S C

IE N

T IF

IC H

IG H

LI G

H T

S E

L E

C T

R O

N IC

S T

R U

C T

U R

E ,

M A

G N

E T

IS M

A N

D D

Y N

A M

IC S

9 7 I H I G H L I G H T S 2 0 2 2

PRINCIPAL PUBLICATION AND AUTHORS

From an antiferromagnetic insulator to a strongly correlated metal in square-lattice MCl2(pyrazine)2 coordination solids, P. Perlepe (a,b), I. Oyarzabal (a,c,d,e), L. Voigt (f), M. Kubus (f), D.N. Woodruff (g), S.E. Reyes-Lillo (h), M.L. Aubrey (i), P. Négrier (j), M. Rouzières (a), F. Wilhelm (k), A. Rogalev (k), J.B. Neaton (l,m,n), J.R. Long (i,o,p), C. Mathonière (a), B. Vignolle (b), K.S. Pedersen (a,f), R. Clérac (a), Nat. Commun. 13, 5766 (2022); https:/doi.org/10.1038/s41467-022-33342-5 (a) Univ. Bordeaux, CNRS, Centre de Recherche Paul Pascal, UMR 5031, Pessac (France) (b) Univ. Bordeaux, CNRS, Bordeaux INP, ICMCB, UMR 5026, Pessac (France) (c) Chemistry Faculty, University of the Basque Country, Donostia-San Sebastián (Spain) (d) BCMaterials, Basque Center for Materials, Applications and Nanostructures, Leioa (Spain) (e) IKERBASQUE, Basque Foundation for Science, Bilbao (Spain) (f) Department of Chemistry, Technical University of Denmark, Lyngby (Denmark) (g) Department of Chemistry, University of Oxford (UK) (h) Departamento de Ciencias Físicas, Universidad Andres Bello, Santiago (Chile) (i) Department of Chemistry, University of California Berkeley (USA) (j) Univ. Bordeaux, CNRS, Laboratoire Ondes et Matière d Aquitaine, UMR 5798, Talence (France) (k) ESRF (l) Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley (USA) (m) Department of Physics, The University of California (USA) (n) Kavli Energy Nanosciences Institute at Berkeley (USA) (o) Department of Chemical and Biomolecular Engineering, University of California Berkeley (USA) (p) Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley (USA)

REFERENCES

[1] K.S. Pedersen et al., Nat. Chem. 10, 1056-1061 (2018). [2] P. Perlepe et al., Polyhedron 153, 248-253 (2018). [3] P. Perlepe et al., Science 370, 587-592 (2020).

Unravelling the origin of the intermediate spin ground state in a Cr10 single molecule magnet

In a molecular magnetic compound of 10 Cr atoms with wheel structure, the origin of its unusual intermediate spin state is unravelled using experimental X-ray techniques, including XMCD, and theoretical methods. The magnetic behaviour is related to subtle changes in the interactions due to the molecular geometry.

The molecular wheel [Cr10(OMe)20(O2CCMe3)10] (Figure 88a) [1], in short {Cr10}, with an unusual intermediate total spin S = 9 and non-negligible cluster anisotropy, D/kB = 0.045(2) K [2], is a rare case among wheels based on an even number of 3d-metals, which usually present an antiferromagnetic (S = 0), or more rarely ferromagnetic ground state (with maximal S). The origin of such a behaviour has been unveiled using a combination of experimental techniques including high-field X-ray

magnetic circular dichroism (XMCD), single-crystal angle-dependent SQUID magnetometry and inelastic neutron scattering (INS) spectroscopy with an exhaustive theoretical approach including both ab-initio and density functional theory (DFT) calculations, and Monte Carlo (MC) simulations.

X-ray absorption spectroscopy (XAS) and XMCD spectra were collected at the Cr K-edge at beamline ID12 using the Apple II undulator and a double Si(111) crystal monochromator. The K-edge signal mainly originates in dipolar 1s 4p transitions (Figure 89a), but the pre- peak signal (Figure 89b) originates in 1s 3d transitions (both direct quadrupolar transitions and dipolar ones through 4p-3d hybridisation). This channel opens a direct probe to the Cr3+ 3d magnetism. By fixing the incident photon energy at the Cr pre-peak, the low-temperature XMCD magnetisation curve up to 17 T (Figure 89c), once scaled using SQUID data at 5 T, made it possible to fit the exchange interactions in a model Hamiltonian using classical and quantum MC.

Fig. 87: a) Ti K-edge, (b) V K-edge and (c) Cl K-edge XAS spectra of polycrystalline TiCl2(pyz)2, VCl2(pyz)2 materials and the relevant reference compounds recorded at room temperature.