Assembly of 1D, 2D and 3D lanthanum() coordination polymers with perchlorinated benzenedicarboxylates: positional isomeric effect, structural transformation and ring-opening polymerisation of glycolide

Utilizing a series of positional isomers of tetrachlorinated benzenedicarboxylic acid ligands, seven La( iii )-based coordination polymers were solvothermally synthesized and structurally characterized. Their structural dimensionalities varying from 1D double chains, to the 2D 3,4,5-connected network, to 3D 6-connected pcu topological nets are only governed by the positions of carboxyl groups on the tetrachlorinated benzene ring. A comprehensive analysis and comparison reveals that the size of the carbonyl solvent molecules (DMF, DEF, DMA, and NMP) can affect the coordination geometries around the La( iii ) ions, the coordination modes of carboxylate groups, the packing arrangements, and the void volumes of the overall crystal lattices. One as-synthesized framework further shows an unprecedented structural transformation from a 3D 6-connected network to a 3D 4,5-connected net through the dissolution and reformation pathway in water, suggesting that these easily hydrolyzed lanthanide complexes may serve as precursors to produce new high-dimensional frameworks. The bulk solvent-free melt polymerisation of glycolide utilizing these La( iii ) complexes as initiators has been reported herein for the first time. All complexes were found to promote the polymerization of glycolide over a temperature range of 200 to 220 °C, producing poly(glycolic acid) (PGA) with a molecular weight up to 93 280. Under the same experimental conditions, the different catalytic activities for these complexes may result from their structural discrepancy. Eight La( iii ) coordination polymers were prepared from isomeric perchlorinated benzenedicarboxylate ligands, and their catalytic activities have been described.