IJIRST –International Journal for Innovative Research in Science & Technology| Volume 3 | Issue 12 | May 2017 ISSN (online): 2349-6010
XAFS Study of Copper (II) Complexes of PAnisidine Jaishree Bhale Shree Cloth Market Institute of Professional Studies, Indore(M.P), India
Pradeep Sharma Govt. Holkar Science College, Indore(M.P), India.
A.Mishra School of Physics, DAVV, Indore(M.P), India
Abstract X-ray K-absorption spectroscopic studies have been carried out on three copper (II) mixed-ligand complexes .The complexes are [Cu(L6)2(H2O)2(Cl)](0.2)H2O, [Cu(L6)2(H2O)2(SO4)](0.2)H2O and [Cu(L6)2(H2O)2(Br)](0.2)H2O where ligand L6= (pmethoxy anilino) –P– chloro phenyl acetonitrile. XAFS spectra have been recorded at the K-edge of Cu using the dispersive beam line at 2.5GeV Indus-2 synchrotron radiation source RRCAT(Raja Ramanna Center for Advance Technology ), Indore, India. The data obtained has been processed using XAFS data analysis program Athena and the computer software Origin 6.0 professional. Various X-ray absorption parameters e.g., chemical shift, edge-width and shift of the principal absorption maximum have been obtained in the present study. The chemical shift data have been utilized to estimate effective nuclear charge on the absorbing atom. Further the observed chemical shifts have been correlated with percentage covalency in these complexes. The studies establish significant correlation between various parameters for these complexes. The XAFS data obtained has also been used to determine the bond length by using four different methods, i.e., Levy’s, Lytle, Lytle, Sayers and Stern’s (LSS) and Fourier transformation methods. The results of the study have been reported in this paper. Keywords: Compatibility, Superplasticizers, Silica fume ________________________________________________________________________________________________________ I.
INTRODUCTION
X-ray absorption fine structure (XAFS) refers to the details of how x-rays are absorbed by an atom at energies near and above the core-level binding energies of that atom. Specifically, XAFS is the modulation of an atom’s x-ray absorption probability due to the chemical and physical state of the atom. The x-ray absorption spectrum is typically divided into two regimes: X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine-structure spectroscopy (EXAFS). X-ray absorption spectroscopy has been extensively used to obtain information about the molecular structure viz. the oxidation state and the effective nuclear charge of the absorbing atom in compounds and complexes. The Fourier transform of an EXAFS spectrum provides information on the distribution of atomic shells as a function of distance from the target absorber. The bond lengths have also been determined by three graphical methods, namely, Levy’s [1], Lytle’s [2], and Lytle, Sayers and Stern’s (LSS) [3, 4]methods. The results of the comparative study have also been reported in this paper. XANES and EXAFS studies of some of the copper (II) complexes of p-anisidine have been already discussed in previous literature [5-7]. The XAFS characterization of some more complexes had been carried out and their results have been reported in this paper. II. EXPERIMENTAL DETAILS The three complexes studied in the present investigations are [Cu(L6)2(H2O)2(Cl)](0.2)H2O, [Cu(L6)2(H2O)2(SO4)](0.2)H2O and [Cu(L6)2(H2O)2(Br)](0.2)H2O .The ligand L6= (p-methoxy anilino) –P– chloro phenyl acetonitrile was synthesized. The ligand was prepared by Strecker's procedure [8 -9] which included the reaction of p-chlorobenzaldehyde with p-anisidine. All the complexes were prepared according to the standard methods reported in literature and their purity was checked [10]. The X-ray absorption spectra at the K-edge of copper of these complexes have been recorded at BL-8 Dispersive EXAFS beamline at the 2.5-GeV INDUS-2 Synchrotron Source, Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, India [11 - 13]. The experimental data have been analyzed using the available computer software packages Origin 6.0 professional and Athena [14]. Table – 1 Abbreviation and molecular formulae of copper (II) complexes Complexes I II
Abbreviation [Cu(L6)2(H2O)2(Cl)](0.2)H2O [Cu(L6)) 2 (H 2O) 2(SO 4)](0.2)H2O
Molecular formulae [Cu(C15H14N2 OCl )2(Cl)2] 0.2H2O [Cu(C15H14N2OCl)2(SO4)2] 0.2H2O
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XAFS Study of Copper (II) Complexes of P-Anisidine (IJIRST/ Volume 3 / Issue 12/ 016)
III
[Cu(L6)2(H2O)2(Br)](0.2)H2O
[Cu(C15H14N2 OCl )2(Br)2] 0.2H2O
Fig 1. The XANES region of the absorption spectrum at the K-edge of copper metal and in the complexes indicating positions of the absorption edge K and the principal absorption maxima A.
Fig. 2. Derivative of the XANES region of the absorption spectrum at the K-edge of copper metal and in the complexes indicating positions of the absorption edge K and the principal absorption maxima A.
Complexes Copper metal [Cu(L6)2(H2O)2(Cl)](0.2)H2O
Table – 2 XANES data for the K absorption edge of copper in the complexes. Shift of the principal Edge-width EK EA Chemical shift absorption maximum (EA_EK) (eV) (eV) (eV) (eV) (eV) 8980.12 8996.21 16.088 8986.99 8998.30 6.87 2.09 11.31
ENC Electron/ atom 0.71
% Covalency
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65.15
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XAFS Study of Copper (II) Complexes of P-Anisidine (IJIRST/ Volume 3 / Issue 12/ 016)
[Cu(L6)2(H2O)2(SO4)](0.2)H2O [Cu(L6)2(H2O)2(Br)](0.2)H2O
8988.37 8990.22
8997.78 9001.55
8.32 10.10
3.55 5.34
9.41 11.33
0.82 0.95
55.45 35.65
III. RESULTS AND DISCUSSION The shapes of the copper K-absorption discontinuity and the associated near edge structure (XANES) for all the complexes are shown in Fig 1.The curves in this figure represent the normalized K absorption spectra. The energies of the copper K-edge (EK) and the principal absorption maximum (E A) along with the values of the edge-width (EA-EK), effective nuclear charge Zeff and the chemical shift ΔEK are given in Table 2. The EXAFS spectra converted into k space have been given in Figure 6. The values of energy E and wave vector k corresponding to these maxima and minima have been shown in Table 3. The slopes of energy level Q Vs energy E curves, shown in Figure 7, have been used to evaluate the bond length by Lytle method. The slopes of channel number n Vs wave vector k curves, shown in Figure 8, have been used to evaluate the bond length by LSS method. The magnitudes of Fourier transform of Figure 6 are shown in Figure 9. Chemical Shift The shifts of the K-absorption edge of copper in the complexes with respect to that of copper metal have been determined according to the eqn. ΔEK = EK(complex) - EK(metal) The results are given in Table 2. For computing the chemical shift, the value of EK (Cu metal) has been taken as 8980.12 eV. For the complexes under study, the order in which the ligands contribute to the chemical shift is: [Cu(L6)2(H2O)2(Br)](0.2)H2O > [Cu(L6)2(H2O)2(SO4)](0.2)H2O > [Cu(L6)2(H2O)2(Cl)](0.2)H2O In Table 2, the complexes have the values of chemical shifts as 6.87, 8.32 and 10.10 eV. Hence, on the basis of values of the chemical shifts, the complexes are found to have copper in oxidation state +2 [15]. As compared to the K-absorption edge in the metal, the K-absorption edge of copper has been found to be shifted towards the high-energy side in all the complexes studied. IV. EFFECTIVE NUCLEAR CHARGE AND CHEMICAL SHIFT In the present work, Zeff has been obtained from the measured chemical shift by using the semi-experimental method by employing the procedure suggested by Nigam and Gupta [16]. The data is presented in Table 2. The effective nuclear charge on the copper in the complexes under present study varies between 0.71 – 0.95 electrons/atom. An attempt was made to establish a co–relation between ENC and chemical shift. A parabolic co–relation is observed between them. The results show that chemical shift increases then ENC also increases.
Chem ical shift eV
10
5 0 .5
1
E N C e le c tro n /a to m
Fig. 3: Correlation between ENC and chemical shift
Percentage Covalence and Chemical Shift To calculate the percentage covalency of the bonds, a theoretical graph is plotted between the calculated value of binding energy of 1s electron using Clementi’s results of atomic function and percentage covalency for copper [17]. An attempt was made to establish a co–relation between percentage covalency and chemical shift. A parabolic co–relation is observed between them .It is clear from the Table 2 that the chemical shift decreases as the percentage covalency increases.
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XAFS Study of Copper (II) Complexes of P-Anisidine (IJIRST/ Volume 3 / Issue 12/ 016)
C hem ical shift (eV )
10
5 40
70
P e rc e n ta g e c o v a le n c y
Fig. 4: Correlation between percentage covalency and chemical shift
V. PERCENTAGE COVALENCY AND ENC It is clear from the data that the percentage covalency increases as effective charge decreases. . A parabolic co–relation is observed between them.
ENC electron/atom
1
0 .5 40
70
P e rc e n ta g e c o v a le n c y
Fig. 5: Correlation between percentage covalency and ENC
Principal Absorption Maximum The data for the principal absorption maximum EA for the complexes is also included in Table II. The shifts of the principal absorption maximum at the K-absorption edge of copper in the complexes with respect to that of copper metal have been determined according to the eqn. ΔEA = EA(complex) – EA(metal) For computing the chemical shift the value of EA(Cu metal) has been taken as 8996.21 eV. It has been observed that the value of EA is shifted towards the higher energy side with respect to copper metal [18]. EDGE-WIDTH In Table.2 the values of the edge-width (EA-EK) have been reported. The experimental data of edge-width of Cu (II) complexes (Table 2) show that the edge-width decreases as follows: [Cu(L6)2(H2O)2(SO4)](0.2)H2O < [Cu(L6)2(H2O)2(Cl)](0.2)H2O < [Cu(L6)2(H2O)2(Br)](0.2)H2O
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XAFS Study of Copper (II) Complexes of P-Anisidine (IJIRST/ Volume 3 / Issue 12/ 016)
Fig. 6: Ï&#x2021; (k) versus k curves for the copper complexes
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XAFS Study of Copper (II) Complexes of P-Anisidine (IJIRST/ Volume 3 / Issue 12/ 016)
[Cu(L6)2(H2O )2(Cl)](0.2)H2O [Cu(L6)2(H2O )2(Br)](0.2)H2O [C u(L6)2(H 2O )2(S O 4)](0.2)H 2O
6
6 8
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-1
k(Å )
6
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-1
K(Å )
k(Å )
Fig. 7: n versus k curves for the copper complexes
[Cu(L6)2(H2O)2(SO4)](0.2)H2O
160
[C u(L6)2(H 2O )2(C l)](0.2)H 2O
[C u(L6)2(H 2O )2(B r)](0.2)H 2O 250
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Q
Fig. 8: Q versus E curves for the copper complexes
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XAFS Study of Copper (II) Complexes of P-Anisidine (IJIRST/ Volume 3 / Issue 12/ 016)
Fig. 9: Magnitude of Fourier transform of the χ(k) versus k curve for Cu(II) complexes Table – 3 Energy E (eV) and wave vector k (Å-1) for EXAFS maxima and minima at the K absorption edge of copper in the complexes and their corresponding values of n and energy level Q [Cu(L6)2(H2O)2(Cl)](0.2)H2O [Cu(L6)2(H2O)2(SO4)](0.2)H2O [Cu(L6)2(H2O)2(Br)](0.2)H2O Structure n Q E (eV) k (Å-1) E (eV) k (Å-1) E (eV) k (Å-1) A 0 2.04 19.249 2.25 13.01 1.85 18.403 2.2 α 1 54.904 3.80 38.93 3.2 43.954 3.4 B 2 6.04 127.908 5.80 63.91 4.1 63.916 4.1 β 3 240.313 7.95 108.83 5.35 93.165 4.95 C 4 12.0 291.112 8.75 146.15 6.2 119.239 5.6 γ 5 160.646 6.5 Table – 4 Values of first shell bond lengths (in Å) calculated from Levy’s, Lytle’s, LSS and Fourier transform methods for the copper (II) complexes Complexes Levy’s method Lytle’s method LSS method Fourier transform [Cu(L6)2(H2O)2(Cl)](0.2)H2O 2.09 1.87 1.50 1.48 [Cu(L6)2(H2O)2(SO4)](0.2)H2O 2.0 1.67 1.43 1.41 [Cu(L6)2(H2O)2(Br)](0.2)H2O 2.24 1.06 1.16 1.46
VI. CONCLUSIONS X-ray absorption spectra of mixed ligand copper complexes at the K-edge of copper have been recorded at the recently developed EXAFS beamline setup at the Indus-2 synchrotron source at RRCAT, Indore. The energy of K-edge (EK), and principal absorption maxima (EA) have been reported. From these, the shift of the K-edge (chemical shift), shift of the principal absorption maximum and edge-width has been obtained. The chemical shift has been used to determine the effective nuclear charge on the absorbing atom and percentage covalency. The values of the chemical shifts suggest that copper is in oxidation state +2 in all of the complexes.
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XAFS Study of Copper (II) Complexes of P-Anisidine (IJIRST/ Volume 3 / Issue 12/ 016)
From the positions of the EXAFS maxima and minima, the bond lengths in the complexes have been determined by three different methods viz. Levy’s, Lytle’s and LSS methods. From the Fourier transforms of the EXAFS spectra, the bond lengths (uncorrected for phase shift) have been determined. It has been observed that the values of the phase-uncorrected bond length, i.e. R1-α1, as determined from LSS method and that determined from the Fourier transformation method, agree with each other within the limits of experimental error. ACKNOWLEDGEMENT The authors are thankful to Dr. S. N. Jha for his help in recording the spectra. The authors are also grateful to Mr. Nihar Patel (Prashant group of industries) for his valuable support for this research work. REFERENCES [1] [2] [3] [4] [5] [6] [7]
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