Structural Diversity and Thermochromic Properties of Iodobismuthate Materials Containing d-Metal Coordination Cations: Observation of a High Symmetry [Bi3I11]2− Anion and of Isolated I− Anions

Six new inorganic−organic salts, all containing iodobismuthate anions and d-metal coordination cations, were synthesized solvothermally from reactions of bismuth iodide, a transition metal (M) nitrate salt (M = Co, Fe or Zn), and a heterocyclic, chelating organic ligand: 1,10-phenanthroline (1,10-phen), 3,4,7,8-tetramethyl-1,10-phenanthroline (TMphen), or 2,2′:6′,2′′-terpyridine (tpy). All six compounds were structurally analyzed by single crystal X-ray diffraction, including variable temperature crystallographic analysis to monitor for structural changes. Furthermore, those containing novel anions and achieved in high yield were additionally characterized by solid-state UV visible spectroscopy at room temperature. [Co(1,10-phen)3][Bi3I11] (1), [Fe(1,10-phen)3][Bi3I11] (2), and [Zn(1,10-phen)3][Bi3I11] (3) are isostructural. They crystallize in the monoclinic space group P21/n and contain the unprecedented iodobismuthate anion, [Bi3I11]2−, which exhibits near D3h symmetry and has an unusual arrangement of three cis face-sharing BiI6 octahedra. [Co(TMPhen)3]2[Bi2I9][I] (4), which crystallizes in the trigonal space group P-31c, and [Co(tpy)2]2[Bi2I9][I] (5) and [Zn(tpy)2]2[Bi2I9][I] (6), which are isostructural and crystallize in the monoclinic space group C2/c, contain the discrete binuclear [Bi2I9]3− anion, common in previously reported iodobismuthate compounds. In addition they contain unusual isolated I− anions, which are rarely encountered in iodobismuthate phases. Compounds 1−6 show constitutional similarities while utilizing different organic ligands and illustrate the sensitive dependence of reaction conditions on the identity of the halometalate anion formed. Additionally, all six compounds and the starting material BiI3 are thermochromic; the origin of this behavior is spectroscopically and crystallographically investigated.