The Structure of 2,3-Butanedione Dihydrazone and IR Study of Higher Polyazines: A New Class of Polymeric Conductors
Charles R. Hauer, Gregory S. King, Erica L. McCool, William B. Euler, Joseph D. Ferrara, Wiley J. Youngs, Journal of the American Chemical Society, 1987, 109, 5760 – 5765
Abstract
Polyazines, H2N–[N=C(CH3)–C(CH3)=N]x–NH2, of various chain lengths have been prepared and studied by IR spectroscopy. An X-ray crystal structure was done on the monomer of this series, 2,3-butanedione dihydrazone (x = 1). It crystallized in space group P42/n with cell constants a = 12.172 (3) Å and c = 4.115 (1) Å and Z = 4; intensity data were collected from 3.0° ≤ 2θ ≤ 65.0°. Refinement to convergence on the 1195 independent reflections, I ≥ 3σ(I), resulted in final anisotropic R = 0.043 and Rw = 0.048. The monomer is planar with long carbon-nitrogen double bonds (1.291 (1) Å) in the E conformation, the methyl groups are anti across the short carbon-carbon single bond (1.474 (2) Å), and the lone pairs across the nitrogen-nitrogen single bond are gauche. The anomalous bond lengths indicate a degree of π-bond conjugation in this molecule. The higher molecular weight materials are yellow to brown powders, are stable to air, have high melting points, and are surprisingly resistant to hydrolysis. Correlation of the IR spectra of the monomer and sequentially increasing chain length polymers shows that the highest molecular weight material is at least 45 monomer units long and is planar with double bonds in the E conformation and all single bonds in the anti conformation. As in the monomer, the position of the C=N resonance indicates conjugation of the π system along the polymer chain. The polymer can be doped with iodine to give air-stable electrically conducting materials with room-temperature conductivities as high as 1.3 Ω–1cm–1. IR spectra of the doped materials show that the polymer retains its structural integrity, and two new doping-induced absorptions appear.