Probing the Local Magnetic Structure of the [FeIII(Tp)(CN)3]- Building Block Via Solid-State NMR Spectroscopy, Polarized Neutron Diffraction, and First-Principle Calculations

International audienceThe local magnetic structure in the [Fe (Tp)(CN) ] building block was investigated by combining paramagnetic Nuclear Magnetic Resonance (pNMR) spectroscopy and polarized neutron diffraction (PND) with first-principle calculations. The use of the pNMR and PND experimental techniques revealed the extension of spin-density from the metal to the ligands, as well as the different spin mechanisms that take place in the cyanido ligands Spin-polarization on the carbon atoms and spin-delocalization on the nitrogen atoms. The results of our combined density functional theory (DFT) and multireference calculations were found in good agreement with the PND results and the experimental NMR chemical shifts. Moreover, the ab-initio calculations allowed us to connect the experimental spin-density map characterized by PND and the suggested distribution of the spin-density on the ligands observed by NMR spectroscopy. Interestingly, significant differences were observed between the pseudo-contact contributions of the chemical shifts obtained by theoretical calculations and the values derived from NMR spectroscopy using a simple point-dipole model. These discrepancies underline the limitation of the point-dipole model and the need for more elaborate approaches to break down the experimental pNMR chemical shifts into contact and pseudo-contact contributions

93Nb and 17O NMR chemical shifts of niobiophosphate compounds

International audienc

A very sensitive high-resolution NMR method for quadrupolar nuclei: SPAM-DQF-STMAS

We show that by combining the intrinsically larger (with respect to MQMAS) efficiency of Double-Quantum Filtered Satellite-Transition MAS (DQF-STMAS), with the large S/N gain of the Soft-Pulse Added Mixing (SPAM) concept, a new very sensitive high-resolution solid-state NMR method can be obtained for semi-integer quadrupolar nuclei

RMN de l'oxygène-17 et nouvelles méthodologies de RMN des solides appliquées à la caractérisation des matériaux phosphates

Ce travail concerne l'étude des verres de phosphate par RMN du solide et principalement par RMN de l' oxygène-l7. D'abord, nous proposons une méthode d'enrichissement en 17O, basée sur un échange isotopique sous vapeur d'eau enrichie. Cette méthode permet d'enrichir en 17O aussi bien des composés phosphates que des composés oxydes. Puis, nous avons adapté le concept SPAM afin d'améliorer la sensibilité des spectres haute résolution 3Q- et SI -MAS en 17O des verres de niobiophosphate. La résolution des spectres RMN du 31P de niobiophosphates cristallisés est aussi améliorée par découplage de l'interaction J entre le 31P et le 93Nb Enfin, les verres du système xNb2O5-(100-x)NaPO3 ont été caractérisés par une approche RMN multi-nucléaire. Un changement structural observé entre 20 et 30% molaire de Nb2O5 explique l'évolution des propriétés optiques non-linéaires. Ces résultats confortent les études structurales réalisées à partir d'autres techniques spectroscopiques.LILLE1-BU (590092102) / SudocSudocFranceF