Dual Structure of a Vanadyl-Based Molecular Qubit Containing a Bis(β-diketonato) Ligand

We designed [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]. The synthesis afforded three different crystal phases, 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 temperatures through quantum tunneling and Raman mechanisms. Angle-resolved electron paramagnetic resonance (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). According to 1H diffusion ordered spectroscopy (DOSY) and EPR experiments, the complex adopts the desired monomeric structure in organic solution and its geometry was inferred from density functional theory (DFT) calculations. Spin relaxation measurements in a frozen toluene-d8/CD2Cl2 matrix yielded Tm values reaching 13 μs at 10 K, and coherent spin manipulations were demonstrated by Rabi nutation experiments at 70 K. The neutral quasi-macrocyclic structure, featuring nuclear spin-free donors and additional possibilities for chemical functionalization, makes 1′ a new convenient spin-coherent building block in quantum technologies.

我们设计了[VO(bdhb)] (1')作为一种新型电子量子比特 (electronic qubit)，其包含被单个双(β-二酮根)配体[H2bdhb = 1,3-双(3,5-二氧代-1-己基)苯]包覆的氧钒(IV)离子（自旋S=1/2）。该合成反应得到三种不同的晶相，所有晶相均意外地包含分子式为[(VO)2(bdhb)2] (1)的二聚体结构。具有蜂窝状结构与46%溶剂可及空隙的三方晶型(1h)会随时间定量转变为单斜溶剂化物晶型1m，以及少量三斜无溶剂相1a。在静磁场中，1h与1m在低温下通过量子隧穿与拉曼机制表现出可观测的慢磁弛豫行为。单晶体的角分辨电子顺磁共振 (angle-resolved electron paramagnetic resonance, EPR) 光谱揭示了低维磁行为特征，该特征依赖于溶剂化物晶型：其二聚体间钒-钒间距（6.7–7.5 Å）远短于分子内钒-钒间距（11.9–12.1 Å）。基于氢核扩散有序波谱 (1H diffusion ordered spectroscopy, DOSY) 与电子顺磁共振实验，该配合物在有机溶剂中呈现目标单分子结构，其几何构型可通过密度泛函理论 (density functional theory, DFT) 计算推导得到。在冷冻氘代甲苯-d8/二氯甲烷-d2基质中开展的自旋弛豫测量显示，其在10 K下的Tm值可达13 μs；70 K下的拉比章动实验证实了相干自旋操控的可行性。该中性准大环结构具备无核自旋给体位点，且拥有进一步化学功能化的潜力，使其成为量子技术领域中一种新型便捷的自旋相干构建单元。