Before the advent of the present computer age,"" chemistry was almost exclusively an experimental science. The bonding in molecules, particularly those involving carbon, could be described (and new molecules conceived) using rather simple concepts. Organic compounds are based on tetrahedral, trigonal, and linear digonal building blocks. Systems distorted from these ideal geometries are strained,"" according to the textbooks. Drastic deviations are too high in energy to exist.
Beginning in the1970''s, quantum chemical computations afforded opportunities to examine basically different bonding arrangements, such as those with carbon atoms in planar tetracoordinate environments. Computer predictions of such unconventional bonding led to numerous experimental verifications. The computational design of even more outlandish structures then led to the prediction of planar pentacoordinate, planar hexacoordinate, and even planar heptacoordinate carbon molecules! Possibilities for the computational exploration of molecules with many different types of unconventional structures abound. Examples involving extended systems with planar and nonplanar hypercoordinate carbons and other elements, novel sandwich structures including those with multiple layers and other extensions, with monolayer metal atom sheets, and those comprised of cage molecules are among those suggested in the proposal. The anticipated impact may be considerable. While truly new compositions of matter cannot have any immediate use, such uses often develop later based on the unusual properties which often accompany unusual bonding. The immediate impact is the realization that the chemical bonding principles long held to be inviolate can be extended and can reveal new worlds of chemical structures.
These projects are particularly instructive to undergraduates and to graduate students, since they demonstrate how fundamental chemical research can be carried out with computers (which involves far more than black box"" applications) and illustrates how imaginative, rule-breaking research lines can developed intellectually. Representative examples are included in graduate courses given by the senior personnel, and these courses also feature hands-on exercises such as the computation of planar tetracoordinate methane.
