Nuclear-spin-pattern control of electron-spin dynamics in a series of V(iv) complexes

Achieving control of phase memory relaxation times (T(m)) in metal ions is an important goal of molecular spintronics. Herein we provide the first evidence that nuclear-spin patterning in the ligand shell is an important handle to modulate T(m) in metal ions. We synthesized and studied a series of five V(iv) complexes with brominated catecholate ligands, [V(C(6)H(4–n)Br(n)O(2))(3)](2–) (n = 0, 1, 2, and 4), where the (79/81)Br and (1)H nuclear spins are arranged in different substitutional patterns. High-field, high-frequency (120 GHz) pulsed electron paramagnetic resonance spectroscopic analysis of this series reveals a pattern-dependent variation in T(m) for the V(iv) ion. Notably, we show that it is possible for two molecules to have starkly different (by 50%) T(m) values despite the same chemical composition. Nuclear magnetic resonance analyses of the protons on the ligand shell suggest that relative chemical shift (δ), controlled by the patterning of nuclear spins, is an important underlying design principle. Here, having multiple ligand-based protons with nearly identical chemical shift values in the ligand shell will, ultimately, engender a short T(m) for the bound metal ion.