Pentanuclear [2.2] spirocyclic lanthanide(III) complexes: slow magnetic relaxation of the Dy(III) analogue.

The reaction of LnCl3·6H2O (Ln = Dy(3+), Tb(3+) and Ho(3+)) with the multisite coordinating ligand N'-(2-hydroxy-3-(hydroxymethyl)-5-methylbenzylidene)acetohydrazide (LH3) in the presence of pivalic acid (PivH) leads to the formation of three isostructural homometallic pentanuclear complexes, [Dy5(LH)4(η(1)-Piv)(η(2)-Piv)3(μ2-η(2)η(1)Piv)2(H2O)]·Cl·9·5H2O·5MeOH (1), [Tb5(LH)4(η(1)-Piv)(η(2)-Piv)3(μ2-η(2)η(1)Piv)2(H2O)]·Cl·10.5H2O·2MeOH·2CHCl3 (2) and [Ho5(LH)4(η(1)-Piv)(η(2)-Piv)3(μ2-η(2)η(1)Piv)2(H2O)]·Cl·14.5H2O·2CHCl3 (3). 1-3 are monocationic and are comprised of four doubly deprotonated [LH](2-) ligands along with six pivalate ions. These complexes possess a [2.2] spirocyclic topology formed by the fusion of two triangles of Ln(III) ions at a common vertex. The magneto chemical analysis reveals the presence of antiferromagnetic exchange interactions at low temperature, and the Dy(III) complex 1 gives an out-of-phase signal with a small curvature in alternating current (ac) magnetic susceptibility measurement. Application of a 3000 G static field during ac measurement intensifies the signals, revealing a second slow relaxation process in the Dy(III) analogue.