New members of the [Ru(diimine)(CN)(4)](2-) family: structural, electrochemical and photophysical properties

A series of complexes of the type K-2[Ru(NN)(CN)(4)] has been prepared, in which NN is a diimine ligand, and were investigated for both their structural and photophysical properties. The ligands used ( and the abbreviations for the resulting complexes) are 3-(2-pyridyl) pyrazole (Ru-pypz),2,2'-bipyrimidine (Ru-bpym), 5,5'-dimethyl-2,2'-bipyridine (Ru-dmb), 1-ethyl-2-(2-pyridyl)benzimidazole (Ru-pbe), bidentate 2,2':6, 2'''-terpyridine (Ru-tpy). The known complexes with NN = 2,2'-bipyridine (Ru-bpy) and 1,10-phenathroline (Ru-phen) were also included in this work. A series of crystallographic studies showed that the [Ru(NN)(CN)(4)](2-) complex anions form a range of elaborate coordination networks when crystallised with either K+ or Ln(3+) cations. The K+ salts are characterised by a combination of near-linear Ru-CN-K bridges, with the cyanides coordinating to K+ in the usual 'end-on' mode, and unusual side-on pi-type coordination of cyanide ligands to K+ ions. With Ln(3+) cations in contrast only Ru-CN-Ln near-linear bridges occurred, affording 1-dimensional helical or diamondoid chains, and 2- dimensional sheets constituted from linked metallamacrocyclic rings. All of the K-2[Ru(NN)(CN)(4)] complexes show a reversible Ru(II)/Ru(III) couple (ca. + 0.9 V vs. Ag/AgCl in water), the exception being Ru-tpy whose oxidation is completely irreversible. Luminescence studies in water showed the presence of (MLCT)-M-3-based emission in all cases apart from Ru-bpym with lifetimes of tens/hundreds of nanoseconds. Time-resolved infrared studies showed that in the (MLCT)-M-3 excited state the principal C-N stretching vibration shifts to positive energy by ca. 50 cm(-1) as a consequence of the transient oxidation of the metal centre to Ru( III) and the reduction in back-bonding to the cyanide ligands; measurement of transient decay rates allowed measurements of (MLCT)-M-3 lifetimes for those complexes which could not be characterised by luminescence spectroscopy. A few complexes were also examined in different solvents compared to water.