The salt-cocrystal continuum is well illustrated by a
neutron diffraction study on a pentachlorophenol/4-methylpyridine
complex (¢pKa ) 0.77) at variable temperatures.
The data showed that the shared proton moved closer to the
oxygen (more cocrystal or non-ionized character) with
increasing temperature (Figure 2).14a,18 Variable temperature
neutron diffraction studies were also reported for a carboxylic
acid/pyridine 1:2 cocrystal, where the proton in an OâââN
hydrogen bond moved toward the oxygen with increasing