Large d-d luminescence energy variations in square-planar bis(dithiocarbamate) platinum(ii) and palladium(ii) complexes with near-identical MS4 motifs: a variable-pressure study.

We present the variable-pressure luminescence spectra of crystals of isostructural palladium(ii) and platinum(ii) complexes with bis-N-benzyl-N'-3-methylpyridyldithiocarbamate (bmpDTC) ligands. The d-d luminescence band maxima Emax for these complexes are compared to others with different peripheral substituents on the dithiocarbamate ligands in the solid state. The comparison reveals significant variations of Emax despite very similar metal coordination geometries. Emax varies by 3000 cm-1 and 1300 cm-1 among four dithiocarbamate complexes of platinum(ii) and palladium(ii), respectively. Variations of Emax with pressure reveal the effects of intermolecular MH-C interactions on several complexes. ΔEmax/ΔP values are negative for the bmpDTC complexes, unprecedented in the dithiocarbamate family. Static orientation and pressure-induced movement of the C-H bonds involved in intermolecular interactions have a significant effect on Emax and ΔEmax/ΔP, with a stronger impact on platinum(ii) complexes than on their palladium(ii) analogs.