| Abstract
| - The compounds of formula {Ln2[Ni(opba)]3}·S (opba being o-phenelynebis(oxamato), LnlanthanideIII ions, and S solvents molecules) have been structurally and magneticallycharacterized for Ln = La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, and Er. These compounds crystallizepoorly, and structural information has been obtained from EXAFS and wide-angle X-rayscattering (WAXS) techniques. The EXAFS studies have shown that the Ni site may adoptsquare planar geometry (with a spin SNi = 0) or octahedral geometry (with SNi = 1). Thecompounds are orange when the Ni sites are mostly square planar or green for Ni sitesmostly octahedral. The WAXS studies have shown that the compounds present the sameladder-like motif as that previously described for Tm2[Cu(opba)]3}·4H2O·10DMF. Themagnetic properties of the compounds with magnetic octahedral Ni sites have been studiedand compared with those of the {Ln2[Zn(opba)]3}·S series for each Ln ion. This comparisonallows us to determine the nature of interactions in LnIII−NiII pairs. It is clearly establishedthat the interaction is ferromagnetic when LnIII is GdIII, TbIII, DyIII, and perhaps HoIII. Onthe contrary, the interaction seems to be antiferromagnetic for LnIII = CeIII, PrIII, NdIII, ErIII.These results are discussed with those obtained recently in LnIII−CuII pairs.
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