Influence of the solvent medium on formation of Cu(II), Zn(II) and Ni(II) hexacyanocobaltates

Tu/ut,nf. Vol. 26. PP. 157 159 0 Pcrgamon Press Ltd 1979. Printed in Great Britain

INFLUENCE OF THE SOLVENT MEDIUM ON FORMATION OF Cu(II), Zn(I1) AND Ni(I1) HEXACYANOCOBALTATES* ALE~ANDRO

DE ROBERTIS,Anlos BELLQMOand DOMENICODE MARCO Institute of Analytical Chemistry, University of Messina, Messina, Italy 14 June 1978. Accepted

(Received

14 August

1978)

Summary-Investigations on precipitation of metal hexacyanocobahates from mixed solvent media have confirmed the earlier interpretation of the mechanism and provided further insight into it.

In an earlier investigation’ we studied the formation of I complete the data reported in the hterature.2-s The results were interpreted as implying a precipitation reaction in insoluble compounds between K,Co(CN), and various and the metal ions in aqueous medium, with the purpose of identi- ,t 1: 1 ratio between the ion-pair’ K+-Co(CN):’ cation, any further transformation then occurring in the fying the reaction stoichiometry for various concentrations of the reacting species and order of addition, to verify and ” solid phase. Since the equilibrium constant of ion-pair formation increases with decreasing dielectric constant of the solvent * Supported by C.N.R., Rome.

-_

I

cl.3 Cdll)

w An

-.-O-O-~-O--n-O

I

-0-o

q-o-

--

R Q

0-O /

,0-o -0 GB&Z)-+O-~-O-kVIf l.6

1.0

1

2

2.!s

J 2.63

R=l.OOlo-aoml

I

1

1.3s S pAn

A’

.A’

f/ 0

PAM

3.5

1

I

-oR=l.~Ok~=o.ooo~lO

a pAn

S 3.43

R=1.50(0-0.0066)

0

5 pAn

5 3.46

R voriobh

140

S pAn

S 2.58

R-l.OOlo-0.0064)

2.~6

*

S 342

R voriobk

pAn

/AA 3

‘t2.,3 1.42

. 1 IA1

homC1.OO

from >l.OO

to!@ 1.60

lo S 1.50

k -1%

An

_

*

.-133

cua).

_ -1.0

0-cka-o-onR 0

0 PCU

1

2

1.5

I

1

I

CUKCO(CN)~

_

for Rfor

tronsformotion

0 =10X; 0 = 20%

I

3

I

3.6

I

for R = 1.00

Cu,K~o
2.5

1.33

R- I.50 occurrod

: A=30%

in the solid photo

dioxon - wotor. vlv

Fig. 1. Cu(II)-water-dioxan system. R values and relative standard deviations as obtained for different Cu(I1) and An concentrations at varying dielectric constant of solvent medium. (A) An titrated with Cu(I1); (B) Cu(I1) titrated with An. T*L.26,2-F

157

158

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L + NKII) -”

)+---or-o-R-o

z

L

-1.33

~R-&e-4-&e-R-~-A

.-.

-1.0

0-0-0-0--0-&0-coCO-0-0-&~-0-0-.+0A-lJ-0-a 1.5 2

.

An 0 PAn 1

I

I

0 1.15s pAn s 3.44

R = 1.00 (a -aooW

U 1.30SpAnS

3.32

A 1.41SpAnS3.53

-_,

0

R=l.OO

(O-0.0041) _,

R

R-1.00

(a-o.oWr)

-

I

1.30

spAn

I 2A4SpAn

.

R=t.33

I

t

s l.95

R = 1.33 ((I -o.oo.%ol

13.32

R=l.50 (O=aoo4?)

kJ=O.CCW

p -1.5 An

O-O-_O-O--Oa/a-O-D--n-o-O.a-O-n-O

.

/

A’

0’

Ni(ll) .

+

_ E f .-1.33 o-&o-a-&a’ I &-a--a -1.0 1

0 Hi

1s

2

I

0 1.22 5 pNi

4

S 3.40

R = 1.50

R=1.33 R = 1.50 lo-0.00391 la =o.oow)

pNi 5 1.40

R = 1.00 (a = o.ww)

A 1.49 I pNi 2.30

5 1.90

R = 1.33 (a -o.oo&q

5 3.33

R = 1.50 (0

5 pNi

NiKCo(CN)6

for for

Ni3[Co(CN)d,

for

0=10%:

0=20X:

3.5

I

-W,046)

R = 1.00

Ni.,K~o(CN)&

transformation

3

Io=o.oon)

1.36 1.70 5 S pNi pNi SS 1.60 3.24 1.15 5

A

2.5

1

R= 1.33 R= 1.50

occurred in the wlid a=30%

fnhase

dioxan-water,vfv

Fig. 2. Ni(II)-water-dioxan system. R values and relative standard deviations as obtained for different Ni(lI) and An concentrations at varying dielectric constant of solvent medjum. (A) An titrated with Ni(I1): (B) Ni(I1) titrated with An. medium.“’ the influence of the K+-Co(CN)ispecies on the precipitation stoichiometry should become morel marked as the dielectric constant of the solvent medium shifts from 80 (for water) to lower values (for mixtures of water with organic solvents of low dielectric constant). We have therefore decided to examine this experimentally as an extension of the earlier work.

always 100 ml and the reactant concentrations were chosen accordingly. All precipitates with a defined composition were analvsed for cation and cobalt content by atomicabsorption spectrophotometry. For titration resuhs leading to the same compound, the standard deviation. cr. was calculated. Rrt~ctions between Cu(ll)

EXPERIMENTAL

The dielectric constant of the solvent medium (4 was varied by using 10, 20 and 30”,, v/v dioxan solutions in water. Stock solutions of copper, nickel and zinc sulphates were prepared and standardized; the working solutions containing the desired amounts of dioxan were prepared by dilution. The hexacyanocobaltate solutions were similarly prepared and periodically standardized. The equivalence point of the precipitation reactions (performed at 20 k 1’) was detected with an oscillometric digithe ratio (R) tal read-out apparatus. ” For each titration of the analytical metal ion and hexacyanocobaltate concentrations at the equivalence point was calculated. The concentration range examined was the widest consonant with reagent solubility and the instrumental sensitivity. No buffer solutions were added and therefore the titration.pH was that engendered by the solutions used in the reaction. The. initial volume of solution titrated was

ad

K3Co(C&,

(Fig. I)

The compounds found were all intensely blue, with R = 1.00 corresponding to CuKCo(CN),. R = 1.50 corresponding to Cu,[Co(CN),], and R = 1.33 corresponding to Cu,K[Co(CN),], and stoichiometrically equivalent to CuKCo(CN), + Cu,[Co(CN),],. besides intermediate values in passing from one species to another. When the Cu(II) is used as titrant for 1.35 < pAn $ 2.63 in IO”, dioxan solution (An = anion), the compound first formed has R = 1.00. and is transformed in the solid phase. by addition of Cu(II). into the compound with R = 1.50. When Cu(l1) is the titrand. the species having R = 1.33 is preferentially formed. the range of conditions for its formation increasing as E decreases. In aqueous medium. the species with R = 1.50 was always obtained. Reactior~s berwen

Zn(II)

ad

K,Co(CN),

The only species found were those with R = 1.00 and R = 1.50, just as in aqueous medium. Decrease in E. how-

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ever, increased the tendency to formation of ZnKCo(CN),. In fact, with Zn(II) as the titrant, the compound with R = 1.00 was always precipitated irrespective of the conditions, and then underwent transformation in the. solid phase to Zns[Co(CN)& In contrast, in aqueous medium this transformation was limited to a restricted concentration range, only the species with R = 1.50 being normally obtained. With Zn(I1) as titrand the species with R = 1.00 was stabilized at the lowest l value. This species was not obtained in purely aqueous medium. The precipitates were white.

159

is present in the spatial group (4 Co, 4 Me,, 2 Me,,, 24 C, 24 N) in I : 1 ratio with Co(CN)z- and bound in an Me,-N-C-Co chain; the other two Me,, ions are statistically distributed and very weakly co-ordinated. Therefore, for the empirical formula, the configuration Me, Me,, iI2Co(CN), occurs. Consequently, the ions in the Me,, positions, because of these characteristics, are mobile and can be partially or totally substituted by potassium, to give the MeKCo(CNk and Me,K[Co(CN),], species: this can occur both during the precipitation as well as later in the solid phase, and is favoured by the pre-existence of K+-Co(CN):ion-pairs.

Reactions between Ni(ll) and K,Co(CN),

(Fig. 2) Precipitates with R = 1.00, R = 1.33 and R = 1.50 were found, as in aqueous medium, but decrease in E stabilized the first two compounds over a wider range of conditions. Thus with Ni(I1) as titrand in aqueous medium, the Ni,[Co(CN)& species was exclusively obtained, but in 30% dioxan medium, at high Ni(I1) concentrations the NiKCo(CN), species was stabilized. An analogous trend occurred with Ni(I1) as titrant. The precipitates were blue. DISCUSSION

The results show that the dielectric constant of the medium influences the stoichiometry by favouring the presence of potassium in the precipitates. Decrease in E causes an increase of the K+-Co(CN):ion-pair formation constant, so that for a fixed K,Co(CN), analytical concentration, the effective ion-pair concentration is the higher the smaller the E value. Consequently, the reactions with K+Co(CN)iare favoured rather than those with Co(CN): -. Also the structure of the precipitates plays a positive role in formation of the mixed hexacyanocobahates, as can be verified through localization of the metal ion and bonds in the crystal lattice. In fact, two types of environment for the metal ion can be distinguished,” denoted by Me, and Me,,. The former

REFERENCES 1.

A. De Robertis,

A. Bellomo

and

D. De Marco,

Taianta, 1976, 23, 732. 2. A. Malagudi and T. Labianca, Gazz. Chim. Ital., 1954,

84, 979. 3. M. A. Rallier and E. Arreghini, ibid., 1939, 69, 499. 4. J. Richardson and N. Elliot, J. Am. Chem. Sot., 1940, 62, 3 182. 5. S. C. Saraiya and A. K. Sundaram, Currenf Sci. Indiu, 1969, 38, 337. 6. J. Csaszar and A. Felvegi, Acta Chim. Acad. Sci. Hung., 1966, 47, 499. 7. A. Ferrari, M. E. Tani and G. Mangano, Gazz. Chim. Ital., 1959, l39, 2512. 8. J. Krtil, CoBection Czech. Chem. Commun., 1967, 32, 4496. 9. J. C. James and C. B. Monk, Trans. Faraday Sot., 1950, 46, 1041.

10. G. H. Nancollas, Interactions in Electrolyte Solutions, p. 17. Elsevier, Amsterdam, 1966. 11. A. Bellomo, A. De Robertis, A. Casale and D. De Marco, Anal. Chem., 1974, 46, 1158. 12. A. Ludi and H. U. Guedel, He/u. C&n. Acta, 1968, 51, 2006.