We report the synthesis, crystal structures, and optical properties of two new compounds, KBiI(I)·14HO (1) and (NH)BiI(I)·4.5HO (2), as well as the electronic structure of the latter. They crystallize in tetragonal space group P4/ mmm with the unit cell parameters a = 12.974(1) and c = 20.821(3) Å for 1 and a = 13.061(3) and c = 15.162(7) Å for 2. Though 1 and 2 are not isomorphous, their crystal structures display the same structural organization; namely, the BiI octahedra are linked by I units to form disordered layers in 1 and perfectly ordered chains in 2. The I-I bond distances in the thus formed I-I-I-I linear links are not uniform; the central bond is only slightly longer than in a standalone I molecule, whereas the peripheral bonds are significantly shorter than longer bonds typical for various polyiodides, which is confirmed by Raman spectroscopy. The analysis of the electronic structure shows that the atoms forming the I-I-I-I subunits transfer electron density from their occupied 5p orbitals onto their vacant states as well as onto 6s orbitals of bismuth atoms that center the BiI octahedra. This leads to low direct band gaps that were found to be 1.57 and 1.27 eV for 1 and 2, respectively, by optical absorption spectroscopy. Luminescent radiative relaxation was observed in the near-IR region with emission maxima of 1.39 and 1.24 eV for 1 and 2, respectively, in good agreement with the band structure, despite the strong quenching propensity of I moieties.

Phenylenediammonium polyiodobismuthate­(III), [PDA­(BiI4)2·​I2] (PDA = phenyl­ene­diam­monium, [NH3­C6H4­NH3]2+), represents a new hybrid halometallate synthesized in a form of black well-shaped crystals by a facile reaction in aqueous solution of HI containing dissolved I2. It crystallizes in triclinic space group P1̅ with the unit cell parameters a = 7.761(1) Å, b = 9.259(1) Å, c = 9.689(1) Å, α = 95.68(3)°, β = 103.19(3)°, γ = 93.56(3)°, and Z = 1. Its crystal structure comprises three levels of organization discriminated by a type of chemical bonding. The first level is provided by covalently bonded [BiI6] octahedra linked into [BiI4]∞ – one-dimensional anionic chains; the second level features secondary bonds between the chains and I2 bridging molecules, whereas the third level is specified by the weak hydrogen N–H···I bonds involving a diammonium cation and I···I intermolecular interactions that additionally link anionic chains. Altogether, these three interaction types ensure the formation of a complex pseudo-three-dimensional crystal structure. According to optical absorption study, [PDA­(BiI4)2·​I2] is a semiconductor with the band gap of 1.45 eV.