Charge separation study in bisbenzene complexes of metals by theoretical analysis of infrared intensities

255

JournalofMolecularStructure,218 (1990)255-260 ElsevierSciencePublishersB.V.,Amsterdam-PPrintedinTheNetherlands

CHARGS

SEPARATION

STUDY

IN BISBENZENE

BY THEORETICAL

ANALYSIS

OF INFRARED

I.I.GREENWALD,

B.V.LOKSHIN

COMPLEXES

OF METALS

INTENSITIES

A.N.Nesmeyanov Institute of organoelement sciences, Vavilova Str.28, 117813 I%SCOW

compounds, (USSR)

Academy

of

SUMMARY Using the first approximation of the effective charges model from the experimental IR integrated intensities the effective charges on atoms in bisbenzene complexes of V, Cr and MO have been calculated. The charges on the metal atoms in the complexes studied are somehigher than in corresponding metallocenes and have the values about 0.5-0.9 electron charge units.

INTRODUCTION Considerably in molecules IR bands

intensities

effective

charges

systematic plexes ults

study

Cp2M

have

Therefore

model

(refs.l,2).

showed

have been made

that metallocenes

and calculations

compounds-

bisbenzene

the cyclopentadienyl

opinion, duse

complexes

are unstable

data

on stated

the picture

small

of charge

effective

distribution

atomic

class

Bz=q6-C6H6

make

The res-

chemical

pro-

charges.

of sandwich and M=V,Cr,

the majority

temperature.

compounds

a

com-

out a new seriebof

important

Bz2M, where

at room

three

(ref.2)

this model.

different

to carry

complexes

work

of

of the

in cyclopentadienyl

using

for a very

MO. Unlike

approximation

with

it interesting

charges

on the analysis

In our earlier

charges

and relatively

of effective

based

of first-order

of the effective

similar

ne compounds

to the study

by the method,

in terms

we considered

experiments

approach

(Cp=$-C5H5)

obtained

perties

correct

is represented

of bisbenze-

Nevertheless, it possible

in bisbenzene

in our

to repro-

complexes.

EXPERIMENTAL IR measurements

were

in tne reegion 4000-50 tions.

Sample

atmosphere

made

on IR spectrometer

"Perkin-Elmer"-180

cm -1 in octane , cy=lonex;.ne and benzei:e solu-

preparation

or in vacuum

and cell using

filling

special

was performed

procedure

in inert

(ref.3).The

for the intensity

measurements

did not exceed6-8%.

0022-2860/90/$03.50

0 1990ElsevierSciencePublishersB.V.

error

256

RESULTS

AND DISCUSSION

Measurement

of absolute

Measurements

were

IR band

made

le 1). The intensities because

these

values

and for comparison that the tendency

CP2Fe

lower

than

not influence

values

are summarized

It schould

be noticed

zene modes

3, and

bands were

(ref.Z):the

intensities

of skeletal

that the forbidden

of charges

l.These

in Bz2M

(Tab-

not studied

intensities

in Table

intensities

the intensities

modes

the accuracy

of integrated

of vibrational

fers from metallocenes much

from ten IR active

of two CH stretching should

The obtained

calculation.

intensities

for eight

for Bz2M data

show

complexes

of ligand

modes

metal-ligand

by symmetry

difare

modes.

for "free"ben-

the bisbenzene

9 have a very low intensities. In this respect 10 complexes are closer to "ionic" Cp-compounds (Cp2Mn,

CP2Yg)

as to "covalent"

TABLE

as well

ferrocene.

1

Frequencies (S,cm-') and integrated intensities (A,l.mole of bands in IR spectra of Bz2M (M=V,Cr,Mo) and Cp2Fe.

Bz2V NO

-lcm-2

Bz2Mo

Bz2Cr

)

Cp2Fe

Assignment $

A.104

A.104

$

3

A.104

$

A.104

. $26

, sLML

E.

$25 $23 311

48 *c

Normal

coordinate

There

analysis

are several

benzene

complexes

lations

are available

scheme

Bz2Cr

force

81 frequencies available. diagonal

Data force

coordinate

analysis

of bis-

However

complete

calcu-

0.21 0.02 0.05 0.02 0.14

1005 1431

normal

of force

Norma1

field was

elements

of force matrix

The prosedure

for deuterated from refs.6,8 field

(ref.2).

derivatives

0.18

were

analysis

In this work

for Bz2Cr

varied

is resonable,

were

constants.

coordinate

field was made

force

0.06

complexes

(refs.4-7).

for Bz2Cr.

Diagonal

field.

0.31 0.55 0.11 0.12 0.32 0.22_

to that of Cp2iY complexes

variation

-derivative. d10 but nondiagonal

0.05 172 1.21 481 0.65 498 0.06 815 0.12 845 0.03 1108 0.17 1000 0.02 1423

1.84

820 970

where

140 380 435 785 812 970 1045 1420

2.08

of bisbenzene

works,

only

0.08

159 462 492 795

are described

is similar

the complete

0.06 2.20 0.69 0.55 0.06 0.26 0.11 0.08

150 430 473 745 775 960 992 1440

for Bz2V

transferred since

of Bz2V

and its and Bz2Mo, from the

the experimen-

and Bz2Mo

used as zero order

are not

approach

of

257

TABLE

2

Frequencies and normalized modes Bz2M complexes, M=V,Cr and MO.

Compound

$,cm -1

Assignment

Cal

Bz_Cr L

)ML

Bz2Cr-d10

456

Qcc

459

0.05 -0.04 0.27 -0.09

f CH -0.04 1.06 0.26 -0.03

2252

0.04 0.01 0.25 -0.13

0 0 0.06 0.76

-0.28 -0.25 0.24 -0.09

-0.19 0.80 0.10 -0.05

SML .9cD

422 627

420 637

-kD

2283

920

A2u 0

LML -0.34 -0.18 0.23 -0.06

970 3058

xc

'CH

0 0.03 1.04

3074

928

of

Mode

Exp

795 SCH

of A2u and Elu vibrations

BCH

SLML

Bz2V

&l L 430 $H 742 -kc 963 SCH 3093

430 745 960 3100

0.04 -0.02 0.27 -0.08

0 -0.34 0 -0.17 0.03 0.22 1.04 -0.06

-0.05 1.06 0.20 -0.03

Bz,Plo

$ PL 374 814 QCH see 970 $CH 3083

380 812 970 3100

0.03 -0.07 0.25 -0.09

-0.37 0 -0.18 0.03 0.19 1.04 -0.06

0.02 1.02 0.36 -0.03

0 0 0 -0.32 0 0.07 0.04 0.15 0.03 -0.09 1.04 -0.06

0.01 -0.05 1.07 0.14 -0.05 -0.03

0 0.15 0.03 0.05 -0.03 -0.04 0.70 0.07 1.46 0.04 -0.04 0.03

L

0

Elu Bz2Cr

z LML 163 SML 493 QCH 817 P CH 1003 kc 1437 SCH 3071

Bz2Cr-d10

sLE 8

159 490 820 1005 1431 3058

4'::

SCD 630 CD 795 CC 1278 CD 2272

802 1282 2252

0 0.04 0 0.13 -0.30 -0.12

SLML 149 +IL 472 3CH 779 PCH 995 3cc 1441 ?CH 3080

150 473 775 992 1440 3100

0003 -0.11 0.22 -0.27 -0.07

: 0 0.05 0.02 1.03

-0032 -0.06 0.14 -0.09 -0.06

0 -0.04 1.07 0.13 -0.05 -0.03

0 0.15 0.04 0.05 -0.03 -0.04 0.83 -0.06 1.39 0.05 -0.02 0.03

SLML 138 SML 436 9CH 787 @CH 1037 kc 1418 3CH 3080

140 435 785 1045 1420 3100

: 0 0.04 0.05 1.04

0.01 -0.33 -0.06 0.15 -0.05 -0.06

0.01

0003 -0.02 0.29 -0.19 -0.07

-0.04 1.07 0.13 -0.04 -0.03

0.15 0% 0.06 -0.01 -0.05 0.38 -0.07 1.57 0.03 -0.05 0.03

480

Bz2V

Bz2Mo

0 0.03 -0.02 0.24 -0.24 -0.07

0 0 0 0.05 -0.03 0.76

0.01 -0.29 -0.12 0.13 -0.11 -0.09

0.02 -0.16 0.80 0.06 -0.05 -0.05

0 0.14 0.07 0.07 0 -0.06 0.76 -0.05 0.94 0.05 0.04 0.04

Results the close plexes.

of normal

coordinate

similarity

of the normal

It is important

(SLML) is highly intensity in Bz2M

of this mode

depends

as in Cp2M

data of A2u

ted eigenvectors

and hydrogen

It is well

known

is aggravated ves matrix

that

There

from each

for Bz2M

maining

MO

that

com326

the IR

distribution

intensities were

the method

and calculafor detennina-

charges

described

of dipole

hence

on metal,

in refs.l,2. problem

moment

derivati-

the 2n solutions

correspond

of the

order)each

satisfy-

to 2n possible

for Eiu species,but

in sign.

represented

used

of the electrooptical

(where n- matrix

which

are close

atomic

charges

Practical

sign com-

16 of them

calculations

can be reduced

in their

effective

in Table

3.

(in units

of electron

Variant

Atomic 1

to four. charge

showed The re-

values

charge)

to

in Bz2M

ofsolution

2

3

,4

QC.10

-1.03

-0.91

-1.16

-0.91

QB.10

0.54

0.23

0.36

-0.02

Q,, Cr

exist

only

charge

V

to conclude

mode

3

Effective

M __

using

all the 16 solutions

four,

frequency

and effective

are 32 solutions other

of Cp2M and Bz2M

on charge

coordinates

the solution

values,

indicate

problem

are not known.

12 solutions

one of those

TABLE

atoms

equation

ing the intensity

differ

practically

by the fact that the signs

elements

electrooptical

binations.

permits

parameters

that

vibrations

that the lowest

and Elu bands

in Cartesian

tion of elrctrooptical

and eigenvectors

compounds.

of the electrooptical

Experimental

carbon

to note

characteristic.It

as well

Solution

analysis

0.49

0.68

0.80

0.92

Qc-10

-1.20

-1.34

-1.41

-0.65

QR-10

0.40

0.63

0.30

-0.12

QCr

0.80

0.71

0.91

0.77

QC'10

-0.99

-1.04

-1.07

-0.36

QB.10

0.16

0.27

0.26

-0.42

0.77

0.81

0.78

the calculations

do not give

QMo

0.83

As it has been value

noted

of the charges.

Nevertheless

for all solutions

the absolute the calcula-

259 tion proves are opposite.

that the signs of the metal and carbon atomic charges The data of table 3 permit the following conclusions:

the absolute

values

no defenite series found

of the carbon

e. The charges

exceedO.15

tendency

sponding

in effective

For different

of metals.

to lie between

0.49

Cp-complexes.

se the formal

valence

zero and in Cp2M-

and hydrogen

of the metal

charge

atomic

changes

that

The result

these

and

in the

charges

than

is rather

never

values

is observed

is higher

obtained

charges

are closein

sets of solutions

and 0.92e,

state

atoms

are

for corre-

strange

of the metal

atoms

in Bz2M

to 2+ and the opposite

order

of charges

becau-

is equal was

to

expe-

cted. It is interesting tive

charges

refs.9,10

with

to compare

the quantum

the average

values

the results

chemical

ween

Di value

energy

dissosiation

cyclopentadienyl

to suppose

that

TACLE

are presented

energy

to the valence

E(M-L)

in the series

in Table

is

s-tate.The

from spectroscopic

and benzene

close

In

bet-

data

the energies

are not avaiSable.Nevertheless

as ber~zei,c cui.lpounds they have

for Ei(M-L)

molecule.Thedifference

taken

radical

state

data.

energies

of the metal-ligand boMand L remain in the

dissosiation

atom were

to the valence

is reasonable well

average

from the standard

for the metal

(ref.ll).For transition

as in the initial

and the usual

the excitation last vaiues

state

for the effec-

and thermodinamic

of "inner"

??i(N-L) were proposed as the characteristic nd. It is supposed that after dissosiation same electronic

obtained

of it

of cyclopentadienyl

values.

The obtained

as data

4.

4

Average (rd) and "inner" average (5.) dissosiation energies of M-L bond, metal excita tion energies toithe valence state (&)(~cal/mcle) and Wiberg indexes for Cp2M and Bz2M complexes. Ligand

!"I l5(X-L)

.&

E$Y-L)

SC

‘72i5.

97

V

38+1

58

Co ___ Ni -x--I--_I~ " ;; 68+1 40+1 101 :;

.__~-f-C6H5

W4S,4#PL

W3d_L

1.20

1.5

117 119 116 120

1.4 1.4 1.4 1.4 1. 5 1.5

0.5 0.6 0.6 0.6 O"6 0.6 0.6

ii

0.9 0.8

,g;l -.

.-

_ I-___

2 .O 2.0 2.0 2.0 2.0 2 . ;. 2.1 ------_0.8 1.6 _

~-____-_.-_-__I

wPl-L

117

260

In the series llY_t3

stant

of Cp-complexes

Kcal/mole.

these values

For Bz2X

are approximately the values

complexes

con-

are 94+3;;cal/ -

mole . In the Table presented between

3 the calculated

(ref.12).

The W3d_i_ value

3d A0 and W4s

4h_L-

ligands.

The Wiberg

13) with

parametrization

ain approximately the average

bonds

ato:ns. Taking valent both

covalent, charges

is in agreement

is rather to some

and to a decrease

1

atoms. larger

increase

with

as

ind.:xes of cyc-

charges

(1,"

on met& the co-

that in the

are predominantly

the relatively

small

complexes

fbr cyclopsntadienyl

in the effective

(ref. rem-

as well

characterizes

bonds

charge

or ci((M-L) val:kcs for this

W(M-L)

"ini1e.r'energies

it may be supposed

For bisbenzene than

Wiberg

effective

t'nat W(M-L)

MO of

IXDO method

of complexes

to nigher

the metal-ligand

with

The values

?Yi((M-L). higher

to M-L bond

on the metal

tribution responds

what

series

and to the smaller

of complexes

the interaction

using

(ref.14).

correspond

into consideration

contribution

series

W(P!m.L)z-e also

characterizes

calculated

in both

energies

complexes

metal-iigand

were

of Clack

constant

indexes

4s and 4p A0 of the metal

i;dexes

"inner"

lopentadienyl

Wiberg

class

atomic

the ionic

con-

ones

cor-

on metal

that

atoms

of c0mpOunds.

S.Kh.Samvelyan, V.T.Alexanyan, P.V.Lokshin, J.Mol.S~cctrcsc., 48(1973)47,566. 2 V::'.Alexacyan, l.i.GreenwalJrJ. ?oi.StrL:c-t.,3ij(lT;c%2) 35. .I .G.reenwald,A.S. ir'.'T.A~.exinyan,T'.I.Arser~ieva r X.N. J>~rshinsk~y,I 3 Smirnov Izv.Acad.Sci.USS" rY,ser.kchim.,(1981)299 (in Russian). 4 L:Schafdr,J.i Soutern S .ci.~~~~in,Spc?ctrochj.,7!.Acta,27~(1972)13i~3. 3 3 .;!.Cyi:ir?:a.i:.C;'~i3, ?.ca:l Moleci?ia~- Orbital Theory, ?41:*i:r;-:w HFll,N.Y.,i970. 14 D.C.Lack ,nol..i'!;ys.,27(j.974)ljl3.