A calcium(II) coordination polymer based on a tricyclic dicalcium-bis(2-nitrobenzoate) building block

Abstract

The reaction of CaCO 3 with 2-nitrobenzoic acid (2-nbaH) results in the formation of a coordination polymer, [Ca(2-nba) 2(H 2O) 2] n ( 1) (2-nba = 2-nitrobenzoate), which can be dehydrated to [Ca(2-nba) 2] ( 2). Compound 2 can be rehydrated to 1 on exposure to water vapor. Compounds 1 and 2 were characterized by elemental analysis, IR and UV–Vis spectra, and TG-DSC thermograms. Compound 1 crystallizes in the triclinic space group P 1 ¯ and its structure consists of an eight coordinated calcium(II), two terminal aqua ligands and two crystallographically independent 2-nba anions, both of which function as μ 2–η 2:η 1 bridging ligands. Each unique 2-nba ligand is linked to Ca(II) in a bidentate fashion via the carboxylate oxygen atoms and is further linked to a symmetry related Ca(II) via one of the oxygen atoms. A pair of such μ 2–η 2:η 1 2-nba ligands are bridged to two symmetry related Ca(II) ions, resulting in the formation of a tricyclic dicalcium-bis(2-nitrobenzoate) moiety, which constitutes the basic building block of the polymer. In the crystal structure of 1, alternating pairs of bridging 2-nba ligands link pairs of {Ca(H 2O) 2} 2+ units into a 1-D polymeric chain extending along the a-axis. The oxygen atoms of the coordinated water, and the carboxylate and nitro groups of 2-nba are involved in O–H···O and C–H···O interactions.