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Studies of a Molecular Hourglass: Synthesis and Magnetic Characterisation of a Cyclic Dodecanuclear {Cr 10 Cu 2 } Complex
Author(s) -
Shanmugam Muralidharan,
Engelhardt Larry P.,
Larsen Finn K.,
Luban Marshall,
McInnes Eric J. L.,
Muryn Christopher A.,
Overgaard Jacob,
Rentschler Eva,
Timco Grigore A.,
Winpenny Richard E. P.
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.200600827
Subject(s) - excited state , electron paramagnetic resonance , antiferromagnetism , ferromagnetism , chemistry , copper , crystallography , ground state , magnetic susceptibility , metal , exchange interaction , chromium , condensed matter physics , physics , atomic physics , nuclear magnetic resonance , organic chemistry
The synthesis, structure, EPR, and magnetic studies of two dodecanuclear heterometallic cyclic clusters are reported. The compounds have the general formula [R 2 NH 2 ] 2 [Cr 10 Cu 2 F 14 (O 2 CCMe 3 ) 22 ] (R=Me, 1 or i Pr, 2 ). Both structures contain an array of metal centers which describe an approximate “hourglass”, with an ammonium cation in the center of each half of the figure. The chromium sites are all six‐coordinate, with the two copper sites five‐coordinate. The majority of metal–metal edges are bridged by a single fluoride and two pivalate ligands, while two CrCu edges are bridged by a single fluoride and a single pivalate. Magnetic studies show that 1 and 2 exhibit similar (but not identical) behavior, which can be attributed to ten antiferromagnetic and two ferromagnetic exchange interactions around the ring which gives an S =0 ground state. Quantum Monte Carlo calculations have been used to quantify the exchange interactions by successfully simulating the susceptibility for the full temperature range and thus clarifying the distinction between 1 and 2 . EPR spectroscopy shows signals due to excited states, and a variable‐temperature study has provided an estimate of the energy gap between the first excited state ( S =1) and second excited state ( S =2) for 1 that is consistent with the value obtained using the QMC method.