Magnetic measurements on dimeric and tetrameric fluoro-bridged cobalt and manganese compounds

Smit, J.; Nap, G. M.; Jongh, L.J. de; Ooijen, J. A. C. Van; Reedijk, J.

doi:10.1016/0378-4363(79)90087-1

Cited by 9 publications

(7 citation statements)

References 8 publications

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“…An intermediate of F stoichiometry [CoF(DMPz)3]2(BF 4)2 can be isolated from the above reaction, and this material is dimeric with bridging fluorides. The exchange constant in the dimer is -1 K or smaller, which reflects the constrained geometry ofthe Co-F 2-CO core, as well as the poor superexchange path furnished by fluoride [80]. Several copper compounds with CuF 2 Cu cores [81] likewise have essentially zero exchange interaction.…”

Section: Some Other Dimersmentioning

confidence: 99%

Introduction to Magnetic Exchange: Dimers and Clusters

Carlin

1986

Magnetochemistry

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Energy Levels and Specific Heats 71configurational mixing of states such as M+ F M2+. The electron on Fin (c) and (d) can now couple with the lone electron in a d z 2 orbital on an adjoining Ni2+ . The preferred coupling is to give a singlet state [(c), called antiferromagnetic] rather than a triplet, (d). This in turn stabilizes the singlet state (a) with respect to the triplet (b). The strength of the interaction will depend on the amount of overlap, and we present here only a model of 180° superexchange. Metal ion orbitals can also overlap with p" ligand orbitals at a 90° angle, and much recent research effort has gone into finding the factors which influence this superexchange interaction.This model, which has been applied to a variety of systems [1,2] is somewhat similar to that which is used for explaining spin-spin coupling in NMR spectroscopy [3]. The Hamiltonian in use for metal-metal exchange interaction in magnetic insulators is of the form (5.2) where the sum is taken over all pair-wise interactions of spins i and j in a lattice. For the moment, we shall restrict our attention to dimers, and thereby limit the summation to the two atoms 1 and 2 in the dimeric molecule, so thatThis is called an isotropic (note the dot product between the two spins, S) or Heisenberg Hamiltonian, and we adopt the convention that negative J refers to antiferromagnetic (spin-paired or singlet ground state in a dimer) interactions, and positive J refers to ferromagnetic (spin-triplet ground state) interactions. The exchange constant J is given in energy units (Kelvins) and measures the strength ofthe interaction. The reader must be careful in comparing different authors, for a variety of conventions (involving the negative sign and even the factor of 2) are in use. (The symbol J now takes a different meaning from its earlier use as the quantum operator for total angular momentum.) Energy Levels and Specific HeatsAn antiferromagnetic interaction ofthe type given in Eq. (5.3), when applied to two ions each of!/ = t gives a spin-singlet ground state and a spin-triplet 2J in energy above the singlet ( Fig. 5.2). Naturally, ifthe interaction were ferromagnetic, the diagram is simply inverted. For an external field applied along the z-axis of the pair, the complete Hamiltonian will be taken as

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Section: Some Other Dimersmentioning

confidence: 99%

Introduction to Magnetic Exchange: Dimers and Clusters

Carlin

1986

Magnetochemistry

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“…Thus, numerous tetranuclear complexes have been prepared and studied with overall oxidation state for the four manganese ions comprised between +8 and +16 and a variety of nitrogen- and/or oxygen- containing ligands affording diverse topological arrangements of the four manganeses. They are usually described with reference to known structures or to the overall shape of the complex like adamantane (tetrahedral), cubane, butterfly shaped, and bis-dinuclear with either arrangement of the two dinuclear units in two superposed planes 5 or in the same plane leading to approximately linear or chainlike clusters . However, owing to the large variety of tetranuclear manganese assemblies, a number of them do not pertain to previously described arrangements…”

Section: Introductionmentioning

confidence: 99%

Synthesis, Structure, and Magnetic and Redox Properties of Linear Bis-Dinuclear Complexes Afforded by Schiff Base Ligands Containing Catecholate and Pyridine or Imidazole Groups

et al. 1997

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3-[(((2′-pyridyl)methyl)imino)methyl]benzene-1,2-diol, H 2 L 2 ) 3-[((2-(2′-pyridyl)ethyl)imino)methyl]benzene-1,2-diol, and H 3 L 3 ) 3-[((2-(4′-imidazolyl)ethyl)imino)methyl]benzene-1,2-diol, have been synthesized and studied. 1 crystallizes in the monoclinic system, space group P2 1 /c, Z ) 2, a ) 11.396(1) Å, b ) 18.583(2) Å, c ) 9.888(1) Å, and ) 103.51(1)°. The structure was solved by direct methods and refined to conventional agreement indices R ) 0.028 and R w ) 0.029. The molecular structure of 1 consists of discrete [Mn II 2 L 1 (CH 3 CO 2 ) 2 (CH 3 OH)] 2 molecules. 1 is a chainlike bis-dinuclear Mn(II) complex involving an unprecedented arrangement of pentacoordinated (N 2 O 3 ) and hexacoordinated (O 6 ) manganese ions as the outer and inner pairs of metal centers, respectively. The different Mn‚‚‚Mn distances result from significant differences in bridging moieties, two catecholato bridges for the shortest distance between inner manganese ions, and one catecholato and two acetato bridges for the longer distances between inner and outer manganese ions. The symmetry of the N 2 O 3 donor set around the outer Mn(1) is close to a trigonal bipyramid while the O 6 ligand environment of the inner Mn(2) can be described as a rhombically distorted octahedron. The synthesis, IR, EPR, and magnetic susceptibility of 1-3 suggest a similar bis-dinuclear structure for all three complexes. Variabletemperature magnetic susceptibility studies establish the presence of antiferromagnetic exchange interactions between Mn(II) centers of 1-3 with predominence of the interactions between inner and outer metal ions (-3.4 to -5 cm -1 ) over the interaction between inner manganese ions (-0.5 to 0.5 cm -1 ). EPR spectroscopy indicates that the bis-dinuclear arrangement of complexes 1-3 is retained in aprotic solvents. As shown by EPR, O 2 oxidation leads to the release of the constitutive Mn(II) dinuclear units, prior to formation of mononuclear Mn(II) and finally Mn(III) species. Observation of two irreversible two-electron oxidation waves in the CV profiles of 1-3 is consistent with a similar splitting of the bis-dinuclear complex molecules induced by electrochemical oxidation. These studies suggest that complexes resulting from the reaction of manganese with the fully oxidized form of such electroactive ligands may afford interesting new higher oxidation-state polynuclear Mn species.

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“…A similar oxo bridge has been observed in the compound B III 4 (2,2'-biimidazole) 2 (O)(C 2 H 5 ) 6 reported by Niedenzu et al [10a] The B À O, B À N, and B À C bond lengths in A and B are similar and typical. [10,11] The structure of A is similar to that of B III 2 (O)(7-azain) 2 (C 2 H 5 ) 2 where the environment around both boron centers is identical. In 1 H and 13 C NMR spectra of A, only one set of resonances due to the phenyl group are observed, while one resonance is present in 11 B NMR spectrum of A, indicating that the structure of A in solution is the same as that in the solid state.…”

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confidence: 98%