Crystal structure of the low temperature phase of bis(hexylammonium) zirconium bis(nitrilotriacetate) dihydrate, (CH₃(CH₂)₅NH₃)₂ Zr (N(CH₂COO)₃)₂ · 2 H₂O

Abstract

The crystal structure of the low temperature phase of bis(hexylammonium) zirconium bis(nitrilotriace-tate) dihydrate was investigated at 100 K by means of X-ray single crystal diffraction. Although the zirconium bis(nitrilotriacetate) anion representing the dominant part of the crystal structure shows only minor changes during the phase transition, a strong change in respect to the oriäentation of the hexylammonium cations takes place. These are now statically disordered over two geometrically quite different conformations at 100 K. The distance between the terminal carbon atoms of the two possible conformations of the hexylammonium cation is as large as 5.7 Å. The space group remains C2/c after passing the phase transition from the high temperature phase to the low temperature phase with the lattice parameters a = 18.8708 (6) Å, b = 11.2229 (3) Å, c = 16.1895 (5) Å, β = 112.726 (1)°. In addition heat capacity measurements were performed, which yielded broad peaks at about 275 K indicating the phase transition temperature T_c.