Magnetic interactions in the three copper(II)-complex polymers, [Cu(PZ)(NO
3)
2]
n, [Cu(PM)(NO
3)
2(H
2O)
2]
n, and [Cu(PM)
2(NO
3)
2]
n are discussed on the basis of extended Hückel calculations inthe formulas PZ and PM stand for pyrazine and pyrimidine, respectively. Interactions between the Cu-3d orbitals and the
lone-pair orbitals of pyrazine and pyrimidine are analyzed from the viewpoint of `through-space'' and `through-bond'' interactions using binuclear complexes to model the three copper(II) polymers. Three conclusions can be drawn from the orbital interaction analysis: (1) in the first polymer, a superexchange pathway is formed with the
bond of Cu–-N and the through-bond interaction between the lone pairs of the nitrogen atoms of pyrazine will lead to an antiferromagnet state; (2) in the second polymer a superexchange pathway is formed with the
bond of Cu–-N and the through-space interaction between the lone pairs of the nitrogen atoms of pyrimidine, and as a result an antiferromagnetic state will be preferred; and (3) in the third polymer., there is no effective pathway in respect of overlap interaction and the HOMO and the LUMO are actually degenerate, and thus a ferromagnetic state will arise. The band structures are analyzed to characterize the magnetic properties of the antiferromagnetic polymers, [Cu(PZ)(NO
3)
2]
n and [Cu(PM)(NO
3)
2(H
2O)
2], and the ferromagnetic polymer, [Cu(PM)
2(NO
3)
2]
n.
Molecular magnetism - superexchange interaction - copper(II)-complex polymer - ferromagnetic polymer - extended Hückel method