A Series of New Copper Iodobismuthates: Structural Relationships, Optical Band Gaps Affected by Dimensionality, and Distinct Thermal Stabilities

Three new copper iodobismuthates, red tetranuclear [n-Bu4N][Cu2(CH3CN)2Bi2I10] (1), dark-red infinite linear
[Et4N]2n[Cu2Bi2I10]n (2), and black polymeric ladderlike [Cu(CH3CN)4]2n[Cu2Bi2I10]n (3), crystallize from solutions of
BiI3 and CuI in the presence of different cations. A regular structural relationship from 0-D (1) to 1-D linear anion
chains (2) to 1-D ladderlike anion chains (3) is observed. The self-assembly of the basic building unit Cu2Bi2I10 as
altered by different cations is proposed to be the driving force for their formation. The optical band gaps exhibit a
structure-related decrease from 1 to 2/3, in agreement with their color changes and the density functional theory
(DFT) calculation results. The electronic structures and the relationship with corresponding monobismuth analogues
and the Ag−Bi isotypes are discussed on the basis of DFT calculations. In spite of their structural similarities, the
compounds are distinctive thermally:  2 is stable to 230 °C, 1 undergoes a solvent loss at 85 °C to form a new
phase that is thermally stable to 230 °C, and 3 releases a solvent molecule and decomposes at 80 °C into BiI3
and CuI. The essential reasons for these differences are discussed.