The structural chemistry of lithium, sodium and potassium anthranilate hydrates

Abstract

Lithium, sodium and potassium anthranilates (2-aminobenzoates) have been prepared by neutralization of anthranilic acid with the corresponding alkali hydroxides in aqueous solution. Li(Anth) and Na(Anth) crystallize as hemihydrates, K(Anth) as the monohydrate. A single crystal structure determination has shown that Li(Anth)(H2O)0.5 forms a chain structure composed of unique polyhedral compartments with ten-membered ring rims sharing two opposite rectangular faces. The strings are connected via hydrogen bonds involving the amino groups which are not part of the inner coordination sphere of the penta-coordinated lithium atoms. By contrast, Na(Anth)(H2O)0.5 has a layer structure with the hexa- and hepta-coordinated sodium atoms O,N-chelated by anthranilate anions and interconnected via bridging carboxylate groups and water molecules. Hydrogen bonding contributes to the connectivity within a given sheet with its corrugated double-layer of sodium atoms, but not beyond the layers which are shielded by the arene rings. K(Anth)(H2O) also forms a sheet structure with a single corrugated layer of seven-coordinated potassium cations O,O-chelated and bridged by the anthranilate anions and by the water molecules. The amino groups have no contact with the metal centres and are involved solely in hydrogen bonding. The hydrocarbon rings extending above and below the sheets show no π���π-stacking and are not indented.