Synthesis and structural characterization of a new open-framework zinc terephthalate Zn3(OH)2(bdc)2 .2DEF, with infinite Zn-(μ3-OH)-Zn chains

A new zinc carboxylate Zn-3(OH)(2)(bdc)(2 center dot)2DEF was synthesized under mild hydrothermal conditions (100 degrees C, 40h) in the presence of 1,4-benzenedicarboxylic (bdc) acid, in N,N'-diethylformamide (DEF) solvent. Its structure, characterized by means of single-crystal XRD analysis, consists of connection of ZnO2(OH)(2) tetrahedra corner-sharing with ZnO4(OH)(2) octahedra. Two adjacent ZnO2(OH)(2) tetrahedra have a common edge corresponding to hydroxy group, which is also linked to the octahedrally coordinated zinc atoms with a mu(3) configuration. This resulting connection mode generates infinite chains running along the c-axis, and connected to each other via the We ligand. Three-dimensional framework is therefore formed with channels running along the c-axis, parallel to the infinite Zn-OH-Zn chains. Within the tunnels are trapped the DEF species, which interacts via hydrogen-bond to the mu(3)-hydroxy of the zinc chains with the terminal oxygen atom of the formamide function. Analysis by solid state NMR (1 H and 13 Q has confirmed both the presence of occluded solvent molecules within the pores and the incorporation of carboxylate moieties into the framework. The structure of Zn-3(OH)(2)(bdc)(2) center dot 2DEF is closely related to those of MOF-69 series, constructed with longer organic linkers (4,4'-biphenyldicarboxylate and 2,6-naphthalenedicarboxylate). The structure is observed to loose crystallinity upon heating and removal of the occluded DEF moieties. Crystal data for [Zn-9(OH)(6)(O2C-C6H4-CO2)(6)] center dot 6[(CH3-CH2)(2)NCHO]: a 17.7374(3) angstrom, b = 15.2605(2) angstrom c = 18.2635(2) angstrom, beta = 113.071(1)degrees, V = 4548.2(1) angstrom , P2(1)/n (no. 14), Z = 1, R-1 = 0.0510, wR(2) = 0. 1302 for 11877 reflections I > 2 sigma(I). (c) 2005 Elsevier Inc. All rights reserved.