Two new Zn2+-based metal–organic frameworks (MOFs) based on biphenyl-2,2′,5,5′-tetracarboxylic acid, i.e. H4(o,m-bpta), and N-donor ligands, namely, poly[[(μ4-biphenyl-2,2′,5,5′-tetracarboxylato)bis{[1,3-phenylenebis(methylene)]bis(1H-imidazole)}dizinc(II)] dimethylformamide monosolvate dihydrate], {[Zn2(C16H6O8)(C14H14N4)2]·C3H7NO·2H2O}
n
or {[Zn2(o,m-bpta)(1,3-bimb)2]·C3H7NO·2H2O}
n
(1) {1,3-bimb = [1,3-phenylenebis(methylene)]bis(1H-imidazole)}, and poly[[(μ4-biphenyl-2,2′,5,5′-tetracarboxylato)bis{[1,4-phenylenebis(methylene)]bis(1H-imidazole)}dizinc(II)] monohydrate], {[Zn2(C16H6O8)(C14H14N4)2]·H2O}
n
or {[Zn2(o,m-bpta)(1,4-bimb)2]·H2O}
n
(2) {1,4-bimb = [1,4-phenylenebis(methylene)]bis(1H-imidazole)}, have been synthesized under solvothermal conditions. The complexes were characterized by IR spectroscopy, elemental analysis, single-crystal X-ray diffraction and powder X-ray diffraction analysis. Structurally, the (o,m-bpta)4− ligands are fully deprotonated and combine with Zn2+ ions in μ4-coordination modes. Complex 1 is a (3,4)-connected porous network with honeycomb-like [Zn2(o,m-bpta)]
n
sheets formed by 4-connected (o,m-bpta)4− ligands. Complex 2 exhibits a (2,4)-connected network formed by 4-connected (o,m-bpta)4− ligands linking Zn2+ ions in left-handed helical chains. The cis-configured 1,3-bimb and 1,4-bimb ligands bridge Zn2+ ions to form multi-membered [Zn2(bimb)2] loops. Optically, the complexes show strong fluorescence and display larger red shifts compared to free H4(o,m-bpta). Complex 2 shows ferroelectric properties due to crystallizing in the C
2v
polar point group.
Γ-point group velocity of lossy Dirac cone composite right/left-handed metamaterials
