Antonio Cinti

Cobalt Electrolyte/Dye Interactions in Dye-Sensitized Solar Cells: A Combined Computational and Experimental Study

We report a combined experimental and computational investigation to understand the nature of the interactions between cobalt redox mediators and TiO(2) surfaces sensitized by ruthenium and organic dyes, and their impact on the performance of the corresponding dye-sensitized solar cells (DSSCs). We focus on different ruthenium dyes and fully organic dyes, to understand the dramatic loss of efficiency observed for the prototype Ru(II) N719 dye in conjunction with cobalt electrolytes. Both N719- and Z907-based DSSCs showed an increased lifetime in iodine-based electrolyte compared to the cobalt-based redox shuttle, while the organic D21L6 and D25L6 dyes, endowed with long alkoxy chains, show no significant change in the electron lifetime regardless of employed electrolyte and deliver a high photovoltaic efficiency of 6.5% with a cobalt electrolyte. Ab initio molecular dynamics simulations show the formation of a complex between the cobalt electrolyte and the surface-adsorbed ruthenium dye, which brings the [Co(bpy)(3)](3+) species into contact with the TiO(2) surface. This translates into a high probability of intercepting TiO(2)-injected electrons by the oxidized [Co(bpy)(3)](3+) species, lying close to the N719-sensitized TiO(2) surface. Investigation of the dye regeneration mechanism by the cobalt electrolyte in the Marcus theory framework led to substantially different reorganization energies for the high-spin (HS) and low-spin (LS) reaction pathways. Our calculated reorganization energies for the LS pathways are in excellent agreement with recent data for a series of cobalt complexes, lending support to the proposed regeneration pathway. Finally, we systematically investigate a series of Co(II)/Co(III) complexes to gauge the impact of ligand substitution and of metal coordination (tris-bidentate vs bis-tridentate) on the HS/LS energy difference and reorganization energies. Our results allow us to trace structure/property relations required for further development of cobalt electrolytes for DSSCs.

New pentanuclear mixed valence Co(II)–Co(III) complexes of “short” salen homologues

We describe herein a series of novel pentanuclear Co(II)–Co(III) mixed-valence cationic complexes of formula [Co5L4(μ3-OH)2]+ {L2− = 2,2′-[1,1-methanediylbis(nitrilomethylidene)diphenate] or its arylmethane analogues}, obtained by controlled oxidation of [Co2L2] precursors. The [Co5(μ3-OH)2(salNO2ben)4]I·2(CH3)2CO and [Co5(μ3-OH)2(salClben)4]I·2DMF·CH2Cl2 compounds have been studied by X-ray methods and turn out to be isostructural. The structural data show that the cobalt atoms in the pentanuclear units are bridged by μ-O(phenolato) atoms and μ3-OH groups and approximate three types of co-ordination geometries: tetrahedral, octahedral and trigonal-bipyramidal. The X-ray structure of one proligand, namely 2,2′-[1,1-(4-nitrophenylmethanediyl)bis(nitrilomethylidene)diphenol] is also reported. The χT(T) behaviour of the complex with this ligand has been studied in the 4–300 K range. The data clearly show that ferromagnetic as well as (much weaker) antiferromagnetic exchange interactions occur within the cluster. A simple exchange model has been developed which nicely reproduces the experimental data.

Structure and Magnetism of a New 2-D Bimetallic Compound of Mn(II) and Cu(II)

Abstract We present the X-ray structure and the magnetic properties of the new compound {[Cu(en)2]3[Mn(NCS)6]} (NCS)2 (en═H2N-CH2-CH2-NH2).

Binuclear Co(II)Co(II), Co(II)Co(III) and Co(III)Co(III) complexes of “short” salen homologues derived from the condensation of salicylaldehyde and methanediamine or phenylmethanediamines. Synthesis, structures and magnetism

Binuclear Co(II)Co(II), Co(II)Co(III) and Co(III)Co(III) complexes are reported of dianionic ligands, L2−, derived from the condensation of two mol of salicylaldehyde, or substituted salicylaldehydes, and one mol of methanediamine or phenyl substituted methanediamines. Direct evidence for the binuclear nature of the compounds is provided by X-ray structural and FAB mass spectroscopy data. Oxidation of the Co(II)Co(II) complexes, [Co2L2], with iodine, in the presence of pyridine, produces two types of compounds depending on the nature of L: mixed valence Co(II)Co(III) dimers of [Co2L2(py)2](I3) stoichiometry, in the case of the phenylmethane derivatives and fully oxidised Co(III)Co(III) dimers, [Co2L2(py)4](I3)2, obtained from the complexes with methanediamine. The crystal structures of [Co2(salben)2(py)2](I3) and [Co2(salmen)2(py)4](I3)2 (salben = N,N′-phenylmethanediyldiphenato, salmen = N,N′-methanediyldiphenato) have been determined. In both dimers the Co atoms are bridged by two bis-bidentate ligands. The coordination geometry of the Co(II) chromophore, CoN2O2, was found to be distorted tetrahedral, as preliminarily suggested by near infrared and room-temperature magnetic susceptibility data. The Co(III) environments, CoO2N4, involving two additional pyridine nitrogens, are regular octahedral. The magnetic behaviour of representative compounds has been determined and discussed.

Next-Nearest Neighbor Exchange Interactions in the Bimetallic Chain Compound Cu(en)2MnCl4

Abstract The magnetic properties of the title compound reveal antiferromagnetic coupling between the next-nearest neighbor Mn(II) ions and no discernible MnCu coupling.