Discontinuous high spin ⇌ low spin transition in an iron(II) complex [FeL2(NCS)2] with the pharmaceutical agent bromazepam

Abstract

A temperature-dependent susceptibility and Mössbauer effect study of the iron(II) complex [FeL2(NCS)2], where L is the psychotherapeutic agent bromazepam, has been performed. The Mössbauer spectra demonstrate that two lattice sites are present. One of them undergoes a high spin (5T2g)⇌ low spin (1A1g) transition around ca. 240 K, the other remains in the low-spin state over the whole temperature range. This is consistent with the temperature dependence of the effective magnetic moment µeff·, which varies between a pure low-spin value of 0.9 µB in the low-temperature region and an intermediate value of 4.2 µB as a high-temperature plateau. A small hysteresis for the high spin ⇌ low spin transition has been observed. It is suggested that two stereoisomers of [FeL2(NCS)2] with different magnetic properties are present in the lattice.