Syntheses, characterization, and crystal structures of nickel complexes derived from tridentate schiff bases and thiocyanate mixed ligands

Article abstract of DOI:10.1080/15533174.2013.776610

The self-assembly and construction of specific Schiff base nickel complexes are important in the exploration of new functional materials. In the present work, in the presence of thiocyanate ligands, two mononuclear Schiff base nickel(II) complexes, [NiL1(NCS)] (1) and [Ni(L2)2] (2) (L1 = 2-bromo-6-[ (2-dimethylaminoethylimino)methyl]phenolate, L2 = 2-bromo-6-[(3- dimethylaminopropylimino)methyl]phenolate), with different coordination modes, have been synthesized and characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction. The Ni atom in (1) is four-coordinated in a square planar configuration, with three donor atoms of L1 and one nitrogen atom of thiocyanate ligand. The Ni atom in (2) is six-coordinated in an octahedral configuration, with six donor atoms from two L2 ligands. The relationship between the ligands and the final structures of the complexes is discussed.

Full text of DOI:10.1080/15533174.2013.776610

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Syntheses, Characterization, and Crystal Structures of
Nickel Complexes Derived From Tridentate Schiff Bases
and Thiocyanate Mixed Ligands
Chun-Lan Yuan a
a Department of Chemistry and Chemical Engineering , Baoji University of Arts and
Sciences , Baoji , P. R. China
Accepted author version posted online: 23 Sep 2013.Published online: 21 Nov 2013.
To cite this article: Chun-Lan Yuan (2014) Syntheses, Characterization, and Crystal Structures of Nickel Complexes Derived
From Tridentate Schiff Bases and Thiocyanate Mixed Ligands, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-
Metal Chemistry, 44:4, 482-485, DOI: 10.1080/15533174.2013.776610
To link to this article: http://dx.doi.org/10.1080/15533174.2013.776610
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 44:482–485, 2014
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2013.776610
Syntheses, Characterization, and Crystal Structures
of Nickel Complexes Derived From Tridentate Schiff Bases
and Thiocyanate Mixed Ligands
Chun-Lan Yuan
Department of Chemistry and Chemical Engineering, Baoji University of Arts and Sciences, Baoji,
P. R. China
nation modes of the thiocyanate ligand, this pseudohalide ligand
was usually used in the preparation of metal complexes.[11–13]
Previously, I have reported a few thiocyanate coordinated Schiff
base complexes.[14] In order to explore the relationship between
the ligands and the final structures of nickel complexes, espe-
cially in the presence of thiocyanate ligands, in the present
work, two mononuclear Schiff base nickel(II) complexes,
[NiL1(NCS)] (1) and [Ni(L2)2] (2) (L1 = 2-bromo-6-[(2-
dimethylaminoethylimino)methyl]phenolate, L2 = 2-bromo-6-
[(3-dimethylaminopropylimino)methyl]phenolate), have been
successfully synthesized and characterized.
The self-assembly and construction of specific Schiff base
nickel complexes are important in the exploration of new func-
tional materials. In the present work, in the presence of thio-
cyanate ligands, two mononuclear Schiff base nickel(II) com-
plexes, [NiL1(NCS)] (1) and [Ni(L2)2] (2) (L1 = 2-bromo-6-[
(2-dimethylaminoethylimino)methyl]phenolate, L2 = 2-bromo-6-
[(3-dimethylaminopropylimino)methyl]phenolate), with different
coordination modes, have been synthesized and characterized by
elemental analysis, IR spectra, and single-crystal X-ray diffraction.
The Ni atom in (1) is four-coordinated in a square planar config-
uration, with three donor atoms of L1 and one nitrogen atom of
thiocyanate ligand. The Ni atom in (2) is six-coordinated in an oc-
tahedral configuration, with six donor atoms from two L2 ligands.
The relationship between the ligands and the final structures of the
complexes is discussed.
EXPERIMENTAL
Materials and Measurements
Keywords crystal structure, mononuclear complex, nickel complex,
Commercially available 3-bromosalicylaldehyde, N,N-
dimethylethane-1,2-diamine, and N,N-dimethylpropane-1,3-
diamine were purchased from Lancaster and used without fur-
ther purification. Other solvents and reagents were made in
China and used as obtained. C, H, and N elemental analyses
were performed with a Perkin-Elmer 240 C elemental analyzer.
IR spectra were measured with a FT-IR 170-SX (Nicolet) spec-
trophotometer.
Schiff base, self-assembly
INTRODUCTION
Schiff base ligands and their metal complexes are easily syn-
thesized, and such complexes have been extensively used as
catalyst in various organic reactions.[1–3] The study of nickel
compounds attracts considerable attention in various aspects of
chemistry, because these compounds are present in active sites
of urease and widely used in the design and construction of
novel biological, catalytic, and magnetic materials.[4–7] Nickel
complexes derived from the tridentate Schiff base ligands bear-
ing 2-[(2-dimethylaminoethylimino)methyl]phenolate and 2-
[(3-dimethylaminopropylimino)methyl]phenolate moieties are
not uncommon in the reported literature.[8–10] However, even
though the above ligands are similar to each other, the final
nickel complexes are much more different with respect to the
coordination modes. In addition, owing to the versatile coordi-
Synthesis of L1 and L2
The ligands L1 and L2 were prepared by the conden-
sation of 3-bromosalicylaldehyde (1.0 mmol, 201 mg) with
N,N-dimethylethane-1,2-diamine (1.0 mmol, 88 mg) and N,N-
dimethylpropane-1,3-diamine (1.0 mmol, 102 mg), respectively,
in methanol (20 mL) at room temperature. Anal. Calcd. for
C11H15BrN2O (L1, FW 271.2): C, 48.7; H, 5.6; N, 10.3. Found:
C, 48.6; H, 5.7; N, 10.4%. Yield, 203 mg (75%). Anal. Calcd. for
C12H17BrN2O (L2, FW 285.2): C, 50.5; H, 6.0; N, 9.8. Found:
C, 50.3; H, 6.1; N, 9.8%. Yield: 226 mg (79%).
Synthesis of [NiL1(NCS)] (1) and [Ni(L2)2] (2)
The complexes are synthesized by the similar method as de-
scribed subsequently. To a stirred methanol solution (10 mL) of
the Schiff base ligand (0.1 mmol) was added a methanol solu-
tion (5 mL) of NH4NCS (0.1 mmol), and a methanol solution
Received 28 January 2013; accepted 10 February 2013.
Address correspondence to Chun-Lan Yuan, Department of Chem-
istry and Chemical Engineering, Baoji University of Arts and Sciences,
Baoji 721007, P. R. China. E-mail: chunlanyuan@163.com
482

NICKEL COMPLEXES WITH TRIDENTATE SCHIFF BASES
483
TABLE 2
(5 mL) of NiCl2.6H2O (0.1 mmol). The mixtures were stirred
for 30 min at room temperature to give a clear red solution for
(1) and green solution for (2). Single crystals of the complexes,
suitable for X-ray single-crystal analysis, were formed at the
bottom of the vessel on slow evaporation of the solvents for sev-
eral days. The isolated crystals were washed three times with
cold methanol, and dried in a vacuum over anhydrous CaCl2.
Anal. Calcd. for C12H14BrN3NiOS (1, FW 386.9): C, 37.2; H,
3.6; N, 10.9. Found: C, 37.4; H, 3.6; N, 10.7%. Yield, 15.0 mg
(39% on the basis of L1). Anal. Calcd. for C24H32Br2N4NiO2
(2, FW 627.1): C, 46.0; H, 5.1; N, 8.9. Found: C, 46.2; H, 5.2;
N, 8.8%. Yield: 14.5 mg (46% on the basis of L2).
Selected bond lengths (Å) and bond angles (◦) for complexes
(1) and (2)
(1)
Ni1-N1
Ni1-N3
N1-Ni1-O1
O1-Ni1-N3
O1-Ni1-N2
1.842(4)
1.874(4)
94.0(1)
88.5(1)
179.0(1)
Ni1-N2
Ni1-O1
1.958(3)
1.848(3)
172.3(2)
87.0(2)
N1-Ni1-N3
N1-Ni1-N2
N3-Ni1-N2
90.5(2)
(2)
Ni1-O1
2.028(7)
2.266(7)
180
86.7(3)
91.2(3)
98.3(3)
180
Ni1-N1
2.056(7)
Ni1-N2
Crystal Structure Determination
O1-Ni1-O1A
O1-Ni1-N1
O1-Ni1-N2
N1-Ni1-N2A
N2-Ni1-N2A
O1-Ni1-N1A
N1-Ni1-N1A
O1-Ni1-N2A
N1-Ni1-N2
93.3(3)
180
88.8(3)
81.7(3)
Diffraction intensities for the complexes were collected at
298(2) K using a Bruker SMART APEX 1000 CCD area-
detector with MoKα radiation (λ = 0.71073 Å). The collected
data were reduced using the SAINT program,[15] and multiscan
absorption corrections were performed using the SADABS pro-
TABLE 1
Crystallographic and experimental data for complexes (1)
and (2)
gram.[16] The structures were solved by direct methods and re-
fined against F2 by full-matrix least-squares methods using the
SHELXTL version 5.1.[17] All of the non-hydrogen atoms were
refined anisotropically. Hydrogen atoms in the two complexes
were placed in calculated positions and constrained to ride on
their parent atoms. Crystallographic data for the complexes are
summarized in Table 1. Selected bond lengths and angles are
given in Table 2. Crystallographic data for the two complexes
have been deposited with the Cambridge Crystallographic Data
Centre (CCDC 921134 and 921135).
(1)
(2)
Formula
C12H14BrN3NiOS C24H32Br2N4NiO2
FW
386.94
627.07
Crystal
Block/red
Block/green
shape/color
Crystal size/mm
Crystal system
Space group
0.37 × 0.32 × 0.30 0.13 × 0.10 × 0.10
Monoclinic
C2/c
Monoclinic
P21/n
RESULTS AND DISCUSSION
a/Å
b/Å
33.082(2)
6.212(1)
14.323(1)
97.569(2)
2918.0(3)
8
8.814(2)
7.677(1)
19.281(2)
103.21(2)
1270.1(3)
2
Preparation of the Ligands and the Complexes
c/Å
The tridentate Schiff base ligands were synthesized by
1:1 condensation reaction of 3-bromosalicylaldehyde with
N,N-dimethylethane-1,2-diamine and N,N-dimethylpropane-
1,3-diamine, respectively, in methanol according to Scheme 1.
The nickel(II) complexes were prepared by treatment of the lig-
ands H2L with nickel chloride and ammonium thiocyanate in
molar ratio 1:1:1 in methanol according to Scheme 2.
β/◦
V/Å3
Z
λ (MoKα)/Å
0.71073
298(2)
4.206
0.71073
298(2)
3.938
T/K
μ/mm−1 (Mo-Kα)
Tmin
Tmax
0.3052
0.3651
0.6285
0.6942
1644/153
994
CHO
N
MeOH
Reflections/parameters 3164/174
N
N
H2N
+
Independent
reflections
F(000)
2464
OH
OH
Br
Br
Br
(L1)
1552
636
Goodness of fit on
1.055
1.119
F2
CHO
OH
MeOH
N
N
H2N
N
+
R1, wR2 [I ≥
2σ(I)]a
0.0447, 0.1045
0.0557, 0.1437
OH
R1, wR2 (all data)a
ꢀ
0.0648, 0.1161
0.1227, 0.2087
Br
(L2)
ꢀ
ꢀ
ꢀ
aR1 = ||Fo|-|Fc||/ |Fo|, wR2 = [ w(Fo2-Fc2)2/ w(Fo2)2]1/2
.
SCH. 1.

484
C.-L. YUAN
SCH. 2.
From the results of X-ray determination and infrared spectra,
it can be observed that the thiocyanate anion coordinates to the
Ni atom in (1). However, as for complex (2), the thiocyanate an-
ion was not participating in coordinating. This phenomenon is in
agreement with the similar complexes reported previously.[9,10]
Detailed comparison on the relationship between the Schiff base
ligands and the final structures can observe that the flexibility
of the former might contribute to the difference. There form a
rigid five-membered chelate ring for (1) with the Schiff base
L1, while a flexible six-membered chelate ring for (2) with the
Schiff base L2. Thus, the slightly difference, for example, the
flexibility, of the Schiff base ligands used in the preparation of
the complexes with nickel chloride and ammonium thiocyanate
can result in different structures of the final complexes.
FIG. 1. The structure of (1), showing the atom-numbering scheme. Displace-
ment ellipsoids are drawn at the 30% probability level.
of L1, and the N atom of the thiocyanate ligand. The significant
distortion of the coordination is revealed by the bond lengths
and angles related to the nickel center. The bond lengths are
range from 1.842(4) to 1.958(3) Å. The perpendicular and trans
bond angles are range from 87.0(2) to 94.0(1)◦, and 172.3(2)
to 179.0(1)◦, respectively, as a result from the strain created by
the five-membered chelate ring Ni1/N1/C8/C9/N2. The Ni N
and Ni O bond lengths are in agreement with those found pre-
viously in similar nickel(II) complexes[9,18,19] and, as expected,
the bond involving amine N atom is longer than that involving
imine N atom. The thiocyanate ligand is nearly linear and show
bent coordination mode with the metal atom.
Stability in Air and Solubility in General Solvents
The yellow gummy products of the Schiff base ligands L1
and L2 are stable in air at room temperature and soluble in polar
organic solvents, such as MeOH, EtOH, MeCN, and Me2CO, but
insoluble in water and Et2O. The two complexes are also stable
in air at room temperature; soluble in DMF, DMSO, MeOH,
EtOH, and MeCN; and insoluble in water and Et2O.
Infrared Spectra
In the infrared spectra of the complexes, weak absorption
bands at about 2930 and 2860 cm−1 are due to the coordinated
NMe2 groups. The strong absorption appeared at 1623 cm−1 for
(1) and 1625 cm−1 for (2) are due to the azomethine groups.
The C–O stretching vibrations in free ligands are observed at
about 1220 cm−1. The frequencies shift in the complexes toward
higher values as a result of coordination of the oxygen to the
metal ion [1231 cm−1 for (1) and 1228 cm−1 for (2)]. Com-
plex (1) shows an intense peak due to the thiocyanate ligand at
2101 cm−1
.
Structure Description of (1)
The molecular structure of (1) is shown in Figure 1. The
complex is a Schiff base and thiocyanate mixed ligands coordi-
nated mononuclear nickel species. The Ni atom in the complex
is in a square planar coordination configuration and is four-
coordinated by the phenolate O, imine N, and amine N atoms
FIG. 2. The structure of (2), showing the atom-numbering scheme. Displace-
ment ellipsoids are drawn at the 30% probability level. H atoms have been
omitted for clarity. Atoms labeled with the suffix A are at the symmetry posi-
tions –x, 1 – y, –z.

NICKEL COMPLEXES WITH TRIDENTATE SCHIFF BASES
485
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The molecular structure of (2) is shown in Figure 2. The
complex is a centrosymmetric mononuclear nickel species, with
the inversion center located at the metal atom. The Ni atom
in the complex is in an octahedral coordination configuration
and is six-coordinated by two phenolate O and two imine N
atoms at the equatorial plane, and two amine N atoms at the ax-
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distortion of the coordination is revealed by the bond lengths
and angles related to the nickel center. The bond lengths are
range from 2.028(7) to 2.266(7) Å, which are much longer than
those in (1). The perpendicular bond angles are range from
81.7(3) to 98.3(3)◦. The Ni N and Ni O bond lengths are
in agreement with those found previously in similar nickel(II)
complexes[10,20] and, just as described for (1), the bonds in-
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