Molecular structures of tris(dipivaloylmethanato) complexes of the lanthanide metals, Ln(dpm)3, studied by gas electron diffraction and density functional theory calculations: a comparison of the Ln-O Bond distances and enthalpies in Ln(dpm)3 complexes and the cubic sesquioxides, Ln2O3

The molecular structures of tris(dipivaloylmethanato)neodymium(III), Nd(dpm)3, and tris(dipivaloylmethanato)ytterbium(III), Yb(dpm)3, have been determined by gas electron diffraction (GED) and structure optimizations through density functional theory (DFT) calculations. Both molecules were found to have D3 molecular symmetry. The most important structure parameters (r(a) structure) are as follows (GED/DFT): Nd-O = 2.322(5)/2.383 A, Yb-O = 2.208(5)/2.243 A, O-Nb-O = 72.1(3)/71.3 degrees , and O-Yb-O = 75.3(2)/75.8 degrees . The twist angles of the LnO6 coordination polyhedron, defined as zero for prismatic and 30 degrees for antiprismatic coordination, were theta = 19.1(3)/14.2 degrees for Nd and 20.4(2)/19.2 degrees for Yb. Structure optimizations of La(dpm)3, Gd(dpm)3 Er(dpm)3, and Lu(dpm)3 by DFT also yielded equilibrium structures of D3 symmetry with bond distances of La-O = 2.438 A, Gd-O = 2.322 A, Er-O = 2.267 A, and Lu-O = 2.232 A. The Ln-O bond distances in 12 Ln(dpm)3 complexes studied by GED decrease in a nearly linear manner with the increasing atomic number (Z) of the metal atom, as do the Ln-O bond distances in the cubic modifications of 14 sesquioxides, Ln2O3. The bond distances in the dpm complexes are, however, about 2% shorter. The mean Ln-O bond rupture enthalpies of the cubic sesquioxides calculated from thermodynamic data in the literature vary in an irregular manner with the atomic number; the La-O, Gd-O, Tb-O, and Lu-O bonds are nearly equally strong, and the remaining bonds are significantly weaker. The Ln-O bond rupture enthalpies previously reported for 11 Ln(dpm)3 complexes are on the average 13 kJ mol(-1) or about 5% smaller than in the sesquioxides, but they vary in a similar manner along the series: it is suggested that the pattern reflects variations in the absolute enthalpies of the gaseous Ln atoms.     

Investigation of molecular structure of KNO3 by means of gas-phase electron diffraction

Ivanovo Chemical Technology Institute. Ivanovo State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 4, pp. 51–55, July–August, 1991.     

Electron diffraction study of the In-I system. III. Indium diiodide

Ivanov Chemical Engineering Institute. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 1, pp. 51–55, January–February, 1988.     

Geometrical and electronic structure of LaI3 molecule from the gas electron diffraction data and quantum chemical calculations

The saturated vapor over LaI₃ has been studied using the electron diffraction method with mass-spectral monitoring. It was determined that at a temperature 1142(10) K, along with monomer molecules, dimers are present in the vapor in the quantity of 0.7 mol.%. Effective configuration parameters of LaI₃ molecule were obtained: r _g(La-I) 2.961(6) Å, ∠_g(I-La-I) 116.5(9)°, l(La-I) 0.106(1) Å and l(I…I) 0.412(7) Å. A small deviation of the valence angle ∠_g(I-L-I) from 120° can be totally caused by a contraction effect of the distance r _g(I…I) of LaI₃ molecule with planar equilibrium configuration. The electronic structure of LaI₃ molecule was examined by the B3LYP/SDD method. In terms of the NBO-analysis, the participation of lanthanum 4f-AO in bonding orbitals La-I is noted. It is shown that the NBO-analysis describes the bond La-I in LaI₃ molecule as predominantly ionic one with a noticeable covalence component. The energy of the heterolytic bond breakage E(La-I)_het = 1216 kJ/mole was calculated.     

Electron diffraction study of the structure the NbBr4 molecule

The structure of the NbBr₄ molecule is studied in synchronous electron diffraction and mass spectrometry experiments. Gaseous niobium tetrabromide is synthesized in the course of the experiment during the interaction of niobium chips with bromine at 496°C. Analysis of the geometrical models of the NbBr₄ molecules of C_2v, C_3v, D_2d, and T_d symmetries shows that the tetrahedral model is preferable. The thermally averaged parameters of the effective configuration of the NbBr₄ molecule are as follows: r_g(Nb?Br)=2.418(5) Å, l(Nb?Br)=0.074(2) Å, r_g(Br?Br)=3.921(16) Å, l(Br?Br)=0.271(12) Å, δ(Br?Br)=0.027(18) Å.     

Molecular structure of dipivaloylmethane and the intramolecular hydrogen bond problem

Molecular structure of dipivaloylmethane was investigated by X-ray electron diffraction at 24°C. The C_2v and C_s geometrical models involving an intramolecular hydrogen bond are considered. The C_2v model with enol hydrogen lying symmetrically relative to the oxygen atoms has several advantages over the classical model of the enol tautomer. Translated from Zhumal Struktumoi Khimii, Vol. 41, No. 1, pp. 58-66, January–February, 2000     

Molecular structure of lutetium trichloride monomer and dimer

This paper reports on a simultaneous electron diffraction and mass spectrometric study of the saturated vapor of lutetium trichloride at T = 1070(10) K. It is found that the vapor consists of the monomer LuCl₃ [91.6(1.2) mol. %] and dimer Lu₂Cl₆. The following parameters were obtained for LuCl₃ (r_g configuration): r_g(Lu-Cl) = 2.403(5) Å, r_g(CL.Cl) = 4.119(18) Å,_g(Cl-Lu-Cl) = 117.9(1.3)?. Calculation of vibrational corrections for a transition from r_g to r_α geometry gave a planar equilibrium configuration for LuCl₃ with D_3h symmetry, whereas our previous electron diffraction study recommended a pyramidal configuration. Possible reasons for this controversy are discussed. The geometry of the Lu₂Cl₆ molecule of D_2h symmetry is described by the following parameters (ra configuration): r_α(Lu-Cl_t) = 2.366(5) Å, r_α(Lu-Clα) = 2.589(24) Å, ZCl_t-rLu-Cl_t = 119(7)?, ZCl_b-Lu-Cl_b = 84(2)?. The mean energies of the terminal [E(Lu-Cl_t) = 485 kJ/mole] and bridging [E(Lu-Cl_b) = 292 kJ/mole] bonds of Lu₂Cl₂₆ are estimated.     

Structure and force field of the NbOCl3 molecule

The structure of the NbOCl₃ molecule is studied by electron diffraction at 743(6) K. It is established that the molecule is characterized by C_3v symmetry and the following structural parameters: r_α(Nb=0) 1.682(6) Å, r_α(Nb?Cl) 2.276(5) Å, ?(ONbCl) 107.5(5)°, and ?(ClNbCl) 111.3(4)°. Comparison with the other niobium oxytrihalide molecules shows that these values of the Nb=O bond and the bond angles are characteristic. The assignment of the ?₃ frequency of the NbOCl₃ molecule is refined, and the vibration frequencies of the NbOF₃ molecule are estimated.     

Molecular structure of WO2Br2

Molecular structure of WO₂Br₂ has been studied by electron diffractometry. Structural parameters for the molecule with C_2v symmetry are: r_α(W=O)=1.710(6) Å, r_α(W?Br)=2.398(5) Å, r_α(O?O)=2.815(30) Å, r_α(Br?Br)=4.021(16) Å, r_α(O?Br)=3.347(10) Å. The OWO and BrWBr bond angles are close to tetrahedral:L _αOWO=110.8(2.0)°, L_αBrWBr=113.9(1.0)°. The W=O bond was found to be characteristic in the series of tungsten dioxyhalides.