Synthesis and structural characterization of three new mixed ligand alkaline-earth metal picrates

Abstract

The dissolution of alkaline-earth metal carbonate in aqueous picric acid followed by reaction with nicotinamide results in the formation of [M(H sub(2)O) sub(n) (nic) sub(2)(pic) sub(2)] (nic = nicotinamide; pic = picrate; n = 1 and M = Ba 1; n = 2 and M = Ca (or Sr) 2 (or 3)). In [Ba(H sub(2)O)(nic) sub(2)(pic) sub(2)] 1, the barium and the oxygen atoms of a terminal aqua ligand are located on a two-fold axis. Compound 1 exhibits a {BaO sub(7)N sub(2)} coordination sphere, where the barium atom is bonded to a unique bidentate picrate and the crystallographically independent nicotinamide bridges to two symmetry related barium atoms with a Ba...Ba separation of 9.799 Angstrom via the pyridine nitrogen and the amide oxygen atoms leading to the formation of a two-dimensional coordination polymer. The compounds 2 and 3 are isostructural with discrete molecules. The central Ca atom in 2 (or Sr in 3) located on a two-fold axis is bonded to a crystallographically unique terminal aqua ligand, an independent monodentate nicotinamide and a unique bidentate picrate anion resulting in a distorted {MO sub(8)} polyhedron. The mixed ligand alkaline-earth metal picrates 1-3 exhibit three varieties of hydrogen bonding and Pi-Pi stacking interactions. Several alkaline-earth metal picrates are compared in this study.