This award in the Chemical Synthesis (SYN) program supports work by Professor Philip P. Power at the University of California, Davis to carry out fundamental studies on the reversible reactions of unsaturated molecules with multiple bonded heavier main group and transition metal species. These studies focus on how small molecules containing multiple bonds interact in reversible processes with a group of elements that have not been well studied up to now. Examples of the small unsaturated (that is, multiple bonded) molecules to be studied include ethylenes, acetylenes, carbon monoxide and carbon dioxide. These molecules are of great importance in industrial catalytic cycles which usually use transition metal compounds of metals such as titanium, rhodium or platinum as catalysts.
The studies will focus on abundant and inexpensive elements such as aluminum or silicon whose use may achieve better catalysis together with energy savings. In addition, the award supports the training of several undergraduate and graduate students and postdoctoral fellows in numerous practical research skills as well as in independent scientific thinking.
The main objectives of the work were to synthesize, characterize, and investigate the physical and chemical properties of new compounds of the main group and transition metals (two different classes of elements in the periodic table) whose central atom is bound only to two other atoms or groups of atoms called ligands. Such two-coordinate compounds are of interest because they are expected to possess unusual bonding, high reactivities, or magnetism as a result of the fact that the central atom environment is more open and accessible than that which is normally found in compounds where the central atom is usually bound to four or more ligands. During the period of the award, numerous two-coordinate transition metal (e.g. chromium, iron, cobalt, or nickel) compounds were synthesized which exhibited previously unknown high levels of magnetism for compounds of these elements. This is due to the fact that the electrons on the central atom can circulate freely, since they are bound to only two neighboring atoms that do not interfere with electron circulation. The circulating electrons generate a magnetic field such that the molecule can display some of the characteristics of a miniature magnet. This property is called molecular magnetism. Due to the extremely small size of the molecule and their magnetic character, they have the potential to greatly enhance data storage capability, and may eventually find use in data storage devices. At present, the compounds only exhibit molecular magnetism at very low temperatures. We have been able to show that changing the type of groups attached to the central atom affect the temperature at which they can display molecular magnetism. We have also shown that angles at which the groups are attached to the central atom have a large effect on the magnetism. In addition, we have shown that weak interatomic forces (called dispersion forces) can exert a strong influence on the structure of the molecules, often in ways that are counterintuitive. The main group molecules, derivatives of elements such as aluminum or silicon, are generally non-magnetic, but they display a highly unusual reactivity with industrially important small molecules such as hydrogen, ammonia, ethylene, or carbon monoxide. These findings are of importance for the development of inexpensive new catalysts that are based on earth-abundant elements, rather than precious metals.
