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Molecular addition compounds of tin (IV) chloride—III preparation and infra-red spectra of the complexes of stannic chloride with ortho-, meta- and para-aminobenzoic acids
J. Inorg. Nucl. Chem., 1965, Vol. 27, pp. 2593 to 2596. PergamonPress Ltd. Printedin Northern Ireland
MOLECULAR
ADDITION COMPOUNDS CHLORIDE--III
OF
TIN
(IV)
PREPARATION AND INFRA-RED SPECTRA OF THE COMPLEXES OF STANNIC CHLORIDE WITH ORTHO-, META- AND PARAAMINOBENZOIC ACIDS R. C. AGGARWAL and P. P. SINGH Department of Chemistry, Lucknow University, Lucknow (India)
(Received 14 December 1964) Abstract--1:2-complexes of tin (IV) chloride with anthranilic and methyl anthranilic acids, and 1 : 1complexes with meta- and para-aminobenzoic acids have been prepared by direct interaction in suitable organic solvents. The former are molecular addition compounds while the latter are ionic complexes. Negative shifts of ~(N--H) and positive shifts of v(C----O) indicate nitrogen-metal bonding in all these complexes.
CURRAN and coworkers t1'2) have prepared chelates of anthranilic acid with certain metal ions in aqueous solution, and from an infra-red study of the complexes have shown the existence of covalent bonding between nitrogen and the metal ion and ionic bonding between metal and carboxylate ions. No work has been reported on the preparation and structural studies of complexes of aminobenzoic acids with Lewis acids in a non-aqueous medium. The present communication reports the preparation and infra-red study of the complexes of stannic chloride with amino-benzoic acids. EXPERIMENTAL
Material and man~ulations Stannic chloride (Laboratory Reagent grade) was purified as described by HILDEBRAND and CASTER.~s~ Reagent grade ortho-, meta- and para-aminobenzoic acids were purified by standard methods. N-methyl anthranitic acid was prepared and purified as described by MANN and SAUr,rOER.c*~ Chloroform, dichloroethane, dioxan and carbon tetrachloride were dried before use, and watersensitive compounds were handled in a dry box. Infra-red spectra of donor acids were measured in Nujol mull or in solution on a Perkin-Elmer Infra Cord fitted with sodium chloride optics, and those of the complexes on a Beckman Spectrophotometer I R A using KBr optics.
Preparation of complexes Complexes were prepared by the reaction of dilute non-aqueous solutions of stannic chloride and of the organic acids; stannic chloride and the solvents were directly distilled to exclude moisture. Precipitates formed immediately in all cases and were washed with the solvent until free from the unreacted components before drying in vacuum. * Copies of the spectra may be obtained from Dr. R. C. AGGARWAL. ~1~ G. F. SAVATOS,C. CURRANand J. V. QUAGLIANO,J. Amer. Chem. Soc. 77, 6159 (1955). (8) A. G. HILL and C. CUggAN, J. Phys. Chem. 64, 1519 (1960). ~3~j. H. HILDEBRANDand J. M. CASTER,J. Amer. Chem. Soc. 54, 3592 (1932). ~4~ F, G. MANN and B. C. SALrNDERS,Practical Organic Chemistry (4th Ed), p. 220. Longmans, London (1960). 2593
2594
R . C . AGGARWAL and P. P. SINGH
Analyses The complexes were analysed for tin, chloride and nitrogen as described earlier ~5) with the analytical results in Table 1. TABLE 1 Tin
1. 2. 3. 4.
Compounds
m.p. (°C)
Calc. (~)
SnC14.20AB SnCI4-2MA SnCI~-MAB SnCI4-PAB
208 * * *
22-2 21.0 29.8 29.8
Obs. (9/oo)
Nitrogen Calc. Obs. (~) (~o)
Chloride Calc. Obs. (9/oo) (~)
22.0 20.9 29.0 29'2
5'2 4.47 3"52 3-52
26"5 25"2 35"7 35-7
5.0 4-8 3.5 3"7
26.2 24.9 34.9 35'1
* Does not melt below 245°C. OAB = o-aminobenzoic acid, MA = methyl anthranilic acid, MAB = m-aminobenzoic acid, PAB = p-ambinobenzoic acid. All the complexes are dull, white-coloured, non-hygroscopic solids. The anthranilic and methyl anthranilic acid complexes are insoluble in non-polar solvents but soluble in dioxan, m- and paminobenzoic acid complexes are insoluble in polar as well as non-polar organic solvents, but are soluble in water.
Indicator titrations These were carried out as described earlier c5~with the results in Table 2. TABLE 2 (a) Stannic Chloride-OAB SnCI4(A) (ml) (0"0506 M)
OAB (B) (ml) (0.1007 N)
Moles B/A
2"00 2"50 3.00
1 '98 2"48 2-98
1.97 1 '97 1.97
SnCl4(A) (ml) 0.0506 M
(B) (ml) 0.10 M
Moles B/A
2.00 2-50 3'00
1 '80 2-25 2-70
1 '77 1 "77 1-77
(b) Stannic Chloride-MA
(c) Stannic Chloride-PAB SnC14(A) (ml) 0"0506 M
0.037 M
5'00 6"00 7.00
7"10 8"60 10"40
is) R. C. AGGARWAL and P. P. SING, J.
PAB (B) (ml) Moles B/A
lttorff. NucL Chem. 26,
1"04 1"04 1"08 2185 (1964).
Molecular addition compounds of tin (IV) chloride--IlI
2595
These results show that while anthranilic and methyl anthranilie acids form 1:2-complexes SnC14'2A. a 1 : 1-complex is formed byp-aminobenzoic acid. Indicator titrations failed with m-aminobenzoic acid because of its insolubility in dichloroethane.
Molecular weight determinations Molecular weights of complexes soluble in dioxan were determined by the freezing-point method; the values recorded in Table 3 show that SnCI~'20AB and SnC1. 2 MA are monomeric. TABLE 3 Compound
Molecular weight (found)
SNC14"20AB SNC14-2 MA
Molecular weight (calc)
522 553
534-7 562.7
Infrared spectra The assignments of various bands in the infra-red spectra of the aminobenzoie acids and their complexes are given in Table 4. TABLE 4 Assignments
OAB (in KBr)
N - - H (st) N - - H (st) C = O (st) Anilino Phenyl
3480 (s) 3370 (s) 1665 (s) 1615 (s) 1575"(s)
3420 (s) -1700 (s) 1620 (s) 1580 (s)
Assignments
MA (Soln. CHCIa)
SNC14'2 MA (in KBr)
N - - H (st) N - - H (st)
C~---O (st) Anilino Phenyl Assignments N - - H (st) N - - H (st)
~0
(st)
Anilino Phenyl Assignments N - - H (st) C - - O (st) Anilino Phenyl
-3295 1665 1638 1588
(m) (s) (s) (s)
MAB (emulsion in nujol) --1640 (s) 1575 (s) 1515 (s) PAB (Soln. CHCI~) 3375 (s) 1665 (s) 1605 (s) 1592 (sh)
SNC14"20AB (in KBr)
3380 (s) 3090 (s) 1680 (s) 1610 (s) 1570 (s) SnCI4- MAB (in KBr) 3400 3060 1700 1600 1500
(w) (s) (s) (s) (s)
SnC14, PAB (in KBr) 3040 (s) 1710 (s) 1610 (s) 1550 (s)
Shift (cm -1) --60 +35
Shift (cm -1) --205 + 15
Shift (cm -1)
+60
Shift (cm -1) --335 +45
Note: st = stretching, s = strong, m = medium, w -----weak, sh = shoulder. The peaks for N - - H (st) vibrations are not well resolved in case of MAB.
2596
R.C. AGGARWALand P. P. SIN~H
DISCUSSION Aminobenzoic acids may co-ordinate to Lewis acids either through carbonyl oxygen or through amino nitrogen, or else may undergo condensation through the NH 2 group. Co-ordination through oxygen will decrease the double-bond character of the carbonyl group, resulting in a decrease in ~ ( ~ O ) . Co-ordination through nitrogen, on the other hand, would increase the double-bond character of the carbonyl group with a consequent increase in its stretching frequency. Positive shifts in the carbonyl stretching frequency in all these complexes show that the carbonyl oxygen is not involved in co-ordination. They are rather indicative of co-ordination or condensation reactions through the amino group. Negative shifts or disappearance of the N--H stretching bands in the complexes show conclusively that co-ordination or condensation occurs through NH 2 group. In anthranilic and methyl anthranilic acids the existence of intramolecular hydrogen bonding between the adjacent carbonyl and amino groups results in a decreased liability of hydrogen attached to nitrogen, reducing the chances of the amino group being involved in condensation reactions. Furthermore, co-ordination through carbonyl oxygen in the above acids seems very unlikely, because of the decrease in the electron density on this oxygen atom due to intramolecular hydrogen bonding. The absence of intramolecular hydrogen bonding in the m- and p-aminobenzoic acids enables the amino group to act independently of the carbonyl group, and would explain the adduct formation (by coordination through nitrogen) in the case of anthranilic and methyl anthranilic acids and salt formation (by condensation through the amino group) by m- and p-aminobenzoic acids. 1: 2-adducts are expected to be octahedral, with cis- or trans-arrangement of the ligands, while the l:l-complexes are ionic, and presumably possess the structures (SnClaNH~COOHC6H4)+C1-. The solubility of the anthranilic and methyl anthranilic acid complexes in polar organic solvents and their insolubility in water, and the insolubility of the m- and p-aminobenzoic acid complexes in organic solvents and their solubility in water, confirm that former are adducts and the latter salts.
Acknowledgement We are indebted to Head of the Department of Chemistry, LucknowUniversity, for providinglaboratoryfacilitiesfor this work and to the Chairman Sadtler Research Laboratories Philadelphia, U.S.A. for recordingthe infrared spectra of our complexes.
MOLECULAR
ADDITION COMPOUNDS CHLORIDE--III
OF
TIN
(IV)
PREPARATION AND INFRA-RED SPECTRA OF THE COMPLEXES OF STANNIC CHLORIDE WITH ORTHO-, META- AND PARAAMINOBENZOIC ACIDS R. C. AGGARWAL and P. P. SINGH Department of Chemistry, Lucknow University, Lucknow (India)
(Received 14 December 1964) Abstract--1:2-complexes of tin (IV) chloride with anthranilic and methyl anthranilic acids, and 1 : 1complexes with meta- and para-aminobenzoic acids have been prepared by direct interaction in suitable organic solvents. The former are molecular addition compounds while the latter are ionic complexes. Negative shifts of ~(N--H) and positive shifts of v(C----O) indicate nitrogen-metal bonding in all these complexes.
CURRAN and coworkers t1'2) have prepared chelates of anthranilic acid with certain metal ions in aqueous solution, and from an infra-red study of the complexes have shown the existence of covalent bonding between nitrogen and the metal ion and ionic bonding between metal and carboxylate ions. No work has been reported on the preparation and structural studies of complexes of aminobenzoic acids with Lewis acids in a non-aqueous medium. The present communication reports the preparation and infra-red study of the complexes of stannic chloride with amino-benzoic acids. EXPERIMENTAL
Material and man~ulations Stannic chloride (Laboratory Reagent grade) was purified as described by HILDEBRAND and CASTER.~s~ Reagent grade ortho-, meta- and para-aminobenzoic acids were purified by standard methods. N-methyl anthranitic acid was prepared and purified as described by MANN and SAUr,rOER.c*~ Chloroform, dichloroethane, dioxan and carbon tetrachloride were dried before use, and watersensitive compounds were handled in a dry box. Infra-red spectra of donor acids were measured in Nujol mull or in solution on a Perkin-Elmer Infra Cord fitted with sodium chloride optics, and those of the complexes on a Beckman Spectrophotometer I R A using KBr optics.
Preparation of complexes Complexes were prepared by the reaction of dilute non-aqueous solutions of stannic chloride and of the organic acids; stannic chloride and the solvents were directly distilled to exclude moisture. Precipitates formed immediately in all cases and were washed with the solvent until free from the unreacted components before drying in vacuum. * Copies of the spectra may be obtained from Dr. R. C. AGGARWAL. ~1~ G. F. SAVATOS,C. CURRANand J. V. QUAGLIANO,J. Amer. Chem. Soc. 77, 6159 (1955). (8) A. G. HILL and C. CUggAN, J. Phys. Chem. 64, 1519 (1960). ~3~j. H. HILDEBRANDand J. M. CASTER,J. Amer. Chem. Soc. 54, 3592 (1932). ~4~ F, G. MANN and B. C. SALrNDERS,Practical Organic Chemistry (4th Ed), p. 220. Longmans, London (1960). 2593
2594
R . C . AGGARWAL and P. P. SINGH
Analyses The complexes were analysed for tin, chloride and nitrogen as described earlier ~5) with the analytical results in Table 1. TABLE 1 Tin
1. 2. 3. 4.
Compounds
m.p. (°C)
Calc. (~)
SnC14.20AB SnCI4-2MA SnCI~-MAB SnCI4-PAB
208 * * *
22-2 21.0 29.8 29.8
Obs. (9/oo)
Nitrogen Calc. Obs. (~) (~o)
Chloride Calc. Obs. (9/oo) (~)
22.0 20.9 29.0 29'2
5'2 4.47 3"52 3-52
26"5 25"2 35"7 35-7
5.0 4-8 3.5 3"7
26.2 24.9 34.9 35'1
* Does not melt below 245°C. OAB = o-aminobenzoic acid, MA = methyl anthranilic acid, MAB = m-aminobenzoic acid, PAB = p-ambinobenzoic acid. All the complexes are dull, white-coloured, non-hygroscopic solids. The anthranilic and methyl anthranilic acid complexes are insoluble in non-polar solvents but soluble in dioxan, m- and paminobenzoic acid complexes are insoluble in polar as well as non-polar organic solvents, but are soluble in water.
Indicator titrations These were carried out as described earlier c5~with the results in Table 2. TABLE 2 (a) Stannic Chloride-OAB SnCI4(A) (ml) (0"0506 M)
OAB (B) (ml) (0.1007 N)
Moles B/A
2"00 2"50 3.00
1 '98 2"48 2-98
1.97 1 '97 1.97
SnCl4(A) (ml) 0.0506 M
(B) (ml) 0.10 M
Moles B/A
2.00 2-50 3'00
1 '80 2-25 2-70
1 '77 1 "77 1-77
(b) Stannic Chloride-MA
(c) Stannic Chloride-PAB SnC14(A) (ml) 0"0506 M
0.037 M
5'00 6"00 7.00
7"10 8"60 10"40
is) R. C. AGGARWAL and P. P. SING, J.
PAB (B) (ml) Moles B/A
lttorff. NucL Chem. 26,
1"04 1"04 1"08 2185 (1964).
Molecular addition compounds of tin (IV) chloride--IlI
2595
These results show that while anthranilic and methyl anthranilie acids form 1:2-complexes SnC14'2A. a 1 : 1-complex is formed byp-aminobenzoic acid. Indicator titrations failed with m-aminobenzoic acid because of its insolubility in dichloroethane.
Molecular weight determinations Molecular weights of complexes soluble in dioxan were determined by the freezing-point method; the values recorded in Table 3 show that SnCI~'20AB and SnC1. 2 MA are monomeric. TABLE 3 Compound
Molecular weight (found)
SNC14"20AB SNC14-2 MA
Molecular weight (calc)
522 553
534-7 562.7
Infrared spectra The assignments of various bands in the infra-red spectra of the aminobenzoie acids and their complexes are given in Table 4. TABLE 4 Assignments
OAB (in KBr)
N - - H (st) N - - H (st) C = O (st) Anilino Phenyl
3480 (s) 3370 (s) 1665 (s) 1615 (s) 1575"(s)
3420 (s) -1700 (s) 1620 (s) 1580 (s)
Assignments
MA (Soln. CHCIa)
SNC14'2 MA (in KBr)
N - - H (st) N - - H (st)
C~---O (st) Anilino Phenyl Assignments N - - H (st) N - - H (st)
~0
(st)
Anilino Phenyl Assignments N - - H (st) C - - O (st) Anilino Phenyl
-3295 1665 1638 1588
(m) (s) (s) (s)
MAB (emulsion in nujol) --1640 (s) 1575 (s) 1515 (s) PAB (Soln. CHCI~) 3375 (s) 1665 (s) 1605 (s) 1592 (sh)
SNC14"20AB (in KBr)
3380 (s) 3090 (s) 1680 (s) 1610 (s) 1570 (s) SnCI4- MAB (in KBr) 3400 3060 1700 1600 1500
(w) (s) (s) (s) (s)
SnC14, PAB (in KBr) 3040 (s) 1710 (s) 1610 (s) 1550 (s)
Shift (cm -1) --60 +35
Shift (cm -1) --205 + 15
Shift (cm -1)
+60
Shift (cm -1) --335 +45
Note: st = stretching, s = strong, m = medium, w -----weak, sh = shoulder. The peaks for N - - H (st) vibrations are not well resolved in case of MAB.
2596
R.C. AGGARWALand P. P. SIN~H
DISCUSSION Aminobenzoic acids may co-ordinate to Lewis acids either through carbonyl oxygen or through amino nitrogen, or else may undergo condensation through the NH 2 group. Co-ordination through oxygen will decrease the double-bond character of the carbonyl group, resulting in a decrease in ~ ( ~ O ) . Co-ordination through nitrogen, on the other hand, would increase the double-bond character of the carbonyl group with a consequent increase in its stretching frequency. Positive shifts in the carbonyl stretching frequency in all these complexes show that the carbonyl oxygen is not involved in co-ordination. They are rather indicative of co-ordination or condensation reactions through the amino group. Negative shifts or disappearance of the N--H stretching bands in the complexes show conclusively that co-ordination or condensation occurs through NH 2 group. In anthranilic and methyl anthranilic acids the existence of intramolecular hydrogen bonding between the adjacent carbonyl and amino groups results in a decreased liability of hydrogen attached to nitrogen, reducing the chances of the amino group being involved in condensation reactions. Furthermore, co-ordination through carbonyl oxygen in the above acids seems very unlikely, because of the decrease in the electron density on this oxygen atom due to intramolecular hydrogen bonding. The absence of intramolecular hydrogen bonding in the m- and p-aminobenzoic acids enables the amino group to act independently of the carbonyl group, and would explain the adduct formation (by coordination through nitrogen) in the case of anthranilic and methyl anthranilic acids and salt formation (by condensation through the amino group) by m- and p-aminobenzoic acids. 1: 2-adducts are expected to be octahedral, with cis- or trans-arrangement of the ligands, while the l:l-complexes are ionic, and presumably possess the structures (SnClaNH~COOHC6H4)+C1-. The solubility of the anthranilic and methyl anthranilic acid complexes in polar organic solvents and their insolubility in water, and the insolubility of the m- and p-aminobenzoic acid complexes in organic solvents and their solubility in water, confirm that former are adducts and the latter salts.
Acknowledgement We are indebted to Head of the Department of Chemistry, LucknowUniversity, for providinglaboratoryfacilitiesfor this work and to the Chairman Sadtler Research Laboratories Philadelphia, U.S.A. for recordingthe infrared spectra of our complexes.