Dr. Robert H. Crabtree, Department of Chemistry, Yale University, is supported by the Inorganic, Bioinorganic, and Organometallic Program of the Chemistry Division for a study of novel types of hydrogen bonding that occur between a conventional proton donor, an OH or NH group, and an unconventional acceptor, an M-H or B-H bond (M = Re, Ir). Preliminary data show that these bonds are short, strong, and bent at the MH or BH unit. During this project examples of inter- and intramolecular M-H...H-M' and M-H...M' complexes will be synthesized and the hydrogen bonding in them analyzed using spectroscopic and kinetic data. Specific issues that will be addressed target include the stabilization of HF complexes, restricting rotation in dihydrogen complexes by inducing H-bond formation, perturbing the fluxionality rates of polyhydrides, and increasing the rate of nucleophilic attack at CO. A solvatochromic method will be evaluated for characterizing outer sphere H-bonding interactions. Interactions between atoms and molecules are the most important phenomena that determine the properties of matter. One type of interaction is called 'hydrogen bonding.' Hydrogen bonding has been known for many years and is responsible, for example, for many of the properties of ice and liquid water. Recently, new types of hydrogen bonds that involve metal-hydrogen units have been discovered. This project aims at discovering general trends in these new types of hydrogen bonds and at developing novel hydrogen bonding situations in order to effect useful chemical transformations.