Dibromidobis(N,N,N′,N′-tetramethylthiourea-κS)cadmium(II)

In the title compound, [CdBr2(C5H12N2S)2], the CdII atom lies on a twofold rotation axis. It exhibits a distorted tetrahedral coordination environment defined by two S atoms of two tetramethylthiourea (tmtu) ligands and two bromide ions. The crystal structure is consolidated by C—H⋯N and C—H⋯S hydrogen bonds.


Comment
The coordination chemistry of thioureas with metal ions has been the subject of several recent investigations because of their variable binding modes and because of the relevance of their binding sites to those in living systems. Crystallographic reports about d 10 metal complexes of thioureas established that these ligands are coordinated via the sulfur atom (Al-Arfaj et al., 1998;Moloto et al., 2003). Spectroscopic data is also consistent with this finding Ali et al., 2009). Herein, we report the crystal structure of a cadmium bromide complex with tetramethylthiourea (tmtu), [Cd(C 5 H 12 N 2 S 2 ) 2 Br 2 ], (I).
The crystal structure of (I) consists of discrete molecular species in which the cadmium atom is located on a twofold rotation axis (Fig. 1). It exhibits a distorted tetrahedral coordination environment defined by two tetramethylthiourea (tmtu) ligands and two bromide ions. The tmtu ligand is terminally bound to the Cd II atom via coordination of the S1 atom. The Cd-S and Cd-Br bond lengths are 2.5580 (6) and 2.5735 (3) Å, respectively. These values are in agreement with those reported for related compounds, e.g. (Al-Arfaj et al., 1998;Lobana et al. 2008;Marcos et al., 1998;Moloto et al., 2003). The bond angles around Cd are indicative of a slight tetrahedral distortion, with the S-Cd-S angle showing the largest deviation (117.70 (3)°) from the ideal value. The SCN 2 -moiety of the tmtu ligand is essentially planar, the maximum deviation from the mean plane being 0.007 (2) Å for the carbon atom. The fragments N1-C1-C2-C3 and N2-C1-C4-C5 are also close to planarity. The maximum deviations from the mean planes are 0.072 (2) Å and 0.065 (2) Å for N1 and N2, respectively. These values are consistent with a significant C-N double bond character and electron delocalization in the SCN 2 -moiety. The steric effect of the two adjacent 1,3-methyl groups imposes a dihedral angle of 47.4 (2) ° for the two mean planes and therefore a tilted conformation. The latter is likely stabilized by non-classical intramolecular hydrogen bonding interactions involving methyl H atoms with sulfur and nitrogen atoms (C2-H2A ···N2 and C5-H5A···S1). The molecules pack to form columns approximately parallel to [110] direction (Fig. 2).
The structure of (I) is isotypic with [Cd(tmtu) 2 I 2 ] (Nawaz et al., 2010a), with an equivalent degree of distortion from the ideal tetrahedral configuration and similar Cd-S and C-N bond lengths. The tmtu bond lengths are also consistent with those found for the likewise isotypic compound [Hg(tmtu) 2 Cl 2 ] (Nawaz et al., 2010b), in which a significantly higher distortion of the metal ion coordination sphere is observed.
Experimental 0.35 g (1.0 mmol) cadmium(II) bromide tetrahydrate dissolved in 10 ml water were added to two equivalents of tetramethylthiourea in methanol. A white precipitate formed and was filtered off. The filtrate was kept for crystallization. As a result, an off-white crystalline product suitable for single crystal X-ray diffraction was obtained.

Refinement
H atoms were placed in calculated positions with a C-H distance of 0.96 Å and U iso (H) = 1.5 U eq (C). Fig. 1. The molecular structure of title compound with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. H-atoms are omitted for clarity.