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.