Copper complexes antiferromagnetism

The structures of the examined complexes are proved by x-ray diffraction, for example Refs. 115-117. Magnetochemical properties of these complexes, especially those of copper (mostly antiferromagnetic compounds), are reported in Refs. 104, 111, and 112. 

Multimetallic complexes (tetranuclear and pentanuclear with complicated structures) of these ligands which could have unique magnetic properties were prepared and studied. It is noted [125a] that, in the copper complex with H2L, Cu5(0H)2(L)2(N03)4, all magnetic interactions within the complex unit H2L appear to be antiferromagnetic, as well as in copper complexes with two other ligands, [Cu(HL1)(N03)]4 and [Cu2(L2)(OAc)2]2 [187,188],... 

In a later article, complexes of Ni(II), Cu(II), Pd(II), and V02+ ions with the same tetra-substituted porphyrin were reported. Stepwise oxidation of these complexes gave products for which the authors proposed quinonoid, monoradical, and diradical structures. The most prolonged oxidations yielded the diradical products, which were isolated as dark purple crystals, relatively stable in air (40). The monoradical vanadyl complex was observed to be diamagnetic, suggesting antiferromagnetic coupling between the phenoxyl radical and unpaired electron on vanadium, whereas in the copper complex no such coupling was observed. More detailed studies of these systems seem warranted. 

The copper complex of the diaminodiol (98) functions as a model foT galactose oxidase.A related diamidodiol (99) has been reported binding to high-valent Os and Ru, as well as in mixed [Cu L M(bipy)2] (M = Co, Ni, Zn) compounds, some of the latter being antiferromagnetically coupled. A number of diamine-diacid ligands have appeared, such as (100), ... 

Type 2 Cu(II) weak absorption spectrum EPR spectrum characteristic of square-planar Cu(II) complexes Type 3 Cu(II) di-copper centre strong absorption in the near UV CXmax 330 nm) no EPR spectra, the two coppers are antiferromagnetically coupled. 

There are three reasonable combinations of metal oxidation states for oxidized Type 3 copper that are consistent with spectral and redox data (1) Cu(I) Cu(I) with some other group, e.g., disulfide, functioning as a two-electron acceptor (2) Cu(I)-Cu(III) where Cu(III) is low spin and (3) an antiferromagnetically coupled Cu(II)-Cu(II) dimer. Magnetic susceptibility studies on Rhus vernicifera laccase have established that the two Type 3 copper atoms in this enzyme are present as an antiferromagnetically coupled Cu(II) dimer (4). The Type 3 copper atoms of hemocyanin and tyrosinase appear to be similarly coupled and separated by 3-5 A (5,6,7). Further structural information on the Type 3 copper chromophore is scanty neither the identity of the ligands nor the geometry of the site has been ascertained. There is likewise a paucity of literature on binuclear copper complexes that exhibit structural features expected for Type 3 copper. 

Fig. 14. Electron paramagnetic resonance spectra of low molecular mass copper complexes in the presence and in the absence of bovine serum albumin (BSA). All four copper concentrations are identical. Cu-EDTA served as standard. Cu flonazolac) displays no EPR-signal due the antiferromagnetic coupling of the two copper-centers. After addition of BSA, a signal of the biuret-type is obtained, indicating that the original complex was disrupted. A similar signal is seen after addition of CuSO, to BSA...

Tyrosinase-catalyzed transformations of catechols and o-benzoquinones were modeled by copper complexes which mimic both the spectroscopic characteristics [44-48] and the chemical behavior [49,50] of the biological systems. Tyrosinases have so-called copper type 3 centers, which are strongly antiferromagnetically coupled. The multicopper concept has emerged as an important feature in the modeling approach. 

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