Coordination motifs in modern supramolecular chemistry

In this paper we describe the contribution of coordination chemistry to the creation and development of supramolecular chemistry. Both discrete- and infinite buildups are examined. The first group comprises metal-containing host molecules and organic acceptors for metal cations; the second includes coordination polymers, ionic -and liquid crystals. Their potential- and practical applications are briefly explained.     

Coordination structures and supramolecular architectures in a cerium(III)-malonamide solvent extraction system

The process chemistry and solution structures investigated in the title system bridge the three ostensibly disparate fields of separation sciences, soft matter research, and coordination chemistry. We have explored this subject with synchrotron radiation research and advanced analyses leading to original insights into aggregation phenomena in solvent extraction. Herein we present findings showing the coagulation of reverse micelles into wormlike aggregates in organic phases (N,N'-dimethyl-N,N'-dibutyltetradecylmalonamide-abbreviated as DMDBTDMA-in n-dodecane) obtained by liquid-liquid extraction following contact with acidic and neutral aqueous media containing trivalent cerium. The growth of solute architectures was shown to prelude phase transition (i.e., the formation of a "third phase"). The presence of acid was shown to promote the growth of these micellar chains and, therefore, promoted third-phase formation. Acid was also shown to hydrate and swell the reverse micelle units, preorganizing them to allow for incorporation of cerium, leading to different coordination structures and enhanced metal extraction. The approach of linking both the coordination environment and supramolecular structures to the process properties of a solvent extraction system in a single study provides perspectives that are not available from independent, uncorrelated experimentation. Moreover, the analysis of small-angle X-ray scattering data from a solvent extraction system using the generalized indirect Fourier transform method to gain real-space information led to insights not otherwise available, showing that micellar assemblies are larger and more ordered than previously thought. This multipronged and multidisciplinary investigation opens new avenues in the evolving understanding of solute architectures in organic phases of practical relevance to solvent extraction and, simultaneously, of fundamental relevance to structured fluids and, in particular, phase transition phenomena.     

Mechanism of N-octadecyl-N'-maleoyl-L-phenylalanine self-assembled into supramolecular structures

N-Octadecyl-N'-maleoyl-L-phenylalanine (ODMA-L-Phe) was synthesized through the condensation, deprotection and aeid-ylation reaction of BOC-L-phenylalanine, octadecylamine and maleic anhydride. ODMA-L-Phe can self-assemble in some organic solvents and turned them into thermally reversible physical supramolecular organogels. The morphology of ODMA-L-Phe aggregates was characterized by polarized optical microscopy (POM) and field emission scanning electron microscope (FE-SEM). The aggregates of ODMA-L-Phe were needle-like fibrils with diameters of approximately 100-200 nm. The mechanism of ODMA-L-Phe self-assembly in organic solvents was investigated using 1H NMR and circular dichroism (CD). The results indicated that hydrogen bonding was one of the main driving forces for the self-assembly of ODMA-L-Phe.     

Topology of supramolecular structures in ethanol solutions

A quantitative topological analysis of supramolecular structures in ethanol solutions with methanol, propanol, water, benzene, and hexane is performed by the MDGT method previously proposed by the authors. The method is based on a combination of molecular dynamics calculations and the graph theory, which enables the recognition and memorization of supramolecular structures observed in each snapshot of the molecular dynamic trajectory, the averaging of data for any number of these snapshots. Thus, the averaged concentrations of associates (dimers, trimers, etc.) are represented and then the concentrations and characteristics of isomers (e.g., chains, branched chains, rings, etc.), bond lengths, angles, etc. are determined in each group of associates.     

Macromolecules with specific constitution and supramolecular structures

Segmented triblock and multiblock copolymers consisting of highly flexible polydisperse segments and molecularly uniform segments of well defined architecture capable of either the formation of a mesophase, chainfolded crystallites or double-helical metal complexes have been synthesized; the bulk superstructure as well as the physical and material properties correlated with the primary structure: block copolymers with liquid crystalline segments formed microphase separated systems, and the phase behaviour depended on the constitutional composition. Multiblock copolymers with symmetrically chain-folded polyurethane hard segments and associative groups in the chain fold led to specially shaped lamellar superstructures. Block copolymers with bipyridine containing segments gave tetracoordinated and double-helical copper(I) complexes which segregated resulting in supramolecular polymer systems.     

Assembly of ethylzincate compounds into supramolecular structures

Sodium and potassium triethylzincate were isolated by Wanklyn in 1858, and are corner stones in the history of organometallic chemistry. Crystallisation of organozincates from neat dialkylzinc, in the absence of a coordinating solvent, can be expected to result in assembly of supramolecular structures, rather than formation of discrete molecules in the crystalline state. This inspired us to reinvestigate Wanklyn’s classical compounds. Crystallisation of sodium triethylzincate from benzene led to metallation of benzene and the formation of diethylphenylzincate anions. The compound is a two-dimensional network where Na⁺ ions link the zincate anions by coordination to both ethyl- and phenyl groups. We have also, accidently, isolated crystals of the two-dimensional coordination network [K₂(ZnEt₂)₄O]_n, displaying a rare oxo-centred core with an octahedral oxide ion surrounded by four zinc atoms and two potassium atoms.     

Solid-state supramolecular structures of resorcinol-arylboronic acid compounds

[structure: see text] An X-ray crystallographic study of unique hydrogen-bonded supramolecular solid-state networks comprised of a tetraarylboronic acid resorcinarene is described. When 1 is recrystallized from 9:1 MeOH:EtOH, partial esterification takes place to give compound 2, the corresponding half methyl ester, which forms an infinite two-dimensional array. Each molecule participates in 12 hydrogen bonds with other macrocycles. These hydrogen bonds are both B-OH- - - OH (phenolic) and OH (phenolic)- - -OH (phenolic).     

Hydrogen-bonded supramolecular structures constructed from trinuclear copper units

Four copper complexes with similar trinuclear copper units, [Cu₆(Bmshp)₂(SO₄)₂(H₂O)₇]·2H₂O (1), [Cu₃(Bmshp)(ClO₄)₂(H₂O)₄]·5H₂O (2), [Cu₃(Bmshp)(DMF)₄(H₂O)₂]·H₂O·2DMF·2ClO₄ (3) and [Cu₃(H₂Bcshp)(ClO₄)₂(H₂O)₄]·3H₂O (4) (H₄Bmshp = 2,6-bis[(3-methoxysalicylidene)hydrazinocarbonyl]pyridine, H₆Bcshp = 2,6-bis[(3-carboxylsalicylidene)hydrazinocarbonyl]pyridine), were synthesized and characterized by elemental analysis, IR and single crystal X-ray diffraction analysis. Due to the different anions, solvents and ligands used in the syntheses, complexes 1–4 exhibit diverse supramolecular structures constructed from the corresponding trinuclear copper units via H-bonds.     

Self-assembly of heterogeneous supramolecular structures with uniaxial anisotropy

Uniaxial anisotropy in two-dimensional self-assembled supramolecular structures is achieved by the coadsorption of two different linear molecules with complementary amine and imide functionalization. The two-dimensional monolayer is defined by a one-dimensional stack of binary chains, which can be forced to line up along steps in vicinal surfaces. The competing driving forces in the self-organization process are discussed in light of the structures observed during single molecule adsorption and coadsorption on flat and vicinal surfaces and the corresponding theoretical calculations.     

Coordination chemistry of phosphole ligands: From supramolecular assemblies to OLEDs

The synthesis and properties of organophosphorus π-conjugated chromophores incorporating metallic ions are described. Their optical and electrochemical properties depend on the metal centre linked to the organophosphorus atom. Moreover, the introduction of metallic ions induces a control of the supramolecular organization of the organophosphorus π-conjugated systems. The specific properties of these complexes make them valuable materials for organic light-emitting diodes and interesting building blocks for the tailoring of novel NLO-phores.     

Coordination studies on supramolecular chiral ligands and application in asymmetric hydroformylation

In this study we introduce a series of monodentate pyridine-based ligands for which the phosphorus coordination mode to rhodium can be controlled by the binding of Zn(II)-templates to the pyridyl group. A series of monodentate phosphoroamidite and phosphite ligands have been prepared and studied under hydroformylation conditions by in situ high-pressure NMR and IR techniques. These studies reveal the exclusive formation of rhodium hydride complexes in which the phosphorus atom of the ligand resides in an axial position, trans to the hydride, but only after addition of Zn(II)-template. In the absence of these templates the usual mono-coordinated rhodium hydrido complexes are formed, with the phosphorus ligated in the equatorial plane, cis to the hydride. The catalytic performance of these complexes is evaluated in asymmetric hydroformylation of unfunctionalised internal alkenes in which the supramolecular change is reflected in higher activity and selectivity.     

Coordination polymers and supramolecular structures in Ag(I)triflate-dppf systems (dppf=1,1-bis(diphenylphosphino)ferrocene)

The interaction of silver triflate (OTf⁻=SO₃(CF₃)⁻) and dppf [(C₅H₄PPh₂)₂Fe)] gave different complexes, depending on the stoichiometric proportions and reaction conditions. Under limiting dppf conditions, three different forms (1-3) of [Ag₂(OTf)₂(dppf)]_x were isolated. Single crystal X-ray diffraction analyses showed that the structure of 1 (x=2n) consists of a 2-D polymer comprising a tetra-silver basic unit, while that of 2 (x=2) possesses a discrete tetra-silver framework and that of 3 (x=n) is a linear polymer based on a di-silver repeating unit. The structures are supported by bridging dppf ligands and triflate groups. The crystal lattices of the compounds are stabilized by extensive intermolecular C-H?X hydrogen bonding (H=ring proton of Cp or Ph of dppf; X=O or F of OTf). [Ag(dppf)(OTf)] (4) and the structurally characterized mononuclear [Ag(dppf)₂](OTf) (5) were the sole products obtained from treatment of AgOTf with dppf in molar ratios of 1:1 and 1:2, respectively.     

Hydrogen-bond-assisted supramolecular 1-D tape-like structures of mesogenic bis-pyrazoles

Two new series of isomeric bis-pyrazoles 1a–b are prepared, characterized, and their mesomorphic properties investigated. These pyrazoyl derivatives were obtained from the condensation of α,β-diketones 2a–b with hydrazine monohydrate in refluxing THF. Two single crystallographic structures of compounds mesogenic 1a (n=14) and nonmesogenic 1b (n=8) were determined by X-ray analysis. Both 1a–14 and 1b–8 crystallize in a triclinic space group P?1 and monoclinic C2/c group, respectively. An extended H-bonded structure was formed in both crystal lattices, giving a pseudo 1D-polymeric tape-like structure. Derivatives 1a exhibited smectic A/C mesophases, in contrast, derivatives 1b were all nonmesogenic. The difference in mesomorphic behavior was attributed to the between linear conformation and the coplanarity of the five rings over than in 1a. The correlation between the molecular structures and the mesomorphic properties is discussed.     

New titanium imido synthons: syntheses and supramolecular structures

Reactions of Ti(NMe(2))(2)Cl(2) with a wide range of primary alkyl and arylamines RNH(2) afforded the corresponding 5-coordinate imido titanium compounds Ti(NR)Cl(2)(NHMe(2))(2) (R = (t)Bu (1), (i)Pr (2), CH(2)Ph (3), Ph (4), 2,6-C(6)H(3)Me(2) (5), 2,6-C(6)H(3)(i)Pr(2) (6), 2,4,6-C(6)H(2)F(3) (7), 2,3,5,6-C(6)HF(4) (8), C(6)F(5) (9), 4-C(6)H(4)Cl (10), 2,3,5,6-C(6)HCl(4) (11), 2-C(6)H(4)CF(3) (12), 2-C(6)H(4)(t)Bu (13)). The compounds 1-13 are monomeric in solution but in the solid state form either N-H...Cl hydrogen bonded dimers or chains or perfluorophenyl pi-stacked chains, depending on the imido R-group. The compound 13 was also prepared in a "one-pot" synthesis from RNH(2) and Ti(NMe(2))(4) and Me(3)SiCl. Reaction of certain Ti(NR)Cl(2)(NHMe(2))(2) compounds with an excess of pyridine afforded the corresponding bis- or tris-pyridine analogues [Ti(NR)Cl(2)(py)(x)](y) (x = 3, y = 1; x = y = 2), and the structure of Ti(2)(NC(6)F(5))(2)Cl(2)(mu-Cl)(2)(py)(4) shows pi-stacking of perfluorophenyl rings. Reaction of Ti(NMe(2))(2)Cl(2) with cross-linked aminomethyl polystyrene gave quantitative conversion to the corresponding solid-supported titanium imido complex. This paper represents the first detailed study of how supramolecular structures of imido compounds may be influenced by simple variation of the imido ligand N-substituent.     

Solution NMR techniques for large molecular and supramolecular structures

Transverse relaxation-optimized spectroscopy (TROSY) or generation of heteronuclear multiple quantum coherences during the frequency labeling period and TROSY during the acquisition period have been combined either with cross-correlated relaxation-induced polarization transfer (CRIPT) or cross-correlated relaxation-enhanced polarization transfer (CRINEPT) to obtain two-dimensional (2D) solution NMR correlation spectra of (15)N,(2)H-labeled homo-oligomeric macromolecules with molecular weights from 110 to 800 kDa. With the experimental conditions used, the line widths of the TROSY-components of the (1)H- and (15)N-signals were of the order of 60 Hz at 400 kDa, whereas, for structures of size 800 kDa, the line widths were about 75 Hz for (15)N and 110 Hz for (1)H. This paper describes the experimental schemes used and details of their setup for individual measurements. The performance of NMR experiments with large structures depends critically on the choice of the polarization transfer times, the relaxation delays between subsequent recordings, and the water-handling routines. Optimal transfer times for 2D [(15)N,(1)H]-CRIPT-TROSY experiments in H(2)O solutions were found to be 6 ms for a molecular weight of approximately 200 kDa, 2.8 ms for 400 kDa, and 1.4 ms for 800 kDa. These data validate theoretical predictions of inverse proportionality between optimal transfer time and size of the structure. The proton longitudinal relaxation times in H(2)O solution were found to be of the order of 0.8 s for structure sizes around 200 kDa, 0.4 s at 400 kDa, and 0.3 s at 800 kDa, which enabled the use of recycle times below 1 s. Since improper water handling results in severe signal loss, the water resonance was kept along the z-axis during the entire duration of the experiments by adjusting each water flip-back pulse individually.     

Construction of nonanuclear supramolecular structures from simple modular units

A porphyrazine based supramolecule with a nonanuclear structure has been prepared by the ready coordination of pyridine donor sites in octakis(4-pyridoxyethylthio)porphyrazinatomagnesium with vanadyl bis(acetylacetonate) and characterized by EPR spectroscopy.     

Mechanism of N-octadecyl-N1-maleoyl-L-phenylalanine self-assembled into supramolecular structures

N-Octadecyl-N1-maleoyl-L-phenylalanine （ODMA-L-Phe） was synthesized through the condensation, deprotection and acid- ylation reaction of BOC-L-phenylalanine, octadecylamine and maleic anhydride. ODMA-L-Phe can self-assemble in some organic solvents and turned them into thermally reversible physical supramolecular organogels. The morphology of ODMA-L-Phe aggregates was characterized by polarized optical microscopy （POM） and field emission scanning electron microscope （FE-SEM）. The aggregates of ODMA-L-Phe were needle-like fibrils with diameters of approximately 100-200 nm. The mechanism of ODMA- L-Phe self-assembly in organic solvents was investigated using XH NMR and circular dichroism （CD）. The results indicated that hydrogen bonding was one of the main driving forces for the self-assembly of ODMA-L-Phe.