CRYSTAL-STRUCTURE, THERMAL-EXPANSION AND ELASTIC PROPERTIES OF TRICLINIC BETAINE HYDROGEN AMMONIUM-SULFATE, ((CH3)(3)NCH2COOH)NH4SO4

Large single crystals of optical quality of betaine hydrogen ammonium sulfate have been grown from aqueous solutions. An X-ray structure ana lysis yielded space group P (1) over bar, a(1) = 6.829(1)% Angstrom, = 7.239(2) Angstrom, a(3) = 10.282(2) Angstrom, alpha(1) = 88.78(2)degr ees, alpha(2) = 88.18(2)degrees, a(3) = 82.71(2)degrees, Z = 2, rho(ca lc) = 1.531 g cm(-3) rho(obs) = 1.530 g cm(-3). The structure is built up from ammonium ions and betaine hydrogen sulfate groups which are a rranged in three different layers parallel to (001). The constituents of each three-layer package are linked by ionic interactions and hydro gen bonds. Between adjacent packages van der Waals interactions are im portant. Complete elastic and thermoelastic tensors were determined by the aid of ultrasonic methods. Further, the tensor of thermal expansi on has been studied in the range between 200 K and 350 K. The physical properties investigated show a strong anisotropy, which is closely re lated to the crystal structure.