Far infrared spectra of metal complexes in aqueous solutions

Joumal of bfolecultzrStrz~ciuure. 79 (1982) 261-265

FAR INFRARED SPECTRA

OF METAL COMPLEXES

261

in The Netherlands

Ekevier Scientific Publishing Company, Amsterdam -Printed

IN AQUEOUS

SOLUTIONS

C. CARR and P.L. GOGGIN Department

of Inorganic Chemistry,

The University,

Bristol

BS8 1TS (Gt. Britain)

ABSTRACT Using F.t.i.r.

and multiple

acquisition

methods,

good S/N ratios can be obtained from aqueous are presented

for some concentrated

colour precludes separate

cations,

quantitative

bromide

in about 4 hours.

chloride

systems

To obtain spectra without

removal of each component.

halide and gallium(II1)

solutions

ruthenium(II1)

Raman spectroscopy.

water or hydrated

far 1.r. spectra with fairly

subtraction

techniques

Results are presented

where

Spectra the

interference are employed

from for

for some indium( III)

systems.

INTRODUCTION Because of technical i.r. have attracted have reported solutions

of

in examining features results

difficulties,

relatively

and discussed strong

the broad profiles (ref.

aqueous

due to ZnCl vibrations here which demonstrate

readily observed

little attention.

electrolytes

concentrated

studies on aqueous

Dudley Williams

in the far and co-workers

for water (ref. 1) and -1 . Tyler and Querry, down to 75 cm

2)

solutions

observed

of ZnC12 were unable to locate soecific

(ref. 3) in a study-down that metal-halide

from concentrated

solutions

to 300 cm-'.

stretching

(> 1M) aqueous

solutions

features

We report can be

of metal-halide

complexes. METHODOLOGY

AND RESULTS

One difficulty obtaining

ln studying far i-r. spectra

cell windows

with thin films.

which are both transparent

Nicolet 7199A F.t.i.r.

of water

spectrometer

and polyethylene-windowed here are 4 hours

solutions

and sufficiently

Silicon proves to be a suitable material

Fig. 1 shows the spectrum

presented

of aqueous

(12.14 p thickness) Typical

so obtained

acquisition

(1500 scans).

nO22-2860/82/000D-Q000/$02.75@1982Elsevier

rigid for work

for this purpose.

with 6.25 p Mylar beamsplitter,

T.G.S. detector.

has been

Scientifichbli&ingCompany

using a Globar

source

times for examples

a .

b

sbo

430

lbo

‘0

l.lm&&eERs

Fig. 1. Far i.r. spectrum of water (12.14 p in silicon cell). Fig. 2. Far i-r. spectrum of 1.6M RuC13 in water: (A) as measured and (B) after water subtraction. One area where deeply coloured example,

the i-r. method may prove particularly

solutions

concentrated

shown in Fig. 2. water profile;

for which Raman spectroscopy

aqueous

As measured

ruthenium

(B) is obtained

by subtracting

to the formation features shows

the

at 400 cm of

water

spectrum

in

of

8.33M

LiCl

it.

Assuming

systems containing quantitative

4H20

LiCl.

spectrum

GaBr stretching

of

to

quantitatively

(Fig.

3),

where

“free”

water

to remove solvent

example.

Fig. 4

the feature

despite

water,

the is

due

doubtless

the spectrum

lo thickness)

Li+,

on the

less 3H20 per ruthenium,

as in the preceding

pure

on the

1 ower

still rising concentration

subtracted

to

give

which is used for further processing

Fig. 3(B) is the result of carrying water and LiCl respectively;

of

out two separate

the shoulder

at 272 cm

-1

of RuClRu bridging. 2M GaBr3

in

water

does

not

show

since the two broad bands observed

to those found for the other gallium

of 4.6 mol equivalents established

bound

[Li(H20)4]f"

subtractions,

may be indicative

wavenumbers

(12.12

Processing

is much more intense than in

the spectrum of "dissolved

The

complexes.

is

On adding LiCl to RuC13, the

band moves to lower wavenumber

of anionic

etc. IS not as straightforward -1

is superimposed

of the solution

One such

is dark red-brown,

"free".water

that to be the amount of bound water.

intense RuCl stretching

is that of very

is inapplicable.

which

(A) the solute spectrum

basis of the known water concentration assuming

trichloride

valuable

of

LiBr

shows

by Raman spectroscopy

the

formation

(ref. 4).

in CDC13 is shown in Fig. 5 for comparison.

any

features

attributable

below 400 cm"

trihalides. of

[GaBr4]-

The i.r. spectrum

correspond

However,

to

in

addition

(Fig. 5), as also of [~u4~][GaBr4]

263

8 I

_

2ba 3bO l.tfmmd

*JO

btl

r50

‘0

abo

b0

l!iO

abo URVENUMBERS

Fig. 3. Far i.r. spectrum of aqueous RuCl, t 3LiCl (1.7M in Ru): (A) as measured and (B) with water and [Li(H20)4] cation contributions

Fig. 4. Far 1.r. spectrum of 8.33M LiCl in water: (A) as measured and (B) after subtraction of "free" water assuming [Li(H20)4] cation.

subtracted

Silicon

separately.

windowed

cell

(12.12

~1.

187

URVENUtIBERS

solvent

and

(C) spectrum of (CDC13 subtracte

cation

subtraction.

Bu,+N]LGaBr,] in CDC13

Indium iodide with excess NaI shows In contrast

tetrahedral

as the ultimate

[In14]-

[InBr4]- is not formed

ln the aqueous

at Br:In ratios of 4 or more the InBr stretching -1 with no significant contribution around 190 cm ion absorbs.

The substantially

number presumably subtractlon

procedures

whilst this could,

lower wavenumber

due to hydration

(Fig. 6).

InBr3 + LiBr system;

implies a higher coordination

absorption

in part, be due to imperfections a significant

complex

band maximum in the i-r. IS -1 where the tetrahedral at 236 cm

(e.g, [InBrq(H20)2]-).

leave substantial

seems likely that it contains

'0

Fig. 6. Far i.r. spectra of (A) 1.5M “Nal.sInIb.s” in water and (5) [Pentyl,N] [InI,] in CDCIJ . Solvent etc. have been subtracted ln both cases.

FSg. 5. (A) Far i.r. spectrum of 1.5M nLi1.6GaBr4.6" as measured and (B) after

rbo

In this case the

in the 400 cm

-1

region and

in the subtraction

contribution

from hydrated

model

it

indium species.

The

+ Cl- system shows progressive changes with added Cl- (Fig. 7). position reached (InCl stretching maximum at can be reconciled with a hydrated InC14- complex, the currently accepted

In(II1)

We do not believe that the ultimate 255 cm") view

(ref.

5);

reported

that this is close

we note

for solid

[MeSNH] 3[InC16]

2.cm

i!!

(ref.

to

the

i-r.

acti

we stretching

wavenumber

6).

INCL6.S2

Zi%

$’

e w 990

.

I*

b 2bo ibo w%dJnBeRS

kbo

abo

ibo Fig.

b

WFI&JtL

7.

Effect

lb0

Fig. 8. (A) Far i-r. spectrum of 1.7M InI in water (water subtracted) and (8) the result of interactively subtracting the spectrum of [InIb] .

‘0

on far

i.r.

spectra

of

addition of Li Cl to aqueous InCl (Solvent and cation contributionshave been subtracted quantitatively). 3

.

Where several species are present together different

metal:halide

isolating

the

techniques,

spectra

through

conditions of

shown with the spectrum visible,

Fig.

bq

If

simultaneous

of aqueous

the

complexes

of

this

-

arises from a hydrated cationic the

Raman spectrum

frequency, system

ion

the data for

addition

and

A rudimentary There

subtraction

example

is

are two In1 stretches

to [InI,]- as also identified is

interactively

subtracted

from

the result is Fig. 8(B).

This residue

indium iodide complex.

In addition to

has an additional

polarised

by

feature at about the same

as a shoulder on w, of the anion.

We recently published chloride

by multiple

one corresponding

spectrum

should constitute

(Fig. 8).

InI

the spectra under

solution,

equations.

8(A) until it is no longer visible

probably

In-I

of

the higher wavenumber

the Raman spectrum.

or on dilution

individual

a set

in

a preliminary

(ref. 7) where

peaks predominantly

account of measurements

qua1 i tative use of interactive

arising from tetra-,

for the thallium(II1) subtractions

penta- and hexa-chlorothallates

enabled

to be seen.

265 ACKNOWLEDGEMENT We thank

the

S.E.R.C.

for

a grant

to

purchase

the

F.t.i.r.

spectrometer.

REFERENCES 1 2 3 4 5 6 7

D.A. Draegert, N.W.B. Stone, B. Curnette, and D. Williams, J.Opt.Soc.Am., 56 (1966) 64-69. D.A. Draegert and D. Williams, J.Chem.Phys., 48 (1968) 401-407. I.L. Tyler and M.R. Cjuerry, J.Chem.Phys., 68 (1978) 1230-1236. L.A. Woodward and A.A. Nord, J.Chcm.Soc., (1955) 2655-2656. T. Jarv, J.T. Bulmer, and D.E. Irish, J.Phys.Chem., 81 (1977) 649-656. 3. Gislason, M.M. Lloyd, and D.G. Tuck, Inorg.Chem., 10 (1971) 1907-1910. CZZ2C;;;, P.L. Goggin, and M. Sandstrijm, J.Chem.Soc.,Chem.Corun.~ (1981) .