J. Tremmel

Combined electron diffraction/mass-spectrometric investigation of the molecular structure of germanium dichloride

Abstract Germanium dichloride was produced by reaction of Ge + GeCl 4 at 660°C in a combined electron diffraction/quadrupole mass-spectrometric experiment. The structure of germanium dichloride can be characterized by the following parameters: r a (GeCl): 2.183 (4) A, l (GeCl): 0.080 (2) A, ∠ClGeCl: 100.3(4)°, l (ClċCl): 0.166 (4) A. The geometrical variations observed in Group IV dihalides are consistent with the VSEPR model, and with considerations based on non-bonded interactions.

The molecular geometry of iron trifluoride from electron diffraction and a reinvestigation of aluminum trifluoride

The molecular geometry of iron trifluoride has been determined at 1260 K by gas-phase electron diffraction. Use of a platinum envelope during the experiment prevented the iron trifluoride sample from partial reduction otherwise observed at high temperatures. The molecular geometry of aluminum trifluoride has been reinvestigated at 1300 K. The electron diffraction results for both AlF3 and FeF3 are compatible with planar bond configuration (D3hsymmetry) with bond lengths (rg): Al-F 1.630±0.003 Å and Fe-F 1.763±0.004 Å. Experimental vibrational frequencies support the notion of planarity for aluminum trifluoride. There is no such additional spectroscopic evidence available for iron trifluoride.

A nozzle system for broad temperature range and versatile applicability in gas electron diffraction

A high-temperature (up to 1500K) nozzle system is described. Its utility is shown for electron diffraction experiments on products of reaction, dissociation and decomposition as well as on moisture-sensitive samples.

Electron diffraction study of the molecular structure of germanium dibromide

Abstract The molecular structure of ground-state monomeric germanium dibromide (rg 2.337 ± 0.013 A, ∠101.2 ± 0.9°) has been determined by electron diffraction. The GeBr2 is produced by a reaction between Ge metal and GeBr4 vapour. Experimental data may indicate the presence of another state.

High temperature electron diffraction investigation and the bending vibrational frequency of cobalt (II) chloride

Abstract The structure of CoCl2 was studied by high-temperature gas electron diffraction. The linear shrinkage effect was determined in particular and compared to values calculated by spectroscopical methods. By this approach the v2 vibrational frequency was determined to be 78 ± 8 cm −1, which is significantly larger than a previous estimate from the literature. The present; value is fairly well compatible with a recent matrix-isolation infrared frequency, viz. 94 cm−1.

Two independent gas electron diffraction investigations of the structure of plumbous chloride

Abstract The results of two independent electron diffraction analyses of PbCl 2 are compared. The bond lengths ( r g ) and angles ( r α ) were found to be 2.447 ± 0.005 A and 98.7 ± 1.0° (nozzle temperature 853 K, Budapest), and 2.444 ± 0.005 A and 98.0 ± 1.4° (nozzle temperature 963 K, Moscow), respectively.

Molecular structure of monomeric manganese (II) bromide with evidence on the structure of the dimer from electron diffraction

Abstract An electron diffraction investigation (at 608° C) determined r g (Mn-Br) = 2.344 ± 0.006 A in MnBr 2 . Assuming a linear equilibrium configuration, the observed vibrational amplitudes and shrinkage effect allowed estimation of the vibrational frequencies. The dimer has a four-membered ring and a bridging bond longer than the bond of the monomer by 0.23 A.

The use of the rotating sector for observation of electron intensities in gas electron diffraction

Observation of the primary beam and scattered electrons is important for centring the electron beam and establishing the optimum conditions in a gas electron diffraction experiment. Electronic control utilizing the beam stop and the rotating sector (see e.g. Schafer 1976) as electron collectors seems to be a suitable method. Such a detecting device, using a centrally friction driven sector which needs no additional contacts, is described.

Gas electron diffraction apparatus at the University of Antwerpen

Abstract A description is given of the Antwerpen gas electron diffraction unit. Its electron optical system maintains a stability of the electron wavelength of about 0.01% over several hours and of about 0.3% over at least one year. Differences with respect to the well-known Balzers unit are the following. The electron beam is shielded from external magnetic fields by a mu metal cylinder, and the machine background is reduced by a movable aluminum disk in addition to graphite coating of the diffraction chambers interior. Furthermore, features enhancing the serviceability are: (i) built-in means to accurately measure the nozzle-to-photographic plate distances, (ii) a processor controlled vacuum system, (iii) means for easy adjustment of beam centring and estimation of exposure time, (iv) semi-automatic recording of the diffraction pattern, and marking of the diffraction centre on the photographic plate, and (v) built-in safety measures in case of a vacuum breakdown. Two gas-inlet systems are available with active temperature ranges between −190 and +30°C, and between +20 and +200°C, respectively.

Molecular structures of monomeric gallium trichloride, indium trichloride and lead tetrachloride by gas electron diffraction

Gas electron diffraction data for monomeric GaCl3, monomeric InCl3 and PbCl4 have been recorded with nozzle temperatures of about 380, 480 and 20 °C respectively. The data for GaCl3 and InCl3 are consistent with equilibrium structures of D3h symmetry and bond distances ra= 210.8(3) and 228.9(5) pm respectively. The data for PbCl4 are consistent with an equilibrium structure of Td symmetry and ra= 237.3(3) pm. Bond energies and distances from the literature show that the M–Cl bonds in MCl(g) are stronger, but longer, than in MCl3(g) for M = Al, Ga or In, and that M–Cl bonds in MCl2(g) are stronger, but longer, than in MCl4(g) for M = Ge, Sn or Pb. It is suggested that the relative weakness of the bonds in group-valent chlorides is due to the energy required to promote the Group 13 metal atoms from the 2P (s2p) ground states to 4P(sp2) valence states, or to promote the Group 14 metal atoms from 3P(s2p2) ground states to 5S(sp3) valence states. Further that the decreasing stability of the group-valent relative to subvalent chlorides as the Groups are descended is due both to increasing promotional energies and to decreasing M–Cl bond strengths.