Three‐Dimensional Open‐Frameworks Based on Ln^IIIIons and Open‐/Closed‐Shell PTM Ligands: Synthesis, Structure, Luminescence, and Magnetic Properties

Abstract

A series of isostructural open-framework coordination polymers formulated as [Ln(dmf)(3)(ptmtc)] (Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5); PTMTC = polychlorotriphenylmethyl tricarboxylate) and [Ln(dmf)(2)H(2)O(αH-ptmtc)] (Ln = Sm (1'), Eu (2'), Gd (3'), Tb (4'), Dy (5')) have been obtained by treating Ln(III) ions with PTMTC ligands with a radical (PTMTC(3-)) or a closed-shell character (αH-PTMTC(3-)). X-ray diffraction analyses reveal that these coordination polymers possess 3D architectures that combine large channels and fairly rare lattice complex T connectivity. In addition, these compounds show selective framework dynamic sorption properties. For both classes of ligands, the ability to act as an antenna in Ln sensitization processes has been investigated. No luminescence was observed for compounds 1-5, and 3' because of the PTMTC(3-) ligand and/or Gd(III) ion characteristics. Conversely, photoluminescence measurements show that 1', 2', 4', and 5' emit dark orange, red, green, and dark cyan metal-centered luminescence. The magnetic properties of all of these compounds have been investigated. The nature of the {Ln-radical} exchange interaction in these compounds has been assessed by comparing the behavior of the radical-based coordination polymers 1-5 with those of the compounds with the diamagnetic ligand set. While antiferromagnetic {Sm-radical} interactions are found in 1, ferromagnetic {Ln-radical} interactions propagate in the 3D architectures of 3, 4, and 5 (Ln = Gd, Tb, and Dy, respectively). This procedure also provided access to information on the {Ln-Ln} exchange existing in these magnetic systems.

Three‐Dimensional Porous Metal–Radical Frameworks Based on Triphenylmethyl Radicals

“…Indeed, room-temperature reactions between acids aHÀPTMTCÀH 3 or PTMTCÀH 3 and Ln III nitrates in the presence of pyridine afforded 3D open-framework architectures that showed large 1D channels and a particularly rare extended T connectivity when realized in DMF/ethanol mixtures. [31] In an extension of this work, we have explored the possibility of forming porous open-framework coordination polymers with various topologies by simply modifying the preparation procedures; that is, using carboxylate salts (instead of forming them in situ from the acid) and/or different solvents. aH À PTMTC À H 3 and PTMTC À H 3 molecules were prepared in good yields following a previously reported multistep procedure.…”

“…These supramolecular motifs have not been observed previously for Ln/PTM-based coordination polymers, which were accordingly less robust. [31] Photoluminescence properties: In coordination polymers, rare-earth-based luminescence is usually achieved through an antenna effect, where organic molecules (ligands, auxiliary ligands and/or guests) act as light collectors and transfer energy to the Ln III ions. [34] Most energy transfer occurs from the organic molecule triplet excited state to emissive states of the Ln ions, [44] and the process efficiency closely depends on the gap between related energy levels.…”

“…Radical molecules are dark red solids that show characteristic absorptions at around 370-395 and 500-575 nm. [24,31,46] Upon excitation at 385 nm, a PTM radical www.chemeurj.org emission spectrum is characterized by one single broad band located between 600 and 675 nm. When compounds 1 (Tb) and 3 (Eu) are irradiated at 385 nm, only the radical signature is observed without the characteristic bands expected for Ln ion luminescence.…”

“…With the aim of accessing materials that combine open-frameworks with magnetic and/or luminescence properties, we have recently explored the coordination chemistry of carboxylated PTM radicals with rare-earth metal ions. [25,26,31] However, this strategy has led to examples of 3D open-framework architectures constructed from rare-earth ions and organic radicals which exhibit a porosity but only when guest solvent molecules fill the void volume of the pores. [26,31] Such materials show reversible guest-induced crystal-to-amorphous transformations, and therefore lack permanent porosity.…”

“…[25,26,31] However, this strategy has led to examples of 3D open-framework architectures constructed from rare-earth ions and organic radicals which exhibit a porosity but only when guest solvent molecules fill the void volume of the pores. [26,31] Such materials show reversible guest-induced crystal-to-amorphous transformations, and therefore lack permanent porosity. Herein, we report the first example of a series of PTMbased metal-organic frameworks (MOFs) that have permanent porosity in which the molecular scaffolds do not collapse when the guest solvent molecules are evacuated.…”