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)
Abstract
The reaction of copper(II)-praseodymium(III) 3d-4f precursors with nitrogenated ligands yields to a 3d-4f-4f-3d pseudo-1D 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 PrIII ion. Two intramolecular exchange interactions [3d(CuII)-4f(PrIII) and 4f(PrIII)-4f(PrIII)] and one intermolecular exchange interaction [3d(CuII)-3d(CuII)] 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*3H2O, and the dinuclear [Cu(salen)Pr(hfac)3(H2O)n] {hfac- = 1,1,1,5,5,5-hexafluoroacetylacetonate, H2salen = N,N′-ethane-1,2-diylbis(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 PrIII 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 CuII-PrIII interaction.