Steric and electronic effects of N -coordinated NC − and NCS− on NiS2PN: synthesis, spectral and single crystal X-ray structural studies on N , N ′-di- n -butyldithiocarbamate complexes of nickel(II) with phosphorus and nitrogen donor ligands

Abstract

Planar nickel(II) complexes involving N,N′-dibutyldithiocarbamate, such as [Ni(bu2dtc)(PPh3)(NC)] (1) and [Ni(bu2dtc)(PPh3)(NCS)] (2) (where bu2dtc = N,N′-dibutyldithiocarbamate anion) have been prepared, characterized by electronic, IR and NMR spectra and their structures determined by single crystal X-ray crystallography. Cyclic voltammetric characterizations of the complexes are also reported. IR spectra of the two complexes indicate the isobidentate coordination (νc-s ≃ 1095 cm−1 without splitting) of the dithiocarbamate moiety. The important stretching mode characteristic of the thioureide bond (νC–N) occurs at higher wave numbers compared to that of the parent dithiocarbamate complex [Ni(bu2dtc)2]. The electronic spectra of 1 and 2 show signature bands at 426 nm and 478 nm, respectively. NMR spectra show large 31P chemical shifts in both compounds and the most important N13CS2 chemical shift appears at 204.86 ppm and 203.23 ppm for 1 and 2, respectively. The CV studies clearly show the presence of reduced electron density on the nickel ions in mixed-ligand complexes 1 and 2 compared to the parent dithiocarbamate. Single crystal X-ray structure studies show that 2 crystallizes as a new triclinic polymorph, whose molecular structure closely resembles that of the previously reported monoclinic form. Both complexes contain a planar NiS2PN chromophore in keeping with the observed diamagnetism. In both complexes the Ni-S distances are significantly different. The thioureide C–N distances of the complexes are shorter than those observed in the parent [Ni(bu2dtc)2]. The two compounds allow comparison of the influence of NCS− in place of NC−.