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Ga1.4Ge2.86Mn3.6O12Sio.14 (1), cubic, laid (No. 230), a = 12.043(3) k,V= 1746.6 Â, Ζ = 8, Rgt(F) = 0.028, wRrdF 2 ) = 0.062, 7 = 300 K. Gai.56Ge3Mn3.440i2 (2), cubic, Ia3d (No. 230), a = 12.049(3) Â, V = 1749.3 À, Ζ = 8, Rgt(F) = 0.023, utfref(F) = 0.052, Τ =300 Κ. Gao.7Geo.4Mn6.30i2Sio.6 (3), tetragonal, /4i/acd(No. 142), a = 9.464(4) À, c = 18.78(3) À, V = 1682.1 À 3 , Z = 8 , Rgt(F) = 0.023, wRTef(F) = 0.053, T= 300 K. Source of material Solid solution compounds of garnet and braunite type in the system Mn0/Mn203/Ga203/Ge02/Si02 were obtained accidentally by annealing M n 2 0 3 (99.9 %, ChemPur), Ga 2 03 (99.5 %, Merck) and GeÛ2 (99.9 %, Merck) in the stoichiometric ratio of 2:1:6. The experiment was performed inside a closed quartz tube at 1273 Κ which contained the amount of hydrochloric acid gas corresponding to the pressure of 500 mbar at reaction temperature. The reaction time was 145 h. Aiming at a selective preparation of Mn3Ga2Ge30i2 the corresponding stoichiometric mixture of MnO, G a 2 0 3 (99.5 %, Merck) and G e 0 2 (99.9 %, Merck) was annealed in an open corundum cup inserted in a closed quartz tube. Reaction temperature and the pressure of hydrochloric acid gas were chosen as in the previous experiment. The reaction time was 315 h. MnO was prepared by decomposing MnCÛ3 under hydrogen flow at 823 K. Red single crystals of garnet type were obtained and a second non single crystalline phase which was not identified. Experimental details For 1, six crystals in random orientation were measured with similar results. Therefore, the merged reflections of the six measurements were combined for the last refinement. For 2 and 3 two crystals were measured with similar results, and the merged reflections of the two measurements were combined for the last refinement. The compositions of the crystals were derived from the refined occupation factors, and the results of EDX analyses were only used qualitatively. For 1, in more detail, the differences of most of the parameters of each individual result lie in the range 2 to 4 e.s.d. Although one can expect crystals of variable composition in a solid solution synthesis, in our case the observed differences in the composition are not sig* Correspondence author (e-mail: wartchow@aca.uni-hannover.de) nificant. We therefore consider the differences in the results as random and believe that merging of the reflection data for the final refinement is justified in order to obtain a result which is more representative for the whole sample. The merged F0bs data set of each single measurement was scaled against Fecale, therefore, it can be expected that the relative scale factors for the various data sets are nearly 1.0. In an empirical way, relative scale factors in the range 0.97 1 . 0 3 were tested, and the scale factor chosen was the one that improved both the Rmt as well as the final residual wRref(F). Other data reported in the CIF (e.g. lattice parameters) were averaged too. The reported number of 'measured' reflections in Table 1 is the sum of the merged reflections of the six crystals. Similarly, for 2 and 3 cases, for the final refinement the merged reflection data sets of the two measured crystals were compiled in one file and merged again. Lattice parameters were averaged too. The data relevant for the absorption correction reported in the CIF file are taken from the larger crystal. The reported number of reflections in Tables 3 and 5 is the sum of the merged reflections of the two crystals. Details of each individual measurement are contained in the deposited CIF. Discussion The next end-member garnet nearest in composition to our garnets (compound 1 and 2) is Mn3Ga2Ge30i2, of which the lattice constant is known from powder diffraction data (PDF 13-5) as a = 12.043 A in good agreement with our average value of compound 1. Its colour is described as beige. A single crystal structure refinement is not available. The comparison with Mn3Fe2Ge30i2 instead (see [1]) is in good agreement as regards interatomic distances taking into account that the ionic radius of Ga is assumed to be 2-3% smaller than that of Fe. The anisotropic displacement ellipsoid of Mn 2 (U3/U1 = 2.6 to 2.8, this work) agrees fairly well with that of spessartine (U3/U1 = 3.1, ICSD #83458) and its longest half axis points to the midpoint of two oxygen neighbours with the longest Mn—O distances within the peculiar 4 + 4 coordination sphere as one would expect. The refinement shows that the electron density at the Ga 3 site is reduced. We assume that Ga J is partially substituted by Mn . This was not proven by other means, but we believe that the red colour of our garnet crystals is caused by this substitution. The observation of crystals of braunite type (compound 3) confirms the statement on the stability of braunite Mn 2 + Mn6SiOi2 (see [2]) and shows that in braunite Mn + J can be partially substituted by Ga 3 and Si by Ge. The situation of the Mn 2 ion in braunite is quite similar to that in garnet. The anisotropy of the displacement ellipsoid (U3/U1 = 4.7) is still more pronounced because there are larger differences in the Mn + 2 —O 374 Manganese gallium germanium silicon oxides distances of the 4 + 4 coordination polyhedron. The Mn —O distances are : 2.30 Â (4x) and 2.42 Â (4x) in 1, 2.30 À (4x) and 2.43 Â (4x) in 2, and 2.18 Â (4x) and 2.52 Â (4x) in 3. 1. M a n g a n e s e g a l l i u m g e r m a n i u m silicon ox ide ( g a r n e t type) , M M G a ^ M n ^ X G e s z S y O i a (y = 0 .6 , ζ = 0 .14 ) Table 1. Data collection and handling.

zeitschrift für kristallographie. new crystal structures/zeitschrift für kristallographie. new crystal structures

Crystal structure of manganese gallium germanium silicon oxide (garnet type), Mn 3 (Ga 2-ζ ,Mn,)(Ge 3-z Si z )O 12  (y = 0.6, ζ = 0.14; j=0.44, z=0), and of manganese gallium germanium silicon oxide (braunite type), Mn(Mn 6-y Ga y )(Si 1-z Ge z )O 12  (y = 0.7, z = 0.4)