Synthesis, crystal structure and luminescent properties of isoreticular lanthanide-organic frameworks based on a tetramethyl-substituted terphenyldicarboxylic acid

A series of 3D metal-organic frameworks derived from 2',3',5',6'-tetramethyl-[1,1':4',1 ''-terphenyl]-4,4 ''-dicarboxylic acid (H2L) as organic linker and various lanthanides have been prepared. The resulting coordination polymers [Ln(3)L(4)(NO3)(DMF)(x)(H2O)](n) (where x = 2 or 3) were characterized by elemental analysis, thermogravimetric investigations, IR and TG-FTIR spectroscopy, as well as powder X-ray diffraction measurements. The crystal structure for six of these isostructural networks based on La(III), Ce(III), Nd(III), Sm(III), Tb(III) and Dy(III) was established using single crystal X-ray crystallography. As an example, the asymmetric part of [La3L4(NO3)(DMF)(3)(H2O)](n) consists of two deprotonated ligand molecules L2- and two La(III) ions, one of them occupying a general position with full site occupancy, while the other one has a fractional occupancy of 0.5. Investigation of the luminescence of these coordination polymers showed that compounds containing La3+, Nd3+ and Gd3+ possess only the emission associated with the anion of the organic ligand (L2-), polymers containing Eu3+ and Tb3+ show pure metal-centered radiation, while networks containing Dy3+ and Sm3+ display dual metal- and ligand-centered luminescence. The organic linker acts as a good antenna for Tb3+, Eu3+, Dy3+ and Sm3+ ions. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

A series of 3D metal-organic frameworks were synthesized using 2',3',5',6'-tetramethyl-[1,1':4',1 ''-terphenyl]-4,4 ''-dicarboxylic acid (H2L) as the organic linker and various lanthanides. The resulting coordination polymers were characterized through various methods, and the crystal structure for six isostructural networks was determined using single crystal X-ray crystallography. Luminescence investigation showed different emission properties for compounds containing different lanthanide ions.