2 Study on molecular complexes of aliphatic amines with HF and F2

105

Advances in Molecular Relaxation and Interaction Processes, 11(1/2) (1977)105-l14 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

CNDO/2

STUDY ON MOLECULAR

KRYSTYNA

ROMANOWSKA,

Institute

*

HENRYK

of Chemistry,

50-383 Wroclaw,

Department

OF ALIPHATIC

RATAJCZAK

University

AMINES

WITH HF AND F2

and W. J. ORVILLE-THOMAS*

of Wroclaw,

14 Joliot-Curie

Street,

(Poland)

of Chemistry

Salford M5 4WT, (Received

COMPLEXES

and Applied

Chemistry,

University

of Salford,

(Gt. Britain)

13 October

1976)

ABSTRACT

Properties

of molecular

complexes

formed between

HF and F2, respectively,

have been evaluated

amine-HF

hydrogen-bonded

complexes

energy,

amount of charge

fairly

constant

transfer

complexes

the binding

transferred

slightly

potential.

The results

nic structure

transferred,

increases

of the complexes

properties

enhancement studied.

energy decreases

are discussed

In the

(binding

of dipole moment)

are

In the amine-F2

charge

and the amount of charge

with the lowering

obtained

amines with

by the CNDO/Z method.

the calculated

in the series of systems

aliphatic

of the amine's

in relation

ionization

to the electro-

formed.

INTRODUCTION

Molecular

charge-transfer

xes, have been extensively subject

[l].

Recently

complexes.

charge

transfer

the electronic importance

However,

structure

in chemistry,

and properties physics

bond

at various

of hydrogen-

have been attempted

for

since the elucidation

for such complexes

of

are of great

and biology.

in the study of interactions

the relationship

and the electron-donor-acceptor

ents.

Recently

empirical

(HB) comple-

exists on this

calculations

out for a variety

fewer calculations

plexes

several

literature

orbital

This is regrettable

approach

is to examine

and a vast

have been carried

complexes.

One interesting complexes

studied

many SCF molecular

levels of approximation bonded

(CT), as well as hydrogen

between properties

correlations

in molecular

the properties

of the com-

of their isolated

between

certain

compon-

physico-

chemical

properties

of weak and moderately

have been found and discussed theory

on the basis of Mulliken's

These correlations

[l-7].

basis of quantum

chemical

might be further

calculations

ever, so far, no such systematic of structurally

similar

bonds

good model

in relation

amines.

systems

the molecular

of the literature

to provide

correlation

between

the molecular

ionization

potentials

tal geometries [17].

of the constituent

of charge

transfer

series of model

properties

of complexes

which has been successfully

complexes

in this work. complexes

systems when a

and the amine

the properties

applied

for a number

of molecular

complexes

AND RESULTS

with the usual parameters

for the amines

in the F2 molecule

and is equal to 1.1 w.

to be unchanged

during

[16].

Experimen-

are taken from the literwas determined

The geometry

by the

of the amines The following

the complexation.

is geometrical

the bond of the electron-acceptor

for the complex was chosen:

F2) was taken to be collinear

is used

and the HF molecule

The F-F distance

CNDO/Z method

model

of strong hydrogen

here.

The CNDO/Z method,

assumed

an important

It

amines might

[8-151 that the amine-halogen

is used to calculate

MO CALCULATIONS

ature

bond.

HF and aliphatic

properties

How-

is being sought.

The CNDO/Z MO method,

discussed

transfer on the

systems.

a strong hydrogen

properties

complexes

out for a series

amines have also been studied

shows

might be considered

of applications,

involving

for the study of properties

F2 and aliphatic

formed between

out for model

formed between

to the electron-donor

In addition

A review

carried

charge

investigated

studies have been carried

complexes

seems to us that the complexes provide

strong hydrogen-bonded

with

the symmetry

@F,

axis of the N lone pair

charge cloud of the amine. The dipole moments Table

1 together

calculated

with the values

and the ionization

potentials

The energy of formation erence between ted energies the complexes cular

the computed

studied

magnitude

of the complex,

components.

the change

transfer,

the change of dipole moment

are given in

for dipole moments

for the amines. AE, was obtained

Other properties

calculated

equilibrium

in the H-F bond length,

Aq; the dipole moment

due to the complex

as the diff-

and the sum of the compu-

in this paper are as follows:

R(N...F);

of charge

experimentally

energy of the complex

of the isolated

distances,

for the isolated molecules

obtained

intermole-

Ar(HF);

of the complex,

formation,

for

the

pN and

An, calculated

as

107

The results hydrogen-bonded-and

TABLE

in Table

obtained

are given in Table 2 for

3 for charge-transfer

complexes.

1

Molecular

parameters

for the isolated

molecules

and for amine-iodine

complexes

ionization

dipole moment

potential

molecule

Ii

experimental b value

a

(D)

enthalpy of complex

calculated c value

formationd (kcal/mol)

10.15

1.47

2.096

- 4.8

methylamine

ammonia

a.97

1.29

2.042

- 7.1

ethylamine

8.86

1.00

2.034

- 7.4

dimethylamine

8.24

1.03

1.805

- 9.8

trimethylamine

7.82

0.63

1.704

-12.1

1.736

1.861

HF

a

experimental

value

from ref.[37]

b c

experimental

value

from ref.[38]

d

experimental

calculated

TABLE

value

in this work

value

from ref.[9]

2

Physico-chemical

parameters

for amine-HF

hydrogen-bonded

systems by the

CND0/2 method

electron

donor

ammonia

F *** (2)

ArHF

AE

lJ

Au

*q

(G

(kcal/mol)

(D)

(D)

(e)

2.45

0.026

19.69

5.11

1.15

0.0986

%I

methylamine

2.45

0.026

20.13

5.05

1.15

0.0978

ethylamine

2.45

0.026

20.13

5.14

1.25

0.1006

dimethylamine

2.45

0.026

19.02

4.84

1.22

0.0985

trimethylamine

2.45

0.026

19.36

4.74

1.18

0.0978

108

TABLE 3 Physico-chemicalparameters for amine-F2 charge transfer complexes by the CNDO/Z method

electron donor

p

%...F

ArF-F 'E

(2)

(8)

(kcal/mol) (D)

Au

Aq

(D)

(e)

ammonia

2.85

0

1.88

2.44 0.35

methylamine

2.85

0

1.68

2.38 0.33 0.0174

ethylamine

2.85

0

1.61

2.40 0.37

0.182

dimethylamine

2.85

0

0.78

2.15 0.35

0.0183

trimethylamine 2.85

0

0.95

2.06 0.35 0.0190

*

0.0172

Here F signifies the fluorine atom mearest to the nitrogen nucleus.

DISCUSSION

Amine-HF hydrogen-bonded complexes

The results obtained show, as one might expect, that in the complexes studied a strong hydrogen bond is formed. The values obtained for the change of dipole moment (s 1 D) in the series studied indicates the formation of molecular hydrogen-bonded complexes rather than hydrogen-bonded ion-pair species [2]. Unfortunately, there are no experimental or ab initio data available for the complexes of alkylamines with HF.

However some indication of the

expected reliability of these calculated results may be obtained from a comparison with the results obtained for the F-H...NH3 complex since this entity has been extensively studied by using semiempirical as well as ab initio methods. The literature data obtained for the F-H...NH3 complex are given in Table 4. Examination of Table 4 shows that the binding energy value of the F-H ...NH3 complex obtained from ab initio calculations depends strongly upon the basis set used in the calculations. The minimal basis set (STO-3G) gives a AE value of ~8 kcal/mol, but an extended set (4-31G) predicts a binding energy of ~(16-18) kcal/mol. Our AE value (19.64 kcal/mol) is in fairly good agreement with those obtained from the (4-31G) set. Our AE values given in Table 3 are obtained by first minimizing the energy of the system calculated as a function of the hydrogen bond distance, R(N..F), and then minimizing the energy as a function of r(HF) in the complex. It

109 TABLE 4 Theoretical

values

enhancement

of dipole moments

of binding

energies

(AE), intermolecular

(Au), for ammonia-HF,

distances

(R),

F2 and trimethylamine-

F2 complexes.

method complex

of

RN..F (2)

calculations

NH3-HF

AE

*q

A!J

(&

(kcal/mol)

(e)

(D)

ref.

STO-3G

2.77

8.3

4-31G

2.77

18.0

1.14

19

2.69

16.3

0.84

19

HFAO

2.75

11.7

6-31G*

2.77

12.2

4-31G*

2.68

16.3

21

perturbation

2.65

12.17

22

STO-3G

2.75

8.5

23

4-31G

NH3-F2

ArHF,FF

(0)

0.93

20 0.79

INDO

2.45

0.04

31.7

0.149

24

2.45

0.026

20.0

0.097

25

CND0/2

2.47

13.08

26

CND0/2

2.45

11

27

STO-3G

2.81t

0.43

double-zeta

3.08t

0.60

28

extended

3.08t

0.62

28

polarized

3.04t

0.79

28

4-31G

3.00t

1.05

INDO

2.74t 0.01

Here F signifies

is interesting enhancement

the fluorine

0.34

the ab initio

atom closest

distance

calculations;

24

0.11

28

nucleus

is also obtained

lower in comparison

this discrepancy

0.078

to the nitrogen

Au,of the ammonia-HF

is much

28

29

10.4

to note that fairly good agreement

of dipole moment,

intermolecular

results

19

CND0/2

0.32

t

19

complex.

for the

However,

the

with that obtained

is usually

observed

from

for CND0/2

[30].

From an examination that all the calculated

of the results preperties

given in Table

2 it can be seen

(AE, R(N . ..F). Ar(HF),

Au, Aq) in the

110 series of complexes

studied

upon the ionization

potential

expect

from the charge

are fairly constant

of the lone pair of the amines as one might

transfer

behaviour

has been demonstrated

complexes

of aliphatic

Certainly

[321.

to be a purely

charge transfer Full agreement

(ES), charge

action.

However,

(CT) and exchange

basis,

useful

in these studies.

that the H3N-HF

static supplemented

complex

that the electrostatic

transfer complex.

contribution However,

the enhancement systems

results transfer

since the calculated

of dipole moment,

studied one may suggest

contributions

to the binding

obtained

may suggest

contribution

have recently

been obtained

Amine-fluorine

charge

The results

This

but that the charge

amount of charge

Au, are fairly constant transfer

energy of the

transfer,

Aq, and

in the series of

and polarization as well.

that for a strong hydrogen

bond the charge

energy

The

is fairly constant

is very interesting bond.

in con-

strong hydrogen and throws a new Analogous

from the energy decomposition

conclusions

studies

carried

[21].

transfer

obtained

electro-

contribution.

in the stabilization

of the strong hydrogen

and Morokuma

the formation

is dominant

Moro-

[Zl], on this

as strongly

transfer

found for weak and moderately

out by Umeyama

that

[35] is

energy are fairly constant

This conclusion

light on the properties

interinter-

question

(ECDD) scheme

he has shown

that the charge

the stabilization

trast to the indications [4,25,36].

charge

contribution

in molecular

to form the complex.

should be classified

is also important

(ER) [1,21].

repulsion

The important

decomposition Recently

by a substantial

impor-

terms depend on the properties

come together

energy and charge distribution

extremely

repulsion

forces

[33,34].

is how do these various which

of a 11,211.

bonds: viz.,

has been paid to the exchange

has not been well established

of the isolated molecules

bonds

transfer

energy of hydrogen

struc-

bond was con-

The importance

that at least three terms make

so far the role of dispersion

has to be answered

chloride

is now well established

to the stabilization

less attention

means

interaction.

The same molecular

the electronic

In early days the hydrogen

has now been reached

much

[l-7].

[31] and with hydrogen should reflect

contribution

electrostatic

bond

for the hydrogen-bonded

observed

bond.

Hitherto

kuma's

recently

electrostatic

interaction

tant contributions

actions

model of the hydrogen

amines with water

the behaviour

ture of the strong hydrogen sidered

and that they do not depend

complexes

(table 3) show that the CNDO/Z method

of weak complexes

between

F2 and alkylamines.

predicts

So far no

111

experimental

data are available

tion of the expected be obtained

for these complexes.

reliability

from a comparison

of the calculated

of data for F2-NH3

(table 4) which have been recently Examination the F2-NH3 closer

of Tables

and F2-N(CH3)3

to those obtained

the INDO method

slightly

obtained

from CNDO/Z

from ab initio studies

transfer

potential

theory

cement of the dipole moment the series of complexes

value monotonically

decreases

with

out by Lucchese

Similar

results

with

structure

interactions

have recently

charge

ant contributions

(ER)

from the enhan-

of amines.

published

[28] where

in

is for the bind-

of the amine's

The AE ionization

STO-3G calcula-

it has been shown

has a smaller binding ammonia

been obtained

complex

(see

by Morokuma

should be related

complexes.

The origin

in the literature

has now been reached complexes

to the stabilization

(ES), charge

result

potential

observed

discussed

transfer

depends

et al

complexes.

of the molecular

It seems to us that agreement

electrostatic

by

is fairly constant

striking

for the corresponding

has been widely

gen bondandin

formation

trimethylamine

and CH3H2N-ClF

transferred

unexpectedly,

the recently

As has been shown the behaviour electronic

of charge

the lowering

with

and Schaefer

of fluorine

[29] for the H3N-ClF

The most

to the ionization

than that calculated

Table 4).

of

are

than the ones evaluated

However,

due to complex

This is consistent

that the complex energy

energy values calculations

of the amines as expected

[13].

studied.

in relation

tions carried

complexes

[24].

charge

potential.

given here may

and F2-N(CH3)3

3 and 4 shows that the binding complexes

upon the ionization

ing energies

results

some indica-

studied by the ab initio method.

As one can see from Table 3 the amount

Mulliken's

However,

transfer

to the

of molecular

[1,8,10,27,29].

that both in the hydro-

at least three terms make

energy

of the complex.

import-

They are:

(CT) and short range exchange

repulsion

interactions. Recently

decomposition weak ES-CT

analyses,

partly

substitution

is reflected charge

by the exchange

one should expect

an increase

of the donor's

and charge ground

repulsion

ionization

potential

show that upon successive

transfer They

forces.

Due to

transfer

potential.

This

in the amount

decreases.

methylation

as a

state.

in the charge

ionization

studied by a slight increase

as the amine's

obtained

should be classified

that electrostatic

compensated

in the systems

system

ones in the electronic

due to a lowering

transferred

the results

that the H3N-F2

are the dominant

are, however,

stabilization

et al [29] have shown, on the basis of their energy

This means

complex.

interactions

methyl

Morokuma

of

Thus

of NH3 in the

112 H3H-F2

complexes

bution

greater

one observes

an increase

than the increase

stabilization

of the exchange

in the attractive

repulsion

contributions

contri-

to the

energy of the complex.

It is interesting dipole moment,

to note that the calculated

Au, for the complexes

studied

enhancement

of the

is fairly constant

and equal

to QO.35 D. Thus the amine-fluorine to the amine-iodine between

molecules enthalpy moment

charge

their properties is concerned of complex

transfer

transfer

[8,9].

complexes.

potential

the theoretical

Hence

the results

only with the experimental

(gas phase)

or perhaps with

obtained

question

mental

the electronic

matrix

structure

effects

of dipole

reported

in that

car-

here

here should strictly

data obtained

to be answered,

the

of the amines

from experiments

calculations

low temperature

leaves an important

systems

it should be noted

However,

systems were obtained

be compared

on the one hand, and solvent

of electron-donor

[9] as well as the enhancement

to the amine-fluorine

refer to the gas phase.

differently

insofar as the relations potential

depend upon the ionization

ried out in solution whereas

behave

In the case of the amine-iodine

the data for the amine-iodine

data reflect

complexes

complexes

with the ionization

formation

[13] strongly

contrast

charge

in isolated

isolation

conditions

data.

This

viz., how far does the experiof the amine-iodine

complexes

on the other?

ACKNOWLEDGMENTS

The authors assistance

and Professor

publication. Academy

thank Miss M. Redshaw K. Morokuma

H. Ratajczak

of Sciences

and Miss M. Szczesniak

for sending his papers

and K. Romanowska

for support

are thankful

for computer to us prior to

to the Polish

(PAN-3).

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