Interface Group Assembly Of Polymer Nano-structured Materials

Coordination polymers are compounds with infinite one-,two-,and three-dimensional (1D,2D,and 3D) networks constructed from metal ions as connectors and ligands as linkers.They were first named in 1960s,since then great efforts have been made to design,synthesize,and assemble the coordination building blocks with desired architectural,physical,and chemical properties.Not only the inorganic-organic hybrid but also the porous structures make coordination polymers become one kind of unique functional materials toward wide applications of catalysis, chirality,conductivity,luminescence,magnetism,non-linear optics,porosity or zeolitic behavior,and molecular devices.In the present work,coordination polymer nanostructural materials were assembled at air-liquid,solid-liquid,and liquid-liquid interfaces.According to the geometric features of metal ions and multi-dentate ligands,we can achieve several kinds of coordination frameworks with different structures through the interfacial assembly. Metal ions such as Cd²⁺,Ag⁺,Hg²⁺,and PdCl₄^2- were used as connectors and multi-dentate ligands containing pyridyl ligand such 4,4'-bipyridyl,tri(4-pyridyl)triazine, and tetra(4-pyridyl)porphyrin were used as linkers.Excellent works have been reported in the field of assembly coordination polymers,however,almost all of them focused on crystalline compounds and synthesized in solutions.The information of microscopic morphology and growth dynamics was lacking.Herein,the coordination polymer nanostructural materials were assembled at the interface in mild conditions.These interfaces provide defect-free junction,where the products are highly mobile and can rapidly achieve equilibrium.The coordination polymers assembled at the interface are unable to dissolve into solutions so that one can easily separate the products from the reactants.Furthermore,dynamics of the coordination polymer growth can be monitored by simply removing the products from the interface after appropriated reaction time.Finally,the structure of coordination polymer can be controlled by tailoring the interfacial reaction conditions such as reaction time, concentration of reagents,etc.Hence,the present interfacial assembly method could create a convenient route for construction of coordination polymers,leading to easily design and assembly unique coordination frameworks at the interface by selecting the connectors and linkers with different coordinate geometric features. This paper was divided into two major parts.In the first part,interfacial assembly of coordination polymer nanostructural materials containing porphyrin linkers were investigated.The second parts discussed the coordination polymers constructed by chiral ligand and metal-complex-like ligand at the air-water interface.Partâ… .The water-chloroform interface was used as a mediator for assembly of metaltetrapyridylporphyrin (TPyP) coordination polymer nanocrystals,and the Langmuir-Blodgett (LB) method was used to transfer the nanocrystal layer to solid surfaces.The nanocrystal formation process and its frameworks were characterized by using transmission electron microscopy(TEM),electron diffraction(ED) and X-ray diffraction(XRD).It was found that single-/micro-crystals were formed at first,and then they grew into polycrystals.Moreover,X-ray photoelectron spectra(XPS) and UV-vis absorption spectra were used to analyze the composition and porphyrin arrangement of the nanocrystals.Rod-or wire-like nanocrystal frameworks could be formed by the interfacial coordination reaction of HgCl₂,AgNO₃ and K₂PtCl₄ with TPyP,and square nanocrystal formed by CdCl₂ and K₂PtCl₆ with TPyP.Based on the consideration of Hg²⁺,Ag⁺ and PtCl₄^2-(tetrahedral) and of Cd²⁺ and PtCl₆^2- (octahedral) geometric features,it can be concluded that the frameworks of coordination polymers produced are dominant by the geometric features of the metal ions.Mixtures of 4,4'-bipyridyl(BPy) and TPyP chloroform solution were used for the liquid-liquid assembly with HgCl₂ aqueous solution,resulting in formation of comb-like micro-/nano-structural coordination polymers.Scan electron microscopic images revealed that the coordination polymer nanocombs assembled closely depended on the mixed molar ratios of TPyP to BPy in the reactants,as well as the interfacial reaction time.Both the XPS and energy dispersive X-ray(EDX) spectroscopic measurements confirmed that the as-prepared nanocombs were composed of Hg,Cl,C and N elements.When the 4,4'-bipyridyl ligand was replaced by its derivatives,2,2'-bipyridyl or 4,4'-trimethylenedipyridine,coordination polymer nanocombs could not be obtained.The central metal ions of TPyP had little influence on the nanocombs assembled.BPy was replaced by ligand tris(4-pyridyl)-1,3,5-triazine(TPyTa) and mixed with TPyP in chloroform solution with different molar ratios as organic phase.The mixture was reacted with Hg²⁺ at the water-chloroform interface and unique coordination polymer nanotubes were obtained.TEM images revealed that the outer diameter of the nanotubes was about 60～80 nm and inner diameter about 30～40 nm.The wall thickness of the nanotube was about 15～25 nm.Furthermore,the nanotubular structure formed only when the molar ratios of TPyP/TPyTa were in the range of 1:3 to 1:4.When the molar ratios of TPyP/TPyTa were below 1:2 or above 1:6, tubular structures were not found.Composition of the Hg-TPyP/Hg-TPyTa nanotubes was estimated by XPS and elemental analysis.ED,UV-vis,and fluorescence spectra confirmed that the as-prepared nanotubes were composed of TPyP and BPy ligands. The formation mechanism of the tubular structure was considered by rolling the TPyTa-Hg-TPyP nonplanar coordination unit.Layer-by-layer(LBL) assembly of Iron(â…¢) 5,10,15,20-tetra-(4-pyridyl)porphyrin (FeTPyP)as linkers and PdCl₄^2- as connectors was performed at solid-liquid interface. The assembly process was in situ investigated by UV-vis absorption spectra.It was found that the Pd-FeTPyP LBL films were stable at acidic,alkaline,and organic solvent,these properties made it possible for a catalyst system because the metalloporphyrins are effective catalysts for selective oxidation of alkanes and alkenes under mild conditions.GC-MS measurement found when the Pd-FeTPyP LBL films modified substrate was immersed in the cyclooctene solution with hydrogen peroxide as oxidant,epoxidation of cyclooctene could be observed;when the substrates were removed,the reaction stopped.That is,the oxidation reaction is easily switched "on" and "off",just by immersing or removing the multiporphyrin arrays modified substrates in or from the reaction system.According to the Beer-Lambert rule,we calculated that the catalytic efficiency of Pd-FeTPyP LBL film was higher than that for the FeTPyP in solution.Partâ…¡Chiral linkers R(S)-binaphthyl-bis(amidopyridyl)[R(S)BNBP]were synthesized and used for construction of coordination polymers films with PdCl₄^2- at the air-liquid interface.The surface pressure-area isotherms indicated that the RBNBP and SBNBP presented very similar monolayer behavior.That is,stable monolayers of Pd-R(S)BNBP coordination polymer could be formed on the K₂PdCl₄ subphase surface instead of pure water surface.XPS measurement confirmed the elemental composition of the Pd-R(S)BNBP coordination polymer LB films.TEM images revealed that the films were composed of large amount of closely packed round domains,which were then connected into nanowires under high surface pressures. Circular dichroism(CD) spectra indicated the signals appeared in the range of 300～340 nm for the R(S)BNBP solution,but were silent in the Pd-R(S)BNBP films.New CD signals at about 240 nm were found in the Pd-R(S)BNBP coordination polymers. This difference of the CD signals might be due to the different arrangement of R(S)BNBP in Pd-R(S)BNBP coordination polymer LB films compared with that in solutions.4'-(4-pyridyl)-2,2':6',2"-terpyridine(pyterpy) was synthesized and used to form a complex-like coordination linker of Fe(pyterpy)₂[BF₄]₂ with Fe(BF₄]₂.Then,an interfacial assembly of bimetallic coordination polymer of Cd-Fe(pyterpy)₂ was performed at the air-liquid interface.The surface pressure-area and area-time isotherms indicated that stable monolayers of Fe(pyterpy)₂[BF₄]₂ could be formed on the 0.1 mol/L CdCl₂ subphase surface after an interfacial coordination reaction over 12 h,though it was difficult to form stable monolayers on the pure water surface.By using the LB method,monolayers of the Cd-Fe(pyterpy)₂ coordination polymers were transferred on the substrate surfaces,and characterized by using the UV-vis,XPS,as well as TEM.The spectral data revealed that the LB film was composed of C,Cl,Cd, N and Fe elements,which was in agreement with the composition of the coordination polymer.Electrochemical measurements revealed a couple of reversible wave corresponding to the iron(â…¡)/iron(â…¢) reduction-oxidation process in the films of the bimetallic coordination polymers.