Spin Crossover Star-Shaped Metallomesogens of Iron(II)

Three
new types of spin crossover (SCO) metallomesogens of FeII 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
(mpyN, N (number of carbon atoms in n-alkyl chains) = 8, 18), 1-alkyl-1H-imidazole (imN, N = 4, 16, 18, 20, 22), or 1-alkyl-1H-benzimidazole (bimN, N = 6, 14, 16, 18, 20). A complex
derived from 1-octadecyl-1H-naphtho­[2,3-d]­imidazole (nim18) 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.