Showing papers in "CrystEngComm in 2003"

Extended motifs from water and chemical functional groups in organic molecular crystals

Abstract: The probability of organic compounds crystallising as hydrates increases with increasing number of polar chemical groups in the molecule. The extended patterns of H-bonding involving chemical groups and water molecules have been studied and classified. The most frequent ring, chain, tape and layer patterns displayed between the water molecules alone in organic molecular crystals are also predominant patterns in the larger H-bond network when other donor/acceptors are included.

Borromean links and other non-conventional links in ‘polycatenated’ coordination polymers: re-examination of some puzzling networks

Abstract: A number of coordination networks, exhibiting novel and fascinating types of entanglements of individual motifs have been reported throughout the years by many groups. The structural complexity of these species has caused, in some cases, misinterpretations regarding the correct nature of the entanglement. In this article, we analyse the structures of some polymeric networks of the ‘polycatenanes’ class, which have the peculiar feature of all the constituent motifs having lower dimensionality than that of the overall array. Unexpected topological features and new linkages, that had previously been overlooked, have been discovered. The most relevant finding concerns the first observation of examples of Borromean links in 3D and 2D arrays. These systems are comprised of layers that are not catenated but, nonetheless, inseparably entangled in an uncommon topological fashion.

Crystal engineering: from weak hydrogen bonds to co-ordination bonds

Abstract: This article highlights the importance of crystal engineering in designing functional materials. Various rational design strategies will be discussed for controlling the molecular architectures of the materials using C–H⋯O, C–H⋯π, O–H⋯O, N–H⋯O and O–H⋯N hydrogen bonds and co-ordination bonds. The results described here show the role of guest molecules in templating the isomeric network structures with one set of molecular components. In particular, the materials that are designed based on strong hydrogen bonds and coordination bonds exhibited zeolite like and clay like properties.

Crystal and co-crystal

Abstract: Problems with nomenclature are necessary evils in the development of a new subject. As the subject of crystal engineering progresses, it is possible and indeed advantageous to assess terminology, keep what is good, and discard what is not required. Names are coined easily in the early days of a subject. This arises partly from enthusiasm and partly because it is difficult to describe new concepts with old names. Or so we seem to feel. As crystal engineering has evolved into a more mature discipline, one also realizes that some of the terms that we used during the last 15 years or so in describing crystals and their design and properties might not have been really necessary and that standard terminology in the existing chemical and crystallographic literature might well have sufficed. More particularly, I refer to the term co-crystal (also written as cocrystal). I do not know exactly when this term came into the literature. Perhaps it was in the paper of Etter and Panunto on the complexing ability of 1,3-bis(m-nitrophenyl)urea. Whatever the case, the term gained easy acceptance. The operational word here is ‘easy’. Anyone could understand that a co-crystal was what one got in a co-crystallization experiment, and gradually the term came to be used for just about any twoand higher-component crystal. At this point, it would do one good to remember that we had (and still have) a perfectly good word to describe multi-component crystals, which have specific noncovalent interactions between the distinct molecules, and this is molecular complex. For someone whose serious early chemical education included the study of Foster’s book on donor– acceptor complexes and Herbstein’s illuminating work in this area (for those too young to know or care, my Ph.D. topic was in the area of quinone–hydroquinone donor acceptor complexes), the term molecular complex was perfectly acceptable and I have used it invariably in my papers. Recently, however, the term co-crystal slipped into a paper (that too in the title) where I was not the corresponding author and this has prompted the present letter. I was always uncomfortable with the term co-crystal but not in ways I could express satisfactorily. For a start, the word crystal is too important, too meaningful and too evocative. For those in the subject of crystal engineering, it is a sacrosanct word—something like bond to a chemist. Given the centrality of the concept of a crystal, what is a co-crystal? I never had any problems with co-crystallization or co-crystallize and indeed I use these terms regularly. It was the simple, easy word cocrystal that caused me problems. Now, a crystal is described both by a lattice, which gives us the symmetry information, and also by the atoms/ions/molecules that are contained in it, the chemical information. So how can something like 1 : 1 1,3bis(m-nitrophenyl)urea–triphenylphosphine oxide masquerade as a co-crystal, when it has nothing in common with the crystal of either 1,3-bis(m-nitrophenyl)urea or that of triphenylphosphine oxide? What is coto what? In the end, would brass become a co-crystal of copper and zinc? Or are my questions too naı̈ve? It was Herbstein again who, through his recent paper on composite crystals of 5-oxatricyclo[5.1.0.0]octan-4-one, resolved my nebulous doubts and brought my objections to the present use of the term co-crystal into sharper focus. He defines a composite crystal as something that is formed by ‘ordered agglutination of crystals of the same or different type’. He is speaking literally about two different crystals stuck together at the molecular level. This to my mind is a real cocrystal—two crystals that are joined together. In his paper written 40 years ago on hexabromobenzene, he provides us with another beautiful example of a composite crystal. Because this crystal is pseudo-hexagonal with c/a y 1/d3, planes like (101) and (1 0 21) or (301) and (001) coincide, but not exactly, and what one gets is a mosaic of crystals joined along these nearly common planes. In a recent authoritative work, Chapuis and his group discuss urotropin azelate. These authors actually call this an ‘unwilling co-crystal’ in their paper title because each of the components, urotropin and azelaic acid, retain many of their original crystal traits in the conjunction of these substances. Now this is what I would call a good co-crystal because, once more, vestigial influences of former beings persist. However, so prevalent has the present connotation of the term co-crystal become that something that is a really good example of a co-crystal is referred to in almost exactly the opposite terms! The Chapuis group have another paper on the s-structure of b-tantalum, and here the composite portions of a true co-crystal have different space groups. This is not all. Alivisatos and co-workers have recently shown how a nanocrystal tetrapod of CdTe grows. When it nucleates, it starts off as a cubic phase and when it branches out it switches to a hexagonal phase. Two crystals living together—I’d call this a co-crystal for sure. I will round off this selection of examples with Boese’s fascinating studies of what he calls oligodiffractometry. Here we have crystals of polymorphs that are necessarily examined together in the diffraction experiment and their patterns deconvoluted later—a different type of cocrystal maybe but still a co-crystal. In none of these cases, however, has my image of a crystal been dimmed and yet we have two or more crystals somehow connected with each other intimately. So what do we do with the 1 : 1 1,3-bis(m-nitrophenyl)urea– triphenylphosphine oxide co-crystal? For a start, I’d revert to calling it the 1 : 1 1,3-bis(m-nitrophenyl)urea–triphenylphosphine oxide molecular complex. This is a good term and a clear one at that. It tells us what is happening, and it is general enough. It may be distinguished from the terms solid solution or inclusion compound and the reader who is further interested in all these terminologies is well advised to read Kitaigorodskii’s book. To conclude, when new terms enter the literature in a big way, and there is some controversy regarding their use, I would suggest that there are two possible courses of action. If the term is merely ambiguous, it may be easiest to just retain it because it has become too common. A good example of this situation is the use of the term pseudopolymorph. But if something is scientifically suspect it must go, howsoever popular it might be. What is easy is sometimes not what is best. Letter

Should solid-state molecular packing have to obey the rules of crystallographic symmetry?

Abstract: About 8% of crystal structures contain more than one independent molecule or formula unit; the number being denoted by the parameter Z′. To most chemists and crystallographers such structures are nothing but a pain in the scientific rear! The crystallographer has to waste valuable data collection and computing power determining the structure of two or more often almost identical molecules, while the chemist writing a paper has to go to the trouble of making sure that “the second independent molecule does not differ significantly from the first”. With the advent of modern data collection and computational hardware these irritations have been to some extent ameliorated. Moreover, to a slowly growing body of ‘crystal chemists’ the interactions between crystallographically independent molecules represent a rich hunting ground for understanding solid state packing. Why should such structures form when nine times out of ten, crystallographic symmetry results in perfectly decent packing arrangements? Most importantly, can we learn something about the phase behaviour and materials properties of solids by understanding these special cases, perhaps with a view to using them in a predictive fashion? This survey sets out to collate existing data and interpretations on structures with high Z′ values as well as to highlight some interesting case studies and make some suggestions about future directions.

Solid-state molecular syntheses: complete reactions without auxiliaries based on the new solid-state mechanism

Abstract: Molecular crystals including salts undergo gas–solid, solid–solid, thermal, photochemical and catalyzed reactions if the crystal lattice allows for long-range anisotropic molecular migrations, if the product phase can form fast enough and if crystal disintegration provides fresh surface. This ingenious three-step solid-state mechanism is derived from atomic force microscopy (AFM) studies, the results of which correlate strictly with the crystal packing. It is secured by the results of various supporting experiments. The experimental mechanism is at variance with Schmidt's “topochemistry” hypothesis with its well-known failures which are now easily settled. Topotactic reactions without molecular migrations are very rare and not at all typical for solid-state reactions. AFM scrutiny excluded several alleged cases of topotaxy and secured three of them with molecular precision. Very detailed solid-state effects that go down to the molecular level emerge from AFM investigations with single crystals on their different faces and are discussed. The efficiency of gas–solid and solid–solid reactions is unexpectedly high. Thus, the yield in one product is 100% due to favorable kinetics in most cases. These waste-free syntheses are fast, require rather simple equipment, save resources and are unbeatable in their wealth for sustainable environmental protection, inasmuch as they do not require workup procedures. The scaling up for industrial application is prepared at the kg level. Numerous selected examples of preparative interest out of more than 1000 are presented.

Molecular architecture and supramolecular association in the zinc-triad 1,1-dithiolates. Steric control as a design element in crystal engineering?

Abstract: A survey of the fascinating structural chemistry of the zinc-triad 1,1-dithiolates is presented. A total of twelve distinct structural motifs are delineated ranging from monomeric, dimeric, tetrameric, linear polymeric, layer to 3-dimensional network architectures. Such diversity arises from the prevalent secondary bonding interactions, i.e. A⋯S, operating in the solid state. While the variation in structure suggests that the control of secondary interactions is difficult, a possible design tool for crystal engineering is identified, namely by moderating the steric profile of thiolate-bound organic substituents, at least for the systems described herein.

Supramolecular synthons in phenol–isonicotinamide adducts

Abstract: Molecular complexes of four phenols (hydroquinone, resorcinol, phloroglucinol and 4-hydroxybenzoic acid) with isonicotinamide are characterized by X-ray diffraction. (Hydroquinone)0.5·(isonicotinamide) 1 and (resorcinol)·(isonicotinamide)22 have tapes of O–H⋯N and amide N–H⋯O dimer synthons. In (phloroglucinol)·(isonicotinamide)2·(H2O)23, six component self-assembly results in stacked dimers with four O–H⋯N and four amide N–H⋯O hydrogen bonds and the third phenol OH aggregates with two water molecules in a supramolecular chair cyclohexane array. Phenol⋯pyridine and amide N–H⋯O dimers are robust synthons in 1–3 for the self-assembly of 0D discrete aggregates and infinite 1D chains. Hydrogen bonding of amide dimers via N–H⋯Ophenol/water is ascribed to cooperative effects. The crystal structure of (4-hydroxybenzoic acid)·(isonicotinamide) 4 establishes the robustness of phenol⋯pyridine hydrogen bonding in the presence of carboxylic acid groups. Molecular components in 4 are arranged as zigzag tapes of O–H⋯N hydrogen bonds and acid⋯amide heterodimers. Supramolecular synthesis with phenol–isonicotinamide adducts expands the versatility of isonicotinamide as a co-crystallizing agent in crystal engineering.

Structural trends in one and two dimensional coordination polymers of cadmium(II) with halide bridges and pyridine-type ligands

Abstract: Cadmium dihalides were reacted with pyridine derivatives as Lewis bases, and the solid state structures of 15 reaction products were studied by X-ray diffraction; all but one of these structures are reported for the first time. Among the 15 complexes there are 13 coordination polymers containing six-coordinated cadmium with four bridging halides in the equatorial and two pyridine ligands in the axial positions of a pseudo octahedron. For unidentate ligands such as pyridine and 3-chloro-, bromo- or methylpyridine chain polymers of composition [CdX2(L)2]1∞ were formed. The six combinations of Cl, Br, or I as bridging halides with 3-halopyridine and the two of chloride and bromide bridges with 3-methylpyridine lead to eight isomorphous compounds in the space group P21/c. In a second structure type 4,4′-bipyridyl was used to link neighbouring chains to two-dimensional nets with [CdX2(bpy)]2∞ stoichiometry. The chloro and bromo derivatives are isomorphous and crystallise in a space group Pban whereas the iodide bridged complex was obtained in the supergroup Cmmm. The halogen substituted pyridines represent the most versatile ligands for the formation of coordination polymers—they can be accommodated in the whole range of halide bridged [M(μ-X)2]1∞ chains (M = Zn, Cd) covering metal⋯metal distances between 3.654 and 4.143 A. In contrast to the above mentioned halide bridged topologies terminal rather than bridging iodide ligands occur in [CdI2(py)2] and [CdI2(3-Mepy)2]: these complexes are mononuclear with the metal center in tetrahedral coordination.

Involving metals in halogen–halogen interactions: second-sphere Lewis acid ligands for perhalometallate ions (M–X⋯X′–C)

Abstract: Lewis-acidic halocarbon groups (X–C) serve as effective second-sphere ligands for perhalometallate ions and provide an alternative means to hydrogen bonds for developing the supramolecular chemistry of such ions, exemplified here by short directional M–X⋯X′–C halogen bond linkages used in conjunction with hydrogen bonds for crystal synthesis

New architectures from the self-assembly of MIISO4 salts with bis(4-pyridyl) ligands. The first case of polycatenation involving three distinct sets of 2D polymeric (4,4)-layers parallel to a common axis

Abstract: New network structures and topologies have been obtained from the reactions of different metal(II) sulfates with three bis(4-pyridyl) spacer ligands, that illustrate the influence of the SO42− anions in the self-assembly of polymeric coordination architectures. The products include [Fe(bpp)2(SO4)] [bpp = bis(4-pyridyl)propane] (1), [Cd(bpethy)(SO4)] [bpethy = bis(4-pyridyl)ethyne] (2), [Cu(bpe)(SO4)(H2O)]·2H2O [bpe = bis(4-pyridyl)ethane] (3), [Co2(bpe)3(SO4)2(MeOH)2]·xSolv (4) and [Ni6(bpe)10(H2O)16](SO4)6·xH2O (5). In compounds 1–4 the SO42− anions are directly involved in the polymeric frameworks, forming bridges that connect different metal centres. Compound 1 contains one-dimensional ribbons of rings joined by the anions to give a 3D array with the CdSO4-type topology. In compound 2 the Cd2+ cations are connected by μ4–η4-bridging anions to give 2D layers of linked octahedra and tetrahedra, that are joined by the bpethy ligands into a 3D array. The structure of compound 3 consists of simple Cu(bpe) chains linked by the anions into 2D sheets. Compound 4 is a complex polymer comprised of highly undulated 2D layers of folded quadrilateral meshes; the layers are deeply interdigitated and joined together by the anions, thus resulting in an unique 3D architecture containining 6- and 4-connected cobalt centres. Compound 5 is the more interesting species in that it is an entangled array of three distinct sets of layers. It contains two different types of 4-connected 2D motifs, i.e. undulated layers of rectangular meshes and square grid layers, in a ratio of 2 ∶ 1. The three sets are parallel to a common axis but show a relative rotation of ca. 120° about it, giving a common axis, giving inclined interweaving in an unprecedented ‘parallel/parallel/parallel’ fashion, to generate a unique 3D architecture.

Towards a realistic model for the quantitative evaluation of intermolecular potentials and for the rationalization of organic crystal structures. Part I. Philosophy

Abstract: Calculations on prototypical dimer structures and representative crystal structures of organic compounds have been carried out by SCDS-Pixel, a new method for the evaluation of intermolecular potentials. Systems not included in the set originally employed in calibration of the method are considered, and a significant improvement in performance is obtained by adjustment of the disposable parameters over a wider collection of experimental and computational evidence. The results cast some new light on the organization of molecular crystals, and suggest that the density sums method is an advantageous alternative to atom–atom potential techniques, as concerns both detailed quantitative results and general ways of thinking about crystal packing. While the SCDS-Pixel method, as it is now, is general and applicable to a wide range of chemical systems, further development and improvements are possible and a few sensitive points in this respect are examined.

Inorganic intermolecular motifs, and their energies

Abstract: This article focuses on materials containing inorganic molecules and coordination complexes, assembled via intermolecular interactions. For inorganic systems that can contain the full range of elements and exhibit the full diversity of chemistry, some clarification is needed for fundamental concepts about molecular and non-molecular structure. An underlying theme is the need for knowledge of intermolecular energy potentials as a prerequisite for reliable design and preparation of molecular materials. Relationships between intermolecular potentials, histograms of intermolecular distances, and van der Waals surfaces, are discussed. A density functional method for efficient calculation of intermolecular potentials is evaluated, and some results presented, particularly for compounds with high-Z atoms where the integrity of molecular surfaces is diminished. In the context of the higher ordering of molecular assemblies, the main types of concerted intermolecular embraces between arylated molecules and representative coordination complexes are reviewed. When charged polyatomic molecules are assembled, and homo-charged molecules are segregated, there are basic questions about the relative magnitudes and influences of electrostatic energies: this issue is considered in the context of observed embraces between homo-charged polyatomic molecules and coordination complexes.

Supramolecular assemblies in salts and co-crystals of imidazoles with dicarboxylic acids

Abstract: Two new salts 2-phenyl imidazolium hydrogen cyclobutane-1,1-dicarboxylate 1, imidazolium hydrogen malonate 2, and two new co-crystals benzimidazole/succinic acid co-crystal (1 ∶ 1) 3 and benzimidazole/isophthalic acid co-crystal (1 ∶ 1) 4 were synthesized and characterized by X-ray crystallography in order to analyze their supramolecular architecture. The results are examined and compared with the structures present in the Cambridge Structural Database.

[Cobalt(II)L-glutamate(H2O)·H2O]∞: a new 3D chiral metal–organic interlocking network with channels

Abstract: A monometallic assembly of composition [Cobalt(II)L-glutamate(H2O)·H2O]∞ (I) has been prepared and structurally and magnetically characterized. Assembly I crystallizes in the orthorhombic space group P212121 with a = 7.149(9), b = 10.468(3), c = 11.295(5) A, V = 845.3 A3 and Z = 4. The crystal structure analysis reveals a three-dimensional network with channels parallel to the a-axis. The observed structure suggests that highly isolated Co(II) cations are present in the solid state structure – a fact verified by the temperature-dependent magnetic susceptibility (298–5 K) which is that of a classical, isolated paramagnet with μ(eff) ranging from 4.1 to 5.2 BM.

Towards a realistic model for the quantitative evaluation of intermolecular potentials and for the rationalization of organic crystal structures. Part II. Crystal energy landscapes

Abstract: Many crystal structures were generated by a computer predictor for naphthalene, naphthoquinone, 1,2-dichlorobenzene, 2,3-dimethylbenzoic acid, parabanic acid and pyridine, and the lattice energies were then calculated by standard atom–atom potentials, by point-charge models, and by the SCDS-Pixel method. Using results from the latter approach, the relative importance of coulombic, polarization, dispersion and repulsion energies in crystals is discussed in relationship with the chemical characteristics of the constituent molecule, with crystal density, and with some key crystal structural factors like interplanar angles and some intermolecular distances believed to be indicators of crystal stabilization. In general, intermolecular interactions are better discussed when considering the electron density of large molecular moieties or of entire molecules, than when considering atom–atom distances. Significant comparisons between atom–atom energies and the more accurate Pixel energies are presented. The performance of the Pixel-SCDS method in ranking crystal energies against experimental structures, in the so-called crystal structure prediction exercise, is comparable to, and sometimes better than that of atom–atom force fields.

Synthesis and structural characterisation of two coordination polymers (molecular ladders) incorporating [M(OAc)2]2 secondary building units and 4,4′-bipyridine [M = Cu(II), Zn(II)]

Abstract: We report herein the synthesis and structural characterisation of two coordination polymers: {[Cu(4,4′-bipy)(OAc)2]·2.5H2O}n1 and {[Zn(4,4′-bipy)(OAc)2]}n2, which feature dissimilar dimeric metal acetate secondary building units linked through 4,4′-bipyridine to yield 1D molecular ladders. In 1, the ladders connect via (C–H⋯O) hydrogen bonds to generate 2D sheets, which further link via (C–H⋯π) hydrogen bonds to give a 3D supramolecular network. A 3D network in 2 results directly from a combination of (C–H⋯O) and (C–H⋯π) hydrogen bonding. Variable temperature magnetic susceptibility measurements reveal very weak antiferromagnetic coupling between Cu(II) centres across the acetato bridges in 1 (J = −1.18 cm−1).

When is template directed mineralization really template directed

Abstract: In-situ synchrotron X-ray scattering clarifies the role of templating on calcium carbonate mineralization. Fatty acid monolayers are reorganized by Ca2+ in the subphase, into structures with no epitaxial relation to CaCO3 planes. Crystals are not oriented relative to the film; kinetics dominates polytype selection.

Analysis of pi–halogen dimer interactions present in a family of staircase inclusion compounds

Abstract: The family of staircase inclusion compounds formed by the tetrahalo aryl hosts 1 and 2 are re-evaluated in terms of the pi–halogen dimer interactions present in their structures.

Supramolecular equivalence of halogen, ethynyl and hydroxy groups. A comparison of the crystal structures of some 4-substituted anilines

Abstract: Chloro, bromo and ethynyl substituents play exactly the same role in the crystal structures of the corresponding 4-substituted anilines and this is related to their similar polarisations. The iodo derivative is, however, distinct and this may be related to its greater size.

Supramolecular association in organomercury( ii ) 1,1-dithiolates. Complementarity between Hg⋯S and hydrogen bonding interactions in organomercury( ii ) 2-amino-cyclopent-1-ene-1-carbodithioates

Abstract: A survey of the supramolecular associations operating in the crystal structures of organomercury 1,1-dithiolates shows that owing to the presence of Hg⋯S interactions, dimeric, 1-, 2- and 3-dimensional architectures are generated. Introducing hydrogen-bonding functionality into the 1,1-dithiolate ligand allows for the formation of both intra- and intermolecular hydrogen bonds as well as Hg⋯S interactions, so that 2- and 3-dimensional architectures are formed that are distinct for each of the two polymorphic forms of MeHg(S2CC5H6NH2-2) and for PhHg(S2CC5H6NH2-2).

CH/π interactions as disclosed on the fullerene convex surface. A database study

Abstract: A systematic search in the Cambridge Structural Database has disclosed that many CH groups are involved in the interaction with the fullerene convex surface; aliphatic as well as aromatic CHs are concerned. CH/π interactions in C60 fullerene and C60 fulleride inclusion compounds were surveyed and compared. The mean CH/C60 intermolecular distance has been shown to be shorter in the fulleride complexes than in the fullerene complexes. The face-to-face type interaction was also surveyed, programmatically. The present study has demonstrated that the CH/π interaction plays a considerable part in fullerene supramolecular chemistry, together with the van der Waals interaction. The concept of the CH/π interaction will be of help in designing fullerene- and nanotube-based materials and in exploring the electronic structure of nonclassical π-systems.

High-dimensional malonate-based materials: Synthesis, crystal structures and magnetic properties of [M2(mal)2(L)(H2O)2]n·n(H2O) M = Zn(II), Co(II); H2mal = malonic acid, L = pyrimidine, pyrazine

Abstract: Four novel coordination polymers [M2(mal)2(pym)(H2O)]n·nH2O, M = Zn (1), Co (2) and [M2(mal)2(pyz)(H2O)]n·nH2O, M = Zn (3), Co (4) (H2mal = malonic acid, pym = pyrimidine, pyz = pyrazine), have been synthesized. Compounds 1 and 2 are isomorphous, as are compounds 3 and 4. X-ray diffraction experiments reveal that 1–4 exhibit an interesting 3D-network, containing malonate and either pyrimidine (1 and 2) and pyrazine (3 and 4) as organic ligands. Variable-temperature magnetic susceptibility measurements indicate the occurrence of weak antiferromagnetic interactions between Co(II) ions in 2 and 4.

Molecular recognition at the interface between crystals and biology: generation, manifestation and detection of chirality at crystal surfaces

Abstract: An intimate historical and conceptual association exists between crystals and chirality. Yet the relationships between crystal symmetry and crystal morphology are not fully understood. In biological environments, molecular recognition between biological macromolecules and crystal surfaces can affect crystal morphological symmetry, or can be modulated by the symmetry expressed at the surfaces. The transfer of chiral information between biological macromolecules and ordered surfaces is considered here through several examples. Certain biogenic crystals of calcium oxalate exhibit a chiral morphology, although both molecular and crystal structures are non-chiral. This reduction in symmetry is believed to be induced by proteins during crystal nucleation. In contrast, crystals of calcium-{R,R}- and -{S,S}-tartrate tetrahydrate are inherently chiral, but their morphologies are symmetric. The chirality expressed by the crystal faces is however detected by cells, which selectively adhere to the {R,R} crystals. Structural insight into stereo- and enantio-selective recognition of chiral surfaces is provided by comparison between the degrees of recognition of four antibodies, raised and selected against crystal surfaces. A general framework is presented, where chirality can be understood at a length-scale larger than molecular, namely the length-scale of crystal surfaces, crystal morphology and the relations between them.

Supramolecular Sn⋯Cl associations in diorganotin dichlorides and their influence on molecular geometry as studied by ab initio molecular orbital calculations

Abstract: A number of supramolecular architectures based on hypervalent Sn⋯Cl interactions are observed in a series of eight R2SnCl2 structures ranging from tetrameric assemblies to a variety of polymeric motifs. The absence of Sn⋯Cl interactions in the crystal lattice of tBu2SnCl2 may be attributed to the bulky size of the tin-bound t-butyl groups that precludes such interactions. The influence of the supramolecular aggregation upon molecular geometry has been investigated using ab initio molecular orbital calculations. These show that invariably more symmetric structures are observed in the absence of hypervalent Sn⋯Cl interactions.

Supramolecular organisation via hydrogen bonding in trimethoprim sulfonate salts

Abstract: The present study deals with the crystal structures of four organic salts, namely, trimethoprim benzene sulfonate monohydrate 1, trimethoprim sulfanilate monohydrate 2, trimethoprim p-toluene sulfonate 3 and trimethoprim 3-carboxy-4-hydroxybenzene sulfonate dihydrate 4. Trimethoprim (TMP) is protonated at one of the ring nitrogens of the pyrimidine ring. Generally, in the TMP carboxylate complexes, the protonated pyrimidine ring is hydrogen-bonded to the carboxylate group forming a cyclic fork-like hydrogen-bonded bimolecular motif. In structures 1–3, the sulfonate group plays the role of the carboxylate anion. In compounds 1 and 2, there is no pairing of the pyrimidine rings because the pairing sites are blocked by water molecules donating hydrogen to the unprotonated ring nitrogen. Two of the cyclic motifs are bridged by the water molecule donating two hydrogen atoms, leading to a hydrogen-bonded supramolecular chain. This chain pairs with another chain running in the opposite direction. These two chains are cross-linked by O–H⋯O hydrogen bonds. In compound 2, two of the hydrogen atoms of the amino group of the sulfanilate bridge two methoxy oxygen of the two TMP cations via N–H⋯O hydrogen bonds resulting in a supramolecular zig-zag chain. In compound 3, two inversion related cyclic motifs are paired through a pair of N–H⋯N hydrogen bonds involving the 4-amino group and the N3 atom of the pyrimidine ring. In addition to the pairing, one of the sulfonate oxygen atoms bridges the 2-amino and 4-amino groups on either side of the paired bases, resulting in a self-complementary DADA (D represents the hydrogen bond donor and A represents hydrogen bond acceptor) array of quadruple hydrogen bonding patterns. In compound 4, one of the water molecules forms a hydrogen-bonded dimer with the inversion-related water molecule. The 3-carboxy-4-hydroxybenzene sulfonate moiety self-assembles into a supramolecular chain along the c axis through O–H⋯O hydrogen bonds. Two such oppositely running supramolecular chains are connected by dimeric and monomeric water molecules. The variation of supramolecular organization via hydrogen bonding in the four different trimethoprim sulfonate salts has been discussed.

Multiple molecules in the crystallographic asymmetric unit. Self host–guest and doubly interpenetrated hydrogen bond networks in a pair of keto-bisphenols

Abstract: The presence of two molecules in the crystallographic asymmetric unit in a pair of closely related keto-bisphenols that differ by a methyl substituent only, leads to open frameworks that fill space through self-inclusion in one case, and through interpenetration in the other.

Supramolecular architecture of a novel salt of trimesic acid and 1,2-bis(4-pyridyl)ethane

Abstract: We report the transformation of [(BPEH2)(H2BTC)2(H3BTC)2·(H2O)] (I) (the first organic salt of trimesic acid with 1,2-bis(4-pyridyl)-ethane recently reported by us), into [(BPEH2)2(H2BTC)2(H3BTC)2·(H2O)14] (II), a new salt which was characterized structurally using single-crystal X-ray diffraction. II has increased crystal symmetry (monoclinic P21/n) when compared to I, and is formed by an extensive and very complex hydrogen bond network containing both homo- and heteronuclear neutral and ionic interactions. Water molecules play an important role in the hydrogen-bonding network, linking together adjacent zigzag ionic trimesic acid tapes leading to the formation of a 2D supramolecular anionic layer; connecting the BPEH22+ cations to the layers, and also acting as bridges between adjacent, close-packed layers.

Structural relationship of two coordination polymers of Cu(I) with the ligand ethanediyl bis(isonicotinate)

Abstract: The flexible ligand ethanediyl bis(isonicotinate), L, is used as linking unit for Cu(I) ions in a coordination polymer. Two different structures of one-dimensional chains can be obtained, mainly depending on the co-crystallising solvent. Weak interactions such as hydrogen bonding and pi–stacking, and the exclusion of solvent molecules are responsible for the slow transformation of one compound into the other in the mother liquor.