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Journal of Organometallic Chemistry 751 (2014) 356e360

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Journal of Organometallic Chemistry

journal homepage: www.elsevier .com/locate/ jorganchem

Synthesis of mixed-valence trinuclear carbonylmanganese dithiolates:Promoting vacant coordination sites in tricarbonyl[(1-5-h)-pentadienyl]manganese

Karla P. Salas-Martin a, Marisol Reyes-Lezama a, Herbert Höpfl b, Noé Zúñiga-Villarreal a,*a Instituto de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, Circuito Exterior, 04510 México, D.F., MexicobCentro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, C. P. 62210 Cuernavaca, Morelos, Mexico

a r t i c l e i n f o

Article history:Received 14 May 2013Received in revised form19 June 2013Accepted 11 July 2013

Keywords:Manganese carbonylsPentadienyl ligandAlkanedithiolsMixed-valence complex

* Corresponding author.E-mail addresses: noe.zuniga.villarreal@gm

(N. Zúñiga-Villarreal).

0022-328X/$ e see front matter � 2013 Elsevier B.V.http://dx.doi.org/10.1016/j.jorganchem.2013.07.036

a b s t r a c t

Mixed-valence complexes Mn3(CO)6(m-S(CH2)nS-k2-S,S0)3 n ¼ 2, 3, and 4 were prepared upon reaction oftricarbonyl[(1-5-h)-pentadienyl]manganese with the respective alkanedithiols at room temperature ingood yields. The three metal centers are bound by thiolate bridges with no metalemetal bonds; onemanganese atom exhibits a formal oxidation state of þ4; while the other two possess an oxidation stateof þ1. EPR and X-ray analysis showed an octahedral environment around the manganese centers.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

Metal carbonyl complexes containing thiolate ligands comprisea well-defined group among organometallic compounds [1]. Alka-nedithiolates stand out as stabilizing ligands in carbonyl clusters oftransition metals due to their bridging and chelating capacities [2].The anion [Mn(CO)5]� [3] and to a lesser extent Mn2(CO)10 [4] havebeen used as common starting material for manganese dithiolatecarbonyls. Tricarbonyl[(1-5-h)pentadienyl]manganese has provenin our hands to be a suitable starting material for the preparation ofmanganese carbonyl thiolates [5]; alkanedithiols caught ourattention and, as a result, we found an expeditious room temper-ature method for the synthesis of mixed-valence trinuclear car-bonylmanganese dithiolates. We report here on the details.

2. Results and discussion

Complexes Mn3(CO)6(m-S(CH2)nS-k2-S,S0)3 n ¼ 2, (2); n ¼ 3, (3);and n ¼ 4, (4).

Complexes (2)e(4) were synthesized upon reaction of the cor-responding alkanedithiol and Mn(h5-C5H7)(CO)3 (1) [6] at room

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temperature according to Scheme 1 in 86.0, 85.0, and 85.0% yieldsresp.

Equimolar ratios were used in all cases. The products are darkgreen solids partially soluble in dichloromethane, chloroform, andthf; in air they decomposed within days, under nitrogen atmo-sphere they resisted decomposition for approximately one month;in solution they decomposed in approximately two days, longertimes led to materials insoluble in all standard organic solvents.(2)e(4) were prepared at room temperature since higher temper-atures led to intractable mixtures wherein the trinuclear com-pounds were present in small quantities.

The IR n(CO) spectra of (2)e(4) show two strong bands in theterminal carbonyl region (see Experimental). Dinuclear hex-acarbonyl complexes with the carbonyls in an anti-disposition (D3dlocal symmetry) present two IR active bands due to the A2u þ Eumodes, while for a carbonyl-eclipsed conformation (D3h localsymmetry) the A00

2 þ E0 modes give also rise to two IR active bands[7]. In the present case, notwithstanding the nuclearity of thecomplexes (the central manganese has no bound carbonyls, asshown in the X-ray structure below); it can be proposed thatcomplexes (2)e(4) possess a D3d local symmetry that straightfor-wardly relates to the solid state structure. The wave numbers ofthe n(CO) bands of (2)e(4) lie in the range of the standard man-ganese carbonyl complexes with chalcogen ligands [5] and contrastwith the wave numbers reported for the 16e� complex [N(PPh3)2]

Scheme 1.

K.P. Salas-Martin et al. / Journal of Organometallic Chemistry 751 (2014) 356e360 357

[Mn(CO)3(S,S-C6H4)] (1986 vs, 1887 s cm�1 in thf) with a CO’s C3vlocal symmetry, where it has been proposed that such lower wavenumbers are caused by the strong p-donating ability of thebidentate [S,S-C6H4]2� ligand [3c].

Complex (3) has been synthesized upon reaction of Mn2(CO)10with 1,3-propanedithiol in the presence of Me3NO$2H2O at roomtemperature in 20% yield [4a]; interestingly, when the reactionwasconductedwith 1,2-ethanedithiol a dinuclear complexMn2(CO)6(m-SCH2CH2S-k2-S,S0)2, instead of trinuclear complex (2), was ach-ieved. It was suggested that the nuclearity of the complexes syn-thesized under the reported reaction conditions depends on thechain length of the alkanedithiol. Such dependence was notobserved in the preparation of mixed valence trinuclear complexeswith alkanedithiols HSe(CH2)neSH, n ¼ 2, 3 and 4 in the presentcase.

(2)e(4) are trinuclear complexes as evidenced from the struc-ture of (2), depicted in Fig. 1, determined by an X-ray analysis.

Oxidation states of the carbonyl bound manganese atoms,Mn(2) and Mn(3), are assigned as þ1; while Mn(1) is assignedas þ4. The Mn(1)eMn(2) and Mn(1)eMn(3) lengths (2.9662(6);2.9776(6) �A, resp.) are quite similar and are non-bonding. Adamset al. have reported aMneMn bond length of 2.6470(6)�A inMn2(m-SCH2CH2S)(CO)7 [4b]; in Mn2(CO)10 the MneMn bond distance is

Fig. 1. Molecular structure of (2) including the atom numbering scheme (ORTEPdrawing with 50% probability ellipsoids). Selected bond lengths [�A]: Mn(1)eS(1)2.3279(8); Mn(1)eS(2) 2.3111(9); Mn(1)eS(3) 2.3637(9); Mn(1)eS(4) 2.3608(8);Mn(1)eS(5) 2.3393(9); Mn(1)eS(6) 2.3614(9); Mn(2)eS(2) 2.3975(9); Mn(2)eS(3)2.3709(9); Mn(2)eS(4) 2.3902(9); Mn(3)eS(1) 2.3971(9); Mn(3)eS(5) 2.3830(9);Mn(3)eS(6) 2.3845(9); Mn(1)eMn(2) 2.9662(6); Mn(1)eMn(3) 2.9776(6). SelectedBond angles [�]: S(4)eMn(1)eS(1) 169.63(3); S(2)eMn(1)eS(6) 166.27(3); S(3)eMn(1)eS(5) 174.00(3); C(9)eMn(2)eS(2) 177.93(11); C(7)eMn(2)eS(4) 173.32(11);C(8)eMn(2)eS(3) 170.11(12); S(6)eMn(3)eC(10) 170.72(11); S(1)eMn(3)eC(12)178.88(11); S(5)eMn(3)eC(11) 168.59(11), Mn(2)eMn(1)eMn(3) 166.95(2).

2.9038(6)�A [8]. The Mn(2)eMn(1)eMn(3) angle, 166.95(2)�, showsa bent backbone in (2) in contrast with the reported structure of (3)wherein the manganese atoms lie nearly linear (177.56(3)�) [4a].This can be attributed to the shorter chain length in 1,2-ethanedithiolate. Interestingly the MneCO distances [1.814(4) �A(average)] (Supplementary material) are longer than those re-ported for the MneCO distances [1.767(4) �A (average)] in thecomplex [N(PPh3)2][Mn(CO)3(S,S-C6H4)]. The MneS distance([2.230(1) �A (average)] is shorter compared to the present case(Fig. 1) pointing to the strong p-donating ability of the bidentate[S,S-C6H4]2� ligand [3c].

The UVeVis spectrum of (2) in dichloromethane shows ab-sorption maxima at 234 ( 3 ¼ 24212.22 L cm�1 mol�1), 327( 3 ¼ 5853.49 L cm�1 mol�1), and 674 nm ( 3 ¼ 2798.84 Lcm�1 mol�1), the band at 234 nm is attributed to a charge transfer;while the band at 674 nm stems from the electronic transitionresponsible of the green color of the complexes (for complex (3)this band appears at 613 nm, Supplementary material for bothspectra).

The central manganese atom in complexes (2)e(4) possesses ad3 configuration in an octahedral environment. The room temper-ature experimental magnetic moments of (2), 3.81 mB, (3), 3.86 mB,and (4), 4.14 mB, lie within the range for Mn(IV) species having threeunpaired electrons.

The method of choice for the detection of the paramagneticMn(IV) is EPR spectroscopy since Mn(IV) complexes give well-characterized EPR signals [9].

100 200 300 400 500 600-1500

-1000

-500

0

500

1000

1500

Inte

nsity

(a. u

.)

Magnetic Field (mT)

Fig. 2. EPR spectra of Mn3(CO)6(m-S(CH2)2S-k2-S,S0)3, (2), in powder form at 77 K.

100 200 300 400 500 600

-1000

-500

0

500

1000

Inte

nsity

(a.u

)

Magnetic Field (mT)

Fig. 3. EPR spectra of Mn3(CO)6(m-S(CH2)2S-k2-S,S0)3, (2), in thf solution at 77 K.

K.P. Salas-Martin et al. / Journal of Organometallic Chemistry 751 (2014) 356e360358

The EPR spectrum of Mn3(CO)6(m-S(CH2)2S-k2-S,S0)3 reveals thatthe effective electronic environment of manganese(IV) lies close tothe ideally octahedral situation. Spectra were run in powder form(298 K) (Fig. 2) as well as in dilute frozen THF solutions (77 K)(Fig. 3). The major feature is the same in compounds (2)e(4): Astrong signal at gz 2 and aweak broad signal at lower field (gz 4).The g z 2 signal displays a complex 55Mn hyperfine structure infrozen solution with A z 95 G for complexes (2) and (3)(Supplementary material).

For Mn(IV) complexes, a d3 system, two EPR resonancescentered at g ¼ 4 (strong) and g ¼ 2 (weak) are typically observed[9]. In the present case the dominating signal is at g z 2 attendedby one or more weak broad signals at low fields (1000e1500 G).This behavior has been accounted for by assuming that the axialparameter D takes the limiting form 2D << hn (hn ¼ 0.317 cm�1 forX-band) causing a decrease in the intensity of the g ¼ 4 resonance[10]. The low solubility of complex (4) in thf and dichloromethaneprevented analysis by EPR in solution. The spectra of (4) and (2) inpowder at 77 K are similar (see Supplementary material).

Preparation of complexes (2)e(4) were monitored by IR(Supplementary material). Reaction intermediates were difficult topin down; in the case of IR the Mn(CO)3 fragments were ubiquitousduring the reaction time rendering the n(CO) band region ratherobscure. 1H NMR monitoring showed the formation of cys-piper-ylene (Supplementary material); while resonances in the methy-lene region were of no use in detecting reaction intermediates. Weadvance a plausible reaction sequence for the realization of (2)e(4)based on the chemical behavior of the pentadienyl ligand: Hydro-thiolation of complex (1) proceeds at room temperature condi-tions; an implication thereof is h5,h3 isomerization of thepentadienyl ligand to open a coordination site due to initial dithiol

Scheme

monocoordination to the Mn(h5-C5H7)(CO)3 metal center togenerate intermediate A (Scheme 2).

A-like species are well known as intermediates in carbonylsubstitution reactions of (1) by tertiary phosphines and phosphites[11]. Hydrogen migration from the coordinated sulfur atom to theh3-pentadienyl ligand of A would afford intermediate B (oxidativeaddition of sulfhydryl group to the Mn center cannot be ruled out).The formation of cis-piperylene suggests the presence of B. It isapparent from IR and 1H NMR reaction monitoring that dithiols’coordination as well as intramolecular hydrogen migration arerelative fast processes that preclude detection of intermediates Aand B. It must be pointed out that upon reaction of Mn(h5-C5H7)(CO)3 with tertiary phosphines the pentadienyl ligand in theintermediate species adopts an S-h3-conformation (Scheme 3) [11].

The presence of cis-piperylene would indicate that hydrogenmigrated to a pentadienyl ligand with a U-h3-conformation ratherthan to a pentadienyl with an S-h3-conformation.

3. Conclusions

The present method constitutes a reliable synthetic procedurefor preparing trinuclear mixed-valence carbonyl complexes start-ing from tricarbonyl[(1-5-h)pentadienyl]manganese and alka-nedithiols. The reaction’s apparent driving force is the saturation ofthe pentadienyl ligand to cis-piperylene. It must be highlighted thesuitability of tricarbonyl[(1-5-h)-pentadienyl]manganese as astarting material for diverse manganese carbonyls with 15 and 16groups’ ligands in the same coordination sphere:We anticipate thatthe synthetic approach here reported has great potential in thepreparation of manganese chalcogen carbonyls; further work isunderway.

4. Experimental

4.1. General considerations

All reactions were conducted under oxygen free nitrogen at-mosphere using standard vacuum line and Schlenk techniques. Thereactions were monitored by IR spectroscopy in the n(CO) regionand the reaction times reported correspond to the time when nofurther changes were observed in the CO groups’ patterns. Complex(1) was prepared according to literature procedures [5]. 1,2-Ethanedithiol, 1,3-propanedithiol, and 1,4-butanedithiol were ac-quired from Aldrich Chemical Co. and used as received. Single-crystal X-ray diffraction studies were performed on a BrukereApex diffractometer equipped with a CCD area detector(lMoKa ¼ 0.71073 �A, monochromator: graphite). Frames werecollected at T ¼ 100 K. The measured intensities were reduced to F2

and corrected for absorption with SADABS (SAINT-NT). Structuresolution, refinement, and data output were carried out with theSHELXTL-NT program package [12]. Non-hydrogen atoms were

2.

PR3

Mn

(OC)3

Scheme 3.

K.P. Salas-Martin et al. / Journal of Organometallic Chemistry 751 (2014) 356e360 359

refined anisotropically; CeH hydrogen atoms were placed ingeometrically calculated positions using the riding model. EPRspectra were recorded on a JEOL JES-TE300 spectrometer. Magneticsusceptibilities were measured on a Magway MSB MK1 magneticbalance. IR spectra were obtained in solution (4000e400 cm�1)using a Nicolet FT-IR 55X spectrometer and in KBr disk (4000e400 cm�1) in a Perkin Elmer 283B spectrometer. NMR spectra wereobtained at room temperature on Varian Unity 300, Perkin Elmer283B, and Jeol GX300 spectrometers. 1H NMR spectra were refer-enced to residual solvent peaks with chemical shifts (d) reported inppm downfield of tetramethylsilane. 31P{1H} NMR spectra wereexternally referenced to 85% H3PO4. FAB(þ) mass spectra wererecorded on a JEOL SX-102A instrument. Elemental analyses wereperformed on a CE-440 analytical analyzer. Melting points weredetermined on a FishereJohns apparatus and are uncorrected.

4.2. Synthesis of Mn3(CO)6(m-S(CH2)nS-k2-S,S0)3 (2)e(4)

Complex (1) (1.0 mmol, 206.0 mg) was dissolved in 100 mL ofdry cyclohexane in a 250 mL round bottom flask with a magneticstirrer previously purged with nitrogen. Alkanedithiol was added(1.0 mmol). The reaction mixture was left at room temperature for4 h (except for (4), see below). Samples were taken every 30min formonitoring purposes. As the reaction progressed there was achange in color from light yellow to dark green. At the end of thereaction a green precipitate was formed. The mixture was filteredthrough a cannula. The filtrate was washed with hexane (to elim-inate unreacted (1)) and dissolved in dichloromethane. Eliminationof dichloromethane under reduced pressure gave complexes (2)e(4) as green solids.

Table 1Crystal data for (2).

(2)

Empirical formula C12H12Mn3O6S6M 609.4Temperature (K) 100(2)Crystal size (mm) 0.48 � 0.42 � 0.36Crystal system TriclinicSpace group P�1

a (�A) 8.8657(5)b (�A) 12.3924(7)c (�A) 19.524(1)a (o) 74.554(1)b (o) 84.091(1)g (o) 82.859(1)V (�A3) 2046.1(2)Z 4q Range for data collection (�) 1.71e25.00Reflections collected 12,580Independent reflections 7096 (Rint ¼ 0.0228)Final R indices [F2 > 2s(F2)]a R1 ¼ 0.0322, wR2 ¼ 0.0783R indices (all data)b R1 ¼ 0.0347, wR2 ¼ 0.0805

a R1 ¼ SjjFoj � jFcjj/SjFoj.b wR2 ¼ [Sw (Fo2 � Fc

2)2/S(Fo2)2]1/2.

Complex Mn3(CO)6(m-S(CH2)2S-k2-S,S0)3 (2) was obtained in86.0% yield; m.p. 125 �C dec. Anal. Calc. for C12H12Mn3O6S6: C,23.65; H, 1.98%; Found: C, 23.10; H, 2.33%. IR (KBr): n(CO) 2009 s,1922 m cm�1. IR (CH2Cl2): n(CO) 2014 s, 1945 m, br cm�1. Anal. Calc.for C12H12Mn3O6S6: C, 23.65; H, 1.98%; Found: C, 23.10; H, 2.33%.meff: 3.81 MB. UVeVis (CH2Cl2) 674, 327, and 234 nm. MS (m/e): 609[M]þ, 608 [M � 1]þ, 525 [M � 3CO]þ, 441 [M � 6CO]þ, 381[M � 6COeSCH2CH2e]þ, 289 [M � 6COe(SCH2CH2S)2]þ.

Crystallization by diffusion of a dichloromethane solution of (2)and hexane at �4 �C afforded suitable crystals to conduct an X-raydiffraction analysis. This method was used for complex (4); how-ever, its low solubility led to small crystals not suitable for an X-rayanalysis.

Complex Mn3(CO)6(m-S(CH2)3S-k2-S,S0)3 (3) was obtained in asimilar manner as (2) with a yield of 85%. The spectroscopiccharacterization partially matches with that of the reported com-plex [4a].

For complex Mn3(CO)6(m-S(CH2)4S-k2-S,S0)3 (4) the reactiontime was 6 h. Yield of 85%. M.p. 150 �C dec. Anal. Calc. forC18H24Mn3O6S6: C, 31.17; H, 3.49%; Found: C, 30.70; H, 3.25%. IR(KBr): n(CO) 2014 s, 1935 s cm�1. IR (CH2Cl2): n(CO) 2018 s, 1942 s, brcm�1. meff: 4.14 MB. MS (m/e): 693 [M]þ, 665 [M � CO]þ, 609[M � 3CO]þ.

4.3. Crystal data

See Table 1.

Acknowledgments

The authors thank I. Chávez-Uribe, B. Quiroz-García, V. Gómez-Vidales, M. A. Peña-Gonzáles, L. Velasco-Ibarra, E. García-Ríos, S.Hernández-Ortega, M. P. Orta-Pérez, (Instituto de Química, UNAM)and A. Núñez-Pineda (CCIQS) for technical assistance. K. P. S.-M.gratefully acknowledges a student grant from CONACyT. N. Z.-V.expresses gratitude to CONACyT for funding of this projectthrough grant CB 2009/131329.

Appendix A. Supplementary material

CCDC 938296 contains the supplementary crystallographic datafor this paper. These data can be obtained free of charge from TheCambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Appendix B. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.jorganchem.2013.07.036.

References

[1] (a) W. Gao, J. Liu, C. Ma, L. Weng, K. Jin, C. Chen, B. Akermark, L. Sun, Inorg.Chim. Acta 359 (2006) 1071e1080;(b) R.B. King, T.E. Bitterwolf, Coord. Chem. Rev. 206e207 (2000) 563e579;(c) D. Sellmann, J. Sutter, Acc. Chem. Res. 30 (1997) 460e469;(d) P.M. Treichel, P.C. Nakagaki, Organometallics 5 (1986) 711e716.

[2] (a) M.M. Hasan, M.B. Hursthouse, Shariff E. Kabir, K.M.A. Malik, Polyhedron 20(2001) 97e101;(b) K.M. Hanif, M.B. Hursthouse, S.E. Kabir, K.M.A. Malik, Md. A. Mottalib,E. Rosenberg, Polyhedron 19 (2000) 1073e1080;(c) G.M.G. Hossain, Md. I. Hyder, S.E. Kabir, K.M.A. Malik, Md. A. Miah,T.A. Siddiquee, Polyhedron 22 (2003) 633e640;(d) S.E. Kabir, K.M.A. Malik, E. Rosenberg, T.A. Siddiquee, Inorg. Chem. Com-mun. 3 (2000) 140e142.

[3] (a) W.F. Liaw, C.H. Hsieh, S.M. Peng, G.H. Lee, Inorg. Chim. Acta 332 (2002)153e159;(b) W.F. Liaw, C.H. Hsieh, G.Y. Lin, G.H. Lee, Inorg. Chem. 40 (2001)3468e3475;

Dr. Marisol Reyes-Lezama, Centro Conjunto de Inves-tigación en Química Sustentable UAEM-UNAM, B.Sc.;2002; Facultad de Química, Universidad Nacional Autón-oma de México, Ph.D.; 2008; Instituto de Química, Univer-sidad Nacional Autónoma de México

Prof. Herbert Höpfl, Centro de Investigaciones Química.Universidad Autónoma de Estado de Morelos, M.Sc.; 1994;Ludwig-Maximilians-Universität München, Germany,Ph.D.; 1997; Chemistry Department, CINVESTAV-IPN,México

K.P. Salas-Martin et al. / Journal of Organometallic Chemistry 751 (2014) 356e360360

(c) W.F. Liaw, C.H. Hsieh, G.Y. Lin, G.H. Lee, S.M. Peng, C.M. Lee, C.H. Hu,J. Chem. Soc. Dalton Trans. (1999) 2393e2398;(d) W.F. Liaw, C.H. Hsieh, G.Y. Lin, G.H. Lee, Inorg. Chem. 37 (1998)6396e6398.

[4] (a) N. Begum, Md. I. Hyder, S.E. Kabir, G.M.G. Hossain, E. Nordlander,D. Rokhsana, E. Rosenberg, Inorg. Chem. 44 (2005) 9887e9894;(b) R.D. Adams, O.-S. Kwon, M.D. Smith, Isr. J. Chem. 41 (2001) 197e206.

[5] M. Reyes-Lezama, H. Höpfl, N. Zúñiga-Villarreal, Organometallics 29 (2010)1537e1540 and references cited therein.

[6] D. Seyferth, E. Goldman, J. Pornet, J. Oganomet. Chem. 208 (1981) 189e193.[7] F. Pruchnik, Organometallic Chemistry of the Transition Elements, Plenum,

New York, 1990, pp. 32e41.[8] M.R. Churchill, K.N. Amoh, H.J. Wasserman, Inorg. Chem. 20 (1981) 1609e

1611.[9] (a) S. Chandra, A. Chakravorty, Inorg. Chem. 31 (1992) 760e765;

(b) S. Pal, P. Ghosh, A. Chakravorty, Inorg. Chem. 24 (1985) 3704e3706;(c) K.L. Brown, R.M. Golding, P.C. Healy, K.J. Jessop, W.C. Tennant, Aust. J.Chem. 27 (1974) 2075e2081.

[10] B.C. Dave, R.S. Czernuszewics, J. Coord. Chem. 33 (1994) 257e269.[11] M.A. Paz-Sandoval, P. Powell, M.G.B. Drew, R.N. Perutz, Organometallics 3

(1984) 1026e1033.[12] (a) Bruker Analytical X-ray Systems, SAINT þ NT, Versions 6.01 and 6.04, 1999

and 2001. (b) G.M. Sheldrick, SHELX86, Program for Crystal Structure Solution,University of Göttingen, Germany, 1986;(c) SHELX, G.M. Sheldrick, Acta Crystallogr. Sect. A 64 (2008) 112e122.

Karla P. Salas-Martin, B.Sc.; 2008; Facultad de Química,Universidad Nacional Autónoma de México, M.Sc.; 2010;Instituto de Química, Universidad Nacional Autónoma deMéxico, Currently Ph.D. student at Instituto de Química(UNAM) under the advisory of Dr. Noé Zúñiga Villarreal

Prof. Noé Zúñiga Villarreal (Corresponding author),Inorganic Chemistry Department. Instituto de Química,UNAM, Circuito Exterior, Ciudad Universitaria. DelegaciónCoyoacan 04510 México, D.F. México, Tel.: þ52 (55) 56224431, Fax: þ52 (55) 5616 2203. B.Sc.; 1981; Escuela Su-perior de Ingeniería Química e Industrias Extractivas, IPN.México, Ph.D.; 1991; Chemistry Department, CINVESTAV-IPN, México.