Spectroscopic studies and structures of trans-ruthenium(II) and ruthenium(III) bis(cyanide) complexes supported by a tetradentate macrocyclic tertiary amine ligand.
ABSTRACT trans-[Ru(16-TMC)(C[triple bond]N)2] (1; 16-TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane) was prepared by the reaction of trans-[Ru(16-TMC)Cl2]Cl with KCN in the presence of zinc powder. The oxidation of 1 with bromine gave trans-[Ru(16-TMC)(CN)2]+ isolated as PF6 salt (2.PF6). The Ru-C/C-N distances are 2.061(4)/1.130(5) and 2.069(5)/1.140(7) A for 1 and 2, respectively. Both complexes show a Ru(III/II) couple at 0.10 V versus FeCp2+/0. The UV-vis absorption spectrum of 1 is dominated by an intense high-energy absorption at lambda(max) = 230 nm, which is mainly originated from dpi(RuII) --> pi*(N[triple bond]C-Ru-C[triple bond]N) charge-transfer transition. Complex 2 shows intense absorption bands at lambda(max) <or= 228 nm and weaker vibronically structured absorption bands with peak maxima at 315-441 nm (epsilon(max) approximately (5-8) x 10(2) dm3 mol-1 cm-1), which are assigned to dpi(RuIII) --> pi*(N[triple bond]C-Ru-C[triple bond]N) and sigma(-CN) --> d(RuIII) charge-transfer transition, respectively. Density functional theory and time-dependent density-functional theory calculations have been performed on trans-[(NH3)4Ru(C[triple bond]N)2] (1') and trans-[(NH3)4Ru(C[triple bond]N)2]+ (2') to examine the Ru-cyanide interaction and the nature of associated electronic transition(s). The 230 nm band of 1 has been probed by resonance Raman spectroscopy. Simulations of the absorption band and the resonance Raman intensities show that the nominal nuC[triple bond]N stretch mode accounts for ca. 66% of the total vibrational reorganization energy. A change of nominal bond order for the cyanide ligand from 3 to 2.5 is estimated upon the electronic excitation.
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ABSTRACT: The study of paramagnetic compounds based on 4d and 5d transition metals is an emerging research topic in the field of molecular magnetism. An essential driving force for the interest in this area is the fact that heavier metal ions introduce important attributes to the physical properties of paramagnetic compounds. Among the attractive characteristics of heavier elements vis-à-vis magnetism are the diffuse nature of their d orbitals, their strong magnetic anisotropy owing to enhanced spin-orbit coupling, and their diverse structural and redox properties. This critical review is intended to introduce readers to the topic and to report recent progress in this area. It is not fully comprehensive in scope although we strived to include all relevant topics and a large subset of references in the area. Herein we provide a survey of the history and current status of research that has been conducted on the topic of second and third row transition metal molecular magnetism. The article is organized according to the nature of the precursor building blocks with special topics being highlighted as illustrations of the special role of heavier transition metal ions in the field. This paper is addressed to readers who are interested in molecular magnetism and the application of coordination chemistry principles to materials synthesis (231 references).Chemical Society Reviews 03/2011; 40(6):3213-38. · 24.89 Impact Factor
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ABSTRACT: By reacting metal cyanide complexes with NaBPh(4) in the presence of acid at room temperature, a new class of neutral isocyanotriphenylborate-containing complexes trans-Ru(L)(4)(CNBPh(3))(2) (L = pyridine, 1; 4-methylpyridine, 2; 4-tert-butylpyridine, 3), cis-Ru(bipy)(2)(CNBPh(3))(2) (4, bipy = 2,2'-bipyridine) and cis-M(phen)(2)(CNBPh(3))(2) (M = Ru, 5; M = Fe, 6; phen = 1,10-phenanthroline) have been synthesized. These new complexes are characterized by IR, UV spectroscopy and single-crystal X-ray diffractions. The electron withdrawing triphenylborate group on the isocyanide ligands has a pronounced effect on the photophysical properties of complexes 1-6 in comparison with other ruthenium(II) and iron(II) isocyanide complexes. The excitation energies corresponding to metal-to-ligand charge transfer (MLCT) shift to higher energies while the (3)MLCT emissions are quenched at room temperature.Dalton Transactions 12/2009; · 3.81 Impact Factor