Synthesis, crystal structures, phase transition characterization and thermal decomposition of a new dabcodiium hexaaquairon(II) bis(sulfate):: (C6H14N2)[Fe(H2O)6](SO4)2

The crystal structures of 1.4-diazabicyclo[2.2.2]octane (dabco)-templated iron sulfate, (C6H14N2)[Fe(H2O)(6)](SO4)(2), were determined at room temperature and at -173 degrees C from single-crystal X-ray diffraction. At 20 degrees C, it crystallises in the monoclinic symmetry, centrosymmetric space group P2(1)/n Z = 2, a = 7.964(5), b = 9.100(5), c = 12.065(5) angstrom, beta = 95.426(5)degrees and V = 870.5(8) angstrom(3). The structure consists of [Fe(H2O)(6)](2 divided by) and disordered (C6H14N2)(2 divided by) cations and (SO4)(2-) anions connected together by all extensive three-dimensional H-bond network. The title compound undergoes a reversible phase transition of the first-order at -2.3 degrees C, characterized by DSC. dielectric measurement and optical observations, that Suggests a relaxor-ferroelectric behavior. Below the transition temperature, the compound crystallizes in the monoclinic system, non-centrosymmetric space group Cc, with eight times the volume of the ambient phase: a = 15.883(3) b = 36.409(7), c = 13.747(3) angstrom, beta = 120.2304(8)degrees, Z = 16 and V = 6868.7(2) angstrom(3). The organic moiety is then fully ordered within a supramolecular structure. Thermodiffractometry and thermogravimetric analyses indicate that its decomposition proceeds through three stages giving rise to the iron oxide. (c) 2007 Elsevier Inc. All rights reserved.