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

Hydro(solvo)thermal reactions between 1,1'-biphenyl-2,2',3,3'-tetracarboxyl acid (H(4)bptc) and Cd(NO3)(2).4H(2)O 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 [Cd-9(bptc)(4)(mu(3)-OH)(2)(H2O)(14)].(bpydo).2H(2)O (2), [Cd-2(bptc)(bpe)(H2O)(2)]. H2O (3), [Cd-4(bptc)(Hbptc)(bpp)(mu(3)-OH)(H2O)(4)] (4), [Cd-2(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 Schlafli symbol of (4.6(2))(4(3).6(3))(4(4).6(10).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 Schlafli symbol of (4(3))(2)(4(6).6(6).8(3)). 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.