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

Adams, H., Alsindi, W. Z., Davies, G. M., Duriska, M. B., Easun, Timothy, Fenton, H. E., Herrera, J. M., George, M. W., Ronayne, K. L., Sun, X. Z., Towrie, M. and Ward, M. D. 2006. New members of the [Ru(diimine)(CN)(4)](2-) family: structural, electrochemical and photophysical properties. Dalton Transactions (1) , pp. 39-50. 10.1039/B509042C

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A series of complexes of the type K2[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[triple prime]-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 Ln3+ 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 π-type coordination of cyanide ligands to K+ ions. With Ln3+ 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 K2[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 3MLCT-based emission in all cases apart from Ru-bpym with lifetimes of tens/hundreds of nanoseconds. Time-resolved infrared studies showed that in the 3MLCT 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 3MLCT lifetimes for those complexes which could not be characterised by luminescence spectroscopy. A few complexes were also examined in different solvents (MeCN, dmf) and showed much weaker emission and shorter excited-state lifetimes in these solvents compared to water.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Publisher: Royal Society of Chemistry
Last Modified: 04 Jun 2017 07:58

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