Abstract

Growing efforts to construct new MOFs (metal-organic frameworks) have been focused at developing functional materials exhibiting applicable catalytic, gas storage and separation, magnetic, and sensing properties. Currently, one of the most challenging goals in the field of MOF chemistry is to build the frameworks by design in order to endow them those properties or improved functions. Several research groups have developed and demonstrated rational design sterategies toward desired framework structures and in turn better functional materials. However, as there are many framework structures that do not follow nature’s default network types, many examples for the unprecedented structures need to be explored and classfied to figure out their assembling patterns or rules as demonstrated by the cases of 1D infinite chains. Here we present a rare example that 1D metal-organic frameworks containing an unusual copper tetranuclear inorganic building block are assemlbed to form a 3D framework. Before our work, two MOFs sharing similar structural features as our case were reported. However, our preparation method is simpler and milder than the reported ones, and in addition, the crystal strcuture is slightly different from those due to the changes in the additional coordinating ligands. Reaction of 5-sulfoisophthalic acid sodium salt with Cu(NO3)2·2.5H2O in a mixed solvent of DMF and water at 85 °C for 2 days produced large rectangular blue crystals of 1 formulated as {[Cu4L2(OH)2(DMF)2]·3(DMF)}n (1) (L = 5-sulfoisophthalate, DMF = N,N-dimethylformamide). The X-ray crystal structure of 1 revealed the formation of infinite 1D chains or “tapes” composed of tetracopper clusters held by two μ3-hydroxo groups as inorganic building blocks, and 5-sulfoisophthalates as organic linkers (Scheme 1). The crystallographic asymmetric unit of 1 contains two independent half-occupied copper ions and also a halfoccupied L (Figure 1). Cu(1) sits on a crystallographic mirror plane (m) and Cu(2) does on a 2-fold rotation axis, which requires two symmetry-related copper atoms. These four copper atoms are held by two μ3-bridging hydroxo groups to form a tetranuclear cluster. These hydroxo oxygen atoms also sit on a mirror plane, and are placed opositely by 0.375(4) A above and below the mean plane defined by the four copper atoms. Cu(1) and Cu(2) show a sqare-pyramidal and a distorted octahedral coordiantion geometry, respectively. Cu(1) is coordinated by two oxygen atoms (O(2) and its symmetryrelated O(2)) of carboxylate of L, one oxygen atom O(1C) of μ3-bridging hydroxo group, one oxygen atom (O(1S)) of DMF in the equatorial positions. The axial oxygen atom (O(4)) is provided by the sulfonate group of the neighboring

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