In this review an exhaustive crystallochemical analysis of copper(I) π-complexes with allyl derivatives of heterocyclic compounds has been performed. Structural genesis of inorganic constituents starting from the simplest units to the most complicated aggregates was considered taking into account the specific role of Cu-(C=C) interaction, the construction of the organic ligands, the basicity and nucleophilic activity of their heteroatoms, as well as olefin Cu(I) π-complex preparation route.

As an important class of heterocyclic compounds, 1,3,4-thiadiazoles have a broad range of potential applications in medicine, agriculture and materials chemistry, and were found to be excellent precursors for the crystal engineering of organometallic materials. The coordinating behaviour of allyl derivatives of 1,3,4-thiadiazoles with respect to transition metal ions has been little studied. Five new crystalline copper(I) π-complexes have been obtained by means of an alternating current electrochemical technique and have been characterized by single-crystal X-ray diffraction and IR spectroscopy. The compounds are bis[μ-5-methyl-N-(prop-2-en-1-yl)-1,3,4-thiadiazol-2-amine]bis[nitratocopper(I)], [Cu₂(NO₃)₂(C₆H₉N₃S)₂], (1), bis[μ-5-methyl-N-(prop-2-en-1-yl)-1,3,4-thiadiazol-2-amine]bis[(tetrafluoroborato)copper(I)], [Cu₂(BF₄)₂(C₆H₉N₃S)₂], (2), μ-aqua-bis{μ-5-[(prop-2-en-1-yl)sulfanyl]-1,3,4-thiadiazol-2-amine}bis[nitratocopper(I)], [Cu₂(NO₃)₂(C₅H₇N₃S₂)₂(H₂O)], (3), μ-aqua-(hexafluorosilicato)bis{μ-5-[(prop-2-en-1-yl)sulfanyl]-1,3,4-thiadiazol-2-amine}dicopper(I)–acetonitrile–water (2/1/4), [Cu₂(SiF₆)(C₅H₇N₃S₂)₂(H₂O)]·0.5CH₃CN·2H₂O, (4), and μ-benzenesulfonato-bis{μ-5-[(prop-2-en-1-yl)sulfanyl]-1,3,4-thiadiazol-2-amine}dicopper(I) benzenesulfonate–methanol–water (1/1/1), [Cu₂(C₆H₅O₃S)(C₅H₇N₃S₂)₂](C₆H₅O₃S)·CH₃OH·H₂O, (5). The structure of the ligand 5-methyl-N-(prop-2-en-1-yl)-1,3,4-thiadiazol-2-amine (Mepeta), C₆H₉N₃S, was also structurally characterized. BothMepetaand 5-[(prop-2-en-1-yl)sulfanyl]-1,3,4-thiadiazol-2-amine (Pesta) (denotedL) reveal a strong tendency to form dimeric {Cu₂L₂}²⁺fragments, being attached to the metal atom in a chelating–bridging modeviatwo thiadiazole N atoms and an allylic C=C bond. Flexibility of the {Cu₂(Pesta)₂}²⁺unit allows the Cu^Iatom site to be split into two positions with different metal-coordination environments, thus enabling the competitive participation of different molecules in bonding to the metal centre. ThePestaligand in (4) allows the Cu^Iatom to vary between water O-atom and hexafluorosilicate F-atom coordination, resulting in the rare case of a direct Cu^I...FSiF₅²⁻interaction. Extensive three-dimensional hydrogen-bonding patterns are formed in the reported crystal structures. Complex (5) should be considered as the first known example of a Cu^I(C₆H₅SO₃) coordination compound. To determine the hydrogen-bond interactions in the structures of (1) and (2), a Hirshfeld surface analysis has been performed.