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Free keywords:
Framework structure; Lone-pair element; Phosphate; Hydroxide; Antiferromagnetic
Abstract:
The new compound Co(3)Te(2)O(2)(PO(4))(2)(OH)(4) was synthesized using hydrothermal techniques. It crystallizes in the monoclinic space group C2/m with the unit cell a=19.4317(10) angstrom, b=6.0249(3) angstrom, c=4.7788(2) angstrom, beta=103.139(5)degrees. The crystal structure is an open framework having chains of edge sharing [Co(1)O(6)] octahedra. Other building blocks are [TeO(3)(OH)(2)], [PO(4)] and [Co((2))O(2)(OH)(4)] connected mainly via corner sharing. The -OH groups protrude into channels in the structure. The magnetic susceptibility measured from 2 to 300 K shows two broad anomalies at around 21 K and 4 K. respectively. The peak at similar to 20 K is ascribed to a two-dimensional antiferromagnetic ordering of linear [Co(1)O(6)] chains coupled by interchain interaction via [PO(4)] groups in the Co(1) sheets. The second transition at 4 K is ascribed to a second antiferromagnetic ordering of the moments of the Co(2) entities via super-super exchange involving [PO(4)] and [TeO(3)(OH)(2)] groups. This assignment is strongly supported by low-temperature heat capacity measurements indicating an entropy removal within the high-temperature transition of about twice the magnitude of the low-temperature transition. (C) 2011 Elsevier Inc. All rights reserved.
