Complexation of cis-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine with the first row transition metal ions cobalt(III), chromium(III), and nickel(II)

The syntheses and characterization of the Co(III), Cr(III), and Ni(II) complexes of the pendant arm macrocyclic hexaamine cis-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (cis-diammac) are reported and their spectroscopic and structural properties are compared with those of the known isomeric trans-diammac complexes with the aid of molecular mechanics and angular overlap model calculations. In contrast to the [M(trans-diammac)]n+ analogues, the [M(cis-diammac)]n+ complexes do not display short M-N bond lengths, nor are particularly high energy electronic maxima a feature. The [M(cis-diammac)]n+ complexes exhibit trigonally twisted geometries and more positive M(III/II) redox couples than their trans-diammac relatives. The X-ray crystal structure of [Cr(cis-diammac)](ClO4)3.2H2O is reported: C12H34Cl3CrN6O14, orthorhombic, space group Pc2(1)n, a = 10.455(4) angstrom, b = 14.262(4) angstrom, c = 16.905(7) angstrom, Z = 4.