Structural analysis of molten Na2BeF4 and NaBeF3 by X-ray diffraction

Abstract

The structures of molten Na₂BeF₄(923 ± 10 K) and NaBeF₃(743 ± 5 K) have been investigated by X-ray diffraction analysis. BeF₄ tetrahedra existing in the crystalline state persist as the fundamental structural unit in the molten state. Molten Na₂BeF₄ contains mainly monomeric BeF^2–₄ with four unshared F^– corners. A configuration for four Na⁺ cations around a BeF₄ tetrahedron is suggested for molten Na₂BeF₄. In molten NaBeF₃, short-chain anions, such as the common F^– corner sharing dimeric Be₂F^3–₇ and/or trimeric Be₃F^4–₁₀, mainly occur.