Syntheses and electronic and optical properties of complexes of the bis(2,2′-bipyrazyl)ruthenium unit
作者:Benjamin J. Coe、Martyn K. Peers、Nigel S. Scrutton
DOI:10.1016/j.poly.2015.04.028
日期:2015.8
Seven new complexes of the form cis-[Ru-II(bpz)2(L-L)(n+) (bpz = 2,2'-bipyrazyl: n = 2; L L = 4,4'-bis (tert-butyl)-2,2'-bipyridyl, 4,4'-dipheny1-2,2'-bipyridyl, 4,4'-dichloro-2,2'-bipyridyl, 4,4'-diamino-2, 2'-bipyridyl, 4,4'-bis(trifluoromethyl)-2,2'-bipyridyl, 4,4'-bis(methoxycarbonyl)-2,2'-bipyridyl: n = 4; L-L = N '',N'"-dimethy1-4,4':2',2 '':4 '',4'''-quaterpyridinium) are prepared and isolated as their PF6- and Cl- salts. Improved methods for synthesising bpz and 4,4'-bis(trifluoromethyl)-2,2'-bipyridyl are described also. Characterisation involves various techniques including H-1 NMR spectroscopy and mass spectrometry. The new compounds are studied alongside the known species where n = 2 and L-L = 2,2'-bipyridyl, 4,4'-dimethy1-2,2'-bipyridyl or 2,2'-bipyrimidine. Their UV-Vis spectra display intense intraligand pi -> pi* absorptions, and also metal-to-ligand charge-transfer (MLCT) bands with two resolved maxima in the visible region. Red-shifts in the MLCT bands occur as the electron-donating strength of L L increases. Cyclic voltammograms show reversible Ru-III/II oxidation waves, and several ligand-based reductions that are also mostly reversible. The variations in the redox potentials correlate with changes in the MLCT energies. Time-dependent density functional theory calculations give relatively good correlations with the experimental UV Vis spectra for selected complexes when using the MOB functional and basis sets Def2-QZVP (on Ru) and Def2-SVP (on all other atoms) in acetonitrile. The lowest energy visible absorption band is confirmed to be due to Ru-II -> bpz MLCT, while further such transitions occur along with MLCT to L L at higher energies. (C) 2015 The Authors. Published by Elsevier Ltd.