Three-dimensional porous metal-radical frameworks based on triphenylmethyl radicals

Abstract

Lanthanide coordination polymers {[Ln(PTMTC)(EtOH)(2)H(2)O]·x H(2)O, y EtOH} [Ln=Tb (1), Gd (2), and Eu (3)] and {[Ln(αH-PTMTC)(EtOH)(2)H(2)O]·x H(2)O, 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 (PTMTC(3-)) or closed-shell (αH-PTMTC(3-)) character, respectively. X-ray diffraction analyses reveal 3D architectures that combine helical 1D channels and a fairly rare (6,3) connectivity described with the (4(2).8)·(4(4).6(2).8(5).10(4)) 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)(2)H(2)O] and [Tb(αH-PTMTC)(EtOH)(2)H(2)O] 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.