Comparative study of salts Cs₂B₁₀H₁₀ and Cu₂B₁₀H₁₀ by X-ray spectroscopy methods

Conclusions

• 1. From a comparison of the$CuL_{\alpha _{1, 2} }$ and BK^α, spectra of Cu₂B₁₀H₁₀ it follows that the upper valence MO in this salt are build mainly from Cu⁺ 3d orbitals (G and H maxima). The deeper MO are represented mainly by the 2p orbitals of the B atoms. The BK^α and CuL$CuL_{\alpha _{1, 2} }$, overlap of the spectra indicates that MO of the mixed p-d type are present, which can be explained by the participation of the Cu⁺ 3p orbitals in forming the chemical bond.

• 2. A charge transfer of ∼0.5 e from the B₁₀H₁₀ ²⁻ ion to the Cu⁺ ions occurs in the salt Cu₂B₁₀H₁₀ when compared with Cs₂B₁₀H₁₀.

• 3. Two vertex and four equatorial B atoms of the anion participate in forming the bond in Cu₂B₁₀H₁₀. The equatorial atoms undergo the greatest change in the bond energy, which can be explained by assuming their participation in the simultaneous formation of both the three-center B-Cu-B bond and the B-H-Cu bridge bond.

• 4. From an estimate of the charge value of the Cu⁺ ion and the x-ray spectral data it can be postulated that the bond with Cu₂B₁₀H₁₀ bears a partially covalent character, which is caused by the donor-acceptor mechanism for the interaction of the Cu ion with the B₁₀H₁₀ ²⁻ ion.