Andrew D. U. Hardy

Crystal and molecular structure of an OH ⋯π hydrogen-bonded system : 2,2-bis-(2-hydroxy-5-methyl-3-t-butylphenyl)propane

The crystal structure of the title compound (I) has been determined by three-dimensional X-ray analysis. Crystals are orthorhombic, a= 14.089, b= 18.190, c= 8.896 A, Z= 4, space group P212121. The structure was solved by direct methods employing 1 646 significant diffractometer data, and refined by least-squares methods to a final R of 0.038. The structure possesses two independent intramolecular OH ⋯π hydrogen bonds, mean 2.09 A, for the perpendicular distance between the hydroxy-hydrogen atom and its corresponding π-electron-dono rring.

A new approach for the design of inclusion compounds

A new strategy for the design of inclusion compounds is described. The approach is based on the analogy between the hydrogen-bonded hexamer unit present in the clathrates of phenol, quinol, Dianins compound, and other hydroxyaromatic hosts, and a hexasubstituted benzene. Suitable hexasubstituted benzenes have been prepared, and on recrystallisation from various solvents, a wide range of inclusion behaviour has been found for compounds (I), (III), (VIII)–(XIII), (XV), and (XVIII)–(XX), In addition, several of these hosts, for example, (III), (VIII), (IX), and (XIII), exhibit remarkable guest selectivity properties when recrystallised from solvent mixtures. A detailed X-ray study of the carbon tetrachloride adduct of hexakisphenylthiobenzene (I) has been carried out. The crystals are trigonal, space group R, with a= 14.263; c= 20.717 A, and three host and six guest molecules in the hexagonal unit cell. A true clathrate structure is found and two CCl4 guest molecules fit snugly into a cavity of effective length ca. 17 A, a C–Cl bond of each guest being collinear with the c axis of the crystal.

Design of inclusion compounds: systematic structural modification of the hexa-host molecule hexakis(benzylthiomethyl)benzene

A study of the inclusion behaviour of the title compound (I) and eleven structurally related compounds (II)–(XII) is described. Substitution of each of the six outer aromatic rings of (I) with a single methyl group gives new hosts, the most general of which is the meta-analogue (III). A parallel situation is found for the hexachloro-compounds (X)–(XII) where inclusion is again favoured by meta-substitution. The versatile host (VII) favours inclusion of o-xylene from an equimolar mixture of o- and p-xylene, in contrast to host (III) which selectively includes the para-isomer. A detailed X-ray study of the 1,4-dioxan adduct of the parent (I) has been carried out. The crystals are monoclinic, space group P21/c, with a= 10.542, b= 20.863, c= 12.496 A, β= 95.48°, and 2 host and 2 guest molecules in the unit cell. A true clathrate structure is found, the chair-shaped dioxan guest molecules being accommodated in effectively closed cages.

Structure and transformation of products of the reactions of 2,2″-thiodi-isobutyrophenone with hydrazine

The novel course of the reaction of the title dioxo-sulphide (II) with hydrazine is described. In absence of acid none of the expected dihydrothiadiazepine (Ia) could be detected; the major product, a monohydrazone (IV), being accompanied by other products including 2,2,4,4-tetramethyl-1,5-diphenyl-8-oxa-3-thia-6,7-diazabicyclo[3.2.1]octane (III) whose structure was elucidated by spectroscopic and X-ray crystallographic methods: compound (III) crystallises in the triclinic space group P with a= 9·911, b= 15·297, c= 6·257 A, α= 103·02°, β= 106·15°, γ= 81·17°, Z= 2, and the structure was refined to a final R value of 7·7% for 2055 independent reflections. The thiadiazepine (Ia) could, however, be obtained by treatment of a crude reaction mixture in pyridine with strong mineral acid, or by dehydration of (III) with acetic acid. The reaction of (III) with molecular oxygen gives, depending on temperature, either the ozonide (VI) or the epoxide (VII) in good yield.

Synthesis and crystal structures of normethyl analogues of Dianin's compound

As part of a study of inclusion behaviour, chromans (II) and (III) have been prepared, normethyl analogues of the versatile host Dianins compound (I). Compound (II), which lacks the 2-methyl group cis to the p-hydroxyphenyl substituent, retains the ability to form clathrates. Crystals of the carbon tetrachloride clathrate of (II) are trigonal, space group R, with a= 26.936(6), c= 10.796(1)A, and 18 host and 3 guest molecules in the hexagonal unit cell. An X-ray study has shown that the new cavity-shape is markedly different from that of the parent (I). In contrast to (II), the 4-nor-analogue (III) crystallises unsolvated in the tetragonal system, space group P21c, with a= 12.640(2), c= 17.254(4)A, and Z= 8. This structure has infinite chains of molecules linked head-to-tail by O–H ⋯ O hydrogen bonds of length 2.82(1)A.

A synthetic and structural investigation of the role of hydrogen bonding in clathrate formation

A study of molecules related to Dianins compound (I) in which the hydroxy-function is replaced by another group capable of forming hydrogen bonds is described. The amine (II) crystallises with spontaneous resolution, without incorporation of solvent. The thiol (III) shows an interesting duality of behaviour, crystallising unsolvated with spontaneous resolution from cyclohexane, but forming a true clathrate with carbon tetrachloride. This clathrate crystallises in the trigonal space group R , with a= 27.063, c= 12.074 A, with 18 host and 6 guest molecules in the unit cell. The structure was solved by direct methods, and refined to a final R value of 10.4% for 1 475 independent diffractometer data. Near planar hexagons of sulphur atoms, linked by SH ⋯ S hydrogen bonds, form the top and bottom of each closed cage in the clathrate structure.

Alteration of cage geometry by systematic structural modification of a clathrate host molecule

A study of compounds structurally related to the versatile host compound, 4-p-hydroxyphenyl-2,2,4-trimethyl-thiachroman (I) is described. The compounds (II)–(IV) which possess an additional methyl group at the 6-, 7-, or 8-position of (I) have been synthesised and found to exhibit an interesting spectrum of behaviour. The previously described 7-methyl analogue (III) forms spontaneously-resolved unsolvated crystals while (II) and (IV) are new hosts. A single-crystal X-ray investigation of the trigonal crystals of the cyclo-octane clathrate of the 8-methyl analogue (IV), space group R, a= 33.629(9), c= 8.239(3), and Z= 18 (host), has established the formation of a fundamentally new cage-shape. Compound (V) has also been synthesised in the present study, as have analogues (VII) and (VIII) of the host Dianins compound (VI), but in these three cases no inclusion behaviour has been found.

Synthesis and X-ray structural analysis of 4-p-hydroxyphenyl-2,2,4,7tetramethylthiochroman

The title compound has been prepared and its crystal and molecular structure determined by three dimensional X-ray analysis. Crystals are orthorhombic, a= 11.777(1). b= 16.501 (2), c= 8.479(1)A, Z= 4, space group P212121. The structure was solved by a combination of conventional Patterson and direct methods, and refined by least-squares methods to a final R of 0.091, employing 1 136 diffractometer data. The crystal structure possesses infinite chains of molecules linked head-to-tail by OH ⋯ S hydrogen bonds of length 3.34 A. such that no voids are left for solvent inclusion.

Synthesis and properties of the inclusion compound 2-phenyl-3-p-(2,2,4-trimethylchroman-4-yl)phenylquinazolin-4(3H)-one; use of quartets in the crystal structure determination of the methylcyclohexane clathrate

The title compound (III) has been found to form stable adducts with a wide range of solvents, important classes of guest being cycloalkanes, cyclic ethers and ketones, alcohols, and aromatic molecules. An X-ray investigation of the inclusion compound formed with methylcyclohexane has been carried out. A key feature of the solution of this complex structure, which has 79 non-hydrogen atoms in the asymmetric unit, was the use of quartet relationships in the direct-method analysis. Crystals are triclinic, space group P, with a= 18.649(25), b= 19.443(25), c= 9.390(15)A, α= 78.88(5), β= 98.97(5), γ= 118.16(10)°, with four host and two guest molecules in the unit cell. The structure was refined by least-squares methods to a final R of 0.098, employing 3 432 significant diffractometer data. The packing of host molecules of (III) is such that large closed cages are formed : in each of these clathrate voids two methylcyclohexane guest molecules are accommodated. Compound (V), a thio-analogue of (III), has also been prepared and found to exhibit inclusion behaviour.

X-Ray crystal structure of the novel bis-quaternary dispiro system obtained from the reaction of morpholine with hexakis(bromomethyl)benzene

In contrast to the six-fold substitution of hexakis(bromomethyl)benzene (Ia) by aniline to give the hexa-amine (Ib), reaction of (Ia) with morpholine occurs with dispiro-annelation yielding (II); the structure of this novel product was deduced spectroscopically and its detailed molecular geometry was determined by X-ray crystallography.