A Computational Study on Closed‐Shell Molecular HexafluoridesMF₆(M=S, Se, Te, Po, Xe, Rn, Cr, Mo, W, U) – Molecular Structure, Anharmonic Frequency Calculations, and Prediction of the NdF₆Molecule

Abstract

Quantum chemical methods were used to study the molecular structure and anharmonic IR spectra of the experimentally known closed‐shell molecular hexafluorides MF6 (M=S, Se, Te, Xe, Mo, W, U). First, the molecular structures and harmonic frequencies were investigated using Density Functional Theory (DFT) with all‐electron basis sets and explicitly considering the influence of spin‐orbit coupling. Second, anharmonic frequencies and IR intensities were calculated with the CCSD(T) coupled cluster method and compared, where available, with IR spectra recorded by us. These comparisons showed satisfactory results. The anharmonic IR spectra provide means for identifying experimentally too little studied or unknown MF6 molecules with M=Cr, Po, Rn. To the best of our knowledge, we predict the NdF6 molecule for the first time and show it to be a true local minimum on the potential energy surface. We used intrinsic bond orbital (IBO) analyses to characterize the bonding situation in comparison with the UF6 molecule.

Structure and Excitation Spectra of Third-Row Transition Metal Hexafluorides Based on Multi-Reference Exact Two-Component Theory

“…Another important aspect is including static correlation effects to treat the degeneracy in the MF 6 molecules. Most previous studies of MF 6 [25][26][27][28][29][30][31][32][33][34][35][36][37][38] were based on single-reference methods such as the density functional theory (DFT) or coupled cluster theory. These methods are sufficient for closed-shell systems but may encounter problems when there is significant multi-reference effect In the context of the vibrational coupling with the JT effect, multi-reference methods with the SOC were employed by Balasubramanian's group for metal clusters [39][40][41][42], by Mondal for the first-row transition-metal trihalides 43, 44, and by Koseki's group for third-row transition-metal tetrahydrides [45,46].…”