1,2,5-Thiadiazole 1,1-dioxides and Their Radical Anions: Structure, Properties, Reactivity, and Potential Use in the Construction of Functional Molecular Materials

This work provides a summary of the preparation, structure, reactivity, physicochemical properties, and main uses of 1,2,5-thiadiazole 1,1-dioxides in chemistry and material sciences. An overview of all currently known structures containing the 1,2,5-thiadiazole 1,1-dioxide motif (including the anions radical species) is provided according to the Cambridge Structural Database search. The analysis of the bond lengths typical for neutral and anion radical species is performed, providing a useful tool for unambiguous assessment of the valence state of the dioxothiadiazole-based compounds based solely on the structural data. Theoretical methodologies used in the literature to describe the dioxothiadiazoles are also shortly discussed, together with the typical 'fingerprint' of the dioxothiadiazole ring reported by means of various spectroscopic techniques (NMR, IR, UV-Vis). The second part describes the synthetic strategies leading to 1,2,5-thiadiazole 1,1-dioxides followed by the discussion of their electrochemistry and reactivity including mainly the chemical methods for the successful reduction of dioxothiadiazoles to their anion radical forms and the ability to form coordination compounds. Finally, the magnetic properties of dioxothiadiazole radical anions and the metal complexes involving dioxothiadiazoles as ligands are discussed, including simple alkali metal salts and d-block coordination compounds. The last section is a prospect of other uses of dioxothiadiazole-containing molecules reported in the literature followed by the perspectives and possible future research directions involving these compounds.

Transition metal complexes and radical anion salts of 1,10-phenanthroline derivatives annulated with a 1,2,5-tiadiazole and 1,2,5-tiadiazole 1,1-dioxide moiety: multidimensional crystal structures and various magnetic properties

Advances in the molecular variety and the elucidation of the physical properties of 1,10-phenanthroline annulated with 1,2,5-thiadiazole and 1,2,5-thiadiazole 1,1-dioxide moieties have been achieved, and are described herein. A 1,2,5-thiadiazole compound, [1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline (tdap), was used as a ligand to create multidimensional network structures based on S•••S and S•••N intermolecular interactions. A 1,2,5-thiadiazole 1,1-dioxide compound, [1,2,5] thiadiazolo[3,4-f][1,10]phenanthroline, 1,1-dioxide (tdapO₂), was designed to create a stable radical anion, as well as good network structures. Single crystal X-ray structure analyses revealed that transition metal complexes of tdap, and radical anion salts of tdapO₂ formed multidimensional network structures, as expected. Two kinds of tdap iron complexes, namely [Fe(tdap)₂(NCS)₂] and [Fe(tdap)₂(NCS)₂]•MeCN exhibited spin crossover transitions, and their transition temperatures showed a difference of 150 K, despite their similar molecular structures. Magnetic measurements for the tdapO₂ radical anion salts revealed that the magnetic coupling constants between neighboring radical species vary from strongly antiferromagnetic (J = −320 K) to ferromagnetic (J = 24 K), reflecting the differences in their π overlap motifs.