Linkage and geometrical isomers of dichloridobis(triphenylphosphine) ruthenium(II) complexes with quinoline-2-carbaldehyde (pyridine-2-carbonyl) hydrazone: Their molecular structures and electrochemical and spectroscopic properties

Asami Mori, Takayoshi Suzuki, Yukinari Sunatsuki, Atsushi Kobayashi, Masako Kato, Masaaki Kojima, Kiyohiko Nakajima

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Abstract

The reactions of quinoline-2-carbaldehyde (pyridine-2-carbonyl)hydrazone (HL) and [RuCl2(PPh3)3] in various solvents at different temperatures gave the three geometrical isomers trans(Cl,Cl)-, cis(Cl,Cl),trans(P,N)-, and trans(P,P)-[RuCl2(PPh3) 2{HL-κO(amide),κN(imine)}] (1, 2, and 3, respectively) as well as a linkage isomer trans(P,P)-[RuCl2(PPh3) 2{HL-κN(imine),κN(quin)}] (4). The molecular and crystal structures of 1-4, together with both E and Z configurational isomers (with respect to the C=N double bond) of the free ligand HL, were determined by X-ray analysis. The ligand HL adopted a Z form and acted as a κO(amide), κN(imine) bidentate ligand in 1-3, whereas it was an E isomer with a κN(imine),κN(quin) coordination mode in 4. The gradual thermal conversions of 1 to 2 and of 2 to 3 were observed in dichloromethane and ethanol, respectively, but an interconversion between 3 and 4 was not detected. In dichloromethane, all complexes have a reversible RuIII/II redox couple in the range 110-412 mV (vs. Ag/Ag+), and the redox potential was largely dependent on the coordination mode of HL and on the mutual configuration of the two PPh3 ligands. Such a potential shift can be interpreted as a combination of Cl-/amide O π-donor and PPh 3/quinoline N π-acceptor orbital contributions to the Ru II dπ orbitals [highest occupied molecular orbitals (HOMOs)]. Complexes 3 and 4 in acetonitrile showed a gradual spectral change, probably because of the substitution of the Cl- ligand by the acetonitrile solvent. In addition, 2-4 showed solvatochromic behavior even in noncoordinating solvents that resulted from a blueshift of the metal-to-ligand charge-transfer (MLCT) transition band in polar solvents. These electrochemical and spectroscopic properties are also supported by DFT and time-dependent DFT (TD-DFT) calculations.

Original languageEnglish
Pages (from-to)186-197
Number of pages12
JournalEuropean Journal of Inorganic Chemistry
Issue number1
DOIs
Publication statusPublished - Jan 2014

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Keywords

  • Hydrazones
  • Isomerization
  • Isomers
  • Ruthenium
  • Solvatochromism

ASJC Scopus subject areas

  • Inorganic Chemistry

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