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 Re F is present in the gas phase. The geometric structure of the Re F 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 Re F , 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 Re X 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 Re F molecule and the [Re F ] dianion in the crystal corresponds to the concept of a triple σ π (Re -Re ) bond and a quadruple σ π δ (Re -Re ) bond, respectively, which are formed between rhenium atoms due to the interaction of d-atomic orbitals. The enthalpy of dissociation of the Re F molecular form in two monomers ReF (Δ H°(298) = 109.9 kcal/mol) and the bond energies E(Re-Re) and E(Re-X) in the series Re F →Re Cl →Re Br 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 Re Br (D ) geometric configuration differs from the symmetry of the Re F and Re Cl (D ) molecules.