Superexchange mechanism in polymeric heterocyclic diamine bridge copper(II) complexes. 2

Synthesis, crystal structure and magnetic property of a one-dimensional copper(II) complex with 2,5-dimethylpyrazine-1,4-dioxide as bridging ligand

“…In order to evaluate the coupling intensity the experimental magnetic data have been fitted using uniform one-dimensional equation (2), derived from the Bonner-Fisher calculation [15] based on the isotropic Heisenberg Hamiltonian (1):Ĥ [8], which may be attributed to the different structural factors. Compared with complexes with pyrazine as bridging ligand, the distance between the bridged Cu(II) ions in this complex is larger [16][17][18], and the magnetic interaction of the present complex is larger than that of the Cu(II) complexes with pyrazine as a bridging ligand. …”

Synthesis, crystal structure and properties of bis(hexafluoroacetylacetonato)tetrazinecopper(II)

“…Hatfield and co-workers studied the magnetism of two related linear chain copper(II) complexes with pyrazine bridges. In the coordination polymer [Cu(hfac) 2 (pz)] n , no superexchange interaction was observed in the magnetic susceptibility data down to 1.8 K [7]. The absence of exchange interaction was attributed to the fact that the pyrazine plane lies in the xz plane of the Cu(hfac) 2 unit, where the copper(II) ground state is d x 2 Ày 2 and there is no effective -orbital pathway available on the pyrazine.…”

“…The absence of exchange interaction was attributed to the fact that the pyrazine plane lies in the xz plane of the Cu(hfac) 2 unit, where the copper(II) ground state is d x 2 Ày 2 and there is no effective -orbital pathway available on the pyrazine. On the other hand, the pyrazine-bridged coordination polymer [Cu(pz)(NO 3 ) 2 ] [7] has shown antiferromagnetic chain-like behavior which was described by the Heisenberg linear-chain model [8]. In this case, the pyrazine groups lie canted about 50 from the copper xy plane, which allows for d x 2 Ày 2 -(b 1g ) overlap and leads to a -orbital pathway for pyrazine superexchange interactions.…”

Derivation of effective low-energy Hamiltonians for chemically complex materials from first principles

“…The details of the pyrazine-mediated Cu-Cu superexchange have been under investigation and debate for some time [29,[180][181][182][183]. Having a number of chemically similar materials gives us the opportunity to use the different structures to investigate the physical mechanisms of magnetic exchange.…”

“…When superexchange was initially observed via pyrazine, it was proposed that the superexchange pathway would be via the π-orbitals of the pyrazine [181]. However, extended Hückel calculations [183] and the investigation of experimental spin and charge densities [180] have revealed a different pathway via the lone-pair σ-orbitals on the nitrogen atoms.…”