Preparation and Characterization of Novel Inorganic−Organic Hybrid Materials Containing Rare, Mixed-Halide Anions of Bismuth(III)

Three new hybrid inorganic−organic salts containing novel mixed haloanions of bismuth were synthesized by the solvothermal reaction of bismuth iodide with a haloacid, HX (X = Cl or Br), and the alkylamine 4,4‘-trimethylenedipiperidine (TMDP). All three compounds were structurally characterized by single-crystal X-ray diffraction. Reaction of TMDP and BiI₃ with HCl yielded two crystalline products:  [H₂TMDP]₂[(Bi₂I₉)(BiCl₂I₂)] (1, major yield) and [H₂TMDP]₂[Bi₂Cl_10-xI_x] (2, x = 3.83, minor yield). Compound 1 crystallizes in the monoclinic space group Cc (a = 22.8586(11) Å, b = 15.5878(7) Å, c = 17.6793(9) Å, β = 118.7010(10)°, Z = 4) and contains the mononuclear mixed-halide anion BiCl₂I₂^- in addition to a face-sharing bioctahedral Bi₂I₉^3- anion and two independent H₂TMDP²⁺ cations. The BiCl₂I₂^- anion has a sawhorse geometry (equatorially vacant trigonal bipyramidal geometry) that is not commonly observed in bismuth chemistry. Compound 2 crystallizes in the monoclinic space group P2₁/c (a = 14.9471(7) Å, b = 12.7622(6) Å, c = 13.3381(7) Å, β = 116.1030(10)°, Z = 2) and contains an edge-sharing bioctahedral mixed-halide anion in which iodide occupies one and chloride occupies two of the five crystallographically independent halide sites. The remaining two sites have mixed-chloride and -iodide occupancy. Reaction of TMDP and BiI₃ with HBr yielded the crystalline product [H₂TMDP][BiBr_5-xI_x] (3, x = 0.99), which contains, in addition to the organic cation, a polymeric, mixed-haloanion of bismuth(III). Compound 3 crystallizes in the chiral, orthorhombic space group P2₁2₁2₁ (a = 8.5189(5) Å, b = 14.8988(9) Å, c = 17.9984(11) Å, Z = 4) and consists of an H₂TMDP²⁺ cation in addition to the anion, which is built up of corner-sharing BiX₆ octahedra. Of the five crystallographically independent halide sites in this anion, two are occupied solely by Br and the remaining three have mixed-bromide and -iodide occupancy. Other anion stoichiometries have been observed crystallographically for 3, as the specific stoichiometry is dependent on the relative concentration of the haloacid starting material used.