Experimental and Computational Study on the Structure and Properties of Herz Cations and Radicals: 1,2,3-Benzodithiazolium, 1,2,3-Benzodithiazolyl, and Their Se Congeners

Salts of 1,2,3-benzodithiazolium (<b>1</b>), 2,1,3-benzothiaselenazolium (<b>3</b>), and 1,2,3-benzodiselenazolium (<b>4</b>) (Herz cations), namely, [<b>1</b>]­[BF₄], [<b>1</b>]­[SbCl₆], [<b>3</b>]­[BF₄], [<b>3</b>]­[GaCl₄], [<b>3</b>]­[SbCl₆], and [<b>4</b>]­[GaCl₄], were prepared from the corresponding chlorides and NaBF₄, GaCl₃, or SbCl₅. It was found that [<b>1</b>]­[SbCl₆] and [<b>3</b>]­[SbCl₆] spontaneously transform in MeCN solution to [<b>1</b>]₃[SbCl₆]₂[Cl] and [<b>3</b>]₃[SbCl₆]₂[Cl], respectively. [<b>1</b>]­[BF₄], [<b>1</b>]₃[SbCl₆]₂[Cl], [<b>3</b>]­[BF₄], [<b>3</b>]₃[SbCl₆]₂[Cl], and [<b>4</b>]­[GaCl₄] were structurally characterized by X-ray diffraction (XRD). In solution, these [BF₄]⁻ and [GaCl₄]⁻ salts as well as [<b>1</b>]­[GaCl₄], [<b>2</b>]­[GaCl₄], [<b>3</b>]­[GaCl₄], [<b>3</b>]­[Cl], and [<b>4</b>]­[Cl] were characterized by multinuclear nuclear magnetic resonance (NMR). The corresponding Herz radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b> were obtained in toluene and DCM solutions by the reduction of the appropriate salts with Ph₃Sb and characterized by EPR. Cations <b>1</b>–<b>4</b> and radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b> were investigated computationally at the density functional theory (DFT) and second-order Møller–Plesset (MP2) levels of theory. The B1B95/cc-pVTZ method was found to satisfactorily reproduce the experimental geometries of <b>1</b>–<b>4</b>; an increase in the basis set size to cc-pVQZ results in only minor changes. For both <b>1</b>–<b>4</b> and <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b>, the Hirshfeld charges and bond orders, as well as the Hirshfeld spin densities for the radicals, were calculated using the B1B95/cc-pVQZ method. It was found for both the cations and the radicals that replacing S atoms with Se atoms leads to considerable changes in the atomic charges, bond lengths, and bond orders only at the involved and the neighboring sites. According to the calculations, 60% of the positive charge in the cations and 80% of the spin density in the radicals is localized on the heterocycles, with the spin density distributions being very similar for all radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b>. For the cations <b>1</b>–<b>4</b>, the NICS values (B3LYP/cc-pVTZ for B1B95/cc-pVTZ geometries) lie in the narrow range from −5.5 ppm to −6.6 ppm for the carbocycles, and from −14.4 ppm to −15.5 ppm for heterocycles, clearly indicating the aromaticity of the cations. Calculations on radical dimers <b>[1</b>^<b>•</b><b>]</b>₂–[<b>4</b>^<b>•</b><b>]</b>₂ revealed, with only one exception, positive dimerization energies, i.e., the dimers are inherently unstable in the gas phase

Experimental and Computational Study on the Structure and Properties of Herz Cations and Radicals: 1,2,3-Benzodithiazolium, 1,2,3-Benzodithiazolyl, and Their Se Congeners

Salts of 1,2,3-benzodithiazolium (<b>1</b>), 2,1,3-benzothiaselenazolium (<b>3</b>), and 1,2,3-benzodiselenazolium (<b>4</b>) (Herz cations), namely, [<b>1</b>]­[BF₄], [<b>1</b>]­[SbCl₆], [<b>3</b>]­[BF₄], [<b>3</b>]­[GaCl₄], [<b>3</b>]­[SbCl₆], and [<b>4</b>]­[GaCl₄], were prepared from the corresponding chlorides and NaBF₄, GaCl₃, or SbCl₅. It was found that [<b>1</b>]­[SbCl₆] and [<b>3</b>]­[SbCl₆] spontaneously transform in MeCN solution to [<b>1</b>]₃[SbCl₆]₂[Cl] and [<b>3</b>]₃[SbCl₆]₂[Cl], respectively. [<b>1</b>]­[BF₄], [<b>1</b>]₃[SbCl₆]₂[Cl], [<b>3</b>]­[BF₄], [<b>3</b>]₃[SbCl₆]₂[Cl], and [<b>4</b>]­[GaCl₄] were structurally characterized by X-ray diffraction (XRD). In solution, these [BF₄]⁻ and [GaCl₄]⁻ salts as well as [<b>1</b>]­[GaCl₄], [<b>2</b>]­[GaCl₄], [<b>3</b>]­[GaCl₄], [<b>3</b>]­[Cl], and [<b>4</b>]­[Cl] were characterized by multinuclear nuclear magnetic resonance (NMR). The corresponding Herz radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b> were obtained in toluene and DCM solutions by the reduction of the appropriate salts with Ph₃Sb and characterized by EPR. Cations <b>1</b>–<b>4</b> and radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b> were investigated computationally at the density functional theory (DFT) and second-order Møller–Plesset (MP2) levels of theory. The B1B95/cc-pVTZ method was found to satisfactorily reproduce the experimental geometries of <b>1</b>–<b>4</b>; an increase in the basis set size to cc-pVQZ results in only minor changes. For both <b>1</b>–<b>4</b> and <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b>, the Hirshfeld charges and bond orders, as well as the Hirshfeld spin densities for the radicals, were calculated using the B1B95/cc-pVQZ method. It was found for both the cations and the radicals that replacing S atoms with Se atoms leads to considerable changes in the atomic charges, bond lengths, and bond orders only at the involved and the neighboring sites. According to the calculations, 60% of the positive charge in the cations and 80% of the spin density in the radicals is localized on the heterocycles, with the spin density distributions being very similar for all radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b>. For the cations <b>1</b>–<b>4</b>, the NICS values (B3LYP/cc-pVTZ for B1B95/cc-pVTZ geometries) lie in the narrow range from −5.5 ppm to −6.6 ppm for the carbocycles, and from −14.4 ppm to −15.5 ppm for heterocycles, clearly indicating the aromaticity of the cations. Calculations on radical dimers <b>[1</b>^<b>•</b><b>]</b>₂–[<b>4</b>^<b>•</b><b>]</b>₂ revealed, with only one exception, positive dimerization energies, i.e., the dimers are inherently unstable in the gas phase

Experimental and Computational Study on the Structure and Properties of Herz Cations and Radicals: 1,2,3-Benzodithiazolium, 1,2,3-Benzodithiazolyl, and Their Se Congeners

Salts of 1,2,3-benzodithiazolium (<b>1</b>), 2,1,3-benzothiaselenazolium (<b>3</b>), and 1,2,3-benzodiselenazolium (<b>4</b>) (Herz cations), namely, [<b>1</b>]­[BF₄], [<b>1</b>]­[SbCl₆], [<b>3</b>]­[BF₄], [<b>3</b>]­[GaCl₄], [<b>3</b>]­[SbCl₆], and [<b>4</b>]­[GaCl₄], were prepared from the corresponding chlorides and NaBF₄, GaCl₃, or SbCl₅. It was found that [<b>1</b>]­[SbCl₆] and [<b>3</b>]­[SbCl₆] spontaneously transform in MeCN solution to [<b>1</b>]₃[SbCl₆]₂[Cl] and [<b>3</b>]₃[SbCl₆]₂[Cl], respectively. [<b>1</b>]­[BF₄], [<b>1</b>]₃[SbCl₆]₂[Cl], [<b>3</b>]­[BF₄], [<b>3</b>]₃[SbCl₆]₂[Cl], and [<b>4</b>]­[GaCl₄] were structurally characterized by X-ray diffraction (XRD). In solution, these [BF₄]⁻ and [GaCl₄]⁻ salts as well as [<b>1</b>]­[GaCl₄], [<b>2</b>]­[GaCl₄], [<b>3</b>]­[GaCl₄], [<b>3</b>]­[Cl], and [<b>4</b>]­[Cl] were characterized by multinuclear nuclear magnetic resonance (NMR). The corresponding Herz radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b> were obtained in toluene and DCM solutions by the reduction of the appropriate salts with Ph₃Sb and characterized by EPR. Cations <b>1</b>–<b>4</b> and radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b> were investigated computationally at the density functional theory (DFT) and second-order Møller–Plesset (MP2) levels of theory. The B1B95/cc-pVTZ method was found to satisfactorily reproduce the experimental geometries of <b>1</b>–<b>4</b>; an increase in the basis set size to cc-pVQZ results in only minor changes. For both <b>1</b>–<b>4</b> and <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b>, the Hirshfeld charges and bond orders, as well as the Hirshfeld spin densities for the radicals, were calculated using the B1B95/cc-pVQZ method. It was found for both the cations and the radicals that replacing S atoms with Se atoms leads to considerable changes in the atomic charges, bond lengths, and bond orders only at the involved and the neighboring sites. According to the calculations, 60% of the positive charge in the cations and 80% of the spin density in the radicals is localized on the heterocycles, with the spin density distributions being very similar for all radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b>. For the cations <b>1</b>–<b>4</b>, the NICS values (B3LYP/cc-pVTZ for B1B95/cc-pVTZ geometries) lie in the narrow range from −5.5 ppm to −6.6 ppm for the carbocycles, and from −14.4 ppm to −15.5 ppm for heterocycles, clearly indicating the aromaticity of the cations. Calculations on radical dimers <b>[1</b>^<b>•</b><b>]</b>₂–[<b>4</b>^<b>•</b><b>]</b>₂ revealed, with only one exception, positive dimerization energies, i.e., the dimers are inherently unstable in the gas phase

Coordination of Halide and Chalcogenolate Anions to Heavier 1,2,5-Chalcogenadiazoles: Experiment and Theory

New products of coordination of anions X^– (X = F, I, PhS) to the Te atom of 3,4-dicyano-1,2,5-telluradiazole (<b>1</b>) were synthesized in high yields and characterized by X-ray diffraction (XRD) as the salts [(Me₂N)₃S]⁺[<b>1</b>-F]⁻ (<b>9</b>), [K­(18-crown-6)]⁺[<b>1</b>-I]⁻ (<b>10</b>), and [K­(18-crown-6)]⁺[<b>1</b>-SPh]⁻<b>·</b>THF (<b>11</b>), respectively. In the crystal lattice of <b>10</b>, I atoms are bridging between two Te atoms. The bonding situation in anions of the salts <b>9</b>–<b>11</b> and some other adducts of 1,2,5-chalcogenadiazoles (chalcogen = S, Se, Te) and anions X^– (X = F, Cl, Br, I, PhS) was studied using DFT, QTAIM, and NBO calculations, for <b>9</b>–<b>11</b> in combination with UV–vis, IR/Raman, and MS-ESI techniques. In all cases, the nature of the coordinate bond is negative hyperconjugation involving the transfer of electron density from X^– to the heterocycles. The energy of the bonding interaction varies in a range from ∼30 kcal mol^–1 comparable with energies of weak chemical bonds (e.g., internal N–N bond in organic azides) to ∼86 kcal mol^<b>–</b>1 comparable with an energy of the C–C covalent bonds. The thermodynamics of the anions’ coordination to <b>1</b> and their Se and S congeners was also studied by quantum chemical calculations. The general character of this reaction and favorable thermodynamics in the case of heavier chalcogens (Se, Te) were established. Comparison with available data on acyclic analogues, i.e. the chalcogen diimines RNXNR, reveals that they also coordinate various anions but in addition reactions across XN (X = S, Se, Te) double bonds. Attempts to prepare the anion [<b>1</b>-TePh]⁻ led to disintegration of <b>1</b>. The only unambiguously identified product was a rather rare tellurocyanate that was characterized by XRD and elemental analysis as the salt [K­(18-crown-6)]⁺[TeCN]⁻ (<b>13</b>)

Bis(toluene)chromium(I) [1,2,5]Thiadiazolo[3,4‑<i>c</i>][1,2,5]thiadiazolidyl and [1,2,5]Thiadiazolo[3,4‑<i>b</i>]pyrazinidyl: New Heterospin (<i>S</i>₁ = <i>S</i>₂ = ¹/₂) Radical-Ion Salts

Bis­(toluene)­chromium­(0), Cr⁰(η⁶-C₇H₈)₂ (<b>3</b>), readily reduced [1,2,5]­thiadiazolo­[3,4-<i>c</i>]­[1,2,5]­thiadiazole (<b>1</b>) and [1,2,5]­thiadiazolo­[3,4-<i>b</i>]­pyrazine (<b>2</b>) in a tetrahydrofuran solvent with the formation of heterospin, <i>S</i>₁ = <i>S</i>₂ = ¹/₂, radical-ion salts [<b>3</b>]⁺[<b>1</b>]⁻ (<b>4</b>) and [<b>3</b>]⁺[<b>2</b>]⁻ (<b>5</b>) isolated in high yields. The salts <b>4</b> and <b>5</b> were characterized by single-crystal X-ray diffraction (XRD), solution and solid-state electron paramagnetic resonance, and magnetic susceptibility measurements in the temperature range 2–300 K. Despite the formal similarity of the salts, their crystal structures were very different and, in contrast to <b>4</b>, in <b>5</b> anions were disordered. For the XRD structures of the salts, parameters of the Heisenberg spin Hamiltonian were calculated using the CASSCF/NEVPT2 and broken-symmetry density functional theory approaches, and the complex magnetic motifs featuring the dominance of antiferromagnetic (AF) interactions were revealed. The experimental χ<i>T</i> temperature dependences of the salts were simulated using the Van Vleck formula and a diagonalization of the matrix of the Heisenberg spin Hamiltonian for the clusters of 12 paramagnetic species with periodic boundary conditions. According to the calculations and χ<i>T</i> temperature dependence simulation, a simplified magnetic model can be suggested for the salt <b>4</b> with AF interactions between the anions ([<b>1</b>]⁻···[<b>1</b>]⁻, <i>J</i>₁ = −5.77 cm^–1) and anions and cations ([<b>1</b>]⁻···[<b>3</b>]⁺, <i>J</i>₂ = −0.84 cm^–1). The magnetic structure of the salt <b>5</b> is much more complex and can be characterized by AF interactions between the anions, [<b>2</b>]⁻···[<b>2</b>]⁻, and by both AF and ferromagnetic (FM) interactions between the anions and cations, [<b>2</b>]⁻···[<b>3</b>]⁺. The contribution from FM interactions to the magnetic properties of the salt <b>5</b> is in qualitative agreement with the positive value of the Weiss constant Θ (0.4 K), whereas for salt <b>4</b>, the constant is negative (−7.1 K)

Synthesis and Properties of the Heterospin (<i>S</i>₁ = <i>S</i>₂ = ¹/₂) Radical-Ion Salt Bis(mesitylene)molybdenum(I) [1,2,5]Thiadiazolo[3,4‑<i>c</i>][1,2,5]thiadiazolidyl

Low-temperature interaction of [1,2,5]­thiadiazolo­[3,4-<i>c</i>]­[1,2,5]­thiadiazole (<b>1</b>) with MoMes₂ (Mes = mesitylene/1,3,5-trimethylbenzene) in tetrahydrofuran gave the heterospin (<i>S</i>₁ = <i>S</i>₂ = ¹/₂) radical-ion salt [MoMes₂]⁺[<b>1</b>]⁻ (<b>2</b>) whose structure was confirmed by single-crystal X-ray diffraction (XRD). The structure revealed alternating layers of the cations and anions with the Mes ligands perpendicular, and the anions tilted by 45°, to the layer plane. At 300 K the effective magnetic moment of <b>2</b> is equal to 2.40 μ_B (theoretically expected 2.45 μ_B) and monotonically decreases with lowering of the temperature. In the temperature range 2–300 K, the molar magnetic susceptibility of <b>2</b> is well-described by the Curie–Weiss law with parameters <i>C</i> and θ equal to 0.78 cm³ K mol^–1 and −31.2 K, respectively. Overall, the magnetic behavior of <b>2</b> is similar to that of [CrTol₂]⁺[<b>1</b>]⁻ and [CrCp*₂]⁺[<b>1</b>]⁻, i.e., changing the cation [MAr₂]⁺ 3d atom M = Cr (<i>Z</i> = 24) with weak spin–orbit coupling (SOC) to a 4d atom M = Mo (<i>Z</i> = 42) with stronger SOC does not affect macroscopic magnetic properties of the salts. For the XRD structure of salt <b>2</b>, parameters of the Heisenberg spin-Hamiltonian were calculated using the broken-symmetry DFT and CASSCF approaches, and the complex 3D magnetic structure with both the ferromagnetic (FM) and antiferromagnetic (AF) exchange interactions was revealed with the latter as dominating. Salt <b>2</b> is thermally unstable and slowly loses the Mes ligands upon storage at ambient temperature. Under the same reaction conditions, interaction of <b>1</b> with MoTol₂ (Tol = toluene) proceeded with partial loss of the Tol ligands to afford diamagnetic product