Titelbild

Abstract

Das Titelbild zeigt schematisch die Synthese und Zersetzung von Strontiumdiazeniden. Die Kristallstrukturen der unter hohen N2‐Drücken (bis 5500 bar) phasenrein hergestellten Diazenide wurden durch Neutronenbeugung bestimmt. Im Bildhintergrund ist ein Ausschnitt des Beugungsdiagramms von SrN2, rechts oben die Koordination der Diazenid‐Ionen abgebildet. Der N‐N‐Abstand in den Diazenid‐Ionen beträgt in beiden Verbindungen 122 pm. Einzelheiten zur Synthese und Charakterisierung der Strontiumdiazenide sind in der Zuschrift von G. Auffermann, Y. Prots und R. Kniep auf S. 565 ff. zu finden.

Inelastic Neutron Scattering Spectroscopy of Diazenides: Detection of the NN Stretch

“…[1] Recently, high-pressure synthesis led, for the first time, to single-phase products of diazenides, thus showing that [N 2 ] 2À ions are stable in binary systems. [2,3] Using this method, it was possible to synthesise nitrogen-rich compounds such as SrN (black-grey) and SrN 2 (brown), which are free of impurities such as oxygen, hydrogen or carbon. [4] The samples were prepared by heating the ambient pressure nitride Sr 2 N in a molybdenum boat under a N 2 atmosphere at 920 K for 72 hours in an autoclave, varying the reaction pressure from 400 bar (SrN) up to 5500 bar (SrN 2 ).…”

“…[4] The samples were prepared by heating the ambient pressure nitride Sr 2 N in a molybdenum boat under a N 2 atmosphere at 920 K for 72 hours in an autoclave, varying the reaction pressure from 400 bar (SrN) up to 5500 bar (SrN 2 ). [2] After structural characterisation by elastic neutron diffraction experiments [2] , the N 2 dumbbells became obvious. The crystal structures of both diazenides can be topologically deduced from that of Sr 2 N (CdCl 2 structure type): in SrN (Sr 4 [N] 2 [N 2 ]) one half of the free octahedral holes between the Sr 2 N layers are occupied by diazenide ions in an ordered manner, whereas in SrN 2 all octahedral holes of the nearly close-packed strontium matrix are occupied by N 2 dumbbells.…”

“…To assign the remaining features, we use the correlation method. [9] From the crystal structure, [2] this predicts two acoustic modes (A 2u and E u ), two optic translational modes (A 2u and E u ) and a librational mode of the diazenide ion (E g ) in addition to the NN stretch (A 1g ). Since librations usually occur at higher energies than translations, we assign the libration to the band at 337 cm À1 .…”

“…[13] To test the validity of the approach, we calculated a number of N 2 species in the gas phase as shown in Table 1, and as can be seen, the calculations well reproduce the observed frequencies and bond lengths. For the N 2 2À species we additionally assumed singlet N 2 2À because for both compounds magnetic susceptibility measurements [2] show a weak temperature-independent paramagnetism, thus indicating singlet N 2…”

“…except for N 2À 2 , where the bond length is from ref [2]. and the frequency is from this present work.…”