Andrea Pascui - Dinuclear Complexes Containing Linear M–F–M [M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)] Bridges: Trends in Structures, Antiferromagnetic Superexchange Interactions, and Spectroscopic Properties

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  Inorg. Chem., 2012, 51 (21), pp 11820–11836


  The reaction of   M(BF4)2·xH2O, where M   is Fe(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II), with the   new ditopic ligand   m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene   (Lm*) leads to the formation   of monofluoride-bridged dinuclear metallacycles of the formula   [M2(μ-F)(μ-Lm*)2](BF4)3.   The analogous manganese(II) species,   [Mn2(μ-F)(μ-Lm*)2](ClO4)3,   was isolated starting with   Mn(ClO4)2·6H2O using   NaBF4 as the source of the bridging fluoride. In all   of these complexes, the geometry around the metal centers is   trigonal bipyramidal, and the fluoride bridges are linear. The   1H, 13C, and 19F NMR spectra of   the zinc(II) and cadmium(II) compounds and the 113Cd   NMR of the cadmium(II) compound indicate that the metallacycles   retain their structure in acetonitrile and acetone solution. The   compounds with M = Mn(II), Fe(II), Co(II), Ni(II), and Cu(II) are   antiferromagnetically coupled, although the magnitude of the   coupling increases dramatically with the metal as one moves to   the right across the periodic table: Mn(II) (−6.7   cm–1) < Fe(II) (−16.3 cm–1) < Co(II)   (−24.1 cm–1) < Ni(II) (−39.0 cm–1)   << Cu(II) (−322 cm–1). High-field EPR spectra of   the copper(II) complexes were interpreted using the coupled-spin   Hamiltonian with gx = 2.150,   gy = 2.329,   gz = 2.010, D = 0.173   cm–1, and E = 0.089 cm–1.   Interpretation of the EPR spectra of the iron(II) and   manganese(II) complexes required the spin Hamiltonian using the   noncoupled spin operators of two metal ions. The values   gx = 2.26,   gy = 2.29,   gz = 1.99, J = −16.0   cm–1, D1 = −9.89 cm–1,   and D12 = −0.065 cm–1 were   obtained for the iron(II) complex and   gx = gy  = gz = 2.00, D1  = −0.3254 cm–1, E1 = −0.0153,   J = −6.7 cm–1, and D12 =   0.0302 cm–1 were found for the manganese(II) complex.   Density functional theory (DFT) calculations of the exchange   integrals and the zero-field splitting on manganese(II) and   iron(II) ions were performed using the hybrid B3LYP functional in   association with the TZVPP basis set, resulting in reasonable   agreement with experiment.

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