Probing the excited states of d6 metal complexes containing the 2,2'-bipyrimidine ligand using time-resolved infrared spectroscopy. 1. Mononuclear and homodinuclear systems

This paper reports time-resolved infrared (TRIR) spectroscopic studies on a series of weakly luminescent or nonluminescent 2,2‘-bipyrimidine-based complexes to probe their electronic structure and the dynamic behavior of their excited states on the picosecond and nanosecond time scales. The complexes are mononuclear [Re(CO)3Cl(bpm)] (1), [Ru(CN)4(bpm)]2- (2), and [Ru(bpyam)2(bpm)]2+ (3) [bpm = 2,2‘-bipyrimidine; bpyam = 2,2‘-bipyridine-4,4‘-(CONEt2)2] and their homodinuclear analogues [{Re(CO)3Cl}2(μ-bpm)] (4), [{Ru(CN)4}2(μ-bpm)]2- (5), and [{Ru(bpyam)2}2(μ-bpm)]4+ (6). Complex 1 shows the characteristic shift of the three ν(CO) bands to higher energy in the Re → bpm triplet metal-to-ligand charge-transfer (3MLCT) state, which has a lifetime of 1.2 ns. In contrast, the dinuclear complex 4 shows ν(CO) transient bands to both higher and lower energy than the ground state indicative of, on the IR time scale, an asymmetric excited state [(OC)3ClReI(bpm•-)ReII(CO)3Cl] whose lifetime is 46 ps. The cyanoruthena...