AKIRAKUBOYAMA
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gratefully acknowledge the use of the facilities of the Indiana University Research Computing Center. Thanks are also due N r . Ralph Christofferson for read-
[CONTRIBUTION FROM
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Vol. 86
ing some of the microphotometer traces and Mrs. Joanne Knight for her help in preparing the manuscript.
LABORATORY OF MOLECULAR STRUCTURE A N D SPECTRA, DEPARTMENT OF PHYSICS,THE UNIVERSITY OF CHICAGO, CHICAGO 37, ILL.]
Molecular Complexes and Their Spectra. XVII. The Iodine and the Chloranil Complexes with Thianthrene Analogs BY AKIRAKUBOYAMA' RECEIVED FEBRCARY 25, 1963 The thermodynamic properties of the iodine complexes with the thianthrene analogs I , 11, and I11 in solution were spectroscopically studied. Their charge transfer bands were also studied in comparison with the ones of the chloranil complexes with the thianthrene analogs. From the obtained results, i t is concluded t h a t the thianthrene analogs are essentially n-donors for iodine. Furthermore, referring to the energies of the charge transfer bands of the chloranil complexes, the appropriate integral values for the thianthrene analogs in the Huckel MO method were studied.
Introduction Many studies have hitherto been carried out with various charge-transfer type molecular complexes. But there have been only few works in which unsaturated heterocyclic compounds except for azines were used as donors. Recently, Lang* studied spectroscopically the iodine complexes with five-membered unsaturated heterocyclic compounds. Since thianthrene analogs have two heteroatoms, it is particularly interesting to study the charge transfer interaction between iodine and these molecules, the principal reason for undertaking the present study. In the present study, thianthrene (I), phenoxathiin (11),and diphenylene dioxide (111) were used as donors.
I
I1
I11
Experimental Materials.-Fisher certified iodine was resublimed under reduced pressure. Fisher spectrograde dichloromethane and carbon tetrachloride were dried with Drierite and distilled with a Podbielriiak column. Phillips 66 "pure" grade n-heptane was washed twice with concentrated sulfuric acid, then severa, times with water, dried with Drierite, and distilled with a Podbielniak column. Eastman Pure Chemicals of thianthrene, phenoxathiin, and chloranil were purified by recrystallization from n-heptane-ethanol (1: 1) mixture, n-heptane, and toluene, respectively ( m . p . 158.5-159.5" for thianthrene, 57-57.5" for phenoxathiin). Commercially available diphenylene dioxide was washed twice by dilute aqueous sodium hydroxide solution and, after drying, recrystallized repeatedly from n-heptane ( m . p . 119-120'). Method.-Absorption spectra were measured with a Beckman spectrophotometer Model DK-2 attached with a thermostated cell jacket. Square silica cells of 1-cm. path length were used. The molar extinction coefficients near the peaks of the charge transfer absorption bands3 and the equilibrium constants were obtained by the formula of Ketelaar, et aZ.+ In the cases of thianthrene and phenoxathiin, the concentrations of iodine were 4.6 5.3 X M and those of the donors 0.05 0.20 M . In the case of diphenylene dioxide the concentration of iodine was 3.7 X 10-3 A4 and those of the donors were 0.21 0.36 M . Since the tail of the long wave length absorption band of thianthrene and the C T band of its iodine complex considerably overlap with each other, especially in carbon tetrachloride, ET in the formulas of Ketelaar, et d.,? was obtained by dividing the difference between the absorption of thianthrene and t h a t of the complex solution by the iodine conccntration. The absorption
-
-
( 1 ) On leave of absence from the Government Chemical Industrial Research I n s t i t u t e , Tokyo, Shibuya-ku, T o k y o , Japan. (2) R.P. Lang, J . A m . Chem. Soc., 84, 4438 (19621. (3) In t h e following, t h e term "the charge transfer absorption banal.' is abbreviated as "the CT hand." (4) J. A. A. Ketelaar, C. van de Stolpe, A . Goudsmit, and W. Dzcubas, Rec I Y ~ u . chim.. 71, 1104 (1952).
intensities of thianthrene were always less than 7.570 those of the complex solutions. The C T bands of the complexes between chloranil and the thianthrene analogs were measured with equal volume mixtures of the chloranil and the thianthrene analogs solutions, both nearly saturated. The C T band shapes of the iodine and the chloranil complexes were obtained by subtracting the absorptions corresponding t o the added quantities of both components of the complexes from the absorptions of the complex solutions. The oscillator strengths of the C T bands were calculated by the approximate formula given by Tsubomura and Lang.6,0
Results Since the formula of Ketelaar, et ~ l . was , ~ satisfied in all cases, it is clear that the one-to-one charge transfer complexes were formed in the concentration ranges used in this work. Table I shows the equilibrium constants and the molar extinction coefficients obtained. In the calculation of the equilibrium constants, the molarity was used as the units of the concentrations of iodine and the donors. As shown in Table I , the obtained molar extinction coefficients of the complexes somewhat fluctuated over the temperature range adopted in the present study, but it is likely that in all cases the molar extinction coefficients are independent of temperature. Therefore, the equilibrium constants shown in Table I were evaluated using the average values of the molar extinction coefficients obtained a t various temperatures. As shown in Fig. I , good linearities between the logarithms of the equilibrium constants and the reciprocals of temperatures were obtained in all cases. The binding energies ( A H ) and the entropies of formation(AS) of the complexes are obtained from the slope and the intercept of the straight lines shown in Fig. 1. The thermodynamic constants and the features of the C T bands obtained are shown in Tables I1 and 111, respectively. The features of the C T bands of the chloranil complexes with the thianthrene analogs a t 20' are also shown in Table 111 for the purpose of comparison; Avand Avf in the sixth and the seventh columns of Table I11 are the differences in wave number between the peak positions of the CT bands and their half-height positions of the C T bands a t the longer and the shorter wave length sides, respectively, and the sums of these two values are the half-widths (Avl,a) of the C T bands which are shown in the eighth column. The peak positions of the C T bands and the C T band shapes of the iodine complexes with the thianthrene analogs are almost independent of temperature. In the last column the oscillator strengths of the C T bands, f-values, are ( 5 ) H. Tsubomura and R. P. Lang, J . Ant. Chem. S O L . 83, , 2085 (1961). W. B. Person, Ann. Rev. P h y s . Chem., 13, 107
(6) R . S. Mulliken and (1962).
IODINE AND CHLORANIL COMPLEXES WITH THIANTHRENES
Jan. 20, 1964
shown. I n the iodine-thianthrene complex, Av+ could not be obtained owing t o the overlap of the CT band with the absorption band of thianthrene. As in the chloranil-thianthrene complex the first and the second C T bands considerably overlap each other; both the apparent and the true peak positions of the C T bands are shown. Therefore, the peak positions of the C T band of the iodine-thianthrene complex in Table I11 are thought to be the apparent ones. Thermodynamic and spectroscopic data on the iodine complexes with the aliphatic thioethers and ethers by other authors are shown in Table IV for the purpose of comparison. The ionization potentials of electron donors can be evaluated from the energies of the C T bands of the chloranil complexes in carbon tetrachloride by the aid of the Briegleb-Czekalla f o r m ~ l a . The ~ actual evaluated values are 7.9, 7.6, and 7.7 e.v. for thianthrene, phenoxathiin, and diphenylene dioxide, respectively.
0.3;
( 21 ) Thionthrene Thianthrene (CH,CI,) (CC14]
0.2
( 4 ) Phenoxathiin (CH,CI,)
( 3 1 Phenoxathiin [
165
/
CC14)
/-i
-0.2c
3.3
3.4
(l/T)
Fig. 1.-The
3.5
x
3.6
10'.
plot of log K O vs. 1 / T for the iodine complexes with the thianthrene analogs.
Discussion
TABLE I
As seen in Tables I11 and IV, the energies of the CT EQUILIBRIUM CONSTANTS ASD MOLAR EXTINCTION COEFFICIENTS bands of the iodine complexes with the thianthrene OF THE IODINECOMPLEXES WITH THE THIANTHRENE ANALOGS analogs are nearly equal to each other and far smaller than the ones of the iodine complexes with the ali--c, 1. mole-' cm.-l-Temp., -Kc, 1. mole-'Av. 375 mp 380 mp 385 mp OC. 375 mp 380 mp 385 mp phatic thioethers and ethers. These facts show t h a t in the thianthrene analogs the a-electronic conjugation ( a ) Donor, thianthrene; solvent, carbon tetrachloride occurs to a considerable extent. In Tables I1 and 111, 1 . 6 2.11 2.12 2.115 13100 12400 it is noticeable that the binding energies and the in1 0 . 0 1 . 7 2 1 . 7 3 1 . 7 2 1 . 7 2 12750 12200 11100 tensities of the C T bands of the iodine complexes with 2 0 . 0 1 . 3 4 1 . 3 5 1 . 3 3 1 . 3 4 14400 13700 13450 thianthrene and phenoxathiin are nearly equal to each 3 1 . 4 1 . 0 5 1 . 0 6 1 . 0 5 1 . 0 5 13200 13000 12400 other, whereas the equilibrium constant and the inAv. 13350 12800 12300 tensity of the C T band of the iodine-diphenylene di( b ) Donor, thianthrene; solvent, dichloromethane oxide complex are considerably smaller than the ones of the iodine complexes with thianthrene and phenox1 . 9 1 . 5 6 1 . 6 9 1 . 6 8 1 . 6 4 12200 10050 10200 athiin. These marked facts are unambiguously related 1 0 . 5 1 . 3 0 1 . 3 7 1 . 3 8 1 . 3 5 12200 12200 11400 to the absence of a sulfur atom in diphenylene dioxide. 2 0 . 0 1 . 0 5 1.11 1.11 1 . 0 9 12400 12400 12150 On the other hand, as seen in Table IV, the equilibrium Av. 12300 11550 11250 constants, the binding energies, and the intensities of (c) Donor, phenoxathiin; solvent, carbon tetrachloride the C T bands of the iodine complexes with the ali3110 mp 395 mp 400 mp Av. 390 mp 395 m p 400 mw phatic thioethers (diethyl sulfide, 1,4-dithiane, and 1,41 . 8 1 . 5 6 5 1 . 5 0 1 . 5 5 1 . 5 4 13400 14950 13850 thiodioxane) are far larger than the iodine complexes 10.0 1 . 2 6 1.225 1 . 2 4 5 1 . 2 4 14250 14900 15100 with the corresponding aliphatic ethers (diethyl ether 2 0 . 5 0 . 9 6 0 . 9 3 0 . 9 5 0 . 9 5 14100 14600 13950 and 1,4-dioxane), respectively. It is known that 12200 13400 13700 31.0 0.76 0 . 7 3 0.74 0.74 aliphatic thioethers and ethers are n-donors for iodine and in the iodine complexes with 1,4-dithiane analogs Av. 13900 14500 14150 in solution the iodine molecule coordinates one of two ( d ) Donor phenoxathiin; solvent, dichloromethane heteroatoms of 1,4-dithiane analogs. From these 395 mp 400 mp 405 mp Av. 395 mu 400 mp 405 mn facts, it is concluded that the thianthrene analogs are 1 . 1 1 . 2 2 5 1 . 2 2 1 . 1 6 1.205 14000 14500 15500 essentially n-donors for iodine like aliphatic thioethers 5 . 7 1 . 0 7 1 . 0 7 5 1 . 0 2 1 . 0 5 5 14200 13800 15300 and ethers, and the iodine molecule coordinates one 1 0 . 0 0 . 9 8 0 . 9 7 5 0.935 0.965 13800 14700 15000 of the two heteroatoms of the thianthrene analogs. 15.0 .84 .84 .81 . 8 3 15200 14250 14250 The equilibrium constants and the binding energies .75 .72 20.0 .75 .74 15500 16000 16000 of the iodine complexes with thianthrene and phenoxaAv. 14550 14650 15200 thiin are smaller than those of the iodine complexes with the aliphatic thioethers, and the equilibrium con( e ) Donor, diphenylene dioxide; solvent, carbon tetrachloride stant of the iodine-diphenylene dioxide complex is 2 0 . 1 0 . 3 0 0 . 2 5 0 . 2 7 5 0.275 3030 3580 3230 smaller than those of the iodine complexes with the aliphatic ethers. In the iodine complexes with n-donors, the TABLE I1 strength of the charge transfer interaction may be sensiTHERMODYNAMIC CONSTANTS OF THE IODINE COMPLEXES WITH tive to the lone-pair orbital hybridization of the heteroTHE THIANTHRENE ANALOGS atoms in the donors, which depends upon the bond angles - AHO of the heteroatoms. The bond angles of the sulfur atoms f0.1, -ASc of thianthrene, phenoxathiin, and 1,4-dithiane are kcal./ rt0.5, Kc, looo,* 92-94°,9 and 990j10 respectively. Therefore, Donors Solvents l./mole mole e.u. it is thought that the lone-pair orbital hybridizations1' Thianthrene CCI, 1.34 3.82 12.4 of the sulfur atoms in thianthrene and 1,4-dithiane are Thianthrene CHzClz 1.09 3.71 12.5 ZOO,
Phenoxathiin Phenoxathiin Diphenylene dioxide
cclp CHzClz CClr
0.95 .74 .27
4.12 4.12
(7) G. Briegleb a n d J. Czekalla, Z . Elcktrochem., 63, 6 (1959).
14.3 14.6
(8) H. Lynton and E. G. Cox, J . Chem. Soc., 488 (1966); I. Rowe and B. P o s t , Acta C ~ y s l . 11, , 372 (1958). (9) S. Hosoya. Dissertation, University of Wales, 1958, Aclo Cry.rt., 16, 310 (1963). (10) R. E. Marsh, ibid., 8, 91 (1955). (11) R . S. Mulliken, J . A m . Chem. SOL.,7 7 , 887 (1955).
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Vol. 86
AKIRAKUBOYAMA THEFEATURES OF
Acceptors
Iodine
Chloranil
THE
CT BANDSOF
THE
Donors
Solventsa
Thianthrene Thianthrene Phenoxathiin Phenoxathiin Phenoxathiin Diphenylene dioxide Diphenylene dioxide
CCl4 CHzClz CHzClz C7Hl6 CCla CHzClz
Thianthrene
cc14
TABLE I11 IODINE AND THE CHLORANIL COMPLEXES WITH Amax, m r
emax
371 375 396 400 390 399.5 -394
cc1,
13350 12300 14200 14800 3280
-520( 515)b -418( 420)* Thianthrene CHiClz -525 Phenoxathiin CClr 580
