Novel Ba(II) and Pb(II) coordination polymers based on citric acid: Synthesis, crystal structure and DFT studies

Two new Ba(II) and Pb(II) citrate coordinate polymers have been synthesized and structurally characterized. The crystalline complexes have been obtained using the gel method. The high purity of synthesized compounds has been confirmed by the X-ray photoelectron study. The deprotonation of citric acid and metal-carboxylate ligand binding has been observed in the XPS as well as IR spectra. The crystal structure of both complexes has been determined by X-ray crystallography, thus being the first crystal structure of Ba(II) citrate and only the second one of Pb(II) citrate reported in literature. Both hydrated complexes: {[5Ba(C6H5O7)(2)(C6H6O7)(2)center dot 6H(2)O]center dot 2H(2)O}(n) and {[5.5Pb(C6H5O7)(3)(C6H6O7)center dot 5H(2)O]center dot 4.5H(2)O}(n) are three-dimensional polymers with four crystallographically distinct citrate groups, which differ in charges and chelating modes. The O-atoms from organic and aqua ligands are nearly symmetrically distributed around the Ba(II) anions, whereas the Pb(II) cations display hemidirected coordination geometries. These metal-citrate moieties as well as the very complex hydrogen-bonding scheme, which arises from the super-abundance of donors and acceptors, lead to the stable structures of both complexes. Additional insight into the electronic structure of the studied compounds, and in particular the properties of stereochemically active lone electron pair on Pb(II) ion, has been gained from the periodic density functional theory calculations. (C) 2017 Elsevier Ltd. All rights reserved.