A celebration of Harry B. Gray's 75th birthday

Harry B. Gray is one of the towering figures in modern chemistry. Harry's career has touched nearly every area of inorganic chemistry. His early research led to the development of molecular orbital theory for inorganic molecules. In a 1962 paper with C. J. Ballhausen, he first formulated the concept of metal–ligand multiple bonding. The Ballhausen–Gray model for metal–oxo bonding remains the standard to this day, receiving thousands of citations in the scientific literature since 1982. In this paper, along with two later papers, Harry derived valence orbital ionization energies and analytical orbital wave functions that enabled a generation of computational chemists to perform molecular-orbital calculations of the structures and reactivity of inorganic molecules. After a decade studying bonding, electronic structure, and spectroscopy in transition metal complexes, Harry moved into bioinorganic chemistry with investigations of the active sites and reactivity of metalloproteins. Harry's singular achievement in bioinorganic chemistry is the demonstration of the phenomenon of long-range electron tunneling in proteins, and his experimental elucidation of the chemical principles that regulate the efficiencies of these vital transformations. The current understanding of long-range electron tunneling in biology derives in large measure from a 30-year research effort in Harry's laboratory. During a 50-year research career marked repeatedly by groundbreaking innovations in both theory and experiment, Harry Gray has earned a position among that elite group of scientists who have fundamentally changed the way chemists look at their field