A Field Induced High-Spin Molecule: {Fe(Ⅱ)-Fe(Ⅲ)_6} Cluster

摘要

A blue heptanuclear complex [Fe~(Ⅱ){(CN)Fe~(Ⅲ)(~5L)}_6]Cl_2 resulted by combining the mononuclear precursor [Fe~(Ⅲ)(~5L)Cl] and [Fe(CN)_6]~(4-). In the role of the pentadentate blocking ligand the Schiff-condensation product of 1,7-diamino-4-azaheptane with the salicyaldehyde has been used. The mixed-valence cluster has been characterized by its Mossbauer spectra and the powder diffraction patterns. The magnetization measurements until B = 1 T indicate S=6 ground state. The susceptibility has been fitted with J/k = -0.0284 K, g = 1.825 when all 46656 magnetic states of the cluster are considered assuming that six s = 5/2 centers take part in the exchange coupling. With such a small exchange coupling constant the ground S = 0 molecular state is crossed by the Zeeman term so that the molecular ground state depends upon the magnetic field strength, progressively reaching the maximum value S = 15 for large field/temperature ratio.