Photodimerization of a 1D hydrogen-bonded zwitter-ionic lead(II) complex and its isomerization in solution.

A pair of bpe-H(+) ligands in a zwitter-ionic complex undergoes photochemical cycloaddition quantitatively accompanied by proton transfer and the cyclobutane ring isomerizes slowly in solution to two more isomers, catalyzed by CF(3)CO(2)H acid.