Crystal field and exchange interactions in rare earth transition metal salen compounds containing bipyridine, pyrazole complexes

Crystal field parameters for Pr3+ in {[Ni(salen)Pr–(hfac)3](H2O)} (noted as NiPr) and {[Ni(salen)Pr(hfac)3(pyr)]–(CHCl3)} (noted as NiPrpyr) have been found from a fit to the thermal variation in the magnetic susceptibility of NiPr and NiPrpyr. The nature of exchange interaction in [Cu(salen)Pr(hfac)3(pyr)] (noted as CuPrpyr), {[{Cu(salen)Pr(hfac)3}2(pyz)](H2O)3} (noted as Cu2Pr2pyz) and {[{Cu(salen)Pr(hfac)3}2(bpy)]–(CHCl3)2} (noted as Cu2Pr2bpy, bpy=4,4_-bipyridine) have been found using the derived results for NiPr and NiPrpyr. All the exchange interactions give significant contribution to the thermal variation in magnetic susceptibility below 50 K. The contribution due to Pr–Cu interaction is positive while that of the Cu–Cu and Pr–Pr interactions are negative. The behaviors below 10 K for Pr–Cu and Pr–Pr are difficult to explain, and point to a possible change in structure of CuPrpyr, Cu2Pr2pyz and Cu2Pr2bpy below 10 K. The theoretical thermal variations in the magnetic specific heat of NiPr and NiPrpyr are computed and discussed.