Building 1D lanthanide chains and non-symmetrical [Ln(2)] “triple-decker” clusters using salen-type ligands: magnetic cooling and relaxation phenomena.

A solvothermal reaction between Ln(NO3)(3)center dot 6H(2)O (Ln: Gd, Tb and Dy), 2-hydroxy-1-naphthaldehyde, 2-OH-naphth, and ethylenediamine, en, in MeOH in the presence of a base, NEt3, led to the formation of the 1D coordination polymers [Ln(L)(MeO)(MeOH)(0.5)](n)center dot MeOH (Ln = Gd (1 center dot MeOH), Tb(2), Dy (3 center dot MeOH); H2L = 1,1′-((1E,1’E)-(ethane-1,2-diylbis(azanylylidene)) bis(methanylylidene)) bis(naphthalen-2-ol), the Schiff-base ligand derived from the condensation of 2-OH-naphth and en), while a similar reaction in an excess of NaN3 yielded 1D coordination polymers [Ln(L)(N-3)(0.75)(MeO)(0.25)(MeOH)](n) (Ln = Gd (4), Tb (5), Dy (6)). Finally, upon replacing ethylenediamine with o-phenylenediamine, o-phen, we managed to isolate the discrete dimers [Dy-2(L’)(3)(MeOH)]center dot 2MeOH (7.2MeOH) and [Gd-2(L’)(3)(MeOH)]center dot 2MeOH (8.2MeOH) (H2L’ = 1,1′-((1E,1’E)-(1,2-phenylenebis(azanylylidene)) bis(methanylylidene)) bis (naphthalen-2-ol), the Schiff-base ligand from the condensation of 2-OH-naphth and o-phen). Polymers 1-3 describe one-dimensional chains, containing alternating seven-and eight-coordinate Ln(III) metal centers, polymers 4-6 contain eight-coordinate lanthanide ions, while in both 7 and 8 the two Ln(III) centers are eight- and seven-coordinate, adopting square antiprismatic and “piano-stool” geometry, respectively. The magnetocaloric properties of the three Gd-III analogues were determined from magnetic measurements, yielding the magnetic entropy change -Delta S-m = 21.8, 23.0 and 16.0 J kg(-1) K-1 at T = 3.0 K on demagnetization of 7 T to 0, for 1, 4 and 8, respectively. The study of the magnetic properties also revealed that all three Dy-III analogues (3, 6 and 7) display out-of-phase signals, therefore suggesting slow magnetic relaxation, while such behaviour was not established in the Tb-III analogues.