Structural and Diffraction Properties of Incommensurate Solid Inclusion Compounds Formed between α,ω-Dihalogenoalkanes and Tri-ortho-thymotide

Abstract

Structural properties of incommensurate solid inclusion compounds formed between long-chain α,ω-dihalogenoalkanes [1,10-dibromodecane, Br(CH2)10Br; 1,8-diiodooctane, I(CH2)8I; 1,10-diiododecane, I(CH2)10I] and tri-ortho-thymotide (TOT) are reported, together with a detailed discussion of the diffraction properties of these inclusion compounds. At ambient temperature, all three inclusion compounds have essentially the same TOT “host” structure, within which there are linear, parallel tunnels. The α,ω-dihalogenoalkane “guest” molecules form an ordered arrangement along these tunnels, with an incommensurate relationship between the periodicities of the host and guest structures along the tunnel direction. However, the guest molecules do not exhibit strong inter-tunnel ordering (in contrast to the situation for the same guest molecules in urea inclusion compounds). As a consequence of the partially disordered guest substructures in these TOT inclusion compounds, the single-crystal X-ray diffraction patterns contain substantial diffuse scattering. The results reported here provide evidence for a weak superstructure of the host in the 1,10-dibromodecane/TOT and 1,10-diiododecane/TOT inclusion compounds and evidence for a low-temperature phase transition in the 1,8-diiodooctane/TOT inclusion compound. The diffraction properties of these inclusion compounds and their corresponding structural implications are assessed in detail.