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

The local magnetic structure in the [FeIII(Tp)(CN)3]− 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. Spinning tops! A deep understanding of the spin‐density distribution in the molecular building block [FeIII(Tp)(CN)3]− has been gained by using polarized neutron diffraction, paramagnetic NMR spectroscopy, and quantum chemistry calculations (see figure). The connection, via ab‐initio calculations, of the PND and pNMR experimental pictures of the magnetism, is particularly suitable in the rationalization and development of magnetic materials.