ELECTRICAL CONDUCTIVITY OF POTASSIUM THIOCYASATE
May, 1963 TABLE IV Temp., 'C.
149 175 203 245 266 289 318
Relative volatility
s.95 7.93 6.71 4.89 4.33 3.69 3.04
Density, g./cc.
0.00248 .00462 .00833 .0183 .0265 .0389 .0632
g. NHa(v) per I.(v)
per p.p.m. NHa(1)
2 . 2 x 10-6 3 . 7 x 10-6 5.6 X 9 . 0 x 10-6 11 x 10-5 14 X 10-5 19 x 10-6
Since the concentration of ammonia in the condensed steam was the quantity actually measured, it was preferable to calculate a value that did not involve a pressure (which would have required a gas law assumption). I n calculating these values, it has been assumed that the density of the water vapor over the ammonia solution
1i15
was equal t o the saturation pressure over pure water. This should be a good approximation since the liquid phase contained only 13 to 19 p.p.m. ammonia. I t should also be pointed out that the values in Table IV only apply to a liquid phase concentration in this range since it has been shown in the previous paragraphs that the ammonia distribution is concentration dependent. The increase in concentration of ammonia in the vapor phase as the temperature increases (for a given liquid phase concentration) is very different behavior from that of gases such as helium, nitrogen, oxygen, and xenon. All of the latter have less tendency t o be in the vapor phase as the temperature is raised in the range of 100 to 315".6 (6) J. M. Smith and D. 1 2 Katz, "Physical Behavior of the H-Oz-HtO System Under Pressure," ORNL-1069.
ELECTRICAL COXDUCTIVITY OF POTASSIUM THIOCYASATE BY JTJAN M. LOMELIN~ AND THEODORE J. KEU,BERT Department of Chemistry, Illinois Inststute of Technology, Chicago 16, Illinozs Received December 3, 196.9 The electrical conductivity of polycrystalline K S C S was studied as a function of temperature from room temperature to the melting poin t (175")using zone refined, analytical reagent grade, and impurity doped samples. Unless all traces of HzO Fere removed, conductivities a t low temperature were anomalously high. Log conductivity 11s. reciprocal temperature curves for carefully dehydrated samples showed two straight line portions with a sharp bend a t ca. 120". The activation energy for the conduction process in the high temperature (intrinsic) region is 2.13 e.v.; that for the low temperature (extrinsic) region is 1.30 e.v. Addition of 10-2% BaClz enhances the conductivity in the lorn temperature region, indicating that positive ion vacancieg play a role in the conduction process; addition of 10-270 NanS caused no change in conductivity. The implications of these observations are discussed and the conductivity behavior of KSCN is shoxn in relation to that of KCl and CsBr.
Some time ago we became curious to know whether KSCN by virtue of its lorn melting point (175') exhibited any unusual behavior with regard to its electrical conductivity. The work to be reported extends some previous conduct,ivity nieasurements by Plester, et aL2 X-ray diffraction studies by Klug3" have shown KSCN to have an orthorhombic unit cellocontaining 4 J$3CS with la$tice parameters: a = 6.66 A., b 6.635 A., c = 7.58 A. Analysis of the infrared spectrum of solid KSCN by Jones3 indicates that the S C W ion is linear and that the S-C azd S-C distances are approximately 1.17 and 1.61 A,, respectively. The arrangement of K + and SCX- ions in crystalline KSCN resembles the arrangement of ions in CsCl and CsBr. The SCN- ion lie in parallel planes, alternating with planes of K + ions. I n the anion planes, each SCNion is perpendicular t o its neighboring SCN- ions. A drawing depicting the crystal structure is given in Jones' pamper.3b Experimental =2
Conductivity Measuring Apparatus.-Preliminary tests indi.. cated that conductivities in the range 10-la to 10-5 mho would be encountered and that measuring currents would have to be kept smaller than ca. 10-7 amp. (a) Low conductivities (10-13 to 10-7 mho) were measured by observation of the current which flowed through the sample (1) Instituto Mexican0 de Investigaoiones Technologicas, Calsada Legaria 694, Mexico 10, D. F. Mexico. ( 2 ) D. W. Plester, S. E. Rogers, and A. R. Ubbelohde, Proe. R o y . Soc. (London), 235, 469 (1956). ," ( 3 ) (a) H. P. Klue, 2. Krist., 81, 214 (1938); (b) L. K. Jones, J . Chem. Phys., 25, 1069 (1956).
upon application of a known e.m.f. (1.5-7.5 v.). The current sensing instrument was! a Keithley Model 210 electrometer with a Keithley Model 2008 decade shunt. The working batteries and the necessary switches were housed in a shielded junction box which was provided with Teflon-insulated connectors and internal desiccant in order that the "no sample" conductivit,y be less than mho. In shielding leads t o the conductivity cell, care was taken to keep lead capacitances low so that the time constant of the circuit would not be disagreeably long. Measurements were made with current flow of each sign, and were averaged. ( b ) High ccnductivities (10-7 to 10-6 mho) were determined by matching the current through the sample with that through a standard variable resistance using a galvanometer to indicate amp./mm.; period, 3 sec). The operatequivalence (4.3 X ing potential (0.01-0.75 v.) was applied by means of a set of motor driven switches in a cycle of four pulses: two pulses alternating in sign applied to the sample and two pulses alternating in sign applied t o the variable resistance per cycle. The kind of switches and the switching circuit used were of the sort in which all thermal e.m.f.'s were opposed by presumably equal but opposite thermal e.m.f.'s. Conductivity Cells.-The typical conductivity cell envelope consisted of a (vertical) Pyrex glass tube (44 cm. long X 25 mm. 0.d.) having, approximately half way along its length, an inclined side arm for introduction of sample. The upper end of the cell fitted into a standard taper cap which was connected to EL vacuum line and into which were waxed three long glass tubes; two for platinum electrodes, one for a copper-constant thermocouple. The electrode aiurfaces (6 mm. diam. X 0.26 mm. thick) were oriented vertically with a spacing of ca. 7 mm. and were positioned ca. 3.5 cm. from the bottom of the cell envelope, which r a s normally filled t o a depth of ca. 9 cm. Sample Materials.-'The principal sample material waB J. T. Baker Chemical Co. Reagent Grade potassium thiocyanate, Lot 1125. Some measurements, however, were made with zone refined KSCN. Typical conditions of refinement were: ( a ) horizontal glass tube (45 cin. long X 25 mm. 0.d.) half filled with
Juss ill. LOMELIX ASD THEODORE J. NEUBERT
2.2
a4
2.6
-/ooo/
-
2.8
7-
5.0
32
Fig. 1.-Electrical conductivity (G in ohm1- cm.-l) of dry polycrystalline KSCN as a function of temperature: ( a ) run 27 (round points) on zone refined KSCX; ( b ) run 12 (triangular points) on stock bottle KSCK; ( c ) run 8 (square points) on material of stock bottle quality to which mole fraction of Na2S had been added. salt; (b) heattx speed, 4 cm./hr.; (c) width of melted zone, 20 mm.; ( d ) vacuum atmosphere, (3) 32 zone passes. Routine of Measurement.-In beginning a set of measurements, after the electrodes had been cleaned with HNOI and their alignment checked, sample was placed in the inclined sidearm of the cell and the system closed and evacuated. After a while the XSCX was melted by gently warming with a flame and permitted to run down into the electrode region where it was held as a liquid in vacuo a t ca. 180” for ca. 15 hr., i.e., until all traces of water had been removed. Following the dehydration operation, in order t o have homogeneity in grain size and composition, the molten salt was quenched by means of a water bath at room temperature. Only four-fifths of the salt was permitted t o freeze rapidly; enough liquid phase was left in order to provide by slower cooling sufficient material for filling the depressed central core which formed. Finally a heater furnace was put in place and the system was heated at ca. 165” for an hour or so. Conductivities were then measured, in most cases with decreasing temperatures. Calculation of Conductivity Values.-Specific conductivities G, ought to be computed from measured conductivities G, using the relation G, = G,(L/A)/(F), which in addition to the term describing the ratio of electrode separation to electrode area includes a further term ( F ) to take account of the “fringing field.’’ The ( L / A )term for the electrode geometry used is ca. 2.5 cm.-l; the ( F ) term calculated by relations due to Kirchhoff4 is of the order of 2.5-3.7 cm.-’. Since these two terms so nearly compensate one another, and in view of uncertainties arising from poly-. crystallinity of samples, it was decided to use the measured conductivities in lieu of specific conductivities. Bt low temperatures, measurod conductivities were corrected by subtracting the “no sample” conductivity of the apparatus. This correction ohm-’ cm. -l. was trivial for conductivities above
Experimental Results Figure 1 shows three sets of data: (a) run 27 (round (4) “American Institute of Physics Handbook,” McGraw-HdI Book Co., New York, N. Y., 1967, pp. 6-14.
Vol. 67
points) on zone refined KSCX, (b) run 12 (triangular points) on stock bottle KSCX, and (c) run 8 (square points) on material of stock bottle quality to which mole fraction WazS had been added. I n preparing the figure the data for the zone refined sample were taken as standard and the other curves superimposed by matching the high temperature linear portions. This was achieved by lowering the data for SF2 doped KSCN by 0.1 log unit and raising those for stock bottle material by 0.4 log unit. Such manipulation is presumed to be justified by the vagaries of polycrystalline samples. It is evident from Fig. 1 that the log G vs. 1000/T data for each of the three samples may be represented by two straight line segments. For zone refined material the high temperature line obeys the relation G = 3.1 X lo1*exp (-24,70O/T); the low temperature line obeys the relation G = 4.4 X lo7exp (- 15,00O/T). Conductivities in the high temperature region are expected to be intrinsic and independent of impurities, whereas conductivities in the low temperature region are expected to be impurity sensitive.6 Such is the case in alkali halide systems, where conductivities in the low remperature regions are enhanced roughly in proportion to the concentration of divalent cationic impurities. The fact that the zone refined data are lower than the other data in the low temperature region by 0.2 log unit suggested that the concentration of divalent cationic impurities has been decreased relative to stock bottle material. The data for S-2 doped KSCN indicate no change in conductivity as a result of adding ?;a& to the system. This may be explained in three ways: (a) The S-2 failed to be incorporated substitutionally either because of lack of solubility in KSCN or because of chemical reaction with some impurity. (b) The substitutionally incorporated S+ was bound in an immobile complex with the negative ion vacancy which accompanies its introduction into the crystal or with a divalent cationic impuritye6 (c) Free negative ion vacancies in KSCN are not very mobile. In order to be certain of the influence of divalent cation impurities the conductivity of Ba+2 doped KSCK was investigated. Doping was done in two ways: (1) by adding the requisite amount of BaClz in aqueous solution to solidified stock bottle KSCN in the coiiductivity cell and then heating, melting, and dehydrating in the manner already described, and (2) by adding to molten KSCN the requisite amount of a previously fused concentrated mixture of anhydrous KSCX and anhydrous BaClz which will be referred to as a “solid solution.” Figure 2 shows three sets of data relating to doped stock bottle KSCX: (a) run 13 (triangular points) containing 2 x 10-5 mole fraction BaClz added as “solid solution,” (b) run 14 (square points) containing mole fraction BaClz added as “solid solution” and (c) run 18 (circular points) containing mole fraction BaClz added ~ i aaqueous solution. Conductivities were measured with decreasing temperatures, except for run 13 in which measurements were made in both directions. The dotted portions of Fig. 2 reproduce the data for zone refined KSCN from Fig. 1, and in prepaTing Fig. 2 the plotted points were shifted (run 13 by +0.2 unit, run 14 by ( 5 ) A. B. Lidlard, “Encyclopedia of Physics,” Tol. XX, Spiinger Verlag, 1057, pp. 246-349. (6) H. W.bIorgan and P. A. Staats, J. A p p l . Phys., 33, 3G4 (1902).
May, 1963
ELECTRICAL CONDUCTIVITY OF POTASSIUM THIOCYANATE
$0.4 log unit, and run 18 by -0.05 log unit) to give agreement with the zone refined sample in the high temperature region. It is clear from Fig. 2 that doping with Ba+2enhances the conductivity of KSCN in the low temperature impurity sensitive region. Further, the mehhod of doping causes no discernable diff ereiices in behavior provided the drying is effective. As is the case with purer material (Fig. 1) the data are satisfactorily represented by two straight lines. The low temperature and mole fraction lines in Fig. 2 for 2 X Ba+2,however, are separated from one another by 0.3 log unit instead of the expected 0.7 long unit. Experiments were done a t other doping levels but the results are confusing. At lower Ba+2 ion concentrations the changes mere difficult to discern because of scattering of experimental points. At higher concentrations the enhancements of conductivity observed in the low temperature region were larger, but, although the samples had been dried as previously described, the general shape of the curves was such as to suggest that the drying operation had been ineffective. Traces of water have a strong influence on the electrical conductivity of polycrystalline KSCX’. For example, upon completion of run 18 (circular points of Fig. 2) a few drops of mater were added to the cell, the sample mas melted, held in vacuo for only 1 hr. instead of the usual 15hr., frozen, and quickly remeasured. As a result of the small amount of water residual in the sample the entire conductivity curve was raised above that shown in Fig. 2 . The slope in the high temperature region was approximately the same as before; the slope at low temperature was smaller by more than a factor of two and the transition between regions was very gradual making a resolution into two straight line segment difficult. These effects depend upon the amount of water present and are not limited to doped KSCN. Similar observations were made in other samples, both doped and pure.
Discussion A comparison of the electrical conductivity of KSCN with that of KCl and of CsBr is shown in Fig. 3. The KSCK data are for zone refined material; the KC1 data are for a sample of Harshaw Chemical Co. single crystal measured in this Laboratory in an experiment preliminary to other work; the CsBr curve has been taken from a recent paper by Lynch.7 Although conductivities of polycrystalline and single crystalline material are compared, early work by Phipps, et aZ.,8 showed that polycrystalline and single crystalline results were reasonably concordant. The gross aspects of the three sets of data in Fig. 3 are seen to be qualitatively similar. Apart from the displacement of the KSCN curve to lower temperature, there are three notable differences. (a) At the melting points, the conductivity of polycrystalline KSCN is about two orders of magnitude lower than that of KCl single crystal and three orders of magnitude lower than that of CsBr single crystal. (b) The activation energy for the conduction process in the high temperature region is 2.13 e.v. for KSCS, ca. 2.0 e.v. for KCl, and 1.29-1.44 e.v. for CsBr. (c) The activation energy for (7) D W.Lynch, Phys. R e t . , 118, 468 (1960). ( 8 ) T. E Phlpps, et al., J 4m. Chem S o c , 48, 112 (1920), SO, 2412 (1928); 81, 1331 (1929).
2.4
2.2
1l:li
2.8
2.6
-- / O O O / T
9.2
30
7
Fig. 2.-Electrical conductivity ( G in ohm-’ cm.-’ of Ba+2 doped dry polycrystalline KSCN as a function of temperature: mole fraction ( a ) run 13 (triangular points) containing 2 X BaC12 added as “solid solution”; (b) run 14 (square points) containing mole fraction BaCL added as “solid solution”; (e) mole fraction BaC12 added run 111 (circular points) containing oia aapeous solution. KC1
YI
c
I
I
CsBr 1
‘\
1.0
’
I. 4
--
KSCK I
I
I
I.8 /a00
I
2.2
I
I
2.6
I
11
3.0
/ T-
Fig. 3.-Comparison of the electrical conductivities (G in ohm-‘ cm. -l) of dry polycrystalline KSCN, single crystalline CsBr (curve taken from ref. 7 ) ,and single crystalline (Harshamr) KC1.
the conduction pyocess in the low temperature region is 1.30 c2.v. for KSCK, 0.77 e.v. for KC1, and 0.53 e.v. for CsBr. Plester, et al., report the activation energies to be 2.05 e.v. a t high temperature and ea. 0.3 e.v. a t low
1118
D. H A D ~ A. I , SOVAII, AND J. E. GORDON
temperature. Although the agreement a t high temperatures is satisfactory, the shape of their log G os. 1/ T curve and the very low value of 0.3 e.v. for the slope in the low temperature region indicate that their samples were not entirely free of mater contamination. I n the case of CsBr, which has a crystal structure similar to that of KSCN, Lynch' was able to conclude, on the basis of electrical conductivity and diffusion coefficient measurements, that electrical conductivity is ionic and probably proceeds via a vacancy mechanism. The diffusion coefficient measurements, however, indicated that both positive and negative ion vacancies were mobile. I n the case of KSCK, since the crystal structure resembles that of CsBr, it is perhaps possible that electrical conduction proceeds via a vacancy mechanism and that both positive and negative ion vacancies may have comparable transport numbers. The mobility of positive ion vacancies is demonstrated by the fact that the low temperature conductivity is enhanced by
Vol. 67
doping with Ba+2. At the moment, however, not enough is known about the KSCN system to come to any definite conclusion with regard to the details of the conduction process or the meaning to be ascribed to the energies, 2.13 and 1.30 e.v., calculated from the slopes of the straight line portions of the KSCN log G vs. 1/T curves. Diffusion coefficient and transport number measurement would be required in addition to further electrical conductivity measurements, and these would have to be carried out on a single crystalline zone refined material in an atmosphere completely devoid of water. Acknowledgment.-VC-e are grateful to the Atomic Energy Commission, Division of Research, Chemistry Branch, Contract No. AT(l1-1)-1044, which provided the apparatus and materials required in this investigation. J. M .L. also wishes to acknowledge a Bank of Mexico Fellowship which with a leave of absence from the Iiisituto Mexican0 de Investigaciones Technologicas enabled him to undertake the iiivestigation.
INFRARED SPECTRA OF, AND HYDROGEK BONDING IN, SORrlE ADDUCTS OF PHESOLS WITH THEIR PHENOXIDES AND OTHER OXYGEN BASES BY D. H A D ~ A. I , YOVAK, AXD J. E. GORDON The Chemical Institute Boris Kidrit, Ljubljana, Yugoslavia, and iUellon Institute, Pittsburgh 13, Pa. Received December 6 , 1962 Adducts of phenols with the corresponding phenoxides, some carboxylates, and with trimethylamine oxide have been prepared and their infrared spectra examined. Very strong hydrogen bonds occur in these adducts and may be classified into three different types: asymmetrical intermolecular, symmetrical intermolecular, and symmetiical intramolecular. Behavior of the hydroxylic bands of the bonded OH. . 0 groups as a function of the type of hydrogen bond is discussed.
It has been shown that acid salts of carboxylic acids of the general formula (RCOOH, RCOO-lIe+) contain very strong hydrogen bonds of various types joining the carboxylic and carboxylate g r o u p ~ . l - ~We were interested in compounds where similar hydrogen bonds, Le., between a hydroxylic group and a negatively charged oxygen atom, are expected. Some adducts of phenols with their phenoxides and with neutral salts of carboxylic acids have been reported in the earlier literature and their stoichiometric formulas have been but no systematic investigation of their infrared spectra or hydrogen bonding has been published. We have therefore prepared several adducts of phenols with their phenoxides of the general formula (ROH, RO-Me+), with potassium acetate and oxalate (ROH, R' COO-Me.+), and with trimethylamine oxide (ROH, (CHJ&O) and recorded their spectra in the solid state (1) J. C. Speakman, et al., J . Chsm. Soc., 3367 (1949); 185 (1951); 180 1954); 1151, 1164 (1961). (2) D. Hadii and A. Novak, "Infrared Spectra of, and Hydrogen Bonding in, Some Acid Salts of Carboxylic Bcids," University of Ljubljana, 1960. (3) R . Blinc and D. Hadii, Spectrochim. Acta, 16, 853 (1960). (4) R. Blinc, D. Hadti, and 4 . Novak, Z . Elektrochem., 64, 567 (1960). ( 5 ) J. Fritzsche, J . prakt. Chem., 1, 75, 268 (1858); Ann., 110, 150 (1859). (6) E. van Gorup-Besanez, Ann., 148, 129 (1867). (7) J. C. W. Fraser, Am. Chem. J . , SO, 309 (1903). (8) C. Gentsch, D.R.P. 166761, Chem. Zentr., I , 313 (1905). (9) J. Potratz, D.R.P. 237019, ibid., 11, 405 (1911). (10) R . F. Weinland and W.Denrel, Ber., 47, 737, 2244, 2990 (1914). (11) R. F. Weinland and G. Barlacher, ibid., 62, 148 (1919). (12) D. Goddard and A. E. Goddard, J . Chem. Soc., 54 (1922). (13) H. Meyer, Z. anal. Chem., 64, 72 (1924). (14) P. Pfeiffer. "Organische Molekiilverbindungen," Verlag von F.Enke, Stuttgnrt, 1927, p. 50.
and in solution in dimethyl sulfoxide (DMSO). The spectral features make it possible to divide the adducts into two groups. The spectra of the first group are characterized by the appearance of two distinct bands near 2500 and 1800 cm.-l, respectively, one of which is clearly attributable to the OH stretching vibration. The second group has no such bands; i n fact the only candidate for an OH stretching mode is the absorption observed for some of them near 1600 cm.-'. This and some other evidence leads us to the conclusion that symmetrical hydrogen bonds connect the phenoxide groups in these cases. From changes on dissolution it can be shown that some of these hydrogen bonds are intramolecular and others intermolecular, the symmetry of the latter being destroyed on dissolving the adduct, Assignments of the hydroxylic bands of the bonded OH. .O group have been made in most cases, and it is shoxn that the r-OH band increases in frequency with the strength of the hydrogen bond as estimated from the position of the v-OH band, but that 110 such trend is observed for 6-013 bands. The adducts may be divided according to their composition into phenol-phenoxide, phenol-carboxylate, and phenol-trimethylamine oxide groups. However, we shall follow the division according to the type of hydrogen bonding as demonstrated by the spectral features and the changes in state. Adducts with Asymmetrical Intermolecular Hydrogen Bonds.-This group comprises phenol-phenoxide adducts (potassium hydrogen di-(4-cyanophenoxide) and
