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Chelate polymers of copper(II) with various dihydroxyquinoid ligands
J. inorg, nucl. Chem., 1974, Vol. 36, pp. 1049-1053. Pergamon Press. Printed in Great Britain.
CHELATE POLYMERS OF COPPER(II) WITH VARIOUS
DIHYDROXYQUINOID LIGANDS H. DWAIN COBLE and HENRY F. HOLTZCLAW, Jr. Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68508
(Received 13 July 1973) Abstract--The polymeric copper(II) chelates of 2,5-dihydroxy-p-benzoquinone, 5,8-dihydroxy-l,4naphthoquinone, 1,4-dihydroxyanthraquinone, 1,5-dihydroxyanthraquinone, 1,2,5,8-tetrahydroxyanthraquinone, and 6,1 l-dihydroxynaphthacenequinone have been prepared and the thermal stabilities studied. The compounds were prepared under similar conditions and relative thermal stabilities were determined by differential thermal analysis. The thermal stability is not related to the thermodynamic stability, as indicated by shift in carbonyl absorption frequency, but is an almost linear function of the number of fused rings in the ligand portion of the chelate.
INTRODUCTION THE DIHYDROXYQUINONES are capable of being tetrafunctional and should form linear polymers when allowed to react with suitable metal ions. Examples are the ligands 2,5-dihydroxy-p-benzoquinone (hereafter referred to as HzA), 5,8-dihydroxy-l,4-naphthoquinone (HzB), 1,4-dihydroxyanthraquinone (HzC), 1,5-dihydroxyanthraquinone (HzD), 1,2,5,8-tetrah y d r o x y a n t h r a q u i n o n e (HzE), and 6,ll-dihydroxyn a p h t h a c e n e q u i n o n e (H2F), each of which reacts with copper(II) ion to produce a linear uncharged polymer. Copper(If) polymers with H2A , H2B, H2C, a n d H2D have been prepared a n d the thermal stabilities have been studied by various a u t h o r s [ i - 9 ] , Differences in a variety of factors such as conditions of preparation, methods of determining the thermal stabilities, solvents, temperatures, and concentrations can affect chain length a n d thermal stability. These factors make comparisons of data from different sources difficult. The purpose of this investigation was to prepare the polymers under the same conditions and to determine the relative thermal stabilities by means of differential thermal analysis at the same heating rate using similar size samples.
solvents were used without further purification. The dimethylformamide (DMF) was reagent grade.
Preparation qf compounds The polymers were typically prepared by adding 0.010 mole of the ligand in 100 ml of hot DMF to 0.010 mole of copper acetate l-hydrate in 100 ml of hot DMF and refluxing the mixture for 3 4 hr. The solution immediately darkened and particles were observed on the sides of the flask. The products were separated either by allowing the solution to set for several days or by centrifugation. In each case, the precipitate was a dark powder. The compounds were all insoluble in common solvents and were purified by extraction in a Soxhlet apparatus with acetone until the wash solution was clear. The analytical data are summarized in Table l.
2,5-Dihydroxy-p-benzoquinonecopper(lI) chelate polymer (Cu-A) A dark olive powder was obtained by adding 1-40 g (0.010 mole) of 2,5-dihydroxy-p-benzoquinone dissolved in 100 ml of hot DMF to 2.00 g (0.010 mole) of copper acetate 1-hydrate dissolved in 100 ml of hot DMF. Yield, 1.60 g.
5,8-Dihydroxy-l,4-naphthoquinonecopper(II) chelate polymer (Cu-B)
Materials
EXPERIMENTAL
The method described above was used. The product is a dark purple powder. Yield, 2.32 g (from 0.01 mole ligand and copper acetate 1-hydrate in 100 ml DMF).
The ligands H2A, HzC, H2D, and H2F were purchased from Eastman Organic Chemicals; ligands HzB and H2E were purchased from L. Light & Co. All were purified by extraction and recrystallization using xylene as the solvent. The coper(II) acetate 1-hydrate was reagent grade and was used without further purification. Common laboratory
(Cu-C)
1,4-Dihydroxyanthraquinonecopper(II) chelate polymer The product is a dark purple powder. Yield, 19.27 g (from 0.080 mole each reactant in 800 ml DMF).
1049 J.I.N.C., Vol. 36, No. 5 • G
H. DWAINCOBLEand HENRYF. HOLTZCLAW,Jr.
1050
Table 1. Summary of analytical data Polymer %Cu Cu-A(Cu-C6H204) Cu-B(Cu-CloH404)
Cu-C(Cu-C14H604) Cu-D(Cu-CI4H604)
Cu-E(Cu-C14H606) Cu-F(Cu-C 1sHsO4)
31.52 25.25 21.06 21.06 19.04 18.07
Calcd %c 35.74 47.73 55.73 55.73 50.39 61.47
°JoH 0.99 1-59 1.99 1.99 1.80 2.27
l-5,-Dihydroxyanthraquinonecopper(lI) chelate polymer
Analyses C/Cu %Cu 6.0 9.0 14.0 14.0 14.0 18.0
29.0 26.0 19.95 21.02 18.60 16.9
Found %C %H 35-58 44.41 55.72 54.01 48.13 61.24
1-64 2.05 2.10 2.20 2.80 2.70
C/Cu 6.5 9.1 14-8 13-6 13-7 19.2
RESULTS
(Cu-D) The product is a purple powder. Yield, 16.0 g (from 0.060 mole each reactant in 600 ml DMF). 1,2,5,8-Tetrahydroxyanthraquinonecopper(ll)-chelate
polymer (Cu-E) The product is a dark purple powder. Yield, 1.78 g (from 0.010 mole each reactant in 100 ml DMF). 6,11-Dihydroxynaphthacenequinonecopper(II) chelate
polymer (Cu-F) The product is a dark purple powder. Yield, 3.53g (from 0.010 mole each reactant in 100 ml DMF).
Infrared absorption spectra 1.R. absorption spectra were obtained on a Perkin-Elmer 237 recording spectrophotometer using the KBr pellet method.
Thermal analyses The thermal stabilities of the polymers were investigated by means of differential thermal analysis (dta). The dta apparatus consisted of a 300-W tube furnace, a steel sample block 1¼in. in diameter and 3¼in. long, Vycor sample tubes 7 mm o.d. and 35 mm long, and appropriate thermocouple wiring. The differential temperature was amplified and recorded by a Sargent SR recorder. The absolute temperature (vs ice bath temperature) was recorded by a Sargent SR recorder (usually 25 my range). Samples ordinarily were 70 mg and covered with ignited alumina to exclude free access of oxygen.
Physical characteristics of the polymers All of the compounds are dark infusible powders. Cu-A is a dark olive-green whereas the rest are dark purple. All are insoluble in common organic solvents, and hence molecular weight determinations are not possible by usual methods. The analytical results, Table 1, are indicative of polymeric composition in that the values are near those expected for a 1 : 1 polymer. All of the complexes were somewhat difficult to analyze because constant weight could not be readily obtained. Apparently drying in air does not result in complete drying, due to a tendency to absorb moisture. Absorbed D M F is very difficult to remove and does not appear to be completely removed even after drying at 250 ° for several hours. At still higher temperatures, slow decomposition was observed. Because of these difficulties, the analytical data cannot be used to establish chain length definitely, but do indicate that chain length probably is 10 or greater repeating units.
Differential thermal analysis The dta results are listed in Tables 2 and 3. The ligands all sublime with decomposition. Ligands H2E and H2F apparently do not melt at the heating rate used, showing only one thermal effect, and were observed subliming from the sample tubes. The temperatures listed are those of first indication of thermal
Table 2. Differential thermal analysis results for ligand Ligand
T(°C)
H2A
210 222 215 230 194 416 262 400 315 344
H2B H2C H2D H2E HzF
Heat effect endothermic endothermic endothermic exothermic endothermic endothermic endothermic endothermic endothermic endothermic
Identification (reaction) melting vaporization with decomposition melting or sublimation decomposition melting vaporization with decomposition melting vaporization with decomposition sublimation with decomposition sublimation with decomposition
Chelate polymers of copper(II)
1051
Table 3. Differential thermal analysis results for copper polymer Compound
Decomposition temperature*
Cu-A Cu-B Cu-C Cu-D Cu-E Cu-F
345 420 485 485 400 565
Observations? exothermic endothermic endothermic endothermic endothermic endothermic
sublimation sublimation sublimation sublimation sublimation
of ligand~ of ligand§ of ligand§ of ligand § of ligand §
*Decomposition temperature taken as point of deviation from baseline. tBlack residue in sample tube at end of run. Copper mirror also except Cu-A. ++Violet substance observed -presumed to be due to ligand. §Sublimate collected, i.r. spectrum identical with that of ligand. change (the point at which the curve leaves the baseline). With the exception of Cu-A, the polymer decompositions are slow and are accompanied by the evolution of a colored gas which quickly condenses. For Cu-C, Cu-D, and Cu-F the condensate was collected and, by comparison of i.r. spectra, identified as ligand. The polymers Cu-B and Cu-E produce a colored gas but the gas is produced sufficiently slowly that it sublimes away from the thermocouple leads and cannot conveniently be collected. It is assumed in these cases also that the gases are ligand molecules. Low heats of decomposition and slow rates of reaction make reproducibility difficult; the dta results are the average of two or more determinations reported to the nearest 5° .
Infrared spectra The ligand carbonyl absorption frequencies and the shifts in these frequencies which occur on chelation are given in Table 4. Only the 2,5-dihydroxy-p-benzoquinone has any appreciable absorption in the 3300 cm-1 region. This absorption is missing in the copper chelate and indicates
that the enolic hydrogen atoms are lost on chelation. The chelates show little, if any, absorption in the region where carbonyl absorption occurs in the free ligand, indicating that, if ligand molecules are the end groups, the chain length must be great enough to make the end group absorption negligible. DISCUSSION Elemental analyses, physical properties, and i.r. data provide good evidence that the compounds are polymeric. The structure of polymer Cu-A is probably similar to those proposed by Kanda and Saito[3, 4] for various M C 6 H 2 0 4 derivatives, as shown in structure I. The structure of Cu-B has been proposed to be as shown in IIE6], while the structure Cu-C has been proposed as III[9]. We are proposing that Cu-D has structure IV and thus a staggered chain rather than a straight chain
/ 7:o o 1
Table 4. Infrared spectral data (carbonyl absorption frequencies). Comparison of ligand and chelate polymer Compound
vC=O (cm 1)
H 2A Cu-A H2 B Cu-B H2C Cu-C H2D Cu-D H2 E Cu-E H2F Cu-F
1640 1460 1620 1535 1625 1540 1639 1585 1611 1545 1623 1538
A/,C=O (cm 1) - 150
It
-85 85 -54 - 66 -85
Itl
1052
H. DWAIN COBLEand HENRY F. HOLTZCLAW,JR.
It is not surprising that the carbonyl shifts of Cu-B, Cu-C, and Cu-F are very similar. A comparison of carbonyl absorption frequencies of the quinone from which the ligand is derived, the ligand, and the copper chelate (Tables 4 and 5) indicates that increasing the number of fused rings affects the carbonyl absorption only slightly for the unsubstituted quinone. In addition, the two hydroxy groups and the resultant hydrogen bonding causes approximately the same shift in 1V carbonyl frequency for all the compounds except for structure. The structure of Cu-E could be similar to ligand H2D. In this case any resonance in one portion III or IV and may consist of both inasmuch as the OH of the molecule is acting independently of resonance in groups in the ligand are so located as to make both another part of the molecule. The relative thermal stabilities (Table 3) show the structures possible. The structure of Cu-F is assumed to be similar to III with another fused ring in the ligand order of decreasing thermal stability to be Cu-F > Cu-D ~ Cu-C > Cu-B > Cu-E > Cu-A. Except for portion of the compound. The copper(II) ion in all of these compounds is the Cu-E polymer, the thermal stability is seen to assumed to have a coordination number of four and to increase regularly with the number of fused rings in the ligand. The increase is presumably due to greater be located in a square planar arrangement. The i.r. spectral data (Table 4) show that a pro- delocalization of the electrons from the metal atom into nounced change in the carbonyl absorption occurs on the aromatic n-system. Kenney[10] and Tomic[ll] chelation. For the compounds Cu-B, Cu-C, and Cu-E, have both noted that aromatic complexes containing the shift in the carbonyl frequency is identical (85 cm- ~) n-electron systems are more thermally stable than their within experimental error, whereas the Cu-A polymer aliphatic counterparts. The data here suggest that the shows a much greater shift in frequency (150 cm- 1) and more extensive the n-electron system the greater is the thermal stability. the Cu-D polymer a slightly smaller shift (54 cm- 1). The relatively low decomposition temperature of If shift in carbonyl frequency is related to the Cu-E compared to that of Cu-C and Cu-D must be due stability of the chelates, Cu-B, Cu-C and Cu-E, would be expected to be of comparable stability. Cu-A should to a difference in the mode of decomposition. The be of greater stability and Cu-D of lesser stability. The presence of the two free hydroxyl groups could allow a very large shift in carbonyl absorption frequency for dehydration reaction with resultant rupture of the Cu-A is unexpected in that five-membered unsaturated ligand portion of the polymer. The thermal stability as indicated by dta and the chelate rings are generally less stable than corresponding unsaturated six-membered chelate rings. This thermodynamic stability as indicated by infrared data frequency shift (increased stability) may be due to the are not directly related in that the thermodynamic copper(I1) ion being large enough to bridge between the stability of the Cu-B, Cu-C, and Cu-F polymers two oxygen atoms, whereas hydrogen may not be would be very nearly the same while the thermal sufficiently large. The strong OH absorption frequency stability increases greatly for this series. That the at 3300 cm ~indicates that the hydrogen is not bridged stabilities are not comparable is expected in that for between the two oxygen atoms. The low frequency thermodynamic stability the breaking of the C u - O shift for compound Cu-D is probably due to the fact bond is the important factor whereas for thermal that resonance in one chelate ring does not involve stability the bond broken can be either the C u - O the other chelate ring and thus the resonating system bond or one of the several bonds within the ligand. for Cu-D is not as great as when the rings are t r a n s to Hence the thermal stability of the ligand is an important determining factor in the thermal stability of the polyone another (Cu-C).
Q -o/
Table 5. Infrared spectral data tcarbonyl absorption frequencies). Comparison of the quinone from which ligand is derived and ligand Compound p-Benzoquinone Dihydroxybenzoquinone 1,4-Naphthoquinone 5,8-Dihydroxy- 1,4-naphthoquinone Anthraquinone 1,4-Dihydroxyanthraquinone 1,5-Dihydroxyanthraquinone Naphthacenequinone 6,11 -Dihydroxynaphthacenequinone
vC=O (cm- 1) 1665 1610 1675 1620 1678 1625 1639 1682 1623
AvC=O (cm- 1) - 55 - 55 - 53 - 39 - 59
1053
Chelate polymers of copper(II) mer. Possibly the "splitting out" of hydrogen from adjacent ligand portions is the important step. Charles [12] found for alkaline earth quinolinates that the evolution of hydrogen gas accompanied the decomposition and proposed the loss of hydrogen from adjacent ligands to be the important step in the decomposition. The high thermal stability of the compounds, especially of the polymer Cu-F, would indicate potentially useful polymers. The problem of insolubility of these coordination polymers makes their study difficult. Additional studies are in progress with other metal ions with a view toward obtaining more tractable polymers.
Acknowledgement--The authors wish to thank the American Chemical Society for a PRF grant which provided for construction of the dta apparatus and for a fellowship to H.D.C.
REFERENCES
1. J. P, Collman, M.S. Thesis, University of Nebraska (1956). 2. H. D. Coble, M.S. Thesis, University of Nebraska, 1962; Ph.D. Thesis, University of Nebraska, 1966. 3. S. Kanda, Kogyo Kagaku Zasshi 66, 641 (1963) [Chem. Abstr. 60, 3109g (1964)]. 4. S. Kanda and Y. Saito, Bull chem, Soc. Japan 30, 192 (1957). 5. R. S. Bottei and P. L. Gerace, J. inorg, nuel. Chem. 23, 245 (1961). 6. R. S. Bottei and J. T. Fangman, J. inorg, nueL Chem. 28, 1259 (1966). 7. D. N. Chakravarty and W. C. Drinkard, Jr., 3. Indian chem, Soc. 37, 517 (1960). 8. W. C. Drinkard and D. N. Chakravarty, WADC Tech. Rept. 59/761, 1960, p. 232. (B. P. Block, Inorganic Polymers (Edited by F. G. A. Stone and W. A. G. Graham), p. 500. Academic Press, New York (1961). 9. V. V. Korshak, S. V. Vinogradova and V. S. Artemova, Vysokomolek. Soedin. 2, 492 (1960). 10. C. N. Kenney, Chem. Ind. Lond. 880 (1960). 11. E. A. Tomic, J. Appl. Polymer Sci. 9, 3745 (1965). 12. R. G. Charles, J. inorg, nucl. Chem. 20, 211 (1961).
CHELATE POLYMERS OF COPPER(II) WITH VARIOUS
DIHYDROXYQUINOID LIGANDS H. DWAIN COBLE and HENRY F. HOLTZCLAW, Jr. Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68508
(Received 13 July 1973) Abstract--The polymeric copper(II) chelates of 2,5-dihydroxy-p-benzoquinone, 5,8-dihydroxy-l,4naphthoquinone, 1,4-dihydroxyanthraquinone, 1,5-dihydroxyanthraquinone, 1,2,5,8-tetrahydroxyanthraquinone, and 6,1 l-dihydroxynaphthacenequinone have been prepared and the thermal stabilities studied. The compounds were prepared under similar conditions and relative thermal stabilities were determined by differential thermal analysis. The thermal stability is not related to the thermodynamic stability, as indicated by shift in carbonyl absorption frequency, but is an almost linear function of the number of fused rings in the ligand portion of the chelate.
INTRODUCTION THE DIHYDROXYQUINONES are capable of being tetrafunctional and should form linear polymers when allowed to react with suitable metal ions. Examples are the ligands 2,5-dihydroxy-p-benzoquinone (hereafter referred to as HzA), 5,8-dihydroxy-l,4-naphthoquinone (HzB), 1,4-dihydroxyanthraquinone (HzC), 1,5-dihydroxyanthraquinone (HzD), 1,2,5,8-tetrah y d r o x y a n t h r a q u i n o n e (HzE), and 6,ll-dihydroxyn a p h t h a c e n e q u i n o n e (H2F), each of which reacts with copper(II) ion to produce a linear uncharged polymer. Copper(If) polymers with H2A , H2B, H2C, a n d H2D have been prepared a n d the thermal stabilities have been studied by various a u t h o r s [ i - 9 ] , Differences in a variety of factors such as conditions of preparation, methods of determining the thermal stabilities, solvents, temperatures, and concentrations can affect chain length a n d thermal stability. These factors make comparisons of data from different sources difficult. The purpose of this investigation was to prepare the polymers under the same conditions and to determine the relative thermal stabilities by means of differential thermal analysis at the same heating rate using similar size samples.
solvents were used without further purification. The dimethylformamide (DMF) was reagent grade.
Preparation qf compounds The polymers were typically prepared by adding 0.010 mole of the ligand in 100 ml of hot DMF to 0.010 mole of copper acetate l-hydrate in 100 ml of hot DMF and refluxing the mixture for 3 4 hr. The solution immediately darkened and particles were observed on the sides of the flask. The products were separated either by allowing the solution to set for several days or by centrifugation. In each case, the precipitate was a dark powder. The compounds were all insoluble in common solvents and were purified by extraction in a Soxhlet apparatus with acetone until the wash solution was clear. The analytical data are summarized in Table l.
2,5-Dihydroxy-p-benzoquinonecopper(lI) chelate polymer (Cu-A) A dark olive powder was obtained by adding 1-40 g (0.010 mole) of 2,5-dihydroxy-p-benzoquinone dissolved in 100 ml of hot DMF to 2.00 g (0.010 mole) of copper acetate 1-hydrate dissolved in 100 ml of hot DMF. Yield, 1.60 g.
5,8-Dihydroxy-l,4-naphthoquinonecopper(II) chelate polymer (Cu-B)
Materials
EXPERIMENTAL
The method described above was used. The product is a dark purple powder. Yield, 2.32 g (from 0.01 mole ligand and copper acetate 1-hydrate in 100 ml DMF).
The ligands H2A, HzC, H2D, and H2F were purchased from Eastman Organic Chemicals; ligands HzB and H2E were purchased from L. Light & Co. All were purified by extraction and recrystallization using xylene as the solvent. The coper(II) acetate 1-hydrate was reagent grade and was used without further purification. Common laboratory
(Cu-C)
1,4-Dihydroxyanthraquinonecopper(II) chelate polymer The product is a dark purple powder. Yield, 19.27 g (from 0.080 mole each reactant in 800 ml DMF).
1049 J.I.N.C., Vol. 36, No. 5 • G
H. DWAINCOBLEand HENRYF. HOLTZCLAW,Jr.
1050
Table 1. Summary of analytical data Polymer %Cu Cu-A(Cu-C6H204) Cu-B(Cu-CloH404)
Cu-C(Cu-C14H604) Cu-D(Cu-CI4H604)
Cu-E(Cu-C14H606) Cu-F(Cu-C 1sHsO4)
31.52 25.25 21.06 21.06 19.04 18.07
Calcd %c 35.74 47.73 55.73 55.73 50.39 61.47
°JoH 0.99 1-59 1.99 1.99 1.80 2.27
l-5,-Dihydroxyanthraquinonecopper(lI) chelate polymer
Analyses C/Cu %Cu 6.0 9.0 14.0 14.0 14.0 18.0
29.0 26.0 19.95 21.02 18.60 16.9
Found %C %H 35-58 44.41 55.72 54.01 48.13 61.24
1-64 2.05 2.10 2.20 2.80 2.70
C/Cu 6.5 9.1 14-8 13-6 13-7 19.2
RESULTS
(Cu-D) The product is a purple powder. Yield, 16.0 g (from 0.060 mole each reactant in 600 ml DMF). 1,2,5,8-Tetrahydroxyanthraquinonecopper(ll)-chelate
polymer (Cu-E) The product is a dark purple powder. Yield, 1.78 g (from 0.010 mole each reactant in 100 ml DMF). 6,11-Dihydroxynaphthacenequinonecopper(II) chelate
polymer (Cu-F) The product is a dark purple powder. Yield, 3.53g (from 0.010 mole each reactant in 100 ml DMF).
Infrared absorption spectra 1.R. absorption spectra were obtained on a Perkin-Elmer 237 recording spectrophotometer using the KBr pellet method.
Thermal analyses The thermal stabilities of the polymers were investigated by means of differential thermal analysis (dta). The dta apparatus consisted of a 300-W tube furnace, a steel sample block 1¼in. in diameter and 3¼in. long, Vycor sample tubes 7 mm o.d. and 35 mm long, and appropriate thermocouple wiring. The differential temperature was amplified and recorded by a Sargent SR recorder. The absolute temperature (vs ice bath temperature) was recorded by a Sargent SR recorder (usually 25 my range). Samples ordinarily were 70 mg and covered with ignited alumina to exclude free access of oxygen.
Physical characteristics of the polymers All of the compounds are dark infusible powders. Cu-A is a dark olive-green whereas the rest are dark purple. All are insoluble in common organic solvents, and hence molecular weight determinations are not possible by usual methods. The analytical results, Table 1, are indicative of polymeric composition in that the values are near those expected for a 1 : 1 polymer. All of the complexes were somewhat difficult to analyze because constant weight could not be readily obtained. Apparently drying in air does not result in complete drying, due to a tendency to absorb moisture. Absorbed D M F is very difficult to remove and does not appear to be completely removed even after drying at 250 ° for several hours. At still higher temperatures, slow decomposition was observed. Because of these difficulties, the analytical data cannot be used to establish chain length definitely, but do indicate that chain length probably is 10 or greater repeating units.
Differential thermal analysis The dta results are listed in Tables 2 and 3. The ligands all sublime with decomposition. Ligands H2E and H2F apparently do not melt at the heating rate used, showing only one thermal effect, and were observed subliming from the sample tubes. The temperatures listed are those of first indication of thermal
Table 2. Differential thermal analysis results for ligand Ligand
T(°C)
H2A
210 222 215 230 194 416 262 400 315 344
H2B H2C H2D H2E HzF
Heat effect endothermic endothermic endothermic exothermic endothermic endothermic endothermic endothermic endothermic endothermic
Identification (reaction) melting vaporization with decomposition melting or sublimation decomposition melting vaporization with decomposition melting vaporization with decomposition sublimation with decomposition sublimation with decomposition
Chelate polymers of copper(II)
1051
Table 3. Differential thermal analysis results for copper polymer Compound
Decomposition temperature*
Cu-A Cu-B Cu-C Cu-D Cu-E Cu-F
345 420 485 485 400 565
Observations? exothermic endothermic endothermic endothermic endothermic endothermic
sublimation sublimation sublimation sublimation sublimation
of ligand~ of ligand§ of ligand§ of ligand § of ligand §
*Decomposition temperature taken as point of deviation from baseline. tBlack residue in sample tube at end of run. Copper mirror also except Cu-A. ++Violet substance observed -presumed to be due to ligand. §Sublimate collected, i.r. spectrum identical with that of ligand. change (the point at which the curve leaves the baseline). With the exception of Cu-A, the polymer decompositions are slow and are accompanied by the evolution of a colored gas which quickly condenses. For Cu-C, Cu-D, and Cu-F the condensate was collected and, by comparison of i.r. spectra, identified as ligand. The polymers Cu-B and Cu-E produce a colored gas but the gas is produced sufficiently slowly that it sublimes away from the thermocouple leads and cannot conveniently be collected. It is assumed in these cases also that the gases are ligand molecules. Low heats of decomposition and slow rates of reaction make reproducibility difficult; the dta results are the average of two or more determinations reported to the nearest 5° .
Infrared spectra The ligand carbonyl absorption frequencies and the shifts in these frequencies which occur on chelation are given in Table 4. Only the 2,5-dihydroxy-p-benzoquinone has any appreciable absorption in the 3300 cm-1 region. This absorption is missing in the copper chelate and indicates
that the enolic hydrogen atoms are lost on chelation. The chelates show little, if any, absorption in the region where carbonyl absorption occurs in the free ligand, indicating that, if ligand molecules are the end groups, the chain length must be great enough to make the end group absorption negligible. DISCUSSION Elemental analyses, physical properties, and i.r. data provide good evidence that the compounds are polymeric. The structure of polymer Cu-A is probably similar to those proposed by Kanda and Saito[3, 4] for various M C 6 H 2 0 4 derivatives, as shown in structure I. The structure of Cu-B has been proposed to be as shown in IIE6], while the structure Cu-C has been proposed as III[9]. We are proposing that Cu-D has structure IV and thus a staggered chain rather than a straight chain
/ 7:o o 1
Table 4. Infrared spectral data (carbonyl absorption frequencies). Comparison of ligand and chelate polymer Compound
vC=O (cm 1)
H 2A Cu-A H2 B Cu-B H2C Cu-C H2D Cu-D H2 E Cu-E H2F Cu-F
1640 1460 1620 1535 1625 1540 1639 1585 1611 1545 1623 1538
A/,C=O (cm 1) - 150
It
-85 85 -54 - 66 -85
Itl
1052
H. DWAIN COBLEand HENRY F. HOLTZCLAW,JR.
It is not surprising that the carbonyl shifts of Cu-B, Cu-C, and Cu-F are very similar. A comparison of carbonyl absorption frequencies of the quinone from which the ligand is derived, the ligand, and the copper chelate (Tables 4 and 5) indicates that increasing the number of fused rings affects the carbonyl absorption only slightly for the unsubstituted quinone. In addition, the two hydroxy groups and the resultant hydrogen bonding causes approximately the same shift in 1V carbonyl frequency for all the compounds except for structure. The structure of Cu-E could be similar to ligand H2D. In this case any resonance in one portion III or IV and may consist of both inasmuch as the OH of the molecule is acting independently of resonance in groups in the ligand are so located as to make both another part of the molecule. The relative thermal stabilities (Table 3) show the structures possible. The structure of Cu-F is assumed to be similar to III with another fused ring in the ligand order of decreasing thermal stability to be Cu-F > Cu-D ~ Cu-C > Cu-B > Cu-E > Cu-A. Except for portion of the compound. The copper(II) ion in all of these compounds is the Cu-E polymer, the thermal stability is seen to assumed to have a coordination number of four and to increase regularly with the number of fused rings in the ligand. The increase is presumably due to greater be located in a square planar arrangement. The i.r. spectral data (Table 4) show that a pro- delocalization of the electrons from the metal atom into nounced change in the carbonyl absorption occurs on the aromatic n-system. Kenney[10] and Tomic[ll] chelation. For the compounds Cu-B, Cu-C, and Cu-E, have both noted that aromatic complexes containing the shift in the carbonyl frequency is identical (85 cm- ~) n-electron systems are more thermally stable than their within experimental error, whereas the Cu-A polymer aliphatic counterparts. The data here suggest that the shows a much greater shift in frequency (150 cm- 1) and more extensive the n-electron system the greater is the thermal stability. the Cu-D polymer a slightly smaller shift (54 cm- 1). The relatively low decomposition temperature of If shift in carbonyl frequency is related to the Cu-E compared to that of Cu-C and Cu-D must be due stability of the chelates, Cu-B, Cu-C and Cu-E, would be expected to be of comparable stability. Cu-A should to a difference in the mode of decomposition. The be of greater stability and Cu-D of lesser stability. The presence of the two free hydroxyl groups could allow a very large shift in carbonyl absorption frequency for dehydration reaction with resultant rupture of the Cu-A is unexpected in that five-membered unsaturated ligand portion of the polymer. The thermal stability as indicated by dta and the chelate rings are generally less stable than corresponding unsaturated six-membered chelate rings. This thermodynamic stability as indicated by infrared data frequency shift (increased stability) may be due to the are not directly related in that the thermodynamic copper(I1) ion being large enough to bridge between the stability of the Cu-B, Cu-C, and Cu-F polymers two oxygen atoms, whereas hydrogen may not be would be very nearly the same while the thermal sufficiently large. The strong OH absorption frequency stability increases greatly for this series. That the at 3300 cm ~indicates that the hydrogen is not bridged stabilities are not comparable is expected in that for between the two oxygen atoms. The low frequency thermodynamic stability the breaking of the C u - O shift for compound Cu-D is probably due to the fact bond is the important factor whereas for thermal that resonance in one chelate ring does not involve stability the bond broken can be either the C u - O the other chelate ring and thus the resonating system bond or one of the several bonds within the ligand. for Cu-D is not as great as when the rings are t r a n s to Hence the thermal stability of the ligand is an important determining factor in the thermal stability of the polyone another (Cu-C).
Q -o/
Table 5. Infrared spectral data tcarbonyl absorption frequencies). Comparison of the quinone from which ligand is derived and ligand Compound p-Benzoquinone Dihydroxybenzoquinone 1,4-Naphthoquinone 5,8-Dihydroxy- 1,4-naphthoquinone Anthraquinone 1,4-Dihydroxyanthraquinone 1,5-Dihydroxyanthraquinone Naphthacenequinone 6,11 -Dihydroxynaphthacenequinone
vC=O (cm- 1) 1665 1610 1675 1620 1678 1625 1639 1682 1623
AvC=O (cm- 1) - 55 - 55 - 53 - 39 - 59
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Chelate polymers of copper(II) mer. Possibly the "splitting out" of hydrogen from adjacent ligand portions is the important step. Charles [12] found for alkaline earth quinolinates that the evolution of hydrogen gas accompanied the decomposition and proposed the loss of hydrogen from adjacent ligands to be the important step in the decomposition. The high thermal stability of the compounds, especially of the polymer Cu-F, would indicate potentially useful polymers. The problem of insolubility of these coordination polymers makes their study difficult. Additional studies are in progress with other metal ions with a view toward obtaining more tractable polymers.
Acknowledgement--The authors wish to thank the American Chemical Society for a PRF grant which provided for construction of the dta apparatus and for a fellowship to H.D.C.
REFERENCES
1. J. P, Collman, M.S. Thesis, University of Nebraska (1956). 2. H. D. Coble, M.S. Thesis, University of Nebraska, 1962; Ph.D. Thesis, University of Nebraska, 1966. 3. S. Kanda, Kogyo Kagaku Zasshi 66, 641 (1963) [Chem. Abstr. 60, 3109g (1964)]. 4. S. Kanda and Y. Saito, Bull chem, Soc. Japan 30, 192 (1957). 5. R. S. Bottei and P. L. Gerace, J. inorg, nuel. Chem. 23, 245 (1961). 6. R. S. Bottei and J. T. Fangman, J. inorg, nueL Chem. 28, 1259 (1966). 7. D. N. Chakravarty and W. C. Drinkard, Jr., 3. Indian chem, Soc. 37, 517 (1960). 8. W. C. Drinkard and D. N. Chakravarty, WADC Tech. Rept. 59/761, 1960, p. 232. (B. P. Block, Inorganic Polymers (Edited by F. G. A. Stone and W. A. G. Graham), p. 500. Academic Press, New York (1961). 9. V. V. Korshak, S. V. Vinogradova and V. S. Artemova, Vysokomolek. Soedin. 2, 492 (1960). 10. C. N. Kenney, Chem. Ind. Lond. 880 (1960). 11. E. A. Tomic, J. Appl. Polymer Sci. 9, 3745 (1965). 12. R. G. Charles, J. inorg, nucl. Chem. 20, 211 (1961).