Inorganica Chimica Acta 367 (2011) 9–14

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Inorganica Chimica Acta

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Coordination chemistry of two new tetraaza Ni(II) and Cu(II) macrocyclic andtwo new Co(II) and Zn(II) macroacyclic Schiff base complexes containingpiperazine moiety: X-ray crystal structures of Ni(II) and Zn(II) complexes

Hassan Keypour a,⇑, Parisa Arzhangi a, Nasibeh Rahpeyma a, Majid Rezaeivala b, Yalcin Elerman c,Hamid Reza Khavasi d

a Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65174, Iranb Department of Chemical Engineering, Hamedan University of Technology, Hamedan 65155, Iranc Department of Engineering Physics, Faculty of Engineering, University of Ankara, Besevler 06100, Ankara, Turkeyd Department of Chemistry, Shahid Beheshti University, G.C., Evin, Tehran 1983963113, Iran

a r t i c l e i n f o a b s t r a c t

Article history:Received 25 April 2010Received in revised form 4 November 2010Accepted 19 November 2010Available online 4 December 2010

Keywords:Piperazine moietyMacroacyclic Schiff base complexX-ray crystal structureTetraaza macrocycle

0020-1693/$ - see front matter � 2010 Elsevier B.V. Adoi:10.1016/j.ica.2010.11.033

⇑ Corresponding author. Tel.: +98 811 8242044; faxE-mail address: haskey1@yahoo.com (H. Keypour)

A new potentially tetradentate (N4) Schiff base ligand (L), 1,9,12,20-tetraazatetracyclo[18.2.2.02,7.014,19]tetracosa-2(7),3,5,8,12,14(19),15,17-octaene containing a piperazine moiety is described. MacrocyclicSchiff base complexes, [NiL](ClO4)2 (1) and [CuL](ClO4)2 (2) have been obtained from equimolar amountsof ligand (L) with nickel(II) and copper(II) metal ions. While the equilibrium reaction in the presence ofcobalt(II) and zinc(II) metal ions with ligand L in a 1:1 molar ratio yielded the open-chain Schiff basecomplexes, [CoL0](ClO4)2 (3) and [ZnL0](ClO4)2 (4) containing two terminal primary amino groups. Theligand L0 is 1,4-bis(2-(2-aminoethyliminomethyl)phenyl)piperazine. The crystal structures of (1) and(4) have been also determined by X-ray diffraction. It was shown that the Ni(II) is coordinated to theligand L by two nitrogen atoms of piperazine group and two nitrogen atoms of the imine groups, in aslightly distorted square-planar geometry. Also single crystal X-ray analysis of (4) confirmed a distortedoctahedral arrangement in the vicinity of Zn atom with N6 donor set. The spectroscopic characterizationof all complexes is consistent with their crystal structures.

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1. Introduction

The Schiff base ligands are one of the most widely used ligandsdue to the ease of formation and remarkable versatility, and there-fore they have played an important role in the development ofcoordination chemistry as they readily form stable complexes withmost of the transition metals. The research field dealing with Schiffbase metal complexes is very broad due in part to their potentialinterest for a number of interdisciplinary areas that include bioin-organic chemistry, catalysis, and magnetochemistry [1–5]. Pipera-zine is a water soluble cyclic diazine with rigid preorganizedcyclohexane conformation [6]. As an amine, piperazine readilyundergoes nucleophilic substitution reactions with proper halides.The hexaatomic piperazine ring may exhibit a boat or a chair con-formation, the latter one is 17.2 kJ mol�1 more stable [7]. The boatconformation is stabilized when the piperazine ring coordinatesone metal ion through both the nitrogen atoms forming biden-tate–chelate complexes. However, the structural character ofpiperazine causes some rigidity.

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In previous works [8–12] synthesis and characterization ofsome N4 macrocyclic and macroacyclic Schiff base complexes inthe presence of Co(II), Ni(II) and Cu(II) were reported. We have re-cently reported the synthesis and crystal structure study of somenew macrocyclic and macroacyclic Schiff base complexes contain-ing piperazine moiety [13–19]. Herein we report the synthesis andphysical properties of the complexation capability towards Ni(II),Cu(II), Co(II) and Zn(II) transition metal ions with a new 14-mem-bered N4 macrocyclic ligand L having a piperazine moiety (Scheme1). In addition, the X-ray crystal structures of [NiL](ClO4)2 and[ZnL0](ClO4)2 are also described.

2. Experimental

2.1. Starting materials

1,4-Bis(2-formylphenyl)piperazine was obtained according toliterature method [18,20]. All solvents were of reagent grade qual-ity and purchased commercially. Metal salts, piperazine, 2-fluoro-benzaldehyde and 1,2-diaminoethane were obtained from Merckand were used without further purification.

[ML']2+

N

N

N

NM2+

H2N NH2

NH2

H2N

N N

O O

+ M= Co, ZnN N

N N

L

[ML]2+

N N

N N

M2+

M= Ni, Cu

/ Reflux

+

C2 H

5 OH/ Reflux

H2O

CH3CN

Scheme 1. Synthetic pathway followed to obtain complexes.

10 H. Keypour et al. / Inorganica Chimica Acta 367 (2011) 9–14

2.2. Physical measurements

Infrared spectra were collected as liquid films between NaClplates, using a BIO-RAD FTS-40A spectrophotometer (4000–400 cm�1). Electron impact mass spectrum for ligand was recordedon a QP-1100EX Shimadzu GC–MS (EI at 70 eV) spectrometer. FABmass spectra were recorded using a Kratos-MS-50T spectrometerconnected to a DS90 data system using 3-nitrobenzyl alcohol asthe matrix. CHN analyses were carried out using a Perkin–Elmer,CHNS/O elemental analyzer model 2400. Conductance measure-ments were performed using a Hanna HI 8820 conductivity meter.1H and 13C NMR spectra were obtained using a Jeol 90 MHzspectrometer.

2.3. X-ray crystallography

Suitable crystals of 1 and 4 were obtained by slow diffusion ofdiethyl ether vapour into a acetonitrile solution of the appropriatecomplex. The details of the X-ray crystal data and of the structuresolution and refinement are given in Table 1. The X-ray diffractionmeasurements were made on a STOE IPDS-G diffractometer withgraphite monochromated Mo Ka radiation (k = 0.71073 Å). For 1yellow rod shape and 4 colorless block shape crystals with dimen-sions of 0.49 � 0.31 � 0.07 mm and 0.5 � 0.13 � 0.09 mm, respec-tively, were mounted on a glass fiber and used for datacollection. Cell constants and an orientation matrix for data collec-tion were obtained by least-squares refinement of diffraction datafrom 2028 unique reflections for 1, and 7092 for 4. The structureswere solved by direct methods and refined by full-matrix least-squares techniques on F2 using the solution program SHELXS-97and refined using SHELXL-97 [21]. For 1 empirical absorption correc-tion was applied by the integration method via X-RED software [22],while for 4 it was applied numerically using X-RED [23] and X-SHAPE

[24]. All non-hydrogen atoms were refined with anisotropic dis-placement parameters and hydrogen atoms were located in theircalculated positions and refined using a riding model.

2.4. Synthesis of free Schiff base ligand (L)

The macrocyclic ligand L was prepared by Schiff base condensa-tion of 1,4-bis(2-formylphenyl)piperazine and 1,2-diaminoethanein acetonitrile.

1,4-Bis(2-formylphenyl)piperazine (0.294 g, 1 mmol) in aceto-nitrile (30 ml) was added dropwise with stirring to a solution of1,2-diaminoethane (0.06 g, 1 mmol) in acetonitrile (50 ml), over aperiod of 2 h. The mixture was stirred and heated to reflux for24 h. A white precipitate was obtained that was filtered off andwashed with cold ethanol and dried in vacuo. Yield: 0.22 g (71%).Anal. Calc. for C20H23N4O0.5: C, 73.37; H, 7.08; N, 17.11. Found: C,73.4; H, 7.0; N, 17.0%. IR (Nujol mull, cm�1): 1637 [m(C@N)],1596, 1482 [m(C@C)ar]. EI-MS: (m/z): 318, [L]+.

2.5. Synthesis of complexes

Safety note: Perchlorate complexes are potentially explosive.While we have not experienced any problems with the compoundsdescribed, they should be treated with caution and handled insmall quantities.

2.5.1. [NiL](ClO4)2 (1)Ni(ClO4)2�6H2O (0.182 g, 0.5 mmol), dissolved in 15 mL ethanol,

was added to a warm solution of L (0.16 g, 0.5 mmol) in ethanol(50 ml), and the reaction mixture was stirred and heated to refluxfor 6 h. The solvent was allowed to evaporate slowly to produce ayellow solid. The resultant product was collected by filtration andwashed with cold methanol. Crystals suitable for X-ray diffractionwere grown by slow diffusion of diethyl ether into a solution of thecomplex in acetonitrile. Yield: 0.11 g (48%). Anal. Calc. forC20H22Cl2NiN4O8: C, 41.70; H, 3.85; N, 9.73. Found: C, 41.5; H,4.0; N, 9.8%. IR (Nujol mull, cm�1):1650 [m(C@N)], 1598, 1501[m(C@C)ar], 1099, 620 ½mðClO4

�Þ�. Km/X�1 cm2 mol�1(in CH3CN):234 (2:1).

Table 1Crystal data and structure refinement for [NiL](ClO4)2 and [ZnL’](ClO4)2.

[NiL](ClO4)2 [ZnL0](ClO4)2

Empirical formula C20 H22N4O8Cl2Ni C22H30N6O8Cl2ZnFormula weight 576.03 642.81T (K) 296(2) 298(2)k (Å) 0.71073 0.71073Crystal system hexagonal monoclinicSpace group P6122 P21/n

Unit cell dimensionsa (Å) 9.8796(5) 12.0063(7)b (Å) 9.8796(5) 16.7213(13)c (Å) 40.279(2) 13.1699(8)a (�) 90.00 90.00b (�) 90.00 92.85(5)c (�) 120 90V (Å3) 3404.8(3) 2640.7(3)Z 6 4Dcalc (Mg/m3) 1.686 1.617Absorption coefficient (mm�1) 1.147 1.191F(0 0 0) 1776 1328Crystal size (mm) 0.49 � 0.31 � 0.07 0.5 � 0.13 � 0.09h range for data collection (�) 1.01–25.69 1.97–29.30Limiting indices �9 6 h 6 11, �11 6 k 6 11, �47 6 l 6 47 �16 6 h 6 16, �22 6 k 6 21, �18 6 l 6 17Reflections collected 19 188 19 590Independent reflections (Rint) 2028 (0.0499) 7092 (0.0465)Completeness to h 99.5% (25.13�) 98.3% (29.30�)Absorption correction integration numericalMaximum and minimum transmission 0.9413 and 0.8314 0.956 and 0.915Refinement method full-matrix least-squares on F2 full-matrix least-squares on F2

Data/restraints/parameters 2028/0/160 7092/24/368Goodness-of-fit (GOF)on F2 1.002 1.049Final R indices [I > 2r(I)] R1 = 0.0291, wR2 = 0.0632 R1 = 0.0579, wR2 = 0.1373R indices (all data) R1 = 0.0376, wR2 = 0.0655 R1 = 0.0818, wR2 = 0.1506Largest difference in peak and hole(e �3) 0.122 and �0.214 0.690 and �0.512

H. Keypour et al. / Inorganica Chimica Acta 367 (2011) 9–14 11

2.5.2. [CuL](ClO4)2 (2)The copper(II) complex was prepared by the same procedure as

complex 1. L (0.16 g, 0.5 mmol) and Cu(ClO4)2�6H2O (0.184 g,0.5 mmol) yielded the product as brown crystals. Yield: 0.21 g(75%). Anal. Calc. for C20H22Cl2CuN4O8: C, 41.35; H, 3.82; N, 9.65.Found: C, 41.7; H, 3.9; N, 9.6%. IR (Nujol mull, cm�1):1658[m(C@N)], 1597, 1493 [m(C@C)ar], 1088, 622 ½mðClO4

�Þ�. FAB-MS(m/z): 481 [CuL+1](ClO4)+, 381 [CuL]+. Km/X�1 cm2 mol�1(inCH3CN): 272 (2:1).

2.5.3. [CoL0](ClO4)2 (3)Co(NO3)2�6H2O (0.146 g, 0.5 mmol), dissolved in 15 mL ethanol,

was added to a warm solution of L (0.16 g, 0.5 mmol) in ethanol(50 ml), and the reaction mixture was stirred and heated to refluxfor 6 h. The solution was reduced to ca. 20 ml, then sodium per-chlorate was added and the precipitate was filtered. Crystallinecompound was obtained by slow diffusion of diethyl ether vapourinto the acetonitrile solution of the above solid. Yield: 0.13 g (42%).Anal. Calc. for C22H30Cl2CoN6O8: C, 41.52; H, 4.75; N, 13.21. Found:C, 41.4; H, 4.8; N, 12.9%. IR (Nujol mull, cm�1): 3313, 3269[m(NH2)], 1644 [m(C@N)], 1597, 1490 [m(C@C)ar], 1091, 620½mðClO4

�Þ�. FAB-MS (m/z): 538 [CoL0+1](ClO4)+, 439 [CoL0+2]+. Km

/ X�1 cm2 mol�1(in CH3CN): 240 (2:1).

2.5.4. [ZnL0](ClO4)2 (4)The zinc(II) complex was prepared similarly to 3 but using

Zn(NO3)2�6H2O (0.148 g, 0.5 mmol) instead of Co(NO3)2�6H2O.The resulting solution was worked up as previously described. Sin-gle crystals of 4 suitable for X-ray diffraction were grown by slowdiffusion of diethyl ether into a solution of the complex in acetoni-trile. Yield: 0.10 g (31%). Anal. Calc. for C22H30Cl2ZnN6O8: C, 41.11;H, 4.70; N, 13.07. Found: C, 41.6; H, 4.7; N, 13.3%. IR (Nujol mull,cm�1): 3319, 3274 [m(NH2)], 1650 [m(C@N)], 1597, 1490 [m(C@C)ar],

1089, 620 ½mðClO4�Þ�. FAB-MS (m/z): 541 [ZnL0�2](ClO4)+, 442

[ZnL0�1]+. Km/X�1 cm2 mol�1(in CH3CN): 248 (2:1).1H NMR (CD3CN, ppm) dH: 2.4–3.17 (m, 8H), 3.27–3.59 (m, 8H),

3.93 (s, 4H), 7.51–7.66 (m, 8H), 8.62 (s, 2H). 13C NMR (CD3CN, ppm)dC: 40.61, 54.66, 56.05, 121.87, 123.52, 128.47, 135.40, 137.61,148.14, 171.08.

3. Result and discussion

3.1. Synthesis and characterization

The macrocycle ligand L containing a piperazine moiety hasbeen easily prepared from [1+1] cyclocondensation of 1,4-bis(2-formylphenyl)piperazine and 1,2-diaminoethane and character-ized by microanalysis, IR and mass spectra. Since this ligand wasinsoluble in most organic solvents, we could not obtain a properNMR spectrum of this ligand. The EI mass spectrum confirms thepresence of the desired final product as it shows a peak at m/z318 corresponding to [L]+.

According to the previous paper from the reaction of similardialdehyde containing piperazine moiety with 1,2-diaminoethane,1,2-diaminobenzene and 1,3-diaminopropane, the 1:2 linear con-densation products were obtained instead of the macrocyclic dii-mines. Structure determination of these ligands showed thatthese adopt an extended configuration which minimizes nitrogenlone-pair–lone-pair repulsion [25].

In this work from the reaction of a 1:1 (metal:ligand) stoichiom-etry L and appropriate metal salts in ethanol because of the elec-tronic nature of the metal ion and the requirement of preferredgeometry of the complex [26], in the case of Ni2+ and Cu2+ macro-cyclic ring closure will occur but when using Zn2+ or Co2+ onlymacroacyclic complex is the final product (Scheme 1). The isolatedcomplexes were characterized by a combination of microanalysis,

a

b

c d

e

fg

h

i

a'

N

N

N

N

Zn2+

H2N NH2

j

Scheme 2. Schematic structures of the [ZnL0]2+ cation showing the lettering schemefor NMR assignments.

12 H. Keypour et al. / Inorganica Chimica Acta 367 (2011) 9–14

IR and FAB-MS spectroscopy, conductivity measurements and inthe case of Zn(II) complex, by 1H and 13C NMR spectroscopy. Also,crystals of [NiL](ClO4)2 and [ZnL0](ClO4)2 complexes suitable to bestudied by X-ray diffraction were obtained. The solid compoundsare air stable, moderately soluble in CH3CN and elemental analysesare consistent with the formulations given in Section 2.

3.2. Infrared spectra

The infrared spectra of the resulting compounds recorded in theregion 4000–400 cm�1. The presence of the water molecules isconfirmed by the appearance of a broad band centered about3400–3300 cm�1 in the IR spectrum of the ligand L. The absenceof m(C@O) absorptions in the IR spectrum of the ligand L togetherwith the appearance of m(C@N) absorptions at ca. 1637 cm�1

clearly indicated that a cyclic Schiff base had formed. The bandsfor C@N groups present in all the complexes are distinct and occurwithin 1644–1658 cm�1. The shift of the C@N band of the ligand toa higher frequency, supports the suggestion of coordination

Fig. 1. Crystal structure of the cation [NiL]2+. Hydrogen atoms are

Fig. 2. Crystal packing diagr

through the imine nitrogen atoms [12]. The bands at about 1597and 1490 cm�1, attributable to the m(C@C) of the aromatic ringsof the complexes are also observed [27,28]. For all the complexesabsorptions attributable to perchlorate ions were found at approx-imately 1100 and 620 cm�1 [29]. The lack of splitting of thesebands suggests that the perchlorate anions are not coordinated[30]. In addition, the presence of m(NH2) bands at 3269 and3313 cm�1 for Co complex and 3274 and 3319 cm�1 for Zn com-plex, attributed to the presence of two primary amino groups inthese compounds.

3.3. Molar conductivity

The molar conductivity (Km) of 10�3 M solutions of thecomplexes in acetonitrile was measured at 25 �C. Metal chelateshave molar conductivity of 237–272 X�1 cm2 mol�1 indicatingthe 1:2 ionic nature in all cases [31]. These values are indicativeof the presence two outer sphere perchlorate anions and are inagreement with the results obtained from the IR and X-raystudies.

3.4. NMR studies

The 1H and 13C NMR data of the [ZnL0](ClO4)2 dissolved inCD3CN is shown in Section 2 which uses the lettering schemeshown in Scheme 2.

The 1H NMR spectrum of the [ZnL0]2+ complex shows the imineresonance at d 8.62 ppm (Hh), demonstrating the equivalence ofthe two imine environments. The absorption signals of aromaticprotons appeared in the region of 7.51–7.66 ppm. Unfortunately,since the protons do not show scalar-coupling, we were not ableto assign explicitly the signals to each of the aromatic systemspresent in the molecule. In the aliphatic region, the 1H NMRspectrum of this complex shows a signal resonance at d 3.93 ppm

omitted for clarity. Symmetry code: #1: 1�x + y, y, 3/2 � z.

am of 1 in b-direction.

H. Keypour et al. / Inorganica Chimica Acta 367 (2011) 9–14 13

corresponding to the (–NH2) protons, piperazine protons in theregion of 3.27–3.59 ppm and the (–CH2–) protons appeared inthe region of 2.41–3.17 ppm (Hi and Hj). The 13C NMR spectrumshows also the resonance at d 171.08 ppm demonstrating theequivalence of the two imines environments. In the region corre-sponding to the signals of aromatic ring carbons (121.87, 123.52,128.47, 135.40, 137.61 and 148.14 ppm), six peaks are observed,

Table 2Selected bond lengths (Å) and angles (�) for [NiL]2+ (1) and [ZnL’]2+ (4)

1 4

Bond lengths (Å) Bond lengths (Å)Ni(1)–N(1) 1.845(2) Zn(1)–N(1) 2.167(4)Ni(1)–N(2) 1.918(2) Zn(1)–N(2) 2.149(3)

Zn(1)–N(3) 2.253(3)Zn(1)–N(4) 2.270(3)Zn(1)–N(5) 2.139(3)Zn(1)–N(6) 2.117(3)

Bond angles (�) Bond angles (�)N(1)–Ni(1)–N(1) 87.02(16) N(1)–Zn(1)–N(2) 78.01(14)N(1)–Ni(1)–N(2) 97.25(10) N(1)–Zn(1)–N(3) 147.65(13)N(1)–Ni(1)–N(2) 175.27(10) N(1)–Zn(1)–N(4) 98.89(13)N(2)–Ni(1)–N(2) 78.56(14) N(1)–Zn(1)–N(5) 91.01(13)

N(1)–Zn(1)–N(6) 108.53(16)N(2)–Zn(1)–N(3) 80.63(11)N(2)–Zn(1)–N(4) 111.39(11)N(2)–Zn(1)–N(5) 165.14(12)N(2)–Zn(1)–N(6) 94.31(13)N(3)–Zn(1)–N(4) 66.95(10)N(3)–Zn(1)–N(5)N(2)–Zn(1)–N(4)

113.40(10)

N(3)–Zn(1)–N(6) 97.00(13)N(4)–Zn(1)–N(5) 79.93(10)N(4)–Zn(1)–N(6) 145.82(12)N(5)–Zn(1)–N(6) 79.58(12)

Fig. 3. Weak intermolecular C–H(aromatic)���O(perchlora

Table 3Geometry of the C–H���O hydrogen bonds (Å) of complex (1).

D–H���A d(D–H) d(H���A)(Å) (Å)

C7–H7���O1 0.93 2.59C8–H8A���O4 0.97 2.36C9–H9B���O4 0.97 2.59C10–H10A���O4v 0.97 2.46

also in the region corresponding to the signals of aliphatic carbons(40.61, 54.66 and 56.05 ppm), three peaks are observed.

3.5. Description of the crystal structures

The crystal structures of [NiL](ClO4)2 and [ZnL0](ClO4)2 com-plexes have been determined by X-ray diffraction. The projectionview of the molecular structures of the atoms represented by50% thermal ellipsoids are shown in Figs. 1 and 4, respectively, to-gether with selected bond lengths and angles relating to the coor-dination environment of the metal (Table 2).

The [NiL](ClO4)2 complex crystallizes in the hexagonal P6122

space group and shows that the metal atom is four coordinatedin a slightly distorted square-planar geometry, arising from coordi-nation to the ligand by two nitrogen atoms of piperazine group andtwo nitrogen atoms of the imine groups. A similar four coordinategeometry has been found for other Ni(II) complexes with N4 mac-rocyclic ligands [32]. The Ni(G) is coplanar with the four nitrogenatoms with an r.m.s. deviation of 0.034 Å for the four donor atoms.The sum of the four N–Ni–N chelate angles (360.08�) is almost 360�for an ideal planar structure. The imino nitrogen bond lengths areequivalent [Ni–N(1) 1.845(2) Å] and 0.073 Å, shorter than the Ni–N–piperazine distances [Ni–N(2) 1.918(2) Å].

The perchlorate ion is non-coordinating reflecting the low coor-dination ability of this anion.

The packing diagram of [NiL](ClO4)2 is shown in b-direction inFig. 2. This compound represents helical structure with alternationof cationic and anionic rows. It is notable that the presence of bulkypiperazine rings precludes the overlapping of the adjacent ions. Asit is clear from Fig. 3, each cation is surrounded by 10 perchlorateanions by weak intermolecular C-H(aromatic)���O(perchlorate) andC–H (aliphatic)���O(perchlorate) bonds that are effective in the sta-bilization of the packing, Table 3.

te) and C–H(aliphatic)���O(perchlorate) bonds in (1).

d(D���A) (D-H���A) Sym. Code(Å) (�)

3.398(5) 146.00 y, �x + y, �1/6 + z3.278(5) 158.00 1 � x + y, y, 3/2 � z3.135(4) 116.00 1 + y, 1 � x+y, �1/6 + z3.048(3) 119.00 1 � x, 1 � x+y, 5/3 � z

Fig. 4. Crystal structure of the cation [ZnL0]2+. Hydrogen atoms are omitted forclarity.

14 H. Keypour et al. / Inorganica Chimica Acta 367 (2011) 9–14

The [ZnL0](ClO4)2 complex crystallizes in the monoclinic P21/nspace group and shows that the Zn(G) ion is lying in a six-coordi-nated environment formed by coordination to the two piperazinenitrogen atoms, two imine nitrogen atoms and two nitrogen atomsof terminal primary amino groups, that is best described as dis-torted octahedral geometry. Where the equatorial plane is com-prised by N(1) N(3) N(4) N(6) donor atoms, while the axialpositions occupied by the two imine N atoms, N(2) and N(5),[(N(2)–Zn1–N(5) 165.14(12)] (see Fig. 4).

The six Zn–N bond lengths are in the range 2.117–2.270 Å. TheN(6) aminic nitrogen atom provides the shortest distance to themetal [Zn(1)–N(6) 2.117(3)], while the longest one belongs to theN(4) piperazine nitrogen atom [Zn(1)–N(4), 2.270(3)]. Variationin bond lengths indicates the different strength of the bond formedby each of the coordinated nitrogen atoms. The perchlorate ion isnon-coordinating reflecting the low coordination ability of thisanion.

4. Conclusion

A new tetraaza macrocyclic Schiff base ligand (L) has beensynthesized and it’s complexation capacity towards Ni(II), Cu(II),Co(II) and Zn(II) has been studied. In the presence of nickel(II)and copper(II) metal ions, because of the electronic nature of themetal ion and the requirement of preferred geometry of thecomplex, our attempts were successful and macrocycliccomplexes were obtained, while in the presence of cobalt(II) andzinc(II) metal ions, open-chain Schiff base complexes with twoterminal primary amino groups were isolated. The crystal struc-tures of [NiL](ClO4)2 and [ZnL0](ClO4)2 were determined and indi-cated that in the solid state, their complex structures adopted aslightly distorted square-planar and a distorted octahedral geome-try, respectively.

Acknowledgements

We are grateful to the Faculty of Chemistry of Bu-Ali Sina Uni-versity, National Foundation of elites (BMN) and Ministry of Sci-ence, Research and Technology of Iran, for financial support.

Appendix A. Supplementary material

CCDC 754029 and 754030 contain the supplementary crystallo-graphic data for [ZnL0](ClO4)2 and [NiL](ClO4)2, respectively. Thesedata can be obtained free of charge from The Cambridge Crystallo-graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.ica.2010.11.033.

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