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Crystals of the title compound are monoclinic with a= 15·199, b= 23·814, c= 13·383 A, β= 119·07°, Z= 4 space group P21/m. 7113 visually estimated intensities were used, and the structure refined to R 9·83%. There are two crystallographically independent cations each possessing a mirror plane. The iridium atoms are at the centre of a trigonal bipyramid with the PPh3 ligands at the apices and the CO and CS groups co-planar with the iridium atoms in the equatorial plane. Mean thiocarbonyl bonding parameters are: Ir–C(S) 1·867, C–S 1·511 A; Ir–C–S = 178·2°. The σ and π bonding properties of the CO and CS groups are compared.

SummaryThe use of lanthanum hydroxide tracers permitted the demonstration of two distinct types of alterations in the ultrastructural appearance of the glomerular basement membrane in aminonucleoside nephrosis. In some capillary loops an increase in the number and size of lanthanum aggregates were observed, in others portions of the basement membrane measuring in length 600-1000 A the entire thickness of the membrane appeared to be filled with tracer molecules. It is concluded that the lanthanum method is a useful approach for the demonstration of ultrastructural changes in the basement membrane in instances where the use of conventional electron microscopic techniques fail to do so.

Crystals of the title compound are orthorhombic with a= 11·310, b= 14·799, c= 7·690 A, Z= 4, space group P212121. 1511 Visually estimated X-ray reflexions were refined by least squares to R 6·25%; the structure was solved by direct methods. The stereochemistry of the molecule is of the allene type with the two C-NC planes approximately normal to each other, with C–NC angles of 127·2(3)°, and with an NCN angle of 170·4(4)°.

Crystals of the title compound (I) are orthorhombic with a= 24·738, b= 3·827, c= 13·277 A, Z= 4, space group Pna21. The structure was solved by direct methods. 1205 Visually estimated X-ray intensities were refined by full-matrix least-squares to R 7·73%. The molecule differs markedly from an idealised allene type. Important differences (idealised values in parentheses) are: C–NC 129·6 and 134·4°(120°), NCN 169·7°(180°), and C–N ⋯ N–C torsion angle 113·5°(90°).

IN a recent paper Gaydon and Wolfhard1 state: “In stationary pre-mixed flames of hydrocarbons at pressures between 1 atm. and a few mm. of mercury . . . the flame speed is independent of pressure". Reference is made to determinations by Wolfhard2 of the effect of pressure on the burning velocities of acetylene/air, acetylene/oxygen and acetylene/oxygen/argon mixtures and also of butane/air mixtures. Some experiments of ours and various recorded measurements of the effect of pressure on burning velocity, excluding those in tubes, had led us to a different view.

RECENTLY, Bradley has proposed a theory which correlates and predicts the structures of metallic alkoxides1. At the moment, Bradley's theory cannot be fully developed because of the lack of direct structural information. In particular, it is not known whether lithium methoxide is ionic, as generally assumed, or whether it is a giant polymer2. This communication describes the structure of lithium methoxide, which is shown to be similar to that of lithium hydroxide3. Although the structure has some features reminiscent of a giant two-dimensional polymer, it would normally be considered ionic.

A three-dimensional X-ray diffraction analysis of the structure of triphenylphosphoranylideneketen (C6H5)3PCCO, has been completed. The crystals are monoclinic, space group P21/n, with a= 14·527, b= 10·299, c= 10·794 A, β= 94° 10′. The structure was solved by direct methods. All fifteen hydrogen atoms were located from a difference synthesis. The final R factor for 2106 reflexions collected with a Hilger and Watts diffractometer is 9·2%. The bond lengths in the cumulene chain are remarkably short, and the chain is bent to an angle of 145·5° at the carbon atom nearest the phosphorus. A dπ–ππ type of interaction is postulated to account for the molecular geometry.

A three-dimensional X-ray diffraction analysis of the structure of nitrilotrimethylene triphosphonic acid N(CH2PO3H2)3, has been carried out. The crystals are monoclinic, space group P21/c, with a= 12·050, b= 7·474, c= 11·868 A, β= 104° 10′, Z= 4. The solution of the crystal structure presented considerable difficulties since all three phosphorus atoms lie close to special positions. However, once a reasonable trial structure had been obtained, refinement proceeded smoothly until the final R factor for 2236 independent reflexions measured with a Hilger–Watts linear diffractometer was 5·76%. All twelve hydrogen atoms were located from a difference synthesis, and their disposition shows that the molecules exist as zwitterions in the crystal. A true representation of the molecular structure is thus NH+(CH2PO3H2)2(CH2PO3H)–. All except the methylene hydrogen atoms are involved in an efficient and complex system of intermolecular hydrogen bonds. The bonds and angles round the nitrogen atom show no deviations from each other and are close to the expected values, but the angles at all three phosphorus atoms diverge very significantly from a regular tetrahedral value. The P–O distances split into three recognisable groups. The shortest, with a mean value of 1·477 A, correspond to PO bonds. The longest (1·534 A) are associated with P–OH bonds. Intermediate between these two extremes (1·501 A) are two bonds which may be described as P–O– bonds, each oxygen atom carrying a fractional negative charge.

A three-dimensional X-ray diffraction analysis of an azacyclotrisiloxane has been completed. The crystals are monoclinic, space group P21/a, with a= 17·412, b= 16·287, c= 13·725 A, β= 116° 31′. The solution to the structure was obtained by direct methods with a ratio of reflexions to atoms of less than 5 : 1. Positional parameters and individual isotropic temperature factors were refined until R reached a final value of 12·5% for 2337 independent reflexions. Anomalous lengths were obtained in the ethyl group for a reason which is not known, but other molecular parameters are close to standard or expected values. The central six-membered ring adopts a distorted boat form.

The structure of the title compound has been determined. The crystals are monoclinic with a= 15·362, b= 9·483, c= 20·054 A, β= 95° 6′, Z= 4, space group C2. 3292 Visually estimated X-ray reflections were refined to R 8·88%. There are two crystallographically independent molecules, each possessing a two-fold axis. The PCP angle is 143·8° in one of these molecules and 130·1° in the other. The results are compared with those obtained for related species, including the isoelectronic cation Ph3PNPPh3 and the cumulene ylides.