Dual structure of a vanadyl-based molecular qubit containing a bis(β-diketonato) ligand

We report [VO(bdhb)] (1') as a new electronic qubit containing an oxovanadium(IV) ion (S = 1/2) embraced by a single bis(β-diketonato) ligand [H₂bdhb = 1,3-bis(3,5-dioxo-1-hexyl)benzene]. ¹H-DOSY and EPR experiments in organic solution confirmed a quasi-macrocyclic structure, whose geometry was inferred from DFT calculations. Spin relaxation measurements in frozen toluene-d₈/CD₂Cl₂ solution yielded T_m values reaching 13 μs at 10 K, and coherent spin manipulations were demonstrated by Rabi nutation experiments at 70 K. Three different crystal phases were obtained from CH₂Cl₂/Et₂O solvent mixtures, all of which unexpectedly contain dimers with formula [(VO)₂(bdhb)₂] (1). A trigonal form (1h) with a honeycomb structure and 46% of solvent accessible voids quantitatively transforms over time into a monoclinic solvatomorph 1m and minor amounts of a triclinic solventless phase (1a). In a static magnetic field, 1h and 1m have detectably slow magnetic relaxation at low temperature through quantum-tunnelling and Raman mechanisms. Angle-resolved EPR spectra on single crystals revealed signatures of low-dimensional magnetic behavior, which is solvatomorph dependent, being the closest interdimer V···V separations (6.7-7.5 Å) much shorter than intramolecular V···V distances (11.9-12.1 Å). The neutral quasi-macrocyclic structure, featuring nuclear-spin free donors and additional possibilities for chemical functionalization, make 1' a new convenient spin-coherent building block in quantum technologies.