DOI•
Structure and magnetism of an exchange coupled system: An NMR approach
01 Aug 1995-Vol. 107, Iss: 4, pp 281-295
TL;DR: A binuclear copper(II) complex [Cu2L(OH)](C1O4)2·2H2O has been synthesized and characterized by X-ray crystallography and 1H-NMR studies.
Abstract: A binuclear copper(II) complex [Cu2L(OH)](C1O4)2·2H2O has been synthesized and characterized by X-ray crystallography and1H-NMR studies The crystal structure shows that the bridging angles between Cu(l)-O(l)-Cu(2) and Cu(l)-O(2)-Cu(2) are 989(2)° and 1022(2)° respectively The Cu(l)-Cu(2) distance is 30097(12)A This indicates that the interaction between the two copper atoms is antiferromagnetic in nature The geometry around Cu(l) is distorted square-pyramid with one water molecule occupying the axial fifth position, whereas, the geometry around Cu(2) is distorted square-planar with weak interactions of one of the perchlorate anion There are eight molecules present in the unit cell There is an interdimer interaction between the dimers The temperature-dependent1H-NMR chemical shift studies have been performed on six different protons of this complex which reveals that the exchange coupling constant (− 2J) is same for all protons (208 ± 1 cm−1) However, the hyperfine coupling constant (A′) was found to be different in magnitude as well as in sign We also report solvent dependent NMR properties
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TL;DR: In this article, the theory of double exchange was applied to perovskite-type manganites and detailed qualitative predictions about the magnetic lattice, the crystallographic lattice and the electrical resistivity were made.
Abstract: The theory of semicovalent exchange is reviewed and applied to the perovskite-type manganites $[\mathrm{La}, M(\mathrm{II})]\mathrm{Mn}{\mathrm{O}}_{3}$. With the hypothesis of covalent and semicovalent bonding between the oxygen and manganese ions plus the mechanism of double exchange, detailed qualitative predictions are made about the magnetic lattice, the crystallographic lattice, the electrical resistivity, and the Curie temperature as functions of the fraction of ${\mathrm{Mn}}^{4+}$ present. These predictions are found to be in accord with recent findings from neutron-diffraction and x-ray data as well as with the earlier experiments on this system by Jonker and van Santen.
3,148 citations
TL;DR: In this article, the sign of the superexchange interaction is closely connected with the symmetry of the electron orbitals and the cation orbital state when the cations are subject to the crystalline field arising from octahedral or tetrahedrally surrounding anions.
2,477 citations
TL;DR: In this article, the general formalism of Kramers indicating the existence of superexchange interaction has been reduced, under simplifying assumptions, to the point where actual formulas for the interaction can be written down directly in terms of spin operators, with certain exchange and transition integrals as parameters.
Abstract: In this paper the general formalism of Kramers indicating the existence of superexchange interaction has been reduced, under simplifying assumptions, to the point where actual formulas for the interaction can be written down directly in terms of spin operators, with certain exchange and transition integrals as parameters. Two results of physical interest are the following: (a) superexchange must be expected to show the directional properties (as far as directional relations of interacting magnetic ions are concerned) of the orbitals in the outer shell of the non-magnetic connecting ions; and (b) the sign of the effective exchange integral depends upon the sign of the internal exchange coupling of an added electron on the magnetic ion.
1,304 citations
TL;DR: In this paper, the effect of geometrical distortions, electronegativity, and variation of substituents on the magnetic interaction in dimeric systems is examined in detail for singly bridged L,M-X-ML, (n = 3, 4, 5); Cu~C16~ and other doubly bridging species where the bridging ligands are halogens, OR, pyridine N-oxides, oxalate, squarate; and the acetate bridged dimers C u ~ (R C 0 0 ) 4.
Abstract: A molecular orbital analysis shows that the antiferromagnetic contributions to magnetic coupling, favoring a lowspin ground state for a dimer containing two weakly interacting metal centers, can be analyzed in terms of pairwise interactions of dimeric molecular orbitals, with the square of the splitting in energy between the members of a pair being a measure of the stabilization of the low-spin state. The effect of geometrical distortions, electronegativity, and variation of substituents on the magnetic interaction in dimeric systems is examined in detail for singly bridged L,M-X-ML, ( n = 3 , 4 , 5); Cu~C16~and other doubly bridged species where the bridging ligands are halogens, OR, pyridine N-oxides, oxalate, squarate; and the acetate bridged dimers C u ~ ( R C 0 0 ) 4 . The emphasis is on d9 Cu(I1) dimers, but other transition metal systems are also analyzed. Transition metal complexes containing more than one metal atom with unpaired electrons can generally be categorized according to their magnetic behavior into three main groups depending on the strength of the metal-metal interaction. In the noninteracting type the magnetic properties of the dimer (or polymer) a re essentially unchanged from the paramagnetic monomer. In the strongly interacting type formation of relatively strong metal-metal bonds occurs, and the molecule will display simple diamagnetic behavior (for even numbers of electrons). In this paper the properties of weakly interacting metal ions will be investigated. In such compounds this weak coupling between the electrons of the two metal ions leads to low-lying excited states of different spin which can be populated a t thermal energies (SI000 cm-I). The resulting magnetic behavior will be antiferromagnetic or ferromagnetic, depending on whether the low spin (spins paired) or high spin (spins parallel) state is the ground state, respectively. These interactions-often termed superexchange because of the large distances involved (3-5 A) between the metal ions-have been observed in a wide variety of compounds. I 5 In experimental studies the magnetic interaction between spins SA and Sg for atoms A and B is usually written in a form suggested originally by Heisenberg, Dirac, and Van
1,224 citations
TL;DR: In this paper, a review of subnormal magnetic moments of copper(II) compounds with subnormal magnet moments can be found, which can be roughly divided into two types: those with direct copper-to-copper interaction and those with super-exchange interaction.
Abstract: : On the basis of present investigations, copper(II) compounds with subnormal magnetic moments can be roughly divided into two types. Those with direct copper-to-copper interaction have short copper-to-copper distances. In these compounds, of which copper(II) acetate monohydrate is an example, the bonding is postulated to be of the delta-bond type. In the second group, represented by acetylacetone-mono(o-hydroxyanil)copper(II), super-exchange interaction produces the lowering of the magnetic moments. It is hoped that this review will initiate structural and other investigations of these extremely interesting compounds. (Author)
597 citations