Structure of an adduct between diammonium dihydrogendiphoshate and telluric acid: (NH4)2H2P2O7.Te(OH)6

Abstract

Telluric acid-diammonium dihydrogen- diphosphate (1/1), Te(OH)6.(NH4)2H2P207, Mr = 441.677, monoclinic, P21/n, a-- 7.651 (2), b = 21.790 (10), c = 6.689 (2) A, /3 = 113.85 (3) °, V= 1020 (1)/~3, Z = 4, Dx = 2.876 Mg m -3, A(Ag Ka) = 0.5608 A, /z = 1.766 mm-~, /7(000) = 864, T= 294 K, final R = 0.033 for 3602 reflections. The title compound is the second example of an adduct between telluric acid and a diphosphate. Thick layers containing infinite (H2P207) n chains and layers of Te(OH)6 octahedra alternate perpendicular to the b axis. The hydrogen-bond scheme which includes very short bonds inside the (HEP207) n chains is described. Crystal data for the isotypic Rb salt are given. Introduction. During the past 20 years the authors have characterized a great number of addition com- pounds between telluric acid and various alkali phos- phates, condensed or not. A good review of the present state of crystal chemistry of this class of adducts was recently given by Boudjada (1985). The main feature of these compounds is the coexistence within the atomic arrangement of both Te(OH)6 groups and phosphoric anions as independent units (not sharing O atoms). Among this important class of addition compounds K3HP207.Te(OH)6.H20 (Averbuch-Pouchot & Durif, 1983) was up to now the only one involving a diphosphate group. In the present work we report the chemical preparation and crystal structure determination for the second example of coexistence of Te(OH)6 octahedra and diphosphate groups in an atomic arrangement: Te(OH)6.(NHa)2H2 P207. The corresponding Rb salt, Te(OH)6.Rb2H2P207, is isotypic, with the following unit-cell dimensions: a = 7.652 (2), b = 21.758 (10), c = 6.674 (2) A, fl = 114.12 (5) ° .