That composition and structure can so profoundly impact the properties of crystalline materials has provided impetus for exponential growth in the field of crystal engineering over the past 30 years. Crystal engineering has evolved from structure design (form) to control over bulk properties (function). Today, when coupled with molecular modeling, crystal engineering offers a paradigm shift from the more random, high-throughput methods that have traditionally been utilized in materials discovery and development. Simply put, custom-design of the right crystalline material for the right application is now at hand. An overview of the evolution of crystal engineering will be followed by the detailing of two classes of porous materials that offer potential to address global challenges:

1. Ultramicroporous Materials are built from metal or metal cluster “nodes” and combinations of organic and inorganic “linkers”; their pore chemistry and size (< 0.7 nm) can overcome some of the weaknesses of existing classes of porous material, especially for trace separations such as CO2,[1] C2H2[2] and C6H6[3] capture. Water harvesting applications will be addressed.

2. Non-porous solids that reversibly switch between closed and open (porous) phases can exhibit isotherms that, perhaps counterintuitively, are advantageous in terms of working capacity vs. rigid porous materials. New examples of 2D[4] and 3D[5] switching materials that offer excellent gas storage and/or separation performance along with unusual isotherms will be presented.