Novel metal-organic and supramolecular 3D frameworks constructed from flexible biphenyl-2,5,3′-tricarboxylate blocks: Synthesis, structural features and properties

Biphenyl-2,5,3′-tricarboxylic acid (H3L) was selected as an unexplored tricarboxylate building block and applied for the hydrothermal synthesis of three novel coordination compounds, namely a 0D tetramer [Co4(HL)2(μ3-HL)2(phen)6(H2O)2]·3H2O (1) and two 3D metal-organic frameworks (MOFs) [Cd3(μ5-L)(μ6-L)(py)(μ-H2O)2(H2O)]n·H2O (2) and [Zn3(μ4-L)2(2,2′-bpy)(μ-4,4′-bpy)]n·2H2O (3). These products were easily generated in aqueous medium from the corresponding metal(II) chlorides, H3L, and various N-donor ancillary ligands, selected from 1,10-phenanthroline (phen), pyridine (py), 2,2′-bipyridine (2,2′-bpy), and 4,4′-bipyridine (4,4′-bpy). Compounds 1-3 were isolated as stable crystalline solids and were fully characterized by IR and UV-vis spectroscopy, elemental, thermogravimetric (TGA), powder (PXRD) and single-crystal X-ray diffraction analyses. Compound 1 possesses a discrete tetracobalt(II) structure, which is extended into a 3D H-bonded network with the pcu topology. In contrast, MOF 2 discloses a very complex trinodal 4,5,12-connected net with an undocumented topology, while MOF 3 features the nce/I topological framework. The magnetic (for 1) and luminescence (for 2 and 3) properties were also studied and discussed. The present study thus widens a still very limited family of metal-organic and supramolecular frameworks driven by flexible biphenyl-2,5,3′-tricarboxylate building blocks.