Molecular dynamics calculations were performed on two liquid ionic solutions, M3AX6and MA3X10, containing a total of about 500 ions. Four different sets of radii for the M+, A3+, and Xminus;ions were considered in a simplified Tosindash;Fumi potential; the cationndash;anion distances were kept constant but the cationndash;anion radius ratios varied. These sets generated configurations in which the coordination of A3+by Xminus;ranged from octahedral to tetrahedral. Our goal was to investigate typical complexing molten salt solutions such as fluoroyttriates and chloroaluminates. In all the melts studied, A3+tended to have preferential even coordination numbers, 4 or 6, and to form independent AX3minus;nnmoieties in very dilute solutions. As the concentration of AX3increased, these moieties became interconnected by close to linear Andash;Xndash;A bridges to form larger species. In the octahedrally coordinated melts, this led to a threehyphen;dimensional network with intermediate range order and to the formation of bridged species containing A3+equilateral triplets, even in M3AX6. In the tetrahedrally coordinated M3AX6melts, the value for the equilibrium constant of 2AXminus;4rlarr2;A2Xminus;7+Xminus;was found to be 4times;10minus;2which is close to the value obtained previously for MAX4. Consequently, the Andash;Xndash;A bridges were most stable in the octahedrally coordinated melts. For three of the four sets of ionic radii investigated, a composition dependent distribution of the coordination numbers of A3+cations by Xminus;was observed.
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