Determination of the Nature of Exchange Interactions in the 3d-4f Magnetic Chain {[Cu(salen)Pr(hfac)3]2(L)}n (L=4,4′-Bipyridine, Pyrazine)

The reaction of copper(II)-praseodymium(III) 3d-4f precursors with nitrogenated ligands yields to a 3d-4f-4f-3d pseudo-ID compound with the formula {[{Cu(salen)}{Pr(hfac)(3)}(2)(pyz)](H2O)(3)} (pyz = pyrazole). A "comparative method" was used to determine the nature of the magnetic interactions in this magnetic chain, by analysing the magnetic behaviour of diamagnetic or building-block analogues, This method allows the estimation of the nature of all the magnetic interactions in the compound even in the presence of the orbitally degenerate Pr-III ion. Two intramolecular exchange interactions [3d(Cu-II)-4f(Pr-III) and 4f(Pr-III)-4f(Pr-III)] and one intermolecular exchange interaction [3d(Cu-II)3d(Cu-II)] have been identified, and they have been found to be antiferromagnetic. The buildings blocks were obtained by reaction of Cu(salen) complexes with Pr(hfac)(3)center dot 3H(2)O, and the dinuclear [Cu(salen)Pr(hfac)(3)(H2O)(n)] {hfac(-) = 1,1,1,5,5,5-hexafluoroacetylacetonate, H(2)salen = N,N'-ethane-1,2-diyl-bis(salicylidenamine), n = 0 or 1} or the heterotetranuclear {[{Cu(Salen)}{Pr(hfac)(3)}(2)(bpy)](CHCl3)(2)} compounds were formed. The diamagnetic analogues were obtained by substituting copper(II) by nickel(II). Evidence of a change of the crystal field around the Pr-III ion as a result of the presence of a nitrogenated ligand in its coordination sphere is provided. The change in the crystal field leads to a different energy distribution of the Stark sublevels and allows the determination of the Cu-II-Pr-III interaction.