X-ray studies of the phase transitions of bis(guanidinium)zirconium bis(nitrilotriacetate) hydrate, (C(NH2)3)2Zr(N(CH2COO)3)2 · H2O

Abstract

Abstract The structural differences of phase I (at 193 K) and phase III (293 K) of bis(guanidinium)zirconium bis(nitrilotriacetate) hydrate were investigated by means of X-ray diffraction. The phase transition III → I is characterised by a loss of translational symmetry as it is indicated by the change of space group symmetry from C2221 to P212121 passing from 293 K to 287 K. In respect to bond lengths and bond angles the structural changes are very small. The transition is mainly caused by the hydrogen bridges O–H…O1 and N–H12…O5 of the high temperature phase III which both split into two non-equivalent hydrogen bonds of different strengths in phase I. Apparently the mechanism of this splitting is responsible for the softening of the longitudinal stiffness c 22 along [010] and the strong attenuation of elastic modes which accompanies the transition from phase III to phase I.