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Infrared spectra of some bivalent metal complexes of mandelic acid
Notes
4301
substituting Eqn (2) into Eqn (1) yields an expression for D in which only the concentration of the aqueous phase need be determined. moles Min - moles M~q D
l/i'rg nloles Maq
(3)
The use of this equation is valid only if there is a mass balance for the metal ion. Should this not be the case, the calculated values for D would be erroneous. The absence of a metallic mass balance can be encountered depending upon the particular characteristics and conditions of the particular solvent extraction system. For example, in the extraction of metals with long-chain carboxylic acids, the efficiency of extraction is greatest at a pH range just below the point at which the metal hydroxide begins to precipitate[2]. Should the insoluble gelatinous hydroxide form, it would tend to settle on the interface between the aqueous and organic layers being neither a part of each phase, and it can be mistaken for an emulsion which is frequently present shortly after the completion of shaking the phases. In a study of the solvent extraction of Fe(lll) with chlorendic acid into benzene, the formation of a polymeric, possibly micellar, substance has been observed to settle at the interface after shaking for 24 hr and longer[3]. Subsequent analysis of both phases indicated the absence of a mass balance. Considering the scope of this problem, it seems advisable to check the existence of the mass balance tor the metals when the study of the properties of a particular system is to be undertaken. The analytical data obtained for both phases would provide a more reliable determination for the value of D than the method of differences described by Eqn (3), especially if equilibrium studies are undertaken. The analysis of the organic phase is usually a very difficult technique requiring the evaporation of the solvent followed by the oxidation of the chelate, usually by a wet digestion with HC10~, to convert the metal ion to an uncomplexed form suitable for analysis. However, with the introduction of the technique of atomic absorption, the analysis of both phases may be done reliably and rapidly with the preparation of calibration curves for each of the two phases[4].
Department o f Sciences John Jay College of Criminal Justice City University of New York 455 West 59 Street New York, New York 10019
SELMAN A. BERGER
2. A. W. Fletcher and D. S. Flett, J. appl. Chem, 14, 250 (1964). 3, S. A. Berger, J. B. McKay and H. L. Finston, A paper presented at the Eighth Annual Middle Atlantic Regional Meeting of the A.C.S., Washington, D.C., 15-17 January, 1973. 4. S. A. Berger, At. Absorpt. Newslett. 12, 30 (1973).
J. inorg, nucl. Chem., 1973, Vol. 35, pp. 4301-4304. Pergamon Press. Printed in Great Britain.
Infrared spectra of some bivalent metal complexes of mandelic acid (Received 26 January 1973) 1.R. SPECTRA of Cu(ll), Ni(ll), Co(II), Mn(lI), Zn(ll), Fe(II) and Be(I1) complexes o f mandelic acid in KBr matrix were recorded. The bonding in these complexes has been discussed on the basis of change in hydroxyl and carboxyl group frequencies. No linear relationship is observed between the ionized carboxyl
4302
Notes
group stretching frequency and the stability of the complexes. However, the difference between the antisymmetric and symmetric carboxyl stretching frequency of the complexes showed a linear relationship with the stability of the complexes. In continuation to our previous investigation[l, 2] the present work deals with the i.r. spectra studies of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Fe(II) and Be(II) complexes of mandelic acid. All these complexes were isolated by the method described by Khadikar et al.[3]. The important results obtained are discussed here. EXPERIMENTAL All chemicals used were either of B.D.H., AnalaR or of an equivalent quality. The i.r. spectra of the complexes were recorded on Perkin-Elmer Spectrophotometer-237, in KBr matrix. I.R. spectrum of the ligand has also been obtained for comparison. RESULTS AND DISCUSSION All the complexes were isolated by the method described by Khadikar et al.[3]. The composition of the complexes was found to be ML2.2H20. The characteristic absorption bands of the ligand and the complexes are given in Table 1. The i.r. spectra of the complexes show bands corresponding to the vibrational modes of the ligand present and also the M - O stretching vibrations. Table 1. Characteristic infrared frequencies in cm- 1 Mand. acid
Cu(II) mand.
Ni(lI)mand.
Co(II)mand.
Mn(II) mand.
Zn(II)mand.
Fe(II)mand.
Be(II)mand.
3420s 2956sb 1702s 1490m 1442s 1355s 1280s 1215s 1172s 1065sh 1070s 1018w 990w 928s 872s 840w 755m 718s
3300sb 1610s 1355sb 1105s 940vw 665w 654s
3250s 3040sh 1575s 1490vw 1405s 1358s 1338m 1275s 1245s l190s 1068m 1020sh 988s 942s 908w 788s 740s 688s 645s
3270s 1575s 1490vw 1410s 1358s 1338w 1275s 1248s 1192s 1072m 1020sh 1000s 945s 912w 858vw 788s 742s 688s 650s
3250sb 1555s 1490vw 1408s 1360w 1262w 1180m 1070vw 1060s 994sh 935m 900vw 768m 748m 728s 705vw 680s 658w
3260sb 1590s 1400s 1355s 1275s 1248s 1192s 1095wb 1072vw 1020sh 992s 940w 910vw 785s 740s 788s 550w
3250sb 1565s 1450sh 1410s 1360s 1335vw 1270m 1245w l190s l105s 1070vw 1020sh 1000s 992sh 940s 908m 782s 738s 685s 640w
3400sb 1600s 1480s 1385w 1360vw 1320s 1100sb 940s 925w 890m 855vw 780m 735vw 690w 635w
s, sharp; m, medium; v, very; w, weak; b, broad; sh, shoulder. The important bands are recorded in Table 2. Considerable shift in the hydroxyl group frequency from 3420 cm- ~ in mandelic acid to approximately 3260 cm- t in the complexes was observed. The ionized carboxyl group stretching frequency is also found I. P. V. Khadikar and R. L. Ameria, J. Indian chem. Soc. 47, 1201 (1970). 2. P. V. Khadikar and R. L. Ameria, J. Indian chem. Soc. 49, 717 (1972). 3. P. V. Khadikar and R. L. Ameria, Sci. Cult. 37, 491 (1971).
4303
Notes Table 2. Important bands of the infrared spectra of the complexes
Complex
Carboxyl antisymm, stretch, freq. (cm- 1)
Hydroxyl group freq. (cm- 1)
M 0 stretch, freq. (cm- 1)
Ligand Cu(lI)--mand. Zn(II)-mand. Ni(II) mand. Co(lI)- mand. Fe(II) mand. Mn(II)-mand. Be(ll) mand.
1702s 1610s 1590s 1575s 1575s 1565s 1555s 1600s
3420s 3300sb 3260sb 3250s 3270s 3250sb 3250sb 3400sb
654s 550w 645s 650s 640w 658w 635w
to have been shifted to approximately 1575 cm I (ligand 1702 cm ~ 1). This suggests that the chelation has taken place involving coordination of both, hydroxyl and carboxyl, groups of mandelic acid. The weak band at approximately 800 cm- a in all the complexes may be attributed to the rocking mode of vibration of water molecules ---in agreement with Fujita et al.[4I. Bellamy and BranchE5] have shown a linear relationship between the carboxy group frequency and the stability of the chelates of salicylaldehyde with different bivalent metal cations. Bellamy and Beecher[6] have shown that in acids also there should be a linear relationship between ionized carboxyl group stretching frequency and the stability of the complexes. Perusal of Table 2 shows that no direct relationship could be traced between ionized carboxyl group stretching frequency and the stability of the complexes. The absence of a linear relationship is not entirely unexpected. In comparing the complexes formed by a particular ligand with various metal cations, the action of the ligand is essentially the same in each case and except for the differences in the masses of metals, any effect which strengthens the metal oxygen bond weakens the carbon oxygen bond at the same time. The difference in resonance, inductive and mass effects between the various chelates must be attributed essentially all to the ligand. In Table 3 are recorded the antisymmetric and symmetric carboxyl group frequencies of the various mandelate chelates studied in the present investigation along with their separation. These frequencies are most sensitive to changes in the strength of the metal-oxygen interaction[7]. The data in Table 3 show that in general, the antisymmetric band shit~s to higher frequencies and the symmetric band to lower frequencies, as proceeds from Mn(II)- to Cu(lI)-mandelates except the Be(II) complex. The frequency separation follows the order : Cu(I1) > Zn(II) > Ni(I1) > Co(ll) > Fe(I1) > Mn(II) > Be(It). Table 3. Antisymmetric and symmetric carboxyl stretching frequencies and their separation
Complex
Antisymm.
Cu(II) mand. Zn(II) mand. Ni(II)- mand. Co(ll) mand. Fe(II) mand. Mn(II) mand. Be(II) mand.
1610s 1590s 1575s 1575s 1565s 1555s 1600s
4. 5. 6. 7.
Carboxyl stretching frequencies (cm Symm. 1355sb 1400s 1405s 1410s 1410s 1408s 1480s
J. Fujita, K. Nakamoto and M. Kbayaski, J. Am. chem. Soc. 78, 3963 (1956). L. J. Bellamy and R. F. Branch, J. chem. Soc. 4491 (1954). L. J. Bellamy and L. Beecher, J. chem. Soc. 4487 (1954). K. Nakamoto, Morimoto and A. E. Martel, J. Am. chem. Soc. 83, 4528 (1961).
~) Separation 255 190 170 165 155 147 /20
4304
Notes
This order of separation is in accordance with the Irving-Williams rule[8] established for the order of stability of bivalent metal complexes. The antisymmetric carboxylate stretching frequencies of the metal chelates of some amino acids have been interpreted in a variety of ways in recent years[9]. Saraceno et a/.[9] claimed that the metal-oxygen bond in Cu(II), Ni(II) and Zn(II) glycinates are essentially ionic, since their frequencies are almost the same as those of potassium glycinate and sodium acetate. On the other hand Rosenberg[10] and Nakamoto et al.[7] have concluded that the shift of the carboxylate band to higher frequencies is in the order Ni(II) < Cu(II) < Pt(II); this indicates the increasing covalent character of the metal-oxygen bond. Following the work of Nakamoto et al.[7] it is suggested that the mandelate complexes of the bivalent metal cations studied in the present investigation can be either of the fol!owing structures: H
H
H
I
I
I
C6H,--C--O \m/0--~=0
o=c-o /
"O--C--H [ H
I
I
C6Hs--C
H
I 0,.
~ C
I/O-..>M~'" C
"'0
"0
C6H 5
"0 I C--H
I
H
L
C6H 5
II
X-ray structure data indicate that symmetrical carboxylic groups (formula II) exist in certain metal complexes such as Mn(CHaCOO)4.2H20, where M n- --Cr(II), or Cu(II)[ll]. The results reported have supported formula I rather than the II for the mandelate chelates. In formula I the covalent character of the metal-oxygen bond will lead to more asymmetric vibrations of the carboxylate group and would result in an increased frequency separation of the two carboxylate bands as has been observed in the present investigation. The progressive shift to higher frequencies of the antisymmetric band and the progressive increase in the frequency separation as one proceeds from Be(II) to Cu(II) are not compatible with the theory of symmetrical co-ordination of the carboxylate ion represented by formula II. If such were the case the antisymmetric and the symmetric bands would be expected to shift in the same direction with an increase in the co-ordination bond strength. Acknowledgements--Authors' thanks are due to Prof. W. V. Bhagwat and Principal H. N. Sharma for their keen interest and to Dr. V. S. Mehta for providing the i.r. spectra. Madhav Science College Ujjain (M.P.) India
P.V. KHADIKAR* R.L. AMERIA M.G. KEKRE S. D. CHAUHAN
* Present address: School of Studies in Chemistry, Vikram University, Ujjain (M.P.), India. 8. M. Irving and R. J. P. Williams, J. chem. Soc. 3192 (1963). 9. A. S. Saraceno, I. Nagawaka, S. Mizushisma, C. Curran and J. V. Quagliano, J. Am. chem. Soc. 80, 5018 (1958). 10. A. Rosenberg, Acta. chem. scand. 10, 840 (1956). 11. J. N. Van Niekerk and F. R. L. Schoening, Acta. crystallogr. 6, 277 (1953).
4301
substituting Eqn (2) into Eqn (1) yields an expression for D in which only the concentration of the aqueous phase need be determined. moles Min - moles M~q D
l/i'rg nloles Maq
(3)
The use of this equation is valid only if there is a mass balance for the metal ion. Should this not be the case, the calculated values for D would be erroneous. The absence of a metallic mass balance can be encountered depending upon the particular characteristics and conditions of the particular solvent extraction system. For example, in the extraction of metals with long-chain carboxylic acids, the efficiency of extraction is greatest at a pH range just below the point at which the metal hydroxide begins to precipitate[2]. Should the insoluble gelatinous hydroxide form, it would tend to settle on the interface between the aqueous and organic layers being neither a part of each phase, and it can be mistaken for an emulsion which is frequently present shortly after the completion of shaking the phases. In a study of the solvent extraction of Fe(lll) with chlorendic acid into benzene, the formation of a polymeric, possibly micellar, substance has been observed to settle at the interface after shaking for 24 hr and longer[3]. Subsequent analysis of both phases indicated the absence of a mass balance. Considering the scope of this problem, it seems advisable to check the existence of the mass balance tor the metals when the study of the properties of a particular system is to be undertaken. The analytical data obtained for both phases would provide a more reliable determination for the value of D than the method of differences described by Eqn (3), especially if equilibrium studies are undertaken. The analysis of the organic phase is usually a very difficult technique requiring the evaporation of the solvent followed by the oxidation of the chelate, usually by a wet digestion with HC10~, to convert the metal ion to an uncomplexed form suitable for analysis. However, with the introduction of the technique of atomic absorption, the analysis of both phases may be done reliably and rapidly with the preparation of calibration curves for each of the two phases[4].
Department o f Sciences John Jay College of Criminal Justice City University of New York 455 West 59 Street New York, New York 10019
SELMAN A. BERGER
2. A. W. Fletcher and D. S. Flett, J. appl. Chem, 14, 250 (1964). 3, S. A. Berger, J. B. McKay and H. L. Finston, A paper presented at the Eighth Annual Middle Atlantic Regional Meeting of the A.C.S., Washington, D.C., 15-17 January, 1973. 4. S. A. Berger, At. Absorpt. Newslett. 12, 30 (1973).
J. inorg, nucl. Chem., 1973, Vol. 35, pp. 4301-4304. Pergamon Press. Printed in Great Britain.
Infrared spectra of some bivalent metal complexes of mandelic acid (Received 26 January 1973) 1.R. SPECTRA of Cu(ll), Ni(ll), Co(II), Mn(lI), Zn(ll), Fe(II) and Be(I1) complexes o f mandelic acid in KBr matrix were recorded. The bonding in these complexes has been discussed on the basis of change in hydroxyl and carboxyl group frequencies. No linear relationship is observed between the ionized carboxyl
4302
Notes
group stretching frequency and the stability of the complexes. However, the difference between the antisymmetric and symmetric carboxyl stretching frequency of the complexes showed a linear relationship with the stability of the complexes. In continuation to our previous investigation[l, 2] the present work deals with the i.r. spectra studies of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Fe(II) and Be(II) complexes of mandelic acid. All these complexes were isolated by the method described by Khadikar et al.[3]. The important results obtained are discussed here. EXPERIMENTAL All chemicals used were either of B.D.H., AnalaR or of an equivalent quality. The i.r. spectra of the complexes were recorded on Perkin-Elmer Spectrophotometer-237, in KBr matrix. I.R. spectrum of the ligand has also been obtained for comparison. RESULTS AND DISCUSSION All the complexes were isolated by the method described by Khadikar et al.[3]. The composition of the complexes was found to be ML2.2H20. The characteristic absorption bands of the ligand and the complexes are given in Table 1. The i.r. spectra of the complexes show bands corresponding to the vibrational modes of the ligand present and also the M - O stretching vibrations. Table 1. Characteristic infrared frequencies in cm- 1 Mand. acid
Cu(II) mand.
Ni(lI)mand.
Co(II)mand.
Mn(II) mand.
Zn(II)mand.
Fe(II)mand.
Be(II)mand.
3420s 2956sb 1702s 1490m 1442s 1355s 1280s 1215s 1172s 1065sh 1070s 1018w 990w 928s 872s 840w 755m 718s
3300sb 1610s 1355sb 1105s 940vw 665w 654s
3250s 3040sh 1575s 1490vw 1405s 1358s 1338m 1275s 1245s l190s 1068m 1020sh 988s 942s 908w 788s 740s 688s 645s
3270s 1575s 1490vw 1410s 1358s 1338w 1275s 1248s 1192s 1072m 1020sh 1000s 945s 912w 858vw 788s 742s 688s 650s
3250sb 1555s 1490vw 1408s 1360w 1262w 1180m 1070vw 1060s 994sh 935m 900vw 768m 748m 728s 705vw 680s 658w
3260sb 1590s 1400s 1355s 1275s 1248s 1192s 1095wb 1072vw 1020sh 992s 940w 910vw 785s 740s 788s 550w
3250sb 1565s 1450sh 1410s 1360s 1335vw 1270m 1245w l190s l105s 1070vw 1020sh 1000s 992sh 940s 908m 782s 738s 685s 640w
3400sb 1600s 1480s 1385w 1360vw 1320s 1100sb 940s 925w 890m 855vw 780m 735vw 690w 635w
s, sharp; m, medium; v, very; w, weak; b, broad; sh, shoulder. The important bands are recorded in Table 2. Considerable shift in the hydroxyl group frequency from 3420 cm- ~ in mandelic acid to approximately 3260 cm- t in the complexes was observed. The ionized carboxyl group stretching frequency is also found I. P. V. Khadikar and R. L. Ameria, J. Indian chem. Soc. 47, 1201 (1970). 2. P. V. Khadikar and R. L. Ameria, J. Indian chem. Soc. 49, 717 (1972). 3. P. V. Khadikar and R. L. Ameria, Sci. Cult. 37, 491 (1971).
4303
Notes Table 2. Important bands of the infrared spectra of the complexes
Complex
Carboxyl antisymm, stretch, freq. (cm- 1)
Hydroxyl group freq. (cm- 1)
M 0 stretch, freq. (cm- 1)
Ligand Cu(lI)--mand. Zn(II)-mand. Ni(II) mand. Co(lI)- mand. Fe(II) mand. Mn(II)-mand. Be(ll) mand.
1702s 1610s 1590s 1575s 1575s 1565s 1555s 1600s
3420s 3300sb 3260sb 3250s 3270s 3250sb 3250sb 3400sb
654s 550w 645s 650s 640w 658w 635w
to have been shifted to approximately 1575 cm I (ligand 1702 cm ~ 1). This suggests that the chelation has taken place involving coordination of both, hydroxyl and carboxyl, groups of mandelic acid. The weak band at approximately 800 cm- a in all the complexes may be attributed to the rocking mode of vibration of water molecules ---in agreement with Fujita et al.[4I. Bellamy and BranchE5] have shown a linear relationship between the carboxy group frequency and the stability of the chelates of salicylaldehyde with different bivalent metal cations. Bellamy and Beecher[6] have shown that in acids also there should be a linear relationship between ionized carboxyl group stretching frequency and the stability of the complexes. Perusal of Table 2 shows that no direct relationship could be traced between ionized carboxyl group stretching frequency and the stability of the complexes. The absence of a linear relationship is not entirely unexpected. In comparing the complexes formed by a particular ligand with various metal cations, the action of the ligand is essentially the same in each case and except for the differences in the masses of metals, any effect which strengthens the metal oxygen bond weakens the carbon oxygen bond at the same time. The difference in resonance, inductive and mass effects between the various chelates must be attributed essentially all to the ligand. In Table 3 are recorded the antisymmetric and symmetric carboxyl group frequencies of the various mandelate chelates studied in the present investigation along with their separation. These frequencies are most sensitive to changes in the strength of the metal-oxygen interaction[7]. The data in Table 3 show that in general, the antisymmetric band shit~s to higher frequencies and the symmetric band to lower frequencies, as proceeds from Mn(II)- to Cu(lI)-mandelates except the Be(II) complex. The frequency separation follows the order : Cu(I1) > Zn(II) > Ni(I1) > Co(ll) > Fe(I1) > Mn(II) > Be(It). Table 3. Antisymmetric and symmetric carboxyl stretching frequencies and their separation
Complex
Antisymm.
Cu(II) mand. Zn(II) mand. Ni(II)- mand. Co(ll) mand. Fe(II) mand. Mn(II) mand. Be(II) mand.
1610s 1590s 1575s 1575s 1565s 1555s 1600s
4. 5. 6. 7.
Carboxyl stretching frequencies (cm Symm. 1355sb 1400s 1405s 1410s 1410s 1408s 1480s
J. Fujita, K. Nakamoto and M. Kbayaski, J. Am. chem. Soc. 78, 3963 (1956). L. J. Bellamy and R. F. Branch, J. chem. Soc. 4491 (1954). L. J. Bellamy and L. Beecher, J. chem. Soc. 4487 (1954). K. Nakamoto, Morimoto and A. E. Martel, J. Am. chem. Soc. 83, 4528 (1961).
~) Separation 255 190 170 165 155 147 /20
4304
Notes
This order of separation is in accordance with the Irving-Williams rule[8] established for the order of stability of bivalent metal complexes. The antisymmetric carboxylate stretching frequencies of the metal chelates of some amino acids have been interpreted in a variety of ways in recent years[9]. Saraceno et a/.[9] claimed that the metal-oxygen bond in Cu(II), Ni(II) and Zn(II) glycinates are essentially ionic, since their frequencies are almost the same as those of potassium glycinate and sodium acetate. On the other hand Rosenberg[10] and Nakamoto et al.[7] have concluded that the shift of the carboxylate band to higher frequencies is in the order Ni(II) < Cu(II) < Pt(II); this indicates the increasing covalent character of the metal-oxygen bond. Following the work of Nakamoto et al.[7] it is suggested that the mandelate complexes of the bivalent metal cations studied in the present investigation can be either of the fol!owing structures: H
H
H
I
I
I
C6H,--C--O \m/0--~=0
o=c-o /
"O--C--H [ H
I
I
C6Hs--C
H
I 0,.
~ C
I/O-..>M~'" C
"'0
"0
C6H 5
"0 I C--H
I
H
L
C6H 5
II
X-ray structure data indicate that symmetrical carboxylic groups (formula II) exist in certain metal complexes such as Mn(CHaCOO)4.2H20, where M n- --Cr(II), or Cu(II)[ll]. The results reported have supported formula I rather than the II for the mandelate chelates. In formula I the covalent character of the metal-oxygen bond will lead to more asymmetric vibrations of the carboxylate group and would result in an increased frequency separation of the two carboxylate bands as has been observed in the present investigation. The progressive shift to higher frequencies of the antisymmetric band and the progressive increase in the frequency separation as one proceeds from Be(II) to Cu(II) are not compatible with the theory of symmetrical co-ordination of the carboxylate ion represented by formula II. If such were the case the antisymmetric and the symmetric bands would be expected to shift in the same direction with an increase in the co-ordination bond strength. Acknowledgements--Authors' thanks are due to Prof. W. V. Bhagwat and Principal H. N. Sharma for their keen interest and to Dr. V. S. Mehta for providing the i.r. spectra. Madhav Science College Ujjain (M.P.) India
P.V. KHADIKAR* R.L. AMERIA M.G. KEKRE S. D. CHAUHAN
* Present address: School of Studies in Chemistry, Vikram University, Ujjain (M.P.), India. 8. M. Irving and R. J. P. Williams, J. chem. Soc. 3192 (1963). 9. A. S. Saraceno, I. Nagawaka, S. Mizushisma, C. Curran and J. V. Quagliano, J. Am. chem. Soc. 80, 5018 (1958). 10. A. Rosenberg, Acta. chem. scand. 10, 840 (1956). 11. J. N. Van Niekerk and F. R. L. Schoening, Acta. crystallogr. 6, 277 (1953).