Insight Into the Intermolecular Factors Responsible for theZ,ZConfiguration of Ar–X–N=S=N–X–Ar (X = S, Se) Derivatives in the Solid State

Abstract

The molecular and crystal structures of three new derivatives of Ph–S–N=S=N–S–Ph (1), with 2,4,6‐(tert‐C4H9)3C6H2 (4), C6F5 (5) and 4‐CF3C6F4 (6) as peripheral rings, respectively, and one new derivative of Ph–Se–N=S=N–Se–Ph (2), with C6F5 (7) as peripheral rings, are reported and discussed in connection with those of the two parent structures 1 and 2 and those of the previously studied derivative of 1 containing 4‐ClC6H4 (3) as peripheral rings. For these seven compounds the Z,Z configuration is the only one of the three theoretically possible configurations observed in the solid state and this configurational preference can not be explained by intramolecular stereoelectronic effects. Calculation of the packing energies and densities for the six most common space groups revealed that the crystal packing of the parent structure 1 in the Z,Z configuration has a systematic preference over the corresponding packing of 1 in the Z,E configuration by 0.3–4.9 kJ mol–1. As a result, packing forces are most likely responsible for the dominance of the Z,Z configuration of the title compounds in the crystal.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

A Brave New World: The Heteroatom Chemistry of 1,3,2,4‐Benzodithiadiazines and Related Compounds

“…[29b,29c,44,46a-46c] This system features a notably low IE 1 , low-lying π*-excited states, and enhanced magnetic shielding of the 1 H, 13 C, and 19 F nuclei attached to C5 and C8, i.e., those closest to the heterocycle, probably due to paratropic ring currents in the latter. All these peculiarities can be associated with antiaromaticity.…”

“…The most interesting feature of the NMR spectra of compounds 1 is the enhanced shielding of the 1 H, 13 C, and 19 F nuclei (for the monofluoro derivatives) attached to C5 and C8 -i.e., those closest to the heterocycle -as compared to those attached to C6 and C7. [23c,29] For 1h, δ( 1 H) is 5.90 and 5.79 for H5 and H8, and 6.63 and 6.79 for H6 and H7, respectively.…”

“…However, it is necessary to take into account that the acyclic derivatives normally exist in solution as equilibria of isomers (mainly Z,E and Z,Z) with slightly different λ max values. [11][12][13] …”

The First Observation of theE,ZConfiguration Of Ar–X–N=S=N–X–Ar (X = S, Se) Chains in the Crystalline State

“…packing forces) are the main driving force behind the experimentally observed Z,Z configurations. [7] In this situation, the stabilization of the E,Z isomer in the crystal can be considered as a challenge for the structural and supramolecular chemistry and crystal engineering of chalcogen-nitrogen compounds. One way to address the problem is by affecting the crystal packing through specific intermolecular interactions, [10] which are different from the X···X interactions observed in the crystal lattices of the already studied Z,Z isomers.…”

“…both (substituted) hydrocarbon and fluorocarbon groups], only the Z,Z configuration was found in the solid state, while the coexistence of the Z,Z and E,Z isomers was observed by NMR spectroscopy in solution and predicted by quantum chemical calculations in the gas phase. [7] Ph-N=S=N-S-N=S=N-Ph [8] and Ph-S-N=S=N-S-N=S=N-S-Ph [9] possess the E,Z,E,Z and Z,E,Z,Z configurations in the crystal, respectively, whereas the macromolecular (SN) x adopts the ...E,Z,E,Z... configuration. [1] For the Ar-X-N=S=N-X-Ar (X = S, Se) derivatives, it was shown that their configurational preference in the solid state cannot be explained by intramolecular stereoelectronic effects, and that intermolecular factors (i.e.…”