Hans J. Lindner

Crystal structure of mono[3-(2-imidazolylthio)]-altro-β-cyclodextrin: elliptical distortion of the cavity and unique ‘Yin–Yang’ stacking

The title compound is elliptically distorted due to the unusual 1C4 geometry of the altrose portion. In packing, a unique fourfold helical structure is elaborated with head-to-head dimers as the repeating motif. The imidazolyl moieties mutually reside on each others cavities thereby resembling the Yin-Yang type balancing of antagonisms.

A 2-C-fructosyl-propanone locked in a 2,7-dioxabicyclo[3.2.1]octane framework

Abstract Condensation of d -fructose with pentane-2,4-dione in mildly alkaline aqueous solution generates a novel sugar-based scaffold: a 2-C-fructosyl-propanone compressed by formation of a cycloacetal into a 2,7-dioxabicyclo[3.2.1]octane framework.

Topography of the 1:1 α-cyclodextrin–nitromethane inclusion complex

Abstract Dissolution of α-cyclodextrin (α-CD) in 9:1 water–nitromethane smoothly generates the title compound, which crystallizes as the pentahydrate in the orthorhombic space group P212121 with a=9.452(4), b=14.299(3), c=37.380(10) A, and Z=4. Its crystal structure analysis revealed the α-CD macrocycle in an unstrained conformation stabilized through a ring of O-2⋯O-3′ hydrogen bonds between five of the six adjacent glucose residues. The nitromethane is located in the α-CD cavity in an orientation parallel to the plane of the macrocycle, and assumes two sites of equal population with the nitro group in excessive thermal motion; the guest is held by van der Waals contacts and C-H⋯O-type hydrogen bonds to the pyranose H-3 and H-5 protons. The packing of the macrocycles in the crystal lattice is of cage herringbone-type with an extensive intra- and intermolecular hydrogen bonding network. The ready formation of a nitromethane inclusion complex in aqueous nitromethane, and the subtleties of its molecular structure amply demonstrate the ease with which water is expelled from the α-CD cavity by a more hydrophobic co-solvent.

Synthesis, characterization and magnetochemical studies of some imidazole and imidazolate copper(II) complexes derived from N-salicylideneacetylhydrazine: X-ray crystal and molecular structures of [imidazole-(N-salicylidenatoacetylhydrazinato)-ONO′ (-2)]copper(II) and potassium [mono(μ-imidazolate) bis(N-salicylidenatoacetylhydrazinato)] dicopper(II)

Three new copper(II) complexes, [Cu(Sah)HIm], [Cu(HSah)Cl·HIm] and K[{Cu(Sah)}2Im], have been prepared and characterized by elemental analyses, infrared and ultraviolet–visible spectroscopy (HSah and Sah refer to mono- and dinegative N-salicylideneacetylhydrazine anions, respectively, while HIm and Im refer to neutral imidazole and mononegative imidazolate anion). The X-ray crystal and molecular structures of [Cu(Sah)HIm] and K[{Cu(Sah)}2Im] have been determined. In [Cu(Sah)HIm], the copper(II) atom is in a distorted square-planar environment and coordinated to the hydrazone ligand via phenoxy oxygen, imine nitrogen and deprotonated enolimine oxygen. The fourth coordination site is occupied by the imidazole nitrogen. The imidazole N–H is involved in an intermolecular hydrogen bond with the hydrazide nitrogen forming a 1-D supramolecular structure. In the (μ-imidazolate) dicopper(II) complex K[{Cu(Sah)}2Im], each copper(II) atom is in a distorted square-planar environment where the hydrazone ligand acts as an ONO tridentate dianion. The imidazolate anion acts as a bridged coligand connecting the two tricoordinated copper(II) units. The K+ is six coordinate, coordinated to four (μ-imidazolate) dicopper(II) units giving rise to a supramolecular network. Both [Cu(Sah)HIm] and [Cu(HSah)Cl·HIm] show normal magnetic moments of 1.82 and 1.85 µβ respectively. The dicopper complex K[{Cu(sah)}2Im] shows antiferromagnetic spin–spin coupling mediated via the μ-imidazolate with −J = 17.0 cm−1.

The 2,3-anhydro-α-cyclomannin−1-propanol hexahydrate: topography, lipophilicity pattern and solid-state architecture

Abstract As evidenced by its X-ray structural analysis, 2,3-anhydro-α-cyclomannin 6 , a cyclooligosaccharide consisting of six α-(1→4)-linked 2,3-anhydro -d- mannopyranose units, readily incorporates 1-propanol into its cavity such that hydrophobic and hydrophilic surface regions of guest and host match at their interfaces. Together with water, the macrocycle and its guest assemble into a unique solid-state architecture, featuring layers of head-to-head dimers of the macrocycle with its guest, separated by equally distinct layers of water molecules, which are engaged in an intense hydrogen bonding network with the 6-CH 2 OH and the propanol-OH groups. The overall guest–host topography is thus reverse to that of the respective ethanol inclusion complex. 1

Structure and Lipophilicity Profile of 2, 3‐Anhydro‐α‐cyclomannin and Its Ethanol Inclusion Complex

Readily available from alpha-cyclodextrin in three steps, 2,3-anhydro-alpha-cyclomannin composed of six alpha-(1-->4)-linked 2,3-anhydro-D-mannopyranose residues, crystallizes well when precipitated from aqueous ethanol. An X-ray structure reveals the macrocycle to contain ethanol in its cavity, thus representing the first inclusion complex of a non-glucose cyclooligosaccharide. The wider rim of the torus-shaped macrocycle holds the six epoxide rings whose oxygens point away from the cavity, thereby sculpturing the unique over-all shape of a six-pointed star.

Hydroxymethyl-substituted crown acetals with 35-C-14 and 40-C-16 skeletal backbones: synthesis and molecular geometries

Abstract An oxidation/reduction sequence readily converts β- and γ-cyclodextrin into hydroxymethyl-substituted crown acetals with 35-C-14 and 40-C-16 skeletal cores. X-Ray analysis of their well crystallizing peracetates reveals the 40-membered ring of the γ-CD derived octaacetal to mould into an undulated four-loop structure with alternating gauche and anti-conformations of the eight meso-butanetetrol units, the overall shape resembling a four-leaf clover. In the β-CD derived, 35-membered crown heptaacetal, six of the seven glycolaldehyde/butanetetrol segments are lined up in alternating gauche/anti arrangements with the seventh, uneven unit inserted in gauche orientation. In solution, however, the macrocycles are highly flexible as evidenced by their 1H and 13C NMR spectra, which at 300 K show only one set of signals for the respective -CHR-CHR-O-CHR-O- units (R=CH2OH or CH2OAc).

Synthesis and Molecular Geometry of an Achiral 30-Crown-12 Polyacetal fromα-Cyclodextrin

Periodate oxidation of alpha-cyclodextrin followed by borohydride reduction readily provided an octadeca-hydroxymethyl-substituted 30-crown-12 polyacetal 1, its 30-membered macrocycle being composed of six meso-butanetetrol/glycolaldehyde acetal units, which is, consequently, optically inactive. Its solid-state molecular geometry emerged from the X-ray structural analysis of the well-crystallizing octadeca-acetate 2, which revealed the undulated macrocycle to be molded into three loops with a unique order of succession of the -CHR-CHR-O-CHR-O- units: alternating gauche- and anti-conformations of the meso-butanetetrol portions and consecutive disposition of the glycolaldehyde-acetoxymethyl groups above and below the mean-plane of the macrocycle. In solution, however, as evidenced by 1H- and 13C-NMR spectra, the macrocycle is highly flexible at ambient and higher temperatures, its mobility becoming distinctly restricted only below -20 degrees C.