Monatsh Chem (2012) 143:753–761 DOI 10.1007/s00706-011-0629-9
ORIGINAL PAPER
A novel mononuclear square-planar copper(II) complex (Pip-H+)2[CuL4]22 with 2-cyano-3-(2,5-dimethoxyphenyl)acrylic acid as ligand: synthesis, crystal structures, spectral and thermal studies Aliakbar Dehno Khalaji • Karla Fejfarova Michal Dusek • Debasis Das
•
Received: 7 September 2010 / Accepted: 19 August 2011 / Published online: 18 November 2011 Ó Springer-Verlag 2011
Abstract 2-Cyano-3-(2,5-dimethoxyphenyl)acrylic acid and its novel mononuclear square-planar copper(II) complex dipiperidinium tetrakis[2-cyano-3-(2,5-dimethoxyphenyl)acrylic acid]copper(II) ((Pip-H?)2[CuL4]2-) were synthesized and characterized by elemental analyses, FT–IR, UV–Vis spectroscopy, and thermogravimetric analysis. Moreover, the ligand was characterized by 1H and 13C NMR spectroscopy. The structures of the ligand and its copper(II) complex were confirmed by single-crystal X-ray crystallography. Whereas the ligand crystallizes in the triclinic space ˚, group Pı¯ with unit cell parameters a = 4.6911(2) A ˚ , c = 13.7084(6) A ˚ , a = 74.946(4)°, b = b = 9.0181(4) A ˚ 3, and Z = 2, 87.152(4)°, c = 89.220(4)°, V = 559.34(4) A the complex crystallizes in the orthorhombic space group ˚, b = Pccn with unit cell parameters a = 27.5486(5) A ˚ ˚ ˚ 3, and 12.9484(2) A, c = 15.8822(3) A, V = 5,665.34(17) A Z = 4. Keywords Copper(II) complex Spectroscopy Crystal structure Thermogravimetric analysis
A. D. Khalaji (&) Department of Chemistry, Faculty of Science, Golestan University, Gorgan, Iran e-mail:
[email protected] K. Fejfarova M. Dusek Institute of Physics of the ASCR, v.v.i, Na Slovance 2, 182 21 Prague 8, Czech Republic D. Das Department of Chemistry, The University of Burdwan, Burdwan, West Bengal, India
Introduction The ability of carboxylate compounds [1–4] to convert solar light into electricity in dye-sensitized solar cells [5–9] has raised the demand to design and synthesize this class of compounds with improved properties. Transition metal complexes with these ligands have special properties and applications [10–18]. Carboxylate ligands, an important family of O-donor ligands, can coordinate to different metal ions, viz. Cd(II), Mn(III), Cu(II), Tl(I), Ni(II), Pb(II), and Co(II), forming versatile structures with different topologies and stabilities [10–18]. Wein et al. [14] reported dinuclear paddle-wheel-type copper(II) complexes by reacting Cu(OH)2 with bridging carboxylate ligands to study the effect of ligand environment on the structure and properties of copper(II) complexes. Copper, an essential trace element, plays an important role in living organisms [19, 20] as a part of different metalloenzymes. This fact boosted us to study the coordination chemistry of Cu(II) complexes. Herein, we report a novel mononuclear square-planar copper(II) complex (Pip-H?)2[CuL4]2- (1) with a new carboxylate ligand, 2-cyano-3-(2,5-dimethoxyphenyl)acrylic acid (HL) (Fig. 1). Systematic characterization of the ligand and its Cu(II) complex was performed by elemental analyses, FT–IR, UV–Vis spectroscopy, X-ray crystallography, and thermal studies.
Results and discussion 2-Cyano-3-(2,5-dimethoxyphenyl)acrylic acid (HL), an airstable carboxylate ligand, was prepared under mild conditions. The reaction of this ligand with CuI or Cu(NO3)23H2O in the presence of piperidine resulted in
123
754 Fig. 1 Chemical structure of ligand HL and its copper(II) complex [CuL4]2- (1)
A. D. Khalaji et al. H O H
H3C O
O
O
O
CH3CN + CH3OH + Pip
O
+
H3C O CN
H2C CN
O CH3
O CH3
CH3CN + Pip CuI
Cu(NO3)2
2– H3C O
CH3
NC
O
O CH3 O
O 2
CH3
⊕ N H
O
O
CH3
O
O
H
CN
O Cu O
NC
O
O
H3C O CN
O CH3
O CH3
the novel mononuclear square-planar copper(II) complex (Pip-H?)2[CuL4]2- (1) in 73% yield (Fig. 1). The compositions of the ligand 2-cyano-3-(2,5-dimethoxyphenyl)acrylic acid (HL) and its Cu(II) complex 1 were confirmed by microanalytical data. Both HL and 1 are completely soluble in coordinating solvents such as N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and CH3CN, but partly soluble in chloroform, methanol, and ethanol. Spectral characterization FT–IR spectra of HL displayed a sharp strong peak at 2,220 cm-1 corresponding to the cyanide group, which undergoes a blue shift to 2,216 cm-1 in the complex, indicating complexation. HL showed two other bands at 1,697 and 1,678 cm-1 assigned to mas(COO) and ms(COO), respectively, which are also blue-shifted to 1,617 and 1,578 cm-1 in the Cu(II) complex. HL and 1 show several weak bands at 2,855–3,060 cm-1 corresponding to aromatic and aliphatic C–H stretching, and at 1,450–1,580 cm-1 corresponding to aromatic C=C stretching. The electronic spectra of HL and 1 were measured in DMSO. In the UV spectrum of HL, two peaks are found at 301 and 397 nm, attributed to the p–p* and n–p* transitions of the ligand. These peaks are shifted to lower
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wavelength, 295 and 384 cm-1, relative to the free ligand in the UV–Vis spectrum of the complex as a result of the coordination of the carboxylate group to the central copper (II) ion. In the UV–Vis spectrum of 1, a d–d transition is observed in the visible region at 695 nm. A 1H NMR spectrum of HL was recorded using DMSOd6 (Fig. 2a). In this spectrum the methoxy protons appear as singlets at 3.74 and 3.83 ppm. The multiplet peaks in the region of 6.60–7.65 ppm were assigned to hydrogens of the symmetrical aromatic ring. The singlet peak at 8.49 ppm was assigned to the ethylene proton. The proton of the carboxylic acid group appears at 14.08 ppm. A 13C NMR spectrum of HL was recorded using DMSO-d6 (Fig. 2b). Peaks at 55.47 and 56.29 ppm are assigned to two methyl carbons. The peak at 103.11 ppm is due to the cyanide carbon. Peaks at 112.40, 113.18, 116.26, 120.12, 121.14, and 147.79 ppm are assigned to six aromatic carbons and peaks at 152.74 and 153.31 ppm are assigned to two ethylene carbons. The peak at 163.45 ppm is due to the carboxylic acid carbon. Thermal behavior Thermogravimetric (TG) analysis of HL and 1 was performed under a N2 atmosphere. The TG curves, determined
A novel mononuclear square-planar copper(II) complex (Pip-H?)2[CuL4]2Fig. 2 a 1H NMR and b NMR spectra of HL
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13
C
at a heating rate of 20 K min-1, are shown in Fig. 3a and b, respectively. Three thermal stages can be observed for the degradation of HL. The first stage is observed at 508–566 K. The mass loss in the reaction corresponds to the loss of 2,5-dimethoxyphenyl. It is not possible to estimate the changes in the second (566–640 K) and the third (640–1,013 K) stage. Complex 1 is stable up to 443 K and on further heating undergoes decomposition in three stages. In the first stage, complex 1 shows a mass loss of 28.25% in the temperature range 443–464 K, corresponding to the elimination of two pip? and eight methoxy groups (calcd. 30.74%). In the second stage, complex 1 shows a mass loss of 49.04% in the temperature range 464–534 K, which corresponds to
the major stage of the decomposition–elimination of four Ph–C=C–CN groups (calcd. 48.60%). The third decomposition stage of complex 1 is a partial one and shows a mass loss of 17.03% in the temperature range 534–1,013 K (four CO2 molecules, calcd. 15.12%). The final decomposition product is Cu (Fig. 4, supported by the absence of any stretching frequencies of the ligand of the final residue). Description of the crystal structure of HL The molecular structure of 2-cyano-3-(2,5-dimethoxyphenyl)acrylic acid (HL) with the atom numbering scheme is presented in Fig. 5. HL crystallized in a triclinic system.
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Fig. 3 TG curves of HL (a) and 1 (b)
Fig. 4 Part of the probable decomposition pathway of complex 1 on TG analysis
NC O
O O
O 1
O
NC O
Cu O O
CN
O O
O
O
O Cu O
Cu
O O
CN
The phenyl ring and the chain connecting the ring to the CN and COOH groups are roughly coplanar. The angle between the plane of the phenyl ring (C1–C6) and the plane defined by C11–C10–C12 is 4.528(85)°. This degree of coplanarity allows for increased p-conjugation in this compound. HL adopts a trans configuration with respect to the C=C double bond. The bond lengths and angles are within the normal ranges [21]. Selected bond lengths and angles are
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given in Table 2. Bond lengths and angles within the aromatic rings and ethylene group are consistent with those expected for sp2 carbon atoms. The bond length C9–C10 of ˚ is consistent with double bonds and the bond 1.359(2) A ˚, lengths C9–C1, C10–C11, and C10–C12 of 1.4452(19) A ˚ , and 1.480(2) A ˚ , respectively, are consistent 1.435(2) A with single bonds. The bond angles C1–C9–C10, C9–C10– C11, and C9–C10–C12 of 131.41(15)°, 126.03(13)°, and 118.32(14)° confirm the sp2 character of C9 and C10
A novel mononuclear square-planar copper(II) complex (Pip-H?)2[CuL4]2-
757
Fig. 5 ORTEP diagram of ligand HL, showing the atom labeling scheme and 50% probability ellipsoids for the non-hydrogen atoms. Dashed line is a hydrogen bond
atoms, respectively. The bond angles C10–C12–O4, C10– C12–O3, and O4–C12–O3 of 121.58(13)°, 114.37(14)°, and 124.05(13)° confirm the sp2 character of C12. The bond angle C10–C11–N1 of 177.24(15)° confirms the sp character of C11. All bond lengths and angles are slightly different in complex 1 as a result of the coordination of HL to the central copper(II) ion. The mean value of the torsion angle C1–C9=C10–C12 is about 178°, and the dihedral angle between the phenyl ring (C1–C2–C3–C4–C5–C6) and the plane defined by C11–C10–C12 is 4.53(6)°, indicating the coplanarity of these moieties in the ligand HL. The molecules of HL create layers as shown in Fig. 6. The best plane through the layers has indices hkl = (0.69, ˚ to the neighboring 0.37, -0.62) with a distance of 3.22 A plane. The layers are connected by C8–H8cN1 and C7– H7bN1 weak hydrogen bonds. The other hydrogen bonds listed in Table 1 occur within the layer. Description of the crystal structure of 1 The molecular structure of (Pip-H?)2[CuL4]2- (1) with the atom numbering scheme is presented in Fig. 7. The crystallographic data reveal that there are two piperidinium cations and one CuL42- anion in the unit cell of 1. The copper(II) ion is coordinated by four donor oxygen atoms of four ligands. Whereas a square-planar geometry might be expected for a four-coordinated copper(II) center, the geometry around the copper(II) ion in complex 1 is distorted from square-planar [22], as indicated by the unequal
Fig. 6 Layers found in the structure of HL connected by C8–H8cN1 and C7–H7bN1 weak hydrogen bonds
Table 1 Inter- and intramolecular hydrogen bonds of HL H-bonds
D–HA
˚ D–H/A
˚ HA/A
˚ DA/A
D–HA/°
Intramolecular
C6–H6N1
0.960
2.671
3.539
150.634
Intermolecular
C8–H8aN1
0.960
2.744
3.693
170.032
Intermolecular
C7–H7aO4
0.960
2.847
3.700
148.549
Intermolecular
C4–H4O2
0.960
2.437
3.394
174.846
Intermolecular
C8–H8cN1
0.960
2.822
3.662
146.662
Intermolecular
C7–H7bN1
0.960
2.920
3.736
143.513
metal–ligand bond distances and angles: Cu1–O1 = ˚ and Cu1–O5 = 1.9895(10) A ˚ , O1–Cu1– 1.9752(10) A i O5 = 91.23(4)°, O1–Cu1–O5 = 89.37(4)°, O1–Cu1-O1i = 172.81(4)°, and O5–Cu1–O5i = 170.32(5)°. The Cu1–O1 and Cu1–O5 distances agree well with the same distances in other copper(II) carboxylate complexes [14]. The mean values of the torsion angles C13–C14=C16– C17 and C1–C2=C4–C5 are about 177° and 172°, respectively. The dihedral angles between the phenyl ring (C5–C6–C7–C8–C9–C10) and the plane subtended by C1–C2–C3 is 29.81(9)°, whereas the corresponding angle defined by the phenyl ring (C17–C18–C19–C20–C21–C22) and the plane subtended by C13–C14–C15 is 8.63(8)°. This means that the coplanarity of these respective moieties in complex 1 is fulfilled only in one of two cases.
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Fig. 7 ORTEP diagram of complex 1, showing the atom labeling scheme and 50% probability ellipsoids for the non-hydrogen atoms. Hydrogen atoms and one pip? molecule are omitted for clarity
Table 2 and Fig. 8 show the hydrogen bonding between the molecules of complex 1. There are no direct connections between the molecules of complex 1. The hydrogen bonds are formed between CuL4 and Pip-H (indicated black). Thus Pip-H mediates the connection of CuL4 molecules into a one-dimensional chain along c.
Table 2 Intermolecular hydrogen bond geometry of 1 ˚ D–H/A
˚ HA/A
˚ DA/A
D–HA/°
C10–H10N1
0.960
2.737
3.473
134
C25–H25aN1
0.960
2.695
3.434
134
C29–H29aO7
0.960
2.934
3.561
124
N3–H3aO6
0.960
1.821
2.763
166
C22–H22N2
0.960
2.533
3.403
151
D–HA
Conclusion We synthesized a novel square-planar Cu(II) complex with a new acrylic acid derivative. Both the ligand and the complex are well characterized by different spectroscopic techniques and microanalytical data. Their structures were confirmed by X-ray crystallographic analysis. The thermal stability and decomposition patterns of the ligand and Cu(II) complex are described in detail.
Experimental All organic solvents used are commercially available and used as received without further purification. 2,5-Dimethoxybenzaldehyde and cyanoacetic acid were purchased from Merck Chemical Company. CuI and piperidine were purchased from Acros Chemical Company. FT–IR spectra were recorded from KBr disks on a FT–IR Perkin-Elmer spectrophotometer. Elemental analyses were carried out using a Heraeus CHN-O-Rapid analyzer. Thermogravimetric
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analyses were done on a Perkin-Elmer TG/DTG lab system l (Technology by SII) in a nitrogen atmosphere at a heating rate of 20 °C/min from 308 to 1,013 K. 13C and 1H NMR spectra were measured on a Bruker DRX-500 Avance spectrometer at 500 MHz. All chemical shifts are reported in d units downfield from TMS. UV–Vis absorption spectra were recorded on a Jasco V-570 spectrophotometer. 2-Cyano-3-(2,5-dimethoxyphenyl)acrylic acid (HL, C12H11NO4) 2,5-Dimethoxybenzaldehyde (0.4 mmol) and cyanoacetic acid (0.4 mmol) were dissolved in 20 cm3 methanol/ acetonitrile (1:1, v/v) containing piperidine (0.4 mmol). The mixture was stirred and refluxed for 1.5 h to give a clear yellow solution. The mixture was cooled and the product was allowed to crystallize by slow evaporation at room temperature. After 5 days, a yellow precipitate of HL was formed which was collected by filtration and dried at room temperature. Recrystallization of the yellow precipitate from 30 cm3 acetonitrile/chloroform (2:1, v/v) by
A novel mononuclear square-planar copper(II) complex (Pip-H?)2[CuL4]2-
759
precipitate was filtered and washed with a small amount of acetonitrile/methanol (1:1). Recrystallization of the resulting precipitates from 30 cm3 acetonitrile/chloroform (2:1) afforded green crystals of 1 in 55% yield. Method B: a solution of HL (0.4 mmol) in 15 cm3 acetonitrile was stirred with Cu(NO3)23H2O (0.1 mmol) at room temperature for 30 min. The mixture turned to a clear green solution. Then 0.5 cm3 of piperidine was added slowly with stirring. The resulting mixture was refluxed for about 2 h to obtain a green precipitate. The green precipitate was filtered and washed with a small amount of acetonitrile/methanol (1:1). Recrystallization of the resulting precipitates from 30 cm3 acetonitrile/chloroform (2:1, v/v) afforded green crystals of 1 in 73% yield. IR (KBr): v = 2,949–3,044, 2,840, 2,216, 1,617, 1,578, 1,496, 1,469, 1,454, 1,446, 1,423, 1,368, 1,335, 1,304, 1,259, 1,229 cm-1; UV–Vis: kmax (e) = 295 (11,365), 384 (7,869), 695 (167) nm (mol-1 dm3 cm-1). X-ray structure determination Single crystals of HL and 1 with dimensions of 0.39 mm 9 0.18 mm 9 0.11 mm and 0.35 mm 9 0.09 mm 9 0.04 mm, respectively, were chosen for X-ray diffraction study. Crystallographic measurements were done at 120 K using a Table 3 Crystal data and summary of experimental details for HL and 1
Fig. 8 One-dimensional chain in complex 1
adding acetic acid afforded yellow crystals of HL. Yield 91%; FT–IR (KBr): v = 2,922–3,059, 2,839, 2,220, 1,697, 1,678, 1,571, 1,497, 1,469, 1,458, 1,425, 1,381, 1,364, 1,297, 1,248, 1,234 cm-1; UV–Vis: kmax (e) = 301 (12,457), 397 (8,321) nm (mol-1 dm3 cm-1); 1H NMR (500 MHz, DMSO-d6): d = 3.74 (s, 3H), 3.83 (s, 3H), 7.12 (d, 1H), 7.20 (dd, 1H), 7.69 (d, 1H), 8.49 (s, 1H), 13.98 (br, 1H) ppm; 13C NMR (125 MHz, DMSO-d6): d = 55.47, 56.29 (CH3), 103.11 (CN), 112.40, 113.18, 116.26, 120.12, 121.14, 147.79 (aromatic), 152.74, 153.31 (ethylene), 163.45 (COOH) ppm. Dipiperidinium tetrakis(2-cyano-3-(2,5-dimethoxyphenyl)acrylic acid) copper(II) (1, C58H64CuN6O16) Method A: a solution of HL (0.4 mmol) in 15 cm3 acetonitrile was stirred with CuI (0.1 mmol) at room temperature for 30 min during which the mixture turned to a clear yellow solution. Then 0.5 cm3 of piperidine was added slowly with stirring. The stirring was continued for another 15 min and then the reaction mixture was refluxed for about 2 h to obtain a green precipitate. The green
HL
1
Empirical formula
C12H11NO4
C58H64CuN6O16
Formula weight Crystal system
233.2 Triclinic
1,164.7 Orthorhombic
Space group ˚ a/A ˚ b/A
Pı¯
Pccn
4.6911(2)
27.5486(5)
9.0181(4)
12.9484(2)
˚ c/A
13.7084(6)
15.8822(3)
a/°
74.946(4)
90.00
b/°
87.152(4)
90.00
c/° ˚3 V/A
89.220(4)
90.00
559.34(4)
5,665.34(17)
Z
2
4
l/mm-1
0.89
1.17
Rint
0.019
0.029
S
2.28
1.82
Reflection with I [ 3r(I) 1,573
3,862
R[F2 [ 2r(F2)] wR(F2)
0.038 0.118
0.029 0.093
Index ranges
-5 B h B 5
-31 B h B 31
-10 B k B 10
-14 B k B 14
-16 B l B 16
-17 B l B 17
Crystal size/mm3
0.39 9 0.18 9 0.11 0.35 9 0.09 9 0.04
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˚ ) and angles (°) for HL Table 4 Selected bond lengths (A O1–C2
1.359(2)
O3–C12
1.3009(18)
O1–C7
1.432(2)
O4–C12
1.236(2)
O2–C5
1.369(2)
N1–C11
1.148(2)
O2–C8
1.429(2)
C2–O1–C7
117.93(12)
N1–C11–C10
177.24(15)
C5–O2–C8
117.32(12)
O3–C12–O4
124.05(13)
O1–C2–C1
116.75(12)
O3–C12–C10
114.37(14)
O1–C2–C3
123.60(14)
O4–C12–C10
121.58(13)
O2–C5–C4
115.45(12)
O2–C5–C6
124.68(14)
˚ ) and angles (°) for 1 Table 5 Selected bond lengths (A Cu1–O1
1.9752(10)
Cu1–O5
1.9895(10)
Cu1–O1i
1.9752(10)
Cu1–O5i
1.9895(10)
O1–C1
1.2745(18)
O5–C13
1.2702(19)
O2–C1
1.2368(19)
O6–C13
1.2468(19)
O3–C6
1.367(2)
O3–C11
1.430(2)
O4–C12
1.393(3)
O4–C9
1.386(2)
O7–C18
1.3672(19)
O7–C23
1.424(2)
O8–C21
1.368(2)
O8–C24
1.427(2)
N1–C3
1.149(2)
N2–C15
1.149(2)
O1–Cu1–O1i
172.81(4)
O1i–Cu1–O5
89.37(4)
O1–Cu1–O5
91.23(4)
O1i–Cu1–O5i
91.23(4)
O1–Cu1–O5
i
i
89.37(4)
O5–Cu1–O5
Cu1–O1–C1
109.16(9)
Cu1–O5–C13
170.32(5) 109.60(9)
C6–O3–C11
117.81(13)
C9–O4–C12
113.40(14)
C18–O7–C23 N1–C3–C2
117.67(12) 179.49(19)
C21–O8–C24 N2–C15–C14
116.32(13) 179.28(17)
O7–C18–C19
123.22(15)
O7–C18–C17
116.63(13)
O8–C21–C22
123.94(16)
O8–C21–C20
116.49(14)
O3–C6–C5
115.77(14)
O3–C6–C7
123.84(15)
O4–C9–C10
120.39(16)
O4–C9–C8
119.63(15)
O1–C1–O2
124.83(14)
O5–C13–O6
124.43(13)
O1–C1–C2
116.44(13)
O5–C13–C14
117.36(13)
O2–C1–C2
118.73(14)
O6–C13–C14
118.20(14)
Symmetry codes: (i) -x?1/2, -y?1/2, z
four circle CCD Gemini diffractometer (Oxford Diffraction Ltd.) with mirror-collimated Cu Ka radiation (k = ˚ ). The crystal structures were solved by direct 1.54184 A methods with the SIR2002 program [23] and refined with the Jana2006 program package [24] by full-matrix leastsquares technique on F2. The molecular structure plots were prepared by ORTEP III [25]. Hydrogen atoms were mostly discernible in difference Fourier maps and could be refined to reasonable geometry. According to common practice they were nevertheless kept in ideal positions during the refinement. The isotropic atomic displacement parameters of hydrogen atoms were evaluated as 1.2Ueq of
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the parent atom. Crystallographic data and details of the data collection and structure solution and refinements are listed in Table 3. Selected bond lengths and angles of HL and 1 are listed in Tables 4 and 5, respectively. Crystallographic data (excluding structure factors) for the structures reported in this paper were deposited with the Cambridge Crystallographic Data Center, CCDC Nos. 779236 (HL) and 796345 (1). Copies of the data can be obtained free of charge on application to The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, fax: ?44-1223-336033, e-mail:
[email protected] or http://www.ccdc.cam.ac.uk. Acknowledgements We acknowledge the Golestan University (GU) for partial support of this work, the institutional research plan no. AVOZ10100521 of the Institute of Physics, and the project Praemium Academiae of Sciences of the Czech Republic.
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