The structure and complex formation of concentrated aqueous gallium(III) bromide (GaBr
3) solutions have been investigated over a temperature range 80–333 K by Raman spectroscopy, X-ray absorption fine structure (XAFS), and X-ray diffraction. The Raman spectra obtained at various [Br
?]/[Ga
3+] molar ratios and temperatures have shown that complex formation between Ga
3+ and Br
? occurs as a predominant species, with [GaBr
4]
? at [Ga
3+] as high as 1~2
M (
M =
mol?
dm ?3) and [Br
?]/[Ga
3+] ratios > ~2, and that cooling of the solutions favors the formation of the aqua Ga
3+. The intermediate species were not seen in the Raman spectra. The XAFS data have revealed that the aqua complex has a sixfold coordination as [Ga(H
2O)
6]
3+ with a Ga
3+–H
2O distance of (1.96 ± 0.02) Å, whereas the [GaBr
4]
? complex has a Ga
3+–Br
? distance of (2.33± 0.02) Å, and that vitrification of the aqueous GaBr
3 solution at liquid nitrogen temperature shifts the equilibrium toward the aqua complex. The X-ray diffraction data at different subzero temperatures have shown a tendency of decreasing Ga
3+–Br
? and increasing Ga
3+–H
2O interactions with lowering temperature, confirming the preference of aqua Ga
3+ in the supercooled liquid state as well as in the glassy state. The Ga
3+–H
2O distance of ~1.8 Å for the tetrahedral coordination was found in a 2.01
M gallium(III) bromide solution with a [Br
?]/[Ga
3+] ratio of 3.7 and gradually increased to a value of 1.92 Å for octahedral geometry with decreasing temperature, suggesting that equilibrium shifts from [GaBr
4]
? to [Ga(H
2O)
6]
3+ through intermediate species, [GaBr
n ]
(3?n)+ (
n = 2 and 3). The Ga
3+–Br
? and Br
?–Br
? distances within [GaBr
4]
? with an almost tetrahedral symmetry are (2.35± 0.02) and (3.82± 0.03) Å, respectively. The Ga
3+ has the second hydration shell at (4.03± 0.03) Å and the hydration of Br
? is characterized with a Br
?–H
2O distance of (3.35± 0.02) Å at all temperatures investigated.
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