Sha

ND

a

ARRA

KACC

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opaosMiTahactpppappaae

1d

Spectrochimica Acta Part A 79 (2011) 1154– 1161

Contents lists available at ScienceDirect

Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

jou rn al hom epa ge: www.elsev ier .com/ locate /saa

pectral studies of copper(II) complexes of tridentate acylhydrazone ligands witheterocyclic compounds as coligands: X-ray crystal structure of onecylhydrazone copper(II) complex

ancy Mathew, Maheswaran Sithambaresan, M.R. Prathapachandra Kurup ∗

epartment of Applied Chemistry, Cochin University of Science and Technology, Kochi 682022, Kerala, India

r t i c l e i n f o

rticle history:eceived 4 February 2011eceived in revised form 22 March 2011

a b s t r a c t

Six copper(II) complexes of 2-hydroxy-4-methoxybenzaldehyde nicotinoylhydrazone (H2hmbn), 2-hydroxy-4-methoxyacetophenone nicotinoylhydrazone (H2hman), 2-hydroxy-4-methoxybenzaldehyde

ccepted 15 April 2011

eywords:cylhydrazonesopper(II) complexes

benzoylhydrazone (H2hmbb) and 2-hydroxy-4-methoxyacetophenone benzoylhydrazone (H2hmab)have been synthesized. The complexes viz. [Cu(hmbn)]2·2H2O (1), [Cu(hman)]2 (2), [Cu(hmbb)]2·2H2O(3), [Cu(hmbb)phen]·1(1/2)H2O (4), [Cu(hmbb)(bipy)·H2O] (5) and [Cu(hmab)phen] (6) were charac-terized by different physicochemical techniques. The crystal structure of [Cu(hman)phen] is obtainedand it has a distorted square pyramidal geometry with �–� stacking interactions and significant C–H �interactions.

rystal structure

. Introduction

Over the past few decades, there is growing interest in the studyf coordination chemistry of acylhydrazones and their metal com-lexes, as they offer a wide spectrum of applications, includingnalytical, biological and photochemical fields. The coordinationf bioactive ligands to metal might increase their activity whileome bioinactive ligands acquire activity through coordination.any complexes derived from hydrazones have potential biolog-

cal activities and hence they are pharmacologically important.he presence of heterocyclic rings in the metal complexes playn important role in their pharmacological properties [1,2]. Acyl-ydrazones display radioprotective properties and a range ofcylhydrazones have been shown to be cytotoxic while copperomplexes of them show enhanced activity [3]. Among the differentransition metals, copper has gained a special position because of itsresence in biological systems, which are crucial to many biologicalrocesses. Recently Chen et al. have shown that the copper com-lexes of plumbagin (an extract from the plant Plumbago zeylanicand used as traditional Chinese medicine) have higher anticancerroperties and are less toxic to healthy cells than commonly usedlatinum-based drugs, such as cisplatin [4]. The biomimetic cat-

lytic activity of copper complexes towards the catechol oxidationnd aerobic oxidation of ascorbic acid is reported [5,6]. The inter-st in the study of chemistry of copper complexes of hydrazones

∗ Corresponding author. Tel.: +91 484 2862423; fax: +91 484 2575804.E-mail addresses: mrp k@yahoo.com, mrp@cusat.ac.in (M.R.P. Kurup).

386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.saa.2011.04.036

© 2011 Elsevier B.V. All rights reserved.

has been deepened by the findings of Johnson et al. which revealsthat the copper(II) complex of the most potent of the chelators,salicylaldehyde benzoyl hydrazone exhibits appreciably greaterinhibitory activity than salicylaldehyde benzoyl hydrazone itself[7]. There are so many reports on the studies of Cu(II) complexeswith ligands containing O, N and S donor atoms [8–10]. All the abovesaid facts stimulate our interest in the study of transition metalcomplexes with O and N donor ligands and an extension of our workon hydrazones [11–16], we report the synthesis and characteriza-tion of some copper(II) complexes with four different ONO donorligands and some heterocyclic compounds as coligands. The crystalstructure of one of the copper(II) complexes is also discussed.

2. Experimental

2.1. Materials

2-Hydroxy-4-methoxyacetophenone (Aldrich), 2-hydroxy-4-methoxybenzaldehyde (Aldrich), nicotinic acid hydrazide(Aldrich), benzhydrazide (Aldrich), copper (II) acetatemonohydrate (Qualigens), 2,2′-bipyridine (Qualigens), 1,10-phenanthroline (Ranchem) were used without further purification.Solvent used was methanol.

2.2. Synthesis of acylhydrazones

The acylhydrazones were synthesized by earlier reported meth-ods [15,16]. Scheme 1 describes the syntheses of acylhydrazones.

N. Mathew et al. / Spectrochimica Acta Part A 79 (2011) 1154– 1161 1155

OH

O

R

OCH3 +

reflux 4 h methanol

- H2O

R = H & X=N; H2hmbnR = CH3 & X= N; H2hmanR = H & X=C; H2hmbb

NHONH2

X

OH

NNH

OO

CH3

RX

eses o

2

[CHpaCi3aCss

2

cS4p1MmTDtfqwtmm5

2

f0sm[msXdi

these complexes [21]. The observed magnetic susceptibility valuesof the complexes 4, 5 and 6 are in close agreement with the spinonly value for a d9 copper system.

Table 1Crystal data and structure refinement parameters for [Cu(hmab)phen] (6).

Empirical formula C28H22CuN4O3

Formula weight 526.04Temperature 100(2) KWavelength 0.71073 ACrystal system MonoclinicSpace group P21/cUnit cell dimensions a = 16.0239(14) A

b = 10.4971(6) Ac = 14.4246(12) A˛ = 90◦

= 106.347(9)◦

� = 90◦

Volume 2328.2(3) A3

Z 4Density (calculated) 1.501 Mg/m3

Absorption coefficient 0.978 mm−1

F(0 0 0) 1084Crystal size 0.11 mm × 0.08 mm × 0.05 mm� Range for data collection 2.94–25.00◦

Index ranges −19 ≤ h ≤ 19,−12 ≤ k ≤ 12,−17 ≤ l ≤ 17

Reflections collected 19,930Independent reflections 4100 [R(int) = 0.1638]Refinement method Full-matrix least-squares on F2

Data/restraints/parameters 4100/0/327Goodness-of-fit on F2 1.020Final R indices [I > 2�(I)] R1 = 0.0832, wR2 = 0.1611R indices (all data) R1 = 0.1633, wR2 = 0.2004

Scheme 1. Synth

.3. Synthesis of complexes

The complexes [Cu(hmbn)]2·2H2O (1), [Cu(hman)]2 (2) andCu(hmbb)]2·2H2O (3) were prepared by refluxing 1 mmol ofu(OAc)2·H2O and 1 mmol of the corresponding ligand (H2hmbn,2hman or H2hmbb) in alcoholic medium for 3–5 h. The com-lexes [Cu(hmbb)phen]·1(1/2)H2O (4), [Cu(hmbb)(bipy)·H2O] (5)nd [Cu(hmab)phen] (6) were prepared by refluxing 1 mmol each ofu(OAc)2·H2O, heterocyclic base (bipy/phen) and the correspond-

ng ligand (H2hmbb or H2hmab) in alcoholic medium for about–5 h. We tried to prepare the heterocyclic analogous of the lig-nds (H2hmbn and H2hman) with copper, but our attempts failed.omplex [Cu(hmab)phen] (6) crystallized from methanol and itstructure has been determined by single crystal X-ray diffractiontudies.

.4. Physical measurements

Elemental analyses of the acylhydrazones and their copper(II)omplexes were carried out using a Vario EL III CHNS analyzer atAIF, Kochi, India. Infrared spectra were recorded on a JASCO FT/IR-100 type A spectrometer in the range 4000–400 cm−1 using KBrellets. Electronic spectra were recorded on a Cary 5000 version.09 UV–vis spectrophotometer using acetonitrile as the solvent.agnetic susceptibility measurements at room temperature wereade using a vibrating sample magnetometer at IIT Roorkee, India.

he EPR spectra of the complexes in the solid state at 298 K, inMF at 298 K and at 77 K were recorded on a Varian E-112 spec-

rometer using TCNE as the standard, with 100 kHz modulationrequency, modulation amplitude 2 G and 9.1 GHz microwave fre-uency at the SAIF, IIT Bombay, India. The spectra of the complexesere simulated using Easy Spin package [17]. TG-DTG analyses of

he prepared complexes were carried out on a Perkin Elmer, Dia-ond thermogravimetric analyzer. The heat flow was 10 ◦C perinute under nitrogen atmosphere over a temperature range of

0–1000 ◦C.

.5. X-ray crystallography

Single crystals of the compound [Cu(hmab)phen] (6) suitableor X-ray diffraction studies having approximate dimensions of.11 mm × 0.08 mm × 0.05 mm obtained by slow evaporation of theolution of compound in CH3OH over two days was selected andounted on a CrysAlis CCD, Oxford Diffraction Ltd. diffractometer

18], equipped with a graphite crystal, incident-beam monochro-ator, and a fine focus sealed tube, Mo K� (� = 0.71073 A) X-ray

ource at a temperature of 100(2) K at the National Single Crystal-ray diffraction Facility, IIT, Bombay, India. The crystallographicata along with details of structure solution refinements are given

n Table 1.

R = CH3 & X=C; H2hmab

f acylhydrazones.

The trial structure was solved using SHELXS-97 and refinementwas carried out by full-matrix least squares on F2 using SHELXL-97[19] and all the hydrogen atoms were fixed in calculated positionsfor compound 6. The molecular graphics employed was DIAMOND[20].

3. Results and discussion

In all the complexes the acylhydrazones are in the doublydeprotonated form. The colors, magnetic susceptibility and partialelemental analyses of the complexes are presented in Table 2. Theelemental analyses values are in good agreement with the generalformula of the complexes. Complexes 1, 2 and 3 show substantiallow magnetic moment in the range of 1.05–1.2 �B may be due tothe coupling of two magnetic centers suggesting dimeric nature to

Largest diff. peak and hole 1.374 and −0.521 e.A−3

R1 = �||Fo| − |Fc||/�|Fo|

wR2 =[

˙w(F2o −F2

c )2

˙w(F2o )

2

]1/2

1156 N. Mathew et al. / Spectrochimica Acta Part A 79 (2011) 1154– 1161

Table 2Colors and partial elemental analyses data of copper(II) complexes.

Compound Color �eff (B.M) Found (calculated) %

C H N

[Cu(hmbn)]2·2H2O (1) Green 1.27 48.33(47.93) 4.19(3.74) 11.98(11.98)[Cu(hman)]2 (2) Dark green 1.34 52.50(51.95) 3.68(3.78) 12.16(12.12)[Cu(hmbb)]2·2H2O (3) Green 1.05 51.87(51.50) 4.30(4.03) 8.45(8.01)

60.20(60.16) 3.78(4.30) 10.82(10.39)59.18(59.34) 3.85(4.38) 11.40(11.07)63.37(63.93) 3.87(4.22) 10.74(10.65)

3

balcnsiN

eOpTtpNses

iiacuptbsla

[Cu(hmbb)phen]·1(1/2)H2O (4) Green 1.90

[Cu(hmbb)(bipy)·H2O] (5) Green 1.95

[Cu(hmab)phen] (6) Green 1.96

.1. Crystal structure of [Cu(hmab)phen] (6)

The crystal structure of the compound along with atom num-ering scheme is given in Fig. 1. The complex crystallizes into

monoclinic P21/c space group. In this complex the dinegativeigand, 2-hydroxy-4-methoxyacetophenone benzoylhydrazone isoordinated to Cu(II) through the phenolic oxygen O2, azomethineitrogen N1 and deprotonated enolate oxygen O3, forming five andix membered chelate rings. The heterocyclic base phenanthrolines coordinated to the central metal ion through two nitrogen atoms3 and N4 and forms a five membered chelate ring.

The five coordinated complex adopts a square pyramidal geom-try, and the basal coordination positions are occupied by O2, N1,3 and N3 atoms. The Cu–N4 bond distance is larger when com-ared with others suggests that N4 occupies an apical position.his complex is somewhat distorted to square pyramidal geome-ry with the angular structural parameter = 0.1366 [22]. The meanlane deviation calculations show that the atoms O2, N1, O3 and3 are nearly planar with a mean plane deviation of 0.2059 A. The

ignificant deviation from regular square pyramidal geometry isvident from the observed values of bond angles and bond lengthsummarized in Table 3.

A beautiful arrangement of molecules in the crystal systemn a quadruple cell along b axis is shown in Fig. 2. The �–�nteractions play an important role in controlling the packing orssembly of compounds. Analyses of complexes with nitrogenontaining heterocyclic compounds reveal that �–� stacking issually an offset or slipped facial arrangement of the rings. Hereacking of the compound is stabililized by �–� stacking interac-ions and C–H· · ·� interactions. The interchain stacking interactionetween the phenanthroline rings in the compound is remarkably

trong and it may be due to larger � system in phenanthro-ine ligand [23]. In this compound all the phenanthroline ringsre arranged parallel to each other within the unit cell and the

Fig. 1. Structure and labeling scheme for [Cu(hmab)phen)] (6).

Fig. 2. Quadruple cell packing of the compound [Cu(hmab)phen)] (6) viewed alongthe b axis.

phenanthroline rings Cg(5) and Cg(8) are involved in �–� stack-ing with a distance of 3.507 A. Fig. 3 shows the �–� stackingin [Cu(hmab)phen]. In addition to the �–� stacking interactionssignificant C–H· · ·� interactions are also present in the unit cell,they are C15–H15· · ·Cg(3) and C21–H21· · ·Cg(6). These interactionparameters are listed in Table 4. Weak intramolecular hydrogenbonding is observed between C(9)–H(9C)· · ·N(2) [with a H· · ·N dis-tance of 2.19 A and an angle of 111◦]. Intermolecular hydrogenbonding is C(17)–H(17)· · ·O(1) [with a H· · ·O distance of 2.51 A andan angle of 120◦] and C(19)–H(19)· · ·O(2) [with a H· · ·O distance of2.58 A and an angle of 167◦].

3.2. Infrared and electronic spectral studies

The vibrational bands of the free ligands and their copper com-plexes, which are useful for determining the mode of coordinationof the ligands, are given in Table 5. In the IR spectra of the freeligands, the carbonyl and azomethine bands are observed in the

Fig. 3. �–� stacking of [Cu(hmab)phen)] (6).

N. Mathew et al. / Spectrochimica Acta Part A 79 (2011) 1154– 1161 1157

Table 3Selected bond lengths (Å) and bond angles (◦) for the compound [Cu(hmab)phen] (6).

Bond lengths Bond angles Bond angles

Cu(1)–O(2) 1.902(5) O(2)–Cu(1)–N(1) 92.6(2) C(2)–O(2)–Cu(1) 127.2(5)Cu(1)–N(1) 1.940(6) O(2)–Cu(1)–O(3) 163.5(2) C(10)–O(3)–Cu(1) 109.5(5)Cu(1)–O(3) 1.950(5) N(1)–Cu(1)–O(3) 82.7(2) C(8)–N(1)–Cu(1) 128.1(5)Cu(1)–N(3) 2.012(6) O(2)–Cu(1)–N(3) 90.4(2) N(2)–N(1)–Cu(1) 112.8(4)Cu(1)–N(4) 2.350(6) N(1)–Cu(1)–N(3) 171.7(2) C(10)–N(2)–N(1) 111.0(6)O(2)–C(2) 1.300(8) O(3)–Cu(1)–N(3) 92.3(2) C(28)–N(3)–Cu(1) 120.0(5)O(3)–C(10) 1.308(9) O(2)–Cu(1)–N(4) 97.3(2) C(17)–N(3)–Cu(1) 122.3(5)N(1)–C(8) 1.306(9) N(1)–Cu(1)–N(4) 111.0(2) C(26)–N(4)–Cu(1) 134.3(5)N(1)–N(2) 1.400(8) O(3)–Cu(1)–N(4) 99.2(2) C(27)–N(4)–Cu(1) 107.9(5)N(2)–C(10) 1.327(9) N(3)–Cu(1)–N(4) 76.2(2) C(8)–C(1)–C(2) 125.0(7)C(1)–C(8) 1.425(10) C(4)–O(1)–C(5) 117.6(6) O(2)–C(2)–C(1) 124.0(7)

Table 4Interaction parameters of the compound [Cu(hmab)phen] (6).

�–� interactionsCg(I)· · ·Cg(J) Cg–Cg (Å) (◦) (◦) � (◦) Cg(I)⊥ Cg(J)⊥

Cg(2)· · ·Cg(5) a 3.981(4) 2.21 32.53 31.42 3.397 3.356Cg(4)· · ·Cg(5) b 3.676(4) 17.11 27.76 11.70 3.600 3.253Cg(5)· · ·Cg(5)a 3.738(4) 0.00 24.50 24.50 3.402 3.401Cg(5)· · ·Cg(8)a 3.507(4) 0.85 14.21 14.16 3.401 3.400

C–H· · ·� interactions

C· · ·H(I) Cg(J) H· · ·Cg (Å) C–H· · ·Cg (◦) C· · ·Cg (Å)

C(15)–H(15)· · ·Cg(3)c 2.90 141 3.666C(21)–H(21)· · ·Cg(6)d 2.65 157 3.526

Equivalent position codes: a = 1 − x, −y, −z; b = 1 − x, 1/2 + y, 1/2 − z Cg(2) = Cu(1) N(3), C(28), C(27), N(4); Cg(4) = N(3), C(17), C(18), C(19), C(20), C(28) Cg(5) = N(4), C(26),C(25), C(24), C(23), C(27); Cg(8) = C(20), C(21), C(22), C(23), C(27), C(28); c = x,1/2 − y, −1/2 + z; d = 1 − x,1/2 + y,1/2 − z Cg(3) = Cu(1), O(2), C(2), C(1), C(8), N(1); Cg(6) = C(1),C(2), C(3), C(4), C(6), C(7).

Table 5Selected IR bands (cm−1) with tentative assignments of copper(II) complexes.

Compound (C O) (C N) (N C) (Cu–N) (N–N) Heterocyclic breathing (C–O)

H2hmbn·H2O 1643 1604 – – 1027 – 1284[Cu(hmbn)]2·2H2O (1) – 1594 1525 420 1060 – 1233H2hman 1638 1602 – – 1024 – 1262[Cu(hman)]2 (2) – 1591 1531 419 1080 – 1244H2hmbb 1630 1600 – – 1031 – 1286[Cu(hmbb)]2·2H2O (3) – 1588 1547 419 1067 – 1225[Cu(hmbb)phen]·1(1/2)H2O (4) – 1589 1532 420 1089 1428, 728 1214

rO3

Nlb–Tt1weinba4r

pe

[Cu(hmbb)(bipy)·H2O] (5) – 1588 1529H2hmab 1650 1600 –[Cu(hmab)phen] (6) – 1590 1524

egions 1630–1650 cm−1 and 1600–1605 cm−1, respectively. The–H and N–H stretching frequencies are observed around 3250 and035 cm−1.

In all the six copper(II) complexes the bands due to O–H and–H are absent which is a clear evidence for the coordination of

igands in deprotonated form. In all the complexes the azomethineands are shifted to lower wavenumbers and the newly formedC N–N C– moiety gave bands between 1520 and 1550 cm−1.he bands around 415 cm−1 indicate the coordination of azome-hine nitrogen to copper centre. A new band appears in the region230–1255 cm−1 in complexes was assigned to the (C–O) mode,hich is also an evidence for the coordination of ligands in the

nolic form. The increase in (N–N) bands in complexes, due to thencrease in double bond character is another proof for the coordi-ation of the ligands through the azomethine nitrogen. There areroad bands observed around 3400 cm−1 in all complexes except 2nd 6 indicate the presence of water in structures. In compounds, 5 and 6, bands due to heterocyclic breathing are observed in the

egion 750–1450 cm−1.

The electronic absorption bands of the free ligands and com-lexes, recorded in acetonitrile are presented in Table 6. Thelectronic spectra of all the four acylhydrazones show bands in

407 1070 1438, 774 1214– 1025 – 1265

420 1080 1425, 726 1246

the region 30,500–46,000 cm−1 due to �–�* transitions. The con-jugation of azomethine chromophore with olefinic or aryl groupschange the spectrum significantly, since rather weak bands dueto n–�* transitions are submerged by strong absorptions associ-ated with �–�* transitions [24]. These intraligand transitions wereslightly shifted on complexation. In all the complexes an intenseband at 25,670 cm−1 is assignable to the ligand to metal chargetransfer transition. The d–d bands of complexes except 1 appearedas weak bands around 15,710 cm−1 [25].

3.3. EPR spectra

The EPR spectral assignments of the complexes are presented inTable 7.

The EPR spectra of the compounds recorded in polycrystallinestate at room temperature provide information about the coor-dination environment of Cu(II) species in these complexes. Inpolycrystalline state at room temperature complexes 2, 4 and 6

show typical axial symmetry with well defined g|| and g⊥ valueswhereas the compounds 1 and 5 gave three g values g1, g2 andg3 which indicate rhombic distortion in their geometry. In addi-tion to this, a half field signal obtained for compound 1 (Fig. 4)

1158 N. Mathew et al. / Spectrochimica Acta Part A 79 (2011) 1154– 1161

Table 6Electronic spectral assignments (cm−1) of copper(II) complexes.

Compound Intraligand transitions LMCT d–d

H2hmbn·H2O 30,450, 33,370, 40,860, 45,800 – –H2hman 30,710, 33,810, 41,660, 45,720 – –H2hmbb 30,630, 33,450, 41,920, 45,540 – –H2hmab 30,710, 33,890, 42,100, 45,800 – –[Cu(hmbn)]2·2H2O (1) 30,350 (sh), 33,260 (sh), 37,680, 43,520 25,310 –[Cu(hman)]2 (2) 30,488, 38,020, 44,150 24,630 14,990[Cu(hmbb)]2·2H2O (3) 32,530, 37,310, 42,980 26,150 16,210[Cu(hmbb)phen]·1(1/2)H2O (4) 32,125, 37,490, 43,320 25,870 15,700

, 36,31, 37,49

dgmtpmttfcet

G

a

w

4ces

2ath

TE

[Cu(hmbb)(bipy)·H2O] (5) 31,363 (sh)[Cu(hmab)phen] (6) 32,180 (sh)

ue to forbidden transition �Ms = ±2 at 1600 G with g = 4.074, sug-ests a dimeric species [26] and the separation between these twoetal centers is less than 3.5 A as there is an interaction between

hese copper nuclei [27]. The compound 3 gave no EPR signal inolycrystalline state at room temperature due to strong antiferro-agnetic interactions between copper centers. The consistency of

hese giso values with the gav values of the spectra in frozen solu-ion show the existence of the same geometry in both states exceptor the compound 3 for which we obtained no EPR signal at poly-rystalline state. The geometric parameter G, which is a measure ofxchange interaction between copper centers, is calculated usinghe equation

= g|| − 2.0023g⊥ − 2.0023

for axial spectra

nd G = g3 − 2.0023g⊥ − 2.0023

here g⊥ = (g1 + g2)/2 for rhombic spectra [28].If G > 4.4, exchange interaction is negligible, and if it is less than

.4 considerable exchange interaction is there [29]. G values for theompounds 1, 2, 4 and 5 are less than 4.4 indicating considerablexchange interactions, but for compound 6 the value exceeds 4.4howing negligible exchange interactions.

The solution spectra of all complexes were recorded in DMF at

98 K. For all the complexes except 2 isotropic spectra are obtainednd this is due to the tumbling motion of molecules in DMF. Allhe complexes in DMF solution clearly showed four well resolvedyperfine lines (63,65Cu, I = 3/2). In complexes 3 and 5 the signal

able 7PR spectral assignments of copper(II) complexes in polycrystalline state at 298 K, in DM

1 2 3

Polycrystalline (298 K)g|| g1 = 2.050 2.192

g3 = 2.187

g⊥ 2.060

giso/gav 2.108 2.104

G 2.748 3.288

DMF (298 K)giso 2.115 –

Aisoa 73.3 – 8

AN – – 1DMF (77 K)g|| 2.235 –

g⊥ 2.055 –

gav 2.115

A||a 198.0 – 21˛2 0.817 –

ˇ2 – –

�2 – –

K|| – –

K⊥ – –

a Expressed in units of cm−1 multiplied by a factor of 10−4.

0, 42,290 26,010 15,8500, 43,460 26,280 15,800

corresponding to MI = + 3/2 split into three with superhyperfinecoupling constant AN = 12.5 and 15 G, respectively indicating thatthe azomethine nitrogen dominates the bonding in solution [30].

The expected half field signal is not obtained in the frozen statefor compound 1. However, a four fold splitting in the parallel regionis obtained (Fig. 5). The spectrum obtained for complex 2 wasnot good to interpret due to poor glass formation. The hyperfinesplitting is due to the interaction of the electron spin with the cop-per nuclear spin (63,65Cu, I = 3/2). In all complexes g|| > g⊥ > 2.0023indicating the presence of dx2−y2 ground state. The g|| < 2.3 is anindication of significant covalent character to the M–L bond [31].The EPR spectrum of compound 3 in DMF showed the presence oftwo copper species in the system and we are unable to simulatethis spectrum. This may be due to the cleavage of the compound inDMF and the coordination of solvent molecule to some copper cen-ters [32]. In the EPR spectra of the compounds 4, 5 and 6 (Figs. 6–8)expected superhyperfine splitting due to three nitrogen atoms areabsent. But g|| > g⊥ suggest a distorted square pyramidal geometryand rules out the possibility of a trigonal bipyramidal structure.This is confirmed by the crystal structure of compound 6.

The EPR parameters g||, g⊥, A|| and the energies of d–d transitionswere used to evaluate the bonding parameters ˛2, ˇ2 and �2 whichmay be regarded as measure of covalency in the in-plane �-bonds,in-plane �-bonds and out-of-plane �-bonds. The orbital reduc-tion factors K|| and K⊥ were also used to calculate these bonding

parameters.

According to Hathaway [33] for pure �-bonding K|| ≈ K⊥ ≈ 0.77and for in-plane �-bonding K|| < K⊥, while for out-of-plane �-bonding K⊥ < K||. Here in compounds 3 in DMF and 6, it is observed

F solution at 298 K and in DMF solution at 77 K.

4 5 6

– 2.146 g1 = 2.047 2.221g2 = 2.117g3 = 2.163

– 2.080 2.066– 2.102 2.109 2.163– 1.849 2.016 5.584

2.117 2.118 2.117 2.1093.3 75.0 80.0 76.72.5 – 15.0 –

2.209 2.256 2.223 2.1462.038 2.074 2.058 2.0122.095 2.135 2.113 2.0560.0 200.0 195.0 163.00.845 0.879 0.826 0.6410.841 0.881 0.879 0.9140.782 0.937 0.883 0.4750.711 0.775 0.727 0.5850.661 0.824 0.730 0.304

N. Mathew et al. / Spectrochimica Acta Part A 79 (2011) 1154– 1161 1159

lex 1

t��fi

3

toc

Fig. 4. EPR spectrum of comp

hat K⊥ < K|| which indicates the presence of significant out-of-plane-bonding and the compounds 4 and 5 (K|| < K⊥) show in-plane-bonding. The value of bonding parameters ˛2, ˇ2 and �2 < 1 con-rms the covalent nature of complexes.

.4. Thermal studies

Thermal analyses provide valuable information regarding thehermal stability and nature of water molecules in complexes werebtained. It helps us to distinguish the lattice water molecules andoordinated water molecules present in the compound. Reports

Fig. 5. Experimental and simulated best fit EPR

in polycrystalline state at RT.

show that the weight losses for lattice water are in the range of50–130 ◦C and weight losses due to coordinated water moleculesare in the range of 130–250 ◦C [34,35]. Here in complexes 1, 3and 4 there are weight losses in the region 90–130 ◦C indicate thepresence of lattice water molecules and weight loss is observed inbetween 160 ◦C and 210 ◦C in compound 5 indicating the presenceof coordinated water molecule in structure. In compounds 2 and

6 there are no weight loss in these regions indicating the absenceof water molecules. All the complexes decompose in the temper-ature range 250–550 ◦C. Above 550 ◦C a plateau is observed whichcorresponds to the formation of CuO.

spectra of the complex 1 in DMF at 77 K.

1160 N. Mathew et al. / Spectrochimica Acta Part A 79 (2011) 1154– 1161

Fig. 6. Experimental and simulated best fit EPR spectra of the complex 4 in DMF at 77 K.

Fig. 7. Experimental and simulated best fit EPR spectra of the complex 5 in DMF at 77 K.

t EPR

S

d6tr

Fig. 8. Experimental and simulated best fi

upplementary data

Crystallographic data for the structural analysis has been

eposited with the Cambridge Crystallographic Data centre, CCDC96921 for compound [Cu(hman)phen]. Copies of this informa-ion may be obtained free of charge at www.ccdc.cam.ac.uk/conts/etrieving.html [or from Cambridge Crystallographic Data Centre

spectra of the complex 6 in DMF at 77 K.

(CCDC), 12 Union Road, Cambridge, CB2, IEZ, UK; Fax: +44(0)1223-336033; e-mail: deposit@ccdc.cam.ac.uk].

Acknowledgements

M.R.P. Kurup is thankful to the Kerala State Council for Sci-ence, Technology and Environment, Thiruvananthapuram, Kerala,

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N. Mathew et al. / Spectrochimi

ndia for financial assistance. Nancy Mathew is thankful to theniversity Grants Commission, New Delhi, India for the award ofenior Research Fellowship. Maheswaran Sithambaresan gratefullycknowledges the Indian Council for Cultural Relations (ICCR) fornancial support. The authors are thankful to the Sophisticatednalytical Instrumentation Facility, Cochin University of Sciencend Technology, Kochi 22, India for elemental analyses and Nationalingle Crystal X-ray Diffraction Facility, IIT, Bombay, India for pro-iding single crystal XRD data.

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