Premium
Single‐Ion versus Dipolar Origin of the Magnetic Anisotropy in Iron( III )‐Oxo Clusters: A Case Study
Author(s) -
Abbati Gian Luca,
Brunel LouisClaude,
Casalta Helene,
Cornia Andrea,
Fabretti Antonio C.,
Gatteschi Dante,
Hassan Aia K.,
Jansen Aloysius G. M.,
Maniero Anna Lisa,
Pardi Luca,
Paulsen Carley,
Segre Ulderico
Publication year - 2001
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 - 10.1002/1521-3765(20010417)7:8<1796::aid-chem17960>3.0.co;2-y
Subject(s) - anisotropy , magnetic anisotropy , dipole , ion , condensed matter physics , materials science , nuclear magnetic resonance , physics , chemistry , magnetization , magnetic field , quantum mechanics
Abstract A multitechnique approach has allowed the first experimental determination of single‐ion anisotropies in a large iron( III )‐oxo cluster, namely [NaFe 6 (OCH 3 ) 12 (pmdbm) 6 ]ClO 4 ( 1 ) in which Hpmdbm=1,3‐bis(4‐methoxyphenyl)‐1,3‐propanedione. High‐frequency EPR (HF‐EPR), bulk susceptibility measurements, and high‐field cantilever torque magnetometry (HF‐CTM) have been applied to iron‐doped samples of an isomorphous hexagallium( III ) cluster [NaGa 6 (OCH 3 ) 12 (pmdbm) 6 ]ClO 4 , whose synthesis and X‐ray structure are also presented. HF‐EPR at 240 GHz and susceptibility data have shown that the iron( III ) ions have a hard‐axis type anisotropy with D Fe =0.43(1) cm −1 and E Fe =0.066(3) cm −1 in the zero‐field splitting (ZFS) Hamiltonian H = D Fe [ S z 2 − S ( S + 1)/3] + E Fe [ S x 2 − S y 2 ]. HF‐CTM at 0.4 K has then been used to establish the orientation of the ZFS tensors with respect to the unique molecular axis of the cluster, Z. The hard magnetic axes of the iron( III ) ions are found to be almost perpendicular to Z , so that the anisotropic components projected onto Z are negative, D Fe ( ZZ )=−0.164(4) cm −1 . Due to the dominant antiferromagnetic coupling, a negative D Fe ( ZZ ) value determines a hard‐axis molecular anisotropy in 1 , as experimentally observed. By adding point‐dipolar interactions between iron( III ) spins, the calculated ZFS parameter of the triplet state, D 1 =4.70(9) cm −1 , is in excellent agreement with that determined by inelastic neutron scattering experiments at 2 K, D 1 =4.57(2) cm −1 . Iron‐doped samples of a structurally related compound, the dimer [Ga 2 (OCH 3 ) 2 (dbm) 4 ] (Hdbm=dibenzoylmethane), have also been investigated by HF‐EPR at 525 GHz. The single‐ion anisotropy is of the hard‐axis type as well, but the D Fe parameter is significantly larger [ D Fe =0.770(3) cm −1 , E Fe =0.090(3) cm −1 ]. We conclude that, although the ZFS tensors depend very unpredictably on the coordination environment of the metal ions, single‐ion terms can contribute significantly to the magnetic anisotropy of iron( III )‐oxo clusters, which are currently investigated as single‐molecule magnets.