Intramolecular Chalcogen−Nitrogen Interactions:  Molecular and Electronic Structures of Geometrical Isomers of the Diazenes RSNC(R‘)NNC(R‘)NSR

Abstract

The sulfur-containing diazenes ArSNC(Ar‘)NNC(Ar‘)NSAr (1d, Ar = Ar‘ = 4-CH3C6H4; 3b, Ar = Ph, Ar‘ = 2-BrC6H4; 3c, Ar = Ph, Ar‘ = 2-CF3C6H4) are obtained by the reaction of Ar‘CN2(SiMe3)3 with 3 molar equivs of ArSCl in CH2Cl2. X-ray structural determinations have shown that 1d exists as a Z,E,Z isomer with a weak intramolecular S···N interaction [2.607(10) Å], whereas 3b adopts an E,E,E configuration. Crystals of 1d are monoclinic, space group P21/n, with a = 6.140(2) Å, b = 10.492(6) Å, c = 20.728(9) Å, β = 96.56(4)°, V = 1325(1) Å3, Z = 2, R = 0.056, and R w = 0.052. Crystals of 3b are orthorhombic, space group Ccca, with a = 13.884(5) Å, b = 24.763(7) Å, c = 14.500(3) Å, V = 4985(2) Å3, Z = 8, R = 0.043, and R w = 0.044. Density functional theory calculations for the model diazenes HENC(H)NNC(H)NEH (E = S, Se, Te) show that (a) Z,E,Z isomers with an intramolecular E···N interaction are more stable than the E,E,E isomers, (b) the intramolecular interaction involves donation from the σ(N) lone pairs into both σ*(S−H) and σ*(S−N) and back-donation from a chalcogen π lone pair into the π*(NN) orbital, and (c) the intense visible absorption bands (λmax 500−550 nm, ε = 1 × 104 M-1 cm-1) can be attributed to the π-HOMO (3au) → π*-LUMO (3bg) transition. Variable-temperature 1H NMR spectra of PhSNC(H)NNC(H)NSPh in toluene-d 8 and in CD2Cl2 provide evidence for the co-existence and interconversion of several geometrical isomers.

O⋯S vs. N⋯S intramolecular nonbonded interactions in neutral and radical cation salts of TTF-oxazoline derivatives: synthesis, theoretical investigations, crystalline structures, and physical properties

“…Indeed, theoretical studies on a series of chalcogen containing diazenes undoubtedly demonstrated the important role of the p type orbital interactions in the stabilization of intramolecular EÁ Á ÁN contacts. 26 It is thus clear that in the case of our TTF-SMe-OX the stabilization of This demonstrates once again that the 3c-4e model accurately describes also the NÁ Á ÁS nonbonded interaction in our case.…”

“…Indeed, theoretical studies on a series of chalcogen containing diazenes undoubtedly demonstrated the important role of the p type orbital interactions in the stabilization of intramolecular EÁÁÁN contacts. 26 It is thus clear that in the case of our TTF-SMe-OX the stabilization of 20 ; r B = electron density at the BCP (au); r 2 r B = Laplacian at the BCP (au). planar structures, be they s-cis or s-trans, is largely favored also by p interactions such as p(S)-p(CQC) and p(CQC)-p(CQN).…”

The supramolecular chemistry of 1,2,5-chalcogenadiazoles

“…Divalent chalcogen atoms frequently engage in SBIs with other atoms that contain lone pairs of electrons [10,11], these interactions are the result of a combination of electrostatic, covalent, and dispersion contributions that overcome the strong Pauli repulsion between lone pairs [12][13][14]. A thorough computational (DFT) study of the association of 1,2,5-chalcogenadiazoles showed that the covalent interactions represent the largest contribution to the stabilization of the (E-N) 2 supramolecular synthon.…”

A survey of tellurium-centered secondary-bonding supramolecular synthons

“…1). The fundamentals of this model derived from empirical observation have been validated by modern quantum mechanical methods [15,16] but a complete bonding description does require the inclusion of all orbital, electrostatic and dispersion contributions [6]. While mixing of occupied and unoccupied orbitals corresponds to the donor-acceptor character of the interaction and confers directionality to the SBI, an unavoidable destabilizing contribution (the Pauli repulsion) results from the mixing of all-occupied orbitals.…”