Probing the Excited States of d6 Metal Complexes Containing the 2,2'-Bipyrimidine Ligand Using Time-Resolved Infrared Spectroscopy. 1. Mononuclear and Homodinuclear Systems
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- 作者：Wassim Z. Alsindi ; Timothy L. Easun ; X.-Z. Sun ; Kate L. Ronayne ; Michael Towrie ; Juan-Manuel Herrera ; Michael W. George ; Michael D. Ward
- 刊名：Inorganic Chemistry
- 出版年：2007
- 出版时间：April 30, 2007
- 年：2007
- 卷：46
- 期：9
- 页码：3696 - 3704
- 全文大小：138K
- 年卷期：v.46,no.9(April 30, 2007)
- ISSN：1520-510X
文摘
This paper reports time-resolved infrared (TRIR) spectroscopic studies on a series of weakly luminescent ornonluminescent 2,2'-bipyrimidine-based complexes to probe their electronic structure and the dynamic behavior oftheir 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(
-bpm)] (4), [{Ru(CN)4}2(-bpm)]2- (5), and[{Ru(bpyam)2}2(-bpm)]4+ (6). Complex 1 shows the characteristic shift of the three 
(CO) bands to higher energyin 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 (CO) transient bands to both higher and lower energy than the ground stateindicative of, on the IR time scale, an asymmetric excited state [(OC)3ClReI(bpm
ll.gif">-)ReII(CO)3Cl] whose lifetime is46 ps. The cyanoruthenate complexes 2 and 5 show comparable behavior, with a shift of the (CN) bands tohigher energy in the excited state for mononuclear 2 but two sets of transient bands-one to higher energy andone to lower energy-in dinuclear 5, consistent with an asymmetric charge distribution [(NC)4RuII(bpmll.gif">-)RuIII(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, bothhigher-energy Ru bpyam and lower-energy Ru bpm 3MLCT states are formed following 400 nm excitation;the former decays rapidly (
= 6-7 ps) to the latter, and the subsequent decay of the Ru bpm 3MLCT stateoccurs with a lifetime of 60 or 97 ns in D2O or CH3CN, respectively. Similar behavior is shown by dinuclear 6 inboth D2O and CH3CN, with initial interconversion from the Ru bpyam to the Ru bpm 3MLCT state occurringwith ~ 7 ps and the resultant Ru bpm 3MLCT state decaying on the nanosecond time scale.
-bpm)] (4), [{Ru(CN)4}2(-bpm)]2- (5), and[{Ru(bpyam)2}2(-bpm)]4+ (6). Complex 1 shows the characteristic shift of the three (CO) bands to higher energyin 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 (CO) transient bands to both higher and lower energy than the ground stateindicative of, on the IR time scale, an asymmetric excited state [(OC)3ClReI(bpmll.gif">-)ReII(CO)3Cl] whose lifetime is46 ps. The cyanoruthenate complexes 2 and 5 show comparable behavior, with a shift of the (CN) bands tohigher energy in the excited state for mononuclear 2 but two sets of transient bands-one to higher energy andone to lower energy-in dinuclear 5, consistent with an asymmetric charge distribution [(NC)4RuII(bpmll.gif">-)RuIII(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, bothhigher-energy Ru bpyam and lower-energy Ru bpm 3MLCT states are formed following 400 nm excitation;the former decays rapidly ( = 6-7 ps) to the latter, and the subsequent decay of the Ru bpm 3MLCT stateoccurs with a lifetime of 60 or 97 ns in D2O or CH3CN, respectively. Similar behavior is shown by dinuclear 6 inboth D2O and CH3CN, with initial interconversion from the Ru bpyam to the Ru bpm 3MLCT state occurringwith ~ 7 ps and the resultant Ru bpm 3MLCT state decaying on the nanosecond time scale.