Medium-range order in liquids: Interactions in supercooled electrolyte solutions system Zn(NO3)2 - DMSO)

l 12

Journal of Non-Crystalline Solids 106 (1988) 112 115 North-Holland, Amsterdam

MEDIUM-RANGE

Ladislav

ORDER

~ERVINKA

IN L I Q U I D S : INTERACTIONS IN S U P E R C O O L E D SOLU'I~IONS ,SYSTEM Zn(NO3) 2 -DMSO)

and

Zden6k

ELECTROLYTE

I~JELICI-IAR §

stitute of P h y s i c s , C z e c h o s l o v a k ~Institute of Inorganic Chemistry,

Academy of S c i e n c e s , 1 8 0 4 0 P r a h a 8, C z e c h o s l o v a k i a Czechoslovak Academy of S c i e n c e s , 1 6 0 O O P r a h a 6,

C ze c h o s l o v a k i a

X - r a y analysis of s u p e r c o o l e d electrolyte solutions in the s y s t e m d i m e t h y l s u l p h o x i d e (DMSO)Zn(NO~) o was made for p u r e D N [ S O (chemical formtlla ( 6 H 3 ) 2 S : O ) a n d for c o m positions charac~e~'ized b y m o l a r ratios R = D M S O / Z n ( N O _ ) _ j >, = 6, 3 a n d 2 T h e X - r a y scattering picture in the ~,hole c o m p o s i t i o n interval is d o m i n a t e d b y a m a s s i v e peak which shifts with i n c r e a s i n g Z n ÷ content from 1.44 ~ - i (for p u r e D M I S O ) to 1.54 ~ - i (for R--2) and describes a decrease of intermolecular d i s t a n c e s in this s y s t e m from 5.4 to 5.0 ~ . Clusters are identified a s D]V[SO m o l e c u l e s w h i c h d e c r e a s e their intermolecular distance a s a result of a four-fold solvation of the Z n 2÷ ion in D M S O . T h i s m o d e l is s u p p o r t e d b y the analysis of c o r r e s p o n d i n ~ radial electron density distribution c u r v e s w h i c h exhibit with i n c r e a s i n g Z n 2e content a d e v e l o p m e n t of a Z n - O coordination s p h e r e located at 2.3 ~ . The proposed structural m o d e l h e l p s also in the u n d e r s t a n d i n g of the a n o m a l o u s behaviour of the viscosity v s c o m p o s i t i o n d e p e n d e n c e .

ft. I N T R O D U C T I O N Up

to

lutions ones

now

with has

less

is

Lions

the a

structure

special

received

known

in

other

-

to dissolve

extremely

high

led

can

ganic

salts the

unusual

scosiby, plots

i.e.

the

exhibit

=

a

2, w h i c h

currently

a

structural

solutions

of p u r e in D M S O

6.

hexahydrate

kia, analytical

in a n

to R = 2 .

analyst",

were

and

of D M S O

mixture

!

was

o~

zinc

Czechoslova-

used

Zn(NO3)2.6H20

amount

The

(Lachema,

grade)

The

Merck)

without was

dissol-

corresponding heated

to 8 0 - 9 0 ° 6

s°c

45~c

\=-o 6oocI

// has

of vi-

concentration

a

mole

described

these we

ratio

minimum

e q u a t i o n I, figure

point of v i e w

inor-

with D N I S O

the

2 = 3 and

to explain

("pro

solu-

region

Among

DNISO

Zn(NO3) 2 was

vs

nitrate

analysis

2. E X P E R I M E N T A L

purification.

supercoo-

at

be

9, 3 a n d

ved

easily

dependence

viscosity

zinc

=

stu-

that m a n y

nitrate

maximum

cannot

used

In o r d e r

enabled

to

shown

its solution

concentration

R=DMSO:Zn(NO3)

IR

be

and

R

nitrate

formula salts u p

temperature.

zinc

because

solu-

electrolyle

have

DI%'IZO with

of dime-

exist in the m e t a s t a b l e

the liquidus

an

ability

inorganic

of o u r X - r a y

Much of

(chemical

can

below

chosen

The

so-

aqueous

structure

concentrated studies

solutions

and

on

colucentrations

of highly

tions. T h e s e

electrolyte

of interest.

the

DI%']SO

(6H3)2SO)

of these

lot

solvents.

thyIaulphoxide

dies

focus

a

about

of

pret results

by

at

any

i.

properties

!

z

o~'i o!, . 0~2 654

,

3

F I G U R E

from

tried to i n t e r -

0 0 2 2 - 3 0 9 3 / 8 8 / $ 0 3 . 5 0 © Elsevier Science Publishers B.V. ( N o r t h - H o l l a n d Physics Publishing Division)

o;3, ~4

,,

2 R MOLAR RATIO 1

Viscosity i s o t h e r m s in the Z n ( N O _ ) 2 - D M S O J systeml; R is the m o l a r ratio a n d x is the m o l e fraction of Z n ( N O 3 ) 2.

L. Cervinka, Z. Melichar / Medium-range order in liquids

in v a c u u m water.

in o r d e r

The

prepared DMSO

by

samples

vessels

moisture

and

durin~

put in a

solution

then

held

contamination

the m e a s u r e m e n t

in clo-

with air was

ne~lec we-

hol-

analysis

with a lead covered

foil (16}/m). T h e

X-ray

sample

at l o w e r

shielding

with a

at

with

scatterin~

foil g a v e

an~les

diffraction

peak

lO0 ~n .~_ c- 90 80 ~'70

SUPERCOOLED

ELECTROLYTE

SOLUTIONS R= (CH3)2SO:Zn(N03) 2

2°/II1%,

of a ma-

than

110

3°/ht

thin plastic

scatterin 9 picture

holder

first s h a r p

and

/

120

in

sample

provided

massive

the R = 2

130

polymethylmetacrylate

front side

ximum

6 were

samples

the

empty

remaining

and

the

der

the

the

R=3

were

the

ted. F~or the X - r a y re

with

dissolvi.ng

I. T h e

sed

to r e m o v e

solutions

113

R=2

-~ ,oL II I ~'%-.,. ol-;f'~l " - \

R=3

the R=6

(FSDP)

of D M S O . In figure -ray

2 we

scattering

we

show

conventional

way

The

X-ray

DMSO

tO a n

scatterin~

at 1.44

~,

corrected

lume

of liquid D M S O

void

space

structure

an

and 2.

intense

each

in ~ o o d

PSDP

distance

from in

of

agreement

of the D M S O

r~K)-

the m o l a r account

molecule

F'SDI ° to h i ~ h e r a value

ratio lq

DMSO

, .

,

DMSO J , 15, S [A'] 60 70 e

L

.

&0

30

vothe

50

assumed

to be

hedrally

(figure

ly a s same

of Z n ( N O 3 ) 2 is

of 1.54 /<~-i for

the

shift c o r r e s p o n d s

for lq=2 a v a l u e

way:

either

molecules

study

3

2

plateau

I~SDP position s 1 _-4"0.02 }~-i

1.44

1.49

1.47

1.54

real s p a c e dist a n c e _+O.OT .~

5.36

5.18

5.26

5.02

(table

tion n u m b e r the

salvation

the

sample

of the

part of

i). S u p p o s i n ~ DNqSO

in

electrostricresults

in

between solvent.

1q=3 is a n

in the PSDP

the

at the c o n -

This

it s h o w s

of Z n 2 + i n

almos%

in the p u r e

the

simil:nr-

~reater

distances

than

spheres

be is

find U ] e m s e l v e s

under

of Z n 2 + i o n s .

tration d e p e n d e n c e

has Thus

the

should

intermolecular

because

can

Zn2÷ion

in D M S O

Z n 2+

spheres

molecules

which qualita-

oclahedrally 3 or tetra-

as

In this s e q u e n c e

6

The

4) solvafed

under

ling influence smaller

1

5.02 /~. i

the Li + cation 4, w h i c h

salvation

to a

distance

of this o b s e r v a t i o n

ionic radius

centrations

in the

s-values

i. T h i s

of the intercluster

exception Molar

i , 10 . .

,

in a followin~

DMSO TABLE

,

20

tive explanation Ziven

DR{SO

concentration

reachin~

•

10

reaches

of the liquid 2.

shift of the

L

decrease

corresponds

(intercluster)

taking

around

~

FIOURE 2 C o r r e c t e d a n d s c a l e d X - F a y scattering curv e s in the Z n ( N O )- DMSO s y s t e m for m o 32 lar ratios R = 6, 3, 2 a n d for p u r e DS~qSO.

in a

of p u r e

value

diameter

With increasin~

observed,

by

calculated

0

lq=2, table

picture

bein~

molecular

(5.46 ~ )

lecule

3

of figure

/~-i. T h i s

this value

the

in figure

DISCUSSION

intermolecular

5.36

a

the

is c h a r a c t e r i z e d

located

with

AND

X-

calculated

intensity functions

3. l q E S U L T S

our

radl~l electron

curves

from

of

and

correspondin~

distribution

scaled

results

experiments

the

density

present

concen-

position

that the

a

salva-

i5 four, then

of Z n 2 + a r e

lust safu-

L. Cervinka, Z. Melichar / Medium-range order in liquids

1 14

,,°[ 1 01

/li l,"~

[ SYSTEM DMS0: ZnIN0a)2 sos

Zn,,,0 0

FIGURE 4 M o l e c u l a r c l u s t e r s in the Zn(NO3) 2- DMSO system In this schematic picture a f o u r " ~4-. - f o l d c o o r d i n a t e d Zn ion is supposed.

z40! o

i

2,0 ...."

i~

/i

1/ ."

bond

dis~nces

ponding

C-S-C

94°and are

i I~16~'B~2Bs. s ".-'" //" 2 r[~] 0

3

--I

4

5

and

The

O-S-C

bond

i O O 0 respectively.

These

in a g r e e m e n t

talline D M S O lutions

6

respectively.

with t h o s e

angles

found

in solutions

of c a d m i u m

in crys-

and

perchlorates

in so-

in D M S O

iodide

are

values

5, in liquid D M S O

of metal

corres-

3 and

complexes

i n D M ~ O 6. Radial

F'IOURE 3 electron density distribution curves in the Zn(NO3)2-DMSO system.

With peak

increasing

at 2.25 ~

attributed rated

at R = 4 .

tion s p h e r e s

(NO3)-

by

cannot

For

of the a b o v e

R=2

we

observe

a

approximately heights

sudden

twice

for both

concentrations

power

trast to t h e

The

radial

for pure cated can

DMSO

at 1.15, be

1,60,

ascribed

Zn-S

R=3 Zn-O

as

peak

This

is a n

salt suppose

medium

scat-

in c o n -

well

distribution

3, s h o w s

1.85

to C - H ,

and S-O,

peaks

lo-

peaks

2.65 ~ , w h i c h S-C

a n d C,-O

The

Zn-(H20 )

located

at

that it descri-

bond by

into the

the

clear

separation

sphere

from S-C

the

distance

that for this c o n c e n -

R=2

sphere we

located

observe

a very

of Z n - O

probably

lengths

of Z n 2÷ i s

at a p p r o x i m a t e l y

overlapping

is c a u s e d

in Z n - O

Hence

For

maximum

2.10 ~:

a

coordination

defined.

broad

above

density

i.e.

peak

the D M S O

indication

tration t h e

being

We

observe

characterizing

FSDP

similar v a l u e

suppose

coordination

peak

the

DMSO.

we

in

with l o w e r

i.e.

interactions in the Z n 2 + - O = S ( C H 3 ) 2

For

]5"SDP

a be

complexes.

one.

figure

bes

we

can

Z n ( N O 3 ) 2 solutions 7.

a massive

appears;

of the

distances

greater

in a q u e o u s

of the

(NO3)-cluster

electron

DMSO,

K'or

3.20 ~

i

peak of Z n - O ,

found for Zn-O,

Simultaneously

prevailing

the

large

pure

the rea-

decrease

increase,

as

to a

of the

in the solbe

to t h e

solutions

and

that this is d u e tering

a

due

Simultaneously

shows

interactions

plateau.

of (NO3)-intercluster

the material. height

again

interactions,

however,

the intermolecu-

mentioned

Zn-(DMSO)

(2.17 v~)was

molecules

distance

solva-

concentration

This

to the d e v e l o p m e n t

penetrated

process,

of Z n 2+, but m a y

son

intercluster

This

of D M S O

sphere

I~ the

inevitably

dramatically

lar d i s t a n c e s

influence

be

anions.

change

vation

decreasing

must

Zn(NO3) 2

develops.

by

evoked

and

S-C

fluctuations as

mentioned

penetration

solve[ion

of ( N O 3 ) - c l u s t e r s 2+ shell of the Z n ion.

Zn2C'-(m03)-

actions via o x y g e n

and atoms

Zn2~'_ (n~vlSO) i n t e r ~ contribute

to

b r o a d p e a k at 2.10/0~. T h i s l e a d s a t the

the

same

L. Cervinka, Z. Melichar / Medium-range order in liquids

time

to a

charge

gradual

by

probable

a

neutralization

of the Z n 2+ 1 of c o m p l e x e s with a

formation

composition

/Zn(NO3)(DMSO~/-

or /Zn(NO3)2(DMSO)2/. complexes

(which serve

in v i s c o s i t y

decrease

of viscosity

concentration figure

kinetic entities

vation

sphere,

"free"

DMSO

in the

reason

particles

is gradually

for the

plexes

with i n c r e a s i n g interval

R=3

salt

to 2, s e e

The

above

mentioned

coordinated

Z n 2÷

the

for lq=3.

The

observe

5.75 ~ the

clusters

distance

possible A

deve-

at 4.20,

the

5.02 ~)

packing

of

detailed

smallest

intermo-

reached

i t s highest

of the

structure of

description

constituting

in this w o r k

needs,

of m o r e

4 a lack

of D M S O

Z n 2+ salvation

solvation less

documented

by

a

broad

plateau

on

of the

peak

at 2.1 ~ peaks

the i n c r e a s i n g

and

consequently

analysis

salvation

of Z n 2+ ions

um-range

order

the

solutions

however,

terized

by

f r o m 5.4 • lecules

intermolecular

(in p u r e

in the

a fur-

The

anomalous

of viscosity

four-fold

liquids

The

developed 2.3 ~.. of the

of the

leads

in a

Z n 2+

to a l o w e r

RE 5"ERENCES i. P. P a c d k , Z. K o d e j £ a n d H. ~ p a l k o v & , Z. L P h y s i k a l i s c h e Chemie, Neue lmolge 1 4 2 (1984) 157. 2. P. Pacelk,

J. Solution

Chem.

of Z n 2~" a n d

composition

concentration

R=2. dependence

a

consequence

16

and A32

(1987)%%. S. A h r (1978)

J.P. Toth, G. Ritzhaupt a n d J.P. Devlin, J. P h y s . C h e m . 85 (1981) 1387.

5. lq. T h o m a s , A c t a Cryst.

C.B. S h o m a k e r 21 (1966) 12.

and

6.

S. P a c e r , R. Triolo a n d Acts Chem. Scand. A33

7.

S.P. Dagnall, D.N. H a g u e and Towl, J. C h e m . Sac., F a r a d a y 78 (1982) 2 1 6 1 .

ranging

to 5 X f o r m o -

sphere

is in this s y s t e m

medi-

is c h a r a c -

distances

mEsa)

salvation

c o L * r e p o n d i n g to t h e

of a

in D M S O .

in these

(for R = 2 ) b y

vi s c o sity.

of Z n ( N O 3 ) 2 - D M S O

in f a v o u r

is

concen-

to 2 results

4.

points

of

position

which

4. C O N C L U S I O N S X-ray

to

This

at 1.9 a n d

3. H. S a n d s t r ~ m , I. P e r s s o n land, A c t s C h e m . S c a n d . 607.

The

the

5"SDP

partial or full neutralization charge

sphere

concentration

salt in the interval R = 3

R

groups

regular.

simultaneously

well defined

leads

of ( N O 3 ) -

becomes

com-

For

molecules

sphere

penetration

ther study.

solutions

massive

increases.

of

(characterized

degree.

particles/clusters treated

by

the liquid

(for R = S ) a n d

confirm that for this

medium-range

for this c o m p o s i t i o n lecular

located

expense

Z n 2+ w h i c h

from

Z n 2+ sal-

at the

into the we]/ d e f i n e d

the

of D M S O

in the

hence

already

a

bound

increases

tration d e p e n d e n c e

it e q u a l s

concentration.* number

molecules;

would

of Z n 2* is

where

moreover

which

(NO3)-

and

case

are

built u p

increased

Thus

concentration DMSO

number

in water,

of distinct p e a k s

and

we

at 2.10 ~

solvation than

]5~or ]q=2 w e

5.05

peak

point

four-fold

in the

coordination

broad

thus smaller 7 six .

lopment

of a

Z n 2÷ ion, b e c a u s e

six-fold

observe

observations

time in f a v o u r

salt

its v i s c o s i t y

than

to fill the an

same

and

smaller

Z n 2+ s a l v a t i o n

s i x to f o u r t h e

i s in c o m p a r i s o n

i.

at the

of a

the

in t h e

with i n c r e a s i n g

F'or R from

m o b i l i t y of ~ s e

/Zn(DMSO)4/2-

- this i s

and

sphere

changes

molecules, which

as

measurements)

to d o u b l e - c h a r g e d greater,

The

and

of g r a d u a l

115

K.

Eriks,

O. J o h a n s s o n , (1979) 1 7 9 . A.D.C. Trans.

2