Slow Magnetic Relaxation and Luminescent Properties of Mononuclear Lanthanide-Substituted Keggin-Type Polyoxotungstates with Compartmental Organic Ligands.

Estibaliz Ruiz-Bilbao,José A García,Leire San Felices,Luis Lezama,Beñat Artetxe,Juan M Gutiérrez-Zorrilla,Enrique Colacio,Markel Pardo-Almanza,José Manuel Seco,Itziar Oyarzabal

doi:10.1021/acs.inorgchem.1c03214

Abstract

The reaction of mid to late lanthanide ions with the N,N′-dimethyl-N,N′-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylene-diamine organic ligand and monolacunary Keggin type [α-SiW11O39]8– anion affords a series of isostructural compounds, namely, K5[LnIII(α-SiW11O39)(C20H22Br2N2O4)]·14H2O (1-Ln, Ln = Sm to Lu). The molecular structure of these sandwich-type complexes is formed by the LnIII ion in a biaugmented trigonal prismatic geometry, which occupies the external O4 site of the organic ligand and the vacant site of the lacunary polyoxometalate (POM) unit. The empty N2O2 coordination site of the organic ligand allows its unprecedented folding, which displays a relative perpendicular arrangement of aromatic groups. Weak Br···Br and π–π interactions established between adjacent molecular units govern the crystal packing, which results in the formation of assemblies containing six hybrid species assembled in a chairlike conformation. 1-Gd and 1-Yb display slow relaxation of the magnetization after the application of an external magnetic field with maxima in the out-of-phase magnetic susceptibility plots below ∼5–6 K, which is ascribed to the presence of various relaxation mechanisms. Moreover, photoluminescent emission is sensitized for 1-Sm and 1-Eu in the visible region and 1-Er and 1-Yb in the NIR. In contrast, the quenching of metal-centered luminescence in the 1-Tb derivative has been attributed to the out-of-pocket coordination mode of the lanthanide center within the POM fragment. It is demonstrated that the 1-Yb dual magneto-luminescent material represents the first lanthanide-containing POM reported to date with simultaneous slow magnetic relaxation and NIR emission. Solution stability of the hybrid molecular species in water is also confirmed by ESI-mass spectrometry experiments carried out for 1-Tb and 1-Tm.

Highlights

Their high solution, thermal, and chemical stability together with remarkable redox properties enables the growing family of polyoxometalates (POMs)[1,2] to be useful for a wide range of applications in areas like catalysis,[3] biomedicine,[4] and material science.[5]
In the past few years, the combination of lacunary polyoxotungstates that can act as multidentate oxygen donor inorganic ligands with lanthanide (Ln) cations has resulted in some of the most spectacular architectures in terms of size and complexity.[9]
Considering all of the above, we report on the synthesis, structure, and solution stability of a series of 10 hybrid anions formed by mid-to-late lanthanide-containing Keggin-type polyoxotungstates and the compartmental organic ligand

Summary

Introduction

Their high solution, thermal, and chemical stability together with remarkable redox properties enables the growing family of polyoxometalates (POMs)[1,2] to be useful for a wide range of applications in areas like catalysis,[3] biomedicine,[4] and material science.[5]. All compounds 1-Ln are isostructural and crystallize in the triclinic P1̅ space group containing three crystallographic independent SiW11O39)]5− ({Ln}) clusters in molecular [Ln(H2L)(αeach asymmetric unit

Results

Conclusion