Polyhedron 30 (2011) 2171–2180

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Polyhedron

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Synthesis and characterization of Cu(II) complexes of pyrazine-2,3-dicarboxylicacid

Sülin Tas�cıoglu a,⇑, Adnan Aydın a, Bahattin Yalçın a, Esra Kakı a, Ömer Andaç b, Orhan Büyükgüngör c,Bas�ak Kos�ar d

a Marmara Üniversitesi, Fen-Edebiyat Fakültesi, Kimya Bölümü, Göztepe, _Istanbul, Turkeyb Ondokuzmayıs Üniversitesi, Fen-edebiyat Fakültesi, Kimya Bölümü, Atakum, Samsun, Turkeyc Ondokuzmayıs Üniversitesi, Fen-edebiyat Fakültesi, Fizik Bölümü, Atakum, Samsun, Turkeyd Sinop Üniversitesi, Egitim Fakültesi, Sinop, Turkey

a r t i c l e i n f o

Article history:Received 14 December 2010Accepted 6 May 2011Available online 27 May 2011

Keywords:Pyrazine-2,3-dicarboxylic acidCopper(II) bromide complexesCopper(II) mixed ligand complexesTwin structure

0277-5387/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.poly.2011.05.018

⇑ Corresponding author. Tel.: +90 0216 3487759; faE-mail address: stascioglu@marmara.edu.tr (S. Tas�

a b s t r a c t

Four copper(II) coordination polymers, {[Cu(pz(COO)2)(H2O)]4�HBr}n (1), {[Cu(pz(COO)2)(NH3)2]�H2O}n

(2), {[Cu3H2(pz(COO)2)4(H2O)3]�2H2O}n (3) and {[Cu2(pz(COO)2)2(NH3)2(H2O)3][Cu(pz(COO)2)(NH3)(H2O)2][Cu(pz(COO)2)(NH3)(H2O)]�2H2O}n (4) were synthesized using pyrazine-2,3-dicarboxylic acid,CuBr2, 2-(2-aminoethylamino)ethanol/triethanol amine/ammonia in a methanol:water (1:1) solution,and the mixed ligand complexes were characterized by spectroscopic methods, thermal and elementalanalysis, and magnetic susceptibility. Complexes 2 and 4 were also characterized by means of single crys-tal X-ray crystallography. The characterizations show that the complexes have polynuclear molecularstructures, except for complex 2, and all of the complex structures form polymeric chains. Complex 4has a pseudo-merohedral twin structure.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Pyrazine-2,3-dicarboxylic acid (H2pzdc) and its complexes arethe subject of many studies in which coordination polymers withspecial electronic and magnetic properties have been synthesizedas linear chains or infinite networks. Pyrazine [1–5] itself and car-boxylate groups are used to bridge transition metal atoms to formbinuclear or polynuclear complexes [6–11]. Thus, one, two or threedimensional molecular structures can be constructed. Pyrazine-2,3-dicarboxylic acid bears both kinds of bridging species and iscapable of building polynuclear complexes [12–14]. It is a dianion-ic tetradentate ligand with two potential nitrogens of pyrazine andtwo carboxylate-oxygens. The other two oxygens of carboxylategroups also may participate in bridging. The coordination modesas well as the hydrogen bonding between monomeric units deter-mine the kind of polymerization.

An aqueous solution of Na2pzdc and Cu(ClO4)2 gives a onedimensional polymeric chain built up by pentacoordinated Cu(II)ions, pzdc as a bridging ligand and water molecules, [Cu(pzdc)2

(H2O)2]�H2O, in which lattice water molecules give rise to a 3Dstructure via hydrogen bonding [15]. The lack of one of the car-boxylic acid protons, as in the case of the mono methyl ester of

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x: +90 0216 3478783.cıoglu).

H2pzdc, with aqueous CuCl2 causes the formation of a twodimensional coordinating polymer with CuL2 monomeric units[16]. However, H2pzdc reacts with aqueous CoCl2 solution to giveCo(Hpzdc)2 (H2O)2 in which mononuclear units are bridged onlyby hydrogen bonds through pyrazine–carboxylate ligands[12,13].

Although there are a number of bis-bidentate complexes ofH2pzdc with two copper atoms, only one example of a ladder-likepolymeric manganese(II) complex, [Mn(pzdc)(H2O)2]n, has beenreported. The ladder-like chain is formed via bridging the twoMn(II) atoms with one of the carboxylates of two parallel pzdcunits and the chains are linked by hydrogen bonds of water mole-cules [14].

Pyrazine-2,3-dicarboxylic acid reacts with CuCl2 in 6 N HCl togive a one dimensional coordination polymer [12] with monomericCu(pzdc)�HCl units, in which Cu(II) is pentacoordinated and theligand coordinates to two Cu atoms in a bis-bidentate mode. Theacid hydrogen of one carboxylic acid moiety forms intramolecularhydrogen bonds with another carboxylate oxygen.

H2pzdc, Cu(II) and bidentate ligands with nitrogen atoms giveligand coordinated mono-, di- and polynuclear complexes, whichlead to polymer chains [17–20]. In continuation of our work onpolynuclear complexes [21], now we report the results of theCuBr2–H2pzdc interaction in weakly alkaline and neutralsolutions to give polynuclear coordination oligomers, whichreact with 5 N NH3 solution to give ammonia coordinatedcomplexes.

2172 S. Tas�cıoglu et al. / Polyhedron 30 (2011) 2171–2180

2. Experimental

2.1. Physical and chemical measurements

2.1.1. UV–Vis and IRThe electronic and infrared spectra were recorded on Shimadzu

UV–Vis 240, Varian Cary Eclipse Fluorescence and Hyper IR Shima-dzu Infrared (KBr disc) spectrophotometers, respectively.

Thermogravimetric analysis experiments were performed using aNetzsch STA 409C/CD in a nitrogen atmosphere with a nitrogenflow rate of 50 mL min�1 in the temperature range 20–400 �C, witha 5 �C min�1 heating rate.

Magnetic susceptibility measurements were carried out at roomtemperature on a magnetic balance of the Faraday type withHg[Co(SCN)4] as the standard.

Elemental analyses and mass measurements were performed inthe analytical laboratory, Tübitak, Ankara on a LECO CHNS 932Analyzer and the LC/MS system of an Agilent1100 MSD spectrom-eter, respectively.

Copper analysis was carried out with an Analytikjena Zeenit 700AAS.

Melting points were measured by using a Gallenkamp meltingpoint apparatus.

Single crystal X-ray structural analyses were performed on a STOEIPDS 2 diffractometer with graphite monochromated Mo Ka radia-tion at 296 and 110 K.

2.2. Syntheses

2.2.1. ReagentsPyrazine-2,3-dicarboxylic acid was from Fluka and CuBr2 was

from Riedel-de Haen. The solvents used in the preparations wereall Merck p.a. products.

2.2.2. Preparation of {[Cu(pz(COO)2)(H2O)]4�HBr}n (1)CuBr2 (4.46 g, 0.02 mol), pyrazine-2,3-dicarboxylic acid (3.36 g,

0.02 mol), 2-(2-aminoethylamino)ethanol or triethanolamine (ap-prox. 0.02 mol) were dissolved in 20 mL methanol/water (1/1),and the solution was heated at 70–80 �C for 2 h with continuousstirring under a reflux condenser. The green precipitate obtainedin the powder form was filtered, washed with chloroform anddried in air.

Yield: 4.97 g (93%), Mw: 1071.524 g mol�1, m.p.: >250 �C,leff = 3.27 BM. TGA data (�C) (weight loss%) (calcd. weight loss%):129 (6.94) (6.72; calcd. for – 4H2O): 129–269 (45.22) (45.64; –HBr, –8CO2, –2N2). UV (nm) (H2O): 388; 533; 634. IR (KBr,m/cm�1): 3418 (m, br, O–H str.), 3090, 3067 (m, pz-C–H str.),1680 (m, COO�), 1643 (s, C@N), 1580 (m, asym. COO� str.), 1329(s, sym. COO� str.), 889 (m, H2O), 853 (m, C–H bend. of ring), 496(m, Cu–N str.), 231 (s, Cu–N). Mass (positive pol., m/e): 1028.4(1%, m⁄-CO2 + H); 740.5 (0.7%, [pz(COO)2Cu(H2O)]3–2H); 495.6(2.6%, [pz(COO)2Cu�H2O]2); 284.3 (100%, pz(COOH)CuBr�H2O+);230.3 (8.3%, Hpz(COO)2Cu+). Anal. Calc. for C24H17N8O20Cu4B: C,26.90; H, 1.60; N, 10.46; Cu, 23.72. Found: C, 27.42; H, 1.14; N,11.05; Cu, 22.57%.

2.2.3. Preparation of {[Cu(pz(COO)2)(NH3)2]�H2O}n (2)Cu4[pz(COO)2]4�HBr�4H2O (0.5 g, 1.78 mmol) (1) was dissolved

in 20 mL 5 N NH4OH and 25% of the solution was evaporated atatmospheric pressure. Green needles of {[Cu(pz(COO)2)(NH3)2](H2O)}n crystallized out on cooling down to room temperature.The green crystals were filtered and washed with chloroform.

Yield: 0.24 g (88%), Mw: 281.72 g mol�1, m.p.: >300 �C,leff = 2.05 BM. TGA data (�C) (weight loss%) (calcd. weight loss%):137–270 (56.44) (54.7; –H2O, –2NH3, –2CO2, –N); 270–400

(1.48). IR (KBr, m/cm�1): 3462 (m, br, O–H str. of H2O), 3090 (m,pz-CH str.), 3321 (s), 3274 (m), 3239 (m) (N–H str. of NH3), 3171(m, pz-C–H str.), 1659 (s, C@N ring), 1628 (m, sh, O–H bend ofH2O), 1591 (s, asym. COO� str.), 1450 (m, C@C ring), 1386 (s,sym. COO� str.), 1350 (m, sym. COO� str.), 1313, 1265 (m, sym. de-form.mode of N–H of coord. NH3), 888 (m, H2O), 845 (m, C–H bendof ring), 735 (rocking mode of N–H of coord. NH3), 547 (w, H2O),471 (m, Cu–N str.), 448 (m, Cu–N of NH3), 259 (s, Cu–O asym.str.). UV (nm) (H2O): 389; 487; 532; 631. Mass (negative pol.,m/e): 841 (0.2%, m⁄-4H), 283.2 (36.3%, pz(COOH)2Cu(NH3)2�H2O);281.1 (32.5%, pz(COO)2Cu(NH3)2�H2O); 255.2 (100%), 253.30(46%). Anal. Calc. for C6H10N4O5Cu: C, 25.58; H, 3.58; N, 19.89;Cu, 22.55. Found: C, 25.90; H, 3.13; N, 19.74; Cu, 21.91%.

2.2.4. Preparation of {[Cu3H2(pz(COO)2)4(H2O)3]�2H2O}n (3)CuBr2 (0.5025 g, 2.3 mmol) and pyrazine-2,3-dicarboxylic acid

(0.5040 g, 3 mmol) were dissolved in 20 mL methanol/water(1/1) and the solution was heated at 70–80 �C for 2 h with contin-uous stirring under a reflux condenser. The light green precipitateobtained in the powder form was filtered, washed with chloroformand dried in air.

Yield: 0.61 g (88%). Mw: 947.092 g mol�1, m.p.: >250 �C.leff = 3.4 BM. TGA data (�C) (weight loss%) (calcd. weight loss%):132 (4.32) (3.80; –2H2O); 132–261 (14.66) (15.00; –2CO2–3H2O),261–280 (35.44) (35.48; –7CO2, –N2); 280–400 (4.17%) (4.43%;–3/2N2). IR (KBr, m/cm�1): 3385 (m, br, O–H str. of H2O), 3231 (m,br, O–H str. of COOH), 3090, 3067 (m, pz-C–H str.), 2650–2500(O–H str., bonded), 1674 (m, COO�), 1651 (s, C@N), 1640 (s, O–Hbending), 1584 (s, asym. COO� str.), 1425 (s, C@C ring), 1354,1333 (s, sym. COO� str.), 889 (s, H2O), 853 (m, C–H bend. of ring),538 (m, H2O), 494 (m, Cu–N str.), 423 (w, Cu–O–aqua complex),260 (s, Cu–O). UV (nm) (H2O): 391; 533; 630. Mass (positive polar-ity) (m/e): 715.2 (1.5%, m⁄-[pz(COO)2Cu + 2H]), 503.9 (21.7%, m⁄-[(pz(COO)2)2Cu + CO2 + 4H]); 425.0 (53.6%, m⁄-[(pz(COO)2)2Cu +HpzCOOH + 2H]); 423.0 (100%); 323.9 (26.5%, m⁄-[(pz(COO)2)2-

Cu2 + pz(COO)2–2H]); 321.9 (22.4%); 258.3 (5.2%, m⁄-[pz(COO)2]3-

Cu3); 79.2 (61.2%, HPz). Anal. Calc. for C24H20N8O21Cu3: C, 30.44;H, 2.13; N, 11.83; Cu, 20.13. Found: C, 30.48; H, 1.36; N, 12.02;Cu, 19.96%.

2.2.5. Preparation of {[Cu2(pz(COO)2)2(NH3)2(H2O)3][Cu(pz(COO)2)(NH3)(H2O)2] [Cu(pz(COO)2)(NH3)(H2O)]�2H2O}n (4)

{[Cu3H2(pz(COO)2)4(H2O)3]�2H2O}n (0.3 g, 0.33 mmol) (3) wasdissolved in 10 mL 5 N NH4OH solution and 25% of the solutionwas evaporated at atmospheric pressure. Light blue crystals werefiltered, washed with chloroform, and methanol/water (1/1) anddried in air. Complex 4 was also obtained via the addition of CuBr2

and 5 N ammonia solution (75–80 �C, 1 h) to the 2-(2-aminoeth-ylamino)ethanol salt of pyrazine-2,3-dicarboxylic acid, whichwas isolated from a dimethylsulfoxide solution of the reactants.The mixture yields bright blue crystals in a month.

Yield: 0.063 g (68%). Mw: 1130.81 g mol�1, m.p.: >300 �C.leff = 3.19 BM. TGA data (�C) (weight loss%) (calcd. weight loss%):72–182 (12.10) (12.74, –8H2O); 182–252 (40.40) (40.87; –4NH3,–8CO2, –3/2N2); 252–400 (4.09 (3.72; –3/2N2). IR (KBr, m/cm�1):3449 (m, br, O–H str. of H2O), 3343 (s), 3262 (m), 3180 (m, N–Hstr. of NH3), 3067 (m, pz-CH str.), 1650 (s, C@N ring), 1643 (s,N–H bend), 1635, 1622 (m, sh, O–H bend of H2O), 1580 (s, asym.COO� str.), 1454 (m, C@C ring), 1387 (s, sym. COO� str.), 1350(m, sym. COO� str.), 1305, 1283, 1265 (w, sym. deform. mode ofN–H of coord. NH3), 893 (m, H2O), 849 (s, C–H bend. of ring), 756(rocking mode of N–H of coord. NH3), 559 (w, H2O), 486 (w, Cu–N str.), 448 (w, Cu–N of NH3), 274 (s, Cu–O asym.str.). UV (nm)(H2O): 388, 534, 634; UV (nm) (solid): 390, 479, 532, 632. Mass(positive pol.) (m/e): 1127 (0.2%, m-4), 1053 (0.3%, m⁄-(NH3+3H2O),1026 (0.5%, m⁄-(3NH3 + 3H2O), 954 (0.4%, m⁄-(4NH3 + 6H2O–H),

S. Tas�cıoglu et al. / Polyhedron 30 (2011) 2171–2180 2173

919 (0.3%, m⁄-(4NH3 + 8H2O), 830 (0.8%, m⁄-(4NH3 + 8H2O + 2-CO2 + H), 230 (3.9%, pz(COO)2Cu), 179 (18.1%), 101.1 (100%,C4H5O2N + 2H), 79.15 (1.1%, Hpz). Anal. Calc. for C6H9N3O6Cu: C,25.49; H, 3.21; N, 14.86; Cu, 22.48. Found: C, 25.43; H, 3.21; N,14.85; Cu, 21.31%.

2.3. X-ray structural analyses of the complexes

Of the synthesized complexes, complexes 2 and 4 were ob-tained as suitable crystals for X-ray analysis. Single crystals of 2and 4 were mounted on a glass fibre, and data collection processeswere performed on a STOE IPDS 2 diffractometer with graphitemonochromated Mo Ka radiation at 296 and 110 K, respectively.Relevant crystallographic data for 2 and 4 are listed in Table 1. Datacollection: X-AREA; cell refinement: X-AREA; data reduction andabsorption correction: X-RED32 [22]. The structures were solvedby direct methods using SHELXS-97 [18] and refined by full-matrixleast-squares methods on F2 using SHELXL-97 [23,24]. All non-hydro-gen atoms were refined with anisotropic parameters. Geometriccalculations were performed on PLATON [25]. Molecular drawingswere obtained using ORTEP-III for Windows [26]. Materials were pre-pared for publication using WINGX software [27].

In complex 2, all hydrogens were obtained from the differencemap and refined isotropically but dfix constraints [18], 0.83 Å for

Table 1Crystal data and structure refinement for 2 and 4.

Complex 2 4

Formula C6H10CuN4O5 C24H36Cu4N12O24

Molecular weight 281.72 1130.81T (K) 296(2) 110(2)k (Å) 0.71073 0.71073Crystal system orthorhombic monoclinicSpace group Pbca P21Unit cell dimensions

a (Å) 7.1291 (7) 10.7993(3)b (Å) 14.4806 (12) 14.5563(5)c (Å) 18.974 (3) 12.0617(4)

b (�) 90.159(3)V (Å3) 1958.8 (4) 1896.1(1)Z 8 2Dcalc (g cm�3) 1.911 1.981Absorption coefficient 2.245 2.324F(0 0 0) 1144 884Crystal size (mm) 0.50 � 0.28 � 0.03 0.56 � 0.46 � 0.32h range for data

collection2.81–26.00 1.89–27.37

Index ranges �7 < h < 8;�17 < k < 17;�18 < l < 23

�13 < h < 13;�18 < k < 18;�15 < l < 12

Reflections collected 9272 13 611Independent reflections

(Rint)1908 (0.0975) 8501 (0.0333)

Reflections observed(>2r)

1251 8087

Data completeness 0.992 0.993Absorption correction Integration IntegrationMaximum and

minimumtransmission

0.3948 and 0.2215

Refinement method full-matrix least-squares on F2

full-matrix least-squares on F2

Data/restraints/parameters

1908/3/185 8501/19/614

Goodness-of-fit on F2 1.034 1.033Final R indices [I > 2r(I)] R1 = 0.0464,

wR2 = 0.0694R1 = 0.0352,wR2 = 0.0859

R indices (all data) R1 = 0.0918,wR2 = 0.0794

R1 = 0.0382,wR2 = 0.0889

Largest difference peakand hole (e �3)

0.374 and �0.396 0.479 and �0.665

O–H and 1.30 Å for H� � �H distances, were applied to waterhydrogens.

In complex 4, the intensity statistics revealed the presence ofpseudo-merohedral twinning and a twin matrix of 1 0 0 0–1 0 0 0–1 was used for the refinement. Hydrogen atoms bondedto carbon and amine hydrogens were placed in calculated positions(C–H 0.95 Å and N–H 0.91 Å) and refined using riding model [23]with U = 1.2 U of the parent atom for CH and U = 1.5 U for aminehydrogens. The hydrogens of the four water molecules were ob-tained from the difference map and refined using dfix constraints[23], 0.90 Å for O–H and 1.40 Å for H� � �H distances, with U 1.5times that of the attached oxygen atoms. However, the hydrogensof two water molecules were found to be disordered over severalpositions and were involved in very strong hydrogen bonding withthe neighbouring oxygen and nitrogen atoms. Therefore, the posi-tions of the two water hydrogens were not resolved.

3. Results and discussion

3.1. Synthesis

Pyrazine-2,3-dicarboxylic acid (H2pzdc or pz(COOH)2) reactswith CuBr2 in the presence of a base, such as an aliphatic amine,namely 2-(2-aminoethylamino)ethanol (AE) or triethanolamine,to give a polynuclear copper(II) complex. The carboxylic acidgroups of pyrazine-2,3-dicarboxylic acid have different aciditieswith pKa1 = 0.8 and pKa2 = 2.84 [28]. Thus, the pH of the reactionmedium affects the coordination modes of H2pzdc [14,28]. Thepresence of 2-(2-aminoethylamino)ethanol in less than an equimo-lar amount necessary for full neutralization causes the partial neu-tralization of H2pzdc, followed by the formation of complex 1(Fig. 1), which includes aquabromo carboxylatocopper (II) coordi-nation at one of the terminal pzdc molecules. The same complexhas also been obtained in the presence of triethanolamine

4PzðCOOHÞ2 þ 4CuBr2 þ 4H2Oþ 2ðBaseÞ! fH½pzðCOOÞ2CuðH2OÞ�3ðOOCÞpzgfðCOOÞCuðH2OÞBrg ð1Þ

However, the absence of a base in the reaction medium helps tokeep free COOH groups at both of the terminal pz moieties. Thepresence of excess H2pzdc (around 36% excess) makes the reactionmedium more acidic and causes the formation of complex 3. Com-plex 3 (Fig. 2) is constructed from 4 mol pzdc and 3 mol Cu(II).Thus, in complex 3 one undissociated COOH group is kept at bothof the terminal pz moieties.

4PzðCOOHÞ2 þ 3CuBr2 þ 5H2O! f½HðpzðCOOÞ2Þ3Cu3ðH2OÞ3�� ½ðOOCÞpzðCOOH� � 2H2Ogþ 6HBr ð3Þ

Fig. 1. Complex 1.

Fig. 2. Complex 3.

Table 2Selected bond distances (Å) and angles (o) in 2 and 4.

Complex 2Cu1–N1 2.064 (3) Cu1–N3 2.002 (4)Cu1–N4 1.977 (5) Cu1–O1 1.977 (3)Cu1–O3i 2.307 (3) Cu1–O2ii 2.930 (4)C5–O1 1.273 (5) C5–O2 1.225 (5)

2174 S. Tas�cıoglu et al. / Polyhedron 30 (2011) 2171–2180

The bis-pyrazinedicarboxylato bridged complexes 1 and 3 reactwith ammonia, where the ammonia nitrogen attacks and breaksone of the two N-Cu bonds of each pz moiety via introduction ofan ammonia molecule. During this action, the terminal pzdc2-

and, in the case of 1, bromocopper ions are also eliminated. Thus,NH3 participation in the coordination either results in the substitu-tion of coordinated water molecules entirely, as in complex 1, oroccurs by binding one NH3 molecule to each copper atom, half ofwhich atoms are also coordinated by additional water moleculesto enhance some of the copper coordination numbers to six, as incomplex 4. Consequently, bluish green and light blue 1D coordina-tion polymers (2 and 4) are obtained. The substitution of the coor-dinated water of complex 4 with ammonia gives the diamminecomplex 2. (4) + 3NH3 ? (2) via another way, in strong basic med-ium, CuBr2 and H2pzdc were also reacted to form complex 2 in 5 NNH3 and in the absence of AE.

C6–O3 1.245 (6) C6–O4 1.255 (6)N4–Cu1–N3 95.4 (2) O1–Cu1–N3 87.37 (16)N4–Cu1–N1 95.33 (18) O1–Cu1–N1 80.48 (13)N3–Cu1–N1 166.03 (16) N4–Cu1–O1 169.3 (2)N4–Cu1–O3i 87.16 (19) N3–Cu1–O3i 95.97 (18)O1–Cu1–O3i 102.90 (14) N1–Cu1–O3i 93.45 (13)O2–C5–O1 126.5 (4) O3–C6–O4 125.8 (4)

Complex 4Cu1–O1 1.991(3) Cu1–N9 1.994(4)Cu1–O7 2.007(3) Cu1–N1 2.038(4)Cu1–O1W 2.289(4) Cu1–O8 2.816(4)C5–O1 1.286(6) C5–O2 1.243(6)C6–O3 1.272(6) C6–O4 1.246(6)Cu2–O3iii 1.990(3) Cu2–O4iii 2.834(4)Cu2–N3 2.054(4) Cu2–N10 1.998(4)Cu2–O5 1.980(4) Cu2–O3W 2.558(4)Cu2–O2W 2.785(4) C11–O5 1.265(6)C11–O6 1.252(6) C12–O7 1.284(6)C12–O8 1.226(6) Cu3–O11iv 1.977(3)Cu3–O9 1.967(4) Cu3–N5 2.042(4)Cu3–N11 2.011(4) Cu3–O5W 2.899(5)Cu3–O4W 2.485(3) Cu3–O12iv 2.832(4)C17–O9 1.283(6) C17–O10 1.237(6)C18–O11 1.279(6) C18–O12 1.251(6)Cu4–O15v 2.013(3) Cu4–O16v 2.763(4)Cu4–O13 1.981(4) Cu4–N12 1.975(4)Cu4–N7 2.054(4) Cu4–O6W 2.254(4)C23–O13 1.296(6) C23–O14 1.234(6)C24–O15 1.282(6) C24–O16 1.246(6)O7–Cu1–N1 169.1(2) O1–Cu1–N9 166.0(2)N9–Cu1–O7 91.2(2) O1–Cu1–O7 87.1(1)N9–Cu1–N1 99.5(2) O1–Cu1–N1 82.0 (2)O1–Cu1–O1W 103.4(2) N9–Cu1–O1W 90.7 (2)O7–Cu1–O1W 96.3(1) N1–Cu1–O1W 85.8(2)

3.2. Infrared spectra of the complexes

The coordination modes of pyrazine-2,3-dicarboxylic acid in thecomplexes were determined by IR spectra, by comparing the sepa-rations between the mas(COO) and ms(COO) bands. In the copper (II)complexes of pyrazine-2,3-dicarboxylic acid, the carboxylategroups individually behave as monoanionic monodentate ligands.For example, in the IR spectrum of the green crystalline complex2, the asymmetric COO� band of the ligand at 1578 cm�1 shiftsto 1591 cm�1. In the meantime, the symmetric COO� absorptions,appearing at 1394 and 1354 cm�1, shift to 1386 and 1350 cm�1,respectively. Thus, the separations between the mas(COO) andms(COO) bands (D = 205 and 241 cm�1) are consistent with themonodentate coordination of the carboxylate groups [29–31]. Sim-ilar observations are made for the other complexes, indicating asimilar coordination mode of the carboxylate groups.

All the complexes show a band in the range 502–460 cm�1 [32]which is associated with the copper–nitrogen asymmetricstretching vibrations. The pyrazine ring C–H bending absorptionsat 868 cm�1 shift 15–23 cm�1 down to lower frequencies aftercoordination.

The coordinated ammonia bands for asymmetric deformation,symmetric deformation and rocking modes of the molecule, whichare found in the ranges 1627–1585, 1300–1210 and 740–700 cm�1

[32], respectively, have been observed for complexes 2 and 4, ex-cept were they are obscured by the strong ring absorption bands.

O5–Cu2–N10 171.4(2) O3iii–Cu2–N3 167.7(2)O5–Cu2–O3iii 89.3(2) O3iii–Cu2–N10 90.6(2)N10–Cu2–N3 99.1(2) O5–Cu2–N3 82.3(2)O5–Cu2–O3W 97.4(1) O3iii–Cu2–O3W 89.7(1)N10–Cu2–O3W 91.2(2) N3–Cu2–O3W 82.53(14)O5–Cu2–O2W 95.44(15) O3iii–Cu2–O2W 118.7(1)N10–Cu2–O2W 77.2(2) N3–Cu2–O2W 71.3(1)O3W–Cu2–O2W 148.9(1) O2–C5–O1 125.6(4)O4–C6–O3 126.5(5) O6–C11–O5 125.0(4)O8–C12–O7 126.7(5) O11iv–Cu3–N5 168.2(2)O9–Cu3–N11 170.1(2) O11iv–Cu3–N11 90.8(2)O9–Cu3–O11iv 88.9(2) N11–Cu3–N5 99.9(2)O9–Cu3–N5 81.5(2) O9–Cu3–O4W 100.1(1)N11–Cu3–O4W 89.8(2) N5–Cu3–O4W 87.5(2)O11iv–Cu3–O4W 87.6(1) O9–Cu3–O5W 101.1(2)

iv

3.3. Electronic spectra of the complexes

All the complexes exhibit d-d transition bands in the region550–670 nm, which indicates five coordinate complexes with asquare pyramidal geometry [33–36]. Cu2 and Cu3 in 4 are octahe-drally coordinated in the solid-state, according to the results of thesingle crystal X-ray analysis, but the electronic spectrum of 4 doesnot confirm an octahedral geometry in the solution phase. Theelectronic spectra of the complexes in MeOH show broad bandscentred at 649 and 642 nm, suggestive of a square pyramidal coor-dination geometry of the Cu(II) ion [37].

O11 –Cu3–O5W 117.5(1) N11–Cu3–O5W 70.4(2)N5–Cu3–O5W 71.3(2) O4W–Cu3–O5W 147.2(1)O10–C17–O9 125.2(4) O12–C18–O11 127.7(4)O15v–Cu4–N7 169.1(2) N12–Cu4–O13 164.8(2)O13–Cu4–O15v 87.0(1) N12–Cu4–N7 98.9(2)O13–Cu4–N7 82.3(2) N12–Cu4–O15v 91.1(2)N12–Cu4–O6W 96.4(2) O13–Cu4–O6W 98.9(2)O15v–Cu4–O6W 96.5(2) N7–Cu4–O6W 86.8(2)O14–C23–O13 125.9(4) O16–C24–O15 127.1(5)

Symmetry codes: i = x + 1/2, y, �z + 1/2; ii: x � 1/2, y, �z + 1/2; iii: x, y � 1, z; iv:�x + 1, y + 1/2, �z + 2; v: �x + 1, y + 1/2, �z + 2.

3.4. Magnetic measurements

The magnetic moment of the mononuclear complex 2 (leff:2.05BM) is within the range for d9 systems [38], but the slightlyhigher magnetic moment indicates polymeric chain formation.The magnetic moments of the other complexes (1, leff: 3.27; 3, leff:3.4; 4, leff: 3.19) indicate polynuclear structures and molecularassociations.

3.5. Thermogravimetric analysis

The thermogravimetric experiments were performed under anitrogen atmosphere, with a nitrogen flow rate of 50 mL min�1,in the temperature range 20–400 �C, with a 5 �C min�1 heatingrate. According to the TGA curves, which have many decomposi-tion stages, the weight losses correspond to the liberation of water,hydrobromic acid, ammonia, carbon dioxide and nitrogen.

S. Tas�cıoglu et al. / Polyhedron 30 (2011) 2171–2180 2175

The thermal decomposition curves of complexes 1 and 2 arevery simple, showing one onset temperature (205.9 �C) for 2 andtwo onset temperatures (54.7 and 216.6 �C) for 1. Complexes 3and 4 both have three onset temperatures (92.5, 205.4, 260.4 �Cfor 3 and 104.9, 152, 213 �C for 4). The decomposition starting tem-peratures may give information about the stability of the com-plexes and the possible dynamic exchanges of the neutral ligandsor lattice molecules in the environment of the central atoms. Incomplexes 1 and 3, the neutral ligands are water molecules andtheir decomposition starts at temperatures below 70 �C, fromwhich the possibility of dynamic exchange of water molecules tosome extent between the lattice and coordination sphere can bededuced. However, in complexes 2 and 4, the neutral ligands areammonia and water molecules. Although, complex 2 only hasammonia molecules, the units of complex 4 have both ammoniaand water molecules in the copper coordination sphere of its allunits, which form polymeric chains. Thus, complex 2 is the moststable, the decomposition of which starts at 137 �C. The thermalstability of complex 4 is lower, with the initial decomposition ob-served between 72 and 128 �C, lattice waters being lost first, fol-lowed by the loss of six coordinating water molecules in thetemperature range 128–182 �C. In all the complexes, pzdc decarb-oxylations are observed in the temperature range 140–280 �C, inwhich partial pyrazine ring decompositions also occur.

3.6. Structural descriptions of 2 and 4

3.6.1. Crystal structure of {[Cu(pz(COO)2)(NH3)2]�H2O}n (2)Compound 2, namely poly[diamminepyrazine-2,3-dicarboxyla-

tocopper(II)]hydrate, crystallized in the orthorhombic space groupPbca and its structure is identical with poly[diaquapyrazine-2,3-dicarboxylatocopper(II)]hydrate, {[Cu(pz(COO)2)(H2O)2]H2O}n, re-ported by Konar et al. [15]. Crystal data and refinement resultsare listed in Table 1. The asymmetric unit of complex 2 containsone divalent copper ion, one pyrazinedicarboxylate (pzdc) ion,two ammine ligands and one lattice water molecule.

Although, the cell parameters and the distances around thecoordination environment of complex 2 and its analogous struc-ture are same to within the error limits, there are some differences:The colour of complex 2 is green, but the colour of its analogouscomplex is blue. Complex 2 was prepared in concentrated

Fig. 3. The polymeric chain of {[(OOC)pz(COO)Cu(NH3)2](H2O)]3}n (2) with the atom-numsmall spheres of arbitrary radii. i: x + 1/2, y, �z + 1/2; ii: x � 1/2, y, -z + 1/2; iii: x � 1, y,

ammonia solution, but its analogue was obtained in mild aqueousammonia [15]. Although it is not easy to distinguish nitrogen andoxygen atoms from X-ray data, as their scattering factors are sim-ilar, ammonia and water molecules can be distinguished by theirhydrogen atoms. In both analogous structures, the hydrogen atomsof coordinated water and ammonia molecules were placed fromthe difference map and refined isotropically without applyingany constraints. The obtained N–H and O–H bond lengths, andH–N–H and H–O–H angles are acceptable. The coordination dis-tances of Cu–N (NH3) and Cu–O (H2O) and the angles (H3N)N–Cu–N(NH3) and (H2O)O–Cu–(OH2), including other data of thetwo complexes, are different, being affected by the kind of ligand(NH3 or H2O). Konar et al. stated that the hydrogen atoms wereplaced at their calculated positions and did not mention how theywere refined [15]. The values in the cif file deposited with CCDCNo. 217834 indicate that the hydrogen atoms of all water mole-cules were refined isotropically without applying any constraintor restrain. It can be concluded that the composition of both anal-ogous structures are different. The composition of complex 2 wasalso confirmed by elemental analysis, IR, TGA and other data.

The coordination environment at the copper is an ideal{CuO2N3} square pyramid, which is reflected by the s value of0.054, defined by Addison et al. [39] (s = 0 for an ideal square-pyr-amid, and s = 1 for ideal trigonal bipyramid, s = (H �U)/60 whereH and U are the two largest angles around the central atom). The svalue of the analogous structure is 0.066. The apical site of squarepyramid is taken up by the carboxyl oxygen of a symmetry relatedneighbouring pyrazine dicarboxylate ion. The mean plane formedby N1, N3, N4 and O1 has an r.m.s. deviation of 0.0172 Å, showingit to be essentially planar. The Cu(II) ion is 0.1577 Å above theplane, towards the apical site. The Cu(II) polyhedron may also beconsidered as a distorted octahedron with a long Cu1� � �O2(x � 0.5,y, �z + 0.5) distance of 2.930(4) Å. However, bond valance analysis[40,41] by the PLATON program [25] showed that the coordinationnumber of Cu(II) is five. The geometric parameters related to thecoordination environment are listed in Table 2.

The copper-nitrogen bond lengths are 1.977 and 2.002 Å. Thus,the copper-nitrogen bond lengths are within the range 1.93–2.03 Åreported for other diammine complexes [42]. The copper–nitro-gen(pz) bond length is 2.064 Å, which is longer than the am-mine–N–Cu bond. The pyrazine group of pzdc ligand is almost

bering scheme and 40% probability displacement ellipsoids. H atoms are shown asz; iv: x + 1, y, z.

Table 3Hydrogen-bonding geometries (Å, �) for 2 and 4.

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

Complex 2O5–H5A� � �O2 0.83(2) 2.01(3) 2.795(5) 158(7)N3–H3A� � �N2i 0.92(6) 2.35(7) 3.268(6) 177(5)N3–H3B� � �O5ii 0.83(7) 2.45(7) 3.257(8) 165(6)N3–H3C� � �O4iii 0.87(5) 2.12(5) 2.985(6) 170(5)N4–H4A� � �O3iii 0.75(6) 2.33(6) 3.002(6) 149(6)N4–H4B� � �O5iii 0.80(7) 2.30(7) 3.027(6) 151(7)N4–H4C� � �O4iv 0.87(6) 2.21(6) 3.055(7) 165(5)O5–H5B� � �O4v 0.82(2) 2.22(6) 2.840(5) 133(8)

Complex 4N9–H9A� � �O4viii 0.91 2.13 2.976(5) 153.5N9–9B� � �O15vi 0.91 2.44 3.193(6) 140.1N9–H9C� � �O6 0.91 2.21 3.094(6) 165.3N10–H10A� � �O2xi 0.91 2.28 3.173(6) 167.8N10–H10B� � �O7ix 0.91 2.21 3.110(5) 171.98N10–H10C� � �O10x 0.91 2.47 3.166(6) 133.9N10–H10C� � �O2W 0.91 2.52 3.046(6) 117.4N11–H11A� � �O1Ovii 0.91 2.35 3.222(6) 161.5N11–H11B� � �O15vi 0.91 2.83 3.157(5) 162.0N11–H11C� � �O5W 0.91 2.31 2.923(6) 124.5N12–H12A� � �O12vi 0.91 2.11 2.956(5) 154.1

2176 S. Tas�cıoglu et al. / Polyhedron 30 (2011) 2171–2180

planar (the r.m.s. deviation is 0.0125 Å). The dihedral angles be-tween the pyrazine and the carboxyl groups are 82.3(2)� and10.9(7)� and that between the two carboxyl groups is 87.3(4)�.

The pzdc ligand is coordinated to the copper atoms through twooxygen atoms from its two carboxylate groups and one nitrogenatom. The pzdc ligand links one copper ion, forming a chelate,and bridges another copper ion with a second carboxylate groupin a monodentate fashion, as shown in Fig. 3. The neighbouringcopper centres are combined together by bridging pzdc ligandsto form a 1D covalently bonded chain along the a-axis. The 1Dpolymer is further stabilized by weak face-to-face p� � �p interac-tions from the pyrazine rings [Cg1–Cg1i separation: 3.566(3) Å,vertical displacement of Cg: 3.288(2) Å; i = x + 1/2, y, �z + 1/2;[Cg1@N1–C1–C2–N2–C3–C4].

The compound has both intramolecular and intermolecularhydrogen bonds, and the geometric parameters are given in Table 3.The 1D subunits are linked into a 3D coordination frameworkthrough these intermolecular O–H� � �O, N–H� � �N and five N–H� � �Ohydrogen bonds. Complex 2 molecule forms a polymeric chain(Fig. 4). Fig. 5 shows the stacking of molecules in the unit cell downthe a-axis. The structure contains no solvent accessible voids.

N12–H12B� � �O4viii 0.91 2.31 2.997(6) 132.6N12–H12C� � �O14vi 0.91 2.17 3.083(6) 177.0O1W–H1W1� � �O1Ovii 0.89(2) 1.87(2) 2.759(5) 173(6)O1W–H1W2� � �O7Wvi 0.89(2) 1.88(2) 2.760(5) 167(5)O2W–H2W1� � �O14x 0.89(2) 2.05(3) 2.929(5) 168(6)O2W–H2W2� � �O4wx 0.90(2) 2.02(3) 2.851(5) 153(7)O3W–H3W1� � �O1ix 0.89(2) 2.17(3) 2.994(5) 154(5)O3W–H3W2� � �N4ix 0.88(2) 2.08(3) 2.853(5) 146(6)O4W–H4W1� � �O13 0.91(2) 2.06(3) 2.922(5) 159(5)O4W–H4W2� � �N8vi 0.89(2) 2.11(3) 2.974(6) 163(6)O5W–H5W1� � �O2ix 0.90(2) 2.04(4) 2.871(5) 153(7)O5W–H5W2� � �O3W 0.89(2) 1.93(2) 2.808(6) 172(7)O6W–H6W1� � �O8Wviii 0.89(2) 1.88(2) 2.743(5) 164(6)O6W–H6W2� � �O6 0.89(2) 1.90(3) 2.768(5) 164(7)

i: �x + 1, y,+1/2, �z + 1/2; ii: x + 1/2, y, �z + 1/2; iii: x, �y + 3/2, z + 1/2; iv: x � 1/2, y,�z + 1/2; v: 3/2 � x, ½ + y, z; vi: �x + 1, y + 1/2, �z + 2; vii: �x + 1, y + 1/2, �z + 1;viii: �x, y � 1/2, �z + 2; ix: �x, y � 1/2, �z + 1; x: x � 1, y, z; xi: x, y � 1, z.

3.6.2. Crystal structure of {[Cu2(pz(COO)2)2(NH3)2(H2O)3][Cu(pz(COO)2)(NH3)(H2O)2][Cu(pz(COO)2)(NH3)(H2O)]�2H2O}n (4)

The complex 4 crystallizes in the monoclinic space group P21. bis 90.159(3)� and the structure is twinned. It is common that thepseudo-merohedral twin is seen with monoclinic cells with anglesnear to 90�. Crystal data and refinement results are listed in Table1. The unit cell consists of three 1D coordination polymers and twolattice water molecules. An explanation for the coordination poly-mers are depicted in Schemes 1–3. As illustrated in Fig. 6, there arefour crystallographically independent metal sites. Cu1 and Cu4atoms display a square-pyramidal geometry with two oxygenatoms of two pzdc ligands, one nitrogen atom of an ammine ligandand one water oxygen atom, {CuO3N2}, while Cu2 and Cu3 atomshave an octahedral geometry with two oxygen atoms of two pzdcligands, one nitrogen atom of an ammine ligand and two wateroxygen atoms, {CuO4N2}.

The determination of the coordination numbers of the metalcentres in 4 was not straightforward. Analysis of the coordinationspheres around the copper centres in 4 by the PLATON [25] programreveals that the coordination numbers of Cu1 and Cu4 are six; butthe coordination numbers of Cu2 and Cu3 are seven, i.e. one of the

Fig. 4. Polymeric chain of complex 2

carboxylate groups is coordinated in a bidentate manner throughthe two oxygen atoms and water molecules with a distance of lessthan 2.92 Å (sum of the van der Waals radius) to copper ions are allcoordinated. Checkcif, a service of the International Union of Crys-tallography, reports the moiety formula of C12H16Cu2N6O11,C6H9CuN3O6, C6H7CuN3O5, 2(H2O). This moiety formula shows that

along the a-axis, down to b-axis.

Fig. 5. A packed diagram of {[Cu(OOC)pz(COO)(NH3)2](H2O)]3}n (2) down to a-axis. Dashed lines show the stacking with intra- and intermolecular hydrogen bonds.

N

N

Cu

OO

O

O

NN

O

O

O

O

CuOH2

OH2

NH3

NH3

n

NN

O

O

O

O

OH2

Scheme 1. Catena-Poly-[[ammineaquacopper(II)amminediaquacopper(II)-l-pyrazine-2,3-carboxylato-j3N1,O2:O3]-l-Pyrazine-2,3-carboxylato-j3N1,O2:O3].

S. Tas�cıoglu et al. / Polyhedron 30 (2011) 2171–2180 2177

one water molecule is coordinated to Cu1 and Cu4 but two watermolecules are coordinated to Cu2 and Cu3. In order to clarify thecoordination numbers, bond valence analysis has also been con-ducted by the PLATON program. The bond valence parameters [40]R used for the calculations are 1.6790 and 1.7510 for Cu2+� � �O2�

and Cu2+� � �N3�, respectively. 0.37 Å is used for the B parameterin all calculations. Bond valence analysis results suggest that allcopper centres in 4 have square-pyramidal geometries with a{CuO3N2} coordination.

A literature survey reveals that copper atoms in square-pyrami-dal geometries are generally placed above the basal plane towardsthe apical atoms [43–45]. As summarised in Table 4, Cu1 and Cu4are placed above the basal plane, but the displacement of Cu2 and

Cu3 from the defined planes is negligible. The bond lengths in theequatorial planes are �2 Å on average. The axial coordination sitesof the copper atoms are occupied by the water oxygen, with aninteratomic Cu� � �O distance ranging from 2.254 to 2.899 Å; theCu–Oax distances are longer than those of Cu–Oeq. The Cu1–O1Wand Cu4–O6W bonds are 2.289 and 2.254 Å, respectively. In gen-eral, Cu� � �L bonds in the range 2.5–2.9 Å may be considered assemi-coordinating [46]. The Cu2–O3W, Cu2–O2W, Cu3–O4W andCu3–O5W bonds are 2.558, 2.785, 2.485 and 2.899 Å, respectively,indicative of weak coordination bonds. Hence, the geometry maybe considered to be intermediate between an asymmetric distortedoctahedral geometry and a distorted square-based-pyramidalfive-coordinate geometry, plus an additional long bond to the sixth

N

N

Cu

OO

O

O

OH2

OH2

NH3

N

N

OO

O

O

n

Scheme 2. Catena-Poly-[[amminediaquacopper(II)]-l-pyrazine-2,3-carboxylato-j3

N1,O2:O3].

N

N

Cu

OO

O

O

OH2

NH3

N

N

OO

O

O

n

Scheme 3. Catena-Poly-[[ammineaquacopper(II)]-l-Pyrazine-2,3-carboxylato-j3

N1,O2:O3].

Fig. 6. Copper coordination spheres in complex 4 with lattice water molecules O7W and O8W. The thermal ellipsoids were drawn at 40% probability. i: x, y � 1, z; ii: �x + 1,y + 1/2, �z + 1; iii: �x + 1, y + 1/2, �z + 2.

Table 4Basal planes, r.m.s. deviations and Cu(II) positions relating to planes in 4. Planesdefined treating all metal centers as square-pyramidally coordinated.

Mean planedefined byatoms

r.m.s. deviations from thebest least-squares planes(Å)

Centralatom

Cu(II) positionsabove the plane(Å)

O1, 7, N1, N9 0.113 Cu1 0.129(2)O3i, O5, N3,

N100.147 Cu2 0.001(2)

O11ii, O9, N5,N11

0.136 Cu3 0.035(2)

O15iii, O13, N7,N12

0.104 Cu4 0.158(2)

Symmetry codes: i: x, y � 1, z; ii: �x + 1, y + 1/2, �z + 1; iii: �x + 1, y + 1/2, �z + 2.

2178 S. Tas�cıoglu et al. / Polyhedron 30 (2011) 2171–2180

ligand. Therefore, the coordination geometry around the Cu2 andCu3 atoms can thus be viewed as 4 + 1 + 1⁄ [47–49], an elongatedoctahedron which may be attributed to the well-known Jahn–Tell-er effect observed in this system. The coordination environments atCu1 and Cu4 are ideal {CuO3N2} square pyramids with s values of0.052 and 0.072, respectively. All he pyrazine groups in 4 areessentially planar, and the dihedral angles between the carboxyl-ate groups and pyrazine planes are summarized in Table 5.

The three dimensional structure is formed by both intramolec-ular and intermolecular hydrogen bonds, and the geometricparameters are given in Table 3. The 1D parts are linked throughthese extensive hydrogen bonds. Fig. 7 shows the stacking ofmolecules in the unit cell down the c axis. The structure containsno solvent accessible voids.

Table 5The planes and their dihedral angles.

Pyrazine ring of Pzdc ligands r.m.s. Carboxylate planes Angle to pyrazine plane (o) Angle between carboxylate planes (o)

C1, C2, C3, C4, N1 N2 0.0156 O1, O2, C5 14.8(7) 72.1(4)O3,O4, C6 71.4(3)

C7, C8, C9, C10, N3, N4 0.0122 O5, O6, C11 6.1(8) 89.6(4)O7, O8, C12 87.6(2)

C13, C14, C15, C16, N5, N6 0.0035 O9, O10, C17 3.7(9) 83.3(4)O11, O12, C18 83.8(3)

C19, C20, C21, C22, N7, N8 0.0195 O13, O14, C23 14.7(7) 78.8(5)O15, O16, C24 78.5(2)

Fig. 7. A packed diagram of complex 4 showing 1D coordination polymers and intra- and intermolecular hydrogen bonds.

S. Tas�cıoglu et al. / Polyhedron 30 (2011) 2171–2180 2179

4. Conclusion

Since the carboxylic acid groups of pyrazine-2,3-dicarboxylicacid have different acidities, the pH of the reaction medium affectsthe coordination modes of H2pzdc. Complex 1 is formed in thepresence of 2-(2-aminoethylamino)ethanol or triethanolaminewith insufficient amounts for full neutralization, however complex3 is formed in the absence of any base. When the reactants (CuBr2

and H2pzdc) are reacted in 5 N NH3 solution, because of the strongbasic medium, all of the acidities have been neutralized and com-plex 2 is formed. In 5 N ammonia solutions of complexes 1 and 3,different NH3 coordinations occur; complex 1 forms complex 2,

while complex 3 forms complex 4 with partial replacements togive oligomers with different coordination geometries. Recrystalli-zation of complex 4 from 5 N NH3 results in complex 2. All thecomplexes exhibit 1D coordination polymers. Only the structureof complex 1 has a bromide ion; complexes 1, 3 and 4 have poly-nuclear structures; the complex 2 molecule has a mononuclearand five-coordinating molecular structure that forms a polymericchain and crystallises in the orthorhombic crystal system. Themolecular structure of complex 4 has 3 linear polymeric chainswhich include different units with different copper ion–ligandcoordinations and are bonded to each other by intra- and inter-molecular hydrogen bonding, and thus three dimensional struc-

2180 S. Tas�cıoglu et al. / Polyhedron 30 (2011) 2171–2180

tures are formed. Complex 4 crystallises in the monoclinic systemand has a pseudo-merohedral twin formation. The high values ofthe magnetic susceptibilities may indicate polynuclear and poly-meric structures.

Appendix A. Supplementary material

CCDC 727014 and 727015 contain the supplementarycrystallographic data for 2 and 4. These data can be obtained freeof charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, orfrom the Cambridge Crystallographic Data Centre, 12 Union Road,Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:deposit@ccdc.cam.ac.uk.

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