Nonbridging and monodentate carboxylate coordination of calcium(2+) through the use of intramolecular hydrogen bonding in a new sterically hindered carboxylate ligand

The sterically hindered carboxylate ligand 2,6-bis(2,2-dimethylpropionylamino)benzoic acid (HL) has been prepared. The two intramolecular hydrogen bonds in HL are exploited to restrict the corresponding carboxylate anion (L-) to non-bridging coordination and to preorganise its sterically bulky substituents proximal to the first and second coordination sphere of the bound metal ion. The crystal structures of the ligand anion as the ammonium salt [NH4][L] and the distorted octahedral calcium complex CaL2(H2O)(2), in which L-binds to the calcium(2+) ion in a monodentate, mode, are described. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Germany, 2004).