Structure of diiodide salts of N-heteroaromatic dications

The structures of 2,2'-dimethyl-1,1'-biisoquinolinium diiodide monohydrate (I) and 1,1'-dimethyl-4,4'-biquinolinium diiodide (II) have been determined. Both biisoquinolinium and biquinolinium dications have a twofold rotation axis. The two N-heteroaromatic planes in (I) are twisted from each other to a greater extent than those in (II); this can be explained by steric repulsion of the N-methyl groups in (I). In both crystals each I - anion is in arelatively close contact with one of the positively charged N atoms of the dications. These interionic interactions seem to be responsible for the deep red color of the crystals