From Condensed Lanthanide Coordination Solids to Microporous Frameworks Having Accessible Metal Sites

Abstract

The combination of terbium nitrate and 1,4-benzenedicarboxylic acid (H 2 BDC) in the presence of triethylamine yields the compound Tb 2 (BDC) 3 ·(H 2 O) 4, which has an extended nonporous structure constructed from copolymerized BDC and Tb(III) units. The multidentate functionality of BDC and the tendency of Tb to have a high coordination number has allowed water to act as a terminal ligand to Tb in the structure. Upon thermally liberating the water ligands, a microporous material, Tb 2 (BDC) 3, is achieved, which has extended 1-D channels and the same framework structure as that of the as-synthesized solid as evidenced by XRPD. Water sorption isotherm data proves that Tb 2 (BDC) 3 has permanent microporosity, and points to the presence of accessible metal sites within the pores, which also allows the sorption of ammonia to give Tb 2 (BDC) 3 ·(NH 3 ) 4 . Luminescence lifetime measurements confirm that resorbed water and sorbed ammonia are bound to Tb and that they give distinctly different decay constants.