J P, Harohally NV, Krishnamurthy C, Jathi K, Ahmad A, Alshammari MB, Lokanath NK. Structural Investigation of Schiff Base Ligand and Dinuclear Copper Complex: Synthesis, Crystal Structure, Computational, and Latent Fingerprint Analysis

The structural studies of the fluorinated Schiff base ligand and its copper complex were synthesized and characterized by Fourier transform infrared, UV-visible, and photoluminescence spectroscopy. Single-crystal X-ray diffraction analysis unveils a dinuclear copper complex arising from double bridging acetate anions to copper ions that are chelated by the tridentate Schiff base ligand Cu(LS). The trigonality index τ5 of 0.080 indicates a distorted square pyramidal coordination geometry for the metal. The SL ligand and complex exhibit intra- and intermolecular interactions, leading to unique supramolecular architectures. The structural changes between the free halogenated Schiff base ligand and upon coordination with the metal were extensively studied by experimental and theoretical approaches. The intra- and intermolecular interactions have been analyzed by Hirshfeld surface and quantum theory of atoms in molecules analysis, and the enrichment ratio highlights the most favored interactions in the formation of molecular packing. The chemical and physical properties, such as the HOMO - LUMO energy gap, chemical reactivity, and electron density topology, are studied using density functional theory studies. In addition, the Schiff base ligand compound is used to study the latent fingerprint analysis.

Tunable Construction of Sandwich-Type Double-[1 + 1] and Half-Folded [2 + 2] Schiff-Base Complexes Controlled by the Combination of Primary and Secondary Template Effects

The first-row transition-metal ions Mn²⁺-Cu²⁺ could serve as effective templates to construct three types of double-[1 + 1], [2 + 2], and [1 + 1] Schiff-base dinuclear macrocyclic complexes in the presence of dialdehydes with different pendant arms and a common 1,8-diamine. The extremely flexible nature of macrocyclic ligands allows for the multiple template-directed syntheses, but the final products could be finely tuned by the subtle variations of Mn²⁺-Cu²⁺ ions in a 3d-electronic configuration, radius, and coordination number/geometry as well as the auxiliary (pendant-armed and anionic) template effect at the same time. Two borderlines are observed at the Co²⁺ ion for forming double-[1 + 1] and [2 + 2] metallacycles involving the H₂pdd precursor and the [1 + 1] Cu²⁺ complex for double-[1 + 1] and [2 + 2] macrocycles containing the H₂hpdd unit, respectively. The structural diversity is originated from the non-perfect match between [1 + 1]/[2 + 2] Schiff-base macrocycles and dinuclear metal centers; hence, a compromise between the metal coordination modes and alterations of the ligand conformation takes place.

A novel Schiff base macrocycle based on 1,1'-binaphthyl for fluorescence recognition

A novel chiral polyimine macrocycle C-1 was designed and synthesized by the self-condensation of the dialdehyde of the chiral dinaphtho[2,1-d:1',2'-f][1,3]dioxepine derivative and o-phenylenediamine by Schiff base formation, and the corresponding polyamine macrocycle C-1H was obtained by the reduction of the polyimine macrocycle. The UV-vis and fluorescence spectral studies indicated that both C-1 and C-1H form the complex with metal ions in a 1:2 ratio. The fluorescence behaviour of C-1 upon the addition of Zn²⁺ or Cd²⁺ showed a 'turn-on' response accompanied by fluorescence enhancement at 510 nm six times for Cd²⁺ and 13 times for Zn²⁺ . In contrast, C-1H revealed a 'turn-off' response upon the addition of Co²⁺ , Ni²⁺ , and Cu²⁺ .

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.