Carbon anions in solution: C(2)(2-) dumbbells are well-known in solid-state compounds. The crystallization of the title compounds now shows that acetylide ions are existent in solution and therefore chemistry with small dissolved carbon anions may be within reach.

Structural changes of Li2C2 under pressure were studied by synchrotron x-ray diffraction in a diamond anvil cell under hydrostatic conditions and by using evolutionary search methodology for crystal structure prediction. We show that the high pressure polymorph of Li2C2, which forms from the Immm ground state structure (Z = 2) at around 15 GPa, adopts an orthorhombic Pnma structure with Z = 4. Acetylide C2 dumbbells characteristic of Immm-Li2C2 are retained in PnmaLi2C2. The structure of Pnma-Li2C2 relates closely to the anticotunnite type structure. C2 dumbbell units are coordinated by 9 Li atoms, as compared to 8 in the antifluorite structure of ImmmLi2C2. First principles calculations predict a transition of Pnma-Li2C2 at 32 GPa to a topologically identical phase with a higher Cmcm symmetry. The coordination of C2 dumbbell units by Li atoms is increased to 11. The structure of Cmcm-Li2C2 relates closely to the Ni2In type structure. It is calculated that Cmcm-Li2C2 becomes metallic at pressures above 40 GPa. In experiments, however, Pnma-Li2C2 is susceptible to irreversible amorphization.

Three new alkali metal acetylides CsNaC 2 , CsKC 2 , and CsRbC 2 have been synthesized and characterized by means of synchrotron powder diffraction studies. As a new synthetic approach, the binary alkali metal acetylides were reacted at relatively low tempera-* Prof. Dr. U. Ruschewitz

Professor Paul Hagenmuller zum 80. Geburtstag gewidmet Inhaltsu È bersicht. Die phasenreinen Verbindungen auf dem quasibina È ren Schnitt Nd 2 O 3 ±SeO 2 : Nd 2 Se x O 3+2x im thermodynamischen Gleichgewicht wurden durch Festko È rperreaktion dargestellt und durch Ro È ntgendiffraktometrie, IR-Spektroskopie und DSC-Messungen charakterisiert. Dabei wurde neben den bereits bekannten Phasen Nd 2 Se 4 O 11 , Nd 2 Se 3,5 O 10 , Nd 2 Se 3 O 9 und Nd 2 SeO 5 die Existenz einer wei-teren Phase Nd 2 Se 1,5 O 6 nachgewiesen. Die thermische Zersetzung der Phasen wurde durch Gesamtdruckmessungen beschrieben und aus den Zersetzungsdruckfunktionen wurden mit Hilfe der gemessenen C p -Funktionen die thermodynamischen Daten hergeleitet. Das Zustandsdiagramm und das Barogramm wurden aus den DSC-und Gesamtdruckmessungen ermittelt.Abstract. The ternary pure phases on the line Nd 2 O 3 ±SeO 2 : Nd 2 Se x O 3+2x in the thermodynamically equilibrium have been synthesized by solid state reactions and characterized by X-ray powderdiffration, IR-spectroscopy and DSCmeasurements. The existence of a new phase Nd 2 Se 1,5 O 6 was demonstrated beside the known phases Nd 2 Se 4 O 11 , Nd 2 Se 3,5 O 10 , Nd 2 Se 3 O 9 and Nd 2 SeO 5 . The thermical decomposition properties of the compounds have been determined by total pressure measurements and the thermodynamical data of the compounds have been derived from their decomposition function and C p -values, which were measured too. The phase diagram and the phase barogram have been established using the result of DSC and total pressure measurements.

Kohlenstoffanionen in Lösung: C22−‐Hanteln sind in Festkörperverbindungen seit langem bekannt. Mit der Kristallisation der Titelverbindungen konnte nun gezeigt werden, dass Acetylidionen auch in Lösung existieren. Dadurch rückt eine Chemie mit kleinen gelösten Kohlenstoffanionen in greifbare Nähe.