Subtle Control in Solution and Crystal Structures with Weak Hydrogen Bonds: The Unusual Profile of Dimethyl 3,12-Dioxo-7,8-dithia-4,11-diazabicyclo[12.2.2]octadeca-1(16),14,17-triene-5,10-dicarboxylate (TDA1)

Abstract

The structural features of the title compound were determined or examined by three diverse procedures: single crystal X-ray diffraction analysis, solution spectroscopic procedures and Quantum mechanical theoretical calculations. The conformational asymmetry of the macrocycle provides the opportunity to form one strong NH···OC intermolecular hydrogen bond, as well as, a number of weak CH···OC bonds. The interior of the macrocycle has short approaches for NH(...)π and NH···S. The many weak hydrogen bonds cooperate to form a very hard, robust crystal. Crystal parameters: C(18)H(22)N(2)O(6)S(2), P2(1)2(1)2(1), a = 5.108(1) Å, b = 18.948(4) Å, c = 21.029(3) Å, α = β = γ = 90°. Quantum chemical calculations have provided a strong foundation for weak hydrogen bonds. Contrary to popular belief the present work has conclusively proved that the importance of weak hydrogen bonds are perhaps underestimated since calculations show that the energy of duplex are significantly lower then estimated from the identified hydrogen bonding.