Crystal structure of N,N'-diphenylguanidinium dihydrogenphosphite, (C13H14N3)(H2PO3)

C13H16N3O3P, tetragonal, P4 3 (No. 78), a = 10.775(4) Ä, c = 12.572(2) Ä, V = 1459.6 Ä , Ζ = 4, R&(F) = 0.027, wRretfF) = 0.073, T = 293 K. Source of material The compound was synthesized by neutralizing a saturated ethanolic solution of iV^V-diphenylguanidine (Aldrich, 97 % purity) with phosphoric acid (Aldrich, 85 wt% water solution). After slow evaporation over a period of a few weaks single crystals grew from the solution and were recrystallised from ethanol. Experimental details The coordinates of the Η atoms were placed at idealized positions and refined as riding using the SHELXL-97 defaults [1], except for the Η atom attached to the Ρ atom which was freely refined isotropicaly. The absolute structure was refined by the Flack method [2], taking advantage of the anomalous dispersion of the Ρ atom. The final structure was examined with PLATON [3] showing that there are no solvent-accessible voids in the crystal lattice. Discussion Di-aryl-guanidine compounds have pharmacological applications [4]. In addition, diphenylguanidine (dpg) salts are interesting because the cation dpg exhibits different atropisomers depending on the counter-ion, both in solution and in crystalline form [5]. These atropisomers differ in the conformation of the phenyl rings which may have a syn-syn, anti-anti or syn-anti position with respect to the unsubstituted Ν atom of the guanidinium group. Theoretical calculations have shown that there is an easy interchange between the different conformations in solution, due the low potential barrier of rotation of the phenyl rings [5]. Using different counter-ions, the three atropisomers of the dpg cation may be isolated by crystallisation. This work is part of a research project on atropisomerism in dpg salts, aiming at studying the interplay between the structure and physical properties of these compounds. In the title compound, the phenyl rings have a syn-anti conformat i on , as s h o w n by t h e v a l u e s of t he t o r s i o n s a n g l e s N2-C1-N3-C8 (170.4(2)°) and N 2 C 1 N 1 C 2 (0.1(3)°). This conformation is similar to that of the free base [6 ,7] and was also found in dpg + Perchlorate [8] and dpg + f luor ide hydrogen-fluoride [9]. A syn-syn conformation occurs in the nitrate, trifluoroacetate, m-chlorobenzeneseleninate, hydrogenselenite monohydrate, tartrate and formate salts of dpg [10-15]. An anti-anti conformation was found in the phosphate and oxalate salts [16-17]. In a few cases, co-crystallization of two different conformations of the dpg cation was observed, namely in bis(dpg) sulfate monohydrate [18] and in bis(N,/V'-diphenylguanidinium) d ihydrogenphosphi te -phosphor ic acid-water (1/1/1) [19], The C—Ν bond lengths of the guanidinium group are within the range 1.324 Ä -1 . 336(2) Ä, typical for a delocalized C—Ν bond. The guanidinium group is planar, the sum of the valence angles around C1 adds exactly to 360°. However, it should be noted that the angle opposite to the Ν1 atom is smaller (118.0(2)°) than the other two valence angles. In other compounds where the cation has a syn-anti conformation, the N C N angle opposite to the N-phenyl group in yyn-position has always been found to be somewhat shorter than the other N C N valence angles. The dihedral angles between the central planar guanidinium fragment N3C and the least squares-planes of the phenyl rings are 86.61(9)° (C2-C7) and 48.34(9)° (C8-C13). The dihedral angle between the planes of the two phenyl rings is 59.83(9)°. In the crystal s t ructure of b i s (N, /V ' -d iphenylguanid in ium) d ihydrogenTable 1. Data collection and handling. colourless block, size 0.20 χ 0.37 χ 0.39 mm Mo Ka radiation (0.71073 Ä) 1.99 cm" Enraf-Nonius CAD-4, ω/2θ 50° 2860,2578 U s > 2 a(lobi), 2388 188 SHELXS-97 [20], SHELXL[1], PLATON [3] Crystal: Wavelength: μ: Diffractometer, scan mode: 26max: WlWAntasured, Wl*/A,mque: Criterion for lobs, N(hkl)gi: N(param),tfmtd'. Programs: * Correspondence author (e-mail: jap@pollux.fis.uc.pt) Unauthenticated Download Date | 9/26/19 7:23 PM iV,/V'-Diphenylguanidinium dihydrogenphosphite 417 phosphite—phosphoric acid—water (1/1/1) the angle between the two phenyl rings of the dpg cation having the syn-atiti conformation is 80.9(2)°, and in the Perchlorate and bifluoride salts the corresponding angles are 63.6(2)° and 77.18(8)°, respectively. which shows the flexibility of the cation to addapt to different crystalline environments. The geometry of the anion is unexceptional. It features two short Ρ — Ο bonds and a larger one ( P I — O l ) , corresponding to the unionized P O H group. The anions and cations are l inked by an intrincate threedimensional network of hydrogen bonds. The strongest H-bond interconnects the anions with an O—O distance of 2.547(3) Ä. The Ν · · Ό distances of the Η-bonds involving the amino groups are in the range 2 . 716 Ä 2 . 747(2) Ä. The two bare Ο atoms of the dyhydrogenphosphite anion accept two protons each. One of the Η-atoms of the guanidnium NH2 group is not involved in hydrogen bonding, which is unusual, as dpg compounds typically fully exhaust the potential for hydrogen-bonding of the NH