The Reticular Chemistry Structure Resource (RCSR) Database of, and Symbols for, Crystal Nets

Abstract

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.

Secondary building units, nets and bonding in the chemistry of metal–organic frameworks

“…In the archetypical and iconic MOF, MOF-5, OZn 4 cationic SBUs are linked by the benzenedicarboxylate (BDC) anion to form a continuous cubic neutral framework of composition Zn 4 O(BDC) 3 . 4 The zinc carboxylate unit has formula Zn 4 O(CO 2 ) 6 , and the six carboxylate carbons (the points of extension) are at the vertices of a regular octahedron. The underlying topology of a MOF framework is also that of a net.…”

“…5 We have developed a system of nomenclature for common nets and some of their properties are conveniently accessed through a web-based database known at the Reticular Chemistry Structure Resource (RCSR). This system has recently been described in detail elsewhere; 6 here we are content to note that net topologies are assigned a three-letter symbol in bold lower-case; thus the MOF-5 and MOF-177 topologies have symbols pcu and qom, respectively. Some derived nets have symbols with extensions, a good example is the so-called augmented net in which the vertices of the original net are replaced by a cluster of vertices corresponding to the vertex figure of the original net.…”

Unprecedented Zeolite-Like Framework Topology Constructed from Cages with 3-Rings in a Barium Oxonitridophosphate

“…Interconnecting the novel CBUs via their 4-rings (forming additional 3-rings) yields 8-ring channels along AE100ae with a free diameter of 292 pm (calculation considering r(N) = 147 pm). The coordination sequences and the vertex symbols for the framework (RCSR symbol fuv) 42 are given in the Supporting Information (Table S4). …”

Reticular Synthesis of HKUST-like tbo-MOFs with Enhanced CH4 Storage

“…3b, 8 Successful implementation of reticular chemistry and the molecular building block approach offer nowadays potential to ideally target MOFs with desired and appropriate structural features. For example, HKUST-1 9 material that has an underlying tbo-a topology, can be further interpreted and regarded as constructed from a 2-periodic arrays of squares, each consistent with an augmented 4,4 square lattice (sql-a), that are cross-linked through 4-connected pillars containing copper paddle wheels. This underlying layer, isolated through deconstruction of the crystal structure, can be targeted and constructed from judiciously selected metals and ligands.…”