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.

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 μ(3)-oxido clusters [Fe(2)RuCl(4)(μ(3)-O)(μ-OMe)(μ-pz)(2)(NO)(Hpz)(2)] (6) and [Fe(2)RuCl(3)(μ(3)-O)(μ-OMe)(μ-pz)(3)(MeOH)(NO)(Hpz)][Fe(2)RuCl(3)(μ(3)-O)(μ-OMe)(μ-pz)(3)(DMF)(NO)(Hpz)] (7·MeOH·2H(2)O) and the heterotetranuclear μ(4)-oxido complex [Ga(3)RuCl(3)(μ(4)-O)(μ-OMe)(3)(μ-pz)(4)(NO)] (8) were prepared from trans-[Ru(OH)(NO)(Hpz)(4)]Cl(2) (5), which itself was prepared via acidic hydrolysis of the linear heterotrinuclear complex {[Ru(μ-OH)(μ-pz)(2)(pz)(NO)(Hpz)](2)Mg} (4). Complex 4 was synthesized from the mononuclear Ru complexes (H(2)pz)[trans-RuCl(4)(Hpz)(2)] (1), trans-[RuCl(2)(Hpz)(4)]Cl (2), and trans-[RuCl(2)(Hpz)(4)] (3). 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 Mössbauer 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 spectrum. The electronic structure of 6 was also studied by an X-ray charge density analysis.