X-ray diffraction study of phase transitions in iron(II) trisnioximate hexadecylboronate clathrochelate complex

Crystals of the iron(II) nioximate hexadecylboronate clathrochelate complex -FeNx(3)(BHd)(2) [tris(mu ,1,2-cyclohexanedionedioximato-O:O')di-n-hexadecy ldiborato(2-)-N,N',N " ,N''',N'''',N''''']iron(II)-are investigated by diff erential scanning calorimetry and X-ray diffraction. Two structural phase t ransitions are revealed at T-cr1 = 290(3) K and T-cr2 = 190(3) K. The cryst al structures of phases I, II, and III are determined by X-ray diffraction analysis at 303, 243, and 153 K, respectively. It is demonstrated that the I <----> II phase transition is due to a change in the system of translatio ns, and the II <----> III phase transition is accompanied only by a jumpwis e change in the unit cell parameters. The possible mechanisms of phase tran sitions are discussed in terms of geometry and molecular packing of FeNx(3) (BHd)(2) in all three phases, (C) 2001 MAIK "Nauka/Interperiodica".