STRUCTURE AND MAGNETISM OF ELECTRONICALLY DISTORTED IRON(III) SCHIFF-BASE COMPLEXES

The reaction of [Fe(salen)Cl] [H2salen = N,N'-bis(salicylidene)ethane) -1,2-diamine] with an excess of L [imidazole (Him), 1-,2- or 4-methyli midazole (1-,2- or 4-mim)] in acetone resulted in the isolation of het erobisadducts, [Fe(salen)L(Cl)] (L = Him, 1- or 2-mim) and a homobisad duct, [Fe(salen)L2]Cl (L = 4-mim). The structures of [Fe(salen)(1-mim) Cl] and [Fe(salen)(4-mim)2]Cl were determined by single-crystal X-ray diffraction: [Fe(salen)(1-mim)Cl], monoclinic, space group P2(1)/c, Z = 4, a = 9.8510(10), b = 15.9830(10), c = 12.8350(10) angstrom, beta = 107.610(10)-degrees; [Fe(salen)(4-mim)2]Cl, orthorhombic, space group Fdd2, Z = 8, a = 21.7650(10), b = 12.5040(10), c = 18.508(2) angstrom . The structures were refined by full-matrix least-squares methods on F2 to R = 0.0537 and 0.0537 and 0.0338 for 2609 and 1207 reflections, respectively. A significant difference between the two structures is t hat the dihedral angle between the two phenyl rings of the salen ligan d is 17.5-degrees for [Fe(salen)(1-mim)Cl] and 4.4-degrees for [Fe(sal en)(4-mim)2]Cl. All of the complexes were characterized by variable-te mperature magnetic susceptibility and Mossbauer spectroscopy. The hete robisadducts, which have a N3O2Cl donor set, exhibit an admixed electr onic ground state whereas the homobisadduct is high spin. Another N3O2 Cl donor set molecule has been found to exhibit a temperature-dependen t spin equilibrium, T-2 reversible A-6, as evidenced by variable-tempe rature magnetic susceptibility, ESR and Mossbauer spectroscopies.