Structural and physical properties of bis(guanidinium) X bis(nitrilotriacetate) hydrate, (C[NH₂]₃)₂X(N[CH₂COO]₃)₂·H₂O (X = Zr, Sn, Hf) and bis(methylammonium) X bis(nitrilotriacetate dihydrate, (CH₃NH₃)₂X(N[CH₂COO]₃)₂·2 H₂O (X = Sn, Zr)

Abstract

Single crystals of bis(guanidinium) tin bis(nitrilotriacetate) hydrate (GuSN) and bis(methylammonium) tin bis(nitrilotriacetate) dihydrate (MetamSN) having optical quality and dimensions up to 15 × 15 × 20 mm were grown from aqueous solutions. The isotypy with the corresponding zirconium and hafnium compounds (GuZN, GuHN, and MetamZN, respectively)) was proved by X-ray structure analyses (GuSN: space group Ccc2₁, a₁ = 11.338 Å, a₂ = 20.285 Å, a₃ = 10.178 Å, Z = 4, density 1.796 g cm^-3; MetamSN: space group P2₁2₁2₁, a₁ = 9.851 Å, a₂ = 14.164 Å, a₃ = 15.548 Å, Z = 4, density 1.821 g cm^-3). Distinct differences in the dimensions of the tin bis(nitrilotriacetate) and zirconium bis(nitrilotriacetate) anions could be derived from structural features. The molecular volume of the latter is about 6 ų larger than that of the tin complex. Along one direction perpendicular to the twofold or quasi-twofold axis the diameter of the tin complex is about 0.18 Å shorter. Thermal expansion, dielectric, piezoelectric, elastic, thermoelastic and piezo elastic properties of corresponding tin, zirconium and hafnium compounds are quite similar. The small differences in the dimensions of the anions, however, are clearly reflected in the elastic longitudinal stiffnesses. The earlier described phase transitions in GuZN exist also in GuSN as confirmed by X-ray analysis at 100 K. The temperature of the transition region II is shifted to lower temperatures by about 4 and 6 K, if Zr is substituted by Sn and Hf, respectively. All anomalous phenomena observed during the transition in GuZN and GuHN are also found in GuSN.