Comparative spectroscopic and magnetic studies of two types of Ln and Ln:Cu trichloroacetates

Abstract

Heteronuclear copper–lanthanide complexes have attracted much attention as models for the theoretical investigation of magnetic exchange involving d and f electrons and because of their potential application in superconducting ceramics. Synthesis, structural, spectroscopic and magnetic characterization of one-dimensional polymeric Ln(Cl3CCOO)3·2H2O (Ln=Nd, Eu, Dy) (I) and heteronuclear CuNd2(Cl3CCOO)8⋅6H2O (II) single crystals was undertaken. The structure of (II) is constructed from dimers of two crystallographically independent types of NdO8(9) polyhedra linked by carboxyl bridges. These dimers are separated by square planar coordinated copper ions which are bridged to the lanthanide by four carboxyl groups and two water molecules. The chains are further connected via a hydrogen bonding system to layers. The optical and magnetic properties were investigated in the 4.2–293K temperature range and are discussed on the basis of X-ray data. Electronic spectra reveal marked differences in the structures of these two types of compounds. The spectra allow the determination of the splitting pattern of the ground state multiplet of the Nd3+ ion. Vibronic components were detected in the europium excitation spectra and their assignments were made on the basis of Raman data. The temperature dependence of χM and μeff shows a decrease of the magnetic moment with temperature and the reverse relation for magnetic susceptibility in mixed Nd:Cu crystals. The cooperative interaction of ion-pairs coupled in polymeric chains could be considered based both on spectroscopic and magnetic investigations.