Crystal structure, thermal expansion and elastic properties of triclinic betaine hydrogen dihydrogen triiodate, ((CH3)3NCH2COOH)H2(IO3)3

Abstract

Abstract Large single crystals of optical quality of betaine hydrogen dihydrogen iodate have been grown from aqueous solutions. An X-ray structure analysis yields space group P[unk], a 1 = 6.232(1) Å, a 2 = 9.478(1) Å, a 3 = 12.252(2) Å, α 1 = 87.94(1)°, α 2 = 84.59(1)°, α 3 = 85.88(1)°, Z = 2, Q calc = 2.982g cm−3, Q obs = 2.977 g cm−3. The structure consists of puckered layers which are built up from edge- and corner-sharing [IO6] and [IO7] polyhedra, respectively. Between adjacent layers van der Waals interactions are important. The complete elastic stiffness tensor was determined by the aid of ultrasonic methods. The tensors of thermoelastic constants and thermal expansion have been studied in the range between 290 K and 350 K. Both the elastic properties and the thermal expansion exhibit a distinct anisotropy, which is closely related to the anisotropy of the structural bonding system. No electric conductivity could be detected near room temperature.