Bismuth Polycations Revisited: Alternative Synthesis and Electronic Structure of Bi6Br7, and Bonding in Main-Group Polyatomic Ions from a Direct Space Perspective
A bismuth subbromide, Bi6Br7, was synthesized in the form of single crystals using the reaction between Bi and Hg2Br2 in a gradient furnace. Its crystal structure was reinvestigated by low-temperature single-crystal X-ray diffraction (Pnnm, a = 15.4996(6) Å, b = 23.6435(7) Å, c = 9.0231(2) Å, Z = 8, R1 = 0.041, wRall = 0.087). Based on the diffraction data, the structure description was revised as containing Bi95+ cluster polycations and 1∞[Bi3Br145−] ladder-like anions. DFT calculations of
... structure showed the compound to be a narrow-gap semiconductor with a band gap of ca. 1.3 eV, with the nature of the compound as ionic salt confirmed by charge density analysis. Direct-space bonding analysis based on the ELF topology and QTAIM partitioning, performed for all known homoatomic bismuth polycations, as well as isoelectronic main-group metal ions, shows patterns of localized pairwise and three-center bonding forming the frameworks of the clusters. In addition to obtaining new data, the use of highly augmented basis sets allowed us to revise and amend several previously made conclusions regarding bonding in such species.