Millennium Nucleus
Molecular Engineering for Catalysis and Biosensors

What we learned...


Heavy Element Metallacycles: Insights into the Nature of Host-Guest Interactions Involving Dihalide Mercuramacrocycle Complexes
Miguel Ponce-Vargas, and Alvaro Muñoz-Castro
J. Phys. Chem. C, 2014, 118 (48), pp 28244–28251 [4.772, 2014]
DOI:   10.1021/jp5092625
Host-guest chemistry is a relevant issue in materials science, which encompasses the study of highly structured molecular frameworks composed of at least two complementary entities associated through noncovalent interactions, where structures involving several metallic centers, namely, metallacycles, acting as host species, offer significant advantages over organic systems due to the high versatility of their binding sites in terms of ion recognition. In this context, we study via relativistic density functional calculations the host–guest formation of systems involving a heavy element metallacycle, [HgC(CF3)2]5, which binds to several halide anions to give [(HgC(CF3)2)5 2X]2 (X = Cl, Br, I). Our results reveal an interesting case where the expected soft acid–soft base pair is not the more stable situation. Instead, a surprising hard–soft pair arises as the preferred species, with stronger forces toward Cl- than those corresponding to I- by about 24 kcal/mol. To understand such a situation, the use of a detailed analysis of the energy decomposition analysis (EDA) terms suggests the electrostatic character of the host–guest pair, which is ruled by the ion–dipole term by about 97%, favoring the inclusion of the hard base, namely, Cl-, instead of the softer counterpart, I-. The current approach allows determining the role of certain Coulombic terms in the electrostatic nature of the interaction, leading to a clear rationalization of the soft–soft or hard–soft preferences into the formation of host–guest pairs, which can be extended to the study of the behavior of several organic or inorganic systems.

Understanding the Influence of Terminal Ligands on the Electronic Structure and Bonding Nature in [Re63-Q8)]2+ clusters
Walter Alfonso Rabanal-León , Juliana Andrea Murillo-Lopez , Dayán Páez Hernández , and Ramiro Arratia-Perez
J. Phys. Chem. A, Just Accepted Manuscript [2.693, 2014]
DOI:   10.1021/jp508892r
Since the synthesis of the first molecular cluster [Re63-Q8)X6]4- and the substitutional lability of the terminal ligands prompted new developments in their chemistry, that makes these molecular clusters a reasonable point of departure for building new materials. The development of novel inorganic materials of technological interest certainly requires an understanding of the electronic structure, bonding, spectroscopy, photophysical and structural properties of these clusters. Taking into account the potential applications in material sciences, and the lack of systematization on the study of these kind of clusters, the proposal of the present work is to perform a detailed theoretical study of the[Re63-Q8)X6]4- (Q = S2-, Se2-, Te2-; X = F-, Cl-, Br-, I-, CN-, NC-, SCN-, NCS-, OCN-, NCO-) clusters based on the deeply description of the electronic structure of these complexes and the bonding nature between the [Re63-Q8)]2+ core and several donor/acceptor terminal ligands. All this work was developed on the framework of the relativistic density functional theory (R-DFT), where relativistic effects were incorporated by means of a two-component Hamiltonian with the zeroth-order regular approximation (ZORA). To describe the relative stability of these complexes, we employed the global descriptors of chemical hardness (η) and softness (S) introduced by Pearson. Moreover, an analysis of bonding energetics were performed by combining a fragment approach to the molecular structure with the decomposition of the total bonding energy (EBE), according to the Morokuma-Ziegler energy partitioning scheme. After an analysis of these results we found in all cases an extensive ionic character in the bonding between the core an each peripheral ligand. The interaction between the halide ligand and the core gives about 75% ionic character while the other ligands shows a more covalent interaction due to effective synergic mechanisms. We conclude that the most stable clusters are those which present the stronger ?-donor terminal ligands, while the cluster stability start to decrease when the ?-acceptor effect will be stronger; this fact is directly related with the terminal ligand lability and with the strong electrophilic character of the [Re63-Q8)]2+ core.

Covalent lanthanide(III) macrocyclic complexes: the bonding nature and optical properties of a promising single antenna molecule
Walter A. Rabanal-León, Dayán Páez-Hernández and Ramiro Arratia-Pérez
Phys. Chem. Chem. Phys., 2014, 16 (47), 25978 - 25988 [4.493, 2014]
DOI:   10.1039/C4CP03882G
The present work is focused on the elucidation of the electronic structure, bonding nature and optical properties of a series of low symmetry (C2) coordination compounds of type [LnIIIHAM]3+, where "LnIII" are the trivalent lanthanide ions: La3+, Ce3+, Eu3+ and Lu3+, while "HAM" is the neutral six-nitrogen donor macrocyclic ligand [C22N6H26]. This systematic study has been performed in the framework of the Relativistic Density Functional Theory (R-DFT) and also using a multi-reference approach via the Complete Active Space (CAS) wavefunction treatment with the aim of analyzing their ground state and excited state electronic structures as well as electronic correlation. Furthermore, the use of the energy decomposition scheme proposed by Morokuma-Ziegler and the electron localization function (ELF) allows us to characterize the bonding between the lanthanide ions and the macrocyclic ligand, obtaining as a result a dative-covalent interaction. Due to a great deal of lanthanide optical properties and their technological applications, the absorption spectra of this set of coordination compounds were calculated using the time-dependent density functional theory (TD-DFT), where the presence of the intense Ligand to Metal Charge Transfer (LMCT) bands in the ultraviolet and visible region and the inherent f-f electronic transitions in the Near-Infra Red (NIR) region for some lanthanide ions allow us to propose these systems as "single antenna molecules" with potential applications in NIR technologies.

Reactivity trends of Fe phthalocyanines confined on graphite electrodes in terms of donor-acceptor intermolecular hardness: Linear versus volcano correlations
C. Linares-Flores, J. Espinoza-Vergara, J.H. Zagal, R. Arratia-Perez
Chemical Physics Letters 614 (2014) 176-180 [1.897, 2014]
DOI:   10.1016/j.cplett.2014.09.033
In this work, we have studied the interaction between the hydrazine N2H4 molecule with several FeN4 macrocyclic complexes (FePc's). In order to modulate the electron density located on the metal center using iron-phthalocyanine (FePc) as the reference, we used substituted iron-phthalocyanines with different types of substituents electron-donating groups such as iron-tetraamino-phthalocyanine (4β(NH2)FePc) and iron-octamethoxyphthalocyanine (8β(OCH3)FePc), and with electron-withdrawing groups such as iron-tetranitrophthalocyanine(4β(NO2)FePc) and iron-hexadecachlorophthalocyanine (16(Cl)FePc), respectively. We have found that the energy of interaction between hydrazine and the Fe center in the macrocycle increases as the electron-withdrawing power of the substituents increases. When rate constants instead of currents are compared in a semilog plot versus ΔεD-A, a linear correlation is found where log k increases as the intermolecular hardness of the systems decreases.

Advances in Nanomedicine Towards Clinical Application in Oncology and Immunology
Eduardo Herreros, Sebastián Morales, Cristian Cortés, Mauricio Cabaña, Juan Pablo Peñaloza, Lilian Jara, Daniela Geraldo, Carolina Otero and Ricardo Fernández-Ramires
Current Pharmaceutical Biotechnology, 2014, 15(9), 864-879 [2.511, 2014]
DOI:   10.2174/1389201015666140909122727
Recent advances in nanotechnology and nanobiotechnology have contributed to the development of nanomaterials, able to be used as drug carriers, probes, targets or cytostatic drugs by itself. Nanomedicine is now the leading area in nanotechnology where a large number and types of nanoparticles (NPs) has been developed and several are already in the clinical practice. Chemotherapy is one of the most widely used strategies to treat cancer. Most chemotherapeutic agents have poor solubility, low bioavailability, and are formulated with toxic solvents. NPs have been designed to overcome the lack of specificity of chemotherapeutic agents as well to improve circulation time in blood, taking advantages on tumor cells characteristics. In immunology, recent advances regarding the activation of the innate immune system artificially enhanced by NPs functionalized with immune-stimulators open a new window as novel methods in vaccines. Also, viruses and virus-like particles (VLPs) engineered to stimulate immune response against their similar virus or as molecular platforms for the presentation of foreign epitopes have been described. In this review we focused in the use of different types of NPs in oncology and immunology, pinpointing the main novelties regarding their development and use of nanotechnology in a broad array of applications, ranging from tumor diagnostics, immune-modulation up to cancer therapeutics

Predicting the electronic structure and magnetic properties of UO2+, UO2(CO)5+ and UO2(Ar)2+ using wavefunction based methods
Dayán Páez-Hernández
Journal of Electron Spectroscopy and Related Phenomena 197 (2014) 1-6 [1.436, 2014]
DOI:   10.1016/j.elspec.2014.08.002
The electronic structure and magnetic properties of UO2+, and two complexes, UO2(CO)5+ and UO2(Ar)2+ in D5h symmetry are studied with a combination of relativistic theoretical methods: ab-initio wavefunction calculations, density functional theory (DFT), and crystal-field (CF) models with parameters extracted from the ab-initio calculations. The model Hamiltonian techniques are employed to describe theoretically the state interaction and the "competition" between Crystal field (CF) and spin-orbit coupling (SO), this is important besides for a correct description of the sign of the g-factors using also a symmetry criteria.

Understanding Planar Ligand-Supported MAu5 and MAu6 Cores. Theoretical Survey of [MAu5(Mes)5] and [MAu6(Mes)6] (M = Cu, Ag, Au; Mes = 2,4,6-Me3C6H2) Under the Planar Superatom Model
A. Muñoz-Castro and R. Guajardo Maturana
J. Phys. Chem. C, 2014, 118 (36), pp 21185–21191 [4.772, 2014]
DOI:   10.1021/jp5057557
The planar superatom model has been applied to the case of planar ligand-supported MAu5 and MAu6 cores, where M = Cu(I), Ag(I), and Au(I), in order to increase the understanding of the electronic structure and bonding properties of planar golden clusters. The study of [Au5(Mes)5], [Au6(Mes)6], [MAu5(Mes)5], and [MAu6(Mes)6] has been carried out by using relativistic DFT calculations, which describe the short d10–d10 contacts due to the bonding stabilization within the Aun core in addition to the respective aurophilic phenomena. The results under the planar superatom approach allow us to characterize the electronic structure in all the systems as formally 10 valence electron cores, depicting an overall 1s21px,y41dxy,x2–y24 configuration as a result of the ligand–metal interaction. The inclusion of the respective M(I) closed shell center increases the number of superatomic shells as 1s1p1d ? 1s1p1d2s, denoting the interaction between each concentric section. Our results suggest that the MAun cores could be conveniently viewed as the combination of concentric structures denoted by [M@Aun]. In addition, the role of the inclusion of the spin–orbit term into the planar superatom model is discussed.

sp3-hybridization in superatomic clusters. Analogues to simple molecules involving the Au6 core
A. Muñoz-Castro
Chem. Sci., 2014,5, 4749-4754 [9.211, 2014]
DOI:   10.1039/C4SC01719F
The electronic and structural properties of [Au6{Ni3(CO)6}4]2- pave the way to describe a superatom analogue of the most simple and archetypical hydrocarbon, CH4. In this sense, our interest relies on the plausibility of finding superatomic clusters as analogues for archetypical molecules in organic chemistry, preserving relevant concepts of chemical significance, such as the hybridization of atomic orbitals. In [Au6{Ni3(CO)6}4]2-, a central Au6 core exhibits the formation of superatomic SP3 hybridized orbitals in order to account for the molecular shape and bonding. Inspired by this finding, several clusters were proposed exploring the capabilities of the metallic core to exhibit SP2 and SP superatomic hybrid orbitals. In addition, we include the evaluation of superatomic bonding involving SP3SP3, SP2SP2 and SPSP hybridized cores, which denote single, double and triple superatomic bonds. Our results describe the extension of the localized Lewis structure model to the understanding of clusters according to the superatom model, contributing to the tremendous opportunities for the design of functional clusters and nanoparticles.

In Search of the Best Iron N4-Macrocyclic Catalysts Adsorbed on Graphite Electrodes and on Multi-walled Carbon Nanotubes for the Oxidation of l-Cysteine by Adjusting the Fe(II)/(I) Formal Potential of the Complex
Cristian A. Gutierrez, J. Francisco Silva, F. Javier Recio, Sophie Griveau, Fethi Bedioui, Claudia A. Caro, José H. Zagal
Electrocatalysis, 2014, 5(4), 426-437 [2.089, 2014]
DOI:   10.1007/s12678-014-0209-y
The redox potential of macrocyclic complexes is a very predictive reactivity index for the electrocatalytic activity of these molecules, and it can be easily measured under the same conditions of the catalysis experiments. It reflects directly the activity of a given complex. We have investigated the effect of the Fe(II)/(I) formal potential on the catalytic activity of a series of Fe porphyrins and Fe phthalocyanines for the electrooxidation of l-cysteine, with the complexes directly adsorbed on ordinary pyrolytic graphite or adsorbed on multi-walled carbon nanotubes (MWCNTs) deposited on graphite. A correlation of log j (at constant potential) versus the Fe(II)/(I) formal potential of the catalysts gives a volcano curve for both systems without and with MWCNTs with higher activities in the latter case. Our results clearly show that the highest catalytic activity is achieved in a rather narrow potential window of Fe(II)/(I) formal potentials of N4-macrocyclic complexes. The use of MWCNTs as supporting material for the catalysts does not change the reactivity trends of the Fe complexes.

A study on the versatility of metallacycles in host-guest chemistry: Interactions in halide-centered hexanuclear copper(II) pyrazolate complexes
M. Ponce-Vargas, A. Muñoz-Castro
Phys. Chem. Chem. Phys., 2014,16, 13103-13111 [4.493, 2014]
DOI:   10.1039/C4CP01238K
Hexanuclear copper(II) pyrazolate complexes have shown the ability to encapsulate different halide ions, leading to [trans-Cu6{μ-3,5-(CF3)2pz}6(μ-OH)6X]- (X = F, Cl, Br, I). They offer an interesting case study for variation in local properties at host binding sites, due to the presence of a six membered ring involving Cu(II) centers considered as the borderline Lewis acid according to the Pearson Hard and Soft Acids and Bases (HSAB) principle. Here, we describe the host-guest interactions via relativistic density functional calculations, involving the graphical description of local dipole and quadrupole moments, energy decomposition analysis, non-covalent indices, and magnetic behavior. The observed variation in the copper local dipole and quadrupole moments suggests that a metallacycle host offers great advantages in comparison to their organic counterparts, prompted by the versatility of the metallic centers to modulate the surrounding electron density accordingly. According to our results, the contribution of ion-dipole forces in the halide-centered series decreases from 95.0% to 77.0% from the fluoride to the iodide complex, whereas the contribution of higher order interactions such as quadrupole-dipole and quadrupole-quadrupole, goes from 5.0% to 23.0% towards a softer guest. In addition, the through-the-space magnetic response of trans-Cu6{μ-3,5-(CF3)2pz}6(μ-OH)6, reveals a noteworthy aromatic structure, which is driven by the superexchange through the ligands leading to a singlet ground state.

Direct Spectroscopic Evidence for Constituent Heteroatoms Enhancing Charge Recombination at a TiO2?Ruthenium Dye Interface
Ke Hu, Holly A. Severin, Bryan D. Koivisto, Kiyoshi C. D. Robson, Eduardo Schott, Ramiro Arratia-Perez, Gerald J. Meyer, and Curtis P. Berlinguette
J. Phys. Chem. C 2014, 118 (30), pp 17079-17089 [4.772, 2014]
DOI:   10.1021/jp500879p
A series of three bis(tridentate) cycloruthenated sensitizers with furyl, thiophene, or selenophene units attached to the cyclometalated ligand were designed to examine how chalcogen atoms effect interfacial electron transfer events that occur following the absorption of visible light by the sensitizers when attached to mesoporous titania thin films immersed in CH3CN electrolytes. Spectroelectrochemistry established that the RuIII/II reduction potentials were confined to the 0.954–0.965 V vs NHE range for the series and that the density of TiO2 acceptor states were sensitizer-independent. Pulsed light excitation into the metal-to-ligand charge transfer band of the sensitized thin films resulted in rapid excited state injection, kinj > 108 s–1. Charge recombination (RuIII/TiO2(e) ? RuII/TiO2) rate constants were insensitive to the identity of the cyclometalated compound, yet the open circuit photovoltages were markedly lower for the compound containing selenophene. These lower photovoltages appear to be a manifestation of a 4-fold-larger, second-order rate constant measured for the reaction between triiodide and TiO2(e) in the case that the selenophene comprises the donor fragment of the dye. Adduct formation between oxidized iodide(s) and the selenophene moiety of the sensitizer is implicated.

Optimization of the electrocatalytic activity of MN4-macrocyclics adsorbed on graphite electrodes for the electrochemical oxidation of L-cysteine by tuning the M (II)/(I) formal potential of the catalyst: an overview
Francisco J. Recio, Cristian A. Gutierrez, Ricardo Venegas, Cristian Linares-Flores, Claudia A. Caro, José H. Zagal
Electrochimica Acta 2014, 140, 482-488 [4.504, 2014]
DOI:   10.1016/j.electacta.2014.04.098
The M(II)/(I) formal potential of MN4 macrocyclic complexes dictates their electrocatalytic activity for many reactions and L-cysteine oxidation is not an exception. In this work we review the literature related to this reaction and propose a semi-empirical model that can describe the catalytic activity of these chelates in terms of their formal potential. A correlation of log i (at constant potential) versus the M(II)/(I) formal potential for M= Fe,Co) of the catalysts gives a volcano curve. Our results clearly show that the M (II)/(I) formal potential of N4-macrocyclic complexes needs to be adjusted to values around -1.0 V vs. SCE to obtain the highest catalytic activity for the oxidation of L-cysteine. When comparing chelates of different metals (M= Cr, Mn, Fe, Co) of tetrasulphonated phthalocyanines only a linear correlation is obtained.

Synthesis, characterization and computational studies of (E)-2-{[(2-Aminopyridin-3-yl) imino]-methyl}-4,6-di-tert-butylphenol
Alexander Carreño, Andrés Vega, Ximena Zarate, Eduardo Schott, Manuel Gacitúa, Ninnette Valenzuela, Marcelo Preite, Juan M. Manríquez, and Ivonne Chávez
Quim. Nova, 2014, 37(4), 584-588 [0.658, 2014]
DOI:   10.5935/0100-4042.20140098
(E)-2-{[(2-Aminopyridin-3-yl)imino]-methyl}-4,6-di-tert-butyl-phenol (3), a ligand containing an intramolecular hydrogen bond, was prepared according to a previous literature report, with modifications, and was characterized by UV-vis, FTIR, 1H-NMR, 13C-NMR, HHCOSY, TOCSY and cyclic voltammetry. Computational analyses at the level of DFT and TD-DFT were performed to study its electronic and molecular structures. The results of these analyses elucidated the behaviors of the UV-vis and electrochemical data. Analysis of the transitions in the computed spectrum showed that the most important band is primarily composed of a HOMO-LUMO transition, designated as an intraligand (IL) charge transfer.

Linear versus volcano correlations for the electrocatalytic oxidation of hydrazine on graphite electrodes modified with MN4 macrocyclic complexes
Federico Tasca, F. Javier Recio, Ricardo Venegas, Daniela A. Geraldo, Mamie Sancy, José H. Zagal
Electrochimica Acta, 2014, 140(10), 314–319 [4.504, 2014]
DOI:   10.1016/j.electacta.2014.04.059
For electrochemical reactions catalyzed by electrodes modified with MN4 macrocyclic transition metal complexes, it is commonly accepted that d-band vacancy, surface lattice strain, and eg-orbital filling the transition metals are essential parameters to take in account for an optimum catalysis. These parameters affect the formal potential of the catalyst which is related to the free energy of the adsorption of the reacting molecule to a point that volcano correlations have been reported when plotting the activity of the catalyst versus the Mz+/M(z-1)+ formal potential of the catalyst (M (II) = Fe, Co). The highest catalytic activity is achieved when the formal potential of the catalyst is close to ?0.5 V vs SCE regardless of whether the central metal is Fe or Co. In this work, we review the work done until now on the oxidation of hydrazine in alkaline medium at metallophthalocyanines modified graphite electrodes and we show that for some complexes the redox potential of the MN4 macrocyclic transition metal complex can be varied changing the concentration of the catalyst at the electrode surface. Therefore we show that if log i (normalized for the actual surface concentrations of M(II) active sites (M = Fe, Co) at constant potential is plotted versus the M(II)/(I), the correlations is linear with a slope close to 2RT/F.

Preparation and Characterization of Electrodes Modified with Pyrrole Surfactant, Multiwalled Carbon Nanotubes and Metallophthalocyanines for the Electrochemical Detection of Thiols
Magdalena Rangel Argote, Elizabeth Sánchez Guillén, Ana Gabriela Gutiérrez?Porras, Oracio Serrano Torres, Cyrille Richard, José H. Zagal, Fethi Bedioui, Silvia Gutierrez Granados, and Sophie Griveau
Electroanalysis, 2014, 26(3), 507–512 [2.138, 2014]
DOI:   10.1002/elan.201300578
Our aim was to prepare hybrid electrodes active towards the electrooxidation of thiols by the co-immobilization of native carbon nanotubes (CNTs) and cobalt phthalocyanine (CoPc) from aqueous solutions. This strategy was adopted to avoid the oxidation of CNTs that can induce a modification of their exceptional properties. To do so, a hydrosoluble pyrrole surfactant was used to get homogeneous aqueous dispersions of CNTs and CoPc and to trap both materials on the electrode via the electropolymerization of the pyrrole surfactant. The hybrid electrodes exhibit a good electrocatalytic activity towards the oxidation of L-cysteine and glutathione. Their performances in terms of limit of detection (0.01?mM) are compatible with the detection of these thiols in biological samples.

Application of a planar superatom model on [Hg5(C(CF3)2)]. Bonding and magnetic response considerations into a five-fold d10-d10 metal cycle
Alvaro Muñoz-Castro
Phys. Chem. Chem. Phys., 2014, 16, 7578-7583 [4.493, 2014]
DOI:   10.1039/C3CP55482A
Application of the planar superatom model to describe the electronic structure, and to gain insights into the stabilization of metal macrocycles supporting closed-shell d10-d10 interactions, is studied through analysis of the membered ring composed by Hg(II) atoms, namely, [Hg(C(CF3)2)]5. Its electronic structure resembles the level sequence given for a planar jellium model, revealing an electronic configuration given by 1s2 1p4x,y 1d4xy,x2-y2. The analysis of the population of each level of the Hg5core, denotes a slight net bonding into the [Hg(C(CF3)2)]5 ring. However, stabilization is mainly supported by the balance given by a similar population of the jellium levels, which is suggested to be a different scheme for stabilizing d10 macrocyclic clusters with metallophilic interactions, in the category of long d10-d10 contacts. The extension of the planar jellium model to the relativistic case, including spin–orbit coupling considering the D5h* point group, denotes the consequent splitting for levels with l ? 0, namely, 1px,y and 1dxy,x2-y2. In this framework, the electronic configuration is given by 1s1/22 1p3/22 1p1/22 1d5/22 1d3/22, which contribute to the analysis of the electronic structure of planar clusters in terms of spin–orbit coupling, involving molecular spinors (j = l ± s) instead of molecular orbitals (pure l).

Towards a unified way of comparing the electrocatalytic activity MN4 macrocyclic metal catalysts for O2 reduction on the basis of the reversible potential of the reaction
José H. Zagal, F. Javier Recio, Cristian A. Gutierrez, Cesar Zuñiga, Maritza A. Páez, Claudia A. Caro
Electrochemistry Communications, 41, 24–26, 2014 [4.847, 2014]
DOI:   10.1016/j.elecom.2014.01.009
We have revisited correlations between catalytic activity and formal potentials of MN4 catalysts for the reduction of O2 (ORR). When comparing the activities of Cr, Mn, Co and Fe MN4 complexes for ORR as a plot of (log i/n)E versus the M(III)/(II) formal potential of the catalyst (n = number of electrons involved in the ORR), two linear correlations are obtained: one for Cr, Mn and Fe complexes and another for Co complexes. Mn and Fe are 4-electron reduction catalysts and Cr and Co are 2-electron reduction catalysts for ORR in alkaline media. We show that instead of plotting the formal potential E°? of the catalyst but the difference between this parameter and the reversible potential Erev of the corresponding catalytic reaction (O2/OH?) or (O2/HO2?), as (E°? ? Erev) and using the Co(II)/(I) formal potential for cobalt macrocyclics, instead of the Co(III)/(II) redox couple, all data points merge into one single linear correlation of slope + 0.170 V/decade. It is possible that when (E°? ? Erev) approaches zero, the maximum activity could be achieved and this is especially important for 4-electron catalysts and the linear correlation might be part of an incomplete volcano correlation.

Intramolecular and Lateral Intermolecular Hole Transfer at the Sensitized TiO2 Interface
Ke Hu, Kiyoshi C. D. Robson, Evan E. Beauvilliers, Eduardo Schott, Ximena Zarate, Ramiro Arratia-Perez, Curtis P. Berlinguette, and Gerald J. Meyer
J. Am. Chem. Soc., 2014, 136 (3), pp 1034–1046 [12.113, 2014]
DOI:   10.1021/ja410647c
Characterization of the redox properties of TiO2 interfaces sensitized to visible light by a series of cyclometalated ruthenium polypyridyl compounds containing both a terpyridyl ligand with three carboxylic acid/carboxylate or methyl ester groups for surface binding and a tridentate cyclometalated ligand with a conjugated triarylamine (NAr3) donor group is described. Spectroelectrochemical studies revealed non-Nernstian behavior with nonideality factors of 1.37 ± 0.08 for the RuIII/II couple and 1.15 ± 0.09 for the NAr3•+/0 couple. Pulsed light excitation of the sensitized thin films resulted in rapid excited-state injection (kinj > 108 s–1) and in some cases hole transfer to NAr3 [TiO2(e)/RuIII–NAr3 → TiO2(e)/RuII–NAr3•+]. The rate constants for charge recombination [TiO2(e)/RuIII–NAr3 → TiO2/RuII–NAr3 or TiO2(e)/RuII–NAr3•+ → TiO2/RuII–NAr3] were insensitive to the identity of the cyclometalated compound, while the open-circuit photovoltage was significantly larger for the compound with the highest quantum yield for hole transfer, behavior attributed to a larger dipole moment change (?? = 7.7 D). Visible-light excitation under conditions where the RuIII centers were oxidized resulted in injection into TiO2 [TiO2/RuIII–NAr3 + hν → TiO2(e)/RuIII–NAr3•+] followed by rapid back interfacial electron transfer to another oxidized compound that had not undergone excited-state injection [TiO2(e)/RuIII–NAr3 → TiO2/RuII–NAr3]. The net effect was the photogeneration of equal numbers of fully reduced and fully oxidized compounds. Lateral intermolecular hole hopping (TiO2/RuII–NAr3 + TiO2/RuIII–NAr3•+ → 2TiO2/RuIII–NAr3) was observed spectroscopically and was modeled by Monte Carlo simulations that revealed an effective hole hopping rate of (130 ns)–1.

New mono and bimetallic iron complexes derived from partially methylated s-indacene. Evidence of a trinuclear iron s-indacene complex
César Morales-Verdejo, Iván Martínez-Díaz, Christopher Adams, Juan Felipe Araneda, Luciano Oehninger, Desmond Mac-Leod Carey, Alvaro Muñoz-Castro, Ramiro Arratia-Pérez, Ivonne Chávez, Juan Manuel Manríquez
Polyhedron, 2014, 69, 15–24 [2.011, 2014]
DOI:   10.1016/j.poly.2013.11.023
The preparation and characterization of new mono- and multinuclear iron complexes derived from s-indacene partially alkylated has been achieved by the development of rational synthetic routes. The synthesis of the new multimetallic complexes are based on the employment of 1,5-dihydro-2,4,6,8-tetramethyl-s-indacene (Ic’H2) as ligand to obtain two monometallic complexes, namely, [Cp*–Fe-(η5-2,4,6,8-tetramethyl-5-hydro-s-indacenide)] (1), and [Fe-bis(η5-2,4,6,8-tetramethyl-5-hydro-s-indacenide)] (2) (Cp* = pentamethylcyclopentadiene), as well as, the new bimetallic [Cp*Fe-(μ:η55-2,4,6,8-tetramethyl-s-indaceneiide)-FeCp*] (3) and trimetallic [Fe-bis{Cp*Fe-(μ:η55-2,4,6,8-tetramethyl-s-indaceneiide)}] (4) complexes. All complexes here reported were characterized by means of 1H, 13C NMR, mass spectrometry, elemental analysis, together with cyclic voltammetry. In addition, these complexes have been studied by DFT methods in order to gain further knowledge about its electronic structure. In addition, the possibility to generate organometallic polymers employing the complexes here reported, is proposed theoretically with the study of an oligomer titled as [Cp*{Fe(Ic’)}4FeCp*], 6t.