Hydrogen Bonds Involving Transition Metal Centers Acting As Proton Acceptors

A short review of the most remarkable results which have recently reported M----H-X hydrogen bonds, along with a systematization of their structural and spectroscopic properties, is provided in this paper. These M----H interactions are substantially different from the "agostic" M----H ones, and their differences are commented on, setting up criteria that permit their clear differentiation in order to avoid some of the misidentifications that occurred in the past.