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 their excited-state properties in a nanosecond time domain have been investigated. These new compounds were synthesized by following a “building 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 investigated. These new trimetallic complexes, [(CN) 4 Fe II (BL(1))Ru II (bpy)(BL(2))Rh III (tpy)(MQ + )](PF 6 ) 4 (tpy = 2,2‘:6‘:2‘‘-terpyridine; BL(1) = 2,3-bis(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 group, the tetracyanoferrate(II) unit; (ii) an antenna fragment, the Ru(II) polypyridyl moiety; and (iii) an electron acceptor group. The electron acceptor group is a Rh(III) polypyridyl that contains the ligands tpy and MQ + . No emission was observed in any of the reported complexes either in fluid solutions at room temperature or in glassy solutions at 77 K. Time-resolved experiments conducted on these triads showed formation of a transient intermediate within the laser pulse. Redox properties and transient absorption observations helped us to identify the nature of this intermediate as an Fe(III)/Ru(II) mixed-valence species that decays exponentially by following a first-order law with a lifetime of τ ≤ 70 ns in fluid solution at room temperature.