The ruthenium nitrosyl moiety in clusters: Trinuclear linear μ-hydroxido magnesium(II)-diruthenium(II), $μ_3$-oxido trinuclear diiron(III)–ruthenium(II), and tetranuclear $μ_4$-oxido trigallium(III)-ruthenium(II) complexes
Résumé
The ruthenium nitrosyl moiety, {RuNO}$^6$, is important as a potential releasing agent of nitric oxide and is of inherent interest in coordination chemistry. Typically, {RuNO}$^6$ is found in mononuclear complexes. Herein we describe the synthesis and characterization of several multimetal cluster complexes that contain this unit. Specifically, the heterotrinuclear $\mu_3$-oxido clusters [Fe$_2$RuCl$_4$($\mu_3$-O)($\mu$-OMe)($\mu$-pz)$_2$(NO)(Hpz)$_2$] and [Fe$_2$RuCl$_3$($\mu_3$-O)($\mu$-OMe)($\mu$-pz)$_3$(MeOH)(NO)(Hpz)][ Fe$_2$RuCl$_3$($\mu_3$)-O)($\mu$-OMe)($\mu$-pz)(3)(DMF)(NO)(Hpz)] ((7·MeOH·2H$_2$O) and the heterotetranuclear $\mu_4$)-oxido complex [Ga$_3$RuCl$_3$($\mu_4$-O)($\mu$-OMe)(3)($\mu$-pz)$_4$(NO)] were prepared from trans-[Ru(OH)(NO)(Hpz)$_4$]Cl-$_2$, which itself was prepared via acidic hydrolysis of the linear heterotrinuclear complex {[Ru($\mu$-OH)($\mu$-pz)$_2$(pz)(NO)(Hpz)]$_2$Mg}. Complex 4 was synthesized from the mononuclear Ru complexes (H$_2$pz)[trans-RuCl$_4$(Hpz)$_2$], $trans$-[RuCl$_2$(Hpz)$_4$]Cl, and trans-[RuCl$_2$(Hpz)$_4$]. The new compounds 4-8 were all characterized by elemental analysis, ESI mass spectrometry, IR, UV-vis, and $^1$H NMR spectroscopy, and single-crystal X-ray diffraction, with complexes 6 and 7 being characterized also by temperature-dependent magnetic susceptibility measurements and Mossbauer spectroscopy. Magnetometry indicated a strong antiferromagnetic interaction between paramagnetic centers in 6 and 7. The ability of 4 and 6-8 to form linkage isomers and release NO upon irradiation in the solid state was investigated by IR spectroscopy. A theoretical investigation of the electronic structure of 6 by DFT and ab initio CASSCF/NEVPT2 calculations indicated a redox-noninnocent behavior of the NO ancillary ligand in 6, which was also manifested in TD-DFT calculations of its electronic absorption spectr$um. The electronic structure of 6 was also studied by an X-ray charge density analysis.
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