Structure and magnetism of bis(2-chloropyridine)tetrakis(.mu.-trichloroacetato(O,O')-dicopper(II). Influence of the bridging ligand on magnetic properties of dimeric copper(II) carboxylate adducts

Moreland, James A.; Doedens, Robert J.

doi:10.1021/ic50181a033

Cited by 42 publications

(15 citation statements)

References 31 publications

(11 reference statements)

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“…The results described above on the dimeric 2-chloropyridine adduct of copper trichloroacetate [23] and tribromoacetate [24], especially concerning the influence of the -CX3 groups, would tend to argue in favor of a superexchange mechanism for exchange interaction in these molecules, rather than a direct metal-metal interaction. Indeed, it was found that the ordering of the exchange constants is identical to the ordering of the group polarizabilities of the substitutuents on the acetate group (R=-H, -CF 3, -CH 3 , -CC1 3 or -CBr 3).…”

Section: +E(s;-s;)mentioning

confidence: 94%

“…The hydrated and anhydrous formates, however, are distinctly different, both in structural and magnetic properties [22]. The structure and magnetism of the 2-chloropyridine adducts of both copper trichloroacetate [23] and copper tribromoacetate [24] have been reported. The dimeric molecules have the bridged copper(II) acetate structure, with a long Cu---Cu distance of 0.2766 nm in both molecules (recall that the separation is 0.2616 nm in [Cu(OAch· (H20)]2).…”

Section: +E(s;-s;)mentioning

confidence: 99%

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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: +E(s;-s;)mentioning

confidence: 94%

Section: +E(s;-s;)mentioning

confidence: 99%

Introduction to Magnetic Exchange: Dimers and Clusters

Carlin

1986

Magnetochemistry

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“…When the methyl group in acetate is replaced by CCl 3 the coupling constant is reduced from À 296 to less than À 200 cm À1 . [14,94,95] A more spectacular change is obtained if R SiR' 3 , enhancing the antiferromagnetic coupling to a strong value (J %À 1000 cm À1 ). [96] The experimental value for a given bridging ligand is not unique since the compounds that have been magnetically characterized with different axial ligands have slightly different structural data.…”

Section: Computational Methodologymentioning

confidence: 99%

“…[13,94,95,108,109] To study the effect of this distortion on the coupling constant we have considered a model structure with ammonia molecules in the axial position and a Cu´´´Cu distance of 3.22 , the average value found for compounds with this distorted geometry. The only parameters that have α β 8 been changed from the ideal to the distorted structure are the two N-Cu-O angles (a and b in 8), while all other structural parameters, including the Cu´´´Cu distance, are kept fixed.…”

Section: Computational Methodologymentioning

confidence: 99%

Exchange Coupling in Carboxylato-Bridged Dinuclear Copper(II) Compounds: A Density Functional Study

et al. 2001

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A computational study of the exchange coupling is presented for a selected sample of carboxylato-bridged dinuclear copper(II) compounds. Model calculations have been used to examine the influence of several factors on the coupling constants: a) the electron-withdrawing power of the bridging ligands; b) the nature of the axial ligands; c) the number of bridging carboxylato groups; d) some structural distortions frequently found in this family of compounds; and e) the coordination mode of the carboxylato bridge. Coupling constants calculated for some complete structures, as determined by X-ray diffraction, are in excellent agreement with experimental data, confirming the ability of the computational strategy used in this work to predict the coupling constant for compounds for which experimental data are not yet available.

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“…[5] Strong antiferromagnetic coupling was observed at the Cu II À Cu II bond between the two S = 1/2 spins. [4][5][6] Two axial sites of the paddle-wheel [Cu II 2 A C H T U N G T R E N N U N G (CH 3 COO) 4 ] unit were further coordinated by two H 2 O molecules, which could easily be replaced by DMF, pyridine, picoline, urea, etc. [4] The introduction of the bidentate ligand pyrazine into the axial sites of [Cu (2) crystals were examined by X-ray crystallography, 1 H NMR spectroscopy, and measurements of the dielectric constants and magnetic susceptibilities (ADCOO = adamantane carboxylate, DMF = N,N-dimethylformamide, and AcOEt = ethyl acetate).…”

Section: -A C H T U N G T R E N N U N G (Rcoo)mentioning

confidence: 99%

Huge Dielectric Response and Molecular Motions in Paddle‐Wheel [Cu^II₂(Adamantylcarboxylate)₄(DMF)₂]⋅(DMF)₂

Takahashi

Hoshino

et al. 2011

Chemistry A European J

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The temperature-dependent dynamic properties of [Cu(II)(2)(ADCOO)(4)(DMF)(2)]⋅(DMF)(2) (1) and [Cu(II)(2)(ADCOO)(4)(AcOEt)(2)] (2) crystals were examined by X-ray crystallography, (1)H NMR spectroscopy, and measurements of the dielectric constants and magnetic susceptibilities (ADCOO = adamantane carboxylate, DMF = N,N-dimethylformamide, and AcOEt = ethyl acetate). In both crystals, four ADCOO groups bridged a binuclear Cu(II)-Cu(II) bond, forming a paddle-wheel [Cu(II)(2)(ADCOO)(4)] structure. The oxygen atoms of two DMF molecules in crystal 1 and two AcOEt molecules in crystal 2 were coordinated at axial positions of the [Cu(II)(2)(ADCOO)(4)] moiety, forming [Cu(II)(2)(ADCOO)(4)(DMF)(2)] and [Cu(II)(2)(ADCOO)(4)(AcOEt)(2)], respectively. Two additional DMF molecules were included in the unit cell of crystal 1, whereas AcOEt was not included in the unit cell of crystal 2. The structural analyses of crystal 1 at 300 K showed three-fold rotation of the adamantyl groups, whereas rotation of the adamantyl groups of crystal 2 at 300 K was not observed. Thermogravimetric measurements of crystal 1 indicated a gradual elimination of DMF upon increasing the temperature above 300 K. The dynamic behavior of the crystallized DMF yielded significant temperature-dependent dielectric responses in crystal 1, which showed a huge dielectric peak at 358 K in the heating process. In contrast, only small frequency-dependent dielectric responses were observed in crystal 2 because of the freezing of the molecular rotation of the adamantyl groups. The magnetic behavior was dominated by the strong antiferromagnetic coupling between the two S = 1/2 spins of the Cu(II)-Cu(II) site, with magnetic exchange energies (J) of -265 K (crystal 1) and -277 K (crystal 2).

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Structure and magnetism of bis(2-chloropyridine)tetrakis(.mu.-trichloroacetato(O,O')-dicopper(II). Influence of the bridging ligand on magnetic properties of dimeric copper(II) carboxylate adducts

Abstract: Structure and Magnetism of Bis(2-chloropyridine)tetrakis(yu-trichloroacetato(0,0/)

Cited by 42 publications

References 31 publications

Introduction to Magnetic Exchange: Dimers and Clusters

Introduction to Magnetic Exchange: Dimers and Clusters

Exchange Coupling in Carboxylato-Bridged Dinuclear Copper(II) Compounds: A Density Functional Study

Huge Dielectric Response and Molecular Motions in Paddle‐Wheel [Cu^II₂(Adamantylcarboxylate)₄(DMF)₂]⋅(DMF)₂

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Structure and magnetism of bis(2-chloropyridine)tetrakis(.mu.-trichloroacetato(O,O')-dicopper(II). Influence of the bridging ligand on magnetic properties of dimeric copper(II) carboxylate adducts

Abstract: Structure and Magnetism of Bis(2-chloropyridine)tetrakis(yu-trichloroacetato(0,0/)

Cited by 42 publications

References 31 publications

Introduction to Magnetic Exchange: Dimers and Clusters

Introduction to Magnetic Exchange: Dimers and Clusters

Exchange Coupling in Carboxylato-Bridged Dinuclear Copper(II) Compounds: A Density Functional Study

Huge Dielectric Response and Molecular Motions in Paddle‐Wheel [CuII2(Adamantylcarboxylate)4(DMF)2]⋅(DMF)2

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Huge Dielectric Response and Molecular Motions in Paddle‐Wheel [Cu^II₂(Adamantylcarboxylate)₄(DMF)₂]⋅(DMF)₂