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A Family of Ferro‐ and Antiferromagnetically Coupled Decametallic Chromium( III ) Wheels
Author(s) -
Low David M.,
Rajaraman Gopalan,
Helliwell Madeleine,
Timco Grigore,
van Slageren Joris,
Sessoli Roberta,
Ochsenbein Stefan T.,
Bircher Roland,
Dobe Christopher,
Waldmann Oliver,
Güdel HansUlrich,
Adams Mark A.,
Ruiz Eliseo,
Alvarez Santiago,
McInnes Eric J. L.
Publication year - 2006
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.200501041
Subject(s) - ground state , antiferromagnetism , ferromagnetism , diamagnetism , chemistry , inelastic neutron scattering , condensed matter physics , chromium , cluster (spacecraft) , crystallography , coupling (piping) , physics , neutron scattering , atomic physics , materials science , neutron , magnetic field , quantum mechanics , organic chemistry , computer science , metallurgy , programming language
The synthesis and crystal structures of a family of decametallic Cr III “molecular wheels” are reported, namely [Cr 10 (OR) 20 (O 2 CR′) 10 ] [R′=Me, R=Me ( 1 ), Et ( 2 ); R′=Et, R=Me ( 3 ), Et ( 4 ); R′=CMe 3 , R=Me ( 5 ), Et ( 6 )]. Magnetic studies on 1 – 6 reveal a remarkable dependence of the magnetic behaviour on the nature of R. In each pair of complexes with a common carboxylate (R′) the nearest neighbour Cr⋅⋅⋅Cr magnetic exchange coupling is more antiferromagnetic for the ethoxide‐bridged (R=Et) cluster than for the methoxide analogue. In complexes 2 , 4 and 6 the overall coupling is weakly antiferromagnetic resulting in diamagnetic ( S =0) ground states for the cluster, whilst in 1 and 5 it is weakly ferromagnetic thus resulting in very high‐spin ground states. This ground state has been probed directly in the perdeuterated version of 1 ([D] 1 ) by inelastic neutron scattering experiments, and these support the S =15 ground state expected for ferromagnetic coupling of ten Cr III ions, and they also indicate that a single J ‐value model is inadequate. The ground state of 5 is large but not well defined. The trends in J on changing R are further supported by density functional calculations on 1 – 6 , which are in excellent agreement with experiment. The very large changes in the nature of the ground state between 1 and 2 , and 5 and 6 are the result of relatively small changes in J that happen to cross J =0, hence changing the sign of J .