Impact of Counter Ion Methyl Groups on Spin Relaxation in[V(C6H4O2)(3)](2-)

A detailed understanding of how counterion methylgroups affect electron spin relaxation is key to using these chemicalspecies in the design of new molecular qubits. Here, we study thecoherent spin dynamics of the V(IV) complex [V(C6H4O2)3]2-withfive different countercations: (Et3NH)+(1), (n-Bu3NH)+(2),(n-Bu3N-2H)+(2-d2), (n-Hex3NH)+(3), and (n-Oct3NH)+(4).These counterions systematically increase the distance between theV(IV) spin and the methyl group of the alkyl chains. Pulsedelectron paramagnetic resonance investigations in both glassysolutions and solid-state dilutions show that (1) the counterionsare bound via hydrogen bonding to the [V(C6H4O2)3]2-unit, evenin frozen solutions, and that (2) the methyl group of thecounterion has a dominant role in dictating the spin-spin (or phase memory) relaxation. We can reproduce the rate of the spin echodecay with a model that is based on the distance-dependent impact of the counterion methyl groups, and we note that in1, themethyl groups generate a modulation of the echo decay. We also show that an important instrumental setting of the spin echomeasurement, the shot repetition time, can have a dramatic impact on the shape of the echo decay curve and thus the measuredrelaxation times. Finally, the spin-lattice relaxation times are independent of cation and are the same, within experimentaluncertainty, in glassyo-terphenyl and in the V(IV) complexes doped into the closed-shell Ti(IV) analogue, (n-Bu3NH)2[Ti-(C6H4O2)3](2-Ti). Together, these data provide a mechanistic picture of how counterion CH3groups modulate phase memory spinrelaxation in open-shell metal complexes.