Spin Crossover Star-Shaped Metallomesogens of Iron(II)

Abstract

Three new types of spin crossover (SCO) metallomesogens of Fe^II based on symmetric tripod ligands and their magnetic and structural properties are reported here. These were obtained by condensation of tris­(2-aminoethyl)­amin (tren) with the aldehyde derived from 3-alkoxy-6-methylpyridine (<b>mpyN</b>, N (number of carbon atoms in <i>n</i>-alkyl chains) = 8, 18), 1-alkyl-1<i>H</i>-imidazole (<b>imN</b>, N = 4, 16, 18, 20, 22), or 1-alkyl-1<i>H</i>-benzimidazole (<b>bimN</b>, N = 6, 14, 16, 18, 20). A complex derived from 1-octadecyl-1<i>H</i>-naphtho­[2,3-<i>d</i>]­imidazole (<b>nim18</b>) retains the high spin state at any temperature. Single crystals of the short-chain complexes were investigated by a combination of X-ray crystallography, magnetic measurements and Mössbauer spectroscopy. Generally, in comparison with the short-chain complexes the long-chain complexes display more gradual SCO and undergo a phase transition crystal–liquid crystal that is reflected in their magnetic properties. Characterization by X-ray powder diffractometry and differential calorimetry reveal formation of a smectic mesophase upon melting