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Journal of Molecular Structure 834–836 (2007) 336–344

Synthesis, structure, spectroscopic and electrochemical propertiesof (2-amino-4-methylpyrimidine)-(pyridine-2,6-dicarboxylato)

copper(II) monohydrate

_Ibrahim Ucar *, Bunyamin Karabulut, Ahmet Bulut, Orhan Buyukgungor

Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayıs University, Kurupelit, 55139 Samsun, Turkey

Received 11 September 2006; received in revised form 27 October 2006; accepted 27 October 2006Available online 19 January 2007

Abstract

The (2-amino-4-methylpyrimidine)-(pyridine-2,6-dicarboxylato)copper(II) monohydrate complex was synthesized and characterizedby spectroscopic (IR, UV/Vis, EPR), thermal (TG/DTA) and electrochemical methods. X-ray structural analysis of the title complexrevealed that the copper ion can be considered to have two coordination spheres. In the first coordination sphere the copper ion formsdistorted square-planar geometry with trans-N2O2 donor set, and also the metal ion is weakly bonded to the amino-nitrogen in the layerover and to the carboxylic oxygen in the layer underneath in the second coordination sphere. The second coordination environment onthe copper ion is attributed to pseudo octahedron. The powder EPR spectra of Cu(II) complex at room and liquid nitrogen temperaturewere recorded. The calculated g and A parameters have indicated that the paramagnetic centre is axially symmetric. The molecular orbi-tal bond coefficients of the Cu(II) ion in d9 state is also calculated by using EPR and optical absorption parameters. The cyclic voltam-mogram of the title complex investigated in DMSO (dimethylsulfoxide) solution exhibits only metal centered electroactivity in thepotential range �1.25 to 1.5 V versus Ag/AgCl reference electrode.� 2007 Elsevier B.V. All rights reserved.

Keywords: Copper-dipicolinate complexes; X-ray crystal structure; EPR; Thermal analysis; IR and cyclic voltammetry

1. Introduction

It has been reported that dipicolinic acid (pyridine-2,6-dicarboxylic acid) is a key component for the high heatresistance of bacterial spores, owing to its ability to buildstabilizing with divalent metals [1]. It is implicated as a fac-tor in spore resistance properties and germination that theCa2+ chelate of this organic compound is a major constit-uent of the dormant spore core [2,3]. From the crystal engi-neering point of view, dipicolinic acid is also a useful toolfor constructing crystalline architectures due to its rigidand planar nature, and its proton donating and acceptingcapabilities for hydrogen bonding via the oxygen atomsof its carboxylate groups [4]. Having potential donor

0022-2860/$ - see front matter � 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.molstruc.2006.10.061

* Corresponding author.E-mail address: [email protected] (_I. Ucar).

oxygen and nitrogen atoms, dipicolinic acid has attractedthe scientist from the coordination chemistry and numbersof studies have been carried out with dipicolinate (dpc)ligand by both inorganic and bioinorganic chemists duringthe past few years [5,6]. Dipicolinates commonly coordi-nate to transition metals by either carboxylate bridgesbetween metal centres, to form polymeric or dimeric com-plexes [7–9], or tridentate (O, N, O 0) chelation to one metalion [10–12]. To investigate the antitumor effects [13], a ser-ies of isomorphous dipicolinate complexes with rare-earthmetals were synthesized and the structures were reported[14–16]. The dipicolinic ligand with Cu(II) ions commonlyhas one or two coordination modes. In one coordinationmode, a single planar dpc ligand binds in the equatorialplane of a Cu(II) cation and other ligands such as H2Oor pyridine based heterocycles occupy the remaining sites,thereby forming a square planar or square pyramidal

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_I. Ucar et al. / Journal of Molecular Structure 834–836 (2007) 336–344 337

coordination geometry [17]; or two planar dpc moleculescoordinate perpendicularly generating a distorted octahe-dral coordination geometry [18].

In our ongoing research on determination of furthercoordination modes of chelates of dipicolinic acid withbiogically important transition metal ions, we have recentlysynthesized mixed-ligand metal (II) complexes of dipicoli-nic acid and theirs structures have been reported [19]. Inthis paper, we report the syntheses, structures, thermalbehaviours and redox properties of new copper-dpc (dpc:dipicolinic acid) complex with the ampym ligand (ampym:2-amino-4-methylpyrimidine), namely [Cu(ampym)(dpc)]ÆH2O.

2. Experimental

2.1. General method

All chemical reagents were analytical grade commercialproducts. Solvents were purified by conventional methods.The EPR spectra were recorded using a Varian E-109Cmodel X-band spectrometer. The magnetic field modula-tion frequency was 100 kHz and the microwave powerwas around 10 mW. The g values were obtained by com-parison with a diphenylpicrylhydrazyl sample ofg = 2.0036. The optical absorption spectra of title complexwere recorded at room temperature in DMF solution on aCINTRA 20 UV/Vis spectrometer working between 300and 900 nm. The thermal decomposition of �10 mg ofthe prepared complexes were measured under the nitrogenair atmosphere with PRIS Diamond TG/DTA thermalanalyser at a heating rate of 10 �C/min. in the temperaturerange 35–1000 �C for both complexes using platinum cruci-bles. The IR spectra were recorded on a Jasco 430 FT/IRspectrometer using KBr pellets and operating in4000–200 cm�1 range. An EcoChemie Autolab-30 poten-tiostat with the electrochemical software package GPES4.9 (Utrecht, Netherlands) was used for voltammetric mea-surements. A three electrode system was used: a Pt counterelectrode, an Ag/AgCl reference electrode and a Pt wireelectrode as working electrode. The potentiostat/galvonas-tat have an IR-compensation option. Therefore, the resis-tance due to the electrode surface was compensatedthroughout the measurements. Oxygen-free nitrogen wasbubbled through the solution before each experiment. Allexperiments were carried out at room temperature.

2.2. Syntheses of [Cu(ampym)(dpc)]ÆH2O

To an ethanole/water (30 ml, ca 1:1 v/v) containingCuCl2Æ4H2O (1 mmol) and disodium dipicolinate(1 mmol), ampym (1 mmol) was added slowly with contin-uous stirring. The resulting solution was refluxed for 1 hand then filtered. The blue filtrate was allowed abouttwo weeks at room temperature, and then the blue crys-tals of title complex suitable for X-ray diffraction analysiswere collected.

2.3. X-ray crystallography

A suitable single crystal was mounted on a glassfiber and data collection was performed on a STOEIPDSII image plate detector using Mo Ka radiation(k = 0.71019 A) at 297 and 113 K. Details of crystal struc-tures are given in Table 1. Data collection: Stoe X-AREA[20]. Cell refinement: Stoe X-AREA [20]. Data reduction:Stoe X-RED [20]. The structure was solved by direct-meth-ods using SIR-97 [21] and anisotropic displacement param-eters were applied to non-hydrogen atoms in a full-matrixleast-squares refinement based on F2 using SHELXL-97[22]. All carbon hydrogens were positioned geometricallyand refined by a riding model with Uiso 1.2 times that ofattached atoms and remaining hydrogen atoms were foundby Fourier difference. Molecular drawings were obtainedusing ORTEP-III [23].

3. Results and discussion

3.1. Molecular structure

The structure of the title compound (Fig. 1) consists of aneutral [Cu(ampym) (dpc)] unit and one solvent water mol-ecule. The dpc anion, with its two carboxylate groups inortho-positions with respect to the pyridine N atom, ispotentially tridentate. The copper ion is bonded to the pyr-idine N atom [Cu1AN1 = 1.900(2) A], as well as to one Oatom of each carboxylate group [Cu1AO1 = 1.995(2) andCu1AO2 = 2.001(2) A] and to pyrimidine N atom of2-amino-4-methylpyrimidine [Cu1AN2 = 1.979(2) A],which is in trans-position to the nitrogen atom of the dip-icolinic acid, adopting a distorted square planar geometry.A similar coordination arrangement and bond distances(Table 2) were found in dipicolinate copper complexes with4-dimethylaminopyridine and N-methyl-imidazole [24]. Inthe second coordination sphere the copper ion of the titlecompound is weakly bonded to the amino-nitrogen N4i

in the layer over (Cu1AN4i = 2.861(3) A; symmetry code(i) 1 � x, 2 � y, �z) and to the carboxylic O3ii oxygen inthe layer under (Cu1AO3ii = 2.801(3) A; symmetry code(ii) 1 � x, 1 � y, �x) the regarded monomer. In this casethe coordination environment of the copper ion is signifi-cantly elongated octahedron (Fig. 2), forming one dimen-sional polymeric structure along the crystallographic b

axis. The significant difference between the CuAL bonddistances in the equatorial plane and the CuAL distancesin the axial positions has also been observed in other cop-per complexes [25–27]. Sieron and Bukowska-Strzyzewska[28] established a correlation between the equatorial CuALbond lengths and the average axial CuAL distances in themixed-ligand complexes of copper pyridine-2-carboxam-ide. The correlation clearly indicated that the CuAL dis-tance in the equatorial plane is inversely proportional tothe axial CuAL distance. In title copper(II) complex thecorresponding bond distances are well-adjusted with thiscorrelation. Axial elongation can easily be explained if

Table 1Crystal data and structure refinement for [Cu(C7H3NO4)(C5H7N3)]ÆH2O complex

Formula C12H12CuN4O5 C12H12CuN4O5

Formula weight 355.81 355.81Temperature (K) 297(2) 113(2)Wavelength (Mo Ka) 0.71073 0.71073Crystal system Triclinic TriclinicSpace group P�1 P�1Unit cell dimensionsa, b, c (A) 7.423(5), 9.993(5), 10.645(5) 7.393(9), 9.918(2), 10.604(2)a, b, c (�) 102.364(5), 107.020(5),110.416(5) 102.712(10), 106.507(10), 111.381(10)Volume (A3) 662.1(6) 646.94(14)Z 2 2Calculated density (g cm�3) 1.785(2) 1.827(5)l (mm�1) 1.681 1.721F(000) 362 362Crystal size (mm) 0.25 · 0.30 · 0.42 0.22 · 0.30 · 0.40h range (�) 2.49–26.48 1.54–27.18Index ranges �9 6 h 6 9 �23 6 h 6 23

�13 6 k 6 13 �12 6 k 6 12�13 6 l 6 12 �13 6 l 6 13

Reflections collected 10134 5456Independent reflections 3119 [R(int) = 0.075] 2804 [R(int) = 0.035]Reflections observed (>2r) 2654 2388Absorption correction Integration IntegrationRefinement method Full-matrix least-squares on F2 Full-matrix least-squares on F2

Data/restrains/parameters 3119/0/227 2804/0/227Goodness-of-fit on F2 1.049 1.114Final R indices [I > 2r(I)] 0.035 0.035R indices (all data) 0.044 0.048Largest diff. peak and hole (A�3) 0.42, �0.67 0.72, �1.04

Fig. 1. The molecular structure of title complex, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level andH atoms are shown as small spheres of arbitrary radii. Dashed line indicates the intra-molecular hydrogen bond.

338 _I. Ucar et al. / Journal of Molecular Structure 834–836 (2007) 336–344

one considers the Jahn-Teller distortion observed in mostoctahedral copper(II) complexes.

In order to observe changing in Jahn-Taller distortionwe have also carried out the diffraction experiment at113 K. The results indicated that there are no essential dif-ferences between the molecular structures of title com-pound at both temperatures. However, we have noticedthat the axial CuAL bond distances (Cu1AO3ii =

2.749(3) A, Cu1AN4i = 2.787(3) A) at 113 K became con-siderably shorter than the corresponding bond distancesat 297 K, whereas the CuAL distances in equatorial planeare slightly different compare to those at 297 K (Table 2).This changing in the CuAL distances with decreasing tem-perature can be ascribed to the effects of rigid-body libera-tion motions. The fact that at both temperatures theCu1ANpyridine distance is significantly shorter than the

Table 2Selected bond lengths and angles, and hydrogen bonding geometry of [Cu(C7H3NO4)(C5H7N3)]ÆH2O complex

Bond lengths (A) and angles (�) at 297 K

Cu1AO1 1.995(2) O1ACu1AO2 161.07(9) O1ACu1AN1 80.66(9)Cu1AO2 2.002(2) O1ACu1AN2 102.19(9) O2ACu1AN1 80.54(9)Cu1AN1 1.900(3) O2ACu1AN2 96.69(8) O2ACu1AO3ii 81.07(7)Cu1AN2 1.980(3) N1ACu1AN4i 89.57(9) O3iiACu1AN1 87.89(8)Cu1AN4i 2.861(3) N2ACu1AN4i 87.99(8) N1ACu1AN2 176.17(9)Cu1AO3ii 2.801(3) O3iACu1AN2 94.31(8) O2ACu1AN4i 94.08(8)

Bond lengths (A) and angles (�) at 113 K

Cu1AO1 1.998(2) O1ACu1AO2 161.27(12) O1ACu1AN1 80.67(13)Cu1AN1 1.897(4) O1ACu1AO3ii 95.91(10) O2ACu1AN4 93.94(11)Cu1AN2 1.975(4) N1ACu1AN4i 90.24(12) N1ACu1AN2 176.57(14)Cu1AN4i 2.787(3) O2ACu1AN1 80.76(12) O3iiACu1AN2 94.25(11)Cu1AO3ii 2.749(3) N2ACu1AN4i 87.84(12) O3iiACu1AN1 87.42(12)Cu1AO2 2.006(3) O2ACu1AN2 96.53(12) O2ACu1AO3i 80.86(10)DAH d(DAH) d(H. . .A) <DHA d(D. . .A) A Symmetry codes

Hydrogen bonds (A, �) at 297 K

N4AH4B 0.80(4) 2.27(4) 113(4) 3.063(4) N3 [�x, �y + 2, �z]N4AH4A 0.85(4) 1.96(4) 158(4) 2.762(4) O1O5AH5A 0.74(6) 2.25(6) 113(6) 2.975(4) O4 [�x, �y + 1, �z]O5AH5B 0.82(6) 2.18(6) 172(4) 2.992(5) O3 [�x + 1, �y + 1, �z + 1]

Hydrogen bonds (A, �) at 113 K

N4AH4B 0.77(5) 2.28(5) 174(3) 3.050(5) N3 [�x, �y + 1, �z + 1]N4AH4A 0.87(6) 1.92(6) 163(5) 2.765(5) O1O5AH5A 0.81(8) 2.13(8) 179(9) 2.938(5) O4 [�x, �y, �z]O5AH5B 0.74(8) 2.21(8) 113(6) 2.953(4) O3 [�x + 1, �y, �z + 1]

Symmetry codes (i) 1 � x, 2 � y, �z; (ii) 1 � x, 1 � y, �z.

Fig. 2. The second coordination sphere of title complex is pseudo octahedral geometry (symmetry codes (i) 1 � x, 2 � y, �z; (ii) 1 � x, 1 � y, �x).


Cu1ANpyrimidine distance indicates that atom N1 is thestrongest donor site, since the two carboxylate groups inortho positions enhance the basicity of this atom. Thedpc chelate angles are 80.67(8)�, 80.54(8)� at 297 K and

80.66(11)�, 80.76(10)� at 113 K, which are comparable tothose found in other Cu-dipicolinate complexes [19]. Allatoms in the dpc anion are nearly coplanar, with a maxi-mum deviation of �0.190(2) A and �0.191(2) A for atom


O3 at 297 and 113 K, respectively, resulting from the weak-ly bonded to metal ion. The dihedral angle between thepyridine and pyrimidine ring of the ligands is 6.14(19)� at297 K, whereas this angle is 6.31(3)� at 113 K. In the poly-meric chain the intrachain Cu1� � �Cu1i and Cu1� � �Cu1ii dis-tances are 4.741(3), 5.357(4) A at 297 K and 4.694(2),5.331(2) A at 113 K, respectively.

The intermolecular contacts (including the some hydro-gen bonds) are shortened at 113 K (see Table 2), resultingin changes of unit cell parameters and reduction of the cellvolume. It can be seen from Fig. 3 that the two dipicolinatemolecules are joined by two N4AH4B. . .N3 intermolecularhydrogen bonds, which lead to the formation of a centro-symmetric dimer of title compound in the crystal unit cell.These centrosymmetric dimers are linked by the crystal lat-tice water molecules through the OAH� � �O hydrogenbonding. In the crystal packing there is also strong intra-molecular hydrogen bonding interaction between thedonor N4 and acceptor O1 atoms.

3.2. Thermal investigation

Thermal behaviour of the complex taken in the temper-ature range 30–1000 �C is shown in Fig. 4, while the ther-moanalytic results are given in Table 3. It can be seenfrom Table 3 that the complex has five thermal decompo-sition stages.

The dehydration of lattice water molecule forms the firststage in which DTGmax is 116 �C. The dehydrated com-

Fig. 3. Three dimensional structure of copper comp

pound stable up to 165 �C starts to decompose from thatpoint to further up to 272 �C forming the second stage.In this endothermic second stage, 2-amino-4-methylpyrim-idine (ampym) ligand coordinated to metal ion iscompletely removed (found: 30.45%, calcd. 30.67%). Thethird stage is exothermic and starts with decompositionof dpc at 272 �C. In this stage 25.13% mass lost is observedoriginating possibly from removing of carboxylate groupsof dpc. The fourth decomposition stage starts at 307 �Cwhere Cu-py (py: pyridine) is formed. The 17.48% massobtained at 910 �C corresponds to metallic copper (calcd.17.86%).

The decomposition enthalpies of the stages are obtainedby converting DTA signals to DSC data. According to theresults, the decomposition enthalpies for the first threestages are 334.24, 380.18, and �208.93 J/g, respectively.Since fourth and fifth decomposition stages overlaps eachother and show a broad peak, the decomposition enthal-pies of these two stages are calculated in total as9474.59 J/g. Observing rather large enthalpy values forthese final two stages comparing with the first three decom-position stages is most probably due to thermal stability ofCu-py compound.

3.3. EPR and optical absorption investigation

The powder EPR spectra of Cu(II) complex at room andliquid nitrogen temperature were recorded (Fig. 5). As canbe seen from Fig. 5a there is only one g// and one g^

lex. Dashed lines indicate the hydrogen bonds.

Fig. 4. Thermal analysis curves for copper complex.

Table 3Thermoanalytical data for the [Cu(C7H3NO4)(C5H7N3)]ÆH2O complex

Complex Stage Temparature range(�C)

DTGmax

(�C)DH (J/g) Mass loss,

Dm (%)Total mass loss,Dm (%)

Decompositiongroups

Found Calcd. Found Calcd.

[Cu(C7H3NO4)(C5H7N3)]ÆH2O 1 70–144 116 334.24 5.13 5.06 H2O2 165–272 243 380.18 30.45 30.67 ampym3 272–307 289 �208.93 25.13 24.74 2COO4 307–479 413 9474.59 9.29 21.665 479–910 718 12.52 82.52 82.13 py


components were obtained due to the influence of exchangeinteraction which makes the hyperfine lines smaller. In theEPR spectrum of Cu(II) complex in DMF (dimethylform-amide) solution at liquid nitrogen temperature, four paral-lel together with one broadened perpendicular componentshave been observed (Fig. 5b). The g and A parameters arecalculated. As can be seen from Table 4 the g values are inthe order of g//æg^æge (free electron g value, g = 2.0023)Considering these values together with the observed char-acteristic g// and g^ values for Cu2+ ions, it can be conclud-ed that the paramagnetic centre is axially symmetric, theground state of unpaired electron is dx2�y2 (2B1g state)and the Cu2+ ions are located in distorted octahedral sites(D4h) elongated along the z-axis [29,30].

It is well known that d orbitals of a d ion split into adoublet of Eg and a triplet of T2g symmetry states in anoctahedral crystal field. The base functions of Eg, aredx2�y2 and d3z2�r2 orbitals and the degeneracy of the energy

levels are removed in a distorted crystal field. The groundstate wavefunction, including also the covalency effect ofthe metal ion, is written [31–33] as

W ¼ ½a02�1=2½ajx2 � y2i þ bj3z2 � r2i�; ð1Þ

where a02 is the probability of finding the unpaired electron

in the metal d orbital and is a measure of the covalency.The normalization condition for mixing coefficient a andb is

a2 þ b2 ¼ 1: ð2Þ

Using the experimental values for Cu complex, theground state wave function can be constructed for the com-plex as,

WI ¼ ð0:3211=2½0:853jx2 � y2i þ 0:521j3z2 � r2i�: ð3Þ

Table 5Selected IR spectral data for [Cu(C7H3NO4)(C5H7N3)]ÆH2O complex

Assignment IR (cm�1)

NH2 asy. str. 3523 m, 3467 mNH2 sym. str + H2O 3255 mCAH str. 3079, 3045 mC@O str. 1685, 1639 vsRing str. 1550 sCAH def. 1463 sCAO str. 1340 sCAN str. 1222 si.p.def. OACAO 736 wNH2 wagging 682 w

s, strong; vs, very strong; m, medium; w, weak; asy, asymmetric; sym,symmetric; str, stretch; def, deformation; i.p, in plane.

Fig. 5. EPR spectra of copper complex (a) powder at room temperature and (b) in DMF solution at liquid nitrogen temperature.

Table 4Principle g//, g^ and hyperfine values (A) of [Cu(C7H3NO4)(C5H7N3)]ÆH2Ocomplex

Temperature (K) g// g^ A// A^

Powder 293 and 113 2.247 2.061 – –DMF solution 113 2.247 2.052 129 G 41 G


The value of the covalency parameter a02 (0.321) indi-

cates that the unpaired electron spends 67.9% of its timeon the ligand orbitals, whereas the rest is spent on thed orbitals of the Cu2+ ion. Also, the coefficients of thedx2�y2 are greater than that of the d3z2�r2 . This means thatthe unpaired electron spends most of its time on thedx2�y2 orbital of Cu2+ ion.

The optical absorption study of the title complex inDMF solution shows two bands centered at 730 nm(13698 cm�1) and 796 nm (12562 cm�1) at room tempera-ture confirming the nearly axial symmetry. The bandat 13698 cm�1 and 12562 cm�1 can be assigned tothe d–d transition, ð2B1g ! 2EgÞdxz;yz $ dx2�y2 andð2B1g ! 2B2gÞdxy $ dx2�y2 of Cu2+ ion, respectively. By

correlating the EPR and the optical absorption data, themolecular orbital coefficients a2, b2

1 and b22 are expressed

by using the formula given in the literature [34,35] asfollows:

a2 ¼ 7

12

A== � AP

� �� 2

3g==

5

14g? þ

6

7

� �ð4Þ

g== ¼2:0023 1� 4kc2b21

B1g $ B2g

� �ð5Þ

g? ¼2:0023 1� kc2b21

B1g $ Eg

� �ð6Þ

where p is a constant (0.036 cm�1), k is the spin-orbit cou-pling constant (�828 cm�1 for Cu2+ ion) and ge is the freeelectron g value, (ge = 2.0023) and A = (A// + 2A^)/3.

If a2 = 1, the bond is completely ionic. Nevertheless, ifthe overlapping integral is vanishingly small and a2 = 0.5,the bond is completely covalent. The parameters a2, b2

1

and b22 can be taken as a measure of the in-plane r bond-

ing, in-plane p bonding and out of plane p-bondingbetween d orbital of the central metal ion and p orbitalsof the ligands [36,37]. The values of a2, b2

1 and b22 were cal-

culated by using the above equations, and were found as0.55, 0.84 and 0.74, respectively. The calculated values ofa2, b2

1 and b22 indicate that the in-plane r bonding is mod-

erately covalent whereas the in-plane p bonding and out ofplane p-bonding are significantly in ionic character.

3.4. IR investigation

Infrared-spectra of dipicolinate-containing complexeshave quite characteristic absorption bands. The most char-acteristic IR bands of title complex are given in Table 5.The characteristic carboxyl vibrations in the free pyri-dine-2,6-dicarboxylicacid were found at 1132 cm�1 as astrong and broad vibration and at 1331 and 1299 cm�1

Fig. 6. The FT-IR spectrum of copper complex.

Fig. 7. The cyclic voltammogram of 5 · 10�3 M copper complex at a Ptwire elecrode in 0.1 M DMSO-Bu4NClO4, potential scan rate 100 mV s�1

(potential scanning starting at 0 V towards catodic potential and back to0 V and towards anodic potential).


for which the former is assigned to the m(C@O) and the lat-ter two to the m(CAO) stretching vibrations [38,39].

The strong bands at 1685 and 1639 cm�1 in IR spectraof title complex are assigned to m(C@O) and the otherstrong absorption at 1340 cm�1 is attributed to m(CAO)vibration (Fig. 6). The difference between m(C@O) andm(CAO) of dpc ligand is at near 300 cm�1 indicating thatthe carboxyl groups are monodentate-coordinated [40],consistent with the XRD results. Significant m(NAH)absorption bands due to the amine group in pyrimidineare appeared at 3523, 3467 cm�1. This region of the NH2

stretching vibrations is relatively broadened by partialsuperposition of the OAH vibrations of the crystal watermolecule. The antisymmetric and symmetric stretchingvibrations of the NH2 group together with OH stretchingvibrations are listed in Table 5. The d(OACAO) in-planedeformation vibration which occurs as a sharp band at701 cm�1 in free H2dpc ligand, shifts to 736 cm�1 in titlecomplex, as is also found in the literature [38]. The bandmedium intensity at 1463 cm�1 corresponds to CAH defor-mation vibration and weak band centered at 1222 cm�1 isattributed to the CAN stretching vibrations [41]. On theother hand, medium intensity ring stretching is observedat 1550 cm�1.

3.5. Electrochemical investigation

The redox behaviour of complex was studied using cyc-lic voltammetry at a Pt working electrode at a scan rate of100 mV s�1. n-Bu4NClO4 (0.1 M) was used as a supportingelectrolyte in dimethylsulfoxide (DMSO) solution of2 · 10�3 M complex. The cyclic voltammogram of the com-plex is displayed in Fig. 7.

The observed oxidation and reduction waves are due tothe metal-centred process in title complex. The copper(II)

ion yields two quasi-reversible redox couple, located atE1

1=2 ¼ 0:245 V and E21=2 ¼ 0:605 V which are assignable

to Cu(II)/Cu(I) and Cu(II)/Cu(III), respectively(E1/2 = (Epa + Epc)/2). The criteria of reversibility werechecked by observing constancy of peak–peak separation(DEp = Epa � Epc 6 59 mV) and the ratio of peak heights(ipa/ipc � 1) with variation of scan rates. In the title com-plex this ratio is not equal to 1 and DEp P 59 mV. There-fore, the electron transfer process is not in equilibrium andshown to be slow. From the voltammetric data two redoxcouples can be attributed to a quasi-reversible one electrontransfer process. The Ip/m1/2 value is almost constant for allscan rates. This establishes the electrode process as diffu-sion controlled. Any redox behaviour of the ligand in therange �1.25 to 1.50 V is rule out because dipicolinic acid


showed quasi-reversible and irreversible process onlyaround �1.58 V in its complexes [42]. Furthermore, no vol-tammetric signal for ampym is observed in the selectedpotential range in DMSO.

4. Supplementary data

Crystallographic data (excluding structure factors) forthe structure in this paper have been deposited with theCambridge Crystallographic Data Centre as the supple-mentary publication no. CCDC 617658. Copies of the datacan be obtained, free of charge, on application to CCDC,12 Union Road, Cambridge, CB12 1EZ, UK, fax: +441223 366 033, E-mail: [email protected] or on the webwww: http://www.ccdc.cam.ac.uk

References

[1] L. Chung, K.S. Rajan, E. Merdinger, N. Grecz, Biophys. J. 11 (1971)469.

[2] W.G. Murrel, Adv. Microb. Physiol. 1 (1967) 133.[3] W.G. Murrel, A.D. Warth, in: L.L. Cambell, H.O. Halvor (Eds.),

Spores III, American Society for Microbiology, Washington, DC,1965, pp. 1–24.

[4] L. Wang, L. Duan, E. Wong, D. Xiao, Y. Li, Y. Lan, L. Xu, C. Hu,Trans. Met. Chem. 29 (2004) 212.

[5] W.Z. Wang, X. Liu, D.Z. Liao, Z.H. Jiang, S.P. Yan, G.L. Wang,Inorg. Chem. Commun. 4 (2001) 327.

[6] C. Yue, Z. Lin, L. Chen, F. Jiang, M. Hong, J. Mol. Struct. 779(2005) 16.

[7] C. Ma, C. Chen, Q. Liu, D. Liao, L. Li, Eur. J. Inorg. Chem. (2003)1227.

[8] M. Ranjbar, H. Aghabozorg, A. Moghimi, Acta Cryst E. 58 (2002)m304.

[9] M. Devereux, M. McCann, V. Leon, V. McKee, R.J. Ball, Polyhe-dron 21 (2002) 1063.

[10] C. Ma, C. Fan, C. Chen, Q. Liu, Acta Cryst. C 58 (2002) m553.[11] M. Koman, M. Melnik, J. Moncol, Inorg. Chem. Commun. 3 (2000)

262.[12] L. Mao, Y. Wang, Y. Qi, M. Cao, C. Hu, J. Mol. Struct. 688 (2004) 197.[13] J. Zhou, L.F. Wang, J.Y. Wang, N. Tang, J. Inorg. Biochem. 83

(2001) 41.[14] J.A. Lindsay, W.G. Murrell, Curr. Microbiol. 13 (1986) 255.

[15] J.H. Hwang, R.K. Larson, M.M. Abu-Omar, Inorg. Chem. 42 (24)(2003) 7967.

[16] S. Ogata, M. Takeuchi, H. Fujita, K. Shibata, K. Okumura, H.Taguchi, Biosci. Biotechnol. Biochem. 64 (6) (2000) 1142.

[17] J.C. MacDonald, P.C. Dorrestein, M.M. Pilley, M.M. Foote, J.L.Lundburg, R.W. Henning, A.J. Schultz, J.L. Manson, J. Am. Chem.Soc. 122 (2000) 11692.

[18] E.E. Sileo, G. Rigotti, B.E. Rivero, M.A. Blesa, J. Phys. Chem. Solids8 (7) (1997) 1127.

[19] _I. Ucar, A. Bulut, O. Buyukgungor, Acta Cryst. C61 (2005) m479.[20] Stoe & Cie X-AREA (Version 1.18) and X-RED (Version 1.04), Stoe

& Cie, Darmstadt, Germany, 2002.[21] A. Altomera, M.C. Burla, M. Camalli, G.L. Cascarano, C. Giaco-

vazzo, A. Guagliardi, A.G.G. Moliterni, G. Polidori, R. Spagna, J.Appl. Crystallogr. 32 (1999) 115.

[22] G.M. Sheldric, SHELXL97, University of Gottingen, Germany,1997.

[23] M.N. Burnett, C.K. Johnson, ORTEPIII. Report ORNL-6895, OakRidge National Laboratory, TN, USA, 1996.

[24] C.C. Su, S.Y. Chiu, Polyhedron 15 (15) (1996) 2623.[25] K.J. Kim, J.H. Lee, S.H. Lee, J. Magn. Magn. Mater. 279 (2004) 173.[26] B. Murphy, B. Hathaway, Coord. Chem. Rev. 243 (2003) 237.[27] G.A. Abada, I. Mutakainen, U. Turpeinen, J. Reedjik, Acta Cryst. E

58 (2002) m55.[28] L. Sieron, M. Bukowska-Strzyewska, Acta Cryst. C 53 (1997) 296.[29] H. Hosono, H. Kawazoe, T. Kanazawa, J. Non-Cryst. Solids 29

(1978) 173.[30] H. Hosono, H. Kawazoe, T. Kanazawa, J. Non-Cryst. Solids 34

(1979) 339.[31] R.T. Bhaskar, M. Narayana, Phys. Status Solidi 106 (1981) 601.[32] N. Satyanarayana, J. Phys. Chem. Solids 47 (1986) 55.[33] B. Karabulut, R. Tapramaz, A. Bulut, Z. Naturforsch. 54a (1999)

256.[34] S.K. Hoffmann, J. Goslar, J. Solid State. Chem. 44 (1982) 1982.[35] R.P. Sreekanth Chakradnar, K.P. Ramseh, J.L. Rao, J. Rama-

krishna, J. Phys. Cond. Matt. 115 (2003) 1469.[36] D. Kivelson, R. Neiman, J. Chem. Phys. 35 (1961) 149.[37] H.A. Kuska, M.T. Rogers, R.E. Drullinger, J. Phys. Chem. 71 (1967)

109.[38] P. Carmona, Spectrochim. Acta A 36 (1980) 705.[39] G.A. Van Albada, J.G. Haasnoot, J. Reedijk, M. Biagini-Cingi, M.

Manotti-Laanfredi, F. Ugozoli, Polyhedron 17 (1995) 2467.[40] S.D. Robinson, M.F. Uttley, J. Chem. Soc. Dalton Trans. 18 (1973)

1912.[41] L. Levi, C.E. Hubley, Anal. Chem. 28 (1956) 1591.[42] M. Chatterjee, M. Maji, S. Ghosh, T.C.W. Mak, J. Chem. Soc.

Dalton Trans. (2000) 2875.

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