Polyhedron 30 (2011) 913–922

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Polyhedron

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Synthesis, structure, spectroscopic properties, electrochemistry, and DFT correlativestudies of N-[(2-pyridyl)methyliden]-6-coumarin complexes of Cu(I) and Ag(I)

Suman Roy a, Tapan Kumar Mondal a, Partha Mitra b, Elena Lopez Torres c, Chittaranjan Sinha a,⇑a Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, Indiab Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700 032, Indiac Departamento de Química Inorgánica, c/ Francisco Tomás y Valiente, 7, Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain

a r t i c l e i n f o

Article history:Received 30 September 2010Accepted 15 December 2010Available online 9 January 2011

Keywords:N-[(2-Pyridyl)methyliden]-6-coumarinCopper(I)Silver(I)Structures and spectraElectrochemistryDensity functional theory (DFT)

0277-5387/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.poly.2010.12.037

⇑ Corresponding author.E-mail address: c_r_sinha@yahoo.com (C. Sinha).

a b s t r a c t

6-Aminocoumarin reacts with pyridine-2-carboxaldehyde and has synthesized N-[(2-pyridyl)methyl-iden]-6-coumarin (L). The ligand, L, reacts with [Cu(MeCN)4]ClO4/AgNO3 to synthesize Cu(I) and Ag(I)complexes of formulae, [Cu(L)2]ClO4 and [Ag(L)2]NO3, respectively. While similar reaction in the presenceof PPh3 has isolated [Cu(L)(PPh3)2]ClO4 and [Ag(L)(PPh3)2]NO3. All these compounds are characterized byFTIR, UV–Vis and 1H NMR spectroscopic data. In case of [Cu(L)(PPh3)2]ClO4 and [Ag(L)(PPh3)2]NO3, thestructures have been confirmed by X-ray crystallography. The structure of the complexes are distortedtetrahedral in which L coordinates in a N,N0 bidentate fashion and other two coordination sites are occu-pied by PPh3. The ligand and the complexes are fluorescent and the fluorescence quantum yields of[Cu(L)(PPh3)2]ClO4 and [Ag(L)(PPh3)2]NO3 are higher than [Cu(L)2]ClO4 and [Ag(L)2]NO3. Cu(I) complexesshow Cu(II)/Cu(I) quasireversible redox couple while Ag(I) complexes exhibit deposition of Ag(0) on theelectrode surface during cyclic voltammetric experiments. GAUSSIAN 03 computations of representativecomplexes have been used to determine the composition and energy of molecular levels. An attempthas been made to explain solution spectra and redox properties of the complexes.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Coumarin is found in a variety of plants such as Tonka bean, lav-ender, sweet clover grass, licorice and also occurs in food plantssuch as strawberries, apricots, cherries, cinnamon. Coumarin deriv-atives have blood-thinning, anti-fungicidal, anti-tumor and antico-agulant activities [1–10]. Photophysics and photochemistry ofcoumarin derivatives are also important and have been used asdye lasers [11–14]. Considerable effort has now been given at pres-ent to functionalize coumarin so that metal–coumarin complexesmay be synthesized that could display interesting excited stateproperties and be used in designing artificial photosynthetic sys-tems, chemical sensors and molecular level devices [15–17]. Weare interested to anchor diimine (–N@C–C@N–) function tocoumarin backbone so that the molecule may act as bidentateN,N-chelator. We have prepared coumarin based ligand, N-[(2-pyr-idyl)methyliden]-6-coumarin (L), which reacts with [Cu(MeCN)4]-ClO4 and AgNO3 to synthesize [M(L)2]+ (M = Cu(I), Ag(I)) whilesimilar reaction in the presence of PPh3 has isolated [Cu(L)(PPh3)2]-

ll rights reserved.

ClO4 and [Ag(L)(PPh3)2]NO3, respectively. All these compounds arecharacterized by spectroscopic data. In case of [Cu(L)(PPh3)2]ClO4

and [Ag(L)(PPh3)2]NO3, the structures have been confirmed byX-ray crystallography. In the last decade Quantum chemical calcu-lations using density functional theory (DFT) have been carried outto the theoretical and experimental structure, spectroscopic, andthermodynamic properties of different type of compounds.Time-dependent density functional theory (TD-DFT) is openingnew perspectives in this field [18–20]. In this work the DFT andTD-DFT calculations have been performed on the optimized geom-etry of the selective complexes to pursue the electronic propertyand redox activity of the complexes.

2. Experimental

2.1. Materials

AgNO3 and pyridine-2-carboxaldehyde were purchased fromAldrich Chemical Co. Coumarin was available from S.D. Fine Chem.Ltd., Boisar. [Cu(MeCN)4]ClO4 was prepared by standard procedure[21]. PPh3 was purchased from Merck, India. Dinitrogen was puri-fied by bubbling through an alkaline pyrogallol solution. Solventswere purified by standard procedure [22]. All other chemicals

914 S. Roy et al. / Polyhedron 30 (2011) 913–922

and solvents were of reagent grade and were used without furtherpurification.

2.2. Physical measurements

Microanalytical data (C, H, and N) were collected on Perkin–Elmer 2400 CHNS/O elemental analyzer. Spectroscopic data wereobtained using the following instruments: UV–Vis spectra byPerkin–Elmer UV–Vis spectrophotometer model Lambda 25; FTIRspectra (KBr disk, 4000–400 cm�1) by Perkin–Elmer FT-IR spectro-photometer model RX-1; the 1H NMR spectra by Bruker (AC)300 MHz FTNMR spectrometer. Electrochemical measurementswere performed using computer-controlled CH-Instruments, Elec-trochemical workstation, Model No CHI 600D (SPL) with Pt-diskelectrodes. All measurements were carried out under nitrogenenvironment at 298 K with reference to SCE electrode in acetoni-trile using [n-Bu4N]ClO4 as supporting electrolyte. The reportedpotentials are uncorrected for junction potential. Emission wasexamined by LS 55 Perkin–Elmer spectrofluorimeter at room tem-perature (298 K) in CH3CN solution under degassed condition.

The fluorescence quantum yield of the complexes was deter-mined using carbazole as a reference with known /R of 0.42 inMeCN [23]. The complex and the reference dye were excited atsame wavelength, maintaining nearly equal absorbance (�0.1),and the emission spectra were recorded. The area of the emissionspectrum was integrated using the software available in the instru-ment and the quantum yield is calculated according to the follow-ing equation:

/S=/R ¼ ½AS=AR� � ½ðAbsÞS=ðAbsÞS� � ½g2S=g

2R� ð1Þ

Here, /S and /R are the fluorescence quantum yield of the sam-ple and reference, respectively. AS and AR are the area under thefluorescence spectra of the sample and the reference, respectively,(Abs)S and (Abs)R are the respective optical densities of the sampleand the reference solution at the wavelength of excitation, and gS

and gR are the values of refractive index for the respective solventused for the sample and reference.

Fluorescence lifetimes were measured using a time-resolvedspectrofluorimeter from IBH, UK. The instrument uses a picoseconddiode laser (NanoLed-07, 370 nm) as the excitation source andworks on the principle of time-correlated single photon counting[24]. The instrument responses function is �230 ps at FWHM. Toeliminate depolarization effects on the fluorescence decays, mea-surements were done with magic angle geometry (54.7�) for theexcitation and emission polarizers. The observed decays of[Cu(L)2]ClO4 (1), [Ag(L)2]NO3 (3) and [Ag(L)(PPh3)2]NO3 (4) com-plexes fit with single exponential decay whereas [Cu(L)(PPh3)2]-ClO4 fits with a bi-exponential decay as in the followingequation: where s’s are the fluorescence lifetime and a is thepre-exponential factor. For the fits, the reduced v2 values werewithin 0.99–1.07 and the distribution of the weighted residualswere random among the data channels. sf is mean fluorescence lifetime (meaning of the symbols are usual) [25].

IðtÞ ¼ ½a1 expð�t=s1Þ � a2 expð�t=s2Þ� ð2Þsf ¼ a1s1 þ a2s2 ð3Þ

3. Synthesis

3.1. Synthesis of N-[(2-pyridyl)methyliden]-6-coumarin (L)

There are three steps in the preparation of ligand (Scheme 1): 6-nitrocoumarin (step 1), 6-aminocoumarin (step-2) and condensa-tion with pyridine-2-carboxaldehyde (step-3). All the steps areshown in Scheme 1.

3.1.1. Step-1: synthesis of 6-nitrocoumarinCoumarin was nitrated with mixed acid in an ice bath. Couma-

rin (8 gm, 54.8 mmol) was dissolved in conc. H2SO4 (40 cm3) andtemperature was maintained at �5 �C and then 16 cm3 mixed acid(HNO3 and H2SO4 (conc.) in 1:3 volume ratio) was added. The mix-ture was stirred keeping at room temperature for 1 h and then to itice was added. A white precipitate of 6-nitrocoumarin was ob-tained. It was then filtered and washed thorough with cold water(10 cm3 � 10) and dried over CaCl2 and recrystallized from aceticacid. Yield, 9.2 g (88%). m.p. 185 ± 2 �C; 1H NMR (300 MHz, CD3CN)d 8.54 (1H, s), 8.38 (1H, d, 7.5 Hz), 7.98 (1H, d, 7.5 Hz), 7.49 (1H, d,7.0 Hz), 6.55 (1H, d, 8.0 Hz); IR (KBr, cm�1) 3096, 3071, 1751, 1620,1564, 1536, 1480, 1436; UV (kmax, nm (e, 103 M�1 cm�1) in CH3CN)327 (1.80), 314 (2.13), 268 (6.93), 259 (9.51); Anal. Calc. forC9H5NO4: C, 56.54; H, 2.62; N, 7.33. Found: C, 56.45; H, 2.67; N,7.28%.

3.1.2. Step-2: synthesis of 6-aminocoumarinReduction of 6-nitrocoumarin was done using iron powder and

ammonium chloride in water. 6-Nitrocoumarin (8 g, 41.9 mol) inwater (150 cm3) was treated with Fe-powder (20 gm) and ammo-nium chloride (2.6 g, 48.6 mmol). The mixture was kept in waterbath for 2 h with stirring. A dark brown precipitate was obtainedwhich was then extracted with acetone. Evaporation of acetoneyielded silky yellow precipitate of 6-aminocoumarin (m.p.158 �C). It was then recrystallized from dil HCl solution as 6-aminocoumarin hydrochloride. Yield, 5.1 g (76%). m.p. >260 �C;1H NMR (300 MHz, CD3CN) d 7.71 (1H, d, 7.5 Hz), 7.09 (1H, d,7.5 Hz), 6.88 (1H, d, 7.5 Hz), 6.77 (1H, s), 6.30 (1H, d, 8.0 Hz),4.26 (2H, s); IR (KBr, cm�1) 1705, 1635, 1570, 1490, 1451; UV (kmax,nm (e, 103 M�1 cm�1) in CH3CN) 370 (3.54), 280 (11.43), 253(21.44); Anal. Calc. for C9H7NO2: C, 67.08; H, 4.35; N, 8.70. Found:C, 67.12; H, 4.25; N, 8.65%.

3.1.3. Step-3: N-[(2-pyridyl)methyliden]-6-coumarin (L)6-Aminocoumarine (0.5 g, 3.1 mmol) and pyridine-2-carboxal-

dehyde (0.26 cm3, 3.1 mmol) was taken in dry methanol (15 cm3)and was refluxed for 8 h. Slow evaporation of the solution sepa-rated a straw color crystalline compound of yield 0.7 g (90%);m.p. 152 ± 2 �C; MS m/z = 249 (M+); FT-IR (KBr, m, cm�1) m(COO),1714; m(C@N), 1629; m(C@C), 1581, 1566, 1472, 1437. Anal. Calc.for C15H10N2O2: C, 72; H, 4; N, 11.2. Found: C, 71.8; H, 4.1; N,11.15%

3.2. Preparation of complexes

The complexes are prepared as per Scheme 2. Detail procedureis given below.

3.2.1. Preparation of [Cu(L)2]ClO4 (1)[Cu(MeCN)4]ClO4 (0.025 g, 0.076 mmol) was taken in a 100 cm3

double neck round bottom flask dissolved in dry MeOH by mag-netic stirring under N2 atmosphere. Then L (0.038 g, 0.152 mmol)under N2 atmosphere and stirring is continued for 2–3 h. A brown-ish black precipitate was collected by filtration and dried. The com-plex was isolated in 0.035 g (70%) yield; decompositiontemperature >162 �C. FT-IR (KBr, cm�1) 1721, 1560, 1100. Anal.Calc. for [Cu(L)2]ClO4 (1): C30H20N4ClO8Cu: C, 54.3; H, 3.02; N,8.45. Found: C, 54.2; H, 2.85; N, 8.35 %.

3.2.2. Preparation of [Cu(L)(PPh3)2]ClO4 (2)[Cu(MeCN)4]ClO4 (0.025 g, 0.076 mmol) was taken in a 100 cm3

double neck round bottom flask dissolved in dry MeOH by mag-netic stirring under N2 atmosphere. Then PPh3 (0.040 g,0.152 mmol) was added to this solution and stirred magnetically.After half-an-hour L was added to the reaction mixture and stirred

O OO O

O2N

O O

N2

O O

N

N H

Conc HNO3

Conc H2SO4

Fe powder NH4Cl

Pyridine-2-Carboxaldehyde

Dry MeOH

CoumarinNitrocoumarin

C

6-Nitrocoumarin

6-Aminocoumarin L,Reflux

H

Scheme 1.

[Cu(MeCN)4]ClO4

L (1:2) in Dry MeOH

Reflux with stirringunder N2 atmosphere

[Cu(L)2]ClO4

(1)

PPh3,L(1:2:1)in Dry MeOH

Reflux with stirringunder N2 atmosphere

[Cu(L)(PPh3)2]ClO4

(2)

AgNO3

L (1:2) in MeOHand dark atmosphere

[Ag(L)2]NO3

(3)

PPh3,L(1:2:1) in MeOHand dark atmosphere

[Ag(L)(PPh3)2]NO3

(4)

Scheme 2.

S. Roy et al. / Polyhedron 30 (2011) 913–922 915

for another 2 h. An orange precipitate was collected by filtrationand was purified by crystallization from acetonitrile solution. Aftera week single crystals were collected. The complex was obtained in0.057 g (80%) yield; decomposition temperature >212 �C. FT-IR(KBr, cm�1) 1722, 1560, 1100. Anal. Calc. for [Cu(L)(PPh3)2]ClO4

(2): C51H40N2ClO6P2Cu: C, 65.3; H, 4.3; N, 2.9. Found: C, 65.25; H,4.33; N, 3.0%.

3.2.3. Preparation of [Ag(L)2]NO3 (3)To AgNO3 (0.025 g, 0.15 mmol) solution in MeOH wrapped with

carbon paper, L (0.0735 g, 0.30 mmol) was added in MeOH. Thesolution was magnetically stirred for 2 h, light yellow precipitatefiltered, residue was collected and dried. The complex was ob-tained in 0.090 g (90%) yield; decomposition temperature>250 �C. FT-IR (KBr, cm�1) 1721, 1561, 1384. Anal. Calc. for[Ag(L)2]NO3 (3): C30H20N5O7Ag: C, 53.7; H, 2.98; N, 10.44. Found:C, 53.65; H, 3.12; N, 10.34%.

3.2.4. Preparation of [Ag(L)(PPh3)2]NO3 (4)To AgNO3 (0.025 g, 0.15 mmol) solution in MeOH (20 cm3) in

stirring condition PPh3 (0.0775 g, 0.30 mmol) was added and stir-red for 1 hr. Then L (0.0368 g, 0.15 mmol) was added to this solu-tion and was magnetically stirred for 2 h. The reaction mixturewas transferred in a beaker which was wrapped with carbon paperand evaporated in air. After 2 weeks crystals were deposited on thewall of beakers. The complex was obtained as a yellow crystallinesolid in 0.113 g (80%) yield; decomposition temperature >175 �C.FT-IR (KBr, cm�1) 1724, 1630, 1590, 1383. Anal. Calc. for[Ag(L)(PPh3)2]NO3 (4): C51H40N3O5P2Ag: C, 64.79; H, 4.23; N,4.44%. Found: C, 64.65; H, 4.35; N, 4.32%. The preparative routeof all the complexes is shown in Scheme 2.

3.3. X-ray crystallography of [Cu(L)(PPh3)2]ClO4 (2) and[Ag(L)(PPh3)2]NO3 (4)

The crystals of 2 and 4 were obtained by slow evaporation ofacetonitrile and methanol solution, respectively. Crystallographicrefinement data and selected geometric parameters are collectedin Table 1. Data for 2 were collected by Bruker Smart Apex IICCD Area Detector. Fine-focus sealed tube was used as the radia-tion source of graphite-monochromatized Mo Ka radiation. Inten-sity data for 4 was collected on a Bruker Smart CCD area detectorusing Cu Ka radiation source. Data were corrected for Lp and anempirical absorption correction. Data processing and empiricalabsorption correction were accomplished with the programs CRYS-

TAL CLEAR and ABSCOR [26], respectively. The structure was solved byheavy-atom methods and followed by successive Fourier and dif-ference Fourier syntheses. Full matrix least squares refinementson F2 were carried out using SHELXL-97 [27,28] with anisotropic dis-placement parameters for all non-hydrogen atoms. Hydrogenatoms were constrained to ride on the respective carbon atomswith isotropic displacement parameters equal to 1.2 times theequivalent isotropic displacement of their parent atom in all casesof aromatic units. Figures are drawn using ORTEP [29], PLATON [30]and MERCURY 2.2 [31] softwares.

3.4. Theoretical calculations

Full geometry optimization of [Cu(L)(PPh3)2]ClO4 (2) and[Ag(L)(PPh3)2]NO3 (4) were carried out using density functionaltheory (DFT) at the B3LYP level [32]. All calculations were carriedout using the GAUSSIAN 03 program package [33] with the aid ofthe GaussView visualization program [34]. For C, H, N, O and Pthe 6-31G(d) basis set were assigned, while for Cu and Ag the

Table 1Summarized crystallographic data of [Cu(L)(PPh3)2]ClO4 (2) and [Ag(L)(PPh3)2]NO3

(4).

[Cu(L)(PPh3)2](ClO4) (2) [Ag(L)(PPh3)2] (NO3) (4)

Empiricalformula

C51H40N2ClO6P2Cu C52H44N3O6P2Ag

Formulaweight

937.79 976.71

T (K) 150(2) 100(2)Crystal system triclinic triclinicCrystal size

(mm)0.22 � 0.19 � 0.17 0.20 � 0.20 � 0.15

Space group P�1 P�1Unit cell

dimensionsa (Å) 11.668(3) 11.5500(7)b (Å) 13.177(3) 13.1591(8)c (Å) 15.255(4) 15.3330(11)a (�) 88.116(3) 81.980(4)b (�) 79.476(3) 78.976(5)c (�) 82.800(3) 76.936(4)

V (Å)3 2287.6(9) 2216.9(2)Z 2 2k (Å) 0.71073 1.54178l (mm�1) 0.658 (Mo K) 4.782 (Cu K)h Range 1.36–26.55 2.95–67.77Index range �12 6 h 6 13;

�15 6 k 6 15; �18 6 l 6 18�13 6 h 6 12;�15 6 k 6 15; �18 6 l 6 16

Dcalc (mg m�3) 1.361 1.463Refine

parameters568 582

Totalreflection

9432 7671

Unique data[I > 2r(I)]

7983 7484

R1a [I > 2r(I)] 0.0447 0.0329

wR2b 0.1102 0.0865

Goodness of fit 1.025 1.090Dmax (e �3) 0.800 0.965Dmin (e �3) -0.553 -0.545

a R =P

Fo � Fc/P

Fo.b wR ¼ ½

PwðF2

o � F2c Þ=P

wF4o �

1=2 are general but w are different, w ¼ 1=½r2ðF2oÞþ

ð0:0623PÞ2 þ 1:4952P� for (2); w ¼ ½r2ðFoÞ2 þ ð0:0420PÞ2 þ 2:4478P��1 for (4)where P ¼ ðF2

o þ 2F2c Þ=3.

916 S. Roy et al. / Polyhedron 30 (2011) 913–922

LANL2DZ basis set with effective core potential were employed[35]. The vibrational frequency calculations were performed to en-sure that the optimized geometries represent the local minima andthere are only positive eigen values. Vertical electronic excitationsbased on B3LYP optimized geometries were computed using thetime-dependent density functional theory (TD-DFT) formalism

Table 2UV–Vis, fluorescence, lifetime and cyclic voltammetric data of L, copper(I) and silver(I) co

Compound UV–Vis spectral data kmax(nm)(10�3 2 (dm3 mol�1 cm�1) in CH3CN

FluorescenCH3CN

kex

(nm)ke

(n

L 280(18.5), 289(15.6), 328(8.15) 328 4[Cu(L)2]ClO4 (1) 278(56.8), 327(26.5), 492(19.7) 327 5

[Cu(L)(PPh3)2]ClO4

(2)266(16.73), 337(5.76), 405(14.07) 337 4

[Ag(L)2]NO3 (3) 278(43.3), 330(19.9) 330 5

[Ag(L)(PPh3)2]NO3

(4)254(36.2), 277(30.6), 330(9.8), 400(3.2) 330 4

a Solvent, MeCN Pt-working electrode, SCE reference Electrode, Pt-auxiliary electrEM = 0.5(Epa + Epc), V, DEp = Epa � Epc, mV; EL refers to ligand reduction.

b Epa (anodic-peak-potential).c Epc (cathodic-peak-potential).

[18–20] in acetonitrile using conductor-like polarizable continuummodel (CPCM) [36]. Gauss Sum was used to calculate the fractionalcontributions of various groups to each molecular orbital [37].

4. Results and discussion

4.1. Synthesis and formulation

4.1.1. N-[(2-pyridyl)methyliden]-6-coumarin (L)Nitration of coumarin and its subsequent reduction to 6-amino-

coumarin has been carried out by Fe powder/NH4Cl. The condensa-tion of pyridine-2-carboxaldehyde with 6-aminocoumarin inalcohol under refluxing condition has isolated straw yellow crys-talline compound (Scheme 1). Infrared spectra of 6-aminocouma-rin shows two m(NH2) bands at 3329 and 3409 cm�1 which iseliminated in the condensation product and a new band appearsat 1582 cm�1 that is corresponding to m(C@N) along with lactonem(COO) at 1714 cm�1. Absorption spectrum shows intense bandat 328 and 289 nm in acetonitrile. These are assigned to n ? p⁄

and p ? p⁄ transitions (Table 2). The structural characterizationhas been carried out by 1H NMR spectral data (Table 3). The CH@Nshows singlet signal in 1H NMR spectrum at 8.63 ppm. Pyridyl pro-tons appear at d 7.4–8.8 ppm while coumarin protons appear at d6.4–8.2 ppm. DFT computation has been done to interpret elec-tronic transitions (vide infra, pictures of MOs and transitions are gi-ven as Supplementary material).

4.1.2. The complexesThe reaction of L with [Cu(MeCN)4]ClO4 in dry methanol under

N2 environment for 2 h has isolated dark brown colored [Cu(L)2]-ClO4 (1) (Scheme 2). The reaction of L and [Cu(MeCN)4]ClO4 inthe presence of PPh3 (2 equiv.) in dry methanol under N2 environ-ment for 2 h has separated orange precipitate of [Cu(L)(PPh3)2]ClO4

(2). Single crystal is also obtained from CH3CN solution of this com-pound. Silver(I) complexes are also prepared by similar procedurein the absence of light. The reaction of AgNO3 and ligand L in 1:2mole ratio has separated [Ag(L)2]NO3 (3). Upon addition of 2 equiv-alent of PPh3 to methanolic solution of AgNO3 and L in 1:1 molarratio has isolated the complex, [Ag(L)(PPh3)2]NO3 (4). Molarconductance (M) in CH3CN record in the range of 150–160 X�1 cm2 mol�1. This is in support of 1:1 electrolytic natureof the complexes. The structures of 2 and 4 are confirmed by singlecrystal X-ray diffraction study.

mplexes.

ce data in Fluorescence decay data in CH3CN Cyclic voltammograma

E (V) (DEP, mV)

m

m)/ v2 s

(ns)kr � 10�9 knr � 10�9 EM EL

84 0.018 5.41 0.92 0.0028 0.18214 0.003 1.06 1.82 0.0017 0.562 1.0

(100)�0.77 (160),�1.45

14,438 0.021 1.07 3.1 0.0023 0.55 1.30c �0.63 (155),�1.32

18 0.002 1.06 1.7 0.0012 0.588 0.40b �0.72 (160),�1.40

87 0.09 0.99 1.7 0.053 0.535 0.44b �0.70 (170),�1.45

ode; [n-Bu4N](ClO4) supporting electrolyte, scan rate 50 mV/s; metal oxidation

Table 31H NMR spectral data of ligand and the complexes.

Compd d ppm (J, Hz)

3-He 4-He 5-Hd 7-He 8-He 10-Hd 13-He 14-Hf 15-He 16-He PPh3

La 6.48 (9.55) 7.75 (9.50) 7.37 7.38 (8.65) 7.51 (8.66) 8.63 8.74 (6.8) 7.87 7.87 8.20 (7.89)1c 6.46 (9.09) 7.82 (9.85) 7.57 7.41 (8.82) 7.48 (8.66) 8.96 8.86 (6.8) 8.19 8.19 8.10 (7.79)2a 7.70 (9.38) 6.41 (9.57) 7.40 7.35 (6.75) 7.38 (7.41) 9.38 8.49 (6.48) 7.66 7.99 8.15 (7.75) 6.95–7.403b 6.43 (9.60) 7.76 (9.64) 7.54 7.32 (8.68) 7.59 (8.68) 8.84 8.86 (6.7) 8.13 8.13 8.00 (7.73)4a 6.45 (9.52) 7.78 (9.57) 7.49 7.35 (8.71) 7.61 (8.75) 9.02 8.82 (6.2) 7.92 7.92 8.30 (7.92) 7.29–7.42

a In CDCl3.b In DMSO-d6.c In CD3CN.d Singlet.e Doublet.f Multiplet.

Table 4Selected bond lengths and bond angles of [Cu(L)(PPh3)2]ClO4 (2) and [Ag(L)(PPh3)2]NO3 (4).

(M = Cu) (2) (M = Ag) (4)

Bond lengths (Å)M(1)–N(2) 2.095(3) 2.338(2)M (1)–N(8) 2.101(3) 2.365(2)M (1)–P(1) 2.2730(12) 2.4420(6)M (1)–P(2) 2.2695(11) 2.4447(6)C(7)–N(8) 1.278(4) 1.283(3)C(9)–N(8) 1.431(4) 1.422(3)

Bond angles (�)N(2)–M(1)–N(8) 79.42(11) 71.25(8)N(2)–M(1)–P(1) 107.01(8) 111.54(5)N(8)–M(1)–P(1) 119.85(8) 123.24(5)N(2)–M(1)–P(2) 120.36(8) 121.65(5)N(8)–M(1)–P(2) 110.75(8) 110.54(5)P(1)–M(1)–P(2) 115.07(4) 113.15(2)

S. Roy et al. / Polyhedron 30 (2011) 913–922 917

4.2. Molecular structures of [Cu(L)(PPh3)2]ClO4 (2) and[Ag(L)(PPh3)2]NO3 (4)

The molecular structures of [Cu(L)(PPh3)2]ClO4 (2) and[Ag(L)(PPh3)2]NO3 (4) and are shown in Fig. 1a and b. The bondparameters are listed in Table 4. Each discrete molecular unit con-sists of mononuclear fragment MN2P2. The charges of the cationiccomplexes [M(L)(PPh3)2]+ are satisfied by either ClO4

� or NO3�.

Solvent of crystallization, CH3OH present in the structural arrange-ment of 4 and generates supramolecular hydrogen bonded net-work with NO3

� and lactone C@O of coumarin unit of thechelated ligand (Table 5 and Fig. 2). Ligand, L, acts as N,N0-donor(N refers to N(pyridine) and N0 refers to N(imine)) end cappingagent. The atomic arrangements M, N(2), C(1), C(7), N(8) constitutea chelate plane with a deviation <0.01 Å. M(I) is present at the cen-tre of a distorted tetrahedron. The pendant coumaryl ring makes adihedral 33.21(15)� for 2 and 24.21(8)� for 4 with chelated diimine

ring, -(M-N=C-C=N-) and may assist distortion from ideal platonic

geometry. The acute bite angle, M(N, N0), 79.53(15)� for 2 and71.25(8)� for 4 are extended by L on coordination to M(I) and iscomparable with reported results in the series of chelated arylazo-imidazoles of d10 metal complexes [38]. The small chelate anglemay be one of the reasons for geometrical distortion. The P(1)–M(1)–P(2), 115.12(5)� (2) and 113.15(2)� (4) supports this struc-tural deviation from ideal tetrahedral geometry. The ligand showsdistortion that may be due to steric demand of pendant coumarylgroup. The M–N(pyridine), 2.088(4) (2) and 2.338(2) Å (4), areshorter than M(I)–N(imine) (2.098(3) and 2.365(2) Å) that reflectspreferentially stronger interaction of M(I) with N(pyridine)

Fig. 1. (a) The molecular structure of [Cu(L)(PPh3)2]ClO4(2) and

compared to exocyclic N (imine). M–P distances, M(1)–P(1),2.2674(14) Å (2, Cu), 2.4420(6) Å (4, Ag); M(1)–P(2), 2.2721(14) Å(2, Cu), 2.4447(6) Å (4, Ag) are comparable with the reported re-sults [39].

Crystallization solvent CH3OH and counter ion, NO3� forms

hydrogen bonded unit, O(6)–H� � �O(4)(NO2); O(4) and O(5) ofNO3

� form bifurcated hydrogen bonds with coumaryl-H (C(10–H(10)). Pyridyl-H, C(3)–H(3) and C(4)–H(4) form hydrogen bondwith O(3) and O(4) of NO3

�. O(5) of NO3� is again bonded with

C(32)–H(32) of PPh3. Thus NO3� serves to bridge complex ion,

[Ag(L)(PPh3)2]+ and forms supramolecular network. Coumaryl-O(O(2)) belongs to carbonyl (C@O) acts as H-acceptor and helps to

(b) [Ag(L)(PPh3)2]NO3 (4) with atom numbering scheme.

Table 5Hydrogen bonding interactions in [Ag(L)(PPh3)2]NO3 (4).

D–H� � �A D–H H� � �A D� � �A \D–H� � �A

O(6)–H(6)� � �O(4) 0.89(3) 1.93(4) 2.801(4) 165(5)C(10)–H(10)� � �O(4)i 0.9504 2.5516 3.329(4) 139.13C(10)–H(10)� � �O(5)i 0.9504 2.3686 3.303(4) 167.66C(3)–H(3)� � �O(3)ii 0.9506 2.4466 3.143(4) 129.99C(4)–H(4)� � �O(4)ii 0.9496 2.4006 3.288(4) 155.40C(19)–H(19)� � �O(2)iii 0.9504 2.4665 3.243(3) 138.89C(32)–H(32)� � �O(5)iv 0.9498 2.4655 3.400(4) 168.02C(37)–H(37)� � �O(2)v 0.9504 2.3212 3.122(3) 141.60

C–H� � �Cg H� � �Cg C� � �Cg C–H� � �CgC(19)–H(19)� � �Cg(1)vi 3.177 4.030 150.32C(25)–H(25)� � �Cg(5)vi 2.996 3.762 138.79C(29)–H(29)� � �Cg(10)vi 2.700 3.598 158.05C(47)–H(47)� � �Cg(1)vi 3.057 3.955 158.13C(52)–H(52)� � �Cg(9)ii 3.110 3.957 149.24

Symmetry: i1 + x,y,z; ii1 � x,1 � y,1 � z; iii2 � x,1 � y,2 � z; ivx,1 + y,z;v1 � x,1 � y,2 � z; vix, y, z.Cg(1): Ag(1)–N(2)–C(1)–C(7)–N(8); Cg(5): C(18)–C(19)–C(20)–C(21)–C(22)–C(23);Cg(9): C(42)–C(43)–C(44)–C(45)–C(46)–C(47); Cg(10): C(48)–C(49)–C(50)–C(51)–C(52)–C(53).

Fig. 2a. Unit cell packing diagram of [Ag(L)(PPh3)2]NO3 (4).

Fig. 2b. Supramolecular chain via hydrogen bonds and p� � �p interactions in[Ag(L)(PPh3)2]NO3 (4).

300 400 5000

1x104

2x104

3x104

4x104

5x104

6x104

7x104

(d)

(c)

(b)

(a)

(e)

Mol

ar E

xtin

ctio

n C

oeffi

cien

t

Wavelength

400 500 600 700 8000.0

2.0x104

4.0x104

6.0x104

(b)

(c)

(e)

Mol

ar E

xtin

ctio

n C

oeff

icie

nt

Wavelength

Fig. 3. UV–Vis spectra of (a) L, (b) [Cu(L)2]ClO4, (c) [Cu(L)(PPh3)2]ClO4, (d)[Ag(L)2]NO3 and (e) [Ag(L)(PPh3)2]NO3 in MeCN.

918 S. Roy et al. / Polyhedron 30 (2011) 913–922

strengthen the hydrogen bonded polymer. The C–H� � �Cg interac-tions also help to ensure rigidity in the supramolecular structure(Fig 2b and Table 5). The – interaction is observed between pen-dant coumaryl groups (Cg(2)� � �Cg(4), 3.696 Å; Cg(4) � � �Cg(4),3.607 Å) where Cg(2): O(1)–C(14)–C(13)–C(12)–C(11)–C(15) andCg(4): C(9)–C(10)–C(11)–C(15)–C(16)–C(17)) of adjacent mole-cules and a -cube is generated via interaction between phenylgroups (Cg(2)� � �Cg(10), 3.668 Å) (Cg(10): C(48)–C(49)–C(50)–

C(51)–C(52)–C(53)) of coordinated PPh3. Unit cell packing diagram(Fig. 2) shows these interactions.

4.3. The spectral characterization

The main vibrational bands are m(COO) at 1720–1724 cm�1 andm(C@N) at 1590–1600 cm�1. Presence of ionic ClO4

� in (1 and 2) issupported by strong single stretch at 1100 cm�1 with a weakstretch at 625 cm�1.

The electronic spectra of the complexes are recorded in CH3CNsolution in the wavelength range 200–600 nm (Fig. 3 and Table 2).The electronic transitions have been assigned based on the TDDFTresults calculated in acetonitrile. The complexes exhibit transitionbelow 400 nm corresponding to intraligand charge-transfer (ILCT)transitions. The transitions are shifted only to longer wavelengthregion by 5–10 nm compare to free ligand values. A broad bandis observed at >400 nm but intensity is about one order below thanthat of transitions <400 nm. This transition does not observed infree ligand, L, and is assigned to admixture of MLCT and LLCT band,Cu(dp)/PPh3 ? L(p⁄) on comparing with reported copper(I) com-plexes which is a characteristic feature of the copper complexeswhen bonded with conjugated organic chromophore [21,40,41].In case of Ag complexes only [Ag(L)(PPh3)2]NO3 (4) shows elec-tronic transition at near about 400 nm which is also assigned toILCT band with partial contribution from Ag(dp) ? L(p⁄) transition.

The 1H NMR spectra were recorded in CDCl3 for [Cu(L)(PPh3)2]-ClO4 (2) and [Ag(L)(PPh3)2]NO3 (4). DMSO-d6 is used to study NMRof [Cu(L)2]ClO4 (1) and [Ag(L)2]NO3 (3). The spectra are analyzed oncomparing with free ligand value (Table 3). Pyridine protons (13-Hto 16-H) experience significant downfield shift by 0.1–0.5 ppmwhile coumarin protons (3,4-H; 5-H; 7-H, 8-H) perturbed by0.05–0.15 ppm only. Imine proton (–CH@N–) appears as a singletat most downfield side, 8.8–9.8 ppm. The proton movement is inassociation with coordination of L with metal ion(s). PPh3 protonsappear at 6.9–7.4 ppm.

4.4. Emission spectroscopy

Photoluminescence study of N-((2-pyridyl)methyliden)-6-aminocoumarin (L) and the complexes are carried out at roomtemperature in CH3CN (Fig. 4). The compounds exhibit fluores-cence when they are excited at p–p⁄ band 328–337 nm (Table 2).Free ligand exhibits transition at 484 nm at 298 K upon excitation

350 400 450 500 550 600-20

0

20

40

60

80

100

120

140

160

180

200

220

(b)

(d)

(a)

(e)

(c)

Flu

ores

cenc

e In

tens

ity

Wavelength

Fig. 4. Emission spectra of (a) L, (b) [Cu(L)2]ClO4, (c) [Cu(L)(PPh3)2]ClO4, (d)[Ag(L)2]NO3 and (e) [Ag(L)(PPh3)2]NO3 in MeCN.

S. Roy et al. / Polyhedron 30 (2011) 913–922 919

at 328 nm. The complexes, 1–4, do not emit significant emissionwhen they are excited at MLCT band maxima (>400 nm, Table 2).It is because of the difficulty to oxidize or reduce metal ions ofd10 configuration. The emission is referred to p� � �p⁄ emission, i.e.,it may belong to intraligand charge transfer (ILCT), ligand-to-ligandcharge transfer (LLCT) transitions or combination of both. The fluo-rescence quantum yield of the complexes are higher (/ = 0.021 (2),0.09 (4)) than that of the ligand (/ = 0.018 (L)). It is curious to findhigh quantum yield of the complexes containing coordinated PPh3

group. [Ag(L)2]NO3 (3) shows lowest / (0.002) in the series and[Ag(L)(PPh3)2]NO3 (4) gives highest/, 0.09. The mechanism of fluo-rescence enhancement for the complexes is believed to workthrough photo induced electron transfer (PET) and rigidity to che-lated L in the complexes may suppress vibrational relaxation. InPET, the complex fails to fluoresce or very weakly fluoresces be-cause the excited state is quenched by electron transfer, unlessthe relative energies of the fluorophore are perturbed. Heteroatomcontaining fluorophores develop partial charges due to internalcharge transfer (ICT) and interaction with charged groups can af-

(a)

0 20 40 60 80 100 120

1

10

100

1000

Log

(cou

nts)

Time (ns)

Fig. 5. Exponential decay profile ( ) and fitting curve (—) of (a) [Cu(L)(PPh3)2]ClO4

fect its energy. It has been reported that the metal ions can en-hance or quench the fluorescence emission of pyridine containingcompounds [42]. In the complexes, the PET process is effectivelyreduced due to the presence of metal and p-acidic PPh3 moleculeswhich also helps to populate the excited states [38]. This may bethe probable reason for the increased fluorescence quantum yieldof the complexes than ligand in the presence of PPh3. Intersystemcrossing due to spin-orbit coupling introduced by the metal centremay also influence the emission intensity. This enhances fluores-cence intensity upon coordination to the metal ion. The quantumyield of [Ag(L)2]NO3 is lower than that of [Cu(L)2]ClO4. That maybe explained considering heavy atom effect to the promotion ofquenching [25].

Lifetime data are obtained upon excitation at 370 nm and aresummarized in Table 2. The observed decays of [Cu(L)2]ClO4 (1),[Ag(L)2]NO3 (3) and [Ag(L)(PPh3)2]NO3 (4) complexes fit with sin-gle exponential decay whereas [Cu(L)(PPh3)2]ClO4 (2) fits with abi-exponential function (Fig. 5) which may be due to decaythrough both high energy and MLCT states. The average lifetimevalue for the complexes is higher than free ligand value. The me-tal–ligand orbital mixing in the complexes (DFT computation sup-ports, vide infra) state may be the reason for passing longer time atexcited state.

4.5. Redox properties

Copper(I) complexes show quasi-reversible oxidation-reductionCu(II)/Cu(I) couple at ca. 0.6–0.7 V vs SCE (at 100 mV s�1 scan rate)at a Pt-bead working electrode. The quasi-reversible character isaccounted from the DEp (Epa – Epc) (130–160 mV) values underthe condition of measurements (Fig. 6 and Table 2). Presence ofPPh3 coordination in [Cu(L)(PPh3)2]ClO4 (2) shows higher redoxCu(II)/Cu(I) couple than that of [Cu(L)2]ClO4 (1) which is due tobetter p-acceptability of PPh3 than L. The electrochemistry of silvercomplexes is not very informative. The cathodic progress followedby scan reversal in anodic side gives an irreversible oxidative re-sponse on the positive side to SCE which may be due to the oxida-tion of adsorbed silver on the electrode bed [43] produced on thecathodic scan. The reductive responses at �0.70 to �0.77 V and�1.40 to �1.45 V may be assigned to the reduction of diiminegroup of the chelated ligand. Free ligand does not show any oxida-tion but irreversible reductive responses appear at <�1.5 V.

(b)

0 20 40 60 80 100 120

1

10

100

1000

log

(cou

nts)

Time (ns)

and (b) [Ag(L)(PPh3)2]NO3 in acetonitrile. Excitation is carried out at 370 nm.

Fig. 6. Cyclic voltammogram of [Cu(L)2]ClO4 in acetonitrile using Pt-bead electrode,SCE reference and Pt-auxiliary electrodes in the presence of [n-Bu4N]ClO4 support-ing electrolyte in MeCN solution at 100 mV scan rate.

920 S. Roy et al. / Polyhedron 30 (2011) 913–922

4.6. DFT computations: explanation of spectral and redox properties

DFT calculation has been performed for the complexes 2 and 4.The optimized structure of these molecules are developed usingGAUSSIAN 03 analyses package. The structural agreement has beenobserved from the comparison of bond distances and angles be-tween calculated and X-ray determined structures. The orbital

HOMO

E, -6.14 eV

HOMO-1

E, -6.86 eV

L

HOMO

E, -8.14 eV; L, 5 %; Cu,

31 %; PPh3 , 64 %

HOMO-1

E, -8.40 eV; L, 87 %; Cu, 8

%; PPh3 , 5 %

HOMO-2

E, -8.53 eV; L, 12 %;

Cu, 34 %; PPh3 , 54 %

LUMO

E, -5.06 eV; L, 96 %; Cu,

3 %; PPh3 , 1 %

[Cu(L)(PPh3)2]ClO4 (2)

Fig. 7. Contour plots of some selected MOs of L

energies along with contributions from the ligands and metal aregiven in the supplementary material and Fig. 7 which depicts se-lected occupied and unoccupied frontier orbitals.

The HOMO � 1 is constituted by >85% contribution from Lwhereas HOMO is contributed 60% from PPh3 and 20% from metalion in the complexes. The LUMO, LUMO + 1, LUMO + 2 are com-posed of L function (>80%). Thus, HOMO ? LUMO is consideredas major transition which is M(dp)/PPh3 ? L(p⁄) transition. Theother transitions are HOMO � 1 ? LUMO [L(p) ? L(p⁄)] andHOMO � 2 ? LUMO [M(dp)/PPh3 ? L(p⁄)] that is intraligand andligand to ligand charge transfer transitions are also observed.

In the free ligand the electronic transition at 331 is n ? p⁄

(HOMO � 2 ? LUMO) while at 328, 324.6, 286.9 nm are p ? p⁄

those are ascribed to HOMO ? LUMO + 1, HOMO/HOMO -1 ? LUMO. Solvent polarity stabilizes occupied MOs more effi-ciently than unoccupied MOs. Thus, the energy separation (DE)between HOMO and LUMO are increasing on going from gas phaseto MeCN phase. The occupied MOs are significantly contributedfrom metal (>30% of 2 and >20% of 4). Triphenyl phosphine contrib-utes 64% to HOMO and 54% to HOMO � 2 but only 1% to LUMO incomplex 2 whereas 72% to HOMO and 69% to HOMO � 2 but only2% to LUMO in 4. The chelating ligand L, in general, is main constit-uent of unoccupied MOs: LUMO, LUMO + 1, LUMO + 2 (2: LUMO toLUMO + 2, 96–98% and 4: LUMO to LUMO + 2, 92–98%). The calcu-lated transitions are grouped in Table 6. The intensity of these tran-sitions has been assessed from oscillator strength (f) (Table 6). InMeCN the longest wavelength band calculated at >481 nm (f,

LUMO

E, -2.05 eV

LUMO+1

E, -1.84 eV

HOMO

E, -8.12 eV ; L, 4 %; Ag,

24 %; PPh3 , 72 %

HOMO-1

E,-8.48eV; L, 92 %; Ag,

2 %; PPh3 , 6 %

HOMO-2

E, -8.58 eV ; L, 10 %;

Ag, 21 %; PPh3, 69 %

LUMO

E, -5.07 eV; L, 96 %;

Ag, 2 %; PPh3 , 2 %

[Ag(L)(PPh3)2]NO3(4)

, [Cu(L)(PPh3)2]ClO4 and [Ag(L)(PPh3)2]NO3.

Table 6Selected electronic excitation for L, [Cu(L)(PPh3)2]ClO4 (2) and [Ag(L)(PPh3)2]NO3 (4) MLCT = M(dp) ? L(p⁄); ILCT = L(p) ? L(p⁄) and LLCT = PPh3 ? L(p⁄) transitions.

k (nm) f Key transition Character AssignmentL331.0 0.2817 (46%)HOMO � 2 ? LUMO n ? p⁄ ILCT328.9 0.1418 (70%)HOMO ? LUMO + 1 p ? p⁄ ILCT324.6 0.5398 (47%)HOMO ? LUMO p ? p⁄ ILCT286.9 0.4945 (81%)HOMO � 1 ? LUMO p ? p⁄ ILCT

[Cu(L)(PPh3)2]ClO4 (2)455.2 0.0368 (88%)HOMO ? LUMO Cu(dp)/PPh3 ? L(p⁄) MLCT, LLCT445.6 0.0333 (70%)HOMO � 2 ? LUMO Cu(dp)/PPh3 ? L(p⁄) MLCT, LLCT369.0 0.3820 (68%)HOMO � 3 ? LUMO Cu(dp)/PPh3 ? L(p⁄) MLCT, LLCT343.9 0.0254 (38%)HOMO�15 ? LUMO L(p) ? L(p⁄) ILCT, LLCT

(22%)HOMO � 12 ? LUMO L(p)/PPh3 ? L(p⁄)325.4 0.0791 (77%)HOMO � 1 ? LUMO + 1 L(p) ? L(p⁄) ILCT317.6 0.0556 (48%)HOMO � 9 ? LUMO L(p)/PPh3 ? L(p⁄) ILCT, LLCT

(21%)HOMO � 10 ? LUMO

[Ag(L)(PPh3)2]NO3 (4)456.9 0.0684 (95%)HOMO ? LUMO Ag(dp)/PPh3 ? L(p⁄) MLCT, LLCT386.4 0. 2953 (77%)HOMO � 1 ? LUMO L(p) ? L(p⁄) ILCT377.3 0. 0486 (65%)HOMO � 2 ? LUMO Ag(dp)/PPh3 ? L(p⁄) MLCT, LLCT339.8 0.2323 (38%)HOMO � 8 ? LUMO L(p)/PPh3 ? L(p⁄) ILCT, LLCT

(35%)HOMO � 6 ? LUMO PPh3 ? L(p⁄)303.1 0.0272 (45%)HOMO � 1 ? LUMO + 1 L(p)/PPh3 ? L(p⁄) ILCT, LLCT

(28%)HOMO � 9 ? LUMO302.5 0.0506 (42%)HOMO � 9 ? LUMO PPh3 ? L(p⁄) ILCT, LLCT

(34%)HOMO � 8 ? LUMO L(p)/PPh3 ? L(p⁄)301.1 0.0710 (51%)HOMO � 10 ? LUMO L(p)/PPh3 ? L(p⁄) ILCT, LLCT,

MLCT(23%)HOMO � 2 ? LUMO + 1 Ag(dp)/PPh3 ? L(p⁄)

S. Roy et al. / Polyhedron 30 (2011) 913–922 921

0.0768) for 2 followed by transitions at 455, 445 along with largenumber of transitions in UV region (<400 nm). In 4 the calculatedtransitions are 457 (f, 0.0684), 386 (f, 0.2953), and 377 (f,0.0486) nm. The observed transitions (Fig 3 and Table 2) are moreor less closer to the calculated one in both the complexes. Thecharge transfer may not be assigned only to pure MLCT ratheradmixture of d(M) ? ⁄(L) and (PPh3) ? ⁄(L) transitions involvingHOMO/HOMO � 2/HOMO � 3 ? LUMO (in complex 2) andHOMO/HOMO � 2 ? LUMO (in complex 4).

Cyclic voltammetric behavior are readily accountable from DFTcalculation. Because of higher metal (Cu) function in occupied MOsthe complexes show metal oxidation which is observed indeed.Unoccupied MOs are significantly dominated by diimine function(>90%), thus reduction may refer to electron accommodation at dii-mine dominated orbital of the ligand. So the assignment, diiminereductions are justified.

5. Conclusion

Copper(I) and silver(I) complexes of N-[(2-pyridyl)methyliden]-6-coumarin (L) and with co-ligand PPh3 are prepared and charac-terized by spectroscopic techniques. The complexes of formula,[M(L)2](X) (M = Cu, Ag and X = ClO4, NO3), [Ag(L)(PPh3)2]NO3 and[Cu(L)(PPh3)2]ClO4 are reported in this work. In case of[Ag(L)(PPh3)2]NO3 and [Cu(L)(PPh3)2]ClO4, the structures havebeen confirmed by X-ray crystallography. The structure of thecomplex is distorted tetrahedral in which the coumarin ligandcoordinates in a bidentate fashion and other two coordination sitesare occupied by PPh3. The ligand and the complexes are fluorescentand the quantum yield of [M(L)(PPh3)2]+ are higher than [M(L)2]+.Cu(I) complexes show Cu(II)/Cu(I) quasireversible couple whileAg(I) complexes exhibit deposition of Ag(0) on the electrode sur-face during cyclic voltammetric experiments.

Acknowledgements

Financial support from CSIR and UGC, New Delhi, are thankfullyacknowledged. Thanks to Prof. Nitin Chattopadhyay, Departmentof Chemistry, Jadavpur University for lifetime study.

Appendix A. Supplementary data

CCDC 794830 and 794829 contain the supplementary crystallo-graphic data for [Cu(L)(PPh3)2]ClO4 (2) and [Ag(L)(PPh3)2]NO3 (4).These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge CrystallographicData Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementarydata associated with this article can be found, in the online version,at doi:10.1016/j.poly.2010.12.037.

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