Journal of Molecular Structure 1045 (2013) 55–61

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Journal of Molecular Structure

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Synthesis, structure and electrochemistry behavior of a cobalt(III)compound with azide and methyl 2-pyridyl ketone semicarbazoneligands

0022-2860/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.molstruc.2013.03.049

⇑ Corresponding authors. Tel.: +98 411 3393144; fax: +98 411 3340191 (B.Shaabani), tel.: +351 220402576; fax: +351 220402659 (L. Cunha-Silva).

E-mail addresses: b.shaabani@yahoo.com (B. Shaabani), l.cunha.silva@fc.up.pt(L. Cunha-Silva).

Behrouz Shaabani a,⇑, Ali Akbar Khandar a, Farzaneh Mahmoudi a, Salete S. Balula b, Luís Cunha-Silva b,⇑a Department of Inorganic Chemistry, Faculty of Science, Tabriz University, 51666-14766, Iranb REQUIMTE & Department of Chemistry and Biochemistry, Faculty of Chemistry, University of Porto, 4169-007 Porto, Portugal

a r t i c l e i n f o

Article history:Received 5 November 2012Received in revised form 23 March 2013Accepted 25 March 2013Available online 18 April 2013

Keywords:Semicarbazone ligandAzide compoundCobalt(III) centerCrystal structureCyclic voltammogram

a b s t r a c t

An unprecedented cobalt(III) compound with methyl 2-pyridyl ketone semicarbazone (HL) and the aux-iliary azide ligand, [Co(L)2] [Co(L)(N3)3] (1) was synthesized and further characterized crystallographi-cally and spectroscopically. Compound 1 crystallizes in the triclinic system and space group of P-1 andits structure consists of two mononuclear crystallographic units with metal chromophore comprisingtwo cobalt(III) centers revealing distorted octahedral geometries and formed by distinct ligands in theinner coordination spheres. Interestingly, compound 1 represents the first complex formed by two dis-tinct mononuclear units involving this ligand. As consequence of various donor and acceptor groups inboth crystallographic units, there are several strong NAH� � �N and NAH� � �O hydrogen bonding interac-tions interconnecting adjacent moieties, ultimately leading to a three-dimensional supramolecular net-work. Furthermore, the electrochemical behavior of the HL and compound 1 were investigated.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

For decades, Schiff bases have been played an extraordinaryrole as chelating ligands in main group and transition metal coor-dination chemistry, due to their uncomplicated synthesis, wideavailability and structural versatility associated with their poten-tial in diverse applications [1–10]. Numerous Schiff bases andcoordination complexes with this extensive family of ligands haverevealed remarkable antimicrobial activity, being potent antibac-terial, antifungal, anticancer and antiviral compounds [2,11–20].In particular the semi and thiosemicarbazones are versatile ligandsthat have attracted the scientific interest of researchers, not onlydue to their interesting coordination proprieties since they cancoordinate in both neutral and anionic forms [21–23], but also asconsequence of their potential in pharmacological applications[24–30,13,31, 32,11,33]. Frequently, their metal complexes re-vealed enhanced antimicrobial activities than the free Schiff baseligands. Consequently, the design and preparation of novel coordi-nation complexes with transition metals and semicarbazones li-gands to improve and tune the proprieties trough the discoveryof new structures is still a notable scientific challenge. In an earlierpaper [33] we have reported the synthesis of ligand namely

pyridine-2-carbaldehyde semicarbazone, here we report thesynthesis and characterization of a novel ligand methyl 2-pyridylketone semicarbazone (HL) (Scheme 1) and the cobalt(III) com-pound of it. The methyl 2-pyridyl ketone semicarbazone ligandhas been utilized in the preparation of metal complexes. A surveyin the Cambridge Structural Database showed demonstrated fivecrystal structures involving this ligand, all of them featuringmononuclear complexes. On the other hand, a basic possibility toimprove the structural features of the semicarbazones based coor-dination complexes is the use of auxiliary bridging ligands, such aspseudohalides. These can form bridging complexes with transitionmetals where the groups N�3 , NCS�, NCO� coordinate in the end-to-end and end-on bridging modes [34–43]. Recently mono and dinu-clear complexes of Schiff base ligands and pseudohalides like azidewith cobalt(III), have been well established [41–43,38,39,44].

Following our interest in the design and development ofunprecedented transition metal coordination complexes withsemicarbazone-type ligands and a second bridging ligand, we syn-thesized the Co(III) compound [Co(L)2] [Co(L)(N3)3] (1), with the HLand azide ligand. This compound was characterized by IR and UVspectroscopies and the solid-state structure was unveiled by sin-gle-crystal X-ray diffraction revealing two distinct mononuclearCo(III) unites, [Co(L)2] and [Co(L)(N3)3]. The supramolecular intera-tions between the different unities were investigated, and the elec-trochemical behavior of the free semicarbazone ligand and thecompound 1 was studied.

Scheme 1. The Schiff base ligand methyl 2-pyridyl ketone semicarbazone (HL).

Table 1Crystal data and structure refinement parameters for [Co(L)2][Co(L)(N3)3] (1).

Chemical formula C24H27Co2N21O3

Formula weight 775.53Crystal description Plate, brownCrystal size (mm) 0.17 � 0.09 � 0.03Temperature (K) 150Crystal system TriclinicSpace group P-1a (Å) 8.6140(4)b (Å) 13.2566(7)c (Å) 13.6042(7)a (�) 86.445(4)b (�) 84.286(3)c (�) 82.026(3)Volume (Å3) 1529.00(13)Z 2qcalculated (g cm�3) 1.684l (mm�1) 1.154h range (�) 3.66–25.41Final R indices [I > 2r(I)] 0.0432(4292)Final R indices (all data) 0.1115(5551)Largest diff. peak and hole (eÅ�3) 0.574 and �0.692

56 B. Shaabani et al. / Journal of Molecular Structure 1045 (2013) 55–61

2. Experimental

2.1. Materials and general methods

All chemicals and solvents were of reagent grade and used asreceived from Merck or Fluka. Microanalyses were carried outusing a Heraeus CHNAOA Rapid analyzer. Melting points weremeasured on an Electrothermal 9100 apparatus and are uncor-rected. IR spectra were recorded on a FT-IR Spectrometer BrukerTensor 27 in the region 4000–400 cm�1 using KBr pellets. UV spec-tra were recorded on a Shimadzu, UV-1650 PC spectrophotometer.The solid state electronic absorption spectra were recorded by dif-fuse reflectance spectra (DRS) on a Scinco 4100 in the range of200–1100 nm using BaSO4 as reference. Cyclic voltammetric mea-surements were performed using an AMEL Instruments Model2053 as potentiostate connected with a function generator (AMELModel 568). In all electrochemical studies, a three-electrode sys-tem was used consisting of a glassy carbon as the working elec-trode, a platinum wire auxiliary electrode, and an Ag/AgCl as thereference electrode. All of the electrochemical experiments werecarried out under nitrogen atmosphere at room temperature usingsolution of compounds with concentration about 10�3 M in DMSOsolvent containing 0.1 M lithium perchlorate as the supportingelectrolyte. Electrochemistry of HL and its metal compound andazide, were studied by cyclic voltammetry in scan rate of0.01 V s�1. Ferrocene (Fc) was used as the internal standard andall redox potentials were referenced to the Fc+/0 couple.

2.2. Synthesis of methyl 2-pyridyl ketone semicarbazone (HL)

The HL was prepared by condensation of methyl 2-pyridyl ke-tone with semicarbazide hydrochloride [21,22]. 0.8 g (7 mmol) ofsemicarbazide hydrochloride was added to a solution of 2-methylPyridyl ketone (0.85 ml, 7 mmol) in 20 ml of methanol in a roundbottom flask under continuous stirring. The mixture was refluxedfor 5 h to produce a white suspension. The final reaction mixturewas filtered off and the filtrate was kept in room temperature for10 h. The resulting white precipitation (m.p. 206 �C) was filteredoff, washed with methanol and dried in air. Yield: 1.30 g (5 mmol,80%), Anal. Calc. for C8H10N4O: C, 44.72; H, 4.66; N, 26.08. Found: C,44.65; H, 4.46; N, 26.08. Characteristic IR absorbtions (cm�1):3431, 3279 m, m(NH2); 3192 m, m(NAH); 1578 s, m(C@N); 1105 s,m(NAN); 1685 s, m(C@O).

2.3. Synthesis of [Co(L)2][Co(L)(N3)3] (1)

Crystals of 1 are obtained by slow diffusion in an H-shaped Tubealready described in the literature [34,45,46]. By using 0.2 mmol ofHL, 0.8 mmol of Co(OAC)2�4H2O and 1.5 mmol of NaN3 in ethanol,dark brown crystals of 1 were formed (decomposition at 300 �C)after seven days, which were isolated, filtered off, washed withacetone and diethyl ether and dried in air. Yield: 0.12 g, 30%. Anal.Calc. for C24H27Co2N21O3: C, 37.13; H, 3.48; N, 43.32. Found: C,37.03; H, 3.28; N, 43.20. Characteristic IR absorbtions (cm�1):3441, 3301 m, m(NH2); 1604 s, m(C@N); 1182 m, m(NAN); 591 m,m(CoAN azomethine), 2023 s, m(N�3 ).

2.4. X-ray crystallography

Crystalline material suitable for single-crystal X-ray diffractionanalysis of the complex [Co(L)2][Co(L)(N3)3] (HL is methyl 2-pyri-dyl ketone semicarbazone) was manually harvested and mountedon a CryoLoop using appropriated oil [47]. Data were collected at150(2) K on a Bruker X8 Kappa APEX II Charge-Coupled Device(CCD) area-detector diffractometer (Mo Ka graphite-monochro-mated radiation was used, k = 0.71073 Å) controlled by the APEX2software package [48], and equipped with an Oxford CryosystemsSeries 700 cryostream monitored remotely by the Cryopad soft-ware [49]. Images were processed with SAINT+ [50], and data werecorrected for absorption by the multi-scan method implemented inSADABS [51]. The structure was solved by the direct methods ofSHELXS-97 [52,53] .allowing the immediate location of the Coatoms, with the remaining non-hydrogen atoms being identifiedin the difference Fourier maps calculated from successive full-ma-trix least-squares refinement cycles on F2 using SHELXL-97[53,54]. All non-hydrogen atoms were successfully refined withanisotropic displacement parameters, and hydrogen atomsbounded to the carbon atoms were placed in geometrica geometri-cal position [53–56]. Hydrogen atoms of the NH2 groups weremarkedly visible in difference Fourier maps and included in thestructure with the NAH and H���H distances restrained to 0.90(2)and 1.50(2) Å, respectively, and with Uiso fixed at 1.5 � Ueq of theparent nitrogen atom. The highest peak (0.59 eÅ�3) was found at1.09 Å from Co2 and the deepest hole (�0.69 eÅ�3) at 0.71 Å fromCo2. Refinement details are summarized in Table 1.

3. Results and discussion

3.1. IR spectra

The IR spectra of HL and compound 1, and the shifts of IR bandsof ligand due to its coordination to Co(III) cation are given in Ta-ble 2. For more information the FT-IR spectra curves of HL and 1are presented in Fig. 1a and b. A medium band in 3192 cm�1 inthe free ligand HL, due to a m(2NAH) vibration, disappears in thespectra of 1, providing strong evidence for ligand coordination tothe Co(III) ion in the deprotonated enolate form [19,26,13]. Thestrong bands at 3431 and 3279 cm�1 in the spectra of HL, assignedto m(4NAH), shifts to higher energies in 1. Bands in 1578 and1485 cm�1 suffer significant shifts in the spectra of 1, which canbe attributed to m(C@N) and m(C@C) vibration modes, and their

Table 2IR spectral assignment (cm�1) for HL and 1.

Compound m(C@N) m(NAN) m(C@O) m2ðNAHÞ m4

ðNAHÞ m(CoAN azomethine) m(N3)

HL 1578 1105 1685 3192 3431, 3279 – –1 1604 1182 – – 3441, 3301 591 2023

Fig. 1. The FT-IR spectral curves for HL (upper) and compound 1(lower).

B. Shaabani et al. / Journal of Molecular Structure 1045 (2013) 55–61 57

Table 3Electronic absorption data of HL and 1.

Compound p! p�pyridine e (M�1 cm�1) p! p�imine e n! p�imine e LMCT e d–d e

HL (DMSO) 260(sh) 8000 320 25,000 365(sh) 2000 – –HL (DMF) 261(sh) 7000 323 24,000 362(sh) 2000 – –HL (Solid state) 278(sh) 351 – – –Compound 1 (DMSO) 263(sh) 10,000 336 16,000 – 420 14,000 600 250Compound 1 (DMF) 265 8000 340 15,000 – 423 13,000 604 100Compound 1 (Solid state) 280 361 – 462 643

Fig. 2. The two neutral mononuclear crystallographic units that compose the structure of 1, showing the labeling scheme for the Co(III) coordination centers. For clarityreasons only the hydrogen atoms of the amine groups are shown.

Table 4Selected bond lengths (Å) and angles (deg) for 1.

Co1AN2 1.860(3) Co2AN10 1.862(3)Co1AN6 1.861(3) Co2AN9 1.917(3)Co1AO2 1.896(2) Co2AO3 1.944(3)Co1AN5 1.909(3) Co2AN16 1.949(3)Co1AN1 1.916(3) Co2AN19 1.956(3)Co1AO1 1.922(2) Co2AN13 1.971(3)

N2ACo1AN6 177.83(12) N10ACo2AN9 83.13(13)N2ACo1AO2 95.16(10) N10ACo2AO3 82.03(11)N6ACo1AO2 82.68(10) N9ACo2AO3 165.15(11)N2ACo1AN5 98.67(12) N10ACo2AN16 177.61(13)N6ACo1AN5 83.50(12) N9ACo2AN16 98.81(13)O2ACo1AN5 166.15(10) O3ACo2AN16 96.02(12)N2ACo1AN1 83.15(11) N10ACo2AN19 87.44(12)N6ACo1AN1 97.04(11) N9ACo2AN19 88.59(12)O2ACo1AN1 89.80(11) O3ACo2AN19 90.36(12)N5ACo1AN1 90.98(11) N16ACo2AN19 91.21(13)N2ACo1AO1 82.09(10) N10ACo2AN13 90.65(12)N6ACo1AO1 97.74(10) N9ACo2AN13 90.92(12)O2ACo1AO1 92.39(10) O3ACo2AN13 89.64(11)N5ACo1AO1 90.38(11) N16ACo2AN13 90.72(12)

58 B. Shaabani et al. / Journal of Molecular Structure 1045 (2013) 55–61

mixing patterns are different from that in the spectra of HL. The po-sitive shift of bands corresponding to m(C@N) in the range1578 cm�1 in the HL to 1604 cm�1 in 1, is consistent with the coor-dination of the azomethine nitrogen to the Co(III) ions [20–23,11].Medium bands at 591 cm�1 corresponding to m(CoAN) further sup-port azomethine nitrogen coordination [11,35,36]. The enolizationof HL is supported by the increase in m(NAN) by 77 cm�1. The ab-sence of the m(C@O) bands, present in HL at 1685 cm�1, indicatesthe enolization of the amide functionality upon coordination tothe Co(III) center. Instead strong bands at 1645 cm�1 are observedwhich are characteristic of the coordination of HL in enolate forms[23–26]. Presence of a band at 1552 for 1, is assigned to the newlyformed m(N@C) after enolization [23]. The low energy pyridine ringin-plane and out-of-plane vibrations observed in the spectra of HLat 625 and 432 cm�1 are shifted to higher frequencies at 638 and445 cm�1 but for 1, which is a good indication of the coordinationof nitrogen of pyridine heterocycle to the metal center [23,26]. In 1,the well resolved peak at 2023 cm�1 were obtained, which are as-signed to coordinated azido group [37–44].

N1ACo1AO1 165.21(10) N19ACo2AN13 178.06(12)

Table 5Selected hydrogen bonding parameters for 1.

DAH� � �A d(DAH)(Å)

d(H� � �A)(Å)

d(D� � �A)(Å)

(DAH� � �A)(�)

N4AH4A� � �N11i 0.886(17) 2.09(2) 2.943(4) 161(3)N4AH4B� � �O1ii 0.874(17) 2.028(19) 2.898(3) 174(3)N8AH8A� � �N13 0.869(17) 2.12(2) 2.969(4) 164(3)N8AH8B� � �N3iii 0.868(17) 2.12(2) 2.963(4) 165(3)N12AH12B� � �N7iv 0.880(18) 2.55(3) 3.322(4) 147(4)

Symmetry transformations used to generate equivalent atoms: (i) x � 1, y, z; (ii) �x,�y + 1, �z + 1; (iii) x + 1, y, z; and (iv) �x + 1, �y + 1, �z + 1.

3.2. Electronic spectra

Electronic spectral data of HL and 1 are presented in Table 3.The UV absorption bands of HL in DMSO solvent exhibits chargetransfer transitions at 260 and 320 nm attributed to intra-ligandp ? p⁄ transitions of the pyridyl ring and imine function of thesemicarbazone moiety and a band at 365 nm attributed to n ? p⁄

transition of imine function. Metallation of HL, causes a red shiftof these electronic transitions for 1 (see Table 3). Also the absorp-tion band at 420 nm is attributed to LMCT from azido ligand to co-balt(III) ions. For 1, containing distorted octahedral cobalt(III)centers, the absorption band at 600 nm appeared due to d–d tran-sition as reported in the literature [41,42,38] and the higher energyband was overlapped by ligand to metal charge transfer bands. As

B. Shaabani et al. / Journal of Molecular Structure 1045 (2013) 55–61 59

seen in Table 3 and comparing the results of electronic spectra ofHL and 1 in DMSO, DMF and solid state, the results demonstratethat with dissolving, intense charge-transfer bands of HL and 1 ap-pear at low wavelengths. Such a large blue shift may be attributedto the strong interaction between the solvent molecules with 1.Also by comparing the electronic spectra of HL and 1 in DMSOand DMF, it is concluded that by using a polar solvent the absorp-tion bands are shifted to short wavelength which is known as hyp-sochromic shift.

3.3. Crystal structure of [Co(L)2][Co(L)(N3)3](1)

The structure of 1 is depicted in Fig. 2, and the crystallographicdata and structure analysis for it, is summarized in Table 1. Thestructure of 1 consists of two distinct mononuclear crystallo-graphic units, which will be denoted as parts A and B. In part Awith formula [Co(L)2], the cobalt(III) center is uniquely coordinatedby two deprotonated HL. The structural study reveals that the Co1center exhibit a distorted octahedral environment and the equato-rial sites of Co1 center are occupied by two nitrogen and one eno-late oxygen atoms of the HL (N5, N6 and O2) and one nitrogenatom of the second HL (N2), and the axial sites are occupied byone nitrogen and one enolate oxygen atoms of the second HL(N1,O1). The coordination polyhedron around Co1 may be de-scribed as an axially elongated octahedral (for more informationabout the bond length see Table 4). The Co(III)AN distances areshorter for the azomethine nitrogen atoms, indicating their stron-ger coordination than pyridyl nitrogens. The angles around the Co1center deviate significantly from 90�, the N2ACo1AO2 andN5ACo1AN2 angles have opened up to 95.16� and 98.67�, respec-tively and the N6ACo1AO2 and N5ACo1AN6 angles have reducedto 82.68� and, 83.18� indicating distortion from a regular octahe-dron [41,43]. The chelate bite angles in the two five-memberedrings are close [O1ACo1AN2, 92.09�; N2ACo1AN1, 93.12� andO2ACo1AN6, 82.68�; N6ACo1AN5, 83.51�]. In part B with formula[Co(L)(N3)3], the Co2 center is uniquely hexa coordinated by a tri-dentate Schiff base HL and three terminal azides. The coordinationpolyhedron around Co2 is best described as distorted octahedral.Distortion from the ideal octahedral geometry is mainly due tothe asymmetric nature of the bond tridentate Schiff base ligand.Three atoms (N9, N10 and O3) of the tridentate HL in combination

Fig. 3. (a) NAH� � �N and NAH� � �O hydrogen bonds interconnecting adjacent parts A anHydrogen bonds are represented as dashed lines (golden color) and for clarity only threferences to color in this figure legend, the reader is referred to the web version of thi

with three nitrogen atoms (N13, N16 and N19) of three differentazides in a meridional alignment complete octahedral coordinationof the Co2 ion. The equatorial positions are occupied by the twonitrogen and one enolate oxygen atoms of the HL (N9, N10 andO3) and one nitrogen atom of the terminal azide (N16), while othernitrogen atoms of the remaining azides (N13 and N19) are placedat the axial positions with the angle of N13ACo2AN19;178.05(12)�. The chelate bite angles in the two five-memberedrings are very close [O3ACo2AN10 is 82.00�, N10ACo2AN9 is83.15�]. The coordination polyhedron around Co2 may be de-scribed as an axially elongated octahedral. As seen, the Co(III)ANdistance is shorter for the azomethine nitrogen atom indicatingits stronger coordination than pyridyl and azide nitrogens. The ter-minal azide ligands show asymmetric NAN distances of 1.198(4)/1.160(4) Å, 1.207(4)/1.167(4) and 1.208(4)/1.144(4) Å with thelonger NAN bonds involving the N atoms coordinated to the metalcenter. The bond length for CoAN(azido) with CoAN13; 1.971(3) Å,CoAN16; 1.949(3) Å, CoAN19; 1.956(5) Å are similar with that re-ported in the literature [41–43,38]. The azides are quasi-linearwith NANAN angles: [N13AN14AN15; 176.7(4)�, N16AN17AN18;177.9(4)� and N19AN20AN21; 176.6(4)�], these NANAN anglesare similar with that reported in the literature [41,38].

As consequence of various donor and acceptor groups in boththe parts, there are several strong NAH� � �N and NAH� � �O hydrogenbonds interconnecting adjacent moieties. The details about thehydrogen bonds interconnecting are summarized in Table 5. WhileN4AH4B� � �O1ii and N8AH8B� � �N3iii interconnect only crystallo-graphic equivalent parts of type A, the remaining hydrogen bonds(N4AH4A� � �N11i, N8AH8A� � �N13 and N12AH12B� � �N7iv) areinteraction involving distinct parts, i.e. between parts A and B.These strong hydrogen bonding network lead to the formation ofa three-dimensional supramolecular network. These hydrogeninteractions and a three-dimensional supramolecular network forthe compound are shown in the Fig. 3a and b.

3.4. Electrochemistry

3.4.1. Electrochemistry of the HL and azide ligandsIt is evident from the cyclic voltammogram of HL displayed in

Fig. 4a, that HL is electroactive over a range from 1.5 to �2.0 V indimethylsulfoxide solvent. Two ligand-centered redox waves

d B. (b) Extended crystalline packing showing the 3D hydrogen bonding network.e H-atoms involved in the hydrogen bonds are shown. (For interpretation of the

s article.)

Fig. 4. Cyclic voltammogram of 10�3 mol/l HL (a) and azide (b) ligands in DMSO and lithium perchlorate (0.1 mol/l); scan rate 10 mV s�1.

Fig. 5. Cyclic voltammogram of 10�3 mol/l [Co(L)2][Co(L)(N3)3](1) in DMSO andlithium perchlorate (0.1 mol/l); scan rate 10 mV s�1.

60 B. Shaabani et al. / Journal of Molecular Structure 1045 (2013) 55–61

observed at �1.15 and 1.18 V are attributed to the pyridine rings.The azo group (AN@NA) is known as a potential electron transfercenter [41] and the cyclic voltammogram of azide ligand displaysonly one irreversible oxidation wave at 0.85 V (see Fig. 4b).

3.4.2. Electrochemistry of [Co(L)2][Co(L)(N3)3](1)As seen in Fig. 5, the compound 1 exhibits both metal and ligand

centered electroactivity in the potential range �2 to 1 V. The cyclicvoltammogram of 1 in DMSO, displays two cathodic potentials atabout �0.54 V (Ic1) and �1.68 V (Ic2). The cathodic peaks of 1 at�0.54 (Ic1) and �1.68 (Ic2) (versus Ag/AgCl) can be attributed forthe reduction of two cobalt(III) ions in different environment to co-balt(II). During the reverse scan oxidation waves (Ia1, Ia2 and Ia3)appear at �1.68, �0.54 and 0.94 V. The oxidation waves (Ia1, Ia2)which are associated with the cathodic peaks Ic2 and Ic1, respec-tively. These processes are completely reversible, characterizedby a peak to peak separation (DEp = EPa � Epc) of 0.18 and 0.16 V,respectively, which remains unchanged upon changing the scanrate. There is also an equality in the anodic peak current and thecathodic peak current of 1 (ia1/ic2 = 0.35, ia2/ic1 = �.080), as ex-pected for a reversible electron transfer process. The oxidationwaves (Ia3) displays at 0.94 V is attributed to the oxidation of azideligand [28,31].

4. Conclusion

A cobalt(III) compound [Co(L)2] [Co(L)(N3)3] (1), involving Schiffbase methyl 2-pyridyl ketone semicarbazone (HL) and the auxil-iary azide ligand, has been synthesized and characterized. Compar-ison of the IR spectra of HL and 1, indicates that HL acts as atridentate Schiff base and is chelated to the cobalt(III) centers in

enolate form, which is confirmed by the solid-state structuredeterminate by single crystal X-ray diffraction. In fact, compound1 consists of two Co(III) mononuclear crystallographic units withdifferent coordination spheres, but both the Co(III) centers are sixcoordinated with distorted octahedral geometries. This compoundis the first compound formed by two mononuclear units based inthe methyl 2-pyridyl ketone semicarbazone ligand. As conse-quence of various donor and acceptor groups in the two distinctunits, there are several strong NAH� � �N and NAH� � �O hydrogenbonds interconnecting adjacent moieties, ultimately leading to athree-dimensional supramolecular network. Cyclic voltammetricexperiments of 1 in DMSO reveals oxidation of azide at 0.94 Vand two oxidation potentials at �1.68, �0.54 V for two differentcobalt(III) centers. Currently, we are investigating other bridgingauxiliary ligands to be used with semicarbazone based moleculesin the preparation of new metal coordination compounds, in orderto increase their structural complexity and improve theirproperties.

Supplementary data

Crystallographic data (excluding structure factors) for all thestructures reported in this paper have been deposited with theCambridge Crystallographic Data Centre as supplementary publi-cation no. CCDC-894063. Copies of these data can be obtained freeof charge on application to CCDC, 12 Union Road, Cambridge CB22EZ, UK; FAX: +44 1223 336033, or online via www.ccdc.cam.a-c.uk/data_request/cif or by emailing data_request@ccdc.cam.ac.uk.

Acknowledgements

We are grateful to Tabriz University of Research council for thefinancial support of this research. We are grateful to the Fundaçãopara a Ciência e a Tecnologia, (FCT, MEC, Portugal) for their generalfinancial support under the strategic project PEst-C/EQB/LA0006/2011.

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