Solvatomorphism, CO2 adsorption and luminescence properties of non-aromatic bis-hydroxamate-based metal–organic frameworks

Abstract

Two new Tb(III) metal–organic frameworks with an aliphatic bis-hydroxamate linker have been synthesized and structurally characterized. The title compounds have [Tb₂(H₂O)₂(OAc)₂(L)₂]·2Solv formulae, where L²⁻ is a deprotonated form of 1,4-dihydroxy-3,3,6,6-tetramethylpiperazine-2,5-dione and Solv is N,N-dimethylacetamide or ethanol. Both compounds possess layered sql-type structures and appear to be solvatomorphic crystal phases, but with a significant change in the pore volume fraction from 35% for the DMA-based structure down to 23% for the EtOH-based one. The activation of the ethanol-based compound led to a porous network demonstrating hysteretic adsorption of carbon dioxide with a BET surface area of 493 m² g⁻¹. A narrow-banded emission in the green region, typical for Tb(III)-based metal–organic complexes, was found for both obtained compounds with ca. 1% photoluminescence quantum yields, showing an ability of the first MOF-related example of a non-aromatic bis-hydroxamate strut presented herein to sensitize the phosphorescence of Tb(III) ions.