Changes in excited-state character of M(L1)(L2)(CO)2(-diimine) (M=Ru, Os) induced by variation of L1 and L2

J. VAN SLAGEREN; F. HARTL; D.J. STUFKENS; D.M. MARTINO; H. VAN WILLIGEN

COORDINATION CHEMISTRY REVIEWS

Año: 2000 vol. 208 p. 309 - 320

0010-8545

The character of the lowest excited state of the d6-complexes [M(L1)(L2)(CO)2(a-diimine](MRu, Os) varies with L1 and L2. In the case of [Ru(Cl)(Me)(CO)2(a-diimine)] it haspredominant metal-to-ligand charge transfer (MLCT) character. For [M(SnPh3)2CO)2(a-diimine)](MRu, Os), having two axial SnPh3 ligands, it has s(SnMSn)p*(a-diimine)(Sigma-Bond-to-Ligand Charge Transfer, SBLCT) character. In a glass at 90 K the emissionlifetimes of the [Ru(SnPh3)2(CO)2(a-diimine)] complexes are nearly a thousand times longerthan those of the corresponding [Ru(Cl)(Me)(CO)2(a-diimine)] compounds, although theiremission energies are very similar. In fact, these lifetimes are extremely long (e.g. t1070 msfor [Ru(SnPh3)2(CO)2(4,4%-dimethyl-2,2%-bipyridine)]) for a CT state. Although replacementof Ru by Os decreases both the emission energy and lifetime of complexes such as[M(bpy)3]2 (MRu, Os), only the emission lifetime decreases in the case of the[M(SnPh3)2CO)2(a-diimine)] compounds. The latter effect is due to the increase of spin-orbitcoupling (SOC), the influence of which could thus be studied without taking into accountany energy-gap-law effect. Preliminary photophysical data are presented for[Pt(SnPh3)2(Me)2(i-Pr-DAB)], which has very similar excited state properties as the corresponding Ru- and Os-complexes. Replacement of a SnPh3 ligand by a methyl group to give[Ru(Me)(SnPh3)(CO)2(i-Pr-DAB)] increases the photoreactivity of the complex. The weakerRuMe bond is broken homolytically and the formation of methyl radicals was studied indetail with FT-EPR spectroscopy. © 2000 Elsevier Science S.A. All rights reserved.