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Structural and Energetic Properties of Haloacetonitrile - GeF₄ Complexes.

ABSTRACT: The 1:1 and 2:1 complexes of FCH₂CN and ClCH₂CN with GeF₄ have been investigated by M06/aug-cc-pVTZ calculations, low-temperature, thin-film IR spectroscopy, and an x-ray structure has been obtained for (FCH₂CN)₂-GeF₄. Theoretical structures and binding energies for FCH₂CN-GeF₄ and ClCH₂CN-GeF₄ demonstrate that halogen substitution significantly weakens the Ge-N dative bonds. The Ge-N distances for the F-and Cl-complexes (2.447 and 2.407 Å, respectively) are about 0.2 Å longer than in CH₃CN-GeF₄, and the binding energies (6.5 and 6.9 kcal/mol) are 2 to 3 kcal/mol less. Furthermore, the Ge-N potential curves are flatter for the halogenated complexes, exhibit a greater response to dielectric media, and thus these systems are more prone to structural change in condensed-phases. For the 2:1 complexes, experimental and theoretical structure and frequency data are consistent with differences in the (calculated) gas-phase and solid-state structures. For (FCH₂CN)₂-GeF₄ the calculated gas-phase structure has Ge-N distances about 0.3 Å longer those in the x-ray structure (2.366 Å vs. 2.059 Å (ave)). Also, low-temperature IR spectra of CH₃CN/GeF₄, FCH₂CN/GeF_4, and ClCH₂CN/GeF₄ thin films are consistent with the presence of 2:1 nitrile:GeF₄ complexes, and the splitting patterns of the GeF-stretching bands (~700 cm^-1) match predictions for the corresponding complexes, but are red-shifted relative to the gas-phase predictions, and reflect Ge-N bonds that are compressed in the solid-state, relative to predicted gas-phase structures.

SUBMITTER: Waller AW

PROVIDER: S-EPMC8279132 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Ag16B4O10 has been obtained as a coarse crystalline material via hydrothermal synthesis, and was characterized by X-ray single crystal and powder diffraction, conductivity and magnetic susceptibility measurements, as well as by DFT based theoretical analyses. Neither composition nor crystal structure nor valence electron counts can be fully rationalized by applying known bonding schemes. While the rare cage anion (B4O10)8- is electron precise, and reflects standard bonding properties, the silver ion substructure necessarily has to accommodate eight excess electrons per formula unit, (Ag+)16(B3+)4(O2-)10 × 8e-, rendering the compound sub-valent with respect to silver. However, the phenomena commonly associated with sub-valence metal (partial) structures are not perceptible in this case. Experimentally, the compound has been found to be semiconducting and diamagnetic, ruling out the presence of itinerant electrons; hence the excess electrons have to localize pairwise. However, no pairwise contractions of silver atoms are realized in the structure, thus excluding formation of 2e-2c bonds. Rather, cluster-like aggregates of an approximately tetrahedral shape exist where the Ag-Ag separations are significantly smaller than in elemental silver. The number of these subunits per formula is four, thus matching the required number of sites for pairwise nesting of eight excess electrons. This scenario has been corroborated by computational analyses of the densities of states and electron localization function (ELF), which clearly indicate the presence of an attractor within the shrunken tetrahedral voids in the silver substructure. However, one bonding electron pair of s and p type skeleton electrons per cluster unit is extremely low, and the significant propensity to form and the thermal stability of the title compound suggest d10-d10 bonding interactions to strengthen the inter-cluster bonding in a synergistic fashion. With the present state of knowledge, such a particular bonding pattern appears to be a singular feature of the oxide chemistry of silver; however, as indicated by analogous findings in related silver oxides, it is evolving as a general one.

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Structural and Energetic Properties of Haloacetonitrile - GeF4 Complexes.

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Structural and Energetic Properties of Haloacetonitrile - GeF₄ Complexes.