As part of a long-running programme, we have identified many co-crystallisation systems producing hydrogen-bonded molecular complexes yielding fascinating X-ray diffraction and DFT results. Among the molecular building blocks we utilise in creating these complexes are substituted benzoic acids and a series of so-called ¿proton sponge¿ complexes, of which the archetype is DMAN (dimethylaminonaphthalene). The complex of DMAN with 4-chlorobenzoic acid crystallises in a 1:1 ratio, and produces a unique situation where one DMAN is protonated, the other unprotonated. We aim to investigate this unusual situation of H-atom distribution as a function of T, and also the diffuse scattering, likely to be produced by the local arrangement of the chains of DMAN molecules.