1. Departments of Chemistry and Biology, Indiana University, Bloomington, Indiana 47405, A.N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences, 28 Vavilova Street, Moscow 119991, Russia, Institute of Crystallography, Russian Academy of Sciences, 59 Leninsky pr., 117333 Moscow, Russia, EMBL, Outstation, Notkestrasse 85, D-22603 Hamburg, Germany, and Applied Materials Inc., 3330 Scott Boulevard, M/S 0690, Santa Clara, California 95054