August, 1961
SOTES
ing orthorhombic symmetry. The mean refractive index is 1.85 f 0.03, in agreement with the value 1.85 calculated as above. The differences in the optical properties suggest that this compound may not be isomorphic with the isoformular rubidium compound. Cs3PuC16.-This compound melts congruently a t 825 =t 3" and. on cooling, undergoes polymorphic transformation a t 410". Crystals of the roomtemperature modification are green in bulk by reflected light but, immersed in liquid of similar refractive index, are transparent and virtually colorless by transmitted light. They are optically anisotropic and exhibit very fine, complex, polysynthetic twnning. The mean refractive index is around 1.7, in agreement with the value 1.73 calculated as above. Discussion It is interesting to note the similarity between PuC13 and UCljb6in the formation of double salts with alkali chlorides. KO compounds occur in the binary systems involving LiCl or NaC1. There exist iLIPuzC17-type compounds, where hI = Rb or Cs, hlzPuCl5-type compounds where 31 = K or Rb, and R13PuC16-typecompounds where bI = K, Rb or Cs. Acknowledgments.-We are indebted to A. TIT. Morgan and J IT. Anderson for the plutonium metal, and to C . F. AIetz, W. H. Ashley, G. R. Waterbury, R. T . Phelps, C. T. Apel, &I. H. Corker, D. C. Croley, J. A. Mariner, 0. R. Simi, C. H. Ward, K.IT. Wilson and A. Zerwekh for the chemical and spectrochemical analyses.
polyphosphate, previously reported5 a t 25", evaluated a t 65'.
1463 iq
Experimental Materials.-Tetramethylammonium polyphosphates and imidophosphates in 99.9+ and 97+% puiitl , Iebpectively, were prepared as previously d e s c r ~ b e d . ~ The water used for solution make-up was distilled and freshly boiled to remove dissolved COz. Other chemicals were C.P. grade. Procedures.-The aciditv constant determination at a constant temperature and ionic strength WBR carried out ab previously described.3 A Leeds and Sorthiop pH meter with glass and calomd electrodes T T ~ Sutilized, and aa. calibrated a t each temperature with huffer solutions having a pH of 4, 7 and 10 Calibration oi the pH meter nith one buffer solution gave readings ~ i t thr h other two buffers that agreed to within 10.01 pH unit, indicating lineaiity of the pH scale. Temperature B A S controlled to 10.1" using a heater in combination with a heat-sensing Thermotrol unit, manufactured by Hallikainen Instruments, Berkeley, California. In the experiments below room temperature, the solutions were placed in an ice-acetone bath, a i t h the heater supplying enough heat to maintain the desired temperature. During titration the solutions \\err maintained untie1 :i nitrogen atmosphere. The magnesium coniplr\ing I)\ p\ iophosphate and tripolyphosphate vas measiirrd ti\ the same procedui e de,~ that the measurescribed by Lambert and W a t t t ~ sexcvpt ments \\-ere made a t 25 and 65'. The p H mrasurements in the presence of excess magnesium nere made within a few minutes to aboid precipitntion of niagnefiirim phoqphates
Results and Discussion Acidity Constants.-Stepwise titration curves with definite breaks for the weakest two hydrogens were obtained with all of the investigated acids. The other hydrogens were so strong that no inflection points ~ e r eobserved. The acid-base titration dhta, obtained at a constant temperature and total ionic strength, were fit to a least-squares program of an IB3I 704 computer, as previously (5) C J Baiton R J Shell A B milkerson and W R. Grimes. described.3 The resultant acid dissociation conORNL-2548 or E M Leiin and H F RZcMurdie, "Phase Diagrams for Ceramists Part 11, %m Ceram Soc , 1959. stants with the statistical 95y0 confidence limits (6) J J Katz and E Rabinowitch 'The Chemistry of Uranium are listed in Table I. Part I , N N E S Di\ V I I I , Vol 5, RIcGraw-Hill, New York, N Y.. pu'o attempt was made to extrapolate the acid 1951, p 480 dissociation constants to infinite dilution since they were only determined a t fewer than four ionic strengths. For the polyphosphoric acids (H0)zOP METAL CORIPLEXISG BY PHOSPHORUS CORIPOUKDS. T'. TEMPERATURE [ ~ H ] ~ - P O ( O € € ) 2with n varying from 0-60, D E P E S D E S C E OF ACIDITY AND MAGSESIUM COMPLEXISG CONSTA4NTS no significant temperature dependence of the dissociation of the weakest two hydrogens was obBY RIYADR. 1 ~ 4 x 1 served. with the apparent, molal AH for dissociation RrseaTch Department, Inorganir Chemicals Dzuzszon, Monsanto Chemibeing between -1 and 0 kcal. The apparent A H cal Company, St. Louzs 66, Missourz for the dissociation of the stronger hydrogens lies Received April 3 , 1961 between - 2 and 0 kcal. As was previously3 found The acidity c ~ n s t a n t s l -of ~ polyphosphoric and at 25', the ratio of the dissociation constants of the imidophosphoric acids hare been reported at 25'. two weakest hydrogens approaches the value of However, the evaluation of the temperature de- four7 as the chain length of the phosphate chain appendence of metal complexing at pH values where proaches infinity. two hydrogen forms of a ligand coexist4requires the The acid dissociation constants of imidodiphosavailability of acid dissociation constants in the phoric and diimidotriphosphoric acids show sigsame temperature range. nificant temperature dependence, as was observed I n the present study the aciditj constants of poly- with their calcium complexes. Thus, the apparent phosphoric and imidophosphoric acids are presented molal AH for the dissociation of the weakcst hydroa t several temperatures and ionic strengths. Rlag- gen ( K J at :in ionic strength of 0.1 is -6.4 and nesiuni complexing by pyrophosphate and tri- - 4.5 kcal. for imidodiphosphorir and diimidotriphosphoric acids, respectively, where "
"
(1) J. I. Watters, E. D. Loughran and S. M. Lambert, J . A m . Chem. SOC.,78, 4855 (1956). ( 2 ) S. M. Lambert and J. I. Watters. ibid.,79, 4262 (1957). (3) R. R. Irani and C. F. Calli@,J . Phys. Chem., 6S, 934 (1961). (4) R. R. Irani and C. F. Callis, ibid., 64, 1398 (1960).
(5) S. ILl. Lambert and J. I. T a t t e r s , J. A m . Chem. Soc., 7 9 , 5608 (1957). (6) R. R. Irani and C. F. Callis, J . Phgs. Chem., SS,296 (1961). (7) S. W. Benson, J . A m . CAem. Soc., 80, 5151 (1958).
VOI. 63.5
XOTES
L
FOR
n
0
Ionic strength
Temp., O C .
0
0.1
10
.1
25
.I 1.0 0.1 .2 .3 .1 .2 .3 .1 1.o 0.1
05
Ib
0 10 25
.1 1.o 0.1 .2 .3 .1 .2 .3 0.1 1.o
50
05
4
14
58
1.o
25 37 50 25 37 50 25 37 50
pKa
9.08 f 0.16 8 . 9 7 f .13 8.95 rt .10 S . 7 4 f .07 8 . 9 4 f .OS 8 . 9 3 z t .09 8.88rt .09 s . 9 i r t .os 8 . 9 0 f .os 8.88rt .09 8 . 9 2 f .09 8 . 7 2 f .07 8 . 5 1 f .12 8 . 7 0 f .07 8 . 6 5 f .05 8 . 5 6 f .10 8 . 5 0 3 ~.OS 8.51 f .OS 8 . 5 2 f .08 8 . 5 5 f .OS 8 . 4 8 f .OS 8 . 4 8 f .OS 8 . 4 8 f .06 8 . 3 9 f .OG 8 . 1 3 f .14 8 . 0 2 f .2 8 . 0 0 f .15 8 . 0 S f .I0 8 . 0 2 f .13 8 . 1 5 f .10 8 . 1 7 f .04 8.033Z .OS 8 . 0 3 f .08
.1
37
Y = OXYGEN
PKi
1.0 1.o 1.o 1.0 1.0 1.0 1.0 1 .o
FORX 0
0.1 .3 .I .3 .1 .3
25 37 50
lb
25
.I
37 .I 50 .1 Est,imnted, large errnrs may exist.
b
6 . 1 i f 0.15 6 . 0 3 f .18 6 . 1 2 f .10 5 . 9 S f .07 6 . 1 3 3 ~ .07 6 . 1 2 5 .08 6 . 0 8 f .09 6 . 1 3 f .07 (i.06rfi .07 6 . 0 4 f .08 6 . 1 6 f .08 6 . 0 1 f .OS 5 . 7 f .1 5 8 4 f .05 5 . 7 5 f .14 5 . 6 9 f .ll 5 . 7 7 f .07 5 . 7 7 i .07 5 . 7 8 3 ~ .07 5 . 9 0 f .07 5 . 8 0 f .OS 5 . 8 4 f .07 5 . 8 8 f .07 5 . 8 0 3 ~ .05 5 . 9 8 3 ~ .18 5 . 8 3 & .15 5.81 f .20 6 . 4 8 i .07 6 . 4 8 f .OS 6.50f .OS 7 . 2 2 f .04 7 . 2 8 f .08 7 . 2 8 4 ~ .OS
PKZ
2 . 5 f0.1 2.3 f . I 2.0 f . 1 1 . 9 5 3 ~ .04 1 . 9 5 f .05 1 . 9 7 f .OF 1 . 9 1 f .oc, I . 9 S I .of; 1 . 9 2 f .08 2.123~.Oi 2 . 1 2 f .0; 2 , 1 7 + .05 2.3 f .1 2.31 f .04 2 . 1 3 k .10 2 . 0 4 k .09 1 . 8 9 f .OG 1 . 9 5 3 ~.06 1 . 9 S f .oo 2 . 1 2 f .07 1 . 9 5 f .OG 2 . 6 2 f .05 2 . 1 5 3 ~ .05 2 . 1 0 f .08 2 . 1 9 f .10 2 . 2 2 f .07 2 . 2 2 i .12 2 . 9 2 3 ~ .09 2 . 6 4 f .05 2 . 5 2 f .13
..... .....
2.3 2.2 2 1.7 I .(I1 I .7 1.7
I !I I .:I 1.2
1.3 1.2 2.2 2.2 2 1.2 1.7 1.7 1.7 1 .7 1.7 1.7 1. 7 1.7 2 .I 1.3 1.3 2 2 2 .. ..
..
= NH
7.32 f 0.12 2.66 f 0.09 1 0 . 2 2 f 0.09 7 . 0 5 3 ~.I2 2.81 f .06 9 . 7 7 f .I2 7 . 1 6 f .04 2 . 6 0 + .OS 9 . 7 9 3 ~ .03 6 . 9 9 f .05 2 . 6 8 f .07 9 , 5 2 5 .05 6 . 9 0 f .06 2 . 8 1 f .07 9 . 4 1 3 ~ .06 6 . S 8 f .06 2 . 8 3 f .07 9 . 3 2 f .03 6 . 6 1 f .09 3 . 0 3 f .10 9 . 8 4 f .OS 6 . 8 0 f .OS 3 . 2 4 f .OS 9 . 5 0 f .OS 7 . 0 2 f .08 3.59* .09 9 . 2 8 f .OS p K j is estimated to be 1 f 0.5 at the various temperatures.
d In K , dT ICn = (H+) ( H ~ - I L - ( ~ - ” + ” ) (H,L -b -))
pKda
1.5 2 1.8 1.8
1.8 1.8 2 2.2 2.4
weakest hydrogens (&), the vahieq of AH at an ionic strength of 0.1 are -3.2 and +3.2 kcal. for imidodiphosphoric and diimidotriphosphoric ncids (2) respectively. Magnesium Comp1exing.-The nephelomet,ric and parentheses indirate concentration. The difference hetwecn A H I , and the thermodynamic value, titrations, previously utilized* in evaluating calcium complexing constants were not found as AH‘n, is suitable for magnesium complexing because of the d In f absence of a well defined magnesium precipitate. AH’n AH,, = R T 2 - - (3) dt Therefore, the pH-lowering technique was used. wheref is the o~cti~7ity cocfficient8ratio of the species The acid-base titrations in the presence of magin equation 2 . For the dissociation of the second nesium still showed stepwise complex formation. A H n = RT2--
-
August, 1961
NOTES
In Table I1 the pH values are given after adding 1/2 and 3/2 equivalents of hydrogen ion per mole of ligand in the presence of magnesium. Utilizing the appropriate acidity constants, the, formation constants for the following equilibria, previously proposed bv 1,xmbert and Wattersls were evahinted a t 25 arid Go, using the techniques previously described.
to a need for polarizability and molar volume data for substituted ammonium salts in particular. We report here the results of refractive index and density measurements for the systems tetra-nbutylammonium picrate (Bu4NPi) in nitrobenzene and in chlorobenzene, tetra-n-butylammonium iodide (BaNI) in o-dichlorobenzene and in water, and sodium tetraphenylboride, tetra-n-propylammonium iodide (Pr4NI), tetraethylammonium bromide and tetramethylammonium chloride in water.
1465
TABLE I1 COMPLEXINGOF MAGNESIUMBY PYROPHOSPHATE AND Experimental TRIPOLYPHOSPHATE ANIONS Salts.-These were from current laboratory stock and, "a" is the number of equivalents of H + per mole of ligand, with the exception of sodium tetraphenylboride and tetra-nand L is the polyphosphate ligand. Total ionic strength was adjusted to 1.0 with tetramethylammonium bromide. Neg. log of formation constant of MgL MgzL MgHI, 5.42 2.33
r l
Ligand
I emp., "C.
''
[' y ro 1111os 111, a tr ,
.,_.j
li5
Tripolyphosphateb
25 65
"a" pH U . 5 C.30
..
1.55.11
..
1.5 5.00 0.5 6.10 1 . 5 4.52
..
.. ..
5.81
2.13
0.5 1.5
..
5.97 4.60
5.76
..
+ M g + HL
..
.. 2.12 ..
0 Total magnesium concentration = 9.930 X Total pyrophosphate concentration = 2.955 X 6 Total magnesium concentration = 9.980 X Total tripolyphosphate concentration = 2.553 X
Mg f L 2Mg L
3.05 4.13 3.36
..
3.40
lo-'
*
MgL MggL MgHL
M. M. M. ill. (4) (5) (6)
where L is the polyphosphate anion. At 65' and pH values over 7 a precipitate formed rapidly in solutions containing pyrophosphate and an excess of magnesium, so that no values for MgP2072-, and Mg,P207are reported a t that temperature. The results a t 25' agree very well with those previously reported. The formation constants for the magnesium complexes a t 65' are very close to those a t 25') and the AH for complex formation is 0 zt 1 kcal. Previous extensive work8 with calcium complexing by pyrophosphate and tripolyphosphate showed the AH values to be less than 4 kcal. and attributed complex formation to positive entropy changes. Obviously, in magnesium complexing by polyphosphat'es the same interpretation applies. These results suggest that a relationship may exist between the heats of dissociation of a hydrogen and a metal ion from a ligand. This is not surprising since the two processes are somewhat similar. Acknowledgment.-The author thanks Mr. William W. Illorgenthaler for making some of the measurements. POLARIZABILITIES AXD MOLAR VOLUMES
OF A NUMBER O F SALTS I N SEVERAL SOLVENTS AT 25'1 BY W. R. GILBERSON AND J. L. STEW ART^ Depurtment of Chemistry, University of South Carolina, Columbia, South Carolina Received April 7, 1961
Recent interest3+ in obtaining dipole moments of ion pairs from dielectric measurements has led
propylammonium iodide, were considered of sufficient purity to use without further treatment. The sodium tetraphenylboride was recrystallized from water, and the tetran-propylammonium iodide was recrystallized from ethanol. Solvents.-The solvents were purified by recrystallization (nitrobenzene), distillation (water), and in the case of chlorobenzene and o-dichlorobenzene, passed through an alumina column and then distilled. Apparatus.-Densities were determined with a reproducibility of 0.02% using a Lipkin pycnometer, the volume of the stems having been calibrated with mercury a t 25", and the volume of the bulb with water a t 25". Solutions were equilibrated in an oil thermostat set at 25.0'. Refractive indices were obtained with a reproducibility of 0.01% using a Bausch and Lomb Abbe-3L refractometer. The light source waB an ordinary 40 watt incandescent lamp. The refractometer was connected to a circulating 25" water thermostat.
Results The solution densities were plotted us. molar concentration of solute. All of the plots were linear within the concentration range used (0.005 to 0.05 M ) . From the relation d = do
+ (ill, - & ~ ) C / l O O O
(1)
where d is the solution density, do that of pure solvent, M o the formula weight for the solute, V,' the partial molar volume of solute a t infinite dilution, and C the molar concentration of solute, the values of Vi shown in Table I were obtained using the slopes of the d versus C plots. The specific refractions, R, of the salt solutions were determined from the relation
where rllz is the refractive index of solution, q1 that of pure solvent, C1the molar concentration of solvent; and CIois the molar concentration of pure solvent. Plots of specific refraction 2's. salt concentration were linear in all cases. From the slopes of these plots, the solute polarizabilities, at, werc calculated from the relation CYZ
= 3000 X s l o p e / 4 ~ N
These results are listed in Table I. Discussion A comparison of the molar volumes of BulNPi and B a N I in the two solvents used for each is interesting. I n nitrobenzene, the picrate has an (I) This work has been supported in part by contract with the Office of Ordnance Research, U. 9.Army. (2) N. S. F. Summer Research Participant, 1960. (3) E. A. Richardson and K. H. Stern, J. Am. Chem. Soc.. 89, 1296 (1960). (4) M. Davies and G. Williams, Trans. Faraday Soc., 66, 1610 (1960). (5) W. R. Gilkerson and K. K. Srivsstsva, J . Phys. Chem.. 65, 272 (1961).
