Exploring the Organometallic Route to Molecular Spin Qubits: the [CpTi(cot)] case.

The coherence time of the 17-electron, mixed sandwich complex [CpTi(cot)], (η 8 -cyclooctatetraene)(η 5 -cyclopentadienyl)- titanium, was found to reach 34 ms at 4.5 K in a frozen deuterated toluene solution. This result represents a remarkable coherence time for a highly protonated molecule. We here confirm that the intramolecular distances between the Ti and H atoms provide a good compromise between instantaneous and spin diffusion sources of decoherence. In addition, ab initio calculations at the molecular and crystal packing levels reveal that the characteristic low-energy ring rotations of the sandwich framework do not yield a detrimental spin-lattice relaxation because of their small spin-phonon coupling. Much shorter and almost temperature-independent phase memory times T m were observed when [CpTi(cot)] was diluted in the diamagnetic (16-electron) crystalline host [CpTi(cht)], (η 7 -cycloheptatrienyl)(η 5 -cyclopentadienyl)titanium. Such finding reinforces the deactivating role of both intermolecular interactions involving the hydrogen atoms of neighboring molecules and cluster formation in the host crystal lattice. The volatility of [CpTi(cot)] and the accessibility of the semi-occupied, non-bonding d z 2 orbital make this neutral compound an ideal candidate for single-qubit addressing on surface and quantum sensing in combination with scanning probe microscopies.