The opening of an icosanderal boron cage in the periodinated closo-dodecaborate B12I122- upon deiodination is studied using cryogenic ion trap vibrational spectroscopy combined with electronic structure calculations. Comparison of simulated vibrational spectra to the infrared photodissociation spectra of messenger-tagged B12I122- and B12In- (n = 7-9) formed by skimmer collision induced dissociation shows that the larger clusters absorb exclusively below 975 cm(-1) and hence exhibit quasi-icosahedral B-12-cage structures, while the higher energy absorptions in-between 1000 and 1300 cm(-1) observed for n = 7 can only be recovered by considering a breakup of the icosahedral cage upon deiodination from n = 8 to n = 7. (C) 2015 Elsevier B.V. All rights reserved.