Polyselenide Chemistry of Indium and Thallium in Dimethylformamide, Acetonitrile, and Water. Syntheses, Structures, and Properties of the New Complexes [In₂(Se₄)₄(Se₅)]⁴⁻, [In₂Se₂(Se₄)₂]²⁻, [In₃Se₃(Se₄)₃]³⁻, and [Tl₃Se₃(Se₄)₃]³⁻

The reaction of InCl₃ with Na₂Se₅ in dimethylformamide (DMF) in the presence of PluPCl gave (Ph₄P)₄[In₂(Se₄)₄(Se₅)] (I) in 75% yield. Under the same conditions, InCl₃ reacted with Na₂Se₅ in the presence of Pr₄NBr or Et₄NBr and afforded (Pr₄N)₄[In₂(Se₄)4(Se₅)] (II) in 65% yield and (Et₄N)₄[In₂(Se₄)4(Se₅)] (III) in 72% yield, respectively. (I) crystallizes in the triclinic space group P1̄ (No. 2) with unit cell dimensions a = 11.417(4) Å, b = 12.734(9) Å, c = 20.188(9) Å, α = 96.03(5)^∘, β = 94.69(3)^∘, γ=111.68(4)^∘, V = 2689(2) ų, Z = 1, and R/R_w = 0.073/0.085. (II) crystallizes in the monoclinic space group P2/c (No. 13) with unit cell dimensions a = 15.997(3) Å, b = 17.376(3) Å, c = 15.168(2) Å, β = 94.56(3)^∘, V= 4202(1) ų, Z = 2, and R/R_w = 0.069/0.080. (III) crystallizes in the triclinic space group P1̄ (No. 2) with unit cell dimensions a = 12.428(3) Å, b = 15.781(3) Å, c = 17.540(4) Å, α = 89.47(2)^∘, β = 97.90(2)^∘, γ = 94.47(2)^∘, V= 3397(1) ų, Z = 2, and R/R_w = 0.075/0.084. Single-crystal X-ray diffraction studies show that (I), (II), and (III) contain the same anion, [In₂(Se₄)₄(Se₅)]⁴⁻. The anion consists of In³⁺ centers in trigonal bipyramidal coordination; each In atom is chelated by two bidentate Se₄²⁻ ligands forming a [In(Se₄)₂]⁻ unit. Two of these [In(Se₄)₂]⁻ units are bridged by an Se₅²⁻ chain forming a dimer. The hydrothermal reaction of InCl₃ with Na₂Se₄ in the presence of Pr₄NBr and water at 110 °C for 3 days in an evacuated sealed Pyrex tube afforded deep red crystals of (Pr₄N)₂[In₂Se₂(Se₄)₂] (IV), in 80% yield. Under the same conditions the reaction with [(Ph₃P)₂N]Cl yields [(Ph₃P)₂N]₂[In₂Se₂(Se₄)₂] (V) in 60% yield. (IV) crystallizes in the triclinic space group P1̄ (No. 2) with unit cell dimensions a = 8.938(2) Å, b = 11.290(2) Å, c = 11.528(2) Å, α = 79.19(1)^∘, β = 105.56(1)^∘, γ = 99.84(1)^∘, V = 1093(1) ų, Z = 1, and R/R_w = 0.045/0.049. (V) also crystallizes in the triclinic space group P1̄ (No. 2) with unit cell dimensions a = 10.931(5) Å, b = 11.302(7) Å, c = 15.189(8) Å, α = 84.98(5)^∘, β = 94.15(4)^∘, γ = 93.86(4)^∘, V= 1858(1) ų, Z = 1, and R/R_w = 0.060/0.081. Single-crystal X-ray diffraction studies show that (IV) and (V) contain the same binuclear anion [In₂Se₂(Se₄)₂]²⁻. The anion contains In³⁺ with a tetrahedral coordination, bridged by two monoselenides to form a planar [In₂Se₂]²⁺ core with an inversion center at the middle of the In--In vector of 3.336(2) Å. The remaining two coordination sites on each In atom are occupied by the Se₄²⁻ bidentate chelates. The reaction of InCl₃ with Na₂Se₅ in 1:2 mole ratio in acetonitrile in the presence of Et₄NBr afforded (Et₄N)₃[In₃Se₃(Se₄)₃] (VI). Similar reaction of TlCl with Na₂Se₅ in 1:2 mole ratio in DMFin the presence of Et₄NBr gave (Et₄N)₃[Tl₃Se₃(Se₄)₃] (VII). Single-crystal X-ray diffraction studies show that the two compounds (VI) and (VII) are isostructural and crystallize in the monoclinic space group P2₁/c (No. 14). The unit cell dimensions are a = 16.747(4) Å, b = 13.701(3) Å, c = 22.227(3) Å, β = 94.16(2)^∘, V= 5086(2) ų, Z = 4, and R/R_w = 0.045/0.051 and a = 16.813(3) Å, b = 13.774(3) Å, c = 22.186(4) Å, β = 94.13(1)^∘; V= 5126(2) ų, Z = 4, and R/R_w = 0.072/0.087 for (VI) and (VII), respectively. The trinuclear anion [M₃Se₃(Se₄)₃]³⁻ (M = In, Tl) in (VI) and (VII) contains M³⁺ with a tetrahedral coordination. Each M³⁺ center has a chelating Se₄²⁻ ligand and is bridged to the other two M³⁺ centers by monoselenide, Se²⁻, ligands forming a six-membered [M₃Se₃]³⁺ core. Variable-temperature ⁷⁷Se NMR spectra of (I)–(VII) are reported. All indiumpolyselenide complexes show the same NMR spectrum at room temperature in DMF suggesting that in solution only one In/Se species exists. UV/vis of (I)–(III) are similar, with two absorptions at ∼450 and ∼650 nm, while (IV)–(VII) have a featureless spectra. The electrochemistry of (I) and (VI) is reported. The solid-state far-IR spectra of all the compounds show strong absorptions in the 300−100 cm⁻¹ region due to the Se-Se and M-Se stretching frequencies; tentative assignments are reported herein. Thermal gravimetric analysis data show that the compounds pyrolyze to give single-phase binary metal chalcogenides (β-In₂Se₃ and TlSe).