VdW Mediated Strong Magnetic Exchange Interactions in Chains of Hydrogen-Free Sublimable Molecular Qubits

Sulfur-rich molecular complexes of dithiolene-like ligands are appealing candidates as molecular spin qubits because spin coherence properties are enhanced in hydrogen-free environments. Herein, we employ the hydrogen-free mononegative 1,3,2-dithiazole-4-thione-5-thiolate (dttt-) ligand as an alternative to common dinegative dithiolate ligands. We report the first synthesis and structural characterization of its Cu2+, Ni2+, and Pt2+ neutral complexes. The XPS analysis of thermal deposition of [Cu(dttt)2] in UHV conditions indicates that films of intact molecules can be deposited on surfaces by sublimation. Thanks to a combined approach employing DC magnetometry and DFT calculations, we highlighted AF exchange interactions of 108 cm-1 and 36 cm-1 attributed to the two different polymorph phases. These couplings are exclusively mediated by S center dot center dot center dot S VdW interactions, which are facilitated by the absence of counterions and made particularly efficient by the diffuse electron density on S atoms. Furthermore, the spin dynamics of solid-state magnetically diluted samples was investigated. The longest observed Tm is 2.3 mu s at 30 K, which significantly diverges from the predicted Tm > 100 mu s. These results point to the diluting matrix severely affecting the coherence lifetime of Cu2+ species via different factors, such as the contributions of neighboring 14N nuclei and the formation of radical impurities in a non-completely controllable way. However, the ease of processing [Cu(dttt)2] via thermal sublimation can allow dispersion in matrices better suited for coherent spin manipulation of isolated molecules and the realization of AF-coupled VdW structures on surfaces.