Synthesis and crystal structures of two new schiff base hydrazones derived from biphenyl-4-carbohydrazide

The crystal structures of two novel Schiff base hydrazones have been determined by means of the X-ray diffraction. These compounds: N'-(E)-(2,5-dimethoxyphenyl)methylidene]biphenyl-4-carbohydrazide, C(22)H(20)N(2)O(3) (1) and N'-(E)-(4-fluorophenyl)methylidene]biphenyl-4-carbohydrazide, C(20)H(15)FN(2)O (2), are the first structurally characterized biphenyl derivatives of phenylmethylidene-carbohydrazide. Both compounds crystallize in the monoclinic space groups, 1 in P2(1)/c space group with a = 13.987(2) , b = 16.426(3) , c = 8.214(2) , beta = 98.12(2)A degrees, and 2 in C2/c with a = 37.163(5) , b = 10.696(2) , c = 8.098(2) , beta = 101.18(2)A degrees. Both molecules have very similar bond lengths and angles pattern, even in the differently substituted phenyl ring. However, the conformations of the molecules differ significantly, the more crowded molecule 1 is much more folded than 2. The dihedral angle between the terminal ring planes is 56.17(6)A degrees in 1 while in 2 it is as small as 2.83(14)A degrees. In both structures relatively short and linear N-H center dot center dot center dot O hydrogen bonds (created by the best available hydrogen bond donor and acceptor) connect molecules into the chains along the unit cell parameter of ca. 8 in length. The next stage of the crystal architecture determination, the secondary interactions, are however quite different: in 1 there are almost solely dispersion van der Waals interactions while in 2 some more specific C-H center dot center dot center dot F and C-H center dot center dot center dot pi interactions are also involved in the crystal packing