Two new quadridentate Schiff base complexes of nickel(II) and cobalt(III): Synthesis, structure and spectral characterisation

Article abstract of DOI:10.1515/znb-2006-1004

Two novel quadridentate Schiff base complexes, [Ni^IILH](ClO ₄)₂·H₂O (1) and [Co^IIIL]- (ClO₄)₂·H₂O (2) [LH, a Schiff base ligand: Ph(OH)C(Me)=NCH₂CH₂N(CH₂CH ₂NH₂)₂] have been synthesised and characterised by elemental analyses, spectroscopic and electrochemical studies. The structures of both have been unequivocally established from single crystal X-ray diffraction studies. 1 and 2 crystallise in the monoclinic space group P2 ₁/n having cell parameters a = 8.536(1), b = 13.832(4), c = 18.194(2) A?, β= 100.00(10)°, Z = 4 for 1, and a = 10.819(5), b = 14.301(2), c = 14.224(1) A?, β = 97.04(2)°, Z = 4 for 2. The complexes expose a square planar geometry around the metal centers chelated with three different types of nitrogen donor centers of the ligand.

Full text of DOI:10.1515/znb-2006-1004

Two New Quadridentate Schiff Base Complexes of Nickel(II) and
Cobalt(III): Synthesis, Structure and Spectral Characterisation
Joy Chakrabortya, Raj K. Bhubon Singhb, Brajagopal Samantaa,
Chirantan Roy Choudhurya, Subrata K. Deya, Pritha Talukdera, Manob J. Borahb,
and Samiran Mitraa
a Department of Chemistry, Jadavpur University, Kolkata: 700 032, W.B., India
b Department of Chemistry, Nagaland University, Mokokchung 798601, Nagaland, India
Reprint requests to Prof. Samiran Mitra. Fax: 91-033-2414 6414. E-mail: smitra 2002@yahoo.com
Z. Naturforsch. 61b, 1209 – 1216 (2006); received April 10, 2006
Two novel quadridentate Schiff base complexes, [NiIILH](ClO4)2·H2O (1) and [CoIIIL]-
(ClO4)2·H2O (2) [LH, a Schiff base ligand: Ph(OH)C(Me)=NCH2CH2N(CH2CH2NH2)2] have been
synthesised and characterised by elemental analyses, spectroscopic and electrochemical studies. The
structures of both have been unequivocally established from single crystal X-ray diffraction stud-
ies. 1 and 2 crystallise in the monoclinic space g◦roup P21/n having cell parameters a = 8.536(1),
˚
b = 13.832(4), c = 18.194(2) A, β = 100.00(10) , Z = 4 for 1, and a = 10.819(5), b = 14.301(2),
◦
˚
c = 14.224(1) A, β = 97.04(2) , Z = 4 for 2. The complexes expose a square planar geometry around
the metal centers chelated with three different types of nitrogen donor centers of the ligand.
Key words: Nickel(II)/Cobalt(III), Schiff Base Chelator, X-Ray Structure, Spectral Characterisation
Introduction
bases have also drawn considerable attention in the
past due to their important biological applications.
Many model complexes of cobalt in both 2+ and
3+ oxidation states have been prepared and investi-
gated. Ni(II) complexes with tetradentate N2O2 Schiff
base ligands derived from salicylaldehyde have been
studied, but complexes with tetradentate Schiff base
ligands having an N3O donor set are not that much
frequent. Also, Co(III) complexes with uni-negative
tetradentate Schiff base ligands have received less at-
tention [27, 28]. It was shown that N2O2 ligand sys-
tems may act as tridentate as well as bidentate ligands
in Cu(II) and Co(III) complexes [24, 29].
In continuation of these studies, we report herein
the synthesis, characterisation, spectral studies and
structural aspects of two metal complexes of Ni(II)
and Co(III) with a quadridentate Schiff base lig-
and Ph(OH)C(Me)=NCH2CH2N(CH2CH2NH2)2. The
structures have been confirmed by X-ray crystallog-
raphy, which shows two square planar complexes
of Ni(II) and Co(III) incorporating N3O donor sets
with an interesting feature of three different types of
nitrogen donor centers in the same ligand.
In recent years, an increasing effort has been ded-
icated to the preparation of mono- or dinuclear tran-
sition metal complexes containing chelating nitrogen
ligands. Early and late transition metal complexes of
this type have extensively been used as catalysts for a
wide variety of reactions, including olefin polymeri-
sation [1 – 3] and oxygen activation [4 – 7]. In this
context, Schiff base complexes have a diverse range
of applications in inorganic synthesis [8 – 11], as li-
quid crystals [12] and heterogeneous catalysts [13].
Nickel(II) and cobalt(III) complexes of multidentate
Schiff base ligands have been extensively used [14–
17] because such ligands can bind with one, two or
more metals involving various coordination modes
and allow the synthesis of homo- and/or heteronu-
clear metal complexes with interesting stereochem-
istry [18, 19]. The chemistry of nickel complexes with
multidentate Schiff base ligands has attracted par-
ticular attention because this metal can exhibit sev-
eral oxidation states [20] and such complexes have a
strong role in bioinorganic chemistry and redox en-
zyme systems [21, 22] and may provide the basis of
models for active sites of biological systems [23, 24]
or act also as catalysts [25, 26]. Co(III) complexes
derived from symmetrical and unsymmetrical Schiff
Results and Discussion
The complexes were synthesised following the con-
ventional literature method, viz. the reaction of ethano-
0932–0776 / 06 / 1000–1209 $ 06.00 © 2006 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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J. Chakraborty et al. · Two New Quadridentate Schiff Base Complexes of Nickel(II) and Cobalt(III)
1.2
1.8
1.6
1.4
1.2
1.0
1.0
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
200
300
400
500
600
700
800
-0.2
200
300
400
500
600
700
800
Wavelength ( nm )
Wavelength ( nm )
Fig. 1. Room temperature UV/vis spectrum for 1.
Fig. 2. Room temperature UV/vis spectrum for 2.
lic solutions of nickel or cobalt salts with the Schiff
base ligand under reflux condition.
the lowest energy state of Ni(II) becomes a singlet,
resulting in a diamagnetic complex. Diamagnetism is
a consequence of eight electrons being paired in the
four low-lying d-orbitals (dxz, dyz, dz2 and dxy). The
lower four orbitals are often so close together in en-
ergy that individual transitions from there to the up-
per dx −y orbital can not be clearly distinguished, re-
Infrared spectra
The FT-IR spectra of 1 and 2 are fully consistent
with the structural data obtained from X-ray diffrac-
tion studies. The broad absorption peaks for ν(O-H)
appear at 3504 and 3448 cm−1 for 1 and 2 respectively,
indicating the presence of lattice water molecules and
phenolic O-H groups (for 1), suggesting the coordina-
tion of the metal atom through the phenolic oxygen
atom (without deprotonation). The strong absorption
bands at 1586 and 1617 cm−1 for complexes 1 and 2,
respectively, may be assigned to the coordination of
the nickel(II) and cobalt(III) ion by the azomethine
(C=N) nitrogen atom [27, 30]. Strong absorption bands
found at 626 and 680 cm−1 for 1 and 2, respectively,
may be due to ν[Ni-N(imino)] / ν[Co-N(imino)], and
peaks at 374 and 364 cm−1 to ν(Ni-NH2), at 362
and 355 cm−1 to ν(Co-NH2) [31]. The bands in the re-
gion 1086 cm−1 for both complexes may be assigned
to ν(C-O) stretching [30].
2
2
sulting in a single absorption [32]. Two main bands,
1
1
1
1A1g → T1g and A1g → T2g, are normally observed
in the d-d spectrum of Co(III) complexes. In the
present case, we observed only the lower energy band
at 554 nm (Fig. 2). The higher energy band was prob-
ably obscured by the ligand to metal charge transfer
band [32].
Cyclic voltammetry
The electrochemical behavior of 1 has been inves-
tigated by cyclic voltammetry (Fig. 3) in acetonitrile
solution (HPLC grade) under N2 atmosphere to ex-
plore the extent of redox stabilisation of the Ni(II)
state towards electrochemical oxidation. The CV scan
of 1 in acetonitrile shows one irreversible Ni(III/II)
couple at E1/2 = 0.72 V vs. SCE with a ∆Ep value
of 200 mV, which suggests that the Ni(III) species is
unstable and undergoes rapid decomposition. The data
obtained agrees well with those for a Ni(II) species.
In the cyclic voltammogram for the complex 2
UV/vis spectra
Among the two complexes, 1 possesses a square
planar geometry with diamagnetic nature that is re-
flected by the electronic spectrum (Fig. 1). It shows
two absorption bands at 307 and 374 nm. The first one (Fig. 4), one reductive response appears on the nega-
may be assigned to an LMCT transition, usually ob- tive side of SCE at −0.71 V and is tentatively assigned
served in metal Schiff base complexes containing phe- to the reduction of the coordinated Schiff base ligand.
nolato ligands due to “phenolato-to-M” charge trans- Another irreversible reductive response found on the
1
fer, and the second one may be due to a 1Ag → Eg negative side of SCE (at −0.55 V) may be due to the
transition. Due to the strong metal ligand interaction, reduction of the Co(III) centre.
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J. Chakraborty et al. · Two New Quadridentate Schiff Base Complexes of Nickel(II) and Cobalt(III)
1211
Fig. 5. ORTEP view of 1 showing intramolecular H-bondings
(with 40% ellipsoid probability level for non-hydrogen
atoms).
1.2
0.8
0.4
0.0
-0.4
-0.8
Potential / V
Fig. 3. Cyclic voltammogram for 1.
1.2
0.8
0.4
0.0
-0.4
-0.8
Potential / V
Fig. 4. Cyclic voltammogram for 2.
Room temperature magnetic susceptibility studies
The effective magnetic moments at r. t. (300 K)
for 1 and 2 are 0.001 and 0.013 B.M., respectively,
which match well the spin-only values of nickel(II) and
cobalt(III) ions in a square-planar environment.
Fig. 6. Packing view of 1 in a direction normal to the (001)
plane.
X-ray crystal structures
The crystal structures of the complexes consist of
discrete molecules held together by hydrogen bonds views and atom numbering schemes are shown in
and van der Waal’s interactions only. The ORTEP Figs. 5 and 7, respectively. The most important and
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J. Chakraborty et al. · Two New Quadridentate Schiff Base Complexes of Nickel(II) and Cobalt(III)
Fig. 7. ORTEP view of 2 showing intramolecular H-bondings
(with 40% ellipsoid probability level for non-hydrogen
atoms).
interesting feature of the ligand is that it has an
N3O donor set with three different types of nitrogen
donor centers in a square planar geometry for both
complexes around the metal centers. The nature of the
ligand is strikingly different in the two complexes.
In the case of complex 1, the Schiff base is behaving
as a neutral chelating ligand while in complex 2 it is
an anionic chelating ligand due to the deprotonation
of the phenolic OH group. So, in both cases two
perchlorate anions are present in the lattice to give a
charge balance to their dicationic complex counter-
Fig. 8. Packing view of 2 in a direction normal to the (001)
plane.
parts. The square planes in the complexes suffer from For tertiary amine nitrogen atoms N(1) the bond
a tetrahedral distortion as indicated by the deviations lengths are Ni(1)-N(1), 1.919(3) and Co(1)–N(1)
˚
of the relevant atoms from the mean planes of the 2.049(17) A. Here, it may be noted that Ni-N and
N3O atoms. The distortions are quite large and sig- Co–N (amine) distances in the present square pla-
˚
nificant, thereby reflecting the greater steric demand nar complexes are ca. 0.25 and ca. 0.37 A shorter
of the -CH2CH2NH2 substituents on N(1) in both than Ni-N and Co–N distances found in a number
complexes. Angular distortion in the square plane is of square planar Ni(II) and Co(III) complexes in
caused by different bite angles in the five and six mem- the literature [22, 23], whereas the imino-N-metal
˚
bered chelate rings with the values O(1)-Ni(1)-N(2), distances Ni(1)-N(2) (1.854(3) A) and Co–N(2)
95.51(13)◦; O(1)-Ni(1)-N(1), 176.12(13)◦; N(2)- (1.944(18) A) are nearly the same as reported ear-
˚
Ni(1)-N(1), 88.17(14)◦; O(1)-Ni(1)-N(3), 90.03(15)◦; lier [16]. The unit N(1)-C(3)-C(4)-N(3) for 1 is
N(2)-Ni(1)-N(3), 173.23(16)◦; N(1)-Ni(1)-N(3), puckered with a dihedral angle of ca. 24.3(4) ◦ and
86.39(16)◦ and O(1)–Co(1)–N(2), 95.5(7)◦; O(1)– the unit N(1)-C(1)-C(2)-N(2) has a dihedral angle
Co(1)–N(1), 172.4(7)◦; N(1)–Co(1)–N(2), 86.6(7)◦; of ca. 39.7(4) ◦, whereas N(1)–C(1)–C(2)–N(2) and
N(1)–Co(1)–N(3),
85.2(8)◦;
N(2)–Co(1)–N(3), N(1)–C(3)–C(4)–N(3) for 2 have dihedral angles of
166.8(8)◦; O(1)–Co(1)–N(3), 94.0(7)◦ for 1 and 2, ca. 52(3) and ca. 49(3) ◦, respectively. The Ni-O and
respectively. The bond lengths Ni-N and Co-N are Co-O bond lengths are slightly smaller than for similar
significantly different. For amino nitrogen atoms, e. g. square planar complexes reported earlier [22, 23] and
˚
N(3), they are longer [Ni(1)-N(3) 1.931(4) A] than for seem to be correlated with the slightly longer C-O
imino nitrogen atoms N(2) [Ni(1)-N(2) 1.854(3) A]. bonds C(14)-O(1) (1.320(5) A).
˚
˚
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J. Chakraborty et al. · Two New Quadridentate Schiff Base Complexes of Nickel(II) and Cobalt(III)
1213
◦
Table 2. Selected hydrogen bonding parameters.
˚
Table 1. Selected bond lengths (A) and bond angles ( ) for 1
and 2.
◦
˚
˚
˚
D-H···A
d(D-H) A d(H···A) A d(D···A) A ∠(DHA)
(◦)
1: N(3)-H(3A)···O(2) 0.82(5) 2.25(5)
O(10)-H(10A)···O(3) 0.82(5) 2.16(5)
2.843(7) 130(5)
2.963(6) 165(7)
3.061(6) 115
3.431(7) 151
˚
Bond lengths (A)
Bond angles
1: Ni(1)-O(1)
1.814(3)
O(1)-Ni(1)-N(1) 176.12(13)
O(1)-Ni(1)-N(3) 90.03(15)
N(2)-Ni(1)-N(3) 173.23(16)
C(5)-N(1)-Ni(1) 108.8(2)
C(3)-N(1)-Ni(1) 105.6(3)
C(7)-N(2)-Ni(1) 128.3(3)
C(4)-N(3)-Ni(1) 111.6(3)
O(1)-Ni(1)-N(2) 95.51(13)
N(2)-Ni(1)-N(1) 88.17(14)
N(1)-Ni(1)-N(3) 86.39(16)
C(1)-N(1)-Ni(1) 104.6(2)
C(2)-H(2B)···O(4) 0.91
C(10)-H(10)···O(5) 0.97
2.56
2.55
Ni(1)-N(1)
Ni(1)-N(3)
N(1)-C(1)
N(3)-C(4)
N(4)-C(6)
O(1)-C(14)
N(1)-C(5)
N(2)-C(2)
N(2)-C(7)
N(1)-C(3)
–
1.919(3)
1.931(4)
1.494(5)
1.484(6)
1.490(6)
1.320(5)
1.490(5)
1.483(5)
1.303(5)
1.497(5)
–
2: N(3)-H(3A)···O82) 0.90(11) 1.28(15) 2.07(7)
143
163
153
O(10)-H(10B)···O(1) 0.8(3)
N(3)-H(3B)···O(9A) 0.9(3)
1.8(3)
2.5(3)
2.63(3)
3.36(8)
erature, especially for Co(III). Both complexes have
been characterised by elemental analyses, spectro-
scopic and electrochemical investigations. Structures
have been confirmed by single crystal X-ray diffraction
studies.
C(7)-N(2)-C(2)
118.9(3)
C(2)-N(2)-Ni(1) 112.8(3)
–
–
2: Co(1)-O(1)
1.858(14)
O(1)-Co(1)-N(1) 172.4(7)
O(1)-Co(1)-N(2) 95.5(7)
O(1)-Co(1)-N(3) 94.0(7)
N(2)-Co(1)-N(1) 86.6(7)
N(2)-Co(1)-N(3) 166.8(8)
N(1)-Co(1)-N(3) 85.2(8)
C(5)-N(1)-Co(1) 110.6(12)
C(1)-N(1)-Co(1) 100.0(13)
C(3)-N(1)-Co(1) 103.9(13)
C(2)-N(2)-Co(1) 112.0(14)
C(7)-N(2)-Co(1) 126.8(15)
C(4)-N(3)-Co(1) 110.7(15)
Co(1)-N(1)
2.049(17)
Co(1)-N(3)
2.01(2)
Experimental Section
Co(1)-N(2)
1.944(18)
Materials
N(1)-C(1)
1.46(3)
N(3)-C(4)
1.47(3)
All the chemicals used for the synthesis were of
analytical grade and purchased from Lancaster, UK.
2-Hydroxyacetophenone and tris(2-aminoethyl)amine were
used as received without further purification. Nickel(II) per-
chlorate and cobalt(II) perchlorate were synthesised as de-
scribed in the literature [33]. All solvents were freshly dried
using standard methods.
N(1)-C(3)
1.49(3)
–
–
–
–
–
–
–
–
–
–
The six membered rings are almost planar. Close
scrutiny of the bond lengths in the ligand reveals a
clear trend and this suggests that the N(2)-C(7) bonds
Caution: Although no problems were encountered in
this work, perchlorate salts in presence of organic materials
are potentially explosive. Compounds should be prepared in
small amounts and handled with care.
˚
(1.303(5) A in 1) retain their double bond character.
The mode of H-bondings is more or less similar in
both complexes (Table 2). The type is completely of
intramolecular nature. These H-bondings are mainly
distributed in between hydrogen atoms from the lattice
water molecules or the ligand and the oxygen atoms
Physical techniques
The Fourier Transform Infrared Spectra (400 –
4000 cm−1
) of the complexes were recorded on a
−
Perkin-Elmer Spectrum RX I FT-IR system with KBr
discs. The UV/vis spectra were recorded at 20 ◦C on a
Perkin-Elmer Lambda 40 UV/vis spectrometer using HPLC
grade methanol as solvent with 1 cm quartz cuvettes. C, H,
N analyses were carried out using a Perkin-Elmer 2400 II
elemental analyser. Cyclic voltammetric measurements were
performed using an EG&G PARC electrochemical analysis
system (model 250-5-0) under a dry N2 environment using
conventional, three electrode configurations in purified
acetonitrile (HPLC grade) with tetraethylammonium per-
chlorate as the supporting electrolyte. A planar EG&G
PARC G0229 glassy carbon milli electrode was used as
of the ClO4 anions. Presence of hydrogen bondings
furnished by H-atoms at N or C atoms with perchlo-
rate anions is clear from Fig. 5 and Fig. 7 correspond-
ing to 1 and 2. Packing views of the complexes 1
and 2 have been provided in Figs. 6 and 8, respec-
tively. Relevant bond lengths and bond angles for 1
and 2 have been incorporated in Table 1. A few se-
lected H-bonding parameters are given in the Table 2.
Conclusion
We have reported herein two novel transition metal
complexes of NiII and CoIII prepared from a new Schiff
base ligand incorporating a N3O donor set. The most
striking result is that the complexes are square planar
with three different types of nitrogen donor centers in
the working electrode at a scan rate of ν = 50 mVs−1
.
The Ni content was determined by the standard gravimetric
estimation method using dimethylglyoxime. Magnetic
susceptibilities were measured with a model 155 PAR vi-
brating sample magnetometer fitted with a Waker Scientific
the same ligand which is not very common in the lit- 175 FBAL magnet using Hg[Co(SCN)4] as the standard.
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J. Chakraborty et al. · Two New Quadridentate Schiff Base Complexes of Nickel(II) and Cobalt(III)
Table 3. Crystallographic data and structure refinements.
Parameters
Empirical Formula
M
1
2
C14H26Cl2N4NiO10
540.00
C14H25Cl2CoN4O10
539.21
Crystal system
Space group
monoclinic
P21/n
monoclinic
P21/n
˚
a [A]
8.536(10)
10.819(5)
˚
b [A]
13.832(4)
14.301(2)
˚
c [A]
18.194(2)
100.00(10)
2115.5(7)
14.224(1)
97.04(2)
2184(11)
β [◦]
3
˚
V [A ]
Z
4
4
Temperature [K]
293(2)
293(2)
˚
λMoK [A]
α
0.71073
1.695
1.230
1120
0.71073
1.640
1.089
1112
Calculated density [g cm−3
]
µ [mm−1
F(000)
θ [◦]
]
2.27 to 30.27
2.24 to 30.26
Index ranges
Total data
Unique data
R(int)
0 ≤ h ≤ 12, 0 ≤ k ≤ 19, −25 ≤ l ≤ 25
0 ≤ h ≤ 15, 0 ≤ k ≤ 20, −20 ≤ l ≤ 20
6697
6315
6831
6523
0.0235
0.0291
I ≥ 2σ(I)
3708
6315 / 7 / 302
[σ2(Fo2)+(0.0663P)2 +1.9888P]−1
0.0600 / 0.1333
1.03
0.1286 / 0.1645
0.693 and −0.483
3451
Data / restraints / parameters
Weighting scheme, w
6523 / 584 / 384
[σ2(Fo2)+(0.0798P)2 +1.9099P]−1
0.0673 / 0.1522
1.02
0.1526 / 0.1897
0.654 and −0.626
Final R1/wR2 indices
Goodness-of-fit on F2
R1/wR2 indices (all data)
−3
˚
Max. diff. peak and hole [e.A
]
Syntheses
– C14H26Cl2N4NiO10 (540.0): calcd. C 57.74, H 10.37,
N 4.85, Ni 10.86; found C 57.77, H 10.38, N 4.89, Ni 10.82.
[C6H4(OH)C(CH3)=NCH2CH2N (CH2CH2NH2)2]:
Chelating Schiff base ligand (LH)
[(C6H4O)C(CH3)=N(CH2)2N(CH2CH2NH2)2Co(III)]-
Tris(2-aminoethyl)amine (1.46 ml, 10 mmol) in 10 ml of
ethanol was added to a solution of 2-hydroxyacetophenone
(1.20 ml, 10 mmol) in 15 ml of ethanol. The solution was
refluxed for 1.5 h and cooled to r. t. This solution was used
without further purification.
(ClO4)2·H2O (2)
The complex was synthesised following the same pro-
cedure as in the case of 1 except using Co(ClO4)2·6H2O
(365 mg, 1 mmol). The final brown solution was filtered
twice and the filtrate was kept for slow evaporation at r. t.
Suitable brown rod-shaped single crystals were collected by
mechanical is◦olation after 3 d.
[C6H4(OH)C(CH3)=N(CH2)2N(CH2CH2NH2)2Ni(II)]-
(ClO4)2·H2O (1)
M. p. 135 C. – UV/vis (CH3OH): λmax(lgε) = 235 nm
(3.65). – IR (KBr disc): ν = 3448 (O-H), 1617 (C=N),
1086 (C-O), 680 (Co-Nimino), 362, and 355 (Co-NH2). –
C14H25Cl2N4CoO10 (539.21): calcd. C 57.93, H 10.41,
N 4.67; found C 57.91, H 10.39, N 4.69.
A solution of Ni(ClO4)2 · 6H2O (330 mg, 1 mmol)
in 15 ml absolute EtOH was added dropwise to a gently
warmed 15 ml ethanolic solution of 1 mmol Schiff base lig-
and [1 : 1 molar ratio, M : L]. The solution was stirred for 3 h
at 65 ◦C. The precipitated complex was then filtered and dis-
solved in a CH2Cl2 : CH3CN = 2 : 1 v/v mixture. The result-
ing orange-red solution was filtered twice and the clear fil-
trate was kept for slow evaporation at r. t. Suitable orange
platelet single crystals were collected by mechanical isola-
X-ray crystallography
Cell dimension and intensity data were measured at 293 K
from a good quality air stable orange platelet crystal of 1
(size 0.48 × 0.31 × 0.06 mm) and a brown rod shaped sin-
tion after 15 d.
◦
M. p. 125 C. – UV/vis (CH3OH): λmax(lgε) = 230 nm gle crystal of 2 (size 0.44 × 0.08 × 0.06 mm), mounted on
(2.85). – IR (KBr disc): ν = 3504 (O-H), 1586 (C=N), a fine-focus sealed tube of a FR590 Enraf Nonius Turbo
1086 (C-O), 626 (Ni-Nimino), 374 and 364 (Ni-NH2). CAD4 diffractometer equipped with a LiI scintillation detec-
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J. Chakraborty et al. · Two New Quadridentate Schiff Base Complexes of Nickel(II) and Cobalt(III)
1215
tor and fitted with graphite-monochromated MoKα radiation program and refined by full-matrix least-squares on F2 us-
˚
(λ = 0.71073 A) using non-profiled ω scans. Accurate cell ing all unique data for SHELXL-97 [36]. Partially occupied
parameters were obtained by least squares refinement with hydrogen atoms in the structure were obtained from the dif-
diffractometer angles for the entire data set for 25 reflec- ference map, which were further included in the model. De-
tions in the range of 9.2 < θ < 14.4◦ and 8.9 < θ < 13.7◦ tails of crystal data, collection and refinement are listed in
for 1 and 2, respectively. Measuring standard reflections at Table 3.
fixed intervals during the data collection checked the stabil-
ity of the crystals. However, no significant loss of intensity
was noted. Absorption corrections were carried out by us-
ing multiple and symmetry related measurements with the
REFDELF program [34]. This absorption correction pro-
gram consists of methods which have fallen out of favour
in the recent past. It requires a refined model to provide a
“correction” for the data based on the assumption that any
consistent differences between the calculated and observed
structure factors are due to absorption. When numerical cor-
rections cannot be carried out, and if no extra intensities
were measured, then these methods remain the only capa-
ble ones of providing some sort of correction for absorption.
For most crystals containing elements heavier than the first
row transition metals, it is likely that absorption is the most
important contributor to the systematic errors. Both struc-
tures were solved by direct methods using the SIR-97 [35]
Supplementary material
X-ray crystallographic data in the CIF format correspond-
ing to the complexes 1 and 2 have been deposited with the
Cambridge Crystallographic Data Center (CCDC 296450,
296451). Supplementary crystallographic data can be ob-
tained free of charge from The Cambridge Crystallographic
Data Center via www.ccdc.cam.ac.uk/data request/cif.
Acknowledgements
We gratefully acknowledge University Grants Commis-
sion, New Delhi, Government of India for the fellowship
awarded to Mr. Joy Chakraborty. Financial support from De-
fence Research and Development Organisation, Ministry of
Defence, Government of India, New Delhi is also gratefully
acknowledged.
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