Volume 212, Issue 2

A single crystal of the thermodynamically stable decagonal phase in the system Al–Ni–Co with the nominal composition Al 72.5 Co 11 Ni 16.5 was first studied by neutron diffraction. The diffraction experiment showed that the investigated crystal was a true single crystal. In a preliminary experiment we have measured a selection of Bragg reflections, diffuse scattering and satellite scattering and compared the observations with corresponding X-ray results. From this comparison we may conclude, that the 10 mm symmetry is not due to the indiscernibility of Co and Ni atoms (X-rays), but a true structure feature. The superorder satellite scattering is basically not due to a Co/Ni ordering problem.

Both direct methods and the solvent flattening technique have been proved capable of breaking the phase ambiguity intrinsic in one-wavelength anomalous scattering (OAS) data. However, in theory, while direct methods are better in deriving starting phases from OAS data, the solvent flattening technique is more powerful in the subsequent phase refinement. A procedure is described in this paper which combines direct methods with the solvent flattening technique for phasing of OAS data. The procedure has been tested with the known protein RNase Sa. This protein is of moderate size, and the diffraction data were collected routinely without taking special care for the recording of Friedels. The test proved that the combination of the direct method and the solvent flattening leads to a much better result than that from either method alone.

An approach to indexing is described which uses a cosine Fourier transform to obtain direct space cell vectors. The cosine function has the advantage of being relatively insensitive to small errors. A number of approaches are discussed for the generation of either (i) candidate direct space vectors themselves, or (ii) directional components of such vectors in order to reduce the three-dimensional transform to a one-dimensional one. In addition a method is described which makes effective use of known cell dimensions. It is shown that a modification of this method can be applied to discarded reflections in order to analyze for a rotational satellite or twin.

We report about the crystal structure of Cu 12 P 20 Br 10 , a polyphosphide containing the new polyanionic phosphorus polymer [unk][P 20 2− ]. It crystallizes in the triclinic system, space group P [unk] (No. 2) with a = 9.886(2) Å, b = 13.190(2) Å, c = 14.763 (3) Å, α = 70.83(1)°, α = 82.68(1)°, γ = 80.13(1)°, V = 1786.1 (6) Å 3 and Z = 2. The phosphorus atoms build up one dimensional negatively charged tubes consisting of condensed 5- and 6-membered rings. They are connected via copper atoms to form double tubes oriented parallel [010] and are embedded between wavy layers of copper and bromine atoms. All copper atoms except those that are linked to negatively charged P-atoms are strongly disordered.

The crystal structure of β -YbV 4 O 8 has been determined using a twinned specimen and refined as a commensurate composite structure including V 2 O 4 framework and Yb cations as substructures. The lattice dimensions for V 2 O 4 are a 1 = 9.030(5) Å, b 1 = 10.72(2) Å, c 1 = 2.876(1) Å, α = 89.911(3)°; those for the Yb substructure are a 2 = a 1 , b 2 = b 1 − C 1 , c 2 = 2 c 1 . Both substructures have the space group P 2 1 / n 11. The three-dimensional framework of V 2 O 4 is isostructural with those of Fe 2 O 4 in CaFe 2 O 4 and Ti 2 O 4 in NaTi 2 O 4 . The Yb cations occupy half of the [8]-coordinated sites in the tunnel of the framework running parallel to [001]. α - and β -YbV 4 O 8 are polytypes in which the Yb cations are differently arranged while the V 2 O 4 frameworks are essentially the same.

Single crystals of Ni(py) 4 F 2 · 2H 2 O ( 1 ) and Cu(py) 4 F 2 · 1.33 HF · 2H 2 O ( 2 ) have been synthesized by solving the precipitated metal fluoride hydrates in Pyridine. Both compounds are sensitive to air. They crystallize in the monoclinic space group C 2/ c with lattice parameters a = 13.199(2) Å, b = 10.815(2) Å, c = 15.353(2) Å, β = 108.08(1)° for 1 and a = 28.531 (6) Å, b = 8.767(2) Å, c = 17.572(4) Å, β = 104.43(3)° for 2 . Within both structures the metal atoms are coordinated in form of a distorted square bipyramid. In the case of 1 four Pyridine nitrogen atoms are in the basal plane and two fluorine atoms in the apical positions. Hydrogen bonding via water molecules lead to infinite chains of Ni(py) 4 F 2 molecules connected by doubly ridged [F 2 (H 2 O) 2 ] ring units. In 2 two different complex moieties exist. In one complex two H 2 O molecules are in the inner coordination sphere besides the four pyridine rings; these molecules are interconnected by two F − ions, which may be partially substituted by HF 2 − -groups forming infinite chains along [010]. In the other, HF 2 − -ions occupy the apical positions of the square bipyramid around the copper ion. They are linked to the fluoride ions of the chains by weak hydrogen bonds of water molecules arranged in between. Thus, the formula should be better given as [Cu(py) 4 (H 2 O) 2 ][Cu(py) 4 (HF 2 ) 2 ] · F 1.66 (HF 2 ) 0.33 · 2H 2 O.

The crystals of (BEDT-TTF) 5 [Pt(SCN) 4 ] (BEDT-TTF:4,5:4′,5′-bis (ethylenedithio)-tetrathiafulvalene), C 54 H 40 · N 4 PtS 44 , belong to the monoclinic space group P 2 1 / c , with the lattice constants of a = 18.166(4) Å, b = 11.437(2) Å, c = 21.040(7) Å, β = 111.17(2)°, V = 4076.3(16) Å 3 and Z = 2. The structure is refined to R = 0.061 for 6441 independent reflections. The crystal structure consists of the donor layers and the anion layers alternating along the a axis. BEDT-TTF molecules are stacked face to face along the c axis to form a pentamer. In the anion layer, [Pt(SCN) 4 ] 2− anions lay parallel to the bc plane and four SCN ligands coordinate to one Pt atom at sulfur atoms with Pt–S–CN bond angles of about 110°. This salt exhibits semiconducting behavior with the activation energy value of about 0.18 eV in the temperature dependence of the resistivity.

The crystal structure of 2-(N,N-diethylamino-N-oxymethyl)-4,6-dichlorophenol contains two slightly different molecules A and B, both with very strong intramolecular O … H … O hydrogen bonds, with O–O distances 2.423(4) Å and 2.400(5) Å, respectively, and with no crystallographic symmetry. The bridging oxygen atoms are also chemically different, O1 is bonded to carbon and O2 to nitrogen. The single crystal neutron diffraction study shows quite unambiguously that the proton in both cases is located slightly off-centred. In the A molecule O1–H = 1.167(6) Å, H–O2 = 1.258(6) Å and the angle O–H–O = 175.8(5)°; in the B molecule O1–H = 1.186(7) Å, H–O2 = 1.214(7) Å and the angle O–H–O = 176.5(5)°. As expected the proton is thus closer to the centre in the slightly shorter hydrogen bond.

The crystal structures of the adducts of triphenylphosphine oxide (TPPO) with the carboxylic acids adamantane carboxylic acid (ACA) {the 1:1 monohydrate, [(TPPO)(ACA)(H 2 O)], (1)}, terephthalic acid (PPA) {the 4:1 dihydrate, [(TPPO) 4 (PPA)(H 2 O) 2 ], (2)} and o -phthalic acid (OPA) {the 2:1 anhydrate, [(TPPO) 2 (OPA)], (3)} have been determined and refined to residuals 0.044, 0.040 and 0.064 for 2461, 3096 and 2227 observed reflections, respectively. The adducts (1) and (2) represent the first reported hydrated examples of TPPO-carboxylic acid adducts and in addition have, instead of the expected single directed hydrogen bond between the phosphoryl oxygen and the carboxylic acid proton [such as is found with (3)], unique three-centre interactions between the water molecule, the carboxylic acid groups and either a single triphenylphosphine oxide {the polymeric adamantane carboxylic acid structure, (1) [O–O, 2.654 Å, 2.736 Å, 3.000(5) Å]} or two triphenylphosphine oxides {the monomeric terephthalic acid structure, (2) [O–O, 2.567 Å, 2.707 Å, 2.721(5) Å]}. In contrast, with (3), the two carboxylic acid groups are involved in separate direct interactions with the two TPPO molecules [O–O, 2.574 Å, 2.625(8) Å].