Syntheses, crystal structures, and characterizations of nickel(II) complexes with schiff bases and thiocyanate ligands

Article abstract of DOI:10.1080/15533174.2010.487056

Self-assembly of Schiff base ligands 2,4-dibromo-6-[(3-dimethy laminopropylimino)methyl]phenol (BMP) and 2-[(3-cyclohexyl aminopropylimino) methyl]-6-methoxyphenol (CMP) with nickel (II) acetate and ammonium thiocyanate forms two centrosymmetric mononuclear nickel(II) complexes, [Ni(BMP)2] (1) and [Ni(CMP)2(NCS)2] (2), respectively. Complex 1 crystallizes in a monoclinic space group C2/c, while complex 2 crystallizes in a hexagonal space group R-3. Both crystal structures were characterized by X-ray diffraction analyses and IR spectra. Each NiII center in the complexes has NiN4O2 coordination environment, with the two imine N and two phenolate O atoms located in the base plane. The difference between the two coordinations is the axial donors, viz. amino N atoms for 1, and thiocyanate N atoms for 2. Copyright Taylor & Francis Group, LLC.

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Syntheses, Crystal Structures, and Characterizations
of Nickel(II) Complexes with Schiff Bases and
Thiocyanate Ligands
Xiao-Hui Li a & Gui-Mei Xu b
a College of Chemistry and Chemical Engineering , Liaoning Normal University , Dalian,
P. R. China
b The Vocational School of Penglai , Penglai, P. R. China
Published online: 27 May 2010.
To cite this article: Xiao-Hui Li & Gui-Mei Xu (2010) Syntheses, Crystal Structures, and Characterizations of Nickel(II)
Complexes with Schiff Bases and Thiocyanate Ligands, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-
Metal Chemistry, 40:5, 355-358
To link to this article: http://dx.doi.org/10.1080/15533174.2010.487056
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:355–358, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2010.487056
Syntheses, Crystal Structures, and Characterizations of
Nickel(II) Complexes with Schiff Bases and Thiocyanate
Ligands
Xiao-Hui Li1 and Gui-Mei Xu2
1College of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian, P. R. China
2The Vocational School of Penglai, Penglai, P. R. China
investigate the influence on the coordination mode of the
thiocyanate groups.
Self-assembly of Schiff base ligands 2,4-dibromo-6-[(3-dimethy
laminopropylimino)methyl]phenol (BMP) and 2-[(3-cyclohexyl
aminopropylimino)methyl]-6-methoxyphenol (CMP) with nickel
(II) acetate and ammonium thiocyanate forms two centrosym-
metric mononuclear nickel(II) complexes, [Ni(BMP)2] (1) and
[Ni(CMP)2(NCS)2] (2), respectively. Complex 1 crystallizes in a
monoclinic space group C2/c, while complex 2 crystallizes in a
hexagonal space group R–3. Both crystal structures were charac-
terized by X-ray diffraction analyses and IR spectra. Each NiII
center in the complexes has NiN4O2 coordination environment,
with the two imine N and two phenolate O atoms located in the
base plane. The difference between the two coordinations is the
axial donors, viz. amino N atoms for 1, and thiocyanate N atoms
for 2.
EXPERIMENTAL
Materials and Methods
3,5-Dibromosalicylaldehyde, 3-methoxysalicylaldehyde, N,
N-dimethylpropane-1,3-diamine and N-cyclohexylpropane-
1,3-diamine were analytical pure grade from Aldrich Chemical
Co., Milwaukee, Wisconsin, and used without further purifica-
tion. Other reagents were also analytical pure grade and obtained
from Beijing Reagent Factory, used without further purification.
IR spectra were recorded on a Nicolet IR-470 spectrometer with
KBr pellets in the range 4000–400 cm–1. C, H, N analyses were
carried out using a Perkin-Elmer model 240 analyzer. Crystal-
lographic data were measured on a Bruker APEX-II CCD area-
detector diffractometer with Mo-Kα radiation (λ = 0.71073
Keywords crystal structure, nickel complex, synthesis, thiocyanate
˚
A).
INTRODUCTION
Synthesis of BMP
Schiff base complexes of transition metals have been widely
investigated for many years. Their ready syntheses and versatile
properties have received much attention.[1] Schiff base nickel(II)
complexes have been regarded as models for enzymes such
as urease.[2] Thiocyanate anions can coordinate to the metal
atoms either through the bridging mode or through the terminal
mode.[3] However, one can hardly possibly predict which coor-
dination mode will be adopted by the thiocyanate groups. In
this paper, two mononuclear nickel(II) complexes, [Ni(BMP)2]
(1) and [Ni(CMP)2(NCS)2] (2) (BMP = 2,4-dibromo-6-
[(3-dimethylaminopropylimino)methyl]phenol, CMP = 2-
[(3-cyclohexylaminopropylimino)methyl]-6-methoxyphenol),
have been synthesized and structurally characterized to
A mixture of 3,5-dibromosalicylaldehyde (0.28 g, 10 mmol)
and N,N-dimethylpropane-1,3-diamine (0.10 g, 10 mmol) in
anhydrous methanol (50 mL) was stirred for 3 h under reflux.
After the reaction mixture was cooled, the solvent was removed
by vacuum distillation, and ice-water was added to the residue.
The product was isolated by filtrating to obtain the straw yellow
solid. Yield: 0.32 g, 89%. Anal. calcd. for C12H16Br2N2O: C,
39.6; H, 4.4; N, 7.7. Found: C, 39.3; H, 4.5; N, 7.9%.
Synthesis of CMP
A mixture of 3-methoxysalicylaldehyde (0.15 g, 10 mmol)
and N-cyclohexylpropane-1,3-diamine (0.16 g, 10 mmol) in
anhydrous methanol (50 mL) was stirred for 3 h under re-
flux. After the reaction mixture was cooled, the solvent was
removed by vacuum distillation, and ice-water was added to
the residue. The product was isolated by filtrating to obtain
the straw yellow solid. Yield: 0.23 g, 79%. Anal. calcd. for
Received 9 July 2009; accepted 16 April 2010.
Address correspondence to Gui-Mei Xu, The Vocational School of
Penglai, Penglai 265600, P. R. China. E-mail: guimei xu@126.com
355

356
X.-H. LI AND G.-M. XU
TABLE 1
(15.2 mg, 0.2 mmol) was added to the above mixture with
continuous stirring for 30 min and filtered. The filtrate was
allowed undisturbed evaporation at ambient temperature, and
green block crystals suitable for X-ray diffraction were collected
by filtration and washed with methanol. Yield: 21.2 mg, 56%.
Crystallographic data and structure refinement for the
complexes
Complex
1
2
Empirical formula
Mr
C24H30Br4N4NiO2 C36H52N6NiO4S2
784.87
monoclinic
C2/c
755.67
hexagonal
R–3
X-Ray Structure Determination
Crystallographic data for the complexes were collected on
a Bruker APEX-II CCD area detector diffractometer at 298(2)
Crystal system
Space group
˚
a/A
19.461(6)
9.716(5)
17.959(8)
90
23.259(11)
23.259(11)
20.761(9)
90
˚
K with Mo-Kα radiation (λ = 0.71073 A). Absorption correc-
˚
b/A
tions were applied using SADSBS. The structures were solved
with direct methods and refined with full-matrix least-squares
techniques on F2 using the SHELXTL program package.[4] All
of the non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were included but not refined. Crystal data are
summarized in Table 1. Selected bond lengths and angles are
given in Table 2.
˚
c/A
α /◦
β /◦
γ /◦
122.81(3)
90
90
120
3
˚
V /A
2854(2)
4
9727(8)
9
Z
–3
–1
Dc / g cm
µ / mm
1.827
1.161
6.308
0.586
RESULTS AND DISCUSSION
T /K
298(2)
0.23 × 0.21 ×
0.18
298(2)
0.27 × 0.23 ×
0.23
Both complexes were synthesized according to the same
method and similar materials, except for the minor difference
of the Schiff base ligands. The thiocyanate ligands coordinate
to the Ni atom of 2, but do not coordinate to that of 1, which
might be caused by the large hindrance effects of the terminal
cyclohexyl groups in 2 than those of the dimethyl groups in 1.
Crystal size/mm3
Independent Reflns
Reflns unique
Parameters
F(000)
2434
4874
1105
3947
162
224
1544
3618
Rint
Tmin/Tmax
0.0506
0.325/0.396
0.0273
0.858/0.877
0.0499, 0.1374
0.0606, 0.1488
ꢀ
IR Spectra
R1, wR2 [I ≥ 2σ(I)]a 0.0403, 0.0597
The IR spectra of the Schiff base ligands show the character-
istic ν-OH absorption bands at ca. 3400 cm which disappear
after complexation, as a result of proton substitution by the
R1, wR2 (all data)a
0.1002, 0.0677
–1
ꢀ
ꢀ
aR1
w(Fo2)2]1/2
=
||Fo| – |Fc||/ |Fo|, wR2 = [ w(Fo2– Fc2)2/
ꢀ
TABLE 2
˚
◦
Selected bond lengths (A) and angles ( ) for the complexes
C17H2N2O2: C, 70.3; H, 9.0; N, 9.6. Found: C, 70.7; H, 9.2; N,
9.5%.
1
Ni1–O1
Ni1–N2
2.024(3)
2.311(4)
180.
Ni1–N1
2.054(4)
Synthesis of the Complex [Ni(BMP)2]
O1–Ni1–O1#1
O1–Ni1–N1#1
O1–Ni1–N2#1
O1–Ni1–N2
N2–Ni1–N2#1
2
O1–Ni1–N1
87.47(13)
180
97.86(15)
82.14(15)
At room temperature, a clear methanol solution (5 mL) of
BMP (72.8 mg, 0.2 mmol) was slowly added to a methanol
solution (10 mL) of Ni(CH3COO)2·4H2O (24.9 mg, 0.1 mmol),
then a methanol solution (5 mL) of ammonium thiocyanate
(15.2 mg, 0.2 mmol) was added to the above mixture with
continuous stirring for 30 min and filtered. The filtrate was
allowed undisturbed evaporation at ambient temperature, and
green block crystals suitable for X-ray diffraction were collected
by filtration and washed with methanol. Yield: 27.3 mg, 70%.
92.53(13) N1–Ni1–N1#1
87.49(13) N1–Ni1–N2#1
92.51(13)
180
N1–Ni1–N2
Ni1–O1
Ni1–N3
2.0242(14)
2.123(2)
180
88.72(7)
90.96(7)
89.04(7)
180
Ni1–N1
2.0733(18)
O1–Ni1–O1#1
O1–Ni1–N1
O1–Ni1–N3
O1–Ni1–N3#1
N3–Ni1–N3#1
O1–Ni1–N1#1
N1–Ni1–N1#1
N1–Ni1–N3
91.28(6)
180
90.26(7)
89.74(7)
Synthesis of the Complex [Ni(CMP)2(NCS)2]
N1–Ni1–N3#1
At room temperature, a clear methanol solution (5 mL) of
CMP (58.0 mg, 0.2 mmol) was slowly added to a methanol
solution (10 mL) of Ni(CH3COO)2·4H2O (24.9 mg, 0.1 mmol),
then a methanol solution (5 mL) of ammonium thiocyanate
Symmetry transformations used to generate equivalent atoms:
#1 3/2 – x, 3/2 – y, – z; #2 1/3 – x, 2/3 – y, 2/3 – z.

NICKEL(II) COMPLEXES WITH SCHIFF BASES
357
FIG. 1. Structure of 1 with the atom labeling scheme (ellipsoids at 30% probability). Unlabeled atoms are at the symmetry position 3/2 – x, 3/2 – y, – z.
Hydrogen atoms have been omitted for clarity.
metal atoms coordination to the oxygen atoms. The absorption mononuclear nickel(II) complexes, with the Ni atoms lying on
attributed to the ν-C=N vibration is at ca. 1625 cm–1 in the lig- the inversion centers. Both the coordination polyhedra can be
ands, the corresponding vibrations in the complexes, are shifted described as distorted octahedra. In 1, the Ni atom is coordi-
–1
–1
approximately 8 cm for 1 and 11 cm for 2 to lower wave nated by six donor atoms of two BMP Schiff base ligands, with
number as described in similar complexes.[5] The medium in- the two imine N atoms and two phenolate O atoms defining
tensity bands observed for the Schiff base ligands at about 1280 the base plane, and the two amine N atoms occupying the ax-
–1
cm can be attributed to the phenolic stretch. These bands are ial positions. While in 2, the Ni atom is coordinated by four
–1
observed at lower wave numbers by ca. 10 cm relative to donor atoms of CMP Schiff base ligands at the base plane,
the free ligands for the complexes suggesting involvement of and two N atoms of two thiocyanate ligands at the axial po-
the oxygen atom of the phenolate moiety in coordination. The sitions. The amino N atoms in 2 are prononated, and not co-
strong absorption band indicates the existence of the thiocyanate ordinate to the metal atom. It is obvious that the axial coor-
groups in 2 is at 2093 cm–1, which is absent in 1.
dinate bonds are much longer than those of the basal bonds.
Besides the non-equivalence of the bond lengths, the values of
the bond angles also show some deviations from regularity, the
four base bond angles of each octahedron being 2.53(13)◦ for
1 and 1.28(6)◦ for 2 from the ideal 90o. The distortion of the
Description of the Crystal Structure of the Complexes
The molecular structures of 1 and 2 are shown in Figures
1 and 2, respectively. Both compounds are centrosymmetric
FIG. 2. Structure of 2 with the atom labeling scheme (ellipsoids at 30% probability). Unlabeled atoms are at the symmetry position 1/3 – x, 2/3 – y, 2/3 – z.
Hydrogen atoms have been omitted for clarity.

358
X.-H. LI AND G.-M. XU
octahedral coordinations can also be observed in other similar
complexes.[6]
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CONCLUSIONS
Two mononuclear nickel(II) complexes have been synthe-
sized and structurally characterized. The amino N atoms of such
Schiff base ligands can coordinate to the metal atoms. However,
the bulky terminal groups such as cyclohexyl may prevent the
coordination, which give a chance for the thiocyanate ligands to
coordinate to the metal atoms.
Supplementary Material
Crystallographic data for the complexes have been de-
posited with the Cambridge Crystallographic Data Centre,
CCDC Nos. 727599 for (1) and 727600 for (2). Copies of
these information may be obtained free of charge from: the
Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk or
http://www.ccdc.cam.ac.uk).
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