Volume 204, Issue 2

The article concerns with the pattern of golden jewlery found 1878 by Heinrich Schliemann in the second town of ancient Troy and with the pattern of golden grave gifts from the mycenean shaft graves found 1876 by Schliemann on the acropolis of Mycenae. Though Troy II is dated about 2300 B.C. and the shaft graves of Mycenae are about 700 years younger similarities already observed by Schliemann between both cultures can be shown by the modern method of symmetry classification. These similarities indicate a long tradition of Bronze Age decorative Art in the Aegean world.

The title compound, (HC 4 H 11 N) 4 [Mo 8 O 26 ] · 6 H 2 O, M = 1588.18 crystallizes in the monoclinic system, space group P 2 1 / c , with cell dimensions a = 10.909(3), b = 9.927(2), c = 22.018(4) Å, β = 101.73(2)°, D x = 2.259, D o = 2.257(1) Mg/m 3 , Z = 2. The structure has been refined to R = 0.028 and R w = 0.030 for 3041 observed reflexions with I > 3 σ ( I ). The unit cell contains discrete centrosymmetric polyanions β -[Mo 8 O 26 ] 4− , (HC 4 H 11 N) + cations and water molecules. Both cations and water molecules are oriented to permit hydrogen contacts with either molybdate oxygen atoms and water oxygen atoms to form an extensive network of hydrogen bonds. Seven different types of hydrogen contacts have been found: N–H…O, N–H…O w , O w ,–H w …N, O w –H w …O, O w –H w …O w , C–H…O and C–H…O w . The proposed hydrogen-bonding interactions appear to stabilize the crystal structure. The compound shows a relative low thermal stability and its water molecules are lost between 58 and 150°C in an oxygen-argon atmosphere during an endothermic process.

Abstracts The refinement method using the optimal algorithm has been formulated for crystal structure determination. This method includes, in the criterion, the a priori data consisting of probable interatomic distances by means of a repulsive-attractive term. The minimization mode used is a simplex mode. This method permits to make the refinement even from an incorrect structural hypothesis and also refuses to pass through physically unacceptable intermediate solutions.

Nine new compounds of composition AB 4 C 5 X 12 with distinct elements being among A: K, Rb, Cs; B: Zn, Cd; C: Ga; X: S, Se, Te were prepared by solving ZnGa 2 S 4 , CdGa 2 S 4 , ZnGa 2 Se 4 , CdGa 2 Se 4 , and CdGa 2 Te 4 in KBr, RbBr, and CsBr, respectively. The crystal structure of KCd 4 Ga 5 S 12 was solved and refined to R = 0.03. It crystallizes with space group R 3, the hexagonal lattice parameters being a 0 = 13.782(3) Å and c 0 = 9.330(3) Å [rhombohedral setting: a 0 = 8.543(2) Å, α = 107.53(1)°], and shows a thirteenfold superstructure. KCd 4 Ga 5 S 12 consists of a cubic close packing of sulfur atoms with partially ordered Cd and Ga cations in the tetrahedral interstices. The potassium ion substitutes one sulfur atom and is located inside a cubooctahedral interstice of the sulfur sublattice. Frequently, twinning is observed which leads to a weighted coincidence site lattice in reciprocal space.

The crystal structure of anorthite, CaAl 2 Si 2 O 8 (Val di Fassa, Monzoni, Italy, An, 100%) has been refined by full-matrix least-squares methods using single-crystal neutron diffraction data (sin θ / λ ≤ 0.78 Å −1 ) measured at 514 K. Crystal data: triclinic, space group I [unk] (assumed), Z = 8, a = 8.194(1), b = 12.878(4), c = 14.171(6) Å; α = 93.07(2), β = 115.07(2), γ = 91.47(2)°, V = 1343.6 Å 3 , μ n = 4.2 × 10 −3 cm −1 F (000) = 532.16 fm, λ = 1.0462(1) Å. R ( F 2 ) = 0.049, wR ( F 2 ) = 0.068, S = 1.27 for 5098 reflections and 293 parameters, including 40 third-order thermal tensor coefficients for four oxygen atoms. The aluminosilicate framework is virtually body-centered, whereas the Ca atoms occur in split-positions with unequal site occupancies. The eight tetrahedral sites show complete Al/Si ordering based on refined scattering-lengths values. The 16 distinct Si–O and [Al–O] bonds (e.s.d.'s, 0.001 Å) have average values of 1.617 ± 0.031 Å and [1.741 ± 0.029 Å]. The O–Si–O and [O–Al–O] angles are in the ranges 101.44(6) – 117.60(7)° and [97.87(7)–119.01(7)°] and have averages of 109.42 and [109.31°]. The unique Si–O–Al angles are between extremes 124.16(6) and 154.7(2)°. The two non-equivalent Ca atoms occupy statistically two sites with respective separations, 0.834(5), 0.494(5) Å, and weights equal ⅔, ⅓ within limits of the analysis. These results are interpreted in terms of a dynamical model in which the I [unk] phase is a statistical dynamical average of small mobile P [unk] domains. The unequal Ca occupancy in the split positions results from the persistence of considerable short-range order near T c . Significant anharmonic thermal vibrations of some of the oxygen atoms are attributed to critical fluctuations associated with the phase transition near T c .

Planar equilateral triangle 3 6 , graphite 6 3 and Kagomé nets of atoms occur widely in crystal structures of the hexagonal and rhombohedral classes (the latter set on hexagonal axes). However with appropriate metric and atomic arrangement they can occur in structures of any crystal class. With symbols H , [unk], K respectively to describe these nets, previously developed symbols for the stacking of these nets one above the other and a new symbolism to handle their occurrence in centred orthohexagonal cells, it is possible to describe and compare these similar geometrical arrangements in more than a thousand structure types of any class with simple one-line descriptions.

[Ca(H 2 O) 6 ] [Zn 2 Br 6 ], M r = 758.36, monoclinic, C 2/ m , a = 13.276(6), b = 10.665(3), c = 13.785(7) Å, β = 113.30(3)°, V = 1792.2(12) Å 3 , Z = 4, D x = 2.81 Mg m −3 , Mo Kα radiation, λ = 0.71069 Å, μ = 15.99 mm −1 , F (000) = 1400, room temperature, R = 0.055 ( wR = 0.053) for 640 unique observed [ I > 3 σ ( I )] reflections. The structure consists of independent octahedral Ca(H 2 O) 6 2+ complexes (〈Ca–O〉 = 2.32 Å) and dimeric tetrahedral Zn 2 Br 6 2− complexes [〈Zn–Br〉 = 2.48 (bridging) and 2.35 Å (terminal)] linked together by O–H…Br hydrogen bonds. The structure is related to those of MgZn 2 Br 6 · 6H 2 O and ZnBr 2 · 2H 2 O but the packing of the complex ions (and, hence, the hydrogen bonding) is different.

The preparation and the X-ray single crystal structure determination of [Mg(C 7 H 7 OH) 6 ]Cl 2 are described. The crystals are monoclinic, space group P 2 1 / c (N° 14), with a = 11.739(1) Å, b = 7.583(1) Å, c = 23.172(4) Å, β = 103.92(1)° and Z = 2. The structure was solved by direct methods and refined using full-matrix least-squares leading to final R = 4.22% and wR = 5.22%. The [Mg(C 7 H 7 OH) 6 ]Cl 2 adduct shows a ionic structure in which the Mg ion is coordinated by six benzyl alcohol moieties through the oxygen atoms. Moreover, each chloride ion shows “hydrogen-bonding” type interactions with three coordinated benzyl alcohol molecules through the hydroxylic hydrogens.

The crystal structure of 2,4-dihydro-8-methoxy-4,4-dimethyl-2-f-tolyl-1 H -[1] benzopyrano-[4,3,2- cd ] indol-1-one (C 24 H 21 NO 3 ) was determined from single crystal X-ray diffraction data. The crystal belongs to the triclinic, space group P [unk], with a = 6.060(2), b = 12.276(5), c = 12.889(5) Å, α = 92.63(4), β = 90.78(4), γ = 95.71(3)°, M r = 371.42, V = 952.92 Å 3 , Z = 2, D cal = 1.29 Mg-m −3 , D m = 1.28 Mg-m −3 , λ (Cu K α ) = 1.54178 Å, μ = 0.60 mm −1 , T = 293 K, F (000) = 392. The crystal structure was solved by direct methods and refined by least-squares to R = 0.038 and R w = 0.043 for 2257 independent reflections. The pyran ring assumes a distorted boat conformation.

The crystal structure of the title compound 2gly HCl has been redetermined. Orthorhombic crystals with the P 2 1 2 1 2 1 space group have unit cell dimensions a = 8.0988(7), b = 18.015(1), c = 5.3086(7) Å, Z = 4 and D x = 1.604 Mg m −3 . The structure was refined by a full-matrix least-squares procedure on 1564 reflections to final R = 0.029. The crystal lattice, held together by an extensive hydrogen bonding network, is comprised of chloride anions, Zwitterionic glycine molecules and protonated glycine molecules in the ratio 1:1:1.