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ESR study of vanadyl ion in tripotassium citrate
0038-1098/92 $5.00 + .00 Pergamon Press Ltd
Solid State Communications, Vol. 82, No. 10, pp. 837-839, 1992. Printed in Great Britain.
ESR STUDY OF VANADYL ION IN TRIPOTASSIUM CITRATE M. Venkateshwarlu and T. Bhaskar Rao Department of Physics, Kakatiya University, Warangal 506 009 (A.P), India
(Received 11 January 1992 by P. Burlet) ESR spectra of VO 2+ doped tripotassium citrate are recorded at room temperature. The observed spectra are fitted to a spin Hamiltonian of orthorhombic symmetry with gx = 2.001 + 0.001, gy = 1.997 + 0.001, g~ = 1.945 + 0.001, Ax = (49.0 + 1) x 10-4cm -~, A. = (66.8 + 1) x 10-4cm -I and Az = (168.4 + 1) x 10-4cm -I. ~l'be covalency and Fermi contact terms are evaluated and compared with those of other lattices. 1. INTRODUCTION CITRATES ARE important compounds having biological and medical applications [1,2]. In a systematic study on the growth and characterisation of several citrates we have made use of electron spin resonance as one of the tools. ESR study of VO 2+ in trisodium citrate [3] and in triammonium citrate [4] was undertaken and the results reported. Here we report the ESR study of tripotassium citrate monohydrate doped with vanadyl radical.
ESR spectrometer operating at X-band frequencies with 100 kHz modulation. 3. CRYSTAL STRUCTURE Tripotassium citrate monohydrate has a molecular formula KaC6HsO7 " H20 and belongs to monoclinic class (5) with lattice parameters a = 7.06A, b = 11.72A, c = 13.69A and fl = ll2 °. The unit cell consists of four molecules. It has a space group of P2~/a. Detailed structure of the crystal is not available.
2. EXPERIMENTAL DETAILS
4. RESULTS AND DISCUSSION
Tripotassium citrate monohydrate crystals are grown from saturated aqueous solution to which a small amount of vanadyl sulphate is added as impurity. Well developed good single crystals are obtained between the temperature 35 and 40°C. The crystal has a cleavage plane identified to be (00 l). The axes are identified by rotational X-ray diffraction photographs. The ESR spectra are recorded by using JEOL
As this crystal belongs to monoclinic class, the b-axis is perpendicular to a and c, whereas a and c are not perpendicular to each other. The axis perpendicular to ab plane is taken as c*-axis. The angular variations are recorded by rotating the crystal in the magnetic field around the three mutually perpendicular axes a, b and c*. ESR spectra show two sets of lines in ab and bc* planes whereas only one set of eight
tj
l 3500G
4
H
IOOG
Fig. 1. ESR spectrum of TPC:VO 2+ for H making an angle of 10° with a-axis in ab plane at 9.77 GHz. 837
838
ESR STUDY OF V A N A D Y L ION IN TRIPOTASSIUM CITRATE
Vol. 82, No. 10
+ AxS~I~ + AySyly + AzS~I~,
(I)
with gx =
2.001 _ 0.001,
g~ =
1.945 _ 0.001,
gy =
1.997 + 0.001,
A x
=
(49.0 __+ 1) x 10-4cm -l,
Ay
=
(66.8 + 1) x 10-4cm -I,
=
(168.4 + 1) x 10-acm -1.
and A z
0
20
&0
60
80 100 ANGLE
120
1~0
160
180
Fig. 2. Angular variation of field positions of ESR lines of TPC : VO 2+ in ab plane. lines in ac plane. One such spectrum is shown in Fig. 1. The spectra are recorded with magnetic field in ab, be* and ac planes for every 10° interval and the angular variation of the field positions of the lines in one of these planes is shown in Fig. 2. The observed spectrum can be fitted to a spin Hamiltonian of orthorhombic symmetry with
= fl(g~H~Sx + gyHySy + g,H,S,)
Table I shows the spin Hamiltonian parameters of VO 2+ in different lattices. It can be observed that the spin Hamiltonian paramters of tripotassium citrate monohydrate agree well with the vanadyl complex in other lattices where it is confirmed that it has an octahedral coordination with tetragonal or rhombic distortion. Hence one can safely assume that the VO 2÷ has entered into this lattice in a distorted octahedral environment. And from the angular variation of the spectra observed, it is very clear that the ion has entered into substitutional site. As there is no detailed crystal structure data available on this lattice, one could only venture to say that at least one of the sites has an approximate octahedral arrangement around it. Using the expressions for spin Hamiltonian parameters Air, A± and gtl, g± for VO(H20) 5+ (3) the values offl~ and k are calculated to be 0.946 and 0.712 respectively. Table 2 compares the Fermi contact term k and molecular orbital coefficient//2 obtained for this lattice with other lattices. The Fermi contact term k of VO 2+ ion in this lattice is comparable with that of K2C204 • H20 lattice and is less than all other lattices. As the Fermi contact term arises due to non-zero spin desnity at the site of the nucleus, it indicates that the s-orbital density at the nucleus o f W ÷ ion in this lattice
Table 1. Spin Hamiltonian parameters ofVO(H20)~ + in different lattices S. No.
Lattice
gz
gx
gy
Az
Ax
Ay
Reference
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 13.
K3C6HsO 7 • H~O Na3C6HsO 7 • 5H20 (NH4)3C6HsO7 K2C204 • H20 KHC204 Mg(H20)6H2 EDTA (NH4)AI(SO4) 2 • 12H20 K2 Mg(SO4)2 • 6H20 Ba formate Cs2Zn(SeO4)2 • 6H20 Rb2 SO4 (NH4)2 Mg(SO4)2 • 6H20
1.945 1.934 1.940 1.945 1.936 1.952 1.940 1.930 1.935 1.938 1.931 1.936
2.001 1.998 2.003 1.984 1.989 1.983 1.978 1.997 1.978 1.975 1.976 1.979
1.977 1.992 1.992 1.987 1.989 1.987 1.978 2.005 1.981 1.978 1.975 1.981
168.4 175.4 166.5 161.7 186.5 151.3 176.0 178.5 173.0 178.0 176.7 196.0
49.0 70.0 56.0 65.4 88.5 64.8 67.0 77.0 63.0 71.3 68.1 81.0
66.8 66.6 63.9 53.4 73.5 80.7 67.0 67.0 64.0 70.4 67.0 79.0
Present work [3] [4] [6] [6] [7] [8] [9] [10] [10] [10] [ll]
Vol. 82, No. 10
ESR STUDY OF VANADYL ION IN TRIPOTASSIUM CITRATE
839
Table 2. Fermi contact term and molecular orbital coefficient ofVO(H20)~ + in various lattices
S. No.
Lattice
k
fl~
Reference
1. 2. 3. 4. 6. 7. 8. 9. 10. 11. 12. 13.
K3C6H507 " HzO
0.712 0.785 0.721 0.700 0.840 0.880 0.860 0.766 0.789 0.769 0.830 0.870
0.946 0.900 0.896 0.960 0.880 0.956 0.910 0.969 0.968 0.936 1.000 0.680
Present work [3] [4] [6] [6] [11] [11] [7] [9] [8] [12] [13]
Na3C6HsO7 • 5H20 (NH4)3C6HsO7 K2C204 • H20 KHCzO4 Cs2Mg(SO4) 2 • 6H20 (NH4)2Mg(SO4)2 • 6H20 Mg(HzO)6H2 EDTA I KzMg(SO4) 2 • 6H20 NH4AI(SOa)2 • 12H20 VO(H20)~ + Na2 Zn(SO4)2 • 4HzO
is comparatively small. As far as the molecular orbital coefficient /F is concerned, it is observed that its value is comparable to that of ammonium alum and Cs2Mg(SO4)~" 6H20. The molecular orbital coefficient of p22 indicates the extent of overlap of the vanadium orbitals with ligand orbitals. As the ground state of VO(H20)~ ÷ complex is a non-bonding orbital one should expect a value of unity for fl~. The deviation from unity indicates the overlap o f ligand orbitals. This can happen due to the mixing of higher levels of vanadium ion into the ground state with spin orbit coupling and the lowering of symmetry. Acknowledgements - The authors are thankful to Dr. K.V. Reddy, Principal Scientific officer, Central Lab., University of Hyderabad for providing facilities to undertake this work.
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
REFERENCES 1.
B. Lonerdal, A.C. Stanislowski & L.S. Hurley, J. Inorg. Biochem. 12, 71 (1980).
13.
R. Swanson, W.H. Ilsley & A.C. Stanislowski, J. Inorg. Biochem. 18, 187 (1983). T. Bhaskar Rao & M. Venkateswarlu, Solid State Commun. 44, 1617 (1982). M. Venkateshwarlu, T. Bhaskar Rao & Ahmed Hussain, Solid State Commun. 78, 1073 (1991). D.M. Burns & J. Iball, Acta Cryst. 7, 137 (1954). M. Salagram, Ph.D. thesis, IIT, Madras (1980). M. Narayana, J. Chem. Phys. 72, 4255 (1980). K.V.S. Rao, M.D. Sastry & P. Venkateswarlu, J. Chem. Phys. 49, 4984 (1968). S. Kasturirengan & S. Soundararajan, J. Magn. Res. 19, 357 (1975). Premchand, V.K. Jain & G.C. Upreti, Magn. Res. Rev. 14, 49 (1988). M. Narayana, S.G. Satyanarayana & G.S. Sastry, Mol. Phys. 31, 203 (1976). L.J. Boucher, E.C. Tynan& Teh Fu Yen, Electron Spin Resonance of Metal Complexes, Plenum, New York (1969). S.V.J. Lakshman & A. Sundar Jacob, Solid State Commun. 45, 141 (1983).
Solid State Communications, Vol. 82, No. 10, pp. 837-839, 1992. Printed in Great Britain.
ESR STUDY OF VANADYL ION IN TRIPOTASSIUM CITRATE M. Venkateshwarlu and T. Bhaskar Rao Department of Physics, Kakatiya University, Warangal 506 009 (A.P), India
(Received 11 January 1992 by P. Burlet) ESR spectra of VO 2+ doped tripotassium citrate are recorded at room temperature. The observed spectra are fitted to a spin Hamiltonian of orthorhombic symmetry with gx = 2.001 + 0.001, gy = 1.997 + 0.001, g~ = 1.945 + 0.001, Ax = (49.0 + 1) x 10-4cm -~, A. = (66.8 + 1) x 10-4cm -I and Az = (168.4 + 1) x 10-4cm -I. ~l'be covalency and Fermi contact terms are evaluated and compared with those of other lattices. 1. INTRODUCTION CITRATES ARE important compounds having biological and medical applications [1,2]. In a systematic study on the growth and characterisation of several citrates we have made use of electron spin resonance as one of the tools. ESR study of VO 2+ in trisodium citrate [3] and in triammonium citrate [4] was undertaken and the results reported. Here we report the ESR study of tripotassium citrate monohydrate doped with vanadyl radical.
ESR spectrometer operating at X-band frequencies with 100 kHz modulation. 3. CRYSTAL STRUCTURE Tripotassium citrate monohydrate has a molecular formula KaC6HsO7 " H20 and belongs to monoclinic class (5) with lattice parameters a = 7.06A, b = 11.72A, c = 13.69A and fl = ll2 °. The unit cell consists of four molecules. It has a space group of P2~/a. Detailed structure of the crystal is not available.
2. EXPERIMENTAL DETAILS
4. RESULTS AND DISCUSSION
Tripotassium citrate monohydrate crystals are grown from saturated aqueous solution to which a small amount of vanadyl sulphate is added as impurity. Well developed good single crystals are obtained between the temperature 35 and 40°C. The crystal has a cleavage plane identified to be (00 l). The axes are identified by rotational X-ray diffraction photographs. The ESR spectra are recorded by using JEOL
As this crystal belongs to monoclinic class, the b-axis is perpendicular to a and c, whereas a and c are not perpendicular to each other. The axis perpendicular to ab plane is taken as c*-axis. The angular variations are recorded by rotating the crystal in the magnetic field around the three mutually perpendicular axes a, b and c*. ESR spectra show two sets of lines in ab and bc* planes whereas only one set of eight
tj
l 3500G
4
H
IOOG
Fig. 1. ESR spectrum of TPC:VO 2+ for H making an angle of 10° with a-axis in ab plane at 9.77 GHz. 837
838
ESR STUDY OF V A N A D Y L ION IN TRIPOTASSIUM CITRATE
Vol. 82, No. 10
+ AxS~I~ + AySyly + AzS~I~,
(I)
with gx =
2.001 _ 0.001,
g~ =
1.945 _ 0.001,
gy =
1.997 + 0.001,
A x
=
(49.0 __+ 1) x 10-4cm -l,
Ay
=
(66.8 + 1) x 10-4cm -I,
=
(168.4 + 1) x 10-acm -1.
and A z
0
20
&0
60
80 100 ANGLE
120
1~0
160
180
Fig. 2. Angular variation of field positions of ESR lines of TPC : VO 2+ in ab plane. lines in ac plane. One such spectrum is shown in Fig. 1. The spectra are recorded with magnetic field in ab, be* and ac planes for every 10° interval and the angular variation of the field positions of the lines in one of these planes is shown in Fig. 2. The observed spectrum can be fitted to a spin Hamiltonian of orthorhombic symmetry with
= fl(g~H~Sx + gyHySy + g,H,S,)
Table I shows the spin Hamiltonian parameters of VO 2+ in different lattices. It can be observed that the spin Hamiltonian paramters of tripotassium citrate monohydrate agree well with the vanadyl complex in other lattices where it is confirmed that it has an octahedral coordination with tetragonal or rhombic distortion. Hence one can safely assume that the VO 2÷ has entered into this lattice in a distorted octahedral environment. And from the angular variation of the spectra observed, it is very clear that the ion has entered into substitutional site. As there is no detailed crystal structure data available on this lattice, one could only venture to say that at least one of the sites has an approximate octahedral arrangement around it. Using the expressions for spin Hamiltonian parameters Air, A± and gtl, g± for VO(H20) 5+ (3) the values offl~ and k are calculated to be 0.946 and 0.712 respectively. Table 2 compares the Fermi contact term k and molecular orbital coefficient//2 obtained for this lattice with other lattices. The Fermi contact term k of VO 2+ ion in this lattice is comparable with that of K2C204 • H20 lattice and is less than all other lattices. As the Fermi contact term arises due to non-zero spin desnity at the site of the nucleus, it indicates that the s-orbital density at the nucleus o f W ÷ ion in this lattice
Table 1. Spin Hamiltonian parameters ofVO(H20)~ + in different lattices S. No.
Lattice
gz
gx
gy
Az
Ax
Ay
Reference
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 13.
K3C6HsO 7 • H~O Na3C6HsO 7 • 5H20 (NH4)3C6HsO7 K2C204 • H20 KHC204 Mg(H20)6H2 EDTA (NH4)AI(SO4) 2 • 12H20 K2 Mg(SO4)2 • 6H20 Ba formate Cs2Zn(SeO4)2 • 6H20 Rb2 SO4 (NH4)2 Mg(SO4)2 • 6H20
1.945 1.934 1.940 1.945 1.936 1.952 1.940 1.930 1.935 1.938 1.931 1.936
2.001 1.998 2.003 1.984 1.989 1.983 1.978 1.997 1.978 1.975 1.976 1.979
1.977 1.992 1.992 1.987 1.989 1.987 1.978 2.005 1.981 1.978 1.975 1.981
168.4 175.4 166.5 161.7 186.5 151.3 176.0 178.5 173.0 178.0 176.7 196.0
49.0 70.0 56.0 65.4 88.5 64.8 67.0 77.0 63.0 71.3 68.1 81.0
66.8 66.6 63.9 53.4 73.5 80.7 67.0 67.0 64.0 70.4 67.0 79.0
Present work [3] [4] [6] [6] [7] [8] [9] [10] [10] [10] [ll]
Vol. 82, No. 10
ESR STUDY OF VANADYL ION IN TRIPOTASSIUM CITRATE
839
Table 2. Fermi contact term and molecular orbital coefficient ofVO(H20)~ + in various lattices
S. No.
Lattice
k
fl~
Reference
1. 2. 3. 4. 6. 7. 8. 9. 10. 11. 12. 13.
K3C6H507 " HzO
0.712 0.785 0.721 0.700 0.840 0.880 0.860 0.766 0.789 0.769 0.830 0.870
0.946 0.900 0.896 0.960 0.880 0.956 0.910 0.969 0.968 0.936 1.000 0.680
Present work [3] [4] [6] [6] [11] [11] [7] [9] [8] [12] [13]
Na3C6HsO7 • 5H20 (NH4)3C6HsO7 K2C204 • H20 KHCzO4 Cs2Mg(SO4) 2 • 6H20 (NH4)2Mg(SO4)2 • 6H20 Mg(HzO)6H2 EDTA I KzMg(SO4) 2 • 6H20 NH4AI(SOa)2 • 12H20 VO(H20)~ + Na2 Zn(SO4)2 • 4HzO
is comparatively small. As far as the molecular orbital coefficient /F is concerned, it is observed that its value is comparable to that of ammonium alum and Cs2Mg(SO4)~" 6H20. The molecular orbital coefficient of p22 indicates the extent of overlap of the vanadium orbitals with ligand orbitals. As the ground state of VO(H20)~ ÷ complex is a non-bonding orbital one should expect a value of unity for fl~. The deviation from unity indicates the overlap o f ligand orbitals. This can happen due to the mixing of higher levels of vanadium ion into the ground state with spin orbit coupling and the lowering of symmetry. Acknowledgements - The authors are thankful to Dr. K.V. Reddy, Principal Scientific officer, Central Lab., University of Hyderabad for providing facilities to undertake this work.
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
REFERENCES 1.
B. Lonerdal, A.C. Stanislowski & L.S. Hurley, J. Inorg. Biochem. 12, 71 (1980).
13.
R. Swanson, W.H. Ilsley & A.C. Stanislowski, J. Inorg. Biochem. 18, 187 (1983). T. Bhaskar Rao & M. Venkateswarlu, Solid State Commun. 44, 1617 (1982). M. Venkateshwarlu, T. Bhaskar Rao & Ahmed Hussain, Solid State Commun. 78, 1073 (1991). D.M. Burns & J. Iball, Acta Cryst. 7, 137 (1954). M. Salagram, Ph.D. thesis, IIT, Madras (1980). M. Narayana, J. Chem. Phys. 72, 4255 (1980). K.V.S. Rao, M.D. Sastry & P. Venkateswarlu, J. Chem. Phys. 49, 4984 (1968). S. Kasturirengan & S. Soundararajan, J. Magn. Res. 19, 357 (1975). Premchand, V.K. Jain & G.C. Upreti, Magn. Res. Rev. 14, 49 (1988). M. Narayana, S.G. Satyanarayana & G.S. Sastry, Mol. Phys. 31, 203 (1976). L.J. Boucher, E.C. Tynan& Teh Fu Yen, Electron Spin Resonance of Metal Complexes, Plenum, New York (1969). S.V.J. Lakshman & A. Sundar Jacob, Solid State Commun. 45, 141 (1983).