Synthesis and X-ray structural study of magnesium (1,3-propanediaminetetraacetato)cuprate(II) octahydrate, Mg[Cu(1,3-pdta)] • 8H2O.: Stereochemistry of hexadentate copper(II)-edta-type complexes in relation to the structure of the ligand

The hexadentate complex Mg[Cu(1,3-pdta)]. 8H(2)O (1) (where 1,3-pdta represents the 1,3-propanediaminetetraacetate ion) has been prepared and isolated and its structure established by X-ray crystallography. The structure converged to R = 0.030 for 1537 observed reflections. The Cu(II) ion is surrounded by two nitrogen atoms and four oxygen atoms of the ligand, making a tetragonally elongated octahedron (T=0.868). The Mg cation is bonded octahedrally to six water molecules. Both complex ions utilize a two-fold symmetry axis that is present in the crystal. The conformations of the chelate rings were found to be envelope for the glycinates and skew-boat for the six-membered diamine (T) ring. Comparison of the structures of the hexadentate copper(II)-edta-type complexes shows an expected variation in their stereochemistry, depending on the structure of the ligand. Infrared (carboxylate region) and electronic absorption spectra are also given. (C) 2000 Elsevier Science Ltd All rights reserved.