Donor-acceptor (D-A) complexes between 3,4-dicyano-1,2,5-chalcogenadiazoles [chalcogen=Te (1a), Se (1b), S (1c)] and the pseudohalides CN- and XCN- (X=O, S, Se, Te) were studied experimentally and theoretically. For 1a, they were isolated as [K(18-crown-6)][1a-CN] (2), [K(18-crown-6)][1a-NCO] (3), [K(18-crown-6)][1a-SCN] (4), [K(18-crown-6)][1a-SeCN] (5), and [K][1a-NCSe] (6) and characterized by X-ray diffraction (XRD), UV/Vis and NMR spectroscopy, and DFT and QTAIM calculations. For 1b and 1c, the complexes were not isolated due to unfavorable thermodynamics. In all isolated complexes, the D-A bonds, stabilized by negative hyperconjugation, were longer than the sum of the covalent radii and shorter than the sum of the van der Waals radii of the bonded atoms. In mixtures of 1a, F-, and SeCN-, the complex [1a-F]- was selectively formed in accordance with thermodynamics. The reaction of 1a with SeCN- and the cyclic trimeric perfluoro-ortho-phenylene mercury afforded the complex [K(18-crown-6)][SCN](o-C6F4Hg)3, which was characterized by XRD.