Vibrational spectra of the [Re(CN)7]4−, [V(CN)7]4−, [Nb(CN)6]4−, [Re4S4(CN)12]4− and [Re4 Se4(CN)12]4− ions

JournaIofMokculnrStrrccfure,46(1978) 307-317 OElswierScientificPub~gCompany,Amsterdam-~tedin

VIBRATIONAL

SPECTRA

OF THE

CRe&S&(cN) x21’- m

W.P. GRBFITE,

Inorganic

[Re4Se4CCN)lo]*-

P.M. KIERNAN,

Chemistry

Technology,

cRe(cN) 7 I”-,

London

Research

307

The Netherlands

[VUX)

7

I’-,

[Nh KN)

B

I'-,

IONS

B.P. U'B.ARB

Laboratories,

Imperial

College

of Science

and

SW7 2AY (Great Britain)

and J.-H. B~GEADLT

Laboratoire

de Cinetfque

Chimique,

75230 Parfs

Cedex 05 (France)

Universit&i Pierre

et Marie

Curie,

ABSTRACT

The tibrational

spectra

the solid state and solution, ures of the complexes

of the tftle complexes and fundamental

in solution

have been measured

modes assigned.

are discussed

on the basis

in

The structof these

results.

The cyanide a-donor

ion (CN-) is capable,

and z-acceptor

states and coordination heptaV-VII),

and octacyano

properties, numbers

complexes

and have isolated

and [Nb(CN)e]s-

143.

by exercising

of stabilfsing

[l]-

Recently

of the early

the new species

present

similar

(L = S, Se).

their structures

data on the metal

12-43 we have been study%ng

(Re(CN)Jl]t- [2,3], the vibrational

to assigning

in aqueous

cluster

its

a tide range of oxidation

transitrLon metals

In this paper we discuss

these ions and of fV
a balance between

[Nb(CN),]4' spectra

of

their vibrational

solutions.

complexes

(Groups

We also

[S] [R~K,L~(CN)ZZ]~-

REHJLTS

AND DISCUSSION

(A)

Heptacyano

complexes.

ligands

the three most

monodentate pentagonal capped versions quite

bipyramid

trigonal

[9].

complexes

the DJh and Czv forms data have

SO

have

vibrational

spectroscopy

solid

and Dsh in aqueous

state

reported data

liminary

Raman

to attempt

for heptacyano

found

rules

no and

in the

have hitherto

there are limited

Haman

[14];

[12];and

and

these

three

data

reported

for

pre-

K5bfo(CN),l [Zl.

for Dsh and Cav symmetries between

been

and infrared

infrared

we have

for Kk[Re(CN)7].2Hn0

to distinguish

Though

electronic

for the anion

studies

1151 and RG[Mo(CLQ7].2H20

data

e.p.r.,

only

1141.

spectroscopic but

are

methods

1) [11-U].

a Czv configuration

solution

the mono-

and the related

by X-ray

(Table

the

or distorted

of interconversion

studied

1121 and Na5[Mo(CN)7].10Hz0 and infrared

shapes

with

are

(Csv) and

these

for K4[Mo(CN)7].2Ez0,

complexes,

On the basis of the selection ly feasible

far been

vibrational

for &[V(CN),].2H,O

octahedron

having

been

complexes

stereochemistries-f7-91

of hepta-cyano

have

suggest

for heptacyano

Ks[Mo(CN)7].Hz0

number

which

been presented

No comprehensive

co-ordinate

[lo] and the energies

For the small

hepta-isonitrile

X-ray

Complexes

(Czv).

of them are known

small

likely

the monocapped

(Dsh).

prism

For seven

it is clear-

stereochemistries

complexes.

TABLE1 Structural

data

on hepta-cyano

and -isonitrile

Idealised Complex

'Oint group (anion)

K+[V(CN),].2HzO

D

Na~[Mo(CN)~].lOHIO

D

Ks[Mo(CN)7].HzO

CM0
71(PF,) a

sh sh

cs

C zv

complexes

Equatorial

Axial M-C

distance

(&

M-C

distance

(61) Ref.

2.144(12)

2.149(6)

Cl13

2.129(10)

2.141(7)

1121

2.14(l)

2.15(l)

Cl21

2.179(9)

2.133(7)a

Cl33

2.051(7)l)

Distances

to a capped

face,

b

uncapped

face of capped

trigonal

prism.

309 (i)

The heptacyanorhenate(IV)

salt K4[Re(CN),].2H20 the aqueous closely known work

solution.

similar

a pentagonal

between

&[Re(CN)7].2Hz0

to assume

2), though

solution

in the 2000-2200 state

2Hz0,

suggests

from

the solid

that

there

cm-'

spectra

are observed,

Raman-infrared

require

splitting

effects

will

of

for both

for the infra-

and the close

this,

electronic

are few

spectra

as is the case

spectra

stereochemical

in particular

in agreement

similarity

of K~[Re(CN)7].

change

for the anion

with

good evidence

solution.

prediction

in the CN stretching

fundamentals.

polarised

provides

in the aqueous

coincidences

Raman

more

region;

solution

a symmetry

there

of crystalline

of the Raman

similar,

is no major

[Re(CN)7]rr- has DSh symmetry

the eleven

state

is

X-ray

to solution.

The Raman

bands

solid

the latter

this

and

is

crystal

also has

with

spectra

the solid which

from single

that[Re(CN),14-

The profiles

and aqueous

pattern

[2,3] and since

In agreement

are very

The potassium

from both

powder

anion

and infrared

the results.

and aqueous

of the solid

spectra

has an X-ray

bipyramidal

the Raman

(Table

complicate

red spectra

Raman

to this in the solid.*

coincidences

solid

The solid

it is reasonable

approximating

course

excellent

[Re(CN)7]4-.

to that for Ks[V(CN)7].2Hz0

to contain Ill],

gives

ion,

bands,

Both more

Four polarised

for DSh,

and

region.

We observe

the CSv and Czv point

Raman

that

fundamentals,

there

groups

and many

Raman are no ten of

would

Raman-infra

red coincidences. On the assumption [Re(CN)7]4solution,

and,

assuming

some of the infrared Raman

and I.R.

[1,3] we know Re-C

bands.

Prom previous

that CrN stretches just above

The bands cm-')

are the easiest vz-va.

and is polarised

(2OOC-2200

band

(P - 0.07);

*This has recently been Brdgeault, J.M. Manoli

also,

since

cm-'

studies cyan0

on the

complexes a~?

from 400-650

and Re-C

they contain

stretching

region, cm-'

(400-450

all the polarised

at 2123 cm-' is the strongest

it

to assign

1163.

cm-')

we assign

for the

attempt

in the 2000-2200

deformations

for

bands

comprehensive

Re-C-N

100-200

to assign

The Raman

structure Raman

[16] and of other

are expected

400 cm-',

from

in the C=N

modes

in the solid

of [Re(CN)c]s-

deformations

bipyramidal

some of the observed

symmetry

DSh

spectra

stretches

and C-Re-C

of a pentagonal

we can now assign

to the totally

verified by a single crystal X-ray and C. PoMn, unpublished work).

Al'

in the spectrum symmetric

study

(J.M.

I

v,_,(ax.)

VM_C(ex.)

vpi_&eqe)

vs

~4

vc_N(eq.)

va

VL

&+.C(eq~)

v~

243s

1

1

VI 4 ~c_N_Cbio

VLS

4

-

_

_

.”

_

vrr(Aa’) &Vaa,Vpr( (EJ’)’ are inactive,

varFv2a fiC_M_C(eq.)

v20 y+CGwI

-

GC_M_C~axX'~@s')

me

~19 vC_N(eq.)

GEI_(&m*I

6M_C_N(eqa)

v17

z Vl6

455~ --

~19 vM,C(ecl~)

163 (2)

155w

10%

“.

-

-

“.

2094~

-

..>

-

in SIR; all

2103(3),

[458w I

observed

407 ($I

Bands underlined

109w

407(i)ap

2115 (3))

472(2)

469(2)dp

PlOb(6)dp

512 (2)

504(l)dp

SW

$&rn

+@%2 6H_C_N(8X’1

Gc_M_cbx’

392m

_2092~s

407w

f434m3

2063(7)

/2144w, 21251~1 --

eoI.id

_2040~~1, _2005~

$&W

grn,

5258

_2101sh,

5328

_2019vs

_2080s

423(3),

438(3)P ,425(4)p

2068(5),

2125(10);

435(3) :

2061[6>p

2123 (lO>p

l~e(CN)~l”*

[M(CN)I I”-

VI* BM_C_N(eqo)

vC_N(eqg)

v&=*)

v6

8 vt0

GM+N(eq’)

VI

Ez’

-

El"

-.

El ’

-

I1 A:, : ‘J6 v,_,b’d

-

Al’

eoZution

Fundamental ,modes for heptacyano complexes, _ _

TABLE2

-

others

--Y_-.I._d_

solid

-._

for soln. from[lSl

402 (-3)

2095 (2)

489 (2)

532(l)

3666, _3315

*m

476m

2088m

444m

urn

20958

378(5)

401(3)

2112 (6)

2106 (10) ; t 21031tiI

in Raman. fIRdata

9Ow

44O(l)dp

2097 (2)dp

14ow

470(3)dp

2072~0’

2104s ’

39712)~

397 COP

2109(6)p

21O$(lO)p

solution

[V(CN),]“-

311 stretching while

mode

pri&rfly

the weaker,

associated

partly~polarised

Comparable

theaxialcyanidestretch. observed

for the corresponding 1.786<7),

closeness

of axial

exes

(Table

bands

near

axial

430 cm-',

tentatively

the higher since

d

orbltals

and

A higher

the axial

axial

sed for the corresponding The Raman the EZ' mode v)10-

band

vL9,

bands

is stronger

than

infrared though

bands

these

ect to solid

and we adopt

are of course state

(i.e., axial modes also postulated

(ii)

despite

will

sequence

Raman

band

We

spectra

for Fe(C0).

higher

on the same assumption lower

are poorer

1153.

at 2103 cm-' and infrared at 2110,

the

(v13) modes, and may

be subj-

[1,3,16],

1211 that equatorial than for the axial

for C-Re-C

frequencies

of the anion

for the anion

(infrared)

for

deformations

than equatorial),

as

[21].

than those

and bands

mode

preferred

cm-l region

frequencies

ion,

2070 cm-=

to

then propose

(v~) and &'

for this complex

solution,

(equatorial)

has been

120, 211.

The heptacyanovanadate(II1)

solution

and is clearly

407 cm-' band

the latter

[V(CN)7]4-.

in solid

for

2104,

for the solid.

They observed bands

The quality

tentative. of DSh

Levenson

We assign

(Raman)

in

polarised

at 2104 and 2072 cm-'

2100 and 2094 cm-'

as being

symmetry

a single

of

so that

[Re(CN)7]4-,

K,,[V(CN)~].2Ea0

symmetry [ll] our assignments are necessarily Of Dsh et al. have provided good evidence for the retention -aqueous

propo-

1201.

fall in the 450-650

the finding

are at slightly

the characterisation

has also been

(p = 0.8)

from solid-state

are at slightly

for Fe(CO)S

in

effects.

deformations

we proceed

to the

the filled'

at 2080 and 2019 cm-' we assign

(v xo) since

in Fe(CO)S

taken

splitting

and 425 cm-'

the depolarised

and a similar

for [Re(CN),14-

Liketise

our spectra

assign

we assign

between

mode

The

Compl-

The polarised

on the z axis

is depolarised

C-N stretches

Co0 stretches

deformations

modes.

lying

120,211

8 1221).

valid.

mode

were'

heptacyano

stretches;

x-interaction

at 417 and 455 cm-' as the AZ"

The Re-C-N

Fe-C-O

Fe(CO)S

to an axial

ligands

("6) and El'

the axial,

the corresponding

1.8270)

in IF, 1171 and Fe(CO),

at 2106 cm"

and we likewise

to AZ"

with

to

(DSh symmetry;

in known

than equatorial M-X

The two infrared-active

respectively

equatorial

rhenium-carbon

be strong

groups,

we assign

and polarisation

[17,18]

distances

438 cm-' band

there will

cyanide

(P = 0.55)

1 [19]) and in Fe(CO)S

Fe-C

a comparison

are clearly

equatorial, xzandd JTs [Re(CN)T]"-.

1.807(l),

make

in IF7

1.858(4)

and equatorial M-C

I) [l&12]

the equatorial

intensities

Ar' modes

I-F equatorial

Impaxial Fe-C 'Dsh sJTnrmetry;

tith

2061 cm-' band

for the

and 2100,

the 2104 and 2072 cm-l bands

312 1153 to the A=" and suggest spectra

(us) and Er'

assignments

of the solids,

200 cm-' have

for these

the presence against axial D

data.agree

separation

between

V=

purely

two in [Re(CN)v]4-) causing

where

and

on their

reports

with

[Re(CN)i]&-. of the infrared

those

to

of-ref.

U= is surprising:

relative

163.

our assign-

intensities.

Possibly

in each of the dxz and d

gives

less metal

v 1 and vz to become

there

with

f6] and K~[V(CN),].H&[23],

and our

of only one electron

molecule,

TGo other

for K4[V(CN),].ZHzO

are based

positions

by comparison

reported,

been

The lack of clear ments

(u,o) modes

for other-bands.

are no electrons

to carbon very

close

orbitals (as y= rr-bonding.in the [in Rep,,

another

only one A,'

in the Dxz or d YZ'

rnzie is observed

(B) evidence

[13]].

The octacyanoniobate(IS7) based

primarily

(Dzd) symmetry

Archimideaen more

known

vibrational

a distinction

to be drawn the

"spread"

example,

as to whether

there

The Raman number

and infrared

strongly

infrared

suggest

configuration however,

spectra

We observe bands

indicated

the Raman

by e.p.r.

spectrum

resolution

(slits

three bands

were

assign

observed

structure.

one polarised

band

symmetric

present

different

to

two likeliest in particular

controversy,

[23] a Dad

for

+ Dad change

from the solid

to

at 2131

is observed

twelve

configuration

and nineteen coincidences,

under

twelve modes

the conditions

12 cm-l min-', (polarised)

For the aqueous

only

moderwhich the Dad

solution,

being

8 sets)

2124 and 2ll6 cm-'-which

stretching

The infrared

of

of the highest

time constant

respectively

at 425 cm-', which (A,).

bands

data.

radically,

In the metal-carbon

vS

Raman

Did

than DSd and supporting

and K-ray

to A =, Err and Es modes

stretch

K,,[NIJ(CN)~].~H~O show a

the supposed

sixteen

region,

2 cm, scan rate

tentatively

of solid with

grouping

changes

In the CN stretching

-carbon

We here

to

this conclusion.

frequencies

or is not

for the solid with

a less symmetric

observed.

matic

[24])changing

these

(M = Mo, W) on passing

in accordance

in the solid.

ate or strong

is [25-271

with

phase.

of coincidences

the anion

between

There has been much

in R4[M(CN)s].2Hz0

presented

has dodecahedral

[4].

to support

of CN stretching

complexes.

solution

anion

solution

data

in principle

for octacyano

aqueous

[Nb(CN)a]4-

for Dad and Dkd are sufficiently

is amall

for the anion

We have

(this is isomorphous

(Did) in aqueous

rules

but

that

a dodecahedral

spectroscopic

The selection

possibilities,

data

[Nb(CN)s]4-.

K4[Nb(CN)s].2H10

to contain

antiprismatic

detailed

allow

on e.p.r.

in the solid

K~fMo(CN)~].2H~O,

ion,

we

for the Ded antipri-

region

(ca. 400 cm-') -

we assign spectrum

only

as the rhenium-

of the solution

313

314

315 in the-CN stretching octacyano

species

be assigned

region

is broad and rather uninformative

[27], but the bands at 2120 and 2112 cm-' may tentatively

to the B2 and Er modes.

Their lack of coincidence

Raman modes also supports a DLd rather tra are too complex

the

The spec-

we assume

to admit of further interpretation;

that, as

and Nb-C modes lie in the

region with C-Nb-C deformations

cm"

with

than a Did configuration.

in IG.[Mo(CN)s].2Ha0 [26], Nb-C-N deformation 330400

as in most

from SO-200 cm-'.

ions, The tetra-us-thio- and -seleno-dodecacyanotetrarhenate(IV) 4We have recently described the preparation and crystal [RekL4(CN)~23 . (C)

structures cyanide

of the tetraphenylphosphonium

ligands are attached

(Re-Re 2.755(S) 8 for L = S, 2.805(5)

sulphur or selenium

Three terminal

to each rhenium atom which fs effectively

the Re4L4 unit is a cubane-like

nine-coordinates -metal bonds

salts of these.

cluster with direct metal8 for L = Se) and the

atoms lie on the threefold axes of the Rer. tetrahedron

(Re-S 2.34(l) 61, Re-Se

2.46(l) 8 151).

The Raman spectra of the solids could not be measured position

in the laser beam, but the solutions

The assignment suggested

of some modes,

in Table 4.

the "spread"

is much smaller

reflects

capacity of CN- compared with CO.

quite close in frequency

strong polarised breathing

mode of the tight Reb tetrahedron;

The polarised the A, C-N stretch

(Se) we assign

The

to the A,

they have no counterparts

and this is also true of the depolarised

110 (S) and 106 cm-' (Se) which we tentatively Re4 octahedron.

but

in part the

to those found in [Re
bands at 215 (S) and 197 cm-'

the 1-R. spectra,

are observed,

than that for the comparable

bands at 2169 (L = S) and 2157 cm-' (L = Se) are clearly ing modes,

for the anion, is

CN stretches

[291 or Rer.(SMe)4(CO)I~, [30] which

much smaller r-bonding

gave good spectra.

overall Td symmetry

All four Raman-active

of frequencies

species Ir4(CO)Iz

assuming

in methanol

owing to decom-

assign

in

Raman bands at

to the E mode for the

The Raman band at 177 cm-' is found in the far I.R. spec-

trum of the thio complex also, so we assign it to the Pz mode of the Rer. tetrahedron. distance

In Ir4(CO),,,

which has a longer but unbridged

of 2.68 E(, the A,, E and FO modes are respectively

105 cm-= [ZPI, and their relative

intensities

find for the rhenium complexes.

The polarised

and 280 cm-' (Se) we tentatively

assign

an analogous

complex,

at 275 cm-' 1311).

are similar

to those which we

bonds in the Raman at 335 (S)

to the A x Re-L stretching

[Fe&4(SCRzCaH~)4]2-.

the corresponding

The I.R. bands at 358 (S) and 207 cm-'

the infrared active I?= modes,

metal-metal at 208, 164 and

observed weakly

modes

(in

Fe-S mode is

(Se) we assign

in the Raman spectrum

of the

to

thio complex difference

(these

involve

movement

may be due to the deformation

of the

The salts KG[Re(CN),].2HaO

characterised

(30-4000

cm-')

ed solids

red

sample

tubes

(6471 ,%).or yellow

measured

in aqueous

fluorite

plates,

Perkin

Elmer

spectra

tubes under

made

or methanol

by the cited Raman with

a Cl?&52

solutions

between

in polythene

solutions,

krypton-ion

(1800-2300 mulls

were

detector

(40-400

cm-')

on powde=

were

as films between

plates.

cm-')

methods measured

in quartz

spectra

from 250-4000

iodide

and

laser was used with

The infrared

caesium discs

(Se)

[3,5]

literature

spectra

DPC-2

for the saturated

and Voltalef

the large

[6],

(Ph~P)~tRe&~(CN)1z].3H10

5 instrument

and,

hence

(S) and 229 cm-'

system.

analyses.

argon;

and as Nujol

measured

at 317

(5682 8) excitation.

325 instrument

were

[4l,

by elemental

on a Spex Ramalog

in capillary

spinning

(us-L)

[3,5] were

(Ph4P)4[Re4Se4(CN)lz].3H10 and were

bands

[2,3], K4[V(CN),].2Ha0

141, KsCN~(CN)BI

Ks[Nb(Oo].2HnO

of the S or Se atoms,

The infrared

in frequency).

cm-' on a

Far infrared

on a FS-720

inter-

ferometer.

ACKNOWLEDGEMEHIS

We (J-M.B.)

thank

the Science

for grants

Research

Council

(P.M.K.)

and the Royal

Society

to two of us.

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