Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 348–356

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Theoretical spectroscopic study of seven zinc(II) complex with macrocyclic Schiff-base ligand Koray Sayin ⇑, Sultan Erkan Kariper, Tuba Alagöz Sayin, Duran Karakasß Chemistry Department, Faculty of Science, Cumhuriyet University, 58140 Sivas, Turkey

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 The agreement is found between

experimental and theoretical results.  The optimized structures of zinc

complexes are demonstrated by using structural parameters, IR and NMR spectra.  The UV–VIS spectrum of mentioned complexes are predicted and explained by using orbital character and transition character analysis.  Ranking of biological activity of relevant zinc complexes is predicted by using quantum chemical descriptors.

a r t i c l e

i n f o

Article history: Received 12 March 2014 Received in revised form 27 May 2014 Accepted 30 May 2014 Available online 12 June 2014 Keywords: Zn(II) complexes Macrocyclic Schiff-base ligand Spectroscopic studies DFT studies

a b s t r a c t Seven zinc complexes, which are [ZnL1]2+, [ZnL2]2+, [ZnL3]2+, [ZnL4]2+, [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+, are studied as theoretically. Structural parameters, vibration frequencies, electronic absorption spectra and 1 H and 13C NMR spectra are obtained for Zn(II) complexes of macrocyclic penta and heptaaza Schiff-base ligand. Vibration spectra of Zn(II) complexes are studied by using Density Functional Theory (DFT) calculations at the B3LYP/LANL2DZ. The UV–VIS and NMR spectra of the zinc complexes are obtained by using Time Dependent-Density Functional Theory (TD-DFT) method and Giao method, respectively. The agreements are found between experimental data of [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions and their calculated results. The geometries of complexes are found as distorted pentagonal planar for [ZnL1]2+, [ZnL2]2+ and [ZnL3]2+ complex ions, distorted tetrahedral for [ZnL4]2+ complex ion and distorted pentagonal bipyramidal for [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions. Ranking of biological activity is determined by using quantum chemical parameters and this ranking is found as: [ZnL7]2+ > [ZnL6]2+ > [ZnL5]2+ > [ZnL3]2+ > [ZnL2]2+ > [ZnL1]2+. Ó 2014 Elsevier B.V. All rights reserved.

Introduction Schiff base ligands play an important role in inorganic coordination chemistry as these ligands form stable complexes with most transition metals in a variety of oxidation states [1–5]. There are great interest about multi-dentate Schiff base ligands because their binding selectivity can be altered subtly by having the ligand ⇑ Corresponding author. Tel.: +90 346 219 10 10x2851; fax: +90 346 219 11 86. E-mail addresses: [email protected], [email protected] (K. Sayin). http://dx.doi.org/10.1016/j.saa.2014.05.097 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

enforce a specific spatial arrangement of donor atoms. The metal complexes with Schiff base ligand have been widely studied because of their industrial, antifungal, and biological applications [6]. Schiff base macrocycles have been of great importance in macrocyclic chemistry [7]. Currently, a great deal of attention is being focused on macrocyclic ligands because they play an important role in many aspects of chemistry, medicine and the chemical industry [8,9]. In recent years, many metal complexes with macrocyclic Schiff base ligand have been reported as experimentally [10–20]. In these studies, metal complexes with macrocyclic

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Schiff base ligand have been synthesized and examined as spectroscopically. Zinc(II) macrocyclic pentaaza and heptaaza Schiff base complexes have been synthesized by Keypour et al. [21]. According to their report, structural parameters of [ZnL5]2+ have been reported while vibration frequencies, 13C and 1H NMR of [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complexes have been demonstrated. The macrocyclic pentaaza and heptaaza Schiff base ligands are represented in Fig. 1. There are not any experimental data about [ZnL1]2+, [ZnL2]2+, [ZnL3]2+ and [ZnL4]2+ complexes in Ref. [21]. However, the biological activities of these complexes have not been investigated as experimentally. The structural parameters, ranking of biological activity, IR, UV–VIS, 1H and 13C NMR spectra can be obtained by using computational chemistry methods. In this paper, the agreement between experimental and theoretical results is investigated by using structural parameters, IR and NMR spectra. After that, complex geometries, structural parameters, IR, UV, 1H and 13C NMR spectra are examined for other zinc complexes. The transition character and orbital character analysis are used to explain the UV–VIS spectra. The ranking of biological activity of mentioned zinc complexes is investigated by using quantum chemical descriptors which are the highest occupied molecular orbital energy (EHOMO), the energy gap (EGAP), hardness (g), softness (r), electronegativity (v) and dipole moment (l). Calculation method All computational processes of relevant zinc complexes were made by using GaussView 5.0.8 [22], Gaussian 09 IA32W Revision-A.02 [23] and Gaussian 09 AML64-G09 Revision-C.01 [24]. Geometries of mentioned zinc(II) complexes were fully optimized at the B3LYP [25,26] method with LANL2DZ [27,28] basis set and mix basis set (with GEN keyword) in the gas phase. For mix basis set, LANL2DZ (for Zn atom) and 6-31G(d,p) [29] (for H, C and N atoms) basis sets were selected. The vibrational frequency analyses indicate that optimized structures of all zinc complexes are at stationary points corresponding to local minima without imaginary frequencies. UV–VIS calculations were performed by using Time Dependent-Density Functional Theory (TD-B3LYP) method with LANL2DZ basis set. The GIAO method was used for 1H and 13C NMR spectra. Tetramethylsilane were selected as reference for NMR spectra at B3LYP/LANL2DZ level. Orbital character (OC%) [30,31] and transition character analyses (TC%) [32,33] were calculated to explain the UV–VIS spectra by using Eq. (1) and (2), respectively.

n2 OC% ¼ P 2  100 n

ð1Þ

t2 TC% ¼ P 2  100 t

ð2Þ

Fig. 1. Schematic structures of the macrocyclic Schiff-base ligands.

P

where n is the atomic orbital coefficient, n2 is the sum of the squares of all atomic orbital coefficients in a specific molecular orbiP tal, t is coefficient of the wavefunction for each excitation and t2 is the sum of the squares of all coefficient of the wavefunction for each excitation in a specific band. Additionally, some quantum chemical parameters (EGAP, g, r and v) were calculated with Eq. (3)–(6) [34–37],

EGAP ¼ ELUMO  EHOMO E E g ¼ LUMO HOMO 2 1 r¼

ð3Þ ð4Þ ð5Þ

g

v¼

ðEHOMO þ ELUMO Þ 2

ð6Þ

Result and discussion Geometry optimization The mentioned seven zinc complexes have been synthesized by Keypour et al. but the structural parameters of these complexes have not been reported except [ZnL5]2+ complex ion. As experimentally, some bond lengths and angles of [ZnL5]2+ complex ion have been demonstrated in their report [21]. All complexes are optimized at B3LYP method with LANL2DZ and mix basis sets. Calculated structural parameters and experimental data of [ZnL5]2+ are given in Table 1. For bond lengths and angles, correlations between experimental and calculated data are investigated by using linear regression analysis. Correlation constants (R2) for bond lengths and angles are calculated for each basis set. According to Table 1, the correlation constants of bond lengths are equal to 0.997 and 0.993 for Table 1 Calculated and experimental structural parameters of [ZnL5]2+ complex ion.

a

B3LYP/LANL2DZ

B3LYP/GEN

Exp.a

Bond lengths (Å) 1Zn–2N 1Zn–13N 1Zn–14N 1Zn–28N 1Zn–32N 1Zn–45N 1Zn–47N 11C–13N 12C–14N

2.291 2.341 2.350 2.382 2.397 2.237 2.237 1.301 1.301

2.277 2.323 2.333 2.381 2.395 2.272 2.270 1.285 1.285

2.223 2.289 2.274 2.365 2.337 2.149 2.155 1.261 1.272

Bond angles (°) 2N–1Zn–13N 2N–1Zn–14N 2N–1Zn–28N 2N–1Zn–32N 2N–1Zn–45N 2N–1Zn–47N 13N–1Zn–14N 13N–1Zn–28N 13N–1Zn–32N 13N–1Zn–45N 13N–1Zn–47N 14N–1Zn–28N 14N–1Zn–32N 14N–1Zn–45N 14N–1Zn–47N 28N–1Zn–32N 28N–1Zn–45N 28N–1Zn–47N 32N–1Zn–45N 32N–1Zn–47N 45N–1Zn–47N

69.77 69.65 141.41 141.27 90.32 92.24 139.42 73.51 145.84 90.43 89.36 145.74 73.32 90.10 91.89 77.32 78.35 98.90 100.80 77.87 177.18

69.86 69.71 141.55 141.33 91.76 93.05 139.57 73.64 145.53 90.78 90.22 145.48 73.38 90.92 91.39 77.12 76.88 98.85 100.04 76.55 175.14

70.20 71.00 141.53 142.32 93.82 89.99 141.10 72.72 144.84 91.37 92.60 144.25 73.40 88.58 89.97 76.15 77.08 101.63 97.27 77.98 175.25

Experimental values are taken from Ref. [21].

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B3LYP/LANL2DZ and B3LYP/GEN, respectively. According to the correlation constants of bond lengths, B3LYP/LANL2DZ level is better than other level. As for the bond angles, the correlation constants are equal to 0.996 and 0.997 for B3LYP/LANL2DZ and B3LYP/GEN, respectively. Although B3LYP/GEN level is better than B3LYP/LANL2DZ, these values are too closed to each other. Therefore, it is difficult to make a selection between levels. The graphs about linear regression analyses are given in supplementary material. As a result, B3LYP/LANL2DZ level is more appropriate for mentioned zinc(II) complexes than other level. The optimized structures of mentioned zinc(II) complexes are given in supplementary material at B3LYP/LANL2DZ level. The calculated bond lengths and angles of mentioned zinc(II) complexes are given in Table 2 except [ZnL5]2+ complex ion. According to Table 2, coordination number value is equal to five in [ZnL1]2+, [ZnL2]2+ and [ZnL3]2+ complex ions, this value is equal to four in [ZnL4]2+ complex ion and seven for other zinc(II) complexes. The bond lengths and angles of mentioned zinc(II) complexes is close to each other except [ZnL4]2+ complex ion. According to these results, there are five nitrogen atoms, which are coordinate to metal atom, in equatorial position in [ZnL1]2+, [ZnL2]2+, [ZnL3]2+ complex ions. It can be said that the geometry of these complexes is distorted pentagonal planar. As for the [ZnL4]2+, there is an interaction between 1Zn and 13N atoms while there are coordinate-covalent bonds between other nitrogen atoms and metal atom. As can be seen from optimized structure of this complex, the geometry is similar to distorted tetrahedral. In [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions, there are five coordinate-covalent bonds in equatorial position while two bonds in axial position. According to this result, the geometry of these complexes is distorted pentagonal bipyramidal.

Table 2 Some calculated bond lengths (Å) and bond angles (°) of other zinc complexes at B3LYP/LANL2DZ level in gas phase.

Bond lengths (Å) 1Zn–2N 1Zn–13N 1Zn–14N 1Zn–28N 1Zn–32N 1Zn–45N 1Zn–47N 11C–13N 12C–14N Bond angles (°) 2N–1Zn–13N 2N–1Zn–14N 2N–1Zn–28N 2N–1Zn–32N 2N–1Zn–45N 2N–1Zn–47N 13N–1Zn–14N 13N–1Zn–28N 13N–1Zn–32N 13N–1Zn–45N 13N–1Zn–47N 14N–1Zn–28N 14N–1Zn–32N 14N–1Zn–45N 14N–1Zn–47N 28N–1Zn–32N 28N–1Zn–45N 28N–1Zn–47N 32N–1Zn–45N 32N–1Zn–47N 45N–1Zn–47N

[ZnL1]2+

[ZnL2]2+

[ZnL3]2+

[ZnL4]2+

[ZnL6]2+

[ZnL7]2+

2.246 2.300 2.300 2.324 2.324 – – 1.301 1.301

2.175 2.225 2.225 2.204 2.204 – – 1.302 1.302

2.221 2.270 2.270 2.280 2.281 – – 1.302 1.302

2.005 3.446 2.090 2.142 2.132 – – 1.352 1.488

2.354 2.383 2.380 2.428 2.499 2.244 2.215 1.302 1.302

2.251 2.326 2.468 2.628 3.230 2.143 2.140 1.302 1.306

70.39 70.39 142.32 142.44 – – 140.78 72.72 145.89 – – 145.96 72.76 – – 75.24 – – – – –

72.72 72.72 135.07 135.05 – – 145.44 75.36 132.32 – – 132.33 75.35 – – 89.87 – – – – –

71.18 71.18 141.01 141.01 – – 142.36 74.41 140.39 – – 140.39 74.40 – – 77.98 – – – – –

59.83 88.22 133.94 123.12 – – 144.11 79.56 104.71 – – 119.71 106.64 – – 85.57 – – – – –

68.13 68.26 134.10 136.58 86.25 89.48 136.33 71.37 146.34 96.03 84.83 148.19 72.24 83.31 92.64 89.31 77.31 107.62 106.54 74.87 174.97

75.19 69.79 140.85 132.42 100.82 106.54 140.95 71.15 152.25 97.51 97.88 147.24 64.22 91.40 91.43 86.73 73.93 88.87 92.00 64.22 151.72

IR spectra The infrared spectroscopy is one of the important methods to determination of functional groups in molecular structure. However, this spectroscopy is one of the popular methods to illuminate the molecular structure. The IR spectrum can be obtained by using computational chemistry methods and vibration frequencies can be assigned. The vibration frequencies in IR spectra are harmonic frequencies and these frequencies can be approximated experimental frequencies by using scale factors. As experimentally, the vibration frequencies of [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ have been reported by Keypour and co-workers. But these frequencies have not been assigned in their report [21]. B3LYP/LANL2DZ level is selected as the best level for our complexes in Section ‘Geometry optimization’ Therefore, stretching vibrations of relevant zinc(II) complexes are calculated at this level in vacuum (gas phase). Theoretical frequencies are scaled by 0.9611 [38–41]. The experimental frequencies and calculated anharmonic frequencies are given in Table 3 and IR spectrum of each zinc complex is given in supplementary material. The experimental frequencies, which are demonstrated by Keypour et al., and calculated frequencies are subjected to linear regression analyses. The correlation constants are calculated as 0.998 for [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions. These results show that there is a good agreement between experimental and calculated frequencies. Therefore, the vibration frequencies of [ZnL1]2+, [ZnL2]2+, [ZnL3]2+ and [ZnL4]2+ complexes are acceptable. All frequencies are assigned and presented in Table 3. The bond stretching frequencies which are mN–H, m(C–H)pry, mC=N, m(C=C)pry, m(C–C), m(C–N), mZn–N and m(Zn–N)pry of each zinc(II) complex are close to each other. These results mean that the geometric structures of zinc complexes are similar to each other except [ZnL4]2+ complex ion. There is an agreement between results of IR spectra and geometry optimization.

UV spectra and character analysis Molecular orbitals (MO) comprises from the linear combinations of atomic orbitals. Different atomic orbitals contribute to each MO. This contribution to each MO can be determined with atomic orbital coefficient. In this study, atomic orbital coefficients are calculated at B3LYP/LANL2DZ level for each zinc(II) complex. Percentages of contributions to MO’s (OC%) are calculated by using atomic orbital coefficient with Eq. (1). Excitation wavelength values and the coefficient of transitions are calculated for all zinc complexes by using TD-B3LYP method with LANL2DZ basis set in vacuum. A band in the UV spectra comprises from a lot of electronic transitions which are between different molecular orbitals. The percentages of transition characters (TC%) are calculated by using Eq. (2). For [ZnL1]2+ complex ion, a band (216.4 nm) and shoulder (301.4 nm) are observed in UV– VIS spectra. The electronic transitions, TC% and OC% of these bands are listed in Table 4 and the UV–VIS spectrum of [ZnL1]2+ complex ion is represented in Fig. 2. At UV spectra, the main band has maximum oscillator strength. We selected the main bands and shoulder in order to evaluate the spectrum of [ZnL1]2+. For this complex ion, the maximum percentage of electronic transition at 216.4 nm is calculated as 81.27%. Electron transfers form ground state (HOMO6) to excited state (LUMO). The orbital characters of HOMO6 and LUMO have been represented in brackets where are at ground state and excited state in the same table. This result shows that electrons transfer from L1 ligand’s orbital to L1 ligand’s orbital. At 301.4 nm, electrons transfer from L1 ligand’s orbital to L1 ligand’s orbital, too. No band is observed in visible region. Because there is not any empty d orbital in zinc(II) ion. Natural electron configuration of zinc(II) ion in complex is calculated as follows:

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Table 3 Some calculated vibration frequencies (cm1) of mentioned zinc(II) complexes at B3LYP/LANL2DZ level in vacuum and experimental frequencies of [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions.

[ZnL1]2+ [ZnL2]2+ [ZnL3]2+ [ZnL4]2+ [ZnL5]2+ [ZnL5]2+a [ZnL6]2+ [ZnL6]2+a [ZnL7]2+ [ZnL7]2+a a

mN–H

m(C–H)pry

mC=N

m(C=C)pry

m(C–C)

m(C–N)

mZn–N

m(Zn–N)pry

3304 3301 3292 3275 3340 3342 3335 3330 3319 3316

3141 3137 3141 3137 3138 3287 3138 3287 3144 3263

1618 1612 1618 1492 1611 1656 1607 1650 1606 1642

1561 1557 1559 1482 1555 1591 1554 1591 1559 1589

1069 1072 1060 1066 1064 1085 1070 1093 1110 1085

1032 990 987 961 979 1015 974 1012 981 1013

719 727 709 552 645 658 646 659 644 658

630 632 627 531 626 622 425 623 629 622

Experimental vibration frequencies are taken from Ref. [21].

9:98

Zn2þ : ½core 4s0:40 3d

4p0:2 ðin ½ZnL1 

2þ

complex ionÞ 1 2+

The process which is explain for [ZnL ] is done for other zinc(II) complexes. Transition types (ligand to ligand, metal to ligand, etc.) are determined for each zinc(II) complexes. The wavelengths of selected band and shoulder with their oscillator strength and the transition type of these bands and shoulders of each zinc(II) complex are given in Table 5. According to Table 5, the transition types are calculated as ‘‘Ligand ? Ligand’’. These types of transition are known as intraligand charge transfer (ILCT). 1

H and

13

Fig. 2. The calculated UV–VIS spectrum of [ZnL1]2+ complex ion at TD-B3LYP/ LANL2DZ level in vacuum.

C NMR spectra

The NMR spectra have become a classy and powerful nondestructive analytical technology that has found a variety of applications in many different research fields. Chemical shifts are recognized as an important part of the information contained in NMR spectra. They are precious for structural interpretation due to their sensitivity to conformational variations. The chemical shifts of hydrogen atoms in [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions have been reported as experimentally in Ref. [21]. The 1H and 13C NMR spectra of mentioned zinc(II) complex are calculated at GIAO/B3LYP method with LANL2DZ basis set in vacuum. The 1H and 13C NMR spectra of zinc(II) complexes in vacuum are represented in supplementary material. All chemical shifts are reported in d (ppm) relative to the tetramethylsilane as internal standard. All atomic labeling for NMR spectrum are represented in Fig. 3. The experimental chemical shift values of [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions and theoretical chemical shift values of carbon atoms and hydrogen atoms are given in Tables 6 and 7 for each zinc(II) complex, respectively. The chemical shifts values of carbon atoms in zinc(II) complexes are presented in Table 6. The 13C NMR of [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions have been given by Keypour et al. [21]. The agreement between experimental and calculated chemical shifts of carbon atoms in [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions are investigated by using linear regression analysis. The

Table 5 The wavelengths (nm) and their transition types of bands in UV–VIS spectra of each zinc complexes. Complexes

Wavelength (nm)

Oscillator strength

Transition type

[ZnL2]2+

215.5 294.2 214.7 298.6 249.9 297.9 213.6 284.7 214.8 285.4 247.8 290.1

0.3888 0.0795 0.4628 0.0725 0.3165 0.0811 0.2756 0.0856 0.2593 0.0830 0.1644 0.0964

Ligand ? Ligand Ligand ? Ligand Ligand ? Ligand Ligand ? Ligand Ligand ? Ligand Ligand ? Ligand Ligand ? Ligand Ligand ? Ligand Ligand ? Ligand Ligand ? Ligand Ligand ? Ligand Ligand ? Ligand

[ZnL3]2+ [ZnL4]2+ [ZnL5]2+ [ZnL6]2+ [ZnL7]2+

correlation constants (R2) are obtained for each analysis and their values are equal to 0.997, 0.996 and 0.995 for [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions, respectively. The results indicate that there is a good agreement between experimental and calculated 13 C NMR spectra. For other zinc(II) complexes, chemical shifts values are given in same table. For [ZnL4]2+ complex ion, the chemical shifts values of carbon atoms are different from other complexes while the chemical shifts values of carbon atoms in [ZnL1]2+,

Table 4 The calculated wavelengths, oscillator strength (OS) of bands and percentage of transition characters.

a

Wavelength (nm)

Oscillator strength

Ground state

Excited state

Transition %

216.4

0.4127

HOMO6 HOMO3 HOMO2 HOMO1

(99.82%)a (99.79%)a (98.12%)a (99.74%)a

LUMO (98.12%)a LUMO+3 (96.01%)a LUMO+2 (81.49%)a LUMO+1 (99.79%)a

81.27 4.06 2.65 12.02

301.4

0.0908

HOMO3 (99.79%)a HOMO1 (99.74%)a

LUMO (98.12%)a LUMO+1 (99.79%)a

63.88 36.12

OC% value of L1 ligand.

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Table 6 The calculated chemical shifts values of carbon atoms in

13

C NMR spectra for each zinc(II) complexes.

Atoms

[ZnL1]2+

[ZnL2]2+

[ZnL3]2+

[ZnL4]2+

[ZnL5]2+

[ZnL5]2+ Exp.

[ZnL6]2+

[ZnL6]2+ Exp.

[ZnL7]2+

[ZnL7]2+ Exp.

C(a) C(b) C(b0 ) C(c) C(c0 ) C(d) C(d0 ) C(e) C(e0 ) C(f) C(f0 ) C(g) C(g0 ) C(h) C(h0 ) C(i) C(i0 ) C(j) C(j0 ) C(l) C(l0 ) C(s) C(s0 )

141.2 122.6 122.6 140.9 140.9 172.5 172.5 12.1 12.1 45.5 45.5 44.7 44.7 44.7 44.7 – – – – – – – –

141.6 122.1 122.1 141.3 141.3 172.9 172.9 12.1 12.1 43.8 43.8 43.7 43.7 42.1 42.1 – – – – 14.0 – – –

141.3 122.5 122.5 141.1 141.1 170.7 170.7 11.5 11.5 48.5 48.5 46.3 46.3 47.4 47.4 – – – – 23.9 23.9 – –

123.2 148.1 137.3 139.3 151 127.8 167.5 12.6 17.0 47.2 31.7 53.2 46.7 47.7 44.4 – – – – – – 22.4 22.1

138.3 121.7 121.6 143.6 143.9 169.3 169.6 11.5 11.8 45.0 46.2 52.7 55.3 55.5 54.5 49.0 51.4 37.0 36.2 – – – –

142.5 124.7 124.7 148.7 148.7 165.1 165.1 15.3 15.3 46.3 46.3 57.3 57.3 56.5 56.5 52.9 52.9 39.3 39.3 – – – –

138.7 121.7 121.7 143.9 144.2 169.8 169.4 11.6 11.8 44.9 45.9 52.3 51.6 64.5 65.0 51.7 56.8 34.3 35.7 23.8 – – –

142.4 124.9 124.9 149.2 149.2 166.3 166.3 15.4 15.4 45.9 45.9 55.8 55.8 62.3 62.3 52.2 52.2 38.5 38.5 24.1 – – –

139.2 121.6 122.4 143.8 144.9 171.9 171.8 11.9 11.9 46.9 50.7 54.4 55.3 60.9 58.8 46.1 47.3 36.4 37.8 23.7 24.1 – –

143.1 125.6 125.6 149.1 149.1 166.6 166.6 15.5 15.5 47.9 47.9 55.5 55.5 55.3 55.3 50.7 50.7 38.9 38.9 24.3 24.3 – –

[ZnL2]2+ and [ZnL3]2+ complex ions are similar to [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions. These results mean that environment of central atom in equatorial position of mentioned zinc(II) complexes are similar to each other, except [ZnL4]2+ complex ion. The complex geometry of [ZnL4]2+ complex is different from other complexes. These results are in agreement with results of Sections ‘Geometry optimization’ and ‘IR spectra’. As for Table 7, chemical shifts of hydrogen atoms of [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions have been reported by Keypour et al. [21]. The experimental and calculated chemical shifts of hydrogen atoms in these complexes are subjected to the correlation analyses. The correlation constants are obtained for each analysis and their values are equal to 0.976, 0.963 and 0.991 for [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions, respectively. The results indicate that there is an agreement between experimental and calculated 1H NMR spectra. Chemical shifts values of hydrogen atoms in [ZnL1]2+, [ZnL2]2+ and [ZnL3]2+ complex ions are similar to [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions while the chemical

shifts values of hydrogen atoms in [ZnL4]2+ complex ion are different from other complexes. These results in 1H NMR spectra mean that position of hydrogen atoms in zinc(II) complexes are similar to each other, except [ZnL4]2+ complex ion. The complex geometry of [ZnL4]2+ complex is different from other complexes. These 1H NMR results are in agreement with 13C NMR results. Determination of chemical reactivity ranking Biological activity of chemical species can be provided with experimental methods and computational methods. There are many studies in the determination of biological activities as theoretically [42–47]. Quantum chemical parameters or descriptors are used to determine the activity ranking. These parameters are highest occupied molecular orbital energy (EHOMO), the energy gap (EGAP), hardness (g), softness (r), electronegativity (v) and dipole moment (l). Environment of central atom is too much important for determination the activity ranking. It is possible

Table 7 The calculated chemical shifts values of hydrogen atoms in 1H NMR spectra for each zinc(II) complexes. Atoms

[ZnL1]2+

[ZnL2]2+

[ZnL3]2+

[ZnL4]2+

[ZnL5]2+

[ZnL5]2+ Exp.

[ZnL6]2+

[ZnL6]2+ Exp.

[ZnL7]2+

[ZnL7]2+ Exp.

C(a)H C(b)H C(b0 )H C(e)H3 C(e0 )H3 C(f)H2 C(f0 )H2 C(g)H2 C(g0 )H2 C(h)H2 C(h0 )H2 C(i)H2 C(i0 )H2 C(j)H2 C(j0 )H2 C(k)H2 C(k0 )H2 C(l)H2 C(l0 )H2 C(s)H2 C(s0 )H2

8.42 7.94 7.94 2.04 2.04 3.27 3.27 2.72 2.72 2.56 2.56 – – – – – – – – – –

8.44 7.90 7.90 2.03 2.03 3.36 3.36 2.98 2.98 2.95 2.95 – – – – – – 1.88 – – –

8.42 7.96 7.96 1.98 1.98 3.28 3.28 2.54 2.54 2.49 2.49 – – – – – – 1.70 1.70 – –

6.70 7.70 7.11 1.45 1.90 2.73 3.15 2.59 2.70 2.52 2.32 – – – – – – – – 1.26 1.46

8.30 7.87 7.87 1.95 1.96 3.28 3.38 2.48 2.58 2.29 2.32 2.25 2.26 2.36 2.09 0.69 0.44 – – – –

8.33 8.19 8.19 2.52 2.52 3.81 3.66 3.15 3.15 2.99 2.80 2.86–2.76 2.86–2.76 2.70 2.40 2.20 2.20 – – – –

8.28 7.87 7.89 1.92 1.92 3.51 3.21 2.53 2.60 2.48 1.43 2.24 1.93 1.95 2.38 0.56 0.72 1.43 – – –

8.32 8.19 8.19 2.47 2.47 3.81–3.76 3.81–3.76 3.45 2.78–2.50 2.99–2.81 2.99–2.81 2.78–2.50 2.78–2.50 2.78–2.50 2.43 2.32 2.32 1.81 – – –

8.28 7.90 7.99 1.96 1.96 3.27 3.41 2.31 2.55 2.20 2.13 2.26 2.31 2.05 2.16 1.02 1.12 1.13 1.11 – –

8.36 8.24 8.24 2.51 2.51 3.80–3.70 3.80–3.70 3.16 2.83–2.55 2.83–2.55 2.83–2.55 2.83–2.55 2.83–2.55 2.83–2.55 2.44 2.16 2.16 1.98 1.75 – –

353

K. Sayin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 348–356

Fig. 3. The structures of mentioned zinc(II) complexes with atomic labeling for NMR spectra.

that the ranking of activity can be provided between mentioned zinc(II) complexes which have similar structures. The environments of central atom in equatorial position are similar in mentioned zinc(II) complexes, except [ZnL4]2+ complex ion. Therefore, this complex ion is not taken into account to determine the ranking of activity. The quantum chemical parameters are given in Table 8. EHOMO is a quantum chemical parameter and mainly associated with electron donating ability of molecule. High value of EHOMO indicates the tendency of electron transfer to appropriate acceptor molecule which is low empty molecular orbital [30]. If EHOMO is decisive for the biological activity, the activity ranking of mentioned complexes should be:

½ZnL7 

2þ

2þ

> ½ZnL6 

> ½ZnL5 

2þ

> ½ZnL3 

2þ

> ½ZnL2 

2þ

2þ

> ½ZnL1 

The other important parameter is the energy gap (EGAP). The smaller value of this parameter means that molecule is more active [48]. According to the EGAP values, the ranking of mentioned complexes should be:

½ZnL7 

2þ

> ½ZnL6 

2þ

2þ

> ½ZnL5 

> ½ZnL3 

2þ

> ½ZnL1 

2þ

> ½ZnL2 

2þ

The hardness and softness are other important parameters. The biological activity tendency of complexes toward appropriate molecules can be discussed with HSAB (hard–soft-acid–base) approximation [49]. Hard molecules have a big EGAP value and soft molecules have small EGAP. Biological molecules, which are enzyme, protein, etc., are known as soft molecules. Therefore, soft complexes can interact easily with biological molecules. The

354

K. Sayin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 348–356

Table 8 Quantum chemical parameters with B3LYP/LANL2DZ level in gas phase for mentioned zinc complexes except [ZnL4]2+ complex ion. Complexes 1 2+

[ZnL ] [ZnL2]2+ [ZnL3]2+ [ZnL5]2+ [ZnL6]2+ [ZnL7]2+

EHOMO (eV)

EGAP (eV)

g (eV)

13.578 13.556 13.238 12.350 12.080 11.405

4.607 4.638 4.345 4.177 3.928 3.147

2.303 2.319 2.172 2.088 1.964 1.573

r

v (eV)

(eV1) 0.434 0.431 0.460 0.479 0.509 0.636

l (Debye)

11.275 11.237 11.066 10.262 10.116 9.832

0.561 0.804 1.611 1.678 2.595 4.496

½ZnL7 

½ZnL7 

2þ

> ½ZnL6 

2þ

> ½ZnL5 

2þ

> ½ZnL3 

2þ

> ½ZnL1 

2þ

2þ

> ½ZnL2 

The other important parameter is electronegativity. The electronegativity is related with freedom of the electrons in the molecule. The small electronegativity value means that electrons in molecule are freer than others. Inhibitors coordinate to appropriate acceptor molecules by giving electrons. Therefore, the biological activity increases with decreasing of electronegativity value. According to the electronegativity values, the activity ranking should be as follow:

> ½ZnL6 

2þ

> ½ZnL5 

2þ

> ½ZnL3 

2þ

> ½ZnL2 

2þ

> ½ZnL1 

2þ

The last parameter is dipole moment and this parameter related to electron mobility. The high value of this parameter means that electrons more active than other and the biological activity is increased with the increasing of dipole moment values [50]. According to the dipole moment values, the ranking of mentioned complexes should be:

½ZnL7  biological activity is increased with the increasing of softness value and decreasing of hardness value. According to the softness values, the ranking of biological activity should be as follow:

2þ

2þ

> ½ZnL6 

2þ

> ½ZnL5 

2þ

> ½ZnL3 

2þ

> ½ZnL2 

2þ

> ½ZnL1 

2þ

Additionally, the distribution graphs are plotted for each mentioned parameter and represented in Fig. 4. According to Fig. 4, the correlation constants are calculated as 0.940, 0.854, 0.778, 0.920 and 0.872 for EHOMO, EGAP, r, v and l, respectively. There is an agreement between mentioned parameters. According to parameters and Fig. 4, the ranking of biological activity should be:

½ZnL7 

2þ

> ½ZnL6 

2þ

> ½ZnL5 

2þ

> ½ZnL3 

2þ

> ½ZnL2 

2þ

> ½ZnL1 

2þ

According to this ranking, [ZnL7]2+ complex ion is the most active complex while [ZnL1]2+ is the most inactive complex. For [ZnL4]2+ complex ion, the complex geometry is different from others. Therefore, this complex is not taken into account to determine

Fig. 4. The distribution graphs for regression analysis.

K. Sayin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 348–356

the ranking of biological activity. The ranking of biological activity shows that the biological activity increases with increasing coordination number and surface area of complex.

[9]

Conclusions DFT calculations are performed on the relevant complexes, which are [ZnL1]2+, [ZnL2]2+, [ZnL3]2+, [ZnL4]2+, [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+, by using B3LYP method with LANL2DZ and mix basis sets. The LANL2DZ basis set is more appropriate with experimental results than mix basis set. For [ZnL1]2+, [ZnL2]2+ and [ZnL3]2+ complex ions, geometry is obtained as distorted pentagonal pyramidal, distorted tetrahedral for [ZnL4]2+ and geometry of [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ is obtained as distorted pentagonal bipyramidal. The electronic absorption spectra are calculated by using TD-DFT method with LANL2DZ basis set. The percentages of electronic transitions have been calculated and orbital character analysis show that bands in UV–VIS spectra are resulted from ligand to ligand electronic transitions for all zinc(II) complexes. The 1H and 13 C NMR spectra are calculated at GIAO/B3LYP method with LANL2DZ basis set. For [ZnL1]2+, [ZnL2]2+, [ZnL3]2+ and [ZnL4]2+ complex ions, none experimental data have been reported by Keypour and co-workers. For these complexes, structural parameters, vibrational frequencies and chemical shifts values of hydrogen and carbon atoms in NMR spectra are reported in this paper. For mentioned zinc(II) complexes, electronic absorption spectra are calculated and interpreted. The geometry of [ZnL4]2+ complex ion is different from [ZnL1]2+, [ZnL2]2+ and [ZnL3]2+ complexes. This result is proven by NMR spectra. For mentioned zinc complexes, except [ZnL4]2+ complex ion, the ranking of biological activity is provided as follows:

½ZnL7 

2þ

[8]

2þ

> ½ZnL6 

> ½ZnL5 

2þ

> ½ZnL3 

2þ

> ½ZnL2 

2þ

2þ

[10]

[11]

[12]

[13]

[14]

[15]

[16]

[17]

> ½ZnL1 

Acknowledgments We are grateful the office of scientific research projects of Cumhuriyet University (Project No.: F-372) for financial supports. This research is made possible by TUBITAK ULAKBIM, High Performance and Grid Computing Center (TR-Grid e-Infrastructure).

[18]

[19]

[20]

Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2014.05.097.

[21]

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