A double salt of cesium platinum and cesium hydride has been made for the first time. Simple salts, like sodium chloride, contain one positively charged element and one negatively charged element. This double salt contains two anions (Pt2- and H-) and one cation (Cs+). Einstein’s Theory of Relativity helps explain how this is possible. The average radial velocity of electrons closest to the nucleus is larger for heavier elements, which leads to a higher effective mass that then leads to a smaller than expected atomic radius, and changes in chemical behavior. The influence of relativity on 6th row element chemistry becomes apparent in the color of gold, and unusually high and low oxidation states, including the possibility to form ionic compounds containing metal anions. Here, the reaction of platinum with cesium hydride in an excess of cesium yielded transparent cherry-red Cs9Pt4H crystals. This is the first reported ternary compound containing platinum in the oxidation state –2 and exhibiting the maximum possible charge separation. This discovery puts into question the boundaries between polar intermetallics and salts.
Cover art showing V. Smetana and A.-V. Mudring's work in Angewandte Chemie
Cesium Platinide Hydride 4Cs2Pt.CsH: An Intermetallic Double Salt featuring Metal Anions