A simple and efficient method to synthesize metal salts of M2[trans-B20H18] (M = Li, Na, K, and Cu)

Abstract

The synthesis of [trans-B₂₀H₁₈]²⁻ from [closo-B₁₀H₁₀]²⁻ based on redox principles has been developed but is still limited. Using different oxidants often leads to various by-products and affects yields. This paper presents a facile and efficient method for synthesizing [trans-B₂₀H₁₈]²⁻ by directly using the alkali metal salt of [closo-B₁₀H₁₀]²⁻ as the precursor. This approach enables the synthesis of the metal salts of [trans-B₂₀H₁₈]²⁻. When Cu(OTf)₂ is used as the oxidant, Cu₂[trans-B₂₀H₁₈] is formed with a yield exceeding 94%. On the other hand, when H₃P(Mo₃O₁₀)₄·xH₂O is used as the oxidant, alkali metal salts of [trans-B₂₀H₁₈]²⁻ (M = Li, Na, and K) are obtained with a yield of up to 85%. All synthesized compounds were characterized by IR, TGA-DSC, and NMR spectroscopy, and M₂[trans-B₂₀H₁₈] (M = K, Cu) was characterized by X-ray single crystal diffraction. Both methods allow for the rapid completion of the reaction in a short time. This synthesis method offers promising potential for further applications, particularly as an all-solid-state electrolyte in battery technology.