Synthesis, structures and properties of a new series of platinum-diimine-dithiolate complexes

The new square-planar platinum–diimine–dithiolate compounds [Pt(mesBIAN)SS] have been synthesised {mesBIAN = bis(mesityl)biazanaphthenequinone; SS = 1,2-dithiooxalate (dto) 1, maleonitriledithiolate (mnt) 2, 1,2-benzenedithiolate (bdt) 3, 3,4-toluenedithiolate (tdt) 4 and 1,3-dithia-2-thione-4,5-dithiolate (dmit) 5}, and the X-ray crystal structures of 3 and 5 determined. Cyclic voltammetry reveals that all the compounds form stable anions, and ESR spectroscopy of these anions shows that the SOMO is based upon the mesBIAN ligand; compounds 2–5 also show a reversible oxidation wave in their CV. Computational studies reveal that charge-transfer processes from orbitals that are combinations of metal and dithiolate ligand to a mesBIAN π*-based LUMO are responsible for the low energy absorptions seen in the UV/visible spectra of these compounds, and that the reverse process is responsible for the observed room-temperature solution luminescence of [Pt(mesBIAN)Cl2] and 1, 2 and 5. Compounds 3 and 4, containing aromatic thiolates, were not found to luminesce under the same conditions. Resonance Raman experiments have shown the origin of band-broadening of the lowest-energy absorption band in the absorption spectra of 2–5 to be due to vibronic structure within one electronic transition