Assembling Polyiodides and Iodobismuthates Using a Template Effect of a Cyclic Diammonium Cation and Formation of a Low-Gap Hybrid Iodobismuthate with High Thermal Stability

Exploiting a template effect of 1,4-diazacycloheptane (also known as homopiperazine, Hpipe), four new hybrid iodides, (HpipeH(2))(2)Bi(2)I(10)·2H(2)O, (HpipeH(2))I(I(3)), (HpipeH(2))(3)I(6)·H(2)O, and (HpipeH(2))(3)(H(3)O)I(7), were prepared and their crystal structures were solved using single crystal X-ray diffraction data. All four solid-state crystal structures feature the HpipeH(2)(2+) cation alternating with Bi(2)I(10)(4–), I(3)(–), or I(–) anions and solvent water or H(3)O(+) cation. HpipeH(2)(2+) assembles anionic and neutral building blocks into polymer structures by forming four strong (N)H···I and (N)H···O hydrogen bonds per cation, with the H···I distances ranging from 2.44 to 2.93 Å and H···O distances of 1.88–1.89 Å. These hydrogen bonds strongly affect the properties of compounds; in particular, in the case of (HpipeH(2))(2)Bi(2)I(10)·2H(2)O, they ensure narrowing of the band gap down to 1.8 eV and provide high thermal stability up to 240 °C, remarkable for a hydrated molecular solid.