{Ru-NO}~6 and {Ru-NO}~7 configurations in [Ru(trpy)(tmp)(NO)]n+ (trpy = 2,2′: 6′,2′′-terpyridine, tmp = 3,4,7,8-tetramethyl-1,10- phenanthroline): An experimental and theoretical investigation

摘要

The ruthenium-nitrosyl complexes [RuII(trpy)(tmp)(NO ~+)](ClO_4)_3 ([4](ClO_4)_3) and [RuII(trpy)(tmp)(NO)](ClO_4)_2 ([5](ClO _4)_2) with {Ru-NO}~6 and {Ru-NO}~7 configurations, respectively (trpy = 2,2′:6′,2′′- terpyridine, tmp = 3,4,7,8-tetramethyl-1,10-phenanthroline) have been isotaled. The nitrosyl complexes [4]~(3+) and [5]~(2+) have been generated by following a stepwise synthetic procedure: [RuII(trpy)(tmp)(X)] ~n, X = Cl/+ (1~+) → CH_3CN/~(2+) (2 ~(2+)) → NO_2/+ (3+) → NO~+/~(3+) (4~(3+)) → NO/2+ (5~(2+)). The single-crystal X-ray structures of two precursor complexes [1]ClO_4 and [3]ClO_4 have been determined. The DFT optimized structures of 4~(3+) and 5 ~(2+) suggest that the Ru-N-O geometries in the complexes are linear (177.9°) and bent (141.4°), respectively. The nitrosyl complexes with linear (4~(3+)) and bent (5~(2+)) geometries exhibit ν(NO) frequencies at 1935 cm~(-1) (DFT: 1993 cm~(-1)) and 1635 cm -1 (DFT: 1684 cm-1), respectively. Complex 4~(3+) undergoes two successive reductions at 0.25 V (reversible) and -0.48 V (irreversible) versus SCE involving the redox active NO function, Ru ~(II)-NO~+ Ru~(II)-NO and Ru~(II)-NO → Ru~(II)-NO~-, respectively, besides the reductions of trpy and tmp at more negative potentials. The DFT calculations on the optimized 4 ~(3+) suggest that LUMO and LUMO+1 are dominated by NO~+ based orbitals of around 65% contribution along with partial metal contribution of ～25% due to (dπ)Ru~(II) → π(NO~+) back-bonding. The lowest energy transitions in 4~(3+) and 5~(2+) at 360 nm and 467 nm in CH_3CN (TD-DFT: 364 and 459 nm) have been attributed to mixed MLLCT transitions of tmp(π) → NO+(π), Ru(dπ)/tmp(π) → NO+(π) and Ru(dπ)/NO(π) → trpy(π), respectively. The paramagnetic reduced species 5~(2+) exhibits an anisotropic EPR spectrum with g1 = 2.018,_(g2) = 1.994, _(g3) = 1.880 (〈g〉 = 1.965 and Δg = 0.138) in CH_3CN, along with ~(14)N (I = 1) hyperfine coupling constant, A2 = 35 G at 110 K due to partial metal contribution in the singly occupied molecular orbital (DFT:SOMO:Ru (34%) and NO (53%)). Consequently, Mulliken spin distributions in 5~(2+) are calculated as 0.115 for Ru and 0.855 for NO (N, 0.527; O, 0.328). The reaction of moderately electrophilic nitrosyl center in 4~(3+) with the nucleophile, OH- yields the nitro precursor, 3~+ with the second-order rate constant value of 1.7 × 10~(-1) M~(-1) s~(-1) at 298 K in CH _3CN-H_2O (10:1). On exposure to light (Xenon 350 W lamp) both the nitrosyl species, 4~(3+) ({Ru~(II)-NO~+}) and 5~(2+) ({Ru~(II)-NO}) undergo photolytic Ru-NO bond cleavage process but with a widely varying kNO, s~(-1) (t ~(1/2), s) of 1.56 × 10~(-1)(4.4) and 0.011 × 10~(-1)(630), respectively.