Recent years have witnessed truly remarkable achievements in many fields of science and technology. Among these, advances in the area of new materials and macromolecules with specific designed features have been particularly dramatic. Theoreticians are now seriously proposing the cognizant design and unidirectional fabrication of atomic and molecular assemblies on the nanometer scale with atomic precision. The design and construction of large-scale molecular arrays is clearly the enabling science for developing the true potential of nanotechnology. While it is expected that the realization of this potential may be far in the future, nonetheless, the structures and molecular assemblies proposed are serving as goals for both theoretical and experimental studies. Along the way, however, many of the smaller molecules and assemblies which are intermediate in the fabrication of larger structures are fully expected to provide significant advances in a variety of areas, including optoelectronic applications, medicine and new advanced materials.
Most of the work thus far in nanoscale design has employed carbon as the primary structural element. Diamondoid and other bucky-based structures are receiving a great deal of attention due to their chemical and physical properties. Boron-based materials, however, have been comparatively neglected in this aspect. Of special interest are the polyhedral boron cluster systems. The design and fabrication of new three dimensional nanoscale molecular architectures may, however, best be accomplished through the use of these polyhedral and related building blocks. When viewed from a nanoscale macrostructural perspective, these polyhedral cluster compounds and assemblies provide extraordinary structures with an unique array of critical nanostructural properties.
One nanomolecular synthon based upon boron polyhedra which we have designed and synthesized is based upon a bis-polyhedral ring structure shown in the figure (left). This simple unit can then be straightforwardly connected through unidirectional synthetic pathways to yield the rings, rods, helices and other more complex architectural components shown. These remarkable structures and compounds are constructed of structurally simple and synthetically viable smaller synthon elements. These structures, along with synthetic pathways and potential applications, will be described in detail in this paper.