Volume 194, Issue 3-4

An approach to structure determination for a crystal from component crystals in equal volume fractions, the most difficult case to the solution, is outlined with precautions for stepwise initialization. Proper selection of a crystal geometrical symmetry space group from a corresponding twin anti-symmetry space group and interpretation of a Patterson space are indispensable prerequisite for the solution. Observations unique to the case are briefly described in a sequence of Patterson synthesis, Fourier approach and least-squares refinement for efficient interpretation and processing.

The crystal structure of the title compound, Ru 3 (CO) 11 P(OC 6 -H 5 ) 3 has been determined at room temperature. Crystals are triclinic, P[unk], a = 9.834(3), b = 11.764(2), c = 13.633(4), α = 91.89(1), β = 107.92(2), γ = 92.02(1)°, Z = 2, D c = 1.94. The structure was refined by a blocked full matrix least squares procedure to final R = 0.061 and R w = 0.065 for 5495 unique reflections used [ I > 2.5 σ ( I )] out of 6280 collected on a Syntex P2 1 diffractometer. The structure shows the P(OPh) 3 group occupying an equatorial position. Interatomic distances of interest are Ru(1) – Ru(2) = 2.844(1), Ru(2) – Ru(3) = 2.848(1), Ru(1) – Ru(3) = 2.852(1) and Ru(1) – P(1) = 2.256(2) Å.

Syntheses under moderate hydrothermal conditions yielded single crystals of the compound Co(PO 3 OH) · H 2 O: a = 15.956(3) Å, c = 7.703(2) Å, space group R [unk], Z = 18. The crystal structure was determined from 932 X-ray reflections with sin θ / λ ≤ 0.70 Å −1 ; Refinement gave R = 0.032. Slightly distorted CoO 6 octahedra (Co – O from 2.052(2) to 2.174(2) Å, 〈2.111 Å〉) share two common O – O edges resulting in helical ∞ 1 [CoO 4 ] rows parallel to [001]. These rows are interconnected by protonated phosphate tetrahedra. Within the phosphate tetrahedron the P – O distance to the hydroxyl group is 1.585(2) Å, the three other P – O distances range from 1.519(2) to 1.530(2) Å. The hydrogen bonds line the surface of unoccupied channels of diameter 4.63 Å running in [001]; O – H … O range from 2.654(4) to 2.720(5) Å.

The crystal structure of Ag 5 Cu 3 (PO 4 ) 2 [(PO 4 )H(PO 4 )] was determined from 2611 single crystal X-ray data [ a = 17.725(6) Å, b = 5.162(2) Å, c = 18.584(6) Å, β = 125.66(2)°, space group C 2/ c , Z = 4, R w = 0.032, sin θ / λ ≤ 0.80 Å −1 ]. (One part of the PO 4 tetrahedra form dimers via a symmetrically restricted, very short O – H – O bond of 2.428(6) Å). Simultaneously this hydrogen bond is a common edge between two coordination polyhedra of Ag atoms. The Cu(1) atom is in a square planar [4] environment. The Cu(2) atom is tetragonal pyramidal [5] coordinated with an uncommon distribution of Cu – O bond lengths [1.933(2), 1.934(2), 1.976(2), 2.105(2) and 2.180(2) Å]. Monoclinic Ag 5 Cu 3 (PO 4 ) 2 [(PO 4 )H(PO 4 )] has topologically the same [Cu 3 (PO 4 ) 4 ] 2− layers as triclinic Na 5 Cu 3 (XO 4 ) 2 [(XO 4 )H(XO 4 )] (X = P, As), but a different stacking sequence. In both cases these layers are connected by hydrogen bonds and by Na and Ag atoms, respectively, to a three-dimensional network structure.

An X-ray diffraction study of single crystals of acuminite, a strontium aluminium fluoride mineral from Ivigtut, Greenland [SrAlF 4 (OH) · H 2 O, a = 13.223(1) Å, b = 5.175(1) Å, c = 14.251(1) Å, β = 111.61(2), C 2/ c , Z = 8, D m = 3.295 g cm −3 , D c = 3.305 g cm −3 ] used 2138 diffraction intensities (CAD-4 diffractometer), and was refined to R (unweighted) = 0.069. The strontium ions are 9-coordinated to 7 fluoride ions and 2 water molecules, the aluminium ions have octahedral coordination, 4 fluoride ions and 2 hydroxyl ions. The structure of acuminite is compared with the structure of tikhoenkovite another modification of SrAlF 4 (OH) · H 2 O.

Coleonol-B a diterpenoid isolated from the roots of the Indian plant Coleus forskohlii crystallizes in the orthorhombic system, space group P 2 1 2 1 2 1 with a = 29.085(5), b = 11.603(2), c = 6.341(1) Å and four molecules in the unit cell. As in Coleonol, the substituents at the 6- and 7-positions are in the β -configuration. 2133 reflections were used, 398 parameters were refined. Final R -values were R w = 0.057 and R = 0.045.

Large single crystals of the isotypic rare-earth formates Y(HCOO) 3 · 2H 2 O (YFD) and Er(HCOO) 3 · 2H 2 O (ErFD) (point group 222) were grown from aqueous solutions containing a surplus of formic acid at 70°C by controlled evaporation of the solvent. The linear electrostrictive tensor [ d ijk ] and the linear electro-optic tensor [ r ijk σ ] (unclamped) were determined at room temperature and λ = 633 nm. High anisotropy, small electro-optic constants (one tenth of corresponding values of KH 2 PO 4 ) and medium electrostrictive constants (3.5 times of d 111 of α -quartz) are the main features of both formates.

A method has been proposed for indexing powder diffraction patterns using a new criterion. An improved version of our previous procedure (Ishida and Watanabe, 1982) is proposed especially for determining the monoclinic unique axis, crystallographic axes of orthorhombic crystals and Q ( h ,0, l ) values. Only when the improved version is not available for indexing monoclinic patterns, another simple procedure is also proposed. Using these two procedures, the method gives excellent results in monoclinic analysis even by use of a personal computer.

The evidencies for the dynamic but not the static nature of “rotary” crystals are given for normal paraffins as an example. Distinctive features of thermal deformations and polymorphic transformations of paraffins as well as breakdown of paraffin solid solutions at rising temperatures (in a limited temperature interval) indicate the leading role played by the rotary thermal motion of aliphatic chains about their axes in these processes.

A bismuth oxide sulfate, [Bi 1 – x Co x O] 2 (SO 4 ) 1 – x 0.14 ≤ x ≤ 0.18 , was prepared by interacting CoSO 4 with Bi 2 O 3 . Single crystals were obtained and investigated by X-ray diffraction. They are monoclinic, C 2, a = 5.615(3) Å, b = 5.535(2) Å, c = 8.080(2) Å, β = 108.97(5)°, Z = 2,244 measured reflexions: R = 0.079. The structure consists of continuous [Bi 1 – x Co x O] n fluorite-like layers separated by SO 4 2− anions. It shows close structural similarity to the mineral nadorite, PbSbO 2 Cl and the already reported [Bi 2 CoO 3 ]SO 4 (Fanariotis and Rentzeperis, 1987).

Ti 2 Cl 8 O 4 C 10 H 20 , Mr = 583.69, triclinic, P [unk], a = 9.372(2) Å, b = 8.979(2) Å, c = 7.812(2) Å, α = 63.5(2)°, β = 76.2(2)°, γ = 77.5(2)°, V = 567(1) Å 3 , D x = 1.71 g cm −3 , λ (Mo K α = 0.71069 Å, μ = 15.53 cm −1 , F (000) = 292, T = 294 K, m.p. 85 – 90°C, final R = 0.036 for 2248 observed reflections with F > 7 σ ( F ). The structure is built up of dimeric molecules and the unit cell contains only one dimeric unit. The dimerization occurs through two chlorine bridges between the titanium atoms which are coordinated by five chlorine atoms and one carbonyl oxygen atom of the ester moiety in an almost perfect octahedral environment.

The title compound is orthorhombic, with space group B 2 mb and Z = 4. The cell dimensions are a = 8.66036(1) Å, b = 14.51489(5) Å and c = 13.25635(6) Å. A total of 1626 independent reflections were measured with a SYNTEX P2 1 automatic diffractometer using Mo Kα radiation. The structure was refined by a full-matrix least-squares procedure to a conventional R = 0.055 for the 1556 unique reflections. The co-ordination around the central copper atom is octahedral with the copper atom 0.78(4) Å above the equatorial plane of the four nitrogen atoms of the ligand molecule. The Cu – N equatorial plane bond lengths are 1.975 and 2.031 Å. The remaining positions of the co-ordination octahedron are occupied by a fluorine atom of one of the fluorophosphate groups and an oxygen of a water molecule. The Cu – F and Cu – O bond lengths are 2.7371 Å and 2.3968 Å respectively.

Diaqua-trans-bis[1,1,1-trifluoro-4-(4′-nitrophenyl)-buta-2,4-dionato-O,O′] copper(II) bis (pyridine-1-oxide) solvate, C 30 H 24 F 6 N 4 O 10 Cu, Cu(nbta) 2 (H 2 O) 2 (pyO) 2 , MW = 810.08, monoclinic, space group P 2 1 / a , a = 15.318(5), b = 9.036(3), c = 13.253(5) Å, β = 114.16(1)°, Z = 2, F (000) = 822, D (calc) = 1.607 Mgm −3 , λ (Mo Kα ) = 0.7107 Å, μ (Mo Kα ) = 0.75 mm −1 , R = 0.063, R w = 0.061 for 1405 observed reflexions with F > 3.0 σ ( F ). The copper ions are positioned at the inversion centres 0,0,0 and 1/2,1/2,0 and their octahedral environments are strongly tetragonally distorted. In contrast to Cu(pyO) 6 (NO 3 ) 2 (H 2 O) 2 the structure of Cu(nbta) 2 (H 2 O) 2 (pyO) 2 comprises coordinated water molecules axially bound with copper and non-coordinated lattice pyridine-1-oxide molecules. Both the hydrogen atoms of each water molecule are involved in hydrogen bonds with pyridine-1-oxide molecules thus giving rise to a two-dimensional array of hydrogen bonds in the ab plane. Single crystal of Cu(nbta) 2 (H 2 O) 2 (pyO) 2 exhibits four or six-line epr spectrum at certain orientations in the magnetic field.

Single-crystal structure determinations of the low-temperature quartz modification of AlAsO 4 were performed up to 4.87(7) GPa. The refinements were carried out in space groups P 3 1 21 and P 3 2 21, respectively. At ambient conditions the lattice parameters are a = 5.028(4) Å and c = 11.228(3) Å. They decrease to a = 4.800(3) Å and c = 11.001(3) Å at 4.87(7) GPa. The high pressure behaviour of AlAsO 4 is similar to that of the homeotypic compounds quartz and GeO 2 and to that of the isotypic compound AlPO 4 . With increasing pressure the c / a axial ratio increases, the AlO 4 and AsO 4 tetrahedra become more and more distorted. The decreasing (Al – O – As) angles indicate a cooperative tilting of the tetrahedra. From the shortening of intertetrahedral O – O distances and the changes of the shape of the Dirichlet domains of the oxygen anions, it can be concluded that the oxygen packing changes with increasing pressure in the direction of an arrangement corresponding to a cubic body-centered lattice. As in the case of SiO 2 , GeO 2 and AlPO 4 it is mainly this effect which is responsible for the high-pressure behaviour of AlAsO 4 . The structural changes of AlAsO 4 at high temperature can be explained in an analogous way.

The crystal structure of rutile (TiO 2 ) has been studied at high temperatures up to about 1600°C based on sets of single crystal X-ray diffraction intensities collected on a four-circle diffractometer. The thermal expansion coefficients for the a - and c -axes in the measured temperature range were α a = 8.9(1) × 10 −6 °C −1 and α c = 11.1(1) × 10 −6 °C −1 , respectively. The thermal response of the octahedra about Ti is such that the thermal coefficient for the four short equatorial Ti – O bonds was 8.4(3) × 10 −6 °C −1 and for the two long apical Ti – O bonds 11.5(3) × 10 −6 °C −1 . The rate of thermal expansion of the octahedral shared edge is relatively large under ∼ 1200°C, while it becomes small above ∼ 1200°C. An l to l o ratio, which we denote shrinkage index, however, decreases with the raise of temperature ( l = the length of the shared edge at a temperature; l o = the edge length of a regular octahedron having the same volume as the Ti octahedron has at the same temperature).

The crystal structure of the low temperature form of cesiumozonide, α -CsO 3 , has been refined using single crystal diffraction data recorded at −60°C. A technique for selecting and sealing crystals into capillaries under dry and cold conditions had to be applied. The structure of CsO 3 is monoclinic P 2 1 / c ; a = 670.9(2) pm, b = 624.4(1) pm, c = 899.7(3) pm, β = 120.85(1)°, V = 323.6(2) 10 6 pm 3 , Z = 4, 1463 independent reflections, R w = 0.048. The O 3 − -anion displays C 2 ν symmetry within the experimental error of the bondlenghts of O1 – O2 [133.3(9) pm] and O1 – O3 [133.2(8) pm]. The bond angle O2 – O1 – O3 is 114.6(6)°. α -CsO 3 is isostructural to RbO 3 and derives from the CsCl type of structure.