Dipicolylamine Complexes of Copper(II): Two Different Coordination Geometries in the Same Unit Cell of
Mallayan Palaniandavar1, Raymond J. Butcher, Anthony W. Addison
1Departments of Chemistry, Drexel University, Philadelphia, Pennsylvania 19104, and Howard University, Washington, D.C. 20059.
Abstract:
Bright blue Cu(Dipica)(2)(BF(4))(2) crystallizes in the monoclinic space group P2(1)/n, with unit cell parameters a = 23.406(6) Å, b = 9.338(2) Å, c = 25.573(7) Å, beta = 95.39(2) degrees, and Z = 8. The structure was solved by conventional Patterson and Fourier methods. The R and R(w) values for 5282 observed reflections were 7.06% and 9.10% respectively. Two structurally different complex cations are present in the same unit cell, one hexacoordinate and the other pentacoordinate. In the hexacoordinate cation, the two tridentate bis(2'-picolyl)amine ligands are trans-facially coordinated with two pyridine nitrogens and the two secondary amine nitrogens situated on four positions in a plane [Cu-N(pyr) = 2.189(6), 2.146(6) Å; Cu-N(sat) = 2.207(6), 2.201(5) Å]. The remaining two pyridine nitrogens constitute the axis [Cu-N(pyr) = 2.035(5), 2.038(5) Å] in an equatorially expanded pseudooctahedral geometry. The pentacoordinate cation possesses a square-pyramidal configuration, the two secondary nitrogens being mutually cis, with one Dipica equatorially tridentate [Cu-N(pyr) = 2.044(5), 2.027(5) Å, Cu-N(sat) = 1.995(5) Å]. The other Dipica functions as a bidentate ligand, with one of the pyridine nitrogens occupying the equator [Cu-N(pyr) = 1.986(5) Å] and the aliphatic nitrogen defining the axial copper position [Cu-N(sat) = 2.344(5) Å]. Its second pyridine is uncoordinated but hydrogen-bonded to the coordinated NH of the other ligand. Solution properties offer no clear distinction between the two cation stereochemistries. The ternary chelates [Cu(Dipica)(Acac)]ClO(4) and [Cu(Dipica)(Bipy)](ClO(4))(2) are also described.
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