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

Wassim Z. Alsindi, Timothy L. Easun, X. Z. Sun, Kate L. Ronayne, Michael Towrie, Juan Manuel Herrera, Michael W. George, Michael D. Ward

Research output: Journal PublicationArticlepeer-review

30 Citations (Scopus)

Abstract

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′-(CONEt 2)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)3CIRe I(bpm•-)ReII(CO)3Cl] whose lifetime is 46 ps. The cyanoruthenate complexes 2 and 5 show comparable behavior, with a shift of the ν(CN) bands to higher energy in the excited state for mononuclear 2 but two sets of transient bands - one to higher energy and one to lower energy-in dinuclear 5, consistent with an asymmetric charge distribution [(NC)4RuII(bpm•-)Ru III(CN)4]4- in the 3MLCT state. These cyanoruthenate complexes have much longer lifetimes in D2O compared with CH3CN, viz., 250 ps and 3.4 ns for 2 and 65 ps and 1.2 ns for 5 in CH3CN and D2O, respectively. In complex 3, both higher-energy Ru → bpyam and lower-energy Ru → bpm 3MLCT states are formed following 400 nm excitation; the formr decays rapidly (τ = 6-7 ps) to the latter, and the subsequent decay of the Ru → bpm 3MLCT state occurs with a lifetime of 60 or 97 ns in D2O or CH3CN, respectively. Similar behavior is shown by dinuclear 6 in both D2O and CH3CN, with initial interconversion from the Ru → bpyam to the Ru → ;bpm 3MLCT state occurring with τ ∼ 7 ps and the resultant Ru → bpm 3MLCT state decaying on the nanosecond time scale.

Original languageEnglish
Pages (from-to)3696-3704
Number of pages9
JournalInorganic Chemistry
Volume46
Issue number9
DOIs
Publication statusPublished - 30 Apr 2007
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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