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

X-Ray crystal structures of 2,2'-bis(pyrazol-1-yl)-4,4'-bipyridine (3) and 2,2'-bis(3,5-dimethyl-pyrazol-1-yl)-4,4'-bipyridine (4) have been determined at 130 K. Crystals of (3) are triclinic, <P(1)over bar>, a 8.061(1), b 9.024(1), c 10.680(1)Angstrom, alpha 102.032(8), beta 107.931(6), gamma 107.355(7)degrees, Z = 2; the structure was refined to a conventional R(I > 2 sigma(I)) = 0.0273. Crystals of (4) are orthorhombic, P2(1)2(1)2(1), a 7.077(2), b 13.906(4), c 16.697(5) Angstrom, Z = 4; the structure was refined to a conventional R(I > 2 sigma(I)) = 0.0386. In both molecules there is significant (33+/-1 degrees) twisting about the central pyridine-pyridine bond. The pyrazole rings of (3) are approximately coplanar (6+/-2 degrees) with their attached pyridine rings, while in (4) the methyl groups induce slightly greater deviations from coplanarity (15+/-3 degrees). Factors which influence the solid-state conformations and molecular packing of these molecules are discussed.