The synthesis of the nanoscaled bismuth oxido clusters [Bi38O45- (NO3)20(DMSO)28](NO3)4⋅4 DMSO (1 a) and [Bi38O45(OH)2(pTsO)8- (NO3)12(DMSO)24](NO3)2⋅4 DMSO⋅ 2 H2O (2) starting from the basic bismuth nitrate [Bi6O4(OH)4](NO3)6⋅H2O is reported herein. Single-crystal X-ray diffraction analysis, ESI mass spectrometry, thermogravimetric analysis, and molecular dynamics simulation were used to study the formation, structure, and stability of these large metal oxido clusters. Compounds 1 a and 2 are based on a [Bi38O45]24+ core, which is structurally related to δ-Bi2O3. Examination of the fragmentation pathways of 1 a and 2 by infrared multi-photon dissociation (IRMPD) tandem MS experiments allows the identification of novel bismuth oxido cluster species in the gas phase.