Comparative magnetic studies of (Sm, Nd) trichloroacetates and their heteronuclear CuLn2(CCl3COO)8·6H2O systems: structure and spectroscopy of a new type of Eu trichloroacetate

Abstract

Two series of compounds: heteronuclear CuLn2(CCl3COO)8·6H2O (Ln = Nd and Sm) and their simple analogues Ln(CCl3COO)3·2H2O (Ln = Eu, Nd, Sm) were synthesized. New Eu(III) trichloroacetate; Eu(CCl3COO)3·3H2O·CH3OH was obtained, its molecular structure was determined by X-ray diffraction and compared with the data of respective systems reported earlier. Magnetization was measured and the susceptibility was derived in the limit of low field. Magnetic susceptibilities were calculated and discussed for series of homo- and hetero-nuclear chloroacetates.Untypical hysteresis was found (two loops) in samarium trichloroacetate. This phenomenon is most probably the effect of flops of spins in magnetic fields of 30,000Oe and very weak (if any) interaction intermediated by weak hydrogen bonding between the chains. A similar magnetic behavior was observed in neodymium carboxylate where the magnetic ordering was observed as a result of Nd–Nd interaction at low temperature (1.6K). For this system, the magnetic moment depends on magnitude of the magnetic field and ferromagnetic ordering appears at low temperatures. The strongest interactions of coupled ions and antiferromagnetic ordering with TN=6.5K were found in CuSm2(CCl3COO)8·6H2O single crystals.Heisenberg model was applied in the calculations for three interacting ions located linearly. The following relation was derived: χM=Ng2μβ2kT(12)+(12)exp(J2/kT)+5exp(J2/kT)−exp(1,5J1/kT)2+2exp(J2/kT)+4exp(J2/kT)−exp(1,5J1/kT) and applied in calculations of the exchange integrals. Mechanism of the exchange interaction was discussed on the basis of the obtained results.