UC Riverside

The open framework materials have emerged as a highly active and rapidly developing domain of research because their rich host-guest chemistry could be utilized to develop promising materials such as absorbents, catalysts, sensors and substrates for mechanistic studies into fundamental surface interactions and catalytic mechanisms.

To better understand, predict and design materials with desired properties and functions, it is often essential to know the detailed structures, crystalline materials with well-defined periodic arrangements that allow for structural studies at the atomic resolution are of special importance. In addition, some properties such as uniform porosity and associated shape- or size-selectivity can be best designed with crystalline materials.

Unlike some other materials such as semiconductors in which properties can be dramatically altered by simple doping, properties of open-framework materials are closely correlated with their general chemical compositions, and structural and geometrical features. As such, a great emphasis has been placed on creating materials with new crystal structures, in contrast with doping of well-known structure types. Hence the focus of this study is on the introduction of novel chemical-physical functions to the crystalline porous solids by fully exploring and understanding fundamental structural features and their possible correlation to properties and functions.

The first part of this work presented here is on creating pure inorganic framework structures, specifically metal-chalcogenide supertetrahedral-cluster-based frameworks, together with a discussion on their structure-property relationships. A series of such molecular architectures have been built by directed assembly of supertetrahedral clusters that can be viewed as artificial atoms with tunable radii. A new class of "hollowed-out bulk semiconductor" materials has been achieved. Both experimental evaluations and theoretical simulations on some pure phase compounds have been performed. Based on these new structures, the relationship between materials' structural features and their optoelectronic properties is discussed.

The later parts of the work presented here deal with hybrid porous solids, specifically synthesis, characterizations and novel functions of metal-organic framework materials (MOF). By designed synthesis, one MOF material with unusual 4-level structural hierarchy was assembled. Its magnetic property was evaluated, revealing an interesting geometry-induced magnetic frustration mechanism. Also, a catalytically active MOF was synthesized and characterized. Most importantly, single-crystal X-ray crystallography has been employed to capture the detailed molecular conformations of reaction intermediates on the active sites, which represents a powerful example of using a MOF-based novel methodology to elucidate catalytic mechanisms.