pubs.acs.org/crystal Published on Web 07/20/2010 r 2010 American Chemical Society DOI: 10.1021/cg1005677 2010, Vol. 10 3843–3846 Generation of 2D and 3D (PtS, Adamantanoid) Nets with a Flexible Tetrahedral Building Block Jian Tian, Radha Kishan Motkuri, and Praveen K. Thallapally* Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 Received April 28, 2010; Revised Manuscript Received July 2, 2010 ABSTRACT: The self-assembly of the flexible tetrahedral linker tetrakis[4-(carboxyphenyl)oxamethyl]methane acid with various transition metals (Cu, Co, and Mg) results in a 2D layered structure and 3D frameworks with PtS and adamantanoid topology. The PtS net exhibits permanent porosity, as confirmed by BET and gas adsorption experiments. Metal-organic frameworks (MOFs) represent a new class of solid-state materials that have great potential in gas separation, catalysis, and controlled dug release applications. 1-11 The concep- tual approach for synthesizing these materials is based on the self- assembly of cationic systems acting as nodes with polytopic organic ligands acting as linkers, resulting in the construction of MOFs with zero- to three-dimensional network structures with pore sizes ranging from 5 to 20 A ˚ . 12-14 Due to the versatile coordination chemistry of metal centers and polytopic organic ligands, MOFs can have an almost infinite variety of structures, and such diversity is not possible with any other solid-state materials known to date. 15-20 One of the biggest advantages of these materials includes postsyn- thetic modification of functional linkers that appears to be a very valuable alternative. 21-24 This approach consists of modifying the organic part of the material by a chemical reaction that takes place within the porous framework. Several research groups, inclu- ding PNNL, have reported storage of various gases such as CO 2 , methane, and hydrogen using these materials. 25-33 The adsorption of various gases in certain MOFs exceeds that of the standard zeolites due to their high surface area and pore volume. In this regard, we have recently reported a few papers on breathing phenomena as a function of gas loading and catalytic properties derived from tetrakis[4-(carboxyphenyl)oxamethyl]methane (1), a semirigid tetracarboxylic linker with a Zn 2 cluster. 28,34 For topolo- gical consideration, combination of a tetrahedral building block and Zn 2 paddlewheel clusters lead to the formation of interpenetrated micro- and mesoporous supramolecular isomers with PtS, adaman- tanoid, and lonsdaleite networks having differences in solid-state packing, amount of gas uptake, selectivity toward other gases, and shape selective catalytic properties. 9,10 Similarly, when auxiliary ligands such as bipyridine were used during the synthesis, a 2-fold interpenetrated PtS network and the two PtS nets connected by a bipyridine were observed with contraction and expansion of the framework upon solvent removal and CO 2 uptake. 9 We herein extend our research toward the synthesis and characterization of nonporous and microporous metal -organic frameworks built upon the copper, magnesium, and cobalt based SBUs and the flexible tetrahedral organic building block, 1. The synthesis of the ligand tetrakis[4-(carboxyphenyl)oxame- thyl]methane (1) was accomplished by the reported procedure. 35 Our initial efforts in getting single crystals for copper, cobalt, and magnesium failed in pure dimethylformamide (DMF) solvent. Thus, after modifying the synthetic procedure, single crystals of 2 (blue rectangular) were obtained by heating the reactants (ligand/ copper nitrate = 1:2 molar ratio) in a solvent mixture of DMF/ ethanol/water (v/v = 2/1/1) at 105 °C for 72 h. It is interesting to note that various attempts have been made to synthesize 2 under different reaction conditions, including pure DMF, pure DMA, and DMA/CH 3 CN, but single crystal quality was only obtained in DMF and in the ethanol and water mixture. Similarly, purple block crystals of 3 were synthesized with cobalt nitrate (ligand/Co = 1:2.5) in a solvent mixture of DMA/CH 3 CN (v/v 2/1) at 110 °C for 72 h in a Teflon lined autoclave. On the contrary, complex 4 was obtained by heating the reactants (ligand/Mg = 1:2) in a mixture of DMF/H 2 O (5/1) at 110 °C for 24 h in a 20 mL glass vial, respec- tively. All of these complexes were successfully reproduced in bulk. The single crystal X-ray measurements on 2 show a tetrahedral ligand connected to two cupper atoms in a paddle-wheel fashion, as shown in Figure 1. In-depth analysis of 2 indicates that each Figure 1. Porous network structure of complex 2, with the corre- sponding PtS network on the bottom. *Corresponding author. E-mail: Praveen.Thallapally@pnl.gov.