Structural characterization of sodium and potassium 3-nitrohydrogenphthalate coordination polymers

Abstract

The synthesis, crystal structures and properties of two alkali metal 3-nitrohydrogenphthalates obtained by a 1:2 reaction of M sub(2)CO sub(3) (M = K or Na) with 3-nitrophthalic acid (LH sub(2)) are reported. In the anhydrous potassium coordination polymer [K(LH)] (LH = 2-carboxy-3-nitrobenzoate) 1, the K sup(+) cation is bonded to nine oxygen atoms from six symmetry related (LH) sup(-) ligands resulting in a distorted {KO sub(9)} coordination polyhedron. Five of the six oxygen atoms including a nitro oxygen atom of the crystallographically unique 2-carboxy-3-nitrobenzoate are involved in metal binding. The Mu 6-bridging mode of (LH)sup(-) places the K sup(+) cations into the layers of the two-dimensional (2D) coordination polymer. Each {KO sub(9)} polyhedron in 1 shares edges with two other polyhedra along the b and c axes. A low temperature structure redetermination of [Na(L sup(#)H)(H sub(2)O)3].H sub(2)O (L sup(#)H = 2-carboxy-6-nitrobenzoate) 2 has revealed that the (L sup(#)H)- anion is bonded to the Na sup(+) cation in a monodentate fashion via the carbonyl oxygen atom of the -COOH group and two of the three unique aqua ligands exhibit a bridging bidentate mode stabilizing a chain polymer. The structure of compound 2 thus consists of chains of edge-sharing {NaO sub(6)} octahedra. Thermal decomposition of 1 or 2 results in the formation of metal carbonate residues.