Crystal structure of catena-poly[N,N,N′,N′-tetramethylguanidinium [(chloridocadmate)-di-μ-chlorido]]

The structure of the title salt, {(C5H14N3)[CdCl3]}n, consists of infinite zigzag polyanionic 1 ∞[CdCl4/2Cl1/1]− chains held together by tetramethylguanidinium cations through N—H⋯Cl hydrogen bonds, leading to a layered structure parallel to (010).


Chemical context
Tetramethylguanidine is known to crystallize in its neutral form, as a Lewis base or as a singly protonated cation. Several cationic complexes of Pd, Ga and Pt have been reported with tetramethylguanidine acting as a ligand (Li et al., 2005;Cowley et al., 2005;Eliseev et al., 2013), and halogenidometalates have been reported with tetramethylguanidinium as a countercation (Bujak et al., 1999;Bujak & Zaleski, 2007). Since none of these complexes has cadmium as a component, we decided to study the interactions between tetramethylguanidine and [CdCl 2 ]ÁH 2 O, which has yielded the title salt, (C 5 H 14 N 3 ) + [CdCl 3 ] À , (I).

Structural commentary
The asymmetric unit of (I) (Fig. 1) consists of a Cd II cation surrounded by four Cl atoms and one N,N,N 0 ,N 0 -tetramethylguanidinium cation. The coordination polyhedron around Cd II can be described best as a distorted trigonal bipyramid where atoms Cl1, Cl2 and Cl4 define the equatorial plane while atoms Cl3 and Cl4 i [symmetry code: (i) 3 2 À x, 1 2 À y, 1 À z] are in axial positions with a Cl3-Cd1-Cl4 i angle of 166.347 (10) . The equatorial Cd-Cl bond lengths range from 2.4829 (4) Å to 2.5829 (4) Å while the axial bond lengths Cd1-Cl3 and Cd1-Cl4 i are 2.5854 (4) Å and 2.6403 (4) Å , ISSN 2056-9890 respectively. The CdCl 4 moieties of the asymmetric unit are related by an inversion center, generating an extended zigzag chain of edge-sharing trigonal bipyramids running parallel to [101]. These 1 1 [CdCl 4/2 Cl 1/1 ] À chains are formed by the bridging atoms Cl2, Cl3, Cl4 and Cl4 i with a Cd-Cd-Cd angle of 137.893 (6) . The corrugation of the chains results in rather short CdÁ Á ÁCd distances of 3.8720 (3) and 3.8026 (3) Å . The same kind of zigzag chain is found, for example, in the [CdCl 3 ] À salt obtained with benzyltriethylammonium as counter-cation (Sun & Jin, 2013) but with a less pronounced corrugation. Accordingly, the angle between two successive rectangular [Cd 2 Cl 2 ] units is 57.928 (3) in the structure of the benzyltriethylammonium compound compared with 129.859 (2) for the present structure. The tetramethylguanidinium cation has the central atom C1 in an almost trigonal-planar configuration. The three N-C-N angles range from 119.26 (14) to 121.14 (14) and the r.m.s deviation from the least-squares plane calculated with atoms C1, N1, N2 and N3 is only 0.005 Å . The corresponding C-N bond lengths of 1.330 (2), 1.3360 (19), and 1.3441 (19) Å indicate a partial double-bond character. Hence the positive charge may be considered as delocalized in the CN 3 plane (Tiritiris, 2012). The two pairs of dimethylammonium groups are twisted by 24.67 (8) and 27.31 (9) with respect to this plane.

Figure 2
Partial packing diagram of (I), viewed along [

Synthesis and crystallization
Crystals suitable for a single-crystal X-ray diffraction study were obtained by mixing stoichiometric amounts of tetramethylguanidine with CdCl 2 ÁH 2 O in ethanol and allowing the solvent to evaporate slowly at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The H-atom positions of all methyl groups were placed geometrically and refined with U iso (H) = 1.5U eq (C). H atoms bonded to the N atoms were located from a Fourier difference map and were refined freely.

Special details
Experimental. X-ray crystallographic data for I were collected from a single-crystal sample, which was mounted on a loop fiber. Data were collected using a Bruker Venture diffractometer equipped with a Photon 100 CMOS Detector, a Helios MX optics and a Kappa goniometer. The crystal-to-detector distance was 4.0 cm, and the data collection was carried out in 1024 x 1024 pixel mode. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.