Multinuclear Ni(II) and Cu(II) complexes of a meso 6 + 6 macrocyclic amine derived from trans-1,2-diaminocyclopentane and 2,6-diformylpyridine

Redox reactions of a pyrazine-bridged RuIII(edta) binuclear complex: spectrochemical, spectroelectrochemical and theoretical studies

The redox reactions of a pyrazine-bridged binuclear [(edta)RuIIIpzRuIII(edta)]2- (edta4- = ethylenediaminetetraacetate; pz = pyrazine) have been investigated spectrochemically and spectroelectrochemically for the first time. The kinetics of the reduction of [(edta)RuIIIpzRuIII(edta)]2- (RuIII-RuIII) with the ascorbic acid anion (HA-) was studied as a function of ascorbic concentration and temperature at a fixed pH 6.0. The overall reaction of RuIII-RuIII was found to consist of two-steps involving the initial formation of the mixed-valence [(edta)RuIIpzRuIII(edta)]3- (RuII-RuIII) intermediate complex (λmax = 462 nm, εmax = 10 000 M-1 cm-1), which undergoes further reduction by ascorbic acid to produce the [(edta)RuIIpzRuII(edta)]4-(RuII-RuII) ultimate product complex (λmax = 540 nm, εmax = 20 700 M-1 cm-1). Our studies further revealed that the RuII-RuIII and RuII-RuII species are formed in the electrochemical reduction of the RuIII-RuIII complex at 0.0 and -0.4 V (vs. SHE), respectively. Formation of RuII-RuIII and RuII-RuII was further corroborated by magnetic moment measurements and DFT calculations. Kinetic data and activation parameters are interpreted in terms of a mechanism involving rate-determining outer-sphere electron transfer between Ru(III) and the ascorbate monoanion (HA-) at pH 6.0. A detailed reaction mechanism in agreement with the spectral, spectro-electrochemical and kinetic data is presented. The results of the spectral and kinetic studies of the reaction of the RuII-RuII complex with molecular oxygen (O2) reveal the ability of the RuII-RuII species to effect the oxygen reduction reaction (ORR) leading to the formation of H2O2, a partial reduction product of dioxygen (O2).

Design, spectral characterization, quantum chemical investigation, biological activity of nano-sized transition metal complexes of tridentate 3-mercapto-4H-1,2,4-triazol-4-yl-aminomethylphenol Schiff base ligand

A tridentate Schiff base ligand, H2MTIP, was produced by condensing salicylaldehyde with 4-amino-4H-1,2,4-triazole-3-thiol. The ligand was then used to create nanosized complexes of Pt(II), Ni(II), Cu(II), and Pd(II). The complexes have the composition [Pt/Ni/Cu/or Pd(MTIP)(H2O)], this conclusion is supported by molar conductance, magnetic moments, elemental analyses, spectral analyses. In DFT analysis, the 6-31+ g(d,p) basis set was used to fully optimize the energy with respect to the shapes of Schiff base ligand and metal complexes. Pt(II), Ni(II), Cu(II), and Pd(II) complexes have been assigned square-planar geometries. At the same time, the intense diffraction peaks in X-ray diffractograms show their crystalline features with particle sizes in the nanoscale range. The binding interaction of calf thymus DNA with these metal complexes and their insulin-like activity was examined in vitro by inhibiting α-amylase. The study investigated the in-vitro activity of several complexes and identified Pt(II) complex as the one with the highest activity. The researchers then tested this complex for in-vivo antidiabetic activity in induced diabetic rats using the STZ model, and it significantly lowered blood glucose levels. The antioxidant activity and toxicity level of Pt(II) complex were also excellent, suggesting that it could be a good candidate for further research as a possible diabetes drug.Communicated by Ramaswamy H. Sarma.

Hexa- and octanuclear copper(II) complexes with a tetraeicosaaza amine macrocycle

One hexa- and two octanuclear Cu(II) complexes were synthesised from different metal salts and a very large (8 + 8) tetraeicosaaza macrocycle. These nitrate, chloride and sulphate coordination compounds were characterised by taking elemental analysis, spectroscopy, crystallography and magnetic susceptibility measurements. Their crystal structures revealed different interesting coordination modes of Cu(II) cations and nuclearity in these centrosymmetric complexes. For the sulphate complex two different, homo- vs. heterochiral, arrangements of the same macrocycle L3 around the same Cu(II) cations take place.

Copper(II) coordination polymer based on l-arginine as a supramolecular hybrid inorganic–organic material: synthesis, structural, spectroscopic and magnetic properties

We report the synthesis and structural, spectroscopic and magnetic properties of new 1D coordination polymeric complex {[Cu(μ-l-Arg)2]SO4⋅1.5H2O}n (1) that contains asymmetric μ−O,O’ carboxylic bridge linking distorted square-pyramidal [Cu(μ-l-Arg)2]2+ coordination units. In 1D, the syn−anti−μ2−η1:η1zigzag polymer conformation, the adjacent Cu(II) ions are distanced by 5.707 Å, and the subsequent Cu∙∙∙Cu proximity in 1D-coordination chain equals 6.978 Å. Detailed interpretation of IR and Raman spectra of l-arginine and 1 was performed. The principal components of the g tensor determined from EPR experiments (gx = 2.059, gy = 2.075, gz = 2.228) indicate nearly axial symmetry of Cu(II) coordination sphere and correspond to the unpaired electron occupying the dx2–y2 orbital. The single broad band at 16,200 cm–1, characteristic of d−d transition, is assigned to the dominant dublet-dublet 2B1g(dx2–y2)→ 2Eg(dyz≈dxz) transition. Magnetic susceptibility measurements have revealed ferromagnetic coupling between the Cu(II) ions within the 1D-coordination chain, while the intermolecular coupling is antiferromagnetic.

Graphical Abstract

New Dinuclear Macrocyclic Copper(II) Complexes as Potentially Fluorescent and Magnetic Materials

Two dinuclear copper(II) complexes with macrocyclic Schiff bases K1 and K2 were prepared by the template reaction of (R)-(+)-1,1'-binaphthalene-2,2'-diamine and 2-hydroxy-5-methyl-1,3-benzenedicarboxaldehyde K1, or 4-tert-butyl-2,6-diformylphenol K2 with copper(II) chloride dihydrate. The compounds were characterized by spectroscopic methods. X-ray crystal structure determination and DFT calculations confirmed their geometry in solution and in the solid phase. Moreover, intermolecular interactions in the crystal structure of K2 were analyzed using 3D Hirshfeld surfaces and the related 2D fingerprint plots. The magnetic study revealed very strong antiferromagnetic CuII-CuII exchange interactions, which were supported by magneto-structural correlation and DFT calculations conducted within a broken symmetry (BS) framework. Complexes K1 and K2 exhibited luminescent properties that may be of great importance in the search for new OLEDs. Both K1 and K2 complexes showed emissions in the range of 392-424 nm in solutions at various polarities. Thin materials of the studied compounds were deposited on Si(111) by the spin-coating method or by thermal vapor deposition and studied by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM), and fluorescence spectroscopy. The thermally deposited K1 and K2 materials showed high fluorescence intensity in the range of 318-531 nm for K1/Si and 326-472 nm for the K2/Si material, indicating that they could be used in optical devices.

Experimental and Theoretical Studies of the Optical Properties of the Schiff Bases and Their Materials Obtained from o-Phenylenediamine

Two macrocyclic Schiff bases derived from o-phenylenediamine and 2-hydroxy-5-methylisophthalaldehyde L1 or 2-hydroxy-5-tert-butyl-1,3-benzenedicarboxaldehyde L2, respectively, were obtained and characterized by X-ray crystallography and spectroscopy (UV-vis, fluorescence and IR). X-ray crystal structure determination and DFT calculations for compounds confirmed their geometry in solution and in the solid phase. Moreover, intermolecular interactions in the crystal structure of L1 and L2 were analyzed using 3D Hirshfeld surfaces and the related 2D fingerprint plots. The 3D Hirschfeld analyses show that the most numerous interactions were found between hydrogen atoms. A considerable number of such interactions are justified by the presence of bulk tert-butyl groups in L2. The luminescence of L1 and L2 in various solvents and in the solid state was studied. In general, the quantum efficiency between 0.14 and 0.70 was noted. The increase in the quantum efficiency with the solvent polarity in the case of L1 was observed (λex = 350 nm). For L2, this trend is similar, except for the chloroform. In the solid state, emission was registered at 552 nm and 561 nm (λex = 350 nm) for L1 and L2, respectively. Thin layers of the studied compounds were deposited on Si(111) by the spin coating method or by thermal vapor deposition and studied by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM), spectroscopic ellipsometry and fluorescence spectroscopy. The ellipsometric analysis of thin materials obtained by thermal vapor deposition showed that the band-gap energy was 3.45 ± 0.02 eV (359 ± 2 nm) and 3.29 ± 0.02 eV (377 ± 2 nm) for L1/Si and L2/Si samples, respectively. Furthermore, the materials of the L1/Si and L2/Si exhibited broad emission. This feature can allow for using these compounds in LED diodes.