The structure of Bi(III) clusters in aqueous concentrated acidic perchlorate solutions has been studied by means of X-ray absorption spectroscopy (XAS). The XAS data show that the polynuclear [Bi6O4(OH)(4)](6+) complex with a cage structure predominates at room temperature in acidic Bi-rich solutions. This complex breaks down to form mononuclear complexes with increasing temperature to 428 K. This behavior is consistent with theoretical predictions based on considerations of the electrostatic repulsion, which increases sharply as the dielectric constant of the solvent decreases with increasing temperature.
Brugger, J., Tooth, B., Etschmann, B. E., Liu, W., Testemale, D., Hazemann, J-L., & Grundler, P. V. (2014). Structure and thermal stability of Bi(III) oxy-clusters in aqueous solutions. Journal of Solution Chemistry, 43(2), 314 - 325. https://doi.org/10.1007/s10953-014-0131-1