Welf Bronger

Rb3ReH10, ein neues Hydrid des siebenwertigen Rheniums - Hochdrucksynthese und Kristallstruktur

Uber eine Reaktion von Rubidiumhydrid mit Rhenium in einer Wasserstoffatmosphare bei einem Druck oberhalb von 4000 bar konnte im Temperaturbereich zwischen 700 und 870 K das ternare Hydrid Rb3ReH10 dargestellt werden. Rontgenographische Untersuchungen an einer pulverformigen Probe sowie Neutronenbeugungsexperimente an der deuterierten Verbindung fuhrten zur Strukturaufklarung. Bei Raumtemperatur existiert eine kubische Atomanordnung, die entsprechend der Schreibweise [ReD9]DRb3 eine dem Perowskit analoge Struktur besitzt. Das von den Deuteriumatomen gebildete Koordinationspolyeder der Rheniumatome kann kristallographisch uber eine statistisch unterbesetzte Belegung von zwei 24-zahligen Punktlagen beschrieben werden. In einer rhombischen Tieftemperaturmodifikation nehmen die Deuteriumliganden die geordneten Positionen eines einfach uberdachten vierseitigen Antiprismas ein. Die Verbindung zeigt diamagnetisches Verhalten. Rb3ReH10, a New Rhenium(VII) Hydride – High Pressure Synthesis and Crystal Structure The ternary hydride Rb3ReH10 can be synthesised by reacting rubidium hydride with rhenium in a hydrogen atmosphere under a pressure of above 4000 bar in a temperature range between 700 and 870 K. X-ray investigations on powder samples and elastic neutron diffraction experiments on the deuterated compound led to the crystal structure. According to the formula [ReD9]DRb3 the atomic arrangement of the room temperature modification corresponds to that of the perowskite structure type. The coordination polyhedron of the hydrogen atoms that surround each rhenium atom can be described crystallographically as a statistical occupation of two 24-fold positions with hydrogen. In the orthorhombic low-temperature modification the deuterium ligands are arranged in ordered positions. They form monocapped square antiprisms. Magnetic susceptibility measurements revealed Rb3ReD10 to be diamagnetic.

Spatial chemistry of the aluminium-platinum compounds: a quantum chemical approach

It was shown by quantum chemical calculations (TB-LMTO-ASA) for the compounds of the system aluminium—platinum that the Baders atomic volumes and charges of platinum and aluminium atoms change with the concentration. This behaviour is in contrast to Vegards approach which assumes constant volume increments of the constituents in the whole concentration region. Introduc ing the variation of the atomic volume with the composition extends the Vegards approach and allows non-linear and even non-monotonic slope of the atomic volume vs concentration dependency, which is observed experimentally in several systems.

New alkali metal osmium- and ruthenium hydrides

Abstract Previously unknown ternary metal hydrides AxOsHz and AxRuHz (A=alkali metal) were synthesized by the reaction of alkali metal hydrides with osmium or ruthenium under a hydrogen pressure up to 6000 bar. The crystal structures of the hydrides were determined using a combination of X-ray and neutron diffraction experiments with deuterated compounds on powdered samples. Na3OsH7 and Na3RuH7 crystallize at room temperature in a tetragonal structure type (space group: P42/mnm), which is characterized by isolated [OsH7]- or [RuH7] anions. The coordination polyhedron formed by the seven hydrogen (deuterium) ligands can be described as a distorted pentagonal bipyramide. Magnetic susceptibility measurements on Na3OsH7 in the temperature range between 3.5 K and room temperature revealed a weak temperature independent paramagnetism. Quantum mechanical calculations confirm these facts and show in detail that the large value of the spin–orbit coupling constant is responsible for the magnetic behaviour of these compounds with the oxidation state +4 for the transition metal atoms. With the heavier alkali metals transition metal(IV) hydrides A3−δOsH7−δ and A3−δRuH7−δ could be synthesized. They crystallize with isotypic atomic arrangements related to the cryolite structure type. Highest hydrogen pressure during the reaction leads to the osmium(VI) hydrides Cs3OsH9 and Rb3OsH9. The atomic arrangement is characterized by [OsH8] polyhedra intercalated in a cubic HA3 framework which corresponds to the ReO3 structure type. Within these polyhedra the hydrogen ligands occupy two 24-fold positions with a statistical distribution.