Water-anion vibrational coupling in some crystallohydrates

Journal of hloiecular Structure, 115 (1984) 359-362 Elsevler Science Publishers B.V., Amsterdam - Printed In The Netherlands

359

WATER-ANION VIBRATIONAL COUPLING IN SOME CRYSTALLOHYDRATES 6.

S~PTRAJAN~V

Facul ty Skopje,

and

f4.

RISTOVA Cyri

of Chemistry, Yugoslavia

1

Methodi

and

us

University.

ABSTRACT In treating the vibrational spectra of crystallohydrates, it is usually assumed that the water molecules vibrate independently (or nearly so) from the rest of the structural units and, consequently, the bands which shift on deuteration are automatically assigned to In a number of hydrates of mewater modes (internal or external). tal carboxylates, however, we were able to de;ect indications of water-anion vibrational coup1 i ng.

INTRODUCTION An

assumption

when

the

that

water

dently the

vibrational

the

exception

which ned cules

to

water do

used

to

not

namely,

shifted

least

to width

higher is

(acetates

and

formates)

factorily

not

fit

interpreted

sumed.

In

the

rates,

similar

OQ22-2860/84/SO3.00

case

if of

conclusions

the

water-anion

some

we

and/or

criterion

the

some

lowering

the but

us

were

by

Tewary

0 1984 Elsevier Science Publishers B.V.

is, study

of

could

metal

formate et

rather

temperature

coupling

by

low-

carboxylates

encountered

vibrational

is

our

the

are,

intensity of

metal

scheme

of ones

and

investigated reached

mole-

examination

temperature

various

assig-

or

additional

course

the

bands

are ions

the

of

established

and

librational

the

with

al 1

deuteration

the

In

however,

deuteration

into

the

decreased

hydrates

[Z],

on

-

on

is indepen-

structure

present

when

111.

the

less

molecules

An

based

frequencies

of

on other

bands

increased

effects

could

the

appreciably

spectra

unexpected which

of

apparently,

vibrational

the

is

studied

or

Consequently

protons.

librations

sensitivity

up

water

position

that

exchangeable

water

make

related,

implicitly,

are more

coordinated.

their

provided

or

vibrate

which

symmetry is

explicitiy

crystallohydrates

structure

water

contain

their

ered,

of

the

change

assign

made,

units

alike,

which

modes,

temperature

the

in

significantly to

usually

structural of

atoms

is spectra

molecules

from

metal

at

which

aZ.

be

satis-

was

as-

dihyd13,41.

360 EXPERIMENTAL All

studied

prepared on

formic red

standard

DzO or acid

were

JRS

For

SIB

used

were

either

laboratory

solvent

was

spectra

a JEOL tra.

by

from

compounds

to

containing

prepare on

the was

infrared

we is

present,

that

of

deuterated used

believe,

nickel

to

on Thus,

protiated

of

bi

is 945

the

found cm-‘)

perature. (C) Raman

deuterate instead almost

:

thermal

this sensi

which

Raman

spec-

vibrational probab-

a2.

infrared

of

this

however. compound

tivi

characteristic

a of

(Fig. exactly

(A) Variation of (B) Infrared spectra spectra of protiated

infrawhile

tetrahydrate

a possibility,

the

of

the

-

a VLT-2

water-anion et

have

izati The

the

were

deutero-

instrument,

record

acetate

ly compound

or

samples. 580

measurments

or

recrystall

deuteroacetic

a Perkin-Elmer

spectrophotometer

low-temperature

available

Repeated

methods.

media

recorded

commercially

of

IR spectra the of protiated and deuterated

this

latter

band

the

of nickel on lowering and deuterated form.

acetate the temform.

361

oned

frequencies.

A doublet is

observed

as

in

that

served

about in

of

the

a little

This other

hand,

band the

spectrum

tivity

and

deuterate)

with

a close

Several

factors

carboxylate led (one the

by

groups

coordination

of

them

water

being

molecules

the

of

the

can

an

and

the

water

to

the

same

only is

261.9

acetate

in

by

to 2,

1530

cm-’

ted

form

(it

perturbed is

frequencies, is

increased

because ration 1500

lx0

with Fig. 2. Changes, on deuterati on, in the acetate v8 region.

the

the

cobalt

of

frequencies.

is,

probably

of 900

in

the

water

all

tetrahydrate, vibrations

cm-’

seems

because

of

the

vibposi-

samples destroyed

bending

respects,

the

mode

higher

the is

lower

acetate above

interaction

aro-

6(HOH)

normal in

shift

situation

interaction

quencies plete,

the

towards

The

cm-1

of

and

its

content

vib-

similar except with

to

seen

protiav6

towards

to

deuterium

As

the

the

shifted

“returning” the

of

not

found

acetate

with

gradually

apparently

band

spectrum

is

requirements.

region.

acetate

interaction

and of

energies

is

the

libthe

mixing

similar

to

around

their

molecules

that

low-frequency

the

bonds

finally,

symmetry

strong

the coup-

field

water so

coupling

in

by

ration) as

with

Thus,

force and,

the

belongs

the

librational

making

low,

strict

the the

und

tion

is

cm-'

vibrational

hydrogen

the

both

vibrational

Fig.

by

probably

of

in

mechanically

and

[71);

states

limitted

if

an

sensi-

band

a water

anharmonic

hindered The

single

are

ion

ions

vibrational not

920

and

plausible.

molecules

symmetry

the

to

assumed.

interaction

highly

due

970

explained

asymmetric,

rations

the

is

be

temperature

and

pm long

very

site

be

metal

ob-

On the

around

to

frequency

such

make

is

V~ mode.

(their

vibration

unperturbed

must

the

bands

simply

where

band

1C).

being

respect

form,

strong

counterpart two

frequencies

protiated

and

compound

acetate

lower)

the

Fig.

candidate

with

vl,

of sharp

(see

protiated

the

between

somewhat

infrared

only

the

position

of

cm-’

its

behaviour

their

spectrum mode

the

(only spectrum

a single,

945 and

of

coupling

same Raman

deuterate

vibration,

the

the the

below

latter

acetate

in

at also

be

lower

that fre-

less water

comli-

362 brational ries

frequencies.

of

decrease, the

on

order

in

the

Ni,

tium

formate

ries

of

this

series

as

Mn,

i.e.

of

the

metal

in

are

There

of

is,

care

should of Hz0

bending)

in

in

the

no

anion

librations

or

the

cobalt

is

that

in

se-

coordinated,

order

of

the

in increase

acetate

to

believe

to

carboxylates

the

vibrational

other

in

appear

water

se-

members et

of [3,4],

al.

of

only,

so

spectra

situations

in

stron-

the

interactions

to

especially

expected

two

that

of

in

Tewary

the

vibrational

that of

when

same

vibra-

region(s)

mode

wa-

(the

paper),

(for by

and

dihydrate

discussed,

reported

limitted

vibrations

accompanying

already

interpreting

some

water

dihydrates

reason

general,

are

as were

be

(81

frequencies

carboxylate

an

formate

would

taken

crystallohydrates

of in

findings

course,

type be

case

metal

which

between

the

shown

librational

ions.

121 and,

same

earlier).

to

discussed

dihydrate the

described

the

coupling

also which

been

water

following

Fe,

isomorphous

the

metal

Co,

mentioned

tions

the

observed

of

namely, the

radii

librations

spectra

has,

compounds

changing

ionic

We have ter

It

isomorphous

as

(e.g.

HOH

(1972)

1663.

.

REFERENCES 1.

M.

Cadene

2.

M.

Ristova,

and

A.M.

Vergnoux,

MS Thesis,

Spectrochim.

University

of

Acta,

Skopje,

28A

Skopje,

1981.

3. G-D.

Tewari, Spectrosc.,

V.P. Tayal, D.P. 36 (1982) 442.

Khandelwal

and

H.D.

Bist,

Appl.

4.

G.D. Tewari, Struct., 96

V.P. (1982)

Khandelwal

and

H.D.

Bist,

J.

Mol.

5.

D. Stoilova, 371.

Khim.,

3

(1976)

6.

P.

7.

T.C. Downie, Cryst., 827

8.

B.

Baraldi

goptrajanov,

G-St. and

G.

Tayal, 45. Nikolov Fabri,

W. Harison, (1971) 706. PhD Thesis,

D.P. and

Ch.

Spectrochim. E.S.

Raper University

Balarev.

Izv.

Acta, and

37A

M.A. of

(1981)

Hepworth,

Skopje,

Skopje,

89. Acta 1973.