Alexandra Lieb

SYNTHESE, KRISTALLSTRUKTUR UND FESTKORPER-NMR-SPEKTROSKOPISCHE UNTERSUCHUNGEN VON K5H(CN2)3

K5H(CN2)3 wurde phasenrein durch Umsetzung von KHCN2 mit metallischem Kalium in flussigem Ammoniak sowie auch durch Reaktion von KNH2 mit Melamin C3N3(NH2)3 bei 320u200a°C synthetisiert. Die Kristallstruktur wurde mit Pulver- und Einkristallmethoden bestimmt: K5H(CN2)3, Raumgruppe Im3m, au200a=u200a795,68(7)u200apm, Zu200a=u200a2, R1u200a=u200a0,025, wR2u200a=u200a0,0438. K5H(CN2)3 ist im Festkorper aus K+ und CN-Einheiten mit der Symmetrie D∞h aufgebaut. Nach 1H- und 13C-Festkorper-NMR-Untersuchungen, temperaturabhangiger Impedanzspektroskopie sowie FTIR-Untersuchungen sind die Protonen nur schwach an die CN22–-Ionen gebunden. Die Protonenleitfahigkeit von K5H(CN2)3 steigt bei 70u200a°C sprunghaft an. n n n nSynthesis, Crystal Structure, and Solid State MAS-NMR Spectroscopic Investigation of K5H(CN2)3 n n n nSingle phase K5H(CN2)3 was synthesized by reaction of KHCN2 with metallic potassium in liquid ammonia or by reaction of KNH2 with melamine C3N3(NH2)3 at 320u200a°C, respectively. The crystal structure was determined from X-ray powder and single crystal data: K5H(CN)3, space group Im3m, au200a=u200a795.68(7)u200apm, Zu200a=u200a2, R1u200a=u200a0.025, wR2u200a=u200a0.0438. In the solid K5H(CN2)3 contains K+ and CN22–, the anions exhibit D∞h symmetry. According to 1H and 13C solid state MAS-NMR investigations, temperature dependent impedance spectroscopy, and FTIR spectroscopy the protons are only loosely bound to the CN22– ions. The proton conductivity shows a sharp increase above 70u200a°C.

Compressibility of the nitridosilicate SrYb Si4N7 and the oxonitridoaluminosilicates MYb Si4-xAlxOxN7-x (x=2; M = Sr, Ba)

The compressibilities of the nitridosilicate SrYb[Si(4)N(7)] and the oxonitridoaluminosilicates MYb[Si(4-x)Al(x)O(x)N(7-x)] (x = 2; M = Sr, Ba) were investigated by in situ high-pressure X-ray powder diffraction. Pressures up to 42 GPa were generated using the diamond-anvil cell technique. The title compounds are structurally stable to the highest pressure obtained. A fit of a third-order Birch-Murnaghan equation-of-state to the p-V data results in V(0) = 302.91 (6) A(3), B(0) = 176 (2) GPa and B = 4.4 (2) for SrYb[Si(4)N(7)]; V(0) = 310.4 (1) A(3), B(0) = 161 (2) GPa and B = 4.6 (2) for SrYb[Si(4-x)Al(x)O(x)N(7-x)]; and V(0) = 317.3 (5) A(3), B(0) = 168 (2) GPa and B = 4.7 (2) for BaYb[Si(4-x)Al(x)O(x)N(7-x)]. While the linear compressibilities of the a and c axes of BaYb[Si(4-x)Al(x)O(x)N(7-x)] are very similar up to 30 GPa, distinct differences were observed for SrYb[Si(4)N(7)] and SrYb[Si(4-x)Al(x)O(x)N(7-x)], with the c axis being the most compressible axis. In all of the investigated compounds the bulk compressibility is dominated by the compression behaviour of the tetrahedral network, while the size of the substituted cation plays a minor role.

Crystal structure of the high-pressure phase of the oxonitridosilicate chloride Ce4[Si4O3 + xN7 − x]Cl1 − xOx, x≃ 0.2

The structural compression mechanism of Ce4[Si4O3u2005+u2005xN7u2005−u2005x]Cl1u2005−u2005xOx, x≃ 0.2, was investigated by in situ single-crystal synchrotron X-ray diffraction at pressures of 3.0, 8.5 and 8.6u2005GPa using the diamond–anvil cell technique. On increasing pressure the low-pressure cubic structure first undergoes only minor structural changes. Between 8.5 and 8.6u2005GPa a first-order phase transition occurs, accompanied by a change of the single-crystal colour from light orange to dark red. The main structural mechanisms, leading to a volume reduction of about 5% at the phase transition, are an increase in and a rearrangement of the Ce coordination, the loss of the Ce2, Ce3 split position, and a bending of some of the inter-polyhedral Si—N—Si angles in the arrangement of the corner-sharing Si tetrahedra. The latter is responsible for the short c axis of the orthorhombic high-pressure structure compared with the cell parameter of the cubic low-pressure structure.