Molecular and Electronic Structure of (L-Histidinato)pentammineruthenium(III) Chloride Monohydrate, (NH3)5Rum(his)Cl3*H20: X-ray Structure, Single-Crystal Polarized Charge-Transfer Spectra, and ab Initio and Semiempirical Molecular Orbital Calculations

Karsten Krogh-jespersen, John D. Westbrook, Joseph A. Potenza, Harvey J. Schugar

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Abstract

The synthesis, X-ray structure, and polarized single-crystal optical spectra are presented for the title complex. Crystals ofruc1302N8C6H24.H20 are orthorhombic, space group P2i2{2\\\\\\\\twith a = 7.113 (2) A, b = 9.990 (1) A, c = 25.717 (3) A, V = 1827.2 (9) A3, Z = 4, and RF(i?wF) = 0.061 (0.063) for 1339 reflections. The structure contains (NH3)5Ru(his)3+cations linked to lattice chloride ions and water molecules by an extensive network of hydrogen bonds. Five ammine and one histidine N atoms provide slightly distorted octahedral coordination for Ru. The Ru-N(his) bond length [2,020 (8) A] is substantially shorter than the average Ru—N(ammine) distance [2.09 (2) A] and the corresponding Ru-N(heterocycle) distances in several related pentammineruthenium(III) complexes. The histidine imidazole ring is staggered with respect to the four equatorial NH3ligands and is approximately perpendicular to a. Polarized single-crystal spectra of the title complex obtained at 80 K reveal that the low-energy LMCT absorption at 22200 cm-1(450 nm) is strongly polarized along the Ru-N(his) direction and suggest that the higher energy LMCT band at 33 000 cm-1(303 nm) may exhibit similar polarization. Ab initio molecular orbital calculations were performed on (NH3)5Rum-imidazole with use of effective core potentials for the inner atomic electrons and valence basis sets of double-Equality. The ground state has been established as2dxz, where dxzis the Ru(4d) orbital capable of interaction with the imidazole 7r-system; the unpaired electron is fully localized in this orbital. The a-donation from imidazole (0,36e) is twice as large as that from any ammine (0.17e), but the imidazole 7r-donation is quite weak (0.06e). Geometry optimization yields good agreement between calculated and experimental Ru-N bond lengths. The relevant Ru parameters required for the semiempirical INDO/S method have been developed from atomic spectral data. Excited state calculations on (NH3)5Ruin-5-methylimidazole provide assignments for the optical charge-transfer spectra as 7t3— dxzand 7t2-dxz, where 7rj and 7r2are the two high-lying occupied imidazole 7r-orbitals. These two LMCT transitions are calculated at 21 200 cm-1(472 nm) and 35 000 cm-1(286 nm), respectively, and both have their largest transition moment components along the Ru-N (heterocycle) axis.

Original languageEnglish (US)
Pages (from-to)7025-7031
Number of pages7
JournalJournal of the American Chemical Society
Volume109
Issue number23
DOIs
StatePublished - Nov 1 1987

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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