Synthesis, NMR and single crystal X-ray structural studies on planar NiS4 and NiS2PN chromophores: Steric and electronic effects

The planar nickel(II) complexes [Ni(echdtc)2] (1) and [Ni(echdtc)(PPh3)(NCS)] (2), (where echdtc = ethylcyclohexyl dithiocarbamate) have been prepared, characterized by elemental analysis, electronic, IR and NMR (1H, 13C, and 31P) spectra, and their structures have been determined by single crystal X-ray crystallography. Both the complexes are diamagnetic and planar. The characteristic thioureide bands occur at 1485 and 1504 cm1 for (1) and (2), respectively. NMR spectra of the complexes show the (N)13CS2- chemical shifts at 206.29 and 202.68 ppm for (1) and (2), respectively. The 31P chemical shift for (2) was observed at 22.51 ppm, indicating a strong interaction. Electronic spectra of complexes (1) and (2) show signature bands at 412 and 478 nm, corresponding to dz 2?dxy/dx2—y2 transitions. Single crystal X-ray structures of [Ni(echdtc)2] (1) and [Ni(echdtc)(PPh3)(NCS)] (2) indicate that the central atom is in a planar environment in the complexes. In both complexes, the Ni–S distances are significantly different due to steric and electronic effects of the donors. Complex (2) is asymmetric with respect to the Ni–S distances, attributed to the trans influence exerted by PPh3 and NCS. The decrease in the S–Ni–S bite angle [78.63(3)] for (2) compared to that of (1) [79.19(2)] is due to steric crowding around the metal center. The P–Ni–S angle, 170.91(3), clearly shows the steric influence of the triphenylphosphine, which contrasts well with the much cramped S–Ni–S angle of 78.63(3).