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 thieno2,3‐b:4,5‐b′]dipyridine ( 1 ) and its monohydroperchlorate salt ( 1a ) 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 going from 1 to 1a the largest changes in bond angles and bond lengths occur in ring A. ¹H and ^l3C nmr spectra of 1 plus the ¹³C nmr spectrum of 1a are reported.