Low-temperature phases of dicalcium barium hexakis(propanoate)

The structure determinations of phases (II) and (III) of barium dicalcium hexakis(propanoate) {or poly[hexa- μ 4-propanoato-bariumdicalcium], [BaCa2(C3H5O2)6]n} are reported at 240 and 130   K, respectively [phase (I) was determined previously by Stadnicka& Glazer (1980). Acta Cryst. B36, 2977 – 2985; our structure determination of phase (I) at room temperature is included in the supporting information]. In the high-temperature phase, the Ba2+ cation is surrounded by six carboxylate groups in bidentate bridging modes. In the low-temperature phases, five carboxylate groups act in bidentate bridging modes and one acts in a monodentate bridging mode around Ba2+. The Ca2+ cations are surrounded by six carboxylate O atoms in a trigonal antiprism in all the structures. The Ba2+ and Ca2+ cations are underbonded and significantly overbonded, respectively, in all the phases. The bonding of the Ba2+ cation increases slightly at the cost of the bonding of Ca2+ cations during cooling to the low-temperature phases. The phase transitions during cooling are accompanied by ordering of the ethyl chains. In room-temperature phase (I), all six ethyl chains are positionally disordered over two positions in the crossed mode, with additional splitting of the ethyl α - and β -C atoms. In phase (II), on the other hand, there are three disordered ethyl chains, one with positionally disordered ethyl α - and β -C atoms, and the other two with positionally disordered ethyl β -C atoms only, and...

Source: Acta Crystallographica Section C - October 19, 2021 Category: Chemistry Authors: F á bry, J. Du š ek, M. Tags: barium dicalcium propanoate positional disorder first-order phase transition second-order phase transition crystal structure research papers Source Type: research