Layered and pillared metal carboxyethylphosphonate hybrid compounds

Abstract

A series of carboxyethylphosphonate hybrid materials has been prepared: Mn^II(O₃PCH₂CH₂COOH)·H₂O (1), Mn^III(OH)(O₃PCH₂CH₂COOH)·H₂O (2), Al₃^III(OH)₃(O₃PCH₂CH₂CO₂)₂·3H₂O (3) and Cr₂^III(OH)₃(O₃PCH₂CH₂CO₂)·3H₂O (4). Compounds 1 and 2 were synthesized from Mn^III(CH₃COO)₃·2H₂O under hydrothermal, or refluxing treatments, respectively. The crystal structures of the manganese-bearing solids have been solved ab initio from laboratory X-ray powder diffraction data and refined by the Rietveld method. 1 crystallises in a orthorhombic cell and 2 in monoclinic symmetry. Both solids have inorganic 2D layered structures with the acid carboxylic groups pointing towards the interlayer space, and the layers linked only through hydrogen bonds. The inorganic layers of these compounds are formed by manganese atoms in distorted octahedral environments linked together by the phosphonate groups. The crystal structure of 3 has been solved ab initio from synchrotron X-ray powder diffraction data. This solid shows a pillared structure with the phosphonate and carboxylate groups cross-linking the inorganic layers. These layers contain chains of aluminium octahedra running parallel to each other. 4 is amorphous and the IR-UV-VIS spectra suggest a framework with Cr(III) cations in octahedral environments. Thermal, spectroscopic and magnetic data for manganese and chromium compounds as well as the structural details of these solids are discussed.