Near Isotropic D_4d Spin Qubits as Nodes of a Gd(III)-Based Metal–Organic Framework

Embedding coherent spin motifs in reproducible molecular building blocks is a promising pathway for the realization of quantum technologies. Three-dimensional (3D) MOFs are a versatile platform for the rational design of extended structures employing coordination chemistry. Here, we report the synthesis and characterization of a gadolinium­(III)-based MOF, [Gd­(bipyNO)₄]­(TfO)₃·xMeOH (bipyNO = bipyridine,N,N′-dioxide; TfO = triflate; and MeOH = methanol) (quMOF-1), which presents a unique coordination geometry that leads to a tiny magnetic anisotropy (in terms of D, an equivalent zero-field splitting would be achieved by D = 0.006 cm^–1) even compared with regular Gd­(III) complexes. Pulsed electron paramagnetic resonance experiments on its magnetically diluted samples confirm the preservation of quantum coherence of single Gd­(III) qubit units in this 3D extended molecular architecture (T₂ = 612 ns and T₁ = 66 μs at 3.5 K), which allows for the detection of Rabi oscillations at 40 K.