- Email: [email protected]
Zn(II), Cd(II) and Hg(I) complexes of cinnamic acid: FT-IR, FT-Raman, 1H and 13C NMR studies
Journal of Molecular Structure 993 (2011) 404–409
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Zn(II), Cd(II) and Hg(I) complexes of cinnamic acid: FT-IR, FT-Raman, 1 H and 13C NMR studies M. Kalinowska, R. S´wisłocka, W. Lewandowski ⇑ Division of Chemistry, Bialystok University of Technology, Zamenhofa 29, 15-435 Białystok, Poland
a r t i c l e
i n f o
Article history: Available online 25 February 2011 Keywords: Cinnamic acid Zinc cinnamate Cadmium cinnamate Mercury cinnamate Spectroscopic studies
a b s t r a c t The effect of zinc, cadmium(II) and mercury(I) ions on the electronic structure of cinnamic acid (phenylacrylic acid) was studied. In this research many miscellaneous analytical methods, which complement one another, were used: infrared (FT-IR), Raman (FT-Raman), nuclear magnetic resonance (1H, 13C NMR) and quantum mechanical calculations. The spectroscopic studies provide some knowledge on the distribution of the electronic charge in molecule, the delocalization energy of p-electrons and the reactivity of metal complexes. In the series of Zn(II) ? Cd(II) ? Hg(I) cinnamates: (1) systematic shifts of several bands in the experimental and theoretical IR and Raman spectra and (2) regular chemical shifts for protons 1H and 13C nuclei were observed. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Zinc ion is a component of over 200 metaloenzymes in human and animal tissues and it is a structural component of various proteins, hormones and nucleotides. Cadmium may actually displace zinc in some of its important enzymatic and organ functions. The toxicity of cadmium, at least partly, can be explained by a competition between cadmium and zinc at cofactor sites in enzymes requiring zinc, resulting in decrease activities of these enzymes. Mercury also poisons some enzyme systems. Mercury also alters the permeability of the membrane of the cells, it replaces structurally or electrochemically important elements in the cells, it blocks sodium currents, inhibits the transport of sugars, inhibits amino acid absorption in the brain, inhibits the synaptic uptake of neurotransmitters in the brain and can cause brain degeneration. The estimation of the electronic charge distribution in metal complexes allows more precise interpretation of the mechanism by which particular metals affect the chemical and biochemical properties of ligands as well as it makes possible to predict, what kind of deformation of an electronic system of ligands would undergo during complexation [1–3]. Cinnamic acid (3-phenyl-2-propenoic acid), a derivative of phenylalanine, composes a relatively large family of organic acid isomers [4]. In nature, cinnamic acid derivatives are important metabolic building blocks in the production of lignins for higher plants. Cinnamic acid possesses antibacterial, antifungal and antiparasitic abilities [5]. A derivative of cinnamic acid is an important pharmaceutical for high blood pressure and ⇑ Corresponding author. Tel.: +48 85 469790; fax: +48 85 7469782. E-mail address: [email protected] (W. Lewandowski). 0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2011.01.063
stroke prevention and possesses antitumour activity [6]. In wine, cinnamic acid and its derivatives join benzoic acid derivatives and flavonoids in creating pigments and tannin agents that give each vintage it characteristic bouquet and color. Cinnamic acid is extensively studied not only due to its important biological activity, but also because of its very specific structure. In the molecule of cinnamic acid the carboxylic group is being separated from the aromatic ring by a double bond. It causes the conjugations between the AC@CA bond and p-electron system. In this work we studied the effect of Zn(II), Cd(II) and Hg(I) on the electronic system of cinnamic acid by means of many complementary methods: infrared (FT-IR), Raman (FT-Raman), nuclear magnetic resonance (1H, 13C NMR). There are few papers concerning the study of the cinnamic acid molecule. The polarized IR spectra of cinnamic acid was used in study of the hydrogen bonds in dimers [7]. The two polymorphic forms of cis-cinnamic acid were compared with that of trans-cinnamic acid by the use of IR, Raman and NMR spectroscopy [8]. Only partial assignment of the bands occurring in the IR and Raman spectra was done. Hsieh et al. studied the molecular structure of cinnamic acid using the B3LYP/6-31G [9]. It is worth mentioning that to our knowledge no spectroscopic data or calculations have been reported so far for zinc, cadmium and mercury cinnamates. 2. Experimental 2.1. Sample preparation The zinc(II) and cadmium(II) cinnamates were obtained by adding salt solutions of ZnCl2 and CdCl2 (concentration 0.25 mol/dm3)
405
M. Kalinowska et al. / Journal of Molecular Structure 993 (2011) 404–409
respectively to the solution of sodium cinnamate (concentration 0.5 mol/dm3) in a stoichiometric ratio 1:2. Mercury(I) cinnamate was synthesised by adding HgNO3 solution (concentration 0.25 mol/dm3) to the solution of sodium cinnamate (concentration 0.5 mol/dm3). White precipitate was washed with distilled water. Water was evaporated at 130 °C in a dryer. The results of elementary analyses are as follows: for zinc cinnamate: %C = 59.31 (calc. %C = 60.11), %H = 3.72 (calc. %H = 3.92); for cadmium cinnamate: %C = 52.32 (calc. %C = 53.16), %H = 3.35 (calc. %H = 3.47); for mercury(I) cinnamate: %C = 32.12 (calc. %C = 31.09), %H = 2.1 (calc. %H = 2.03). Obtained complexes were anhydrous, the metal: ligand ratio was 1:2 in case of Zn and Cd cinnamates and 1:1 in case of Hg cinnamate. 2.2. Measurement The IR spectra were recorded with an Equinox 55 spectrometer (Bruker) within the range of 400–4000 cm 1. Samples in the solid state were measured in KBr matrix pellets obtained with hydraulic press under 739 MPa pressure. Moreover the FT-IR spectra of studied compounds were registered by the use of ATR accessory. Raman spectra of solid samples in capillary tubes were recorded in the range of 100–4000 cm 1 with a FT-Raman accessory of a Perkin–Elmer system 2000. The resolution of spectrometer was 1 cm 1. The NMR spectra of DMSO saturated solution were recorded with a Bruker unit at room temperature. TMS was used as an internal reference. In order to calculate optimized geometrical structures and infrared spectra of cinnamic and its complexes and benzoic acid B3LYP/6-311++G level was used. Theoretical calculations were performed using the GAUSSIAN 03W package of programs [10]. 3. Results and discussion 3.1. IR and Raman spectra of zinc, cadmium and mercury(I) cinnamates The wavenumbers, intensities and assignments of the bands occurring in the IR and Raman spectra of cinnamates are presented
in Table 1. The spectral assignments were done on the basis of the literature data [8,11,12] and calculated IR wavenumbers of studied compounds. The symbol ‘‘m’’ denotes stretching vibrations, ‘‘b’’ denotes in-plane bending modes, ‘‘c’’ designates out-of-plane bending modes; ‘‘u(CCC)’’ denotes the aromatic ring out-of-plane bending modes, and ‘‘a(CCC)’’ designates the aromatic ring in-plane bending modes. Normal vibrations of the aromatic ring were given by Varsànyi [11]. Replacement of the carboxylic group hydrogen with a metal ion causes a breakdown of the intermolecular hydrogen bonding and therefore the characteristic changes in the IR and Raman spectra of the metal cinnamates in comparison with the spectra of acid appeared. Namely, there occurred a disappearance of bands, which originated from stretching m(OH) and deformation b(OH) vibrations; a disappearance of bands assigned to the symmetric and asymmetric stretching m(C@O) vibrations as well as out-of-plane bending c(C@O) vibrations of the carbonyl group were observed; an appearance of bands assigned to the symmetric and asymmetric vibrations of the carboxylate anion mas(COO ), ms(COO ) as well as bas(COO ), bs(COO ), and a disappearance or changes in the positions and intensities of some aromatic bands were also observed. The FT-IR and FT-Raman spectra of cinnamic acid were reported previously [12]. In the experimental FT-IR spectra of cinnamates the wavenumbers of asymmetric and symmetric stretching vibrations of carboxylic anion change their position along the series of metals Zn ? Cd ? Hg (see Table 1). Namely, the band of ms(COO ) is shifted toward lower wavenumbers in spectra of cinnamates, whereas the band of mas(COO ) is shifted towards higher wavenumbers. Two different bands assigned to mas(COO ) occurred in the spectra of cinnamates what suggests two different types of metal coordination. A general tendency in the relationship between Dm(COO ) (the difference between the wavenumbers of the asymmetric (masym) and the symmetric (msym) stretches of carboxylate group from the FT-IR spectra) and the types of coordination of the COO group to metal ions by examining the structures and spectral data was observed for a number of acetate salts in the solid state [13,14]. A general trend in this relationship may be summarised as follows:
Table 1 The wavenumbers [cm 1], intensities and assignments of selected bands that occurred in the FT-IR (recorded in KBr pellets and by the use of ATR accessory), FT-Raman of zinc(II), cadmium(II), mercury(I) and sodium cinnamates. Cinnamic acid [12]
Zn(II) cinnamate
IR KBr
Calc.
Na cinnamate [12] IR KBr
IR KBr
Calc.
3027m 1629vs 1600sh
3210 1661 1649
3027vw 1640m 1599vw
3030w 1644s 1621w
3198 1688 1652
1577m
1623
1577m 1548vs
1495m 1449s
1527 1482
1495m 1451m 1412s
1578m 1531sh 1518vs 1495s 1451s 1418vs
1292vw 1244w 1199vw 1179vw 1074w 1029vw 916vw 852vw 713w 586w
1299w 1256w 1203w 1182w 1073w 1030w 918vw 857w 712m 566w
1624 1418 1417 1529 1484 1445 1437 1274
1286s 1222s 1206m 1176m 1073w 1027w 914m
1307 1252 1226 1108 1054 857
1247 1225 1111 1050 861 750
Cd(II) cinnamate
IR ATR
Raman
1643m 1620w
1647s 1602s
1577m 1533sh 1517vs 1496m 1450s 1417vs
1578w 1524vw
1302w 1256sh 1204w 1179w 1073w 1029w 920w 857w 712s 567m
s – strong; m – medium; w – weak; v – very; sh – shoulder.
1458vw 1441vw
1265w 1205w 1183vw 1032vw 859vw
IR KBr
Calc.
3026w 1640s 162 1vw 1578s 1533vs 1517sh 1496s 1450s 1402vs
3198 1688 1652
1292w 1252m 1204w 1181w 1072w 1028w 918vw 852w 715m 591m
1624 1421 1415 1529 1483 1427 1426 1276 1247 1225 1111 1050 860 741
Hg(I) cinnamate
IR ATR
Assignments
[11]
8a
Raman
IR KBr
IR ATR
Raman
1639m 1622w
1642vs 1602s
3024w 1637s 1620m
1636m 1605w
3020vw 1638vs 1601s
m(CH)ar + m(CH)cinn m(C@C)cinn m(CC)ar
1577m 1533s 1513s 1495s 1450m 1400vs
1579w
1576s 1560s 1526s 1495s 1447m 1358vs
1570w 1555w 1526s 1481s 1447m 1356vs
1579sh
m(CC)ar mas(COO )
8b
1497vw
m(CC)ar m(CC)ar ms(COO )
19a 19b
1290w 1250w 1202w 1180w 1072w 1026w 920w 85 1w 718m 590m
1292w 1254w 1215w
1292w 1252m 1205w 1182w 1071w 1028w 917w 853w 715m 591s
1453w
1256m 1206w 1182w 1030w 854w
1071w 1034w 912w 853w 715m 592m
1363vw 1293vw 1261w 1203w 1182w 1029w 853w 595vw
b(CH)cinn b(CH)cinn b(CH)ar b(CH)ar b(CH)ar b(CH)ar c(CCH)cinn bs(COO ) cs(COO ) bas(COO )
13 9a 18b 18a
406
M. Kalinowska et al. / Journal of Molecular Structure 993 (2011) 404–409
Fig. 1. The crystal hydrated structure of zinc cinnamate [15].
(1) Structure of the carboxylate group is bidentate chelating when the bands of masym(COO ) and msym(COO ) in studied complex are shifted to lower and higher wavenumbers, respectively, compared to those for sodium salt; or Dm(COO )studied complex Dm(COO )sodium salt. (2) Bidentate bridging structure exists when the bands of masym(COO ) and msym(COO ) in studied complex are shifted to higher wavenumbers, compared to those for sodium salt; or Dm(COO )studied complex 6 Dm(COO ) sodium salt. (3) For monodentate geometry of carboxylate group the bands of masym(COO ) and msym(COO ) in studied complex are shifted to higher and lower wavenumbers, respectively, compared to those for sodium salt; or Dm(COO )studied complex Dm(COO )sodium salt. The difference between wavenumbers of asymmetric and symmetric stretches of the carboxylic anion vibrations Dm(COO ) alters in a regular fashion along the metal series Zn ? Cd ? Hg and respectively amounts to: 113, 131 and 202 cm 1 as well as 100, 115 and 168 cm 1. According to spectroscopic criteria the carboxylate group in zinc and cadmium cinnamates seems to be bidentate chelating. Whereas in mercury(I) cinnamate the type of coordination may be monodentate. The literature data for crystal structure of zinc cinnamate Zn(C9H7O2)22H2O was reported and confirms the bidentate chelating coordination (Fig. 1) [15]. Not only the bands which derive from the carboxylic anion vibrations are sensitive to change of metal [16]. Several bands of
aromatic system as well as bands which derive from the AC@CA double bond are shifted towards lower wavenumbers in the spectra of complexes compared with the spectrum of acid. Among these bands are: 3030 cm 1 (IR KBr), m(C@C)cinn (IR KBr, IR ATR, Raman), 8b (IR ATR), 19b (IR KBr, IR ATR), 1295 cm 1 (IR KBr, IR ATR), 1255 cm 1 (IR KBr), 18a (IR KBr, Raman), 918 cm 1 (IR ATR), 775 cm 1 (IR ATR). The bands connected with the AC@CA vibrations undergo larger displacement than the bands derived from ring vibrations. Moreover higher displacement of bands toward lower wavenumbers were observed in the spectra of Hg(I) cinnamate than Zn and Cd cinnamates. Additionally, one can observe a systematic decrease in the wavenumbers of several bands in the series of Zn ? Cd ? Hg cinnamates. These bands are: 3026 cm 1 (IR KBr), m(C@C)cinn (IR KBr, IR ATR, Raman), 19a (IR ATR), 19b (IR KBr, Raman), b(CH)cinn 1292 cm 1 (IR KBr, IR ATR), b(CH)cinn 1252 cm 1 (IR KBr), 18a (IR KBr, Raman), 1132 cm 1 (IR ATR), 1089 cm 1 (IR ATR), 18b (IR ATR), c(CHH)cinn (IR ATR). The displacement of bands toward lower wavenumbers is generally interpreted as a decrease in the force constants of bonds what results from a decrease in electronic charge density around atoms [4]. In Table 2 selected wavenumbers of bands assigned to aromatic ring vibrations of benzoates, cinnamates as well as benzoic and cinnamic acids are gathered [17,18]. The differences between position of appropriate bands are more noticeable in the spectra of benzoic acid and benzoates than cinnamic acid and cinnamates. Several of the aromatic bands disappear in the spectra of sodium and mercury(I) benzoates, but they are present in the spectra of Na and Hg(I) cinnamates. This suggests that influence of metal ions on the structure cinnamic acid is a short range effect and it constrains mainly to the changes in the electronic charge density around atoms of the double bond between aromatic ring and carboxylic group. The differences in electronic charge distribution in benzoic and cinnamic acids are due to the presence of the double bonds between carboxylic group and ring in cinnamic acid molecule. In Fig. 2 the NPA atomic charges calculated at B3LYP6/311++G level for both acids are presented. The electronic charge density around carbon atoms no. C1 is lower in cinnamic acid ( 0.096e) than benzoic acid ( 0.170e). Moreover the close proximity of carboxylic group and aromatic ring in benzoic acid molecule influences the charge density of hydrogen atoms HD (0.226e) and HH (0.230e). Therefore, the presence of the double bond in cinnamic acid molecule is crucial for the effect of metal ions on the charge density in the aromatic ring. A contrary situation takes place in case of picolinic acid and metal picolinates. Wavenumbers of a few bands from FT-IR and
Table 2 Wavenumbers [cm 1] and intensities of selected bands from FT-IR and FT-Raman spectra of benzoic acid and benzoates [17,18], cinnamic acid and cinnamates [16] and picolinic acid and picolinates [19]. 19a
Benzoic acid Na(I) benzoate Zn(II) benzoate Cd(II) benzoate Hg(I) benzoate Cinnamic acid Na(I) cinnamate Zn(II) cinnamate Cd(II) cinnamate Hg(I) cinnamate Picolinic acid Na(I) picolinate Zn(II) picolinate
19b
14
9a
18a
10a
IR
Raman
IR
Raman
IR
Raman
IR
Raman
IR
Raman
IR
Raman
1498w⁄ – 1491w 1494w – 1495m 1495m 1495s 1496s 1495s 1455s – 1476m
– 1493w nd 1494w – 1496vw 1495vw 1496m – 1497vw 1442vw 1475w 1482w
1455s – 1448w 1447w – 1449s 1451m 1451s 1450s 1147m 1439m 1439s 1446m
1460vw 1436m nd 1450vw – 1444vw 1455vw 1458vw 1453m – _ 1440w 1447w
1324vs 1306w 1307w 1310w 1307vw 1334m – – – – 1343s – –
1326w – nd – – 1329vw 1323vw – – – 1358vw – –
1180sh – 1180w 1178w – 1176m 1179vw 1182vw 1181w 1180w 1198s 1169w 1168w
1184m 1185m nd – – 1179m 1180vw 1183vw 1182m 1182w _ 1172w 1170w
1027m 1029m 1026w 1025m nd 1027w 1029vw 1030w 1028w 1026w 1045s 1045w 1048m
1027m 1033m nd nd nd 1027w 103 1w 1032vw 1030w 1029w 105 1w 1050m 1051m
856vw 819m 818m 822vw nd 875w 878w 876w 873w 878w nd nd nd
855vw 825w nd nd nd 876vw 878vw 887vw 875w 880w nd nd nd
s – strong; m – medium; w – weak; v – very; sh – shoulder; nd – no data.
407
M. Kalinowska et al. / Journal of Molecular Structure 993 (2011) 404–409
of complex and acid is higher in case of picolinate than benzoate ligand. It points that presence of nitrogen atom in the ring certainly play an important role in the interactions metal–ligand. The effect of metal ions on the electronic structure of cinnamic acids may be related to selected metal ion parameters. In order to estimate this dependency a linear correlation between wavenumbers of selected bands from FT-IR (recorded in KBr pellets and by the use of ATR accessory) and FT-Raman spectra and metal ion parameters (ionic potential, ionic radius, 1/atomic mass) was done. Because in this paper only tree metal complexes with cinnamic acid were analysed the indispensable additional data to statistical analysis were taken from [12,16,20]. The results of this analysis are presented in Table 3. Only data with correlation coefficients higher than 0.7 are included. The obtained data suggest that the main factor responsible for the interaction metal ion–cinnnamic acid molecule is ionic radius. With an increase in the ionic radius of metal ions the values of the wavenumbers from FT-IR and FT-Raman spectra of selected cinnamates decrease what is caused by a decrease in electronic charge density around atoms (mainly in aromatic ring and double bond AC@CA) in cinnamate molecules. It suggests that the type of metal–ligand coordination determined the effect of metal ions on the electronic charge distribution in ligand molecule.
Fig. 2. The NPA atomic charges calculated at B3LYP/6-311++G level for: (a) benzoic acid and (b) cinnamic acid.
FT-Raman spectra of these compounds are shown in Table 2. Picolinic acid is a pyridine compound with a carboxyl side chain at the 2-position. Both zinc picolinate (covalent bond between metal–ligand) and sodium picolinate (ionic bond) formation causes distinct changes in the location of bands assigned to aromatic ring vibrations. Namely, most of these bands disappear/appear or undergo movement to max. 40 cm 1 in the spectra of zinc picolinate compared with the spectra of acid. The magnitude of difference between location of corresponding bands in the spectra
4. NMR spectra of zinc, cadmium and mercury(I) cinnamates 4.1. 1H NMR spectra In the 1H NMR spectra of Zn(II), Cd(II) and Hg(I) cinnamates signals are slightly shifted upfield in comparison with the appropriate
Table 3 Values of correlation coefficients (R) obtained for the linear correlation between wavenumbers of selected bands from FT-IR spectra (recorded in KBr pellets and by the use of ATR accessory) and FT-Raman spectra and selected metal ions parameters. Li, Na, K, Rb, Cs, Zn, Cd, Hg, Ca, La, Th cinnamates
Ionic potential Ionic radius 1/Atomic mass Bands Ionic potential Ionic radius 1/Atomic mass
b(CH)-C=C- 1290 cm IR KBr 0.544 0.738 0.060
1
b(CH)-C@C- 1250 cm IR KBr 0.645 0.833 0.220
18a IR KBr
1
c(CCH)-C@C- 970 cm IR KBr
1
8a Raman
0.706 0.760 0.191 18a Raman
0.573 0.951 0.500
0.759 0.737 0.001
18b IR KBr
0.485 0.905 0.391
19b IR KBr 0.504 0.785 0.395
11 IR KBr
0.150 0.818 0.708
0.232 0.625 0.748
19b IR ATR 0.671 0.800 0.310
0.655 0.937 0.303
7.4 7.2
Cinnamic acid Cinnamate Na(I)
6.6
Cinnamate Zn(II)
6.4
Cinnamate Cd(II) Cinnamate Hg(I)
6.2 6 C
D. H
F
E. G
0.704 0.704 0.034
0.771 0.710 0.403
7.6
7
0.780 0.689 0.147
9a Raman
bs(COO ) IR KBr
8
6.8
19a IR KBr
Dm(COO ) IR KBr
7.8
[ppm]
Bands
B
proton position Fig. 3. Graphical presentation of chemical shifts from 1H NMR spectra of cinnamic acid and cinnamates.
408
M. Kalinowska et al. / Journal of Molecular Structure 993 (2011) 404–409
175 Cinnamic acid
165
Cinnamate Na(I) Cinnamate Zn(II)
[ppm]
155
Cinnamate Cd(II) Cinnamate Hg(I)
145
135 125
115 7
9
1
4
3.5
2.6
8
carbon position Fig. 4. Graphical presentation of chemical shifts from
COOH A
C H
7
H
8 H
9 1
H 6
GH
5
B
HD 2
4
3 H
E
HF Fig. 5. Atom numbering for cinnamic acid molecule.
signals in the spectra of acid, but the displacement is not as significant as in case of spectrum of sodium cinnamate (Fig. 3). A decrease in the chemical shifts in spectra of metal complexes points at an increase in the screening of aromatic protons as a consequence of the circular current weakening. The signals in the NMR spectra of Zn and Cd cinnamates posses generally the same values, whereas in the spectrum of Hg cinnamate they are located at higher ppm. The differences are small and amount to 0.03–0.05 ppm. It seems that different position of appropriate signals in the spectra of cinnamates are caused by different types of carboxylic group coordination what brings about dissimilar effect of metal ions on the electronic charge distribution in ligand. Namely, the bond between sodium cation and ligand possesses ionic character; deformation of the electronic charge in ligand may be mainly caused by polarization of CAC and CAH bonds. Otherwise, in case of zinc and cadmium cinnamates the infrared data suggest the bridging and chelating types of coordination, and mercury(I) cation is bound by monodentate and bridging carboxylic groups. 4.2.
13
C NMR spectra
On the basis of the chemical shifts of signals from 13C NMR spectra of cinnamic acid and cinnamates we may confirm that metal cations affect mainly the charge distribution around atoms of the double bond, i.e. C8 and C9 (Fig. 4 and 5). The electronic charge density around carbon in position 9 increases, and around carbons no. 8 and 7 decreases in metal complexes compared with acid molecule. The charge densities around the other carbon atoms change insignificantly after replacement of the carboxylic group hydrogen with a metal ion. 5. Conclusions Substitution of metal cations in the carboxylic group of cinnamic acid causes changes in the electronic charge distribution
13
C NMR spectra of cinnamic acid and cinnamates.
of the whole molecule. The alternation in the electronic structure of carboxylate group results from different types of metal ion coordination. According to the spectroscopic criteria the carboxylate group in zinc(II) and cadmium(II) cinnamates is bidentate chelating. Whereas in mercury(I) cinnamates the type of coordination is monodentate. Comparing the 1H NMR results obtained for cinnamic acid and sodium(I), zinc(II), cadmium(II) and mercury(I) cinnamates we may conclude that the differences in the electronic charge distribution of particular molecules depend on the type of metal coordination. Sodium cation causes larger changes in the electronic charge distribution of cinnamic acid than zinc, cadmium and mercury ions. Moreover, a systematic decrease in the wavenumber of several bands in the series of Zn ? Cd ? Hg cinnamates in the FT-IR and FT-Raman spectra was observed. Metal cations affect mainly the charge distribution around atoms of the double bond of cinnamate, the structure of the aromatic ring is affected to a lesser extent. The main factor responsible for the interaction metal ion–cinnnamic acid molecule is ionic radius. On the basis of the FT-IR and FT-Raman spectra of zinc benzoate, cinnamate and picolinate the participation of double bond between the ring and carboxylate group as well as nitrogen atom in the ring in the interaction metal–ligand may be discussed. It occurred that double bond weaken the effect of metal cations on the electronic charge distribution in the ring whereas in case of picolinate molecule this effect is enhanced. Acknowledgement This work was supported by Ministry of Science and Higher Education (Grant no. N N305 384538). References [1] W. Lewandowski, M. Kalinowska, H. Lewandowska, J. Inorg. Biochem. 99 (2005) 1407. [2] R. S´wisłocka, E. Regulska, M. Samsonowicz, T. Hrynaszkiewicz, W. Lewandowski, Spectrochim. Acta A 61 (2005) 2966. [3] G. S´widerski, M. Kalinowska, S. Wojtulewski, W. Lewandowski, Spectrochim. Acta A 64 (2006) 24. [4] L. Bravo, Nutr. Rev. 56 (1998) 317. [5] S. Burt, Int. J. Food Microbiol. 94 (2004) 223. [6] M.G.L. Hertog, D. Kromhout, C. Aravanis, H. Blackburn, R. Buzina, F. Fidanza, S. Giampaoli, Arch. Intern. Med. 155 (1995) 381. [7] H.T. Flakus, M. Jabłon´ska, J. Mol. Struct. 707 (2004) 97. [8] K. Hanai, A. Kuwae, T. Takai, H. Senda, K.-K. Kunimoto, Spectrochim. Acta A 57 (2001) 513. [9] Tiane-Jye Hsieh, Chia-Ching Su, Chung-Yi Chen, Chyong-Huey Liou, Li-Hwa Lu, J. Mol. Struct. 741 (2005) 193.
M. Kalinowska et al. / Journal of Molecular Structure 993 (2011) 404–409 [10] [11] [12] [13] [14] [15]
Gaussian 2003, Revision A.7, in: M.J. Frisch et al. (Eds.), Gaussian, Inc., Pittsburgh, PA, 1998. G. Varsànyi, Assignments for Vibrational Spectra of 700 Benzene Derivatives, Akademiai Kiado, Budapest, 1973. M. Kalinowska, R. S´wisłocka, W. Lewandowski, J. Mol. Struct. 572 (2007) 834– 836. G.B. Deacon, R.J. Philips, Coordin. Chem. Rev. 33 (1980) 227. Ch.R. Choudhury, A. Datta, V. Gramlich, G.M.G. Hossain, K.M.A. Malik, S. Mitra, Inorg. Chem. Commun. 6 (2003) 790. H. Hosomi, S. Ohba, Y. Ito, Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 56 (2000) e123.
409
[16] M. Kalinowska, R. S´wisłocka, W. Lewandowski, W. Ferenc, Nauka i przemysł – _ ´ ci, UMCS, metody spektroskopowe w praktyce, nowe wyzwania i mozliwos Lublin, 2009. [17] W. Lewandowski, Can. J. Spectr. 32 (1987) 41. [18] W. Lewandowski, Arch. Environ. Contam. Toxicol. 17 (1988) 131. [19] W. Lewandowski, G. S´widerski, R. S´wisłocka, S. Wojtulewski, P. Koczon´, J. Phys. Org. Chem. 18 (2005) 918. [20] M. Kalinowska, W. Lewandowski, R. S´wisłocka, E. Regulska, Spectroscopy 24 (2010) 277–281.
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Zn(II), Cd(II) and Hg(I) complexes of cinnamic acid: FT-IR, FT-Raman, 1 H and 13C NMR studies M. Kalinowska, R. S´wisłocka, W. Lewandowski ⇑ Division of Chemistry, Bialystok University of Technology, Zamenhofa 29, 15-435 Białystok, Poland
a r t i c l e
i n f o
Article history: Available online 25 February 2011 Keywords: Cinnamic acid Zinc cinnamate Cadmium cinnamate Mercury cinnamate Spectroscopic studies
a b s t r a c t The effect of zinc, cadmium(II) and mercury(I) ions on the electronic structure of cinnamic acid (phenylacrylic acid) was studied. In this research many miscellaneous analytical methods, which complement one another, were used: infrared (FT-IR), Raman (FT-Raman), nuclear magnetic resonance (1H, 13C NMR) and quantum mechanical calculations. The spectroscopic studies provide some knowledge on the distribution of the electronic charge in molecule, the delocalization energy of p-electrons and the reactivity of metal complexes. In the series of Zn(II) ? Cd(II) ? Hg(I) cinnamates: (1) systematic shifts of several bands in the experimental and theoretical IR and Raman spectra and (2) regular chemical shifts for protons 1H and 13C nuclei were observed. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Zinc ion is a component of over 200 metaloenzymes in human and animal tissues and it is a structural component of various proteins, hormones and nucleotides. Cadmium may actually displace zinc in some of its important enzymatic and organ functions. The toxicity of cadmium, at least partly, can be explained by a competition between cadmium and zinc at cofactor sites in enzymes requiring zinc, resulting in decrease activities of these enzymes. Mercury also poisons some enzyme systems. Mercury also alters the permeability of the membrane of the cells, it replaces structurally or electrochemically important elements in the cells, it blocks sodium currents, inhibits the transport of sugars, inhibits amino acid absorption in the brain, inhibits the synaptic uptake of neurotransmitters in the brain and can cause brain degeneration. The estimation of the electronic charge distribution in metal complexes allows more precise interpretation of the mechanism by which particular metals affect the chemical and biochemical properties of ligands as well as it makes possible to predict, what kind of deformation of an electronic system of ligands would undergo during complexation [1–3]. Cinnamic acid (3-phenyl-2-propenoic acid), a derivative of phenylalanine, composes a relatively large family of organic acid isomers [4]. In nature, cinnamic acid derivatives are important metabolic building blocks in the production of lignins for higher plants. Cinnamic acid possesses antibacterial, antifungal and antiparasitic abilities [5]. A derivative of cinnamic acid is an important pharmaceutical for high blood pressure and ⇑ Corresponding author. Tel.: +48 85 469790; fax: +48 85 7469782. E-mail address: [email protected] (W. Lewandowski). 0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2011.01.063
stroke prevention and possesses antitumour activity [6]. In wine, cinnamic acid and its derivatives join benzoic acid derivatives and flavonoids in creating pigments and tannin agents that give each vintage it characteristic bouquet and color. Cinnamic acid is extensively studied not only due to its important biological activity, but also because of its very specific structure. In the molecule of cinnamic acid the carboxylic group is being separated from the aromatic ring by a double bond. It causes the conjugations between the AC@CA bond and p-electron system. In this work we studied the effect of Zn(II), Cd(II) and Hg(I) on the electronic system of cinnamic acid by means of many complementary methods: infrared (FT-IR), Raman (FT-Raman), nuclear magnetic resonance (1H, 13C NMR). There are few papers concerning the study of the cinnamic acid molecule. The polarized IR spectra of cinnamic acid was used in study of the hydrogen bonds in dimers [7]. The two polymorphic forms of cis-cinnamic acid were compared with that of trans-cinnamic acid by the use of IR, Raman and NMR spectroscopy [8]. Only partial assignment of the bands occurring in the IR and Raman spectra was done. Hsieh et al. studied the molecular structure of cinnamic acid using the B3LYP/6-31G [9]. It is worth mentioning that to our knowledge no spectroscopic data or calculations have been reported so far for zinc, cadmium and mercury cinnamates. 2. Experimental 2.1. Sample preparation The zinc(II) and cadmium(II) cinnamates were obtained by adding salt solutions of ZnCl2 and CdCl2 (concentration 0.25 mol/dm3)
405
M. Kalinowska et al. / Journal of Molecular Structure 993 (2011) 404–409
respectively to the solution of sodium cinnamate (concentration 0.5 mol/dm3) in a stoichiometric ratio 1:2. Mercury(I) cinnamate was synthesised by adding HgNO3 solution (concentration 0.25 mol/dm3) to the solution of sodium cinnamate (concentration 0.5 mol/dm3). White precipitate was washed with distilled water. Water was evaporated at 130 °C in a dryer. The results of elementary analyses are as follows: for zinc cinnamate: %C = 59.31 (calc. %C = 60.11), %H = 3.72 (calc. %H = 3.92); for cadmium cinnamate: %C = 52.32 (calc. %C = 53.16), %H = 3.35 (calc. %H = 3.47); for mercury(I) cinnamate: %C = 32.12 (calc. %C = 31.09), %H = 2.1 (calc. %H = 2.03). Obtained complexes were anhydrous, the metal: ligand ratio was 1:2 in case of Zn and Cd cinnamates and 1:1 in case of Hg cinnamate. 2.2. Measurement The IR spectra were recorded with an Equinox 55 spectrometer (Bruker) within the range of 400–4000 cm 1. Samples in the solid state were measured in KBr matrix pellets obtained with hydraulic press under 739 MPa pressure. Moreover the FT-IR spectra of studied compounds were registered by the use of ATR accessory. Raman spectra of solid samples in capillary tubes were recorded in the range of 100–4000 cm 1 with a FT-Raman accessory of a Perkin–Elmer system 2000. The resolution of spectrometer was 1 cm 1. The NMR spectra of DMSO saturated solution were recorded with a Bruker unit at room temperature. TMS was used as an internal reference. In order to calculate optimized geometrical structures and infrared spectra of cinnamic and its complexes and benzoic acid B3LYP/6-311++G level was used. Theoretical calculations were performed using the GAUSSIAN 03W package of programs [10]. 3. Results and discussion 3.1. IR and Raman spectra of zinc, cadmium and mercury(I) cinnamates The wavenumbers, intensities and assignments of the bands occurring in the IR and Raman spectra of cinnamates are presented
in Table 1. The spectral assignments were done on the basis of the literature data [8,11,12] and calculated IR wavenumbers of studied compounds. The symbol ‘‘m’’ denotes stretching vibrations, ‘‘b’’ denotes in-plane bending modes, ‘‘c’’ designates out-of-plane bending modes; ‘‘u(CCC)’’ denotes the aromatic ring out-of-plane bending modes, and ‘‘a(CCC)’’ designates the aromatic ring in-plane bending modes. Normal vibrations of the aromatic ring were given by Varsànyi [11]. Replacement of the carboxylic group hydrogen with a metal ion causes a breakdown of the intermolecular hydrogen bonding and therefore the characteristic changes in the IR and Raman spectra of the metal cinnamates in comparison with the spectra of acid appeared. Namely, there occurred a disappearance of bands, which originated from stretching m(OH) and deformation b(OH) vibrations; a disappearance of bands assigned to the symmetric and asymmetric stretching m(C@O) vibrations as well as out-of-plane bending c(C@O) vibrations of the carbonyl group were observed; an appearance of bands assigned to the symmetric and asymmetric vibrations of the carboxylate anion mas(COO ), ms(COO ) as well as bas(COO ), bs(COO ), and a disappearance or changes in the positions and intensities of some aromatic bands were also observed. The FT-IR and FT-Raman spectra of cinnamic acid were reported previously [12]. In the experimental FT-IR spectra of cinnamates the wavenumbers of asymmetric and symmetric stretching vibrations of carboxylic anion change their position along the series of metals Zn ? Cd ? Hg (see Table 1). Namely, the band of ms(COO ) is shifted toward lower wavenumbers in spectra of cinnamates, whereas the band of mas(COO ) is shifted towards higher wavenumbers. Two different bands assigned to mas(COO ) occurred in the spectra of cinnamates what suggests two different types of metal coordination. A general tendency in the relationship between Dm(COO ) (the difference between the wavenumbers of the asymmetric (masym) and the symmetric (msym) stretches of carboxylate group from the FT-IR spectra) and the types of coordination of the COO group to metal ions by examining the structures and spectral data was observed for a number of acetate salts in the solid state [13,14]. A general trend in this relationship may be summarised as follows:
Table 1 The wavenumbers [cm 1], intensities and assignments of selected bands that occurred in the FT-IR (recorded in KBr pellets and by the use of ATR accessory), FT-Raman of zinc(II), cadmium(II), mercury(I) and sodium cinnamates. Cinnamic acid [12]
Zn(II) cinnamate
IR KBr
Calc.
Na cinnamate [12] IR KBr
IR KBr
Calc.
3027m 1629vs 1600sh
3210 1661 1649
3027vw 1640m 1599vw
3030w 1644s 1621w
3198 1688 1652
1577m
1623
1577m 1548vs
1495m 1449s
1527 1482
1495m 1451m 1412s
1578m 1531sh 1518vs 1495s 1451s 1418vs
1292vw 1244w 1199vw 1179vw 1074w 1029vw 916vw 852vw 713w 586w
1299w 1256w 1203w 1182w 1073w 1030w 918vw 857w 712m 566w
1624 1418 1417 1529 1484 1445 1437 1274
1286s 1222s 1206m 1176m 1073w 1027w 914m
1307 1252 1226 1108 1054 857
1247 1225 1111 1050 861 750
Cd(II) cinnamate
IR ATR
Raman
1643m 1620w
1647s 1602s
1577m 1533sh 1517vs 1496m 1450s 1417vs
1578w 1524vw
1302w 1256sh 1204w 1179w 1073w 1029w 920w 857w 712s 567m
s – strong; m – medium; w – weak; v – very; sh – shoulder.
1458vw 1441vw
1265w 1205w 1183vw 1032vw 859vw
IR KBr
Calc.
3026w 1640s 162 1vw 1578s 1533vs 1517sh 1496s 1450s 1402vs
3198 1688 1652
1292w 1252m 1204w 1181w 1072w 1028w 918vw 852w 715m 591m
1624 1421 1415 1529 1483 1427 1426 1276 1247 1225 1111 1050 860 741
Hg(I) cinnamate
IR ATR
Assignments
[11]
8a
Raman
IR KBr
IR ATR
Raman
1639m 1622w
1642vs 1602s
3024w 1637s 1620m
1636m 1605w
3020vw 1638vs 1601s
m(CH)ar + m(CH)cinn m(C@C)cinn m(CC)ar
1577m 1533s 1513s 1495s 1450m 1400vs
1579w
1576s 1560s 1526s 1495s 1447m 1358vs
1570w 1555w 1526s 1481s 1447m 1356vs
1579sh
m(CC)ar mas(COO )
8b
1497vw
m(CC)ar m(CC)ar ms(COO )
19a 19b
1290w 1250w 1202w 1180w 1072w 1026w 920w 85 1w 718m 590m
1292w 1254w 1215w
1292w 1252m 1205w 1182w 1071w 1028w 917w 853w 715m 591s
1453w
1256m 1206w 1182w 1030w 854w
1071w 1034w 912w 853w 715m 592m
1363vw 1293vw 1261w 1203w 1182w 1029w 853w 595vw
b(CH)cinn b(CH)cinn b(CH)ar b(CH)ar b(CH)ar b(CH)ar c(CCH)cinn bs(COO ) cs(COO ) bas(COO )
13 9a 18b 18a
406
M. Kalinowska et al. / Journal of Molecular Structure 993 (2011) 404–409
Fig. 1. The crystal hydrated structure of zinc cinnamate [15].
(1) Structure of the carboxylate group is bidentate chelating when the bands of masym(COO ) and msym(COO ) in studied complex are shifted to lower and higher wavenumbers, respectively, compared to those for sodium salt; or Dm(COO )studied complex Dm(COO )sodium salt. (2) Bidentate bridging structure exists when the bands of masym(COO ) and msym(COO ) in studied complex are shifted to higher wavenumbers, compared to those for sodium salt; or Dm(COO )studied complex 6 Dm(COO ) sodium salt. (3) For monodentate geometry of carboxylate group the bands of masym(COO ) and msym(COO ) in studied complex are shifted to higher and lower wavenumbers, respectively, compared to those for sodium salt; or Dm(COO )studied complex Dm(COO )sodium salt. The difference between wavenumbers of asymmetric and symmetric stretches of the carboxylic anion vibrations Dm(COO ) alters in a regular fashion along the metal series Zn ? Cd ? Hg and respectively amounts to: 113, 131 and 202 cm 1 as well as 100, 115 and 168 cm 1. According to spectroscopic criteria the carboxylate group in zinc and cadmium cinnamates seems to be bidentate chelating. Whereas in mercury(I) cinnamate the type of coordination may be monodentate. The literature data for crystal structure of zinc cinnamate Zn(C9H7O2)22H2O was reported and confirms the bidentate chelating coordination (Fig. 1) [15]. Not only the bands which derive from the carboxylic anion vibrations are sensitive to change of metal [16]. Several bands of
aromatic system as well as bands which derive from the AC@CA double bond are shifted towards lower wavenumbers in the spectra of complexes compared with the spectrum of acid. Among these bands are: 3030 cm 1 (IR KBr), m(C@C)cinn (IR KBr, IR ATR, Raman), 8b (IR ATR), 19b (IR KBr, IR ATR), 1295 cm 1 (IR KBr, IR ATR), 1255 cm 1 (IR KBr), 18a (IR KBr, Raman), 918 cm 1 (IR ATR), 775 cm 1 (IR ATR). The bands connected with the AC@CA vibrations undergo larger displacement than the bands derived from ring vibrations. Moreover higher displacement of bands toward lower wavenumbers were observed in the spectra of Hg(I) cinnamate than Zn and Cd cinnamates. Additionally, one can observe a systematic decrease in the wavenumbers of several bands in the series of Zn ? Cd ? Hg cinnamates. These bands are: 3026 cm 1 (IR KBr), m(C@C)cinn (IR KBr, IR ATR, Raman), 19a (IR ATR), 19b (IR KBr, Raman), b(CH)cinn 1292 cm 1 (IR KBr, IR ATR), b(CH)cinn 1252 cm 1 (IR KBr), 18a (IR KBr, Raman), 1132 cm 1 (IR ATR), 1089 cm 1 (IR ATR), 18b (IR ATR), c(CHH)cinn (IR ATR). The displacement of bands toward lower wavenumbers is generally interpreted as a decrease in the force constants of bonds what results from a decrease in electronic charge density around atoms [4]. In Table 2 selected wavenumbers of bands assigned to aromatic ring vibrations of benzoates, cinnamates as well as benzoic and cinnamic acids are gathered [17,18]. The differences between position of appropriate bands are more noticeable in the spectra of benzoic acid and benzoates than cinnamic acid and cinnamates. Several of the aromatic bands disappear in the spectra of sodium and mercury(I) benzoates, but they are present in the spectra of Na and Hg(I) cinnamates. This suggests that influence of metal ions on the structure cinnamic acid is a short range effect and it constrains mainly to the changes in the electronic charge density around atoms of the double bond between aromatic ring and carboxylic group. The differences in electronic charge distribution in benzoic and cinnamic acids are due to the presence of the double bonds between carboxylic group and ring in cinnamic acid molecule. In Fig. 2 the NPA atomic charges calculated at B3LYP6/311++G level for both acids are presented. The electronic charge density around carbon atoms no. C1 is lower in cinnamic acid ( 0.096e) than benzoic acid ( 0.170e). Moreover the close proximity of carboxylic group and aromatic ring in benzoic acid molecule influences the charge density of hydrogen atoms HD (0.226e) and HH (0.230e). Therefore, the presence of the double bond in cinnamic acid molecule is crucial for the effect of metal ions on the charge density in the aromatic ring. A contrary situation takes place in case of picolinic acid and metal picolinates. Wavenumbers of a few bands from FT-IR and
Table 2 Wavenumbers [cm 1] and intensities of selected bands from FT-IR and FT-Raman spectra of benzoic acid and benzoates [17,18], cinnamic acid and cinnamates [16] and picolinic acid and picolinates [19]. 19a
Benzoic acid Na(I) benzoate Zn(II) benzoate Cd(II) benzoate Hg(I) benzoate Cinnamic acid Na(I) cinnamate Zn(II) cinnamate Cd(II) cinnamate Hg(I) cinnamate Picolinic acid Na(I) picolinate Zn(II) picolinate
19b
14
9a
18a
10a
IR
Raman
IR
Raman
IR
Raman
IR
Raman
IR
Raman
IR
Raman
1498w⁄ – 1491w 1494w – 1495m 1495m 1495s 1496s 1495s 1455s – 1476m
– 1493w nd 1494w – 1496vw 1495vw 1496m – 1497vw 1442vw 1475w 1482w
1455s – 1448w 1447w – 1449s 1451m 1451s 1450s 1147m 1439m 1439s 1446m
1460vw 1436m nd 1450vw – 1444vw 1455vw 1458vw 1453m – _ 1440w 1447w
1324vs 1306w 1307w 1310w 1307vw 1334m – – – – 1343s – –
1326w – nd – – 1329vw 1323vw – – – 1358vw – –
1180sh – 1180w 1178w – 1176m 1179vw 1182vw 1181w 1180w 1198s 1169w 1168w
1184m 1185m nd – – 1179m 1180vw 1183vw 1182m 1182w _ 1172w 1170w
1027m 1029m 1026w 1025m nd 1027w 1029vw 1030w 1028w 1026w 1045s 1045w 1048m
1027m 1033m nd nd nd 1027w 103 1w 1032vw 1030w 1029w 105 1w 1050m 1051m
856vw 819m 818m 822vw nd 875w 878w 876w 873w 878w nd nd nd
855vw 825w nd nd nd 876vw 878vw 887vw 875w 880w nd nd nd
s – strong; m – medium; w – weak; v – very; sh – shoulder; nd – no data.
407
M. Kalinowska et al. / Journal of Molecular Structure 993 (2011) 404–409
of complex and acid is higher in case of picolinate than benzoate ligand. It points that presence of nitrogen atom in the ring certainly play an important role in the interactions metal–ligand. The effect of metal ions on the electronic structure of cinnamic acids may be related to selected metal ion parameters. In order to estimate this dependency a linear correlation between wavenumbers of selected bands from FT-IR (recorded in KBr pellets and by the use of ATR accessory) and FT-Raman spectra and metal ion parameters (ionic potential, ionic radius, 1/atomic mass) was done. Because in this paper only tree metal complexes with cinnamic acid were analysed the indispensable additional data to statistical analysis were taken from [12,16,20]. The results of this analysis are presented in Table 3. Only data with correlation coefficients higher than 0.7 are included. The obtained data suggest that the main factor responsible for the interaction metal ion–cinnnamic acid molecule is ionic radius. With an increase in the ionic radius of metal ions the values of the wavenumbers from FT-IR and FT-Raman spectra of selected cinnamates decrease what is caused by a decrease in electronic charge density around atoms (mainly in aromatic ring and double bond AC@CA) in cinnamate molecules. It suggests that the type of metal–ligand coordination determined the effect of metal ions on the electronic charge distribution in ligand molecule.
Fig. 2. The NPA atomic charges calculated at B3LYP/6-311++G level for: (a) benzoic acid and (b) cinnamic acid.
FT-Raman spectra of these compounds are shown in Table 2. Picolinic acid is a pyridine compound with a carboxyl side chain at the 2-position. Both zinc picolinate (covalent bond between metal–ligand) and sodium picolinate (ionic bond) formation causes distinct changes in the location of bands assigned to aromatic ring vibrations. Namely, most of these bands disappear/appear or undergo movement to max. 40 cm 1 in the spectra of zinc picolinate compared with the spectra of acid. The magnitude of difference between location of corresponding bands in the spectra
4. NMR spectra of zinc, cadmium and mercury(I) cinnamates 4.1. 1H NMR spectra In the 1H NMR spectra of Zn(II), Cd(II) and Hg(I) cinnamates signals are slightly shifted upfield in comparison with the appropriate
Table 3 Values of correlation coefficients (R) obtained for the linear correlation between wavenumbers of selected bands from FT-IR spectra (recorded in KBr pellets and by the use of ATR accessory) and FT-Raman spectra and selected metal ions parameters. Li, Na, K, Rb, Cs, Zn, Cd, Hg, Ca, La, Th cinnamates
Ionic potential Ionic radius 1/Atomic mass Bands Ionic potential Ionic radius 1/Atomic mass
b(CH)-C=C- 1290 cm IR KBr 0.544 0.738 0.060
1
b(CH)-C@C- 1250 cm IR KBr 0.645 0.833 0.220
18a IR KBr
1
c(CCH)-C@C- 970 cm IR KBr
1
8a Raman
0.706 0.760 0.191 18a Raman
0.573 0.951 0.500
0.759 0.737 0.001
18b IR KBr
0.485 0.905 0.391
19b IR KBr 0.504 0.785 0.395
11 IR KBr
0.150 0.818 0.708
0.232 0.625 0.748
19b IR ATR 0.671 0.800 0.310
0.655 0.937 0.303
7.4 7.2
Cinnamic acid Cinnamate Na(I)
6.6
Cinnamate Zn(II)
6.4
Cinnamate Cd(II) Cinnamate Hg(I)
6.2 6 C
D. H
F
E. G
0.704 0.704 0.034
0.771 0.710 0.403
7.6
7
0.780 0.689 0.147
9a Raman
bs(COO ) IR KBr
8
6.8
19a IR KBr
Dm(COO ) IR KBr
7.8
[ppm]
Bands
B
proton position Fig. 3. Graphical presentation of chemical shifts from 1H NMR spectra of cinnamic acid and cinnamates.
408
M. Kalinowska et al. / Journal of Molecular Structure 993 (2011) 404–409
175 Cinnamic acid
165
Cinnamate Na(I) Cinnamate Zn(II)
[ppm]
155
Cinnamate Cd(II) Cinnamate Hg(I)
145
135 125
115 7
9
1
4
3.5
2.6
8
carbon position Fig. 4. Graphical presentation of chemical shifts from
COOH A
C H
7
H
8 H
9 1
H 6
GH
5
B
HD 2
4
3 H
E
HF Fig. 5. Atom numbering for cinnamic acid molecule.
signals in the spectra of acid, but the displacement is not as significant as in case of spectrum of sodium cinnamate (Fig. 3). A decrease in the chemical shifts in spectra of metal complexes points at an increase in the screening of aromatic protons as a consequence of the circular current weakening. The signals in the NMR spectra of Zn and Cd cinnamates posses generally the same values, whereas in the spectrum of Hg cinnamate they are located at higher ppm. The differences are small and amount to 0.03–0.05 ppm. It seems that different position of appropriate signals in the spectra of cinnamates are caused by different types of carboxylic group coordination what brings about dissimilar effect of metal ions on the electronic charge distribution in ligand. Namely, the bond between sodium cation and ligand possesses ionic character; deformation of the electronic charge in ligand may be mainly caused by polarization of CAC and CAH bonds. Otherwise, in case of zinc and cadmium cinnamates the infrared data suggest the bridging and chelating types of coordination, and mercury(I) cation is bound by monodentate and bridging carboxylic groups. 4.2.
13
C NMR spectra
On the basis of the chemical shifts of signals from 13C NMR spectra of cinnamic acid and cinnamates we may confirm that metal cations affect mainly the charge distribution around atoms of the double bond, i.e. C8 and C9 (Fig. 4 and 5). The electronic charge density around carbon in position 9 increases, and around carbons no. 8 and 7 decreases in metal complexes compared with acid molecule. The charge densities around the other carbon atoms change insignificantly after replacement of the carboxylic group hydrogen with a metal ion. 5. Conclusions Substitution of metal cations in the carboxylic group of cinnamic acid causes changes in the electronic charge distribution
13
C NMR spectra of cinnamic acid and cinnamates.
of the whole molecule. The alternation in the electronic structure of carboxylate group results from different types of metal ion coordination. According to the spectroscopic criteria the carboxylate group in zinc(II) and cadmium(II) cinnamates is bidentate chelating. Whereas in mercury(I) cinnamates the type of coordination is monodentate. Comparing the 1H NMR results obtained for cinnamic acid and sodium(I), zinc(II), cadmium(II) and mercury(I) cinnamates we may conclude that the differences in the electronic charge distribution of particular molecules depend on the type of metal coordination. Sodium cation causes larger changes in the electronic charge distribution of cinnamic acid than zinc, cadmium and mercury ions. Moreover, a systematic decrease in the wavenumber of several bands in the series of Zn ? Cd ? Hg cinnamates in the FT-IR and FT-Raman spectra was observed. Metal cations affect mainly the charge distribution around atoms of the double bond of cinnamate, the structure of the aromatic ring is affected to a lesser extent. The main factor responsible for the interaction metal ion–cinnnamic acid molecule is ionic radius. On the basis of the FT-IR and FT-Raman spectra of zinc benzoate, cinnamate and picolinate the participation of double bond between the ring and carboxylate group as well as nitrogen atom in the ring in the interaction metal–ligand may be discussed. It occurred that double bond weaken the effect of metal cations on the electronic charge distribution in the ring whereas in case of picolinate molecule this effect is enhanced. Acknowledgement This work was supported by Ministry of Science and Higher Education (Grant no. N N305 384538). References [1] W. Lewandowski, M. Kalinowska, H. Lewandowska, J. Inorg. Biochem. 99 (2005) 1407. [2] R. S´wisłocka, E. Regulska, M. Samsonowicz, T. Hrynaszkiewicz, W. Lewandowski, Spectrochim. Acta A 61 (2005) 2966. [3] G. S´widerski, M. Kalinowska, S. Wojtulewski, W. Lewandowski, Spectrochim. Acta A 64 (2006) 24. [4] L. Bravo, Nutr. Rev. 56 (1998) 317. [5] S. Burt, Int. J. Food Microbiol. 94 (2004) 223. [6] M.G.L. Hertog, D. Kromhout, C. Aravanis, H. Blackburn, R. Buzina, F. Fidanza, S. Giampaoli, Arch. Intern. Med. 155 (1995) 381. [7] H.T. Flakus, M. Jabłon´ska, J. Mol. Struct. 707 (2004) 97. [8] K. Hanai, A. Kuwae, T. Takai, H. Senda, K.-K. Kunimoto, Spectrochim. Acta A 57 (2001) 513. [9] Tiane-Jye Hsieh, Chia-Ching Su, Chung-Yi Chen, Chyong-Huey Liou, Li-Hwa Lu, J. Mol. Struct. 741 (2005) 193.
M. Kalinowska et al. / Journal of Molecular Structure 993 (2011) 404–409 [10] [11] [12] [13] [14] [15]
Gaussian 2003, Revision A.7, in: M.J. Frisch et al. (Eds.), Gaussian, Inc., Pittsburgh, PA, 1998. G. Varsànyi, Assignments for Vibrational Spectra of 700 Benzene Derivatives, Akademiai Kiado, Budapest, 1973. M. Kalinowska, R. S´wisłocka, W. Lewandowski, J. Mol. Struct. 572 (2007) 834– 836. G.B. Deacon, R.J. Philips, Coordin. Chem. Rev. 33 (1980) 227. Ch.R. Choudhury, A. Datta, V. Gramlich, G.M.G. Hossain, K.M.A. Malik, S. Mitra, Inorg. Chem. Commun. 6 (2003) 790. H. Hosomi, S. Ohba, Y. Ito, Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 56 (2000) e123.
409
[16] M. Kalinowska, R. S´wisłocka, W. Lewandowski, W. Ferenc, Nauka i przemysł – _ ´ ci, UMCS, metody spektroskopowe w praktyce, nowe wyzwania i mozliwos Lublin, 2009. [17] W. Lewandowski, Can. J. Spectr. 32 (1987) 41. [18] W. Lewandowski, Arch. Environ. Contam. Toxicol. 17 (1988) 131. [19] W. Lewandowski, G. S´widerski, R. S´wisłocka, S. Wojtulewski, P. Koczon´, J. Phys. Org. Chem. 18 (2005) 918. [20] M. Kalinowska, W. Lewandowski, R. S´wisłocka, E. Regulska, Spectroscopy 24 (2010) 277–281.