Role of hydrogen in stabilizing new hydride phases or altering old ones

The role of hydrogen impurities in many of the more active metals in the formation of ternary compounds has often not been considered or recognized when these reactants do not contain significant metal hydride phases. This is a particular problem because most phase identifications or structure determinations have traditionally depended on X-ray diffraction means. Extended investigations have established that the alkaline-earth metals, plus some other divalent metals, have evidently often contributed substantial amounts of hydrogen. and this feature has led to numerous erroneous reports of supposed binary phases that form with the main-group (p) elements. Methods of detection and some ready means to avoid these problems will be described. The particularly serious examples that occur among phases reported with beta-Yb5Sb3, Mn5Si3, and Cr5B3-type binary structures for pnictogen (As-Bi) and tetrel (Si-Pb) elements are detailed for 32 examples. Fluoride has proven to be useful as a stand-in for hydride in a variety of these systems. (C) 2002 Elsevier B.V. All rights reserved.