Porous metal-organic materials [1] have attracted considerable attention in recent years because of their potential applications in many areas including gas storage, [2] separation, [3] and catalysis. [4] Because high framework stability is essential for many practical applications, the quest for metal-organic materials with rigid frameworks has been a subject of intense research. Since the first reports of metal-organic frameworks with permanent porosity, [5] many metal-organic frameworks have been reported to have stable porous structures; however, only a handful of these materials have a high surface area, [6] which is another important virtue of this class of materials. There is also growing interest in metal-organic materials with flexible and dynamic frameworks, [7] in particular, those that reversibly change their structures and properties in response to external stimuli as they may find applications, for example, in sensors.[8] However, porous materials that have both high framework stability and framework flexibility are rare.[9] Herein we report a novel metalorganic framework with permanent porosity and a high surface area, which also shows unusual guest-dependent dynamic behavior: the framework shrinks upon guest inclusion and expands upon guest release as proved unequivocally by single-crystal X-ray crystallography. These changes are fully reversible and depend on the nature of guests.Heating [10] The structure of 1·4 DMF· 1 = 2 H 2 O was determined by single-crystal X-ray diffraction and the phase purity of the bulk material was independently confirmed by powder X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and elemental analysis. The framework in 1·4 DMF· 1 = 2 H 2 O is composed of dinuclear Zn 2 units with a paddle wheel structure, which are bridged by 1,4-bdc dianions to form a distorted 2D square-grid {Zn 2 (1,4-bdc) 2 }. The axial sites of the Zn 2 paddle wheels are occupied by dabco, which act as pillars to extend the 2D layers into a 3D structure (Scheme 1). The overall topology of the framework in 1·4 DMF· 1 = 2 H 2 O is best described as a compressed primitive cubic (a-Po) net (Figure 1 a). The dabco pillars are disordered along the Scheme 1. The extension of the 2D square-grid of {Zn 2 (1,4-bdc) 2 } into a 3D structure by using dabco, which occupies the axial positions.

A systematic modulation of organic ligands connecting dinuclear paddle-wheel motifs leads to a series of isomorphous metal-organic porous materials that have a three-dimensional connectivity and interconnected pores. Aromatic dicarboxylates such as 1,4-benzenedicarboxylate (1,4-bdc), tetramethylterephthalate (tmbdc), 1,4-naphthalenedicarboxylate (1,4-ndc), tetrafluoroterephthalate (tfbdc), or 2,6-naphthalenedicarboxylate (2,6-ndc) are linear linkers that form two-dimensional layers, and diamine ligands, 4-diazabicyclo[2.2.2]octane (dabco) or 4,4'-dipyridyl (bpy), coordinate at both sides of Zn(2) paddle-wheel units to bridge the layers vertically. The resulting open frameworks [Zn(2)(1,4-bdc)(2)(dabco)] (1), [Zn(2)(1,4-bdc)(tmbdc)(dabco)] (2), [Zn(2)(tmbdc)(2)(dabco)] (3), [Zn(2)(1,4-ndc)(2)(dabco)] (4), [Zn(2)(tfbdc)(2)(dabco)] (5), and [Zn(2)(tmbdc)(2)(bpy)] (8) possess varying size of pores and free apertures originating from the side groups of the 1,4-bdc derivatives. [Zn(2)(1,4-bdc)(2)(bpy)] (6) and [Zn(2)(2,6-ndc)(2)(bpy)] (7) have two- and threefold interpenetrating structures, respectively. The non-interpenetrating frameworks (1-5 and 8) possess surface areas in the range of 1450-2090 m(2)g(-1) and hydrogen sorption capacities of 1.7-2.1 wt % at 78 K and 1 atm. A detailed analysis of the sorption data in conjunction with structural similarities and differences concludes that porous materials with straight channels and large openings do not perform better than those with wavy channels and small openings in terms of hydrogen storage through physisorption.

Novel microporous metal-organic framework material composed of Mn(II) and formate ions displays permanent porosity, high thermal stability, and size-selective gas sorption behavior. The framework is stable enough to maintain single crystallinity after the complete guest removal at 150 degrees C under a reduced pressure. Most importantly, it selectively adsorbs H2 and CO2 but not N2 and other gases with larger kinetic diameters, which appears to be due to the small aperture of the channels. Despite a moderate H2 storage capacity, which is however still higher than that of any zeolite, its H2 surface coverage is one of the highest among the known microporous materials. Thus this new zeolite-like material made of a simple organic building block may find useful applications in gas separation and sensor.

Metal-organic porous materials are receiving growing attention [1] because of their potential applications in gas storage, [2] separation, [3] and many other areas. [4] Although catalysis is one of the most promising applications of such materials, only a handful of examples have been reported to date. [5] Furthermore, despite considerable efforts, attempts to synthesize robust, homochiral metal-organic porous materials capable of enantioselective separation and/or catalysis have met with only limited success. [6,7] Most homochiral metalorganic frameworks are not robust enough to show permanent porosity, nor porous enough to be useful for selective sorption or catalytic transformation of organic molecules. Therefore, the synthesis of robust homochiral metal-organic frameworks with potential for application is still challenging. For the synthesis of homochiral metal-organic open frameworks, two general approaches have been taken: 1) use of a rigid homochiral organic ligand as a spacer to link adjacent metal centers or secondary building units (SBUs), [5b-d, 7] and 2) use of a homochiral ligand as an auxiliary pendant which does not directly participate in the formation of a framework backbone, but forces the framework to adopt a specific chiral topology.[3d] Herein, we introduce another rational approach to the synthesis of homochiral metal-organic frameworks. A metal ion and a readily available homochiral organic ligand are used to form homochiral SBUs, which in turn, are linked together by rigid spacers to build a network structure, in a one-pot reaction (Scheme 1).[8] With a judicious choice of metal ion, homochiral organic molecule, and rigid polytopic linker (that is, a connector with more than one metal coordination site), this approach allows us to synthesize metal-organic open frameworks with stable chiral pores. Herein, we report a new homochiral metal-organic material that has permanent porosity, size-and enantioselective sorption properties, and catalytic activity.[9]