Download IJCA 39A(8) 792-801

Indian Journal of C hemistry
Vol. 39A, August 2000, pp. 792 - 801
MCSCF calculations on metal ion (Li+, Na+, Be2+) affinities of a few carbonyl
molecules in the ground and 1,3 n1t:* excited states
o Dey Adhikari , T Thakuria & C Medhi* ,
Department of Chemistry, Gauhati University, Guwahati 781014, India
Received 16 Jun e 1997; accepted 9 No vember 1999
Metal affinities (MAs) of form al dehyde, acetaldehyde and formamide molecules have been calculated by MCSCF
(OGM ) method. Ground state metal affinities of the mol ecules are larger th an excited state MAs. M n+ induced proximity
effect is prominent in acetaldehyde-metal ion and formamide-metal ion complexes. Bond orders and net charge densities on
different atoms of th e complexes are used to analyse geometrical relaxatio n du e to complex formation . Li+, Na+ and Be 2+
show spectral shift in th e i.3 nn * excited states.
Introduction
Interaction of group IA and group IIA metal ions with
ligands is important in solution chemistry and
transportation through biological membranes . There
are reports on the binding of N2 and CO 2 with Na+.
Hinton et ai.1 have calculated binding energies of Lt
2
with a number of molecules ; Gutmann established
so lvent donicity and chemical shift due to Na+ in a
series of solvents . Berthod et al. 3 calculated Li+, Na+,
46
Be 2+ affinities of NH, molecule. Rao et ai. - have
observed shift in nrr* and rrrr* transi tions of carbonyl
mol ecules due to metal ions. Marschoff et aC
reported that M+ interaction with H 20 is a charge
tran sfer interaction . However, experimental study on
2
solvation (Gutmann ) and variations of chemical shift
due to environment do not give any direct clue to the
dominating factor of such changes. Hence a
systematic theoretical study on metal ion affinity
towards carbonyl group along with the structural
analysis in the ground and I" nrr* excited states on the
basis of the MCSCF(OGM) method are presented in
thi s paper.
Theory
Within the basic framework of single determinant
LCAO-MO-SCF
model
have
the
following
description in terms of a set of n occupied molecular
spin orbitals (<1>;) which are linear combinations of
say, N ( N~n) atom centered non-ortho ~o nal function s
(Xj) :
\If ( I ,2, .. . . ..... , n)
=A
{ <l>j ... , ... •.. ... , <lln }
<ll (<\>1<\>2' ... .. . .... <\>n)=X (XI ........ .... Xn) T,
< \If I \If >= S , rST= I
occ
P = TT+, P = L njTjTj+ = 2P,
j= 1
If all the n occupied spin orbitals are paired, P is a
representation of the one-electron density matrix
(OEDM) in the X basis. Clearly, this representation
corresponds to the closed shell SCF model or the
open shell unrestricted Hartee-Fock theory of the
molecules depending upon the spin state. Within the
limitations of the models mentioned above, one can
define the atomic charge qA on an atom A in the
molecules as the expectation value of an LCAOatomic density operator (ZA-q) 1-2 such that
ZA being the nuclear charge of the atom A. <qA> is
clearly the Mulliken gross charge density on the atom
A and is an atomic invariant. The chemist's notion of
the parti al charges on the atoms of a molecule can
thu s be recovered from the OEDM represented in the
X basis . Along with the so-called partia l charges on
atoms in a molecule, a chemist's model of molecules
involves the very useful notion of bond order between
a pair of atoms in a molecule, a notion which
practicall y corresponds to the notion of the
multiplicity (or the number) of the bonds holding the
pair of atoms together. The quantum chemical
analogue of this quantity, the so-called quantum
793
ADHIKARI et af.: MCSCF CALCULATIONS ON METAL ION AFFINITIES
Table I -Computed geometrical parameters of formaldehyde - Mn+( M n+== Li+, Na+, Be + ) complexes in the ground and t.3 mt * states.
2
Electro nic
state
System
H2COLi+
H 2CONa+
2
H2COBe +
Bond lengths ( in
A)
6
OM n+
CO
CHI
CH 2
ground
2.45
1.26
1.16
1.12
In1t*
2.47
1. 26
1.15
1.12
3 n1t *
2.45
1.27
1.16
1.12
Angles (in
degr~s)
CO
H2CO
q,
73.0
120.5
127.0
0.0
75.4
114.2
123.2
0.0
75.4
11 3.0
124.0
0.0
180.0
121.0
121.0
0.0
Mn+OC
HI
ground
1.94
1.26
1.12
1.12
In1t*
2.24
1.27
1.12
1.12
137.8
117.6
118.0
43.2
117.1
117. 1
45.0
J n1t *
2.21
1.26
1. 12
1.12
180.0
ground
1.66
1.28
1.12
1.12
180.0
118.9
118.9
0.0
116.9
116.9
12.2
116.7
116.7
45 .0
In1t*
1.91
1.26
1.13
1.13
180.0
J n1t *
1.90
1.27
1.13
l.I3
180.0
Table 2-Computed metal affinities (MA) of formaldehyde, acetaldehyde and formamide
( M n+== Li+, Na+, Be2+ ) in the ground and I.3 n1t* states
Metal affi nities ( in a. u. )
Electronic states
H 2CO-Li+
H2CO-Na+
H 2CO-Be 2+
Ground
0. 117
0.115
0.402
In1t*
0.062
0.060
0.342
3n1t *
0.070
0.063
0.330
CH 3CHO-Lt
CH 3CHO-Na+
CH 3CHO-Be 2+
Ground
0. 164
0. 158
0.479
In1t*
0.075
0.060
0.350
3n1t *
0.065
0.055
0.343
NH 2CHO-Li+
NH 2CHO-Na+
NH 2CHO-Be 2+
Ground
0.268
0. 161
0.672
In1t*
0. 122
0.068
0.655
3n1t *
0. 149
0.063
0.667
Formaldehyde-Mn+
Acetaldehyde-M n+
Formamide-M n+
Table 3-Computed bond orders between different atoms and net charge densities on different atoms of formaldehyde-Mn+
( M n+== Lt, Na+, Be 2+ ) complexes in the ground and I.3 n1t * states
System
Electronic
H2CO-Li+
H2CO-Na+
H 2CO-Be +
Net charge on
OM n+
CO
CHI
CM n+
HIM n+
M n+
0
C
H
ground
0.22
1.96
0.77
0.22
0.16
0.67
-0. 12
0.36
0.04
In1t'
3
n1t'
0.09
1.91
0.83
1.16
0.09
-0. 18
0.25
0.41
0.21
0. 11
1.60
0.79
0.22
0. 14
0.66
0.08
0.42
0.21
0.35
1. 90
0.95
0.72
-0.25
0.44
0.11
0.1 1
1.16
0.92
0.88
-0.08
0.41
0.2 1
0.10
1.81
0.89
-0.03
0.22
0.4 1
0.21
0.97
1.61
0.95
1.40
-0. 19
0.55
0.12
0.37
1.71
0.85
0.78
0.19
0.50
0.27
0.37
1. 70
0.78
0.20
0.49
0.28
grou nd
In1t '
J
2
Bond orders
state
n1t '
ground
I ,
n1t
3
n1t '
CO bond order in H2CO
0.85
n1t '
ground
In1t'
3
2.030
1. 150
1. 190
794
INDIAN 1 CHEM, SEC. A, AUGUST 2000
-+---25·60
(b)
H2CO-U+ compiex
_._-- H2CO-Na+ complex
- . - - H2CO-Be++ complex
:J
o
t:
::. -25·80
...
1/1
(]I
.......t:
W
"0 -26·00
(5
I--
Fig. I-Interactions of M"+ (M"+ == Li+, Na+, 8e 2+) with
formaldehyde molecu le in different electronic states. (a) H 2COLt in the ground and I.3 nrc* states. (b) H 2CO-Na+ in the ground
and 3 nrc* states; H 2CO-Be 2+ in the ground and I.3 nrc * states. (c)
H 2CO-Na+ in the I nrc* state.
chemical bond order has been defined for systems
representable by closed shell single determinant wave
functions as follows :
-25·40
---+---
H2Co.U+ complex
------ H2CO • Na+ complex
-t--- H2CO· Se++complex
-25 · 60
A more general definition that covers open-shell
(UHF) states has also been successfully used:
-'25·80
d
;
[b)
~ - 26 ·00 "*
__- - - , - -- -- . - -- -, . ._ ---;
~
BAB thus defined has been an interesting statistical
interpretation, viz., BAB measures the correlation
between the fluctuation of atomjc charges on atoms A
and B from their respective average values 9 .
If the motions of electron are totally uncorrelated the
bond order BAB vanishes. It may be noted that even at
the single determinant level of representation the
electronic motions are geared through Fermi (spin)
correlation which thus seems to play an important
role in shaping the magnitude of the quantum
11
cherrucal bond order (BAB)' In fact, Mayer8.
identifies BAB with the normalization of the relevant
diatorruc component of the exchange part of the
reduced two electron den sity matrix. A qualitative
description of the role pl ayed by Fermi-correlation in
-2 5·40
___
H2C O-LI'· co mplex
.~
___ - H2CO-N a:+ complex
~
---t- -
.,
H2C O-Be++compiex
t;
(3
I-
-25·60
!
-25, 80·
Fig. 2-Plots of total energies versus O-M"+ distances of H 2COM"+, (M"+ == Li+, Na+, 8e 2+) complexes in the (a) ground, (b) Inrc*
and (c) 3nrc* states.
795
ADHIKARl et at.: MCSCF CALCULATIONS ON METAL ION AFFINITIES
5
Table 4---Calculated chemical shifts for 1.3nn* transitions of
forrnaldehyde-Mn+, acetaldehyde-Mn+ and forrnamide-M n+
( M n+'" Li+, Na+, Be 2+ ) complexes
determining bond orders was suggested even earlier .
The idea of a molecular orb ital picture of valency was
first introduced by Wibergl 2. If the gross population
A
of an AO bas is function (X Il ) on an atom A in the
molecul e is qA Il ' the potential bonding power of that
particular AO in the mo lecul e is supposed to be
bAil
=2 (q\) -
Chemical shifts (in a.u.)
System
(qAlli
3nn
H 2CO-Lt
0 . 140
0 . 150
H2CO-Na+
0.074
0.070
H 2CO-Be 2+
Summing over, all the basis functions ce ntered on
atom A we get what has been called valency (V A) of
the atom A in the molecul e.
*
Inn*
0.063
0.032
C H 3CHO-Lt
0.063
0.049
C H 3CHO-Na+
0.D25
0 .015
2
C H3CHO-Be +
0 .062
0.068
NH 2CHO-Li+
0 .045
0.019
NH 2C HO-Na+
0 .085
0.079
NH 2CHO-Be 2+
0.010
0 .005
n
2
Table 5-Co mputed geomelrical parameters of aceta ldehyde - Mn+( M +'" Li +, Na+, Be + ) complexes in the ground and 1.3nn * states
Electroni c
Bond lengths ( in
A)
,.
OM n +
CO
CC
CH,
CHI
ground
2.23
1.29
1.44
1.13
Inn*
2A7
2A5
1.30
1.1 3
1.29
IA4
IA3
gro und
1.90
1.29
Inn*
2. 14
1.28
3ni1 *
2.15
state
Angles (in odegrees)
<'>
,
7 \
ceo
CH 2C H 3
Mn+OC
1.1 2
1.13
163.0
125.1
5.5
1.1 5
1.13
95.3
124.2
5.0
1.1 3
1.15
1.13
98. 1
120.2
5.6
1.43
1.13
1.12
1.1 3
170.5
124.9
4.6
IA2
1.1 3
1.1 4
1.1 3
90.8
125.3
12A
1.30
IA2
1.14
1.1 4
1.13
88 .0
126.9
12. 1
IAI
l AO
lAO
1.1 3
1. 12
1.1 3
180.0
126.3
5.6
1. 13
1.14
1.13
180.0
121.3
5.0
1.1 3
1.14
1.1 3
180.0
127 .7
4.8
<I>
H3CC HO-Li +
3nn *
H3CCHO-Na+
H3CCHO-Be2+
ground
1.64
1.32
Inn*
1. 86
1.3 1
3nn *
1. 86
1.32
a: aldehydic
Tab le 6- Computed bond orders between different atoms of acetaldehyde-M n+( M n+'" Lt, Na+, Be 2+ ) complexes
in th e grou nd and 1.3 nn * states
System
Electroni c
state
Bond orders
OM n +
CI H,
CIO
C 2 HJ
C IC 2
C Hs
C 2 M n+
H,;M n+
HsC I
C 2 H~
CHJCHO-Li +
C H3C HO-Na+
CH3C HO-Be2+
Gro und
I .
nn
Jnn '
OAO
1.74
0.93
1.11
0 .94
0.96
0. 11
1.58
0.87
1.09
0 .85
0 .91
0 . 17
0. 11
0. 12
1.57
0.88
1.09
0.84
0.92
0 . 18
0 .11
Ground
0.75
1.55
0 .94
1.15
0.90
0 .97
Inn'
0 .08
1.58
0 .86
1.11
0 .87
0 .93
0 . 10
0.08
1
. nn •
0.08
1.52
0 .87
1.1 3
0 .87
0 .93
0.11
0 . 11
Ground
I .
1.11
1.31
0.94
1.24
0.89
0.96
OA6
1.39
0.84
1.19
0.92
0 .88
0.51
1.33
0. 82
1. 25
0.92
0.90
1l1t
1
' nn
•
CO bond order in CH 3CHO
a : aldehydi c
0. 12
0. 16
ground
Inn'
3nn '
1.903
1.076
1.114
796
INDIAN J CHEM, SEC. A, AUG UST 2000
Table 7--Computed net charge densities on different atoms of acetaldehyde - Mn+( M n+== Li +, Na +, Be 2+ ) complexes
in the ground and I.3 mt * states
System
Electronic
0
Ca
C
Ha
HI
H2
H3
-0.22
0.41
-0.04
0.07
0 .66
0.07
0.07
-0.03
- 0 .23
0.13
0.48
0 .003
0.16
0.18
-0. 16
0.14
-0.23
0 . 12
0.47
0 .01
0. 15
0.19
0.16
0 .13
ground
0.76
-0 .33
0.43
- 0 .05
- 0.01
0.04
0 .08
0.07
In1t •
3
n1t "
-0.15
0 .10
0.47
-0.11
0 . 15
0 .17
0. 15
0.12
-0 .16
0 .09
0.47
-0.004
0. 15
0 . 18
0 . 16
0.12
- 0. 13
0.38
0.46
0 .08
0.31
0 .27
0 .39
0.25
0 .72
0 .06
0 .51
-0.05
0.20
0.15
0 .2 1
0.19
0 .70
0.05
0.50
-0.03
0 .20
0 . 17
0 .22
0. 19
state
CH.lCHO-Li'
ground
In1t '
,. n1t
CH 3CHO-Na+
CH, CHO-Be 2+
Net charge on
M n+
Ground
In1t "
3
n1t "
a : aldehydic
Table 8--Computed geometri cal parameters of formamide - Mn+( M n+== Li+, Na+, Be 2+ ) complexes in the ground and
Electronic
Bond lengths ( in
state
H2NCHO-Li +
ground
Imt *
J n1t *
H2NCHO-Na+
ground
In1t*
3 n1t *
H2NCHO-Be 2+
ground
In1t*
3n1t *
A)
OM n+
CO
CN
CHa
NH I
NH2
" oc
rvin+
2.21
2.42
2.46
1.30
1.35
1.34
1.37
1.30
1.3 2
1.12
1.12
1.12
1.09
1.24
1.28
1.07
L08
1.08
1.9 1
2.09
2.24
1.29
1.30
1.33
1.36
1.3 2
1.33
1.12
1.13
I. II
1.08
1.08
1.09
1.65
1.81
1.92
1.31
1.33
1.31
1.40
1.36
1.37
1.13
1.14
1.14
1.13
1.13
1.14
1.3 n1t
* states3
An gles (in degrees)
'
.. <
.....
OCN
CNH I
$
106.2
100.1
97.2
122.1
114.9
115.8
12 1.7
11 3.0
114.4
0.0
34.0
32.0
1.07
1.07
1.07
100.0
100.9
89.2
124.0
120.6
126 .5
121.0
11 9.6
11 6. 6
0.0
26.3
22.1
1.08
1.10
1.09
81.2
76.6
75 .3
124.1
127.3
128 .2
12 1.4
11 6 .6
11 8. 7
0.0
24.2
33.1
a: aldehydic
L ·t
••••••• 1 • •• •
••••
' 0.
H'~""
, : :'
/":'0
",'
.
"
/~-c;""
H4
~
H3
H
;: Li+,Na+,Be2+
(a)
(b)
(c)
(d)
Fig. 3-Interaction s of M n+ (M n+ == Li+, Na+, Be 2+) with acetaldehyde molecule in different electronic states. (a) CH 3CHO-M n+ (M"+ ==
Li+, Na+, Be 2 +) in the ground state, (b) CH 3CHO-Li+ in the 1,3 n1t * state, (c) CH 3CHO-Na+ in the I.3 n1t * state and (d) CH3C HO-Be2+ in the
1.3 111t* state
Wiberg's definition of valency was proposed in
connection with ZDO theori.es of 1t electron systems.
The ab initio generalization of the concept by Mayer
is of a rather recent vintage. Mayer's9 definition of
atomic valence (V AM) is a useful definition', which is a
straightforward generalization of Wiberg's valence
when the basis set of expansion is non-orthogonal.
V AM = 2 L (PS)
ILE A
L (PS)f1v (PS)vf1
IlVEA
If the system is in a open-shell state and represented
by an UHF wave function, we have
797
ADHIKARl et at. : MCSCF CALCULATIONS ON METAL ION AFFINITIES
-34'00
__
~
____
~
Cfi;3CHO-U+ complex
-+-
~ CH3CHO-Be++ complex
H""
CH3CHO-Na+ compl.x
~~o
:.
' ) . . .' .
............. .'::~,
~
-34·20
,.,.
HI
::l
"C:
.
~
III
-34'40
M-"E Li+, Na+,Bel+
~
c
.,
(a)
UJ
~
M-".= Li+, Na+
-34·60
:=
(a)
- 3 4 .8 O+..-'TT'TT. . . .--.-.-.--.-.--...,..,,..,..,.-rr-rr--,--,--,--.-,
2·00
lOO
O-M
n+
JOO
4'0{J
(b)
Fig, 5-lnteractions of M"+ (M"+ '" Li +, Na+, Be 2+) with
formamide molecule in different electronic
states, (a) NH 2CHO-M"+ (M o+ '" Li +, Na+, Be 2+) in the ground
state and i.3 nn * states of NH 2CHO-Be h (b) NH 2CHO-M o+ (Mo+:;
Li+, Na+ ) in the 1.3nn * state
0
Bond L~ng'h (A)
P = pU + pP , pS
_ _ - CH3CHO-Li+ complex
_ _ - CH3CHO -Na+ complex
-3400
___ CH3CHO-BeH complex
= pU _ pP
It can be shown that this automatically leads to a
residual or free valence (<I>A) for the atom A given by
~
s
S
<I>A = L ~ (P S)~v (P S)\,~
JJVEA
-34 ·20
r:::l
o
I:
III
.~
(b)
-34'60:f--,-~-.--,--,--,--,-,.....~-~-.--r-.--r'-----'---'­
-34,00
II
--- CH3CHO-Li+ complex
..
__ - CH3CHO-Na+ co mplex
~
\ __
-+-- CH3CHO-Be++ compl ex
'~ -
I:
UJ
a
Clearly <I>A=O for any closed shell system at the HF
level of description. With this theoretical background
in mind we propose to examine the usefulness of the
quantum chemical valence parameters in the context
of structural modelling of some molecules in the
ground and excited states. We represent the molecule
in its lowest singlet and triplet excited states by the
fo llowing wave functions (S=O corresponds to singlet,
S= I to triplet)
U\jli~j
~
I
= 12
[( I</>,</>,
-
-I
.. " </>i</>j .. " </>n</>n )
-J4 ·20
+ (-1)\ I</>,¢, .. " </>j¢i , ... </>n¢n I)]
The variational optImIzation of the orbitals
<1>1 .. " ....... <1>n' which the so luti on of the master
. 0 fM cweeny 13.
equatIOn
-3440
v
= (hTP, + Z) = STA
". (I)
(c)
-34 6O t=====~~~o:;:_:-::_:-::_==_-=_~==:-=====
~_.
' .00
2·00
O-M
n+
300
4·00
and the CI problem requires one to solve the equation
q
Bond Lwglh (A)
HC=CE
Fig. 4-Plots of total energies versus O_M"+ di stances of
CH 3CHO-M"+, (M"+ '" Li +, Na+, Be 2 +) complexes in the (a) ground
(b) Inn* and (c) 3nn* states.
Equation
orthogonal
.. . (2)
is solved iteratively by a variant of
gradient method'4.' 6 which involves
798
[NDIAN J CHEM, SEC. A, AUGUST 2000
construction of the following sequence iteratively
until the desired degree of convergence is achieved
The CI coefficients at convergence are used to
construct the one-electron density matrix (PI) in the
MO (<1» basis . Once PI is determined, the optimized
orbital expansion coefficient (T) can then be
condensed into a representation of the density matrix
in the X basis as follows .
For the simplified choice of 'l' where we have a fixed
(invariant) set of doubly occupied orbitals (core) and
set of singly occupied orbitals, P = pO +ps, pO
represents the component of the OEDM coming from
the doubly occupied orbitals and pS, the component
contributed by the singly occupied orbital. The pO
and pS matrices can now be used for the
determination of the quantum chemical valence
parameters B AB , V A , PA etc .
Results and Discussion
Formaldehyde and metal ion (M"+-=Lt, Na+, Bi+)
interactions
The optimised geometries of form,aldehyde - M"+
(Mn+-=Li+, Na+, Be 2+) are given in Table 1. Li+
interacts with the oxygen atom of the formaldehyde
molecule at an angle <90 0 in the ground and l.3 n1t *
excited states resulting decrease in C=O bond length.
2
Similarly, Be +, Na+ interact along the C=O bond axis
2
where O---Be + distance is found to be much less
compared to other O ___ Mn+ distances. Unlike proton17
formaldehyde system , C=O bond length decreases
in the metal-formaldehyde system. This may be due
to charge transfer interaction between metal ion and
oxygen lone pair electrons. The decreased electron
density is compensated from the other atoms in the
l8
molecule .
So it is important to rationalize cation interacting
power towards formaldehyde molecule and also
Lewis acidities of the ions. From the computed metal
affinities (MA) of formaldehyde (Table 2) in the
ground and several excited states, Be 2+ affinity is
found to be more than those of Li+ and Na+. Ground
state MA is higher than excited state MAs. MA
increases with each methyl substitution and agrees
with reported data I. There is no good correlation
between MA and net charge on oxygen atom in (he
ground and excited states.
Metal ion, on the other hand, increases C=O bond
order and decreases C-H bond order in the · i.3 n1t *
states of formaldehyde molecule (Table 3). The
observation is found to be contrary to that in the case
17
of proton-formaldehyde system . The net charge
densities (Table 3) together with the bond order data
can be taken to imply the structures [Fig. I (a,b,c)] in
the ground and i.3 n1t * excited states. It is observed ·
that considerable electron density has migrated from
oxygen atom to metal ions. This stabilises the charge
transfer interactions, resulting in substantial reduction
of C-H bond order. The minimum energy plots
corresponding to standard geometries with respect to
Table 9---Computed net charge densities on different atoms of formamide - Mn+( Mn+;: Li+ , Na+, Be 2+ ) complexes
in the ground and 1.3 nn:* states
System
NH 2CHO-Li+
NH 2CHO-Na+
NH 2CHO-Be 2+
a : aldehydic
Electronic
Net charge on
state
M n+
0
C
N
Ha
HI
H2
ground
0.67
-0.32
OA7
-0. 18
0.03
0.16
0.18
Inn:'
0.62
-0.08
0.37
-0.01
0.05
-0. 12
0.16
3n n:'
0.6 1
-0.09
0.33
0.02
0.06
-0.10
0.17
ground
0.71
-0.34
0.45
-0.20
0.02
0.15
0.19
Inn:'
-0.10
0.D3
0. 11
0.27
0.24
-0.09
0.03
OA6
OA7
-0.01
3nn:'
-0.02
0. 11
0.27
0.23
ground
0.99
-0.13
0.53
-0.13
0.16
0.25
0.32
Inn:'
OAI
0.16
0.51
0.04
0.22
0.33
0.34
3n n:'
0.44
0. 15
0.52
-0.01
0.24
0.33
0.33
799
ADHIKARI et a/.: MCSCF CALCULATIONS ON METAL ION AFFINITIES
O---M+ distances are given in Figs [2(a,b,c)]. At the
equilibrium geometry both in the ground and excited
states total energies (T.E.) vs ro---8/+ curves are found
to be steeper than the corresponding curves for Li+,
Na+ ions, which reflect t~e stability of Be2+ ion
complexed with the formaldehyde molecule in all the
electronic states . It has been reported 19 that in
aqueous solutions, stability of Li+ is less than that of
Na+ and we obtained similar observations for these
metal ions interacted with formaldehyde molecule
also. We have analysed special shift (Table 4) in
l.3n7t* transitions. Li+ gives large blue shift, whereas
Be2+ and Na+ show a small shift4 in the 1,3 n1t *
transitions.
Acetaldehyde and metal ion (Mn+-=Li+, Na+, Be 2 +)
interactions
Study on the geometrical structure (Table 5) and
energetics of Mn+ interaction with acetaldehyde
shows that M n+ interacts with the oxygen atom of the
carbonyl groupl . Metal affinities of the metal ions
Lt, Na+ and Be2+ in the ground state are higher than
excited state MAs and Be 2+ affinity is more than Lt
and Na+ affinitie s (Table 2) . The computed Li+
affinities in the ground and l.Jn1t * states are found to
be higher th an the corresponding Na+ affinities 4. The
computed MAs of acetaldehyde are found to be
higher than those of formaldehyde molecule in almost
all the cases. These observation agree with the
reported data that with each methyl substitution MA
mcreases. Structural changes of acetaldehyde
molecule in Mn+-acetaldehyde complexes are less
prominent if one considers MA values. There is no
good correlation between MAs and net charge density
on oxygen atom in the ground and I.3 n1t * states for
CH 3CHO-M n+ complexes. Minimum energy search
for the position of M n+ relative to acetaldehyde
molecule shows that C=O-Mn+(Mn+-=Lt, Na+) angles
are less than 100° in all the exci ted electronic states
(Table 5) . rO_Be2+ is much shorter than ro_ .. I./ and
rO---N/ . Be2+ interacts linearly with the >C=O group.
This may be due to strong 1t decolazation in >C=O
group . Methyl group enhances such an effect. From
the bond orders (Tab le 6) and net charge densities
(Table 7) we analyse structural re-organi sations in
acetaldehyde molecule due to M n+ ion s. Structure in
Fig 3(a) is expected in the ground state of CH)CHOMn+ interactions-(Mn+-=Lt, Na+, Be 2+). In the I.3 n1t *
states of CH 3CHO-Lt complex, Lt-C 2 and Lt-H5
bond orders ,are quite large and structure in Fig. [3(b)]
is expected in the excited state. Similarly, in the
CH 3CHO-N'a+ complex, Na+-O, Na+-C 2 bond orders
are found to be the same in the I.3 n1t * states . Fig.
[3(c)] is expected to contribute in these states . In the
CH3CHO-Be2+ interaction, C-C bond order is much
larger in the excited states than the single bond and
expected structure is given in Fig. [3(d)]. Figs [,4(a, b,
c)] show the correlation between total energy and
rOoM n+ in different states. It is obvious that M n+ ions
show small effect in I ,J n1t * states and agree with
experimental findings4 .
It appears that M n+ induced proximity effect
Table I O--Computed bond orders between different atoms of formamide - Mn+( Mn+;: Li+, Na+, Be2+ ) complexes
in the ground and 1.3 n1t * states
System
NH 2CHO.Li +
NH 2CHO.Na+
NH 2CHO.Be2+
Electronic
state
OM n+
CO
CN
ground
0.3 5
1.62
1.24
CHa
0.93
0.07
'n1t'
0.19
1.07
1.80
0.94
0.06
3nn:'
0.19
1.10
1.73
0.93
0.06
ground
0.38
1.59
1.28
0.94
'n1t'
3
n1t '
0.14
1.33
1.57
0.91
0.09
1.26
1.61
0.91
0.03
0.87
ground
0.80
1.40
1.15
0.92
0.28
0.72
'n1t'
3
n1t '
0.40
1.22
1.42
0.86
0.23
0.68
0.31
1.33
1.34
0.82
0.21
0.70
CO bond order in NH 2CHO
a : aldehydic
Bond orders
CM n+
ground
'n1t'
1.753
0.977
NM n+
Ha Mn +
0.87
NH2
0.94
0.01
0. 11
0.24
0.89
0.22
0.13
0.27
0.91
0.21
0.13
0.05
0.91
0.94
0.01
0.06
0.03
0.88
0.91
0.18
0.07
0.92
0. 17
0.07
0.88
0.15
0.42
0.86
0.00
0.42
0.87
0.00
0.43
NH,
3
n1t '
0.998
800
INDIAN J CHEM, SEC. A, AUGUST 2000
contributes in producing the MA of acetaldehyde
molecule. However, dielectric continuum may not be
the appropriate model for metal ion affect in aprotic
l4
solvent . Thorough evaluation of intermolecular
interactions is required in large carbonyl molecules.
Li+, Na+ and Be 2+ show blue shift in the 1.3 n1t *
transition energies 20 (Table 4).
-37045
-.-~
H2NCHO-Li+ complex
-fI-~
H2NCHO-Na+ complex
_~
H2NCHO-BeH complex
-37-65
II!
Formamide and metal ion (Mt/+ == Li+, Na+, Be 2+)
interactions
Geometrical parameters of NH 2CHO-M"+ (Table
8) and metal affinities of formamide molecule at the
oxygen atom (Table 2) have been calculated for the
metal ions Li+, Na+ and Be 2+. The calculated values
provide information about the strength of metal
carbonyl binding as well as geometrical changes due
to metal ion. From the computed data (Table 2), Mn+
ion affinities of formamide molecule are found to be
more than those of other carbonyl molecules 7 . It
appears that extensive electronic reorganization must
have occurred in the metal complex due to charge
transfer interaction between oxygen atom and metal
ion which, on the other hand, influences the electron
density distribution in the other atoms of formamide
molecule (Table 9). Alkali metals have strong affinity
towards amide:! I and Li+ affinity is found to be more
than Na+ affinity whereas Be 2+ affinity is the largest.
In the Li+-formamide complex, Li+-Ha bond order is
found to be much more than Li+-0 bond order in the
excited states (Table 10). Small positive charge on H.
and large negative charge on oxygen atom confirm
these observations. Structure in Fig. 5(a) is expected
in the ground state for all formamide-M"+ complexes
and structure in Fig. 5(b) is expected in the 1.3 n1t *
states of Li+ aIld Na+ complexes with formamide. But
observations are different in Be 2+-formamide
complexes in these states. In the Be2+-formamide
complex, Be 2+-N bond order is found to be
considerably large (almost half the Be2+-Q bond
order in the ground state and greater than those in the
excited states) (Table 10). It may be expected due to
the large charge transfer interactions between oxygen
atom and metal ion which influence the lone pair
electron on nitrogen atom. This can be referred from
the large negative charge on nitrogen atom, and
structure identical to Fig. 5(a) is expected in the
excited states. The presence of metal-oxygen charge
transfer interaction and the absence of simple oxygen
to metal (donor to acceptor) interaction may be the
reason for the absence of correlation between Li+
.~
Ol
:;; -38,05
~
o
o
I-
-38.25
-3 8·45-1' ...,.,..-.-:-,-,-"...,,....,.....,~--,---,-r..,....,,....,.,.,I-;-. .-'-;-...,-,
. I
20'0
3·00
4·00
1· 00
O-M
-37'40
n+ Bond
0
Length (A )
-+-- H;2NCH~U+ complex
-e- ..... H2NCHO-Na+ complex
--+-- HzNCHO-S.ei'+ comolex
- 37·60
-37-80
-38 ·00.
_ -38 ·20
::r
r:i
~~ -38 40 ~~~~~~~~~~~~~
(b)
·~ -37·'O
..
__ - H;zNCHO-li+- compler
w
-.- ...... H:zNCHO-Be+-+ complex
-+-- H24'JCHO-Na + complex
c
...~ -376
(c)
-38'4 ~+O.,...O~·C'T"'--.-r""'i~.00"-- '
, .. ,
rio
n
o- M -'"-Bond Lenglh (Ao)
Fig. 6-Plot of total energies versus O_Mn+ distances of
NH 2CHO-Mn+, (M n+ == Li+, Na+, Be 2+) complexes in the (a)
ground, (b) 'n7t* and (c) 3n7t* states ..
binding energy and Gutmann number of Li+l
formamide system . It seems that theoretical
calculations may be of great importance to classify
geometrical relaxations due to complex formation
which cannot be obtained experimentally. Like Mn+_
)
ADHIKARJ el al. : MCSCF CALCULATIONS ON METAL ION AFFINITIES
fonnaldehyde and Mn+-acetaldehyde complexes,
there is no good correlation between MA and net
charge density on oxygen atom of the Mn+-fonnamide
complexes. The plots of total energy vs rOoM n+
distance [Fig. 6(a, b, c)] reflect the stability of metal
fonnamide complex compared to other carbonyl
l
compounds . From Table 4 we find that Lt and Na+
show favourable blue shift in Inn* state whereas in
CH 3CHO-Be2+ complex indicates a small blue shift
in 1,3 nn * states 20 •
Conclusions
From the computed data
observations can be made:
3.
References
I
2
3
4
5
6
interesting
1. The observed affinities of the carbonyl molecules
toward Li+, Na+ and Be 2+ ions are in the order:
Be 2+> Lt> Na+.
2.
Department of Atomic Energy, Mumbai for providing
partial financial support.
7
following
8
9
10
II
12
13
Metal affinIty value is state dominant and ground
state affinity is higher than excited state affinities
for all the carbonyl molecules.
IS
Nature of the molecule is one of the factors,
determining metal affinities .
16
4 . There is no good correlation between MA and net
charge on oxygen atom of the carbony l molecules
because
of the
proximity
effect
from
fI
neighbouring atoms of M + ion in the complex .
14
17
18
19
20
Acknowledgement
CM acknowledges CSIR, New Delhi for financial
support to carry out the work and DA thanks
801
21
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