Ni₃Te₂O₂(PO₄)₂(OH)₄, an open-framework structure isotypic with Co₃Te₂O₂(PO₄)₂(OH)₄

Abstract

Single crystals of Ni 3 (TeO(OH) 2 ) 2 (PO 4 ) 2 , trinickel(II) bis[(oxidodihydoxidotellurate(IV)] bis(phosphate),were obtained by hydrothermal synthesis at 483 K, starting from NiCO 3 ·2Ni(OH) 2 , TeO 2 and H 3 PO 4 in a molar ratio of 1:2:2. The crystal structure of Ni 3 Te 2 O 2 (PO 4 ) 2 (OH) 4 is isotypic with that of Co 3 Te 2 O 2 (PO 4 ) 2 (OH) 4 [Zimmermann et al. (2011). J. Solid State Chem . 184 , 3080–3084]. The asymmetric unit comprises two Ni (site symmetries \overline{1}, 2/ m ) one Te ( m ), one P ( m ), five O (three m , two 1) and one H (1) sites. The tellurium(IV) atom shows a coordination number of five, with the corresponding [TeO 3 (OH) 2 ] polyhedron having a distorted square-pyramidal shape. The two Ni II atoms are both octahedrally coordinated but form different structural elements: one constitutes chains made up from edge-sharing [NiO 6 ] octahedra extending parallel to [010], and the other isolated [NiO 2 (OH) 4 ] octahedra. The two kinds of nickel/oxygen octahedra are connected by the [TeO 3 (OH) 2 ] pyramids and the [PO 4 ] tetrahedra through edge- and corner-sharing into a three-dimensional framework structure with channels extending parallel to [010]. Hydrogen bonds of medium strength between the hydroxy groups and one of the phosphate O atoms consolidate the packing. A quantitative structure comparison between Ni 3 Te 2 O 2 (PO 4 ) 2 (OH) 4 and Co 3 Te 2 O 2 (PO 4 ) 2 (OH) 4 is made.