Syntheses and single crystal X-ray structural characterizations, together with infrared spectroscopic studies, are recorded for 1 : 1 adducts of silver(I) thiocyanate with thiourea (‘tu’) and N,N′-diethylthiourea (‘detu’≡ (EtNH)₂CS). The two complexes display novel and different polymeric forms. That formed with tu is a double-stranded form, comprising a pair of Ag(μ-S-tu)Ag(μ-… strands linked by pairs of μ-SCN anions, the whole array having quasi-2 symmetry about the polymer axis. The detu adduct takes the ionic form [Ag(detu)₂]_(∞|∞)[Ag(SCN)₂]_(∞|∞), both cation and anion being one-dimensional polymers lying in parallel, and both of the form …Ag(μ-S-L)₂Ag(μ-… (L = SCN or detu), disposed about crystallographic axes. Redeterminations of the structures of AgSCN : tu, etu (1 : 2) (‘etu’ = ethylenethiourea, (CH₂NH)₂CS)) with quasi-trigonal silver atom environments (the etu adduct the more closely so), are also recorded as a basis for an IR spectroscopic characterization of the [(NCS)Ag(S-xtu)₂] array. A mechanochemical/infrared study of the AgSCN:etu (1 : 1) system showed that no 1 : 1 complex exists in this case, the product being a mixture of the 1 : 2 complex and a novel 1 : 0.5 complex. The latter complex was prepared both mechanochemically and from solution, and characterized by infrared spectroscopy. Diagnostic ligand and metal–ligand bands in the IR and far-IR spectra are assigned for all of the complexes studied and for AgSCN and are discussed in relation to the structures of the complexes. The double degeneracy of the δ(SCN) mode of the coordinated thiocyanate is lifted and the first overtone of this band at gains intensity in the IR in the 1 : 1 complexes, behaviour that is not observed for the terminal bonding mode that is present in the 1 : 2 complexes.