DFT-NMR Investigation and 51V 3QMAS Experiments for Probing Surface OH Ligands and the Hydrogen-Bond Network in a Polyoxovanadate Cluster: The Case of Cs4[H2V10O28]·4H2O

摘要

This work shows that the combination of first-principles calculations and 51V NMR experimentsnis a powerful tool to elucidate the location of surface hydroxyl groups and to precisely describe the hydrogennbond network in the complex decavanadate cluster Cs4[H2V10O28].4H2O, enhancing the strength of NMRncrystallography. The detailed characterization of H-bond networks for these kinds of inorganic compoundsnis of primary importance and should benefit from the DFT-NMR predictions by considering explicitly thenperiodic boundary conditions. The determination of the Cs4[H2V10O28] ·4H2O structure by single-crystal X-rayndiffraction was not sufficiently accurate to provide the location of protons. From available diffraction data,nfive different protonated model structures have been built and optimized using DFT-based methods. Thenpossible interconversion of two decavanadate isomers through a proton exchange is evaluated by calculatingnthe energy barrier and recording variable-temperature 1H MAS NMR spectra. First-principles calculationsnof 51V NMR parameters clearly indicate that these parameters are very sensitive to the local intermolecularnhydrogen-bonding interactions. Considering the DFT error limits, the fairly good agreement betweenncalculated and experimental NMR parameters arising from the statistical modeling of the data allows thenunambiguous assignment of the five 51V NMR signals and, thus, the location of OH surface ligands in thendecavanadate cluster. In particular, first-principles calculations accurately reproduce the 51V quadrupolarnparameters. These results are fully consistent with 51V 3QMAS NMR spectra recorded with and without 1Hndecoupling. Finally, correlations are established between local octahedral VO6 deformations and 51V NMRnparameters (Cq and Δδ), which will be useful for the characterization of a wide range of chemical speciesncontaining vanadium(V).