The effect of partial methylation of the glycine amino group on crystal structure in N,N‐dimethylglycine and its hemihydrate

N,N‐Dimethylglycine, C₄H₉NO₂, and its hemihydrate, C₄H₉NO₂·0.5H₂O, are discussed in order to follow the effect of the methylation of the glycine amino group (and thus its ability to form several hydrogen bonds) on crystal structure, in particular on the possibility of the formation of hydrogen‐bonded `head‐to‐tail' chains, which are typical for the crystal structures of amino acids and essential for considering amino acid crystals as mimics of peptide chains. Both compounds crystallize in centrosymmetric space groups (Pbca and C2/c, respectively) and have two N,N‐dimethylglycine zwitterions in the asymmetric unit. In the anhydrous compound, there are no head‐to‐tail chains but the zwitterions form R₄⁴(20) ring motifs, which are not bonded to each other by any hydrogen bonds. In contrast, in the crystal structure of N,N‐dimethylglycinium hemihydrate, the zwitterions are linked to each other by N—H...O hydrogen bonds into infinite C₂²(10) head‐to‐tail chains, while the water molecules outside the chains provide additional hydrogen bonds to the carboxylate groups.     

[Leu2]Gramicidin S preserves the structural properties of its parent peptide and forms helically aligned β‐sheets

For crystallographic analysis, Leu was substituted for Orn in Gramicidin S (LGS) to suppress interactions with hydrophilic solvent molecules, which increased the flexibility of the Orn side chains, leading to disorder within the crystals. The asymmetric unit (C₆₂H₉₄N₁₀O₁₀·1.296C₃H₈O·1.403H₂O) contains three LGS molecules (A, B and C) forming β‐turn and intramolecular β‐sheet structures. With the exception of one motif in molecule C, d ‐Phe‐Pro turn motifs (Phe is phenylalanine and Pro is proline) were classed as type II′ β‐turns. The peptide backbones twist slightly to the right along the long axis of the molecule. The puckering of Pro is in a Cγ‐endo or twisted Cγ‐endo–Cβ‐exo form. Flanking molecules are arranged such that the angles (A…B = 104°, B…C = 139° and C…A = 117°) form helical β‐sheets. Solvent molecules interact with the peptide backbones supporting the β‐sheets. The forms of the replacement Leu side chains are consistent with the e‐form of the Orn side chain in GS analogues. No hydrophilic region composed of solvent molecules, such as that observed in Gramicidin S hydrochloride (GS·HCl) crystals, was found. The perturbation of αH chemical shifts and coupling constants of CONH showed that the structural properties of GS·HCl and LGS are similar to each other in solution. CD spectra also supported the structural similarity. With the sequence cyclo(–Val–Leu–Leu–d ‐Phe–Pro–)₂ (Val is valine and Leu is leucine), LGS lacks the amphiphilicity and antimicrobial activity of parental Gramicidin S (GS). However, the structure of LGS reflects the structural characteristics of GS and no disordering inconvenient for structural analysis was found. Thus, LGS could be a novel scaffold useful for studying β‐turn and sheet structures.     

A novel crystal form of metacetamol: the first example of a hydrated form

We report the crystal structure and crystallization conditions of a first hydrated form of metacetamol (a hemihydrate), C₈H₉NO₂·0.5H₂O. It crystallizes from metacetamol‐saturated 1:1 (v/v) water–ethanol solutions in a monoclinic structure (space group P2₁/n) and contains eight metacetamol and four water molecules per unit cell. The conformations of the molecules are the same as in polymorph II of metacetamol, which ensures the formation of hydrogen‐bonded dimers and R₂²(16) ring motifs in its crystal structure similar to those in polymorph II. Unlike in form II, however, these dimers in the hemihydrate are connected through water molecules into infinite hydrogen‐bonded molecular chains. Different chains are linked to each other by metacetamol–water and metacetamol–metacetamol hydrogen bonds, the latter type being also present in polymorph I. The overall noncovalent network of the hemihydrate is well developed and several types of hydrogen bonds are responsible for its formation.     

Lamivudine hemihydrate

A new lamivudine hydrate, namely, cis‐4‐amino‐1‐(2‐hydroxymethyl‐1,3‐oxathiolan‐5‐yl)pyrimidin‐2(1H)‐one hemihydrate, C₈H₁₁N₃O₃S·0.5H₂O, has been synthesized and structurally characterized by both powder and single‐crystal X‐ray diffraction studies. The hemihydrate crystallizes in the Sohnke space group P2₁, with the asymmetric unit comprising four lamivudine and two water molecules. An extensive network of intermolecular hydrogen bonds involving both lamivudine and solvent water molecules generates a three‐dimensional supramolecular architecture. The structural data and crystal packing of the present lamivudine hemihydrate are compared with those of other hydrated and anhydrous forms of lamivudine.     

Intermolecular interactions and disorder in six isostructural celecoxib solvates

Six isostructural crystalline solvates of the active pharmaceutical ingredient celecoxib {4‐[5‐(4‐methylphenyl)‐3‐(trifluoromethyl)pyrazol‐1‐yl]benzenesulfonamide; C₁₇H₁₄F₃N₃O₂S} are described, containing dimethylformamide (DMF, C₃H₇NO, 1 ), dimethylacetamide (DMA, C₄H₉NO, 2 ), N‐methylpyrrolidin‐2‐one (NMP, C₅H₉NO, 3 ), tetramethylurea (TMU, C₅H₁₂N₂O, 4 ), 1,3‐dimethyl‐3,4,5,6‐tetrahydropyrimidin‐2(1H)‐one (DMPU, C₆H₁₂N₂O, 5 ) or dimethyl sulfoxide (DMSO, C₂H₆OS, 6 ). The host celecoxib structure contains one‐dimensional channel voids accommodating the solvent molecules, which accept hydrogen bonds from the NH₂ groups of two celecoxib molecules. The solvent binding sites have local twofold rotation symmetry, which is consistent with the point symmetry of the solvent molecule in 4 and 5 , but introduces orientational disorder for the solvent molecules in 1 , 2 , 3 and 6 . Despite the isostructurality of 1 – 6 , the unit‐cell volume and solvent‐accessible void space show significant variation. In particular, 4 and 5 show an enlarged and skewed unit cell, which can be attributed to a specific interaction between an N—CH₃ group in the solvent molecule and the toluene group of celecoxib. Intermolecular interaction energies calculated using the PIXEL method show that the total interaction energy between the celecoxib and solvent molecules is broadly correlated with the molecular volume of the solvent, except in 6 , where the increased polarity of the S=O bond leads to greater overall stabilization compared to the similarly‐sized DMF molecule in 1 . In the structures showing disorder, the most stable orientations of the solvent molecules make C—H…O contacts to the S=O groups of celecoxib.     

Four supramolecular isomers of dichloridobis(1,10‐phenanthroline)cobalt(II): synthesis,structure characterization and isomerization

Crystal engineering can be described as the understanding of intermolecular interactions in the context of crystal packing and the utilization of such understanding to design new solids with desired physical and chemical properties. Free‐energy differences between supramolecular isomers are generally small and minor changes in the crystallization conditions may result in the occurrence of new isomers. The study of supramolecular isomerism will help us to understand the mechanism of crystallization, a very central concept of crystal engineering. Two supramolecular isomers of dichloridobis(1,10‐phenanthroline‐κ²N,N′)cobalt(II), [CoCl₂(C₁₂H₈N₂)₂], i.e. (IA) (orthorhombic) and (IB) (monoclinic), and two supramolecular isomers of dichloridobis(1,10‐phenanthroline‐κ²N,N′)cobalt(II) N,N‐dimethylformamide monosolvate, [CoCl₂(C₁₂H₈N₂)₂]·C₃H₇NO, i.e. (IIA) (orthorhombic) and (IIB) (monoclinic), were synthesized in dimethylformamide (DMF) and structurally characterized. Of these, (IA) and (IIA) have been prepared and structurally characterized previously [Li et al. (2007). Acta Cryst. E 63 , m1880–m1880; Cai et al. (2008). Acta Cryst. E 64 , m1328–m1329]. We found that the heating rate is a key factor for the crystallization of (IA) or (IB), while the temperature difference is responsible for the crystallization of (IIA) or (IIB). Based on the crystallization conditions, isomerization behaviour, the KPI (Kitajgorodskij packing index) values and the density data, (IB) and (IIA) are assigned as the thermodynamic and stable kinetic isomers, respectively, while (IA) and (IIB) are assigned as the metastable kinetic products. The 1,10‐phenanthroline (phen) ligands interact with each other through offset face‐to‐face (OFF) π–π stacking in (IB) and (IIB), but by edge‐to‐face (EF) C—H...π interactions in (IA) and (IIA). Meanwhile, the DMF molecules in (IIB) connect to neighbouring [CoCl₂(phen)₂] units through two C—H...Cl hydrogen bonds, whereas there are no obvious interactions between DMF molecules and [CoCl₂(phen)₂] units in (IIA). Since OFF π–π stacking is generally stronger than EF C—H...π interactions for transition‐metal complexes with nitrogen‐containing aromatic ligands, (IIA) is among the uncommon examples that are stable and densely packed but that do not following Etter's intermolecular interaction hierarchy.     

Packing considerations of 10‐oxa‐9‐boraphenanthrene derivatives

The crystal structures of three products of the reaction of 2‐phenylphenol and BCl₃ have been determined. The structures show intriguing packing patterns and an interesting case of pseudosymmetry. In addition, one of the two polymorphs has a primitive monoclinic crystal system, but it is twinned and emulates an orthorhombic C‐centred structure. Tris(biphenyl‐2‐yl) borate, C₃₆H₂₇BO₃, ( III ), crystallizes with only one molecule in the asymmetric unit. The dihedral angles between the planes of the aromatic rings in the biphenyl moieties are 50.47 (13), 44.95 (13) and 42.60 (13)°. The boron centre is in a trigonal planar coordination with two of the biphenyl residues on one side of the BO₃ plane and the remaining biphenyl residue on the other side. One polymorph of 10‐oxa‐9‐boraphenanthren‐9‐ol, C₁₂H₉BO₂, ( V a ), crystallizes with two almost identical molecules (r.m.s. deviation of all non‐H atoms = 0.039 Å) in the asymmetric unit. All non‐H atoms lie in a common plane (r.m.s. deviation = 0.015 Å for both molecules in the asymmetric unit). The two molecules in the asymmetric unit are connected into dimers via O—H...O hydrogen bonds. A second polymorph of 10‐oxa‐9‐boraphenanthren‐9‐ol, ( V b ), crystallizes as a pseudo‐merohedral twin with two almost identical molecules (r.m.s. deviation of all non‐H atoms = 0.035 Å) in the asymmetric unit. All non‐H atoms lie in a common plane (r.m.s. deviation = 0.012 Å for molecule 1 and 0.014 Å for molecule A). Each of the two molecules in the asymmetric unit is connected into a centrosymmetric dimer via O—H...O hydrogen bonds. The main difference between the two polymorphic structures is that in ( V a ) the two molecules in the asymmetric unit are hydrogen bonded to each other, whereas in ( V b ), each molecule in the asymmetric unit forms a hydrogen‐bonded dimer with its centrosymmetric equivalent. 9‐[(Biphenyl‐2‐yl)oxy]‐10‐oxa‐9‐boraphenanthrene, C₂₄H₁₇BO₂, ( VI ), crystallizes with four molecules in the asymmetric unit. The main differences between them are the dihedral angles between the ring planes. Apart from the biphenyl moiety, all non‐H atoms lie in a common plane (r.m.s. deviations = 0.026, 0.0231, 0.019 and 0.033 Å for molecules 1, A, B and C, respectively). This structure shows pseudosymmetry; molecules 1 and A, as well as molecules B and C, are related by a pseudo‐translation of about in the direction of the b axis. Molecules 1 and B, as well as molecules A and C, are related by a pseudo‐inversion centre at ,,. Neither between molecules 1 and C nor between molecules A and B can pseudosymmetry be found.     

Two terphenyl‐based diol hosts and corresponding solvent inclusions with dimethylformamide and acetonitrile

Having reference to an elongated structural modification of 2,2′‐bis(hydroxydiphenylmethyl)biphenyl, (I), the two 1,1′:4′,1′′‐terphenyl‐based diol hosts 2,2′′‐bis(hydroxydiphenylmethyl)‐1,1′:4′,1′′‐terphenyl, C₄₄H₃₄O₂, (II), and 2,2′′‐bis[hydroxybis(4‐methylphenyl)methyl]‐1,1′:4′,1′′‐terphenyl, C₄₈H₄₂O₂, (III), have been synthesized and studied with regard to their crystal structures involving different inclusions, i.e. (II) with dimethylformamide (DMF), C₄₄H₃₄O₂·C₂H₆NO, denoted (IIa), (III) with DMF, C₄₈H₄₂O₂·C₂H₆NO, denoted (IIIa), and (III) with acetonitrile, C₄₈H₄₂O₂·CH₃CN, denoted (IIIb). In the solvent‐free crystals of (II) and (III), the hydroxy H atoms are involved in intramolecular O—H...π hydrogen bonding, with the central arene ring of the terphenyl unit acting as an acceptor. The corresponding crystal structures are stabilized by intermolecular C—H...π contacts. Due to the distinctive acceptor character of the included DMF solvent species in the crystal structures of (IIa) and (IIIa), the guest molecule is coordinated to the host via O—H...O=C hydrogen bonding. In both crystal structures, infinite strands composed of alternating host and guest molecules represent the basic supramolecular aggregates. Within a given strand, the O atom of the solvent molecule acts as a bifurcated acceptor. Similar to the solvent‐free cases, the hydroxy H atoms in inclusion structure (IIIb) are involved in intramolecular hydrogen bonding, and there is thus a lack of host–guest interaction. As a result, the solvent molecules are accommodated as C—H...N hydrogen‐bonded inversion‐symmetric dimers in the channel‐like voids of the host lattice.     

Novel one‐ and two‐dimensional ZnII coordination polymers based on a versatile 3,6‐bis(pyridin‐4‐yl)phenanthrene‐9,10‐dione ligand

Two new Zn^II coordination polymers, namely, catena‐poly[[dibromidozinc(II)]‐μ‐[3,6‐bis(pyridin‐4‐yl)phenanthrene‐9,10‐dione‐κ²N:N′]], [ZnBr₂(C₂₄H₁₄N₂O₂)]_n, (1), and poly[[bromido[μ₃‐10‐hydroxy‐3,6‐bis(pyridin‐4‐yl)phenanthren‐9‐olato‐κ³N:N′:O⁹]zinc(II)] hemihydrate], {[ZnBr(C₂₄H₁₅N₂O₂)]·0.5H₂O}_n, (2), have been synthesized through hydrothermal reaction of ZnBr₂ and a 60° angular phenanthrenedione‐based linker, i.e. 3,6‐bis(pyridin‐4‐yl)phenanthrene‐9,10‐dione, in different solvent systems. Single‐crystal analysis reveals that polymer (1) features one‐dimensional zigzag chains connected by weak C—H...π and π–π interactions to form a two‐dimensional network. The two‐dimensional networks are further stacked in an ABAB fashion along the a axis through C—H...O hydrogen bonds. Layers A and B comprise left‐ and right‐handed helical chains, respectively. Coordination polymer (2) displays a wave‐like two‐dimensional layered structure with helical chains. In this compound, there are two opposite helical –Zn–HL– chains [HL is 10‐hydroxy‐3,6‐bis(pyridin‐4‐yl)phenanthren‐9‐olate] in adjacent layers. The layers are packed in an ABAB sequence and are further connected through O—H...Br and O—H...O hydrogen‐bond interactions to form a three‐dimensional framework. In (1) and (2), the mutidentate L and HL ligands exhibits different coordination modes.     

Synthesis and crystal structures of a 3‐acetylated (20S,24S)‐ocotillol‐type saponin and its C‐24 epimer

In order to study the in vivo protective effect on myocardial ischemia, (20S ,24R )‐epoxydammarane‐12β,25‐diol, (V), and (20S ,24S )‐epoxydammarane‐12β,25‐diol, (VI), were synthesized through a novel synthetic route. Two key intermediates, namely (20S ,24R )‐3‐acetyl‐20,24‐epoxydammarane‐3β,12β,25‐triol, (III) [obtained as the hemihydrate, C₃₂H₅₄O₅·0.5H₂O, (IIIa ), and the ethanol hemisolvate, C₃₂H₅₄O₅·0.5C₂H₅OH, (IIIb ), with identical conformations but different crystal packings], and (20S ,24S )‐3‐acetyl‐20,24‐epoxydammarane‐3β,12β,25‐triol, C₃₂H₅₄O₅, (IV), were obtained during the synthesis. The structures were confirmed by ¹H NMR, ¹³C NMR and HRMS analyses, and single‐crystal X‐ray diffraction. Molecules of (IIIa ) are extended into a two‐dimensional network constructed with water molecules linked alternately through intermolecular O—H…O hydrogen bonds, which are further stacked into a three‐dimensional network. Compound (IIIb ) contains two completely asymmetric molecules, which are linked in a disordered manner through intermolecular C—H…O hydrogen bonds. While the crystal stacks in compound (IV) are linked via weak C—H…O hydrogen bonds, the hydrogen‐bonded chains extend helically along the crystallographic b axis.     

Isomorphism in 1‐(2‐halidobenzyl)‐4‐[(E)‐2‐(3‐hydroxyphenyl)ethenyl]pyridinium halide hemihydrates (halide = Cl,Br)

The crystal structures of two (E)‐stilbazolium salts, namely 1‐(2‐chlorobenzyl)‐4‐[(E)‐2‐(3‐hydroxyphenyl)ethenyl]pyridinium chloride hemihydrate, C₂₀H₁₇ClNO⁺·Cl⁻·0.5H₂O, (I), and 1‐(2‐bromobenzyl)‐4‐[(E)‐2‐(3‐hydroxyphenyl)ethenyl]pyridinium bromide hemihydrate, C₂₀H₁₇BrNO⁺·Br⁻·0.5H₂O, (II), are isomorphous; the isostructurality index is 99.3%. In both salts, the azastyryl fragments are almost planar, while the rings of the benzyl groups are almost perpendicular to the azastyryl planes. The building blocks of the structures are twofold symmetric hydrogen‐bonded systems of two cations, two halide anions and one water molecule, which lies on a twofold axis. In the crystal structure, these blocks are connected by means of weaker interactions, viz. van der Waals, weak hydrogen bonding and stacking. This study illustrates the robustness of certain supramolecular motifs created by a spectrum of intermolecular interactions in generating these isomorphous crystal structures.     

Methyl 2‐acetamido‐2‐deoxy‐β‐d‐glucopyranoside dihydrate and methyl 2‐formamido‐2‐deoxy‐β‐d‐glucopyranoside

Methyl 2‐acetamido‐2‐deoxy‐β‐d ‐glucopyranoside (β‐GlcNAcOCH₃), (I), crystallizes from water as a dihydrate, C₉H₁₇NO₆·H₂O, containing two independent molecules [denoted (IA) and (IB)] in the asymmetric unit, whereas the crystal structure of methyl 2‐formamido‐2‐deoxy‐β‐d ‐glucopyranoside (β‐GlcNFmOCH₃), (II), C₈H₁₅NO₆, also obtained from water, is devoid of solvent water molecules. The two molecules of (I) assume distorted ⁴C₁ chair conformations. Values of ϕ for (IA) and (IB) indicate ring distortions towards B_C2,C5 and ^C3,O5B, respectively. By comparison, (II) shows considerably more ring distortion than molecules (IA) and (IB), despite the less bulky N‐acyl side chain. Distortion towards B_C2,C5 was observed for (II), similar to the findings for (IA). The amide bond conformation in each of (IA), (IB) and (II) is trans, and the conformation about the C—N bond is anti (C—H is approximately anti to N—H), although the conformation about the latter bond within this group varies by ∼16°. The conformation of the exocyclic hydroxymethyl group was found to be gt in each of (IA), (IB) and (II). Comparison of the X‐ray structures of (I) and (II) with those of other GlcNAc mono‐ and disaccharides shows that GlcNAc aldohexopyranosyl rings can be distorted over a wide range of geometries in the solid state.     

Tris(3,5‐di­methyl‐1H‐pyrazole‐1‐thio­carboxamidato‐κ2N2,N)­cobalt(III)

In the crystal structure of the title complex, [Co(C₆H₈N₃S)₃], the Co^III atom is octahedrally coordinated by three monodeprotonated bidentate 3,5‐di­methyl‐1H‐pyrazole‐1‐thio­carbox­amide ligands with two thio­carbox­amide N atoms in axial positions. The asymmetric unit contains two mol­ecules (A and B) and these mol­ecules are arranged in chains in an alternating fashion connected by N—H⋯S interactions.     

Lenalidomide,an antineoplastic drug,and its hemihydrate

The crystal structures of lenalidomide [systematic name: (RS)‐3‐(4‐amino‐1‐oxoisoindolin‐2‐yl)piperidine‐2,6‐dione], C₁₃H₁₃N₃O₃, (I), an antineoplastic drug, and its hemihydrate, C₁₃H₁₃N₃O₃·0.5H₂O, (II), have been determined by single‐crystal X‐ray diffraction analysis. The overall conformation of the molecule defined by the orientation of the two ring portions, viz. pyridinedione and isoindolinone, is twisted in both structures. The influence of the self‐complementary pyridinedione ring is seen in the crystal packing of both structures through its involvement in forming hydrogen‐bonded dimers, although alternate dione O atoms are utilized. An extensive series of N—H...O hydrogen bonds link the dimers into two‐dimensional supramolecular arrays built up from infinite chains. The water molecule in (II) has a cohesive function, connecting three lenalidomide molecules by hydrogen bonds. The significance of this study lies in the analysis of the interactions in these structures and the aggregations occurring via hydrogen bonds in the hydrated and dehydrated crystalline forms of the title compound.     

Two tautomeric polymorphs of 2,6‐dichloropurine

Two polymorphs of 2,6‐dichloropurine, C₅H₂Cl₂N₄, have been crystallized and identified as the 9H‐ and 7H‐tautomers. Despite differences in the space group and number of symmetry‐independent molecules, they exhibit similar hydrogen‐bonding motifs. Both crystal structures are stabilized by intermolecular N—H...N interactions that link adjacent molecules into linear chains, and by some nonbonding contacts of the C—Cl...π type and by π–π stacking interactions, giving rise to a crossed two‐dimensional herringbone packing motif. The main structural difference between the two polymorphs is the different role of the molecules in the π–π stacking interactions.     

Two pseudo‐enantiomeric forms of N‐benzyl‐4‐hydroxy‐1‐methyl‐2,2‐dioxo‐1H‐2λ6,1‐benzothiazine‐3‐carboxamide and their analgesic properties

The fact that molecular crystals exist as different polymorphic modifications and the identification of as many polymorphs as possible are important considerations for the pharmaceutic industry. The molecule of N‐benzyl‐4‐hydroxy‐1‐methyl‐2,2‐dioxo‐1H‐2λ⁶,1‐benzothiazine‐3‐carboxamide, C₁₇H₁₆N₂O₄S, does not contain a stereogenic atom, but intramolecular hydrogen‐bonding interactions engender enantiomeric chiral conformations as a labile racemic mixture. The title compound crystallized in a solvent‐dependent single chiral conformation within one of two conformationally polymorphic P2₁2₁2₁ orthorhombic chiral crystals (denoted forms A and B). Each of these pseudo‐enantiomorphic crystals contains one of two pseudo‐enantiomeric diastereomers. Form A was obtained from methylene chloride and form B can be crystallized from N,N‐dimethylformamide, ethanol, ethyl acetate or xylene. Pharmacological studies with solid–particulate suspensions have shown that crystalline form A exhibits an almost fourfold higher antinociceptive activity compared to form B.     

Manipulation of Molecular and Supramolecular Structure in Cobalt(II) Complexes with Tetrachloroterephthalate through the Influence of Different Solvents

The reactions of cobalt acetates with tetrachloroterephthalic acid (H₂BDC‐Cl₄) in different solvents gave two polymeric and one mononuclear Co^II complexes. X‐ray single‐crystal structural determination revealed that the ligand BDC‐Cl₄ displays a reliable bridging tecton to construct diverse supramolecular architectures through coordinative bonds or secondary hydrogen‐bonding interactions. The complexes [Co(BDC‐Cl₄)(DMF)₂(EtOH)₂]_n ( 1 ) and {[Co(BDC‐Cl₄)(DMF)₂(MeOH)₂] · 2DMF}_n ( 2 ) demonstrate a one‐dimensional (1D) coordination motif with infinite Co^II‐tetrachloroterephthalate chains, which are tuned by different binding solvent systems of DMF/ethanol (EtOH) and DMF/methanol (MeOH). [Co(DMF)₂(H₂O)₄] · (BDC‐Cl₄) ( 3 ) represents a two‐dimensional (2D) metallosupramolecular network by hydrogen‐bonded bridging between the aqua ligand of the mononuclear complex with the uncoordinated BDC‐Cl₄ solvates. The spectroscopic, thermal, and fluorescent properties of 1 – 3 were also investigated.     

Three‐dimensional hydrogen‐bonded structures in the hydrated proton‐transfer salts of isonipecotamide with the dicarboxylic oxalic and adipic acid homologues

The structures of the 1:1 hydrated proton‐transfer compounds of isonipecotamide (piperidine‐4‐carboxamide) with oxalic acid, 4‐carbamoylpiperidinium hydrogen oxalate dihydrate, C₆H₁₃N₂O⁺·C₂HO₄⁻·2H₂O, (I), and with adipic acid, bis(4‐carbamoylpiperidinium) adipate dihydrate, 2C₆H₁₃N₂O⁺·C₆H₈O₄²⁻·2H₂O, (II), are three‐dimensional hydrogen‐bonded constructs involving several different types of enlarged water‐bridged cyclic associations. In the structure of (I), the oxalate monoanions give head‐to‐tail carboxylic acid O—H...O_carboxyl hydrogen‐bonding interactions, forming C(5) chain substructures which extend along a. The isonipecotamide cations also give parallel chain substructures through amide N—H...O hydrogen bonds, the chains being linked across b and down c by alternating water bridges involving both carboxyl and amide O‐atom acceptors and amide and piperidinium N—H...O_carboxyl hydrogen bonds, generating cyclic R₄³(10) and R₃²(11) motifs. In the structure of (II), the asymmetric unit comprises a piperidinium cation, half an adipate dianion, which lies across a crystallographic inversion centre, and a solvent water molecule. In the crystal structure, the two inversion‐related cations are interlinked through the two water molecules, which act as acceptors in dual amide N—H...O_water hydrogen bonds, to give a cyclic R₄²(8) association which is conjoined with an R₄⁴(12) motif. Further N—H...O_water, water O—H...O_amide and piperidinium N—H...O_carboxyl hydrogen bonds give the overall three‐dimensional structure. The structures reported here further demonstrate the utility of the isonipecotamide cation as a synthon for the generation of stable hydrogen‐bonded structures. The presence of solvent water molecules in these structures is largely responsible for the non‐occurrence of the common hydrogen‐bonded amide–amide dimer, promoting instead various expanded cyclic hydrogen‐bonding motifs.     

Effect of Bulkiness on Reversible Substitution Reaction at MnII Center with Concomitant Movement of the Lattice DMF: Observation through Single‐Crystal to Single‐Crystal Fashion

The porous coordination polymer ({[Mn(L)H₂O](H₂O)_1.5(dmf)}_n, 1 ) (DMF=N,N‐dimethylformamide) exhibits variety of substitution reactions along with movement of lattice DMF molecule depending upon bulkiness of the external guest molecules. If pyridine or 4‐picoline is used as a guest, both lattice and coordinated solvent molecules are simultaneously substituted (complexes 6 and 7 , respectively). If a bulky guest like aniline is used, a partial substitution at the metal centers and full substitution at the channels takes place (complex 8 ). If the guest is 2‐picoline (by varying the position of bulky methyl group with respect to donor N atom), one Mn^II center is substituted by 2‐picoline, whereas the remaining center is substituted by a DMF molecule that migrates from the channel to the metal center (complex 9 ). Here, the lattice solvent molecules are substituted by 2‐picoline molecules. For the case of other bulky guests like benzonitrile or 2,6‐lutidine, both the metal centers are substituted by two DMF molecules, again migrating from the channel, and the lattice solvent molecules are substituted by these guest molecules (complex 10 and 11 , respectively). A preferential substitution of pyridine over benzonitrile (complex 12 ) at the metal centers is observed only when the molar ratio of PhCN:Py is 95:5 or less. For the case of an aliphatic dimethylaminoacetonitrile guest, the metal centers remain unsubstituted (complex 13 ); rather substitutions of the lattice solvents by the guest molecules take place. All these phenomena are observed through single crystal to single crystal (SC–SC) phenomena.     

Syntheses,crystal structures and blue emission of three zinc(II) coordination polymers with a 4,4′‐dicarboxybiphenyl sulfone ligand

Three novel zinc complexes [Zn(dbsf)(H₂O)₂] ( 1 ), [Zn(dbsf)(2,2′‐bpy)(H₂O)]·(i‐C₃H₇OH) ( 2 ) and [Zn(dbsf)(DMF)] ( 3 ) (H₂dbsf = 4,4′‐dicarboxybiphenyl sulfone, 2,2′‐bpy = 2,2′‐bipyridine, i‐C₃H₇OH = iso‐propanol, DMF = N,N‐dimethylformamide) were first obtained and characterized by single crystal X‐ray crystallography. Although the results show that all the complexes 1–3 have one‐dimensional chains formed via coordination bonds, unique three‐dimensional supramolecular structures are formed due to different coordination modes and configuration of the dbsf^2? ligand, hydrogen bonds and π–π interactions. Iso‐propanol molecules are in open channels of 2 while larger empty channels are formed in 3 . As compared with emission band of the free H₂dbsf ligand, emission peaks of the complexes 1–3 are red‐shifted, and they show blue emission, which originates from enlarging conjugation upon coordination. Copyright © 2006 John Wiley & Sons, Ltd.