An enantiotropic pair of polymorphs of (H 2 -o-PDA 2+ ) 4 (H 5 O 2 + )(SO 4 2– ) 4 (HSO 4 – )·2H 2 O (1) interconvert at 140–142 K with a concomitant change in Z′. The details of the structural change are studied by single-crystal X-ray and neutron diffraction which shows that both forms are close packed with the difference resulting from the linearization of hydrogen bonds at low temperature as part of an extensive charge-assisted hydrogen-bonding network. The ...
