Synthesis, Crystal Structure, and Catalytic Property of a Copper Coordination Compound Based on In Situ Generated 2-Hydroxynicotinic Acid

Article abstract of DOI:10.1007/s10870-019-00818-0

Abstract: The copper coordination complex [CuCl(2-OHNA)H₂O]·H₂O (1) was synthesized by the reaction of CuCl₂·2H₂O with in situ generated 2-hydroxynicotinic acid and its crystal structure was determined by single X-ray diffraction methods. It was further characterized by FT-IR spectroscopy, elemental analyses, and thermogravimetric analysis. Complex 1 crystallizes in monoclinic space group P2₁/c with a = 8.9797(13), b = 14.196(2), c = 7.0738(11) ?, β = 96.897(2), V = 895.2(2) ?³, M_r = 273.12, D_c = 2.027?g/cm³, and Z = 4. In the structure, complex 1 is linked into 2D sheets via intermolecular hydrogen bonding [N1–H1···O2 (?x+1, y ? 1/2, ? z+1/2); O5–H10···O2 (? x+1, y + 1/2, ? z+1/2); O4–H9···O5 (x, y ? 1, z); O4–H8···O5 (? x+2, y + 1, ? z)]. The catalytic property of 1 was also investigated in the selective oxidation of benzyl-alkanes using TBHP as oxidant. Under optimized conditions, 1 exhibited high catalytic activity and selectivity toward the corresponding aryl ketones. Graphic Abstract: The copper coordination complex [CuCl(2-OHNA)H₂O]·H₂O (1) was synthesized by the reaction of CuCl₂·2H₂O with in situ generated 2-hydroxynicotinic acid and the catalytic property of 1 was also investigated in the selective oxidation of benzyl-alkanes using TBHP as oxidant.[Figure not available: see fulltext.].

Full text of DOI:10.1007/s10870-019-00818-0

Journal of Chemical Crystallography
https://doi.org/10.1007/s10870-019-00818-0
ORIGINAL PAPER
Synthesis, Crystal Structure, and Catalytic Property of a Copper
Coordination Compound Based on In Situ Generated
2‑Hydroxynicotinic Acid
Ren‑Tao Wu1 · Ji‑Kun Li1 · Chuan‑Ping Wei1 · Xian Ma1
Received: 9 October 2018 / Accepted: 10 December 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
The copper coordination complex [CuCl(2-OHNA)H2O]·H2O (1) was synthesized by the reaction of CuCl2·2H2O with in situ
generated 2-hydroxynicotinic acid and its crystal structure was determined by single X-ray difraction methods. It was further
characterized by FT-IR spectroscopy, elemental analyses, and thermogravimetric analysis. Complex 1 crystallizes in mono-
clinic space group P21/c with a=8.9797(13), b=14.196(2), c=7.0738(11) Å, β=96.897(2), V=895.2(2) Å3, Mr =273.12,
Dc =2.027 g/cm3, and Z=4. In the structure, complex 1 is linked into 2D sheets via intermolecular hydrogen bonding [N1–
H1···O2 (−x+1, y−1/2, − z+1/2); O5–H10···O2 (− x+1, y+1/2, − z+1/2); O4–H9···O5 (x, y−1, z); O4–H8···O5 (− x+2,
y+1, − z)]. The catalytic property of 1 was also investigated in the selective oxidation of benzyl-alkanes using TBHP as
oxidant. Under optimized conditions, 1 exhibited high catalytic activity and selectivity toward the corresponding aryl ketones.
Graphic Abstract
The copper coordination complex [CuCl(2-OHNA)H2O]·H2O (1) was synthesized by the reaction of CuCl2·2H2O with
in situ generated 2-hydroxynicotinic acid and the catalytic property of 1 was also investigated in the selective oxidation of
benzyl-alkanes using TBHP as oxidant.
Keywords Coordination compound · Crystal structure · Benzyl-alkanes · Catalytic oxidation
* Ji-Kun Li
lijk0212@163.com
1
College of Chemistry and Chemical Engineering,
Taishan University, Tai’an 271000, Shandong,
People’s Republic of China
Vol.:(0123456789)
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Journal of Chemical Crystallography
Sil capillary column. TGA experiments were carried out
on a Perkin-Elmer TGA 7 analyzer with a heating rate
of 10 °C/min from room temperature to 700 °C under
nitrogen atmosphere.
Introduction
In recent decades, transition-metal complexes have
obtained long-lasting attention due to their variety of
architectures and the potential applications as functional
materials [1–4]. Among transition metals, copper is an
important element in catalysis chemistry, coordination
chemistry, magnetochemistry and its relevance as the
active-site structure of metalloproteins [5–8]. Moreover,
its fexible coordination modes make the copper ion to
form mononuclear, dinuclear and multinuclear complexes.
Functionalized carboxylates can easily be applied to con-
struct functionalized metal–organic coordination com-
pounds with supramolecular architectures. Functional
groups like –OH, –NH2 are frequently used for this pur-
pose [9]. 2-Hydroxynicotinic acid (2-OHNAH) is one of
the most successful functionalized carboxylates due to its
versatile modes of coordination [10].
Synthesis of Complex [CuCl(2‑OHNA)
H2O]·H2O (1)
To a 40 mL methanolic solution of 2-ClNAH (0.95 g,
6 mmol) was slowly added a 20 mL aqueous solution of
CuCl2·2H2O (0.52 g, 3 mmol) with continuous stirring.
The mixture was stirred for 1 h with constant heating at
60 °C. Subsequently, the solution was allowed to cool and
the pH was adjusted to about 7.5 with an aqueous solu-
tion of NaOH. The mixture was then heated over a water
bath for 2 h and subsequently fltered. The solution was
left to over a week at room temperature to evaporate the
solvent and until blue colored translucent crystals formed
(ca. 52% yield based on 2-ClNAH). Anal. calcd. (%) for
C6H8ClCuNO5: C, 26.38; H, 2.95; N, 5.13. Found: C,
26.24; H, 3.11; N, 5.06. IR (KBr) v: 3442, 3338, 1664,
1616, 1552, 1473, 1247, 1148, 1092, 672, 577, 542,
441 cm−1.
Herein, we present a Cu(II) coordination complex
[CuCl(2-OHNA)H2O]·H2O (1) with in situ generated
2-hydroxynicotinic acid. Complex 1 was fully character-
ized by single crystal X-ray difraction (SXRD), FT-IR
spectroscopy, elemental analysis (EA), and thermogravi-
metric (TGA) analysis. The metal contents of 1 were deter-
mined using inductively coupled plasma (ICP) on a JY-
ULTIMA2 analyzer. Complex 1 was obtained by mixing
CuCl2·2H2O and 2-chloronicotinic acid (2-ClNAH) in 1:2
molar ratio in a 1:2 water–methanol mixture under basic
conditions. In 1, the original 2-ClNAH ligand underwent
to a base hydrolysis reaction followed by keto-enol tau-
tomerization (Scheme 1). Importantly, complex 1 was fur-
ther investigated as catalyst for the oxidation of benzylic
sp3 C–H bonds with TBHP as an oxidant.
X‑ray Crystallography
Single-crystal X-ray diffraction data for complex 1 were
collected on a Bruker Smart APEX II CCD diffractom-
eter using graphite-monochromated Mo Ka radiation
(λ = 0.71073 Å) at 298 K. The data were corrected for
absorption using the multi-scan technique [11]. The struc-
ture was solved by the direct method and refined through
full-matrix least-squares techniques method on F2 using
the SHELXTL 97 crystallographic software package [12,
13]. The hydrogen atoms connected to C and N atoms
were placed in calculated positions and refined using a
riding model. Hydrogen atoms on O atoms were located
in the difference Fourier maps and then refined using a
riding model and a dependent displacement parameter
Uiso(H) = 1.5Ueq(O). The distances of O–H bonds and
bond angles of H–O–H were further restrained using the
DFIX command. Crystallographic data for complex 1 are
Experimental
All reagents and solvents were purchased from com-
mercial sources and used without further purification.
The C, H and N elemental analyses were conducted on
a Perkin-Elmer 240C elemental analyzer. The FT-IR
spectra were recorded from KBr pellets in the range of
4000–400 cm−1 on a Nicolet 170 SXFT/IR spectrom-
eter. The GC analyses were performed on Shimadzu GC-
2014C with a FID detector equipped with an Rtx-1701
Scheme 1 Hydrolysis of 2-chlo-
ronicotinic acid in presence of
base and successive keto-enol
tautomerization
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Journal of Chemical Crystallography
Table 1 Crystal data and structure refnement of 1
summarized in Table 1 and selected bond lengths and
bond angles are listed in Table 2.
Chemical formula
C6H8ClCuNO5
CCDC deposit no.
Crystal description
Formula weight
1569265
Blue block
273.12
Catalytic Oxidation of Benzylic sp3 C–H
Bonds
Temperature (K)
298(2)
Crystal system
Space group
Wavelength (Å)
Unit cell dimensions (Å)
a
b
c
Monoclinic
P21/c
0.71073
In a typical experiment, the required amount of catalyst
(1.5 mol%) and benzyl hydrocarbon (0.125 mmol), 70%
TBHP (0.35 mmol) and benzonitrile (1 mL) were succes-
sively added to a round-bottom fask. The reaction mixture
was subsequently heated at 80 °C in a Wattecs Parallel
Reactor for 24 h with stirring. The conversion and selec-
tivity of these reactions were determined by GC analyses
with nitrobenzene as an internal standard. All of the prod-
ucts were confrmed by GC analysis in combination with
GC–MS.
8.9797(13)
14.196(2)
7.0738(11)
90
96.897(2)
90
895.2(2)
4
2.027
α (°)
β (°)
γ (°)
Volume (Å3)
Z
Density (calculated) (mg m−3
)
)
Absorption coefcient (mm−1
F(000)
2.732
548
Results and Discussion
θ range for data collection (°)
Index ranges
2.70–28.21
– 10≤h≥7
– 16≤k≥16
– 8≤l≥8
4527/1582 (Rint =0.0217)
Multi-scan (based on
symmetry-related meas-
urements)
0.7352, 0.5848
1582/6/127
1.092
R1 =0.0253, wR2 =0.0702
R1 =0.0268, wR2 =0.0712
0.339,−0.600
1569265
Thermogravimetric Analysis of [CuCl(2‑OHNA)
H2O]·H2O (1)
Thermogravimetric analysis (TGA) was performed to
study the stability of complex 1 (Fig. 1). Three sepa-
rate weight loss steps were observed: The first weight
loss began at 90 °C and was completed at 160 °C. The
observed weight loss of 19.90% corresponds to the loss
of one lattice water molecule and –Cl− group (calcd
19.95%). The second weight loss of 24.72% occurred in
Refections collected/unique
Absorption correction
Max. and min. transmission
Data/restraints/parameters
Goodness-of-ft on F2
Final R indices [I>2σ (I)]
R indices (all data)
Largest dif. peak and hole (e. Ǻ−3
)
CCDC
Table 2 Selected bond length and bond angles (Å, °) of 1
Selected bond lengths (Å)
Cu(1)–O(1)
Cu(1)–O(3)
Cu(1)–O(4)
O(1)–C(1)
O(2)–C(1)
O (3)–C(3)
Cu(1)–Cl(1)#1
1.275(3)
1.244(3)
1.275(3)
2.801(5)
Cu(1)–Cl(1)
Bond angles (°)
O(3)–Cu(1)–O(1)
O(3)–Cu(1)–O(4)
O(1)–Cu(1)–O(4)
O(3)–Cu(1)–Cl(1)
O(1)–Cu(1)–Cl(1)
O(4)–Cu(1)–Cl(1)
C(1)–O(1)–Cu(1)
C(3)–O(3)–Cu(1)
93.91(5)
89.50(6)
130.97(14)
125.86(14)
Fig. 1 TGA curve for complex 1
Symmetry code: #1: x, − y + 1/2, z+1/2
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Journal of Chemical Crystallography
the range of 310–540 °C, corresponding to the loss of one
coordinated water molecule and one –COO− group (calcd
24.17%). The third and continuous weight loss step began
at 543 °C and can be attributed to the further decomposi-
tion of the 2-OHNA ligand.
connected by the hydrogen bonding interaction formed by
N1 of the pyridine ring and O2 derived from the carboxyl
group of the adjacent 2-OHNA anion with the N1–H1···O2
(− x + 1, y − 1/2, − z + 1/2) distance of 2.825(2) Å to
form a 1D supramolecular chain. Second, the solvent water
molecules along with the coordinated water molecules
connect the neighboring 1D chains to generate 2D lay-
ers by the hydrogen bonding interactions (O5–H10···O2
(− x + 1, y + 1/2, − z +1 /2) = 2.798(2) Å, O4 − H9···O5
(x, y − 1, z) = 2.732(2) Å, O4–H8···O5 (− x + 2, y + 1,
− z)=2.758(2) Å). At last, the 2D layers are stacked by sol-
vent water hydrogen-bonding to Cl to form a 3D supramo-
lecular structure with the O5–H11···Cl1 (− x + 2, y+1/2,
− z + 1/2) distance of 3.193(6) Å. All hydrogen bonds are
shown in Table 3.
Crystal Structure of [CuCl(2‑OHNA)H2O]·H2O (1)
Compound 1 including the hydrogen-bonded solvent
water is shown in Fig. 2. SXRD analysis shows that com-
plex 1 crystallizes in the monoclinic space group P21/c.
The Cu2+ ion is square planar coordination as expected.
Chlorine atoms in the neighboring sheet are at a 2.80
Å distance from Cu. The ligand 2-OHNA exists in keto
form and bidentately coordinates to the metal centre in
O, O′-salicylate manner. The typical square planar coor-
dination around the Cu(II) ion includes three O atoms
(two from the 2-OHNA ligand and one from the coordi-
nated water molecule) and one Cl atom. The chelate bite
angle in the fve-membered ring formed by O1 (carboxyl
group) and O3 (carbonyl group) is 92.9°. The distances
of Cu1–O1 and Cu1–O3 are 1.920(7) Å and 1.914(9) Å
respectively, which are all considerably shorter than the
Cu1–O4 (1.937(1) Å) distance indicating that the coordi-
nation bond between copper and water molecule (O4) is
relatively weaker than the chelate bonds between copper
and the 2-OHNA ligand (O1 and O3). The bond lengths
and angles between the nicotinic acid and Cu are compa-
rable with structurally characterized complexes previously
reported [14–16].
Catalytic Activity of [CuCl(2‑OHNA)H2O]·H2O (1)
Selective oxidation of benzyl-alkanes is a powerful tool to
generate high value organic compounds from less expen-
sive raw materials and represents one of the formidable
challenges in organic chemistry [17, 18]. However, a few
catalysts have shown catalytic activity in the oxidation of
benzylic C–H bonds with unsatisfactory catalytic activity
[19–21]. With the aim to understand the catalytic prop-
erty of the title coordination polymer for developing a
new oxidation system in organic chemistry, the oxidation
of diphenylmethane to benzophenone was selected as a
model reaction (Scheme 2). While molecular oxygen and
hydrogen peroxide were inefcient to promote diphenyl-
methane oxidation, TBHP was a good oxidizing reagent
in terms of the percentage yield of benzophenone. Thus,
TBHP was chosen as the best oxidant in the reaction. After
the preliminary optimization, benzophenone is obtained
as the almost sole product in 97.5% conversion using
TBHP as oxidant in the presence of complex 1 at 80 °C
for 24 h. And indeed, the catalytical activity of complex
1 outperforms those of some transition-metal-based com-
plexes reported to date, i.e. [Cu4L4]4X (L = 1,3,5-tris(1-
benzylbenzimidazol-2-yl)benzene, X = ClO4, OTs, OTf)
[22], NHPI/Cu@PILC [23].
Further, hydrogen bondings are observed as weak
supramolecular interactions to stabilize the lattice struc-
ture (Fig. 3). First, the adjacent mononuclear structures are
The excellent performance in the transformation of diphe-
nylmethane to benzophenone prompted us to extend the
scope of complex 1 as catalyst for other benzylic sp3 C–H
bonds. As illustrated in Table 4, complex 1 exhibits excel-
lent catalytic activity for oxidation of benzyl sp3 C–H bonds,
fuorene and its derivates, 9H-xanthenes are all oxidized to
the corresponding aryl ketones with great conversion rate
(98.5–99.6%) and exceptional selectivity (97.5–99.5%). That
is to say, complex 1 could facilitate the oxidation of benzylic
Fig. 2 ORTEP diagram (50% probability) of complex 1 with atom
numbering
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Journal of Chemical Crystallography
Fig. 3 a 2D layer along (1 0
2) formed by hydrogen bonds.
b Stacked layers with solvent
water hydrogen-bonding to Cl.
c Packing and unit cell, view
along a (left) and c (right)
Table 3 Hydrogen bonds
lengths and bond angles (Å, °)
of 1
D–H···A
Symm.
D–H
H···A
D···A
D–H···A
N(1)–H(1)···O(2)
O(4)–H(8)···O(5)
O(4)–H(9)···O(5)
O(5)–H(10)···O(2)
O(5)–H(11)···Cl(1)
− x+1, y − 1/2, − z+1/2
− x+2, y+1, − z
x, y−1, z
− x+1, y+1/2, − z+1/2
− x+2, y+1/2, − z+1/2
0.86
0.85
0.85
0.85
0.85
1.97
1.91
1.89
1.95
2.35
2.825(2)
2.758(2)
2.732(2)
2.798(2)
3.193(6)
175.0
176.2
168.4
173.4
173.7
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Journal of Chemical Crystallography
The introduction of Cu2+ cation make complex 1 more stable
and can be used as catalysts in the selective oxidation of
alkylbenzenes with high catalytic activity and high selectiv-
ity toward the corresponding aryl ketones. Intramolecular
hydrogen-bonds help to form a 2D layers. Complex 1 shows
excellent generality in converting benzylic sp3 C–H bonds
compounds to corresponding aromatic ketones efciently.
Investigations on the use of this complex for other potential
catalytic reactions are in progress.
Scheme 2 The oxidation of diphenylmethane to benzophenone with
TBHP
sp3 C–H bonds and may serve as highly efcient and selec-
tive catalyst.
Supplementary Material
CCDC 1569265 contains the supplementary crystallo-
graphic data for this paper. This data can be obtained free
of charge via www.ccdc.cam.ac.uk/data_request/cif, by
e-mailing data_request@ccdc.cam.ac.uk.
Conclusion
In summary, we have synthesized a copper coordination
complex [CuCl(2-OHNA)H2O]·H2O (1) by the reaction of
CuCl2·2H2O with in situ generated 2-hydroxynicotinic acid.
Table 4 Results of selective oxidation of benzylic sp3 C–H bonds compounds catalyzed by complex 1
Entry
1
Substrates
Products
Conv. (%)
97.5
Sele. (%)a
98.2
2
3
4
5
99.4
99.5
99.6
98.5
97.5
99.2
99.5
99.4
Reaction conditions: substrates (0.125 mmol), complex 1 (1.5 mol%), TBHP (0.35 mmol), benzonitrile (1 mL), 80 °C, 24 h
aSelectivity to ketones was analyzed by GC using the nitrobenzene as internal standard. The by-products are corresponding alcohols, which was
analyzed by GC–MS
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Journal of Chemical Crystallography
10. Singh SK, Srivastava AK, Srivastava K, Banerjee R, Prasad J
(2017) J Mol Struct 1147:549
Acknowledgements This work was financially supported by the
Natural Science Foundation of Shandong Province (ZR2017LB002)
and project (2018HX207), Taian Municipal Science and Technology
Project (2015GX2057) and the Talent Introduction Project of Taishan
University (Y2015-1-009).
11. Sheldrick GM (1996) SADABS. Göttingen University, Germany
12. Sheldrick GM (2015) Acta Cryst A 71:3
13. Sheldrick GM (2015) Acta Cryst C 71:3
14. Lü Y, Zhang X, Cui XB, Xu JQ (2018) Inorg Chem 57:11123
15. Hu YY, Zhang TT, Zhang X, Zhao DC, Cui XB, Huo QS, Xu JQ
(2016) Dalton Trans 45:2562
16. Zhao DC, Hu YY, Ding H, Guo HY, Cui XB, Zhang X, Huo QS,
Xu JQ (2015) Dalton Trans 44:8971
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