Crystal structures were determined for two compounds, 2-pyridinecarboxaldehydeazine, 1, and biacetylazine, 2. 2-Pyridinecarboxaldehydeazine crystallizes in space group P2(1)/c with a = 10.0487(7) Angstrom, b = 4.6452(7) Angstrom, c = 11.6700(11) Angstrom, beta = 91.030(6)degrees, V = 544.65(10) Angstrom(3), Z = 2, R = 0.0345. Biacetylazine crystallizes in space group C2/c with a = 9.879(7) Angstrom, b = 12.409(4) Angstrom, c = 7.950(6) Angstrom, beta = 98.44(6)degrees, V = 964.0(11) Angstrom(3), Z = 4, R = 0.0496. Comparison of the imine bond lengths of these and other azine and diimine systems found in the literature suggests that conjugation of imines is better through the carbon-carbon bond than through the nitrogen-nitrogen bond. Semiempirical structural calculations demonstrate that the N-N bond in these azines is rotationally soft, thereby allowing significant twisting at little energy cost. This accounts for the observation that 1 is planar and 2 is not.
A new group of controlled chain length oligoazine analogues with pyridine end groups are synthesized and characterized.
Pentaammineruthenium complexes bridged by 2,3-dicyanopyrazine and 2,3-dicyano-5,6-dimethylpyrazine have been prepared and characterized. The bridging ligand binds to the metal atoms through the cyano nitrogen. Complexes can be prepared in the + 4 and + 6 oxidation states but the mixed-valence, + 5, state is not observed experimentally, unlike the previously prepared 1,2-dicyanobenzene dimer which does have a stable + 5 state. A simple electronic model is constructed from the spectroscopic data and is used to show that the electronic perturbations caused by the uncomplexed nitrogen atoms in the pyrazine ring are sufficient to drive the disproportionation reaction of the + 5 state.
