Three Zinc(II) Phosphonates: Syntheses, Structures and Sensing of Copper(II) Ions

Three zinc(II) phosphonocarboxylates, [Zn3 (m-bpc)2 (OH)]⋅(CH3 )2 NH2 ⋅H2 O (1), [Zn2 (m-bpc)(m-Hbpc)(4,4'-bpy)]⋅(CH3 )2 NH2 ⋅H2 O (2) and [Zn3 (m-bpc)2 (4,4'-bpy)(CH3 )2 NH]⋅H2 O (3) (m-H3 bpc=3-phosphonobenzoic acid, 4,4'-bpy=4,4'-bipyridine), have been solvothermally synthesised to generate unique topologies, as characterised by single-crystal XRD. Compound 1 possesses a diamond topology, which has rarely been found among phosphonate-based metal-organic frameworks. Compound 2 shows a 2D layered structure with pendant m-Hbpc and 4, 4'-bpy ligands, in which the layers feature as a zeolite-like network. Compound 3 has a 3D sandwich pillared-layer framework with an interesting double-helix structure. Only 1 shows an adsorption capacity for CO2 of 28.5 cm3 g-1 at 273 K. Luminescence studies revealed that both 1 and 2 could be potential sensors to copper(II) ions.