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

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 BeF2–4 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 Be2F3–7 and/or trimeric Be3F4–10, mainly occur.