Crystal Structures of the Inclusion Complexes of β-Cyclodextrin with Aliphatic Monoacids Tridecanoic Acid and (Z)-Tetradec-7-enoic Acid. Formation of [3]Pseudorotaxanes

Abstract

The structures of the inclusion complexes of beta cyclodextrin with the aliphatic mono-acids tridecanoic acid (1) and (Z)-tetradec-7-enoic acid (2) have been determined at room temperature. Both compounds crystallise in P1, a = 15.654(6) A, b = 15.650(6) A, c = 15.937(6) A, α = 101.58(1)°, β = 101.59(1)°, γ = 103.58(1)°, Z = 1, for 1 and a = 15.6259(9) A, b = 15.623(1) A, c = 15.935(1) A, α = 101.547(2)°, β = 101.555(2)°, γ = 103.642(2)°, Z = 1, for 2. One molecule of the monoacids threads through two cyclodextrin macrocycles arranged in dimers thus forming [3]pseudorotaxanes. The host dimers are aligned along a channel in order to create a hydrophobic environment for the terminal methyl group of the guest and isolate it from the aqueous environment that surrounds the cyclodextrin dimeric units. The guests exhibit disorder over two orientations resulting in hydrogen bonding between the carboxyl groups of adjacent guest molecules along the channel and formation of carboxylic dimers. This crystal packing differs from that of β-CD complexes of homologous dicarboxylic acids.