Andrzej Katrusiak

High-pressure crystallography

Since the late 1950s, high-pressure structural studies have become increasingly frequent, following the inception of opposed-anvil cells, development of efficient diffractometric equipment (brighter radiation sources both in laboratories and in synchrotron facilities, highly efficient area detectors) and procedures (for crystal mounting, centring, pressure calibration, collecting and correcting data). Consequently, during the last decades, high-pressure crystallography has evolved into a powerful technique which can be routinely applied in laboratories and dedicated synchrotron and neutron facilities. The variation of pressure adds a new thermodynamic dimension to crystal-structure analyses, and extends the understanding of the solid state and materials in general. New areas of thermodynamic exploration of phase diagrams, polymorphism, transformations between different phases and cohesion forces, structure-property relations, and a deeper understanding of matter at the atomic scale in general are accessible with the high-pressure techniques in hand. A brief history, guidelines and requirements for performing high-pressure structural studies are outlined.

Shadowing and absorption corrections of single-crystal high-pressure data

Abstract The effect of shadowing the sample crystal enclosed in the diamond-anvil high-pressure cell (DAC) by the gasket edges, i.e. by the walls of the high-pressure chamber, has been described for unrestricted data-collection procedures. A general vector formalism reveals new features of the shadowing and absorption corrections, depending on the primary beam-DAC-reflection configuration. The corrections apply to the data measured with conventional normal-beam-equatorial diffractometers, or with area-detectors. The simple vector approach optimizes computations and affords straightforward corrections of intensities. Feasibility of enhancing the resolution of numerical integration by applying fine grid divisions, has been discussed.

Giant negative linear compression positively coupled to massive thermal expansion in a metal–organic framework

Materials with negative linear compressibility are sought for various technological applications. Such effects were reported mainly in framework materials. When heated, they typically contract in the same direction of negative linear compression. Here we show that this common inverse relationship rule does not apply to a three-dimensional metal-organic framework crystal, [Ag(ethylenediamine)]NO3. In this material, the direction of the largest intrinsic negative linear compression yet observed in metal-organic frameworks coincides with the strongest positive thermal expansion. In the perpendicular direction, the large linear negative thermal expansion and the strongest crystal compressibility are collinear. This seemingly irrational positive relationship of temperature and pressure effects is explained and the mechanism of coupling of compressibility with expansivity is presented. The positive coupling between compression and thermal expansion in this material enhances its piezo-mechanical response in adiabatic process, which may be used for designing new artificial composites and ultrasensitive measuring devices.

Enforcing Multifunctionality: A Pressure-Induced Spin-Crossover Photomagnet

Photomagnetic compounds are usually achieved by assembling preorganized individual molecules into rationally designed molecular architectures via the bottom-up approach. Here we show that a magnetic response to light can also be enforced in a nonphotomagnetic compound by applying mechanical stress. The nonphotomagnetic cyano-bridged Fe(II)-Nb(IV) coordination polymer {[Fe(II)(pyrazole)4]2[Nb(IV)(CN)8]·4H2O}n (FeNb) has been subjected to high-pressure structural, magnetic and photomagnetic studies at low temperature, which revealed a wide spectrum of pressure-related functionalities including the light-induced magnetization. The multifunctionality of FeNb is compared with a simple structural and magnetic pressure response of its analog {[Mn(II)(pyrazole)4]2[Nb(IV)(CN)8]·4H2O}n (MnNb). The FeNb coordination polymer is the first pressure-induced spin-crossover photomagnet.

Compressibility of lysozyme protein crystals by X-ray diffraction

Single-crystal high-pressure X-ray diffraction studies on the protein crystals of orthorhombic and tetragonal hen egg-white lysozyme polymorphs were carried out using a Merrill-Bassett diamond-anvil cell, image-plate detector and synchrotron radiation. The orthorhombic crystal has been squeezed to 85.5% of its ambient pressure volume at about 1.0 GPa; the crystal compresses anisotropically, and neither a glass transition or denaturation was observed. The tetragonal polymorph of lysozyme undergoes amorphization at pressures about 0.2 GPa.

Giant Dielectric Anisotropy and Relaxor Ferroelectricity Induced by Proton Transfers in NH+···N-Bonded Supramolecular Aggregates

A huge dielectric effect has been observed in a pure and water-soluble hydrogen-bonded organic crystal, 1,4-diazabicyclo[2.2.2]octane hydroiodide [C6H13N2]+.I(-) (dabcoHI). In this structure, the dabco cations are NH+...N bonded into linear aggregates, where the protons are disordered at two nitrogen atoms and the crystal acquires the symmetry of space group P6m2. This nonpolar crystal exhibits a barely temperature-dependent dielectric constant exceeding 1000 at ambient conditions. The dielectric response is extremely anisotropic, more than 2 orders of magnitude higher along the linear hydrogen bonded chains than in perpendicular directions. The physics underlying this effect originates from proton transfers in the NH+...N bonds, leading to disproportionation defects and formation of polar nanodomains, which, on the macroscopic scale, results in one-dimensional relaxor ferroelectricity. Such properties are unprecedented for the materials with hydrogen bonds highly polarizable due to proton disorder. The proton disordering in dabcoHI is analogous to this in H2O ice, where the hydrogen bonds remain disordered until the lowest temperature.

High-Pressure (+)-Sucrose Polymorph†

With the exponential rise in interest in the fundamental, commercial, and intellectual-property importance of crystal forms, the late Walter McCrone s provocative statement regarding the propensity for the formation of polymorphs is often cited: “It is at least this author s opinion that every compound has different polymorphic forms and that, in general, the number of forms known for each compound is proportional to the time and money spent in research on that compound.” (italics in original). In response to McCrone, the lack of evidence for more than one crystal form of two very common, indeed paradigmatic and often crystallized compounds, sucrose and naphthalene, has been frequently cited. Sucrose (saccharose, (+)-C12H22O11), common table sugar, is a particularly poignant example because of the well-known difficulty in inducing industrial-scale crystallizations and the countless variety of conditions and number of times it has been crystallized merely for human consumption. Virtually all of these crystallizations have been carried out under ambient pressure, which represents but a small region of phase space. About ten years ago, with the development of relatively straightforward techniques to explore phase space at pressures above ambient, we undertook a search for a highpressure form of sucrose. A second form was elusive for a number of years, and although the search eventually proved successful, as reported herein, the preparation and characterization of the high-pressure form of sucrose required overcoming a number of experimental difficulties and in the end proved to be remarkably different from the ubiquitous common form sucrose I. Although unstable at ambient conditions, sucrose II provides new information about this compound and all sugars in general. Sugars, in their variety of mono-, di-, and polysaccharides, are the main carriers for energy transport and storage in biological systems and the primary building blocks in living tissue. World-wide production of the disaccharide (+)-sucrose exceeds that of all other manufactured organic compounds. The molecule has considerable conformational freedom and many hydrogen-bonding functionalities (Figure 1), which might suggest the possibility or even tendency for the existence of multiple crystal forms, although there are no published statistics on such correlations between hydrogenbonding functionality, molecular flexibility, and the tendency to crystallize in multiple crystal forms. Nevertheless, as for many other widely studied monoand disaccharides, only a few cases of polymorphs were reported, for example for b-dallose. Cellulose, the most abundant polymer on Earth, and starch are also known for structural transformations and polymorphs. However, their macromolecular amorphous and microcrystalline composition allows for the determination of only average structural features. The structures of ribose anomers were revealed only recently. The sucrose crystals were shown to be stable between 20 K and 373 K, when sucrose starts to decompose. So, there are scarcely any data on the polymorphism of sugars, and no direct observation of their phase transitions have been reported. This information is essential for understanding the interplay between properties of sugars with the conformational flexibility and intermolecular interactions. Sucrose is uniquely suitable for investigating the structure–property relations at varied thermodynamic conditions. Our study reveals an extraordinary molecular flexibility combined with transforming hydrogen-bond types and patterns in sucrose I and II. The types and patterns of hydrogen bonds are characteristic Figure 1. Structural formula of sucrose, with hydrogen bonds and their transformations coded in colors described in the legend. A four-digit ORTEP code of symmetry transformations has been used for specifying intermolecular H bonds; the explicit transformation codes have been listed in Table S7 in the Supporting Information. For clarity, only the hydrogen bonds involving the H-donor atom in the molecule have been indicated. All O···O contacts and OH···O bonds, separately in phase I and II, are shown in Figure S5 in the Supporting Information. Letters “g” and “f” in atomic labels denote the glucose and fructose moieties, respectively.

Pressure-frozen benzene I revisited

The crystal structure of benzene, C6H6, in situ pressure-frozen in phase I, has been determined by X-ray diffraction at 0.30, 0.70 and 1.10 GPa, and 296 K. The molecular aggregation within phase I is consistent with van der Waals contacts and electrostatic attraction of the positive net atomic charges at the H atoms with the negative net charges of the C atoms. The C-H...aromatic ring centre contacts are the most prominent feature of the two experimentally determined benzene crystal structures in phases I and III, whereas no stacking of the molecules has been observed. This specific crystal packing is a likely reason for the exceptionally high polymerization pressure of benzene. The changes of molecular arrangement within phase I on elevating the pressure and lowering the temperature are analogous.

Stereochemistry and transformations of NH:N hydrogen bonds Part II. Proton stability in the monosalts of 1,4-diazabicyclo[2.2.2]octane

Abstract Crystal structures of three monosalts of 1,4-diazabicyclo[2.2.2]octane, perchlorate, tetrafluoroborate and bromide, have been studied by X-ray diffraction. The orthorhombic perchlorate and tetrafluoroborate salts are isostructural, while the bromide salt crystallizes in the hexagonal system. Varying stabilities of the acidic proton in the NH:N hydrogen bonds, linking the cations into chains, have been observed: in the perchlorate salt the H-atom is ordered, in the tetrafluoroborate it is 0.75:0.25 disordered at two N-sites, and in the hydrobromide the H-atom is 50:50 disordered between the symmetry-related sites. Possible mechanisms leading to the disorder of the protons and their stabilizing factors are discussed.

Stereochemistry and transformation of -OH…O= hydrogen bonds Part I. Polymorphism and phase transition of 1,3-cyclohexanedione crystals

Abstract The properties of substances or crystals which may depend on the stereochemical configuration of bistable -OH…O= hydrogen bonds are analysed for 1,3-cyclohexanedione crystals and compared with other simple cyclic β-diketoalkane structures (enolized forms). 1,3-Cyclohexanedione (CHD) is known to form monoclinic crystals, space group P 2 1 / c , built up of chains of hydrogen-bonden enol molecules (polymorph CHD1). When cooled to below 287(1) K or subjected to elevated pressures of about 10 MPa, the CHD1 crystal undergoes a phase transition involving an H-atom transfer in the hydrogen bond (structure CHD2). The mechanism of this hydrogen-bond transformation is explained. A new polymorph of 1,3-cyclohexanedione (CHD3) is reported and its structure has been dete The CHD3 cyrstals are monoclinic, space group P 2 1 , with two different stereochemical configurations of the hydrogen bonds. The CHD structures, as well as other simple cyclic β-diketoalkanes and squaric acid, illustrate the interdependence between the stereochemical configuration of bistable -OH…O= hydrogen bonds and the crystal structure, polymorphism, formation of inclusion compounds, phase transitions and other structural transformations, which affect the physical properties of the crystals.