CRYSTAL-STRUCTURES AND HYDROGEN-BONDING F OR BETA-BE(OH)(2) AND EPSILON-ZN(OH)(2)

Crystals of beta-Be(OH)(2) sufficient for x-ray structure determinatio n were grown from a saturated hot solution of freshly prepared Be(OH)( 2) in NaOH by slowly cooling down and in the case of epsilon-Zn(OH)(2) by electrochemical oxidation of zinc in a NaOH/NH3 solution. The stru ctures of the isotypic compounds were determined including the H-posit ions: beta-Be(OH)(2): P2(1)2(1)2(1), = 4, a = 4,530(2) Angstrom, b = 4 ,621(2) Angstrom, c = 7,048(2) Angstrom Z(F-o(2) > 3 sigma F-o(2) ) = 432, Z(Parameter) = 36, R/R-w = 0,044/0,052 epsilon-Zn(OH)2: P2(1)2(1) 2(1), Z = 4, a = 4,905(3) Angstrom, b =5,143(4) Angstrom, c = 8,473(2) Angstrom Z(F-o(2) > 3 sigma F-o(2)) = 1107, Z(Parameter) = 36, R/R-w = 0,025/0,027 beta-Be(OD)(2) was prepared. With time-of-flight data th e D positions were determined giving (d) over bar(O-D) = 0.954(4) Angs trom. The structures are closely related to that of P-cristobalite: As in SiO2 a quarter of tetrahedral interstices in a distorted cubic clo se packed arrangement of O is regularily occupied by the metal atoms. The filled O tetrahedra are twisted against one another in such a way, that O-H ... O-H hydrogen bonds are favoured which are surprisingly s tronger in the zinc than in the beryllium compound.