Complexes of silver perchlorate, antimony trichloride and mercuric chloride with dioxane and benzene

Spectrocllimtca

Act& 1950, No..Q, pp.‘726 to 712. Pergnmon

Press Ltd.

Printed

in Nortllern

Ireland

Complexes of silver perchlorate, antimony trichloride and mercuric chloride with dioxane and benzene In&red spectra and thermodynamics L. W. DAASCE U.S.

Naval

Research

Laboratory,

(Received

29 Januufy

Washington

25, D.C.

1959)

&&act-The formation of complexes between inorganic salts and organic solvents with the following compositions have been observed: SbCl-.&C&H,; AgC10,.3, 2, $, and lC,H,; SbCls.3, 3, 1 and $C,H,O,; HgCl,.B and lC,H,O,; AgC10,.3 and lC,H,O,. The infrared spectra from 650 to 5000 cm-l of most of these complexes in the solid state are presented. Also included are the spectra of solutions of the inorganic salt in an excess of organic solvent. The differences between the spectra of the complexes and a summation of the spectra of their component, parts are discussed in terms of selection rules. The vapor pressures above the complexes are given as a function of temperature and from these data the thermodynamic functions AH, AF” ancl AS0 for the dissociation reactions are calculated. The heats of dissociation range from -7920 to - 15,300 Cal/mole of organic constituent.

Introduction THE nature of intermolecular forces can be investigated by the effects of these forces on the vibrational spectra of the molecules. In addition, it is sometimes possible to obtain from the spectra information on the structure of the intermolecular compounds which may be formed. Certain types of intermolecular bonds as, for example, the hydrogen bond have been extensively investigated by this means. Some information is also available on less specific solute-solvent interactions. Usually, owing to the low stability of the aompounds formed in this latter type of interaction, the investigations have been carried out in solution, although recent spectroscopic studies have reported such interactions taking place in gases [l] and powdered mixtures of solids when they are compressed [2]. A few inorganic salts are remarkably soluble in certain organic solvents, presumably due to solute-solvent interaction. In many cases stable complexes can be isolated as pure solids. On the basis of these rather unusual protierties alone, the complexes are worthy of investigation. This report deals with several of these inorganic salt-organic solvent complexes. It presents their infrared spectra in solution and in the solid state, their combining proportions in the solid state and the heats of the dissociation reactions calculated from measurements of the changes in vapor pressure with temperature. Information on the symmetry of the complexes is d&cussed wherever possible. [l] [2]

J. A. KJSTELAU, Rec. Tfav. Chk 75, 857 (1957). A. W. BAKER, J. Phys. Chent. 61, 450 (1957).

Complexes

of silver

perchlorate,

antimony

trichloride

and

mercuric

chloride

Materials and procedure Preparation

of complexes

All chemicals used in this work were reagent grade. The antimony trichloride was distilled in order to eliminate adsorbed water, and the silver perchlorate was heated to 100°C in a vacuum oven for 12 hr to remove ws$er present as the monohydrate. The dioxane was stored over anhydrous calcium sulfate and the benzene over sodium. However, subsequent manipulations were performed in an atmosphere of 40 per cent relative humidity and therefore the preparations may not have

Fig.

1. Indication

of complex

formation

in rate

of removal

of organic

component.

been completely water free. The complexes are not as hygroscopic as the parent salts and the spectra give no indication that water was incorporated into any of the solid complexes. All the complexes were formed by the simple dissolution of the inorganic salt in an excess of the organic component, except in the case of silver perchlorate and dioxane, where acetone was added according to the procedure of COMYNS and LUCAS [3]. Gradual removal of the excess organic solvent in a vacuum desiccator produced the solid complexes. The rate of removal of the organic component was observed by weighing the sample at regular intervals. Changes in the rate of removal or abrupt drops in vapor pressure indicated where complexes were formed (Fig. 1). I$awd

measurements

The infrared spectra were obtained on a Perkin-Elmer Model 21 spectrophotometer equipped with a sodium chloride prism. Silver chloride plates were used to support .the solid silver perchlorate complexes and their solutions since these complexes attack the sodium chloride plates normally used for this purpose. Vapour pressure measurements on the gaseous organic component above the [3]

A. E. COMUWS

and H. J.

LUCAS, J.

A9u.

Chem.

Sot.

727

70,

1019

(1954).

L. W. DAASCH

solid complex were obtained at various temperatures from intensity measurements on the absorption bands at 1258 cm -l and 581 cm-l for dioxane and 672 cm-l for benzene. During these measurements a flask containing the solid complex was This flask surrounded by a bath whose temperature could be controlled to fl”C. was connected to a conventional 10 cm gas cell and a vacuum pump.

Discussion Antimony trichloride-benzene complex In this work only one molecular ratio was found for the solid complex and it agrees with that given in the original report of the preparation of the complex MELCHIORE [5] has reported that in a solution of SbCl, [4], that is, 2 SbCl,.C,H,. in benzene both 1 : 1 and 2 : 1 complexes are present. ASHKANAZI et al. [6] and RASKIN [7, 81 have reported on the Raman spectrum of a solution of antimony trichloride in benzene. The former authors observed two new lines at 477 cm-l and 1236 cm-l, which they attribute to the bending and stretching vibrations of the bond between antimony and benzene. Both investigators noted small shifts of 3-30 cm-1 in the frequencies associated with the halide ‘molecule in the region between 134 and 360 cm-l. Certain vibrations of benzene which are inactive in infrared absorption appear in its spectrum of the liquid due to a breakdown in the selection rules for that phase. Some of these “inactive” bands are further intensified or perhaps newly appear in the spectra of the complexes investigated here. An analysis of this data on the basis of selection rules has led [9] to a predicted symmetry of C,, for the SbCl,-benzene complex in solution. The solid state spectrum shows more clearly than the solution the inactive benzene frequencies (see Fig. 2), for example, three overlapping absorption bands at 970, 987 and 990 cm-l and intensification of the adsorption around 100s cm-l, 1142 cm-l, 1308 cm-l and 1596 cm-l. From a summary of the data given in Table 1, one would choose the selection rules for C,, as the best fit to the experimental observations on the solid state. In many respects the changes in the spectrum of pure benzene when it is solidified [lo] are similar to those observed here when benzene is complexed with SbC1, and it is significant that in the case of pure benzene the changes can be Confidence explained on the basis of a known site symmetry for solid benzene [ll]. in the selection rule method for determining the site symmetry in the complex is thereby increased. With this data alone, the structures one might postulate to fulfill these symmetries are in all likelihood not exclusive, but it is perhaps of interest that such symmetries can be obtained by placing the antimony trichloride pyramids directly over and under the center of the benzene ring for C,, symmetry and between the two benzene rings for C,, symmetry as shown in Fig. 3. 41 B. N. IYIEPT~EUTI~N,

Zhur.

Rum.

Fiz.-Khim.

Obsohestva

45, 395 (1911).

51 J. 5. MF,LOHOIRE, Dissertation Abst~. 17, 1911 (1967). 61 M.S.ASBXANAZI,P.U.K~RNOSOVA~~V.S.F~KELS~~, J.Phys.Chem.(U.S.S.R.)8,438 T] SE. SH. RASKIN, Doklady AM. Nauk S.S.S.R. 100,485 (1955). ,8] SH. SH. RASKIN, Opticu i Spektroskopiya 1, 516 (1956). 91 L. W. DAASCH, J. Chem. Phys. 28, 1005 (1958). 0] S. ZWERDLINO mdR. S.HALFORD, J.Chem. Phys.22, 2221(1955). l]

E. G. COX, J. Am.

Chem.

Sot. A

135,491

(1932).

728

(1936).

Complexes

of silver

perchlorate,

antimony

trichloride

and mercuric

chlorida

L. W. DAASCR

Sb

Cl Cl 0 Sb

Cl

CW Fig. lines

Table

3. Possible structure of %bCl,.C,H, indicat.e where unit cell edges might

1. Infrared

activitv

of the

fundamentals

D3horl + o* O&K 1”

::"o:

B 2”

of benzene

C,, symmetry. to give correct

Lmder

various

(Note: molecular

svrnmetrv

Symnetry

Vibrntlon clnsa

47 $0

with C,, and be placed in order

-

-

a _-

-

-a

1306 1141

conditions Experimental obscrvntion

SbCl&H, Solution

c SD

-

dotted ratio.)

-

-

n

-

a

a a

:-

+

l *

cm&es

-f :

850 1172

1590 970

+ 0 * ** a -

-

-

iOi

a

-

--

n

900

n

-

--

a

-

n R

Intensity in complex stronger than in liquid benzene. No observable increase in intensity. Two shoulders present on the high frequency side of the 982 cm-1 absorption. Absorption band not observed in either pure benzene or in complex. Active in infrared spectrum. Inactive in infrared spectrum.

730

-

l *

+*

Complexes

of silver

Silver perchlorate-benzene

perchlomte,

antimony

trichloride

and marauric

chloride

complex

The present experiments on the molecular ratios of this combination indicate that the situation is not simple. A graph following the rate at which benzene is removed from a mixture of silver perchlorate and benzene always has an abrupt : 1 molecular ratio [12] but several other less prominent change corresponding to a 1 breaks in the curve were observed although not in a reproducible manner. These occurred at the ratios. 1 : 3, 1 : 2 and 3 : 4 or 2 : 3. The infrared spectrum of silver perchlorate is shown in Fig. 4(a). The only strong infrared active vibration in the 650-5000 cm-l region which is due to the is allowed to absorb perchlorate ion occurs at ~1060 cm-l. If silver perchlorate water the absorption broadens but no new bands appear. The only other fundamental vibration of the perchlorate ion with a frequency in the 670 to 5000 cm-l range is the Raman active symmetric, stretching mode of the Cl-0 bond which The spectrum of a solid silver perchloratehas a frequency of about 930 cm-l. benzene complex is also given in Fig. 4(a). The solid sample can be prepared by flushing dry nitrogen over a film of the benzene solution of silver perchlorate. Since several molecular ratios are possible we hesitate to be definite on the composition for this spectrum. The spectrum given in 4(a) is usually obtained if one regenerates the complex by passing nitrogen saturated with benzene over a sample of silver perchlorate which has been newly formed from a solution of the complex by flushmg with dry nitrogen until all the benzene has been removed. For this reason Fig. 4(a) is believed to be that of the 1 : 1 complex. At times samples were obtained in which the relative intensity of some of the absorption bands was different from that given in Fig. 4(a). For example the doublet at 735 cm-l, 720 cm-l is found with either component being the stronger. Also, the shoulder at 1150 cm-l sometimes attained moderate strength and emerged from the strong band at 1100 cm-l as a very distinct band. These changes are believed to .be spurious occurrences of polymorphic crystal structures or complexes of different molecular ratio but the conditions under which they appear have not been standardized. Two points should be emphasized. (1) Absorption which can be ascribed to benzene in the spectrum of the solid complex is, with the exception of the 1400 cm-l and 3100 cm-l bands, very weak. Indeed it would be difficult to identify the organic component. (2) With the additional exception of what is certainly a perchlorate ion fundamental in one of the two strong adsorptions at 1030 cm-1 and 1100 cm-l and the possibility of an Ynactive” perchlorate adsorption at 930 cm-l, the rest of the spectrum is not common to any of the possible c,omponents ef the co.mplex. Several reasons can be proposed for the differences between the spectrum of the complex and.the summation of the spectra of its component parts. (a) The silver perchlorate-benzene complex may be a different kind of complex from that of antimony trichloride and benzene in the sense that the bonding between the components may be different. The silver ion is supposedly the unifying principle in the structure of the silver perchlorate-benzene complex. This situation has been indicated by recent X-ray diffraction studies of the complex [l3] which show [12] A. E. HILL, J. Am. ChemSoc. 1131 H. G. SMITE 8nd R. E. RUNDLE,

44, 1103 (1922). J. AWL Chem.

Sm.

731

80, 5075

(1953).

L. W. DMSCR

mx -5% E 8

-

732

I

Complexes

of silver

perchlorate,

antimony

triohloride

and mercuric

chloride

L. W. DAASCH

that the solid complex has the silver atoms above two of the carbon-carbon bonds of the benzene ring and the bonding between the molecules is therefore assumed The bonding in the antimony trichlorideto be primarily through this atom. benzene complex may be more strictly between molecules. In’terms of the overlap of orbitals, in silver perchloratebenzene the overlap is between an atomic orbital and a molecular orbital while for antimony trichloride and benzene it is between I molecular orbit&. (b) The interaction between the component parts may have become so strong that vibrations of the components are submerged in what should be considered vibrations of the complex as a whole. Again X-ray diffraction data suggest this explanation because the interaction is strong enough to change the carbon-carbon bond distances in the benzene ring. (c) The perchlorate vibrational frequencies may interact with the benzene vibrations sufficiently to alter the spectrum of both components. In regard to the symmetry of the complex it should be noted that even though the complex is of low symmetry (as shown by the X-ray work) its spectrum still has relatively few absorption bands. This implies that the symmetry of the complex may still be quite high in terms of selection rules for the appearance of infrared absorption as, for example, is found in the symmetry C,,&. The spectra of solutions of silver perchlorate in benzene are also different from a summation of the spectra of the component parts. If water is present as a third component some additional rather striking changes occur in the intensity and position of the bands above 1300 cm-l (Fig. 4(b). The decrease in intensity of the bands at 1538, 2600, 1400, 1825 and 1970 cm-l when water is present and the definite broadening and shifting of the latter three indicate that the-water substantially effects the vibrations of the benzene ring. No further interpretation of these effects in terms of the actual mode of action of water can be given at this time. It perhaps should be mentioned that it is believed to be improbable that a small amount of water, which might be absorbed by these samples during their preparation, is responsible for the new absorption bands in the spectrum of the solid complex or for the spurious intensity changes referred to in the above discussion. Antimony

trichloride-dioxane

Vapor pressure measurements of dioxane indicate that there are four molecular ratios for this combination: 1 : 2, 2 : 3, 1 : 1 and 3 : 2. KELLY and MCCUSKER [l4] have reported finding the Srst two molecular ratios in their preparative experiments but made no mention of the last two. The compound with 3 : 2 molecular ratio sublimed into the cooler parts of the flask during the vapor pressure measurements. Attempts were made to obtain the spectrum of this complex in the gaseous state by completely surrounding a cell containing the solid complex with an oven. The only identifiable component in the gas phase was dioxane. The spectra of dioxane, a solution of antimony trichloride in dioxane, and a solid complex of antimony trichloride and dioxane are shown in Fig. 5. The various molecular [la] C. J.~~~P.A.McCUSKE~.J.

Am.Chem.Soc. 65, 1307 (1043). 734

Complexes

of silver

perchlor&e,

antimony

trichloride

and mercuric

chloride

L. W. DAASCE

ratios all give similar spectra. The only difference noted was the greater intensity of the band at 856 cm-l relative to the 865 cm-l band in the 1 : 1 and 3 : 2 complexes. A change in the symmetry of dioxane by the crystal field or the potential field in solution from its chair form (a,,) to the symmetrical (C,,) or asymmetrical (C,) boat form should produce, in addition to shifts in the frequency of many absorption bands already present, at least nine new active infrared absorptions. Unfortunately a few of these new frequencies are already overlapped by absorption from dioxane of C,, symmetry [l5] which makes the symmetry distinction less favorable. However, since there is much similarity between the spectra of the solid complexes or their solutions in dioxane and the spectrum of dioxane itself, and since only one new adsorption band (835 cm-l) appears in the solution and possibly three new peaks (all in the 800-900 cm-l region) in the solid complex, it would seem that the infrared data does not support either of the boat forms for the dioxane molecule in the complex. Incidentally, some studies on the infrared spectrum of a titanium tetrabromidedioxane complex [16] reported that the C-O-C ring stretching frequency (at 1122 cm-1 in dioxane) is absent in the spectrum of the complex and this was taken as evidence that the ether oxygens are involved in the bonding with titanium tetrabromide. The present work indicates that the C-O-C absorption is present in the solid complexes but is slightly shifted to lower frequencies as are several other bands (1082, 1045 cm-l). This is not to say that the bonding between the inorganic salts and dioxane is not through the ether oxygen, for in all likelihood such is the case. ’ Mercuric chloride-dioxane The preparation of complexes of mercuric chloride and dioxane with the molecular ratios 1 : 2 and 1 : 1 along with the vapor pressure measurements for the 1 : 1 complex were reported in 1935 [17]. Indications of additional molecular ratios of 3 : 4 or 2 : 3 were found in the present study. The recent infrared and Raman work by TARTE and LAURENT [lS] dealt only with the complex of 1 : 1 molecular ratio. The present infrared spectrum of that complex is in agreement with their results. Note in Fig. 6 that the difference between the spectra of the 1 : 1 and 1 : 2 complexes is the absence of bands at 878 cm-l and 1042 cm-l in the 1 : 1 com$lex. Silver perchlorate-dioxane

complexes

TWO complexes of silver perchlorate and dioxane with 1 : 3 and 1 : 1 were prepared. This is the only case where inorganic salt in the organic constituent is so low that a acetone) has to be used [3]. Since both dioxane and acetone with silver perchlorate, it is fortunate that the vapor pressure

molecular ratios of the solubility of the mixed solvent (with [19] form complexes of the acetone above

[I51 F.E.MALEERBE mdH. J. BERNSTEIN,.~. Am.Chem.Soc.74,4408 (1952). [16] R. F. ROLSTEN and H. H. SISLER, J. Am. Chem. SOC. 79, 1819 (1957). 1171J. L. ~~s~w,A.C. COPE, N.FWDLESTE~~~~R.ROGAN,J. Am.Chent.S0~.6Q,2308(1938). [NJ P. TARTE and P. A. LAURENT, BuKSOC. china. PVWLW 24, 403 (1957). [191 A.D. E.Pu~mvmd J.McC.Pouoc~, Tm~~.i%m&ySoc.!j4,11 (1958).

736

Complexes

of silver

perchlorate,

antimony

trichloride

and merouric

chloride

L. W. DAASX

the mixture of the complexes is considerably higher than that of dioxane so that acetone is completely eliminated before much of the dioxane is lost. One can follow the elimination of acetone by the carbonyl absorption band. Due to the low solubility of the complex in dioxane only the infrared spectrum of the solid state is shown in Fig. 7. Furthermore, the spectra of the complexes with the two molecular ratios are so similar that only one spectrum is presented. It is surprising, in view of the results for the silver perchlorate-benzene complex, to find that in the silver perchlorat&lioxane complex the absorption bands of the organic component This seemingly limits the generality are so little affected by complex formation. of one of the explanations regarding a different type of bonding for the silver perchlorate complexes. Table

2. Frequencies

of absorption of inorganic

bands in 800-900 cm-l salt-dioxane complexes

Complex

Frequency

%H*%

882 892 889, 878 890, 880 887

2SbCl,.C,H,O, HgC1,.2C,H,0a AgClO,.C,H,O, TiBr,.C,HsO, * Taken from

article

by R. F. ROLSTER

of the spectra

(cm-l)

870 865, 862, 870, 852, and

region

856, 852, 822 . 855 858 833*

H. H. SISLER [16].

The splitting of the dioxane bands in the 800-900 cm-l region is again observed in these complexes and as can be seen from Table 2 this splitting seems to be a general characteristic of the spectra of the solid complexes between inorganic salts and dioxane and can also be seen in the infrared spectrum of dioxane in the solid state [15]. The additional absorption is therefore believed to originate in the dioxane molecule and requires some explanation which is generally applicable to all these complexes. It seems very likely that in the solid state the crystalline field is imposing slight deformations on the dioxane to produce symmetries lower than C,. X-ray data on the 1 : 1 complex of mercuric chloride and dioxane [20] gives a space group symmetry of Pi under which only sites of Ci symmetry are available for both the mercuric chloride and dioxane molecules. If this symmetry is imposed on dioxane no additional vibrations would become active in the infrared or Raman spectrum. However, small shifts in frequency of active absorptions could take place and the possibility of Fermi resonance could explain the splittings, since under Ci symmetry the infrared active vibrations of dioxane in classes A, and B, would become the same class (A,). Vapor pressures and thermodynamic results

Graphs showing, the change in vapor pressure with temperature the complexes are given in Fig. 8. In those cases where loss-in-weight [20]

0. HASSEL

and

J. HVOSLEF,

Ackc Chem.

Scund.

8, 1953 (1954).

738

for most of experiments

Complexes

of silver

perchlorat+,

antimony

$richloride

and

merauric

chloride

L. W. DAASCE

DATA FDR DETERMINATION OF TKWC t24WnmES

Fig.

S. Change

in vapor

pressure

with

temperature

for the complexes.

indicated that complexes with several molecular ratios were formed, the measured vapor pressures are believed to be the equilibrium pressures for the pairs of complexes given in the reactions listed in Table 3. The free energy changes (APO), entropy changes (AS’) and the heats of dissociation (AH) for these reactions were calculated from the data in Fig. 8, and the results are given in Table 3. Wherever there is a large drop in pressure between successive reactions, as indicated by the temperature at which the pressure is 1 mm (see Table 3), there is a corresponding large increase in the free energy change. There is no correlation between the size of the thermodynamic quantities and the spectral effects previously discussed. If,for example, the relatively large changes in the spectrum of benzene as it forms a complex with silver perchlorate are due to a strong interaction, and if the energy of such an interaction does not appear externally in the thermodynamic quantities listed in the Table, then it must be dissipated internally. SMITH [ 131has made some calculations of lattice energies for 740

Complexes

of silver

perchlorate,

antimony

triohloride

and mercuric

chloride

A summation of the terms in Madehmg energy, this case which are pertinent. dispersion energy, repulsive energy and induction energy for pure silver perchlorate is -169 Cal/mole, while for the silver perchlorate bonded in the complex it is -126.8 Cal/mole (excluding energy terms connected with benzene). This difference in energy is, of course, compensated for by the energy associated with the interaction between the silver ion and benzene and between benzene and benzene. It is suggested that it is the magnitude of these latter terms which will correlate with the severity of the spectral differences. Table

3.

Thermodynamic

quantities

for

dissociation

-

(,cal/mole:

-t 2SbCls + C,H, -+ AgClO, + C&C, - 2SbCl,.3C,H,O, --f 2[SbCl,.C,H,O,] + 3SbCl,.2C,H,O, + HgCl,.C,HsO, + -f HgCl, + C,H,O, -• ~[AgClO,.C,H,O,] - AgClO, + C,H,O,

AS”,

+ C,HsOs + C,H,O, + C,HsO, C&O, +

at which

the vapor

C,H,O,

pressure

1 (:eu/mole) -

-12,100 -7920 -8380 -13,100 -8380 -8830 -15,350 -10,750 -6510

* T is the temperature 0 at temperature T.

reactions

AH

Reaction

ZSbCl,.C,H, AgClO,.C,H, 2[SbC1,.2C,HsO] 2SbC1,.3C,H,O, 3[SbCl,.C,H,O,] Hg’&.2C,H,O, HgCl,.C,H,O, i[AgClO,.SCH,O,] AgClO,.C,H,O,

-

over

-55.6,,, -43.9,,* -46.92,9 -55.6,,, -39.422, -48.0,,5 -60.7,,, -51.5,,, -41.7,,,

of complexes *

AfJ”2lM AP”29s [eu/mole)

I(Cal/mole)

-52.1 -35.7 -35.7 -58.7 -43.3 -37.8 -68.7 -47.0 -42.0

the complex

-

3410 2720 2250 4385 4510 2430 5120 3250 4000 -

pair

is 1 mm,

so that

log P is

It is further suggested that, in the case of antimony trichloride and mercuric chloride, a separation of charges does not take place. That is, the expansion of the crystal to include the organic component is accomplished by a separation of the halide molecules as non-ionized units. For such a mechanism the change in the crystal energy terms such as the Madelung energy should be relatively small and the changes in the externally measured thermodynamic quantities should be more indicative of the actual bond strength between the organic and inorganic parts of the complex.

Conclusions There are indications in the rate at which the organic component can be removed from the combination of certain inorganic salts in organic solvents that the following molecular compounds are formed: SbC!l,.JC,H,; AgC10,.3, 2, 4 and lC,H,; SbC1,.3, Q, 1 and @Z,H,O,; HgCl,.B, Q and lC,H,O,; AgCIO,.3 and lC,H,O,. Selection rules applied to the spectra of SbCl,.*C,Hs indicate that in solution the complex has a symmetry of C,, while in the solid state it has the symmetry where several C 2V’ This is the only instance among the complexes investigated “inactive” frequencies of the pure organic component become active in the complex in such a manner that a correlation between selection rules and symmetry is quite clear. 741

L. W. DAASCH

Spectra of the solid complexes with dioxane give very little evidence that the symmetry of the complex is less than that of dioxane itself. Attention is called, however, to the splitting of certain bands, particularly in the 800 to 900 cm-l ‘region of their spectra, which may be an indication of a distortion and symmetry change for dioxane from C,, to C,. The silver perchloratebenzene spectra are much different from a summation of the component spectra and these differences do not correlate with possible inactive are proposed: frequencies of the component parts. Three possible explanations (a) the bonding in this case may be a different hind; (b) the interaction may be so strong that the group frequency concept for the component parts is no longer valid; or (c) the perchlorate ion vibrations or some overtones or combinations may be interacting with benzene vibrations. The vapor pressures of the complexes as a function of temperature were measured and AH, AF” and AS” are calculated for the dissociation reactions. There seems to be no correlation between these quantities and the changes in the spectra. It is suggested that it will perhaps be necessary to dissect the lattice energies into their component parts to observe this correlation. Values for AH range from -7920 Cal/mole for AgC104.C,H, to - 15,350 cal/molefor HgCl,.C,H,O,

742