Research Interests - Robert D. Pike

        Some Background Concepts

Inorganic Chemistry is the study of compounds based on elements other than carbon.  Strange as it may seem, many inorganic compounds (including virtually all of the ones we study) have carbon-based groups in them.  The distinction between inorganic and organic compounds is sometimes a matter of taste, but if there's at least one metal atom in a compound, it's inorganic to me.  Inorganic compounds are found in the earth (minerals, metal ores, metals, clays), in the water (dissolved salts) and air around us, in living things (salts, metal-containing proteins, such as hemoglobin, bone), and in countless consumer products (metals, semiconductors, concrete, glass).

Why metals?  Metals are notorious for producing interesting chemical behavior. They can catalyze reactions (causing them to proceed much faster).  They can cause electrons to be transferred, they can bind to several molecules at once ("directing traffic" during a reaction), and very often they can reverse the usual reactivity of organic molecules.

Organometallic Chemistry is a subset of inorganic chemistry, in which compounds feature metal-to-carbon bonds.  Organometallic compounds are relatively uncommon in nature, however, one such compound (Vitamin B12, containing cobalt) is an essential human nutrient.  Organometallic compounds have found use in industrial chemistry as catalysts (see below).

Polymer Chemistry is the study of long chain molecules.  Many important biomolecules are polymer, including DNA, RNA, and proteins.  Synthetic polymers are organic (carbon-based) chains that form the basis for most commercial plastics.  Inorganic polymers are far less common than organic polymers, but there are well-known examples, such as silicones.
 

Our Research

Inorganic Polymers. We are interested in producing new inorganic polymers which have metal atoms within the backbone of the polymer chain.  Depending on their chemical construction, these polymeric networks may be chain-like (one dimensional), sheet-like (two dimensional), or fully networked (three dimensional).  These forms are illustrated in the picture below; metal atoms (represented by red dots) are linked together by carbon-based organic units (represented by blue ovals).

Molecular growth in one, two, or three dimensions is controlled by terminating groups (shown as green lines).  Polymers that incorporate metal atoms may combine some of the desirable properties of organic polymers (strength, flexability, etc.) with the desirable properties of metals (electrical and thermal conductivity).  This combination of characteristics could lead to applications as conducting plastics.  It is also apparent that many of these new materials have inherent pores, which are surrounded by metal atoms.  This should increase the "traffic directing" ability mentioned above, and could lead to applications as catalysts for chemical reactions.

Metal-organic networks have potential applications as catalysts for organic reactions. The porous structure of the network can trap the substrate. Next, the active metal center catalyzes the reaction. After the reaction is complete, the metal catalyst can be easily removed by filtration, conserving expensive catalyst and improving product purity.





Shown below is a sampling of some of the metal-organic network compounds that our group has produced. The views are from X-ray crystallography. this technique produces a photograph-like view of the atom positions in space via diffaction of X-rays from a crystal of the compound. The atoms in light blue are copper. The large atoms in purple, red, yellow, or green are halogens (Cl, Br, I) and the structures in grey with occasional red and blue atoms are the organic linker groups.

















Polymer Additives. We are also exploring the used of certain metal compounds to suppress the evolution of smoke and flame during poly(vinyl chloride) (PVC) combustion. PVC is one of the two highest production commercial polymers worldwide.  It is used in construction and electric wiring.  Although PVC itself does not burn, its decomposition at high temperatures produces dangerous smoke and byproducts which do burn.  We are developing metal-based additives which are designed to crosslink the polymer chains of decomposing PVC, rendering them more stable toward decomposition.  This process is illustrated below.