Structure and properties of bis(1-phenyl-1h-tetrazole-5-thiolate)diiron tetranitrosyl

New tetranitrosyl binuclear iron complex [Fe 2 (SС 7 H 5 N 4 ) 2 (NO) 4 ] ( I ) has been synthesized by interaction of aqueous solutions of anionic salts [Fе(S 2 O 3 ) 2 (NO) 2 ] 3− and [SС 7 H 5 N 4 ] − . The latter one was synthesized by reduction of bis -(1-phenyl-1H-tetrazole-5-yl) disulfide with hydrazine hydrate in ethanol at T = 25 °C. Molecular and crystalline structure of I was determined by X-ray analysis; the complex has binuclear structure of “μ-SCN” type with ∼4.02 A between the iron atoms. Shortened О⋯О contacts (2.81 A) between the NO groups of similar type are observed. Parameters of Mossbauer spectrum for I are: isomer shift δ Fe = 0.311(1) mm/s, quadrupole splitting Δ E Q = 1.044(1) mm/s, line width Γ = 0.267(1) mm/s at 85 K. From SQUID magnetometry data, the temperature and field dependences of the magnetic moment of I are well described in the frame of a simple model of binuclear iron complex with magnetic centers S 1 = S 2 = ½. In solution, binuclear structure of the complex remains, though the NO groups are non-equivalent. For solutions of I five-line hyperfine structure of spectrum (HFS) is observed, g-factor = 2.03. For polycrystals of I , no HFS was observed due to averaged exchange interaction between the electron spins of adjacent complexes. In polycrystals of I , the number of spins per one binuclear complex is I in 1% dimethylsulfoxide (DMSO) aqueous solution is ∼13.8 nM, it halves in 8 min after decomposition starts, and reaches ∼3.8 nM in anaerobic conditions at Т = 25 °С, pH 7.0. This is due, according to quantum-chemical calculations, to the presence of a more stable Fe NO bond in I than in its isostructural analog – nitrosyl iron complex with 1-methyltetrazole-5-yl ( II ).