Advances in the chemistry of metal–organic frameworks

An extensive body of research results currently exists from the synthesis of metal–organic frameworks (MOFs), an area that has attracted widespread attention due to the facility with which well-defined molecular building blocks can be assembled into periodic frameworks and the promise that such a process holds for the logical design of materials. The synthesis of MOFs generally involves the copolymerization of organic links and metal ions in a polar solvent under mild temperatures (up to 200 °C) and autogenous pressures (up to 100 atm). Since most products can be considered kinetically driven and lie on local thermodynamic minima, factors such as solubility of the organic link and metal salt, solvent polarity, ionic strength of the medium, temperature and pressure play critical roles in determining the character of products. Indeed, slight perturbations in synthetic parameters have been the basis for the preparation of what seems to be a flood of new MOF compounds. In the spirit of this discussion we advance the following ideas and developments that we believe contribute to the maturity of the field: (I) a conceptual framework that unifies the processes involved in the designed synthesis of MOFs, and which can be extended to other materials with extended structures; (II) a thesis concerning the possible structures that may form from building blocks with various shapes; (III) important considerations for achieving the design and synthesis of frameworks in which it is possible to change chemical functionality and metrics without changing the underlying framework topology; (IV) the inevitability of porosity for designed structures and some factors affecting framework stability; (V) insights on catenation: interpenetration versus interweaving, forbidden catenation, and duals. These points will be presented to an extent that will stimulate discussion—it is not an attempt to be comprehensive or to give a thorough treatment of this rich field.