Showing papers in "CrystEngComm in 2007"

Comparing entire crystal structures: structural genetic fingerprinting

Abstract: This paper describes a proof-of-concept example for a method that allows the calculation of a similarity index between whole molecular crystal structures; this has been termed ‘structural genetic fingerprinting’. It is based on the use of fingerprint plots derived from Hirshfeld surfaces coupled with cluster analysis and associated multivariate statistics. Using this formalism, it is possible to show quantitatively (using correlation coefficients) that, for example naphthalene is more similar to anthracene than to benzene, and moreover that benzodicoronene is more similar to anthrabenzonaphthopentacene than naphthalene is to anthracene. Whereas the correlation coefficients themselves obtained say nothing about the ways in which the patterns of intermolecular interactions are similar or different for two different structures, the fingerprint plots do contain such information. In principle this method for quantifying structural similarities of whole molecular crystal structures should be both robust and generally applicable. This method is potentially applicable to datasets consisting of many hundreds or even thousands of structures.

Homo- and heterometallic coordination polymers from the f elements

Abstract: Lanthanide and actinide based coordination polymers and metal–organic framework materials present a number of interesting opportunities with respect to their syntheses and properties. Ln elements typically display large coordination numbers and roughly spherical bonding environments whereas An elements (specifically U(VI)) tend to form triatomic species with terminal oxo groups. As such, these features may be perceived by some as obstacles to the development of designed architectures of f-metal containing hybrid materials. We argue that these features, when coupled to the luminescent behavior of these elements actually give rise to a diverse family of compounds with a range of interesting topologies. Presented herein is an overview of the structural features and luminescent behavior of these materials, as well as some synthetic strategies toward producing both homo- and heterometallic compounds.

What is a co-crystal?

Abstract: The term “co-crystal” is failing as a clear and consistent scientific descriptor. If it is to be retained, it should be used only as a synonym for “multi-component molecular crystal”.

Hydrogen storage in metal–organic frameworks

Abstract: The role of porous metal–organic frameworks (MOFs) as storage materials for hydrogen (H2) and the current state-of-the-art in this rapidly developing field are reviewed. The significant potential of MOFs to effectively and reversibly store H2 illustrates the great promise that crystal engineering of solid-state materials gives to the next generation of applied multi-functional materials.

On the presence of multiple molecules in the crystal asymmetric unit ( Z ′ > 1)

Abstract: The presence of multiple molecules in the asymmetric unit (Z9) has been noted from the earliest days of crystallography, when such an occurrence might even have prevented structure solution and refinement, till today when the phenomenon is being commented upon regularly and, as some claim, can even be engineered. In the end, however, the fact that some crystals take more than one symmetry independent molecule is still something of an enigma. Is it a matter of no consequence whatsoever, which occurs randomly, or is there a deeper underlying reason why Z9 . 1? Perhaps high Z9 structures appear mysterious simply because there is still not a critical mass of relevant literature on their phenomenological analysis. However, a few authors have attempted to study this difficult problem. Brock has surveyed alcohols and phenols extensively and has given an elegant explanation as to why these compounds have a higher proportion of Z9 . 1 crystal structures when compared with the global sampling of organic molecular crystals. According to her, the tendency of these hydroxy compounds (ROH) to form cooperative hydrogen bonded chains of the O–H...O–H type is countered by the steric demands of the R-groups, and high Z9 is one of the outcomes (the other is crystallisation in a high symmetry system). In general, there seems to be a consensus that when packing problems make it difficult to achieve a structure with Z9 = 1, a higher Z9 is a good alternative option. The idea of interaction frustration has also echoes in the work of Nangia, Steed and Clegg among others. These authors have also elaborated other interesting themes: that structures with high Z9 have a loose packing but good interactions; that crystals which are grown from the melt or by sublimation have a significantly higher proportion of Z9 . 1 structures; that high Z9 structures can be described as modulations; that high Z9 is obtained when the molecule has a large number of equi-energetic conformations, these conformations co-existing in the crystal. Pseudosymmetry is certainly implicated in some cases and the pseudo-elements of symmetry may be either global or local. In the latter category, we noted a very unusual subset more than 15 years ago of P1 crystals which have Z9 = 2, the two symmetry independent molecules being related by a local pseudo-centre of inversion. Why does the crystal take this pseudo-centre, an ‘‘extra’’, almost ‘‘wasted’’ symmetry element? All these observations are undoubtedly interesting, and possibly important, but what struck me as the most unusual fact about high Z9 structures, an observation that seemed almost counter-intuitive, is that the proportion of Z9 . 1 structures relative to all crystal structures has remained practically invariant over the decades. I must admit that I had always felt (and I daresay that this might be true of others, too) that with the advent of CCD diffractometers and high throughput crystallography, the proportion of high Z9 structures should be steadily increasing. Reality is different. During the period 1970–2006, during which time the CSD has become nearly 43 times larger, the proportion of Z9 = 1, Z9 , 1 and Z9 . 1 organic structures has remained virtually constant (i1%) at 73, 16 and 11%. Does this constancy of numbers say anything about the origin of this phenomenon? Is there a basic, universal reason why high Z9 structures are obtained? I would like to suggest that the secrets of high Z9 structures will be most easily revealed through a study of polymorphic systems, wherein a high Z9 structure may be most easily compared with a lower Z9 structure (ideally one with Z9 = 1) of the same chemical substance. We noted that at least in two cases, pentafluorophenol and trans-1,4-bis(phenylethynyl)cyclohexane-1,4-diol, there are two structures with different Z9 values. The structure with the lower Z9 is the more stable structure; the one with the higher Z9 value is obtained under what essentially amount to kinetic conditions: cryo-crystallography for the phenol and melt cooling for the diol. These observations are suggestive. Steed put forth the idea a few years ago that a high Z9 structure is a ‘‘fossil relic’’ of a more stable form. In this way, it is not difficult to associate the higher Z9 polymorphs of these two compounds with kinetic modifications. Indeed, we showed that the discrete O–H...O–H...O–H trimer synthon in the high Z9 polymorph of pentafluorophenol is an ‘‘incomplete’’ version of the infinite O–H...O–H chain in the low Z9 polymorph. Similarly, the high Z9 polymorph of the diol contains a large number of molecular conformations that are essentially ‘‘frozen’’ into the crystal, and these anneal out in the lower Z9 high temperature modification. It is worthwhile to reflect that all the reasons which have been put forward in the past for the adoption of high Z9 structures (packing difficulties and inconsistencies, modulation, pseudosymmetry, equi-energetic conformations, better interactions) are simply different ways of saying the same thing. A high Z9 structure is a crystal ‘‘on the way’’. Many of Brock’s observations on alcohols and phenols follow from the idea that molecules which form stable clusters in solution because of strong hydrogen bonding have a higher tendency to form Z9 . 1 crystals because these clusters are carried forward more or less unaltered into the crystal. Possibly, O–H...O hydrogen bonding in alcohols and phenols is so strong and directional that it becomes difficult to observe a better packed, School of Chemistry, University of Hyderabad, Hyderabad, 500 046, India LETTER www.rsc.org/crystengcomm | CrystEngComm

Organic crystal hydrates : what are the important factors for formation

Abstract: A database study of 34 770 accurate organic crystal structures reveals that the most important factor determining a higher frequency of hydrates is the sum of the average donor and acceptor counts for the functional groups. Different parameter forms for donor/acceptor properties were investigated for correlation with formation of hydrates, and are discussed. We did not find that the donor/acceptor ratio or the molecular weight significantly affects the hydrate formation. We also examined a wide range of calculated molecular properties and found that increasing polar surface is correlated with increasing hydrate formation. The water environment pattern of donor and acceptor hydrogen bonds in the crystal is influenced by the donor/acceptor ratio of the molecule.

Synthesis-dependant structural variations in amorphous calcium carbonate

Abstract: Amorphous calcium carbonate (ACC) was synthesised in the presence of the additives magnesium and poly(aspartic acid) (pAsp) and the structure and crystallisation of these ACC samples was investigated using a range of techniques including X-Ray Absorption Spectroscopy (XAS), X-Ray Diffraction (XRD) and Infra-Red Spectroscopy (IR). The experiments demonstrated that synthetic ACC can be produced with different short-range structures, according to the solution additives used. While the first Mg–ACC precipitates showed short-range structures most similar to aragonite, with monohydrocalcite short-range structures developing with incubation in solution, the initial pAsp–ACC precipitates possessed short-range structures resembling vaterite. The results show that the influence of these additives on the crystallisation of calcium carbonate is apparent even in the precipitation of the first amorphous precursor phase, and that the first stages of recrystallisation involve the expulsion of water from the structure rather than significant changes in the short-range structure around the calcium ions.

Metal–organic frameworks constructed from mixed-ligand 1,2,3,4-tetra-(4-pyridyl)-butane and benzene-polycarboxylate acids: syntheses, structures and physical properties

Abstract: Three novel coordination polymers, [Mn(TPB)0.5(IPA)(H2O)2]n (1), [Zn1.5(TPB)0.5(TMA)(H2O)·(H2O)]n (2), and [Co(TPB)0.5(PMA)0.5(H2O)2·(H2O)]n (3) (TPB = 1,2,3,4-tetra-(4-pyridyl)-butane; H2IPA = isophthalic acid; H3TMA = trimesic acid; and H4PMA = pyromellitic acid), have been synthesized under hydrothermal conditions and structurally characterized. Complex 1 features a 2D infinite layer framework consisting of bi-manganese clusters, which is further stacked along the [11] direction via strong interlayer π⋯π interactions to form a 3D supramolecular architecture. Complex 2 has a 3D complicated framework comprised of two kinds of infinite 1D chains. The 3D framework of complex 3 possesses three topologically nonequivalent 4-connected nodes synchronously and exhibits an unprecedented (64·102)(42·84)(4·65)2 topology. The magnetic susceptibility data of complex 1 show strong antiferromagnetic interactions in the dinuclear Mn(II) units. Complex 2 exhibits strong fluorescent emissions in the solid state at room temperature and may be suitable as a candidate of blue-fluorescent material.

Solvent inclusion in the structural voids of form II carbamazepine: single-crystal X-ray diffraction, NMR spectroscopy and Hirshfeld surface analysis

Abstract: Single-crystal X-ray diffraction and solution 1H NMR spectroscopy, in conjunction with Hirshfeld surface analysis, give evidence of solvent inclusion in the trigonal polymorph of carbamazepine, which in the unsolvated form is characterised by the presence of large structural voids.

How does grinding produce co-crystals? Insights from the case of benzophenone and diphenylamine

Abstract: A benzophenone–diphenylamine co-crystal nucleates from a submerged eutectic—is this a possible mechanism of grinding induced synthesis of such materials?

Crystal structures of quinacridones

Abstract: The crystal structure of the αI-phase of quinacridone was determined from non-indexed X-ray powder data by means of crystal structure prediction and subsequent Rietveld refinement. This αI-phase is another polymorph than the α-phase reported by Lincke [G. Lincke and H.-U. Finzel, Cryst. Res. Technol. 1996, 31, 441–452.]. The crystal structures of the β and γ polymorphs were determined from single crystal data. The knowledge of the crystal structures can be used for crystal engineering, i.e., for targeted syntheses of pigments having desired properties, especially for the syntheses of new red pigments.

Self-assembly of 3-D 4d–4f coordination frameworks based on 1-D inorganic heterometallic chains and linear organic linkers

Abstract: Four novel 4d–4f heterometallic coordination polymers, namely, LnAg(pydc)2(Hnic)0.5 [Ln = Nd (1), Eu (2); H2pydc = pyridine-3,4-dicarboxylic acid, Hnic = nicotinic acid], and LnAg(inic)2(nicO)·0.5H2O [Ln = Nd (3), Eu (4); Hinic = isonicotinic acid, H2nicO = 2-hydroxynicotinic acid], have been synthesized and characterized. Compounds 1 and 2 exhibit three-dimensional (3-D) coordination frameworks constructed by one-dimensional (1-D) inorganic heterometallic chains and linear pydc linkers. The 1-D channels occupied by disordered Hnic molecules emerge. To our knowledge, both compounds represent the first examples of 3-D open-framework 4d–4f heterometallic coordination frameworks. Compounds 3 and 4 display 3-D covalent frameworks composed of 1-D inorganic heterometallic chains joined by inic ligands, representing the first examples of 3-D 4d–4f coordination frameworks constructed by inorganic heterometallic chain and mixed linear and nonlinear ligands with same donors. Furthermore, the luminescent properties of 2 and 4 were studied.

Asprich mollusk shell protein: in vitro experiments aimed at elucidating function in CaCO3 crystallization

Abstract: Acidic proteins are key components of the organic matrix of many biologically formed minerals and are therefore thought to play an important role in their formation Here we study the effect of one unusually acidic protein of the Asprich family, associated with mollusk shell prismatic layer, on the precipitation of CaCO3in vitro We show that Asprich induces and transiently stabilizes the deposition of amorphous calcium carbonate (ACC) Asprich also induces the formation of ACC when adsorbed onto chitin, a major component of the intracrystalline organic matrix of the prismatic layer Based on this evidence, combined with previous studies on the forming prisms in the shell layer, we suggest that the in vivo function of Asprich is inducing and stabilizing ACC particles and inhibiting their uncontrolled crystallization until they undergo secondary nucleation on the growing prisms

A pillared-grid MOF with large pores based on the Cu2(O2CR)4 paddle-wheel

Abstract: We describe a new interpenetrated pillared-grid structure based on Cu(II) paddle-wheels, 4,4′-biphenyldicarboxylate and 4,4′-bipyridine, with 51% non-framework volume and which retains the same structure on desolvation.

Inorganic–organic hybrid materials incorporating primary cyclic ammonium cations: The lead iodide series

Abstract: Six inorganic–organic hybrids have been synthesized and characterised by single-crystal X-ray diffraction experiments. The inorganic component is based on lead(II) iodide units and the organic component various cyclic hydrocarbons with only a primary ammonium group as a ring substituent. If the organic component is cyclopropylammonium, cyclobutylammonium, cyclopentylammonium and cyclohexylammonium, the inorganic motif observed is based on the cubic perovskite structure type and consists of 2-D layers of corner-sharing octahedra, in the ratio of 1∶2 inorganic–organic. lead(II) iodide and cycloheptylammonium combined to give 1-D chains of corner-sharing lead iodide octahedra and similarly, lead(II) iodide and cyclooctylammonium gave 1-D chains of face-sharing octahedra. A quantitative measure of the steric effects of the size of the cyclic rings on the tilting of the inorganic layers is proposed.

Solvent effect in a “solvent free” reaction

Abstract: Vapour digestion of a mixture of solid [Fe(η5-C5H4–C5H4N)2] and solid pimelic acid HOOC(CH2)5COOH in the presence of solvent vapours generates co-crystals of different stoichiometry depending on the protic or aprotic nature of the solvent. The nature of the products has been ascertained by a combined use of SSNMR and X-ray diffraction.

Counter-ion influence on the coordination mode of the 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (bpo) ligand in mercury(II) coordination polymers, [Hg(bpo)nX2]: X = I−, Br−, SCN−, N3− and NO2−; spectroscopic, thermal, fluorescence and structural studies

Abstract: A series of new mercury(II)–organic polymeric complexes generated from 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (bpo) as an angular dipyridyl derivative ligand, [Hg(bpo)nX2]: X = SCN− (1), I− (2), Br− (3), NO2− (4) and N3− (5), was prepared from reactions of the ligand bpo with different mercury(II) salts. All these compounds were characterized by elemental analysis, IR-, 1H NMR-, and 13C NMR spectroscopies and structurally determined by X-ray single-crystal diffraction. The thermal stabilities of compounds 1–5 and also the reported compound, [Hg(μ-bpo)I2]·CH3CN (6), were studied by thermal gravimetric (TG) and differential thermal analyses (DTA). Solid-state luminescent spectra of the compounds 1–6 indicate intense fluorescent emissions at ca. 470 nm. The results show the influence of the counter-ions on the coordination mode of the bpo ligand in the mercury ion as a soft acid that is capable of forming compounds with four-, five- and six coordination numbers and, consequently, acting in different forms of coordination polymers, containing both discrete and divergent (from one-dimensional, 1-D to two-dimensional, 2-D) coordination frameworks.

Synthesis, structures and properties of nickel(II) and cobalt(II) metal–organic frameworks based on a flexible tricarboxylate ligand H3TTG and different pyridyl-containing ligands

Abstract: Along with our recent investigations on Ni and Co coordination frameworks of a flexible tripodal ligand of H3TTG (N,N′,N″-1,3,5-triazine-2,4,6-triyltris-glycine), four new complexes {[Ni(HTTG)(4,4′-bpy)(H2O)3]·(H2O)2}n (1), {[Ni2(HTTG)2(bpe)2(H2O)]·(H2O)6}n (2), {[Co2(HTTG)2(bpe)2(H2O)]·(H2O)6}n (3) and {[Co3(TTG)2(bpe)2]·(H2O)2}n (4) were hydrothermally synthesized through reactions of this ligand with different pyridyl-containing ligands {4,4′-bpy (4,4-bipyridine), bpe [1,2-bi(4-pyridyl)ethane]}, respectively. Due to various coordination modes and conformations of the flexible tricarboxylate ligand and pyridyl-containing coligands, these complexes exhibit structural and dimensional diversity. Complex 1 shows a unique 1D chain bridged by the R22(8) hydrogen bonds between the carboxylate groups, the triazine rings, and hydrogen-bonded networks of the solvent water molecules as well. Complexes 2 and 3 are isomorphous and both exhibit special 2D (8,2)-connected double-layer structures with two kinds of 1D channels constructed by the coordination bonds and hydrogen bonding interactions, respectively. Complex 4 features a 3-D network with scarce (8,3)-connected rutile-related topology with a Schlafli symbol (42,622,7,83)(4,62)2 based on secondary building units (SBUs) of linear cobalt clusters [Co3(CO2)4]2−. Significantly, with increasing flexibility of the pyridyl-containing coligands, these corresponding complexes become more and more complicated. In addition, their physical properties such as thermal, XPRD, and magnetism have also been investigated.

Molecular dynamics simulations of the interaction of citric acid with the hydroxyapatite (0001) and (011ˉ0) surfaces in an aqueous environment

Abstract: Molecular dynamics simulations are employed to investigate the adsorption of citric acid molecules to the (0001) and (010) surfaces of hydroxyapatite. An aqueous environment is added through the explicit introduction of water molecules in the simulation cell. The citric acid is found to attach to the surfaces, rather than remain in the bulk water and the calculated average adsorption energies are +291.4 kJ mol−1 and −17.4 kJ mol−1 for the (0001) and (010) surfaces respectively. Citric acid thus adsorbs to the (010) surface and hence would inhibit growth of this surface more effectively than growth of the (0001) plane with which it does not interact strongly in an aqueous environment where the water competes with the citric acid for adsorption. The implication is that the hydroxyapatite crystal would grow more rapidly in the [0001] direction than in the [010] direction in the presence of citric acid, leading to elongation in the c-direction and more pronounced expression of the (010) surface in the hydroxyapatite morphology.

Mercury(II) coordination polymers generated from 1,4-bis(2 or 3 or 4-pyridyl)-2,3-diaza-1,3-butadiene ligands

Abstract: A series of new polymeric mercury(II) complexes, [Hg(4-bpdb)(SCN)2]n (1), [Hg(3-bpdb)(SCN)2]n (2), [Hg(4-bpdb)Br2]n (3), [Hg(3-bpdb)Br2]n (4) and [Hg2(2-bpdb)Br4]n (5) {4-bpdb = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene, 3-bpdb = 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene and 2-bpdb = 1,4-bis(2-pyridyl)-2,3-diaza-1,3-butadiene} was prepared from reactions of mercury(II) thiocyanate or bromide with three organic nitrogen donor-based ligands under thermal gradient conditions using the branched tube method. All these compounds were structurally characterized by single-crystal X-ray diffraction. The thermal stabilities of compounds 1–5 were studied by thermal gravimetric (TG) and differential thermal analyses (DTA).

Crystal engineering of 3-D coordination polymers by pillaring ferromagnetic copper(II)-methylmalonate layers

Abstract: Three new copper(II) complexes of formula [Cu(Memal)(H2O)]n (1), [Cu2(pyz)(Memal)2] (2) and [Cu2(4,4′-bpy)(Memal)2(H2O)2] (3) (Memal = methylmalonate, pyz = pyrazine and 4,4′-bpy = 4,4′-bipyridine) were obtained and structurally characterized by X-ray diffraction. Complex 1 is a square grid of aquacopper(II) units which are linked by carboxylate-methylmalonate groups in the anti–syn (equatorial–equatorial) coordination mode. The crystal structures of 2 and 3 consist of corrugated layers of copper(II) (2) and aquacopper(II) (3) units with intralayer carboxylate-methylmalonate bridges in the anti–syn (equatorial–apical) coordination mode which are linked through pyrazine (2) and 4,4′-bipyridine (3) ligands; to build up a 3-D network. Magnetic susceptibility measurements of complexes 1–3 in the temperature range 2–300 K show the occurrence of an overall ferromagnetic behaviour with a weak intralayer ferromagnetic coupling (J = +1.61(1) cm−1) in 1 whereas two opposite magnetic interactions occur in 2 and 3, one ferromagnetic through the anti–syn carboxylate (2 and 3) and the other antiferromagnetic through pyz (2) and 4,4′-bpy) (3).

Scorpion-shaped carboxylate ligand tailored molecular square, bilayer, self-threading and (3,6)-connected nets

Abstract: A novel designed scorpion-shaped 5-oxyacetateisophthalic acid (H3OABDC) was used to construct a series of luminescent metal–organic frameworks, namely [Zn2(HOABDC)2(phen)2(H2O)2]n·nH2O (1), [Zn2(OABDC)(4,4′-bipy)(μ2-OH)(H2O)]n·4/3nH2O (2), [Cd3(OABDC)2(4,4′-bipy)4(H2O)4]n·2nH2O (3), [Cd2(OABDC)(phen)2(μ3-OH)]n·1/3nH2O (4), and [Zn8(OABDC)4(2,2′-bipy)4(μ2-OH)4]n·2nH2O (5) (bipy = bipyridine, phen = 1,10-phenanthroline). Complex 1 features a discrete molecular square and π–π and C–H⋯π interactions between molecular squares give rise to a 2D sheet. Complex 2 shows an unusual 2D bilayer architecture with (3,5)-connected topology. A prominent structural feature in 3 is the self-threading 2D layered structure. Both 4 and 5 exhibit (3,6)-connected topology. In 4, an extraordinary folded four-step-ladder Cd4(OH)2 unit acts as 6-connected node and the framework is 2D (3,6)-connected net. While in 5, the Zn2(OH) unit adopts octahedral geometry and the whole framework features a 3D (3,6)-connected rutile (rtl) topology. Photoluminescence studies revealed that these complexes are interesting blue, green and orange luminescent materials. The thermal stabilities of these complexes are also discussed.

Construction of 2-D lanthanide coordination frameworks: syntheses, structures and luminescent property

Abstract: A series of layered lanthanide coordination frameworks [Ln4(NIPH)6(H2O)4]·(4,4′-bipy) [Ln = La (1), Pr (2)], [La(NIPH)2(H2O)2]·0.5(4,4′-H2bipy) (3), Ln(NIPH)2(H2O)2]·0.5(4,4′-H2bipy)·2H2O [Ln =Pr (4), Nd (5)], and [Ln(NIPH)2]·0.5(4,4′-H2bipy) [Ln = Sm (6), Eu (7), Tb (8), Ho (9), Yb (10)] (NIPH = 5-nitroisophthalate and 4,4′-bipy = 4,4′-bipyridine) have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. All the coordination frameworks display identical crystal system (triclinic) and space group (P). Compounds 1 and 2 are isostructural, their coordination sheets are constructed by polynuclear helical-like chains. Compounds 3–5 are extremely similar in structure, in which Ln atoms are bridged into rod-shaped chains by carboxylate groups. For compounds 6–10, the coordination layers are built up from 1-D zig-zag chains. The 3-D supramolecular frameworks of 1–10 are finally formed through the alternate stack of Ln coordination layers and 4,4′-bipy layers based on hydrogen bonding interactions. Compound 7 displays luminescent property.

The composition of the mineralized cuticle in marine and terrestrial isopods: A comparative study

Abstract: The cuticles of four terrestrial and four marine isopods were analyzed. They consist of crystalline magnesian calcite, amorphous calcium carbonate (ACC), amorphous calcium phosphate (ACP), water and an organic matrix. Marine species have a higher concentration of magnesium within the cuticle in comparison to their terrestrial relatives. Flexible cuticles contain ACC in combination with a high concentration of organic material and a rather low concentration of magnesium calcite. Hard cuticles have a low percentage of organic material, and, in terrestrial species, a higher percentage of ACC. The results indicate that the mineral composition of the crustacean cuticle depends on its function and the habitat of the animal.

Structural variations in rare earth benzoate complexes: Part I. Lanthanum

Abstract: A series of lanthanum benzoate complexes have been prepared and structurally characterised as DMF or DMSO solvates. The structures of these complexes vary considerably as a function of the steric bulk of the ligands and the degree of solvation. With one exception, all of the complexes form coordination polymers. These experimental results are compared to reported data from the Cambridge Structural Database (CSD) in order to study the role of sterically bulky substituents in the structures of lanthanum benzoate complexes. Binding modes vary from the η1 coordination of a carboxylic acid co-ligand to carboxylate ligands adopting a bridging μ-η2 : η1 geometry. The nature of the bridging environment between adjacent lanthanum ions varies significantly in the structures and often several different environments exist within the same structure. Solvent effects are also observed, particularly in cases where the solvent is able to partake in intra- or intermolecular hydrogen bonding.

New insights into mechanisms of biomolecular control on growth of inorganic crystals

Abstract: The interactions of biomolecules with atomic features on crystal surfaces lead to dramatic changes in morphology and growth rate. Molecular scale studies based on atomic force microscopy and computational modeling have provided new insights into the mechanisms that lead to these changes. We examine the key factors that are emerging from those studies and link the mechanisms of modification to the underlying structural and chemical relationships between modifier and crystal surface.

The first example of a coordination polymer from the expanded 4,4′-bipyridine ligand [Ru(pytpy)2]2+(pytpy = 4′-(4-pyridyl)-2,2′∶6′,2″-terpyridine)

Abstract: The complex cation ligand [Ru(pytpy)2]2+ (pytpy = 4′-(4-pyridyl)-2,2′∶6′,2″-terpyridine) is an expanded 4,4′-bipyridine; we describe the first example of a coordination polymer in which [Ru(pytpy)2]2+ plays the role of a bridging bidentate ligand.

Oxo-anion binding by protonated (dimethylphenyl)(pyridyl)ureas

Abstract: The anion coordination chemistry of two protonated urea-based ligands, N-(2,4-dimethylphenyl)-N′-(3-pyridy1)urea (1) and N-(2,6-dimethylphenyl)-N′-(3-pyridy1)urea (2) is reported. Reaction of 1 or 2 with inorganic oxo-acids such as perchloric, nitric or sulfuric acid affords the adducts (3–6) of the corresponding anions with protonated ligands (1H+ and 2H+). The solid-state structures of the anion complexes display a rich variety of hydrogen bond motifs involving the urea NH groups, carbonyl, protonated pyridyl NH+ fragment, water molecules, and the anions. While complexes with ligand 1 (3 and 4) crystallize as monohydrate, compounds with 2 (5 and 6) are solvent-free, which leads to notable differences in their hydrogen bond patterns. When crystallized from the acid mixture HClO4/HNO3 or HClO4/H2SO4 both 1 and 2 selectively bind the perchlorate anion.

Interplay of coordinative and supramolecular interactions in engineering unusual crystalline architectures of low-dimensional metal–pamoate complexes under co-ligand intervention

Abstract: This work presents a systematic investigation on coordination chemistry of a pharmaceutical agent pamoic acid (H2PA), and also reveals the significant function of supramolecular interactions in managing the resultant crystalline networks with the incorporation of secondary co-ligands. Assemblies of pamoic acid with transition metal ions under similar conditions yield a series of eleven MnII, CuII, ZnII, and CdII complexes, in the absence/presence of the organonitrogen ligands such as 2,2′-bipyridyl (2,2′-bipy), 1,10-phenanthroline (phen), and 4,4′-bipyridyl (4,4′-bipy). These compounds, together with the DMF solvate of pamoic acid, have been characterized by IR, elemental analysis, and single-crystal X-ray diffraction techniques. Generally, these complexes display similar 1-D pamoate-bridged coordination arrays (or 2-D coordination layers by introducing bridging 4,4′-bipy). Remarkably, distinct extended network architectures are further constructed with the aid of weak secondary interactions especially aromatic stacking. Amongst them, complexes 6, 8, 9, and 12, which exhibit unusual interpenetrating networks of (6,3) layers or 3-D 5-connected frameworks regulated by stacking forces, are representative paradigms of this research. Structural evolution under the co-ligand intervention in this series of complexes, as well as the general coordination rule of pamoate, has been further discussed. Thermal stability of these crystalline materials and fluorescent properties of the polymeric ZnII and CdII complexes have also been explored.