Andrew J. Pell

Lanthanide hexacyanoferrates, LnFe(CN)6·xH2O, combine the structural versatility of cyanidebridged frameworks with the strong spin–orbit coupling and crystal-field effects of lanthanide ions. Yet, the local (ion-specific) origins of the magnetic response of these materials remain difficult to resolve by conventional solid-state chemistry techniques. Here, we report the 1H and 13C solid-state nuclear magnetic resonance (NMR) spectra of LnFe(CN)6·xH2O (Ln = La to Yb), with assignments supported by first-principles calculations and optical spectroscopy. We interpret the 1H NMR spectra in terms of free (interstitial) and bound (Ln-coordinated) water environments within the porous framework. The 1H shifts and shift anisotropies scale approximately linearly with the lanthanide Bleaney coefficients, establishing a direct and quantifiable link between 1H spectra and single-ion anisotropy. Using 13C NMR spectra, we are able to isolate the impact of Ln composition, despite the Ln contribution comprising only a small fraction (up to 3%) of the total paramagnetic NMR shift. The 13C shift anisotropy also tracks linearly with the Bleaney coefficients, whilst the trend against the isotropic shift is weaker, underlining the site-specific effect of Fermi contact and dipolar contributions to the total shift. Together, out results establish solid-state NMR spectroscopy as a sensitive and quantitative probe of single-ion anisotropy in cyanide-based frameworks.

Disorder is generally expected to destabilize a Kitaev quantum spin liquid, yet it can also generate new quantum phases. Na2Co2TeO6, which contains substantial intrinsic Na-site disorder, provides a promising platform to examine how randomness reshapes spin dynamics. Here, by employing 23Na NMR, we reveal a disorder induced softening of the spin excitations. Between 10 K and 100 K, the temperature dependence of the NMR relaxation times is consistent with the presence of gapped fractional spin excitations. Below 10 K, however, they bifurcate into two distinct channels: a slow-relaxing channel, preserving the gapped excitations character, and a fast-relaxing channel that follows a Korringa-like law, indicating the emergence of nearly gapless spin excitations. This two-channels regime is accompanied by ultraslow, microsecond scale spin fluctuations following an Arrhenius activation law. Besides, ab initio NMR lineshape calculations show that a quantum spin liquid-like model reproduces the low-temperature NMR spectra sufficiently better than magnetically ordered models. Together, our findings indicate transition upon cooling to a disorder-driven quantum spin liquid Griffiths phase, comprising slowly fluctuating gapped regions within a matrix of nearly gapless low-energy spin excitations.

The size and shape of crystallites strongly influence the properties of functional materials yet remain challenging to access experimentally. In paramagnetic solids, the bulk magnetic susceptibility (BMS) contributes a part to the measured nuclear magnetic resonance (NMR) shift tensor, which depends strongly on particle shape and packing. Here, we use a Fourier-space approach to quantify BMS shifts in LiFePO4 and use the 7Li magic-angle spinning NMR spectra to directly probe the crystallite shape and size. By disentangling internal and external BMS shift contributions from the crystallite of interest and its neighbors, we show that particle shape anisotropy leaves a clear signature in the NMR line shape. Combining BMS modeling with quantum-chemical local shift parameters yields excellent agreement with experimental spectra and enables the extraction of new morphological insights, highlighting solid-state NMR as a quantitative probe of crystallite morphology in paramagnetic materials.

Metal clusters are of broad interest across fields in that they possess unique properties making them appealing for a variety of applications; additionally, they provide fundamental understanding of the structure, bonding, and reactivity of the extended metal systems at an atomic level. Pioneering studies on metal clusters were directed toward the rationalization of their (electronic) structure from symmetry considerations and computations. The need to relate these theoretical models to specific spectroscopic signatures of metal clusters in relation to their (electronic) structure has not yet been addressed. In this work, we studied a family of structurally related Pt_n(0) species with different nuclearities (up to 15); we were able to show how ¹⁹⁵Pt solid-state NMR can be used as a general tool to distinguish among metal sites in metal clusters and how their computed MO diagrams can be validated experimentally through the analysis of their NMR fingerprints. We applied this approach to known Pt phosphine/carbonyl ‘Chini’ clusters as well as to an unprecedented Pt₅ square-pyramidal cluster. We propose that this approach can be extended to several other classes of metal clusters containing NMR-active centers, as well as (un)supported metal-based nanostructures.

The rational development of molecular catalysts, supported on an inorganic material, requires advanced analytic methodologies to probe the structure, dynamics, and electronic properties of the catalytic center(s). While spectroscopic tools, in particular solid-state MAS NMR, have greatly advanced our understanding of metal sites in molecules and materials, it remains challenging to address the detailed structure and dynamics of paramagnetic centers. Fe(II) sites are ubiquitous across catalytic systems from enzymes to molecular and heterogeneous catalysts. Across supported systems, silica-supported Fe(II) species have recently been shown to enable the nonoxidative coupling of methane, and the surface sites have been investigated via Surface Organometallic Chemistry. Here, we show how state-of-the-art MAS NMR experiments combined with quantum computations enable us to resolve the structure and the dynamics of a dimeric Fe(II) complex, used for the production of isolated iron sites on the surface of amorphous silica. We also show through analysis of the ¹H and ¹³C NMR signatures of the silica-supported species that a large structural difference exists between molecular and supported species; the latter displaying a remarkably homogeneous, monomeric, and highly dynamic single-atom sites.

Lanthanide ions embedded in crystalline hosts are central to modern technologies, where their unique magnetic and optical properties arise from spin-orbit coupling shaped by the local coordination environment. Here, we provide a unified computational-experimental framework to probe these interactions for Nd³⁺ in yttrium aluminum garnet (Nd:YAG). Multiconfigurational variational-perturbative complete active space-based calculations with spin-orbit treatments accurately capture the crystal field splitting, magnetic anisotropy, and intra-4f optical transitions. Complementary low-temperature EPR and ultrahigh-field, fast magic-angle spinning paramagnetic NMR experiments benchmark the calculations and reveal how subtle structural features tune the electronic and magnetic response properties. By linking magnetic observables with optical transitions through the same local environment, our study establishes a general strategy for predicting and rationalizing the multifunctional behavior of lanthanide-doped materials.

Lanthanide ions embedded in crystalline hosts are central to modern technologies, where their unique magnetic and optical properties arise from spin–orbit coupling shaped by the local coordination environment. Here we provide a unified computational–experimental frame- work to probe these interactions for Nd3+ in yttrium aluminum garnet (YAG). Multiconfigurational variational–perturbative complete active space based calculations with spin–orbit treatments accurately capture the crystal-field splitting, magnetic anisotropy, and intra-4f optical transitions. Complementary low-temperature EPR and ultra-high-field, fast-MAS paramagnetic NMR experiments benchmark the calculations and reveal how subtle structural features tune the electronic and magnetic response properties. By linking magnetic observables with optical transitions through the same local environment, our study establishes a general strategy for predicting and rationalizing the multifunctional behavior of lanthanide-doped materials.

Supported metal catalysts that integrate atomically dispersed species with controlled structures lie at the forefront of catalytic materials design, offering exceptional control over reactivity and high metal utilization, approaching the precision of molecular systems^1–3. However, accurately resolving the local metal coordination environments remains challenging, hindering the advancement of structure–activity relationships needed to optimize their design for diverse applications^1,2. Although electron microscopy reveals atomic dispersion, conventional spectroscopic methods used in heterogeneous catalysis only provide average structural information. Here we demonstrate that ¹⁹⁵Pt solid-state nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for characterizing atomically dispersed Pt sites on various supports, so called single-atom catalysts (SACs). Monte Carlo simulations allow the conversion of NMR spectra into SAC signatures that describe coordination environments with molecular precision, enabling quantitative assessment of Pt-site distribution and homogeneity. This methodology can track the influence of synthetic parameters, uncovering the impact of specific steps and support types, and can also monitor changes upon reaction. It offers critical insights for the reproducible development of SACs with targeted structures. Beyond SACs, this approach lays the foundation for studying more complex architectures, such as dual-atom or single-cluster catalysts, containing various NMR-active metals.

Single atom catalysts (SACs) have revolutionized the field of catalysis achieving an unprecedented level of control and metal utilization for solid materials, approaching what is expected with molecular catalysts.1-3 Establishing structure-activity relationships for their wide-ranging applications requires precise elucidation of the metal coordination environment, which remains a grand challenge.1,2 While electron microscopy reveals atomic dispersion, only average coordination environments can be deduced from state-of-the-art spectroscopic methods used in heterogeneous catalysis. Here, we establish 195Pt solid-state nuclear magnetic resonance (NMR) spectroscopy as a powerful methodology to acquire NMR signatures across a series of Pt-SACs dispersed on carbon based supports. Monte-Carlo simulations allow the conversion of NMR signatures into SAC fingerprints that describe local coordination environments with molecular precision and enable to quantitatively assess Pt-site distribution and homogeneity. This methodology can track the influence of synthetic parameters, e.g., specific protocols, synthetic steps and type of supports, on Pt-SAC structures, to guide the reproducible development of SACs with targeted structures; it also enables to monitor the change of coordination environment of SACs upon reaction. Such development provides a blueprint for the quantitative assessment of larger SAC families containing other NMR-active isotopes.

Ultra‐fast magic‐angle spinning (100+kHz) has revolutionized solid‐state NMR of biomolecular systems but has so far failed to gain ground for the analysis of paramagnetic organic and inorganic powders, despite the potential rewards from substantially improved spectral resolution. The principal blockages are that the smaller fast‐spinning rotors present significant barriers for sample preparation, particularly for air/moisture‐sensitive systems, and are associated with low sensitivity from the reduced sample volumes. Here, we demonstrate that the sensitivity penalty is less severe than expected for highly paramagnetic solids and is more than offset by the associated improved resolution. While previous approaches employing slower MAS are often unsuccessful in providing sufficient resolution, we show that ultra‐fast 100+kHz MAS allows site‐specific assignments of all resonances from complex paramagnetic solids. Combined with more reliable rotor materials and handling methods, this opens the way to the routine characterization of geometry and electronic structures of functional paramagnetic systems in chemistry, including catalysts and battery materials. We benchmark this approach on a hygroscopic luminescent Tb³⁺ complex, an air‐sensitive homogeneous high‐spin Fe²⁺ catalyst, and a series of mixed Fe²⁺/Mn²⁺/Mg²⁺ olivine‐type cathode materials.