Measurement of the Quantum Tunneling Gap in a Dysprosocenium Single-Molecule Magnet.

We perform magnetization sweeps on the high-performing single-molecule magnet [Dy(Cp ttt ) 2 ][B(C 6 F 5 ) 4 ] (Cp ttt = C 5 H 2 t Bu 3 -1,2,4; t Bu = C(CH 3 ) 3 ) to determine the quantum tunneling gap of the ground-state avoided crossing at zero-field, finding a value on the order of 10 -7 cm -1 . In addition to the pure crystalline material, we also measure the tunnel splitting of [Dy(Cp ttt ) 2 ][B(C 6 F 5 ) 4 ] dissolved in dichloromethane (DCM) and 1,2-difluorobenzene (DFB). We find that concentrations of 200 or 100 mM [Dy(Cp ttt ) 2 ][B(C 6 F 5 ) 4 ] in these solvents increases the size of the tunneling gap compared to the pure sample, despite a similarity in the strength of the dipolar fields, indicating that either a structural or vibrational change due to the environment increases quantum tunneling rates.