Ion-exchange properties of ceric phosphate-sorption on some metal-ammines and ethylenediammines

Notes Replicate values of Er for each metal and siloxane pair were always within 3% of the mean value. The extraction efficiencies for the cyclosiloxanes with the metals studied are shown in Table 1. Several of the cyclosiloxanes were completely ineffective in extracting metal chlorides and gave E r values of < 1% for all the metals tested; these have been omitted from Table I. The cyclosiloxanes which were ineffective are ((CH3)2SiO), (n = 5-9, 15). RESULTS AND DISCUSSION

The extraction results show that, whereas many siloxanes are ineffective as phase transfer agents for the metal ions considered, the cyclic trimers and the methyl-substituted cyclic dodecamer do show appreciable activity. We conclude from this that extraction of the metal ions is due specifically to complex formation with the active siloxanes. Studies with Catalin models suggest that ((CH3)2SiO)t2 can envelop a metal ion in a similar manner to crown ethers. Only six of the oxygen atoms of the siloxane are in such a position, in the model, to interact with a metal ion. The estimated cavity diameter in the dodecamer is -0.35 nm, similar to that in 18crown-6 polyethers. Possible conformations of the other rings either have very few oxygen atoms in appropriate positions for coordination, or require long metal-oxygen distances. Presumably such poor metal-ligand bonding would not compensate for the loss of part of the hydration sphere of the metal.

289

The trimers have planar rings of small diameter and probably the cation is bonded out of the ring plane. The selectivity orders shown in the binding do not correlate well with cation diameters. though among the alkali metals the smaller cations seem to be preferred.

Faculty of Applied Science Brighton Polytechnic Moulsecoomb Brighton,BN2 4GJ England

C.J. OLLIFF G.R. PICKERING K.J. RUTT

REFERENCES 1. C. J. Olliff and P. Ladbrook, Bioelectrochem Bioenergetics. 6. 105 (1979). 2. C. J. Pederson, Fed. Proc. 27, 1305 (1%8). 3. G. Eisenman, S. M. Ciani and G. Szabo, Fed. Proc., Fed. Am. Exp. Biol. 27, 1289 (1%8). 4. G. Eisenman, S. Ciani and G. Szabo, J. Membrane BioL I, 294 (1%9). 5. H. K. Frensdofff, J. Am. Chem. Soc. 93, 4684 (1971L 6. T. Takiguichi, M. Sakurai, T. Kishi, J. Ichimura and Y. lizuka, J. Org. Chem. 25, 310 (1960). 7. J. F. Hampton, Brit. Pat. 1,162, 075 (1%9). 8. G. R. Pickering, C. J. Olliff and K. J. Rutt, Org. 'class Spectrom. 10, 1035 (1975).

J. inorg, nucL Chem. Vol. 42. pp. 289-292 Pergamon Press Ltd.. 1980. Printed in Great Britain

Ion-exchange properties of ceric phosphate-sorption on some metai-ammines and ethylenediammines (Received 14 February 1978; received for publication 11 July 1979) The selectivity of ceric phosphate is not well understood [1, 2]. In continuation to our work on the exchange properties of hydrous oxides of Si(IV), Zn(IV), Sn(IV) and Ce(1V)[3,4], we report similar studies on ceric phosphate. The sorption of ammine and ethylenediamine(en) complexes of Cu 2+, Ni 2+, Zn2+ and Cd 2+ on eerie phosphate has been studied at different extermal ionic concentrations and pH. It has been found that both qA and kd values, at first increase with increase of either external ionic concentration or pH, attain a maximum and then decrease. The uptake of the en-complexes is appreciably lower than of the corresponding ammine complexes. Selectivity quotients of the exchanger material towards competing pairs, Cu 2+- Ni2÷, Cu 2+- Cd2. and Zn 2+- Cd2+ of both ammine and en-complexes have been measured at different external ionic concentrations and at pH, 10.5, where most of the metal ions show maximum sorption. The qA(max) and selectivity quotients of both ammine and en-complexes follow the order: Cu 2+ > Zn 2+ > Ni 2+ > Cd 2+.

analysis of the sample of CeP indicated the absence of definite hydrates during thermal drying. The X-ray diffraction patterm of the sample indicated its amorphous character. Stock solutions of ammine and ethylenediammine complexes of the metal ions were prepared by dissolving appropriate quantities of water soluble metal salts in aqueous ammonia or ethylenediammine solutions as the case may be, containing ammonium sulphate as buffering salt, [buffer]: [metal], 2:1). The metal salts used were CuSO4. 5H20, NiSO4. 6H20, ZnSO4.7H20 and 3CDSO4. 8H20. The pH measurements were carried out with an Elico pHmeter in conjunction with a Beckmann glass electrode. For the adjustment of pH of the solutions, aqueous ammonia, aqueous ethylenediamine and H2SO4 were used. All the experiments were carried out at a temperature of 25 _+2°C, in a room provided with a "Climatizer" (Blue Star) air conditioner. Determinations of qA and kd values and the selectivity quotients (K°a) were made as reported earlier[3]. RESULTS AND DISCUSSION

An examination of the results in Tables 1--4 show: MATERIALS AND METHODS

All the reagents were of A.R. quality unless otherwise stated. Doubly distilled water was used throughout. Ceric phosphate was prepared by the dropwise (3 ml/min) addition of one volume of a saturated ceric ammonium sulphate solution in 0.5 M H2SO4, to one volume of a well stirred (240 r.p.m.) solution of 6M H3PO4, at room temperature. The precipitate obtained was stirred for an hour at the same temperature, washed free of sulphate and finally dried at 25-+2°C. The ratio of POdCe in the sample when analysed quantitatively [5], was found to be 1.68. Ceric phosphate prepared in this way behaves as a cation exchanger in basic media, as confirmed by pH titrations[6]. Thermogravimetric

(a) qA and k~ values (i) qA and kn values at first increase with increase of pH, attain a maximum and then decrease (Tables 1 and 2). (ii) qA values first increase with the increase in the concentration of the exchanging ion up to a certain limit, then suddenly fall (Table 3). (iii) In both ammine and diammine series, qA(max) for Cu 2. is the maximum, the decreasing order of qA(max) being: Cu 2+ > Zn 2+ > N i 2+ > Cd 2+.

290

Notes Table 1. Effect of pH on the equilibrium sorption of different metalammines. Amount of the exchanger = 100 mg; Total vohime = 25 ml qA values i n m - e q u i v ,

Kd v a l u e s / g

pH Cu2+

Zn 2+

Ni 2+

Cd 2+

a, c o n c e n t r a t i o n

Cu2+

Zn 2+

Ni 2+

Cd 2+

o f the e x t e r n o 1 exchanqinq i o n = 011R

9.0

0.27

0.24

0.14

n.05

14.3

12.6

7.2

2.5

9.5

0.35

0.30

0.15

0.10

18.8

15.9

?.7

5.1

10.0

0.38

0.36

0.16

0.13

20.6

19.4

8.3

9.0

10.5 0.40

0.24

0.22

0.19

21.7

12.6

11.5

10.0

0.23

0.20

0.17

20.6

12.1

11.0

0.38

b. C o n c e n t r a t i o n o f t h e e x t e r n a l

10.4

9.8

~xchanqinq i o n = OtO1R

9.0

0.225

0,355

0.303

0.106

205

612

38l

67

9.5

0.359

0.369

0.325

0°222

636

704

361

200

10.0

0.375

0.400

0.343

0.266

750

1000

542

284

10.5

0.425

0,409

0.222

0.342

1417

200

541

11.0

0.383

0.288

0.142

0.225

818

99

205

1124 335

Table 2. Effect of pH on the equilibrium sorption of different metal diammines. Amount of exchange = 100mg; Total volume = 25 ml. qA v ~ i u e s I n m - o q u i v .

Kd v a l u e s / g

pH Cu2+

Zn 2+

a,

Ni 2÷

Cd 2+

Concentration

Cu2+

Zn 2+

Nl 2+

Cd2+

of the external axchsnoino ion - O~IR

9.0

0.210

0.132

0.100

0.020

10.96

6,78

6.1

1.00

9.5

0.230

0,158

0.125

0.050

12.15

8.16

5.4

2.81

10.0

0.291

0.200

0.184

0,080

15.45

11.62

9.5

4.05

10.5

0.137

0.050

0.105

0.050

?.04

2.81

5.4

2.81

11,0

0,030

0,045

0.025

0.020

1.51

2.52

1.3

1.00

b.

Concontration

of tho, oxtornal oxchanqinq ion = O.01R

9.0

0.015

0.016

0.004

0.013

7.7

8.3

2.0

5.6

9.5

0.050

0.017

0.007

0.017

27.7

8.8

3.5

8.e

10.0

0.102

0.C19

0.011

0.010

64.0

9.9

5.6

g.4

10.5

0.0125

0.021

0.020

0,019

83.S

10.9

10.4

9.9

0.022

0.017

0.011

0.010

14.5

8.8

5.6

5.1

11.0

(b) Selectivity quotients The selectivity quotients which were measured under comparable experimental conditions and at pH = 10.5, parallel the order of qA(max) values (Table 4)

It is well known that the sorption of simple metal ions on the hydrogen form of metal-phosphate exchangers takes place by the following exchange machanism[9].

Cu 2+ > Zn 2+ > Ni2+ > Cd 2+,

where M stands for the exchanger metal ion and X "+ the exchanging metal ion. It is presumed that the sorption of the complex metal ions takes place at the expense of two hydrogen ions.

(c.) In general, the uptake of the en-complex is appreciably lower than that of the corresponding ammine complex.

nMPH + X" ÷ .

• ( M P ) , ( X " +) + n H ÷

291

Notes Table 3. Effect of concentration on the equilibrium sorption of different metal-ammines ar~ diammines. Amount of the exchanger = 100 rag; Total volume = 25 ml; pH = 10.5 Concert-

trmtion

qA v e l u e e o f meteZ =mmlnea

In m-equlv,

Cu 2+

Zn 2÷

NI 2~

Cd 2÷

qA valuee e? motel dlemmlnee in m-mqulu, Cu 2÷

Zn 2+

812+

Cd 2+

O.01R

0.425

0.409

0.222

0.342

0.125

0.021

0.020

0.019

O.02R

0.440

0.419

0.370

0.350

0.175

0,050

0.080

0.025

O.05R

0.435

0.283

0.340

0,225

0.225

0,125

0.120

0.075

O.08R

0.425

0.250

0.280

0.205

0.145

0.075

0.110

0.060

0.10R

0.400

0.240

0.220

0.190

0.137

0.050

0.106

0.050

Table 4. Selectivity quotients for various competing pairs. Amount of exchanger= 100rag; pH = 105: Total Volume = 25 ml; Concentration of the competing pair (each component) = 0.05 M Quotient

K

Eu(NH3)42+

Value

Quotient

Value

3.80

Nl(en)32+ K

4.20

Eu(mn)32+ K Cd(en)32+

2.89

Zn(en)32+ KEd(in)32 +

1.32

1.13

NI(NH3)6 2+

K

Cu(NH3)42÷ Cd(NH3)42+

KZn(NH3)42÷ Cd(NH3)42~

1.43

EFFECT OF ADDITION OF AMMONIA AND ETltYLENEDIAMMINE (TABLE l AND 2) Successive addition of ammonia for the adjustment of pH influenced the overall exchange process in three different ways: (i) Addition of ammonia may enhance metal-ammine forOH

mation, as a consequence of equilibrium NHI=-~NH3+H+; H"

(ii) The additional OH facilitates the forward release of hydrogen ion by exchange; and (iii) beyond a certain limit, the formation of ammonium ions leads to competion with the metal ions for the exchange sites, and thus causes a decrease in qA and ka values at higher pH. Ethylenediammine acts in a similar way. EFFECT OF CONCENTRATION OF EXCHANGING IONS (TABLE 3) The observed decrease in the equilibrium sorption (qa) at higher concentration of the exchanging ion is presumably due to the lowering of ionic activity at higher concentration. Adiminution of exchange potential at higher concentration is well known/Ill. The decreased in the k~ values at higher external concentration of the exchanging ion shows that the efficiency of separation is maximum at lower concentration (Tables 1 and 2). EFFECT OF VARYING THE EXCHANGING IONS

The variation in the qA values for the different exchanging species is intimately connected with the electric charge and size of the exchanging ions. The combined effect of the two factors may be best reflected in the charge/radius ratio, i.e. the ionic potential/12], @, of the exchanging ions. The data indicate that the higher the ionic potential, the greater is the sorption. Since, all the metal ions under study are bivalent their ionic potentials follow the order of their covalent radii. The known stereochemi-

cal covalent radii/14] are square.planar Cu(ll) ammine, 1.28,~; tetrahedral Zn(ll)-ammine, 1.31A; octahedral Ni(ll)-ammine, 1.39/~; tetrahedral Cd(ll)-ammine, 1.48,~. Therefore, the ionic potentials are likely to follow the order: Cu(NH0~+> Zn(NH3)] + > Ni(NH3)62+ > Cd(NH3)] + as is found. The en-complexes of the metal ions under study are all known to have octahedral symmetry. Therefore, order of the covalent radii is again likely to parallel the order of ionic radii of the simple metal ions/13], Accordingly Cu(en)] +>Zn(en)~ +> Ni(en)] + > Cd(en)] ~ as found for the qA(max) values. In the foregoing discussion the equilibrium sorption (qA) has been compared under condition of maximum sorption of the exchanging ions, although the pH values are not the same. Ideally it is better to an identical experimental conditions, including the hydrogen ion activity, provided the concentration of the exchanging complex ions were independent of the hydrogen ion activity in the external solution. Unfortunately, the thermodynamic stability constants of the metal complexes are pH dependent; consequently, maximum activity of the exchanging complex ion is likely to be exhibited at different pH values. In these circumstances the qA maximum values for each of the ions have been compared assuming/3, 20]: (4) The most favourable pH values for the formation of ammine and en-complex corresponds to that at which qA attains a maximum. (b) The fall in the qa values above a certain oH, when the exchanging ionic concentration remains the same, is presumably due to the formation of NHL en-H + and en-H~ + (as discussed earlier at higher pH; these later species competing with the exchanging metal complex ion. SELECTIVITY (TABLE 4)

The observed order of equillibrium sorption values of both ammine and en-complexes on the exchanger material reveals that

292

Notes

the order of selectivity quotients, K~, exhibited by the exchanger towards a series of exchanging ions is decided by the same property as decides their equilibrium sorption (qA), i.e. by the ionic potential. Our findings are similar to those reported by earlier workers [15-19].

THE EN-COMPLEXIONSV/S THE AMMINES The metal-en complexes are larger in size than the corresponding ammine complexes. As a consequence, their equilibrium exchange values (qA) by both film and particle diffusion mechanism[4], are expected to be lower than those for the corresponding ammine complexes, as is observed.

Acknowledgement--The authors are thankful to the University Grants Commission, New Delhi (India), for providing financial assistance. Department o/Chemistry University of Delhi Delhi-110007 India

A. K. BHADURI K. B. PANDEYA K. R. KAR

REFERENC~ 1. K. H. Konig and E. Meyn, J. lnorg. Nucl. Chem. 29, 1519 (1967). 2. K. H. Konig and G. Eckstein, J. lnorg. Nucl. Chem. 31, 1179 (1969). 3. K. R. Kar, K. B. Pandeya and A. K. Bhaduri, J. lnorg. Nucl. Chem. 38, 1211 (1976). 4. A. K. Bhaduri, B. Bhushan, K. B. Pandeya and K. R. Kar, J. Radioanal. Chem. 33, 209 (1976).

5. G. Alberti, U. Censtantino, P. G. Gregorio and E. Torracca, J. Inorg. Nucl. Chem. 30, 295 (1968). 6. R. Kunin, Elements of Ion-Exchange, p. 14. Reinhold, New York (1960). 7. H. A. Flaschka, EDTA Titrations. Pergamon Press, Oxford (1964). 8. o. Glethorpe and Smith, Analyst 68, 325 (1943). 9. J. A. Marinsky and Y. Marcus (Eds), Idn Exchange and Solvent Extraction, Vol. V, pp. 39, 124. Marcel Dekker, New York (1973). 10. C. B. Amphlett, Inorganic Ion Exchangers, p. 2. Elsevier, Amsterdam (1964). I1. R. Kunin, Elements of IonExchange, Vol. 12, pp. 12, 13. Reinhold, New York (1960). 12. G. H. Cartledge, J. Am. Chem. Soc. 50, 2855 (1928). 13. R. B. Heslop and P. L. Robinson, Inorganic Chemistry, 3rd Edn., Elsevier, New York (1%7). 14. L. Pauling, The Nature of Chemical Bond, 3rd Edn, pp. 246252. Cornell University Press, New York (1963). 15. O. Samuelson, Studier rorande Jouhytande fasta ammen, Stockholm (1944). 16. W. C. Bauman, 23rd Nat. Colloid Syrup. Minneapolis (June 1949). 17. H. P. Gregor, J. Am. Chem. Soc. 73, 642 (1951). 18. G. E. Boyd, B. A. Soldano and O. D. Bormer, J. Phys. Chem. Ithaca 58, 456 (1954). 19. D. A. Robinson and G. E. Mills, Ind. Engng Chem. 41, 2221 (1949). 20. A. K. Bhaduri, K. R. Kar and K. B. Pandeya, Current Sci. 45, 444 (1976).

J. inorg, nucl. Chem. Vol. 42, pp. 292-293 Pergamon Press Lid., 1980. Printed in Great Britain

Studies of nitrosyl c o m p o u n d s - - - I . Thermochemistry of nitrosonium tetrachloroborate (Received 15 January 1979; received[or publication 11 July 1979) Nitrosonium tetrachloroborate, NOBCI4, is reported to sublime from the reaction of N204 with excess BCI3[1]. A product of identical stoichiometry is precipitated from a mixture of CF2CI2 solutions of NOC1 and BCI3[2] or by cooling an equimolar mixture of BCI3and NOC1[3]. Neither detailed spectroscopic nor any thermodynamic data are available, and the above preparative procedures lead to apparently different modifications of the product. Dissociation into NOCI and BCI~ is extensive at temperatures over ca. 273°K; melting into two immiscible layers is complete at 297°K. Reaction with atmospheric moisture is immediate, and manipulation is restricted to subambient temperatures and vacuum or rigorously anhydrous conditions. A detailed Raman study of both solid and liquid phases in this Laboratory[4] supports the formulation NO+BCI2, with dissociation into largely unassociated NOCI(g) and BCI3(g). The temperature dependence of dissociation pressure was therefore measured in order to calculate the standard enthalpy of formation and related thermodynamic parameters. EXPI~ENTAL

Reagents. Nitrosy] chloride (Matheson) was pumped through a trap at 195°K to remove N204 prior to condensation and storage at 77°K; any NO present was removed by pumping. Boron trichloride (BDH) was outgassed several times and then used without further purification. Preparation o[ NOBCI4. This was prepared using a modification of a previously-described method. BCI3 (10.tg, 0.090 tool) was condensed at 77°K into a reaction vessel contain-

ing NOCI (6.1 g, 0:093 mol.). The mixture was allowed to warm to 300°K, when two layers separated. Samples for analysis, spectroscopy and pressure measurements were taken by freezing the vapour at 77°K and pumping the condensate gently until a white flocculent solid remained. (Found: B, 5.88; CI, 77.10%; B:CI = 1:3.99. Calc. for NOBCh: B, 5.92; Cl, 77.64%; B:CI = !:4.00). NOBCh was manipulated under vacuum or dry-box conditions at all times. Samples used for pressure measurements were outgassed by pumping at low temperatures under high vacuum in break-seal ampoules sealed to the pressure-measurement system. This was outgassed by flaming and pumping and, as a final precaution, was equilibrated with BCI3(g) to remove surface water residues. Temperature control. Selected temperatures in the range 210.2-253.8°K were maintained by surrounding the NOBCL ampoule with well-stirred slush baths prepared from appropriate freshly-distilled, organic solvents. Temperatures were also checked using a calibrated mercury thermometer. Pressure measurements. A commercial quartz spiral gauge (Texas Instruments Company, Model No. 144) sealed directly to the ampoule and associated high-vacuum system was used. The performance of the gauge was checked and calibrated in separate experiments using rigorously purified samples of water (291.2306.2°K), acetone (210--150°K) and benzene (210-255°K), leading to a gauge factor of 115.26. Where possible, gauge readings were taken over both ascending and descending temperatures. Analyses. Boron was determined as boric acid after hydrolysis by direct potentiometric titration with standard alkali in the presence of mannitol. Chloride ion was determined after