Mn3+ in garnets III. Absence of Jahn-Teller distorition in synthetic Mn3+-bearing garnet

The crystal structure of a ternary Mn3+-bearing garnet, close to the composition Gross34 Spess26 CaMnGt40 has been refined to a weighted R-value of 0.051 for 440 unique reflections. The lattice constant is 11.867(1) A, fractional atomic parameters for oxygen are x=0.0374 (2), y=0.0470 (2), and z=0.6532 (2). Refinement of site occupancies gave 0.81 (3) Ca+0.19 (3) Mn2+ in the eight coordinated site 24c and 0.64 (2) Al+0.36 (2) Mn3+ in the octahedral site 16a. No deviation from the cubic space group Ia3d has been observed, the Mn3+-bearing YO6 octahedron is nearly regular. Thus, the presence of the 3d 4-configurated ion Mn3+ does not cause Jahn-Teller distortion in this garnet structure.

Structure and polarized absorption spectra of Mn3+-substituted andalusites (viridines)

Strukturelle Untersuchungen an Arsenbrackebuschit

Rontgenographische Untersuchungen an Einkristallen von Arsenbrackebuschit, Pb2(Fe, Zn)(OH, OH2) (AsO4)2 (mit Fe∶Zn∼2∶1), ergaben die RaumgruppeP21/m mita 0=7,763(1) A,b 0=6.046(1) A,c 0=9.022(1)A, β=112,5(1)°,V=391,2(1) A3,Z=2 und ρ x =6,54 g/cm3. Dreidimensionale Fouriersynthesen und Verfeinerungen nach der Methode der kleinsten Quadrate bis zu einemR-Wert von 0,073 zeigten, das das neue Mineral strukturell einer Gruppe von Blei-Mineralen der allgemeinen Formel Pb2 Me(Z) (XO4) (YO4) — mitMe=Cu2+, Mn2+, Zn2+, Fe3+;X=S, Cr, V, As;Y=P, As, V;Z=OH, OH2 — zuzuordnen ist. Vertreter dieser Gruppe sind z. B. Tsumebit Pb2Cu(OH) (SO4) (PO4), Vauquelinit Pb2Cu(OH) (CrO4) (PO4) und auch Brackebuschit …

Die Kristallstruktur von Brenkit, Ca2F2CO3

Brenkit, Ca2F2CO3, kristallisiert in der RaumgruppePbcn mita=7,650(2),b=7,550(2) undc=6,548(2) A. Die Kristallstruktur wurde bis zu einemR-Wert von 0,023 fur 840 unabhangige Reflexe verfeinert. Kalzium ist unregelmasig von vier Fluor-und drei Sauerstoff-Atomen koordiniert mit mittleren Ca-F und Ca-O-Abstanden von 2,388 A bzw. 2,426 A. Die CO3-Gruppe ist vollstandig eben mit C-O-Abstanden von 1,279 (2×) und 1,297 A.

New data on the mercury antimony mineral shakhovite: Chemical composition, unit cell and crystal structure

A new investigation of the mercury antimony mineral shakhovite yielded space groupIm witha=4.871(1),b=15.098(3),c=5,433(1) A and β=98.86(2)°. The determination of the crystal structure gave a cell content of Hg8Sb2O12. Since the presence of Hg2-groups indicates that shakhovite is a pure Hg(1) compound and the infrared spectrum shows an absorption band at 3440 cm−1 which is due to the OH-stretching frequency, it is assumed that there are six oxygen atoms and six OH-groups in the unit cell. Thus the chemical formula of shakhovite reads Hg4Sb(OH)3O3 with two formula units per unit cell. The Hg−Hg distance in the Hg2-group is 2.543 A, each mercury atom has a close oxygen neighbour at 2.160 and …