The unexpected synthesis, crystal structure, and thermal stability of a copper(II) complex derived from 2-[(2-phenylaminoethylimino)methyl]benzoic acid

Article abstract of DOI:10.1080/15533174.2012.762678

A new mononuclear copper(II) complex, [Cu(PIBA)₂(OH ₂)], where PIBA is the anionic form of 2-(1-phenylimidazolidin-2-yl) benzoic acid, has been unexpectedly obtained from the reaction of 2-formylbenzoic acid, N-phenylethane-1,2-diamine, and copper perchlorate in methanol. The complex was characterized by elemental analysis, infrared spectrum, and single-cyrstal X-ray diffraction. The complex crystallizes in the triclinic space group P-1, with unit cell dimensions a = 11.812(2) A, b = 11.884(2) A, c = 22.799(3) A, α = 89.168(2)°, β = 87.290(2)°, γ = 88.604(2)°, V = 3195.5(10) A³, Z = 4, R ₁ = 0.0775, and wR₂ = 0.1647. The Cu atom in the complex is five-coordinated in a square pyramidal geometry by two carboxylate O and two imidazolidine N atoms from two PIBA ligands, and by one water O atom. The thermal stability of the complex has also been determined. Copyright Taylor & Francis Group, LLC.

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The Unexpected Synthesis, Crystal Structure, and
Thermal Stability of a Copper(II) Complex Derived from
2-[(2-Phenylaminoethylimino)methyl]benzoic Acid
Shao-Song Qian a , Dong-Mei Xian b , Yu-Ping Ma b , Zhong-Lu You b & Hai-Liang Zhu a
a School of Life Sciences , Shandong University of Technology , ZiBo , P. R. China
b Department of Chemistry and Chemical Engineering , Liaoning Normal University , Dalian ,
P. R. China
Accepted author version posted online: 07 Mar 2013.Published online: 25 Aug 2013.
To cite this article: Shao-Song Qian , Dong-Mei Xian , Yu-Ping Ma , Zhong-Lu You & Hai-Liang Zhu (2013) The
Unexpected Synthesis, Crystal Structure, and Thermal Stability of a Copper(II) Complex Derived from 2-[(2-
Phenylaminoethylimino)methyl]benzoic Acid, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry,
43:10, 1406-1410, DOI: 10.1080/15533174.2012.762678
To link to this article: http://dx.doi.org/10.1080/15533174.2012.762678
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:1406–1410, 2013
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.762678
The Unexpected Synthesis, Crystal Structure, and Thermal
Stability of a Copper(II) Complex Derived from
2-[(2-Phenylaminoethylimino)methyl]benzoic Acid
Shao-Song Qian,1 Dong-Mei Xian,2 Yu-Ping Ma,2 Zhong-Lu You,2
and Hai-Liang Zhu1
1School of Life Sciences, Shandong University of Technology, ZiBo, P. R. China
2Department of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian, P. R. China
(HPIBA; Scheme 1), has been unexpectedly obtained from the
reaction of 2-formylbenzoic acid, N-phenylethane-1,2-diamine,
and copper perchlorate in methanol.
A new mononuclear copper(II) complex, [Cu(PIBA)2(OH2)],
where PIBA is the anionic form of 2-(1-phenylimidazolidin-2-
yl)benzoic acid, has been unexpectedly obtained from the reaction
of 2-formylbenzoic acid, N-phenylethane-1,2-diamine, and cop-
per perchlorate in methanol. The complex was characterized by
elemental analysis, infrared spectrum, and single-cyrstal X-ray
diffraction. The complex crystallizes in the triclinic space group
P–1, with unit cell dimensions a = 11.812(2) Å, b = 11.884(2) Å,
c = 22.799(3) Å, α = 89.168(2)◦, β = 87.290(2)◦, γ = 88.604(2)◦,
V = 3195.5(10) Å3, Z = 4, R1 = 0.0775, and wR2 = 0.1647. The
Cu atom in the complex is five-coordinated in a square pyramidal
geometry by two carboxylate O and two imidazolidine N atoms
from two PIBA ligands, and by one water O atom. The thermal
stability of the complex has also been determined.
SCH. 1. The ligand HPIBA.
EXPERIMENTAL
Materials and Measurements
Keywords copper(II) complex, crystal structure, synthesis, thermal
stability
Commercially available 2-formylbenzoic acid and N-
phenylethane-1,2-diamine were purchased from Aldrich
(Shanghai, China) and used without further purification. Other
solvents and reagents were made in China and used as received.
C, H, and N elemental analyses were performed with a Perkin-
Elmer elemental analyzer (Nanjing University, China). The in-
frared spectra were recorded on a Nicolet AVATAR 360 spec-
trometer (Liaoning Normal University, China) as KBr pellets
in the 4000–400 cm−1 region. Thermal stability analysis was
performed on a Perkin-Elmer Pyris Diamond TG-DTA thermal
analyses system (Nanjing University, China).
INTRODUCTION
Metal complexes containing Schiff bases have been of great
interest for a long time due to their importance in the fields of
coordination chemistry related to catalysis and enzymatic re-
actions, magnetism and molecular architectures.[1–5] In recent
years, a large number of copper(II) complexes with Schiff bases
derived from salicylaldehyde and its derivatives have been re-
ported.[6–9] 2-Formylbenzoic acid is a structurally similar com-
pound to salicylaldehyde, however, no complexes with the Schiff
bases derived from 2-formylbenzoic acid have been reported so
far. As an exploration of the work on the preparation of the com-
plexes with such ligands, in the present paper, a new mononu-
clear copper(II) complex, [Cu(PIBA)2(OH2)], where PIBA is
the anionic form of 2-(1-phenylimidazolidin-2-yl)benzoic acid
Synthesis of the Complex [Cu(PIBA)2(OH2)]
2-Formylbenzoic acid (1.0 mmol, 0.150 g), NEt3 (1.0 mmol,
0.101 g), and N-phenylethane-1,2-diamine (1.0 mmol, 0.136 g)
were dissolved in methanol (20 mL) with stirring. The mixture
was stirred for 30 min at room temperature. To the above mixture
was added with stirring a methanol solution (10 mL) of copper
perchlorate (1.0 mmol, 0.373 g). The final mixture was further
stirred for 1 h, and filtered. Green block-shaped single crystals
of the complex were formed by slow evaporation of the solution.
Yield: 63% on the basis of 2-formylbenzoic acid. Anal. Calcd.
for C32H32CuN4O5 (FW 616.2): C, 62.4; H, 5.2; N, 9.1. Found:
C, 62.2; H, 5.4; N, 9.0%.
Received 20 February 2012; accepted 23 December 2012.
Address correspondence to Hai-Liang Zhu, School of Life Sciences,
Shandong University of Technology, ZiBo 255049, P. R. China. E-mail:
hailiang zhu@163.com
1406

UNEXPECTED SYNTHESIS OF A COPPER(II) COMPLEX
1407
TABLE 1
Crystallographic and experimental data for the complex
TABLE 2
Selected bond lengths (Å) and angles (◦)
Formula
FW
Crystal shape/color
C32H32CuN4O5
616.2
block/green
Bond lengths
Cu1–O2
Cu1–N1
1.947(4)
2.043(6)
2.306(5)
1.954(4)
2.024(6)
Cu1–O3
Cu1–N3
Cu2–O5
Cu2–N5
Cu2–O10
1.947(5)
2.039(6)
1.954(4)
2.034(6)
2.340(5)
Crystal size/mm
Crystal system
Space group
0.25 × 0.23 × 0.23 Cu1–O9
Triclinic
P–1
Cu2–O7
Cu2–N7
Bond angles
O3–Cu1–O2
O2–Cu1–N3
O2–Cu1–N1
O3–Cu1–O9
N3–Cu1–O9
O7–Cu2–O5
O5–Cu2–N7
O5–Cu2–N5
O7–Cu2–O10
N7–Cu2–O10
a/Å
b/Å
11.812(2)
11.884(2)
22.799(3)
89.168(2)
87.290(2)
88.604(2)
3195.5(10)
4
178.9(2)
90.3(2)
90.3(2)
91.3(2)
90.0(2)
178.9(2)
90.0(2)
88.3(2)
87.1(2)
92.1(2)
O3–Cu1–N3
O3–Cu1–N1
N3–Cu1–N1
O2–Cu1–O9
N1–Cu1–O9
O7–Cu2–N7
O7–Cu2–N5
N7–Cu2–N5
O5–Cu2–O10
N5–Cu2–O10
89.5(2)
89.8(2)
177.7(2)
89.8(2)
92.2(2)
90.8(2)
90.9(2)
177.3(2)
93.7(2)
90.1(2)
c/Å
α/◦
β/◦
γ /◦
V/Å3
Z
T/K
298(2)
0.727
1.281
μ/mm−1(Mo-Kα)
Dc/g cm−3
Reflections/parameters
Restraints
13628/781
10
Observed reflections [I ≥ 2σ(I)]
4823
1284
0.8391
0.8506
tions and constrained to ride on their parent atoms. The crys-
tallographic data for the complex are summarized in Table 1.
Selected bond lengths and angles are given in Table 2. Hydro-
gen bonding information is given in Table 3. Crystallographic
data for the complex have been deposited with the Cambridge
Crystallographic Data Center (CCDC 867495).
F(000)
Tmin
Tmax
Goodness of fit on F2
R1, wR2 [I ≥ 2σ(I)]a
R1, wR2 (all data)a
0.941
0.0775, 0.1647
0.2313, 0.2290
ꢀ
ꢀ
ꢀ
ꢀ
2
2 2
2 2 1/2
aR1 = ||Fo|-|Fc||/ |Fo|, wR2 = [ w(Fo -Fc ) / w(Fo ) ]
.
RESULTS AND DISCUSSION
Synthesis of the Complex
Data Collection, Structural Determination,
and Refinement
The complex was prepared by the reaction of 2-
formylbenzoic acid, NEt3, N-phenylethane-1,2-diamine, and
copper perchlorate in ethanol, as shown in Scheme 2. It is in-
teresting that the formyl group of 2-formylbenzoic acid linked
to both the amine and the imine N atoms of N-phenylethane-
1,2-diamine during the reaction, which was seldom seen for the
preparation of complexes with Schiff bases derived from other
aldehydes.
Diffraction intensities for the complex were collected at
298(2) K using a Bruker SMART 1K area detector (Shan-
dong University of Technology, China) with MoKα radiation
(λ = 0.71073 Å). The collected data were reduced using the
SAINT program,[10] and multiscan absorption corrections were
performed using the SADABS program.[11] The structure was
solved by direct methods and refined against F2 by full-matrix
least-squares methods using the SHELXTL program.[12] All of
the non-hydrogen atoms were refined anisotropically. The water
Structure Description of the Complex
The asymmetric unit of the complex contains two indepen-
and amino H atoms in the complex were located in a difference dent mononuclear copper(II) complex molecules, as shown in
Fourier map and refined isotropically, with O–H, N–H, and Figures 1 and 2, respectively. The Cu atom in each molecule is
H···H distances restrained to 0.85(1), 0.90(1), and 1.37(2) Å, in a square pyramidal coordination, with two carboxylate O and
respectively. All other H atoms were placed in idealized posi- two imidazolidine N atoms from two PIBA ligands defining the
SCH. 2. Preparation of the complex.

1408
S.-S. QIAN ET AL.
FIG. 1. The Cu1 complex molecule of the complex at 30% probability displacement. The carbonyl H atoms have been omitted for clarity.
TABLE 3
basal plane, and with one water O atom occupying the apical
position. The angles between the apical and the four basal donor
atoms range from 89.8(2) to 92.2(2)◦ for Cu1 and from 87.1(2)
to 93.7(2)◦ for Cu2, and the perpendicular angles of the basal
plane range from 89.5(2) to 90.3(2)◦ for Cu1 and from 88.3(2) to
90.9(2)◦ for Cu2, indicating the difference from the ideal values
of 90◦. The apical bonds are much longer than the basal bonds.
The Cu atoms deviate from the least-squares planes defined by
the basal donor atoms by 0.029(1) Å for Cu1, and 0.025(1) Å for
Cu2, toward the apical donor atoms. Within the ligands PIBA,
the dihedral angles between the two benzene rings C1-C6 and
C11-C16, C17-C22 and C27-C32, C33-C38 and C43-C48, and
C49-C54 and C59 and C64 are 90.7(3)◦, 88.1(3)◦, 91.9(3)◦, and
92.5(3)◦, respectively. The imidazolidine groups adopt envelope
shape, with the secondary amino N1, N3, N5, and N7 atoms de-
viate from the least-squares planes defined by the remaining
four atoms by 0.509(2) Å, 0.523(2) Å, 0.533(2) Å, and 0.499(2)
Å, respectively. The dihedral angles between the carboxylate
Hydrogen-bond geometry for the complex (Å, ◦)
D–H···A
D–H
H···A
D···A
D–H···A
O10–H10D···O8i
0.85(1) 2.06(3) 2.868(9)
0.90(1) 2.14(4) 2.950(7)
158(7)
149(6)
110(5)
171(7)
125(5)
154(6)
147(6)
149(6)
N7–H7A···O8i
O10–H10C···O6ii 0.85(1) 2.55(6) 2.948(8)
N5–H5A···O6ii
O9–H9D···O1iii
N1–H1A···O1iii
N3–H3A···O4iv
O9–H9C···O4iv
0.90(1) 2.13(2) 3.028(7)
0.85(1) 2.23(5) 2.800(7)
0.90(1) 2.22(3) 3.050(7)
0.90(1) 2.29(4) 3.081(7)
0.85(1) 2.04(3) 2.811(8)
Symmetry codes: (i) 1 – x, 2 – y, 2 – z; (ii) 1 – x, 1 – y, 2 – z;
(iii) 1 – x, 1 – y, 1 – z; (iv) 2 – x, 1 – y, 1 – z.
FIG. 2. The Cu2 complex molecule of the complex at 30% probability displacement. The carbonyl H atoms have been omitted for clarity.

UNEXPECTED SYNTHESIS OF A COPPER(II) COMPLEX
1409
FIG. 3. The crystal structure of the complex, viewed along the c-axis. Hydrogen bonds are shown as dashed lines.
planes with the benzene rings they attached are in the range IR Spectrum
52.3(3)–54.7(3)◦.
The O–H and N–H vibrations are observed as weak bands
at 3468 and 3136 cm−1, respectively. The characteristic feature
of the infrared spectrum of the complex is the positions of the
νas(COO) and νs(COO) bands at 1594 and 1380 cm−l, respec-
tively. Their difference, = 214 cm−1, is characteristic of the
monodentate coordination mode of the carboxylate groups.[14]
The weak bands located at the low numbers may be assigned to
the ν(Cu–O) and ν(Cu–N).
The coordination number 5 for copper(II) complexes is very
common and usually presents either a square pyramidal or a trig-
onal bipyramidal geometry, or any of the distorted intermediate
geometries. For a pentacoordinated metal center, the distortion
of the coordination environment from square pyramidal to trig-
onal bipyramidal can be calculated from the Addison distortion
index, τ, which defined as τ = (β – α)/60, where α and β are
the two largest coordinate angles, and τ = 0 represents perfect
square pyramidal, τ = 1 represents perfect trigonal bipyrami-
dal.[13] In the present complex, the calculated τ values are 0.020
for Cu1 and 0.027 for Cu2, suggesting they are square pyramidal
geometry, instead of trigonal bipyramidal.
Thermal Stability
Differential thermal (DT) and thermal gravimetric analyses
(TGA) were conducted to examine the stability of the com-
plex. The first step started at about 100◦C and was completed
at 130◦C, corresponding to the loss of the coordinated water
molecule. The observed weight loss of 3.1% is close to the cal-
culated value of 2.9%. The second step, from 164◦C to 412◦C,
corresponds to the loss of the benzene and the benzoate groups
of the ligands. The observed weight loss of 63.3% is close to the
calculated value of 64.0%. The last step, from 412◦C to 654◦C,
corresponds to the loss of the imidazolidine groups, and the
formation of the final product (CuO). The observed weight loss
of 19.0% in this step is close to the calculated value of 20.5%.
The total weight loss of 85.3% is close to the calculated value
(87.0%).
CONCLUSION
A new mononuclear copper(II) complex has been unexpect-
edly obtained from the reaction of 2-formylbenzoic acid, N-
phenylethane-1,2-diamine, and copper perchlorate in methanol.
FIG. 4. DT-TGA curve of the complex.

1410
S.-S. QIAN ET AL.
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group of 2-formylbenzoic acid linked to both the amine and
the imine N atoms of N-phenylethane-1,2-diamine during the
reaction.
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