High Luminance of Heterolanthanide-Based Molecular Alloys by Phase-Induction Strategy

Lanthanide-Based Coordination Polymers Molecular Alloys Stability: A Thermochemical Approach

In this study, we investigate the thermodynamics of lanthanide-based coordination polymer molecular alloys. We demonstrate that if lanthanide ions have many chemical similarities, the solubility of homo-lanthanide-based coordination polymers can vary significantly from one lanthanide ion to another. Indeed, we experimentally determine the solubility constants of a series of isostructural homo-lanthanide coordination polymers, with general chemical formula [Ln₂(bdc)₃(H₂O)₄]_∞ with Ln = La-Er plus Y and where bdc^2- symbolizes 1,4-benzene-di-carboxylate. Then, we extend the study to two series of isostructural molecular alloys with general chemical formula [Ln_2xLn'_2 -2x(bdc)₃(H₂O)₄]_∞ with 0 ≤ x ≤ 1 based either on heavy ([Eu_2xTb_2 - 2x(bdc)₃(H₂O)₄]_∞) or light ( [Nd_2xSm_2-2x(bdc)₃(H₂O)₄]_∞) lanthanide ions. We found that whatever the solubility difference of the homo-nuclear compounds is, the configurational entropy is the main driving force of the stabilization of molecular alloys.

Investigation of Intermetallic Energy Transfers in Lanthanide Coordination Polymers Molecular Alloys: Case Study of Trimesate-Based Compounds

Reactions in water at ambient temperature and pressure between a lanthanide ion and benzene-1,3,5-tricarboxylate (or trimesate) lead to two series of iso-structural coordination polymers. Their general chemical formula is [Ln(tma)(H₂O)₆]_∞ for the lightest lanthanide ions (Ln = La-Dy except Pm), while it is [Ln(tma)(H₂O)₅·3.5H₂O]_∞ for the heaviest ones (Ho-Lu plus Y). For the heaviest lanthanide ions, reactions at 50 °C lead to a third structural family with the general chemical formula [Ln(tma)(H₂O)₃·1.5H₂O]_∞ with Ln = Ho-Lu plus Y. Homo-lanthanide coordination polymers that belong to the latter two families do not exhibit luminescence in the visible region. Therefore, we used a phase induction strategy to obtain molecular alloys that belong to these structural families and show sizeable emission. The random distribution of the lanthanide ions over the metallic sites has been investigated using ⁸⁹Y and ¹³⁹La solid-state NMR spectroscopy experiments. Luminescent properties of homo- and hetero-nuclear coordination polymers based on Eu³⁺ and Tb³⁺ have been studied in detail and compared. As a result, this study strongly suggests that exchange-based intermetallic energy transfer mechanisms play an important role in these systems. It also suggests the presence of an intermetallic exchange pathway through π-stacking interactions.

Synthesis, Crystal Structure, and Luminescence Properties of the Iso-Reticular Series of Lanthanide Coordination Polymers Synthesized from Hexa-Lanthanide Molecular Precursors

Microwave-assisted reactions in DMSO, between a hexa-lanthanide octahedral complex ([Ln₆(μ₆-O)(μ₃-OH)₈(NO₃)₆(H₂O)₁₂·2NO₃·2H₂O] with Ln = Nd-Yb plus Y) and either 3-halogenobenzoic acid (hereafter symbolized by 3-xbH with x = f or c for fluoro or chloro, respectively) or 4-halogenobenzoic acid (hereafter symbolized by 4-xbH with x = f, c, or b for fluoro, chloro, or bromo, respectively), lead to 1D lanthanide coordination polymers. These coordination polymers are almost iso-reticular. The crystal structure is described on the basis of the coordination polymer with chemical formula [Tb(4-fb)₃(DMSO)(H₂O)₂·DMSO]_∞ obtained from 4-fluorobenzoic acid (4-fbH) and the Tb³⁺-based octahedral complex: It crystallizes in the triclinic system, space group P1̅ (n°2), with the following cell parameters: a = 9.8561(9) Å, b = 10.5636(9) Å, c = 15.1288(15) Å, α = 100.840(3)°, β = 95.552(3)°, γ = 110.482(3)°, V = 1426.4(3) ų, and Z = 2. It can be described on the basis of 1D molecular chains. Luminescence properties of the Tb and Eu derivatives have been measured and compared vs the halogeno-function and its position (meta or para). Some molecular alloys have also been prepared to estimate the strength of the intermetallic energy transfers. To confirm that the hexa-nuclear complexes (and not the halogenated ligand) have a structuring effect for the formation of the straight chain-like molecular motif, another coordination polymer with chemical formula [Tb(4-npa)₃DMSO·DMSO·H₂O]_∞ where 4-npaH symbolizes 4-nitro-phenyl-acetic acid has been prepared. It crystallizes in the triclinic system, space group P1̅ (n°2) with the following cell parameters: a = 7.8784(8) Å, b = 14.8719(16) Å, c = 15.2753(17) Å, α = 73.612(4)°, β = 86.406(4)°, γ = 83.104(4)°, V = 1703.8(3) ų, and Z = 2. Its crystal structure can be described on the basis of a molecular motif that is similar to the one observed in the five previous crystal structures which confirms the structuring effect of the hexa-nuclear complexes.

Hexanuclear Molecular Precursors as Tools to Design Luminescent Coordination Polymers with Lanthanide Segregation

Solvothermal reactions between hexanuclear complexes with the general chemical formula [Ln₆(μ₆-O)(μ₃-OH)₈(NO₃)₆(H₂O)₁₂]·2NO₃·2H₂O and 2-bromobenzoic acid (2-bbH) lead to a series of isostructural one-dimensional coordination polymers with the general chemical formula [Ln₂(2-bb)₆]_∞ with Ln = Sm, Eu, Tb, Dy, and Y. These coordination polymers crystallize in the orthorhombic space group Fdd2 (No. 43) with the following cell parameters: a = 29.810(3) Å, b = 51.185(6) Å, c = 11.7913(14) Å, V = 17992(4) ų, and Z = 16. The europium- and terbium-based derivatives show sizable luminescence intensities under UV excitation. Isostructural heterolanthanide coordination polymers have also been prepared. Their luminescent properties suggest that during the synthetic process the starting hexanuclear complexes are destroyed but strongly influence the distribution of the different lanthanide ions over the metallic sites of the crystal structure. Indeed, it is possible to prepare heterolanthanide coordination polymers in which lanthanide-ion segregation is controlled.

Highly Luminescent Europium-Based Heteroleptic Coordination Polymers with Phenantroline and Glutarate Ligands

Isostructural lanthanide-based coordination polymers with general chemical formula [Ln(phen)(glu)(NO₃)]_∞ with Ln = La-Tm (except Ce and Pm) have been synthesized by hydrothermal methods (H₂glu stands for glutaric acid and phen stands for 1,10-phenantroline). They crystallize in the monoclinic system with the P2₁/c (no. 14) space group. The crystal structure has been solved on the basis of the La derivative. It can be described as the superimposition of molecular chains of dimeric La(phen)(NO₃)-La(phen)(NO₃) units bridged by glutarate ligands. Luminescent properties have been explored and show that the Eu derivative exhibits the highest luminance observed for Eu-based coordination polymers (85 to 105 cd·m^-2). Effects of the dilution of the Eu³⁺ and Tb³⁺ luminescent ions by Gd³⁺ optically inactive ions are unexpected and to the best of our knowledge unprecedented. This could be related to the different intermetallic energy-transfer mechanisms in competition and to the nonisotropic distribution of the lanthanide ions in these molecular alloys. The investigation of molecular alloys with general chemical formula [Eu_1-xTb_x(phen)(glu)(NO₃)]_∞ with 0 ≤ x ≤ 1 highlights a very sizable and constant Eu³⁺ luminescence whatever the x value, which further confirms the existence of very strong intermetallic energy transfers in this family of compounds. It is also noticeable that some coordination polymers based on weakly emissive lanthanide ions exhibit very well defined emission spectra.

Colloidal suspensions of highly luminescent lanthanide-based coordination polymer molecular alloys for ink-jet printing and tagging of technical liquids

A series of lanthanide-based coordination polymer molecular alloy colloidal dispersions usable for ink-jet printing and tagging of technical liquids.