Synthesis, spectroscopy, thermal and X-structure studies of a seven coordinated hydrated Ca(II)-<i>para</i>-nitrobenzoate complex showing mono and bidentate carboxylate ligation^ψ

Abstract

The reaction of CaCo₃ with 4-nitrobenzoic acid (4-nhaH) results in the formation of a seven coordinated Ca (II) complex [Ca(H₂O)₄(4-nba)₂] <b>1</b>, (4-nba being 4-nitrobenzoate). The compound has been characterized by elemental analysis, IR and UV-Vis spectra and its structure determined. The complex can be dehydrated to the corresponding anhydrous Ca(II)bis-4-nitrobenzoate Ca(4-nba)₂ <b>2</b>, and the anhydrous complex thus formed can he rehydrated as evidenced by IR spectra. The structure of <b>1</b> exhibits both monodentate and bidentate carboxylate ligation of the 4-nitrobenzoate ligand. The coordination by the O atom from four water molecules completes the heptacoordination around Ca(II). The free O atoms of the monodentate 4-nba and one of the coordinated O atom of the bidentate 4-nba in <b>1</b> are linked via H-bonding to one of the coordinated waters of a neighbouring Ca(II) resulting in the formation of psuedo dimers. The dimers thus formed are further linked with the aid of II bonds, along <i>a</i> as well as <i>b </i>resulting in the formation of an intricate supramolecular network.