Chemical Physics 365 (2009) 164–169

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Chemical Physics

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Theoretical study of the binding nature of glassy carbon with nickel(II)phthalocyanine complexes

Luis Cortez a, Cristhian Berríos b, Mauricio Yáñez c, Gloria I. Cárdenas-Jirón a,*

a Laboratorio de Química Teórica, Facultad de Química y Biología, Universidad de Santiago de Chile (USACH), Casilla 40, Correo 33, Santiago, Chileb Laboratorio de Electrocatálisis, Facultad de Química y Biología, Universidad de Santiago de Chile (USACH), Casilla 40, Correo 33, Santiago, Chilec Laboratorio de Recursos Renovables, Centro de Biotecnología, Universidad de Concepción, Casilla-160 C, Concepción, Chile

a r t i c l e i n f o a b s t r a c t

Article history:Received 21 July 2009Accepted 14 October 2009Available online 20 October 2009

Keywords:Glassy carbonOxo bridgeNickel phthalocyanineSemiempiricalQuantum calculations

0301-0104/$ - see front matter � 2009 Elsevier B.V. Adoi:10.1016/j.chemphys.2009.10.016

* Corresponding author.E-mail address: gloria.cardenas@usach.cl (G.I. Cárd

A theoretical study at the semiempirical RHF/PM3(tm) level (tm: transition metal) of the binding naturebetween a glassy carbon (GC) cluster and a nickel(II) complex (nickel(II) phthalocyanine NiPc, nickel(II)tetrasulphophthalocyanine NiTSPc) was performed. Three types of interactions for GC� � �NiPc (NiTSPc)were studied: (a) through an oxo (O) bridge, (b) through an hydroxo (OH) bridge, and (c) non-bridge.One layer (NiPc, NiTSPc) and two layers (NiPc� � �NiPc) of complex were considered. The binding energycalculated showed that in both cases NiPc and NiTSPc, the oxo structures are more stable than thehydroxo ones, and than the non-bridge systems. Charge analysis (NAO) predicted that GC gained moreelectrons in an oxo structure than in the analogues hydroxo. The theoretical results showed an agreementwith the experimental data available, an oxo binding between GC and a nickel complex (NiPc, NiTSPc) inaqueous alkaline solutions is formed.

� 2009 Elsevier B.V. All rights reserved.

1. Introduction

The design of new materials with electrocatalytic propertiesconstitutes a subject of interest for chemical, analytical and photo-chemical applications. New electrode materials composed of nickelmacrocycle complexes, like phthalocyanine, porphyrin, salen, andcyclam, have been prepared in two stages: (1) first an electro poly-merization is carried out on an electrode surface giving place to theformation of a film of the respective complex, (2) then the filmundergoes an electrochemical transformation in aqueous alkalinesolutions [1–23,26,27]. It has been found that these kinds of electropolymerized films behave as efficient electro catalysts for the oxi-dation of several substrates, concerning to the voltammetricbehavior in organic solvents, and led to electrochemists to investi-gate the reason why this occurs [1–23].

Several authors have related the shape of the final cyclic voltam-mogram of the nickel complexes electro polymerized in aqueousalkaline solutions, with that corresponding to electrochemicallyformed Ni(OH)2 electrodes [24,25] because of its similarity. Hence,it has been suggested that the nickel sites in the respective com-plexes lose the coordination with the pyrrolic nitrogen atoms, andpresent changes in the axial occupation of the Ni sites. This factcan be understood in terms of the formation of O–Ni–O oxo bridgesbetween the nickel complexes and between GC and the closestnickel complex layer [1–11,14,16,21,23,26,27,15].

ll rights reserved.

enas-Jirón).

Goux et al. have proved that the formation of a polymeric film oftetraaminophthalocyanine (poly-NiTAPc) deposited on glassycarbon, which after undergoes an electrochemical transformationin alkaline aqueous solutions (poly-NiTAPc(OH)), shows a muchlarger electro catalytic response toward dopamine redox processthan poly-NiTAPc [1]. Analysis of the polymeric films, poly-NiTAPcand poly-NiTAPc(OH), by scanning electron microscopy (SEM) re-vealed a change in the morphology, where the latter film presenteda less porosity and a global thickness slightly increased with re-spect to poly-NiTAPc [1]. These authors have suggested that alongthe electrochemical treatment, NiTAPc in poly-NiTAPc(OH) has abehavior similar to a nickel hydroxide electrode, which can be ex-plained by the coordination in the axial sites of the nickel complex,due to the formation of an oxo bridge (O–Ni–O) between the Ni-TAPc complexes [1]. Other authors have also discussed the mech-anism by which films of nickel complexes are deposited on theelectrode surface, and suggested the formation of oxo bridges be-tween the complexes [1–11,14,16,21,23,26,27,15].

A similar structural behavior of oxo bridge structures has beenobserved for gold and glassy carbon electrodes modified withnickel tetrakis-(benzylmercapto) phthalocyanine (NiTBMPc) andnickel-tetrakis(dodecylmercapto) phthalocyanine (NiTDMPc)[9,10]. In both electrodes, it was found that the complexes increasedtheir catalytic activities in the nitrite electro oxidation when theypresented the oxo bridge structure [9]. In gold electrodes, the samecompounds exhibited an improved catalytic activity toward theoxidation of 4-chlorophenol and trichlorophenol, when were trans-formed as poly-NiTBMPc(OH) and poly-NiTDMPc(OH). The higher

NNN

H

H

HH

H

HR

R

L. Cortez et al. / Chemical Physics 365 (2009) 164–169 165

catalytic activity was observed in a higher peak current and a shift toless positive peak potentials [10].

In order to asses the stability of an oxo bridge in a glassy carbonelectrode modified with nickel complex, we applied the tools of thequantum chemistry on a supermolecule structure composed of aglassy carbon cluster interacting with one (NiPc, NiTSPc) and twolayers (NiPc) of nickel complex, and interconnected with oxo andhydroxo bridges, as also without a bridge.

N

N

NN

N

H

HH

HH

H

Ni

R

R

R=H : NiPc

R=SO3- : NiTSPc

Fig. 2. Structural view of the nickel complexes studied. NiPc: nickel phthalocya-nine; NiTSPc: nickel tetrasulphonated phthalocyanine.

2. Computational and theoretical aspects

Following to O’Malley et al. [28], who modelled a glassy carbon(GC) cluster using the classical mechanic’s Monte Carlo method, webuilt up a GC cluster (Fig. 1) containing some ordered regions, as inthe graphite structure, with 38 hexagonal rings and some disor-dered regions which were modelled as a set of four five-memberedrings, one seven-membered ring and one 11-membered ring.Hydrogen atoms were not included in the corners of the clusteravoiding a distortion of the rings localized in those regions. Inthe modelling of the interaction between GC and the nickel(II)phthalocyanine complexes (Fig. 2), non-substituted (NiPc) and tet-rasulpho substituted (NiTSPc), the size of the GC cluster was cho-sen such that its width was approximately equal to that of thecomplex. Hence, in this work we modelled one GC cluster interact-ing with one molecule NiPc or NiTSPc. In the case of NiPc, a secondmolecule was added because of the smaller size in comparisonwith NiTSPc, allowing that the theoretical calculations beperformed.

We have investigated two types of bridges, oxo (� � �O� � �) and hy-droxo (� � �OH� � �), so the supramolecular systems that we studied(see Fig. 3) correspond to: GC� � �O� � �NiPc (NiTSPc) andGC� � �OH� � �NiPc (NiTSPc), as a model for the interaction of a firstlayer of the complex with the GC carbon surface, and the systemsGC� � �O� � �NiPc� � �O� � �NiPc and GC� � �OH� � �NiPc� � �OH� � �NiPc includ-ing a second layer of the nickel complex NiPc. As a comparisonwe studied the systems without the presence of a bridge.

Fig. 1. Optimized structure of glassy carbon cluster at the semiempirical level RHF/PM3tm (tm: transition metal): (a) front view and (b) side view.

All the calculations were computed in the gas phase at thesemiempirical Restricted Hartree Fock PM3(tm) (transition metal)level [29], which is parameterized for the nickel atom, using thequantum mechanical code Titan [30]. All the molecular structureswere completely optimized at this level: GC, NiPc, NiTSPc,GC� � �O� � �NiPc, GC� � �OH� � �NiPc, GC� � �O� � �NiPc� � �O� � �NiPc, GC� � �OH� � �NiPc� � �OH� � �NiPc, GC� � �O� � �NiTSPc, GC� � �OH� � �NiTSPc,NiPc� � �O� � �NiPc, NiPc� � �OH� � �NiPc, GC� � �NiPc, GC� � �NiTSPc andGC� � �NiPc� � �NiPc. For the optimization of the supramolecularstructures containing GC, the glassy carbon cluster was frozen,and the remaining of the structure was completely optimized.Geometry previously optimized for GC as isolated form was used.Ab initio calculations could not be carried out due to the large sizeof several of these systems. For example, the GC� � �O� � �NiTSPc sys-tem have 2470 basis functions for a calculation at the density func-tional level B3LYP/LACVP(d) [31], LACVP being a pseudopotentialnecessary to calculate the nickel atom [32]. With the aim to iden-tify the most stable interaction for the supramolecular structures,that is energetically favoured, the interaction energies (Eint) wereobtained at the RHF/PM3(tm) calculation level. For the structures:GC� � �O� � �NiPc (NiTSPc), GC� � �OH� � �NiPc (NiTSPc),GC� � �O� � �NiPc� � �O� � �NiPc and GC� � �OH� � �NiPc� � �OH� � �NiPc, we cal-culated the interaction between GC and the complex (NiPc, NiT-SPc), or between GC and the supramolecular structure(NiPc� � �O� � �NiPc, NiPc� � �OH� � �NiPc) through the bridge (oxo, hy-droxo) by:

EGC���½oxoðhydroxoÞ���complexðlayerÞ�int ¼ EGC���oxoðhydroxoÞ���complexðlayerÞ

� ½EGC þ EoxoðhydroxoÞ þ EcomplexðlayerÞ� ð1Þ

where layer is referred to an array of one or two complexes in thesupramolecular structure.

In the case of the non-bridged structures, GC� � �NiPc, GC� � �NiT-SPc and GC� � �NiPc� � �NiPc, a similar equation to Eq. (1) was usedto determine the interaction energy with glassy carbon:

EGC���½complexðlayerÞ�int ¼ EGC���complexðlayerÞ � ½EGC þ EcomplexðlayerÞ� ð2Þ

but in this case the term Eoxo(hydroxo) = 0 because there are notbridges. The bridges are represented by one oxygen atom (oxo),

Fig. 3. Optimized structures obtained at the semiempirical level RHF/PM3tm (tm: transition metal), for the interaction between the glassy carbon (GC) cluster and nickelcomplexes through an oxo bridge (–O–), through an hydroxo bridge (–OH–) and non-bridge: (a) interaction with one layer of NiPc; (b) interaction with one layer of NiTSPc;and (c) interaction with two layers of NiPc.

166 L. Cortez et al. / Chemical Physics 365 (2009) 164–169

with a charge of�2 and by one OH group (hydroxo) with a charge of�1. Following the experimental procedures published at the aque-ous alkaline solution, where the preparation of the modified elec-trodes was carried out, all the sulphonate groups are fully ionized.Hence NiTSPc was calculated using sulphonate groups (�SO�3 ) asthe substituent, thus each NiTSPc molecule has a charge of �4. Allthe supramolecular systems studied have singlet multiplicity, andthe nickel atom in the complexes NiPc and NiTSPc has an oxidationstate of +2.

Finally, for each molecular system we analysed the electrostaticpotential [30] and the electronic population obtained with the nat-ural atomic orbital approximation (NAO) [33].

3. Results and discussion

3.1. Glassy carbon cluster

Fig. 1 shows the optimized structure obtained for the GC clusterin a front view (Fig. 1a) and in a side view (Fig. 1b). The topology isnot ordered, and the region of the 11-membered ring form a holeinside of the structure (Fig. 1a), suggesting a material suitable formodification with chemical compounds of different nature and sizewhich could interact with this kind of GC cluster. The inclusion ofrings with a number of carbons other than six leads to non planarregions with strong distortions (Fig. 1b), indicating that this struc-tural model is a good starting point for simulating a GC electrode.For example, the hillock in Fig. 1b is due to the presence of onefive-membered ring surrounded by five six-membered rings, lead-

ing to a strongly stressed region. This is in agreement with theknown fact that the density of GC is lower than that of graphite,which only has six-membered rings. The ‘‘hole” is similar to a por-ous, making it a very interesting material, where chemical com-pounds of different nature or size could interact with this kind ofGC cluster.

3.2. Interaction with glassy carbon cluster

The interaction between GC cluster and NiPc or NiTSPc complexwas studied considering the presence of an oxo or an hydroxobridge localized between these structures (see Fig. 3). As a calcula-tion strategy for the molecular optimization, a bond was added be-tween the bridge and the nickel atom of NiPc (NiTSPc) and alsobetween the same bridge and one carbon atom in the central re-gion of the GC cluster, so that the GC cluster was fully coveredby the nickel complex. The same carbon atom was used for allthe structures, GC� � �O� � �NiPc (NiTSPc) and GC� � �OH� � �NiPc(NiTSPc).

Fig. 3 shows the optimized structures obtained for all the sys-tems studied. In the case of the mono layer bridged systems(Fig. 3a and b), we found a less distance for the interactionGC� � �O(OH) denoted by r1 (Table 1) (r1 1.4–1.5 Å) than for theinteraction O(OH)� � �NiPc (NiTSPc) denoted by r2 (r2 1.9–2.0 Å).This indicates that the bridge (� � �O(OH)� � �) prefers a positionmore near to the glassy carbon cluster, which can be explainedby the presence of charge in the bridge, �2 for � � �O� � � and �1for � � �OH� � �, whose electronic density could be stabilized

Table 1Optimized values of distancesa (Å) between glassy carbon (GC) cluster and nickelcomplexes calculated at the semiempirical level RHF/PM3tm.

Structure r1 r2 r3

GC� � �O� � �NiPc 1.39 1.97 3.30GC� � �O� � �NiTSPc 1.39 1.98 3.33GC� � �O� � �NiPc� � �O� � �NiPc 1.60 1.97 3.46

GC� � �OH� � �NiPc 1.48 2.04 3.44GC� � �OH� � �NiTSPc 1.50 2.03 3.46GC� � �OH� � �NiPc� � �OH� � �NiPc 1.49 2.00 3.38

r3

GC� � �NiPc 3.70GC� � �NiTSPc 3.64GC� � �NiPc� � �NiPc 5.19

a Distances definition: r1 – distance GC-bridge; r2 – distance bridge-nickel com-plex; r3 – distance GC-nickel complex (first layer).

Table 2Interaction energies (Eint/eV) of glassy carbon (GC) cluster with the nickel complexescalculated at the semiempirical level RHF/PM3tm.

Structure Eint

Oxo bridgeGC� � �O� � �NiPc �20.93GC� � �O� � �NiTSPc �11.34GC� � �O� � �NiPc� � �O� � �NiPc �15.15

Hydroxo bridgeGC� � �OH� � �NiPc �7.15GC� � �OH� � �NiTSPc �3.23GC� � �OH� � �NiPc� � �OH� � �NiPc �6.21

Non-bridgeGC� � �NiPc �0.62GC� � �NiTSPc 0.03GC� � �NiPc� � �NiPc �0.07

L. Cortez et al. / Chemical Physics 365 (2009) 164–169 167

through the rings of GC cluster. One can see that the substituent,H in NiPc and SO�3 in NiTSPc, does not affect the interaction be-tween GC and nickel complex through the bridge, the values ofr1 and r2 are very similar with the change of the substituent.The position of the substituents localized in the periphery ofthe benzene rings of the phthalocyanine ligand is far of thebridge. As it can be seen in Fig. 3, the curvature observed in partof the ligand is produced by the non planarity of the glassy car-bon cluster, making that some regions of the latter are morenear to the nickel complex.

The analysis in the systems with a double layer of nickel com-plex shows that in both oxo and hydroxo bridges, r1 < r2. Althoughr1 and r2 are different, both account of a covalent interaction for thebridged systems, oxo and hydroxo [34]. For the systems with a sec-ond layer of nickel complex, GC� � �O(OH)� � �NiPc� � �O(OH)� � �NiPc, asimilar trend is observed, a less distance for GC� � �O(OH) in compar-ison with O(OH)� � �NiPc, but r1 increases in the oxo structure (1.6 Å)against to the value obtained with one layer nickel complex (1.4 Å).In relation to the distance obtained between the first layer and thesecond layer of NiPc, we also found a covalent distance for the oxosystems, Ni (first layer)� � �O (1.86 Å) and O� � �Ni (second layer)(1.87 Å), as well for the hydroxo systems Ni (first layer)� � �OH(1.86 Å) and for OH� � �Ni (second layer) (1.95 Å). As it can be seen,the total distance between two NiPc complexes (3.7–3.8 Å) is a lit-tle larger than between GC and NiPc, 3.46 Å for oxo and 3.38 Å forhydroxo (see Table 1).

Our results suggests at least two things: (a) the growing of theNiPc layers could lead to very similar distances between layers, (b)making the first guess (a) as true, the second and other layers of thenickel complex could not be considered in the theoretical model-ling, thus reducing the size of the system, which it would allowthat calculations with methods more sophisticated (density func-tional theory) be performed. Currently in our group we are focus-ing in the application of methodologies like ONIOM, that allowsthe inclusion in the theoretical modelling of quantum methods be-sides molecular mechanics.

In the case of the non-bridge systems (Table 1), the distance (r3)between GC and the nickel complex measured between the nickelatom and one carbon atom of GC, the same atom used in thebridged systems, is 3.7 Å for GC� � �NiPc and 3.6 Å for GC� � �NiTSPc,whose values are slightly larger than in the bridged systems (seer3 in Table 1).

All of these results lead to conclude until here that, the interac-tion GC with a nickel complex such as NiPc or NiTSPc in one layersystems occurs at distances following the order: oxo bridge < hy-droxo bridge < non-bridge. A less distance for the oxo bridge sys-tems, could favour the electronic interaction of these nickelcomplexes with glassy carbon.

The interaction of glassy carbon with NiPc (NiTSPc) was quan-tified through the calculation of the interaction energy (Eint) usingEqs. (1) and (2), depending if the systems were bridged or not,respectively. Table 2 shows the results obtained. With the excep-tion of GC� � �NiTSPc, all the systems predicted negative values forEint, indicating that in all the cases studied the interaction be-tween the glassy carbon model used and the nickel complex isenergetically favoured, it is spontaneous. This could be under-stood in terms that the model used for the GC electrode is ade-quate, because it confirms that GC can be modified by a nickelphthalocyanine or by a nickel tetrasulphophthalocyanine, a factthat is widely accepted by electrochemists (see for example Ref.35).

The systems with one layer of nickel complex show a cleartrend toward a higher stabilization of oxo bridge with respect tothe hydroxo bridge, and with the non-bridge systems. Based on Ta-ble 2, the oxo bridge in GC� � �O� � �NiPc is 14 eV (323 kcal/mol) morestable than the hydroxo one, and 20 eV (461 kcal/mol) more stablethan the non-bridge. For NiTSPc, the interaction through an oxobridge in GC� � �O� � �NiTSPc is 8 eV (184 kcal/mol) more stable thanthe hydroxo one, and 11 eV (254 kcal/mol) more stable than thenon-bridge system. The larger value in Eint, presented by the sys-tems GC� � �O� � �NiPc and GC� � �O� � �NiTSPc with respect to the oth-ers, may be attributed to a stabilization of the oxygen charge(�2) corresponding to the oxo bridge on the GC cluster. Whenwe included a second layer of NiPc, the interaction of GC withthe first layer of NiPc in the oxo bridge system is 9 eV (207 kcal/mol) more stable than the corresponding hydroxo bridge. It seemsto be that the presence of a second layer of nickel complex affectsthe stability degree calculated by the interaction energy, in con-trast to that previously discussed about the distance of the com-plexes with respect to glassy carbon, a smaller effect. Thecomparison of the one layer systems (Table 2) shows that NiPchas always a more negative value of Eint than NiTSPc, in 10 eV inoxo bridge, 4 eV in hydroxo bridge and 0.6 eV in non-bridge. Thismeans that NiPc is more stabilized on GC than NiTSPc, suggestingsome properties of these systems useful for experimentalists.

In summary, the theoretical results predicted in comparativeterms that the systems with oxo bridge are the most stable, andled to conclude that the modification of a glassy carbon clusterwith NiPc generated a stronger interaction than NiTSPc, given bya more negative value of Eint.

On the other hand, the electrostatic potential for the systemswith one layer of NiPc bridged and non-bridged was calculated,and a picture of the property mapped on a density surface is shownin Fig. 4. As we are interested in the change that the glassy carbonhas in the presence of some kind of bridge, we show in this figureonly the electrostatic potential of GC for each one of the systemsstudied. It can be seen that GC (Fig. 4a) present an extense positive

Table 3Charge values obtained at the semiempirical level RHF/PM3tm in terms of thefragments of the systems studied.

Structure GC O (OH) Pc TSPc Ni

GC 0.000GC–O–NiPc �1.264 �0.474 +0.795 �1.057GC–OH–NiPc �1.021 +0.083 +0.984 �1.045GC� � �NiPc +0.018 +0.966 �0.984NiPc +0.986 �0.986GC–O–NiTSPc �1.382 �0.449 �3.143 �1.026GC–OH–NiTSPc �1.092 +0.111 �2.983 �1.036GC� � �NiTSPc +0.012 �3.025 �0.988NiTSPc �3.001 �0.991

Fig. 4. Electrostatic potential surface mapped on a density isosurface calculated at the semiempirical level RHF/PM3tm (tm: transition metal): (a) GC; (b) GC� � �O� � �NiPc; (c)GC� � �OH� � �NiPc; and (d) GC� � �NiPc.

168 L. Cortez et al. / Chemical Physics 365 (2009) 164–169

region for the electrostatic potential, denoted by the intense blue1

color in the figure. However, Fig. 4b and c corresponding to the sys-tems GC� � �O� � �NiPc and GC� � �OH� � �NiPc shows green and blue re-gions that quantitatively correspond to negative electrostaticpotential values. In Fig. 4d, again we found intense blue color inall the regions and present positive values. In addition, the theoret-ical results indicated that the existence of a bridge (O, OH), whichis bonded to GC by a covalent form, allows a change in the elec-tronic density of glassy carbon. If there is not a bridge, like happensin GC� � �NiPc, the electrostatic potential is not altered. If there is abridge (O, OH), a change in the sign of the electrostatic potentialoccurs, from positive to negative, indicating the presence of elec-tronic density in GC, which is provided by the bridge. This fact sug-gests that the latter conditions are favourable for the modificationof GC, leading to a stronger interaction with the respective nickelcomplex. Because of the larger size of the systems containing NiT-SPc in comparison with NiPc, the electrostatic potential could notbe obtained, but based in the other theoretical results presentedin this work, we guess that a similar trend would be presented.

Finally the electronic population by using the NAO approxima-tion was obtained and analysed in a convenient form due to thelarge size of the systems. Table 3 shows the charge values for thefragments GC, Ni, Pc, TSPc and the bridges (O, OH) in the systemscontaining one layer of nickel complex. It is clear for both NiPcand NiTSPc that the electron gain (negative charge) of GC followsthe order: oxo bridge systems > hydroxo bridge systems. Thenon-bridge systems do not present an electron gain, a slight elec-tron lost is observed, a little more in the NiPc system than in theNiTSPc one. These results are consistent with those found for theelectrostatic potential of NiPc systems and discussed previously,in the sense that only in the bridged systems exist a negative elec-trostatic potential for GC account of regions rich in electrons. InGC� � �O� � �NiPc, the GC cluster stabilized an amount of 1.26 elec-trons, some more than in GC� � �OH� � �NiPc (1.02 electrons). In theNiTSPc systems happen a similar trend, in GC� � �O� � �NiTSPc theGC cluster stabilized 1.38 electrons and in GC� � �OH� � �NiTSPc theamount is of 1.09 electrons. Ni fragment charge is seen not changemuch if we compare the respective complex (NiPc, NiTSPc) withthe supramolecular systems bridged or not, indicating that thebridges and the presence of GC do not have an important effectin the electronic composition of the nickel atom. In relation tothe ligands, we found that TSPc presents an ability more electronwithdrawing in the oxo system (�3.14) than in the hydroxo one(�2.98), and Pc is less electron donor in the oxo system (+0.79)than in the corresponding hydroxo (+0.98). As it can be seen, theoxo bridges can not stabilize the charge �2, they only can stabilize�0.47 electrons in GC� � �O� � �NiPc and �0.44 electrons inGC� � �O� � �NiTSPc. Hence, we found an electron gain in GC in bothoxo systems, which it was higher than in the hydroxo systems.

1 For interpretation of color in Figs. 3 and 4, the reader is referred to the webversion of this article.

In summary, different properties analysed such as geometry,interaction energy, electrostatic potential and charge, showed thatan oxo bridge between a glassy carbon cluster and a nickel com-plex (NiPc, NiTSPc) stabilizes the interaction between them. Thissuggests a better communication between the systems mentioned,and lead to useful materials which favours a charge transfer in ancatalytic process, in agreement with the already suggested by elec-trochemists [1–27].

4. Conclusions

At theoretical level of RHF/PM3(tm) (tm: transition metal), itwas possible to model the interaction of a glassy carbon clusterwith one nickel complex (NiPc, NiTSPc). Three kind of interactionswere studied, through an oxo bridge, through and hydroxo bridgeand non-bridge. For both nickel complexes, it was found fromthe interaction energy (Eint) calculated between GC and the respec-tive complex, that the oxo bridge structures are more stable thanthe hydroxo bridge ones. Eint in GC� � �O� � �NiPc is 14 eV more nega-tive than GC� � �OH� � �NiPc. For GC� � �O� � �NiTSPc, the Eint value is 8 eVmore negative than GC� � �OH� � �NiTSPc. These results are also ex-plained in terms of the amount of electrons that GC stabilized. InGC� � �O� � �NiPc, the GC cluster stabilized an amount of 1.26 elec-trons, some more than in GC� � �OH� � �NiPc (1.02 electrons). In theNiTSPc systems a similar trend happens, the GC cluster stabilized1.38 electrons in GC� � �O� � �NiTSPc and 1.09 electrons inGC� � �OH� � �NiTSPc. So, the oxo bridge systems present a larger sta-bilization of charge in GC, which suggest that they are better sys-tems for charge transfer processes. All the results obtainedconfirm that suggested by other authors at experimental level[1–27], the catalytic processes are favored in terms of the effi-ciency, when the glassy carbon electrodes are modified with nick-el(II) phthalocyanine through an oxo bridge.

Acknowledgements

The authors thank the financial support of Projects FONDECYT/CHILE No. 8010006/Lineas Complementarias and No. 1060203. The

L. Cortez et al. / Chemical Physics 365 (2009) 164–169 169

computational time provided by the Project DICYT-USACH ApoyoComplementario is also appreciated. L.C., C.B. and M.Y. thank bydoctorate fellowship CONICYT/CHILE.

References

[1] A. Goux, F. Bedioui, L. Robbiola, M. Pontié, Electroanalysis 15 (2003) 969.[2] T.R.I. Cataldi, D. Centonze, G. Ricciardi, Electroanalysis 7 (1995) 312.[3] F. Bedioui, S. Gutiérrez Granados, C. Bied-Charreton, Recent Res. Devel.

Electrochem. 2 (1999) 91.[4] S. Trévin, F. Bedioui, M.G. Gomez Villegas, C. Bied-Charreton, J. Mater. Chem. 7

(1997) 923.[5] G. Roslonek, J. Taraszewska, J. Electroanal. Chem. 325 (1992) 285.[6] T.R.I. Cataldi, E. Desimoni, G. Ricciardi, L. Francesco, Electroanalysis 7 (1995)

435.[7] M. Pontié, H. Lecture, F. Bedioui, Sensor. Actuat. B 56 (1999) 1.[8] A. Alatorre Ordaz, J. Manriquez Rocha, F.J. Acevedo Aguilar, S. Gutiérrez

Granados, F. Bedioui, Analusis 28 (2000) 238.[9] B.O. Agboola, K.I. Ozoemenab, T. Nyokong, Electrochim. Acta 51 (2006) 6470.

[10] B. Agboola, T. Nyokong, Electrochim. Acta 52 (2007) 5039.[11] A. Alatorre Ordaz, F. Bedioui, S. Gutierrez Granados, Bol. Soc. Chil. Quim. 43

(1999) 375.[12] F. Bedioui, S. Trévin, J. Devynck, J. Electroanal. Chem. 377 (1994) 295.[13] J. Oni, T. Nyokong, Polyhedron 19 (2000) 1355.[14] A. Ciszewski, Electroanalysis 7 (1995) 1132.[15] J. Bukowska, G. Roslonek, J. Taraszewska, J. Electroanal. Chem. 403 (1996) 47.[16] A. Ciszewski, G. Milczarek, J. Electroanal. Chem. 413 (1996) 137.[17] A. Ciszewski, G. Milczarek, J. Electroanal. Chem. 426 (1997) 125.[18] J. Taraszewska, G. Roslonek, J. Electroanal. Chem. 364 (1994) 209.

[19] M. Pontié, C. Gobin, T. Pauporte, F. Bedioui, J. Devynck, Anal. Chim. Acta 411(2000) 175.

[20] T. Malinski, L. Czuchakowsky, in: M. Feelish, J. Stamler (Eds.), Methods inNitric Oxide Research, Wiley, Chichester, 1996, p. 319.

[21] J. Manriquez, J.L. Bravo, S. Gutiérrez Granados, S. Sucar Succar, C. Bied-Charretton, A. Alatorre Ordaz, F. Bedioui, Anal. Chim. Acta 378 (1999) 159.

[22] M.A. Ruiz, M.G. Blasquez, J.M. Pingarron, Anal. Chim. Acta 305 (1995) 49.[23] J. Obirai, F. Bedioui, T. Nyokong, J. Electroanal. Chem. 576 (2005) 323.[24] M. Vukovic, J. Appl. Electrochem. 24 (1994) 878.[25] F. Pasquini, P. Tissot, J. Appl. Electrochem. 26 (1996) 211.[26] S.J. Ferrer, S. Gutiérrez Granados, F. Bedioui, A. Alatorre Ordaz, Electroanalysis

15 (2003) 70.[27] A. Ciszewski, G. Milczarek, J. Electroanal. Chem. 469 (1999) 18.[28] (a) D. McCulloch, S. Prawer, A. Hoffman, Phys. Rev. B 50 (1994) 5905;

(b) B. OMalley, I. SnooK, D. McCulloch, Phys. Rev. B 57 (1998) 14148.[29] J.J.P. Stewart, J. Comput. Chem. 10 (1989) 209.[30] Titan, Wavefunction, Inc. and Schrodinger Inc. 18401 Von Karman Avenue,

Suite 370, Irvine, CA 92612, USA.[31] (a) C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785;

(b) B. Miehlich, A. Savin, H. Stoll, H. Preuss, Chem. Phys. Lett. 157 (1989) 200;(c) A.D. Becke, J. Chem. Phys. 98 (1993) 5648.

[32] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 299.[33] E.D. Glendening, J.K. Badenhoop, A.E. Reed, J.E. Carpenter, J.A. Bohmann, C.M.

Morales, F. Weinhold, NBO 5.0. Theoretical Chemistry Institute, University ofWisconsin, Madison, WI, 2001. Available at: <http://www.chem.wisc.edu/_nbo5>.

[34] L.S. Caputi, S.L. Jiang, A. Amoddeo, R. Tucci, Phys. Rev. B 41 (1990) 8513.[35] M.S. Ureta-Zañartu, C. Berríos, J. Pavéz, J. Zagal, C. Gutiérrez, J.F. Marco, J.

Electroanal. Chem. 553 (2003) 147.