Crystal and molecular structure and some properties of pyridinium µ-oxo-bis[trichioroferrate(III)]–pyridine

Abstract

The crystal structure of the title complex, [Hpy]₂[Cl₃Fe–O–FeCl₃]·py, prepared by hydrolysis of FeCl₃ in aqueous ethanol-pyridine, has been determined. Crystals are monoclinic with a= 8.532(6), b= 13.914(11),c= 10.597(11)Å, β= 110.8(1)°, Z= 2, and space group P2₁/m. The structure has been solved by Patterson and Fourier methods and refined by full-matrix least squares to R 0.056 for 1 236 independent above-background reflections measured by diffractometer. In the complex anion which has crystallographically imposed C_s symmetry, the two equivalent FeOCl₃ units are bridged by the oxygen atom via short Fe–O bonds [1.755(3)Å], the Fe–O–Fe angle being 155.6(7)°. The geometry about each metal is close to tetrahedral, the Cl–Fe–Cl and Cl–Fe–O angles being 108–111°. The Fe–Cl distances (2.208–2.219 Å) are somewhat lengthened with respect to those in [FeCl₄]^–. Strong antiferromagnetic coupling between the S=5//₂ spins in the binuclear anion is observed. The coupling constant, J=–92 cm^–1, is not appreciably different from values reported for other binuclear µ-oxo-complexes in which the iron(III) ions are in a square-pyramidal or octahedral environment. Infrared and Mössbauer spectra are reported.