X-ray crystal structures of 2,2'-bis(pyrazol-1-yl)-4,4'-bipyridine and tetramethyl derivative; new bis-bidentate binucleating ligands

X-ray crystal structures of 2,2'-bis(pyrazol-1-yl)-4,4'-bipyridine (3) ad 2,2'-bis(3,5-dimethylpyrazol-1-yl)-4,4'-bipyridine (4) have been determined at 130 K. Crystals of (3) are triclinic, and their structure was refined to a conventional R(I > 2σ(I)) = 0.0273. Crystals of (4) are orthorhombic, and their structure was refined to a conventional R(I > 2σ(I)) 0.0386. In both molecules there is significant (33±1 deg) twisting about the central pyridine-pyridine bond. The pyrazole rings of (3) are approximately coplanar (6±2 deg) with their attached pyridine rings, while in (4) the methyl groups induce slightly greater deviations from coplanarity (15±3 deg). Factors which influence the solid-state conformations and molecular packing of these molecules are discussed. 15 refs., 4 tabs., 3 figs