CONFORMATIONAL STUDIES OF SOME IMIDAZOLE-BASED NON-FUSED BISHETEROCYCLES, X-RAY CRYSTAL-STRUCTURE OF 1,1'-DIMETHYL 2,2'-BISBENZIMIDAZOLE

X-ray crystal structure of 1,1'-dimethyl 2,2'-bisbenzimidazole has bee n reported. Crystals are monoclinic, space group F21/n, a=6.424(2), b= 5.747(2), C=17.185 (3)A degrees, beta=94.43 (2)degrees. 982 Reflection s are refined to R=0.0129. The inter ring twist angle is almost 0 degr ees and this along with other geometrical parameters well tally with t hose calculated from semiempirical MNDO type methods like MNDO, AM1 an d PM3. These methods have been used to analyst molecular structure and conformational behaviour of the aforesaid molecule and some related i midazole-based non-fused bisheterocycles. The abs minimum of the poten tial energy curve corresponds to the planar trans conformation and the maximum in the curve corresponds to the cis-conformation in all the c ases. The preference of trans-form over the cis-form in the ground sta te, in each case, is attributed to the electrostatic repulsions betwee n the non-bonded atoms. The difference in the heats of formation data between two forms of each molecule in the series exhibits their usage as ligating agents for various transition and inner-transition metals.