Complexation with Diol Host Compounds, 12. Synthesis and Solid‐State Inclusion Properties of Bis(diarylhydroxymethyl)1‐Substituted 1,1′‐Binaphthyls. Crystal Structures of a Host and Its Pyridine Clathrate

Abstract

A series of new clathrate host molecules 1-8 containing two bis(diarylhydroxymethy1) groups attached to different positions (2,2' or 8 , 8 ) of a 1,l'-binaphthyl frame have been synthesized. Their clathrate formation properties with organic guests including alcohols, amines, ketones, and other dipolar aprotic compounds or aromatic hydrocarbons are reported (74 examples of clathrates) together with the results of solvent competition experiments for the parent host compound. The inclusion formation and the clathrate stoichiometries depend on the structure of the host molecules in a systematic manner. The crystal structures of the free parent host 1 and its pyridine clathrate (1 : 3) have been determined by X-ray diffraction. The molecular structure of the host is similar in the two species involving an intramolecular hydrogen bond between the host hydroxyls. No other hydrogen bond is involved in the free host case while in the pyridine inclusion compound the second host hydroxyl forms a hydrogen bond with the nitrogen of one pyridine guest which is surrounded by two unbound pyridine species such as to form clusters of three pyridine guests enclosed in the cavities between the host molecules. Thermal analysis corresponds with the two binding states of the pyridine molecules in the clathrate.Organic compounds that form crystalline host-guest inclusions (clathrates)" with secondary molecules are attracting increasing attentionc3] in view of their practical uses. These include chemical separation, stabilization and protection of labile species, topochemistry or development of new solid materials['-71. This has stimulated the development of new strategies in crystalline inclusion formation and motivated the design of novel host types[%31. The most consistent results refer to inclusion compounds which are based on coordination-assisted clathrate formation between functionalized and polar guest molecules[81. The formation and stability of these crystalline complexes are affected by functional as well as by topological complementarity, and consequently are sensitive to small structural variations[9~'01.Among the many new types of polar host structures[',2~8-'01, the hydroxylic group-containing molecules, in particular those involving triarylmethanol and bridged triarylmethanol units, were found to be very effective clathrate formers ['."-'31 . Fr om the geometric point of view, the scissor-type hosts based on the 1,l'-binaphthyl frame proved particular s~c c e s s f u l [~~~~~~~~. We report here on the synthesis of several specified compounds 1-8 that combine both (1 -7) have different polar and apolar substituents in different positions attached to the lateral aromatic rings. Moreover, linkage of the basic construction elements is also different (2,2' or 83' with reference to the binaphthyl unit, cf. 1 vs. 8) making possible a comprehensive evaluation of the host structures. We describe in detail the crystal inclusion properties of 1 -8, including guest competition experiments for 1 and present crystal structures of the ...

Polymorphism, selectivity and reactivity of inclusion compounds

“…The diol host compound under our study is 2,2'-bis-(diphenylhydroxymethyl)binaphthylene (H) (see scheme). Three polymorphous crystalline forms, A, B and C, were discovered during our study, one of which was previously published [2]. All these three forms has been found to coexist in solution of equal mole ratio of acetone/2-butanol solvent mixture at ambient conditions.…”

“…We have previously shown that H1 successfully forms inclusion compounds with 1,4-dioxane[1] and acetone [2]. Here we report on the structures of H1•DMF and H1•DMA where DMF = N,Ndimethylformamide and DMA = N,N-dimethylacetamide.…”

“…Natural cyclodextrins (CDs), cyclic oligosaccharides consisting mainly of six (αCD), seven (βCD) or eight (γCD) α-(1,4)-linked D-glucopyranosyl residues have a hydrophobic, relatively rigid cavity able to host a plethora of molecules. Being chiral compounds, CDs can, in principle, discriminate between enantiomers (guests) forming preferentially with one of the two a more stable inclusion complex [1,2]. X-ray crystallography can provide details of the factors that lead to chiral recognition.…”

“…The selectivity of a host molecule towards a given guest in a binary mixture of guests G1 and G2 can be determined by competition experiments, in which the inclusion compounds are crystallised in a mixture of guests of known composition and the ensuing crystals analysed by a suitable analytical technique. The resulting analysis of the enclathrated guests yields the selectivity profile which may be of three main types : (i) Zero selectivity, where the mole fraction of the captured guest = that in the starting solution; (ii) A given guest is strongly favoured over the complete range; (iii) The selectivity is strongly concentration dependent [2]. The question which arises is what is the structure of the harvested crystals?…”

Controlled host:guest ratio in an inclusion compound

“…1 Single crystals of the inclusion compound HÁG n (s) generally break up to form a fine powder of the intermediate compound HÁG nÀm (s), making it impossible to subject the latter to single-crystal structure analysis. Previous reports have appeared detailing the possibility of growing inclusion compounds with various host:guest ratios by changing the crystallization temperature.…”