Effect of position of methyl substituent in piperidinedithiocarbamate on the ZnS4N chromophore: Synthesis, spectral, valence-bond parameters and single crystal X-ray structural studies on bis(2-methylpiperidinecarbodithioato-S,S′)-(pyridine)zinc(II) and b

Two Zn(II)monomethyl substituted piperidinedithiocarbamates with ZnS4N chromophores have been synthesized ([Zn(2-mpipdtc)2(py)] (1) and [Zn(4-mpipdtc)2(py)] (2) (where 2-mpipdtc = 2-methylpiperidinedithiocarbamate, 4-mpipdtc = 4-methylpiperidinedithiocarbamate and py = pyridine)) from [Zn(2-mpipdtc)2] and [Zn(4-mpipdtc)2], respectively. Their structures and properties have been characterized by IR, 1H and 13C NMR spectroscopy. The structures of both the complexes were determined by single crystal X-ray crystallography. IR spectra of the complexes 1 and 2 show the thioureide νC–N band at 1431 and 1445 cm−1, respectively. In the case of complex 1, the thioureide νC–N values are shifted to lower wave number compared to 2. This may be due to the steric effect of the ortho-methyl group in the 2-mpipdtc resulting in a decrease in the double bond character of the C–N bond. The methyl protons are more deshielded in 1 (1.28 ppm) than that found in 2 (0.98 ppm), due to deshielding decrease with increase in distance from the metal centre. The 13C NMR peaks of the group N13CS2 are found in both cases, at around 202 ppm, which indicates the bidentate character of the ligands. Single crystal X-ray structural analysis of 1 and 2 showed that the zinc atom is pentacoordinated with four sulfur atoms from the dithiocarbamate and one nitrogen atom from the pyridine. Both the complexes adopt a geometry which is intermediate between the tetragonal pyramid (C4v) and trigonal bipyramid (D3h). From the τ values, the coordination geometry of 1 and 2 is described as being 38.9% and 36.1% along the pathway of distortion from tetragonal pyramid toward trigonal bipyramid.