Preparation, crystal structure and infrared spectroscopy of the new compound rubidium beryllium sulfate dihydrate, Rb2Be(SO4)2-2H2O

The solubility in the three-component system Rb2SO4-BESO4-H2O at 25 degrees C was studied by the method of isothermal decrease of supersaturation. A new compound, Rb2Be(SO4)(2)center dot H2O, is formed in a wide concentration range (from solutions containing 27.49 mass% beryllium sulfate and 20.16 mass% rubidium sulfate up to solutions containing 15.08 mass% beryllium sulfate and 39.07 mass% rubidium sulfate). Rb2Be(SO4)(2)center dot 2H(2)O crystallizes in the monoclinic space group P2(1)lc (a = 11.371(2) angstrom, b = 11.858(2) angstrom, c = 7.43 1 (1) angstrom, beta = 96.33(1), V = 996.0 angstrom(3), Z = 4, R1 = 0.039 for 2672F(degrees) > 4 sigma(F-o) and 153 variables). The crystal structure is characterized by three-membered chain fragments, composed of a central BeO2(H2O)(2) Polyhedron sharing corners with two SO4 tetrahedra. These bent [Be(SO4)(2)(H2O)(2)](2-) units are linked by rubidium ions and hydrogen bonds to double layers and further to a three-dimensional framework structure. Rb2Be(SO4)(2)center dot 2H(2)O is isotypic to the respective potassium sulfate and selenate compounds. The strengths of the hydrogen bonds in the title compound as deduced from the infrared wavenumbers of the uncoupled OD stretches of matrix-isolated HDO molecules (isotopically dilute sample) are discussed in terms of the O-w center dot center dot center dot O hydrogen bond distances, the different hydrogen bond acceptor capabilities of the sulfate oxygen atoms and the strong Be-OH2 interactions (synergetic effect). The intramolecular O-H bond lengths are derived from the v(OD) versus r(OH) correlation curve [H.D. Lutz, C. Jung, J. Mol. Struct. 404 (1997) 631]. (C) 2007 Elsevier B.V. All rights reserved.