Structural studies and magnetic properties of polymeric ladder-type compounds {Ln(2)[Ni(opba)](3)}center dot S (Ln = lanthanide element; opba = o-phenylenebis(oxamato), S = solvent molecules)

The compounds of formula {n(2)[Ni(opba)](3)}.S (opba being o-phenelynebis(o xamato), Ln lanthanide(III) ions, and S solvents molecules) have been struc turally and magnetically characterized for Ln = La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, and Er. These compounds crystallize poorly, and structural information has been obtained from EXAFS and wide-angle X-ray scattering (WAXS) techni ques. The EXAFS studies have shown that the Ni site may adopt square planar geometry (with a spin S-Ni = 0) or octahedral geometry (with S-Ni = 1). Th e compounds are orange when the Ni sites are mostly square planar or green for Ni sites mostly octahedral. The WAXS studies have shown that the compou nds present the same ladder-like motif as that previously described for Tm- 2[Cu(opba)](3)}. 4H(2)O . 10DMF. The magnetic properties of the compounds w ith magnetic octahedral Ni sites have been studied and compared with those of the {Ln(2)[Zn(opba)](3)}.S series for each Ln ion. This comparison allow s us to determine the nature of interactions in Ln(III)-Ni-II pairs. It is clearly established that the interaction is ferromagnetic when Ln(III) is G d-III, Tb-III, DYIII and perhaps Ho-III. On the contrary, the interaction s eems to be antiferromagnetic for Ln(III) = Ce-III, Pr-III, Nd-III, Er-III. These results are discussed with those obtained recently in Ln(III)-Cu-II p airs.