Crystal structure, electron spin resonance, and magnetism of tris(o-phenanthroline)iron(III) perchlorate hydrate

Abstract

The crystal structure of the title compound has been determined by the heavy-atom method from diffractometer data and refined by least-squares to R 0·082 for 3449 reflections. Crystals are monoclinic, space group A2/a, a= 23·252(6), b= 18·342(4), c= 17·824(5)Å, β= 92·45(2)°, Z= 8. The iron atom is surrounded by three bidentate ligands, the six Fe–N distances being equal (mean 1·973 Å). The geometries of two of the perchlorate ions are as expected but the third ion is badly disordered, and there may be additional partial occupancy of the lattice by further water molecules. The e.s.r. spectrum has been determined at ca. 85 K and the principal g values are found to be along the molecular pseudo-trigonal axis (g₁ 1·459(5)) and in the plane normal to it [g₂, g₃ 2·615(10), 2·727(10)]. The splitting of the ²T_2g ground term of the Fe³⁺ ion (Δ_Ag^gca. 800 cm^–1) is deduced to be opposite in sign to that predicted by crystal-field theory.