Portraits of Porosity: Porous Structures Based on Metal Salen Complexes

Innovative Application of Salophen Derivatives in Organic Electronics as a Composite Film with a Poly(3,4-Ethylenedioxythiophene)-poly(styrenesulfonate) Matrix

In this work, we present the innovative synthesis of salophen (acetaminosalol) derivatives in a solvent-free environment by high-speed ball milling, using a non-conventional activation method, which allowed obtaining compounds in a shorter time and with a better yield. Furthermore, for the first time, the salophen derivatives were deposited as composite films, using a matrix of poly 3,4-ethylene dioxythiophene:polystyrene sulfonate (PEDOT:PSS) polymer. Significant findings include the transformation from the benzoid to the quinoid form of PEDOT post-IPA treatment, as evidenced by Raman spectroscopy. SEM analysis revealed the formation of homogeneous films, and AFM provided insights into the changes in surface roughness and morphology post-IPA treatment, which may be crucial for understanding potential applications in electronics. The optical bandgap ranges between 2.86 and 3.2 eV for PEDOT:PSS-salophen films, placing them as organic semiconductors. The electrical behavior of the PEDOT:PSS-salophen films undergoes a transformation with the increase in voltage, from ohmic to space charge-limited conduction, and subsequently to constant current, with a maximum of 20 mA. These results suggest the possible use of composite films in organic electronics.

Lewis Acidic Zinc(II) Complexes of Tetradentate Ligands as Building Blocks for Responsive Assembled Supramolecular Structures

This review presents representative examples illustrating how the Lewis acidic character of the Zn(II) metal center in Zn(salen)-type complexes, as well as in complexes of other tetradentate ligands, and the nature of the medium govern their supramolecular aggregation, leading to the formation of a variety of supramolecular structures, either in solution or in the solid state. Stabilization of these Lewis acidic complexes is almost always reached through an axial coordination of a Lewis base, leading to a penta-coordinated square-pyramidal geometry around the metal center. The coverage is not exhaustive, mainly focused on their crystallographic structures, but also on their aggregation and sensing properties in solution, and on their self-assembled and responsive nanostructures, summarizing their salient aspects. The axial ligands can easily be displaced, either in solution or in the solid state, with suitable Lewis bases, thus being responsive supramolecular structures useful for sensing. This contribution represents the first attempt to relate some common features of the chemistry of different families of Zn(II) complexes of tetradentate ligands to their intrinsic Lewis acidic character.

The electrochemical reduction of a flexible Mn(II) salen-based metal-organic framework

A new metal-organic framework (MOF) containing a Mn(II) salen complex (BET surface area = 967 ± 6 m² g^-1) undergoes a reversible crystalline-to-amorphous transformation. Experimental studies and computational calculations show that the MOF is stable to a one-electron reduction at more anodic potentials than the corresponding discrete complex.

Salen-Based Conjugated Microporous Polymers for Efficient Oxygen Evolution Reaction

Exploring high-performance electrocatalysts, especially non-noble metal electrocatalysts, for the oxygen evolution reaction (OER) is critical to energy storage and conversion. Herein, we report for the first time that conjugated microporous polymers (CMPs) incorporating salen can be used as OER electrocatalysts with outstanding performances. The best OER electrocatalyst (salen-CMP-Fe-3) exhibits a low Tafel slope of 63 mV dec^-1 and an overpotential of 238 mV at 10 mA cm^-2 . DFT and Grand Canonical Monte Carlo calculations confirmed that the significantly improved electrocatalytic properties can be attributed to the intrinsic catalytic activity of the salen moiety and the enrichment effect of the pore structures. This work demonstrates that salen-based conjugated polymers are a type of metal-coordinated porous polymer that show excellent catalyst performance.

Structural, Spectroscopic, and Chemical Bonding Analysis of Zn(II) Complex [Zn(sal)](H2O): Combined Experimental and Theoretical (NBO, QTAIM, and ELF) Investigation

The Zn(II) complex of salen-like scaffold [Zn(sal)](H2O) was synthesized and characterized by elemental analysis, IR, UV–Vis, and 1H-NMR spectroscopic techniques. The structure of complex was confirmed by single crystal X-ray diffraction studies. In the complex, Zn (II) was placed in the inner N2O2 compartment of the salen scaffold in square planar geometry and crystallized in the monoclinic space group P21/n. DFT and TDDFT calculations were performed to reproduce the experimentally observed structural and spectroscopic (IR and UV–vis) findings. The bonding of the Zn(II) framework in the [Zn(sal)](H2O) complex was explored in depth. The theoretical approaches employed were perturbation theory within the context of the natural bond orbital (NBO) framework, and quantum theory of atoms in molecule (QTAIM) and electron localization function (ELF) analysis. The study begins by delineating the difference between the NBO and QTAIM approaches. This paper thus exhibits the supportive nature of NBO theory and QTAIM in discussion of the bonding in the [Zn(sal)](H2O) complex, when both the methodologies are used in combination.

A Constrained and "Inverted" [3+3] Salphen Macrocycle with an ortho-Phenylethynyl Substitution Pattern

A [3+3] Schiff-base salphen macrocycle (7 a) was synthesized by imine condensation between ortho-phenylenediamine and ortho-phenylethynyl-bridged bis(5-salicylaldehyde) precursors. The triangular-shaped macrocycle 7 a has a nonclassical (or "inverted") design in which the N₂ O₂ coordination pockets are located at the sides instead of the corners. Compound 7 a could be synthesized in a reasonably good yield (64 %) considering the steric constraints imposed by the ortho substitution pattern. Subsequent zinc metalation afforded the corresponding Zn metallomacrocycle 7 b. Spectroscopic experiments evidenced weak (7 a) to strong (7 b) self-aggregation behavior in solution. Their ability to self-organize at the supramolecular level was further studied in the solid state by AFM and TEM, which revealed the formation of large bundles of fibers with lengths of several micrometers and widths of nanometers.

Compartmentalization of Alkaline-Earth Metals in Salen-Type Cu- and Ni-Complexes in Solution and in the Solid State

The precise arrangement of metal ions in type and number by a ligand represents an important challenge in biology as well as in materials science. The preorganization of different metal ions such as alkaline-earth and transition-metal ions is of particular interest for the design of catalysts or precursors of oxides. This study is based on a Ω-shaped salen-derived ligand comprising N2O2 and O2O2 coordination sites. The selective binding of Cu(II) and Ni(II) and alkaline-earth-metal ions is influenced by many factors such as the size of the cation, the solvent, or the counterion. UV-vis and 1H NMR titrations and single-crystal X-ray structures reveal that the obtained complexes tend to adopt different structures in solution compared to the solid state. Mainly discrete motifs with a stoichiometry 1:1 (LM1 to alkaline-earth-metal ions) have been shown to form in the solid state, whereas in solution, the 2:1 complexes are predominant.

Crystal structure of (2-{[(8-aminona-phthalen-1-yl)imino]-meth-yl}-4,6-di-tert-butyl-phenolato-κ3N,N',O)bromido-nickel(II)

The title compound, [NiBr(C25H29N2O)], contains an NiII atom with a slightly distorted square-planar coordination environment defined by one O and two N atoms from the 2-{[(8-aminona-phthalen-1-yl)imino]-meth-yl}-4,6-di-tert-butyl-phenolate ligand and a bromide anion. The Ni-O and Ni-N bond lengths are slightly longer than those observed in the phenyl backbone counterpart, which can be attributed to the larger steric hindrance of the naphthyl group in the structure of the title compound. The mol-ecule as a whole is substanti-ally distorted, with both the planar naphthalene-1,8-di-amine and imino-meth-yl-phenolate substitutents rotated against the NiN2OBr plane by 38.92 (7) and 37.22 (8)°, respectively, giving the mol-ecule a twisted appearance. N-H⋯Br hydrogen bonds and N-H⋯C(π) contacts connect the mol-ecules into dimers, and additional C-H⋯Br contacts, C-H⋯π inter-actions, and an offset stacking inter-action between naphthyl units inter-connect these dimers into a three-dimensional network.

An in Situ Embedded Square-Planar CuII/NiIIN4 Metalloligand in Coordination Polymers for Visible-Light Photocatalysis

Three coordination polymers (CPs) with square-planar Cu^II/Ni^IIN₄ subunits were formed in one step by subcomponent self-assembly, giving rise to an unprecedented linking variety of in situ embedded metalloligands and Cu^I clusters. All CPs exhibit unusual visible-light adsorption. Enhanced photocatalytic activity and high selectivity were observed in the oxidation of benzene under visible-light irradiation.

Cu(I) complexes of bis(methyl)(thia/selena) salen ligands: Synthesis, characterization, redox behavior and DNA binding studies

Mononuclear cuprous complexes 1 and 2, [{CH₃E(o-C₆H₄)CH=NCH₂}₂Cu]ClO₄; E=S/Se, have been synthesized by the reaction of bis(methyl)(thia/selena) salen ligands and [Cu(CH₃CN)₄]ClO₄. Both the products were characterized by elemental analysis, ESI-MS, FT-IR, ¹H/¹³C/⁷⁷Se NMR, and cyclic voltammetry. The complexes possess tetrahedral geometry around metal center with the N₂S₂/N₂Se₂ coordination core. Cyclic voltammograms of complexes 1 and 2 displayed reversible anodic waves at E_1/2=+0.08V and +0.10V, respectively, corresponding to the Cu(I)/Cu(II) redox couple. DNA binding studies of both the complexes were performed applying absorbance, fluorescence and molecular docking techniques. Competitive binding experiment of complexes with ct-DNA against ethidium bromide is performed to predict the mode of binding. The results indicate the groove binding mode of complexes 1 and 2 to DNA. The binding constants revealed the strong binding affinity of complexes towards ct-DNA.

A Straightforward Electrochemical Approach to Imine- and Amine-bisphenolate Metal Complexes with Facile Control Over Metal Oxidation State

Synthetic methods to prepare organometallic and coordination compounds such as Schiff-base complexes are diverse, with the route chosen being dependent upon many factors such as metal-ligand combination and metal oxidation state. In this work we have shown that electrochemical methodology can be employed to synthesize a variety of metal-salen/salan complexes which comprise diverse metal-ligand combinations and oxidation states. Broad application has been demonstrated through the preparation of 34 complexes under mild and ambient conditions. Unprecedented control over metal oxidation state (M(II/III/IV) where M=Fe, Mn) is presented by simple modification of reaction conditions. Along this route, a general protocol-switch is described which allows access to analytically pure Fe(II/III)-salen complexes. Tuning electrochemical potential, selective metalation of a Mn/Ni alloy is also presented which exclusively delivers Mn(II/IV)-salen complexes in high yield.

Direct C-C coupling of two Ni-salphen complexes to yield dinickel-disalphen complexes with symmetric and non-symmetric substitution-patterns

The synthesis of symmetric and non-symmetric 5,5'-linked disalophen Ni(ii) complexes by the Suzuki-Miyaura-reaction is reported. Also, the synthesis and structural characterization of four Ni(ii)-precursor complexes are presented. The 5-Br-substituted mononuclear complexes and are coupled to the pinacolborane substituted complexes and yielding the four dinuclear dinickel complexes in good yields. The crystal structure of dinuclear complex was obtained revealing a coplanar arrangement between the two salophen fragments. Electronic spectra as well as DFT-calculations on the ground states and excitation energies are reported and they reveal a small coupling between the electronically saturated Ni-salophen complexes.

Surface functionalization of dinuclear clathrochelates via Pd-catalyzed cross-coupling reactions: facile synthesis of polypyridyl metalloligands

Clathrochelates can be decorated with pyridyl groups by cross-coupling reactions. They represent interesting ligands for supramolecular chemistry and materials science.

Asymmetric binuclear Ni(ii) and Cu(ii) Schiff base metallopolymers

We use electrochemistry to polymerise the new asymmetric binuclear Cu(ii)/Cu(ii) and Ni(ii)/Ni(ii) monomers and study their behaviour as modified electrodes.

Enantioselective cyanosilylation of aldehydes catalyzed by a multistereogenic salen–Mn(iii) complex with a rotatable benzylic group as a helping hand

A multistereogenic salen–Mn(iii) complex bearing an aromatic pocket and two benzylic groups as helping hands was found to be efficient in the catalysis of asymmetric cyanosilylation.

Novel uranyl(vi) complexes incorporating propylene-bridged salen-type N2O2-ligands: a structural and computational approach

Synthesis of uranyl complex, [UO₂L(CH₃OH)] showing distorted pentagonal bipyramidal geometry and derived from a tetradentate dianionic ligand is reported. The computational study of the reported complex shows that its LUMO is featured with uranium f orbital character.

Triptycene-based Organic Molecules of Intrinsic Microporosity

Four Organic Molecules of Intrinsic Microporosity (OMIMs) were prepared by fusing triptycene-based components to a biphenyl core. Due to their rigid molecular structures that cannot pack space efficiently, these OMIMs form amorphous materials with significant microporosity as demonstrated by apparent BET surface areas in the range of 515-702 m(2) g(-1). Bulky cyclic 1',2',3',4'-tetrahydro-1',1',4',4'-tetramethylbenzo units placed on the triptycene termini are especially efficient at enhancing microporosity.