Ruthenium(II/III)-bipyridine complexes with four-membered sulphur donor co-ligands: synthesis, metal valence preference, spectroscopic and electron-transfer properties

A group of stable ruthenium(II) and (III) mixed-ligand tris-chelaled comple xes of the type [Run+(bpy)(L)(2)](z+) (1-8. n=2, Z=0; 9, n=3, Z=1) have bee n synthesized and characterized (bpy=2,2'-bipvridine; L = anionic form of t he ligands, ROC(S)SK, (R=Me, Et, Pr-n, Pr-i, Bu-n, Bu-i, CH2-Ph) or (EtO)(2 )P(S)SNH4 or (Et)(2)NC(S)SNa). The complexes 1-8 are diamagnetic and electr ically neutral and the complex 9 is one-electron paramagnetic and behaves a s 1:1 electrolyte in acetonitrile solvent. The complexes. 1-8 and 9 display two MLCT transitions near 530, 370 nm and 663, 438 nm respectively. Intra- ligand bipyridine based pi-pi* transition is observed near 300 nm. The comp lexes 1-8 exhibit room-temperature emission from the highest energy MLCT ba nd (similar to 370 nm). At room temperature the lifetime of the excited sta tes for the complexes 2 and 8 are found to be 90 and 95 ns respectively. In acetonitrile solution the complexes 1-9 show a reversible ruthenium(III)ru thenium(II) couple in the ranee - 0.08 --> 0.40 V and irreversible rutheniu m(III)-ruthenium(IV) oxidation in the ranee 1.19-1.45 V vs Ag/AgCl. One rev ersible bipyridine reduction is observed For each complex in the range -1.7 0 --> -1.85 V vs Ag/AgCl. The presence of trivalent ruthenium in the oxidiz ed solution for one complex 1 is evidenced by the axial EPR spectrum at 77 K, The isolated trivalent complex 9 also exhibits an axial EPR spectrum at 77 K. The EPR spectra of the trivalent ruthenium complexes (1(+) and 9) hav e been analyzed to finish values of distortion parameters (Delta(cm(-1))--> 1(+), 3689; 9. 3699) and energies of the two expected ligand field transiti ons (v(1)(cm(-1))-->1(+), 3489; 9, 3497 and v(2)(cm(-1))-->1(+), 4339; 9, 4 348) within the t(2) shell, One of the ligand field transitions has been ex perimentally observed at 4673 cm(-1) for complex 9 and which close to the c omputed v(2) value (4348 cm(-1)).(C) 1998 Elsevier Science Ltd. All rights reserved.