Chemical, Spectroscopic and Electrical Conduction Properties of Iodinated Nickel Diimine Complexes

Bis(diimine)nickel complexes [diimine = 2,3-diiminonaphthalene (din) and 9,10-diiminophenanthrene (dip)] have been prepared by oxidation of a solution of Ni2+ and the appropriate diamine. The complexes were studied by UV-vis spectroscopy and compared with the well-known bis(o-phenylenediimine)nickel complex. Oxidation with iodine gave Ni(din)2Ix and Ni(dip)2Ix (where x = 0.13–3.30). Thermogravimetric analyses (TGA) provided quantitative information on the iodine content. Weight losses at 100°C were observed for highly iodinated compounds involving the decomposition of I5− to I3− and for all species above 260°C. Raman and IR spectroscopy were used to characterize the iodine-doped complexes. The Raman spectra showed strong scattering attributable to I3− (107 cm−1) and 15− (160 cm−1), the latter only for highly iodinated complexes. The conductivity of iodine-doped materials was studied by using linear two-probe (300 K) and variable temperature (77–300 K) van der Pauw methods on pressed pellets. The conductivity is thermally activated, with an apparent activation energy of 0.25 and 0.075 eV for Ni(din)2Ix and Ni(dip)2Ix, respectively. A large increase of the conductivity for more extended molecules is observed.