Molecular structure of ErCl<Subscript>3</Subscript> and YbCl<Subscript>3</Subscript> according to the data of the simultaneous electron diffraction and mass spectrometric experiment

The saturated vapors of ErCl₃ and YbCl₃ were studied in a simultaneous electron diffraction and mass spectrometric experiment at 1165 K and 1170 K, respectively. In the vapors of these compounds, we found up to 3 mol.% dimers along with the monomers. The parameters of the r _g effective configuration of the monomer molecules were determined. For ErCl₃ and YbCl₃, the internuclear distances r _g(Ln-Cl) were 2.436(5) Å and 2.416(5) Å, and the bond angles ∠_g(Cl-Ln-Cl) were 117.0(10)° and 117.2(10)°, respectively. The equilibrium configurations and vibration frequencies of the monomer and dimer molecules were calculated by the HF, B3LYP, and MP2 methods using the combination of the ECP_D energy-consistent quasirelativistic core potential, including 4f electrons [Kr4d ¹⁰4f ⁿ ], and the contracted [5s4p3d] valence basis set for Er and Yb atoms and the MIDIX [4s3p1d] basis set for Cl atoms. The parameters of the effective r _g configuration of the monomer molecules corresponding to the temperature of the experiment were calculated. The difference between the calculated equilibrium r _e(Ln-Cl) and temperature-averaged r _g(Ln-Cl) distances was found to be 0.001–0.002 Å and did not exceed the error of the r _g(Ln-Cl) parameter determined in the electron diffraction experiment. The experimental parameters of the r _g structure were shown to be consistent with the idea about the planar equilibrium geometrical configuration of ErCl₃ and YbCl₃ molecules.     

Conformers and Electronic Spectra of Dansylamide: Experimental and Theoretical Studies

Particular features of the geometrical and electronic structure of six possible conformers of dansylamide ((CH₃)₂N–C₁₀H₆–SO₂NH₂) are considered. The electronic absorption spectra of the conformers of dansylamide in the free state and taking into account the influence of an aqueous solvent (in terms of the PCM model) are calculated by the TDDFT method. It is shown that, as a result of taking into account solvation, the electronic absorption spectra of the conformers exhibit a bathochromic shift, and the difference in the values of λ of the conformers reaches 16 nm. The calculated electronic absorption spectra in an aqueous medium agree qualitatively with the obtained experimental spectra. An analysis of molecular orbitals involved in the first three electronic transitions of the conformers is carried out. It is suggested that the broadening of the band with λ_max = 326 nm in the experimental spectrum may be caused by the presence of dansylamide conformers in the aqueous solution. It is shown that the calculated values of λ in the electronic absorption spectra of dansylamide in the aqueous solvent depend substantially on the DFT functional type.     

Relationships between geometrical and electronic structures and optical properties of 1,8-naphthosultam substituents and derivatives: TDDFT study

Geometrical and electronic structure and optical properties of several substituents and derivatives of 1,8-naphthosultam are studied by quantum-chemical DFT and TDDFT. It is found that the substituents –NO₂, –CF₃, and –N(CH₃)₂ affect the geometrical and electronic structure the most. It is shown that the Stokes shift is greatest (≈260 nm) for compounds with the strong donor substituent –N(CH₃)₂, while strong acceptor substituents provide a quite small Stokes shift. The dependence of the Stokes shift on the difference in energies of the frontier orbitals of the ground and excited states of molecules is found. Of the 1,8-naphthosultam substituents considered, compounds with –N(CH₃)₂ substituent, which emit in the biological window region, can be advised for use in optical bioimaging. The results can be used as a basis for the development and creation of new functional materials and biologically active compounds.     

The molecular structure of PrI3 and GdI3 as determined by synchronous gas-phase electron diffraction and mass spectrometric experiment assisted by quantum chemical calculations

A gas electron diffraction study of PrI₃ and GdI₃ has been carried out in combination with mass spectrometric vapour monitoring at 1110(10) K and 1100(10) K, respectively. Up to 3 mol.% of dimeric species was observed in addition to the dominating monomeric molecules. The change of the thermal-averaged r _g configuration parameters of the molecules in the series LaI₃ → LuI₃ reflects the lanthanide contraction. A low value of the shrinkage δ(I···I) even at such a high temperatures may be considered due to vibration effects in molecule whose equilibrium geometric nuclear structure is planar and which correspond to configurationally averaged 4f ⁿ electronic state. B3LYP calculations performed in this study with large core potential for lanthanide atoms also resulted in equilibrium geometry of D _3h symmetry. According to the quantum chemical calculations, the potential function the non-planar vibration is essentially anharmonic, which is therefore to be taken into account to correctly describe nuclear dynamics in molecules such as LnI₃.     

Molecular structure of LuBr<Subscript>3</Subscript> according to the data of the simultaneous electron diffraction and mass spectrometric experiment

The saturated vapor of lutetium tribromide was studied in the simultaneous electron diffraction and mass spectrometric experiment at 1161(10) K. Along with the monomer molecular forms, the vapor contained an insignificant (up to 3 mol.%) amount of dimers. The parameters of the effective configuration of the monomer molecule were determined. The internuclear distance r _g(Lu-Br) is 2.553(5) Å, and the effective bond angle ∠_g(Br-Lu-Br) is 115.3(10)°. The temperature-averaged r _g parameters were calculated by the B3LYP method using the potential functions obtained by scanning the PES along the vibration coordinates and compared with similar experimental values. It was shown that the geometrical model of the LuBr₃ molecule of D _3h symmetry was consistent with the experimental data. The dependence of the r _g parameters of the LuBr₃ molecule on the vapor temperature was studied theoretically.