SYNTHESIS OF, CHARACTERIZATION OF, AND PHOTOINDUCED PROCESSES IN POLYMETALLIC TRIAD COMPLEXES CONTAINING FE(II), RU(II), AND RH(III) METAL CENTERS

A series of new trimetallic mixed complexes containing Fe(II), Ru(II), and Rh(III) metal centers have been prepared and characterized, and t heir excited-state properties in a nanosecond time domain have been in vestigated. These new compounds were synthesized by following a ''buil ding block'' strategy from monomeric Rh(III) and Ru(II) polyazines and tetracyanoferrate(II) ions. The products generated in each synthetic step were fully characterized and their excited-state properties inves tigated. These new trimetallic complexes, L(1))Ru-II(bpy)-(BL(2))Rh-II I(tpy)(MQ(+))](PF6)(4) (tpy = 2,2':6':2 ''-terpyridine; BL(1) = 2,3-bi s(2-pyridyl)pyrazine (dpp) or 2,2'-bipyrimidine (bpm); BL(2) = dpp or bpm; MQ(+) = N-methyl-4,4'-bipyridinium (monoquat)), consist of three fundamental parts linked by bridging ligands (i) an electron donor gro up, the tetracyanoferrate(II) unit; (ii) an antenna fragment, the Ru(I I) polypyridyl moiety; and (iii) an electron acceptor group. The elect ron acceptor group is a Rh(III) polypyridyl that contains the ligands tpy and MQ(+). No emission was observed in any of the reported complex es either in fluid solutions at room temperature or in glassy solution s at 77 K. Time-resolved experiments conducted on these triads showed formation of a transient intermediate within the laser pulse. Redox pr operties and transient absorption observations helped us to identify t he nature of this intermediate as an Fe(III)/Ru(II) mixed-valence spec ies that decays exponentially by following a first-order law with a li fetime of tau less than or equal to 70 ns in fluid solution at room te mperature.