6533b7d0fe1ef96bd125b6e3

RESEARCH PRODUCT

Copper(II) and nickel(II) chelates with dihydrogen Trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetate(2−) ion (H2CDTA2−). Synthesis, XRD structure and properties of [Cu(H2CDTA)]·H2O and [Ni(H2CDTA)(H2O)·4H2O

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Abstract Stoichiometric reactions of metal hydroxycarbonates with the acid trans -1,2-cyclohexanediaminotetraacetic acid (H 4 CDTA) in water under reduced pressure yielded [Cu(H 2 CDTA)]·H 2 O ( I ) and [Ni(H 2 CDTA) (H 2 O)]·4H 2 O ( II ). Both compounds were characterized by TG-DTA analysis, spectral properties (IR, reflectance and RSE) and X-ray diffraction. In I the copper(II) atom exhibits a distorted square-base coordination (type 4+1) by chelation of one H 2 CDTA 2− ligand 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 H 2 CDTA 2− remains free. In II the H 2 CDTA 2− chelating 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(H 2 EDTA)(H 2 O)] (M = Ni, Cu complexes suggest that the steric constraints in the H 2 CDTA ligand promotes the distorted five-coordination of the Cu II chelate in I as well as the hydration of the nearly octahedral Ni II derivative ( II ). The double protonation of the ligand H 2 CDTA 2− is carried out over different kinds of chelate rings, G and R, for Cu II and Ni II M(CDTA) derivatives, respectively (where G and R, indicate metal-glycinate rings nearly coplanar or perpendicular to the plane MNN, respectively).