# Self-Assembly of Chromium(II) Metal-Ion and Pyrazine Ligand into One-Dimensional Coordination Polymers

Dandan Lou, Nathan J Yutronkie, Itziar Oyarzabal, Henri Barry, Aaron Mailman, Pierre Dechambenoit, Mathieu Rouzières, Fabrice Wilhelm, Andrei Rogalev, Corine Mathonière, et al.

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## To cite this version:

Dandan Lou, Nathan J Yutronkie, Itziar Oyarzabal, Henri Barry, Aaron Mailman, et al. Self-Assembly of Chromium(II) Metal-Ion and Pyrazine Ligand into One-Dimensional Coordination Polymers. Crystal Growth & Design, 2025, 25 (11), pp.3996 - 4005. 10.1021/acs.cgd.5c00428. hal-05102813

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# Self-Assembly of Chromium(II) Metal-Ion and Pyrazine Ligand into One-Dimensional Coordination Polymers

Dandan Lou, Nathan J. Yutronkie, Itziar Oyarzabal, Henri Barry, Aaron Mailman, Pierre Dechambenoit, Mathieu Rouzières, Fabrice Wilhelm, Andrei Rogalev, Corine Mathonière, and Rodolphe Clérac*

The first examples of a one-dimensional (1D) coordination polymer featuring a chromium/pyrazine (pyz) repeating motif have been synthesized from $Cr(OTf)_2$-based precursors (OTf: triflate). In nitrile-based solvents (RCN), a fine control of the synthesis conditions allows the selective formation of both chain and ladder-like compounds: $\{Cr(pyz)(RCN)_2(OTf)_2\}_n$ (1, R: Ph) and $\{Cr_2(pyz)_3(RCN)_2(OTf)_4\}_n \cdot X_n$ (2, R: Ph; 3, R: Me, X: $CH_3Cl_2$; 4, R: Me), respectively. Single-crystal X-ray diffraction experiments reveal the systematic presence of octahedral Cr(II) ions bridged by pyrazine ligands, forming the 1D

coordination polymers. In 2–4, these Cr-pyrazine chains are paired by additional bridging pyrazines resulting in ladder-like arrangements. In these structures, two triflate ions are coordinated via oxygen atoms to the Cr ions in a *trans*- or *cis*- configuration for 1–3 and 4, respectively. In the *trans*- configuration, the coordinating oxygen atoms of the triflate ions align with the direction of the Jahn–Teller elongation observed at each metal node. In contrast, the chromium Jahn–Teller axis in 4 involves a pyrazine ligand, forming the rungs of the ladder structure and one triflate anion. The +II oxidation state of the Cr ions was further confirmed by X-ray absorption spectroscopy, which demonstrates the lack of intramolecular electron-transfer between the chromium center and the pyrazine and the stability of the Cr(II) ions under the given reaction conditions and coordination environments. Magnetic susceptibility measurements reveal the presence of weak antiferromagnetic interactions, which dominate between $S = 2$ $Cr(II)$ spins in all compounds. Using a Heisenberg chain model for classical $S = 2$ spins, as developed by Fisher ($H = -2J\sum_{i=1}^n \vec{S}_i \cdot \vec{S}_{i+1}$), the exchange interaction (J) through the neutral pyrazine is estimated at –3.1, –3.3, –3.4, and –2.5 K for 1–4, respectively. Combining magnetic and calorimetric measurements at low temperatures, a long-range antiferromagnetic ordering is detected below 20 K in all four materials.

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Molecule-based magnets have attracted considerable attention as promising components for next-generation technologies.¹⁻⁴ These materials, formed through the coordination of metal ions with organic ligands, exhibit characteristic properties of traditional magnetically order systems (i.e., remnant magnetization), while providing numerous opportunities to realize novel structural architectures and functionalities. The versatility and tunability of these molecule-based materials, which are often challenging to achieve in conventional inorganic magnets, enable the combination of magnetism with electrical conductivity, spin crossover, porosity, and more.¹⁻¹⁰ In their molecular design, particular emphasis is placed on the choice of ligands, which can either bridge or decorate metal ions. By selecting appropriate ligands for a given magnetic metal ion, it has been possible to develop unique molecule-based materials such as single-molecule magnets,⁵⁻⁷ single-chain magnets,⁸ and magnetically ordered

two- (2D) and three-dimensional (3D) metal–organic frameworks (MOFs),⁹,¹⁰ all while utilizing inexpensive and readily accessible ligands.

To these ends, our group has utilized pyrazine (pyz) as an effective building block for the construction of molecule-based magnets with remarkable properties.¹¹⁻¹⁶ This simple ditopic ligand is known to bridge metal ions in a diverse range of structural architectures, from discrete multinuclear complexes¹⁴,¹⁷ to coordination polymers¹¹⁻¹³,¹⁵,¹⁶ and networks of all dimensions.¹⁸ Moreover, the existence of a low-lying molecular $\pi$-antibonding orbital can facilitate a one-electron
transfer with redox-compatible metal centers, as previously reported in a few examples containing monoradical pyrazine.<sup>11,12,14–17,19–23</sup> One of these examples is our recent discovery of noninnocent redox behavior in pyrazine-bridged chromium-based coordination networks.<sup>11,12</sup> More specifically, reacting Cr<sup>II</sup>Cl<sub>2</sub> with pyrazine yields a 2D square network featuring Cr(III) sites and a reduction of half the pyrazines in the scaffold, {Cr<sup>III</sup>Cl<sub>2</sub>(pyz<sub>2</sub>)<sup>•−</sup>}<sub>n</sub>. This electronic configuration results from an electron transfer between the Cr(II) ion and one of the two bridging pyrazine ligands. The strong π-d conjugation between orbitals of the ligands and metal ions ensures the formation of an extended network with highly delocalized open-shell frontier orbital states, which enhance magnetic exchange interactions and promote electron mobility. As a result, {Cr<sup>III</sup>Cl<sub>2</sub>(pyz<sub>2</sub>)<sup>•−</sup>}<sub>n</sub> exhibits ferrimagnetic order below 55 K, along with semiconductor properties and high electrical conductivity of 32 mS cm<sup>−1</sup> at room temperature.<sup>11,12</sup> When Cr<sup>II</sup>Br<sub>2</sub> is used, similar results are obtained.<sup>11,22,23</sup> However, substituting chlorine or bromine by iodine<sup>11,22,23</sup> or methylsulfonate<sup>13</sup> anions in analogous materials, {Cr-(pyz<sup>o</sup>)<sub>2</sub>X<sub>2</sub>}<sub>n</sub> (X = I, OSO<sub>2</sub>CH<sub>3</sub>), suppresses the metal-to-ligand electron transfer. Consequentially, these 2D coordination compounds behave as insulating materials and undergo antiferromagnetic (AFM) ordering below 26 and 10 K, respectively. The complete change in the magnetism and conductivity of these four {Cr(pyz)<sub>2</sub>X<sub>2</sub>}<sub>n</sub> networks is solely due to auxiliary ligands located at the chromium apical coordination sites, which influence the ability of the metal ion to reduce the pyrazine ligand.<sup>11–13,22,23</sup> Thus, the judicious choice of these auxiliary ligands provides a synthetic handle for tuning the physical properties of chromium/pyrazine-based materials.

While this body of work has highlighted the potential of pyrazine-bridged chromium 2D systems as magnetic and conductive materials, few studies have explored the synergy between chromium and pyrazine in other dimensional structural assemblies.<sup>14,24</sup> Recently, our group has reported a tetranuclear complex, [Cr<sub>4</sub><sup>III</sup>(pyz<sup>•−</sup>)<sub>4</sub>(DMA)<sub>16</sub>](OTf)<sub>8</sub>·(pyz<sup>o</sup>)-(DMA)<sub>6.7</sub> (DMA: N,N-dimethylacetamide, OTf: triflate), where the reaction between Cr<sup>II</sup>(OTf)<sub>2</sub> and pyrazine triggered in situ redox reactions, producing Cr(III) ions and pyrazine radical bridging ligands. Using DMA as a solvent enabled control over the complex's dimensionality, resulting in a rare molecular unit with pyrazine-radical ligands. Strong antiferromagnetic interactions between spin carriers (about −932 K per theoretical calculations) led to a thermally isolated S<sub>T</sub> = 4 ground state, even at room temperature.<sup>14</sup> Despite these advancements, to the best of our knowledge, no studies have focused on pyrazine-bridged chromium-based one-dimensional (1D) systems. Notably, recent investigations have explored magneto-structural correlations in pyrazine-based structures involving lanthanide and Group 2 metal ions, which form triangular moieties organized into ladder or two-dimensional arrangements.<sup>25–28</sup> For instance, {SmI<sub>2</sub>(pyz)<sub>3</sub>}<sub>n</sub> exhibits a thermally reversible Sm/pyrazine electron-transfer process associated with a hysteretic first-order phase transition.<sup>25</sup> This transition can be tuned between 50 and 200 K by simply adjusting the Yb/Sm ratio in isomorphous {Sm<sub>1-x</sub>Yb<sub>x</sub>I<sub>2</sub>(pyz)<sub>3</sub>}<sub>n</sub> solid solutions (x = 0 to 0.4).<sup>25</sup> The valence interconversion between Sm(II)-pyz<sup>o</sup> and Sm(III)-pyz<sup>•−</sup> pairs in {Sm<sub>1-x</sub>Yb<sub>x</sub>I<sub>2</sub>(pyz)<sub>3</sub>}<sub>n</sub> is also observed in {SmI<sub>1-x</sub>Br<sub>x</sub>(pyz)<sub>2</sub>(THF)}<sub>n</sub> and {Sm<sub>1-x</sub>M<sub>x</sub>I<sub>2</sub>(pyz)<sub>2</sub>(THF)}<sub>n</sub> (THF: tetrahydrofuran; M: Sr or Ca).<sup>28</sup> A similar phenom-

enon is seen in {CrI<sub>2-x</sub>Br<sub>x</sub>(pyz)<sub>2</sub>}<sub>n</sub> alloys.<sup>23</sup> In these systems, a Cr/pyrazine electron-transfer involving Cr(II)-pyz<sup>o</sup> and Cr(III)-pyz<sup>•−</sup> pairs is detected between 100 and 230 K over a specific range of the Br/I ratio (x = 0.35 to 0.75). Remarkably, these thermally induced electron-transfer phenomena mimic the redox process observed during the synthesis of compounds like {Cr<sup>III</sup>X<sub>2</sub>(pyz<sub>2</sub>)<sup>•−</sup>}<sub>n</sub> (X: Cl or Br),<sup>11,12,23</sup> {Ti<sup>III</sup>Cl<sub>2</sub>(pyz<sub>2</sub>)<sup>•−</sup>}<sub>n</sub><sup>15</sup> and [Cr<sub>4</sub><sup>III</sup>(pyz<sup>•−</sup>)<sub>4</sub>(DMA)<sub>16</sub>](OTf)<sub>8</sub>·(pyz<sup>o</sup>)(DMA)<sub>6.7</sub>.<sup>14</sup> Beyond these examples, research on pyrazine-based 1D coordination polymers has predominantly focused on those containing late 3d transition metals,<sup>29–31</sup> with particular emphasis on Cu(II)/pyrazine-based coordination polymers. These systems have garnered significant attention due to their potential as quantum spin-1/2 Heisenberg chains<sup>32–34</sup> and ladders.<sup>35,36</sup> As an initial step in exploring new coordination polymers of various dimension- alities involving chromium metal ions and pyrazine ligands with potential redox synergy, we report herein the preparation and characterization of four new 1D coordination networks formed from the reaction between chromium triflate precursors and neutral pyrazine.

**General Methods.** Pyrazine was obtained commercially and used without further purification. Cr(OTf)<sub>2</sub> and Cr(OTf)<sub>2</sub>(MeCN)<sub>2</sub> were prepared as previously described.<sup>37,38</sup> All solvents were of at least reagent grade. Anhydrous benzonitrile (PhCN) was purchased commercially, while tetrahydrofuran (THF), acetonitrile (MeCN) and dichloromethane (CH<sub>2</sub>Cl<sub>2</sub>) were dried by passing through activated alumina on an Innovative Technology solvent-purification system and subsequently stored over 4-A or 3-A molecular sieves prior to use. All manipulations were performed in a glovebox under a dinitrogen or argon atmosphere and/or by standard Schlenk techniques, due to the air-sensitivity of some of the reagents and final products. IR spectroscopy was performed on solid samples using an Agilent Technologies Cary 630 FT-IR spectrometer in an argon-filled glovebox.

**Preparation of {Cr(pyz)(PhCN)<sub>2</sub>(OTf)<sub>2</sub>}<sub>n</sub> (1).** A solution of Cr(OTf)<sub>2</sub> (150 mg, 0.43 mmol) in PhCN (3 mL) was poured into the bottom of a glass tube (ca. 1 cm diameter), which was subsequently covered with a slowly added layer of neat PhCN (4 mL). A solution of pyrazine (34.4 mg, 0.43 mmol) in THF (3 mL) was slowly layered on top of the two first solutions. After sealing the glass tube with a rubber septum and parafilm, the three-layer mixture was allowed to stand for 10 days at room temperature, from which 1 was isolated as light brown crystals. Yield: 40–45% based on Cr(OTf)<sub>2</sub>. IR (ν<sub>max</sub> ATR, cm<sup>-1</sup>): 3108 (w), 2267 (m), 1596 (m), 1492 (w), 1446 (m), 1420 (m), 1300 (s), 1237 (s), 1216 (s), 1162 (s), 1113 (m), 1094 (w), 1075 (m), 1025 (s), 933 (w), 836 (s), 805 (w), 761 (s), 683 (s), 630 (s), 577 (s), 555 (s), 514 (s), 489 (s). Anal. calcd for C<sub>20</sub>H<sub>14</sub>CrF<sub>6</sub>N<sub>4</sub>O<sub>6</sub>S<sub>2</sub>: C, 37.74; H, 2.22; N, 8.80%; Found: C, 37.83; H, 2.16; N: 8.82%.

**Preparation of {Cr<sub>2</sub>(pyz)<sub>3</sub>(PhCN)<sub>2</sub>(OTf)<sub>4</sub>}<sub>n</sub> (2). Method 1: Single Crystals for X-ray Diffraction.** A solution of Cr(OTf)<sub>2</sub> (150 mg, 0.43 mmol) in PhCN (3 mL) was poured into the bottom of a glass tube (ca. 1 cm diameter), which was subsequently covered with a slowly added layer of neat PhCN (4 mL). A THF solution (3 mL) of pyrazine (170 mg, 2.13 mmol) was slowly layered on top of the two first solutions. After sealing the glass tube with a rubber septum and parafilm, the three-layer mixture was allowed to stand for 1 week at room temperature, from which 2 was isolated as brown crystals.

**Method 2: Bulk Material for Physical Property Measurements.** A PhCN solution (3 mL) of pyrazine (170 mg, 2.13 mmol) was directly added to a PhCN solution (3 mL) of Cr(OTf)<sub>2</sub> (150 mg, 0.43 mmol) with stirring to immediately afford a brown solution. After about 16 h, a brown powder precipitated. The resulting solid was separated as 2. Yield: 40–45% based on Cr(OTf)<sub>2</sub>. IR (ν<sub>max</sub> ATR, cm<sup>-1</sup>): 3100 (w),
2987 (w), 2862 (w), 2254 (m), 1591 (w), 1483 (w), 1454 (m), 1425 (m), 1300 (s), 1255 (m), 1237 (s), 1206 (s), 1145 (m), 1136 (m), 1125 (m), 1114 (m), 1100 (m), 1089 (m), 1071 (m), 1061 (m), 1033 (m), 1022 (s), 940 (w), 835 (s), 762 (s), 686 (m), 631 (s), 571 (m), 560 (s), 514 (s), 489 (m), 474 (m). Anal. calcd for C₃₀H₂₂Cr₂F₁₂N₈O₁₂S₄: C, 31.42; H, 1.93; N, 9.77%; Found: C, 31.72; H, 1.85; N: 9.89%.

**Preparation of trans-{Cr₂(pyz)₃(MeCN)₂(OTf)₄}ₙ•(CH₂Cl₂)ₙ (3).** A CH₂Cl₂ solution (3 mL) of pyrazine (102 mg, 1.28 mmol) was poured into the bottom of a glass tube (ca. 1 cm diameter), which was subsequently covered with a slowly added layer of THF (4 mL). A MeCN solution (3 mL) of Cr(OTf)₂(MeCN)₂ (185 mg, 0.43 mmol) was slowly layered on top of the two first solutions. After sealing the glass tube with a rubber septum and parafilm, the three-layer mixture was allowed to stand for 5 days at room temperature, from which 3 was isolated as brown crystals. Yield: 50–55% based on Cr(OTf)₂(MeCN)₂. IR (νₘₐₓ ATR, cm⁻¹): 3137 (w), 3108 (w), 3062 (w), 3004 (w), 2937 (w), 2316 (w), 2283 (w), 1429 (m), 1311 (w), 1298 (s), 1256 (m), 1240 (m), 1206 (s), 1166 (s), 1150 (m), 1135 (m), 1105 (m), 1070 (w), 1050 (w), 1036 (m), 1018 (s), 946 (w), 915 (w), 833 (s), 761 (m), 733 (m), 701 (w), 631 (s), 580 (w), 573 (w), 488 (m), 475 (m). Anal. calcd for C₂₁H₂₀Cr₂F₁₂N₈O₁₂S₄Cl₂: C, 22.77; H, 1.82; N, 10.12%; Found: C, 23.35; H, 1.80; N: 10.61%. The slight discrepancy between experimental and calculated values is likely due to solvent loss from the structure during sample transportation and handling.

**Preparation of cis-{Cr₂(pyz)₃(MeCN)₂(OTf)₄}ₙ (4).** A THF solution (3 mL) of pyrazine (102 mg, 1.28 mmol) was poured into the bottom of a glass tube (ca. 1 cm diameter), which was then covered with a slowly added layer of pure THF (4 mL). A MeCN solution (3 mL) of Cr(OTf)₂ (150 mg, 0.43 mmol) was slowly layered on top of the two first solutions. After sealing the glass tube with a rubber septum and parafilm, the three-layer mixture was allowed to stand for 1 week at room temperature, from which 4 was isolated as pale-yellow crystals. Yield: 50–55% based on Cr(OTf)₂. IR (νₘₐₓ ATR, cm⁻¹): 3145 (w), 3116 (w), 3062 (w), 3008 (w), 2937 (w), 2329 (w), 2295 (w), 1429 (m), 1372 (w), 1328 (s), 1286 (s), 1261 (s), 1228 (s), 1196 (s), 1123 (s), 1101 (w), 1086 (w), 1075 (m), 1041 (m), 1033 (s), 1018 (s), 951 (w), 806 (s), 766 (w), 760 (m), 690 (w), 630 (s), 590 (w), 578 (w), 520 (w), 515 (s), 483 (s). Anal. calcd for C₂₀H₁₈Cr₂F₁₂N₈O₁₂S₄: C, 23.49; H, 1.77; N, 10.96%; Found: C, 23.35; H, 1.80; N: 10.61%.

**Elemental Analysis.** Samples for C, H, N analysis were prepared in preweighed 6 × 6 × 10 mm Sn foil pans, typically using 3–5 mg of solid material. The samples were transported to the analyzer sealed in a 0.5 mL Eppendorf Flex-Tube microcentrifuge tube under argon. The sample masses were determined by weighing by difference and quickly introduced into the precalibrated Elementar EL III C, H, N analyzer to determine the C, H, and N composition just prior to each sample analysis. The error in the C, H and N values is estimated to be between 0.5 and 0.1% (0.1% corresponds to the error in the ideal standard conditions given by Elementar).

**Powder X-ray Diffraction.** Powder X-ray measurements were performed on a Rigaku Nanoviewer (XRF microsource generator, MicroMax 007HF), with a rotating anode coupled to a confocal Max-Flux Osmic mirror (Applied Rigaku Technologies, Austin, USA) producing beam with a wavelength of 1.5418 Å or an energy of 8 keV. A wide-angle X-ray scattering with transmission geometry setting was chosen. Samples were sealed in glass capillaries (diameter 0.7 mm) (Glaskapillaren GLAS, Glas-Technik & Konstruktion, Schönwalde-Glien, Germany) with a sample–detector distance of 129 mm providing access to angles in the 3–53° range. Images were collected on a MAR345 image plate detector (MARResearch, Norderstedt, Germany) and spectra were integrated with the FIT2D software (ESRF; www.esrf.fr/computing/scientific/FIT2D/).

**Single-Crystal X-ray Diffraction.** The single-crystal diffraction data of 1–4 was collected on a Bruker APEX II Quasar diffractometer using graphite monochromated Mo Kα radiation (λ = 0.71073 Å). Crystals were mounted on cryoloops using NVH oil and cooled down to 120 K prior to data collection. The program SAINT was used to

integrate the data, which were thereafter corrected for absorption using SADABS.³⁹ Using the OLEX2 software,⁴⁰ the structures were solved by direct methods and were refined with full-matrix least-squares procedures based on *F*² using SHELXL-2018/2.⁴¹ All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were calculated to their ideal positions and refined isotropically using a riding model. Figures related to the crystal structures have been generated using Diamond by Crystal Impact GbR, Bonn, Germany (https://www.crystalimpact.com/). The CIF files have been deposited at the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC 2271404–2271407.

**X-ray Absorption Spectroscopy (XAS).** X-ray absorption experiments were performed at the ID12 beamline of the European Synchrotron Radiation Facility (ESRF). For the experiments at the Cr K-edge, we used the second harmonic of a HELIOS type undulator (HU-52) and Si(111) double crystal monochromator. Powdered samples mixed with mineral oil were mounted inside an argon filled glovebox into vacuum tight sample holders covered with 6 µm thick polyethylene film. X-ray absorption near edge structure (XANES) spectra were recorded using total fluorescence yield detection mode and corrected for reabsorption effects.

**Magnetic Susceptibility Measurements.** The magnetic measurements were carried out with a Quantum Design MPMS-XL SQUID magnetometer working between 1.85 and 400 K with applied static fields (H) ranging from –7 to 7 T. The data were collected on fresh-filtered crystalline samples (1: 14.5 and 11.1 mg, 2: 15.6 mg, 3: 13.3 mg and 4: 13.6 and 15.8 mg). In an argon-filled glovebox, the samples were first sealed in a polypropylene bag (size ≈ 1 × 0.5 × 0.02 cm) and subsequently in an additional polypropylene bag (size ≈ 2 × 1 × 0.02 cm) to ensure a complete protection from oxygen and humidity. The resulting data were corrected for the sample holder and intrinsic diamagnetic contributions of the sample. The alternating current (ac) susceptibility measurements down to 1.85 K were performed using an oscillating field of 3 Oe for frequencies (νₐₓ) between 1 to 1.5 kHz in zero-dc field. In the available temperature and frequency ranges, the samples do not display any observable slow relaxation of the magnetization.

**Heat Capacity Measurements.** Heat capacity was measured by the thermal relaxation technique using a Quantum Design Physical Property Measurement System (PPMS-9) on pressed pellets of 1 (11.7 mg), 2 (16.0 mg), 3 (8.9 mg), and 4 (8.5 mg), which were molded under a pressure of 2 tons for 1 h. Measurements were performed on these compounds in zero-dc field between 298 and 2 K using Apiezon N grease for thermal contact. A small amount of Apiezon N grease (1.5 mg) was measured independently to estimate the sample environment correction, which was then subtracted from the total heat capacity of the sample.

**Synthesis.** The formation of Cr/pyrazine 1D coordination polymers was first achieved by reacting chromium triflate precursors with pyrazine in coordinating solvents using layer diffusion techniques (see Experimental Section). Single-crystal X-ray diffraction studies (vide infra) demonstrate that using benzonitrile yields single crystals of chain-like and ladder-like structures {Cr(pyz)(PhCN)₂(OTf)₂}ₙ (1) and {Cr₂(pyz)₃(PhCN)₂(OTf)₄}ₙ (2), respectively. In contrast, the polymeric ladder-like structures, trans-{Cr₂(pyz)₃(MeCN)₂(OTf)₄}ₙ•(CH₂Cl₂)ₙ (3) and cis-{Cr₂(pyz)₃(MeCN)₂(OTf)₄}ₙ (4), are obtained when acetoni-trile is used. Despite the ability to obtain multiple coordination polymers from the same set of reactants, bulk samples of each compound are selectively and reproducibly synthesized by carefully controlling the reaction conditions. For instance, both compounds 1 and 2 are prepared by slow diffusion of a THF solution of pyrazine into Cr(OTf)₂ in PhCN. However,
selectively isolating each compound requires adjusting the pyrazine stoichiometry from one equivalent for 1 to five for 2. Similarly for the MeCN-solvated materials, 3 is obtained by slow diffusion of a MeCN solution of Cr(OTf)₂(MeCN)₂ into a mixture of THF and dichloromethane containing pyrazine in a 1:3 molar ratio, while 4 forms under similar layering conditions when dichloromethane is excluded from the reaction mixture. Comparison of the experimental powder X-ray diffraction data for 1–4 are consistent with the simulated X-ray patterns derived from single-crystal data, confirming that the bulk materials are phase pure (see Figures S1–S4 in the Supporting Information). Additionally, infrared spectroscopy and elemental analysis (C, H, N) provides strong evidence for the successful isolation and composition of the 1D coordination polymers 1–4.

**Crystallography.** Single-crystal X-ray diffraction analyses of 1–4 confirmed that the chromium metal ions are coordinated by bridging pyrazine ligands forming single-chain motifs in 1 and ladder-like structures in 2–4. Selected crystallographic data and key metric parameters are provided in Table 1 and Table S1 of the Supporting Information, while the crystal structures are depicted in Figures 1, 2, S5 and S6.

<table><caption>Table 1. Selected Structural Metrics from Single-Crystal X-ray Diffraction Data for 1–4</caption><thead><tr><th></th><th>1</th><th>2</th><th>3</th><th>4</th></tr></thead><tbody><tr><td>Φ<sub>r</sub>, °<sup>a</sup></td><td>178.930(5)</td><td>177.761(7)<br>179.037(7)</td><td>178.398(5)</td><td>178.575(7)</td></tr><tr><td>Ω<sub>r</sub>, °<sup>b</sup></td><td>180</td><td>176.80(5)</td><td>176.79(6)</td><td>177.15(9)</td></tr><tr><td>d<sub>1</sub>, Å<sup>c</sup></td><td>7.0327(4)</td><td>7.0910(6)</td><td>7.0787(9)</td><td>7.0600(5)</td></tr><tr><td>d<sub>2</sub>, Å<sup>d</sup></td><td>8.975(1)</td><td>7.2293(9)</td><td>7.213(1)</td><td>7.804(1)</td></tr><tr><td>Cr-N<sub>pyz</sub>, Å</td><td>2.1263(9)</td><td>2.146(1)<br>2.153(1)<br>2.208(1)<sup>e</sup></td><td>2.146(1)<br>2.203(2)<sup>e</sup></td><td>2.137(2)<br>2.501(2)<sup>e</sup></td></tr><tr><td>Cr-N<sub>CN</sub>, Å</td><td>2.095(1)</td><td>2.098(2)</td><td>2.085(2)</td><td>2.079(2)</td></tr></tbody></table>

<sup>a</sup>Angle between Cr1-N<sub>pyz</sub>-N'<sub>pyz</sub> (N<sub>pyz</sub> and N'<sub>pyz</sub> belonging to the same pyrazine) along the chains. <sup>b</sup>Angle between N<sub>pyz</sub>-Cr1-N'<sub>pyz</sub> along the chain direction. <sup>c</sup>Intrachain Cr1···Cr1 distance. <sup>d</sup>Interchain Cr1···Cr1' distance. <sup>e</sup>Metal-ligand bonds orthogonal to direction of chain.

Across all compounds, the metal ions along the backbone of each 1D array are consistently arranged in a quasi-linear fashion, as indicated by the Cr1-N<sub>pyz</sub>-pyz<sub>centroid</sub> angle and the trans-N<sub>pyz</sub>-Cr1-N<sub>pyz</sub> angles (Φ and Ω, respectively; Φ: 1 = 178.930(5)°; 2 = 177.761(7) and 179.037(7)°; 3 = 178.398(5)°; 4 = 178.575(7)°; Ω: 1 = 180°; 2 = 176.80(5)°; 3 = 176.79(6)°; 4 = 177.15(9)°). Additionally, the shortest intrachain Cr1···Cr1 distances, d₁, are comparable (1 = 7.0327(4) Å; 2 = 7.0910(6) Å; 3 = 7.0787(9) Å; 4 = 7.0600(5) Å). Moreover, all chromium ions adopt a six-coordinate pseudo-octahedral geometry with a N₄O₂ coordination environment. However, they differ in their ligand environment, which in turn influences the crystal packing of the chain-like arrays.

In compound 1, which crystallizes in the monoclinic space group C2/c, the Cr coordination sphere is completed by benzonitrile molecules and monodentate triflate anions (Figure 1). Each chromium site is located at an inversion center, positioning the three different peripheral ligands in a trans-configuration. The four N-coordinating ligands form the equatorial plane of the Cr-centered octahedron (Cr1-N1 =

2.1263(9) Å; Cr1-N2 = 2.094(1) Å), while the triflate anions bind axially at longer distances (Cr1-O1 = 2.338(1) Å). These chromium structural features are characteristic of a +II metal oxidation state and are indicative of Jahn-Teller elongation occurring along the O1-Cr1-O1 axis.³⁸

The chain-like arrays in 2 similarly crystallize in the monoclinic space group C2/c. However, in this compound, the Jahn-Teller distorted chromium ions are not located on a special position. The chromium coordination environment includes two triflate anions occupying the elongated apical sites of the octahedra, while three pyrazine and one benzonitrile molecules bind along the equatorial plane (Figure S5a; Cr1-N: 2.098(2)-2.208(1) Å; Cr1-O: 2.298(1)-2.336(1) Å). While two of the pyrazine moieties extend the metal ion chain, the third is shared between chromium ions of adjacent chains, forming centrosymmetric ladder-like structures. The Cr-N bond distance between the metal and the orthogonal pyrazine ligand is slightly longer than those along the chain direction (i.e., 2.2085(14) vs 2.1468(15) Å and 2.1531(15) Å, respectively), which is reflected in the larger interchain Cr1···Cr1' distance, d₂ (7.2293(9) Å), compared to the intrachain d₁ distances. In the crystal, the 1D coordination polymers in both 1 and 2 propagate all along the b-direction and are evenly spaced into rows along the a- and c-directions, respectively (Figures 1b and S5b). At the supramolecular level, these 1D coordination polymers are connected along the two other dimensions through weak C-H···O and C-H···F hydrogen bonds between the triflate anions and adjacent C(sp²)-H of the ligands, forming an overall 3D molecular network (d(C<sub>pyz</sub>-O)

Figure 1. (a) Partially labeled ORTEP drawings (with thermal ellipsoids depicted at 50% probability level) of the chain-like coordination polymers in 1 at 120 K. Black arrows indicate the direction of the chromium Jahn-Teller distortion. (b) Unit cell projection of 1 illustrating a top-down view of the chain-like coordination polymers propagating along the b-direction. Faded atoms highlight chains displaced by b/2 relative to the nonfaded ones. Color code: Cr, purple; C, gray; N, blue; O, red; F, green; S, yellow. Hydrogen atoms are omitted for clarity.

<figure><img src="image_4.png" /></figure>
<figure><img src="image_5.png" /></figure>

**Figure 2.** (a) Partially labeled ORTEP drawings (50% thermal ellipsoids) of the ladder-like coordination polymers in 4 at 120 K. Black arrows indicate the direction of the chromium Jahn-Teller distortion. (b) Unit cell projection of 4 illustrating a top-down view of the ladder-like coordination polymers propagating along the *c*-direction. Faded atoms highlight ladders displaced by *c*/2 relative to the nonfaded ones. Color code: Cr, purple; C, gray; N, blue; O, red; F, green; S, yellow. Hydrogen atoms are omitted for clarity.

= 3.03–3.05 Å in **1** and 3.15–3.26 Å in **2**; $d(C_{\text{Ph}}-F) = 3.24$ Å in **1** and **2**).

The 1D coordination polymers 3 and 4 crystallize in the monoclinic space group C2/m and the orthorhombic space group Pnnm, respectively. Both exhibit ladder-like motifs similar to that of 2. However, closer inspection of the spatial arrangement of the auxiliary ligands around the Cr-centered octahedra reveals structural differences between 3 and 4. Comparatively, the coordination environment of the chromium ion in 3 closely resembles that of 2, with primary difference being the substitution of the nitrile-based solvent ligands (Figure S6a; Cr–N: 2.085(2)–2.203(2) Å; Cr–O: 2.288(2)–2.248(2) Å). In 3, the ladder-like motifs extend along the *b*-direction, while being uniformly anchored by an extended network of weak $C_{\text{pyz}}-H···O_{\text{triflate}}$ hydrogen bonds across the *a*-direction ($d(C_{\text{pyz}}-O) = 3.26$ Å). The dichloromethane molecules present in 3 occupy the void spaces between the (*a*,*b*) layers formed by the 1D coordination polymers (along *b*) and the weak hydrogen bonded network (along *a*; Figure S6). In contrast, the OTf anions in 4 are coordinated in a cis-fashion, positioning one of these ligands directly opposite the shared pyrazine in the ladder-like motif (Figure 2). A Jahn-Teller elongation is observed along this triflate-pyrazine axis, as evidenced by the long metal-ligand bond distances (Cr–N2 = 2.501(2) Å; Cr–O2 = 2.308(2) Å) compared to the other bonds (Cr1–N1 = 2.1376(17) Å; Cr–N3 = 2.079(2) Å; Cr–O1 = 2.052(2) Å). As a consequence, the interchain Cr1···Cr1' distance (7.804(1) Å) is the longest among all the three ladder-like coordination networks. At the supramolecular level, the ladder-like structures in 4 extend along the *c*-direction and are arranged in a staggered, criss-cross pattern stabilized by weak $C_{\text{pyz}}-H···O_{\text{triflate}}$ hydrogen bonds ($d(C_{\text{pyz}}-O) = 3.30$ Å; Figure 2b).

**X-ray Absorption Spectroscopy (XAS).** To corroborate the above single-crystal X-ray diffraction analysis, the electronic structure of the four 1D coordination polymers was further examined by XAS at the Cr *K*-edge. Measurements on solid samples of **1–4** in oil are presented in Figure 3. The XANES spectra display similar near-edge features, including weak features in the pre-edge region (inset, Figure 3) and an intense rising edge corresponding to the 1s → 3d and 1s → 4p electronic transitions, respectively. This striking resemblance, particularly the lowest-lying pre-edge transition (1s → 3d $t_{2g}$),

<figure><img src="image_6.png" /></figure>

**Figure 3.** Normalized XANES spectra at the Cr *K*-edge for **1–4** and for the Cr(II) reference compound, ${\{\text{Cr(pyz)}_2(\text{OSO}_2\text{CH}_3)_2\}}_n$, (pink trace) at 295 K. The data were normalized to zero before the edge for the sake of comparison. Inset: magnified view of the pre-edge region.

indicates comparable electronic structures for the chromium ions, despite subtle differences in metal-ligand bond lengths.⁴² Additionally, the XANES spectra were compared to the previously reported 2D network ${\{\text{Cr(pyz)}_2(\text{OSO}_2\text{CH}_3)_2\}}_n$, as a Cr(II) reference due to its similar ligands and $N_4O_2$ coordination sphere.¹³ The superimposable pre-edge features (Figure 3) provide further evidence of a +2 oxidation state for the chromium ions in all four new compounds. As with ${\{\text{Cr(pyz)}_2(\text{OSO}_2\text{CH}_3)_2\}}_n$, the intrinsic metal-to-ligand electron transfer ($\text{Cr}^{\text{II}}-\text{pyz} \rightarrow \text{Cr}^{\text{III}}-\text{pyz}^*$), previously observed in other Cr/pyrazine systems,¹¹,¹²,¹⁴,²²,²³ is not activated along the 1D arrays in these materials, likely due to the ligand field environment imposed by the coordinated sulfonate ligands.

**Magnetic Measurements.** Magnetic susceptibility ($\chi$) measurements for compounds **1–4** were performed under a 0.1 T dc field to investigate the magnetic properties of this class of Cr/pyrazine 1D coordination polymers. As shown in Figure 4, the temperature dependence of $\chi T$ product is consistent across all four compounds. Above 30 K for **1** and **2** and 40 K for **3** and **4**, the magnetic susceptibility follows Curie-Weiss law as illustrated by the $\chi^{-1}$ vs T data shown in Figure S7. The corresponding fits yield Curie constants (C) around 3 cm³ K mol⁻¹, as expected for high-spin S = 2 Cr(II) centers (with g = 2; Table 2), while Weiss constants ($\theta$) range from −34 to −23 K, suggesting dominant antiferromagnetic interactions. This is further reflected in the $\chi T$ product, which
<figure><img src="image_7.png" /><figcaption>**Figure 4.** Temperature (*T*) dependence of the χ*T product at 0.1 T for 1–4 (where χ = M/H is the molar magnetic susceptibility normalized per chromium ion). The fits of the experimental data (between 1.9 and 285 K) to a S = 2 Heisenberg chain model developed by Fisher are shown as solid lines.</figcaption></figure>

<table><caption>**Table 2.** Selected Magnetic and Entropic Parameters
Discussed in the Main Text for 1–4</caption><thead><tr><th></th><th>1</th><th>2</th><th>3</th><th>4</th></tr></thead><tbody><tr><td>C, cm<sup>3</sup> K mol<sup>-1</sup>&alpha;</td><td>3.1(1)</td><td>3.1(1)</td><td>3.0(1)</td><td>3.0(1)</td></tr><tr><td>&theta;, K<sup>a</sup></td><td>-31(1)</td><td>-33.8(8)</td><td>-34(1)</td><td>-23.3(6)</td></tr><tr><td>g<sup>b</sup></td><td>2.00(5)</td><td>2.00(5)</td><td>2.00(5)</td><td>1.98(5)</td></tr><tr><td>J/k<sub>B</sub>, K<sup>b</sup></td><td>-3.08(5)</td><td>-3.28(8)</td><td>-3.36(8)</td><td>-2.47(4)</td></tr><tr><td>T*, K<sup>c</sup></td><td>8</td><td>11</td><td>12</td><td>8</td></tr><tr><td>T<sub>max</sub>, K<sup>c</sup></td><td>19</td><td>21</td><td>22</td><td>16</td></tr><tr><td>T<sub>peak</sub>, K<sup>d</sup></td><td>9.7</td><td>13.7</td><td>14.3</td><td>8.3</td></tr><tr><td>T<sub>onset</sub>, K<sup>d</sup></td><td>14.5</td><td>20.0</td><td>19.8</td><td>13.3</td></tr><tr><td>S<sub>mag</sub>, J K<sup>-1</sup> mol<sup>-1</sup></td><td>0.5</td><td>2.2</td><td>1.9</td><td>1.8</td></tr></tbody></table>

<sup>a</sup>Curie–Weiss fit to the data from 40–290 K for 1–2 and from 30 to 290 K for 3–4. <sup>b</sup>Values extracted from the Heisenberg S = 2 chain model developed by Fisher. <sup>c</sup>Defined in Figure 5. <sup>d</sup>Defined in Figure 6.

gradually decreases from 290 to ~50 K, then sharply drops to near zero at 1.9 K (Figure 4).

Deeper insights into the magnetic behavior of 1–4 were obtained by fitting the χ*T vs T data using spin chain models, selected based on their crystal structure (Figure 4). Given the coordination of Cr(II) ions into chain motifs in 1, a Heisenberg S = 2 chain model developed by Fisher, derived from the spin Hamiltonian $H = -2J \sum_{i=1}^{n} \overleftarrow{S_i} \cdot \overrightarrow{S_{i+1}}$<sup>43</sup> was applied to fit the data from 1.9–285 K. From this fitting, an intrachain exchange interaction, $J/k_B = -3.08(5)$ K, was estimated for 1. However, for compounds 2–4, the chains in these structures are pairwise linked by additional bridging pyrazines, suggesting that the magnetic properties may be influenced by interactions through these linkers. If the exchange coupling between chromium spins along the chain is stronger than those between spins interacting orthogonally, the magnetic behavior would be expected to resemble that of a spin chain, as seen in 1. Conversely, if the orthogonal interaction is stronger, an S = 2 spin dimer model would likely provide a better description of the experimental data. In all

structures, the $d_1$ separations between chromium ions along the chains are shorter than the $d_2$ separations between chains, prompting us to fit the magnetic data according to the same Heisenberg chain model.

This model fits the experimental data well within the temperature range of 1.9–285 K, providing values of $J/k_B$ that are in close proximity to that of compound 1 (2: -3.3 K; 3: -3.4 K and 4: -2.5 K; Table 2). It is worth noting that this rationale was also applied to the fitting of the χ*T data for the previously published {Cr(pyz)$_2$(OSO$_2$CH$_3$)$_2$)$_n$} where the structure exhibits two different intraplanar Cr···Cr' distances (7.121(2) and 8.086(2) Å) due to a Jahn–Teller distortion along one crystallographic axis within the Cr/pyrazine scaffold.<sup>11,13</sup> For this compound, the chain model yielded $J/k_B = -3.26(5)$ K ($g = 2.04(5)$), highlighting similar magnetic properties despite the extension of the Cr/pyrazine structure from 1D to 2D. Although the magnitude of the antiferromagnetic interactions can be attributed to those between chromium spins along the 1D coordination polymers, the presence of interchain interactions (vide supra) between the magnetic chains or ladders spanning the two last dimensions may provide a pathway to an antiferromagnetic ordered state. To explore this possibility, the field-dependence of the magnetization was measured at 1.85 K. At 7 T, the magnetization is nearly seven times smaller than the expected value of 4 $\mu_B$ (Figure S8). Additionally, the magnetic susceptibility of 1–4 was measured under various applied fields ranging from 0.05 to 7 T (Figure 5).

<figure><img src="image_8.png" /><figcaption>**Figure 5.** Temperature (*T*) dependence of the magnetic susceptibility (χ) for 1–4 (where χ = M/H is the molar magnetic susceptibility normalized per chromium ion) at different applied field between 0.05 and 7 T for temperatures below 50 K. Solid lines are provided as visual guides.</figcaption></figure>

A field dependence of χ begins to appear below approximately 20 K for each compound, becoming more pronounced after a broad cusp in χ. These field and thermal behaviors of the magnetic susceptibility strongly suggest the presence of a phase transition toward an antiferromagnetic ground state. In ideal cases, an antiferromagnetic phase transition and its critical temperature (Néel temperature; $T_N$) are typically marked by a maximum in χ, accompanied by its divergence at different fields. However, since these characteristic features are not well-defined in the present χ vs
T plots as expected for low-dimensional systems, it becomes challenging to pinpoint $T_N$ with certainty for each compound based on magnetic susceptibility measurements alone. For this reason, we defined two characteristic temperatures as an initial range to characterize the Néel temperature of the antiferromagnetic phase transition (Table 2). The temperature $T^*$ represents the point where $\chi$ exhibits a significant divergence at each applied field ($<3$ T; $T^* = 8$ K for 1; 11 K for 2; 12 K for 3; 8 K for 4), while $T_{max}$ refers to the temperature at which a local maximum in $\chi$ occurs in this thermal region (at 500 Oe; $T_{max}$ = 19 K for 1; 21 K for 2; 22 K for 3; 16 K for 4).

**Calorimetry.** To further investigate the presence of an antiferromagnetic phase transition in compounds 1–4, heat capacity ($C_p$) measurements were carried out on samples down to 2 K (Figures 6 and S9). For each coordination polymer, no

<figure><img src="image_9.png" /><figcaption>**Figure 6.** Temperature dependence of (a) the heat capacity ($C_p$) black circles, the magnetic component of the heat capacity ($C_{mag}$) blue dots, and (b) the magnetic entropy ($S_{mag}$; green dots) per mole of 2 measured under a zero applied-dc field. The red solid line corresponds to the nonmagnetic component of the heat capacity, modeled with a polynomial law. $C_{mag}$ is deduced from the removal of the nonmagnetic background from the $C_p$ data. $S_{mag}$ is deduced from the integration of $C_{mag}/T$. Solid lines (in blue, green and black) are provided as visual guides.</figcaption></figure>

sharp anomaly is observed in the $C_p$ data; instead, a broad bump appears below 20 K. By subtracting the lattice contributions (simulated by empirical polynomial expression; red line in Figures 6 and S9) from the $C_p$ data, the magnetic component of the heat capacity ($C_{mag}$) is extracted, revealing a more pronounced peak within this temperature range, thereby confirming the presence of an antiferromagnetic phase transition for each compound. It is worth mentioning that the broad shape of this feature is not surprising for low-dimensional materials, as the broadness may arise from thermal excitations of the $S = 2$ microstates$^{44}$ and/or the presence of spin correlations in low-dimensional systems.$^{45}$ Nonetheless, each peak in the $C_{mag}$ vs T plots was characterized by two temperatures: $T_{peak}$ and $T_{onset}$ (Table 2). $T_{peak}$ denotes the temperature of the peak maximum of the broad $C_{mag}$ peak (9.7 K for 1; 13.7 K for 2; 14.3 K for 3 and 8.3 K for 4), while $T_{onset}$ refers to the temperature at which $C_{mag}$ begins to rise upon cooling (14.5 K for 1; 20 K for 2; 19.8 K for 3; 13.3 K for 4).

By comparing these temperatures from both heat capacity and magnetic data, it is evident that $T_{peak}$ aligns closely with $T^*$, while $T_{onset}$ is more closely related to $T_{max}$. Given the less ambiguous features in $C_{mag}$ we believe that $T_{peak}$ more accurately reflects the divergence of $\chi$ at varying fields, which is more widely accepted as the Néel temperature for an antiferromagnetic phase transition.

Therefore, the four compounds exhibit antiferromagnetic ordering in the range of 8.3 K (for 4) and 14.3 K (for 3), temperatures that are comparable to the $T_N$ of the 2D network $\{\text{Cr(pyz)}_2(\text{OSO}_2\text{CH}_3)_2\}_n$ ($T_N$ = 9.7 K).$^{13}$ Additionally, when the magnetic entropy ($S_{mag}$) is derived from the integration of the temperature dependence of $C_{mag}/T$ within this thermal region for each compound (see Figures 6b and S9), at least 83% of the expected $S_{mag}$ (13.4 J K$^{-1}$ mol$^{-1}$ from the $R \ln(2S + 1)$ relation) is released above $T_N$ for each compound. As expected, due to short-range correlations persisting above the ordering temperature,$^{45}$ the $S_{mag}$ values (ranging from 0.5 to 2.2 J K$^{-1}$ mol$^{-1}$, see Table 2) are slightly lower but remain in good agreement with those reported for the related 2D coordination compound $\{\text{Cr(pyz)}_2(\text{OSO}_2\text{CH}_3)_2\}_n$.$^{11,13}$

The first examples of a one-dimensional (1D) coordination polymer featuring an alternating chromium/pyrazine (pyz) motif have been synthesized using $\text{Cr(OTf)}_2$-based precursors. Both chain-like and ladder-like compounds were obtained from reactions carried out in nitrile-based solvents, as confirmed by single-crystal X-ray diffraction analysis. These coordination polymers are constructed from linear arrangements of octahedral Cr(II) ions linked by pyrazine ligands as isolated in 1, while in compounds 2–4, adjacent chains are pairwise connected by orthogonal pyrazine ligands, forming ladder-like motifs. All octahedral metal centers feature a pair of coordinated triflate anions, arranged in a *trans*-configuration for compounds 1–3 and in a *cis*-configuration for compound 4. This difference in coordination geometry not only influences the crystal packing of the coordination polymers but also correlates with the direction of the Jahn–Teller elongation. From a synthetic perspective, the careful selection of building blocks and meticulous control of reaction conditions underscore the precise level of control achievable in the construction of such molecule-based architectures.

In agreement with single-crystal X-ray diffraction data, X-ray absorption spectroscopy confirms the Cr(II) oxidation states for each compound, while magnetic measurements reveal the systematic presence of an antiferromagnetic ordered state below 15 K. These findings highlight the suppression of intramolecular Cr/pyrazine electron transfers previously observed in the square complex $[\text{Cr}_4(\text{pyz})_4(\text{DMA})_{16}](\text{OTf})_8(\text{pyz})(\text{DMA})_{6.7}^{14}$ and the 2D networks $\{\text{Cr(pyz)}_2\text{Cl}_2\}_n^{11,12}$ and $\{\text{Cr(pyz)}_2\text{Br}_2\}_n^{11,22,23}$. This suppression is likely influenced by the electronic effects of the peripheral ligands in the selected solvents, which can modulate the reducing strength of the metal centers. Substituting the labile triflate anions in such low dimensional systems with chlorides or other pseudohalides could offer a pathway to tune the frontier molecular orbitals and potentially reintroduce this intrinsic redox behavior. Additionally, these materials offer opportunities for post-synthetic modifications, such as the reduction of neutral pyrazine ligands, analogous to the postsynthetic reduction of $\{\text{Cr(pyz)}_2\text{Cl}_2\}_n$ that yielded a room-temperature, molecule-based bulk magnet.$^{16}$ Ongoing studies are currently investigat-
ing these synthetic strategies to further our understanding of
how to systematically tune the redox properties between
chromium and pyrazine in coordination solids.

Centre National de la Recherche Scientifique (CNRS) and the
China Scholarship Council (CSC) for the PhD funding of D.L.
I.O. acknowledges financial support from the department of
Education of the Basque Government through the PIBA
project call (PIBA_2023_1_0027). The European Synchro-
tron Radiation Facility (ESRF) is also acknowledged for the
allocated beamtime, CH 6195.

The University of Bordeaux, the Centre National de la
Recherche Scientifique (CNRS), the Region Nouvelle
Aquitaine, Quantum Matter Bordeaux, the European Synchro-
tron (ESRF) and the Association Française de Magnétisme
Moléculaire (https://asso-am2.fr) are acknowledged for their
continuous support.

This paper is dedicated to Professor Marius Andruh on the
occasion of his 70th birthday, for his important and inspiring
contributions to coordination chemistry and molecular
magnetism, and for his great commitment to the development
of these fields in Romania and worldwide.

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**Corresponding Author**

Rodolphe Clérac – Univ. Bordeaux, CNRS, CRPP, UMR 5031, F-33600 Pessac, France; ● orcid.org/0000-0001-5429-7418; Email: rodolphe.clerac@u-bordeaux.fr

Authors

Dandan Lou – Univ. Bordeaux, CNRS, CRPP, UMR 5031, F-33600 Pessac, France

Nathan J. Yutronkie – Univ. Bordeaux, CNRS, CRPP, UMR 5031, F-33600 Pessac, France; Present Address: ESRF-The European Synchrotron, CS 40220, F-38043 Grenoble Cedex 9, France

Itziar Oyarzabal – *BCMaterials, Basque Center for Materials, Applications and Nanostructures, ES-48940 Leioa, Spain; IKERBASQUE Basque Foundation for Science, ES-48009 Bilbao, Spain*; ● orcid.org/0000-0001-9149-2511

Henri Barry – Univ. Bordeaux, CNRS, CRPP, UMR 5031, F-33600 Pessac, France; ● orcid.org/0009-0002-3724-2313

Aaron Mailman – University of Jyväskylä, Department of Chemistry, NanoScience Centre, FI-40014 Jyväskylä, Finland; ● orcid.org/0000-0003-2067-8479

Pierre Dechambenoit – Univ. Bordeaux, CNRS, CRPP, UMR 5031, F-33600 Pessac, France

Mathieu Rouzières – Univ. Bordeaux, CNRS, CRPP, UMR 5031, F-33600 Pessac, France

Fabrice Wilhelm – ESRF-The European Synchrotron, F-38043 Grenoble Cedex 9, France

Andrei Rogalev – ESRF-The European Synchrotron, F-38043 Grenoble Cedex 9, France

Corine Mathonière – Univ. Bordeaux, CNRS, CRPP, UMR 5031, F-33600 Pessac, France

Author Contributions

The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.

Funding

R.C., C.M., P.D., and M.R. received funding from the
University of Bordeaux, the Region Nouvelle Aquitaine,
Quantum Matter Bordeaux, the ANR (HiPerMagnet project,
ANR-20-CE07-0022), the European Synchrotron (ESRF), the
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# Self-assembly of Chromium(II) Metal-ion and Pyrazine Ligand into One-dimensional Coordination Polymers

Dandan Lou,<fnref n="1" /> Nathan J. Yutronkie,<fnref n="1" /> Itziar Oyarzabal,<fnref n="2" />,<fnref n="3" /> Henri Barry,<fnref n="1" /> Aaron Mailman,<fnref n="4" /> Pierre Dechambenoit,<fnref n="1" /> Mathieu Rouzières,<fnref n="1" /> Fabrice Wilhelm,<fnref n="5" /> Andrei Rogalev,<fnref n="5" /> Corine Mathonière,<fnref n="1" /> and Rodolphe Clérac<fnref n="1" />,*

## Contents:

1- Powder X-Ray Diffraction data for **1, 2, 3** and **4** Page S2

2- Single-Crystal X-Ray Diffraction data for **1, 2, 3** and **4**. Page S4

3- Additional magnetic susceptibility data for **1, 2, 3** and **4**. Page S7

4- Heat capacity data for **1, 3** and **4**. Page S9

<footnote n="1">¹ Univ. Bordeaux, CNRS, CRPP, UMR 5031, F-33600 Pessac, France</footnote>

<footnote n="2">² BCMaterials, Basque Center for Materials, Applications and Nanostructures, UPV/EHU Science Park, ES-48940 Leioa, Spain</footnote>

<footnote n="3">³ IKERBASQUE, Basque Foundation for Science, ES-48009 Bilbao, Spain</footnote>

<footnote n="4">⁴ University of Jyväskylä, Department of Chemistry, NanoScience Centre, P.O. Box 35, FI-40014 Jyväskylä, Finland</footnote>

<footnote n="5">⁵ ESRF-The European Synchrotron, CS 40220, F-38043 Grenoble Cedex 9, France</footnote>

<footnote>* Email: rodolphe.clerac@u-bordeaux.fr</footnote>
<figure><img src="image_10.png" /><figcaption>1- Powder X-Ray Diffraction data for 1, 2, 3 and 4.</figcaption></figure>

**Figure S1.** Experimental and calculated PXRD patterns of 1 (blue and red plots, respectively; with $\lambda = 1.5418$ Å). Experimental data were collected at room temperature. Calculated pattern was obtained from single crystal data collected at 120 K.

<figure><img src="image_11.png" /></figure>

**Figure S2.** Experimental and calculated PXRD patterns of 2 (blue and red plots, respectively; with $\lambda = 1.5418$ Å). Experimental data were collected at room temperature. Calculated pattern was obtained from single crystal data collected at 120 K.
<figure><img src="image_12.png" /><figcaption>**Figure S3.** Experimental and calculated PXRD patterns of 3 (blue and red plots, respectively; with $\lambda = 1.5418$ Å). Experimental data were collected at room temperature. Calculated pattern was obtained from single crystal data collected at 120 K.</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>**Figure S4.** Experimental and calculated PXRD patterns of 4 (blue and red plots, respectively; with $\lambda = 1.5418$ Å). Experimental data were collected at room temperature. Calculated pattern was obtained from single crystal data collected at 120 K.</figcaption></figure>
## 2- Single-crystal X-ray diffraction data for 1, 2, 3 and 4.

<table><caption>**Table S1.** Selected crystallographic data and parameters.</caption><thead><tr><th></th><th>1</th><th>2</th><th>3</th><th>4</th></tr></thead><tbody><tr><td>CCDC N°</td><td>2271404</td><td>2271405</td><td>2271406</td><td>2271407</td></tr><tr><td>Formula</td><td>C<sub>20</sub>H<sub>14</sub>CrF<sub>6</sub>N<sub>4</sub>O<sub>6</sub>S<sub>2</sub></td><td>C<sub>30</sub>H<sub>22</sub>Cr<sub>2</sub>F<sub>12</sub>N<sub>8</sub>O<sub>12</sub>S<sub>4</sub></td><td>C<sub>21</sub>H<sub>20</sub>Cr<sub>2</sub>F<sub>12</sub>N<sub>8</sub>O<sub>12</sub>S<sub>4</sub>Cl<sub>2</sub></td><td>C<sub>20</sub>H<sub>18</sub>Cr<sub>2</sub>F<sub>12</sub>N<sub>8</sub>O<sub>12</sub>S<sub>4</sub></td></tr><tr><td>FW, g.mol<sup>-1</sup></td><td>636.47</td><td>1146.79</td><td>1107.59</td><td>1022.66</td></tr><tr><td>Crystal System</td><td>Monoclinic</td><td>Monoclinic</td><td>Monoclinic</td><td>Orthorhombic</td></tr><tr><td>Space Group</td><td>C2/c</td><td>C2/c</td><td>C2/m</td><td>Pnmm</td></tr><tr><td>T, K</td><td>120</td><td>120</td><td>120</td><td>120</td></tr><tr><td>λ/Å</td><td>0.71073</td><td>0.71073</td><td>0.71073</td><td>0.71073</td></tr><tr><td>a, Å</td><td>16.4504(10)</td><td>16.5501(10)</td><td>16.588(2)</td><td>15.3719(10)</td></tr><tr><td>b, Å</td><td>7.0327(4)</td><td>7.0910(5)</td><td>7.0787(9)</td><td>16.1484(9)</td></tr><tr><td>c, Å</td><td>22.1278(14)</td><td>34.471(2)</td><td>17.024(2)</td><td>7.0600(5)</td></tr><tr><td>α, °</td><td>90</td><td>90</td><td>90</td><td>90</td></tr><tr><td>β, °</td><td>104.306(3)</td><td>96.307(3)</td><td>104.808(7)</td><td>90</td></tr><tr><td>γ, °</td><td>90</td><td>90</td><td>90</td><td>90</td></tr><tr><td>V, Å<sup>3</sup></td><td>2480.6(3)</td><td>4020.9(5)</td><td>1932.6(5)</td><td>1752.52(19)</td></tr><tr><td>Z</td><td>4</td><td>4</td><td>2</td><td>2</td></tr><tr><td>Φ, ° (a)</td><td>178.930(5)</td><td>177.761(7)<br>179.037(7)</td><td>178.398(5)</td><td>178.575(7)</td></tr><tr><td>Ω, ° (b)</td><td>180</td><td>176.80(5)</td><td>176.79(6)</td><td>177.15(9)</td></tr><tr><td>d<sub>1</sub>, Å (c)</td><td>7.0327(4)</td><td>7.0910(6)</td><td>7.0787(9)</td><td>7.0600(5)</td></tr><tr><td>d<sub>2</sub>, Å (d)</td><td></td><td>7.2293(9)</td><td>7.2130(11)</td><td>7.8043(10)</td></tr><tr><td>Cr-N<sub>pyz</sub>, Å</td><td>2.1263(9)</td><td>2.1468(15)<br>2.1531(15)<br>2.2085(14) (e)</td><td>2.1460(12)<br>2.2030(16) (e)</td><td>2.1376(17)<br>2.501(2) (e)</td></tr><tr><td>Cr-N<sub>NCR</sub>, Å</td><td>2.0946(11)</td><td>2.0980(17)</td><td>2.085(2)</td><td>2.079(2)</td></tr><tr><td>Cr-O<sub>OTf</sub>, Å</td><td>2.3389(10)</td><td>2.2983(13)<br>2.3363(14)</td><td>2.2881(17)<br>2.3486(16)</td><td>2.052(2)<br>2.308(2)</td></tr><tr><td>R<sub>int</sub></td><td>0.0221</td><td>0.0362</td><td>0.0285</td><td>0.0615</td></tr><tr><td>R<sub>1</sub> (f)</td><td>0.0259</td><td>0.0485</td><td>0.0474</td><td>0.0349</td></tr><tr><td>wR<sub>2</sub> (g)</td><td>0.0700</td><td>0.1097</td><td>0.1343</td><td>0.0889</td></tr></tbody></table>

<footnote>(a) Angle between Cr1-N<sub>pyz</sub>-N'_{pyz} (N<sub>pyz</sub> and N'_{pyz} belonging to the same pyrazine) along the chain direction; (b) Angle between N<sub>pyz</sub>-Cr1-N'_{pyz} along the chain direction; (c) Intrachain Cr1...Cr1 distance; (d) Interchain Cr1...Cr1' distance; (e) Metal-ligand bonds orthogonal to direction of chain; (f) $I > 2σ(I)$, $R_1 = \sum(|F_o| - |F_c|)/\sum|F_o|$; (g) $wR_2 = \{\sum[w(F_o^2 - F_c^2)^2]/\sum[w(F_o^2)^2]\}^{1/2}$</footnote>
<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /></figure>

**Figure S5.** (a) Partially labeled ORTEP drawings (thermal ellipsoids are depicted at 50 % probability level) of the ladder-like coordination polymers in **2** at 120 K. Black arrows indicate the direction of the chromium Jahn-Teller distortion. (b) Unit cell projection of **2** illustrating top-down view of the ladder-like coordination polymers propagating along the *b*-direction. Faded atoms highlight ladders displaced by *b*/2 relative to the non-faded ones. Color code: Cr, purple; C, gray; N, blue; O, red; F, green; S, yellow. Hydrogen atoms are omitted for clarity.
<figure><img src="image_16.png" /></figure>

**Figure S6.** (a) Partially labeled ORTEP drawings (thermal ellipsoids are depicted at 50 % probability level) of the ladder-like coordination polymers in **3** at 120 K. Black arrows indicate the direction of the chromium Jahn-Teller distortion. (b) Unit cell projection of **3** illustrating top-down view of the ladder-like coordination polymers propagating along the *b*-direction. Faded atoms highlight ladders displaced by *b*/2 relative to the non-faded ones. Color code: Cr, purple; C, gray; N, blue; O, red; F, green; S, yellow; Cl, dark green. Hydrogen atoms are omitted for clarity. The dichloromethane molecule (in the center) is disordered on two positions with equal occupancies.
<figure><img src="image_17.png" /><figcaption>3- Additional magnetic susceptibility data for 1, 2, 3 and 4.</figcaption></figure>

**Figure S7.** Temperature (*T*) dependence of the inverse of the magnetic susceptibility (*χ*⁻¹) at 0.1 T for **1–4** (where *χ* = *M*/*H* is the molar magnetic susceptibility normalized per complex). The Curie-Weiss fit (*χ*⁻¹ = (*T* − *θ*)/*C*) of the experimental data (blue circles) between 40-290 K for **1–2** and 30-290 K for **3–4** is shown as the red solid lines. Data below these temperature ranges are shown in green circles.
<figure><img src="image_18.png" /><figcaption>**Figure S8.** Field dependence of the magnetization up to 7 T at different temperatures between 1.85 and 25 K for **1**, **2**, **3**, and **4**. Solid lines are provided as visual guides.</figcaption></figure>
<figure><img src="image_19.png" /><figcaption>4- Heat capacity data for 1, 3 and 4.</figcaption></figure>

**Figure S9.** Temperature dependence of the heat capacity ($C_p$, black circles on the left plots), the magnetic component of the heat capacity ($C_{mag}$, blue dots on the left plots), and magnetic entropy ($S_{mag}$; green dotted line on the right plots) per mole of **1** (a,b), **3** (c,d), and **4** (e,f) measured under a zero applied-dc field. The red solid line corresponds to the non-magnetic component of the heat capacity, modeled with a polynomial law. $C_{mag}$ is deduced from the removal of the non-magnetic background from the $C_p$ data. $S_{mag}$ is deduced from the integration of $C_{mag}/T$. Solid lines are provided as visual guides.