Crystal structure of N,N′-bis(tert-butoxycarbonyl)-5,10-dihydrophenazine and periodic DFT- D3(BJ) analysis of the interplay of π-stacking and C-H···O interactions

Abstract

The crystal structure of N,N′-bis(tert-butoxycarbonyl)-5,10-dihydrophenazine, a valuable synthetic precursor for phenazine chemistry, and the first example of a carbamate derivative of dihydrophenazine, was determined (triclinic space group P \(\:\stackrel{-}{1}\) with Z = 2). The 5,10-dihydrophenazine core adopts a boat, i.e. cis -conformation core, while bulky tert-butyl groups hindering tight packing. Hirshfeld surface analysis shows two groups of interactions, the numerically minor, but relatively stronger CH···O (11.5%) and CH···C (19.7%), which are relatively isolated in comparison to weak H···H (65.7%) vdW interactions. Under these constraints, the concave molecules self-assemble in pairs, with one stronger slip-stacked π···π interaction and two weaker, symmetry-equivalent edge-to-face C-H···π interactions acting cooperatively. Periodic density functional theory (DFT; PBE-D3(BJ), validated against four X23 reference crystals) gives 130.7 kJ mol − 1 lattice energy, dominated by dispersion. The symmetry-adapted perturbation theory (SAPT) analysis of the symmetry-independent molecular pairs allows direct structural rationalization for the given molecular conformation: four relatively strong pairs were found, the second strongest being the π···π slip stacked pair, whose computed distance closely matches the crystallographic value, although the underlying slip angle differs somewhat. Weaker pairwise interactions, mainly H···H contacts of the tert-butyl groups, contribute little to the lattice energy, isolating the concurrence of the stronger CH···O and CH···C interactions. The SAPT decomposition demonstrates a good structural predictability for weakly interacting dimeric aggregates of dihydrophenazines, while the demonstrated Boc-substituted example represents a general rational approach towards supramolecular dimers for fine-tuning of physico-optical properties.

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