Heteroleptic [Os(H)(CO)(N∧N)(tpp)2]+ and [Os(Cl)(CO)(N∧N)(tpp)2]+ 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 (N∧N) ligand were prepared from an OsCl2(CO)2(tpp)2 precursor. The investigated complexes, available in the form of PF6- salts, have been identified by means of FT-IR, 1H and 31P 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 N∧N 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 3*[Os(H)(CO)(N∧N)(tpp)2]+ and 3*[Os(Cl)(CO)(N∧N)(tpp)2]+ species.