1. School of Chemistry & BiochemistryGeorgia Institute of Technology Atlanta, Georgia U.S.A.
2. present address: Intel Corporation, Chandler, AZ U.S.A.
3. X-Ray Crystallography CenterDepartment of Chemistry, Emory University Atlanta, Georgia U.S.A.
4. School of Chemistry & BiochemistryGeorgia Institute of Technology Atlanta, Georgia, U.S.A.