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

Abstract

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···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 T m is 2.3 μs at 30 K, which significantly diverges from the predicted T m > 100 μs. 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.