## 3 Results and Discussion
### Crystal Structure Analyses  
According to the crystal structure analyses, complexes **1** and **2** are mononuclear and crystallize in different space groups (**1** in monoclinic C2/c and **2** in triclinic P-1). In **1**, the asymmetric unit contains three L- ligands coordinated to one Fe\({}^{3+}\) ion (Figure 1), whereas for **2**, the asymmetric unit contains two crystallographically independent metal complex cations--each one constructed from two L- and two chloride ligands coordinated to a Fe\({}^{3+}\) cation--and two non-coordinated triethylammonium counter-ions (Figure 2). In both cases, the iron(III) centers present octahedral-type geometries with N\({}_{3}\)O\({}_{3}\) (in **1**) and N\({}_{2}\)O\({}_{2}\)Cl\({}_{2}\) (in **2**) coordination environments, but the way the L' coordinates to the metal center depends on the structure. Thus, in **1**, the ligands are all the same, and the _trans_-O\({}_{\rm carboxylate}\)/O\({}_{\rm carboxylate}\)the _trans_-Npyrazine/Npyrazine, and the _trans_-Ocarboxylate/Npyrazine arrangements can be found. In the structure of **2**, the configurations around the metals in the two complex cations are different, and the _trans_-Ocarboxylate/Npyrazine, _trans_-Npyrazine/Cl, and _trans_-Ocarboxylate/Cl can be found at the Fe1 center and one _trans_-Ocarboxylate/Ocarboxylate and two _trans_-Npyrazine/Cl at the Fe2 one. The Fe-O bond lengths range from 1.882(12) to 2.047(3) A, the Fe-N from 2.047(14) to 2.236(4) A, and the Fe-Cl distance from 2.2691(16) to 2.2725(14) A. Extensive H-bond interactions occur in both complexes. In **1**, the amine H-atoms intermolecularly connect with the non-coordinated Ocarboxylate generating a 2D zig-zag grid, but in **2**, a 1D chain type network is formed from alternating NamineH\(\cdots\)-Ocarboxylate and NamineH\(\cdots\)-Npyrazine contacts (Figure 2B). Moreover, in both complexes, we observe intramolecular resonance-assisted hydrogen bonding (RAHB) interactions between the Namine\(-\)H and the Ocarboxylate atoms, with the H\(\cdots\)-Ocarboxylate and Namine-\(\cdots\)Ocarboxylate distances in the ranges of 2.080 A-2.145 A and 2.701 A-2.768 A, respectively. The triethylammonium cations in **2** are hydrogen bonded to the complex cations through N-H\(\cdots\)O [d\({}_{\rm D-A}\) 2.844(6)- 2.886(6) A] and C-H\(\cdots\)-O [d\({}_{\rm D-A}\) 3.179(16) A] interactions. Furthermore, the chloro ligands also interact with the amine group [d\({}_{\rm D-A}\) 3.445(5)- 3.663(5) A] and the aromatic carbons [d\({}_{\rm D-A}\) 3.658(6) A]. Figure 1: (**A**) Ball-and-stick representation of **1** with partial atom numbering scheme. (**B**) Its hydrogen-bonded 2D network. The crystal structure analysis revealed that **3** is a dimethoxido-bridged dinuclear Fe(III) complex, its asymmetric unit containing two L' ligands and one methoxido group coordinated to a Fe\({}^{3+}\) metal cation (Figure 3). The L' chelates the metal center through N\({}_{\rm pyrazine}\) [Fe1-N1, 2.167(8) A; Fe1-N4, 2.140(6) A], O\({}_{\rm carboxylate}\) [Fe1-O1, 1.972(6) A; Fe1-O3, 1.991(5) A], and the bridging methoxido is [Fe1-O5, 1.976(5) A] therefore forming, upon symmetry expansion, a dinuclear structure. Thus, the conformations around the metals are equivalent: _trans_-O\({}_{\rm carboxylate}\)/O\({}_{\rm carboxylate}\) and _trans_-N\({}_{\rm pyrazine}\)/O\({}_{\rm methoxo}\). The distance between the two symmetry-related Fe(III) centers is 3.035(2) A and the Fe-O\({}_{\rm methoxo}\)-Fe bond angle is around 100.4\({}^{\circ}\). The hydrogen bond interactions in complex **3** involve the amine groups which donate to pyrazine N-atom, generating a one-dimensional chain spreading along the crystallographic \(a\) axis; further hydrogen contacts via N\({}_{\rm amine}\)-H\(\cdots\)O [d\({}_{\rm D-A}\) 3.026(10) A] lead to the formation of 2D extended network on the _ac_ plane. Moreover, intramolecular resonance-assisted hydrogen bonding (RHB) interactions between the amine and carboxylate groups [d\({}_{\rm D-A}\) 2.719-2.758 A] are also present in this complex.