Synthesis and structural phase transitions of [Mg2Sb2(C4H2O6)2(H2O)8](ClO4)2·5H2O with complex homochiral chains

Abstract

Abstract A new magnesium antimony tartrate perchlorate [Mg2Sb2(C4H2O6)2(H2O)8](ClO4)2·5H2O, 1, was synthesized in single crystal form by slowly evaporating an aqueous solution of potassium antimony tartrate and magnesium perchlorate. In the temperature interval 298 K–123 K, the compound undergoes two reversible structural phase transitions. The transition from phase I to phase II at ca. 236 K is second order and the transition from phase II to phase III at ca. 144 K is first order. Phase I has an orthorhombic structure, P21212, a=11.8658(4) Å, b=16.464(1) Å, c=8.3895(4) Å at 298 K, containing infinite chains of antimony tartrate dimeric clusters bridged by MgO2(H2O)4 octahedra. The ClO4 − anions occupying the interchain space show pronounced dynamic disorder. Phase II is monoclinic, P21, a=8.3813(8) Å, b=11.760(1) Å, c=16.289(2) Å, β=92.442(2)° at 153 K. Phase III has an orthorhombic unit cell with quadrupled cell volume, P212121, a=11.6914(8) Å, b=16.176(1) Å, c=33.426(2) Å at 123 K. While the infinite chains in phases II and III are closely similar to those in phase I, the ClO4 − anions show different orientations and gradual disappearance of dynamic disorder as the temperature is lowered.