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Gas-phase electron diffraction was applied for the molecular structure determination of octamethylporphyrin tin(II), SnN(4)C(28)H(28), at the temperature of 706(10) K. The molecule was found to possess C(4v) symmetry with the Sn atom 1.025(30) Å above the plane of the N atoms and the following main internuclear distances (r(h1), Å): Sn-N = 2.301(9), C(α)-N = 1.360(8), C(α)-C(β) = 1.453(4), C(α)-C(m) = 1.395(4), C(β)-C(CH3) = 1.498(4). Quantum chemical calculations, DFT (B3LYP, BP86, PBE, PBE0) with cc-pVDZ, cc-pVTZ and cc-pVQZ basis sets reproduce the experimental bond distances with accuracy within 0.03 Å. According to NBO(B3LYP/cc-pVTZ) analysis, the direct donation gives a prevailing contribution to Sn-N bonding, decreasing the net charge on Sn from formal +2 to +1.28. The substitution effects at the pyrrole rings are discussed. The ability of different theoretical methods to predict the structure of this compound is analyzed.

The molecular structure of decachloroferrocene has been determined by gas electron diffraction supported by quantum chemical calculations. The equilibrium conformation has staggered ligand rings and D5d symmetry. The barrier to internal rotation is, however, only 0.8(2) kJ mol−1. This barrier is so low that even at room temperature the vast majority of molecules in the gas phase would have sufficient thermal energy to undergo virtually non-hindered internal rotation. While the eclipsed equilibrium conformation of unsubstituted ferrocene is determined by attractive dispersion interaction between the two cyclopentadienyl ligands, the staggered equilibrium conformation of Fe(η-C5Cl5)2 is due to steric repulsion between Cl atoms at different rings. The ligands are non-planar: the C–Cl bonds are bent 3.7(3)° out of the plane of the C5 ring away from the metal atom. The Fe–C, C–C and C–Cl bond distances (ra) are: 205.0(4) pm, 143.4(3) pm and 170.2(4) pm respectively.

The structure of the UF/sub 4/ molecule has been studied by gaseous electron diffraction. An analysis of the values of the mean amplitudes of the vibrations has indicated that its structure is not tetrahedral. The possible models of the molecule C/sub 3v/, D/sub 2d/, D/sub 4h/, C/sub 4v/ have been examined. The experimetal data show best agreement with the models with symmetry D/sub 2d/ and C/sub 3v/.

A survey is presented on electron diffraction by Inl, In13, In21~, Inlnl 4 and on the vapor compositions above indium monoiodide, diiodide, and triiodide. The molecular structures are examined and relationships are derived between the structure parameters. Estimates are made for the lacking vibrational frequencies of In21s, and band assignments are made for Inlnl 4. The electron-diffraction data give the enthalpy and entropy of 21nl 3 $ !n216 and Inl + Inl 3 $ InInl~, from which the heats of formation of gaseous In216 and Inlnl~ can be calculated. These molecules show a correlation between the mean bond energies and the structural characteristics. Heats of reaction are derived for reactions involving indium io ~ dides.

An electron diffraction study was carried out on the saturated vapor above solid indium diiodide. At 284/sup 0/C, this vapor consists of 59 mole % InI/sub 3/, 28 mole % InI, and 13 mole % In/sub 2/I/sub 4/. Structural parameters were obtained for InI/sub 3/ and In/sub 2/I/sub 4/. The In-I internuclear distance r/sub ..cap alpha../ (In-I) = 2.620(6) A in InI/sub 3/ is in accord with the value previously obtained in a study of InI/sub 3/ vapor. Three possible configurations were examined for the In/sub 2/I/sub 4/ molecule. The most favored configuration has C/sub 2v/ symmetry with equal valence indium atoms, InInI/sub 4/ and r/sub ..cap alpha../ (In/sup III/-I/sub t/) = 2.640(6) A, r/sub ..cap alpha../ (In/sup III/-I/sub b/) = 2.740(6) A, r/sub ..cap alpha../ (In/sup I/-I/sub b/) = 3.527(86) A, ..cap alpha..(I/sub t/-In/sup III/-I/sub t/) = 125 (5)/sup 0/, ..beta..(I/sub b/-In/sup III/-I/sub b/) = 97(4)/sup 0/.

Combined mass spectrometric and electron diffraction study of the overheated vapor over calcium dipivaloylmethanate was performed. It was established that one molecular form, Ca(DPM)2, predominates in the vapor at 420–460‡C. The ra, rg and ra parameters of the Ca(DPM)2 molecule were determined, and the symmetry of the molecule was found to be D2d.

The vibrational problem for the Y(DPM)3 and Y(DPM)2 molecular forms that are present in the overheated vapor of yttrium tris-dipivaloylmethanate is solved. For this purpose, the experimental Raman spectra of Y(DPM)3 solutions are interpreted. The force field of the Y(DPM)2 radical is estimated on the basis of the force constants determined for Y(DPM)3. Rms vibrational amplitudes and corrections for perpendicular displacements to the internuclear distances of the two molecular forms needed for interpreting electron diffraction data are calculated.

Simultaneous electron diffraction and mass spectrometric investigation of overheated vapor of strontium dipivaloyl methanate was carned out. It was found that at 437(5)°C one molecular form, Sr(DPM)2, prevails in the vapor. The ra, rg, and rα structural parameters of the Sr(DPM)2 monomeric molecule were determined; the molecule was found to have D2d symmetry. The structural characteristics are compared in the series Ca(DPM)2—Sr(DPM)2—Ba(DPM)2.