Download Heterobimetallic chemistry: Heterobimetallic complexes derived

Indian Journal of Chemistry
Vol. 41A, June 2002, pp. 1157-1162
Heterobimetallic chemistry: Heterobimetallic complexes derived from
monometallic copper(II) complex of bis(2-hydroxy-l-naphthaldehyde )malonoy ldihydrazone
R A Lal*, J Chakraborty & S Bhaumik,
Department of Chemistry, Tripura University, Suryamaninagar 799130, Tripura, India
and
A Kumar
Department of Chemistry, Indian Institute of Technology, Powai 400 076, Mumbai, India.
Received 24 April 2001 ; revised 13 February 2002
Monometallic copper(II) complex [Cu(LH z)(H zO)21 ( 1) and heterobimetallic complexes [MCu(L)(H 20hl (where M =
UO z(2) and Zn(4)) and [MCu(L)(H 20)41 (where M = Mo0 2(3), Ni(5), Co(6) and Mn(7)) and homobimetallic copper(II)
complex [Cuz(L)(H20)41.2HzO(8) have been isolated and characterized by analytical, molecular weight, magnetic moment,
electrical conductance, electronic IR and ESR spectral data. IR spectral evidences indicate that dihydrazone coordinates to
the metal centres in enol forms. The monometallic copper(IJ) complex (1) and the heterobimetallic complexes U0 2Cu (2)
and Mo0 2Cu (3) and Zn-Cu (4) are normal paramagnetic indicating absence of any metal-metal interaction in the structural
unit of the complexes while the remaining heterobimetallic complexes Ni-Cu(5), Co-Cu (6) and Mn-Cu (7) have much less
Ileff va lues than those required for 3, 4 and 6 unpaired electrons indicating considerable metal - metal interactions. Copper
has distorted octahedral geometry in monometallic and heterobimetallic complexes. Uranium has pentagonal bipyramidal
stereochemi stry while zinc has square pyramidal stereochemistry. However, copper(II) has square pyramidal
stereochemi stry in homobimetallic complex (8).
Cooperative interaction between different metal ions
in hetero-polynuclear complexes I constitutes an active
area of research of cooperative interaction between
metal ions in polynuclear complexes 2 • They might
prove helpful in investigating the mutual influence of
the two metal centres on the electronic, magnetic and
redox properties of such systems) . Multidentate
ligands possessing more than one coordination
environment serve as an important means of
synthesizing hetero-metal compounds. They can
selectively bind one metal ion to one site and different
metal ions to another. The dihydrazone derived from
condensation of o-hydroxy-aromatic aldehydes and
ketones with acyl, aroyl and pyridoyl-dihydrazines
are potentially polyfunctional ligands capable of
forming
polynuclear metal
complexes?
The
malonoyl-dihydrazones constitute a special class of
polyfunctional hydrazones, which ossess acti ve
methylene group flanked by keto groups in addition to
phenol and azomethine functions 8 .
ligand systems have been investigated, those derived
from dihydrazones are quite meagre 9.10. In view of
the above importance of hetero-bimetallic complexes
of dihydrazones, the present paper describes the
synthesis and characterization of hetero-bimetallic
complexes of copper(II) with first row transition
metal ions and oxometal species like M00 22+ and
UO/+
derived
from
bis
(2-hydroxy-lnaphthaldehyde) malonoyldihydrazone (LH4).
The literature survey revealed that although heterobimetallic complexes from a variety of metal ions and
Bis(2 -hydroxy-1-naphthaldehyde )malonoyldihydrazone
Materials and Methods
Ammonium heptamolybdate, metal(lI) salts and
uranyl acetate dihydrate, diethylmalonate, hydrazine
1158
INDIAN J CHEM, SEC A, JUNE 2002
hydrate,
acetylacetone
and
2-hydroxy-Inaphthaldehyde were of E.Merck or equivalent grade.
Mo0 2(acach was prepared by the literature method II.
Malonoyldihydrazine was prepared by reacting
diethylmalonate (1 mol) with hydrazine hydrate (2
mol). The bis(2-hydroxy-I-naphthaldehyde) malonoyldihydrazone (LH4) was prepared by reacting a warm
ethanol solution of malonoyldihydrazine (l mol) with
2-hydroxy-I-naphthaldehyde (2 mol) and was suction
filtered , washed with ethanol and dried in vacuo (m.p.
265°C). [Found: C, 68.45; H, 4.62; N, 13.00; Reqd.
for C2s H2oN40 4, C, 68.18; H, 4.55; N, 12.73 %].
Metals in the complexes were determined by
standard literature method 12 . Carbon, hydrogen and
nitrogen were determined microanalytically. Water
molecules were determined by heating the samples in
an oven at 110°C, and passing the vapours through a
trap containing anhydrous copper sulphate, which
turned blue and the weight loss estimated. The
molecular weights of the complexes were determined
in DMSO solution by freezing point depression
method. The molar conductance of the complexes at
1O-3M dilution in DMSO was measured on a direct
reading conductivity meter with a dip-type
conductivity cell.
IR spectra were recorded on a Paragon 500
Spectrophotometer in the range 4000-350 cm-' in KBr
discs . The electronic spectra of the ligand and
complexes in DMSO solution were recorded on a
Milton Roy spectronic 21 spectrophotometer. The
ESR spectra of the compounds in powdered form at
room temperature and liquid nitrogen temperature
were recorded at X-band frequency on a varian E- L12
E-line Century series ESR spectrometer using TCNE
(g = 2.00277) as an internal field marker.
Preparation of the complex [Cu(LH 2 ) (H 2 0hl (1)
In order to prepare the complex [Cu(LH 2)( H20 h ]'
the ligand, LH4 (0.88 g, 2.0 mmol) in ethanol (20 ml)
was allowed to react with CuCh.2H 20 (1.023 g, 6.0
mmol) in ethanol (20 ml) under refl ux for 6 h. The
dark-brown precipitate thus obtained was filtered,
washed with hot water, ethanol and dried over
anhydrous CaCho Yield : 0.8 1g (75 %).
Preparation of the complexes [MCu(L)(H 2 0).d
(where, M = UOl 2) and 2n(4)) and [MCu(L)(H 2 0)41
(where, M = MoO /+(3), Ni (5), Co (6) and Mn (7))
The suspension of the precursor complex
[Cu(LH2)(H 20)2] (0.538 g,I.O mmol) in methanol (30
mL) was added to a solution of U02(OAch2H20 (0.466
g, 1.1 mmol) in methanol (50 mL) containi ng a trace of
acetic acid over a period 10-15 min with constant stirring.
The reaction mixture so obtained was further stirred for
another 30 min. at 70°C followed by refiuxing for 3 h,
which precipitated dark-brown compound of composition
[U02Cu(L)(H20)3] (2). The complexes were crystallized
out from acetonitrile. The compound was dried over
anhydrous CaChoYield: 0.54 g (65 %).
The complexes (3) to (8) were also synthesized by
essentially following the above procedure using either
metal acetates (M = Zn(4), Ni(5), Co(6), Mn (7) and
Cu(II» or Mo0 2(acach instead of uranyl acetate,
respectively. The complexes were crystallized from
acetonitrile. Yield: (70-65 %).
Results and Discussion
The monometallic complex [Cu(LH 2)(H 20 h ] (I)
has been obtained from direct reaction of copper (II)
chloride with preformed dihydrazone in 3: 1 molar
ratio in methanol. When his complex was treated
with Mo0 2(acach or
uranyl acetate or second
metal acetates in methanol, the heterobimetallic
complexes [MCu(L)H 20)] (M=U0 2(2),Zn(4» and
[MCu(L)(H 20)] (M=Mo0 2(3), Ni(S), Co (6) and Mn
(7» were obtained.
The complexes are dark-green and dark-brown in
colour. The complexes are insoluble in water and
common organic so lvents but freshly prepared
complexes are slightly soluble in acetonitrile and
completely sol uble in highly coordinating solvents
like DMF and DMSO. The complexes decompose
above 300°C except the 1 which melts with
decomposition at 280°C. The high decomposition
temperature of the complexes also indicate their good
thermal stability. The molar co nductance of th e
complexes lies in the range 1.8-2.5 ohm-' cm 2 mor' of
10-3 M DMSO solution indicating their nonelectrolytic nature 13 .
None of the complexes shows weight loss at 110°C
ruling out the possibility of lattice water. On the other
hand, the monometallic copper(II) complex (1) shows
weight loss corresponding to two water mol ec ul es
whi le the complexes (2) and (4) show weight loss
corresponding to three water molecules at 180°C and
the remall1l11g complexes show weight loss
corresponding to four water molecules at this
temperature suggesting that they are present in the
first coordination sphere around the metal centre.
The complexes (1) and (3) are found to have
molecular weights equal to (660±30) and (900±40),
respectively. These values are very close to the
LAL ef al.: STUDIES OF HETEROBIMETALLIC COMPLEXES
theoretical
values for monomer formulation,
respectively. On the other hand, for the remaining
complexes, the experimental values were found to be
close to the theoretical values calculated for dimeric
formulation. However, the experimental values are
much higher than the values calculated either for the
monomeric formulation (for 1 and 3) or for the
dimeric formulation (for 2, 4-8). Such a higher
experimental value of molecular weight strongly
suggests that the coordinated water molecules appear
to be substituted by DMSO molecules.
The present ligand shows strong broad bands centred
at 3450, 3200 and 3047 cm·' which are assigned to
stretching vibrations of naphtholic -OH and secondary NH- group. Upon complexation, the bands at 3200 and
3047 cm·' disappear and a single strong broad band is
observed in the 3550-3000 cm-' region. The
disappearance of the bands at 3200 and 3047 cm-' and
appearance of a single strong broad band in the 3550 3000 cm-' region in all of the complexes suggests
enolization of the ligand and presence of water
molecules. As the water molecules are lost at 180°C
upon heating the complexes, this band is assigned to
ari se due to asymmetric and symmetric vibration of
coordinated water molecules.
The vC=O band at 1697 and 1661 cm-' in free
dihydrazone is absent in all of the complexes. This
suggests coordination of the dihydrazone to the metal
centre in the enol form. The free dihydrazone shows a
strong band at 1532 cm-'. This band is assigned to
have composite character due to mixed contribution
of the amide(II) and v(C-O) (naphtholic) bands. The
band in the 1538-1548 cm-' region in the complexes is
very strong and shows a shift of about 6-16 cm-' .
Such a feature associated with thi s band is attributed
to the fact that they have contribution from the
vNCO- band ari sing from enolization' 4. The vC=N
band appears in the 1600-1618 cm-' region as a
couple of bands in the heterobimetallic complexes .
The complexes (2) and (4) to (7) show medium to
weak intensity band in the region 875-869 cm-'. This
o
M/
"
M
band
IS
characteristic of tetraatomic
"0/
species resulted from involvement of naphthol ate
oxygen atom in bridge formation 15. On the other
hand, the complex (3) does not show such a band in
this region, which rules out the possibility of
1159
/0 ,
M
'\.. /
M
species in the structural unit of the
o
complex '6. Further, the heterobimetallic complex (2)
shows a new strong band at 919 cm-' which is
2
assigned
to
trans
V3(U0 2 +).
The
Mo-Cu
heterobimetallic complex (3) shows bands at 939s,
and 912s cm-' characteristic of cis-MoO/+ group'7.
The non-ligand bands appearing in the 525-590
cm-' region have been assigned to v(M-O)
(naphtholic) vibrations '8. The new bands appearing in
the 420-460 cm-' region are attributed to arise due to
v(M-O) band resulting from coordination of carbonyl
oxygen atom'9.
The magnetic moment value for the complexes are
presented in Table 1. The monometallic copper
complex (1) and heterobimetallic complexes U02- Cu
(2), MoOrCu (3) and Zn-Cu (4) have magnetic
moment value in the 1.95-l.71 8.M region . These
values are very close to the spin only value for one
unpaired electron (1.73 8M) which suggest either
there is no interaction or very weak interaction in the
structural unit of the complexes.
On the other hand, /J.B values for the
heterobimetallic copper(II) complexes (5), (6) and (7)
containing nickel(II), cobalt(II) and manganese(II),
are 2.60, 3.50 and 5.40 8M, respectively. These /J.B
values are less than the spin-only value for 3, 4 and 6
unpaired electrons resulting from bivalent heterometal combinations Ni-Cu, Co-Cu and Mn-Cu ,
respectively, indicating that there is an appreciable
metal-metal interaction between hetero-metal atoms in
the structural unit of the complexes 2o. This
observation is also supported from the fact that
copper
(II)
complex
homobimetallic
[Cu2(L)(H20h].2H20 (8) has /J.B value equal to 1.34
8.M, which is much less than the spin-only value
required for two unpaired electrons.
In addition to the ligand band, the electronic
spectra of monometallic copper(II) complex (1) shows
a band at 710 nm (c ma " 35 dm 3 cm-' mor') in the
visible region assigned to 2T2g -'i2Eg transition . Due to
Jahn-Teller distortion, this band is considerably blue
shifted, as has been reported in some olive green
square planar copper (II) chelates 22 . The band position
together with molar extinction coefficient in the
complex suggests that it has tetragonally distorted
octahedral stereochemistry. On the other hand, homo-
1160
INDIAN J CHEM, SEC A, JUNE 2002
bimetallic copper (II) complex (8) shows a shoulder at
540 nm to the charge transfer band which can be
attributed to d-d transition . The position of the band
together with its molar extinction coefficient indicates
its square pyramidal stereochemi stry 22. The electronic
spectra of hetero-bimetallic complexes (2) to (4) and
(7) show a weak broad band in the 600-750 nm region
with maximum absorption in the 675-690 nm region .
The band in the 675-690 nm region in the complexes
is assigned to d-d transition due to copper (IJ)23
because second metal ion i.e. U0 22+, M00 22+, Zn 2+
and Mn 2+ are not expected to show such a weak band
in this region . This shows that the stereochemistry of
copper centre in these complexes remains essentially
the same as that in the precursor copper complex i.e.
distorted octahedral geometry. Further, the heterobimetallic nickel-copper complex (5) shows only one
band at 720 nm. The position of this band again
indicates that both copper and nickel have distorted
octahedral stereochemistry. A comparison of the
position of this band with the corresponding band in
the spectra23 of [Ni(H 20)6]2+ at 740 nm and
[Ni(NH3)6]2+ at 570 nm suggests that it bears
similarity with those of oxygen donor ligands. This
indicates that nickel atom in this hetero-bimetallic .
complex is surrounded, most probably, by oxygen
atoms i.e. nickel is coordinated to carbonyl oxygen
atoms. On the other hand, the hetero-bimetallic
cobalt-copper complex (6) shows two bands at 630
and 540 nm assigned to Cu(II) and Co(II),
respectively. The position and molar extinction
coefficients together indicate that both copper and
cobalt
atoms
have
distorted
octahedral
stereochemistrl4 •
The monometallic copper(IJ) complex (1) shows an
isotropic spectrum in the polycrystalline state with gav
value equal to 2.089 (Table 2), while it shows an
anisotropic spectrum at liquid nitrogen temperature
(77 K). The parallel and perpendicular 63CU features
are resolved in the complex. The essential features of
the spectrum indicates that complex has octahedral
stereochemistry.
Table.l--Characterization data for complexes of bis(2-hydroxy-l-naphthaldehyde) malonoyldihydrazone
SI. No. Complex / Colour
D.P (0C), Yield (%)
3.
[Cu(LH2)(H20)2]
Dark-green
>280, 75%
[U02Cu(L)(H20)3]
Dark-brown
>300,65 %
[Mo02Cu(L)(H20)4]
4.
Dark-brown
>300,70%
[ZnCu(L)(H20)3]
I.
2.
5.
6.
7.
8.
Found (Caled.), %
Mol. wt.
Exptl. (Ther)
Cu
660±30
(537.54)
M
Magnetic Electronic spectral
moment bands
/lB B.M Amax(nm)(Emax)a
C
H
N
11.25
(11.81)
59.35
(58.81 )
4.13
(4.09)
10.00
(10.98)
1.95
I 980±90
(1647 .08)
11 .67
(11.81)
30.10
36.96
(29.55) (58.8 1)
2.63
(2.55)
6.35
(6.80)
1.75
900±40
(699.55)
9.58
(9.08)
13.52
43.08
(13.72) (42.89)
3.47
(3.43)
8.55
(8.01)
1.73
350(9750)
440(8940)
710(35)
420(12750)
500(5670)
675(50)
430(14500)
680(45)
I 540±60
( 1237.86)
10.58
(10.27)
10.98
48.98
(10.56) (48.47)
3.52
(3.56)
9.55
(9.05)
1.71
Dark-brown
>300,65 %
[NiCu(L)(H20)4]
Dark-brow n
>300,65%
[CoCu(L)(H20)4]
425(12570)
690(40)
I 650±55
(1260.50)
11.10
(10.08)
9.81
(9.31)
47.85
(47.60)
3.78
(3.8 1)
9.10
(8.90)
2.60
420(10950)
720(48)
10.85
( 10.08)
9.55
(9.35)
48.61
(47.58)
3.76
(3.81)
8.85
(8 .90)
3.50
Greenish-brown
>300, 70%
[MnCu(L)(H20)4]
Dark-brown >300, 65 %
[Cu2(L)(H20)2].2H20
Brownish - green
I 680±60
(1260.96)
1700±65
(1253 .10)
10.66
(10.14)
20.43
(20.01)
8.55
(8.78)
48 .10
(47.88)
47.01
(47.24)
3.79
(3.83)
3.85
(3.78)
8.54
(8.94)
8.63
(8.82)
5.40
430(15750)
540(48)
680 (38)
425(13780)
690(55)
350(12800)
380(12908)
", L cm· 1 mo)"1
I 390±35
( 1270.20)
1.34
420 (10290)
540 (250)
11 6 1
LAL et at.: STUDIES OF HETEROBIMETALLIC COMPLEXES
according to Kneubuhl's method 27 gave three g-values
g,=2 .140; g2=2.218 and g3= 2.383. The R- parameter
(g2-g,/g3-g2) for the complex is less than 1. This
indicates that dx'-l , is the ground state in this
complex. Thus, the complex may be suggested to be
five-coordinate square pyramidal. The relatively high
values of g-parameters are, most probably, indicative
of binuclear nature of the complex. The powder
spectra of the complex shows a weak signal at g ==
4.450, typical of Cu-Cu interaction with an absorption
corresponding to a ~ms= 2 transition.
The hetero-bimetallic complexes (2) to (4) derived
from monometallic copper(II) complex (1) have
almost similar ESR spectral feature . They exhibit
isotropic spectra similar to that of the precursor
monometallic complex in the solid state at RT with
gay value in the region 2.090-2.051. Further, the
complexes (2) and (4) show isotropic spectra at LNT
also in solid state with g ay value equal to 2.086 and
2.080, respectively, while, the heterobimetallic Mo0 2
-Cu complex (3) shows an anisotropic spectrum in the
solid state at LNT (77K) with gil and & values equal
to 2.265 and 2.070 and metal hyperfine coupling
constant equal to 180G. The magnetic parameters
indicate that gll>g.1> free electron spin (2.0023),
which shows that unpaired electron is in the d X2 - y2
orbital of the copper (II) centre.
The hetero-bimetallic Mn-Cu complex (7) also
The magnetic parameters indicate gll>g.1> free-spin
(2.0023), which shows that the unpaired electron is in
the d./ -/ orbital of the copper(II) centre. The gil and
g.1 values depart considerably from the free ion value.
The presence of strong broad band centred at -710
nm in the visible region of the electronic spectra of
the compound suggests distorted octahedral stereochemistry.
The covalency parameter a 2Cu for the complex is
calculated from gil , g.1 and All by the following
equation25 .
a 2cu = - (AW'P)
+ (g U-2) + 3/7(gr2) + 0.04
where, P is equal to 0.036 cm-'(ref.26) . Its value
has been found to be 0.63 for the complex. The a 2cu
value for the complex suggests considerable covalent
character (37 %) in bonding involving metal ion and
ligand.
The homo-bimetallic copper(II) complexeS) shows
anisotropic ESR spectrum with three signals. The
intensity of the signals in the solid state at room
temperature and LNT (77K) rules out the possibility
of either square planar or distorted octahedral
stereochemistry for the complex and suggests to have
five-coordinate structure. The two basic configuration
TBP and SP for five- coordinate complexes are
characterized by the ground state dz' and d x'-l.,
respectively. Analysis of the anisotropic spectra
Table 2- Magnetic parameters for monometallic, homobimetallic and some heterobimetallic copper complexes
Complex
Temperature
gay
[Cu(LH 2) (H 2O)2]
RT (solid)
2.08g
(1)
LNT (CH 3CN - DMSO)
LNT (Solid)
2.086
LNT (CH 3CN-DMSO)
LNT (Solid)
LNT (CH 3CN-DMSO)
2.110
LNT (Solid)
2.080
LNT (CH 3CN-DMSO)
2.147
LNT (Solid)
2.077
LNT (CH 3CN-DMSO)
2.146
[U 0 2Cu(L) (H 2O)3]
(2)
[Mo0 2Cu(L) (H 2O)4]
(3)
[ZnCu(L) (H 2O)3]
(4)
[MnCu(L) (H 2O)4]
(7)
gil
gl
[Cu2(L)(H20)2].2H20 RT(solid)
a , gay ~or Mn II . b ,Aav for Mn II
LNT
All
Ai
(G)
(G)
(G)
62
136
25
2.189
2.064
2.212
2.235
2.064
160
2.135
2.265
2.070
180
2.223
2.054
160
2.254
2.090
150
2.258
2.090
2.106
2.035 a
(8)
Aav
2.247
2.383 (g3)
2.218(g2)
94 b
2.140 g,)
4.42
2.189
4.480
2.319(g3)
2.149 (g2)
2. 100 (g,)
1162
INDIAN J CHEM, SEC A, JUNE 2002
[Cu(LH2)(H20)z] (1)
(I) I
shows an isotropic spectrum in the solid state at RT as
well at LNT with gav value equal to 2.077. However,
in the CH3CN-DMSO glass at LNT, the complex
shows isotropic splitting into six hyperfine line. This
hyperfine structure is attributed to sSMn (l = 5/2). In
the low field region, a weak signal is observed with gvalue equal to 2.258. The appearance of weak signals
indicates the binuclear nature of Mn(II) complex. This
signal may also arise due to parallel components of
copper hyperfine structure.
On the basis of various physico-chemical data
presented above and spectroscopic studies, the
structures for some of the complexes are suggested
(Structures I and II).
Acknowledgement
We would like to thank the UGC and DST, New
Delhi for financial assistance. Further, we would like to
thank the Head, RSIC, CDRI, Lucknow, for carbon,
hydrogen and nitrogen analyses, and to the Head RSIC,
lIT, Mumbai for ESR spectral studies.
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