Stoichiometry-controlled complexation of o-phenylenebis-(N,N'-dimethyl-N,N'-ethylene)guanidine (BG) and benzoic acid (BA), which is forming 1:1, 1:2, 1:3, and 1:4 BG+BA systems, was observed in solution by using cold-spray ionization mass spectrometry CSI-MS and pulsed field gradient PFG NMR diffusion and in the solid state by X-ray structure analysis.