Dao-Jun Zhang

Two novel lead(II)-tetrazolate frameworks based on cubane [Pb4(OH)4]4+ clusters trapping long lifetime luminescence emission

Two novel Pb(II)-based metal–organic frameworks (MOFs) based on the rigid bitetrazolate ligand 1,4-benzeneditetrazol-5-yl (H2BDT) have been synthesized under hydrothermal conditions and fully characterized. In these two compounds, [Pb4(OH)4(BDT)2]·2H2O (1) and [Pb4(OH)4(BDT)]·BDT·2H2O (2), the H2BDT ligands exhibit three different coordination modes which are firstly reported in M-BDT frameworks, constructing disparate architectures by bridging the same cubane-shaped [Pb4(OH)4]4+ building units. Compound 1 features a 3D supramolecular network with a rare 2-fold interpenetrating (10, 3)-d (or utp) topology which is accomplished by connecting [Pb4(OH)4]4+ clusters to μ4-bridging BDT2− ligands via weak bonds. Compound 2 exhibits a 2D square grid with (4, 4) topology and the adjacent 2D networks are further linked by Pb–O weak bonds to generate the 3D supramolecular structure. Moreover, the structures of these two compounds are highly influenced by the concentration of the starting reagents. Compounds 1 and 2 exhibit strong solid-state fluorescent emission with millisecond luminescence lifetimes at room temperature.

Structure and Characterization of a Novel 3D Lead Phosphonate Metal–Organic Framework with Cationic Layer Based on Weak Pb–O(N) Contact

A novel lead-phosphonate, [Pb2(HL)]·(NO3)·2(H2O) 1 (H4L = H2O3PCH2N(C4H8)NCH2PO3H2 N,N′-piperazinebis(methylenephosphonic acid), so HL = O3PCH2NH(C4H8)NCH2PO3), has been hydrothermally synthesized and characterized by elemental analysis, IR, TG-DTA, and X-ray single-crystal diffraction. Compound 1 possesses a 2D cationic layer structure built from inorganic chains with three types of eight-membered rings arranged in an ABAC manner. In 1, both crystallographic distinct Pb(II) ions adopt three-coordination geometry, and a counter anion NO3 – and two lattice water molecules occupy the voids between 2D layers. After the removal of solvent, the size of tunnel formed by 2D layers is 137.9 A3 per unit cell, comprising 17.0% of the crystal volume based on the crystal structure. When the bond length of Pb–O(N) extended to 3.10 A, a 3D metal–organic framework was constructed via long Pb–O(N) contacts, simultaneously accompanied by the hemi- to holo-directed transition in coordination geometry of Pb(II). Except for the long Pb–O contacts, a 3D supramolecular network is also formed by hydrogen bonds (N–H···O, O–H···O, and C–H···O), van der Waals forces as well as electrostatic interactions. The result of fluorescence measurements indicates that 1 shows a fluorescent emission band at 465 nm (λexcitation = 215 nm).

Solvothermal syntheses, characterizations and properties of three transition metal (Ni(II), Co(II)) imino-carboxylate-diphosphonates

Three compounds have been isolated from solvothermal reactions of a transition metal(II) (Ni(II), Co(II)) with N,N-bis(phosphonomethyl)aminoacetic acid [(HO2CCH2)N(CH2PO3H2)2] (H5L), namely [NH3(CH2)3NH3](NH4)4[Ni(L)(H2O)]2 (1), (H3O)3[Ni(L)(H2O)2]·4H2O (2) and (H3O)[Co(H2L)(H2O)2]·2H2O (3). These compounds were characterized by single crystal and powder X-ray diffraction, infrared spectroscopy, thermal analysis, elemental analysis, fluorescent spectroscopy and magnetic measurements. The structure of compound 1 is composed of binuclear [Ni2O6N2]n4− units, which are further interconnected into a 3D supramolecular network by hydrogen bonds. Compounds 2 and 3 are both mononuclear and consist of similar octahedral [MO5N] units. A 1D dendritic water chain is formed by hydrogen bond interactions in the supramolecular network of compound 2. Compounds 1 and 2 show ferromagnetic properties, while weak antiferromagnetic properties are observed in compound 3. Compounds 1 and 2 also display fluorescent emission excited at 235 nm.

catena-Poly[[aqua­dioxidouranium(VI)]-μ3-4,4′-oxydibenzoato]

The title compound, [UO2(C14H8O5)(H2O)]n, is a polymeric UO2 complex bridged by 4,4′-oxydibenzoate ligands. One carboxylate group of the bridging ligand chelates a uranyl cation while the other carboxylate group of the ligand bridges two other two uranyl cations, forming a double-chain polymeric structure. The central UVI atom is seven-coordinated in a distorted UO7 pentagonal-bipyramidal geometry. In the crystal structure, O—H⋯O hydrogen bonding links the polymeric chains into a three-dimensional supramolecular framework. Within the bridging ligand, the two benzene rings are oriented at a dihedral angle of 59.0 (2)°.