Effect of phenyl and benzyl group in heterocyclic dithiocarbamates on the ZnS4N chromophore: Synthesis, spectral, valence-bond parameters and single crystal X-ray structural studies on (pyridine)bis(1,2,3,4-tetrahydroquinolinedithiocarbamato)-zinc(II) and (pyridine) bis(1,2,3,4-tetrahydroisoquinolinedithiocarbamato)zinc(II)

Two Zn(II)dithiocarbamates with ZnS4N chromophores have been synthesized ([Zn(thqdtc)(2)(py)] (1) and [Zn(thiqdtc)(2)(py)] (2) (where thqdtc = 1,2,3,4-tetrahydroquinolinedithiocarbamate, thiqtc = 1,2,3,4-tetrahydroisoquinolinedithiocarbamate and py = pyridine)) from [Zn(thqdtc)(2)] (3) and [Zn(thiqdtc)(2)] (4), respectively. Their Structures and properties have been characterized by IR and NMR spectra. The structures of both the complexes were determined by single crystal X-ray crystallography. The observed deshielding of the H-2 protons for 1 and 3 and H-1 and H-3 protons for 2 and 4 in the H-1 NMR spectra is attributed to the drift of electrons from the nitrogen of the NR2 group, forcing a high electron density towards sulfur via the thioureide pi-system. In the C-13 NMR spectra, the most important thioureide (N (CS2)-C-13) carbon signals are observed in the region 204-207 ppm. The upfield shift of NCS2 carbon signal for 1 (204.2 ppm) from the chemical shift Value of 2 (206.9 ppm) is due to electron withdrawing resonance effect of phenyl ring thereby decreasing the double bond character in tetrahydroquinolinedithiocarbamate, whereas benzyl group in tetrahydroisoquinolinedithiocarbamate cannot participate in resonance delocalization in the same way. Single crystal X-ray structural analysis of 1 and 2 showed that the zinc atom is pentacoordinated with four sulfur atoms from the dithiocarbamate ligands and one nitrogen atom from the pyridine. VBS values support the correctness of the determined structure. The lower VBS Value of 2 is due to the steric effect exerted by the thiqdtc. The phenyl and benzyl group in the heterocyclic dithiocarbamates influences the electronic properties of 1 and 2. The shift of v(C)-(N)(thioureide) and thioureide (NCS2)-C-13 carbon signals are correlated with the electronic effects of the dithiocarbamate ligands. (c) 2008 Elsevier B.V. All rights reserved.