Heteroleptic [Os(H)(CO)(NN)(tpp)] and [Os(Cl)(CO)(NN)(tpp)] complexes - comparative studies of their luminescence properties.

Two series of cationic heteroleptic osmium(ii) complexes with a coordinated CO molecule, a chloride Cl or hydride H anion, two monodentate triphenylphosphine (tpp) ligands and one bidentate α-dimine (NN) ligand were prepared from an OsCl(CO)(tpp) precursor. The investigated complexes, available in the form of PF salts, have been identified by means of FT-IR, H and P NMR spectroscopy and X-ray diffraction studies. Their photophysical properties have been investigated in dichloromethane solutions at room temperature and 1 : 1 ethanol-methanol matrices at 77 K. The investigated complexes exhibit metal to ligand charge-transfer (MLCT) phosphorescence with the emission characteristics distinctly affected by the nature of coordinated α-diimine NN and Cl or H ligands. Franck-Condon emission spectral band shape analyses and DFT/TD-DFT calculations have been applied to obtain more detailed insight into the nature of emissive *[Os(H)(CO)(NN)(tpp)] and *[Os(Cl)(CO)(NN)(tpp)] species.