Download Synthesis and physico-chemical studies on transition metal

Indian Journal of Chemistry
Vol. 43A. March 2004. pp. 556-561
Synthesis and physico-chemical
studies on transition metal complexes
of macrocyclic ligand derived from
2,6-diacetylpyridine dihydrazone
Mohammad Shakir*, Poonam Chingsubam,
Hamida-Tun-Nisa Chishti, Yasser Azim & Nishat Begum
Division of Inorganic Chemistry. Department of Chemistry.
Aligarh Muslim University, Ali garh 202 002, Indi a
Received 27 December 2002; revised 3 Nowmber 2003
A novel series of Schiff base decaaza macrocyc lic comp lexes
1
[ML X,] [M = Mn(ll), Fe( ll ). Co(ll). Ni( ll ) and Zn (II )] ; and
[CuL' ]:X 2 ( X = Cl. N0 3) have been synt hesized by the reaction
between pre-synthesized 2.6-diacetylpyridine dihydrazone (L) and
formaldehyde in th e presence or metal ions in methanol medium
at room temperature. The formation of li ga nd (L) and the proposed
macrocyclic complexes have been confirmed from the results of
elemental analyses. the comparative band pos itions for v(C=N)
and appearance of proton resonance peaks for secondary amine
1
group (N-NH-C) in H NMR spectra of compl exes. The nature of
the comp lexes and th eir overall geometry have been infe1Ted from
electrical conductivity data, observed band positions in electronic
spectra and magnetic moment values.
The importance of macrocyclic complexes in
coordination chemistry is because of its various
1 7
applications · , in biol :lg ic al processes such as
8
photosynthesis and dioxygen tran s port ; cata lytic
9
properties ; potential appl ications as metal extractants
10
and as radio-therapeutic and medical imaging agents.
In macrocyclic complexes, both the metal ion and the
size of the ring play an important role. Lindoy and co.
wor kers have reporte d ll ·12 a senes
o f' stu d'res on t he
selective complexation of transition metal ions by
polydentate ligands . Metal ions act as templates ,
directing the steric course of the condensation reaction
.
. nng
.
rn
c Iosure 13 · 19 . Th ere f ore, t I1e meta I
resu Ittng
template method has been recognized as high yielding
and se lective routes to new ligands and their
20 21
complexes ' . Several macrocyclic ligands derived
12 ~ "4
from hydrazine precursors have bee n reported - - .
Recently. divalent metal che lates of macrocycle
derived from dihydrazide and aromatic diketone have
25
also been reported • We report herein, a novel series
of decaazamacrocyclic complexes derived from the
26 29
condensation reaction of 2,6-di acety lpyridine . ,
hydrazine hydrate, formaldehyde and metal ions
structure directing agent.
Experimental
II
II
II
The metal salts MX, .nH,O (M =Mn , Fe , Co ,
11
11
11
Ni , Cu and Zn ; X= Cl,- NO: and n=lJ,6) (all BDH)
were commercially pure samples. The chemicals such
as 2, 6-diacetylpyridine (A ldrich), hydrazine hydrate
85l'/r; (Sigma) and formaldehyde so luti on 37 % (E.
Merck) were used as received. Solvents were dried
before use.
Preparation of 2,6-diacetylpyridine dihydrazone, 'L'
To a stirring solution of 2 ,6-diacetylpyridine
(0.3264 g, 2 mmol) in methanol (- 20 ml) was added
a solution of hydrazine (0.242 ml, 4 mmol) dissolved
in methanol(- 20 ml). The stirTing continued for 6-8
h, resulting in a colourless so lution . The resultant
reaction mixture was allowed to stand for48 h resulting
in the isolation of microcrystalline solid.
Synthesis of dichloro/nitrato (1,3:11,13-dipyridyl-4,10,14,20tetra methyl- 2,5,6,8,9,12,15,16,18,19-decaaza-4,9,14,19tetracne cycloeicosane) metal (II), [ML' X,] (M =Mn", Fe", Co",
Ni" and Zn 11 ) and [CuL'] X, (X=CI, NO,).
To a stirTing methanolic solution (-20 ml) of 2, 6diacetylpyridine dihydrazone, 'L'(0.668 g, 4 mmol),
solutions of formaldehyde (0.298 ml , 4 mmol) taken
in 20 ml methanol and MX 2.nHz0 (X=C I, N0 3 , n=
1,3,6) (2 mmol ) dissolved in 20 ml of methanol were
added simultaneously. The reaction mixture was
further stilTed overnight affording the isolation of solid
product, wh ich was filtered, washed several times and
vacuum dried.
E lemental analyses were obtained from the
microanalytical laboratory, Co llege of Sciences King
Saud University Riyadh (KSA). Metals and chloride
1
0
were determined volumetricall/ and gravimetricall/
respectively. The electronic spectra of the compounds
in DMSO were recorded on a Pye-Un icam 8800
spectrophotometer at room temperature. EPR spectra
were record e d on a JEOL JES RX2X EPR
spectrophotometer. Magnetic s uscepti bi Ii ty
NOTES
N1· II and Zn II ; X=CI, NO) have been prepared by the
template condensation reaction of2-6-diacetylpyridine
dihydrazone, ' L ' and formaldehyde in methanol
medium in a 2:2 ratio (Scheme 1). An attempt was
made to synthesize metal free macrocyclic li gand
which resulted in an oily product. All the complexes
are found to be stable to atmo s phere at r oom
temperature. These complexes are soluble in distilled
water, DMSO and DMF. The results of eleme ntal
analyses (Table 1) correspond to the proposed
macrocyclic framework. The low conductivity data
ascertain the non-electrolytic nature of these
measurements were carried out using a Faraday
32
Balance at 25°C. The electrical conductivities of
3
10· M solutions in DMSO were obtained on a Digital
conductivity meter APX 185 equilibrated at 25 °C
± 0.05. 1H NMR spectra were recorded in DMSO-d6
using a Jeol , Eclipse 400 with Me 4 Si as an internal
1
standard. The IR spectra (4000-200 cm- ) were
recorded as KBr discs on a Perkin-Elmer 2400
spectrophotometer.
Results and discussion
A new series of decaazamacrocyclic complexes
I
I
II
II
II
[ML X 2] and [CuL] X 2 (where M = Mn , Fe , Co ,
Me
ra
y~~~
0
Me
557
+
0
HCHO
~
Me
HN
y
\
A"-';:~----:-l
Scheme I
N /L-NNHH
~Cu~
HN-N~
Me
c"x,ru<,o
)
N-NH
N~"l~
~
Me
I
2+
INDIAN 1 CHEM, SEC A, MARCH 2004
558
Table 1- Analytical data and molar conductance values for the compounds
Compound
Yield
M.pt ( 0 C)
Colour
Calcd (Found) %
M
Cl
1\_,
c
H
N
56.54
(56.53)
6.80
(6.79)
36.64
(36.62)
45.19
(45.17)
4.89
(4.88)
26.36
(26.34}
15
41.09
(41.07)
4.45
(4.43)
28.76
(28.75}
15
45 . 11
(45.10)
4.88
(4.87)
26.31
(26.30)
23
41 .02
(41.01)
4.44
(4.43)
28.71
(28.70)
23
45.02
(45.01 )
4.87
(4.86)
26.26
(26.24)
18
40.95
(40.93)
4.43
(4.41)
28.66
(28.65)
18
44.85
(44.83)
4.85
(4.84)
26.16
(26.15)
14
40.81
(40.80)
4.42
(4.41)
28.57
(28.55)
14
44.44
(44.42)
4.81
(4.80)
25.92
(25.91)
100
40.47
(40.45)
4.38
(4.36)
28.33
(28.32)
115
44.28
(44.27)
4.79
(4.78)
25.83
(25 .81)
18
40.33
(40.31)
4.36
(4.34)
28.23
(28.22)
18
(cm 2 ohm·'
mor')
L
45
150
White
[MnL' CI:J
50
290
Dull green
10.16
( 10.15)
[MnL' (N03 ) J
52
290
Dull green
9.24
(9.23)
[FeL' Cl2 ]
60
>300
Wine red
10.33
(10.31)
fFeL' (N0 3) 1J
55
>300
Wine red
9.40
(9.39)
[CoL' Cl 2]
40
>300
Dark brown
10.50
( 10.49)
[CoL' (N0,) 2]
45
>300
Dark brown
9.55
(9.54)
[NiL' CIJ
38
185
Rust
10.84
( 10.83)
[NiL' (NO)J
45
200
Rust
9.86
(9.85)
[CuL'q]
55
220
Yellow
11.66
( 11.65)
[CuL' ](N03) 2
60
200
Yellow
10.62
(10.61 )
[ZnL' Cl 2]
55
>300
Colourless
11 .99
(11.97)
[ZnL' (N0 3 ) 2]
65
>300
Colourless
10.92
(10.91)
complexes, except that of copper compl.exes, which
}?
were found to be 1:2 electrolyte -.
The preliminary information regarding the
formation of 'L ·has been inferred from bands observed
in its IR spectrum. The disappearance of band
corresponding to v(C=O) and appearance of a new
.J
strong intensity band at 1625 em assigned to v(C=N)
of imine group srrongly suggest the formation of 'L' .
•J
A strong doublet around 3360 em may be assigned
to v(N-H) stretching mode of uncondensed primary
amine group of hydrazine moiety. The appearance of
13.37
( 13.35)
13.34
(13.33)
13.32
( 13.30)
13.27
( 13.25)
13. 14
( 13.13)
13.09
(13.07)
.J
bands at 2925 and 985 em may be assigned to
v(C-H), and v(N-N) stretching vibration respectively
in 'L'.
TheIR spectra of all the complexes exhibit no band
corresponding to v(C=O) of formaldehyde group rather
a new strong intensity band appears in the region 32103260 em·' anributable 33 to the v(N-H) stretching mode
of secondary amines. This suggests that condensation
between CO of formaldehyde moiety and NH 2 of
hydrazine moiety has occurred in presence of metal
ion. The IR sp ~ctra of all the macrocyclic complexes
NOTES
exhibit a medium intensity band in the region 15901
34 37
1620 cm- which may be assigned - to a coordinated
imine v(C=N) stretching vibration. The band in the
1
region 1140-1220 cm- may reasonably, be assigned
to v(C-N) stretching vibration. An absorption band
1
appears in the region 2850-2920 cm - in all the
complexes, may reasonably be ascribed to the v(C-H)
stretchi ng vibrational modes. A medium intensity band
1
around 940-975 cm- may be ascribed to the v(N-N)
38
stretching mode • All the comp lexes show bands
1
around 403, 601 and 1578 cm- consistent39 A0 with the
pyridine ring vibrations assignable to out-of-plane ring
deformation and in-plane ring deformation,
respectively. These vib rations do not suffer signiticant
shift towards higher frequencies suggesting that
pyridine nitrogen in the macrocyclic complexes is not
41
coordin ated to the metal atom • The presence of band
1
in the region 330-490 cm - may be due to the
42 3
v(M-N) .4 _ Bands observed in the regions 207-220
559
1
1
44
cm- and 228-240 cm- may be assigned to v(M-CI )
and v(M-0) stretching vibrations respectively.
However, in the copper complex additiona l bands
1
observed at 1630, 1280, 870 and 705 cm- may be
reasonably assigned to the free nitrate group.
1
The H NMR spectrum of 'L' shows peaks at 2.63
ppm which may be assigned to the methyl protons
(CH 3 ; 6H) of the 2,6-diacetylpyri,dine moiety.
Multiplets in the region 7.75 and i38 ppm may be
45
assigned to aryl protons (Hu) and to (2H~) of 'L'.
46
Multiplets in the region 4.99 ppm may be attributed
1
to (N-NH,; 4H) protons of 'L' _ The H NMR spectra
of the Zn(II) complexes show a major peak at 7.747.77 ppm and 7.35-7.39 ppm which may be assigned
~~
to the ary l · protons (2Hu) and (4H11 ) respectively. A
singlet at 2.68-2.70 ppm may be reasonably assigned
to the methyl (CH 3 ; l2H) protons of the 2, 6diacetylpyridine moiety. The multiplets observed at
3.11-3.13 ppm may be assigned to the meth ylen e
Table 2- Magnetic moment values, electronic spectral data assignments and EPR data or the compound
Compound
J..l.n(B .M .)
Band position(cm·')
EPR
Assignments
G
5.80
[MnL' Cl2]
[MnL' (N0 3 )
2]
5.78
22,300
18.750
6
22.350
18,800
6
6
A 1g ~ 'T,g
4
A 1g ~ T 1g
A 1g ~ 7~g
4
A 1g ~ T 1g
4
6
[FeL' Cl 2]
5.44
11,450
5
T2g ~ Eg
[FeL' (NO,) ,l
5.40
II ,850
5
T 2g ~ Eg
[CoL' C I2]
4.55
16.800
22,200
'T,g(F) ~ A 2g(F)
4
4
T 1g(F) ~ T1 g(P)
[CoL' (NO,) 2]
4.54
16,500
22,400
4
[NiL' Cl 2]
3.05
11,500
17,850
1
[NiL' (NO)J
3.06
12,000
17.400
-'A ,g(F) ~ ' T,g(r)
3
3
A 2g(F) ~ T 1g(P)
[CuL' Cl2 ]
1.76
13.000
16,100
21,950
2
1.77
12, 100
16,200
21,600
5
5
4
T 1g( F) ~ A 2g( F)
4
T 1g( F) ~ T 1g( P)
4
4
A 2g(F) ~ -'T,g(F)
A 2g(F) ~ -'T,g(P)
3
2
B ,g --+ l3 2g
2
' B,g ~ A 1 g
2
2
B 1g ~ Eg
2.22
2.06
3.66
's,g ~ ' s ,g
2
l3 1g ~'A,g
2
'B,g ~ Eg
2.24
2.07
3.42
INDIAN J CHEM, SEC A, MARCH 2004
560
protons (N-CH 2-N; 4H) of the aldehyde moiety. The
multiplets observed at 6.83-6.84 ppm may be assigned
to the secondary amino group of the hydrazine moiety.
But, no NMR signal has been observed in the
1
complexes [Zn
Cl 2] and [Zn L (N0 3)z) which
correspond to the NH 2 protons of 'L' suggesting that
condensation has taken place (Scheme 1.)
The EPR spectra of both the polycrystalline Cu(II)
macrocyclic complexes were recorded at room
temperature, and their g 11 and gj_ values were calculated.
Neither of the decaazamacrocyclic Cu(II) complexes
studied shown any hyperfine splitting, but gave only a
derivative curve giving g 11 and gj_ values, (Table 2), as
48
characteristic of square planar copper (II) complexes.
This suggests that the unpaired electron is present in
49
the dx 2-y 2 orbital as g 11 > g j_ > 2.02 • In an axial
symmetry, the g values are related by the expression
G=(g 11 -2)/(gl - 2), which measures the interaction
between copper centres in the unit cell. The calculated
'G' values for the present complexes appeared in the
50
range 3.42 and 3.66, suggest the existence of a
considerable exchange interaction between copper, as
G<4. All the complexes show g 11 < 2.3. It should be
51
noted that for an ionic environment while for a
covalent environment g 11 < 2.3 , indicating that the
present complexes exhibit considerable covalent
character.
T he appearance of two bands in the electronic
spectra (Table 2) of the manganese complex in the
regions 18,750-18,800 em·' and 22,300-22,350 em·'
may reasonably COITespond 52 to the 6A 1 ~ -~ 4 T1 ~ an d
4
6
A18, -7 T2-~ transitions, respectively consistent with an
octahedral geometry around the manganese (II) ion.
The electronic spectra of the iron complexes exhibit a
weak intensity (d-d) transition in the region 1 1,45011 ,850 em·' , which may be reasonably assigned to the
5
5
T 28 -7 E~ transition , consistent with a high-spin
octahedral environment around iron (II) ion. However,
the electronic spectra of the cobalt complexes exhibit
two bands in the regions 16,500-16,800 em·' and
22,200-22,400 em·' which may reasonably correspond
4
4
4
to th_e_ T 1s(F) -7 _ A 2 _.(F) and ~T 1 §~F) -7 T 1 _~(P)
transitions, respectively, suggestmg· an octahedral
geometry for the complexes. The ligand tield spectra
for nickei(II) macrocyclic complexes show two bands
in the regions 11,500- 12,000 em·' and 17,400-17,850
4
3
em·' which may be ascribed 5 to the 3A 2 /F) -7 T1 ~(F)
and 3A 2 _~(F) -7 3T 1/P) transitions, ·rt"spectively,
indicating an octahedral environment around the
e
nickei(II) ion. The copper complexes gave three bands
in their electronic spectra in the regions 12,100-13,000
em-'; 16,100-16,200 em·' and 21,600-21,950 em·' and
2
these bands may reasonably assigned to the 8 1 ~ -7
2
2
2
2
2
B2R; B,R-7 A '·• and B,_~ -7 E~ transitions respecti~ely.
The above results are consistent with the square planar
geometry of copper (TI) complexes.
The observed magnetic moment values (Table 2)
for all these metal complexes are in close agreement
with electronic spectral data which fUJthersuppOit their
proposed geometry.
Acknowledgements
The authors thank Dr. Yamin Siddiqui , College
of Sciences, King Saud UPI .ersity, Riyadh (KSA) for
1
providing elemental analyses. FT-IR and H NMR
facilities. The Department of Chemistry , Amritsar
(GNDU) is a lso highly thanked for the magnetic
measurement facility. The UGC, New Delhi. India is
also thanked for financial supp01t under major research
project No. F.12-116/200l.
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