preparative procedures descrilied here, i t would be necessary to validate the entire set of procedures used b y direct comparison with the isotopic dilution analysis.
and W.11. Wallace for providing some of the biological samples. LITERATURE CITED
(1) Cotlove, E., “Standard Methods of ACKNOWLEDGMENT
The author thanks Sordica D. Green for skillful technical assistance, and J. L. Gamble, Jr., D. S. Horell, J. G. Parker,
Clinical Chemistry,” Seligson, D., ed., Vol. 3, pp. 81-92, -4cademic Press, Yew York and London, 1961. (2) Cotlove, E., - 4 s ~ CHEM. ~. 35, 95 (1963). (3) Cotlove, E., Hogben, C. A. M.,
“Mineral Metabolism,” Comar, C. L. and Bronner, F., eds., Vol. 2, pp. 109-73, Academic Press, Xew York and London, 1962. (4) Cotlove, E., &hi, H. N., C’lin. Chein. 7,285 (1961). ( 5 ) Cotlove, E., Trantham, H. V.,Bowman, R. L., J . Lab. Clin. M e d . 5 1 , 461 (1958). (6) Somogyi, XI., J . Bid. Chem. 86, 655 (1930). RECEIVEDfor review June 27, 1962. Accepted Xovember 11, 1962.
High Temperature Diffuse Reflectance Spectroscopy P. SMITH
WESLEY W. WENDLANDT, PRESTON H. FRANKE, Jr., and JAMES Deparfment of Chemistry, Texas Technological College, Lubbock, Tex.
b A high temperature diffuse reflectance spectra sample holder, capable of operation from ambient temperature to 500” C., in the 350- to 7 5 0 - m p wavelength region is described. The sample holder i s attached to the reflectance attachment of a Bausch & Lomb Spectronic 505 spectrophotometer. Operation of the sample holder is illustrated by the thermal deaquation of [Co(NH3)6H20] Cla and [Co(NH&H20] Brz. This new high temperature sample holder appears to offer a promising technique for the study of the effect of elevated temperatures on coordination and other inorganic compounds, paints and paint pigments, dyes, plastics, fabrics, and other materials.
-
D
REFLECTAXCE SpeCtroScopy, in the visible wavelength region of the spectrum, is a useful technique for the study of coordination compounds ( 2 , 4, 6, IO, 11) and other inorganic substances (1, 3, 5, 7-9, 14). Kormally, the reflectance spectra are obtained on the powdered crystalline samples, either in the pure state or diluted with a matrix substance, a t ambient or low temperatures. The spectra obtained by this technique show good correlation with solution absorption spectra and single crystal spectra (6, 6). This technique can give useful information about unstable compounds for which single crystal spectra would be difficult, if not impossible, to obtain. Also, the technique is potentially useful for studying surface phenomena ( 5 ) because i t is the surface layer which is measured by reflectance. I n connection with our studies in coordination chemistry, it was necessary t o obtain the diffuse reflectance spectra of certain cobalt(II1) complexes a t temperatures from ambient to about 500’ C. This technique is IFFIJSE
described and some further applications in analytical and inorganic chemistry are pointed out. EXPERIMENTAL
Spectrophotometer. A Bausch & Lomb Spectronic 505 ultraviolet a n d visible range spectrophotometer, equipped with a reflectance attachment, S o . 33-28-12, was employed. The high temperature sample holder is schematically illustrated in Figure 1. The main body of the holder was about 6.0 cm. in diameter b y 1.1 cm. thick and was machined from aluminum. The sample was contained in a circular indentation, 2.5 cm. in diameter by 0.1 cm. deep, machined on the external face of the cell. Two circular ridges were cut a t regular intervals on the indentation t o increase the surface area of the holder and to prevent the powdered sample from falling out of the holder when it is in a vertical position. The sample holder was heated by coils of Sichrome resistance wire wound spirally on an asbestos board and then ALUMINUM SbMHPLE
BLOCK-
qJ 4-h THERM ....
THERMAL SPACER
REFERENCE CELL
Figure 1 . Schematic diagram of the high temperature reflectance sample holder, thermal spacer, and reference sample holder
covered with a thin layer of asbestos paper. Enough wire to provide about 15 ohms of resistance was used. T h e temperature of the sample was detected b y a Chromel-Alumel thermocouple contained in a two-holed ceramic insulator tube 0.35 cm. in diameter. T h e thermocouple junction made contact with the aluminum block directly behind the sample indentation. T o prevent heat transfer from the sample holder t o the integrating sphere, a thermal spacer was constructed from a loop of 0.25-inch aluminum tubing and \vet shredded asbestos. After drying, the thermal spacer was glued to the sphere and the sample holder attached by a spring-loaded clip. The power supply employed has previously been described (12). Output from the thermocouple mas recorded on a Varian RIodel G-22 strip-chart recorder as shown in Figure 2 . Fullscale span on t h e recorder corresponded to a sample cell temperature of 500” C. The reference sample holder, Figure 1, 17-as 6niilar in dimensions to the sample holder except that i t mas unheated. Sample Preparation. Difficulties n e r e experienced when some of t h e pure samples mere heated in t h e sample holder. J l a n y of t h e samples qintered or fused when heated, t h u s altering t h e reflecting surface. T o prevent this, t h e samples were finely powdered. b y grinding in a mortar and pestle or a Kig-L-Bug. and t h e n diluted with a suitable matriv material quch a s previously ignited aluminum oxide, powdered potassium chloride, or potassium sulfate. .\ reference sample of the matrix, contained in a similar sample holder, was placed in the reference port of the integrating sphere by a spring-loaded clip. Procedure. About 1 gram of a 20% mixture of t h e cobalt coordination compound in finely powdered potassium sulfate was intimately ground together and then firmly packed i n t o t h e sample holder indentation. T h e exposed sample surface was made as smooth a s possible b y use of a steel spatula blade. T h e holder was then VOL. 35, NO. 1, JANUARY 1963
105
attached to t h e integrating sphere b y a spring-clip. An equivalent amount REFLECTANCE ATTACHMENT of the matrix material was packed into the reference sample holder and attached to the reference port. To observe the condition of the sample and reference RECORDER 0 ' JUNCTION materials after they were attached t o the sphere, the light ports were reI \ ( \ CELL moved and the surface observed visually. A small dental mirror was useful because it could be inserted easily through the light ports. 2 3 The cooling water for the thermal I 1 I spacer was turned on and the heating cycle of the cell begun. Sormally, a I I 5 " C. per minute heating rate was POWER SUPPLY employed but this could be varied by decreasing or increasing the output Figure 2. Schematic diagram of apparatus voltage from the power supply. The spectrum of the sample was scanned from 350 to 750 nip a t various temperature intervals. During the scanning complexes. The therniogravimetry, difwavelength limitation of the instruperiod, the temperature of the sample ferential thermal analysis, and kinetics ment, it could not be obtained. holder n-as held constant by turning The high temperature reflectance of these reactions have preiiously been off the motor drive of the power supply. Using the 600-mp range gears on the curves show very clearly the deaquation reported ( 1 3 ) . Because the reactants spectrophotometer, the complete specof the cobalt complexes. As this is a and products of the above reaction trum could be scanned in about 2 possess different colors, their reflectance rather simple reaction, no intermediate minutes, although this could be varied spectra are different and hence it should species were obtained, only the initial by adjustment of the scan speed conand final products. However, for more be possible to follow the thermal detrol. Best results were obtained by aquation by the changes in reflectance comples systems, intermediate comremoving the brake from the recorderspectra with temperature. pounds could also be detected. removing the 6CM6 electron tube, The changes in reflectance spectra of The nature of the sample surface is V-211. from the electronics rxmel. an extremely important factor in diffuse Preparation of Compleies. The [Co(KH~)~HzO]C13and [ Co(KH3)j[ C O ( S H ~ ) ~ H I Oand ] C ~[ ~C O ( S H ~ ) ~ H ~ O ]HzO]Br3 with temperature are given in reflectance spectroscopy ( 5 ) . Although Br3 were prepared and analyzed as no measurements were taken as to the Figures 3 and 4, respectively. prer-iously described ( I S ) . particle size of the sample-matrix misThe complex, [ C O ( K H ~HzO]C13, )~. at tures in this study, fairly reproducible 25' C., had a single reflectance band RESULTS AND DISCUSSION results were obtained. The peak maxiwith a band maximum at 490 mp. On mas could be obtained to i 5 mp, with heating, the band shifted to longer Use of the high temperature sample the present range gears, and could wavelengths, with a band maximum holder is illustrated by the thermal probably be improled upon by using 540 mp a t 160' C. a t deaquation of several [ C O ( K H ~ ) ~ H ~ O ] X , 150 Similarly. for [ C O ( K H ~ ) ~ H ~ Otwo ] B ~ ~ a, narrower scanning range-Le., (S= C1. Br) type complexes. These 600 mp. The instead of as i t was or 300 mp, distinct bands were observed compounds lose water, when heated, relative reflectance was more adversely heated. At ambient temperature, according to the reaction: affected with different sample prepara25' C., the band maximum was at 495 tions. Changes as great as 10% m r e mp, and shifted to longer wavelengths, observed. 565 mp, at 125"-l5Oo C. There apThe type of matrix material is an peared to be another band maximum important factor in high temperature forming the monoanionic substituted a t about 350 m p but because of the
I\ ~
I
........ .... WNH31,1$0
CI3-
C.IN%I,CI
160.
GI2
+
CdNH3&H;P B3-
m 750
650
A,
w
550
450
Figure 3. High temperature reflectance curves of [CO(NH&HzO]C13 (20%) in a KzS04 matrix Reference substance, KzSO4
106
ANALYTICAL CHEMISTRY
750
I
I
C d N ~ l S B r B r 2 i H20 I
650
Figure 4. High temperature reflectance [Co(NH&H20]Br3 (20%) in a KaS04 matrix Reference substance, KzSOd
I
1
450
curves
of
reflectance spectroscopy. The mat'rix may react, at elevated temperatures, to produce colored intermediates which reflect a t different wavelengths than the initial or final compounds. Or, the sample may absorb on the matrix material and change color as mas sholyn by mercury(I1) iodide on alumina (14). Perhaps the most useful aspect of the matrix was illustrated by Kortum ( 8 ) who showed that by using another sample of tlie matrix for a reference, the regular part of the reflectance spectra could be eliminated. I n this way the regular reflectance component is identical for both the sample and matrix mixture and for the matrix and hence only the pure diffuse reflectance spectrum is measured. High temperature diffuse reflectance spectroscopy is a useful technique for the study of tlie thermal dissociation of coordination nnd other colored inorganic compounds. The technique may be used to characterize the intermediate molecular and ionic species formed dur-
ing the thermal dissociation process as well as the terminal reaction products. I t is useful also for the study of various solid-state reactions in which colored intermediates or terminal products are formed. By use of isothermal sample holder conditions and measuring the change of reflectance with time, the kinetics of the reaction can possibly be determined. Other possible uses are determining both thermochromic transition temperatures for inorganic or organic compounds and the effect of elevated temperatures on the colors of paints and paint pigments, dyes, plastics, fabrics, and other materials.
( 2 ) Bostrup, O., Acta Cheni. Scand. 11,
1097 (1957). (3) Ibid., p. 745. (4) Chao, K. T., Opt. i Spekroskopiya 6, 181 (1959). (5) Griffiths, T. R., Lott, K . A. K., Symons, M. C. R., AXAL. C H m . 31, 1338 (1959). (6) Katzin, L. I., Gebert, E., J . .4m.Chem. SOC.75, 2830 (1953). ( 7 ) Kortum, G., Spectrochzm. '4cta 1957, Suppl. 534. ( 8 ) Kortum, G., Trans. Faraday Sac. 58, 1624 (1962). (9) blazza, L., Iandelli, A., Botti, E., Gazz. Chiin. Ital. 70, 57 (1940). (10) Moncuit, C., Compt. Rend. 249, 2526 (1959). i11) Pioria. T.. Suoncen Kernistilehti 31B, 337 (1958). 112) n'endlandt. W. \Y..J . Chein. Educ. 38, 571 (1961j. (13) Kendlandt, W. R.,Bear, J., J . Phys. Chem. 65, 1516 (1961). 114) Zeitlin. H.. Gol-a, €I., .Valure 183, 1041 (1959). \ -
ACKNOWLEDGMENT
The assistance of Warner Kendall in constructing the sample holder is gratefully acknowledged. LITERATURE CITED
(1) Billy, M.,Berton, A., Compt. Rend. 206, 1958 (1938).
RECEIVEDfor review August 17, 1962. Accepted Xovember 5 , 1962, Work partially supported by the L . S. Atomic E n e r u Commission through Contract KO,At-(40-1)-2482.
Determination of Substitution of Unconjugated Olefins from Pi Complexes with Tetracyanoethylene SIR: The direct qualitative and quantitative determination of unconjugated olefins Iiy electronic absorption spectrometry is limited because the bands of these chromophores appear in a region (< 200 mp) not accessible to many of the more common spectrophotomet,ers. Even when this region is instrument~allyattainable. the wavelengths characteristic of the various substitution patterns vary too little t o make unambiguous structural assignments (9. 8). This communication s h o w that mono-, di-, tri-, and tetrasubstituted unconjugated olefins may he differentiated by the spectra of their pi complexes with tetracyanoethylene (TCXE) (6). I n these spectra a band appears in or near the visible, whose position is strongly dependent on the degree of substitution at the double bond. Although Long and Neuzil ( 5 ) have utilized the pi complexes with iodine in a similar manner, improved differentiation can be obtained with T C S E . Further. the present method is more convenient than the tetranitromethane procedure of Heilbronner
(4).
EXPERIMENTAL
The spectra were determined in the usual fashion on a Cary Model 11 recording spectrophotometer utilizing 1-cm. quartz cells. The solutions were prepared as follows : Approximately 0.002 gram of tetracyanoethylene (Eastman) was dissolved in approximately 3 ml. of methylenechloride (Eastman). Enough olefin (Phillip's Pure Grade or Columbia) was added (about 0.25 ml.) until it was estimated from the color intensity that a satisfactory measurement could be obtained. The T C N E should be purified by sublimation. Generally, with olefins of a higher degree of substitution, more olefin was required for appropriate intensities. This observation is consistent with the postulate that increased substitution decreases the equilibrium constant of complex formation due to steric hindrance. Gaseous olefins (Phillips Research Grade) were liquified prior to use. Their solubilities at room temperature and atmospheric pressure were such that the desired intensities could be maintained unchanged for a number of hours. An alternative procedure which gives equivalent results involves the addition
of olefin t o a saturated methylene chloride solution of T C K E until the appropriate color intensity appears. The latter technique minimizes the introduction of impurities with the olefin, and also requires less olefin than the previously mentioned procedure. RESULTS AND DISCUSSION
The results of the present investigation are given in Tables I and 11. Some representative spectra are also shown in Figures 1, 2, and 3. These tables and figures indicate not only that structural assignments can be made with greater certainty than before, but that in some instances different olefin types can be detected in mixtures. The wavelength variation with substitution is -200 mp in contrast to-65 mp (6) for the iodine complexes and only -20 mp(2) for the olefins themselves. Further, because the colors of the T C N E complexes vary from yellow to blue with increasing substitution on the olefin, structure may be qualitatively assessed by eye. It is estimated that the data in VOL. 35, NO. 1, JANUARY 1963
107
