Search for: All records

Understanding how magnetic nuclei affect spin relaxation is vital for designing robust spin coherence in magnetic materials and molecules. A key question is the extent that magnetic nuclei close to a spin (e.g., in the ligand shell of a metal complex) influence relaxation and how it varies over different classes of nuclei. Herein, we apply high-field EPR, X-band EPR, and ac magnetic susceptibility techniques to a family of five V(IV) complexes of the type [V(C6X4O2)3]2–, featuring five different sets of 12 nuclear spins on the ligand shell: X = 1H (1), 2H (2), 19F (3), 35/37Cl (4), and 79/81Br (5). We found several unanticipated results in these studies. For example, at high-field/-frequency, we found that compound 1, with the highest-magnetic-moment ligand nuclear spins, exhibits the longest phase memory relaxation times of the series. Furthermore, at lower fields, we found that the spin–lattice relaxation time and its field dependence were ligand-dependent, despite no obvious change in electronic structure across the five species. Based on this data, structural comparisons, and Raman spectroscopic data, we tentatively conclude that the spin–lattice relaxation properties of 1–5 stem from fine-tuning of the local magnetic environment with changing identity of the X atoms. 

Quantum objects, such as atoms, spins, and subatomic particles, haveunique physical properties that could be useful for many different applications, ranging from quantum information processing to magnetic resonance imaging. Molecular species also exhibit these quantum properties, and, importantly, these properties are fundamentally tunable by synthetic design, unlike ions isolated in a quadrupolar trap, for example. In this comment, we distill multiple, distinct, scientific efforts into an emergent field that is devoted to designing molecules that mimic the quantum properties of objects like trapped atoms or defects in solids. Mimicry is endemic in inorganic chemistry and featured heavily in the research interests of groups across the world. We describe this new field of using molecular inorganic chemistry to mimic the quantum properties (e.g. the lifetime of spin superpositions, or the resonant frequencies thereof) of other quantum objects as “quantum mimicry.” In this comment, we describe the philosophical design strategies and recent exciting results from the application of these strategies. 

Asymmetric ligands alter the low-energy vibrational spectra of a metal complex and affect the temperature dependence of⁵⁹Co NMR properties. 

Interstitial patterning of nuclear spins is a nascent design principle for controlling electron spin superposition lifetimes in open-shell complexes and solid-state defects. Herein we report the first test of the impact of the patterning principle on ligand-based nuclear spin dynamics. We test how substitutional patterning of 1H and 79/81Br nuclear spins on ligands modulates proton nuclear spin dynamics in the ligand shell of metal complexes. To do so, we studied the 1H nuclear magnetic resonance relaxation times (T1 and T2) of a series of eight polybrominated catechol ligands and six complexes formed by coordination of the ligands to a Ti(IV) ion. These studies reveal that 1H T1 values can be enhanced in the individual ligands by a factor of 4 (from 10.8(3) to 43(5) s) as a function of substitution pattern, reaching the maximum value for 3,4,6-tribromocatechol. The T2 for 1H is also enhanced by a factor of 4, varying by ∼14 s across the series. When complexed, the impact of the patterning design strategy on nuclear spin dynamics is amplified and 1H T1 and T2 values vary by over an order of magnitude. Importantly, the general trends observed in the ligands also match those when complexed. Hence, these results demonstrate a new design principle to control 1H spin dynamics in metal complexes through pattern-based design strategies in the ligand shell. 

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.