Mixed-valency with cyanides as terminal ligands: Diruthenium(III,II) complexes with the 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine bridge and variable co-ligands (CN- vs. bpy or NH3)

作者：Vergara Monica M; Garcia Posse Monica E; Fagalde Florencia; Katz Nestor E^*; Fiedler Jan; Sarkar Biprajit; Sieger Monika; Kaim Wolfgang

来源：Inorganica Chimica Acta, 2010, 363(1): 163-167.

DOI：10.1016/j.ica.2009.09.018

• Cyano ligands
• Mixed-valency
• Ruthenium complexes
• Spectroelectrochemistry
• Tetrazine ligand

New diruthenium complexes (PPN)(4)[(NC)(4)Ru(mu-bptz)Ru(CN)(4)], (PPN)(4) 1, and [(bpy)(2)Ru(mu-bptz)Ru(CN)(4)], 2, (PPN+ = bis(triphenylphospine)iminium; bptz = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine; bpy = 2,2'-bipyridine), were synthesised and characterised by spectroscopic and electrochemical techniques. The comproportionation constant K-c = 10(7.0) of the mixed-valent species [(NC)(4)Ru(mu-bptz)Ru(CN)(4)](3) as obtained by oxidation of 1(4) in CH3CN is much lower than the K-c = 10(15.0) previously detected for [(H3N)(4)Ru(bptz)-Ru(NH3)(4)](5+), reflecting the competition between CN and bptz for the p-electron density of the metals. Comparison with several other bptz-bridged diruthenium(II, III)complexes reveals an approximate correlation between K-c and the diminishing effective pi acceptor capacity of the ancillary terminal ligands. In addition to the intense MLCT absorption at lambda(max) = 624 nm, the main IVCT (intervalence charge transfer) band of 1(3) was detected by spectroelectrochemistry at lambda(max) = 1695 nm (in CH3CN; epsilon = 3200 M (1) cm (1)). The experimental band width at half-height, Delta nu(1/2) = 2700 cm (1), is slightly smaller than the theoretical value Delta nu(1/2) = 3660 cm (1), calculated from the Hush approximation for Class II mixed-valent species. In agreement with comparatively moderate metal-metal coupling, the mixed-valent intermediate 1(3) was found to be EPR silent even at 4 K. The unsymmetrical mixed-valent complex [(bpy)(2)Ru-II(mu-bptz) Ru-III(CN)(4)](+), obtained in situ by bromine oxidation of 2 in CH3CN/H2O, displays a broad NIR absorption originating from an IVCT transition at lambda(max) = 1075 nm (epsilon approximate to 1000 M (1) cm (1), Delta nu(1/2) approximate to 4000 cm (1)). In addition, the lifetime of the excited-state of the mononuclear precursor complex [Ru(bptz)(CN)(4)](2) was measured in H2O by laser flash photolysis; the obtained value of tau = 19.6 ns reveals that bptz induces a metal-to-ligand electronic delocalisation effect intermediate between that induced by bpy and bpz (bpz = 2,2'-bipyrazine)in analogous tetracyanoruthenium complexes.

• 出版日期2010-1-4