X-RAY CRYSTAL-STRUCTURES OF OCTAHEDRAL DIAQUABIS(N,N-DIALKYLETHYLENEDIAMINE)NICKEL(II) COMPLEXES POSSESSING ELONGATED NICKEL(II)-NITROGEN BONDS ALONG AXIAL DIRECTION

The structures of two diaquabis(N,N-dialkylethylenediamine)nickel(II) chlorides ([Ni(H2O)2(diamine)2]Cl2.nH2O) were determined by X-ray crystallographic studies, where diamine is N,N-dimethylethylenediamine(NN-dmen) or N,N-diethylethylenediamine (NN-deen). Both complexes are trans and crystallize in the monoclinic space group P2(1)/n. The unit cell parameters of the NN-dmen complex, NiCl2C8N4O4H32, are a = 7.531(1), b = 13.092(1), c = 9.591(1) angstrom, beta = 107.76(1)-degrees, and Z = 2, and those of the NN-deen complex, NiCl2C12N4O2H36, are a = 9.154(1), b = 8.692(1), c = 12.395(2) angstrom, beta = 104.46(1)-degrees, and Z = 2. In trans-[Ni(H2O)2(NN-dmen)2]Cl2.2H2O and trans-[Ni(H2O)2(NN-deen)2]Cl2, the Ni-NMe2 and Ni-NEt2 bond distances (2.183 and 2.271 angstrom) are much longer than the Ni-NH2 distances (2.078 and 2.064 angstrom), forming tetragonally distorted octahedrons with four close in-plane neighbors(N2O2) and two remote axial ones(N2). It is apparent that this distortion originates from the steric requirement of N-substituted groups. Such a distortion significantly affects the electronic spectra of these complexes.