Pillared lanthanide metal organic frameworks with sinusoidal channels formed from bent mixed-donor phenanthroline based ligands of different length

Abstract

Five new lanthanide MOFs were prepared by solvothermal synthesis to investigate the effect of ligand and pillar length using the unsymmetrical mixed-donor ligands L1H (4′-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-[1,1′-biphenyl]-3-carboxylic acid) and L2H (3-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)benzoic acid) and linear pillaring ligands H₂BDC (terephthalic acid) and H₂BPDC (3,4-dihydro-[1,1′-biphenyl]-4,4′-dicarboxylic acid). Nd-MOF1 and Gd-MOF1, [M(BDC)(L2)]2.5DMA (M = Nd or Gd), were isomorphous. They both presented a 3D pillared framework with bcu topology with a paddlewheel SBU and sinusoidal channels. Nd-MOF2, [Nd(BDC)(L1)]·4DMA, has a pseudo-paddlewheel SBU and formed a 3D pillared pcu framework where 1D double-chains were crosslinked with BDC to provide sinusoidal channels. Gd-MOF2, [Gd₂(BPDC)₂(L1)₂]·9DMA·0.25H₂O, has a pseudo-paddlewheel SBU and the 1D double-chains were cross-linked by BPDC to form a regular pcu 3D network which was interpenetrated and has sinusoidal channels. The solvent rich Nd-MOF3, [Nd₂(BPDC)(L1)₂(DMA)₄](OH)₂·10DMA, has a pseudo-paddlewheel SBU and formed 1D double-chains which were partially cross linked by BPDC to form a 2D sheet. The bound DMA solvent prevented the extension of these sheets into a 3D framework. Interestingly, the double chains do not interfere with the adoption of a regular topology by the networks. The sinusoidal channels appeared to be a consequence of the unsymmetrical nature of the L1H and L2H ligands.