Quantification of distortions associated with planar NiS4, NiS2NP and NiS2P2 chromophores: Synthesis, structural and CSM analysis

Planar, diamagnetic [Ni(dadtc)(PPh 3 )(NCS)] (1), [Ni(dadtc)(PPh 3 ) 2 ]ClO 4 (2) and [Ni(dadtc)(dppb)]ClO 4 (3) (where dadtc = diallyldithiocarbamate, PPh 3 = triphenyl phosphine, NCS = thiocyanate and dppb = (1,4-bis(diphenylphosphino)butane) have been synthesized and characterized by UV–vis, IR, 1 H, 13 C, 31 P NMR, CV, and thermal analysis. Solvothermal decomposition of the compounds yielded NiS. 1 H NMR signals showed the a -CH 2 protons to be the highly deshielded and 13 C NMR spectra showed the characteristic thioureide (N 13 CS 2 ) carbon signals around 200 ppm. 31 P chemical shifts showed the following order: (2) (29.4 ppm) > (3) (22.40 ppm) > (1) (12.7 ppm). Single crystal X-ray analysis of (1), (2) and (3) showed a distorted square planar coordination in the NiS 2 NP and NiS 2 P 2 chromophores. Deviation of the chromophore from square planar geometry towards tetrahedral geometry has been assessed for the first time by Continuous Symmetry Measure calculation in a scale of ‘0’ to ‘100’, which showed the following decreasing order from planarity: NiS 4 (0.894) ? NiS 2 P 2 (0.660) > NiS 2 NP (0.615) > NiS 2 P 2 (chelating dppb) (0.411). The CSM analysis reveals that the deviation from planarity is less than unity for all the chromophores. However, NiS 2 P 2 (chelating dppb) shows relatively the lowest deviation indicating chelate induced stability.