Crystal structure of dichloridobis(1,3-diazinane-2-thione-κS)cadmium

In dichloridobis(1,3-diazinane-2-thione-κS)cadmium(II), the CdII atom is bound to two chloride anions and two thione ligands via their S atoms. The geometry around the CdII atom is distorted tetrahedral, with the bond angles in the range 101.61 (3)–118.00 (3)°. Intramolecular N—H⋯Cl hydrogen-bonding interactions stabilize a butterfly syn molecular conformation.


Chemical context
Cadmium is considered to be a soft Lewis acid and possesses high affininty towards sulfur donor ligands such as thiones. Upon exposure to living systems, it preferablly interacts with sulfur-containing biomoleules. Therefore, complexes of cadmium with thiones are important as structural models to understand metal-sulfur interactions in biological systems (Akrivos, 2001;Bell et al., 2004). In view of this, the crystal structures of several cadmium complexes of thiones, such as imidazolidine-2-thione (Imt) and 1,3-diazinane-2-thione (Diaz), have been reported Al-Arfaj et al., 1998;Bell et al., 2004;Lobana et al., 2008;Malik et al., 2010;Mahmood et al., 2012Mahmood et al., , 2015Wazeer et al., 2007). The complexity of structures of the L 2 CdX 2 type (where L is a thione and X is a halide or pseudohalide) ranges from mononuclear tetrahedral complexes to polymeric octahedral species. We have reported recently the crystal structures of three cadmium complexes of Diaz, namely, [CdI 2 (Diaz) 2 ], [Cd(CH 3 COO) 2 (Diaz) 2 ] and [Cd(Diaz) 4 ]SO 4 Mahmood et al., 2012Mahmood et al., , 2015. To learn more about the structural aspects of cadmium complexes, we report here the crystal structure of a cadmium chloride complex of 1,3-diazinane-2-thione, i.e. [CdCl 2 (Diaz) 2 ], (I). The spectroscopic properties of the compound have been reported previously (Wazeer et al., 2007).

Structural commentary
In the molecular structure of (I) (Fig. 1), the Cd II atom is bonded to two S atoms, each belonging to a Diaz molecule, and two chloride ions. The coordination geometry at the Cd II ISSN 2056-9890 atom is distorted tetrahedral, with the following bond angles: S-Cd-S = 105.08 (3) , Cl-Cd-Cl = 101.61 (3) and S-Cd-Cl in the range 108.91 (2)-118.00 (3) . The Cl-Cd-Cl bond angle is significantly smaller than the other bond angles, which could be due to the involvement of Cl in intramolecular (N-HÁ Á ÁCl) hydrogen bonding. The Cd-S and Cd-Cl bond lengths are in agreement with those reported for related compounds Al-Arfaj et al., 1998;Bell et al., 2004;Lobana et al., 2008;Malik et al., 2010;Mahmood et al., 2012Mahmood et al., , 2015Wazeer et al., 2007). The two Diaz six-membered rings adopt half-chair conformations. In one of the two rings (the one involving atom S2), two of the methylene C atoms (C7 and C8) are disordered over two positions. The SCN 2 moieties of the Diaz ligands are essentially planar and the corresponding C-S and C-N bond lengths are in the ranges 1.730 (3)-1.731 (3) and 1.318 (3)-1.327 (3) Å , respectively. The C-S bond length is slightly longer than in the free ligand [1.720 (2) Å [Popovic et al., 2001]. The shorter N-C(S) bond length compared to N-C(C) [1.456 (4) Å ] is consistent with a significant N-C(S) double-bond character associated with an electronic delocalization towards the metal ion upon coordination. Compound (I) is related to that of the reported complexes [ZnCl 2 (Diaz) 2 ]  and [CdI 2 (Diaz) 2 ]  that both crystallize in space group C2/c. They show an equivalent degree of distortion from tetrahedral configuration as in (I). However, in [CdCl 2 (Dmtu) 2 ] and [CdBr 2 (Dmtu) 2 ] (Dmtu = N,N 0 -dimethylthiourea), the coordination geometry at the Cd II atom is almost perfectly tetrahedral Malik et al., 2010).

Supramolecular features
Compound (I) shows both intra-and intermolecular hydrogen-bonding interactions. One chloride anion (Cl2) is engaged in intramolecular N-HÁ Á ÁCl hydrogen-bonding interactions with one N-H group of each of the two Diaz ligands (Table 1). This results in a butterfly syn conformation, where the two Diaz six-membered rings reside on the same side of the CdS 2 plane. When such interactions are not effective, an anti conformation may be observed, where the two Diaz rings are located anti relative to the CdS 2 plane. This situation is observed in [CdI 2 (Diaz) 2 ] . The second chloride (Cl1) anion undergoes intermolecular hydrogen-bonding interactions with one N-H group of a Diaz ligand belonging to an adjacent complex molecule, hence generating a chain structure along the a axis (Fig. 2). Furthermore, zigzag interchain N-HÁ Á ÁS interactions take place, giving rise to a three-dimensional hydrogen-bonding network.

Figure 1
A view of the molecular structure of the title compound, showing the atom-numbering scheme. The displacement ellipsoids are drawn at the 50% probability level. The minor-occupancy C atoms are connected by dashed lines.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 2. The crystal under investigation was found to be twinned by non-merohedry. The orientation matrices for the two components were identified using the program CELL NOW (Sheldrick, 2005), with the two components being related by a 180 rotation around the real/ reciprocal axis [104]/(001). The two components were integrated using SAINT resulting in the following statistics: 7087 reflections (2024 unique) involved domain 1 only (mean I/ = 23.7), 6799 reflections (1938 unique) involved domain 2 only (mean I/ = 8.6) and 6567 reflections (1969 unique) the two domains (mean I/ = 23.2). The exact twin matrix identified by the integration program was found to be 1.00176 À0.00043 0.00606, À0.00069 À1.00042 0.00237, À0.52475 À0.00141 À1.00198. The structure was solved using direct methods with only the non-overlapping reflections of component 1. The structure was refined using the hklf 5 routine with all reflections of component 1 (including the overlapping ones) resulting in a BASF value of 0.1134 (6).
The C atoms of one Diaz moiety (C6/C7/C8) are disordered over two sets of sites, with an occupancy ratio of 0.715 (11): 0.285 (11). Atoms N3A and N4A were constrained to have identical positions and displacement parameters as their equivalent partners in the major moiety, but their H atoms were included in the disorder model. Major and minor moieties were restrained to have similar geometries [SAME command in SHELX2014 (Sheldrick, 2015)], and their atoms were subjected to a rigid-bond restraint (RIGU command in SHELX2014). The anisotropic displacement parameters of these C atoms were also subjected to a rigid-bond restraint (RIGU).

Dichloridobis(1,3-diazinane-2-thione-κS)cadmium
Crystal data 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 R-factors(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.