Four K, Cs, Ag(I), and TI(I) compounds with a nitrosodicyanomethanide ONC(CN)(2)(-) anion have been obtained and characterized using IR spectroscopy; UV-visible spectroscopy; room temperature, solid-state photoluminescence; and solutions electrical conductivity measurements. Cesium and thallium(I) complexes were obtained for the first time, and crystal structures were determined for Cs{ONC(CN)(2)}, Ag{ONC(CN)(2)}, and TI{ONC(CN)(2)}. These structures indicate the formation of completely different 3D polymeric networks in which the anion acts as a bridging ligand of different capacity. The cyanoxime ligand in all complexes studied is in the nitroso form and adopts a planar configuration. The structure of the cesium salt is ionic. The structure of Ag{ONC(CN)(2)} represents a 3D coordination polymer where the anion acts as a tetradentate ligand with all four bonds between Ag(I) and donor atoms (three N and one O) significantly shorter than the sum of the ionic radii for these elements. The silver(I) atom in this compound has a distorted tetrahedral surrounding. Additionally, Ag{ONC(CN)(2)} is remarkably UV- and visible-light-insensitive. However, after exposure of the solid complex to gases such as H-2, CO, NO, C2H2, and C2H4, the surface of the compound becomes visible-fight-sensitive and changes color with significant darkening, which indicates reduction of the metal. This is reflected in a dramatic decrease of intensity of the photoluminescence of Ag{ONC(CN)(2)} in the presence of these gases, which might be utilized for nonelectric sensor applications. The TI{ONC(CN)(2)} complex represents a transitional species between ionic (Cs) and covalent (Ag) compounds. The thallium(I) center has four shorter bonds than the sum of the ionic radii bonds (three with N and one with O atoms) and three longer electrostatic (ionic) contacts with the anion. The 6s(2) lone pair is stereotactive, and the coordination polyhedron is best described as a distorted square pyramid. Room temperature diffusion reflectance spectra of solid K{ONC(CN)(2)}, Ag{ONC(CN)(2)}, and TI{ONC(CN)(2)} demonstrated a bathochromic shift of the band's lambda(max) depending on the atomic number of the metal center, indicating a significant role of metal centers in electronic transitions in these compounds. This phenomenon was observed for the first time. The latter complex at 293 K exhibited structured metal-based red photoluminescence in the range of 690-800 nm that depends on the excitation wavelengths.