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Origin of Ferromagnetism and Magnetic Anisotropy in a Family of Copper(II) Triangles
Author(s) -
Mathivathanan Logesh,
Rogez Guillaume,
Ben Amor Nadia,
Robert Vincent,
Raptis Raphael G.,
Boudalis Athanassios K.
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202001028
Subject(s) - electron paramagnetic resonance , ferromagnetism , chemistry , ab initio , ab initio quantum chemistry methods , ground state , magnetic anisotropy , anisotropy , crystallography , trigonal bipyramidal molecular geometry , condensed matter physics , magnetic susceptibility , tetragonal crystal system , crystal structure , magnetization , nuclear magnetic resonance , physics , atomic physics , magnetic field , molecule , organic chemistry , quantum mechanics
Previously reported ferromagnetic triangles (N n Bu 4 ) 2 [Cu 3 ( μ 3 ‐Cl) 2 ( μ ‐4‐NO 2 ‐pz) 3 Cl 3 ] ( 1 ), (PPN) 2 [Cu 3 ( μ 3 ‐Cl) 2 ( μ ‐pz) 3 Cl 3 ] ( 2 ), (bmim) 2 [Cu 3 ( μ 3 ‐Cl) 2 ( μ ‐pz) 3 Cl 3 ] ( 3 ) and newly reported (PPh 4 ) 2 [Cu 3 ( μ 3 ‐Cl) 2 ( μ ‐4‐Ph‐pz) 3 Cl 3 ] ( 4 ) were studied by magnetic susceptometry, electron paramagnetic resonance (EPR) spectroscopy and ab initio calculations to assess the origins of their ferromagnetism and of the magnetic anisotropy of their ground S= 3/2 state (PPN + =bis(triphenylphosphine)iminium, bmim + =1‐butyl‐3‐methylbenzimidazolium, pz − =pyrazolate). Ab initio studies revealed the dz2character of the magnetic orbitals of the compressed trigonal bipyramidal copper(II) ions. Ferromagnetic interactions were attributed to weak orbital overlap via the pyrazolate bridges. From the wavefunctions expansions, the ratios of the magnetic couplings were determined, which were indeterminate by magnetic susceptometry. Single‐crystal EPR studies of 1 were carried out to extend the spin Hamiltonian with terms which induce zero‐field splitting (zfs), namely dipolar interactions, anisotropic exchange and Dzyaloshinskii–Moriya interactions (DMI). The data were treated through both a giant‐spin model and through a multispin exchange‐coupled model. The latter indicated that ≈62 % of the zfs is due to anisotropic and ≈38 % due to dipolar interactions. The powder EPR data of all complexes were fitted to a simplified form of the multispin model and the anisotropic and dipolar contributions to the ground state zfs were estimated.