The ethyl orange-based guanidinium sulfonate (GS) compounds [C(NH2)(3)][O3SR] (1), [C(NH2)(2)(NHMe)][O3SR]center dot MeOH (2), [C(NH2)(2)(NHEt)][O3SR] (3), and [C(NH2)(2)(NMe2)][O3SR] (4) (R = C6H4N=NC6H4NEt2) have been prepared and crystallographically characterized. Compound 1 forms GS sheets, but in contrast to the methyl orange analogue [C(NH2)(3)]-[O3SC6H4N=NC6H4NMe2], these are arranged in continuously interdigitated layers as opposed to bilayers in the extended structure. The GS structure is preserved in 3 despite the loss of one NH donor in the cation, but ribbons are formed instead of sheets in 4. Na[O3SC6H4N=NC6H4NEt2] is protonated by dilute hydrochloric acid to form the zwitterionic compound O3SC6H4NH=NC6H4NEt2 center dot 0.75H(2)O (5). Reaction of 4-aniinoazobenzene-4'-sulfonate with a range of substituted guanidinium salts led to the formation of [C(NH2)(3)][O3SR'] (6), [C(NH2)(2)(NHMe)][O3SR'] (7), [C(NH2)(2)(NHEt)](2)[O3SR'][O3SC6H4N=NC6H4O2] (8) and [C(NH2)(2)-(NMe2)][O3SR'] (9) (R' = C6H4N=NC6H4NH2). These compounds typically have more complex structures than their ethyl orange analogues, in part due to the presence of the additional hydrogen-bond donors. The structures of compounds 6 and 7 are based on hydrogen-bonded cylinders, with 7 containing unusual GS loops, consisting of four cations and four anions. Solid-state samples of both 1 and 6 react with HCl gas. X-ray powder diffraction studies reveal that 1 reacts with HCl to give 5 and [C(NH2)3]Cl as separate phases and that this mixture reacts with NH3 gas to reform I together with NH4Cl. This is in contrast to observations on [C(NH2)(3)][O3SC6H4N=NC6H4NMe2], which reacts with HCl under the same conditions to give a product in which O3SC6H4NH= NC6H4NMe2 and [C(NH2)(3)]Cl are not present as separate phases. ; 2