Strongly Coupled, Oxohyphen;Bridged Iron (III) Complexes Magnetically Perturbed Mouml;ssbauer Spectra

摘要

The electric field gradient tensor is used to study structure, spin state, and bonding in some representative binuclear iron (III) systems. Mouml;ssbauer spectra of stronglpar;Jthinsp;ap;thinsp;minus;thinsp;100cmminus;1rpar;exchange coupled intramolecular antiferromagnets have been determined in zero applied field and also longitudinal fields up to 26 kG. The systems studied, Fe(salen)2O (salenhyphen;N, Nprime;hyphen;ethylenebissalicydeneiminate), Fe(phen)2Cl2hyphen;OCl2middot;5H2O (phenhyphen;1, 10hyphen;phenanthroline), and FeB(H2O)2O(ClO4)4{Bequals;the macrocyclic ligant 2, 13hyphen;dimethylhyphen;3, 6, 9ndash;12, 18hyphen;pentaazahyphen;bicyclo12.3.1octadecahyphen;1(18), 2, 12, 14, 16hyphen;pentaene)} contain fivehyphen;, sixhyphen;, and sevenhyphen;coordinate iron (III), respectively, and show approximate axial symmetry. Signs for the principal component of the electric field gradient tensor are discussed in terms of point charge geometry andsgr;bonding considerations. On this basis, acisarrangement of chlorine and oxygen is proposed for Fe(phen)2Cl2hyphen;OCl2middot;5H2O, and the nature of the large quadrupole splitting is discussed. The spin state of the individual iron (III) ions is also considered and is indicated to be52. The absence of relaxation broadening and internal field augmentation at 4.2deg;K are correlated with total spin zero ground states for the binuclear complexes.