Félix Zamora

Covalent organic frameworks based on Schiff-base chemistry: synthesis, properties and potential applications

Covalent organic-frameworks (COFs) are an emerging class of porous and ordered materials formed by condensation reactions of organic molecules. Recently, the Schiff-base chemistry or dynamic imine-chemistry has been widely explored for the synthesis of COFs. The main reason for this new tendency is based on their high chemical stability, porosity and crystallinity in comparison to previously reported COFs. This critical review article summarizes the current state-of-the-art on the design principles and synthetic strategies toward COFs based on Schiff-base chemistry, collects and rationalizes their physicochemical properties, as well as aims to provide perspectives of potential applications which are at the forefront of research in materials science.

Single layers of a multifunctional laminar Cu(I,II) coordination polymer

A multifunctional bidimensional mixed-valence copper coordination polymer [Cu2Br(IN)2]n (IN = isonicotinato) has been characterized in crystal phase and isolated on graphite surface as single sheets.

Delamination of Layered Covalent Organic Frameworks

Nanomaterials, understood as the study of materials having at least one dimension on the nanometer scale, has been a fruitful area of research during the past few years. [ 1 ] The main reason for this increasing interest is that, at this small scale, qualitative changes in physicochemical properties such as surface plasmon resonance in metal nanoparticles, quantum confi nement in semiconductor particles, and superparamagnetism in magnetic nanomaterials, are connected to the number of atoms or molecules forming the material. [ 2 ]

Mechanical Isolation of Highly Stable Antimonene under Ambient Conditions

Antimonene fabricated by mechanical exfoliation is highly stable under atmospheric conditions over periods of months and even when immersed in water. Density functional theory confirms the experiments and predicts an electronic gap of ≈1 eV. These results highlight the use of antimonene for optoelectronics applications.

Highly conductive self-assembled nanoribbons of coordination polymers.

Organic molecules can self-assemble into well-ordered structures, but the conductance of these structures is limited, which is a disadvantage for applications in molecular electronics. Conductivity can be improved by using coordination polymers-in which metal centres are incorporated into a molecular backbone-and such structures have been used as molecular wires by self-assembling them into ordered films on metal surfaces. Here, we report electrically conductive nanoribbons of the coordination polymer [Pt(2)I(S(2)CCH(3))(4)](n) self-assembled on an insulating substrate by direct sublimation of polymer crystals. Conductance atomic force microscopy is used to probe the electrical characteristics of a few polymer chains ( approximately 10) within the nanoribbons. The observed currents exceed those previously sustained in organic and metal-organic molecules assembled on surfaces by several orders of magnitude and over much longer distances. These results, and the results of theoretical calculations based on density functional theory, confirm coordination polymers as candidate materials for applications in molecular electronics.

Few-Layer Antimonene by Liquid-Phase Exfoliation

Abstract We report on a fast and simple method to produce highly stable isopropanol/water (4:1) suspensions of few‐layer antimonene by liquid‐phase exfoliation of antimony crystals in a process that is assisted by sonication but does not require the addition of any surfactant. This straightforward method generates dispersions of few‐layer antimonene suitable for on‐surface isolation. Analysis by atomic force microscopy, scanning transmission electron microscopy, and electron energy loss spectroscopy confirmed the formation of high‐quality few‐layer antimonene nanosheets with large lateral dimensions. These nanolayers are extremely stable under ambient conditions. Their Raman signals are strongly thickness‐dependent, which was rationalized by means of density functional theory calculations.

Solvent‐Induced Delamination of a Multifunctional Two Dimensional Coordination Polymer

A coordination polymer is fully exfoliated by solvent-assisted interaction only. The soft-delamination process results from the structure of the starting material, which shows a layered structure with weak layer-to-layer interactions and cavities with the ability to locate several solvents in an unselective way. These results represent a significant step forward towards the production of structurally designed one-molecule thick 2D materials with tailored physico-chemical properties.

Electrical conductivity and luminescence in coordination polymers based on copper(I)-halides and sulfur-pyrimidine ligands.

The solvothermal reactions between pyrimidinedisulfide (pym(2)S(2)) and CuI or CuBr(2) in CH(2)Cl(2):CH(3)CN lead to the formation of [Cu(11)I(7)(pymS)(4)](n) (pymSH = pyrimidine-2(1H)-thione) (1) and the dimer [Cu(II)(μ-Br)(Br)L](2) (L = 2-(pyrimidin-2-ylamino)-1,3-thiazole-4-carbaldehyde) (2). In the later reaction, there is an in situ S-S, S-C(sp(2)), and C(sp(2))-N multiple bond cleavage of the pyrimidinedisulfide resulting in the formation of 2-(pyrimidin-2-ylamino)-1,3-thiazole-4-carbaldehyde. Interestingly, similar reactions carried out just with a change in the solvent (H(2)O:CH(3)CN instead of CH(2)Cl(2):CH(3)CN) give rise to the formation of coordination polymers with rather different architectures. Thus, the reaction between pym(2)S(2) and CuI leads to the formation of [Cu(3)I(pymS)(2)](n) (3) and [CuI(pym(2)S(3))] (pym(2)S(3) = pyrimidiltrisulfide) (4), while [Cu(3)Br(pymS)(2)](n) (5) is isolated in the reaction with CuBr(2). Finally, the solvothermal reactions between CuI and pyrimidine-2-thione (pymSH) in CH(2)Cl(2):CH(3)CN at different ratios, 1:1 or 2:1, give the polymers [Cu(2)I(2)(pymSH)(2)](n) (6) and [Cu(2)I(2)(pymSH)](n) (7), respectively. The structure of the new compounds has been determined by X-ray diffraction. The studies of the physical properties of the novel coordination polymers reveal that compounds 3 and 5 present excellent electrical conductivity values at room temperature, while compounds 1, 3, and 5-7 show luminescent strong red emission at room temperature.

Palladium(II) compounds of putrescine and spermine. Synthesis, characterization, and DNA-binding and antitumor properties

The reaction of putrescine (Put) with K2PdCl4 and PdCl2 resulted in the synthesis of compounds of formula [PutH2][PdCl4] and [Pd2Cl4(Put)2]. Compounds of formula [PdCl2(SpermH2)][PdCl4] and [Pd2Cl4(Sperm)] have been also synthesized by reaction of spermine (Sperm) with K2PdCl4. The structure of all these compounds has been analyzed by IR and 1H NMR. UV and CD spectroscopic data have shown that all the Pd(II)-polyamine compounds synthesized induce conformational changes in the circular forms of plasmid DNA. Determinations by electrophoresis in agarose gels of the mobility of the DNA in drug:DNA complexes indicated that only the Pd(II)-putrescine compounds have the ability to induce significant conformational changes in the covalently closed circular (ccc) form of the pUC8 plasmid DNA. The Pd(II)-putrescine and Pd(II)-spermine compounds were also assayed for in vitro antiproliferative activity against MDA-MB 468 and HL-60 human cancer cells. The results suggest that the putrescine complexes may be regarded as potential antitumor agents because the ID50 value of all of the Pd(II)-putrescine complexes is twofold lower than the ID50 of cis-DDP. Our data also show that, on the other hand, the Pd(II)-spermine compounds have low antiproliferative activity.

Tuning delamination of layered covalent organic frameworks through structural design

Exfoliation of a family of polyacetylenic porous layered covalent organic frameworks by means of a simple sonication procedure results in the obtention of nanolayer structures as observed by AFM and TEM measurements. Systematic AFM analysis of the isolated nanostructures reveals that the degree of exfoliation depends on the polymer architecture, thinner layers being observed when the pore size decreases.