Solid-state (13)C magic-angle spinning (MAS) NMR spectroscopy is used to investigate the structure of the Cu(II)-based metal-organic frameworks (MOFs), HKUST-1 and STAM-1, and the structural changes occurring within these MOFs upon activation (dehydration). NMR spectroscopy is an attractive technique for the investigation of these materials, owing to its high sensitivity to local structure, without any requirement for longer-range order. However, interactions between nuclei and unpaired electrons in paramagnetic systems (e.g., Cu(II)-based MOFs) pose a considerable challenge, not only for spectral acquisition, but also in the assignment and interpretation of the spectral resonances. Here, we exploit the rapid T(1) relaxation of these materials to obtain (13)C NMR spectra using a spin-echo pulse sequence at natural abundance levels, and employ frequency-stepped acquisition to ensure uniform excitation of resonances over a wide frequency range. We then utilise selective (13)C isotopic labelling of the organic linker molecules to enable an unambiguous assignment of NMR spectra of both MOFs for the first time. We show that the monomethylated linker can be recovered from STAM-1 intact, demonstrating not only the interesting use of this MOF as a protecting group, but also the ability (for both STAM-1 and HKUST-1) to recover isotopically-enriched linkers, thereby reducing significantly the overall cost of the approach.

Ringing the changes: Selenazolines have applications in medicinal chemistry, but their synthesis is challenging. We report a new convenient and less toxic route to these heterocycles that starts from commercially available selenocysteine. The new route depends on a heterocyclase enzyme that creates oxazolines and thiazolines from serines/threonines and cysteines.

H and C pNMR properties of bis(salicylaldoximato)copper(II) were studied in the solid state using magic-angle-spinning NMR spectroscopy and, for the isolated complex and selected oligomers, using density-functional theory at the PBE0-1/3 //PBE0-D3 level. Large paramagnetic shifts are observed, up to δ( H)=272 ppm and δ( C)=1006 ppm (at 298 K), which are rationalised through spin delocalisation from the metal onto the organic ligand and the resulting contact shifts arising from hyperfine coupling. The observed shift ranges are best reproduced computationally using exchange-correlation functionals with a high fraction of exact exchange (such as PBE0-1/3 ). Through a combination of experimental techniques and first-principles computation, a near-complete assignment of the observed signals is possible. Intermolecular effects on the pNMR shifts, modelled computationally in the dimers and trimers through effective decoupling between the local spins via A-tensor and total spin rescaling in the pNMR expression, are indicated to be small. Addition of electron-donating substituents and benzannelation of the organic ligand is predicted computationally to induce notable changes in the NMR signal pattern, which suggests that pNMR spectroscopy can be a sensitive probe for the spin distribution in paramagnetic phenolic oxime copper complexes.

We present a strategy for predicting the unusual 1 H and 13 C shifts in NMR spectra of paramagnetic bisoximato copper(II) complexes using DFT. We demonstrate good agreement with experimental measurements, although 1 H-13 C correlation spectra show that a combined experimental and theoretical approach remains necessary for full assignment.In recent years, paramagnetic NMR (or "pNMR") has developed greatly, with systems from metalloproteins 1 (dilute, isolated spins) to metal-organic frameworks 2-4 (denser networks of potentially coupled spins) and metal oxides 5 (very dense networks of highly coupled spins) being studied. For dilute spins, the NMR conditions can be selected such that the signal from nuclei near the paramagnetic centre is "invisible" owing to rapid relaxation and only the longer-range throughspace pseudocontact shifts are observed. 1 These are generally on the order of a few ppm and occur over distances such that the unpaired electron can be treated as a point spin, resulting in a simple 1/r 3 relationship with the shift. For dense spin networks such as transition metal oxides, it may be possible to assign the NMR spectra by analysis of bonding pathways (via oxygen). 5 However, in the intermediate regime, including materials such as catalytically-active transition metal complexes and metal-organic frameworks (MOFs), both the through-bond Fermi contact and through-space pseudocontact interactions affect the observed NMR spectrum and assignment can be both nontrivial and counterintuitive. 2,6-9 For example, in the 13 C NMR spectrum of the MOF HKUST-1 (Cu3btc2, btc = benzene-1,3,5-tricarboxylate), 10 the broadest resonance, shifted most by paramagnetic interactions, is not the carboxylate C (separated from Cu 2+ by just two bonds), but rather the adjacent quaternary C (three bonds from Cu). This assignment was confirmed using the relatively costly and timeconsuming approach of specific 13 C labelling in conjunction with 1 H-13 C cross polarisation (CP) NMR, which is generally inefficient for paramagnetic materials. 2 It would, therefore, be desirable to have a more general assignment method that does not rely on the development of bespoke synthetic pathways for efficient isotopic enrichment. Owing to the rapid MAS rates (necessitating the use of small rotors with, consequently, small sample volumes) required for highresolution pNMR spectra, sensitivity is inherently low and it would, therefore, also be advantageous to be able to predict shifts prior to the experimental measurement, particularly as resonances can be several hundred ppm away from their typical diamagnetic range.Periodic density functional theory (DFT) calculations have enjoyed great success in solid-state NMR, allowing the optimisation of experimental structures to an energy minimum and the subsequent calculation of highly accurate NMR parameters [11][12][13] However, pNMR DFT calculations are still in their relative infancy, particularly for periodic solids. The field is more advanced for molecular calculations, which have successfull...