Synthesis, spectroscopic characterisation, electron-transfer properties and crystal structure of [Ru^II(bipy)₂(2-SC₅H₄N)] ClO₄ (bipy = 2,2´ -bipyridine)

Abstract

Two new ruthenium(II) mixed-ligand tris-chelated complexes of the type [Ru(bipy) ₂ L]ClO ₄ , (bipy = 2,2'-bipyridine; L = pyridine-2-thiolate 1 or pyridin-2-olate 2) have been synthesized. The complexes are essentially diamagnetic and behave as 1:1 electrolytes in acetonitrile solution. They display two metal-to-ligand charge-transfer (m.l.c.t.) transitions near 500 and 340 nm respectively along with intraligand transitions in the UV region. Both exhibit room-temperature emission from the highest-energy (m.l.c.t.) band. At room temperature the lifetime of the excited states for the thiolato (1) and phenolato (2) complexes are 100 and 90 ns respectively. The geometry of the complexes in solution has been assessed by high-resolution ¹ H NMR spectroscopy. The molecular structure of complex 1 in the solid state has been determined by single-crystal X-ray diffraction. It shows the expected pseudo-octahedral geometry with considerable strain due to the presence of the sterically hindered ligand L ¹ . In acetonitrile solution the complexes show quasi-reversible ruthenium(II)-ruthenium(III) oxidation couples at 0.54 and 0.64 V versus saturated calomel electrode and quasi-reversible ruthenium(III)-ruthenium(IV) oxidations at 1.41 and 1.03 V respectively. Two reversible reductions are observed near -1.6 and -1.9 V for each complex due to electron transfer to the co-ordinated bipy units. The trivalent analogues of 1 and 2 are unstable at room temperature but can be generated in solution by coulometric oxidation at 263 K as evidenced by EPR spectroscopy.