Copper(II) and Copper(I) Complexes with an Open-Chain N₄Schiff Base Ligand Modeling CuZn Superoxide Dismutase:  Structural and Spectroscopic Characterization and Kinetics of Electron Transfer

Abstract

The structure of the complex [CuII(PuPy)](ClO4)2 (PuPy = L = 1,8-bis(2-pyridyl)-2,7-diazaoctadiene-1,7) and the structure of the corresponding copper(I) complex were determined. In CuIIL(ClO4)2, a model compound with CuZnSOD activity, the unit CuIIL2+ has a tetrahedrally distorted square-planar N4 coordination geometry. The copper(I) complex with L was found to be dimeric, (CuIL)2(ClO4)2.DMF (DMF = N,N-dimethylformamide). The binuclear unit (CuIL)2(2+) has a helical structure with two ligands L bridging the two copper atoms to provide tetrahedral N4 coordination of each copper(I). In solutions of (CuIL)2(ClO4)2.DMF, solvent-dependent dissociation occurs according to D reversible 2M (D = (CuIL)2(2+); M = CuILSx+; S = solvent). Stopped-flow spectrophotometry was used to determine the rate constants for the dissociation of the dimer D (kM) and dimerization of the monomer M (kD) for S = acetonitrile and DMF. Equilibrium constants Kdim = kM/kD were determined spectrophotometrically. In aqueous solution, the oxidation of the dimer (CuIL)2(2+) by CoIII(NH3)5Cl2+ and cis- and trans-CoIII(en)2Cl2+ follows a second-order rate law, rate = kox[(CuIL)2(2+)][Co(III)]. Data for rate constant kox and for the activation parameters delta H++ and delta S++ are presented. In DMF, the oxidation of (CuIL)2(2+) by CoIII(NH3)5Cl2+ occurs via the monomer CuIL(DMF)x+ and the dissociation of (CuIL)2(2+) becomes rate-controlling. The reduction of CuIIL2+ by RuII(edta)H2O2- was found to be too fast to be resolved by stopped-flow spectrophotometry. The kinetic results are discussed mechanistically in terms of the redox switch aspects of the system.

Steric and Electronic Factors Affecting the Conformation of Bimetallic CuI Complexes: Effect of the Aliphatic Spacer of Tetracoordinating Schiff‐Base Ligands

“…In the homoleptic series, [Cu I (L 2 )] 2 (ClO 4 ) 2 and [Cu I (L 4 )] 2 (ClO 4 ) 2 have been reported previously by Pal [37] andL ange, [31] respectively.T he molecular structures of both complexes show that they are bimetallic helicates in the solids tate and crystallize as racemic products. As reported by Lange, [Cu I (L 4 )] 2 (ClO 4 ) 2 dissociates in solution yielding the monometallic complex [Cu I (L 4 )] + , in an equilibrium dependent on the nature of the solvent.…”

“…However,l ittle is knowna bout how ag iven conformationa ffects the stabilityo ft he complex in solution, particularly forh elicates or mesocates that experience dissociative reactions upon dissolution. [31,32] Dissociation of helicates when Cu I is oxidized resultsi narearrangement of the geometry around the copperi on in addition to ac hange in the nuclearity of the complexes.S uch processes have been investigated because of their relation to redox switches. [24] Less understood,h owever,a re processes driving helicate dissociation without achange in the oxidation state.…”

Metal-mediated diradical tuning for DNA replication arrest via template strand scission

“…6). The equatorial Cu-N distances range from 1.99 to 2.01 Å, typical for Cu-imine single bonds (76)(77)(78), whereas the axial pyridine shows weaker coordination (2.16 Å) (SI Appendix, Table S1). This solid-state geometry provides an open coordination site trans to the axial pyridine for solvent coordination, forming a tetragonally elongated octahedron that accounts for the low-energy ligand field transitions observed in the electronic absorption spectrum.…”

Spectroscopic characterization of schiff base-copper complexes immobilized in smectite clays

“…27 The crystal structures of both species were determined, indicating a monomeric square-planar tetrahedrally distorted compound for the oxidized species, and a helical structure for the dimeric red-brown reduced species. 27 The dimeric copper(I) species formation is credited to the long chain imine ligand, allowing the coordination of the same ligand to both copper centers, and this reduced form exhibits a maximum absorption at 478 nm (ε = 13.6 x 10 3 M -1 cm -1 ), in aqueous solution.…”

“…The structure with lowest energy, shown in Figure 4b, is more distorted than the almost square planar, shown at Figure 4a, A similar behavior (smaller distortion for the oxidized form when compared to the reduced form), has been observed in analogous copper complexes, with longer chain imine ligands (four CH 2 groups between the N coordinating atoms). 27,31 Since here the focus is to investigate the behavior of these complexes immobilized in two dimensional inorganic matrices, some possible theoretical conformations were considered in order to calculate electronic and optical properties which are then compared to the available measurements. A relevant question to be addressed here is if the complexes can be accommodated between the clay layers.…”