A Porous Metal-Organic Replica of r-PbO 2 for Capture of Nerve Agent Surrogate Ruqiang Zou,* ,†,‡ Ruiqin Zhong, ‡ Songbai Han, § Hongwu Xu, ‡ Anthony K. Burrell, ‡ Neil Henson, ‡ Jonathan L. Cape, ‡ Donald D. Hickmott, ‡ Tatiana V. Timofeeva, | Toti E. Larson,* ,‡ and Yusheng Zhao* ,‡ Department of AdVanced Materials and Nanotechnology, Department of Energy and Resources Engineering, College of Engineering, Peking UniVersity, Beijing 100871, China, Earth and EnVironmental Sciences DiVision, Los Alamos Neutron Science Center, Materials Physics and Applications DiVision, and Theoretical DiVision, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States, Neutron Scattering Laboratory, China Institute of Atomic Energy, Beijing 102413, China, and Department of Chemistry, New Mexico Highlands UniVersity, Las Vegas, New Mexico 87701, United States Received February 18, 2010; E-mail: rzou@pku.edu.cn; tlarson@lanl.gov; yzhao@lanl.gov Abstract: A novel metal-organic replica of R-PbO 2 exhibits high capacity for capture of nerve agent surrogate. Because of the availability of their precursors and their relative ease of synthesis, nerve agents comprise a class of toxic chemicals likely to be used by terrorist groups. The Sarin gas attack at the Tokyo subway station in May 1995 is a demonstration of the toxicity of nerve agents and their accessibility to terrorists. In addition to Sarin, there are a large number of other highly toxic organophosphate compounds that can be utilized as warfare or terror agents. Most of these compounds contain free phosphonic acid terminal groups or their phosphonate ester analogues. These molecules can form strong complexes with divalent metal ions (Ca, Mg, Zn, etc.), which is in part responsible for their toxicity in biological systems. Therefore, there has been an urgent need to develop new filtration technologies that reversibly capture and release a wide range of chemical threat agents, eliminating the need for traditional expendable media. Our approach is to develop novel materials based on metal- organic frameworks (MOFs) to specifically recognize, bind, and capture nerve agents and their precursors. MOFs are a new family of crystalline porous materials, the structures of which are composed of metal-cluster units linked by organic ligands through strong coordination bonds. 1,2 The flexibility with which these components can be varied has led to an extensive class of MOF structures with ultrahigh specific surface areas, far exceeding those achieved by porous activated carbons, and other sorbent materials. 3-5 They also exhibit tunable pore size, a functionalized pore wall, and high thermal stability. Recent research shows that MOFs can be used for efficient sensing/detection and capture of a range of guest molecules, such as harmful gases and high explosives frequently at the ppm level. 6 The specific properties of these MOFs can be optimized by varying their cavity size and their polarity and by incorporating selective binding sites on frameworks. Selective binding can also be achieved by varying the coordination environ- ments of the base metals or the nature of the base metals used in MOF syntheses. In particular, the base metals are commonly accompanied by organic solvent molecules at the coordination sites. These solvent molecules can be easily displaced to create high binding affinity sites that can be tailored to specifically targeted molecules (toxic or nontoxic). Furthermore, the binding capacity of a metal ion toward organophosphate increases with increasing the Lewis acidity of the metal ion. 7 It is, therefore, conceivable to design coordinately unsaturated MOFs based on divalent metal ions that can strongly bind organophosphate molecules containing both the ester and phosphonic acid groups. These materials will contain coordinately unsaturated metal sites that can bind target molecules. In this communication, we report a novel porous MOF with coordinately unsaturated zinc sites on the channel wall for highly efficient capture of one of the most important nerve agent surrogates, methylphosphonic acid (MPA), even at the ppm level. This result will open the door to use tailored MOFs for the capture of a wide range of nerve agents. Treatment of DMF/H 2 O (DMF ) N,N′-dimethylformamide) solution of zinc nitrate, calcium hydroxide, and benzene-1,3,5- tricaboxylic acid (H 3 BTC) at 95 °C inside a Teflon-capped scintillation vial for 10 h yields large needle-like crystals with a composition of [Zn 2 Ca(BTC) 2 (H 2 O) 2 ](DMF) 2 (1). 8 The purities of the bulk products are confirmed by elemental analysis (Found: C, 37.93%; N, 3.49%; Calcd: C, 37.70%; N, 3.67%) and powder X-ray diffraction (PXRD) measurements. 9 The PXRD patterns exhibit that there are some discrepancies of peak intensities and positions in low angles of 1 in comparison with the simulated patterns based on single crystal XRD data. Synchrotron XRD data of 1 were further collected at room temperature to investigate the phase purities. 9 The result indicates that the bulk sample of 1 is the same phase to the single crystal, in which there is a slight crystal structure derivation from Rietveld refinement. The derivation should be ascribed to the difference of test temperatures between a single crystal (183 K) and bulk powder of 1 (room temperature). Notedly, the host framework of 1 displays reasonable flexibility under various temperatures. Unfortunately, the solvent-free sample of 1 decom- posed when exposed to the strong synchrotron beam, so its structure cannot be further refined. Furthermore, upon re-exposing the solvent-free 1 to DMF/H 2 O, the PXRD pattern reverts to the as- made form, implying the open zinc sites are accessible to guest molecules. 9 Structural analysis shows 1 crystallizes in the orthorhombic space group C222 1 and consists of 3-connected BTC ligands coordinating to trinuclear Zn 2 Ca clusters. The central Ca atom lies in a crystallographic 2-fold axis with a half occupation in an asymmetric unit. Each Ca atom is coordinated by six separate BTC ligands Via † Peking University. ‡ Los Alamos National Laboratory. § China Institute of Atomic Energy. | New Mexico Highlands University. Published on Web 12/07/2010 10.1021/ja101440z  2010 American Chemical Society 17996 9 J. AM. CHEM. SOC. 2010, 132, 17996–17999