The coordination properties of aminobenzoate ligands in complexes with alkali metals

The crystal structures of sodium 4-amino-2-hydroxybenzoate dihydrate [NaL.2H(2)O, L = C6H3(NH2)(OH)COO] and potassium 2-aminobenzoate monohydrate [KL*.H2O, L* = C6H4(NH2)COO] were determined by X-ray diffraction methods. The compound NaL.2H(2)O crystallizes in the monoclinic system, space group P2(1)/c with a = 8.820(2) b = 14.632(3), c = 6.948(2) Angstrom, beta = 97.88(3)degrees. The structure consists of sodium ion pairs joined together by tridentate 4-amino-2-hydroxybenzoate moieties creating a polymeric chain. In the metal centres, two water molecules bridge the sodium atoms. Five oxygen atoms and one nitrogen atom form a distorted octahedral environment. The compound KL*.H2O crystallizes in the monoclinic system, space group P2(1)/c with a=14.684(3), b=7.618(2), c=7.512(2)Angstrom, beta=96.95(3)degrees. The structure consists of octacoordinated potassium atoms bonded with three water molecules and five carboxylate oxygen atoms. Water molecules appear as bridging ligands. The 2-aminobenzoate ligand acts as a pentadentate ligand with the molecular network stabilized by hydrogen bonds. Among the polymeric chains in both structures appear noncovalent interactions of type N-H...X.