ONE-DIMENSIONAL AND 2-DIMENSIONAL RARE-EARTH COPPER MOLECULAR MATERIALS

This short review paper deals with the crystal structures and the magnetic properties of molecular materials arising from the reaction of the [Cu(pba)]2- precursor with trivalent rare earth ions M(III); pba stands for 1,3-propylenebis(oxamato). Three families of compounds have been obtained so far, abbreviated as M2Cu3Cu . 1, M2CU3 . 2 and M2Cu3-3, depending on the synthesis method, and/or the nature of the rare earth. The structure 3 is the simplest one; it consists of discrete and infinite ladder-motifs, the edges of which are made of MCu(pba) units (M going from Tb to Yb, and Y), and the rungs of Cu(pba) units linking two rare earth ions. In structure 1 (M going from La to Gd), the ladders are linked together by oxalato groups, promoting a double-sheet two-dimensional pattern. In addition, this structure contains discrete [Cu(H2O)5]2+ cations interspersed in the gap between the layers. Finally, structure 2 (M going again from La to Gd) consists of discrete and infinite tube-like motifs with a pseudo four-fold symmetry, resulting from the condensation of two ladder-motifs associated with a complete rearrangement of the rungs. The temperature dependences of the magnetic susceptibility and the field dependences of the magnetization for all compounds have been investigated. Only some of the findings are discussed. For the compounds with M = Gd, Th, Dy and Er, chi(M)T (chi(M) being the molar magnetic susceptibility, and T the temperature) increases as T is lowered. This result together with the magnetization data indicate that the M(III)-Cu(II) interaction is ferromagnetic. When M=La, the copper(II) spin carriers are weakly antiferromagnetically coupled through the diamagnetic rare earth ion. The same situation holds for M=Eu which has also a diamagnetic ground state. On the other hand, there is no propagation of the interaction through the Y(III) ion. The perspectives in this new field of the molecular materials incorporating rare earth and 3d metal ions are briefly discussed.