ZINC-COMPLEXES OF THE LIGAND DIPICOLYLGLYCINE

N,N-bis(2-picolyl>glycine (L-H) which was not obtained in the free state was introduced into zinc complexes via its ethyl ester (L-Et) which yielded the intermediate complexes (L-Et)ZnBr2 (1), (L-Et)Zn(NO3)(2) (2), and (L-Et)(2)Zn(ClO4)2 . H2O (3). Autocatalytic hydrolysis in the presence of water turned 2 into [L . Zn(H2O)(2)]NO3 . H2O (4) with an octahedral and 3 into trimeric [L . Zn]ClO4 . H2O (5) with a trigonal-bipyramidal coordination of zinc in the solid state. 5 was found to be a good starting material for the introduction of coligands forming complexes that mimic the coordination of zinc in enzymes with a N,N,O donor set: With imidazole the octahedral complex [L . Zn(Im)(H2O)]ClO4 (6) was obtained, with 2-methylimidazole the trigonal-bipyramidal complex [L . Zn(MeIm)]ClO4 (7), and with diphenyl phosphate the trigonal-bipyramidal complex [L . Zn(Phos)]. 2H(2)O (8). The coordination in the solid state was confirmed for 1 and 4-8 by X-ray work. NMR studies (solid state and solution) and conductivity measurements have revealed various states of dissociation and solvation in solution, with the trigonal-bipyramidal cation [L . Zn(H2O](+) probably being a common and major constituent of all aqueous equilibria.