Relation between structures and spectroscopic properties of Group IIB metal [M(chelate)X2] complexes (X = Cl, Br, I). Crystal and molecular structure of [H2NCH2(CH3)2CCH2NH2]MX2 complexes (M = Zn, X = Cl, Br; M = Cd, X = Br)

The synthesis and structural and spectroscopic characterization of a series of d10 metal(II) compounds of the type [M(dmpd)X2] (M = Zn(II), Cd(II), Hg(II); dmpd = 2,2-dimethylpropane-1,3-diamine; X = Cl, Br, I) are described. The different spectroscopic properties, which divide the complexes into two classes, are discussed and unambiguously assigned only on the basis of the knowledge of the crystal structure of compounds representative of each class. Therefore, the crystal structures of [Zn(dmpd)Cl2] (I), [Zn(dmpd)Br2] (II), and [Cd(dmpd)Br2] (III) are determined from three-dimensional single-crystal X-ray data. The complexes are monoclinic, space groups P21/m for I and II and P21 for III, with two formula units in cells of the following dimensions: a = 6.014 (1) Å, b = 7.724 (1) Å, c = 10.483 (1) Å, and β = 91.32° for I; a = 6.234 (2) Å, b = 7.968 (2) Å, c = 10.628 (2) Å, and β = 91.81° for II; a = 11.288 (2) Å, b = 5.893 (1) Å, c = 7.622(1) Å, and β = 92.72° for III. The structures have been refined to R = 0.024, 0.036, and 0.025 for I, II, and III, respectively. The complexes I and II are isomorphous and isostructural. In these complexes the zinc atom is tetrahedrally surrounded by two halogen and two nitrogen atoms. The only difference between these complexes is the strength of hydrogen-bonding interactions. In the complex III the cadmium atom is octahedrally surrounded by four bromine atoms and two nitrogen atoms of a dmpd molecule. The octahedral moieties are linked in infinite chains by bromine bridges. In all the compounds the dmpd molecule acts as a chelating ligand, giving a six-membered chelate ring in a partially flattened chair conformation.