Structure and Electron Counting in Ternary Transition Metal Hydrides

Abstract

A large number of ternary hydrides of transition metals and alkali or alkaline earth metals have been synthesized and structurally characterized in the last twenty years. These compounds exhibit a puzzling variety of compositions, transition metal coordination numbers, transition metal coordination geometries, and distribution of hydrides within and outside of the transition metal coordination sphere. Valence Bond (VB) concepts form a theoretical framework for understanding, at least partially, some of the dominant trends observed among various transition metal hydride structures. Extrapolation of these concepts suggests that synthesis of ternary metal hydrides with formal electron counts at the transition metal exceeding 18 electrons may be feasible.

Phase transformations of Mg2NiH4 at high-pressure thermal treatment

“…In order to create new ternary compounds, Firman and Landis [2] suggested the possibility that ternary metal hydrides with formal electron count at the transition metal of 20 or more can be isolated, especially at higher hydrogen pressures, based on their valence bond model [3,4]. Also Bronger [5] discussed the increasing oxidative power of hydrogen with increasing pressure thus stabilizing higher oxidation states of the transition metals in the complex.…”

Novel Magnesium-Manganese Hydrides Prepared by the Gigapascal High Pressure Technique

“…[4][5][6] These experiments were performed at relatively low hydrogen pressures, and thus the chemical reactions require longer time. Bronger, Friman and Landis 7,8) have reported that the formation of complex metal hydrides with higher hydrogen content can be attributed to increase in the oxidative power of hydrogen with increasing hydrogen pressure. It was also reported that high-pressure techniques were applied to the Mg 2 Ni-H and Ca-Mg-Ni systems under mechanical pressures of 5-6 gigapascal (GPa).…”

On the Extreme Oxidation States of Iridium

“…A useful review of solid hydrides A x M y H z was published by Firman and Landis 25. The formal electron count at M could range from 14 to 18.…”