The Remarkable [ReH₉]^2– Dianion: Molecular Structure and Vibrational Frequencies

Abstract

The equilibrium geometries and vibrational frequencies of the extraordinary [ReH9](2-) dianion (D3h symmetry) are investigated using Hartree-Fock (HF) theory, coupled cluster theory with single and double excitations (CCSD), and coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. The new generation of energy-consistent relativistic pseudopotentials and correlation consistent basis sets [cc-pVXZ-PP (Re) and cc-pVXZ (H) (X = D, T, Q)] are used. Anharmonicity was considered using second-order vibrational perturbation theory. The predicted geometries and vibrational frequencies generally agree with experimental findings. In order to stabilize the [ReH9](2-) dianion, the M2ReH9 (M = Na, K) sandwich complexes (D3h symmetry) are studied at the CCSD(T)/VTZ (VTZ = cc-pVTZ-PP (Re) and cc-pVTZ (H, Na, K)) level of theory. Compared to the [ReH9](2-) dianion, the predicted vibrational frequencies involving Re-H stretching modes are improved, indicating the importance of considering counterions in electronically dense systems. The natural bond orbital analysis shows that each H atom only bonds with the Re center, and the 5d orbitals of Re and 1s orbitals of H are major factors for the covalent Re-H bonding.

LModeA-nano: A PyMOL Plugin for Calculating Bond Strength in Solids, Surfaces, and Molecules via Local Vibrational Mode Analysis

“…119 As listed in Table 3, the Re−H bond length in the gas-phase dianion was underestimated by our calculation compared to the calculated values at the coupled-cluster level by Schaefer and coworkers. 120 However, our calculated Re−H bond length values match quite well with the K 2 ReH 9 structure resolved with the neutron diffraction study by Bronger and co-workers. 121 From the calculation results in Table 3, the cap Re−H bonds are in general shorter than the prism Re−H bonds.…”

Unusual Intramolecular Motion of ReH92– in K2ReH9 Crystal: Circle Dance and Three-Arm Turnstile Mechanisms Revealed by Computational Studies

“…By comparing the AIMD simulation results for the ReH 9 2– dianion in gas phase and in K 2 ReH 9 crystal, we realized that the aforementioned two isomerization processes in the K 2 ReH 9 crystal are susceptible to the potassium cations surrounding the ReH 9 2– dianion . Therefore, the calculated energy barriers of fluxional processes in K 2 ReH 9 are coupled to the prediction of interatomic distances and lattice parameters by DFT.…”

“…However, we believe the direct reason for such barrier difference is on the K···H electrostatic interactions. Calculations by Schaefer and co-workers demonstrated in a model K 2 ReH 9 molecule that there exists electrostatic attraction between the potassium cations and the hydride ligands with partial negative charges . Therefore, such electrastatic attraction could stabilize the ReH 9 2– dianions in K 2 ReH 9 crystal.…”

“…By comparing the AIMD simulation results for the ReH 9 2− dianion in gas phase and in K 2 ReH 9 crystal, we realized that the aforementioned two isomerization processes in the K 2 ReH 9 crystal are susceptible to the potassium cations surrounding the ReH 9 2− dianion. 47 Therefore, the calculated energy barriers of fluxional processes in K 2 ReH 9 are coupled to the prediction of interatomic distances and lattice parameters by DFT. To select a density functional that can best reproduce the experimentally resolved crystal structure of K 2 ReH 9 , we tested four generalized gradient approximation (GGA) density functionals including PBE, 68,69 PW91, 81,82 revPBE, 72 and PBEsol 83 as well as the meta-GGA density functional TPSS 84 to relax the atomic positions and cell parameters of K 2 ReH 9 simultaneously.…”

“…The molecular structure of ReH 9 2– dianion was first resolved in the K 2 ReH 9 crystal by Ginsberg and co-workers using single crystal X-ray and neutron diffraction in 1964. , Bronger and co-workers redetermined the K 2 ReH 9 crystal structure with neutron diffraction analysis in 1999 and obtained the structure with improved accuracy . Over the past six decades, a series of experimental studies have been carried out to delineate the vibrational properties of ReH 9 2– in crystals, − and the high-pressure phases of some ionic ReH 9 2– salts (e.g., BaReH 9 ) were pursued as potential superconductors. , Numerous theoretical studies were conducted on ReH 9 2– including its structure, vibrational spectra, chemical bonding properties, and high-pressure induced structural changes of related crystals. ,,− …”