Zirconium(III) bromide

Zirconium(III) bromide is an inorganic compound with the formula ZrBr₃.

Preparation

Almost all the trihalides of titanium, zirconium and hafnium can be prepared by the high-temperature reduction of the corresponding tetrahalide with the metal. Incomplete reaction and contamination of the product with excess metal often occurs.

Zirconium(III) bromide can thus be prepared from zirconium(IV) bromide and zirconium foil.

Alternatively, zirconium(III) bromide crystallises from a solution of zirconium(III) in aluminium tribromide. The solution is prepared by reducing a eutectic solution of ZrBr₄ in liquid AlBr₃ at a temperature of 230–300 °C with metallic zirconium or aluminium.

Structure and bonding

Zirconium(III) bromide has a lower magnetic moment than is expected for the d¹ metal ion Zr³⁺, indicating non-negligible Zr-Zr bonding.

The crystal structure of zirconium(III) bromide is based on hexagonal close packing of bromide ions with one third of the octahedral interstices occupied by Zr³⁺ ions. The structure consists of parallel chains of face-sharing {ZrBr₆} octahedra with equally spaced metal atoms. There is some elongation of the octahedra along the metal-metal axis, partly due to metal-metal repulsion. ZrCl₃, ZrBr₃ and ZrI₃ all adopt the β-TiCl₃ structure, but the elongation of octahedra is most pronounced in the chloride, moderate in the bromide and negligible in the iodide.

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