Influence of substituents within bidentate nitrogenous bases on the spectra of mixed-ligand (1,1-dithiolato) copper(II) and nickel(II) chelates

A series of mixed-ligand copper(II) and Nickel(II) chelates, [M(enR)(i-MNT)], containing the dianion of 1,1-dicyano-2,2-ethlenedithiole, (i-MNT)(2-), and an N-alkyl substituted 1,2-diaminoethane, enR, were prepared and characterised. From the IR spectra of [M(enR)(i-MNT)] it transpires that the influence of the groups attached to the diamine on group vibrations is not as important as that of substituents linked to the >C=C< entity. It is established that the frequency of a strong band in the 1340 to 1550 cm(-1) region is inversely proportional to the interatomic distance of the >C=C< entity. The magnetic behaviour and the electronic excitation and ESR spectra indicated a square-planar structure. The existence of metal(II) in a square-planar environment was confirmed by the X-ray diffraction of [Ni(Et(2)en)(i-MNT)] determined from a single microcrystal (monoclinic, space group P2(1)/n, a=7.277(2), b=8.793(3), c=21.557(3) angstrom, beta=95.07(1)(0), Z=4, R=0.0491, R-w=0.0551)