We are studying two different groups of transition-metal complexes: polynuclear “host” molecules with well defined cavities, and volatile metal-organic compounds that can be used to prepare electronic materials.

Metal-Organic Supramolecules

Here we use organic bridging ligands to join two or more metal atoms into hollow “hosts” into which “guest” molecules can fit. Our goal is to use the hosts as catalysts for reactions of the guests (similar to the way metalloenzymes work), or as sensors for small guest molecules.

This work began with our studies of host-guest reactions of bis(β-diketone) complexes such as Cu₂(NBA)₂, as shown in the sketch below:

We are now using other β-diketones that can produce larger rings, 3-dimensional molecules, and crystalline porous framework solids. For example, the bis(β-diketone) m-pbprH₂ yields a “molecular square” on reaction with Cu²⁺. This material is just the right size (diameter ~1.4 nm) to fit buckminsterfullerene (C₆₀). See diagram below.

Another ligand we have studied is “pyacH”, which has a β-diketone attached to pyridine so that the two groups can bind to two different metals. This ligand reacts with Cu²⁺ and Cd²⁺ to make a porous metal-organic framework, with still larger pores:

To develop new catalysts based on these supramolecules, we are now preparing “cages” that contain catalytically active metals such as Rh. The sketch below illustrates one approach, with “arms” (shown in blue) that are expected to provide selective access to the catalytic site for specific substrate molecules.

Electronic Materials

New approaches are needed for making copper and other highly conductive materials for use in the next generations of integrated circuits. Our approach is chemical vapor deposition (CVD), in which a volatile “precursor” passes over a hot silicon wafer and reacts to form a thin film of Cu metal. the desired material. For example, the copper(I) cluster amides [CuNR₂]₄ (e.g., R = SiMe₃, i-Pr) can be used for Cu CVD, and they are also photo­sensitive.