ESR spectra of low-symmetry high-spin cobalt(II) complexes

Journal of Molecuh 0 EkevlerSclentific

ESR

SPECTRA

OF LOW-SYMXETRY

HIGH-SPIN

mTbe

COBALT(I1)

tetra-n-butylammonium 2 tensor oE the A

and the calculation

A. BENCINI,

C. BENELLI,

50132 Florence,

tribromo(quinoline)

cobaltate

and C. ZANCHINI

D. GATTESCHI,

Lab. CNR and Istituto di Chimica

Netherlands

COMPLEXES

Pseudotetrahedral

Sk.

Part

401

Structure, 60 (1980) 401-404 Publishing Company, Amsterdam--Printed

Generale,

LJniversit5

di Firenze,

via

Nardi

39,

Italy.

ABSTRACT X-ray

structure

a symmetry crystal angle

near

dependent

are

with

Ligand

the cobalt

the

to C3,

spectra oE ~20~

[N(?z-C4Hq)4][CoBr3(q

OF

Co-N

largely Co-N.

Field

hyperfine

bond

direction

anisotropic:

These

results The

Model.

coupling

being

g1=6.31. are

the complex

the pseudo

Cg axis.

gS=1.61.

interpreted

of

is also

that

g2=2.33,

easily

application

constant

shows

uinoline)l

the model

gj

using

possesses

The

single

makes

an

a symmetry

ip

to the calculation

of

shown.

INTRODUCTION In the

last

attracted

the interest

the complexes Ligand

Field

their

few years

play

compounds

Model

the

had

been

to include

We wish

high

to report

tools

that

in determining

the

Field

spin

as simple

cobalt(I1)

complexes

have

the characterization

feature

of

components

of

the spectra,

oE the

making

a way

by Cerloch et aZ.

of low symmetry to

the

that

they More

the A tensor

and

(ref.

of

1,7,8).

effective

The

investigat -

enough symmetry

possessed recently

for the

transition metal corn -

interpretation

complexes

as possible. of

for

low symmetry

Model, developed applied

in such

cobalt(I1)

(ref.4,5).

susceptibility

the calculation (ref.

as

spin

clear

successfully

chosen

interpretation

published

role

of the magnetic

of low symmetry

become

Ligand

(ref. 61, has been

g values

of high

straightforward

independent

interpretation

been

not

spectra

researchers,

It has

a major

interpretation

plexes

keep

of many

(ref.2,3).

A symmetry

ed

the ESR

we

the relevant

have

extended

equations

to the

has

9).

here the application

single crystal spectra oE the triclinic

of the Model

to the interpretation

[N(n-CqHq)4][CoBr3(quinoline)]

the Zn analogue, which we reported previously

of the

doped into

(ref. lo), but we were unable

to

justify on the basis of the nature of the ground level of the complex. Further we want

to report some examples

of the cobalt hyperfine * For

Part

4 see

reE.1.

of application

coupling constant,

of the new Eormalism

for the calculation

in order to check its ability

to justify

402 the experimental

RESULTS

AND

The

DISCUSSION

single

Zn analogue spin

A values.

crystal

have

been

Hamiltonian

Although crystal

(reE.

(ref.

LL),

and

of C;, symmetry.

principal

to the Co-N

reflecting symmetry)

In

spectra

and

low

are

directions

are

oE

a S=$

effective

Ear

fact

CS asis),

syrmnetry of

and the single 3 interpreted with this

successfully anisotropic

those

direction,

an angle

the chromophore

to c

(g1=6.31,g2=2.33,g3=

from

distant

the gS

makes

is near

anticipated

which

oE s23"

is

with

on

the

the nearest

it,

clearly

(C7 crystallographic

site

-

opinion

Model are

these

previously

used

data

can be

described

justified

(ref.

coordinates

In order

to keep

the number

of parameters

constant

5 and

the orbital

to the Eree ion value r anisotropy

the quinoline

of

plane

reduction -1

('533 cm

and

using

this

k are

the

model

the bonding

to a minimum

factor

ligand

the projection

considered

oE

can

be estimated

the Co-BrL

varied.

and

5 is

12) so

other

over

a wide

1 the results

OF some

the angle

from

(ref.

This angle LS found to be N that ctc/z r;'W.O6 The is espected.

from

direction

data

are

are

coupling

isotropic

bond -14"

the z7 values

Ligand

crystallographic

parameters

the spin-orbit

to L (x axis).

In Figure

the X-ray

eX

orthogonal

range.

low symmetry

>.

the quinoline

and

only

7). With

geometrical

The

been

highly

as

kept

using

interpreted

the chromophore have

spectra

(pseudo

the actual

our

FieLd data

g

of

As a matter

bond

doped into the

[N(~~-C~H9)~][CoBr3(quinoline)]

reported

symmetry

the ESR

1.61)

of

10).

electronic

basis one

the

spectra

previously

the idealized

polarized

symmetry

ESR

the X-ray

parameters

representative

between

in the plane structural

were

varied

calculation

oE

shown.

6 5 9 4 3

2 1

Fig.

1. The

calculated

g values

Ear

IN(tz-But)q[[CoBr3quinl.

From

efEect of changing the indicated parameter, the other ones are: -1 Br BrcO 3 eN ._, rsloz =0.2, .z~~a/e~~=O.O, k-0.9,5 =533 cm-'. cm ,c TT /en

left

to right

Dq "=750,

the

DqN=900

403 10DqL=3e~+Z(e~s+e~c ). Good agreement

In Figure 1 we have defined transitions 750-850 Field

was

cm?;

calculations

insensitive of

found

e;s/eI

ratios

The

and

of e

ligands

-O.-O.4

g tensor

well and

(ref.

with

the electronic 0. -0.1.

N /ez and the era

in good

agreement

efr/eF with

the other

A values

onesto are

less

than

cm-L ). This

which

fit well

the observed

rationalizes

the electronic -1 ; DqR',

previous

Ligand

more

and

other

are

marked

suggests

findings

quite

dependence the

for

use of

pyridine,

L,L2).

[N(n-C4Hg)4][CoBr3(quinoline)]

the values

cm

transitions

The

have

no

shown

so

=9e9pBuNc

with

DqN=900-1000

in accord

in the range

!&a is on

O--0.2)

; k=0.85-0.90;

that a fitting of the A values cannot be made. -3 contact term constant, r B and K , the isotropic

structure

Table

of

The

directions

halogen

cm

+efr-

11).

the range

spectra

(0.0254

(ref.

and

(in

pyrazole,

B=730-750

to a variation

the g values

low

for

=O.-0.3;

-1

the g values

linewidths,

the

fact

even

that

resolved

Nevertheless

P at the

the hyperfine

l),

fixing

the calculated

free

coupling

P

using

as parameters,

(see Table

with

hyperfine

ion

was

value

not

observed.

1

Representative

of g and A values

fittings

for some

high

spin

cobalt(I.1)

complexes

C omplex

[N(n-But4)] [(Zn,Co)Br3quin]b

talc. obs.

6.46 6.31

2.35 2.33

1.65 1.61

~60 39

CL5 0.1

<30 25

[(Zn,Co)(PlePh2AsO)4N03]NO~

talc. obs.

8.6

1.3 1.2

0.9

462 461

c57 12

c40 31

(Zn,Co)(Ph3PO)7CL~

talc. obs.

5.68 5.67

3.68 3.59

2.07 2.16

53


<20 22

-1 a Values in cm x10m4_ -1 =730 cm , k=0.9, K=0.35,

b eBr=34L0 , eBr=682 oN=32L4 , eNrs=322, erc=O,S =533 .B 'u o r-1 P=O.O234 cm . c ezX=6015, e;c"r=1580, ez=3950, E?:'= -1 ezl=2400, 6685, eexq=2765, B=760, &=533, 1c=O.35, P=O.O19 cm , k=0.9. d eC1=5700, 0 0 -P , k=0.9. ez=4750, e rs=1945, eTTC=1555, B=730, 5=53x, uc=O.32, P=0.017 cm

The have

g values

been

have

have be

previously

been

Using

reported

the same

performed

reasonably

The

of Co(Ph3P0)2C12

the values

from

the

free

to be

a quite

allow

us

(ref. method

some

of calculation

calculations

data

ion value

been

covalency

of

fit using

by EIcGarvey of about

as

in order

The results

have

suggested

large

with

Co(PlePh AsO) (NO ) doped into the Zn analogues 2 4 32 the Node1 described and some fitting parameters

7,8).

reproduced.

experimental

with

analized

and

for

the K

calculations in

(ref. in order

effect.

However

the range

are

a good

the scarce

reported

0.30-0.35

13). The P values to have

we

the observed Avalues

to see wether

30%

to discuss more deeply

cN(C4Hg)4][CoBr3(quinoline)],

cm

have

experimental

in Table -1

1.

in agreement

been

fitting.

can

reduced

This

seems

data

do not

this result. As a matter of fact, however,

also

the

404 B parameter in order

reduced

the same

extent

from

the free

ion value

transitions.

value

between

simple

of about

the electronic

the numerical

agreement

a very

been

to fit

Beyond fair

has

of

the parameters,

the observed

and

it is important A values

calculated

to note

had

been

that

reached

a in

way.

CONCLUSIONS The

Ligand

Field

interpretation cobalt(11)

been

line

powder

the

either Eound or

to

developed

spectral

complexes.

distortions, have

of

Model

and

magnetic

In particular

it can

small

or

solution

to characterize

low symmetry

the spectra

be obtained

can

chromophore.

Using

large,

be strongly

glassy

appears

properties easily

from

which

dependent.

This

spectra

only

complexes,

taking

into can

symmetries

and

account

account

spin

points with

much

cases

that

spin

spectra

the policrystal in

order

interpretation

lead

symmetry to

the

geometrical

caution

a full

for

high

cobalt(I1)

out

the actual

in many

method

low symmetry

into

the high fact

powerful

of

take

be used

must

cobalt(I.1)

idealized

to be a very

oE

oE

the

erroneous

interpretations.

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C.Benelli,

D.Gatteschi,

and

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C.J.O'Connor,

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H.A.O.Hill,

48

(1972)

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