The reaction of [C(NH2)(3)] Cl with methyl orange, Na[O3SC6H4N=NC6H4NMe2], leads to formation of [C(NH2)(3)][O3SC6H4N=NC6H4NMe2] 1 in which the sulfonate dye has been incorporated into a guanidinium sulfonate hydrogen- bonded bilayer sheet structure. Similar reactions with substituted guanidinium cations give [C(NH2)(2)(NHMe)][O3SC6H4N=NC6H4NMe2].MeOH2.MeOH, [C(NH2)(2)(NHEt)][O3SC6H4N=NC6H4NMe2] 3 and [C(NH2)(2)(NMe2)][O3SC6H4N=NC6H4NMe2](4). Although substitution disrupts formation of the GS sheets, the gross structures of 2-4 all have pseudo-bilayer structures, with similar gross features to 1. Compound 1 reacts with HCl in solution to generate the zwitterionic compound O3SC6H4NH=NC6H4NMe2 5, but solid samples of 1 react reversibly with HCl gas to give the HCl adduct 1a. This interconversion has been studied by powder X-ray diffraction, IR spectroscopy and diffuse reflectance visible spectroscopy.