Antiferromagnetic behavior

By reaction of cobalt(II) aquacation with triphos and HSR [R = H, He) different dinuclear metal complexes are formed with formulae [(triphosJCoIp-SR Cottriphos)] + and [(triphos)Co(u-S)2 Co[triphos)]0 +. These dinuclear complexes contain from 32 to 34 valence electrons. Those with 34 electrons present antiferromagnetic behavior. These properties are explained in terms of a molecular orbital treatment of the type suggested by Hoffmann and Burdett for unpuckered dinuclear metal complexes. 

Fluorides are suitable 2-D and 1-D magnetic models. In the K2NiF4 series, for instance, the antiferromagnetic behavior of fluorinated compounds can perfectly be explained by means of high-temperature expansion series which is not always the case with the homologous oxides9). 

Note that the undoped cuprate is an antiferromagnet and that doping converts it into a superconductor. We have shown above that antiferromagnetic behavior arises from the z = +1 side of the extended Hiickel-Hubbard spectrum in Fig. 4.1. In the ISB theory the superconducting behavior comes from the z = -1 side of Fig. 4.1 just as does the freeon theory of ferromagnetism. 

Figure 13 Plot providing the superconducting transition temperature versus the strontium content x of the compound La2 j Stj Cu4 y. The region of antiferromagnetic behavior is also indicated. (Ref. 13, with kind permission of Springer Science Business Media)...

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