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6
Ni(II), Cobalt(II), Manganese(II) and Zinc(II)
Complexes of
5,6_Dihydro_5,6_Epoxy_1,10_Phenanthroline_
Synthesis and Spectroscopic Studies.
F.A. OLUWAFUNMILAYO ADEKUNLE1*
1
Department of Pure and Applied Chemistry Ladoke Akintola University of Technology, Ogbomoso, Nigeria
*E-mail: [email protected]
Abstract--
5,6-dihydro-5,6-epoxy-1,10-phenanthroline (L)
reacted with metal(II) perchlorate hydrates in methanol in a 3:1
ligand : metal ratio at ambient temperature. The complexes
obtained were characterized by microanalyses, room
temperature magnetic susceptibility measurements, infrared,
UV-visible spectra, mass spectra and conductivity measurements.
The results of the data from the microanalyses agreed fairly well
with the calculated values. The room temperature magnetic
susceptibility measurement of the nickel complex at 2.87 B.M.
reflected the spin-only magnetic moment in an octahedral field.
The cobalt(II) compound indicates orbital contribution to the
magnet moment (µeff = 4.63 BM) while the manganese(II)
complex in a high-spin configuration showed a moment of 5.48
B.M. The fragmentation pattern in the mass spectra data of the
complexes is in tandem with other spectroscopic and analytical
studies of the complexes. The data obtained from the
conductivity measurements, reveal the complexes to be 1:2
electrolytes.
agents for the development of bioorganic reagents and probes
[1].
6
5
4
7
B
A
C
8
9
N
N
10
3
2
1
(1)
N
I.
INTRODUCTION
1,10- phenanthroline is the parent of an important class of
chelating agents [1]. This chelating ligand which has high
affinity for metal ions also posses π- acceptor capability which
significantly contributes to the stabilization of their low valent
metal complexes [2,3]. 1,10-phenanthroline (1), when
compared with its congener and the more common
2,2’dipyridyl system (2), has several distinct properties: the
rigid structure imposed by the central ring B means that the
two nitrogen atoms are always held in juxtaposition, whereas
in (2), free rotation about the linking bond allows the two
nitrogens to separate (2a
2b), in particular
under basic or strongly acidic conditions [1]. This entropic
advantage of 1,10-phenanthroline means that complexes with
metal ions can form more rapidly, a property of importance
[1]. Another consequence of the planar nature of 1, 10phenanthroline is its ability to participate as either an
intercalating or groove- binding species with DNA and RNA.
In addition to the afore mentioned properties of this ligand, is
the ability to act as a triplet-state photosensitizer [1]. 1,10phenanthroline and its derivatives have been used as chelating
N
N
N
(2b)
(2a)
O
N
N
(L)
The enormous interest in molecular recognition processes and
increased use of 1,10-phenanthroline in this area has renewed
interest in the synthetic manipulation of these systems [1].
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In 1,10-phenanthroline, the 5,6-double bond is most
susceptible to electrophilic attack and even epoxides can be
formed from it [1] . The epoxidation of olefins is of great
interest due to the importance of epoxides in the manufacture
of both bulk and fine chemicals [4]. A derivative of this
nitrogen donor ligand 2,9- Dimethyl-1,10-phenanthroline has
been converted into a range of oxidized derivatives [1].
Epoxides serve as useful starting material in the synthesis of a
variety of functionalized organic compound, as the epoxide
ring reacts readily with a wide range of nucleophiles with high
regioselectivity [4]. The facile and regiospecific opening of
terminal epoxides makes this class of epoxide particularly
useful in the production of industrially important products
such as surfactants, corrossion protection agents and additives
[4].
Much work has been devoted to the study of the ligand
complexes because of their key role in biological process, and
their properties in such areas such as analytical chemistry,
catalysis and magnetochemistry [5]. In addition, copper(II)
complexes of phenanthroline
and its derivatives have
attracted great attention because they exhibit numerous
biological activities such as antitumor, anti-Candida,
antimycobacterial and antimicrobial [3]. Metal chelates have
been used to probe the structure of DNA in solution, as agents
for mediation of strand scission of duplex DNA and as
chemotherapeutic agents [6].
In this work, we synthesized and characterized nickel(II),
cobalt(II), manganese(II) and zinc(II) complexes 5,6-dihydro5,6-epoxy-1,10-phenanthroline (L). A probe was made into
the spectroscopic properties of these compounds.
3.
EXPERIMENTAL
3.1. Materials and physical measurements
5,6-dihydro-5,6-epoxy-1,10-phenanthroline (L) was
purchased from Aldrich. Ni(ClO4)2.6H2O, Co(ClO4)2.6H2O,
Mn(ClO4)2.xH2O and Zn(ClO4)2.6H2O were all obtained from
Aldrich. Molar conductances were measured by a Syntronics
(India) conductivity meter (Model 306) in acetonitrile.
Microanalyses were performed by Perkin-Elmer 240II
Elemental Analyser. The room temperature magnetic
moments of the Ni, Co and Mn complexes were measured by
a magnetic susceptibility balance from Sherwood Scientific,
UK. UV-Visible spectra were recorded on a Perkin-Elmer
Lambda 950 spectrophotometer, FTIR spectra (KBr) on a
Shimadzu FTIR-8400S spectrometer and ESI mass spectra on
a Waters Qtof Micro YA263 spectrometer.
3.1. Synthesis of NiL3(ClO4)2.2H2O
Ni(ClO4)2.6H2O (73mg, 0.2mmol) dissolved in 5ml methanol
was added dropwise to L (79mg, 0.4mmol) dissolved in 10ml
methanol with stirring to obtain a light orange solution.
Precipitation occurred immediately while stirring continued
for 4hrs. Then it was filtered by suction and was dried in air.
Yield: 170mg (96%). ɅM/mho cm2mol-1:347(CH3CN) (1:2
electrolyte). ESIMS (CH3CN)
NiL3.2H2O2+), 322.9 (100%, NiL3 2+)
7
m/z:
340.9
(10%,
3.2. Synthesis of CoL3(ClO4)2.H2O
Co(ClO4)2.6H2O (46mg, 0.125mmol) dissolved in 8ml
methanol was added dropwise to L (74mg, 0.375mmol)
dissolved in 10ml methanol with stirring to obtain a bright yellow turbid solution. Precipitation occurred after 1hr of
stirring and stirring continued for 7hrs. The yellow compound
obtained after stirring was filtered by suction and was dried in
a vacuo. Yield: 76mg (70%). ɅM/mho cm2mol-1: 350 (CH3CN)
(1:2 electrolytes). ESIMS (CH3CN) m/z: 225.6 (100%,
CoL22+), 323.6 (85%, CoL3 2+)
3.3. Synthesis of MnL3(ClO4)2.2H2O
Mn(ClO4)2.xH2O (32mg, 0.125mmol) dissolved in 10ml
methanol was added dropwise to L (74mg, 0.375mmol)
dissolved in 10ml methanol with stirring to obtain a bright yellow turbid solution. The turbid solution stirred for 4hrs
after which it was kept on the bench for slow evaporation to
take place. The yellow compound obtained after 5days was
filtered by suction and dried in a vacuo. Yield: 49mg (45%).
ɅM/mho cm2mol-1:311(CH3CN) (1:2 electrolyte). ESIMS
(CH3CN) m/z: 223.4 (100%, MnL22+), 321.4 (40%, MnL3 2+)
3.4. Synthesis of ZnL3(ClO4)2.2H2O [7]
Zn(ClO4)2.6H2O (186mg, 0.5mmol) dissolved in 20ml
methanol was added dropwise to L (294mg, 1.5mmol)
dissolved in 20ml methanol with stirring ,within 5min of
stirring a white compound started appearing while stirring
continued for 2hrs. The white compound obtained after
stirring was filtered by suction and washed with few drops of
methanol and dried in air. Yield: 275mg (65%). ɅM/mho
cm2mol-1:307(CH3CN) (1:2 electrolyte). ESIMS (CH2Cl2)
m/z: 227.9 (95%, ZnL22+), 321.9 (20%, ZnL3 2+)
4.
RESULTS AND D ISCUSSION
The complexes were all obtained readily from methanolic
solutions at ambient temperature. The nickel(II) complex was
isolated by reacting the ligand, L with Ni(ClO4)2.6H2O in a 2:
1 ligand to metal ratio, while the Co(II), Mn(II) and
zinc(II)complexes were obtained by the reaction of the ligand
with their respective perchlorate salts in 1:3 metal:ligand ratio.
All complexes were analysed for C,H,N and metal and
satisfactory analyses were obtained in each case (Table 1).
The percentage yields of the prepared compounds were found
to be appreciable except in the manganese complex where the
% yield is relatively small. The colours of the complexes are
consistent with similar systems [8].
The C-O stretching
frequency of the epoxide was observed at 1578 cm-1, 1576
cm-1, and 1576 cm-1 for Ni(epoxy)3(ClO4)2.2H2O,
Co(epoxy)3(ClO4)2.H2O,
Mn(epoxy)3(ClO4)2.2H2O and
Zn(epoxy)3(ClO4)2.2H2O respectively [9]. The presence of
these bands is an indication of the presence of the epoxide ring
in the complexes. The C=C of the aromatic ring in both the Zn
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and Nickel complexes were found at 1614 cm while in the
cobalt and manganese compound it is at lower value [9] of
1612 cm-1. The aromatic C-N stretching of the complexes
were at 1026 cm-1 for only the nickel complex while it was at
1030 cm-1 for the remaining three complexes. The C=N bands
in the complexes are found between 1435-1437 cm-1, the shifts
observed in the spectra of these complexes compared with the
literature value of 1600 cm-1 indicate the use of the nitrogen
atom of the ring to form the complexes [11]. The presence of
the water molecules in the complexes is revealed in the broad
bands observed at 3415 cm-1 to 3535 cm-1 in the spectra of the
complexes. The infrared absorption at ca. 624 cm-1 and 1100
cm-1 associated with perchlorates [11] was observed in the
complexes.
Electronic spectra: The electronic spectra of the
NiL3(ClO4)2.2H2O shows two bands at 12,775cm-1 and 19,099
cm-1 attributed to transitions 3A2g→3T2g and 3A2g→3T1g(F)
respectively [12,13] of nickel(II) complex in an octahedral
geometry. The electronic spectrum of the nickel(II) complex
indicates a six- coordinate structure. The peach coloured
complex has a 10Dq(ⱱ1) value of 12,775 cm-1 within the range
of 12,100 – 12,700 cm-1 [10] and for complexes containing
unsaturated nitrogen atoms the value should be of similar
magnitude to that exhibited by 2,2’-bipyridine and 1,10phenanthroline etc, all of which exhibit 10Dq values near
12,700 cm-1 [14].
The electronic spectra of the cobalt(II) complex exhibits two
principal regions of absorption in the vicinity of 20,095 cm-1
and 11,356 cm-1 which may be assigned to ⱱ3 transition,
4
T1g→4T1g(P) and ⱱ1-transition 4T1g→4T2g respectively in the
high spin octahedral geometry [15,16]. The ⱱ2
transition4T1g→4A2g at 18,697 cm-1 was also observed [15,16].
The energy ratio ⱱ2/ ⱱ1 = 1.67 does not fall within 1.9 – 2.2 for
the range of Dq/B values appropriate for cobalt(II), the
information that can be used to determine whether a weak
feature in the spectrum might be the 4A2g transition [16]. The
cobalt ion is assumed to be coordinated to the six N atoms of
the bidentate chelates in an octahedral arrangement, this
arrangement is similar to that of the tris(1,10phenanthroline)cobalt(II) diperchlorate monohydrate [17].
Manganese(II) is normally found in an octahedral
coordination environment [18]. The d-d spectra of the high
spin manganese complex shows two absorptions at 22,727 cm1
and 19,231 cm-1 corresponding to 6A1g→4Eg and
8
A1g→ T1g transitions respectively, which are typical of
Mn(II) complexes with an octahedral coordination geometry
[19].
The
tris(1,10-phenanthroline)
manganese(II)
bis(perchlorate) chloroform disolvate reported has a twisted
octahedral geometry [19]. Thus, the two complexes have
similar geometry despite the modifications in the 5,6-dihydro5,6-epoxy-1,10-phenanthroline ligand.
6
4
The binary complex of Zn(II) is diamagnetic and the
electronic spectra of the complex is dominated only by ligand
bands.
Magnetic moment: The room temperature magnetic moments
of the complexes prepared during the course of this
investigation are listed in Table 1. The magnetic
susceptibilities, all of which are independent of field strength,
were corrected for the diamagnetic contribution of the ligands,
the anions and the metal ions using Pascal’s constants.
The effective magnetic moment of the binary Ni(II) complex
is 2.87 B.M., suggesting its octahedral structure [13]. The
Co(II) chelate has a room temperature magnetic moment of
4.63 B.M as expected for a high - spin octahedral Co(II)
complex [13]. The tris-bidentate complex of manganese(II) is
of the high-spin variety, exhibiting magnetic moment 5.60
B.M [19] .
Mass spectra: In the mass spectra of NiL3(ClO4)2.2H2O, the
peak at m/z = 340.9 and stand for {NiL3.2H2O}2+ and {NiL3
}2+ respectively. CoL3(ClO4)2.H2O has peaks at m/z = 225.6
and m/z = 323.6 for {CoL2 }2+ and {CoL3}2+ respectively. The
peaks at m/z = 223.4 and m/z = 321.4 were observed in the
MnL3(ClO4)2.2H2O complex while the ZnL3(ClO4)2.2H2O
complex showed peaks at m/z = 227.9 and m/z = 321.9
respectively for {ZnL2 }2+ and {ZnL3} 2+. The measured
molecular weights were consistent with expected values.
Conductivity measurement: The conductance of the
solutions of the complexes in acetonitrile, CH3CN (10-3 mol L1
) are shown in Table 1. The molar conductances of the
complexes are 347 Ω-1 cm2 mol-1 , 350 Ω-1 cm2 mol-1 , 311 Ω-1
cm2 mol-1 and 307 Ω-1 cm2 mol-1 for the Ni(II), Co(II), Mn(II)
and Zn(II) complexes respectively indicating the electrolytic
nature of the complexes [19]. The tris-ligand complexes are
1:2 electrolytes and appear to have the ionic structures
[ML3](ClO4)2 on the basis of the conductivity.
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International Journal of Basic & Applied Sciences IJBAS-IJENS Vol:13 No:03
9
T ABLE I
ANALYTICAL DATA OF THE COMPLEXES
µeff
(B.M)
Peach
ɅM
/mho
cm2mol-1
347
70
Yellow
350
4.63
878.27
44
Yellow
311
5.60
888.6
89
White
307
-
Compound
Molecular
Formula
M.M
Yield%
Colour
Ni(epoxy)3(ClO4)2.2H2O
C36H28N6O13Cl2Ni
881.9
96
Co(epoxy)3(ClO4)2.H2O
C36H26N6O12Cl2Co
864.18
Mn(epoxy)3(ClO4)2.2H2O
C36H28N6O13Cl2Mn
Zn(epoxy)3(ClO4)2.2H2O
C36H28N6O13Cl2Zn
2.87
C
49.10
(48.98)
49.57
(49.99)
49.28
(49.18)
48.18
(48.64)
%Observed
(Calculated)
H
3.06
(3.20)
3.26
(3.03)
3.33
(3.21)
3.24
(2.95)
N
9.47
(9.52)
9.62
(9.73)
9.44
(9.57)
9.31
(9.46)
T ABLE II
KEY INFRARED FREQUENCIES AND ELECTRONIC SPECTRAL TRANSITIONS FOR THE COMPOUNDS (CM-1)
Compound
C-Ostr
C=C str
C-N str
C=N str
C-H str
H2O str
ClO4- str
Ni(epoxy)3(ClO4)2.2H2O
1578
1614
1026
1435
3094
3454
623, 1088
Co(epoxy)3(ClO4)2.H2O
1578
1612
1030
1437
3096,
3028
3429
623,1088
Mn(epoxy)3(ClO4)2.2H2O
1576
1612
1030
1435
3096
3433
623 , 1092
Zn(epoxy)3(ClO4)2.2H2O
1576
1614
1030
1437
3096,
3026
3454
624, 1088
ACKNOWLEGEMENT
F.A.O.Adekunle is grateful to Professor Dipankar Datta of
Indian Association for the Cultivation of Science (IACS)
Calcutta for a laboratory space and Third World Academy of
Science (TWAS), Trieste, Italy and Indian Association for the
Cultivation of Science (IACS) Calcutta India for a PostDoctoral Fellowship.
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