The long-standing challenge of designing and constructing new crystalline solid-state materials from molecular building blocks is just beginning to be addressed with success. A conceptual approach that requires the use of secondary building units to direct the assembly of ordered frameworks epitomizes this process: we call this approach reticular synthesis. This chemistry has yielded materials designed to have predetermined structures, compositions and properties. In particular, highly porous frameworks held together by strong metal-oxygen-carbon bonds and with exceptionally large surface area and capacity for gas storage have been prepared and their pore metrics systematically varied and functionalized.

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Reticular synthesis and the design of new materials

Metal-organic frameworks are a recently-identified class of porous polymeric material, consisting of metal ions linked together by organic bridging ligands, and are a new development on the interface between molecular coordination chemistry and materials science. A range of novel structures has been prepared which feature amongst the largest pores known for crystalline compounds, very high sorption capacities and complex sorption behaviour not seen in aluminosilicate zeolites. The development of synthetic approaches to these materials and investigations of their properties are reviewed.

Metal-organic frameworks

The development in the field of coordination polymers or metal-organic coordination networks, MOCNs (metal-organic frameworks, MOFs) is assessed in terms of property investigations in the areas of catalysis, chirality, conductivity, luminescence, magnetism, spin-transition (spin-crossover), non-linear optics (NLO) and porosity or zeolitic behavior upon which potential applications could be based.

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Engineering coordination polymers towards applications

Metal-organic frameworks (MOFs), also known as coordination polymers, represent an interesting type of solid crystalline materials that can be straightforwardly self-assembled through the coordination of metal ions/clusters with organic linkers. Owing to the modular nature and mild conditions of MOF synthesis, the porosities of MOF materials can be systematically tuned by judicious selection of molecular building blocks, and a variety of functional sites/groups can be introduced into metal ions/clusters, organic linkers, or pore spaces through pre-designing or post-synthetic approaches. These unique advantages enable MOFs to be used as a highly versatile and tunable platform for exploring multifunctional MOF materials. Here, the bright potential of MOF materials as emerging multifunctional materials is highlighted in some of the most important applications for gas storage and separation, optical, electric and magnetic materials, chemical sensing, catalysis, and biomedicine.

Emerging Multifunctional Metal-Organic Framework Materials.

The occurrence of interpenetration in metal–organic and inorganic networks has been investigated by a systematic analysis of the CSD and ICSD structural databases. For this purpose, a novel version of TOPOS (a program package for multipurpose crystallochemical analysis) has been employed, where the procedure of recognition of interpenetrating nets is based on the representation of a crystal structure as a finite reduced graph. In this paper we report a comprehensive list (301 Refcodes) of interpenetrating metal–organic 3D structures from CSD, that are analyzed on the basis of their topologies. Interesting trends and novel features have been observed and distinct classes of interpenetrating nets have been envisaged, depending on the relationships of the individual motifs.

Interpenetrating metal–organic and inorganic 3D networks: a computer-aided systematic investigation. Part I. Analysis of the Cambridge structural database

Acentric three-dimensional coordination polymers bis(isonicotinato)zinc (1) and bis(4-pyridylacrylato)cadmium⋅H2 O (2) were synthesized under hydro(solvo)thermal conditions; they exhibit a threefold (see picture) and fivefold diamondoid structure, respectively. Both 1 and 2 are active for second harmonic generation and exhibit remarkable thermal stability.

Crystal Engineering of Acentric Diamondoid Metal–Organic Coordination Networks

Supramolecular Engineering of Chiral and Acentric 2D Networks. Synthesis, Structures, and Second-Order Nonlinear Optical Properties of Bis(nicotinato)zinc and Bis{3-[2-(4-pyridyl)ethenyl]benzoato}cadmium

Reactions of Cd(NO(3))(2).4H(2)O with 4-cyanopyridine in the presence of ethanol or pyrazine guest molecules under hydro(solvo)thermal conditions afford two new cadmium coordination polymers, [Cd(isonicotinate)(2)(EtOH)][EtOH], 1, and [Cd(isonicotinate)(2)(H(2)O)][pyrazine], 2. The Cd centers in both 1 and 2 are seven-coordinate with distorted pentagonal bipyrimidal structures via coordination to two pyridyl nitrogen atoms, one oxygen atom from a solvent molecule, one chelating carboxylate, and one semichelating carboxylate group. The bridging isonicotinate groups link each Cd center to four adjacent Cd centers, resulting in three-dimensional polymeric networks based on doubly interpenetrated diamondoid structures. One molecule of ethanol or pyrazine is also included in 1 or 2, respectively, to fill the void space left within the solid after the twofold interpenetration. Thermogravimetric analyses (TGA) showed that the included and coordinated ethanol molecules in 1 could be removed stepwise at 100 and 160 degrees C, respectively. After the removal of the guest ethanol molecules, the resulting nanoporous solid exhibits the same X-ray powder diffraction (XRPD) pattern as 1. Guest ethanol molecules can be reintroduced into the evacuated sample of 1 via exposure to ethanol vapor at room temperature. Further heating results in the loss of coordinated ethanol molecules and the collapse of the polymeric network structure. On the other hand, XRPD shows that removal of pyrazine in 2 is accompanied by the loss of the coordinated water molecules and, consequently, the collapse of the polymeric network structure. These results demonstrate that nanopores can be designed based on interpenetrated coordinated networks. Crystal data for 1: orthorhombic space group Pbca, a = 12.691(1) A, b = 15.545(1) A, c = 18.342(1) A, and Z = 8. Crystal data for 2: orthorhombic space group Pbca, a = 12.081(1) A, b = 15.323(2) A, c = 19.705(3) A, and Z = 8.

Nanoporous, Interpenetrated Metal-Organic Diamondoid Networks.

The synthesis of a bipyridine ligand with a flexible spacer and a noncoordinating amine group N,N-(2-pyridyl)-(4-pyridylmethyl)amine, L2, and its coordination chemistry with cadmium have been investigated. Two-dimensional (2D) coordination polymers of L2 with empirical formulas [Cd(L2)2(ClO4)2]∞, 1, or [Cd(L2)2(NO3)2]∞, 2, were prepared by hydro(solvo)thermal reactions of L2 and Cd(ClO4)2·6H2O or Cd(NO3)2·4H2O in mixtures of water and ethanol, respectively. Single-crystal X-ray diffraction studies reveal that 1 and 2 have similar structures in which each L2 ligand bridges two cadmium centers with both the 4-pyridyl and 2-pyridyl nitrogen atoms to result in 2D rhombohedral polymeric grids. The two rings of L2 are essentially perpendicular to each other, likely to accommodate the coordination of both pyridyl nitrogen atoms to the Cd centers as well as the “intramolecular” hydrogen bonds between the amine group in the flexible spacer and the coordinated anion group. When the hydro(solvo)thermal reaction was ...

Ren-Gen Xiong

Papers

Crystal Engineering of Acentric Diamondoid Metal–Organic Coordination Networks

Supramolecular Engineering of Chiral and Acentric 2D Networks. Synthesis, Structures, and Second-Order Nonlinear Optical Properties of Bis(nicotinato)zinc and Bis{3-[2-(4-pyridyl)ethenyl]benzoato}cadmium

Nanoporous, Interpenetrated Metal-Organic Diamondoid Networks.

Two- and Three-Dimensional Cadmium Coordination Polymers Based on N,N-(2-Pyridyl)-(4-pyridylmethyl)amine

Kristall‐Engineering azentrischer diamantartiger metallorganischer Koordinationsnetze