Abstract
Ru nitrosyl complexes were isolated in the RuNO6 and RuNO7 configurations, employing the following reaction pathway for Ru(trpy)(bik)(X)n+: X = Cl-, n = 1, 1(ClO4) $\rightarrow$ X = MeCN, n = 2, 2(ClO4)2 $\rightarrow$ X = NO2-, n = 1, 3(ClO4) $\rightarrow$ X = NO+, n = 3, 4(ClO4)3 $\rightarrow$ X = NO·, n = 2, 4(ClO4)2. The single-crystal x-ray structures of 1(ClO4)·(C6H6)·H2O, 2(ClO4)2·H2O, and 3(ClO4)·H2O were detd. The successive NO+/NO· (reversible) and NO·/NO- (irreversible) redn. processes of 43+ appear at +0.36 and -0.40 V vs. SCE, resp. While the n(C:O) frequency of the bik ligand at $\sim$1630 cm-1 is largely invariant on complexation and redn., the n(NO) frequency for the RuNO6 state in 43+ at 1950 cm-1 shifts to $\sim$1640 cm-1 on 1-electron redn. to the RuNO7 form in 42+, reflecting the predominant NO+ $\rightarrow$ NO· character of this electron transfer. However, a sizeable contribution from Ru with its high spin-orbit coupling const. to the singly occupied MO (SOMO) is apparent from the enhanced g anisotropy in the EPR spectrum 42+ (g1 = 2.015, g2 = 1.995, g3 = 1.881; gav = 1.965; Dg = 0.134). The RuNO6 unit in 43+ reacts with OH- via an associatively activated process (DS\# = -126.5 $\pm$ 2 J K-1 mol-1) with a 2nd-order rate const. of k = 3.3 $\times$ 10-2 M-1 s-1, leading to the corresponding nitro complex 3+. On exposure to light both RuNO6 and RuNO7 in 43+ and 42+ undergo Ru-NO photocleavage in MeCN via the formation of Ru(trpy)(bik)(MeCN)2+, 22+. The rate of photocleavage of the RuII-NO+ bond in 43+ (kNO, 8.57 $\times$ 10-1 s-1, t1/2 = 0.80 s) is much faster than that of the RuII-NO· bond in 42+, kNO·, 5.45 $\times$ 10-4 s-1, t1/2 = 21.2 min (= 1272 s). The photoreleased nitrosyl can be trapped as an Mb-NO adduct. (\copyright Wiley-VCH Verlag GmbH and Co. KGaA, 69451 Weinheim, Germany, 2009). on SciFinder(R)
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