Synthesis, structures and speciation studies of ruthenium(iii) hydroxamate/hydroximato complexes. Crystal and molecular structure of hydrated [Ru(H2edta)(2-methoxyphenylhydroxamate)], the first structurally characterised ruthenium(iii)–hydroxamate complex

Jedd Comiskey, Etelka Farkas, Krystyna A. Krot-Lacina, Robin G. Pritchard, Charles A. McAuliffe (the late), Kevin B. Nolan

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Abstract

Reaction of K[Ru(Hedta)Cl]·1.5H2O with various phenylhydroxamic acids, R-PhaH, in aqueous solution affords the hydroxamate complexes [Ru(H2edta)(R-Pha)]·xH2O, the crystal and molecular structure of one of which i.e. hydrated [Ru(H2edta)(2-OMe-Pha)], where 2-OMe-Pha = 2-methoxyphenylhydroxamate, has been determined. In this complex, the first reported structure of a Ru(iii)–hydroxamate, the carboxylato groups of the tetradentate H2edta are trans to each other and the amino nitrogen and hydroxamate oxygen donor atoms are roughly coplanar. Relevant bond lengths (Å) are: Ru–O(carboxylato) 2.016(4) and 2.044(3), Ru–O(hydroxamato O−) 1.964(4), Ru–O (hydroxamato CO) 2.019(4), Ru–N 2.060(4) and 2.156(4). Addition of R-PhaH to an aqueous solution of K[Ru(Hedta)Cl]·1.5H2O resulted in [Ru(edta)(R-Pha)]2− as the major species at pH 4–7. At higher pH the hydroxamate NH groups in these complexes undergo deprotonation to give the hydroximato complexes [Ru(edta)(R-PhaH−1)]3− as the major species at pH 7–11. This deprotonation, which has previously been reported in only a very small number of cases for mononuclear complexes, is accompanied by marked shifts to longer wavelengths in the ligand to metal charge transfer bands. At pH > 10 hydrolysis to give [Ru(edta)(R-PhaH−1)(OH)]4− in which an edta carboxylato group has been replaced by hydroxide ion is observed. Formation constants for the various species in solution are reported. The affinity of Pha for [Ru(edta)(H2O)]− (hexacoordinated) is much greater than for [Fe(edta)(H2O)]− (heptacoordinated) but this is largely due to differences in charge and coordination numbers of the immediate metal ion environments rather than intrinsic affinity differences between Ru(iii) and Fe(iii) for hydroxamate ligands.

Original languageEnglish
Pages (from-to)4243-4249
Number of pages7
JournalJournal of the Chemical Society. Dalton Transactions
Volume3
Issue number22
DOIs
Publication statusPublished - Nov 4 2003

ASJC Scopus subject areas

  • Chemistry(all)

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