COPPER(II) AND NICKEL(II) CHELATES WITH DIHYDROGEN TRANS-I,2-DIAMINOCYCLOHEXANE-N,N,N',N'- TETRAACETATE(2--) ION (H2CDTA2-). SYNTHESIS, XRD STRUCTURE AND PROPERTIES OF [Cu(H2CDTA)] "H20 AND [Ni(H2CDTA) (H20)] • 4H20

-Stoichiometric reactions of metal hydroxycarbonates with the acid trans-l,2cyclohexanediaminotetraacetic acid (H4CDTA) in water under reduced pressure yielded [Cu(H2CDTA)]'H20 (I) and [Ni(H2CDTA)(H20)]'4H20 (II). Both compounds were characterized by TG-DTA analysis, spectral properties (IR, reflectance and RSE) and Xray diffraction. In I the copper(II) atom exhibits a distorted square-base coordination (type 4 + 1) by chelation of one H2CDTA 2ligand through two N and two O (carboxylate) at the square base and one O (carboxylic) at the apex of the coordination polyhedron; a second carboxymethyl group of H2CDTA 2remains free. In II the H2CDTA 2chelating ligand also plays a quinquedentate role, but one water molecule achieves the slightly distorted octahedral coordination of the nickel(II) atom. Appropriate comparisons with the structure of [M(H2EDTA)(H20)] (M = Ni, Cu) complexes suggest that the steric constraints in the HzCDTA ligand promotes the distorted five-coordination of the Cu n chelate in I as well as the hydration of the nearly octahedral Ni II derivative (II). The double protonation of the ligand H2CDTA:is carried out over different kinds of chelate rings, G and R, for Cu" and Ni II M(CDTA) derivatives, respectively (where G and R, indicate metal-glycinate rings nearly coplanar or perpendicular to the plane MNN, respectively). * Author to whom correspondence should be addressed.