Abstract

This work investigates the micro hydration of the beryllium trifluoride anion (BeF3–) with up to three water molecules (BeF3–(H2O)n where n = 1–3). Full geometry optimizations and harmonic vibrational frequencies were computed on various BeF3–(H2O)n stationary points using density functional theory methods (B3LYP-D3BJ, B3LYP, ωB97XD, and M06-2X) as well as the CCSD(T) and MP2 ab initio methods with a triple-ζ correlation-consistent basis set augmented with diffuse functions on all non-hydrogen atoms (haTZ). One BeF3–(H2O)1, five BeF3–(H2O)2 and 11 BeF3–(H2O)3 minima were identified, most of which have not been reported in the literature to date. Two of the new BeF3–(H2O)3 configurations have lower electronic energies than the previously reported trihydrate structure by nearly 1 kcal mol–1, but the previous structure has the lowest energy when harmonic zero-point vibrational energies are included. For the mono- and dihydrates, the water molecule(s) prefer to bind directly to the beryllium trifluoride anion via double ionic hydrogen bonds (DIHBs) to form planar structures with C2v symmetry. With the introduction of a third water molecule, the hydration pattern associated with the lowest-energy structure (with C3 symmetry) changes from solely DIHBs to a hydrogen-bonded network that also includes water–water interactions. The CCSD(T)/haTZ electronic dissociation energies for the BeF3–(H2O)n global minima are 16.0, 30.1, and 43.6 kcal mol–1 for n = 1, 2, and 3, respectively, and these values decrease by about 5% when a counterpoise procedure is applied. The CCSD(T)/haTZ harmonic OH stretching frequencies of H2O decrease appreciably when donating hydrogen bonds to BeF3– and/or H2O molecules. The magnitude of these shifts is strongly dependent on the hydration motif. For the symmetric structures exhibiting only DIHB contacts, the largest shifts at this level of theory are −168 cm–1 for n = 1 (C2v), −138 cm–1 for n = 2 (C2v), and −122 cm–1 for n = 3 (D3h). In contrast, the C3 trihydrate global minimum also has hydrogen bonding between the water molecules, and the largest shift exceeds 200 cm–1. The magnitude can even exceed 300 cm–1 in structures with an H atom that does not participate in hydrogen bonding.

Department(s)

Chemistry

Publication Status

Open Access

International Standard Serial Number (ISSN)

1520-5215; 1089-5639

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2026 American Chemical Society, All rights reserved.

Publication Date

07 May 2026

PubMed ID

42013373

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