During the past decade, interest has grown tremendously in the design and synthesis of crystalline materials constructed from molecular clusters linked by extended groups of atoms. Most notable are metal-organic frameworks (MOFs), in which polyatomic inorganic metal-containing clusters are joined by polytopic linkers. (Although these materials are sometimes referred to as coordination polymers, we prefer to differentiate them, because MOFs are based on strong linkages that yield robust frameworks.) The realization that MOFs could be designed and synthesized in a rational way from molecular building blocks led to the emergence of a discipline that we call reticular chemistry. MOFs can be represented as a special kind of graph called a periodic net. Such descriptions date back to the earliest crystallographic studies but have become much more common recently because thousands of new structures and hundreds of underlying nets have been reported. In the simplest cases (e.g., the structure of diamond), the atoms in the crystal become the vertices of the net, and bonds are the links (edges) that connect them. In the case of MOFs, polyatomic groups act as the vertices and edges of the net. Because of the explosive growth in this area, a need has arisen for a universal system of nomenclature, classification, identification, and retrieval of these topological structures. We have developed a system of symbols for the identification of three periodic nets of interest, and this system is now in wide use. In this Account, we explain the underlying methodology of assigning symbols and describe the Reticular Chemistry Structure Resource (RCSR), in which about 1600 such nets are collected and illustrated in a database that can be searched by symbol, name, keywords, and attributes. The resource also contains searchable data for polyhedra and layers. The database entries come from systematic enumerations or from known chemical compounds or both. In the latter case, references to occurrences are provided. We describe some crystallographic, topological, and other attributes of nets and explain how they are reported in the database. We also describe how the database can be used as a tool for the design and structural analysis of new materials. Associated with each net is a natural tiling, which is a natural partition of space into space-filling tiles. The database allows export of data that can be used to analyze and illustrate such tilings.

A series of metal-organic frameworks representing a non-interpenetrated framework analogue of MOF-14 have been synthesized by using two different linkers, 4,4',4''-benzene-1,3,5-triyl-benzoic acid (H(3)BTB) and 4,4'-bipyridine (Bpy). Interestingly, the transition metal ions in the paddle-wheel metal clusters could be exchanged by other transition metal ions via a direct single-crystal to single-crystal transformation. This post-synthesis route can be used for synthesis of isomorphous metal-organic frameworks that cannot be obtained by direct synthesis.

A comparative analysis of binary compounds and 61 simple anhydrous salts M(y)(LO(3))(z) (L = S, Se, Te, Cl, Br, I) was performed using the crystallochemical program package TOPOS. A topological similarity was found between the salts and six types of binary compounds (NaCl, NiAs, PoCl(2), Tl(2)S(2), ZnTe, rutile). It is notable that these structure relationships are typical for other groups of inorganic salts: borates, carbonates, nitrates, orthophosphates, orthoarsenates, sulfates, selenates, perchlorates, molybdates and halogenides of d-metals. For all the M(y)(LO(3))(z) compounds the topology and uniformity of the ion arrays were investigated. It has been established that in 36 out of the 61 salts at least one ion array has the topology of close packing or the body-centred cubic lattice. The results obtained have allowed us to come to conclusions about the structure-forming role of the arrays of various chemical composition.

Two open-framework germanates, SUT-1 and SUT-2, have been synthesized under hydrothermal conditions using ethylenediamine (en, H(2)NCH(2)CH(2)NH(2)) as templates and Ni(NO(3))(2)·6H(2)O as the transition-metal source. Their frameworks are built with Ge(10) clusters and [Ni(en)(2)](2+) complexes. In both structures, Ge(10) clusters form square nets in the a-c plane, while the [Ni(en)(2)](2+) complexes bridge the square nets via Ni-O-Ge bonds to form 3D networks. They present the first examples to incorporate Ni(2+) complexes into the germanate frameworks. In SUT-2, additional linkages by Ge(2)O(7) clusters between the square nets generate a new type of topology.