Single-crystal To Single-crystal Research Articles

Ligand exchanges and selective catalytic hydrogenation in molecular single crystals

Chemical reactions inside single crystals are likely to be highly selective, but examples of single crystal to single crystal (SC-SC) transformations are uncommon, because crystallinity is difficult to retain following the rearrangement of atoms in the solid state. The most widely studied SC-SC transformations involve solvent exchange reactions in porous coordination polymers or metal-organic frameworks, which take advantage of the robust polymeric networks of the hosts. Examples of reactions occurring within molecular organic crystals generally involve photo-induced reactions, such as the coupling of alkenes or alkynes within the crystal. For nonporous molecular inorganic or organometallic crystals, single-crystal transformations involving the formation or cleavage of metal-ligand bonds are rare; known examples usually involve ligand loss from the single crystal and reversible religation, a process sometimes accompanied by decay of the single crystal to a microcrystalline powder. Here we report a series of SC-SC transformations that involve the interchange of multiple small gaseous ligands (N(2), CO, NH(3), C(2)H(4), H(2) and O(2)) at an iridium centre in molecular single crystals of a pincer Ir(I) complex. The single crystal remains intact during these ligand-exchange reactions, which occur within the crystal and do not require prior ligand extrusion. We reveal a selective catalytic transformation within a nonporous molecular crystal: pincer iridium single crystals ligated with nitrogen, ethylene or hydrogen show selective hydrogenation of ethylene relative to propylene (25:1) when surface sites are passified by CO.

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)H(2)O](H(2)O)(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.

Porous Coordination Polymer with Flexibility Imparted by Coordinatively Changeable Lithium Ions on the Pore Surface

Solvothermal reactions of equimolar zinc acetate, lithium acetate, and 1,3,5-benzenetricarboxylic acid (H(3)btc) in different mixed solvents yielded isostructural three-dimensional frameworks [LiZn(btc)(cG)].lG [cG and lG denote coordinated and lattice guests, respectively; cG = (nmp)(0.5)(H(2)O)(0.5), lG = (EtOH)(0.5) (1a); cG = H(2)O, lG = EtOH (1b); nmp = N-methyl-2-pyrrolidone] with one-dimensional channels occupied by guest molecules and solvent-coordinated, extrusive Li(+) ions. Thermogravimetry analyses and powder X-ray diffraction measurements revealed that both 1a and 1b can lose all lattice and coordinated guests to form a desolvated phase [LiZn(btc)] (MCF-27, 1) and almost retains the original framework structure. Gas adsorption measurements on 1 confirmed its permanent porosity but suggested a structural transformation from 1a/1b to 1. It is noteworthy that only 1a can undergo a single-crystal to single-crystal (SCSC) transformation into 1 upon desolvation. The crystal structure of 1 revealed that the Li(+) ions were retracted into the channel walls via complementary coordination to the carboxylate oxygen atoms in the framework rather than being exposed on the pore surface. Single-crystal X-ray diffraction analyses were also performed for N(2)- and CO(2)-loaded samples of 1, revealing that the framework remained unchanged when the gases were adsorbed. Although the gas molecules could not be modeled, the residue electrons inside the channels demonstrated that the retracted Li(+) ions still behave as the primary interacting site for CO(2) molecules. Nevertheless, solvent molecules such as H(2)O can readily compete with the framework oxygen atom to retrieve the extrusive Li(+) ions, accompanying the reverse structural transformation, i.e., from 1 to 1a/1b.

Single-crystal to single-crystal transformations in discrete hydrated dimeric copper complexes

The single crystals of discrete hydrated [(OAc)Cu(mu-hep)(2)Cu(OAc)].2H(2)O (.2H(2)O) and [(OAc)Cu(mu-hep)(2) Cu(O(n)Pr)].2H(2)O (.2H(2)O) (the lattice H(2)O molecules exist as a tetrameric water cluster, hep-H = 2-(2-hydroxyethyl)pyridine), OAc(-) = acetate and O(n)Pr(-) = n-propionate) undergo single-crystal to single-crystal (SCSC) transformations to the dehydrated and , respectively, under the influence of heat. The reverse SCSC processes of /-->.2H(2)O/.2H(2)O involving the regeneration of the lattice water tetramers take place on exposure of / to water vapour. However, the blue single crystal of discrete hydrated [(O(n)Pr)Cu(mu-hep)(2)Cu(O(n)Pr)].2H(2)O (.2H(2)O), incorporating the two bulkier O(n)Pr(-) terminal bidentate ligands, irreversibly converts to the green single crystal of a unique discrete tetrameric [Cu(4)(mu(3)hep)(2)(mu-hep)(2)(mu-O(n)Pr)(2)(O(n)Pr)(2)] () with double open cubane core either by heating or by a simple vapour diffusion technique via the breaking and forming of multiple covalent bonds.

The central metal ion exchange of a ferrocenyl carboxylate zinc complex

Ferrocenyl carboxylate zinc complex {[Zn(η2-OOCH4C6Fc)(OOCH4C6Fc)(btx)]2(CH3OH)(H2O)2} 1 (FcC6H4COONa=sodium m-ferrocenylbenzoic; btx=1,4-bis(triazol-1-ylmethyl)benzene) has been synthesized and structurally characterized. In order to further investigate the central metal ion exchange reaction, we immersed the selectable single crystal of 1 into aqueous solutions of Pb-(NO3)2, and obtained a single-crystal to single-crystal (SCTSC) transformation product {[Zn(0.83)Pb(0.17)-(η2-OOCH4C6Fc)(OOCH4C6Fc)(btx)]2(H2O)(1.5)} (2). 2 is characterized by EA, IR, XRD, ICP, EDS, atom absorption and X-ray single crystal determination. Our results show that the ferrocenyl carboxylate zinc complex can be used as an effective central metal ion exchange material for removing lead ion and set the stage for using analogous metal carboxylate for selective exchange of other cations.

Diamondoid Three-Dimensional Metal-Organic Framework Showing Structural Transformation with Guest Molecules

The potential of carboxylate and imidazole-based mixed ligands for forming metal organic frameworks (MOFs) is demonstrated with 4-(1H-imidazole-1-yl)benzoic acid (HIBA) to generate a flexible material. Reaction of HIBA with Cd(NO3)2·6H2O under solvothermal condition in N,N-dimethylformamide (DMF), produces a three-dimensional MOF, {[Cd(IBA)2].2DMF}n (1⊃2DMF), which on heating at 60 and 200 °C turns opaque, forming {[Cd(IBA)2]·DMF}n (1⊃DMF) and {[Cd(IBA)2]}n (1), respectively, as characterized by PXRD, TGA, and elemental analysis. Either of these compounds on keeping in dry DMF for 15 days affords the original compound, i.e., showing reversibility deduced from PXRD. When a crystal of 1⊃2DMF is immersed in moist N,N-diethylformamide (DEF) in a vial open to atmosphere, a new compound, {[Cd(IBA)2]·DEF·H2O}n, (2) is formed in 1 month in a single-crystal to single-crystal (SC-SC) fashion. Also, a crystal of 1⊃2DMF on immersing in moist DMF produces another interesting 3D framework {[Cd(IBA)2.H2O]·DMF·3H2O}n, (3) in a SC-SC transformation. These coordination polymers show interesting 4-fold interpenetrating diamondoid 3D network structures.

Study on the Reaction of Polymeric Zinc Ferrocenyl Carboxylate with Pb(II) or Cd(II)

In this paper, the reaction of polymeric zinc ferrocenyl carboxylate, {[Zn(OOCClH3C6Fc)2(H2O)3](CH3OH)}n (1; FcC6H3ClCOONa = sodium 2-chloro-4-ferrocenylbenzoic), with Pb(NO3)2 or Cd(NO3)2 was investigated. By immersion of selected big single crystals of 1 into aqueous solutions of Pb(NO3)2 and Cd(NO3)2, respectively, two central metal ion exchange induced single-crystal to single-crystal (SCTSC) transformation products, {[Zn0.74Pb0.26(OOCClH3C6Fc)2(H2O)3](H2O)}n (2) and {[Zn0.82Cd0.18(OOCClH3C6Fc)2(H2O)3](H2O)}n (3), could be obtained. In contrast to above-mentioned SCTSC products, 1 can dissolve well in THF solution, and the reaction of the solution containing 1 with Pb(NO3)2 or Cd(NO3)2 results in a 1-D Pb(II) polymer, [Pb(μ2-η2-OOCClH3C6Fc)2(CH3OH)2]n (4), and a mononuclear Cd(II) complex, {[Cd(η2-OOCClH3C6Fc)2(H2O)3](CH3OH)2} (5). Our results indicate that metal ion exchange can be implemented through heterogeneous or homogeneous pathways and suggest an easy means to remove lead and cadmium ions. At ...

Vapor-Diffusion-Mediated Single Crystal-to-Single Crystal Transformation of a Discrete Dimeric Copper(II) Complex to a Discrete Tetrameric Copper(II) Complex

The symmetric dimeric complex [Cu(mu(2)-hep)(TFA)(H(2)O)](2) (1) has been synthesized from 2-(2-hydroxyethyl)pyridine (hep-H), trifluoroacetic acid (TFA-H), and copper acetate in a 95:5 (v/v) MeOH-H(2)O mixture at 298 K. Each Cu(II) ion in 1 is linked with two mu(2)-alcoholic oxygen atoms and one pyridine nitrogen atom of hep, and the other two coordination sites are occupied by the oxygen donors of TFA and H(2)O. At room temperature, the blue single crystals of 1 transform to the green single crystals of a tetrameric complex, [Cu(4)(mu(3)-hep)(2)(mu(2)-hep)(2)(mu(2)-TFA)(2)(TFA)(2)] (2), in presence of alcoholic vapor. The facile single crystal-to-single crystal (SCSC) transformation of 1 to 2 is accompanied by the removal of coordinated H(2)O molecules in 1 and concomitant formation of four new covalent bonds, two Cu-O(mu(3)-hep) and two Cu-O(mu(2)-TFA). The SCSC transformation of 1 to 2 is selective to the alcoholic vapor; the exposure of single crystals of 1 to heat or light or in vacuum has resulted in an immediate loss in crystallinity.

Co(ii) and Cr(iii) complexes of formate–formamide mixed ligands: synthesis, structures, single crystal-to-single crystal transformation and magnetic behaviour

Solvothermal treatment of an equimolar mixture of Co(NO(3))(2).6H(2)O, HCONH(2) and NaN(3) in MeOH at 100 degrees C yielded a three-dimensional NaCl type network Co(HCOO)(2)(HCONH(2))(2).HCONH(2) (1a) containing formamides in the pores of the structure. Solvated pink 1a undergoes single crystal-to-single crystal (SCSC) transformation at 215 degrees C to form the desolvated dark brown product Co(HCOO)(2)(HCONH(2))(2) (1b) with the retention of the original framework. Reversible single crystal-to-single crystal transformation of 1b (brown) to 1a (pink) in the presence of excess formamide was also established at room temperature. The coordination environment around Co(II) in both 1a and 1b is octahedral with a CoN(2)O(4) coordination composition. A similar reaction replacing Co(II) by Cr(III) produced a heterometallic 3D extended network Na[Cr(HCOO)(4)(HCONH(2))(2)].2H(2)O (2a) at 100 degrees C. An increase in reaction temperature to 150 degrees C produced a simple mononuclear complex Cr(HCOO)(3)(HCONH(2))(3).3H(2)O (2b). Variable temperature magnetic studies revealed the presence of a canting phenomena in both 1a and 1b, and hysteresis loop in the field dependent magnetisation plot at 2 K whereas complex 2a is simply paramagnetic in nature.

Metal-directed assembly of two 2-D 4d–4f coordination polymers based on elliptical triple-deck cylinders hinged by meso-double helical chains

Two 2-D 4d–4f coordination polymers based on elliptical triple-deck cylinders hinged by meso-helical chains containing an isonicotinate ligand, namely, {[Ag2Ln(IN)4(H2O)2]·(NO3)·(H2O)}n (Ln = Sm and Eu, IN− = isonicotinate), have been successfully constructed through the transformation of a single-crystal to single-crystal (SC-SC) or different metal–organic polymer units, in which the recognition between the organic ligand and two types of metal ions direct the formation of the final productions.

A Rare Thermally Induced Single Crystal to Single Crystal Transformation from a 2D Chiral Coordination Polymer to a 3D Chiral Coordination Polymer

AbstractA rare single‐crystal to single crystal (SCSC) transformation assisted by hydrogen bonding was induced thermally. A2D homochiral coordination polymer {[Ni2(L‐tar)2(H2O)2](H2O)3}∞ was irreversibly converted into a 3D homochiral coordination polymer, and the structure was confirmed by X‐ray crystallography and XRD. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Single-Crystal to Single-Crystal Structural Transformation and Photomagnetic Properties of a Porous Iron(II) Spin-Crossover Framework

The porous coordination framework material, Fe(NCS)2(bped)2 x 3EtOH, SCOF-3(Et) (where bped is dl-1,2-bis(4'-pyridyl)-1,2-ethanediol), displays a spin-crossover (SCO) transition that has been stimulated both thermally and by light irradiation. The one-step thermal SCO (70-180 K) is sensitive to the presence of molecular guests, with a more gradual transition (70-225 K) apparent following the desorption of ethanol molecules that hydrogen bond to the spin centers. Additional intraframework hydrogen-bonding interactions stabilize the vacant one-dimensional pore structure of the apohost, SCOF-3, despite a dramatic single-crystal to single-crystal (SC-SC) structural change upon removal of the guests. Comprehensive structural analyses throughout this transformation, from primitive orthorhombic (Pccn) to body-centered tetragonal (I4/mcm), reveal a flexing of the framework and a dilation of the channels, with an accompanying subtle distortion of the iron(II) coordination geometry. Photomagnetic measurements of the light-induced excited spin state trapping (LIESST) effect have been used to assess the degree of cooperativity in this system.

Solvent‐Free Photosynthesis of Cyclobutanes: Photodimerization of Crystalline Olefins

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Single Crystal to Single Crystal Structural Transformations in Molecular Framework Materials

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Heteroditopic Rebek's Imide Directs the Reactivity of Homoditopic Olefins within Desolvated Quaternary Assemblies in the Solid State

Molecules with two different binding sites are important constructs in supramolecular chemistry. Such heteroditopic molecules are designed, a priori, to assemble two different molecules and/or ions within ternary complexes, a process which is exploitable in areas such as separations, nucleobase recognition, and replication. Whereas recent studies involving heteroditopic molecules have focused largely on the binding of ion pairs and the programmed assembly of metallosupramolecular architectures, the application of heteroditopic molecules as “artificial enzymes” that direct the formation of covalent bonds remains a worthy goal. Indeed, since the work of Kelly et al. that described a heteroditopic molecule that employed hydrogen bonds to orient two different molecules in solution for an SN2 reaction, advances have been made in our understanding of self-assembly such that complexes that transcend the ternary level are now viable targets in supramolecular syntheses and may be used to direct the formation of covalent bonds. With this in mind, we report here the ability of a heteroditopic molecule, in the form of Rebek1s imide (Rebim), to direct a solid-state reaction in which a covalent bond is formed (Scheme 1). Specifically, we reveal that Reb-im assembles two molecules of trans-1,2-bis(4-pyridyl)ethylene (4,4’-bpe) within a solvated quaternary complex, in 1·toluene (where 1= {(Reb-im)·(4,4’-bpe)}2), which reacts through an intermolecular [2+2] photodimerization and a rare single crystal to single crystal (SCSC) transformation to give rctttetrakis(4-pyridyl)cyclobutane (4,4’-tpcb) stereospecifically in up to 100% yield. We demonstrate that Reb-im assembles two identical olefins with two identical recognition sites and, thus, exhibits a novel and unusual form of degeneracy in its recognition abilities. We also provide evidence that supports the structures of such hydrogen-bonded complexes being remarkably robust, being able to operate in the wake of an induced desolvation and phase transition of the solid. 16] To our knowledge, Reb-im is the first example of a heteroditopic molecule that directs a chemical reaction in the solid state. Our choice of Reb-im as a heteroditopic molecule that directs a [2+2] photodimerization stems from the nature and

Single Crystal to Single Crystal Transformations

The past decade has witnessed escalating interest in solidstate phase transitions that involve significant changes in structure without appreciable loss of crystal mosaicity— single crystal to single crystal (SC-SC) transformation.[1–5] Several factors have contributed to these studies: increased general access to X-ray diffraction facilities, softwareassisted demystification of crystallography, technological developments leading to rapid intensity data collection, and the popularization of crystal engineering as a research field. The two most active areas of interest with regard to SC-SC transformations are the development of porous materials and solventless topochemical reactions. Recent new results representing the current state-of-the-art with regard to both of these topics are reported in the Research Front of this issue of the Australian Journal of Chemistry. In 1988 Dunitz, Schomaker, and Trueblood recounted a prior statement by Nobel Laureate (chemistry, 1939) Leopold Ruzicka, that ‘a crystal is a chemical cemetery’. This was interpreted to imply that, in sharp contrast to liquids and gases, the solid state consists of molecules that are lifelessly interred in fixed geometrical arrangements with little prospect of an interesting existence.[6] However, it has long been known that structural rearrangement can occur in the solid state in response to a variety of physical or chemical factors. Provided that these structural changes are subtle, it is reasonable to expect that the relative absence of mechanical stress would allow individual crystals to retain their mosaicity, both during and after transformation. In most cases, though, changes of the chemical composition and/or molecular conformation and/or packing arrangement within crystals are well known to cause catastrophic disruption of packing continuity. Concomitant fracturing of

Single Crystal to Single Crystal Structural Transformations in Molecular Framework Materials

The rapid advance in the synthesis and characterization of molecular frameworks over the past decade has opened an entirely new approach for the generation of nanoporous materials. With this advance has come an increasingly pressing need for the development of new techniques to characterize the guest-dependent structures of these novel and highly complex materials. In this review we highlight some of the relatively rare cases where single crystal diffraction has been used to characterize the flexible structures of molecular frameworks through the investigation of single crystal to single crystal (SC-SC) transformations.