Dimer Rhenium Tetrafluoride with a Triple Bond Re-Re: Structure, Bond Strength.

Based on the data of the gas electron diffraction/mass spectrometry (GED/MS) experiment, the composition of the vapor over rhenium tetrafluoride at T = 471 K was established, and it was found that species of the ReF is present in the gas phase. The geometric structure of the ReF molecule corresponding to D symmetry was found, and the following geometric parameters of the r configuration were determined: r(Re-Re) = 2.264(5) Å, r(Re-F) = 1.846(4) Å, α(Re-Re-F) = 99.7(0.2)°, φ(F-Re-Re-F) = 2.4 (3.6)°. Calculations by the self-consistent field in full active space approximation showed that for ReF, the wave function of the A ground electronic state can be described by the single closed-shell determinant. For that reason, the DFT method was used for a structural study of ReX molecules. The description of the nature of the Re-Re bond was performed in the framework of Atom in Molecules and Natural Bond Orbital analysis. The difference in the experimental values of r(Re-Re) in the free ReF molecule and the [ReF] dianion in the crystal corresponds to the concept of a triple σπ (Re-Re) bond and a quadruple σπδ (Re-Re) bond, respectively, which are formed between rhenium atoms due to the interaction of d-atomic orbitals. The enthalpy of dissociation of the ReF molecular form in two monomers ReF (ΔH°(298) = 109.9 kcal/mol) and the bond energies E(Re-Re) and E(Re-X) in the series ReF→ReCl→ReBr molecules were estimated. It is shown that the Re-Re bond energy weakly depends on the nature of the halogen, while the symmetry of the ReBr (D) geometric configuration differs from the symmetry of the ReF and ReCl (D) molecules.