Inorganica Chimica Acta 395 (2013) 1–10

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Inorganica Chimica Acta

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Three new 1D Cu(II) coordination polymers and a binuclear Cu(II) complexof two pyrazole derived Schiff base ligands: Heterocyclic ring substitutionand anion dependent structural variations – Spectral studies

Saugata Konar a, Atanu Jana a, Kinsuk Das b, Sangita Ray a, Sudipta Chatterjee c, Susanta Kumar Kar a,⇑a Department of Chemistry, University College of Science, University of Calcutta, 92 A.P.C. Road, Kolkata 700009, Indiab Department of Chemistry, Haldia Government College, Debhog, Purba Midnapur 721657, Indiac Department of Chemistry, Serampore College, Serampore, Hooghly 712201, India

a r t i c l e i n f o

Article history:Received 12 June 2012Received in revised form 27 September 2012Accepted 5 October 2012Available online 1 November 2012

Keywords:Copper(II) 1D coordination polymersPyrazole derived Schiff base ligandsX-ray crystal structuresElectrochemistrySpectral studies

0020-1693/$ - see front matter � 2012 Elsevier B.V. Ahttp://dx.doi.org/10.1016/j.ica.2012.10.013

⇑ Corresponding author. Tel.: +91 033 23508386; faE-mail address: skkar_cu@yahoo.co.in (S.K. Kar).

a b s t r a c t

Three new zig-zag 1D coordination polymers and a binuclear complex of Cu(II) involving pyrazole basedtri- and pentadentate schiff base ligands (Z)-2-(2-(5-methyl-1H-pyrazole-3-carbonyl)hydrazono)-2-phenylacetic acid (L01) and (Z)-2-(2-(5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbonyl)hydrazono)-2-phenylacetic acid (L02) are reported in this work. The ligand precursors L1 and L2 have been transformedinto L1

0 and L20 during the course of reaction with metal ions in which the ester groups have been chan-

ged to carboxylate group. The 1D coordination polymers, namely, [Cu(L01)(ClO4)2(H2O)]n (1), [Cu(L02)(-ClO4)]n (3), [Cu(L02)(NO3)]n (4) and a binuclear complex [Cu2(L01)2Cl2] (2) have been synthesized. Thecomplexes 1–3 are of distorted octahedral geometry and the complex 2 is distorted square pyramidal.Interestingly, these structural variations are dependent on counterions and substituent on the pyrazolering. These have been characterized by elemental analyses, UV, IR, single crystal X-ray diffraction, elec-trochemical and photoluminescence studies. L01 serves as tridentate NNO donor where pyrazole nitro-gen, azomethine nitrogen and ligand carboxylate group are coordinatively active, leaving the carbonyloxygen of carbohydrazide part inactive. The same situation (coordination modes) arises in anotherpentadentate NNNOO donor L02 where extra pyridine nitrogen is coordinated. The complexes 3 and 4have considerable fluorescence emission while the rest of the complexes and the ligand molecules arefluorescent silent.

� 2012 Elsevier B.V. All rights reserved.

1. Introduction

Inorganic chemists have shown interest in synthesizing coordi-nation complexes of Schiff base ligands because of their wideapplicability in catalysis, in designing molecular ferromagnets, inbiological modeling as liquid crystals and as heterogeneous cata-lysts [1–7]. It is well known that the careful selection of the organicligands is one of the key factors for the synthesis of the coordina-tion compounds with novel structures. The synthesis and investi-gation of new coordination polymers have been of great interestin the fields of crystal engineering and coordination chemistry be-cause of their potential applications and intriguing architecturesand topologies [8–11]. Over the last two decades, numerousspectacular coordination polymers have been reported, such as1D-chains and ladders, 2D grids, and 3D microporous networks[12–17]. The selection of bridging ligand is one of the key stepsfor these types of syntheses. It is known that rigid ligands may

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x: +91 033 23519755.

allow a controllable growth of the crystal structure [18], whereasflexible ligands are rather used for the formation of coordinationpolymers [19–23]. The 1D chain like complexes is certainly thesimplest topological type of coordination array to be studiedextensively. As a type of multidentate ligands containing N, O do-nors, the pyrazole carbohydrazide derived ligands have attractedmuch attention and have been widely used to construct polynu-clear metal complexes with interesting structural motifs. It is wellknown that the carboxylate group (O@C–O) can function as abridge to bind two metal ions through the oxygen atoms, whichcan coordinate with metal ions in versatile ways.

Herein, we report the syntheses, spectroscopic and electro-chemical properties of the complexes 1–4. With the aim of inves-tigating versatility of Schiff base ligand in coordination chemistryand further research on the supramolecular polymer chemistry,we have designed and synthesized successfully 1D zig-zag coordi-nation polymers with carboxylate group acting as bridge. Moreinterestingly, the structural versatility depends on the counterionsand the presence of substituent in the pyrazole ring.

2 S. Konar et al. / Inorganica Chimica Acta 395 (2013) 1–10

2. Experimental

2.1. Materials

All chemicals were of reagent grade, purchased from commer-cial sources and used without further purification. Tetraethylammonium perchlorate (TEAP) used for electrochemical workwas prepared as reported in the literature [24]. Methyl benzoyl for-mate (98%) was purchased from Aldrich chemical company, USAand used without further purification.

Caution! Although we have not encountered any problem, itshould be kept in mind that perchlorate compounds of metal ionsare potentially explosive in the presence of organic ligands. Only asmall amount of the material should be prepared and it should behandled with care.

2.2. Physical measurements

Elemental analyses (carbon, hydrogen and nitrogen) of the li-gand and metal complexes were determined with a Perkin–ElmerCHN analyzer 2400 at the Indian Association for the Cultivationof Science, Kolkata. The mass spectrum of the ligand was done atIndian institute of Chemical Biology, Kolkata with a JEOLJMS-AX500 MASS spectrophotometer. The electronic spectra of the com-plexes were recorded on a Hitachi model U-3501 spectrophotom-eter. IR spectra (KBr pellet, 500–4000 cm�1) were recorded on aPerkin–Elmer model 883 infrared spectrophotometer. Electro-chemical measurements were carried out using a computer con-trolled AUTOLAB (model: 263A VERSASTAT) electrochemicalsystem with glassy carbon as working electrode, Pt-wire as counterelectrode and saturated calomel as reference electrode. The fluo-rescence spectra were recorded on a Perkin Elmer LS 50Bfluorimeter.

2.3. Syntheses of the ligand precursors (L1 and L2)

The two ligand precursors L1 and L2 were synthesized in asimilar way by refluxing a methanolic solution (30 ml) of5-methylpyrazole-3-carbohydrazide [25] (1.40 g, 10 mmol) and5-methyl-1-(2-pyridyl)pyrazole-3-carbohydrazide [26] (2.17 g,

Scheme 1. Synthetic scheme of lig

10 mmol), respectively, with methyl benzoyl formate (1.64 g,10 mmol), also taken in methanol (10 ml) (Scheme 1). Reflux wascontinued for ca. 4 h at water bath temperature. After slow evapo-ration of the respective reaction mixture a solid microcrystallinecompound separated. It was filtered off, washed several times withcold methanol and dried in vacuo over fused CaCl2. Single crystal ofL1, suitable for X-ray diffraction was obtained by slow evaporationof the respective methanolic solution of the ligand.

L1: (Yield: 69.30%); M.p. (�C) 138; Anal. Calc. for C14H14N4O3: C,56.68; H, 4.89; N, 19.56. Found: C, 56.53; H, 4.71; N, 19.77%. IR(KBr, cm�1): 1705 (COOMe mC@O), 1436(pz mC@N), 1199 (COOMemC–O), 1127 (pz mN@N), 3272 (mN–H), m/z 286.1 (M+, 100%). 1H NMR(in d6-DMSO, d): 13.25(s, 1NH, ring Pz), 13.10(s, 1H, –CONH),7.63–7.37(m, 5H, ring Ph), 6.57(s, 1H, ring Pz), 3.83(s, 3H, –COOCH3), 2.27(s, 3H, –CH3). UV–Vis (DMF): kmax/nm = 277 and 357.

L2: (Yield: 56.50%); M.p. (�C) 142; Anal. Calc. for C19H17N5O3: C,62.80; H, 4.68; N, 19.28. Found: C, 62.64; H, 4.51; N, 19.39%. IR(KBr, cm�1): 1589 (py mC@N), 1436(pz mC@N), 1709 (COOMe mC@O),1167 (pz mN@N), 1212 (COOMe mC–O), m/z 363.1 (M+, 100%). 1HNMR (in d6-DMSO, d): 13.10(s, 1NH, –CONH), 8.56–7.39(m, 9H,rings Py and Pz), 6.88(s, 1H, ring Pz), 3.87(s, 3H, –COOCH3),2.61(s, 3H, –CH3). UV–Vis (DMF): kmax/nm = 285 and 351.

2.4. Preparation of complexes

2.4.1. Preparation of [Cu(L01)(ClO4)2(H2O)]n(1)A methanolic solution (10 ml) of Cu(ClO4)2�6H2O (0.740 g,

2 mmol) was added dropwise to a solution of L1 (0.572 g, 2 mmol)in the same solvent (15 ml) taken in 1:1 M ratio with constant stir-ring for 2 h. It was left for slow evaporation at room temperature.After 2 weeks X-ray quality crystals of 1 were separated out andthey were collected by usual technique. (Yield: 55.5%). Anal. Calc.for C13H13ClCuN4O8: C, 34.49; H, 2.87; N, 12.38. Found: C, 34.27;H, 2.71; N, 12.29%. IR (KBr, cm�1): 1448 (pz mC@N), 1670 (–COOmC@O), 1086 (m of ClO4

� coordinated),1265 (–COO mC–O), 3191(m of H2O coordinated). UV–Vis (DMF): kmax/nm = 396 and 718.

2.4.2. Preparation of [Cu2(L01)2Cl2](2)Complexes 2 was prepared following the same synthetic proce-

dure as that of 1 using CuCl2�6H2O as metal salt. (Yield: 49.2%).

ands (L1 and L2) preparation.

S. Konar et al. / Inorganica Chimica Acta 395 (2013) 1–10 3

Anal. Calc. for C26H22Cl2Cu2N8O6: C, 42.13; H, 2.97; N, 15.12. Found:C, 41.98; H, 2.88; N, 15.02%. IR (KBr, cm�1): 1435 (pz mC@N), 1674(–COO mC@O), 1107 (pz mN@N), 1253 (–COO mC–O). UV–Vis (DMF):kmax/nm = 372 and 644.

2.4.3. Preparation of [Cu(L02)(ClO4)]n (3)A methanolic solution (10 ml) of Cu(ClO4)2�6H2O (0.740 g,

2 mmol) was added dropwise to a solution of L2 (0.726 g, 2 mmol)in the same solvent (15 ml) taken in 1:1 M ratio with constant stir-ring for 2 h. It was left for slow evaporation at room temperature.After 2 weeks X-ray quality crystals of 3 were separated out andthey were collected by usual technique. (Yield: 68.5%). Anal. Calc.for C18H14ClCuN5O7: C, 32.83; H, 3.78; N, 17.66. Found: C, 32.78;H, 3.74; N, 17.64%. IR (KBr, cm�1): 1441 (pz mC@N), 1658 (mC@O of–COO), 1089 (m of coordinated ClO4

�), 1531 (py mC@N). UV–Vis(DMF): kmax/nm = 373 and 706.

2.4.4. Preparation of [Cu(L02)(NO3)]n (4)Complexes 4 was prepared following the same synthetic proce-

dure as that of 3 using Cu(NO3)2�6H2O as metal salt. (Yield: 62.5%).Anal. Calc. for C17H14CuN7O6: C, 42.86; H, 2.94; N, 20.59. Found: C,42.78; H, 2.83; N, 20.50%. IR (KBr, cm�1): 1528 (py mC@N)1441 (pzmC@N), 1639 (mC@O), 1319 (m of NO3

�), 1669 (mC@O of –COO). UV–Vis (DMF): kmax/nm = 377 and 717.

3. Crystallographic measurements

The crystallographic data for L1 and complexes 1–4 are summa-rized in Table 1 and selected metrical parameters of these com-plexes are given in Table 2. Diffraction data were collected on aBruker-APEX II SMART CCD diffractometer at 296 K (for L1), 150 K(for 1, 2 and 3) and 293 K (for 4) using graphite-monochromated

Table 1Experimental data for crystallographic analysis of ligand L1, 1, 2, 3 and 4.

Compound Ligand L1 1

Empirical formula C14H14N4O3 C13H13ClCuN4O8

Formula weight 286.29 452.27T (K) 296(2) 150(2)k (Å) 0.71073 0.71073Crystal system monoclinic orthorhombicSpace group P21/n IcabUnit cell dimensionsa (Å) 9.2653(4) 12.6415(16)b (Å) 12.7937(6) 21.044(3)c (Å) 12.3970(5) 28.970(4)a (�) 90.00 90.00b (�) 97.675(2) 90.00c (�) 90.00 90.00V (Å3) 1456.34(11) 7706.8(18)z 4 16Dcalc (Mg cm�3) 1.306 1.559Absorption coefficient (mm�1) 0.095 1.319F(000) 600.0 3664.0h Range (�) for data collection 2.3–28.2 1.4–31.3Index ranges �11 6 h 6 12 �18 6 h 6 17

�16 6 k 6 16 �29 6 k 6 30�15 6 l 6 16 �38 6 l 6 42

Goodness-of-fit on F2 1.231 1.068Independent reflections [Rint] 3560 [0.030] 6268[0.036]Absorption correction empirical empiricalRefinement method full-matrix least

squares on F2full-matrix leastsquares on F2

Data/restraints/parameters 3560/0/220 6268/0/261Reflections collected 21867 64636Final R indices [I > 2r(I)] R = 0.0455,

WR2 = 0.1663R = 0.0434,WR2 = 0.1260

Largest difference in peak andhole (e �3)

�0.20, 0.19 �0.71, 0.89

Mo Ka radiation (k = 0.71073 Å). Cell parameter refinement anddata reduction were carried out using Bruker SMART [27] and BrukerSAINT softwares for all the complexes. The structures were solved bydirect and Fourier methods and refined by full-matrix least-squares based on F2 using the SHELXS-97 and SHELXL-97 programs[28]. In L1 and complexes 1–4, non hydrogen atoms were refinedanisotropically till the convergence is attained. SQUEEZE within PLA-

TON [29] was used to remove the contribution of the disordered sol-vent molecule for Complexes 1 and 2. For Complex 1 the squeezedvolume was 260 Å3 and contribution of number of electron re-moved in the squeezed volume was 94 and for Complex 2 it is17 Å3 and 2 respectively. All the N–H bond distances are kept fixedat 0.87 Å using DFIX instruction.

4. Result and discussion

4.1. Syntheses

The ligand precursors L1 and L2 were synthesized by the directcondensation reaction of methyl benzoyl formate with 5-methylpyrazole-3-carbohydrazide and 5-methyl-1-(2-pyridyl) pyrazole-3-carbohydrazide respectively, taken in methanol in a 1:1 mol pro-portion. The ligands L1

0 and L20 were generated in situ by treatment

of ligand precursors L1 and L2 with Cu(II) salts. During complex for-mation the ester group (–COOMe) of each precursor has beenhydrolysed to carboxylic acid group. The complexation behaviorof the ligands (L01 and L02) generated in situ towards Cu(II) saltswere investigated. The ligand precursors L1 and L2 and theircomplexes 1–4 were characterized by X-ray crystallographically,elemental analyses, spectral studies, electrochemical and photolu-minescence studies.

2 3 4

C26H22Cl2Cu2N8O6 C18 H14 Cl Cu N5 O7 C18 H14 Cu N6 O6740.52 511.34 473.90150(2) 150(2) 293(2)0.71073 0.7103 0.71073orthorhombic monoclinic monoclinicPbca P21/c P21/n

16.524(4) 14.611(6) 15.0825(6)7.958(2) 15.551(6) 8.2354(3)21.913(4) 8.837(4) 15.4752(7)90.00 90 90.0090.00 102.36(1) 107.587(2)90.00 90 90.002881.5(11) 1961.4(14) 2357.2(16)4 4 41.707 1.732 1.7181.719 1.305 1.2461496 1036 964.01.9–25.7 1.4–24.5 1.6–29.6�20 6 h- 6 20 �15 6 h 6 16 �20 6 h 6 19�9 6 k 6 9 �18 6 k 6 17 �10 6 k 6 11�26 6 l 6 26 �9 6 l 6 10 �21 6 l 6 211.138 1.012 0.9362729[0.057] 3219[0.071] 5121 [0.032]empirical empirical empiricalfull-matrix leastsquares on F2

full-matrix leastsquares on F2

full-matrix leastsquares on F2

2729/0/208 3219/0/290 5121/0/2819863 8647 24612R = 0.0587,WR2 = 0.1497

R = 0.0596,WR2 = 0.1770

R = 0.0323,WR2 = 0.1150

�0.34, 1.00 �0.79,0.56 �0.45,0.35

Fig. 1. Molecular structure of free ligand L1.

Table 3Details of hydrogen bond distances (Å) and angles (o) for complexes.

D–H� � �A d(D–H) d(H� � �A) d(D� � �A) <(DHA)L1

N1–H1� � �O1 0.8600 2.2600 2.9669(15) 139.00N3–H4� � �O2 0.912(18) 1.995(17) 2.6648(15) 129.0(14)

Complex 1N1–H1N� � �O4 0.75(3) 2.48(3) 2.886(2) 116(3)N3–H3N� � �O1 0.84(3) 2.15(3) 2.959(2) 161(2)O4–H4B� � �O2 0.81(4) 1.90(3) 2.656(2) 155(4)

Complex 2N2–H2N� � �O2 0.66(7) 2.24(7) 2.824(8) 149(8)N3–H3N� � �O3 0.72(7) 2.39(6) 3.036(8) 151(6)

Complex 3N4–H4N� � �O1 0.8800 2.1800 2.967(7) 148.00

Complex 4N4–H4� � �O1 0.8600 2.2000 3.0221(19) 160.00

Fig. 2. The molecular structure of complex 1 (asymmetric unit has to be labeled andH-atoms are omitted for clarity).

Table 2Selected bond distances (Å) and angles (�) in L1 and 1–4.

Selected bonds Value (Å) Selected angles (�)

L1

C(7)–O(2) 1.2056(17)C(7)–O(3) 1.3149(18)C(6)–N(4) 1.2873(16)C(5)–O(1) 1.2155(15)C(5)–N(3) 1.3713(16)N(3)–N(4) 1.3577(15)

Complex 1Cu1–O2 1.9152(15) O2–Cu1–O4 95.83(7)Cu1–O4 1.9486(16) O2–Cu1–O5 88.35(8)Cu1–O5 2.550(3) O2–Cu1–N2 173.01(6)Cu1–N2 1.9282(15) O2–Cu1–N4 82.29(6)Cu1–N4 1.9897(15) O2–Cu1–O8_a 91.74(7)Cu1–O8_a 2.514(2) O4–Cu1–O5 93.88(9)

O4–Cu1–N2 91.03(7)O2–Cu1–N4 175.22(7)O4–Cu1–O8_a 83.94(8)O5–Cu1–N2 89.82(8)O5–Cu1–N4 90.47(9)O5–Cu1–O8_a 177.82(10)N2–Cu1–N4 90.98(6)O8_a–Cu1–N2 90.34(7)O8_a–Cu1–N4 91.70(7)

Complex 2Cu1–Cl1 2.3168(19) Cl1–Cu1–O2 93.05(15)Cu1–O2 1.895(5) Cl1–Cu1–N1 95.27(15)Cu1–N1 1.921(5) Cl1–Cu1–N4 147.58(16)Cu1–N4 2.025(5) O2–Cu1–N1 171.5(2)Cu1–Cl1_a 2.5857(19) O2–Cu1–N4 82.3(2)Cd(1)–O(2) 2.302(2) Cl1_a–Cu1–O2 89.62(15)Cd(1)–O(2)_a 2.302(2) N1–Cu1–N4 89.7(2)C(4)–N(2) 1.286(3) Cl1_a–Cu1–N1 91.96(16)C(6)–O(1) 1.230(3) Cl1_a–Cu1–N4 121.22(16)

Cu1–Cl1–Cu1_a 89.34(6)Cl1–Cu–Cl1_a 90.66(6)

Complex 3Cu1–O2 1.897(4) O2–Cu1–O5 97.84(19)Cu1–O5 2.783(6) O2–Cu1–N1 104.6(2)Cu1–N1 1.979(6) O2–Cu1–N3 173.5(2)Cu1–N3 1.880(5) O2–Cu1–N5 85.02(19)Cu1–N5 1.963(5) O2–Cu1–O3_a 93.88(17)Cu1–O3_a 2.462(5) O5–Cu1–N1 79.42(19)

N1–Cu1–N3 80.3(2)N3–Cu1–N5 89.52(19)O3_a–Cu1–N5 79.53(17)N1–Cu1–N5 167.5(2)O3_a–Cu1–O5 164.57(17)

Complex 4Cu01–O2 1.9024(12) O2–Cu01–N1 105.87(6)Cu01–O4 2.4114(16) O2–Cu01–N5 84.80(5)Cu01–N1 2.0138(16) O2–Cu01–O3_b 88.44(5)Cu01–N3 1.8874(13) O3_b–Cu01–O4 173.59(5)Cu01–N5 1.9789(16) N1–Cu01–N3 79.84(6)Cu01–O3_b 2.6380(14) N3–Cu01–N5 89.14(6)

O2–Cu01–N1 105.87(6)O2–Cu01–N3 172.04(6)N1–Cu01–N5 168.53(6)

Symmetric transformation used to generate equivalent atoms: a = [15455.00] = �1/2 + x, 1/2 � y, z for 1, a = [5755.00] = 2 � x, �y, �z for 2, a = [4554.00] = x, 1/2 � y,�1/2 + z for 3, b = [2656.00] = 3/2 � x, 1/2 + y, 3/2 � z for 4.

4 S. Konar et al. / Inorganica Chimica Acta 395 (2013) 1–10

4.2. Structural description

4.2.1. Structural description of ligand precursor L1

Perspective view of the ligand precursor L1 with atom number-ing scheme is shown in Fig. 1 and selected geometrical parametersare listed in Table 2. The structure of L1 (Fig. 1) shows that the pyr-azole nitrogen atom N2, azomethine nitrogen atom N4 and the li-gand oxygen atom O2 are cis oriented to each other. Uponchelation of the ligand, the above donor atoms are also arranged

in a cis-fashion toward the metal center. The cis conformation ofthe ligand is necessary for its participation as a tridentate NNOchelate ligand in the deprotonated form. The packing of L1 is stabi-lized through a network of hydrogen bonding and details of thehydrogen bonds are given in Table 3.

4.2.2. Structural description of [Cu(L01)(ClO4)2(H2O)]n (1)The molecular structure of the complex 1 is shown in Fig. 2 and

selected bond lengths and bond angles are listed in Table 2. Theunit cell comprises of sixteen molecules. The structure of complex

S. Konar et al. / Inorganica Chimica Acta 395 (2013) 1–10 5

1 consists of a quasi-one dimensional zig-zag infinite chain (alongc-axis) with the repeating unit [Cu(L01)(H2O)]+ bridged by perchlo-rate ions. The coordination environment around the central Cu(II)ion in complex 1 is distorted octahedral, with N2O4 chromophore.The equatorial plane is formed by a by one pyrazole ring nitrogenN2, one azomethine nitrogen N4, one water oxygen O4 and an car-boxylate oxygen atom O2 of the same ligand molecule and the ax-ial positions are occupied by oxygen atoms O5 and O8 of differentperchlorate ions lying above and below the equatorial plane. Theoxygen atom O8 of a perchlorate ion again binds the second Cu(II)ion resulting the propagation of the 1D chain. The copper–copperrepeating distance is 6.482 Å along the chain. The distorted octahe-dral arrangement around the copper(II) produce the equatorialbond distances of Cu1–N4 1.9897(15), Cu1–N2 1.9282(15),

Fig. 3. 2D view of 1D coordination polymers in 1 with tra

Fig. 4. The molecular structure of complex 2 (asymmetric un

Cu1–O2 1.9152(15) and Cu1–O4 1.9486(16) Å and Cu–O axial bonddistances of 2.550(3) and 2.514(2) Å. The chelate bite angles varybetween 90.98� and 95.83�. The 2D view along b-axis is shown inFig. 3. The crystal packing is stabilized by intermolecular H-bonddetailed in Table 3.

4.2.3. Structural description of [Cu2(L01)2Cl2] (2)A view of the crystal structure with atom-numbering scheme is

shown in Fig. 4 and selected bond lengths and angles are listed inTable 2. The geometry around each Cu(II) ion exhibit trigonal bipy-ramidal as the bond angle between the axial positions is 171�,additionally the three angles in the equatorial plane (Cl1, Cl1aand N4) add up to 359.5�, so these atoms are lying in the planeperfectly. Complex 2 consists of dichloro-bridged dimeric {Cu(L01)

pped water molecules within the layers along b-axis.

it has to be labeled and H-atoms are omitted for clarity).

6 S. Konar et al. / Inorganica Chimica Acta 395 (2013) 1–10

(l-Cl)}2 unit in which each Cu(II) center is coordinated by a N2OCl2

chromophore. There are two five-coordinate copper(II) centers,each of which is bonded to a tridentate NNO ligand L01 and theremaining coordination sites on each metal are occupied by twobridging chloride ligands. The basal plane is formed by one pyra-zole N atom, one azomethine N atom, one carboxylate O atomand one Cl atom and apical position is occupied by another Cl atomwith Cu–N 1.921(5) and 2.205 (5) Å, Cu–O 1.895 (5) Å, Cu–Cl 2.316(19) Å and axial Cu–Cl 2.586 (2) Å. The equatorial Cu(1)–N[1.921(5) Å and 2.025(5) Å], Cu(1)–O [1.895(5) Å] and Cu(1)–Cl[2.316(19) Å] bond distances are observed in complex 2, the axialCu(1)–Cl bond distance of 2.586(2) Å. The environment aroundeach copper(II) center may be described as a distorted square pyra-midal with the ligand–metal–ligand bite angles varying between

Fig. 5. H bonding in

Fig. 6. The molecular structure of complex 3 (asymmetric un

82.32� and 93.05�. In 2, there are two types of intramolecularand intermolecular hydrogen bonds detailed in Table 3 (Fig. 5).

4.2.4. Structural description of [Cu(L02)(ClO4)]n and [Cu(L02)(NO3)]n (3)and (4)

The representative structures of the asymmetric unit of 3 and 4are shown in Figs. 6 and 7 respectively; selected bond lengths andbond angles are listed in Table 2. The overall geometry around eachCu(II) center can be described as a pseudo octahedral with N3O3

chromophore. For 3 and 4, three nitrogen atoms from N1 of pyri-dine, N3 of pyrazole and N5 of azomethine one and one carboxyl-ate O atom (O2) form equatorial planes and two oxygen atomsfrom another ligand molecule and from a perchlorate ion for 3and a nitrate ion for 4 are in axial positions. The metal atoms in

teraction in 2.

it has to be labeled and H-atoms are omitted for clarity).

S. Konar et al. / Inorganica Chimica Acta 395 (2013) 1–10 7

both cases are little deviated from these equatorial planes. The api-cal atoms in 3 and 4 make 164.6(2)� and 173.59(5)� angles with theCu(II) centers, respectively. The Cu-Cu repeating distance is 5.340 Åfor 3 and 6.104 Å for 4. The equatorial angles are in average 89.85�for 3 and 89.91� for 4. The H bonding interactions are detailed inTable 3 and 2D view of trapped perchlorate and nitrate ions (along‘b’ and ‘a’ axes) within the layers are shown in Figs. 8 and 9.

Fig. 7. The molecular structure of complex 4 (asymmetric un

Fig. 8. 2D view of 1D coordination polymers in 3 with tra

4.3. Electrochemistry

Electrochemical properties of complexes 1–4 have been studiedin HPLC grade DMF with scan rate of 50 mV s�1. Complex 1 and 2exhibit only oxidation response in anodic scan, in which an irre-versible nature is noted at 0.465 and 0.467 V, respectively whichmay be ascribed to a Cu(II) ? Cu(III) oxidation (Figs. 10 and 11).

it has to be labeled and H-atoms are omitted for clarity).

pped perchlorate ions within the layers along b-axis.

Fig. 9. 2D view of 1D coordination polymers in 4 with trapped nitrate ions within the layers along a-axis.

Fig. 10. Cyclic voltammogram of 1.

Fig. 11. Cyclic voltammogram of 2.

8 S. Konar et al. / Inorganica Chimica Acta 395 (2013) 1–10

In cathodic scan of complex 3, a reversible nature is noted forCu(II)/Cu(I) process at �1.02 V and Cu(I)/Cu(II) process at �0.67 V(Fig. 12). The complex 4 exhibits no oxidation response. However,in cathodic scan of complex 4 an irreversible reduction couple at�1.06 V is ascribed to a Cu(II) ? Cu(I) reduction (Fig. 13).

4.4. Electronic spectroscopy

The electronic absorption spectrum of the ligand precursors L1

and L2 and their complexes 1–4 were measured in DMF solution.The electronic spectra of the L1 and L2 shows two intraligandcharge transfer (CT) bands at 357 nm, 277 nm and 351, 285 nmrespectively. The complexes 1, 3 and 4 show L ? M charge transferbands in the region 373–396 nm [30–33] and the d–d transitionbands in six coordinate environments with low intensity in the re-gion 706–718 nm range [30–33]. The another complex 2 showsL ? M charge transfer band at 372 nm and d–d band at 644 nm

which is more consistent Cu(II) complex with square pyramidalgeometry [34].

4.5. Emission behavior

The emission properties of L1 and L2 and its complexes werestudied at room temperature (298 K) using 1 � 10�5 M DMF solu-tion (Fig. 14). The L1 and L2 show no considerable fluorescence atkex = 350 nm probably due to the quenching effect from the lonepair of nitrogen atoms. In between these ligands, fluorescenceintensity of L2 is slightly enhanced because of the presence of 1-(2-pyridyl pyrazole) unit which is responsible for emission[35,36]. Complexes of L2 show enhanced fluorescence due to com-plexation which reduces rotation, vibration of free ligand (com-plexes are rigid). In between 3 and 4, the fluorescence intensityof complex 3 is higher than that of 4, due to inherent quenchingability of nitrate ion, so fluorescence efficiency is less comparedto perchlorate complex 3 having no quenching property [37].

Fig. 12. Cyclic voltammogram of 3.

Fig. 13. Cyclic voltammogram of 4.

Fig. 14. Fluorescence properties of the ligands L1 and L2 and its complexes.

S. Konar et al. / Inorganica Chimica Acta 395 (2013) 1–10 9

5. Conclusion

Pyrazole based tri and pentadentate ligands L01 and L02 havebeen used to synthesize 1D zig-zag coordination polymeric and abinuclear Cu(II) complexes (1, 3, 4 and 2) with perchlorate, nitrateand chloride as counterions repectively. The ligands L1

0 and L20 are

generated in situ during the course of reactions of the ligand pre-cursors L1 and L2 with Cu(II) salts where the ester gr (–COOMe)in each case has been hydrolysed to carboxylic acid group. The nat-ure and nuclearity of the final products are controlled by the stericcongestion caused by the presence of substituents in the pyrazolering and the participating counterions. In case of L01, the pyrazolering in its 1-position is unsubstituted, the tridentate ligand formsa binuclear l2-chloro bridged Cu(II) complex 2 with Cl� as counter-ion and a 1D coordination polymer 1 with ClO4

� as counterion. Thepropagation of polymer chain in 1 becomes favorable via oxygenatoms of ClO4

� ion. In case of ligand L02, the pyrazole contains apyridine substituent in its 1-position. The pentadentate ligand(L02) utilizes three nitrogen functions and two oxygen functions

simultaneously. Among the oxygen functions one is used for coor-dinate bond formation with a Cu(II) ion and another bridges toadjacent Cu(II) centers to form 1D coordination polymers withboth the ClO4

� and NO3� salts. In the formation of 1D coordination

polymer the Cu(II) centers are far apart (Cu–Cu distance 5.34–6.48 Å) reducing the steric crowding.The geometry arround theCu(II) centers depend upon the substituent in 1-position of pyra-zole ring, the ligand functionality and plasticty of Cu geometry.

Acknowledgments

Financial support [Sanc. No. 01(2401)/10/EMR-II, dated05.01.2011] from the Council of Scientific and Industrial Research(CSIR), New Delhi, India, is gratefully acknowledged. S.K. and A.Jthank CSIR for award of SRF. X-ray Crystallography was done atthe DST FIST, India-funded Single Crystal Diffractometer Facilityat the Department of Chemistry, University of Calcutta.

Appendix A. Supplementary material

CCDC 864103, 864104, 864105, 864106 and 864107 containsthe supplementary crystallographic data for ligand precursor L1

and 1–4, respectively. These data can be obtained free of chargefrom The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-ated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ica.2012.10.013.

Reference

[1] C.O. Rodriguez de Barbarin, N.A. Bailey, D.E. Fenton, Q.-Y. He, J. Chem. Soc.,Dalton Trans. (1997) 161.

[2] E.J. Larson, V.L. Pecoraro, J. Am. Chem. Soc. 113 (1991) 3810.[3] M.M. Taqui Khan, D. Srinivas, R.I. Kureshi, N.H. Khan, Inorg. Chem. 29 (1990)

2320 (and references therein).[4] H. Miyasaka, H. Ieda, N. Mastumoto, R. Crescenzi, C. Floriani, Inorg. Chem. 387

(1998) 255.[5] I. Ramade, O. Khan, Y. Jennin, F. Robert, Inorg. Chem. 36 (1997) 930.[6] D. Wohrle, Adv. Polym. Sci. 50 (1983) 45.[7] N. Hoshino, Coord. Chem. Rev. 174 (1998) 77.[8] R.-F. Song, Y.-B. Xie, J.-R. Li, X.-H. Bu, CrystEngComm 7 (2005) 249.[9] R. Peng, T. Wu, D. Li, CrystEngComm 7 (2005) 595.

[10] G. Li, Y. Xing, S. Song, N. Xu, X. Liu, Z. Su, J. Solid State Chem. 181 (2008) 2406.[11] H. Yang, X. Meng, Y. Liu, H. Hou, Y. Fan, X. Shen, J. Solid State Chem. 181 (2008)

2178.

10 S. Konar et al. / Inorganica Chimica Acta 395 (2013) 1–10

[12] C.-Q. Zhao, M.C. Jennings, R.J. Puddephatt, J. Inorg. Organomet. Polym. 18(2008) 143.

[13] W.-W. Dong, J. Zhao, L. Xu, J. Solid State Chem. 181 (2008) 1149.[14] Z. Chen, X. Li, F. Liang, J. Solid State Chem. 181 (2008) 2078.[15] H.L. Gao, L. Yi, B. Zhao, X.Q. Zhao, P. Cheng, D.Z. Liao, S.P. Yan, Inorg. Chem. 45

(2006) 5980.[16] B.L. Chen, F.R. Fronczek, A.W. Maverick, Inorg. Chem. 43 (2004) 8209.[17] C.D. Wu, W.B. Lin, Chem. Commun. (2005) 3673.[18] L.P. Wang, X.R. Meng, E.P. Zhang, H.W. Hou, Y.T. Fan, J. Organomet. Chem. 692

(2007) 4367.[19] B.L. Wu, D.Q. Yuan, B.Y. Lou, L. Han, C.P. Liu, C.X. Zhang, M.C. Hong, Inorg.

Chem. 44 (2005) 9175.[20] G. Mahmoudi, A. Morsali, A.D. Hunter, M. Zeller, CrystEngComm 9 (2007)

704.[21] M.G. Amiri, G. Mahmoudi, A. Morsali, A.D. Hunter, M. Zeller, CrystEngComm 9

(2007) 686.[22] G. Mahmoudi, A. Morsali, Polyhedron 27 (2008) 1070.[23] G. Mahmoudi, A. Morsali, L.-G. Zhu, Polyhedron 26 (2007) 2885.[24] D.T. Sawyer, J.L. Roberts, Experimental Electrochemistry for Chemists, Wiley,

New York, 1974. p. 212.[25] N. Saha, K.M. Dutta, J. Inorg. Nucl. Chem. 43 (1981) 1405.

[26] T.N. Mandal, S. Roy, A.K. Barik, S. Gupta, R.J. Butcher, S.K. Kar, Polyhedron 27(2008) 3267.

[27] Bruker, SMART v5.631, Bruker AXS Inc., Madison, WI, USA, 2001.[28] G.M. Sheldrick, SHELXS-97 and SHELXL-97, University of Göttingen, Göttingen,

Germany, 1997.[29] A.L. Spek, PLATON, A Multipurpose Crystallographic Tool, Utrecht University, The

Netherlands, 2008.[30] D. Volkmer, B. Hommerich, K. Griesar, W. Haase, B. Krebs, Inorg. Chem. 35

(1996) 3792.[31] B.K. Singh, N. Bhojak, P. Mishra, B.S. Garg, Spectrochim. Acta, Part A 70 (2008)

758.[32] M. Jiang, Y.-T. Li, Z.-Y. Wu, Z.-Q. Liu, C.-W. Yan, J. Inorg. Biochem. 103 (2009)

833.[33] M. Ciampolini, N. Nardi, Inorg. Chem. 5 (1966) 41.[34] A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Amsterdam, 1984. p.

553.[35] S.-Z. Zhan, D. Li, X.-P. Zhou, X.-H. Zhou, Inorg. Chem. 45 (2006) 9163.[36] S. Gupta, B.K. Paul, A.K. Barik, T.N. Mandal, S. Roy, N. Guchhait, R.J. Butcher, S.K.

Kar, Polyhedron 28 (2009) 3577.[37] J.R. Lakowicz, Priniples of Fluorescence Spectroscopy, third ed., Plenum, New

York, 2006.