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 (ν_c-s ≃ 1095 cm⁻¹ without splitting) of the dithiocarbamate moiety. The important stretching mode characteristic of the thioureide bond (ν_C–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⁻.

Keywords:

• Nickel(II)
• Dithiocarbamates
• Cyanide-N
• Thiocyanate-N
• Thioureide
• X-ray crystal structure