INFLUENCE OF COORDINATING ANIONS ON THE STEREOCHEMISTRY OF MIXED-LIGAND COPPER(II) COMPOUNDS - CRYSTAL-STRUCTURE AND SPECTRA OF DIONATO)(N,N-DIMETHYL-1,2-DIAMINOETHANE)COPPER(II)

The compound [Cu(CN-acac)Me(2)en(Br)] (Me(2)en denotes N,N-dimethyl-1, 2-diaminoethane) was prepared and investigated by means of structural (X-Ray diffraction) and spectroscopic (IR and electronic) measurements . The compound crystallizes in the monoclinic space group P2(1)/c with a = 5.959(1) Angstrom, b = 7.465(2) Angstrom, c = 19.338(3) Angstrom, beta = 90.89(2)degrees and Z = 4. The structure consists of discrete [Cu(CN-acac)Me(2)en (Br)] monomeric units, in which copper is five-coo rdinated, The 1,2-diamine adopts the gauche conformation with a torsio nal angle of 51.31 degrees, coordinates as bidentate ligand through th e nitrogen atoms, and attains the lambda configuration. The anion of t he 3-cyano-2,4-pentanedione, CN-acac(-), is bonded through the oxygen atoms and the six-membered metallocyclic ring exhibits a semi chair co nformation. The nitrogen and oxygen donor atoms form a square plane. C opper is also bonded to the bromine atom and a distorted square pyrami dal structure around copper exists. The inequalities in the Cu-N dista nces suggest a second-order Jahn-Teller deformation while the elongati on of the Cu - Br bonds implicates d-s orbital mixing. The ligand fiel d excitation energy is appreciably lower than that observed in the [Cu (CN-acac)Me(2)en](+) entity. The principal stretching vibrations are a ssigned and discussed in the light of the structure.