THE CRYSTAL, MOLECULAR AND ELECTRONIC-STRUCTURES OF COPPER(II) DIPROPYLENETRIAMINE THIOCYANATE NITRATE

The crystal and molecular structure of Cu(dpta)(NCS)(NO3) where dpta = dipropylenetriamine is reported. The blue compound which crystallizes in space group P2(1)/c with Z = 4 and a = 9.571(2), b = 10.453(2), c = 13.620(3) angstrom, beta = 108.29(2)-degrees V = 1294(1) angstrom3 gave 4313 reflections with R(w) = 0.068. Cu(II) is four coordinate with three Cu-N contacts (2.017(6), 2.083(5) and 2.009(6) angstrom) from the tri-dentate dpta and one contact (2.005(6) angstrom) from the N-coordinated NCS group. The contact with an O atom from the NO3 group is at > 3.5 angstrom. The CuN4 group is almost planar, slightly rhombically distorted, and Cu is out of the 4N plane, the amine nitrogens being tilted towards the NCS group. The dpta ligand is in a symmetric conformation (k,k') around the central Cu-N and the NCS group is linear but it is at 162-degrees to the plane of the three dpta nitrogens. The observed molecular symmetry is explained by crowding of the CH2 groups on the one side of the CuN4 plane. This is consistent with electronic and ESR spectra and substantiated by MNDO and MM calculations. The red shift (DELTA-E approximately 400 cm-1) with the temperature observed in the electronic spectra and the polarizations can be explained in terms of dynamic Jahn-Teller coupling and displaced excited states.