Crystal and molecular structure of two isomeric N-methyl iodides of thiobinupharidine:trans,trans-N,N′-dmethyl-thiobinupharidine diiodide dihydrate acetone solvate andcis,trans-N,N′-dimethylthiobinupharidine diiodide dihydrate methanol solvate

Abstract

The crystal structures of two quaternary salts,trans,trans- andcis,trans-N,N′-dimethylthiobinupharidine diiodide, whose stereochemistries have been previously characterized by¹³C NMR spectroscopy, have now been determined by X-ray analysis. Differences in the nitrogen atom configuration of the AB quinolizidine fragment result in different conformations of the central part of the cations, the spiro tetrahydrothiophene ring, and specific selectivity toward solvent molecules. Thetrans,trans isomer crystals obtained from an acetone/methanol/water solution contained two water and one acetone molecule, while thecis,trans cocrystallized from the same solvent mixture with methanol and two water molecules. Very weak hydrogen bonds of the C-H⋯I⁻ type determine interactions between the quaternary cations and the I⁻ anions in the solid state. Water molecules form a dimer, and this dimer is hydrogen bonded to the I⁻ anions. Organic solvent molecules included in crystals show different type of interactions with surrounding molecules: (i) the acetone molecule is trapped in the cavity of thetrans,trans cation by very weak C-H⋯O interactions; (ii) methanol is hydrogen bonded to a water molecule while with thecis,trans cation and I⁻ anion interacts only by van der Waals forces.