CO[(CH3)2N~HlCH2NH,]2[CC137C0212 bclongs to thc monoclinic trystal system, spacc group P 2 , l c with LI = 7.216(1) A, O = 12. I 17(3) A, c = 13.616(4) A. 0 = 103.27(2)", V = 1 158.7 A', Z = 2. Thc S~I.LIC~USC was solvccl by ttic licavy atom rncthod and was rcfincd to R = 0.048. K,,. = 0.056 for 1761 rcflcctions with I 2 313 ( I ) . Thc coniplcxcs lic on crystallograpliic centers of syrnmctry. Deviations froni regular octahedral coordination arc cluc to ,stcric crowding and chclatc ring constraints. The Co-NMcl bond is longcr than tlic Co-NH, bond (7-.258(3) The spectra of six-coordinate (1' and d"iietal ions in octahedral and tetragonal symmetries have been the subject of . .. . . numerous studies (1, 2). The splittings of the octahedral Tstates into E and A or B states in tetragonal symmetry are well understood. The band splittings are especially well resolved when there are marked differences in the strengths of the inplane and axial ligand fields.Systems whose symmetries are less than D,,, al-e very numerous, yet detailed treatments of their spectra are few. The situation is complicated by the large number of possible low synimetry point groups which result from loss of the four-fold axis. Detailed X-ray structural information is essential in order to establish which of the many possible types of d~stortlon actually applies to an indiv~dual complex.In our early explorations of thls neglected area, we reported analyses of the electronic spectra of several coniplexes whose C2, symmetry had been previously demonstrated by detailed X-ray work (3). The reduction in symmetry from D,,, to Cz, was explored theoretically by means of the Normalised Spherical Hamiltonian (NSH), and Angular Overlap Model (AOM) methods.More recently, we have studied complexes whose geometry --'To whom corrcspondcncc should bc addressed is very nearly D,,, due to their all-tt.nrrs nature. We have reported the X-ray structure and crystal spectrum of Ni((C2Hi)?NCH2CH?NH2)2(NCS)?. in which the lowest triplet band is clearly resolved into three well separated peaks (4). The X-ray structure of this complex reveals that the Ni-NEt distance is very much longer than usual for Ni-N distances in complexes. This provides an explanation for the rhombic spectrum in terms of a reduced AOM a parameter for the dialkylated nitrogen bond vector. We were thus able to extend the work of Bertini et 01. (5), thereby demonstrating a clear inverse correlation between metal ligand bond length and AOM u bonding parameters.
--As part of an on-going study related to the single crystal spectra of low symmetry transition metal coniplexes (1 -7), we now report the X-ray crystallographic analysis and low temperature electronic spectrum of bis(trich1oroacetato)bis-(N,N-dimethylethylenedian~ine)cobalt(ll).
ExperimentalCrystals were grown following stoichiomctric reaction of cobalt trichloroacctate with N.N-dirnetliylcthylcncdiarnine under a nitrogen blanket. Analyses were satisfactory.Many of thc crystals wcre twinned. Onc rathcr largc rcd crystal, 0.55 X 0.35 X 0.23 rn...