Hydrothermal synthesis and characterisation of amine-templated metal phosphate framework

Abstract

Two coordination polymers [CH₃CH₂NH₃]₂M₃(NH₃C₆H₄CO₂)₂(HPO₄)₄ (H₂O)₂ (M = Ni for compound I and M = Zn for compound II) incorporating ethylammonium-4-aminobenzoate, were hydrothermally synthesized (autogeneous pressure for 5 days) at 105⁰C. The Scanning Electron Micrographs revealed a greenish rectangular block for the Ni(II) complex and a colourless square plate for the Zn(II) complex. The complexes were characterised by IR-spectroscopy and the Infrared spectra of the two compounds exhibited similar essential features. The Spectra clearly showed the presence of co-ordinated water and terminal –NH₃⁺. The broad band at 3914cm^-1 (I) and 3926 – 3760cm^-1 (II) is due to the presence of water molecule in the structure. The bands at 3542 - 3401cm^-1 (I) and 3434cm^-1 are associated with stretching vibration of ν(-NH₂). The strong absorption bands at 1108 - 1014cm^-1 (I) and 1108 – 1018cm^-1 (II) are associated with the asymmetric stretching vibration of ν(PO₄) groups, whereas those at 936 - 629cm^-1 (I) and 934 – 718cm^-1(II) correspond to its bending mode. The complexes were thermally stable up to 300⁰C, after which the organic components starts decomposing. The solubility test in a wide spectrum of solvents (at room temperature) showed that the complexes were insoluble in water, ethanol, DMF and DMSO.

Keywords: Hydrothermal synthesis, metal phosphates, p-aminobenzoic acid, ethylacetoacetate, ethylammonium- 4-aminobenzoate.