Four 2D metal–organic networks incorporating Cd-cluster SUBs: hydrothermal synthesis, structures and photoluminescent properties

Abstract

Hydro(solvo)thermal reactions between 1,1′-biphenyl-2,2′,3,3′-tetracarboxyl acid (H₄bptc) and Cd(NO₃)₂·4H₂O at the presence of the ‘second’ ligands of bpydo, bpe, bpp and bix (bpydo = 4,4′-bipyridine-N,N′-dioxide; bpe = 1,2-bis-(4-pyridyl)ethane; bpp = 1,3-Bis-(4-pyridyl)propane; bix = 1,4-bis(imidazol-1-yl-methyl)benzene) yield four new 2D metal–organic coordination polymers [Cd₉(bptc)₄(μ₃-OH)₂(H₂O)₁₄]·(bpydo)·2H₂O (2), [Cd₂(bptc)(bpe)(H₂O)₂]·H₂O (3), [Cd₄(bptc)(Hbptc)(bpp)(μ₃-OH)(H₂O)₄] (4), [Cd₂(bptc)(bix)(H₂O)] (5). Compound 2 presents a 2D grid structure with heptanuclear cadmium cluster and two kinds of discrete Cd atoms secondary building units (SUBs), 3 has a 2D structure with the novel Schläfli symbol of (4.6²)(4³.6³)(4⁴.6¹⁰.8), 4 gives a 2D grid structure with a pentanuclear cadmium cluster, binuclear cadmium cluster and discrete Cd atom SUBs, and 5 has a 2D distorted CdI₂-type topology structure with the Schläfli symbol of (4³)₂(4⁶.6⁶.8³). The novel achiral crown-ether-like cycles in 2, 4 and 5 are found and occupied by the single Cd atom or binuclear cadmium cluster. All compounds give strong luminescent emission and have potential application as optical materials.