Polyhedron 31 (2012) 386–394

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Polyhedron

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C�H� � �Pd interactions and cyano-bridged heteronuclear polymeric complexes_Ilkay Çaylı a, Günes� Süheyla Kürkçüoglu b,⇑, Okan Zafer Yes�ilel c, Onur S�ahin d, Orhan Büyükgüngör d

a Eskis�ehir Osmangazi University, The Institute of Science and Technology, Department of Physics, TR-26480 Eskis�ehir, Turkeyb Eskis�ehir Osmangazi University, Faculty of Arts and Sciences, Department of Physics, TR-26480 Eskis�ehir, Turkeyc Eskis�ehir Osmangazi University, Faculty of Arts and Sciences, Department of Chemistry, TR-26480 Eskis�ehir, Turkeyd Ondokuz Mayıs University, Faculty of Arts and Sciences, Department of Physics, TR-55139 Samsun, Turkey

a r t i c l e i n f o

Article history:Received 22 July 2011Accepted 25 September 2011Available online 1 October 2011

Keywords:Intermolecular C–H� � �Pd interactionsTetracyanopalladate(II) complexesVibrational spectraHeteronuclear polymeric complexesN-methylimidazole complexes

0277-5387/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.poly.2011.09.030

⇑ Corresponding author. Tel.: +90 222 2393750; faxE-mail address: gkurkcuo@ogu.edu.tr (G.S. Kürkçü

a b s t r a c t

Three new heterometallic complexes, [Cu(N-Meim)4Pd(l-CN)2(CN)2]n (1), [Zn(N-Meim)3Pd(l-CN)2(CN)2]n

(2) and [Cd(N-Meim)2Pd(l-CN)4]n (3), have been isolated from the reactions of M[Pd(CN)4] (M = Cu(II),Zn(II) or Cd(II)) and N-Meim (N-methylimidazole) with in different molar ratios. All complexes have beencharacterized by X-ray analyses, vibrational (FT-IR and Raman) spectra, thermal and elemental analyses.The crystallographic analysis reveals that the crystal structures of 1 and 2 are 1D coordination polymer,while 3 presents a 2D network. In the Cu(II) and Zn(II) complexes, two cyanide groups of [Pd(CN)4]2�

coordinated to the adjacent M(II) ions and distorted octahedral and square pyramidal geometries of com-plexes are completed by four and three nitrogen atoms of N-Meim ligands, respectively. The Cd(II) ion issix-coordinate, completed with the two nitrogen atoms of N-Meim ligands in the axial positions and thefour nitrogen atoms from bridging cyano groups in the equatorial plane. The most striking features ofcomplexes 1–3 are the presence of obvious C–H� � �Pd hydrogen-bonding interactions between the Pd(II)and hydrogen atoms of N-Meim ligand. This weak hydrogen bonding plays a crucial role in the architec-ture of the network polymers. The adjacent chains are held together by C–H� � �Pd, C–H� � �p or p� � �p inter-actions, forming three-dimensional network.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Today, there is an increasing interest in the synthesis and char-acterization of new coordination polymers due to their challengingstructural features. These complexes frequently contain porousstructures and can act as adsorbents for gases [1], as molecularsieves [2], in sensing devices [3], as hosts for smaller guest mole-cules [4], in non-linear optics devices [5] and as magnetic materials[6]. Recently, cyano complexes with various degrees of dimension-ality have been the subject of structural studies. In such a case, thecyano group or cyano complex anion in addition to its structuralfunction, also demonstrates an important function: the particularcharacteristics of the cyano ligand have accorded it wide-ranginginterest in various research areas [7,8]. The well-known one-,two- and three-dimensional cyano-bridged metal complexes,[MLPd(CN)4], are built by stacking the two-dimensional palladiumcyanide sheets in layers [9–22].

For many years there had been considerable interest in the acti-vation of C–H bonds by transition metal complexes. In this connec-tion, many examples of transition metal complexes showing theagostic or anagostic C–H� � �M interaction have been recognized

ll rights reserved.

: +90 222 2393578.oglu).

[13–16]. The C–H� � �M interaction can be viewed as Lewis acid–Le-wis base interactions, wherein the metal center in the formerserves as the Lewis base while in the latter it adopts the role ofthe Lewis acid [16]. Recently a few examples of the three-centerfour-electron agostic interaction have been reported [13,17–22].The C–H� � �M interactions are relevant with d8 systems and consid-ered to be of importance for the understanding of catalytic reac-tions [23]. Furthermore, the C–H� � �M hydrogen bond plays acrucial role in constructing the supramolecular network [24].

In the preceding studies, the complexes of imidazole and itsmethyl derivatives with the metal(II) ion were described in sev-eral papers [25–28]. We have recently reported the vibrationalspectra, thermal properties and crystal structure results of cya-no-bridged heteronuclear polymeric complexes [29–32]. As a partof our continuing research on the syntheses and characterizationsof complexes, we define in this study, the syntheses, spectral (FT-IR and Raman), thermal and elemental analyses of the [Cu(N-Meim)4Pd(l-CN)2(CN)2] (1), [Zn(N-Meim)3Pd(l-CN)2(CN)2] (2)and [Cd(N-Meim)2Pd(l-CN)4]n (3). The molecular and crystalstructures of the cyano-bridged heteronuclear polymeric com-plexes 1–3 have been designated by X-ray single crystal diffrac-tion. The thermal decomposition behaviors of the complexeswere followed up in the temperature range 30–700 �C in the sta-tic air atmosphere.

Table 2The bond distances and angles in the complexes (Å, �).

Selected atoms

Complex 1Pd1–C10 1.992 (3) Cu1–N1 2.0270 (16)Pd1–C9 1.9929 (19) Cu1–N3 2.0214 (16)

Cu1–N5 2.510 (2)

C10–Pd1–C9ii 88.39 (9) N3i–Cu1–N5 88.49 (7)C10–Pd1–C9 91.61 (9) N3–Cu1–N5 91.51 (7)N3–Cu1–N1 88.29 (7) N1–Cu1–N5 89.78 (7)N3–Cu1–N1i 91.71 (7) N1i–Cu1–N5 90.22 (7)

Complex 2Pd1–C13 1.996 (3) Zn1–N1 2.021 (2)Pd1–C14 2.000 (3) Zn1–N3 1.997 (2)Pd1–C15 1.996 (3) Zn1–N5 2.007 (2)Pd1–C16 1.987 (3) Zn1–N7 2.261 (2)

Zn1–N8 2.293 (2)

C16–Pd1–C15 92.20 (10) N5–Zn1–N1 119.98 (10)C16–Pd1–C13 85.79 (10) N3–Zn1–N7 90.90 (9)C15–Pd1–C13 177.97 (10) N5–Zn1–N7 91.65 (9)C16–Pd1–C14 179.12 (11) N1–Zn1–N7 88.87 (9)C15–Pd1–C14 88.53 (11) N3–Zn1–N8 88.05 (9)C13–Pd1–C14 93.47 (10) N5–Zn1–N8 91.23 (9)N3–Zn1–N5 122.51 (9) N1–Zn1–N8 89.18 (9)N3–Zn1–N1 117.49 (9) N7–Zn1–N8 177.06 (9)

Complex 3Pd1–C5 1.984 (2) Cd1–N3 2.377 (2)

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2. Experimental

2.1. Materials

High purity N-methylimidazole (99%), NiCl2�6H2O (98%), CuCl2

(98%), ZnCl2 (99%), CdCl2�H2O (98%) and KCN (96%) were purchasedfrom Aldrich Chemical Co. Inc. and used as received. All otherchemicals were of AR grade.

2.2. Physical measurements

Elemental analyses (carbon, hydrogen and nitrogen) were per-formed using a LECO CHNS-932 analyzer. The FT-IR spectra wererecorded as KBr pellets in the range of 4000–400 cm�1 (2 cm�1 res-olution) on a Perkin Elmer 100 FT-IR spectrometer which was cal-ibrated using polystyrene and CO2 bands. The Raman spectra weremeasured in the range of 3200–100 cm�1 on a Bruker Senterra Dis-persive Raman instrument using laser excitation of 785 nm. PerkinElmer Diamond TG/DTA thermal analyzer was used to recordsimultaneous TG, DTG and DTA curves in the static air atmosphereat a heating rate of 30–700 �C using platinum crucibles.

2.3. Crystallographic data collection and refinement

Diffraction experiments were carried out at 296 K on a StoeIPDS diffractometer. The structures were solved by direct methodsand refined using the programs SHELXS97 and SHELXL97 [33]. All non-hydrogen atoms were refined anisotropically by full-matrix leastsquares methods [33]. Some H atoms (bonded to C8 for 1, C4 andC12 for 2 and C2 for 3) were located in a difference map and refinedfreely. Other hydrogen atoms bonded to carbon were placed in cal-culated positions (C–H = 0.93–0.96 ÅA

0

) and treated using a ridingmodel with U = 1.2 times the U value of the parent atom for CHand CH3. The following procedures were implemented in our anal-ysis: data collection: X-Area, cell refinement: X-Area, data reduc-tion: X-RED [34]; program(s) used for molecular graphics were

Table 1Crystal data and structure refinement parameters for complexes

1 2 3

Empirical formula C20H24CuN12Pd C16H18N10PdZn C12H12CdN8PdFormula weight 602.45 522.17 487.10T (K) 293 (2)Wavelength (Å) 0.71073 MoKaCrystal system triclinic monoclinic monoclinicSpace group P�1 P21/c C2/ma (Å) 8.3038 (6) 8.2748 (3) 16.4032 (10)b (Å) 8.6157 (7) 13.9991 (4) 7.6933 (5)c (Å) 9.9506 (7) 18.4127 (8) 7.3147 (5)a (�) 71.776 (6)b (�) 73.441 (7) 104.688 (3) 115.806 (5)c (�) 87.798 (6)V (Å3) 647.14 (8) 2063.22 (13) 831.02 (9)Z 1 4 2Absorption coefficient

(mm�1)1.55 2.06 2.37

Dcalc (Mg m�3) 1.546 1.681 1.947h Range for data

collection (�)2.5–27.9 1.9–28.1 2.8–27.3

Measured reflections 6822 23803 4601Independent reflections,

Rint

2669, 0.029 4279, 0.048 938, 0.033

Observed reflections[I > 2r(I)]

2317 3901 854

Absorption correction Integration Stoe X-RED (Stoe & Cie, 2001)Refinement method Full-matrix least-squares on F2

Final R indices (all data) R1 = 0.023wR2 = 0.056

R1 = 0.027wR2 = 0.066

R1 = 0.019wR2 = 0.048

Goodness-of-fit on F2 1.02 1.08 1.15Dqmax (e �3) 0.37 0.62 0.33Dqmin (e �3) �0.34 �0.54 �0.43

as follows: MERCURY programs [35]; software used to prepare mate-rial for publication: WinGX [36].

2.4. Synthesis

K2[Pd(CN)4]�H2O was prepared by mixing stoichiometricamounts of palladium(II) chloride (0.71 g, 4 mmol) with potassiumcyanide (1.04 g, 16 mmol) in water solution (25 mL). The mixturewas refluxed with stirring for 3 h at 50 �C in a temperature-con-trolled bath and then the K2[Pd(CN)4]�H2O solution was cooled to

Cd1–N1 2.271 (3)

C5i–Pd1–C5 90.37 (13) N3iv–Cd1–N3 87.18 (12)C5ii–Pd1–C5 89.63 (13) N1–Cd1–N3iii 87.38 (8)N1–Cd1–N3 92.68 (8) N3–Cd1–N3iii 92.82 (12)

Symmetry codes: (i) �x + 1, �y + 1, �z + 1; (ii) �x + 2, �y + 1, �z for 1 and (i) �x + 1,y, �z + 2; (ii) x, �y, z; (iii) �x + 1, �y, �z + 2; (iv) �x + 1, �y + 1, �z + 1 for 3.

Fig. 1. The molecular structure of 1 showing the atom numbering scheme ((i) 1 � x,1 � y, 1 � z; (ii) �1 + x, y, 1 + z).

Fig. 2. C–H� � �Pd interactions (a); C–H� � �p interactions (b) of the complex 1.

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room temperature. To this solution, 4 mmol (0.328 g) of the N-Meim dissolved in ethanol and 1 mmol of the metal chloride(CuCl2 = 0.134 g, ZnCl2 = 0.136 g and CdCl2�H2O = 0.201 g) dis-solved in water were added with continuous stirring for approxi-mately for 3 h at 60 �C in a temperature-controlled bath. Thereaction mixture was cooled down to room temperature. The crys-tals formed were filtered and washed with water and ethanol anddried in the air. Elemental analyses are in good agreement with thecalculated values. Anal. Calc. for C20H24N12CuPd (1) (MA = 602.45 g/mol): C, 39.87; H, 4.02; N, 27.90. Found: C, 39.90; H, 3.76; N,27.40%. Anal. Calc. for C16H18N10ZnPd (2) (MA = 522.19 g/mol): C,36.80; H, 3.47; N, 26.82. Found: C, 36.82; H, 3.28; N, 26.96%. Anal.Calc. for C12H12N8CdPd (3) (MA = 487.11 g/mol): C, 29.59; H, 2.48;N, 23.00. Found: C, 29.71; H, 1.67; N, 22.76%.

Fig. 3. The molecular structure of 2 showing the atom numbering scheme ((i)�1 + x, 1/2 � y, �1/2 + z; (ii) 1 + x, 1/2 � y, 1/2 + z).

3. Results and discussion

3.1. Description of structures

The X-ray structure determinations of complexes 1–3 revealcoordination polymers built up by M(N-meim) units connectedthrough bridging tetracyanopalladate anions. Details of crystalstructures are given in Table 1. The coordination bond lengthsand angles are reported in Table 2 together with other relevantgeometrical data. These values compare well to those found in

the analogous [Ni(CN)4]2� complexes [32]. The X-ray structuresof complexes 1–3 indeed reveal the presence of an apical C–H� � �Pdinteraction [37,38]. In structures 1 and 3 the metal atoms lie on

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special positions. In complex 1 this is an inversion center, while incomplex 3 this is a site with symmetry 2/m.

3.1.1. Complex 1X-ray analysis has revealed that the crystal structure of 1 con-

sists of 1D linear chains running in [111] direction. The molecularstructure of the complex 1 is depicted in Fig. 1 with the atomicnumbering scheme. The Cu(II) and Pd(II) ions are located on a

Fig. 4. C–H� � �Pd interactions (a); C–H� � �

inversion center. The Cu(II) ion is six-coordinate, complexed withthe four nitrogen atoms of N-Meim ligands in the equatorial planeand the two nitrogen atoms from bridging cyano groups in the ax-ial positions. The Cu–N1 and Cu–N3 bond distances on the equato-rial plane have values of 2.0270(16) and 2.0214(16) Å, respectively,while the Cu–N5 bond distance of 2.510(2) Å in the axial positionsis strongly elongated due to Jahn-Teller distortion. The Pd(II) atomadopts square planar geometry and it is coordinated to the four

p interactions (b) of the complex 2.

Fig. 5. The molecular structure of 3 showing the atom numbering scheme. ((i)1 � x, y, 1 � z; (ii) x, 1 � y, z; (iii) 1 � x, 1 � y, 1 � z).

Fig. 6. An infinite

Fig. 7. C–H� � �Pd interactio

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carbon atoms from cyanide ligands (Pd–C = 1.992 Å). The adjacentPd1� � �Cu1 and Pd1� � �Pd1i distances in the 1D chain are 5.497 and10.994 Å ((i) �1 + x, y, 1 + z). These bond distances compare well tothe literature values [9,10,39].

Adjacent 1D chains are further extended to a 2D novel hydro-gen-bonded layered network through the intermolecular C–H� � �Pdhydrogen bond between the Pd1 and H8B atom of methyl group(Fig. 2). The Pd� � �H, C–H� � �Pd distances and C–H� � �Pd angles are3.296, 4.013 Å and 137.02�, respectively. Adjacent 2D layers arethen packed orderly via the intermolecular C–H� � �p interactionsbetween C4–H4C of methyl group and imidazole ring to form a3D supramolecular architecture (H4C� � �Cg1 = 2.99 Å, Cg1 = N1,C2, N2, C3, C1).

3.1.2. Complex 2X-ray diffraction study demonstrates that complex 2 crystal-

lizes in the monoclinic space group P21/c and shows a 1D poly-meric coordination chain structure (Fig. 3). The asymmetric unitcontains a Zn(II) ion, three N-Meim ligands and a tetracyanopalla-date(II) anion. The coordination sphere of Zn(II) ion is a distortedtrigonal-bipyramidal geometry with the s value of 0.91(s = (177.05–122.51)/60 = 0.91) [40,41], in which the equatorialplane is provided by three N-Meim ligands, as well as two N atomsfrom symmetry related cyano ligands occupying the axial sites. ThePd(II) ion is four coordinate with four C atom from cyanide ligands

2D layer in 3.

ns of the complex 3.

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in a square-planar arrangement and the Zn(II) ion is five coordinatewith five N atoms from two cyanide and three N-Meim ligands. In1, the equatorial plane is provided by three nitrogen atoms fromN-Meim ligands [Zn1–N1 = 2.021 (2), Zn1–N3 = 1.997 (2) andZn1–N5 = 2.007 (2) Å]. These bond distances are comparable tothe corresponding bonds lengths in literature [32,42,43]. The axialposition is occupied by two nitrogen atoms from cyano ligands

Fig. 8. The FT-IR (a) and Raman (

[Zn1–N7 = 2.261 (2) and Zn1–N8 = 2.293(2) Å]. These values arecomparable to those observed in other tetracyanopalladate(II)complexes [9,19,44]. The adjacent Pd1� � �Zn and Pd1� � �Pd1i dis-tances are 5.376 and 10.705 Å ((i) �1 + x, 1/2 � y, �1/2 + z).

A noticeable feature of 2 is the presence of weak intermolecularC–H� � �Pd interactions in the molecular packing. As shown in Fig. 4,each 1D polymeric chain is stacking with adjacent 1D chain via the

b) spectra of the complexes.

Table 3The vibrational wavenumbers (cm�1) of N-Meim in complexes.

Assignmenta [49] N-Meim 1 2 3

(Liquid) FT-IR Raman FT-IR Raman FT-IR Raman

m(CH) 3132 sh 3142 s 3152 w 3145 m 3159 w 3139 m 3141vwm(CH) 3107 s 3127 s 3131 w 3121 vs 3114 w 3128 mm(CH) 3016 w 3054 w 3054 s 3058 wm(CH3) 2987 w 2962 w 2962 m 2961w 2964 w 2966 wm(CH3) 2953 s 2925 m 2931 w 2937 w 2934 w 2940 wmring, d(CH3) 1586 w 1590 m 1589 m 1542 m 1581 mmring, d(CH3) 1518 vs 1537 vs 1531 w 1541 s 1529 m 1535 s 1535 wmring, d(CH3), m(N–CH3) 1506 w 1525 w 1520 w 1527 w 1518 wd(CH3), mring 1471 w 1479 w 1480 w 1474 w 1476 m 1477 w 1476 wd(CH3), mring 1421 s 1421 s 1425 w 1419 w 1419 m 1428 w 1423mmring, d(CH3) 1370 w 1379 w 1370 w 1374 w 1376 s 1374vw 1375mmring, d(CH3) 1359 m 1353 w 1385 w 1350 w 1355 s 1354 w 1355mmring, d(CH3) 1330 w 1341 w 1340 m 1337 w 1340 wd(CH), mring 1286 s 1286 s 1287 m 1287 m 1286 s 1285 m 1284mmring, d(CH3), m(N–CH3) 1231 vs 1239 vs 1239 m 1237 m 1237 w 1238 m 1237md(CH3) 1109 s 1107 vs 1107 w 1106 w 1122 m 1107 sd(CH), mring 1078 vs 1100 vs 1082 w 1099 w 1097 s 1092 m 1086md(CH3), mring 1029 s 1028 m 1028 m 1031 w 1031 s 1029 w 1033 sdring, mring 907 s 950 s 958 m 956 s 953 s 941 s 941 wc(CH) 820 s 828 s 825 m 859 s 856 m 835 s 843 wc(CH) 743 s 741 vs 750 w 741 s 740 w 741 s 738 wm(N–CH3), mring 665 vs 666 s 675 m 664 s 673 vs 657 m 676 vsdring 617 s 617 s 622 w 620 m 621 w 615 w 616 w

a Abbreviations used: m, stretching; d, deformation; x, wagging; t, twisting; r, rocking; s, strong; m, medium; w, weak; sh, shoulder; v, very.

Table 4The vibrational wavenumbers (cm�1) of the [Pd(CN)4]2� group in complexes.

Assignmenta

[54][Pd(CN)4]2� [K2Pd(CN)4]�H2O 1 2 3

A1g (2161) (2189) vs (2170)vs

(2179)vs

B1g (2147) (2135 vs) (2158) s (2150)vs

(2163)vs

Eu, m(CN) 2142 2145 m 2181 s,2137 vs

2151vs,2137vs

2156vs

Hot band 2135 vs 2127 vs 2130w

Eu, m(PdC) 503 486 w 502 wA1g (430) (455) m (455)

m(461)m

Eu, d(PdCN) 393 400 m 425 m 490 m 409 m

a Abbreviations used: s, strong; m, medium; w, weak; sh, shoulder; v, very. Thesymbols m, d and p refer to valence, in-plane, and out-of-plane vibrations, respec-tively. The bands observed in the Raman spectra are given in parentheses.

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intermolecular C–H� � �Pd interactions. The Pd� � �H distance(3.118 Å) and C–H� � �Pd angle (138.89�) are similar to those re-ported in the literature [37,38,45]. It is also interesting to note thatone of the C–H groups of the imidazole ring is involved in a C–H� � �p interaction with the imidazole ring (Fig. 4). The H� � �Cg dis-tance and the C–H� � �Cg angle are 3.183 Å and 152.53�, respectively.This weak C–H� � �Pd hydrogen bonding plays a major role in con-structing network polymers.

3.1.3. Complex 3The crystal structure of 3 with the atom labeling is shown in

Fig. 5. Complex 3 reveals a 2D layer coordination arrangement(Fig. 6), which has a similar network as the previously reported[Cd(mim)2Ni(l-CN)4]n [28] and [Cd(N-Meim)2Ni(l-CN)4]n [32]complexes. The Cd(II) and Pd(II) ions are located on a symmetrycenter. The Cd(II) ion has a slightly distorted octahedral geometry,

completed by four nitrogen atoms from l-cyano ligands in equato-rial positions whereas the axial positions are occupied by nitrogenatoms from two N-Meim ligands. The Pd(II) ion is surrounded byfour carbon atoms from l-cyanide ligands in approximately squarecoordination geometry. The Cd1–N1 (2.271(3) Å) and Cd1–N3(2.377(2) Å) bond distances are comparable to those reported forother Cd(II)-tetracyanopalladate(II) complexes [19].

The most striking feature of 3 is the presence of obvious C–H� � �M hydrogen-bonding interactions between the Pd1 and H2atom of imidazole ring (Fig. 7). The 2D layer is extended into athree-dimensional frameworks by C–H� � �Pd interactions. Thestructural parameters related to the C–H� � �Pd(II) interactions in 3are tabulated in Table 1. The Pd(II)� � �H distance is similar that re-ported for the related Pd(II) complexes [19–22]. The interlayer con-tacts of 2.705 Å at C2–H2� � �Pd1 with the C–H� � �Pd(II) angle of159.10�, indicating a stronger interaction in complex 3 than incomplexes 1 and 2. The bond length and angle indicates this inter-action weak intermolecular C–H� � �Pd hydrogen bonding, which isfound in all the three palladium complex crystals. This weakhydrogen bonding plays a crucial role in the architecture of thenetwork polymers and chemical and biological systems [46–48].

3.2. Vibrational (FT-IR and Raman) spectra

The FT-IR and Raman spectra of 1–3 comprise bands confirmingthe presence of all characteristic functional groups in the preparedcomplexes (Fig. 8). As can be seen from Fig. 8, the presence ofbands belonging to the ligand in the FT-IR and Raman spectra ofthe complexes shows the existence of N-Meim in the complexes.The wavenumbers of N-Meim observed in the FT-IR and Ramanspectra of the complexes are given in Table 3 together with vibra-tional data of free N-Meim. Vibration assignments of the N-Meimhave been studied by several authors [32,49–52] and have beenmade according to Sheinker’s studies in Table 3 [49].

As is clear from Table 3, considerable shifts to higher or lowerfrequency occur in the presence of numerous absorption bandsin the spectra of all complexes due to m(CH), m(CH3), mring, d(CH3),m(N–CH3), c(CH) and dring vibration bands. For all complexes, theobserved bands range of 3145–3054 cm�1 and 3159–3054 cm�1

Fig. 9. TG, DTG and DTA curves of complex 2.

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in the FT-IR and Raman spectra can be assigned to m(CH) stretchingbands, respectively. The stretching bands of all complexes have up-ward shifts in frequency when compared to the free moleculewhile the stretching bands of methyl group at 2987 cm�1 and2953 cm�1 were shifted to the low frequency region. Moreover,the bands at 1586–1370 cm�1 are assigned to the stretching ringvibration derived from the similar degenerate mode in complexesand significantly shifted to higher frequency. When the aromaticring nitrogen is involved in complex formation, certain ring modes,particularly at 1359–907 cm�1, increase in value both due to thecoupling with M–N (ligand) bond vibrations and due to alterationsof the ring force field. These shifts can be explained as the couplingof the internal modes of the N-Meim molecule with M–NN-Meim

vibrations. Analogous shifts on coordination were observed in thevibrational spectra of the other metal-coordinated imidazole com-plexes [25–27] and are expounded as the coupling of the internalmodes of the aromatic molecule with the M–N vibrations [53].

The vibrational wavenumbers of the [Pd(CN)4]2� group for thecomplexes studied are illustrated in Table 4. In assigning the bandsattributable to [Pd(CN)4]2� ion in the spectra, we refer to the workof Jones [54]. The presence of [Pd(CN)4]2� anion in the preparedcomplexes is proved by v(C„N) stretching vibrations whose posi-tions are an important tool to distinguish between terminal andbridging character of cyano group. From the FT-IR and Raman spec-tra of produced complexes it is determined that the stretchingvibration of m(C„N) has shifted to approximately 9–39 cm�1 high-er frequency (see Table 4). In-plane bending vibration band d(Pd–CN) shifts to a higher frequency to support the m(CN) stretchingvibration band [55]. Special attention has been paid to the numberand position of the m(C„N) absorption bands in the FT-IR andRaman spectra since they may help to reveal the number and thetype (terminal or bridging) of cyano groups in the complexes. Itis generally known for cyanometallates(II) that upon coordinationof CN group to a metal the m(C@N) shifts to higher frequencies andthe range for terminal cyano ligands extends from 2120 to2140 cm�1. Because cyano nitrogen lone pair resides in a mostlyC@N antibonding orbital, an increase of m(C@N) in bridging cya-

nides is found and it ranges from 2150 to 2210 cm�1 for bridgedcyanopalladates(II) [56]. As a result, one of three absorption bandsrecorded at higher wavenumbers (2181, 2137 and 2127 cm�1 for1) is assigned to the bridging cyano groups. One can infer thatthose C@N groups more strongly bound to the copper atom,C9@N5, gives rise to the band at 2181 cm�1. The bands at2137 cm�1 and 2127 cm�1 are attributed to the terminal cyanogroup, C10@N6. Similarly two strong and sharp absorption bandsat 2151 cm�1 and 2137 cm�1 in the FT-IR spectra of complex 2can easily be attributed to bridging cyano and terminal cyanobands. The band which is observed at a higher frequency is dueto the mechanical coupling, C15@N7 and C13@N8. The bands at2137 cm�1 are imputed to the terminal cyano group, C14@N9and C16@N10. On the contrary CN stretching vibrations are degen-erated and appeared as two or three separate peaks in complexes 1and 2, no splitting of CN stretching mode occurs in complex 3. Theband at 2156 cm�1 frequency belongs to Cd–C@N–Pd type ofbridge cyano ligands and all cyano groups are shown to form bridg-ing cyano ligands [55].

3.3. Thermal analyses

Thermal behavior of the complexes was studied by using ther-mal analysis techniques (TG, DTG and DTA) in the temperaturerange 30–700 �C in the static air atmosphere. Thermal decomposi-tion of the complexes proceeds in three (1 and 2) and two (3)stages. The thermal analyses curves of complex 2 are presentedin Fig. 9. The complexes 1–3 are thermally stable up to 139, 131and 244 �C respectively and then begin to decompose. In the firststage two N-Meim ligands between 139–248 �C (found. 28.31,calcd. 29.36%, DTGmax: 183 �C) for 1 and one N-Meim ligand 131–203 �C (found. 15.86, calcd. 15.72%, DTGmax: 180 �C) for 2 are re-leased. The following stages, remaining two N-Meim ligands andfour cyano groups in 1 and 2 decompose between 248 and507 �C for 1, 203 and 413 �C for 2 (DTAmax: 451 �C for 1 and403 �C for 2). In first stage of 3, two N-Meim ligands (found.34.19, calcd. 33.71%, DTGmax: 312 �C) are released. In the following

394 _I. Çaylı et al. / Polyhedron 31 (2012) 386–394

stage, remaining four cyano groups in 3 decompose between 305and 394 �C for 3 (DTAmax: 376 �C for 3). The total mass loss of alldecomposition process is 68.67% (calcd. 68.20%) for 1, 60.55%(calcd. 60.97%) for 2 and 56.61% (calcd. 55.08%) for 3 suggestingthat MO + PdO are the end products.

4. Conclusion

Three novel cyano-bridged heteronuclear polymeric complexeshave been synthesized and characterized. Structures of all the ob-tained complexes were determined by using vibrational (FT-IR andRaman) spectroscopy, thermal and elemental analysis techniques.Also, structures of complexes 1–3 certainly were designated byX-ray single crystal studies. Using crystallographic data, the crystalstructures of these complexes contains rare intermolecular C–H� � �Pd interactions. It was determined that the crystals packingof complexes 1–3 were a composite of intermolecular C–H� � �Pdand C–H� � �p interactions. Moreover vibrational bands belong tofunctional groups of ligands were examined from vibration spectraof the complexes. Important results about ligands coordination tothe metal through which donor atoms and the coordination formwere inferred.

Acknowledgement

This work was supported by the Research Fund of EskisehirOsmangazi University. Project No. 201019024.

Appendix A. Supplementary data

CCDC 808893, 726604 and 726605 contain the supplementarycrystallographic data for 1, 2 and 3. 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.

References

[1] P. Amo-Ochoa, G. Givaja, P.J.S. Miguel, O. Castillo, F. Zamora, Inorg. Chem.Commun. 10 (2007) 921.

[2] A.J. Fletcher, E.J. Cussen, D. Bradshaw, M.J. Rosseinsky, K.M. Thomas, J. Am.Chem. Soc. 126 (2004) 9750.

[3] N.A. Rakow, K.S. Suslick, Nature 406 (2000) 710.[4] P.V. Bernhardt, E.J. Hayes, Inorg. Chem. 42 (2003) 1371.[5] Q.F. Xu, Q.-X. Zhou, J.-M. Lu, X.-W. Xia, L.H. Wang, Y. Zhang, Polyhedron 26

(2007) 4849.[6] J. Cernak, M. Orendac, I. Potocnak, J. Chomic, A. Orendacova, J. Skorsepa, A.

Feher, Coord. Chem. Rev. (2002) 224.[7] F. Bonadio, M.C. Senna, J. Ensling, A. Sieber, A. Neels, H. Stoeckli-Evans, S.

Decurtins, Inorg. Chem. 44 (2005) 969.[8] S. Bonhommeau, G. Molnar, A. Galet, A. Zwick, J.A. Real, J.J. McGarvey, A.

Bousseksou, Angew. Chem., Int. Ed. 44 (2005) 4069.[9] S.C. Manna, J. Ribas, E. Zangrando, N.R. Chaudhuri, Polyhedron 26 (2007) 3189.

[10] J. Hanko, M. Orendac, J. Kuchar, Z. Zak, J. Cernak, A. Orendacova, A. Feher, SolidState Commun. 142 (2007) 128.

[11] J. Kuchar, J. Cernak, K.A. Abboud, Acta Crystallogr., Sect. C 60 (2004) M492.[12] A.D. Legendre, A.E. Mauro, M.A. de Oliveira, M.T.D. Gambardella, Inorg. Chem.

Commun. 11 (2008) 896.[13] M. Brookhart, M.L.H. Green, L.L. Wong, Prog. Inorg. Chem. 36 (1988) 1.[14] T.S. Thakur, G.R. Desiraju, Chem. Commun. (2006) 552.[15] D. Braga, F. Grepioni, E. Tedesco, K. Biradha, G.R. Desiraju, Organometallics 16

(1997) 1846.[16] L. Brammer, Dalton Trans. (2003) 3145.[17] M. Brookhart, M.L.H. Green, J. Organomet. Chem. 250 (1983) 395.[18] R.H. Crabtree, Angew. Chem., Int. Ed. 32 (1993) 789.[19] H. Zhang, J.W. Cai, X.L. Feng, H.Y. Sang, J.Z. Liu, X.Y. Li, L.N. Ji, Polyhedron 21

(2002) 721.[20] W.B. Yao, O. Eisenstein, R.H. Crabtree, Inorg. Chim. Acta 254 (1997) 105.[21] J. Dehand, J. Fischer, M. Pfeffer, A. Mitschler, M. Zinsius, Inorg. Chem. 15 (1976)

2675.[22] E.C. Alyea, G. Ferguson, S. Kannan, Chem. Commun. (1998) 345.[23] N. Ding, J. Zhang, T.S.A. Hor, Dalton Trans. (2009) 1853.[24] X.F. Shan, L.Z. Wu, X.Y. Liu, L.P. Zhang, C.H. Tung, Eur. J. Inorg. Chem. (2007)

3315.[25] J.B. Hodgson, G.C. Percy, D.A. Thornton, J. Mol. Struct. 66 (1980) 81.[26] Y. Tufan, N. Karacan, J.E.D. Davies, Vib. Spectrosc. 23 (2000) 51.[27] Y. Tufan, J. Incl. Phenom. Macro. 48 (2004) 131.[28] G.S. Kurkcuoglu, O.Z. Yes�ilel, I. Çaylı, O. Buyukgungor, J. Inorg. Organomet.

Polym. 21 (2011) 306.[29] G.S. Kurkcuoglu, O.Z. Yesilel, I. Kavlak, S. Kurtaran, O. Buyukgungor, J. Inorg.

Organomet. Polym. 19 (2009) 314.[30] G.S. Kurkcuoglu, O.Z. Yesilel, I. Kavlak, O. Buyukgungor, J. Mol. Struct. 920

(2009) 220.[31] G.S. Kurkcuoglu, O.Z. Yesilel, I. Cayli, O. Buyukgungor, Z. Kristallogr. 224 (2009)

493.[32] G.S. Kurkcuoglu, O.Z. Yesilel, I. Kavlak, O. Buyukgungor, J. Inorg. Organomet.

Polym. 19 (2009) 539.[33] G.M. Sheldrick, Acta Crystallgr. A64 (2008) 112.[34] Stoe & Cie, X-Area (Version 1.18), X-Red32 (Version 1.04), Stoe & Cie,

Darmstadt, Germany, 2002.[35] C.F. Macrae, I.J. Bruno, J.A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock, L.

Rodriguez-Monge, R. Taylor, P.A. Wood, J. Appl. Crystallogr. 41 (2008) 466.[36] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.[37] T. Kawamoto, I. Nagasawa, H. Kuma, Y. Kushi, Inorg. Chem. 35 (1996) 2427.[38] X.F. Shan, L.Z. Wu, L.P. Zhang, C.H. Tung, Chin. Sci. Bull. 52 (2007) 1581.[39] J. Cernak, J. Skorsepa, K.A. Abboud, M.W. Meisel, M. Orendac, A. Orendacova, A.

Feher, Inorg. Chim. Acta 326 (2001) 3.[40] J.K. Nag, P.K. Santra, C. Sinha, F.L. Liao, T.H. Lu, Polyhedron 20 (2001) 2253.[41] H. Erer, O.Z. Yesilel, C. Darcan, O. Buyukgungor, Polyhedron 28 (2009) 3087.[42] T.A. Zevaco, R. Trotzki, H. Gorls, E. Dinjus, Inorg. Chem. Commun. 1 (1998) 30.[43] S. Abuskhuna, M. McCann, J. Briody, M. Devereux, V. McKee, Polyhedron 23

(2004) 1731.[44] J. Cernak, J. Lipkowski, E. Cizmar, A. Orendacova, M. Orendac, A. Feher, M.W.

Meisel, Solid State Sci. 5 (2003) 579.[45] S. Otsuka, T. Yoshida, M. Matsumoto, K. Nakatsul, J. Am. Chem. Soc. 98 (1976)

5850.[46] T.W. Hambley, Inorg. Chem. 37 (1998) 3767.[47] C. Taubmann, K. Ofele, E. Herdtweck, W.A. Herrmann, Organometallics 28

(2009) 4254.[48] H.V. Huynh, Y. Han, J.H.H. Ho, G.K. Tan, Organometallics 25 (2006) 3267.[49] V.N. Sheinker, D.Y. Movshovich, O.A. Osipov, A.D. Garnovskii, Zh. Obshch.

Khim. (1973) 43.[50] C. Perchard, A. Novak, Spectrochim. Acta A23 (1967) 1953.[51] F.R. Dollish, W.G. Fateley, F.F. Bentley, Characteristic Raman Frequencies of

Organic Compounds, Wiley and Sons, New York, 1974.[52] T. Soma, T. Iwamoto, Inorg. Chem. 35 (1996) 1849.[53] G.S. Kurkcuoglu, O.Z. Yesilel, I. Kavlak, O. Buyukgungor, Struct. Chem. 19

(2008) 879.[54] L.H. Jones, Inorganic Vibration Spectroscopy, Marcel Dekker, 1971, p. 129.[55] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination

Compounds, Wiley and Sons, New York, 1978.[56] A.M. Golub, H. Köhler, V.V. Skopenko, Chemistry of Pseudohalides, Elsevier,

Amsterdam, 1986.