Nov. 5, 1955
NOTES
melting point of these preparations checked to within 0.1" with the literature values. Solvents and Solutions.-Ethylene dichloride was purified by a previously described m e t h ~ d . ~ The boiling point of the purified solvent was 83' at 750 mm. pressure. The specific conductance of the solvent was found to be less than ohm-' cm.-' and was too low to necessitate any corrections even for the most dilute solutions. Approximately lo-* iM stock solutions were prepared by dissolving a weighed amount of solute in an appropriate amount of solvent. Dilutions were made by the addition of a known amount of the stock solution from a weight buret to the solvent. This technique was found to be more accurate than the usual dilution method since solutions down to 10-5 Jf had to be prepared. All of the solutions were found to be stable for a t least 24 hours, but the measurements were made on the solutions prepared on the same day.
rabutylammonium cations in ethylene dichloride a t 25" have been determined by Tucker and Kraus,6 i t is possible to calculate the limiting equivalent conductances of the polyhalogen ions used in this investigation. The results are likewise given in Table 11. As ionic mobilities are equal to X?/F, the mobilities of the polyhalogen ions come in the following sequence, IBrC1-> IC&-> IBr2-> Brs-buttheactual differences are rather small, which indicates that the ions are of approximately the same size. Acknowledgment.-The authors gratefully acknowledge the support of this work by the Research Corporation.
Results and Discussion.-Equivalent conductances obtained for the polyhalide solutions are tabulated in Table I where a typical series of measurements are given. Several runs were made on different sets of solutions, but the results agreed within experimental error. TABLE I EQUIVALENT CONDUCTANCES O F POLYHALOGEN COMPLEXES IN ETHYLENE DICHLORIDE AT 25" c
x
104
A
c
x
104
A
5507
(6) L. M. Tucker and C. A. Kraus, i b i d , 69, 454 (1947).
DEPARTMENT OF CHEMISTRY OF IOWA STATEUNIVERSITY IOWA CITY,IOWA
The Lowering of the Freezing Point of Sodium Hydroxide on Addition of Salts BY R . P. SEWARD JUNE 17, 1955 RECEIVED
From calorimetric measurements, Douglas and Deverl have found the heat of fusion of sodium hydroxide to be 1520 S= 5% cal. per mole. These authors suggest that the figure of 1670 cal. per mole, calculated by the writer2 from freezing points in the NaOH-NaZC03 system, is in error because the effective molecular weight of Na2C03 in solution may deviate from its formula weight. As the value from the freezing point measurements was calcu(n-C1Hs)rNBrs ( ~ - C ~ H Q ) ~ N I C I ~ lated from temperatures determined to the nearest 0.3689 52.70 0.1651 58.98 degree and the greatest lowering employed was 0,9208 47.20 1,199 47.68 13", i t is quite probable that the discrepancy is 1,667 42.54 2.717 40.59 due to the lack of precision in the freezing point 2.566 38.69 4.467 36.22 data. 3.614 35.76 7.132 32.22 Subsequent to the observations on the NaOH8.51" 28.59 14.49 26.79 Na2C03 system, the writer determined the lowering 17.99 23.23 of the freezing point of sodium hydroxide on addition of NaBr, KBr, KzC03 and again NazCOa. Plots of fi vs. A deviated considerably from While these measurements too are not of sufficient straight lines showing appreciable ion-pair associa- precision to define the heat of fusion accurately, it is tion especially in the more concentrated solutions. thought that they may be of interest for their bearThe data were treated by the method of Fuoss ing on the extent of dissociation and ideal behavior F / A vs. cA f 2 / F plots gave in in fused salt solutions. and K r a ~ s . The ~ each case satisfactory straight lines. The interThe data on the lowering of the freezing point of cepts of the lines yield l/bo and the slopes 1/KAi. sodium hydroxide are tabulated below. AT is the The calculated values of the limiting conductance observed lowering, N is the ratio of the number of and of the ion-pair dissociation constants are given formula weights of solute to total formula weights, in Table 11. and i is the ratio of the observed lowering to 460N. TABLE I1 The mole fraction freezing point lowering constant, CONDUCTASCE DATAI N ETHYLENE DICHLORIDE R T z / A H ~ ,using 1520 cal. per mole for A H F , has a Complex A0 A: x, K x 10' value of 460. Within the precision of the measurements, it 42.6 39.0 0.68 (CHa)4NIBrCl 81.6 appears that the above data are consistent with 36.8 2.11 68.3 31.5 (n-C3Hr)4NIBr2 complete dissociation of solute and solvent and 26.2 36.0 2.05 (n-C4H9)4NBrs 62.2 ideal behavior; one formula weight of solute con(n-C4H9)4hTIC12 64.5 26,2 38.3 2.27 tributing one mole of solute ion in the case of NazReference 6. COS and NaBr, two moles of solute ion with KBr, Since the limiting conductances of the tetrameth- and three with KzC03. In view of the possibilities ylammonium, n-tetrapropylammonium and n-tet- of solid solution formation, i t is remarkable that the (CH3)4SIBrCl 0,6074 53.00 1.367 43.88 2.217 38.27 5,727 28.41 7.582 25.93 9.277 24.24 27.02 20.74
(n-CaHr)rNIBrz 0.5185 56.20 1.306 48.86 2,242 44.12 2.972 41.45 3.720 39.35 7.258 33.30 9.013 31.64
5
(4) A. I . Popov and R. F. Swensen, THIS JOURNAL, 77, 3724 (1955). (5) R . M. Fuoss and C. A. Kraus, ibid., 55, 476 (1933); R. M. Fuoss, ibid., 57, 488 (1935).
(1) T. B . Douglas and J. L. Dever, J . Research Null. Bur. Slandards. 53, 81 (1954). ( 2 ) R . P. S e a a r d , THISJOURNAL, 64, 1053 (1942).
5508 THELOWERINGO F
THE
DROXIDES
TABLE I the solid state. The spectrum was interpreted as Cu++ bonds FREEZING FOIST O F SODIUM Hu- indicating essentially covalent N B Y \*ARIOUS SOLIJTES --f
Solute Na2C03
N AT, " C . i
0.00460 1.8 0.85
0.OO912 0.O136 0.0199 0.0261 4.6 7.1 10.0 12.8 1.13 1.09 1.07 1.10
Solute NaBr
N AT,
"c.
i
0.00765 0.0117 6.5 3.2 0,90 0.93
0.02320 O.OR7il 12.1 1i.i) 1.00 1 .OO
Solute K B r
N AT, " e .
i
0.00282 n . 0 0 n~. on021 ~ 0.om 0 ,oi7x 2.5 5.0 7.8 11.1 15.7 1.92 1.92 1.83 LS4 1.92
Solute KICOI
Av
[J,0051,5
AT, "C.
7.0 2.115
i
VOl. 77
hTOTES
0.0081X
11.9 3.17
0.iII IO
1-) . , I 3,!)7
iLl)l,'37 1%:)
3.01)
and essentially ionic C < ---Cu++bonds in which -\O ' O r the carboxylate ion resonance is preserved.
Experimental Bis-(g1ycino)-zinc (11) monohydrate, Zn( NH2CH2COO)?, H20 was prepared according to the method of Dubsky and Rabas.6 The compound prepared in our laboratory was spectroscopically identical with :L samplc kindly supplied by Dr. Low. Spectra were obtained from samples prepared in accord: L I I C ~ with the KRr disk technique described previously.6 The zinc complex gave very well-defined spectra similar to those reported for the Cu(I1) and Si(I1) salts.4 The frequencies in cm.-' observed for bis-(g1pcino)-zinc( 11) monohydrate are as follows: 3450 ( m ) , 3270 ( m ) , 1603 (vs), 1447 (in),I419 ( i n ) , 1101 (in), 1350 (w),1314 (w),1100 (w), 114ii ( i n ) , 1100 ( m ) , lO(j0 (s), 951 (w),907 (w),719 (w). Ahbrrvi:ttiims: 111 = metliurn, s = stroiig, w = c \ . c : L ~ ,v = \-cry.
Discussion It is to be noted that absorption bands are observed a t 3450 cm.-' (2.9 p ) , 3270 cm.-' (3.06 p ) do. and 1G03 cm.-' (6.24 p ) and no absorption band DEPARTMENT O F CHEMISTRY was observed in the region of 1720 cm.-l (,?.S p ) . THEPENNSYLVANIA STATEUNIVERSITE UNIVERSITYPARK,PESNSYLVANIA These regions are critical for the determination of the type of metal-ligand bonding present in amino acid-metal complexe~.~The appearance of the Infrared Absorption Spectra of Inorganic Co- N H stretching absorption maximurn a t Xi0 ordination Complexes. IV. The Infrared Spec- cm.-l, compared to the 3330 maximum in the spectrum of Bis-(g1ycino)-zinc(I1) Monohydrate'"," trum of sodium glycinate, indicates the presence of Zn++ coordination. The absence of an abBY DANIEL Jf. SWEENY,COLUMRA CURRASANI) J. V. N sorption band near 1720 c m - l (5.8 p ) and the presQUAGLIASO ence of a very strong band a t 1603 cm-' (6.24 p ) RECEIVEDJUNE 10, 1955 indicate that the carboxyl to zinc bond has a high In the course of the investigation of metal amino degree of ionic character. acid complexes in progress in this Laboratory, the These observations regarding the spectrum of infrared spectrum of solid bis-(g1ycino)-zinc(I1) his-(g1ycino)-zinc(I1) monohydrate are in accord monohydrate has been obtained. The spatial ar- with the evidence from X-ray diffraction of a square rangement of ligands about the zinc ion has usually planar configuration for the zinc(I1) complex. been considered to be tetrahedral2 corresponding They indicate that linear sp metal bond orbitals to sp3hybridization of the bond orbitals. However, are involved in the nitrogen-to-metal bonds in this the X-ray investigations of Low3 show conclusively complex as well as in the copper(I1) and nickel(I1) that the glycine ligands are arranged in a planar complexes previously reported. It is to be expected that all complexes of the type ZriXz in fashion about the central zinc ion. I n a previous communication4 i t was postulated which X is a bidentate ligand having as one coiirdithat the trans planar configuration of bis- (g1ycino)- nating center a COO- group forming essentially copper(I1) monohydrate complex is the result of an electrostatic COO- -- - -. Zii++.bonds, should have a sp linear hybridization of copper bond orbitals. This trans square planar configuration if the other inetalexplanation was based upon the observed infrared to-ligand bonds are covalent. Further spectral absorption spectrum of the copper(I1) complex in studies on complexes of this type are brinq pursued in this Laboratory. (1) (a) Paper 111 in series, J. Cicm. Phyr., in press. (b) Supported
"2'factors come as close to wholr numbers as they
---f
in p a r t under A E C Contract A T ( l l - l ) - 3 8 , Radiatiou Project of t h e University of Notre Dame. 4 4 , 774 (1922); C . H. Mac( 2 ) R. G. Dickinson, THISJOURNAL, Gillavry and J. M. Bijvoet, Z. Kiisl., 9 4 , 249 (1936). (3) Private communication from Dr. Barbara Low, University Laboratory of Physical Chemistry Related t o Medicine and Piililic Health, Harvard University. (4) D . N. Sen, S . Mizushinia. C . Curran and 1. 1'. Oiiugliuno, 'THIS JOWRNAI., 77,21 1 ( 1 9 5 5 ) .
DEPARTMEST OF CHEMISTRY USIVERSITPOF NOTREDAME NOTREDAXE,INDIANA (3) J. V. Dubsky and A . R a b a s , Spisy vyd6vant privodovbdeckou Fakiiltou hIasarykovy Univ. No. 123, 3 (1930); C. A , , 26, 20.56 (ISXI). ( t i ) hT. 11,Stimson and & J. I. o'I)nnnell, 'THIS J O U R N A L , 74, 1805 (1952); 1. P. Faust unri I. \'. Qliaglianr), ihid, 76, 6340 f l 9 5 4 ) .
