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42594-AC3
Synthesis and Investigation of Chiral, Heterometallic Metal-Organic Frameworks
The major research activities from this grant in the last fiscal year have been in the exploration of metal-organic frameworks (MOFs). Two specific activities were pursued: a) the proposed work, which uses dipyrrinato metalloligands to construct MOFs, and b) a new project, whereby MOFs are functionalized by a postsynthetic modification approach. The latter project is a new, albeit related, research are for this project that we believe will have a significant impact in the area of MOF chemistry. Our findings have been published in high-quality, peer-reviewed journals and presented at conferences and university research talks.
In one report from our studies on tris(dipyrrinato) metalloligands, we showed that racemic and chiral metalloligands can lead to entirely different phases under the solvothermal conditions. Our studies showed that a rac-cobalt(III) tris(dipyrrinato) metalloligand, when combined with zinc(II) under solvothermal conditions, could make two different MOF structures. However, use of the Δ- or Λ- versions of the tris(dipyrrinato) metalloligand under the same reaction conditions produced only amorphous solids (Sergio J. Garibay, Jay R. Stork, Zhenqiang Wang, Seth M. Cohen, and Shane G. Telfer, Chem. Commun. 2007, 4881-4883). In related, unpublished findings, we have found that the same Δ- or Λ-cobalt(III) tris(dipyrrinato) metalloligand can for a chiral MOF under solvothermal conditions when combined with manganese(II). In this case, the rac-metalloligand does not form a MOF. We are currently working to understand these systems in more detail.
In a another study we have described the formation of unusual, group 13/transition metal heterometallic MOFs. We have previously described Ga(III) and In(III) tris(dipyrrinato) complexes that emit green light upon excitation with UV light at room temperature, with lifetimes in the low nanosecond range. In this more recent study we showed that related complexes could be constructed into MOFs using silver(I) ions, generating a number of (6,3) and (10,3) net structures (Jay R. Stork, Van S. Thoi, and Seth M. Cohen, Inorg. Chem. 2007, 46, 11213-11223).
Finally, in a new project area, we have developed a strategy to produce large families of functionalized MOFs, by using a postsynthetic modification approach. Preliminary results demonstrate that a model system, IRMOF-3 (IRMOF = isoreticular metal-organic framework) that contains primary amino groups within its cavities, can be modified with anhydrides (Zhenqiang Wang and Seth M. Cohen, J. Am. Chem. Soc. 2007, 129, 12368-12369) and isocyanates to form amide and urea products, respectively. The products of the reactions with IRMOF-3 have been meticulously characterized, proving that the MOFs remain crystalline with large surface areas. We expect that this approach will have wide-ranging implications in the areas of gas sorption, solid-state catalysts, gas sorption, and drug delivery applications. A current ACS-PRF AC grant is in submission to support these efforts.
The research program under this grant has trained students in the area of inorganic, supramolecular, and solid-state chemistry. Undergraduate students, graduate students, and postdoctoral fellows working on the project have been trained in these areas, as well as in critical thinking and problem solving. Success in undergraduate training is illustrated by Van S. Thoi, who has authored or co-authored several publications on this project and is presently deciding on a university to pursue graduate studies in inorganic chemistry (she has been admitted to U.C. Berkeley, Stanford, M.I.T. and Northwestern U. among others). All participants in this project have presented their results at regional and national meetings.
