Cohesion of BaReH$_9$ and BaMnH$_9$: Density Functional Calculations and Prediction of (MnH$_9)^{2-}$ Salts

TL;DR

This study uses density functional calculations to analyze the bonding and properties of BaReH$_9$ and predicts the potential synthesis of (MnH$_9)^{2-}$ salts with high hydrogen content, based on similarities in bonding.

Contribution

It provides a detailed bonding analysis of BaReH$_9$ and predicts the feasibility of synthesizing (MnH$_9)^{2-}$ salts with high hydrogen content.

Findings

BaReH$_9$ exhibits high coordination due to Re 5$d$ and H $s$ orbital bonding.

BaMnH$_9$ shows similar bonding and cohesion to BaReH$_9$.

Potential for synthesizing high hydrogen content salts exceeding 10 wt%.

Abstract

Density functional calculations are used to calculate the structural and electronic properties of BaReH$_9$ and to analyze the bonding in this compound. The high coordination in BaReH$_9$ is due to bonding between Re 5$d$ states and states of $d$-like symmetry formed from combinations of H $s$ orbitals in the H$_9$ cage. This explains the structure of the material, its short bond lengths and other physical properties, such as the high band gap. We compare with results for hypothetical BaMnH$_9$, which we find to have similar bonding and cohesion to the Re compound. This suggests that it may be possible to synthesize (MnH$_9)^{2-}$ salts. Depending on the particular cation, such salts may have exceptionally high hydrogen contents, in excess of 10 weight %