Band 160, Heft 1-2

Substituted derivatives of dimethyl 2,3-dihydro-2,3-dihydroxybenzo[b]furan-2,3-dicarboxylate ( 1 ) exist in the cristalline state usually as a mixture of cis and trans isomers, exhibiting similar 1 H n.m.r. spectra with regard to the hydroxy and ester signals. The attribution of either type of these spectra to cis or trans forms was not directly possible. For this reason an X-ray diffraction study of a pure stereoisomer of dimethyl 2,3-dihydro-2,3-dihydroxy-4,7-dimethyl-benzo[b]furan-2,3-dicarboxylate ( 1a ) was done. The compound proved to have the cis configuration. Crystals are monoclinic, space group P 2 1 / n , Z = 4, a = 15.376(2), b = 7.397(1), c = 12.598(1) Å, β = 104.91(1)°. The final R is 0.083 for 2309 observed reflections.

A simple polyhedral model of the feldspar framework is presented, and compared with the feldspar sanidine. The feldspar model is derived by a two-dimensional shear operation on a hypothetical member of the phillipsite-harmotome group of tetrahedral frameworks. This description emphasizes a looped tetrahedral chain as the structure-building unit. This chain also exists in a number of chain silicate structures e.g. agrellite, litidionite and fenaksite.

A procedure has been proposed for indexing powder diffraction patterns using a new criterion. The procedure is useful to determine the monoclinic unique axis, crystallographic axes of orthorhombic crystals, Q ( h ,0, l ) values and eventually all lattice parameters. Particularly, in the monoclinic cases, the criterion provides a powerful clew to determine the h O l net in a short time. With a computer program prepared, the procedure has been tested for a number of JCPDS patterns with satisfactory results.

Polycrystalline MGa 2 O 4 (M = Mg, Mn) are cubic, spinel-type double oxides, space group Fd 3 m , Z = 8. For MgGa 2 O 4 , a = 8.2781(3) Å, V = 567.27(7) Å 3 , D x = 5.33 Mg m −3 , x = 0.256, 87% of Ga in 8(a) positions, R = 0.029, and interatomic M – O distances for tetrahedral and octahedral sites 1.878 and 2.021 Å respectively. For MnGa 2 O 4 , a = 8.4577(3), V = 605.02(2), D x = 5.67, x = 0.264, 32% of Ga in 8(a) positions, R = 0.033, and the interatomic distances mentioned above 2.036 and 2.003 respectively.

Racemic phosphinothricin hydrate crystallizes in the monoclinic space group P 2 1 / n with 4 molecules in the cell. Contrary to l -phosphinothricin the racemic compound is in the crystal lattice the betain ammoniumphosphinate. The shortest hydrogen bond (2.576 Å), which is between the carboxy and the phosphinate group, constructs an annular dimer, which is lying on a centre of symmetry. Together with the water molecule the maximum number of hydrogen bonds is built.

The crystal structure of the title compound has been determined (space group Pbca , a = 10.293(4), b = 22.665(8), c = 12.218(4) Å, Z = 8) and refined to R = 0.065. Bond lengths in the acetal group differ appreciably from those in related equatorial 2-aryloxy acetals.

The structures of intermediate phases, such as the β -phase, are shown to be readily derived from that of spinel ( γ ) by the regular insertion of anti-phase boundaries ( apbs ) or mirror planes parallel to (010) of the body-centered tetragonal unit cell of the latter [[unk]10) planes of the face-centred cubic cell]. The process leads eventually to a hypothetical structure, ω , from which γ , β , etc. can be derived by similar apbs . Unit layers parallel to (0[unk]2) in the ω structure are identical to those parallel to (001) in olivine ( α , setting Pnma ). A simple mechanism is proposed for the transformation α ↔ ω . Further transformation to β etc. and γ requires only slip, to generate apbs .

l -Phosphinothricin crystallizes in the monoclinic space group P 2 1 with two molecules in the cell. At least in the crystalline state the α -carbon atom and the phosphorous are chiral, they have the S - and the R -configuration respectively. There is a very short intermolecular oxygen-oxygen hydrogen bond of 2.427 Å.

The title compound C 6 H 15 N 6 P has been synthesized. Its structure has been determined by X-ray single crystal methods. Crystals are monoclinic, space group P 21/ n with a = 8.742(11) Å, b = 11.342(4) Å, c = 10.209(12) Å, β = 90.28(6)°, Z = 4, V = 1012(1) Å 3 , ϱ exp = 1.3g/cm 3 , ϱ x = 1.32g/cm 3 , μ ( λ ) = 2.44cm −1 , F (000) = 432. There is a C 3 axis in the molecule but not in the crystal. The structure suggests that phosphorus is involved in bonding to adjacent atoms largely via its 3 p orbitals and that the lone pair is largely in the 3 s orbital. The pyramidal coordination of the a nitrogen atoms and the relation structure – reactivity is discussed.

The frequency distributions of some important geometrical quantities of 75 BO 3 -groups with estimated standard deviations of d (B ∓ O) of 0.005 Å or less are presented and discussed. The following mean values and spreads have been obtained: [unk](B ∓ O) 225 = 1.370(19) Å, [unk](O ∓ B ∓ O) 225 = 120.0(2.9)°. The deviations from planarity for about 20 of these 75 BO 3 -groups are small but nevertheless experimentally well established. The extreme values of Δ (distance of the B-atom from the oxygen plane) are 0.035 Å. In the few cases where a fourth relatively close (2.7 ∓ 3.0 Å) oxygen lies vertically above the B-atom of the BO 3 -group, there exists a dependence of magnitude and direction of the deviation on the distance d (B ∓ 4 th O).

Metastable lead germanates are obtainable by glass recrystallization and from the melt at a sufficiently high cooling rate. Their hexagonal crystal structure can be explained as unit-cell-twinning of the prototype structure of stable Pb 5 [□|GeO 4 |Ge 2 O 7 ] by inversion involving an apatite-like Pb 4 Ge[□|(GeO 4 ) 3 ] slab. This leads to translation periods in [001] of c = N · c ′ with magic numbers N = 6 n + 2, n ∈ [unk], and c ′ ≈ 3.6 Å; lattice parameters a vary between 10.15 and 10.20 Å. A homologous series of structures with N = 8, 14, 20, and 38 could be found. The unit-cell contains two units of a general formula Pb 15 n +4 Ge[□|(GeO 4 ) n +1 |(Ge 2 O 7 ) n ] 3 . Vacancies of oxygen accompained with replacement of Ge 4+ by Pb 2+ change the ideal composition. The space group is that of apatite, P 6 3 / m , but loss of centrosymmetry and ferroelectric properties are suggested with increasing N. In addition, metastable barysilite-like Pb 3 [Ge 2 O 7 ] was synthesized from the melt with crystal data a = 10.296(1), c = 39.805(4) Å, space group R [unk] c , D x = 7.188 Mg · m −3 for Z = 18.

The crystal structure of a new sulfosalt, Tl 5 Sb 5 As 8 S 22 , has been determined. The crystal is monoclinic with space group P 2 1 / c . Four formula units are contained in a unit cell of dimensions a 0 = 17.441(5), b 0 = 7.363(2) and c 0 = 32.052(7) Å, β = 105.03(7)°. The structure was determined by direct methods and refined to a final R -value of 0.057 for 5665 observed reflections. The Sb and As coordination polyhedra are connected to form a three-dimensional framework. The Tl coordination polyhedra also form a three-dimensional framework interpenetrating the Sb ∓ As framework. The Sb and As coordination polyhedra share common vertices, edges and even one face with the Tl coordination polyhedra. The mean Tl ∓ S, Sb ∓ S and As ∓ S distances are 3.36, 2.55, 2.29 Å respectively.

The structural parameters of potassium disilicate have been determined with single crystal diffractometer data. K 6 Si 2 O 7 is isostructural to K 6 Co 2 O 7 [space group P 2 1 / c ; a = 645.8(2), b = 888.7(4), c = 1087.9(5) pm, β = 125.0(1)°; 1073 reflections, R = 0.033]. The disilicate anions show straight Si ∓ O ∓ Si bridging bonds. The applicability of some concepts on K 6 Si 2 O 7 explaining the relations between Si ∓ O ∓ Si bond-lengths and angles is discussed. Calculated (bond-length-/bond-strength-concept) and observed bond-lengths within the disilicate group are in good agreement.

The so far unknown compounds Zn 3 BPO 7 and Mg 3 BPO 7 both occur in two forms. The transition of the high-temperature form into the low-temperature form is very sluggish for Zn 3 BPO 7 , but prompt for Mg 3 BPO 7 . Therefore, the growing of larger crystals is restricted to β -Zn 3 BPO 7 . β -Mg 3 BPO 7 cannot be quenched to room temperature. The crystal data are given for β -Zn 3 BPO 7 with the hexagonal space group P[unk] m 2 or P[unk]2 m and for the orthorhombic α -phases of both compounds with the probable space group Imm 2.

C 4 H 11 NO 3 , orthorhombic, Pna 2 1 , a = 8.807(6) Å, b = 8.872(7) Å, c = 7.709(7) Å, V = 602 Å 3 , Z = 4, D c = 1.335, D m = 1.335 g cm −3 (in butyl alcohol), λ (Cu Kα ) = 1.5418 Å. The structure was solved using MULTAN and refined by the full matrix least-squares method to a final R value of 0.080. The central carbon atom is coordinated tetrahedrally by the carbon atoms of hydroxymethyls and the nitrogen atom of an amino group. The NH 2 ∓ C ∓ (CH 2 OH) 3 tetrahedra show marked departures from a regular tetrahedron.

Unit-cell dimensions and space group of potassium-iron molybdate, K 3 FeMo 4 O 15 , have been determined. Crystals belong to the orthorhombic system, space group Pbcm , a = 5.676(3), b = 15.896(14), c = 33.01(9) Å. Variation of the lattice constants with the composition of the samples has been observed.