Synthesis, Spectroscopy, and Redox Behavior of the Binuclear Complex Cation [Ni2(6,6‘-spirobi(cyclam))]4+(cyclam = 1,4,8,11-Tetraazacyclotetradecane): Characteristics of a Transient Ni(II)−Ni(III) Species

Degradation of Malachite green by Potassium persulphate, its enhancement by 1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane nickel(II) perchlorate complex, and removal of antibacterial activity

In this study, degradation of Malachite green (MG) (10mg/L) by Potassium persulphate (KPS) (1 g/L), and KPS in presence of (1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane) nickel(II) perchlorate (complex1), (200 μM), was investigated by spectrophotometric and HPLC methods. KPS alone had ability to degrade MG. Interestingly, rate of degradation of MG was enhanced upon addition of complex1. Degradation was effective at pH range of 3-9 and was found to be dependent on initial concentration of KPS, complex1, MG, and pH. Degradation of MG by KPS was not significantly affected in presence of Ni(II) ions whereas in presence of Fe(II) ions degradation was incomplete. Ability of KPS to reduce TOC increased in presence of complex1. Transformation products were analysed by LC-ESI-MS. Finally, treatment of MG with complex1 and KPS resulted in removal of antibacterial activity of MG under in vitro conditions.

Tunable Charge Delocalization in Dinickel Quinonoid Complexes

When a 2,5-diamino-1,4-benzoquinonediimine C6H2(=NR)2(NHR)2 (2) is used as a bridging ligand, new dinickel(II) complexes [(acac)Ni[mu-C6H2(=NPh)4]Ni(acac)] (3a: R=Ph) and [(acac)Ni[mu-C6H2(=NCH2tBu)4]Ni(acac)] (3b: R=CH2tBu) are obtained; upon one-electron oxidation of these complexes delocalized mixed-valence compounds are formed. An X-ray diffraction study on 3b reveals equalization of the bond lengths within each of the ligand 6 systems and a lack of conjugation between them. The oxidized state in 3b+ involves both the bridging quinonoid ligand and the metal centers, with a major contribution coming from the bridging ligand. Electrochemical and spectroscopic methods were used to study the influence of the N-substituents of the tetranitrogen donor ligands 2. In this combined experimental and theoretical (DFT) study, it is also shown that the electronic structure within the dinickel system can be altered by addition of a coordinating ligand such as pyridine. The latter favors the high-spin configuration with semi-occupied metal-centered orbitals, leading to a metal-metal interaction in the mixed-valence Ni(II)-Ni(III) 3b+ system.

Stepwise Complexation of Ni(II) and Cu(II) Ions by 6,6'-C-spirobi(cyclam) (cyclam = 1,4,8,11-Tetraazacyclotetradecane), L(1). Syntheses and Redox Chemistry of [M(H(2)L(1))]X(4) (M = Cu(2+), Ni(2+)), [Cu(2)(L(1))]X(4), and [CuNi(L(1))]X(4) (X = ClO(4)(-)) and the X-ray Crystal Structure of [Cu(2)(L(1))](ClO(4))(4)

In aqueous HClO(4), the cation [H(4)(L(1))](4+) where L(1) is 6,6'-C-spirobi(cyclam) (cyclam = 1,4,8,11-tetraazacyclotetradecane), complexes Cu(2+) and Ni(2+) ions in a stepwise fashion to form [M(H(2)L(1))](ClO(4))(4) (M = Cu(2+) and Ni(2+)) from which [CuNi(L(1))](ClO(4))(4) has been prepared selectively. The preparation and the structure of [Cu(2)(L(1))](ClO(4))(4) (empirical formula, C(19)H(44)N(8)Cu(2)Cl(4)O(16); space group, triclinic; P&onemacr;; a = 8.1815(6) Å, b = 12.6098(9) Å, c = 16.6565(12) Å, alpha = 80.3890(10) degrees, beta = 76.5840(10) degrees, gamma = 87.1750(10) degrees, V = 1647.9(2) Å(3), and Z = 2; of the 9531 total reflections collected, 6779 reflections with I > 2sigma(I) on least-squares refinement provided final R(1) = 0.0657 and wR(2) = 0.1424) are also reported. The cyclic voltammograms (1.0 M NaCl, 0.1 M H(+); Pt electrodes; all E(1/2) vs NHE) of [M(H(2)L(1))](4+) (M = Cu(2+) and Ni(2+)) ions show single waves for the Cu(II)/Cu(III) couple (E(1/2) = 0.79 V, irreversible) and the Ni(II)/Ni(III) couple (E(1/2) = 0.56 V, reversible), respectively. In CH(3)CN (0.1 M Et(4)NClO(4)), the [Cu(2)(L(1))](4+) ion shows a reversible wave for the Cu(II)-Cu(II)/Cu(II)-Cu(III) couple ((1)E(1/2) = 1.120 V) and an irreversible wave for the Cu(II)-Cu(III)/Cu(III)-Cu(III) couple ((2)E(1/2) = 1.430 V). Similarly, a reversible wave for the Cu(II)-Ni(II)/Cu(II) -Ni(III) couple ((1)E(1/2) = 0.750 V) and an irreversible wave for the Ni(III)-Cu(II)/Ni(III)-Cu(III) couple ((2)E(1/2) = 1.20 V) are observed in the case of the [Cu(II)Ni(II)(L(1))](4+) ion. The [Cu(2)(L(1))](4+) ion (g( perpendicular) = 2.120, g( parallel) = 2.256 and 2.196, A( parallel) = 150 G, and D( parallel) = 75 G) and the mixed valent species [Cu(II)Ni(III)(L(1))](5+) (for Cu(2+), g( perpendicular) = 2.060, g( parallel) = 2.219, and A( parallel) = 100 G; for Ni(3+) in sulfate media, g( perpendicular) = 2.204 and g( parallel) = 1.967) and [Cu(II)Cu(III)(L(1))](5+) (g(xx)() = 1.982, g(yy)() = 2.155, g(zz)() = 2.386, A(yy)() = 80 G, and A(zz)() = 120 G) show dipolar-dipolar interaction. In the mixed-valent ions, due to strong electrostatic repulsion from either the Ni(III) or Cu(III) ions, significantly smaller A( parallel) (or A(zz)()) values are observed for the Cu(2+) ion compared to 200 G in the mononuclear ions. Also, the [Cu(II)Ni(II)(L(1))](4+) in aqueous HClO(4) and the [Ni(2)(L(1))](4+) ion in CH(3)NO(2) show a tendency to reduce perchlorate very slowly.