Effect of Chemical Modification in Trigonal Gd(III) Molecular Qubits

Molecular quantum bits (qubits) are often hailed for the tunability of their properties through chemical backbone modifications. This concept has been explored in detail for transition metal-based systems. However, the effect of chemical modifications in the ligand backbone on the spin dynamics of 4f molecular qubits remains relatively unexplored. We present herein a study of the effect of the addition, and topology thereof, of methoxy groups in the ligand backbone of a Gd(III) qubit while maintaining the molecular symmetry. Continuous wave X-band Electron Paramagnetic Resonance measurements on single crystals of two such derivatized Gd-based molecular qubits provide detailed information on their eigenvector composition. Their dynamic properties were examined by pulse electron paramagnetic resonance on single crystals, revealing that both complexes display coherent spin dynamics up to 100 K, where spin-lattice relaxation limits the coherence. Furthermore, we show that tuning of the ligand field-derived anisotropy leads to control of the eigenvector composition, which translates to control of the Rabi nutation frequency and hence of the time for quantum gate implementation. This demonstrates that molecular qubits offer the possibility for synthetic control and tuning of the speed of coherent manipulations.