Coordination polymers with macrocyclic cages and pockets within their backbones

The reaction between the flexible ligand (1,4-bis(pyridine-2-yl-methanethio)benzene) and Ag+ produces two novel coordination polymers with macrocyclic cages or pockets contained within their backbones, depending upon the ratio of starting materials.     

Guest-dependent flexible coordination networks with fluorinated ligands

Guest-dependent flexible coordination networks are formed from 1,4-bis(4-pyridylmethyl)tetrafluorobenzene (bpf), 4,4'-bis(4-pyridylmethyl)octafluorobiphenyl (bpfb), 2,6-bis(4-pyridylmethyl)hexafluoronaphthalene (2,6-bpfn), and 2,7-bis(4-pyridylmethyl)hexafluoronaphthalene (2,7-bpfn) with Cd(NO3)2 in the presence of various organic compounds. The reaction of bpf affords one-dimensional cyclic chains, two-dimensional rhombus grid sheets, and three-dimensional diamond frameworks with threefold interpenetration. The reaction of bpfb mainly affords two-dimensional rhombus grid sheets with twofold parallel interpenetration. The reaction of 2,6-bpfn affords a one-dimensional ladder and two-dimensional rhombus grid, twisted grid, and herringbone sheets. The reaction of 2,7-bpfn affords two-dimensional rhombus grid sheets and grid sheets with dumbbell-shaped cavities. This diversity of network topologies is induced by interactions between the guest molecules and the flexible ligand frameworks.     

Coordination modes of some fluorinated,potentially polydentate,ligands

Through the use of template condensation reactions, we have developed synthetic routes to a number of fluorinated ligands containing a number of donor atoms in combination with a fluorinated alkoxy group. Typical examples are:

We find all of these to be capable of coordination to transition metals, generally giving stable, neutral, complexes. However, the mode of coordination of (i) and (ii) differs according to the donor atoms present in the chain, with a higher degree of coordination for X = N than for X = O. With ligand (iii), a ‘tripod’ mode of coordination is favoured, with the six donor sites surrounding a 3+ metal ion such as iron(III), cobalt(III), or a lanthanide(III) species.     

Nanostructured hybrid networks based on highly fluorinated acrylates

A dual-curing process is described for obtaining highly fluorinated acrylic networks containing nanosilica. The new materials showed improved hardness, while maintaining the hydrophobicity of the fluorinated polymer. They were obtained by UV-curing a suitable mixture of a perfluoropolyetherurethanediacrylate and alkoxysilanes, followed by a thermal treatment during which the sol–gel process took place. The obtained crosslinked networks had a complex morphology: nanometric silica particles were formed, as observed by TEM, and embedded in a biphasic crosslinked matrix made of perfluoropolyether domains and of copolymeric crosslinked domains containing the polyurethane acrylic units and siloxane chains formed by the alkoxides condensation.     

Metal-controlled self-assembly of arsenic-vanadium-cluster backbones with organic ligands

Five new organic-inorganic assemblies, [Co(en)(3)][Co(en)(2)As(8)V(14)O(42)(H(2)O)].16H(2)O (1), [Ni(Meen)(3)](4)[Ni(Meen)(2)][As(8)V(14)O(42)(NO(3))](2).8H(2)O (2), [Cd(en)(3)][Cd(phen)(en)(H(2)O)(2)][(en)CdAs(8)V(13)O(41)(H(2)O)].1.5H(2)O (3), [Cd(phen)(2)(en)](2)[(phen)CdAs(8)V(13)O(41)(H(2)O)].21H(2)O.phen (4), [Zn(en)(2)](2)[(bpe)(2)Zn(2)As(8)V(12)O(40)(H(2)O)] (5) (en = ethylenediamine, Meen = 1,2-diaminopropane, phen = 1,10-phenanthroline, and bpe= 1,2-bis(4-pyridyl)ethylene) have been synthesized and characterized. Among them, compounds 1 and 2 are constructed from the [As(8)V(14)O(42)] cluster; compounds 3 and 4 are constructed from the Cd-substituted polyoxovanadate [CdAs(8)V(13)O(41)] cluster, while compound 5 consists of bizinic-substituted polyoxovanadate [Zn(2)As(8)V(12)O(40)] building units. It can be assumed that the metal ions used in these reaction systems play a crucial role in controlling the formation of the arsenic-vanadium-cluster backbones, and further leading to the formation of hybrids based on these clusters.     

Unique Zn(II) coordination entanglement networks with a flexible fluorinated bis-pyridinecarboxamide tecton and benzenedicarboxylates

Entangled nets in coordination compounds with both self-penetrating and interpenetrating structural features have been first constructed by using a flexible bis-pyridinecarboxamide and isophthalate or 5-methylisophthalate. Distinct entangled systems showing both 3-fold interpenetration and polyrotaxane can also be obtained by altering the 5-substituents of isophthalate.     

Biomimetic facially amphiphilic antibacterial oligomers with conformationally stiff backbones

A foldamer has been designed with a conformationally stiff backbone that is facially amphiphilic. The oligomer has excellent antimicrobial activity and was found to be 18 times more active toward bacterial cells than human red blood cells. The oligomer is built from arylamide bonds around a central 4,6-dicarboxy pyrimidine ring. The conformation was studied by X-ray crystallography and solution NMR spectroscopy. Density-functional (DFT) calculations were performed to guide the design. These calculations accurately predicted the overall conformation as well as NMR chemical shifts. Antibacterial activity was demonstrated against E. coli, a gram-negative strain, and B. subtilis, a gram-positive strain. The minimal inhibitory concentration is 0.8 microg/ml.     

Electronic structures of polydiacetylene backbones

Energies per unit cell for various polydiacetylene backbone sequences are determined. The unrestricted Hartree-Fock approach is used to obtain the lowest energy transitions.     

Structure and reactivity of phosphorus-selenium heterocycles with peri-substituted naphthalene backbones

Reaction of naphthalene-1.8-bis(dichlorophosphine) with sodium selenide and selenium gives naphthalene-1,8-diyl)-1,3,2,4-diselenoxodiphosphetane 2,4-diselenide (27), a molecule with its four-membered PSePSe ring spanned by a naphthalene-1,8-diyl backbone. 27 was fully characterised, including by X-ray diffraction. Unusually, the reaction yielded not only 27, but also a polymeric or oligomeric material that was selenium deficient, containing significant amount of species with phosphorus atoms not fully oxidised to P(V). Reactions of the selenium deficient material with simple alcohols afforded two 1,2-diphosphaacenaphthenes, which were structurally characterised.     

New polyesters with photosensitive backbones based on the triazene unit

The synthesis of photosensitive polymers that contain the triazeno group (Ph NN NR₂) as a sensitive unit in their backbone is reported. The synthesis pathway consists of difunctional alcohols incorporating the photosensitive unit that react with diacyl derivatives to give the respective polyesters. Upon irradiation, the photosensitive chromophores both in monomeric and polymeric surroundings are cleaved fast and irreversibly, as shown in photolytic studies and their kinetic evaluations. Thermogravimetrical investigations indicate the loss of nitrogen being the initial thermal decomposition step and exhibit stabilities sufficient for the requirements in applications as photoresists. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3017–3025, 1997     

Peptide amphiphile nanofibers with conjugated polydiacetylene backbones in their core

The coupling of electronic and biological functionality through self-assembly is an interesting target in supramolecular chemistry. We report here on a set of diacetylene-derivatized peptide amphiphiles (PAs) that react to form conjugated polydiacetylene backbones following self-assembly into cylindrical nanofibers. The polymerization reaction yields highly conjugated backbones when the peptidic segment of the PAs has a linear, as opposed to a branched, architecture. Given the topotactic nature of the polymerization, these results suggest that a high degree of internal order exists in the supramolecular nanofibers formed by the linear PA. On the basis of microscopy, the formation of a polydiacetylene backbone to covalently connect the beta-sheets that help form the fibers does not disrupt the fiber shape. Interestingly, we observe the appearance of a polydiacetylene (PDA) circular dichroism band at 547 nm in linear PA nanofibers suggesting the conjugated backbone in the core of the nanostructures is twisted. We believe this CD signal is due to chiral induction by the beta-sheets, which are normally twisted in helical fashion. Heating and cooling shows simultaneous changes in beta-sheet and conjugated backbone structure, indicating they are both correlated. At the same time, poor polymerization in nanofibers formed by branched PAs indicates that less internal order exists in these nanostructures and, as expected, then a circular dichroism signal is not observed for the conjugated backbone. The general variety of materials investigated here has the obvious potential to couple electronic properties and in vitro bioactivity. Furthermore, the polymerization of monomers in peptide amphiphile assemblies by a rigid conjugated backbone also leads to mechanical robustness and insolubility, two properties that may be important for the patterning of these materials at the cellular scale.     

Adamantanes, nortricyclenes, and dendrimers with extended silicon backbones

By reaction of the hexabromoheptasilane MeSi(SiMe(2)SiMeBr(2))(3) (1 a) with H(2)O, H(2)S, NH(3), and H(2)NMe the heptasilaadamantanes MeSi(SiMe(2)SiMeO)(3) (4), MeSi(SiMe(2)SiMeS)(3) (5), MeSi(SiMe(2)SiMeNH)(3) (6 a), and MeSi(SiMe(2)SiMeNMe)(3) (6 b), respectively, were prepared in good to moderate yields. Molecular structures of 4, 5, 6 a, and 6 b were determined by X-ray crystallography. The symmetry of the cages is approximately C(3v), and the geometry around the nitrogen atoms is essentially planar. Ab initio SCF/HF calculations with the 6-31G* basis set confirm these results. Reduction of MeSi(SiMe(2)SitBuBr(2))(3) (1 b) with lithium naphthalenide afforded the heptasilanortricyclene MeSi(SiMe(2)SitBu)(3) (7). The (29)Si NMR spectrum of 7 consists of three signals with chemical shifts that agree closely with values predicted by ab initio calculations. (29)Si INADEQUATE spectra also strongly support the nortricyclene structure. Ab initio SCF/HF calculations were performed for the parent molecule Si(7)H(10), and the ring strain of the cage was estimated as 168.8 kJ mol(-1) by using the homodesmic reaction Si(7)H(10) + 3 Si(2)H(6)-->Si(13)H(28). Compound 1 a also served as the starting material for the preparation of first-generation dendrimer 2 a by reaction with six equivalents of Ph(2)MeSiLi. Subsequent protodearylation with HBr and reaction with (Me(2)PhSi)(2)SiMeK afforded second-generation dendrimer 3. All dendrimers were characterized by multinuclear NMR spectroscopy.     

Determining concentration depth profiles in fluorinated networks by means of electric force microscopy

By means of electric force microscopy, composition depth profiles were measured with nanometric resolution for a series of fluorinated networks. By mapping the dielectric permittivity along a line going from the surface to the bulk, we were able to experimentally access to the fluorine concentration profile. Obtained data show composition gradient lengths ranging from 30 nm to 80 nm in the near surface area for samples containing from 0.5 to 5 wt. % F, respectively. In contrast, no gradients of concentration were detected in bulk. This method has several advantages over other techniques because it allows profiling directly on a sectional cut of the sample. By combining the obtained results with x-ray photoelectron spectroscopy measurements, we were also able to quantify F/C ratio as a function of depth with nanoscale resolution.     

Chiral peptide nucleic acid monomers (PNAM) with modified backbones

Convenient high yielding syntheses of optically pure PNAMs comprising l- or d-serine, l-lysine and l-arginine units linked to thymine or Cbz-cytosine are described. Simple workup and inexpensive reagents are employed and free amino acids are used as coupling components.     

Use of fluorinated maleimide and telechelic bismaleimide for original hydrophobic and oleophobic polymerized networks

The syntheses of original fluorinated maleimide and telechelic bismaleimide bearing C₆F₁₃ and C₆F₁₂ groups, respectively, and their use as reactive additives in photopolymerizable formulations of telechelic poly(propylene glycol) bismaleimide (PPGBMI) are presented. Fluorinated maleimide was synthetized in five steps in 63% overall yield from C₆F₁₃C₂H₄I precursor, whereas the fluorinated bismaleimide was prepared in six steps in 14% overall yield from IC₆F₁₂I. These latter led to fluorinated azido and diazido intermediates that were reduced into the fluorinated amine and diamines in two steps. The condensation of amine and diamine onto maleic anhydride offered an amic acid and a diamic acid, which were subsequently cyclized into fluorinated maleimide and bismaleimide. Formulations of telechelic PPGBMI containing a low concentration of these fluorinated maleimide and bismaleimide were UV cured and the surface properties of the resulting films were investigated. A deep modification of the surface properties was noted when the monomaleimide was used. In all the cases, a selective enrichment of the fluorinated monomer at the film surface was observed. The dependence of the surface properties on the fluorinated maleimide and bismaleimide concentrations were also studied, and showed an asymptotic behavior of the contact angle with only 1.5 wt % of fluorinated maleimide additive, whatever the conditions. This monomaleimide led to better hydrophobic and oleophobic properties of the resulting material than that containing the telechelic one. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3214–3228, 2008     

N-heterocyclic carbenes with inorganic backbones: electronic structures and ligand properties

The electronic structures of known N-heterocyclic carbenes (NHCs) with boron, nitrogen, and phosphorus backbones are examined using quantum chemical methods and compared to the experimental results and to the computational data obtained for a classical carbon analogue, imidazol-2-ylidene. The sigma-donor and pi-acceptor abilities of the studied NHCs in selected transition-metal complexes are evaluated using a variety of approaches such as energy and charge decomposition analysis, as well as calculated acidity constants and carbonyl stretching frequencies. The study shows that the introduction of selected heteroatoms into the NHC backbone generally leads to stronger metal-carbene bonds and therefore improves the ligand properties of these systems. The backdonation of pi-electron density from the metal to the ligand is found to be strong in complexes of the studied NHCs with group 11 metals, where it constitutes up to nearly 35% of the total orbital interaction energy. The ligand properties of the aluminum analogues of some of the reported NHCs with boron backbones are also assessed.     

Reaction of fluorinated aldehydes with phenylacetylene

Conclusions Fluorinated aldehydes add to phenylacetylene with the formation of mixtures of ,-unsaturated fluoroketones and acetylenic fluoroalcohols.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 212–214, January, 1987.     

Synthesis and properties of some new polyimidosulfides with highly mobile backbones

Various alkanedithiols [HSRSH; R = (CH₂)_3–6 or? CH₂CH₂OCH₂CH₂? ] add to the carbon-carbon double bonds of N,N′-bismaleimido-1,8-octane ( 1 ) at room temperature in m-cresol that contains triethylamine as a catalyst to produce the corresponding polyimidosulfides ( 3 ) in yields of 75–86% and with inherent viscosities (ηinh) of 0.30–1.05 dL/g. In general ( 3 ) are amorphous, elastomeric materials that undergo glass transitions (T_g) within the range of 6.5–13°C but product ( 3a ) [R = (CH₂)₆] is a tough, leatherlike polymer that exhibits T_g = 35°C and a melting transition at 77°C. X-ray analysis indicates that ( 3a ) is ca. 37% crystalline. In addition to further details of the synthesis and properties of polyimidosulfides ( 3 ), comparisons are made between crystalline ( 3a ) and a structurally analogous but morphologically dissimilar, elastomeric polyaspartimide synthesized earlier

1 J. E. White, M. D. Scaia, and D. A. Snider, J. Appl. Polym. Sci., in press.

from ( 1 ) and N,N′-dimethyl-1,6-hexanediamine.