Electron Diffraction by Gases

Abstract

The method of electron diffraction is used for determining the C–O–C valence angle (α) in 4,4′ diiododiphenyl ether [(C6H4I)2O] and the molecular structures of phosphorus (P4) and arsenic (As4). The electron diffraction photographs were analyzed by four different methods as follows: (1) Visual measurements, (2) measurements of densitometer records, (3) conversion of densitometer records into relative intensity curves, (4) comparison of transformed intensity curves obtained by multiplying the intensity of scattering by [(1/λ) sin θ/2]2 which produces prominent maxima for measurement. The valence angle α was found to be 118±3° for 4,4′ diiododiphenyl ether, definitely greater than the oxygen valence angle found for simpler types of molecules. Phosphorus and arsenic molecules were found to have a regular tetrahedral structure within the limits of experimental error, the atomic separations being 2.21A and 2.44A, respectively, [methods (1) and (2) were used for the case of arsenic]. The minimum atomic distances as found by crystal structure analysis for phosphorus and arsenic are approximately the same as the atomic separations obtained for the gas molecules, showing in addition that these distances do not change greatly when the bond angle decreases from 100° to 60°.

The crystal and molecular structure of tetrameric arsenic selenide, As4Se4

“…These values are considerably longer than 2.42 A, the covalent diameter of the As atom (Schomaker & Stevenson, 1941). By comparison, the As-As bond length is 2-44 A in gaseous As4 (Maxwell, Hendricks & Moseley, 1935), 2.477 _+ 0.003 A in As4S3 (Whitfield, 1970), 2.428 + 0.008 A in (MeAs)3 (Burns & Waser, 1957) and 2.456 + 0.005 A in (PhAs)6 (Hedberg, Hughes & Waser, 1961). In rhombohedral As, where the distance between an As atom and its three nearest neighbors is 2.517 A (Schiferl & Barrett, 1969), each As atom also has three other neighbors 3.12 A, away and the lengthening of the As-As bond can be ascribed to partial metallic bonding (Mooser & Pearson, 1958).…”

Conformations of Bridged Diphenyls. I. Crystal Structure of 2-(3′-Methyl-4′-nitrophenoxy)-1,3-diisopropylbenzene

“…Other reports of structural data (20,23,24) are of low accuracy, and most comparisons with our results are of little value. However, the short bond (1.28 A) between the phenyl carbon atoms and the bridging oxygen atom in 4,4'-dibromodiphenyl ether is clearly inconsistent with our data.…”

“…The information obtained by gas phase electron diffraction experiments (20,21) is of limited value because of the relative complexity of this system. Hamilton and Steinrauf (22) have recently .reported the crystal structure of the alkaloid vertaline which contains oxygen bridged phenyl rings and provides information on the geometry in the vicinity of the bridging atom.…”

P3Se4I: 5-Iodo-2,3,6,7-tetraselena-1,4,5-triphosphabicyclo[221]heptan, ein neues Phosphorselenaiodid / P3Se4I: 5-Iodo-2,3,6,7-tetraselena-1,4,5-triphosphabicyclo[221]heptan, a New Phosphorus Selena Iodide

“…Die P-P-Bindungslänge beträgt 219,2 pm. Dieser Bindungsabstand ist deutlich kürzer als der P-P-Bindungsabstand in der Stammverbindung P 4 Se 3 von 225 pm [6] und etwas kürzer als der P-P-Abstand in den P 4 -Tetraedern des weißen Phosphors (221 pm [7]). Verbindungen mit P-P-Einfachbindungen weisen im allgemeinen größere P-P- Die Zuordnung der 31 P-Resonanzen erfolgte anhand der NMR-Daten von a-und /?-P 4 Se 3 I 2 [5].…”