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A series of homologous Schiff bases N,N′-bis[(4-decyloxy-salicylideneamino)-n-propyl]-piperazine] (ZOPPH2), and N,N′-bis[(4-dodecyloxy-benzylideneamino)-n-propyl]-piperazine (DBPP)(1), based on 1,4-bis(3-amino-propyl)-piperazine (APPZ), were designed and synthesized, with APPZ serving as the piperazine core, bilaterally flanked by extended alkyl chain-containing antennae. Driven by the pursuit of metallomesogenic materials bearing liquid crystalline state properties, chemical reactivity toward divalent metals Co(II) and Cu(II), in alcoholic or tetrahydrofuran/dimethylsulfoxide media, led to compounds [{Co(ZOPP)}(ClO4)]2.(CH3OH).2(CH3)2SO(2) and [Cu(APPZ)Cl]Cl(3). All materials were characterized by elemental analysis, spectroscopic techniques (UV–Visible, FT-IR, NMR where appropriate), molar conductivity, and X-ray crystallography. Physicochemical characterization emphasizes the a) importance of N,O-containing Schiff anchors in metal ion binding, b) significance of the phenolic moiety, on the flanks of the Schiff ligands, in promoting either metal ion complexation or dissociation of the Schiff base at the azomethine moiety junction, thereby altering metal ion chemical reactivity, and c) observed oxidation of Co(II) to Co(III) upon mononuclear complex formation. Hybrid DFT calculations on DBPP and ZOPPH2 suggest increased reactivity of the Schiff CH N moiety, in the absence of the phenolic moiety, and concurrent metal ion presence, thereby lending credence to the notion of metal-assisted rupture of the specific bond in DBPP and the emergence of specific metal-ligand product(s). Collectively, the data denote the significance of structural features of piperazine-core Schiff antennae ligands in a) promoting chemical reactivity toward transition metals, b) defining metal-ligand complexation and lattice architecture, and c) parameterizing such chemical reactivity into synthetic advances toward new materials with well-defined solid-state architecture, lattice and physicochemical properties.

New heteroleptic complexes having the general formula (N^N)MQCl, where N^N = 2,2′-bipyridine or 1,10-phenanthroline, M = Cu(II) or Zn(II) and Q = quercetin were synthesized and characterized by analytical and spectroscopic methods. The complexes are more sensitive to air oxygen in solution or solid state than their flavonoid ligand. The increased sensitivity towards oxidation of the metal complexes was evidenced in the solid state by TGA-DTA measurements and in solution by UV–Vis absorption. The Zn(II) heteroleptic derivatives are luminescent in solution, their emission maxima being red-shifted with respect to quercetin precursor. The free radical scavenging activity of the complexes was evaluated using the stable DPPH radical. Cu(II) heteroleptic complexes have higher antioxidant activity than the Zn(II) complexes. Different oxidative mechanisms were evidenced for the Cu(II) and Zn(II) heteroleptic complexes.

The new Schiff base N,N′-bis(4-decyloxysalicyliden-N-n-propyl)-piperazine (ZOPP) was designed and synthesized. Structures were confirmed by elemental analysis and IR, 1H-NMR spectroscopy. ZOPP can act as ligand through the two set of donor atoms (one set: two nitrogen atoms and one oxygen) situated on each side of the piperazine bridge. The nature of the complexes depends strongly on the metal to ligand molar ratio. Thus, starting from metal to ligand of 1 to 1 ratio, where M=Cu(II), Ni(II), binuclear complexes with a polymeric structure have been obtained, whereas at metal to ligand molar ratio of 2 to 1, discrete binuclear complexes were formed.

Mixed-ligand complexes of the type M2L(TAB)nX4 [L = N,N′-bis(4-antipyryl-methyl)piperazine (BAMP), or N,N′-tetra(4-antipyrylmethyl)-l,2-diaminoethane (TAMEN) and 2-aminobenzothiazole (TAB), X - NCS or CIO4, M - Co, n - 2, or M - Cu, n = 4] were synthesized and investigated. The IR and Raman spectra revealed that the ligands L are coordinated through the carbonyl oxygen atom of the antipyrine and the nitrogen atom of the piperazine or 1,2-ethanediaminc bridge, except in Cu2(TAMEN)(TAB)4(ClO4)4, in which case TAMKN is coordinated to the metal only through the carbonyl oxygen. Steric considerations explain the bonding of TAB through the exocyclic or endocyclic nitrogen.

The synthesis and properties of new cobalt, nickel and copper complexes of general formula M2(TAMEN)Cl4 [M = Co, Ni, Cu; TAMEN = N,N,′-tetra(4-antipyrylmethyl)-1,2-diaminoethane; antipyryl- = 2,3-dimethyl-1-phenyl-3-pyrazoline-5-one] and the 1H-NMR spectrum of the ligand TAMEN are reported. TAMEN bridges the two metal centres via two groups of donor atoms, each being formed of the carbonylic oxygens and a 1,2-diaminoethane nitrogen atom.