Ronald Mason

A refinement analysis of the crystallography of the phospholipid, 1,2-dilauroyl-DL-phosphatidylethanolamine, and some remarks on lipid-lipid and lipid-protein interactions

A least-squares refinement analysis of atomic positional and thermal parameters in a single crystal of 1,2-dilauroyl-DL-phosphatidylethanolamine: acetic acid has been based on the X-ray diffraction intensities of 1132 independent reflexions, assessed by automatic microdensitometry. The final unweighted discrepancy index is 0.16 with e.s.ds of the bond lengths ranging from 0.02 to 0.12 A. The general features of our earlier, lessprecise analysis are confirmed. The close-packed arrangement of the phospholipid molecules is discussed in relation to electron microscopy and diffraction studies of the structures of membranes from Acholeplasma laidlawii and Halobacterium halobium.

Geometries of and bonding in bi- and polynuclear metal complexes with bridging ligands

The geometries of binuclear and polynuclear complexes of transition and main group metals having bridging groups X (X = halide), OR, SR, NR2, PR2, H and R (alkyl, aryl) are discussed. Previous rationales of the bridge stereochemistry in, for example, (BeCl2)n and [Be(CH3)2]n are rejected and emphasis is placed on the symmetry of the molecular orbitals and their electron occupancy in electron deficient and electron precise species.

The molecular structures of H2Os3(CO)10, H(SC2H5)Os3(CO)10 and (OCH3)2Os3(CO)10

Abstract X-ray crystallographic analyses of H 2 Os 3 (CO) 10 , H(SC 2 H 5 )Os 3 (CO) 10 and (OCH 3 ) 2 Os 3 (CO) 10 are reported. Although hydrogen atom positions have not been located, the essential isostructural nature of the three commplexes establishes the hydride ligands as bridging two metal atoms, separated by 2.670 A, with a formal bond order of two; the bridging hydrido- and thiolato-ligands span an osmiumosmium bond of length 2.863 A and formal bond order one; the two μ-methoxy ligands bridge two metal atoms separated by 3.078 A which, by simple 18 electron rule counting, has a metalmetal bond order of zero. Some general comments are made on the structures of polynuclear transition metal carbonyls.

The reactions of carbon monoxide at coordinatively unsaturated sites on a platinum surface

Abstract Photoelectron spectroscopy has described the dissociative sorption of carbon monoxide at the steps and kinks of a platinum vicinal surface, the sorption being associative at terrace sites.

Phospholipid arrangements in multilayers and artificial membranes: Quantitative analysis of the X-ray diffraction data from a multilayer of 1,2-dimyristoyl-dl-phosphatidylethanolamine

Abstract The X-ray diffraction data from a multilayer of 1,2-dimyristoyl- dl -phosphatidylethanolamine is interpreted quantitatively ( R 1 = 0.20 ) from a single crystal analysis of the molecular structure of 1,2-dilauroyl- dl -phosphatidylethanolamine.

Oxidative addition reactions in cluster complexes of osmium: Intracluster reactions of benzyne and a novel 'phenyl' complex

Abstract The structures of HOs3(CO)7(PPh2)(PPh3)(C6H4), HOs3(CO)8(PPh3)(PPh2C6H4) and HOs3(CO)7(PPh2)(PPh2C6H4C6H3) are described, the latter illustrating an intracluster reaction of the coordinated benzyne ligand.

Cluster chemistry: XXII. Crystal structures of [M3(μ3-C6H4)(μ-PPh2)2(CO)7], M Ru and Os

Abstract Structure determinations and a comparison of the molecular core geometries of the complexes [M3(μ3-C6H4)(μ-PPh2)2(CO)7] (M  Ru and Os) are reported. The isosceles M3 triangle (MM 2.776, 2.759, 2.956(1) A {2.785, 2.766, 2.975(2) A}) (values for Ru {Os} given) is edge-bridged by two PPh2 groups (MP 2.267, 2.334(2); 2.319, 2.361(2) A {2.280, 2.361(8); 2.333, 2.387(7) A}) and a semi-bridging CO ligand (MC 1.933, 2.625(6) A {2.04, 2.77(3) A}; MCO 164.4(6)° {166(3)°}). A C6H4 moiety is bonded to two metal atoms by σ-bonds (MC 2.127, 2.135(6) A {2.14, 2.18(3) A}) and to the third by a π-bond (MC 2.303, 2.353(6) A {2.30, 2.40(3) A}); CC bond distances within the six-membered ring indicate some localisation of π-electron density.

The stereochemistry of N-methylhydrazido(2)-N′ ligands coordinated to group VIa metals. The structural characterisation of the bis(1,2-bis(diphenylphosphino)ethane)-bromo-N-methylhydrazido(2)-N′-tungsten(IV) and N-ethyl-N-phenylhydrazido(2)-N′-tris-(N,N-pentamethylenedithiocarbamato)molybdenum(VI) cations

Abstract The structure analyses of two substituted hydrazido(2) complexes has revealed the detailed stereochemistry of the uncoordinated nitrogen atom; the ligand electron density in several rhenium, tungsten and molybdenum complexes is commented upon in the light of the results.

A possible carbon dioxide complex of molybdenum and its rearrangement product di-µ-carbonato-bis{carbonyltris(dimethylphenylphosphine)molybdenum}: X-ray crystal structure

Carbon dioxide reacts with cis-[Mo(N2)2(PMe2Ph)4] to form a complex [Mo(CO2)2(PMe2Ph)4] which changes spontaneously in solution into a carbonato-bridged complex, [(PMe2Ph)3(CO)Mo(CO3)2Mo(CO)(PMe2Ph)3], the structure of which has been determined; the planar carbonate ions bridge in an unusual manner, each being bidentate to one molybdenum atom and monodentate to the other.

The dimer of heptafulveneiron tricarbonyl

Abstract The preparation of the fluxional methyltropyliumiron tricarbonyl from two different precursors is described. Attempts to convert the salt into the parent complex of heptafulveneFe(CO) 3 provides a dimer, C 22 H 14 Fe 2 O 6 , whose structure has been determined by extensive deuterium labelling and NMR spectroscopy, and by X-ray diffraction methods. The dimer is formed by addition across the exocyclic double bond, the electrocyclic dimerisation [which is the formally non-allowed (8 + 8) π-cycloaddition] being promoted by the metal tricarbonyl fragment. The intramolecular bonding in 3,3′-ethano-871,1′-bis(cyclohepta-2,4,6-trienyl)diiron hexacarbonyl is discussed together with its mechanism of formation.