Bis{N,N,N-trimethyl-2-oxo-2-[2-(2,3,4- trihydroxybenzylidene)hydrazinyl]ethanaminium} tetrachloridozincate(II) methanol solvate1

The asymmetric unit of the title compound, (C12H18N3O4)2[ZnCl4]·CH3OH, consists of two Girard reagent-based cations, a tetrachloridozincate anion and a molecule of methanol as solvate. These components are interconnected in the crystal structure by an extensive network of O—H⋯O, N—H⋯O, C—H⋯O, O—H⋯N, O—H⋯Cl, N—H⋯Cl and C—H⋯Cl hydrogen bonds. The shortest intermolecular interaction is realized between the cation and anion [H⋯Cl = 2.29 (5) Å; O—H⋯Cl = 167 (3)°]. C—H⋯O interactions also play a important role in the interconnection of the cations.


Comment
The Schiff base derivatives of Girard reagent are recently investigated as ligands in coordination chemistry (Vojinović et al., 2004 and references therein;Leovac et al., 2006Leovac et al., , 2007Revenko et al., 2009;Vojinović-Ješić et al., 2008, 2010. Considering the specific distribution of charge and simultaneous presence of several donor and acceptor atoms these compounds are able to build extensive hydrogen bonding networks consisting of various types of interactions. The asymmetric unit of the title compound is given in Fig. 1. Two crystallographically independent cations (A and B) display very similar geometry. The bond lengths and angles within the aliphatic parts of the cations are consistent with those of two previously reported Girard-T based hydrazones (Leovac et al., 2007;Revenko et al., 2009).
Excluding the quaternary ammonium groups, non-hydrogen atoms of two cations (A and B) lie in plane, i.e. the rootmean-square deviations of fitted atoms 0.1Å or less. These approximately planar forms of the molecules are stabilized by number of intramolecular hydrogen bonds with the shortest being O4-H4···N1 (see Table 1). The C9-N3 bonds are single and allow for free rotation of the N(CH 3 ) 3 ) moiety (as was observed in complexes (Leovac et al., 2007), yet in each of the cations the deviation of the quaternary ammonium groups is restrained due to intramolecular C-H···O interactions.
Anion (ZnCl 4 ) 2exhibits regular tetrahedral geometry with Zn-Cl distances comparable to similar anions (Jin et al., 2005;Valkonen et al., 2006). Through O-H···Cl, N-H···Cl and C-H···Cl hydrogen bonds the anion intermediates between five different cations. The strongest among these interactions is rather short and directional O5A-H5A···Cl2 i (symmetry code: (i) -x, -y+1, -z) (see Table 1). It is worth noticing that the hydroxyl hydrogen involved in this interaction is the only one (from the six in totals) which significantly deviates from the trihydroxybenzyl moiety.
In the crystal packing, centrosymmetrically related cationic molecules, by C-H···O interactions, with H···O distances all shorter than 2.7Å, associate into corresponding AA and BB dimers. The distances between the parallel planes (passing trough all atoms except N(CH 3 ) 3 ) are 3.386 (8) and 3.194 (7)Å for AA and BB dimers respectively. The pairs of AA and BB dimers further arrange in approximately parallel fashion (angle between planes of A and B molecule is 0.92 (8)°) along the c axis with the closest distance between non-H atoms of 3.407 (5)Å (Fig. 2.). The C-H···O hydrogen interactions relating the dimers mainly include the methyl groups from the quaternary ammonium fragment and oxygen O6 which is in para-position concerning the aliphatic fragment.

supplementary materials sup-2 Refinement
The H atoms bonded to O atoms of trihydroxybenzyl groups and H atoms bonded to N2 atoms (cations A and B) were located in difference map and refined isotropically. C-bound H atoms were placed in calculated positions (C-H 0.93Å, 0.96Å & 0.97Å) and refined as riding, with U iso (H) = 1.2(or 1.5)U eq (C). The refinement of the methanol H resulted in unrealistic positional and thermal parameters, therefore the position of this atom was determined geometrically -O7-H7=0.82Å and U iso (H7) equal to 1.5U eq (O7). Fig. 1. The molecular structure of title compound with atom labels. Displacement ellipsoids are drawn at 50% probability level. H atoms are presented as a small spheres of arbitrary radius. The intramolecular H-bonds are indicated as dashed lines. Crystal data (C 12

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.