- Email: [email protected]
Four- and five-coordinate copper(II) complexes containing mixed ligands
0277-5387184 S3.00 + .OO 0 1984 Pcrgamon RrJs Ltd.
PolyhedronVol. 3, No. 5, pp. 595-598, 1984 Printed in Great Britain.
NOTE FOUR- AND FIVECOORDINATE COPPER COMPLEXES CONTAINING MIXED LIGANDS M. AKRAR ALI*, D. A. CHOWDHURY-I and M. NAZIM UDDIN Department of Chemistry, University of Chittagong, Chittagong, Bangladesh (Received
26 April 1983; accepted
15 October
1983)
Abstract-New copper(I1) complexes of general formula, Cu(ONS)B (ONS = the dinegatively charged Schiff base, S-benzyl-B-N-(2-hydroxyphenyl) methylendithiocarbazate; B = pyridine, 2,2’-dipyridyl or 1, lo-phenanthroline) have been synthesized and characterised by magnetic and spectroscopic measurements. The complex, Cu(ONS)py is fourcoordinate and square-planar. Magnetic and spectroscopic data support a five-coordinate, presumably, a trigonal-bipyramidal structure for the [Cu(ONS)dipy] and (Cu(ONS)phen] complexes.
(Cu(ONS)] was found to possess an anomalously low magnetic moment of 1.02 B.M. This was thought to be due to the presence of antiferromagnetic interactions between a pair of copper(I1) ions in an oxygen-bridged binuclear structure.’ Since the subject Schiff base satisfies three coordination positions whilst simultaneously satisfying the dipositive charge of the copper(I1) ion, we thought it worthwhile to study complexes of the type, [Cu(ONS)B], where ONS stands for the dinegatively charged tridentate ligand and B stands for the heterocyclic bases such as pyridine, 2,2’-dipyridyl (dipy) and 1, lo-phenanthroline (phen). Thus, with pyridine, a monomeric fourcoordinate copper(I1) complex is expected, whereas with dipy and phen, five-coordination should result. Our results, shown below, indicate that the compounds do in fact form in this manner.
The preparation and characterisation of the salicylaldehyde Schiff base of S-benzyldithiocarbazate were initially reported by Akbar Ali and Bose’. From IR spectroscopic evidence, the authors postulated that in the solid-state, the Schiff base remains in the thioketo form (Ia), but in solution, it might remain as an equilibrium mixture of both the thioketo and thioenol (Ib) forms.
a
OH
0
CH
(la
a
HONS)
OH
0
CH=N-N-C,
/ SH
EXPERIMENTAL The solid reflectance spectra were obtained with an SP 500 spectrophotometer. IR spectra as KBr discs were recorded on a Perkin-Elmer 577 spectrophotometer. All other physical measurements and analytical procedures employed in the present investigation were similar to those described previously.2 Physical measurements.
‘SCH&,H, (lb
H,ONS)
In all its reactions with metal ions, the Schiff base was found to coordinate as a dinegatively charged tridentate ligand. The copper (II) complex,
Preparation of S-benzyl-/I-N-(2-hydroxyphenyl)methylendithiocarbazate. This compound was pre*Author addressed.
to
PGLY Vol. 3. No. %F
whom
correspondence
should
be
pared according to the method of Akbar Ali and Bose.’ (Found: C, 60.0; H, 4.8; N, 9.3; S, 21.0.
595
596
Notes
C,,H,,N,OS, 21.2%).
requires: C, 59.6; H, 4.7; N, 9.3; S,
General method for the preparation of the copper(ZZ) complexes. The Schiff base (1 .Og) and the
appropriate heterocyclic base (0.5-0.6 g) were dissolved in a 1 : 1 mixture of abs. ethanol (100 cm3) and 2,2_dimethoxypropane (100 cm’). To this was added a hot and filtered solution of copper(I1) acetate dihydrate (0.9 g) in the same solvent (100 cm’). The mixture was heated on a water-bath for ca. 30 min whereupon the volume of the reaction mixture was reduced to about 100 cm3 by slow heating. On cooling to ambient temperature, crystals of the complexes precipitated and were removed by filtration, washed with ethanol and then dried in a vacuum desiccator over P,O,,,. RESULTS AND DISCUSSION
The Schiff base, hereinafter abbreviated as H,ONS was obtained as beautiful long needles. Its relevant IR spectral bands with their tentative assignments are shown in Table 2. The positions of these bands agree well with those reported by Akbar Ali and Bose.’ Reaction of the Schiff base with copper(I1) acetate in the presence of heterocyclic bases such as pyridine, dipy and ophen yields crystalline complexes of empirical formula, Cu(ONS)B. The complexes which were isolated are listed in Table 1 along with their physical properties. The molar conductance data of the complexes (Table 1) indicate that these compounds behave essentially as non-electrolytes in nitrobenzene. The ligand, therefore, must be behaving as a dinegatively charged species. Comparison of the IR spectrum of the ligand with those of the metal complexes (Table 2) reveals the following facts: (i) the phenolic and N-H protons of the ligand are lost on complex formation with copper(II), (ii) the VC = S band at 782 cm-’ of the free ligand3*4disappears in the spectra of the complexes, (iii) the VC = N band is lowered and a new band at 343 cm-’ attributable to the metal-sulphur stretching frequency5v6 appears in the spectra of the complexes. The foregoing facts suggest that the present Schiff base behaves as a tridentate chelating agent coordinating via the phenolic oxygen atom, the azomethine nitrogen atom and the thiolo sulphur atom. The IR spectrum of [Cu(ONS)phen] shows bands at 420,840 and 1522 cm-’ due to the coordinated phenanthroline molecule.7*8 In a similar manner the IR spectra of [Cu(ONS)dipy] and [Cu(ONS)py] (Table 2) are indicative of dipy and pyridine coordinationg. The colour ofthe [Cu(ONS)B] complexes is green in contrast with the red brown colour of the dimeric Cu,(ONS), complex reported by Akbar
Notes
597
Ali and Bose.’ The room-temperature magnetic moments (Table 1) of the copper complexes suggest that these have normal magnetic moments for a 3d9 ion. The position of the d-d band at 530 nm in the electronic spectrum [Cu(ONS)py] is very similar to that displayed by other known squareplanar copper(I1) species.1o Therefore, a squareplanar structure is assigned to [Cu(ONS)py]. Intercomparison of the electronic spectrum of [Cu(ONS)py] with that of [Cu(ONS)phen] (Table 2) shows that the latter has a different structure than the former. The tendency of l,lO-phenanthroline and 2,2’-dipyridyl to act as bidentates and the Schiff base as an ONS tridentate is expected to impose a five-coordinate configuration on the [Cu(ONS)dipy] and [Cu(ONS)phen] complexes. An oxygen-bridged or a sulphur-bridged diemric or polymeric structure is very unlikely since such bridging arrangements generally lead to antiferromagnetic interactions causing a reduction in the room-temperature magnetic moments.lO~” The [Cu(ONS)dipy] and [Cu(ONS)phen] complexes are most probably associated with a five-coordinate configuration. Five-coordinate complexes may have either a square-pyramidal or a trigonal-bipyramidal geometry, but the choice between these two configurations is not clearcut. The electronic spectrum of [Cu(ONS)phen] displays two incompletely resolved bands at 675 and 520 nm (Table 2). Similar incompletely resolved bands in the same region were also observed in the electronic spectrum of bis(N-methylsalicylaldiminato) copper(I1) for which a trigonalbipyramidal structure has been proposed.12 Furthermore, Cu( 1,2-dimethylimidazole),C1,, for which a slightly distorted trigonal-bipyramidal structure has been proposed has been shown to display the main ligand-field band at 757 nm.13 The electronic spectra of the present copper(I1) complexes do not resemble those of other squareplanar or octahedral copper(I1) species, but are very similar to those displayed by five-coordinate trigonal-bipyramidal copper(I1) complexes.‘“” REFERENCES 1. M. Akbar Ali and R. Bose, J. Znorg. Nucl. Chem. 1977, 39, 265. 2. M. Akbar Ali and M. T. H. Tarafder, Ibid. 1977,39, 1785. 3. M. Mashima, Bull. Chem. Sot., Japan 1974, 37. 4. M. J. M. Campbell and R. Grezeskowiak, J. Chem. Sot. A 1967, 396. 5. D. M. Adams Metal-Ligand and Related Vibrations, p. 319. Arnold, London (1967). 6. S. H. H. Chaston and S. E. Livingstone, Aust. J. Chem. 1967, 20, 1965.
598
7. 8. 9. 10.
Notes R. G. Inskeep, J. Znorg. Nucl. Chem. 1962, 24, 763. A. A. Schilt and R. C. Taylor, Ibid. 1959, 9, 217. M. Monoyama, Znorg. Chim. Acta. 1975, 13, 5. M. Akbar Ali, S. E. Livingstone and D. J. Phillips, Znorg. Chim. Acta. 1973, 7, 531.
11. R. S. Nyholm, Proc. Chem. Sot. 1964, 273. 12. L. Sacconi, M. Ciampolini and G. Speroni, J. Am. Chem. Sot. 1965, 87, 3102. 13. D. M. L. Goodgame, M. Goodgame and G. W. Rayner Canham, J. Chem. Sot. A 1971, 1923.
PolyhedronVol. 3, No. 5, pp. 595-598, 1984 Printed in Great Britain.
NOTE FOUR- AND FIVECOORDINATE COPPER COMPLEXES CONTAINING MIXED LIGANDS M. AKRAR ALI*, D. A. CHOWDHURY-I and M. NAZIM UDDIN Department of Chemistry, University of Chittagong, Chittagong, Bangladesh (Received
26 April 1983; accepted
15 October
1983)
Abstract-New copper(I1) complexes of general formula, Cu(ONS)B (ONS = the dinegatively charged Schiff base, S-benzyl-B-N-(2-hydroxyphenyl) methylendithiocarbazate; B = pyridine, 2,2’-dipyridyl or 1, lo-phenanthroline) have been synthesized and characterised by magnetic and spectroscopic measurements. The complex, Cu(ONS)py is fourcoordinate and square-planar. Magnetic and spectroscopic data support a five-coordinate, presumably, a trigonal-bipyramidal structure for the [Cu(ONS)dipy] and (Cu(ONS)phen] complexes.
(Cu(ONS)] was found to possess an anomalously low magnetic moment of 1.02 B.M. This was thought to be due to the presence of antiferromagnetic interactions between a pair of copper(I1) ions in an oxygen-bridged binuclear structure.’ Since the subject Schiff base satisfies three coordination positions whilst simultaneously satisfying the dipositive charge of the copper(I1) ion, we thought it worthwhile to study complexes of the type, [Cu(ONS)B], where ONS stands for the dinegatively charged tridentate ligand and B stands for the heterocyclic bases such as pyridine, 2,2’-dipyridyl (dipy) and 1, lo-phenanthroline (phen). Thus, with pyridine, a monomeric fourcoordinate copper(I1) complex is expected, whereas with dipy and phen, five-coordination should result. Our results, shown below, indicate that the compounds do in fact form in this manner.
The preparation and characterisation of the salicylaldehyde Schiff base of S-benzyldithiocarbazate were initially reported by Akbar Ali and Bose’. From IR spectroscopic evidence, the authors postulated that in the solid-state, the Schiff base remains in the thioketo form (Ia), but in solution, it might remain as an equilibrium mixture of both the thioketo and thioenol (Ib) forms.
a
OH
0
CH
(la
a
HONS)
OH
0
CH=N-N-C,
/ SH
EXPERIMENTAL The solid reflectance spectra were obtained with an SP 500 spectrophotometer. IR spectra as KBr discs were recorded on a Perkin-Elmer 577 spectrophotometer. All other physical measurements and analytical procedures employed in the present investigation were similar to those described previously.2 Physical measurements.
‘SCH&,H, (lb
H,ONS)
In all its reactions with metal ions, the Schiff base was found to coordinate as a dinegatively charged tridentate ligand. The copper (II) complex,
Preparation of S-benzyl-/I-N-(2-hydroxyphenyl)methylendithiocarbazate. This compound was pre*Author addressed.
to
PGLY Vol. 3. No. %F
whom
correspondence
should
be
pared according to the method of Akbar Ali and Bose.’ (Found: C, 60.0; H, 4.8; N, 9.3; S, 21.0.
595
596
Notes
C,,H,,N,OS, 21.2%).
requires: C, 59.6; H, 4.7; N, 9.3; S,
General method for the preparation of the copper(ZZ) complexes. The Schiff base (1 .Og) and the
appropriate heterocyclic base (0.5-0.6 g) were dissolved in a 1 : 1 mixture of abs. ethanol (100 cm3) and 2,2_dimethoxypropane (100 cm’). To this was added a hot and filtered solution of copper(I1) acetate dihydrate (0.9 g) in the same solvent (100 cm’). The mixture was heated on a water-bath for ca. 30 min whereupon the volume of the reaction mixture was reduced to about 100 cm3 by slow heating. On cooling to ambient temperature, crystals of the complexes precipitated and were removed by filtration, washed with ethanol and then dried in a vacuum desiccator over P,O,,,. RESULTS AND DISCUSSION
The Schiff base, hereinafter abbreviated as H,ONS was obtained as beautiful long needles. Its relevant IR spectral bands with their tentative assignments are shown in Table 2. The positions of these bands agree well with those reported by Akbar Ali and Bose.’ Reaction of the Schiff base with copper(I1) acetate in the presence of heterocyclic bases such as pyridine, dipy and ophen yields crystalline complexes of empirical formula, Cu(ONS)B. The complexes which were isolated are listed in Table 1 along with their physical properties. The molar conductance data of the complexes (Table 1) indicate that these compounds behave essentially as non-electrolytes in nitrobenzene. The ligand, therefore, must be behaving as a dinegatively charged species. Comparison of the IR spectrum of the ligand with those of the metal complexes (Table 2) reveals the following facts: (i) the phenolic and N-H protons of the ligand are lost on complex formation with copper(II), (ii) the VC = S band at 782 cm-’ of the free ligand3*4disappears in the spectra of the complexes, (iii) the VC = N band is lowered and a new band at 343 cm-’ attributable to the metal-sulphur stretching frequency5v6 appears in the spectra of the complexes. The foregoing facts suggest that the present Schiff base behaves as a tridentate chelating agent coordinating via the phenolic oxygen atom, the azomethine nitrogen atom and the thiolo sulphur atom. The IR spectrum of [Cu(ONS)phen] shows bands at 420,840 and 1522 cm-’ due to the coordinated phenanthroline molecule.7*8 In a similar manner the IR spectra of [Cu(ONS)dipy] and [Cu(ONS)py] (Table 2) are indicative of dipy and pyridine coordinationg. The colour ofthe [Cu(ONS)B] complexes is green in contrast with the red brown colour of the dimeric Cu,(ONS), complex reported by Akbar
Notes
597
Ali and Bose.’ The room-temperature magnetic moments (Table 1) of the copper complexes suggest that these have normal magnetic moments for a 3d9 ion. The position of the d-d band at 530 nm in the electronic spectrum [Cu(ONS)py] is very similar to that displayed by other known squareplanar copper(I1) species.1o Therefore, a squareplanar structure is assigned to [Cu(ONS)py]. Intercomparison of the electronic spectrum of [Cu(ONS)py] with that of [Cu(ONS)phen] (Table 2) shows that the latter has a different structure than the former. The tendency of l,lO-phenanthroline and 2,2’-dipyridyl to act as bidentates and the Schiff base as an ONS tridentate is expected to impose a five-coordinate configuration on the [Cu(ONS)dipy] and [Cu(ONS)phen] complexes. An oxygen-bridged or a sulphur-bridged diemric or polymeric structure is very unlikely since such bridging arrangements generally lead to antiferromagnetic interactions causing a reduction in the room-temperature magnetic moments.lO~” The [Cu(ONS)dipy] and [Cu(ONS)phen] complexes are most probably associated with a five-coordinate configuration. Five-coordinate complexes may have either a square-pyramidal or a trigonal-bipyramidal geometry, but the choice between these two configurations is not clearcut. The electronic spectrum of [Cu(ONS)phen] displays two incompletely resolved bands at 675 and 520 nm (Table 2). Similar incompletely resolved bands in the same region were also observed in the electronic spectrum of bis(N-methylsalicylaldiminato) copper(I1) for which a trigonalbipyramidal structure has been proposed.12 Furthermore, Cu( 1,2-dimethylimidazole),C1,, for which a slightly distorted trigonal-bipyramidal structure has been proposed has been shown to display the main ligand-field band at 757 nm.13 The electronic spectra of the present copper(I1) complexes do not resemble those of other squareplanar or octahedral copper(I1) species, but are very similar to those displayed by five-coordinate trigonal-bipyramidal copper(I1) complexes.‘“” REFERENCES 1. M. Akbar Ali and R. Bose, J. Znorg. Nucl. Chem. 1977, 39, 265. 2. M. Akbar Ali and M. T. H. Tarafder, Ibid. 1977,39, 1785. 3. M. Mashima, Bull. Chem. Sot., Japan 1974, 37. 4. M. J. M. Campbell and R. Grezeskowiak, J. Chem. Sot. A 1967, 396. 5. D. M. Adams Metal-Ligand and Related Vibrations, p. 319. Arnold, London (1967). 6. S. H. H. Chaston and S. E. Livingstone, Aust. J. Chem. 1967, 20, 1965.
598
7. 8. 9. 10.
Notes R. G. Inskeep, J. Znorg. Nucl. Chem. 1962, 24, 763. A. A. Schilt and R. C. Taylor, Ibid. 1959, 9, 217. M. Monoyama, Znorg. Chim. Acta. 1975, 13, 5. M. Akbar Ali, S. E. Livingstone and D. J. Phillips, Znorg. Chim. Acta. 1973, 7, 531.
11. R. S. Nyholm, Proc. Chem. Sot. 1964, 273. 12. L. Sacconi, M. Ciampolini and G. Speroni, J. Am. Chem. Sot. 1965, 87, 3102. 13. D. M. L. Goodgame, M. Goodgame and G. W. Rayner Canham, J. Chem. Sot. A 1971, 1923.