⁹⁵Mo Solid-State Nuclear Magnetic Resonance Spectroscopy and Quantum Simulations: Synergetic Tools for the Study of Molybdenum Cluster Materials

Abstract

The ability of (95)Mo solid-state nuclear magnetic resonance (SSNMR) spectroscopy to probe the atomic and electronic structures of inorganic molybdenum cluster materials has been demonstrated for the first time. Six cluster compounds were studied: MoBr(2), Cs(2)Mo(6)Br(14), (Bu(4)N)(2)Mo(6)Br(14), each containing the octahedral Mo(6)Br(14)(2-) cluster unit, and MoS(2)Cl(3), Mo(3)S(7)Cl(4), and MoSCl that contain metallic dimers, trimers, and tetramers, respectively. To overcome inherent difficulties due to the low sensitivity of (95)Mo SSNMR, both high-magnetic-field spectrometers and the quadrupolar Carr-Purcell Meiboom-Gill sensitivity enhancement pulse sequence under magic-angle-spinning conditions, combined with a hyperbolic-secant pulse were used. Experimental measurements as well as characterization of the (95)Mo electric field gradient and chemical shift tensors have been performed with the help of quantum-chemical calculations under periodic boundary conditions using the projector augmented-wave and the gauge-including projector augmented-wave methods, respectively. A large (95)Mo chemical shift range is measured, ∼3150 ppm, and the isotropic chemical shift of the Mo atoms is clearly correlated to their formal oxidation degree in the various clusters. Furthermore, a direct relation is evidenced between the molybdenum quadrupolar coupling constant and the bond lengths with its surrounding ligands. Our results demonstrate the efficiency of the combined use of quantum-chemical calculations and (95)Mo SSNMR experiments to study inorganic molybdenum cluster compounds.

Solid-state NMR/NQR and first-principles study of two niobium halide cluster compounds

“…Positive shifts on niobium sites are rare, but they can be found in few compounds, for example in bidendate ligand complexes of NbX 5 (X = Cl, Br) [{o-C 6 H 4 (CH 2 YMe 2 ) 2 }, {MeY(CH ) 2 YMe} or { n BuSe(CH 2 ) 2 Se n Bu} (Y = S, Se)], although with values much smaller than those determined/calculated in this work [36]. We notice that here reported values are similar to those observed for 95 [18]. Indeed, both forms of clusters, edge-bridged niobium and facecapped molybdenum are similar, they both are classified as hexanuclear clusters with π-donor ligands [37] and their electronic structure is explained by the same molecular-orbital scheme [37].…”

“…To the best of our knowledge, this is a first time the solidstate NMR/NQR technique is combined with the PAW/GIPAW calculations to study these unusual cluster environments for niobium and halide atoms. Additionally, this work can be considered as a continuation of the research about ability of solid-state NMR spectroscopy, combined with PAW/GIPAW computations, in the characterisation of hexanuclear halide metal clusters formed by other metals [18]. (2) were prepared according to procedures described in the literature [16,17].…”

High‐field95Mo and183W static and MAS NMR study of polyoxometalates

“…The MAS NMR spectra are dominated by the effect of the second‐order quadrupolar interaction, while the static spectra are dominated by the CSA, which can be as large as 500 ppm for (TBA) 2 Mo 6 O 19 . This is not unusual for 95 Mo nucleus . Therefore, the 95 Mo spectra were reconstructed with both chemical shift and quadrupolar parameters, so as to best agree with the static and the MAS NMR spectra.…”

Phosphorescent Nanocluster Light‐Emitting Diodes

“…However, these materials have also had challenges with stability due to an excess of dangling bonds and are highly sensitive to the diameter distribution that can change with parasitic reactions such as oxidation. [ 19 ] In contrast, nanoclusters are an inorganic molecular species, exactly defi ned in chemical composition and structure at the nanometer scale, analogous to organic molecules without organic bonding.Among various nanoclusters, molybdenum halide nanoclusters are particularly interesting as they have a variety of structures [ 20 ] and their luminescence and phosphorescent properties have been exploited for oxygen sensor applications. [ 21 ] In earlier studies with these clusters, we outlined routes to achieving near-unity phosphorescent quantum yields, superior to those shown for colloidal quantum dot nanocrystals and NIR organic phosphors through cluster-cation-host interactions.…”