Linear Multiselenium Interactions in Dicationic Oligomers of 1,5-(Diselena)canes: Behavior of Semc σ(mc c-ne e) (6≤mc ≤16) Elucidated with QTAIM Dual Functional Analysis

The intrinsic dynamic and static nature mc center-ne electron interactions of the σ-type σ(mc c-ne e) were elucidated for the Se-Se interactions in dicationic oligomers of Se(CH2 CH2 CH2 )2 Se (1 (Se, Se)) [n2+ (Se, Se): n=1-8], especially for mc ≥6, where n2+ (Se, Se: n=1-8) are abbreviated by n2+ (n=1-8), respectively. QTAIM dual functional analysis (QTAIM-DFA) was applied to the interactions. Perturbed structures generated using coordinates derived from the compliance constants (Cii ) were employed for QTAIM-DFA. Each Se-*-Se in 12+ and 22+ has the nature of CT-TBP (trigonal bipyramidal adduct formation through CT) and Cov-w (weak covalent), respectively, which supply the starting points of the investigations. The asterisk emphasizes the existence of a bond critical point on the interaction. All Se-*-Se in 32+ are classified by the regular closed shell (r-CS) interactions and characterized as CT-MC (molecular complex formation through CT), which are denoted as r-CS/CT-MC, except for the central interaction, of which nature is r-CS/CT-TBP. Most interactions in 42+ -82+ are r-CS/t-HBwc (typical-HB with covalency) but some are pure-CS/t-HBnc (t-HB with no covalency). The linear Se2n 2+ interactions in 22+ -82+ seem close to those without any limitations, since the nature of Se-*-Se inside and outside of (CH2 CH2 CH2 )2 are very similar with each other. The linear Se2n 2+ interactions in 32+ -82+ are shown to be analyzed as σ(mc c-ne e: 6≤mc ≤16), not by the accumulated σ(3c-4e).

Dynamic and Static Nature of Br4 σ(4c-6e) and Se2Br5 σ(7c-10e) in the Selenanthrene System and Related Species Elucidated by QTAIM Dual Functional Analysis with QC Calculations

The nature of Br4 σ(4c-6e) of the BBr-∗-ABr-∗-ABr-∗-BBr form is elucidated for SeC12H8(Br)SeBr---Br-Br---BrSe(Br)C12H8Se, the selenanthrene system, and the models with QTAIM dual functional analysis (QTAIM-DFA). Asterisks (∗) are employed to emphasize the existence of bond critical points on the interactions in question. Data from the fully optimized structure correspond to the static nature of interactions. In our treatment, data from the perturbed structures, around the fully optimized structure, are employed for the analysis, in addition to those from the fully optimized one, which represent the dynamic nature of interactions. The ABr-∗-ABr and ABr-∗-BBr interactions are predicted to have the CT-TBP (trigonal bipyramidal adduct formation through charge transfer) nature and the typical hydrogen bond nature, respectively. The nature of Se2Br5 σ(7c-10e) is also clarified typically, employing an anionic model of [Br-Se(C4H4Se)-Br---Br---Br-Se(C4H4Se)-Br]-, the 1,4-diselenin system, rather than (BrSeC12H8)Br---Se---Br-Br---Br-Se(C12H8Se)-Br, the selenanthrene system.

High-resolution X-ray diffraction determination of the electron density of 1-(8-PhSC10H6)SS(C10H6SPh-8')-1' with the QTAIM approach: evidence for S4 σ(4c-6e) at the naphthalene peri-positions

An extended hypervalent S4 σ(4c-6e) system was confirmed for the linear BS-∗-AS-∗-AS-∗-BS interaction in 1-(8-PhBSC10H6)AS-AS(C10H6 BSPh-8')-1' (1) via high-resolution X-ray diffraction determination of electron densities. The presence of bond critical points (BCPs; ∗) on the bond paths confirms the nature and extent of this interaction. The recently developed QTAIM dual functional analysis (QTAIM-DFA) approach was also applied to elucidate the nature of the interaction. Total electron energy densities H b( r c) were plotted versus H b( r c) - V b( r c)/2 for the interaction at the BCPs, where V b( r c) represents the potential energy densities at the BCP. The results indicate that although the data for an interaction in the fully optimized structure corresponds to a static nature, the data obtained for the perturbed structures around it represent the dynamic nature of the interaction in QTAIM-DFA. The former classifies the interaction and the latter characterises it. Although AS-∗-AS in 1 is classified by a shared shell interaction and exhibits weak covalent character, AS-∗-BS is characterized as having typical hydrogen-bond nature with covalent properties in the region of the regular closed shell interactions. The experimental results are supported by matching theoretical calculations throughout, particularly for the extended hypervalent E4 σ(4c-6e) (E = S) interaction.

Behavior of the E-E' Bonds (E, E' = S and Se) in Glutathione Disulfide and Derivatives Elucidated by Quantum Chemical Calculations with the Quantum Theory of Atoms-in-Molecules Approach

The nature of the E–E’ bonds (E, E’ = S and Se) in glutathione disulfide (1) and derivatives 2–3, respectively, was elucidated by applying quantum theory of atoms-in-molecules (QTAIM) dual functional analysis (QTAIM-DFA), to clarify the basic contribution of E–E’ in the biological redox process, such as the glutathione peroxidase process. Five most stable conformers a–e were obtained, after applying the Monte-Carlo method then structural optimizations. In QTAIM-DFA, total electron energy densities H_b(r_c) are plotted versus H_b(r_c) − V_b(r_c)/2 at bond critical points (BCPs), where V_b(r_c) are potential energy densities at BCPs. Data from the fully optimized structures correspond to the static nature. Those containing perturbed structures around the fully optimized one in the plot represent the dynamic nature of interactions. The behavior of E–E’ was examined carefully. Whereas E–E’ in 1a–3e were all predicted to have the weak covalent nature of the shared shell interactions, two different types of S–S were detected in 1, depending on the conformational properties. Contributions from the intramolecular non-covalent interactions to stabilize the conformers were evaluated. An inverse relationship was observed between the stability of a conformer and the strength of E–E’ in the conformer, of which reason was discussed.

Linear Four-Chalcogen Interactions in Radical Cationic and Dicationic Dimers of 1,5-(Dichalcogena)canes: Nature of the Interactions Elucidated by QTAIM Dual Functional Analysis with QC Calculations

The dynamic and static nature of extended hypervalent interactions of the ^BE···^AE···^AE···^BE type are elucidated for four center-seven electron interactions (4c-7e) in the radical cationic dimers (1·⁺) and 4c-6e in the dicationic dimers (1²⁺) of 1,5-(dichalcogena)canes (2: ^AE(CH₂CH₂CH₂)₂^BE: ^AE, ^BE = S, Se, Te, and O). The quantum theory of atoms-in-molecules dual functional analysis (QTAIM-DFA) is applied for the analysis. Total electron energy densities H_b(r_c) are plotted versus H_b(r_c) - V_b(r_c)/2 [= (ℏ²/8m)∇²ρ_b(r_c)] at bond critical points (BCPs) of the interactions, where V_b(r_c) values show potential energy densities at BCPs. Data from the fully optimized structures correspond to the static nature of the interactions. Those from the perturbed structures around the fully optimized ones are also plotted, in addition to those of the fully optimized ones, which represent the dynamic nature of interactions. The ^BE···^AE-^AE···^BE interactions in 1²⁺ are stronger than the corresponding ones in 1·⁺, respectively. On the one hand, for 1²⁺ with ^AE, ^BE = S, Se, and Te, ^AE···^AE are all classified by the shared shell interactions and predicted to have the weak covalent nature, except for those in 1a²⁺ (^AE = ^BE = S) and 1d²⁺ (^AE = ^BE = Se), which have the nature of regular closed shell (r-CS)/trigonal bipyramidal adduct formation through charge transfer (CT-TBP). On the other hand, ^AE···^BE are predicted to have the nature of r-CS/molecular complex formation through charge transfer for 1a²⁺, 1b²⁺ (^AE = Se; ^BE = S), and 1d²⁺ or r-CS/CT-TBP for 1c²⁺ (^AE = Te; ^BE = S), 1e²⁺ (^AE = Te; ^BE = Se), and 1f²⁺ (^AE = ^BE = Te). The ^BE···^AE-^AE···^BE interactions in 1·⁺ and 1²⁺ are well-analyzed by applying QTAIM-DFA.

Nature ofE2X2σ(4c–6e) of theX---E—E---Xtype at naphthalene 1,8-positions and model, elucidated by X-ray crystallographic analysis and QC calculations with the QTAIM approach

The nature ofE2X2σ(4c–6e) of theX-*-E-*-E-*-Xtype is elucidated for 1-(8-XC10H6)E–E(C10H6X-8′)-1′ [(1)E,X= S, Cl; (2) S, Br; (3) Se, Cl; (4) Se, Br] after structural determination of (1), (3) and (4), together with modelA[MeX---E(H)—E(H)---XMe (E= S and Se;X= Cl and Br)]. The quantum theory of atoms-in-molecules dual functional analysis (QTAIM-DFA) is applied. The total electron energy densitiesHb(rc) are plottedversus Hb(rc) –Vb(rc)/2 for the interactions at the bond critical points (BCPs; *), whereVb(rc) show the potential energy densities at the BCPs. Data for the perturbed structures around the fully optimized structures are employed for the plots, in addition to those of the fully optimized structures. The plots were analysed using the polar coordinate (R, θ) representation of the data of the fully optimized structures. Data containing the perturbed structures were analysed by (θp, κp), where θpcorresponds to the tangent line of the plot and κpis the curvature. Whereas (R, θ) shows the static nature, (θp, κp) represents the dynamic nature of interactions.E-*-Eare all classified as shared shell (S) interactions for (1)–(4) and as weak covalent (Cov-w) in nature (S/Cov-w). The nature ofpureCS (closed shell)/typical-HB (hydrogen bond) with no covalency is predicted forE-*-Xin (1) and (3),regularCS/typical-HB nature with covalency is predicted for (4), and an intermediate nature is predicted for (2). The NBO energies evaluated forE-*-Xin (1)–(4) are substantially larger than those in modelAdue the shortened length at the naphthalene 1,8-positions. The nature ofE2X2of σ(4c–6e) is well elucidatedviaQTAIM-DFA.

Nature of S2Se2 σ(4c–6e) at naphthalene 1,8-positions and models, elucidated by QTAIM dual functional analysis

The nature of ^BE–*–^AE–*–^AE–*–^BE σ(4c–6e) is primarily elucidated at naphthalene 1,8-positions: while the weak covalent nature is predicted for all ^AE–*–^AE, the HB nature with covalency or the CT-MC (MC formation through CT) nature is for ^AE–*–^BE.

Dynamic and static behavior of the E–E′ bonds (E, E′ = S and Se) in cystine and derivatives, elucidated by AIM dual functional analysis

AIM-DFA (AIM dual functional analysis) is applied to the E–E′ bonds (E, E′ = S and Se) in R-cystine (1), its derivatives and MeEE′Me. The nature of E–E′ is elucidated by (θ_p, κ_p: dynamic behavior) and (R, θ: static behavior), through AIM-DFA.

Photoinduced solid state conversion of a radical σ-dimer to a π-radical pair

Irradiation in the solid state of the hypervalent 4c-6e S···S-S···S bridged σ-dimer of a bisdithiazolyl radical leads to its photodissociation into a pair of π-radicals. The transformation has been monitored by optical spectroscopy, single crystal X-ray diffraction, and magnetic susceptibility measurements. As a result of the large electronic reorganization involved in the dimer-to-radical interconversion, the photogenerated S = 1/2 radical state is remarkably thermally stable, persisting to 242 K before reverting to the S = 0 dimer.

1-Methyl-2,3-dihydro-1H-benzimidazole-2-selone

The title compound C₈H₈N₂Se, is the product of the reaction of 2-chloro-1-methyl­benzimidazole with sodium hydro­selenide. The mol­ecule is almost planar (r.m.s. deviation = 0.041 Å) owing to the presence of the long chain of conjugated bonds (Se=C—NMe—C=C—C=C—C=C—NH). The C=Se bond length [1.838 (2) Å] corresponds well to those found in the close analogs and indicates its pronounced double-bond character. In the crystal, mol­ecules form helicoidal chains along the b axis by means of N—H⋯Se hydrogen bonds.

1,3-Benzothia-zole-2(3H)-selone

The title compound, C(7)H(5)NSSe, is the product of the reaction of 2-chloro-benzothia-zole with sodium hydro-selenide. The mol-ecule is almost planar (r.m.s. deviation = 0.018 Å) owing to the presence of the long chain of conjugated bonds (Se=C-N-C=C-C=C-C=C). The geometrical parameters correspond well to those of the analog N-methyl-benzothia-zole-2(3H)-selone, demonstrating that the S atom does not take a significant role in the electron delocalization within the mol-ecule. In the crystal, mol-ecules form centrosymmetric dimers by means of inter-molecular N-H⋯Se hydrogen bonds. The dimers have a nonplanar ladder-like structure. Furthermore, the dimers are linked into ribbons propagating in [010] by weak attractive Se⋯S [3.7593 (4) Å] inter-actions.

Hysteretic spin crossover between a bisdithiazolyl radical and its hypervalent σ-dimer

The bisdithiazolyl radical 1a is dimorphic, existing in two distinct molecular and crystal modifications. The α-phase crystallizes in the tetragonal space group P4̅2(1)m and consists of π-stacked radicals, tightly clustered about 4̅ points and running parallel to c. The β-phase belongs to the monoclinic space group P2(1)/c and, at ambient temperature and pressure, is composed of π-stacked dimers in which the radicals are linked laterally by hypervalent four-center six-electron S···S-S···S σ-bonds. Variable-temperature magnetic susceptibility χ measurements confirm that α-1a behaves as a Curie-Weiss paramagnet; the low-temperature variations in χ can be modeled in terms of a 1D Heisenberg chain of weakly coupled AFM S = (1)/(2) centers. The dimeric phase β-1a is essentially diamagnetic up to 380 K. Above this temperature there is a sharp hysteretic (T↑= 380 K, T↓ = 375 K) increase in χ and χT. Powder X-ray diffraction analysis of β-1a at 393 K has established that the phase transition corresponds to a dimer-to-radical conversion in which the hypervalent S···S-S···S σ-bond is cleaved. Variable-temperature and -pressure conductivity measurements indicate that α-1a behaves as a Mott insulator, but the ambient-temperature conductivity σ(RT) increases from near 10(-7) S cm(-1) at 0.5 GPa to near 10(-4) S cm(-1) at 5 GPa. The value of σ(RT) for β-1a (near 10(-4) S cm(-1) at 0.5 GPa) initially decreases with pressure as the phase change takes place, but beyond 1.5 GPa this trend reverses, and σ(RT) increases in a manner which parallels the behavior of α-1a. These changes in conductivity of β-1a are interpreted in terms of a pressure-induced dimer-to-radical phase change. High-pressure, ambient-temperature powder diffraction analysis of β-1a confirms such a transition between 0.65 and 0.98 GPa and establishes that the structural change involves rupture of the dimer in a manner akin to that observed at high temperature and ambient pressure. The response of the S···S-S···S σ-bond in β-1a to heat and pressure is compared to that of related dimers possessing S···Se-Se···S σ-bonds.

Evidence for effective p(Z)-pi(Ar) conjugations (Z = S, Se, and Te, as well as Z = O) in 9-(arylchalcogenyl)triptycenes: experimental and theoretical investigations

The p(Z)-pi(Ar) conjugations must operate fully in the ground states of 9-(arylchalcogenyl)triptycenes (p-YC(6)H(4)ZTpc:1 (Z = O), 2 (Z = S), 3 (Z = Se), and 4 (Z = Te)), where the p-YC(6)H(4) group is placed in the bisected area between two phenyl planes of the triptycyl group with the parallel orientation. The ground-state geometries, which we call (A: pl), are confirmed by X-ray analysis. However, the conjugations never operate in the transition states between (A: pl) and/or the topomeric structures (A': pl'), where the Z-C(Tpc) bond is perpendicular to the plane. The site-exchange processes correlate to the conjugations. Temperature-dependent (1)H NMR spectra are analyzed for 2 and 3 to demonstrate the effective p(Z)-pi(Ar) conjugations. The activation energies for the interconversion between (A: pl) and (A': pl') (GR: gear process) were obtained for 2 (DeltaG(GR)(2)) and 3 (DeltaG(GR)(3)). DeltaG(GR)(3) correlate well with DeltaG(GR)(2), and DeltaG(GR)(2) are well analyzed by the Hammett-type dual parameters. DeltaG(GR)(2) and DeltaG(GR)(3) are demonstrated to be controlled by the resonance interaction of the p(Z)-pi(C(6)H(4))-p(Y) conjugations. QC calculations are performed on the ground and exited states of 1-4, which clarify the effective p(Z)-pi(C(6)H(4))-p(Y) conjugations for Z of heavier atoms.

Fine structures of 8-G-1-(p-YC6H4C identical with CSe)C10H6 (G = H, Cl, and Br) in crystals and solutions: ethynyl influence and Y- and G-dependences

Fine structures of 8-G-1-(p-YC₆H₄C ≡ CSe)C₁₀H₆ [1 (G = H) and 2 (G = Cl): Y = H (a), OMe (b), Me (c), F (d), Cl (e), CN (f), and NO₂ (g)] are determined by the X-ray analysis. Structures of 1, 2, and 3 (G = Br) are called A if each Se–C_sp bond is perpendicular to the naphthyl plane, whereas they are B when the bond is placed on the plane. Structures are observed as A for 1a–c bearing Y of nonacceptors, whereas they are B for 1e–g with Y of strong acceptors. The change in the structures of 1e–g versus those of 1a–c is called Y-dependence in 1. The Y-dependence is very specific in 1 relative to 1-(p-YC₆H₄Se)C₁₀H₇ (4) due to the ethynyl group: the Y-dependence in 1 is almost inverse to the case of 4 due to the ethynyl group. We call the specific effect “Ethynyl Influence.” Structures of 2 are observed as B: the A-type structure of 1b changes dramatically to B of 2b by G = Cl at the 8-position, which is called G-dependence. The structures of 2 and 3 are examined in solutions based on the NMR parameters.