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

Abstract

The reaction of CaCO3 with 4-nitrobenzoic acid (4-nbaH) results in the formation of a seven coordinated Ca(II) complex [Ca(H2O)(4)(4-nba)(2)] 1, (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(Il)bis-4-nitrobenzoate Ca(4-nba)(2) 2, and the anhydrous complex thus formed can be rehydrated as evidenced by IR spectra. The structure of 1 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 1 are linked via H-bonding to one of the coordinated wafers of a neighbouring Ca(II) resulting in the formation of psuedo dimers. The dimers thus formed are further linked with the aid of H-bonds, along a as well as b resulting in the formation of an intricate supramolecular network.