The crystal and molecular structure of sulfur nitride, S4N4

Dissociation Without Detonation: A DFT Analysis of the Thermally Induced Fragmentation of Binary Sulfur-Nitrogen Rings and Cages

Potential thermal dissociation pathways available to binary sulfur nitrides have been explored by density functional theory methods, and the results interpreted in terms of their known thermochemical behavior. The cyclic cation/anion pair S3N3± both undergo concerted (4 + 2) cycloreversions to afford the 3-membered thiadiazirine ring c-NSN and, respectively, the SNS± cation/anions. A similar pathway has been identified for S4N2, leading to S3 and c-NSN. More complex multistep routes for the elimination of c-NSN have been identified for the bicyclic cation/anion pair S4N5±, as well as for the neutral cage structures S4N4 and S5N6. For the S4N5+ cation a transition state for competing skeletal scrambling via a 1,3-nitrogen σ-bond shift has been located. For the multiply charged cations S3N22+ and S4N42+, dissociation mechanisms are driven by charge repulsion effects, affording SNS+/SN+ and S3N3+/SN+ respectively. Channels leading to loss of NS+ from the cyclic cation species S4N3+ and S5N5+ have also been examined, and the possible role of open-chain and cyclic S3N2-based intermediates in the formation of S2N2 during the thermal cracking of S4N4 over silver wool is explored.

Pentathiepins are an understudied molecular prism of biological activities

The pentathiepin core was first synthesized in 1971, and while synthetic techniques have progressed over subsequent decades, the biological applications of this heterocycle have received less attention and are only now becoming more apparent. The first natural product, varacin, was identified in 1991, showing cytotoxicity toward a human colon cancer cell line. More recently, the pentathiepin has acted as a surrogate to replace elemental sulfur, that was discovered as a hit in neurodegenerative animal models. A variety of other medicinal chemistry applications have recently been disclosed. Here, we summarize these indications and highlight the main synthetic pathways to access the pentathiepin core. We offer a concise summary and future perspective of this unique sulfur isosteric replacement.

Photochemistry of tetrasulfur tetranitride: laser flash photolysis and quantum chemical study

The photochemistry of tetrasulfur tetranitride (1) was studied in hexane solution by the laser flash photolysis technique (LFP). The experimental findings were interpreted using the results of previous matrix isolation studies (Pritchina, E.A.; Gritsan, N.P.; Bally, T.; Zibarev, A.V. Inorg. Chem. 2009, 48, 4075) and high-level quantum chemical calculations. LFP produces two primary intermediates, one of which is the boat-shaped 8-membered cyclic compound (2) and the other is the 6-membered S(3)N(3) cyclic compound carrying an exocyclic (S)-N═S group (3). The primary products 2 and 3 absorb a second photon and undergo transformation to the 6-membered S(3)N(3) cycle carrying an exocyclic (N)-S≡N group (4), which is very unstable and converts back to intermediate 3. The quantum yield of the primary product formation is close to unity even though the quantum yield of photodegradation of 1 is low (~0.01). Thus, 1 is a photochromic compound undergoing in solution the thermally reversible photochemical isomerization. The mechanism of the photochromic process was established, and the rate constants of the elementary reactions were measured.

Photochemical study on the reactivity of tetrasulfur tetranitride, S4N4

To elucidate the multifaceted but poorly understood chemistry of the pivotal polysulfur-nitrogen heterocycle, tetrasulfur tetranitride (S(4)N(4), 1), its photochemistry was studied in Ar matrices. Thereby two primary intermediates and a secondary one (2-4) were detected, and their UV-vis and IR spectra were identified through specific interconversions of 1-4 that can be induced by selective irradiations. The structures associated with these spectra were assigned with the help of DFT calculations. From these assignments it follows that, under the conditions of the present experiments, the cage structure of 1 transforms into isomeric structures 2-4, one of which is a boat-shaped 8-membered cycle (2), and the two other are novel 6-membered S(3)N(3) cycles carrying exocyclic (N)S[triple bond]N (3) or (S)N=S (4) groups, respectively, which have not been previously described. These three intermediates probably play a pivotal role in the formation of the diverse products that are observed in the reactions of S(4)N(4) even under mild reaction conditions.

Electronic Structures and Molecular Properties of Chalcogen Nitrides Se2N2 and SeSN2

The electronic structures and molecular properties of S2N2 as well as the currently unknown chalcogen nitrides Se2N2 and SeSN2 have been studied using various ab initio and density functional methods. All molecules share a qualitatively similar electronic structure and can be primarily described as 2pi-electron aromatics having minor singlet diradical character of 6-8% that can be attributed solely to the nitrogen atoms. This diradical character is manifested in the prediction of their molecular properties, in which coupled cluster and multiconfigurational approaches, as well as density functional methods, show the best performance. The conventional ab initio methods RHF and MP2 completely fail to describe these systems. Predictions for the vibrational frequencies, IR intensities, Raman activities, and 14N, 15N, and 77Se chemical shifts, as well as singlet excitation energies of Se2N2 and SeSN2, have been made. The computed high-level spectroscopic data will be of considerable value in future efforts aimed at the preparation of the conducting polymers (SeN)x and (SeNSN)x.

Preparation and structural characterization of (Me(3)SiNSN)(2)Se, a new synthon for sulfur-selenium nitrides

The reaction of (Me(3)SiN)(2)S with SeCl(2) (2:1 ratio) in CH(2)Cl(2) at -70 degrees C provides a route to the novel mixed selenium-sulfur-nitrogen compound (Me(3)SiNSN)(2)Se (1). Crystals of 1 are monoclinic and belong the space group P2(1)/c, with a = 7.236(1) A, b = 19.260(4) A, c = 11.436(2) A, beta = 92.05(3) degrees, V = 1592.7(5) A(3), Z = 4, and T = -155(2) degrees C. The NSNSeNSN chain in 1 consists of Se-N single bonds (1.844(3) A) and S=N double bonds (1.521(3)-1.548(3) A) with syn and anti geometry at the N=S=N units. The N-Se-N bond angle is 91.8(1) degrees. The EI mass spectrum shows a molecular ion with good agreement between the observed and calculated isotopic distributions. The (14)N NMR spectrum exhibits two resonances at -65 and -77 ppm. Both (13)C and (77)Se NMR spectra show single resonances at 0.83 and 1433 ppm, respectively. The reaction of 1 with an equimolar amount of SeCl(2) produces 1,5-Se(2)S(2)N(4) (2) in a good yield, and that of (Me(3)SiNSN)(2)S with SCl(2) affords S(4)N(4) (3), but the reactions of (Me(3)SiNSN)(2)Se with SCl(2) and (Me(3)SiNSN)(2)S with SeCl(2) result in the formation of a mixture of 2 and 3. A likely reaction pathway involves the intermediate formation of E(2)N(2) fragments (E = S, Se).

Preparation, X-ray Structure, and Spectroscopic Characterization of 1,5-Se(2)S(2)N(4)

The reaction of [(Me(3)Si)(2)N](2)S with equimolar amounts of SCl(2) and SO(2)Cl(2) produces S(4)N(4) in a good yield. The new chalcogen nitride 1,5-Se(2)S(2)N(4) has been prepared in high yield by two different reactions: (a) from [(Me(3)Si)(2)N](2)S and SeCl(4) and (b) from [(Me(3)Si)(2)N](2)Se with equimolar amounts of SCl(2) and SO(2)Cl(2). 1,5-Se(2)S(2)N(4) has a cage structure similar to those of S(4)N(4) and Se(4)N(4). The crystal structure is disordered with site occupation factors ca. 50% for selenium in each chalcogen atom position. The 12 eV EI mass spectrum shows Se(2)SN(2)(+) as the fragment with highest mass. Both the (14)N and (77)Se NMR spectra show a single resonance (-238 and 1418 ppm, respectively). These data rule out the possibility that the crystalline sample is a solid solution of S(4)N(4) and Se(4)N(4) and imply the presence of 1,5-Se(2)S(2)N(4). This deduction was further verified by Raman spectroscopy and vibrational analysis.