1. Contribution from the Department of Chemistry and Laboratory of Molecular Structure and Bonding, P.O. Box 30012, Texas A&M University, College Station, Texas 77842-3012, Department of Chemistry and Biochemistry, and Center for Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306-4390, Department of Chemistry, 1101 University Avenue, University of Wisconsin, Madison, Wisconsin 53706-1322, and the Max-Planck-Institut für Bioanorganische Chemie,...