Raman spectroscopic study of BeCl2 in the crystalline, glassy and liquid state of molten BeCl2-CsCl mixtures

E.A. Pavlatou, G.N. Papatheodorou

Physical Chemistry Chemical Physics (2000), 2, 1035-1043

Raman spectra of solid and liquid beryllium chloride and of binary liquid BeCl2–CsCl mixtures have been measured. Systematic investigation of the Raman spectra upon heating the crystalline forms of BeCl2 revealed two different solid phase transitions at 350 and 405°C. A glass phase was also obtained by vapour transport with a crystallisation temperature at ∽250°C. The Raman spectra of the molten and glassy BeCl2 show bands at common frequencies that are correlated to certain vibrational modes of two solid allotropic phases. Temperature dependent measurements of the Raman spectra of a series of BeCl2–CsCl melt compositions suggest that: (a)at XBeCl20.5 the liquid structure is predominated by tetrahedral and trigonal beryllium species in equilibrium, BeCl42−=BeCl3+Cl; and (b) at XBeCl2>0.5 two types of polynuclear beryllium ionic species are formed, one consisting of a "chain" of edge-bridged BeCl4 tetrahedra and the other having a "cluster" like structure of vertex-bridged BeCl4 tetrahedra. The spectra of pure BeCl2 liquid and glass are interpreted in terms of similar neutral "chain" and "cluster" structures having as ending units trigonally coordinated beryllium atoms. On going from the glass to the melt and/or with increasing temperature the "cluster" structures unfold to form "chains". Similarities also exist between the structures of molten BeCl2 and of glassy SiSe2.

doi: 10.1039/A909120C

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