A comparison of crystallographic and NMR data for thieno[2,3-b : 4,5-b ']dipyridine and its monohydroperchlorate salt

X-ray crystallographic studies of thieno[2,3-b:4,5-b']dipyridine (1) and it s monohydroperchlorate salt (la) show that 1 is protonated at N1 in ring A and not at N6 in ring C. In each compound individual rings are planar, but there is a small dihedral angle-of-twist between the A and C rings. On goin g from 1 to la the largest changes in bond angles and bond lengths occur in ring A. H-1 and C-13 nmr spectra of 1 plus the C-13 nmr spectrum of la are reported.