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

Abstract

Lanthanide coordination polymers {[Ln(PTMTC)(EtOH)₂H₂O]⋅x H₂O, y EtOH} [Ln=Tb (1), Gd (2), and Eu (3)] and {[Ln(αHPTMTC)(EtOH)₂H₂O]⋅x H₂O, y EtOH} [Ln=Tb (1′), Gd (2′), and Eu (3′)] have been prepared by reacting Ln^III ions with tricarboxylate-perchlorotriphenylmethyl/methane ligands that have a radical (PTMTC³⁻) or closed-shell (αHPTMTC³⁻) character, respectively. X-ray diffraction analyses reveal 3D architectures that combine helical 1D channels and a fairly rare (6,3) connectivity described with the (4².8)⋅(4⁴.6².8⁵.10⁴) Schäfli symbol. Such 3D architectures make these polymers porous solids upon departure of the non-coordinated guest-solvent molecules as confirmed by the XRD structure of the guest-free [Tb(PTMTC)(EtOH)₂H₂O] and [Tb(αHPTMTC)(EtOH)₂H₂O] materials. Accessible voids represent 40 % of the cell volume. Metal-centered luminescence was observed in Tb^III and Eu^III coordination polymers 1′ and 3′, although the Ln^III-ion luminescence was quenched when radical ligands were involved. The magnetic properties of all these compounds were investigated, and the nature of the {Ln–radical} (in 1 and 2) and the {radical–radical} exchange interactions (in 3) were assessed by comparing the behaviors for the radical-based coordination polymers 1–3 with those of the compounds with the diamagnetic ligand set. Whilst antiferromagnetic {radical–radical} interactions were found in 3, ferromagnetic {Ln–radical} interactions propagated in the 3D architectures of 1 and 2.