Chiral 27-membered [3+3] Schiff-base macrocycles and their reactivity with first-row transition metal ions

The optical properties of 3 + 3 macrocyclic Schiff base thin material obtained by the Molecular Beam Epitaxy method

3 + 3 optically active macrocyclic Schiff bases were synthesized in the reaction between 4-tert-butyl-2,6-diformylphenol with (1R,2R)-(+)-1,2-diphenylethylenediamine (S1) or (1S,2S)-(-)-1,2-diphenylethylenediamine (S1a). The new compounds were spectroscopically characterised by NMR, IR, X-ray (S1a), UV-Vis and fluorescence spectroscopy. The S1a molecule creates channels with distances between oxygen atoms ranging from 5.8-6.3 Å and sufficiently large to host acetonitrile molecule. Both compounds exhibit green-yellow emission in solution and solid state. Thin layers of the S1 compound obtained via Molecular Beam Epitaxy (MBE) were characterised by scanning electron microscopy with energy-dispersive X-ray spectroscopy SEM/EDS and atomic force microscopy (AFM). The optical properties of the S1/Si thin material were analysed using spectroscopic ellipsometry (SE), fluorescence spectroscopy and synchrotron radiation (SR). The time constant for the decay investigated under SR, denoted by τ1, was determined to be approximately 1.02 ns, suggesting a fast deactivation process of the excited electronic state in the S1/Si material. The ellipsometric analysis of the S1/Si layer showed semiconducting behaviour with pronounced absorption features in the UV range, attributed to π → π* and n → π* transitions, characteristic of Schiff bases. The band-gap energy, determined using the Tauc method, is 3.46 ± 0.01 eV. These analyses highlight the material's potential in applications requiring precise control of optical properties. In the emission spectrum of S1a, a significant emission peak of approximately 561 nm indicates the presence of a prominent emissive process within this wavelength. The S1a compound is emissive in the yellow-green region of the spectrum and has a longer decay time, which suggests that it can be used in sensing optical technologies.

Characterization of Diastereomeric Equilibria of Pseudotetrahedral Bis[(R or S)-N-1-(Ar)Ethylsalicylaldiminato-κ2 N,O]zinc(II) with Λ/Δ-Chirality-At-Metal Induction

A family of bis[(R or S)-N-1-(Ar)ethylsalicylaldiminato-κ2 N,O]-Δ/Λ-zinc(II) {Ar=C6 H5 (ZnRL1 or ZnSL1 ), p-CH3 OC6 H4 (ZnRL2 or ZnSL2 ) and p-ClC6 H4 (ZnRL3 or ZnSL3 )} compounds was synthesized and investigated by multiple methods. They feature Λ/Δ-chirality-at-metal induction along the pseudo-C2 axis of the molecules. The chirality induction is quantitative in the solid state, explored by X-ray crystallography and powder X-ray diffraction (PXRD), where R or S-ligated complexes diastereoselectively yield Λ or Δ-configuration at the metal. On the other hand, Λ and Δ-diastereomers co-exist in solution. The Λ⇆Δ equilibrium is solvent- and temperature-dependent. Electronic circular dichroism (ECD) spectra confirm the existence of a diastereomeric excess of Λ-ZnRL1-3 or Δ-ZnSL1-3 in solution. DSC analysis reveals thermally induced irreversible phase transformation from a crystalline solid to an isotropic liquid phase. ECD spectra were reproduced by DFT geometry optimizations and time-dependent DFT (TD-DFT) calculations, providing ultimate proof of the dominant chirality atmetal in solution.

Specific Noncovalent Association of Truncated exo-Functionalized Triangular Homochiral Isotrianglimines through Head-to-Head, Tail-to-Tail, and Honeycomb Supramolecular Motifs

Chiral isotrianglimines were synthesized by the [3 + 3] cyclocondensation of (R,R)-1,2-diaminocyclohexane with C5-substituted isophthalaldehyde derivatives. The substituent's steric and electronic demands and the guest molecules' nature have affected the conformation of individual macrocycles and their propensity to form supramolecular architectures. In the crystal, the formation of a honeycomb-like packing arrangement of the simplest isotrianglimine was promoted by the presence of toluene or para-xylene molecules. A less symmetrical solvent molecule might force this arrangement to change. Polar substituents present in the macrocycle skeleton have enforced the self-association of isotrianglimines in the form of tail-to-tail dimers. These dimers could be further arranged in higher-order structures of the head-to-head type, which were held together by the solvent molecules. Non-associating isotrianglimine formed a container that accommodated acetonitrile molecules in its cavity. The calculated dimerization energies have indicated a strong preference for the formation of tail-to-tail dimers over those of the capsule type.

Synthesis and Conformational Characteristics of Thermosensitive Star-Shaped Six-Arm Polypeptoids

Star-shaped six-arm poly-2-alkyl-2-oxazine and poly-2-alkyl-2-oxazoline with hexaaza [2₆]orthoparacyclophane derivative core were synthesized successfully using cationic ring-opening polymerization. Conformational behavior of prepared polymer stars were investigated by the methods of molecular hydrodynamics and optics in molecular dispersed solutions. It was shown that conformation characteristics of star-shaped polypeptoids depends on arm length, while the chemical structure weakly affects the behavior of the studied polymers in solutions. This behavior is caused by the close equilibrium rigidity of arms. The star-shaped polypeptoids have relatively high intramolecular density. All synthesized stars exhibit LCST behavior. Phase separation temperature depends on arm structure. It is lower for poly-2-alkyl-2-oxazines, monomer units of which contains one methylene group more than monomers of poly-2-alkyl-2-oxazoline.

Stable Fe(iii) phenoxyimines as selective and robust CO2/epoxide coupling catalysts

Air- and moisture-stable Fe(iii)-phenoxyimine complexes catalyse CO₂ coupling reactions with a range of epoxides to selectively form cyclic carbonates.

Dynamic Formation of Noncovalent Calixsalen Aggregates

A procedure for studying "dynamic structural behavior" of large chiral macrocycles is presented. Ion mobility MS, diffusion-ordered NMR spectroscopy (DOSY NMR), and optical rotation (OR) measurements, supported by calculations, are used together as effective complementary methods to study dynamic formation of noncovalent aggregates. It is shown that the monomer-dimer equilibrium is driven by π-π or CH-π interactions and controlled largely by the substitution pattern of the calixsalen skeleton.

2,2'-{[(1E,1'E)-(Cyclo-hexane-1,4-diyl)-bis(aza-nylyl-idene)]bis-(ethan-1-yl-1-yl-idene)}diphenol

The title compound, C22H26N2O2, crystallizes with three independent mol-ecules, two of which are situated on inversion centers, so the asymmetric unit contains two independent half-mol-ecules and one mol-ecule in a general position. The two hy-droxy groups in each mol-ecule are involved in intra-molecular O-H⋯N hydrogen bonds, which generate S(6) rings. In the crystal, weak inter-molecular C-H⋯π inter-actions link the mol-ecules into two crystallographically independent columns propagating along [001]; one column consists of mol-ecules in general positions, while the other column is built from alternating independent centrosymmetric mol-ecules.

Spectroscopic studies and biological activity of some transition metal complexes of unusual Schiff base

Unusual Schiff base ligand, 4-ethanimidoyl-6-[(1E)-N-(2-hydroxy-4-methylphenyl)ethanimidoyl]benzene-1,3-diol, L, was synthesized via catalytic process involving the interaction of some metal ions with a macrocyclic Schiff base (MSB). The transition metal derivatives [ML(H(2)O)(4)](NO(3))(3), M=Cr(III) and Fe(III), [NiL(H(2)O)(4)](NO(3))(2), [ML(H(2)O)(2)](NO(3))(2), M=Zn(II) and Cd(II), [Cl(2)Pd(μ-Cl)(2)PdL], [PtL(Cl)(2)] and [PtL(Cl)(4)] were also synthesized from the corresponding metal species with L. The Schiff bases and complexes were characterized by elemental analysis, mass spectrometry, IR and (1)H NMR spectroscopy. The crystal structure of L was determined by X-ray analysis. The spectroscopic studies revealed a variety of structure arrangements for the complexes. The biological activities of L and metal complexes against the Escherchia coli as Gram-negative bacteria and Staphylococcus aureus as Gram-positive bacteria, and the two fungus Aspergillus flavus and Candida albicans were screened. The cytotoxicity of [PtL(Cl)(2)] complex, a cis-platin analogous, was checked as an antitumor agent on two breast cancer cell lines (MCF7 and T47D) and human liver carcinoma cell line (HepG2).

C3-symmetrical tribenzotriquinacene derivatives: optical resolution through cryptophane synthesis and supramolecular self-assembly into nanotubes

Based on a regioselective tris-formylation of a tribenzotriquinacene (TBTQ) hydrocarbon, the racemic C(3)-symmetrical TBTQ-trialdehyde and the corresponding TBTQ-trimethanol were synthesized along with their C(1)-isomers. Conversion of the C(3)-trialdehyde to three diastereomeric TBTQ-based cryptophanes occurring in high yield enabled the preparation of the optically pure C(3)-symmetrical TBTQ-trialdehydes and the determination of their absolute configuration. The racemic C(3)-symmetrical TBTQ-trimethanol was found to form several stable nanotubular aggregates in the solid state.

Insertion of a hydroxido bridge into a diphenoxido dinuclear copper(II) complex: drastic change of the magnetic property from strong antiferromagnetic to ferromagnetic and enhancement in the catecholase activity

A diphenoxido-bridged dinuclear copper(II) complex, [Cu(2)L(2)(ClO(4))(2)] (1), has been synthesized using a tridentate reduced Schiff base ligand, 2-[[2-(diethylamino)ethylamino]methyl]phenol (HL). The addition of triethylamine to the methanolic solution of this complex produced a novel triple bridged (double phenoxido and single hydroxido) dinuclear copper(II) complex, [Cu(2)L(2)(OH)]ClO(4) (2). Both complexes 1 and 2 were characterized by X-ray structural analyses, variable-temperature magnetic susceptibility measurements, and spectroscopic methods. In 1, the two phenoxido bridges are equatorial-equatorial and the species shows strong antiferromagnetic coupling with J = -615.6(6.1) cm(-1). The inclusion of the equatorial-equatorial hydroxido bridge in 2 changes the Cu···Cu distance from 3.018 Å (avg.) to 2.798 Å (avg.), the positions of the phenoxido bridges to axial-equatorial, and the magnetic coupling to ferromagnetic with J = 50.1(1.4) cm(-1). Using 3,5-di-tert-butylcatechol as the substrate, the catecholase activity of the complexes has been studied in a methanol solution; compound 2 shows higher catecholase activity (k(cat) = 233.4 h(-1)) than compound 1 (k(cat) = 93.6 h(-1)). Both complexes generate identical species in solution, and they are interconvertible simply by changing the pH of their solutions. The higher catecholase activity of 2 seems to be due to the presence of the OH group, which increases the pH of its solution.

Chirality and diastereoselection of Δ/Λ-configured tetrahedral zinc complexes through enantiopure Schiff base complexes: combined vibrational circular dichroism, density functional theory, 1H NMR, and X-ray structural studies

The metal-centered Δ/Λ-chirality of four-coordinated, nonplanar Zn(A(^)B)(2) complexes is correlated to the chirality of the bidentate enantiopure (R)-A(^)B or (S)-A(^)B Schiff base building blocks [A(^)B = (R)- or (S)-N-(1-(4-X-phenyl)ethyl)salicylaldiminato-κ(2)N,O with X = OCH(3), Cl, Br]. In the solid-state the (R) ligand chirality induces a Λ-M configuration and the (S) ligand chirality quantitatively gives the Δ-M configuration upon crystallization as deduced from X-ray single crystal studies. The diastereoselections of the pseudotetrahedral zinc-Schiff base complexes in CDCl(3) solution were investigated by (1)H NMR and by vibrational circular dichroism (VCD) spectroscopy. The appearance of two signals for the Schiff-base -CH═N- imine proton in (1)H NMR indicates an equilibrium of both Δ- and Λ-diastereomers with a diastereomeric ratio of roughly 20:80% for all three ligands. VCD proved to be very sensitive to the metal-centered Δ/Λ-chirality because of a characteristic band representing coupled vibrations of the two ligand's C═N stretch modes. The absolute configuration was assigned on the basis of agreement in sign with theoretical VCD spectra from Density Functional Theory calculations.

Aqua-{6,6'-dieth-oxy-2,2'-[ethane-1,2-diyl-bis(nitrilo-methanylyl-idene)]diphen-olato}zinc

The mononuclear zinc title complex, [Zn(C(20)H(22)N(2)O(4))(H(2)O)], was obtained by the reaction of 3-eth-oxy-salicyl-aldehyde, ethane-1,2-diamine, and zinc acetate in methanol. The Zn atom is five-coordinated by two phenolate O and two imine N atoms of the tetradentate Schiff base ligand and by one water O atom, forming a square-pyramidal geometry. In the crystal, pairs of mol-ecules are linked via inter-molecular O-H⋯O hydrogen bonds, forming dimers.