CFA-18: a homochiral metal–organic framework (MOF) constructed from rigid enantiopure bistriazolate linker molecules

Abstract

In this work, we introduce the first enantiopure bistriazolate-based metal–organic framework, CFA-18 (Coordination Framework Augsburg-18), built from the R-enantiomer of 7,7,7′,7′-tetramethyl-6,6′,7,7′-tetrahydro-3H,3′H-5,5′-spirobi[indeno[5,6-d]-[1,2,3]triazole] (H₂-spirta). The enantiopurity and absolute configuration of the new linker were confirmed by several chiroselective methods. Reacting H₂-spirta in hot N,N-dimethylformamide (DMF) with manganese(II) chloride gave CFA-18 as colorless crystals. The crystal structure with the composition [Mn₂Cl₂(spirta)(DMF)₂] was solved using synchrotron single-crystal X-ray diffraction. CFA-18 shows a framework topology that is closely related to previously reported metal–azolate framework (MAF) structures in which the octahedrally coordinated manganese(II) ions are triazolate moieties, and the chloride anions form crosslinked one-dimensional helical chains, giving rise to hexagonal channels. In contrast to MAFs crystallizing in the centrosymmetric space group R, the handedness of the helices found in CFA-18 is strictly uniform, leading to a homochiral framework that crystallizes in the trigonal crystal system within the chiral space group P3₁21 (no. 152).