Improving the SMM and luminescence properties of lanthanide complexes with LnO₉cores in the presence of Zn^II: an emissive Zn₂Dy single ion magnet

Abstract

Mononuclear complexes of stoichiometry [Ln(HL)(HO)(NO)](NO) (Ln = Tb, 1; Dy, 2, Er, 3), which crystallise with different solvates, and the heterotrinuclear compound [ZnDy(L)(NO)(OH)] (4) can be obtained with the same HL compartmental ligand. The single X-ray crystal structure of the mononuclear complexes shows a LnO core with a muffin-like disposition while the geometry of the DyO core in 4 seems to be closer to spherical capped square antiprism. The analysis of the magnetic properties of all the complexes demonstrates that the mononuclear lanthanide compounds do not show slow relaxation of the magnetization, even when the samples are diluted with a diamagnetic matrix and subjected to a dc applied field of 1000 Oe. Nevertheless, the heterotrinuclear dysprosium complex 4·3HO is a field-induced single ion magnet, with an estimated U barrier of 59 K. The luminescence characterisation of all the metal complexes in methanol solution at 298 K also shows a notable increase in the fluorescence emission of the heterotrinuclear complex with respect to the mononuclear ones, in such a way that 4 can be defined as a fluorescent single ion magnet.

2D Supramolecular Structure for a Chiral Heterotrinuclear ZnII2HoIII Complex through Varied HBonds Connecting Solvates and Counterions

“…Despite the high stability shown by this type of three-armed ligands when we had worked with them ( [11,12] and own references therein), the reason for these fruitless results could be related to reaction and/or crystallisation periods longer than usual, with a partial decomposition of H3L. This fact had been previously detected for another related ligand [18].…”

“…Keeping in mind the magnetic results previously obtained with H3L and H3L', our goal was obtaining heterotrinuclear holmium(III) and zinc(II) complexes with H3L. The synthetic method was designed on the basis of our previous experience with H3L [11], and H3L' [12] (Scheme 1). A template method using appropriate molar ratios of the corresponding aldehyde, tetraamine and metal salts had resulted as being useful to obtain mononuclear and even heteronuclear complexes with H3L' (Scheme 1) [12], but this method was not suitable for H3L, as the previous isolation of the tricondensed ligand was necessary to prepare its complexes.…”

“…Curiously, this complex is noticeably reminiscent of [Zn2Dy(L')(NO3)3(OH)] [12], more so than those ones derived from L 3− and [Zn2(L)(OAc)] [11]. Thus, as occurring in [Zn2Dy(L')(NO3)3(OH)], the tight μ3-η 1 :η 1 :η 1 -HO − bridge leads to the three metal ions to appear as an isosceles triangle, since d(Zn1···Zn2), is ca.…”

“…In this sense, we are particularly interested in obtaining lightluminescent molecular magnets. Thus, we have been recently involved in a research programme aiming to prepare, characterise and study not only discrete pure lanthanoid (Dy, Er, Tb) complexes, but also hybrid Zn-Ln polynuclear complexes containing one of the two polytopic ligands shown in Scheme 1 [11,12].…”

“…As a result of this previous work, we have found that complexes such as {[ZnDy(HL)(NO3)(OAc)(CH3OH)](NO3)}·1.25CH3OH·0.25H2O; [Zn2Dy(L)(NO3)2(OAc)2(H2O)] and [Zn2Er(L)(NO3)2(OAc)2(H2O)]·1.5H2O behave as induced SIMs [11], while [Zn2Dy(L')(NO3)3(OH)] behaves as a fluorescent SIM [12].…”