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Chelates of Cu(II) with some bidentate Schiff bases
3868
Notes
J. inorg, nucL Chem., 1974,Vol. 36, pp. 3868-3870.PergamonPress. Printedin Great Britain.
Chelates of Cu(II) with some bidentate Schiff bases (Received 20 November 1973) DURING the last few years many Schiff base complexes have been prepared[I-3], the best-known of which are those derived from salicylaldimines. Our study included the preparation and characterization of four new complexes of Cu(II) with the following ligands: N=C-CH 3 R
HO
CHa
1. R II. R III. R IV.R
= = = =
H o-CH 3 m-CHs p-CHs
Preparation of complexes An alcoholic solution of 0.01 mole of copper acetate was added to an alcoholic solution of 0.02 mole of Schiff base. The reaction mixture was kept under reflux for about 2-3 hr. The dark brown precipitate was allowed to settle, filtered, washed free from Schiff base with alcohol and dried in vacuum over anhydrous calcium chloride. Analytical data of the chelates are given in Table 1. Magnetic studies
The ligands were prepared by refluxing equimolar quantities of aryl amine and 2-hydroxy-5-methylacetophenone in alcohol[4, 5]. The separated Schiff bases were filtered and recrystallized from alcohol as yellow solids. Copper analyses were made by means of EDTA titration after decomposing the complexes with a mixture of nitric, sulphuric and perchloric acids. Carbon-hydrogen-nitrogen analyses were made using microanalytical techniques. I.R. spectral data were obtained using a Carl Zeiss Model UR-10 spectrophotometer over the range 4000--400 cm-1. The electronic absorption spectra in chloroform were run on a Beckman DK-2A recording spectrophotometer. The visible reflectance spectra of the solid compounds suitably diluted with lithium fluoride were measured using the standard reflectance attachment and lithium fluoride as the reference. The Gouy method was employed in determining the magnetic moments of the complexes. All the values were corrected for diamagnetism according to the method of Selwood[6].
The magnetic moment values (Table 2) observed for the present complexes are in the range 1.80-1-90 B.M. These values are normal and expected for planar stereochemistry. The results are in agreement with the structural information available through the efforts of Baker et al.[7]. Electronic spectral studies These spectra are characterized by a single relatively broad band with its maximum located in the region of 15,000 era-1 (Table 2) and a pronounced absorption band n e a r 22,000cm-L Tetrahedral copper(II) complexes are expected to give a single broad band in the near i.r. and to have no absorption between 10,000 and 20,000era -1. A blank region between 10,000 and 20,000 cm- t is diagnostic of tetrabedral complexes. Bands around 15,000 era- t are most distinct and most of these are the well-known d-d bands of the planar copper(II)[8,9]. Tetracoordinated copper(II) complexes, with ligands of approximately the same strength as those examined here, exhibit t h e (d-d) transition maximum in the same region[10]. The electronic spectra presented here are suggestive of planar geometry.
Table 1. Analytical data for Cu(II)--Schiff base complexes Found
Calculated Complex No. (amine used) 1. Cu(CIsHI4ON)2 (aniline) 2. Cu(C16H16ON) a (o-toluidine) 3. (Cu(CleHI6ON)2 (m-toluidine) 4. Cu(C16016ON)2 (p-toluidine)
Colour
Cu
C
H
N
Cu
C
H
N
Dark brown
12-42
70.39
5-47
5.47
12.36
71.6
5-88
5.90
Brown
11-77
71.17
5-93
5-19
11.69
70.92
6.40
4.90
Brown
11.77
71-17
5.93
5.19
11.70
71.61
6.28
5.0
Dark brown
11-77
71.17
5.93
5.19
11.65
71.78
6.32
5.0
Notes
3869
Table 2. Electronic spectra and magnetic properties (300°K) of Cu(II) complexes with Schiff bases
Amax(nm) chloroform solution*
Complex 1. Cu(ClsH14ON)2 2. Cu(C16H16ON)2 3. Cu(C16H16ON)2 4. Cu(CI6H16ON)2
460 s 675 br 440 s 650 br 448 s 680 br 450 s 650 br
Reflectancet
Mcff(B.M. )
710 br
1.80
700 br
1.89
700 br
1.84
700 br
1-84
1.8-1.9 x 16 -3 M solutions; s = strong; br = broad. t Spectra of solid samples diluted with LiF. *
l#i'ared studies The important i.r. frequencies along with their assignments are given in Table 3. An examination of the i,r. spectra
presence of only one band in this region suggests the possibility of the trans form[16]. In conclusion, the overall evidence reported is in favour of a trans square planar structure of the type shown below.
Table 3. Infrared frequencies (cm -1) of the copper(ll) complexes and their probable assignments Complex No.
v(C=N)
v(Cu-N)
v(Cu-O)
v(Ph-C-O)
1. 2. 3. 4.
1600 1610 1610 1610
530 490 490 485
485 460 460 460
1337 1330 1335 1328
of the ligands and their copper(II) complexes, shows that the N \ metals are coordinated through C - - O and C=N / / groups. The C = N stretching frequency is observed in the region 1620-1630cm -1. Ueno and Martell[ll] have reported this band in the acetylacetone Schiff bases around 1540 cm-1. The C = N stretching vibration of the copper complexes shows a consistent shift towards higher frequency in comparison to that of free ligands, indicating the involvement of the nitrogen atom in bond formation with the copper atom. The disappearance of the stretching of the phenolic OH, observed in the free ligands around 3300 cm-1, clearly indicates the loss of the phenolic proton on coordination and formation of a new bond between metal and oxygen. The phenolic C ~ 3 stretching vibration in Schiff bases occurs as a strong band around 1280cm 112, 11-13]. On chelation, this band is raised to 1328-1337cm -1. This shift towards higher frequency on complexation indicates that the ortho-OH group is involved in coordination[2, 14]. A medium band in the region 460-485 cm-1 may be due to the M~O stretching vibration. Recently Biradar and Kulkarni[15] assigned the band in the region 460-475 cm- 1 to the Pb-O band in the case of lead(IV) complexes of Schiff bases with acetylacetone. The band observed in the region 485-530 cm- 1 is attributed to the v(Cu-N) vibrations. The
H3 ~ CH3~C~---N. ~-x
U
R /
-O~Cu'"N
/
O
~ C-I~
I CH3
I/I CH 3
Acknowledgement--The authors are grateful to Pro1: R. D. Patel, Head of the Department of Chemistry at Sardar Patel University, for constant encouragement and the facilities for carrying out this work. M. N. PATEL C. B. PATEL R. P. PATEL
Post-graduate Department of Chemistry Sardar Patel University Vallabh Vidyanagar 388120 Gujarat State, India REFERENCES 1. R. H. Holm, G. W. Everett, Jr. and A. Chakravorty, Prog. inorg. Chem. 7, 83 (1966). 2. N. S. Biradar and V. H, Kulkarni, J. inorg, nucl. Chem. 33, 2451 (1971). 3. T.N. Waters and P. E. Wright, J. inorg, nucl. Chem. 33, 359 (1971). 4. A. Senier and F. G. Shepheard, J. chem. Soc. 101, 1950 (1912). 5. L. Hunter and J. A. Marriott, J. chem. Soc., 2000 (1937). 6. P. W. Selwood, Magnetochemistry. Interscience, New York (1956).
3870
Notes
7. E. N. Baker, D. Hall and T. N. Waters, J. chem, Soc. (A), 680 (1966). 8. L. Sacconi and M. Ciampolini, J. chem. Soc. 276 (1964). 9. C. M. Harris, H. R. H. Patil and E. Sinn, Inorg. Chem. 6, 1102 (1967). 10. A. N. Speca, L. L. Pytlewski and N. M. Karayannis, J. inorg, nucl. Chem. 34, 3671 (1972). 11. K. Ueno and A. E. Martell, J. phys. Chem. 59, 998 (1955).
12. J. E, Kovacic, Spectrochim. Acta 23A, 183 (1967). 13. N. S. Biradar and V. H. Kulkarni, J. inorg, nucl. Chem. 33, 3781, 3847 (1971). 14. V. A. Kogan, O. A. Osipov, V. I. Minkin and V. P. Sokolov, Russ. J. inorg. Chem. 10, 45 (1965). 15. N. S. Biradar, V. H. Kulkarni and N. N. Sirmokadam, J. ihorg, nucl. Chem. 34, 3651 (1972). 16. S. C. Jain and R. Rivest, J. inorg, nucl. Chem. 32, 1117 (1970).
Z inorg, nucl. Chem., 1974, Vol. 36, pp. 3870-3871. Pergamon Press. Printed in Great Britain.
Spectral properties and structure of a mixed valence molybdenum compound (Received 31 August 1973) MIXED valence molybdenum compounds containing hexaand pentavalent molybdenum have been known for some time, but their preparation at low temperatures is usually complicated due to their lack of stability towards air oxidation and solvation by varying amounts of water, and their tendency to form colloids. In the present study some of these difficulties were avoided by using a tributylphosphate (TBP)-water system as the reaction medium, in which pentavalent molybdenum is stabilized and the mixed valence compound thus obtained is anhydrous (hydrated, unstable compounds were prepared from an aqueous media by Ostrowetsky[1]). The electronic spectrum as well as the ESR spectrum of this compound were measured and interpreted. EXPERIMENTAL
Preparation A 0'5 M hexavalent molybdenum TBP solution was prepared by extraction of Na2MoO 4 in 6 N HC1 into TBP. A 0,5 M solution of pentavalent molybdenum in TBP was prepared by the reduction of MoO3 in conc. HCI by hydriodic acid[2] followed by extraction of the Mo(V) formed into TBP. Stoichiometric quantities of the above solutions were mixed and shaken with an equal volume of water until a dark blue colour was obtained. After the two phases were separated, the organic phase was washed twice with the equal volumes of a 2 N aqueous lithium chloride solution and finally with a saturated sodium chloride solution. The compound was precipitated by addition of an equal volume of aqueous 1 N (C2Hs)4NCI to the TBP solution and shaking. The precipitate was filtered off after addition of ethanol, washed with absolute ethanol and petrol ether, and dried overnight in a vacuum desiccator. The same compound was also obtained by partial oxidation of pentavalent molybdenum in TBP by an aqueous solution of ferric sulphate. Found: Mo, 49.7; C, 16.85; H, 3.46; N, 2.34 per cent. Required for [(C2Hs)4N]2Mo6019H2: Mo, 50-4; C, 16.81 ; H, 3.68; N, 2.45 per cent.
Micro DTA, Model M4 from Bureau de Liason. The Cary recording spectrophotometer, Model 14 was used for measuring the spectrum of the compound in dimethylsulphoxide solution. I.R. spectra were measured on the Perkin-Elmer 457 i.r. spectrophotometer in Nujol mulls between KBr discs. ESR spectra were recorded on a Varian V-4500 X-band spectrometer at a cavity resonance frequency of 9,178 GHz. Measurements were made in D MSO solution and as an undiluted powder. RESULTS
DTA The differential thermal analysis of the compound showed that no reaction takes p/ace up to 280°C, and from this basis it may be concluded that the compound is obtained anhydrous. At 280°C a violent reaction takes place which is most likely due to the pyrolysis of the organic cation.
Infrared spectra The i.r. spectrum obtained was compared with those of (C2Hs)4NCI[3 ] and ((C4Hg)4N)2M0601914]. The main difference between the spectrum of the mixed valence anion and that of the anion containing only hexavalent molybdenum is a large number of additional bands in the range 890-970 cm-1 due to a variety of different Mo-O bonds existing in the mixed valence compound.
Electronic spectra The electronic spectrum shows three bands which may be assigned by comparison with the spectrum of MoOCl~ -. Molybdenum blue E (cm - 1). emol 9 900 13,400
134 512
31,750
7660
Physical measurements Differential thermal analysis was performed on the
MoOCI 2- [5] E (cm- t) emoz 14,050 22,500 28,200 32,200
16 14 500 4400
Assignments 2B2 -~ 2E(I) 2B2 ~ 2B1 2B2 --, 2E(II) 2 B 2 --* 2Bz(I)
Notes
J. inorg, nucL Chem., 1974,Vol. 36, pp. 3868-3870.PergamonPress. Printedin Great Britain.
Chelates of Cu(II) with some bidentate Schiff bases (Received 20 November 1973) DURING the last few years many Schiff base complexes have been prepared[I-3], the best-known of which are those derived from salicylaldimines. Our study included the preparation and characterization of four new complexes of Cu(II) with the following ligands: N=C-CH 3 R
HO
CHa
1. R II. R III. R IV.R
= = = =
H o-CH 3 m-CHs p-CHs
Preparation of complexes An alcoholic solution of 0.01 mole of copper acetate was added to an alcoholic solution of 0.02 mole of Schiff base. The reaction mixture was kept under reflux for about 2-3 hr. The dark brown precipitate was allowed to settle, filtered, washed free from Schiff base with alcohol and dried in vacuum over anhydrous calcium chloride. Analytical data of the chelates are given in Table 1. Magnetic studies
The ligands were prepared by refluxing equimolar quantities of aryl amine and 2-hydroxy-5-methylacetophenone in alcohol[4, 5]. The separated Schiff bases were filtered and recrystallized from alcohol as yellow solids. Copper analyses were made by means of EDTA titration after decomposing the complexes with a mixture of nitric, sulphuric and perchloric acids. Carbon-hydrogen-nitrogen analyses were made using microanalytical techniques. I.R. spectral data were obtained using a Carl Zeiss Model UR-10 spectrophotometer over the range 4000--400 cm-1. The electronic absorption spectra in chloroform were run on a Beckman DK-2A recording spectrophotometer. The visible reflectance spectra of the solid compounds suitably diluted with lithium fluoride were measured using the standard reflectance attachment and lithium fluoride as the reference. The Gouy method was employed in determining the magnetic moments of the complexes. All the values were corrected for diamagnetism according to the method of Selwood[6].
The magnetic moment values (Table 2) observed for the present complexes are in the range 1.80-1-90 B.M. These values are normal and expected for planar stereochemistry. The results are in agreement with the structural information available through the efforts of Baker et al.[7]. Electronic spectral studies These spectra are characterized by a single relatively broad band with its maximum located in the region of 15,000 era-1 (Table 2) and a pronounced absorption band n e a r 22,000cm-L Tetrahedral copper(II) complexes are expected to give a single broad band in the near i.r. and to have no absorption between 10,000 and 20,000era -1. A blank region between 10,000 and 20,000 cm- t is diagnostic of tetrabedral complexes. Bands around 15,000 era- t are most distinct and most of these are the well-known d-d bands of the planar copper(II)[8,9]. Tetracoordinated copper(II) complexes, with ligands of approximately the same strength as those examined here, exhibit t h e (d-d) transition maximum in the same region[10]. The electronic spectra presented here are suggestive of planar geometry.
Table 1. Analytical data for Cu(II)--Schiff base complexes Found
Calculated Complex No. (amine used) 1. Cu(CIsHI4ON)2 (aniline) 2. Cu(C16H16ON) a (o-toluidine) 3. (Cu(CleHI6ON)2 (m-toluidine) 4. Cu(C16016ON)2 (p-toluidine)
Colour
Cu
C
H
N
Cu
C
H
N
Dark brown
12-42
70.39
5-47
5.47
12.36
71.6
5-88
5.90
Brown
11-77
71.17
5-93
5-19
11.69
70.92
6.40
4.90
Brown
11.77
71-17
5.93
5.19
11.70
71.61
6.28
5.0
Dark brown
11-77
71.17
5.93
5.19
11.65
71.78
6.32
5.0
Notes
3869
Table 2. Electronic spectra and magnetic properties (300°K) of Cu(II) complexes with Schiff bases
Amax(nm) chloroform solution*
Complex 1. Cu(ClsH14ON)2 2. Cu(C16H16ON)2 3. Cu(C16H16ON)2 4. Cu(CI6H16ON)2
460 s 675 br 440 s 650 br 448 s 680 br 450 s 650 br
Reflectancet
Mcff(B.M. )
710 br
1.80
700 br
1.89
700 br
1.84
700 br
1-84
1.8-1.9 x 16 -3 M solutions; s = strong; br = broad. t Spectra of solid samples diluted with LiF. *
l#i'ared studies The important i.r. frequencies along with their assignments are given in Table 3. An examination of the i,r. spectra
presence of only one band in this region suggests the possibility of the trans form[16]. In conclusion, the overall evidence reported is in favour of a trans square planar structure of the type shown below.
Table 3. Infrared frequencies (cm -1) of the copper(ll) complexes and their probable assignments Complex No.
v(C=N)
v(Cu-N)
v(Cu-O)
v(Ph-C-O)
1. 2. 3. 4.
1600 1610 1610 1610
530 490 490 485
485 460 460 460
1337 1330 1335 1328
of the ligands and their copper(II) complexes, shows that the N \ metals are coordinated through C - - O and C=N / / groups. The C = N stretching frequency is observed in the region 1620-1630cm -1. Ueno and Martell[ll] have reported this band in the acetylacetone Schiff bases around 1540 cm-1. The C = N stretching vibration of the copper complexes shows a consistent shift towards higher frequency in comparison to that of free ligands, indicating the involvement of the nitrogen atom in bond formation with the copper atom. The disappearance of the stretching of the phenolic OH, observed in the free ligands around 3300 cm-1, clearly indicates the loss of the phenolic proton on coordination and formation of a new bond between metal and oxygen. The phenolic C ~ 3 stretching vibration in Schiff bases occurs as a strong band around 1280cm 112, 11-13]. On chelation, this band is raised to 1328-1337cm -1. This shift towards higher frequency on complexation indicates that the ortho-OH group is involved in coordination[2, 14]. A medium band in the region 460-485 cm-1 may be due to the M~O stretching vibration. Recently Biradar and Kulkarni[15] assigned the band in the region 460-475 cm- 1 to the Pb-O band in the case of lead(IV) complexes of Schiff bases with acetylacetone. The band observed in the region 485-530 cm- 1 is attributed to the v(Cu-N) vibrations. The
H3 ~ CH3~C~---N. ~-x
U
R /
-O~Cu'"N
/
O
~ C-I~
I CH3
I/I CH 3
Acknowledgement--The authors are grateful to Pro1: R. D. Patel, Head of the Department of Chemistry at Sardar Patel University, for constant encouragement and the facilities for carrying out this work. M. N. PATEL C. B. PATEL R. P. PATEL
Post-graduate Department of Chemistry Sardar Patel University Vallabh Vidyanagar 388120 Gujarat State, India REFERENCES 1. R. H. Holm, G. W. Everett, Jr. and A. Chakravorty, Prog. inorg. Chem. 7, 83 (1966). 2. N. S. Biradar and V. H, Kulkarni, J. inorg, nucl. Chem. 33, 2451 (1971). 3. T.N. Waters and P. E. Wright, J. inorg, nucl. Chem. 33, 359 (1971). 4. A. Senier and F. G. Shepheard, J. chem. Soc. 101, 1950 (1912). 5. L. Hunter and J. A. Marriott, J. chem. Soc., 2000 (1937). 6. P. W. Selwood, Magnetochemistry. Interscience, New York (1956).
3870
Notes
7. E. N. Baker, D. Hall and T. N. Waters, J. chem, Soc. (A), 680 (1966). 8. L. Sacconi and M. Ciampolini, J. chem. Soc. 276 (1964). 9. C. M. Harris, H. R. H. Patil and E. Sinn, Inorg. Chem. 6, 1102 (1967). 10. A. N. Speca, L. L. Pytlewski and N. M. Karayannis, J. inorg, nucl. Chem. 34, 3671 (1972). 11. K. Ueno and A. E. Martell, J. phys. Chem. 59, 998 (1955).
12. J. E, Kovacic, Spectrochim. Acta 23A, 183 (1967). 13. N. S. Biradar and V. H. Kulkarni, J. inorg, nucl. Chem. 33, 3781, 3847 (1971). 14. V. A. Kogan, O. A. Osipov, V. I. Minkin and V. P. Sokolov, Russ. J. inorg. Chem. 10, 45 (1965). 15. N. S. Biradar, V. H. Kulkarni and N. N. Sirmokadam, J. ihorg, nucl. Chem. 34, 3651 (1972). 16. S. C. Jain and R. Rivest, J. inorg, nucl. Chem. 32, 1117 (1970).
Z inorg, nucl. Chem., 1974, Vol. 36, pp. 3870-3871. Pergamon Press. Printed in Great Britain.
Spectral properties and structure of a mixed valence molybdenum compound (Received 31 August 1973) MIXED valence molybdenum compounds containing hexaand pentavalent molybdenum have been known for some time, but their preparation at low temperatures is usually complicated due to their lack of stability towards air oxidation and solvation by varying amounts of water, and their tendency to form colloids. In the present study some of these difficulties were avoided by using a tributylphosphate (TBP)-water system as the reaction medium, in which pentavalent molybdenum is stabilized and the mixed valence compound thus obtained is anhydrous (hydrated, unstable compounds were prepared from an aqueous media by Ostrowetsky[1]). The electronic spectrum as well as the ESR spectrum of this compound were measured and interpreted. EXPERIMENTAL
Preparation A 0'5 M hexavalent molybdenum TBP solution was prepared by extraction of Na2MoO 4 in 6 N HC1 into TBP. A 0,5 M solution of pentavalent molybdenum in TBP was prepared by the reduction of MoO3 in conc. HCI by hydriodic acid[2] followed by extraction of the Mo(V) formed into TBP. Stoichiometric quantities of the above solutions were mixed and shaken with an equal volume of water until a dark blue colour was obtained. After the two phases were separated, the organic phase was washed twice with the equal volumes of a 2 N aqueous lithium chloride solution and finally with a saturated sodium chloride solution. The compound was precipitated by addition of an equal volume of aqueous 1 N (C2Hs)4NCI to the TBP solution and shaking. The precipitate was filtered off after addition of ethanol, washed with absolute ethanol and petrol ether, and dried overnight in a vacuum desiccator. The same compound was also obtained by partial oxidation of pentavalent molybdenum in TBP by an aqueous solution of ferric sulphate. Found: Mo, 49.7; C, 16.85; H, 3.46; N, 2.34 per cent. Required for [(C2Hs)4N]2Mo6019H2: Mo, 50-4; C, 16.81 ; H, 3.68; N, 2.45 per cent.
Micro DTA, Model M4 from Bureau de Liason. The Cary recording spectrophotometer, Model 14 was used for measuring the spectrum of the compound in dimethylsulphoxide solution. I.R. spectra were measured on the Perkin-Elmer 457 i.r. spectrophotometer in Nujol mulls between KBr discs. ESR spectra were recorded on a Varian V-4500 X-band spectrometer at a cavity resonance frequency of 9,178 GHz. Measurements were made in D MSO solution and as an undiluted powder. RESULTS
DTA The differential thermal analysis of the compound showed that no reaction takes p/ace up to 280°C, and from this basis it may be concluded that the compound is obtained anhydrous. At 280°C a violent reaction takes place which is most likely due to the pyrolysis of the organic cation.
Infrared spectra The i.r. spectrum obtained was compared with those of (C2Hs)4NCI[3 ] and ((C4Hg)4N)2M0601914]. The main difference between the spectrum of the mixed valence anion and that of the anion containing only hexavalent molybdenum is a large number of additional bands in the range 890-970 cm-1 due to a variety of different Mo-O bonds existing in the mixed valence compound.
Electronic spectra The electronic spectrum shows three bands which may be assigned by comparison with the spectrum of MoOCl~ -. Molybdenum blue E (cm - 1). emol 9 900 13,400
134 512
31,750
7660
Physical measurements Differential thermal analysis was performed on the
MoOCI 2- [5] E (cm- t) emoz 14,050 22,500 28,200 32,200
16 14 500 4400
Assignments 2B2 -~ 2E(I) 2B2 ~ 2B1 2B2 --, 2E(II) 2 B 2 --* 2Bz(I)