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

Siddhartha De (1) , Alexandrine Flambard (1) , Delphine Garnier (1) , Patrick Herson (1) , Frank H Köhler (2) , Abhishake Mondal (1) , Karine Costuas (3) , Béatrice Gillon (4) , Rodrigue Lescouëzec (1) , Boris Le Guennic (3) , Frédéric Gendron (3)

1 IPCM - Institut Parisien de Chimie Moléculaire
2 TUM - Technische Universität Munchen - Université Technique de Munich [Munich, Allemagne]
3 ISCR - Institut des Sciences Chimiques de Rennes
4 NFMQ - LLB - Nouvelles frontières dans les matériaux quantiques

The 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.

Keywords: density functional calculations; magnetic properties; neutron diffraction; spin density; NMR spectroscopy; ab-initio calculations

Domains: Chemical Sciences; Coordination chemistry

Siddhartha De, Alexandrine Flambard, Delphine Garnier, Patrick Herson, Frank H Köhler, et al.. 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. Chemistry - A European Journal, 2019, 25 (52), pp.12120-12136. ⟨10.1002/chem.201902239⟩. ⟨hal-02280844⟩