Magnetostructural studies of palladium(ii) and platinum(ii) complexes of verdazyl radicals

Abstract

The synthesis, structures, and magnetic properties of several Pd(II) and Pt(II) complexes of verdazyl radicals are presented. Reactions of bidentate verdazyl radicals with (RCN)₂MCl₂ (R = Me or Ph; M = Pd or Pt) produced square planar (verdazyl)MCl₂ complexes, three based on palladium and two on platinum. Solution spectroscopic studies indicate that the verdazyl ligand is substitutionally labile in the donor solvent acetonitrile but not in methylene chloride. The EPR and electronic spectra of three palladium complexes suggest minimal perturbation of the verdazyl chromophore, but there appears to be a significant Pt-verdazyl interaction based on perturbations of the electronic and EPR spectra. In the solid state the complexes assemble into different kinds of π-stacked architectures: four of the five complexes are based on weakly associated dimeric units while one is a one-dimensional π stack. In addition there are two modes of π stacking based on close contacts between neighbouring molecules, either M–M or M–N(verdazyl). Variable temperature magnetic susceptibility studies reveal relatively weak magnetic interactions which can be correlated with the mode of stacking. In one instance weak ferromagnetic exchange is observed and is rationalized based on a combination of spin leakage onto the platinum and the mode of stacking which facilitates a ferromagnetic interaction.