Synthesis and crystal structures of N,N'-bis(5-methylsalicylidene)ethane-1,2-diamine and its bromido-, phenolato-, and dicyanoamido-cobridged polymeric copper(II) complex

Article abstract of DOI:10.1134/S1070328417050062

A bis-Schiff base N,N'-bis(5-methylsalicylidene)ethane-1,2-diamine (H₂L) was prepared and characterized by elemental analysis, ¹H NMR and ¹³C NMR spectra, MS, and single crystal X-ray diffraction (CIF file CCDC no. 1022761

Full text of DOI:10.1134/S1070328417050062

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2017, Vol. 43, No. 5, pp. 331–337. © Pleiades Publishing, Ltd., 2017.
Synthesis and Crystal Structures of N,N'-bis(5-
methylsalicylidene)ethane-1,2-Diamine and Its Bromido-,
Phenolato-, and Dicyanoamido-Cobridged
Polymeric Copper(II) Complex1
X. Y. Qiua, *, Y. T. Gub, Y. T. Lib, D. M. Xianb, Z. L. Youb, and H. L. Zhuc, **
aCollege of Science and Technology, Ningbo University, Ningbo, 315212 P.R. China
bDepartment of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian, 16029 P.R. China
cSchool of Life Sciences, Shandong University of Technology, ZiBo, 255049 P.R. China
*e-mail: xiaoyang_qiu@126.com
**e-mail: hailiang_zhu@163.com
Received March 25, 2016
Abstract—A bis-Schiff base N,N'-bis(5-methylsalicylidene)ethane-1,2-diamine (H2L) was prepared and
characterized by elemental analysis, 1H NMR and 13C NMR spectra, MS, and single crystal X-ray diffraction
(CIF file CCDC no. 1022761 (H2L)). Reaction of the Schiff base with copper bromide and sodium dicyano-
amide in methanol gave a novel bromido-, phenolato-, and dicyanoamido-cobridged polymeric copper(II)
complex, ({Cu2LBr[N(CN)2]}2)n (I). Structure of complex I was characterized by elemental analysis and sin-
gle crystal X-ray diffraction (CIF file CCDC no. 1022762 (I)). The smallest repeat unit of complex I is a dicy-
anoamide bridged tetranuclear copper(II) complex moiety, {Cu2LBr[N(CN)2]}2, in which there possesses a
crystallographic inversion symmetry. The tetranuclear moieties are further linked through Br atoms, forming
a zigzag chain. The chains are further linked by dicyanoamide ligands, forming a 2D network. One Cu atom
in complex I is coordinated by two N and two O atoms of the Schiff base ligand and one Br atom, forming
square pyramidal geometry. The other Cu atom is coordinated by two N atoms of the Schiff base ligand, two
N atoms of dicyanoamide ligands, and one Br atom, forming square pyramidal geometry. The bromido-,
phenolato-, and dicyanoamido-cobridged Cu···Cu distances are 4.823(2), 2.955(1), and 7.121(3) Å, respec-
tively. The [Cu2L] units are linked by the bridging groups, to form 2D chains along the xy plane.
Keywords: Schiff base, copper complex, polynuclear complex, crystal structure
DOI: 10.1134/S1070328417050062
INTRODUCTION
dentate Schiff bases derived from salicylaldehyde and
its derivatives with diamines are important in coordi-
nation chemistry. The phenolate oxygen atoms of the
Schiff bases usually act as bridging groups [16–20]. In
the present work, a novel polynuclear complex bearing
simultaneously bromide, phenolate and dicyano-
amide bridging groups, was presented.
Considerable attention has been focused on the
polynuclear copper complexes due to their wide appli-
cations in magnetic fields [1–5]. The preferred way to
construct polynuclear complexes is the use of suitable
bridging groups, such as N–3, NCS–, N(CN)–2 , dicar-
boxylate, 4,4'-bipyridene, etc. [6–10]. Among the
bridging groups, dicyanoamide anion is of great inter-
est for its simple coordination modes:
EXPERIMENTAL
General methods and materials. Starting materials,
reagents and solvents were purchased from commer-
cial suppliers and used as received. Elemental analyses
were performed on a Perkin-Elmer 240C elemental
analyzer. IR spectra were recorded on a Jasco FT/IR-
4000 spectrometer as KBr pellets in the 4000–400 cm–1
region. UV-Vis spectra were recorded on a Perkin-
M
N−
N
N
N
N
N
M
M
M
M
In addition, polynuclear complexes constructed
from halide salts are not uncommon [11–15]. Tetra-
1
Elmer Lambda 900 spectrometer. H and 13C NMR
1
The article is published in the original.
spectra were recorded on a Bruker spectrometer at 300
331

332
QIU et al.
and 75 MHz, respectively. HRMS data was obtained squares method using SHELXTL [23]. All of the non-
with ESI (electrospray ionization) mode. Single crys- hydrogen atoms were refined anisotropically. Hydro-
tal structures were determined by Bruker D8 Venture gen atoms were placed in calculated positions and
single crystal diffraction.
constrained to ride on their parent atoms. The crystal-
lographic data for the complex are summarized in
Table 1. Selected bond lengths and angles are given in
Table 2.
Supplementary material for structure I has been
deposited with the Cambridge Crystallographic Data
Centre (CCDC nos. 1022761 (H2L), 1022762 (I);
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.
ac.uk).
Synthesis of N,N'-bis(5-methylsalicylidene)ethane-
1,2-diamine (H2L). 5-Methylsalicylaldehyde (2.72 g,
0.02 mol) and ethane-1,2-diamine (0.60 g, 0.01 mol)
were mixed in methanol (30 mL). The mixture was
stirred at ambient temperature for 30 min to give yel-
low solution. Then the solvent was evaporated to give
yellow crystalline product with quantitative yield.
IR data (KBr; ν, cm–1): 3439 w, 1636 s, 1586 m,
1491 s, 1371 w, 1282 m, 1231 m, 1157 w, 1037 s, 977 w,
942 w, 827 s, 777 w, 662 w, 567 w, 473 w. UV-Vis data
(methanol; λ, nm (ε, L mol–1 cm–1)): 260 (1.88 × 104),
280 (8.21 × 103), 328 (7.28 × 103). HRMS (ESI): m/z
calcd. for C18H20N2O2 [M + H]+ 297.1598; found:
RESULTS AND DISCUSSION
The Schiff base H2L was readily prepared by the
condensation reaction of 2 : 1 molar ratio of ethane-
1,2-diamine with 5-methylsalicylaldehyde in metha-
nol at ambient condition. The copper complex
was prepared by the one-pot reaction of H2L, copper
bromide and sodium dicyanamide in methanol. Com-
plex I is soluble in methanol, ethanol, DMSO and
DMF. The Schiff base and stable in air at room tem-
perature. Elemental analyses of the compounds are in
good agreement with the components determined by
single crystal X-ray diffraction.
1
297.1593. H NMR (300 MHz; d6-DMSO; δ, ppm):
13.06 (s., 2H), 8.51 (s., 2H), 7.20 (s., 2H), 7.12 (d.,
13
2H), 6.76 (d., 2H), 3.90 (s., 4H), 2.22 (s., 6H). C
NMR (75 MHz; DMSO-d6; δ, ppm): 166.75, 158.21,
133.00, 131.47, 127.10, 118.24, 116.22, 58.92, 19.87.
Yellow block-like single crystals were obtained by slow
evaporation of a methanol solution of the compound.
For C18H20N2O2
The medium and broad absorption at 3439 cm–1 in
the spectrum of H2L substantiates the presence of
anal. calcd., %:
Found, %:
C, 72.9;
C, 73.1;
H, 6.8;
H, 6.7;
N, 9.5.
N, 9.3.
O‒H group. The strong absorption bands at 1636 cm–1
for H2L and 1626 cm–1 for complex I are assigned to
the azomethine groups ν(C=N). The infrared spec-
trum of complex I displays absorption bands at 2313,
2235, and 2171 cm–1, which are attributed to νs +
νas(CN), νas(CN) and νs(CN) modes of the bridging
dicyanamide ligand, respectively [24]. The ligand
coordination to the metal centre is substantiated by
two bands appearing at 552 and 498 cm–1 attributable
to ν(Cu–N) and ν(Cu–O), respectively.
Synthesis of complex I. H2L (0.296 g, 1.0 mmol),
copper bromide (0.223 g, 1.0 mmol) and sodium dicy-
anamide (0.089 g, 1.0 mmol) and were mixed in meth-
anol (30 mL). The mixture was stirred at ambient tem-
perature for 30 min to give blue solution, which was
filtered to avoid minor impurity, and kept still to slow
evaporate of the solvent. A few days later, block-like
single crystals were obtained by filtration. The yield
was 38%.
Electronic spectra of H2L and complex I were
IR data (KBr, ν, cm–1): 1626 s, 1531 m, 1466 m,
1382 m, 1312 m, 1212 w, 1157 w, 1082 w, 967 w, 822 m,
552 w, 498 w. UV-Vis data (methanol; λ, nm (ε, L
mol–1 cm–1)): 230 (2.85 × 104), 275 (1.55 × 104), 367
(6.13 × 103), 560 (538).
recorded in 10–5 M methanol. There are strong bands
centered at 328 nm for H2L and 367 nm for complex I,
which can be assigned to the n–π* transition. The
spectra showed weak and broad d–d electronic transi-
tions at about 560 nm, which are assigned to
2Eg(D) → 2T2g(D) [25]. The broadness of the bands is due
to the ligand field and the Jahn–Teller effects. These
absorptions prefer the distorted octahedral geometry
for the Cu2+ ion. The intense bands observed at about
270–290 nm for H2L and complex I are assigned to
intraligand π–π* transitions.
For C20H18BrN5O2Cu2
anal. calcd., %:
Found, %:
C, 42.3;
C, 42.1;
H, 3.2;
H, 3.3;
N, 12.3.
N, 12.5.
X-ray crystallography. Diffraction intensities for
H2L and complex I were collected at 298(2) K using a
Bruker D8 Venture diffractometer with MoKα radia-
tion (λ = 0.71073 Å). The collected data were reduced
with SAINT [21], and multi-scan absorption correc-
tion was performed using SADABS [22]. Structures of
H2L and the copper complex were solved by direct
The molecular structure of H2L is shown in Fig. 1a.
The compound possesses a crystallographic inversion
center symmetry with the inversion center located at
the midpoint of C(8) and C(8A) atoms (symmetry
code for A: 1 – x, – y, 1 – z). The bond length of C(7)–
N(1) in the Schiff base is 1.276(2) Å, indicating it is a
method and refined against F2 by full-matrix least- typical double bond. The intramolecular O(1)–
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SYNTHESIS AND CRYSTAL STRUCTURES
Table 1. Crystallographic data and structure refinements for H2L and I
333
Value
Parameter
H2L
I
Fw
296.36
Plate; light yellow
0.33 × 0.28 × 0.07
Orthorhombic
Pbca
567.38
Block; blue
0.20 × 0.20 × 0.17
Orthorhombic
Pbca
Crystal shape; colour
Crystal size, mm
Crystal system
Space group
a, Å
7.3233(3)
12.2128(6)
15.4193(7)
22.0274(10)
4148.0(3)
b, Å
6.1007(2)
c, Å
35.4295(11)
1582.9(1)
V, Å3
Z
4
8
μ(MoKα), cm–1
Tmin/Tmax
0.082
4.005
0.9735/0.9943
1.244
0.5014/0.5492
1.817
ρ
calcd, g cm–3
Reflections/parameters
Unique reflections (Rint)
Restraints
1613/102
1303 (0.0208)
0
3862/271
3369 (0.0431)
12
Goodness of fit on F 2
R1 (I ≥ 2σ(I))
1.044
1.040
0.0518
0.1381
0.0295
0.0759
wR2 (I ≥ 2σ(I))
R1 (all data)
0.0611
0.0362
wR2 (all data)
0.1453
0.0802
∆ρmax/∆ρmin, e Å–3
0.186/–0.162
0.602/–0.605
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QIU et al.
Table 2. Selected bond lengths (Å) and angles (deg) for H2L and complex I*
Bond
d, Å
Bond
d, Å
H2L
C(8)–N(1)
C(7)–N(1)
1.276(2)
1.458(2)
I
C(8)–N(1)
C(9)–N(1)
1.273(4)
1.468(4)
1.901(2)
1.908(2)
2.8697(5)
1.988(3)
1.995(2)
C(11)–N(2)
1.273(4)
1.459(4)
1.906(2)
1.9057(19)
1.972(3)
2.042(2)
2.5902(5)
C(10)–N(2)
Cu(1)–N(2)
Cu(1)–O(2)
Cu(2)–N(3)
Cu(2)–O(1)
Cu(2)–Br(1B)
Cu(1)–N(1)
Cu(1)–O(1)
Cu(1)–Br(1)
Cu(2)–N(5)
Cu(2)–O(2)
Angles
ω, deg
Angles
ω, deg
H2L
C(7)N(1)C(8)
118.1(2)
I
C(8)N(1)C(9)
122.6(3)
C(10)N(2)C1(1)
N(1)Cu(1)O(2)
N(1)Cu(1)O(1)
O(2)Cu(1)O(1)
N(2)Cu(1)Br(1)
O(1)Cu(1)Br(1)
N(3)Cu(2)O(2)
N(3)Cu(2)O(1)
O(2)Cu(2)O(1)
N(5)Cu(2)Br(1B)
O(1)Cu(2)Br(1B)
122.2(3)
170.48(10)
95.91(9)
80.25(9)
94.84(8)
96.83(7)
158.32(11)
93.85(10)
75.00(8)
N(1)Cu(1)N(2)
N(2)Cu(1)O(2)
N(2)Cu(1)O(1)
N(1)Cu(1)Br(1)
O(2)Cu(1)Br(1)
N(3)Cu(2)N(5)
N(5)Cu(2)O(2)
N(5)Cu(2)O(1)
N(3)Cu(2)Br(1B)
O(2)Cu(2)Br(1B)
86.43(10)
95.56(9)
167.84(10)
94.97(8)
94.14(7)
88.73(12)
92.85(10)
152.25(10)
98.04(9)
102.45(6)
104.65(9)
102.33(6)
* Symmetry code: (B) –1/2 + x, 1/2 – y, 1 – z.
Table 3. Parameters between the planes for H2L and complex I*
Distance between ring
Perpendicular distance Perpendicular distance
Cg
Dihedral angle, deg
centroids, Å
of Cg(I) on Cg(J), Å
of Cg(J) on Cg(I), Å
H2L
47
47
Cg(1)–Cg(1)i
Cg(1)–Cg(1)ii
4.698
4.834
–2.0695
2.2316
–4.4903
4.6525
I
0
Cg(2)–Cg(2)iii
Cg(2)–Cg(3)iii
Cg(2)–Cg(4)iii
Cg(2)–Cg(6)iii
Cg(3)–Cg(4)iii
Cg(3)–Cg(6)iii
Cg(4)–Cg(4)iii
Cg(4)–Cg(5)iii
Cg(5)–Cg(6)iv
Cg(5)–Cg(6)iii
4.270
4.205
–3.7704
3.7507
3.7349
3.8571
3.4446
3.6359
3.8710
3.7300
–0.4155
3.1046
–3.7704
–3.6290
–3.5891
–3.1099
3.5569
3.0045
3.8710
2.9146
6
8
14
12
16
0
14
73
15
3.9069
4.8676
3.7266
4.3349
4.9532
4.7428
4.8403
–4.7250
3.3412
4.6320
i
ii
iii
iv
* Symmetry codes: 1/2 – x, 1/2 + y, z; 3/2 – x, –1/2 + y, z; –x, 1 – y, –z; 1/2 + x, 1/2 – y, –z. Cg(1) is the centroid of C(1)–
C(2)–C(3)–C(4)–C(5)–C(6) benzene ring of H L. Cg(2), Cg(3), Cg(4), Cg(5) and Cg(6) are the centroids of Cu(1)–N(1)–C(9)–
2
C(10)–N(2), Cu(1)–O(1)–C(2)–C(1)–C(8)–N(1), Cu(1)–O(2)–C(13)–C(12)–C(11)–N(2), C(1)–C(2)–C(3)–C(4)–C(5)–C(6),
and C(12)–C(13)–C(14)–C(15)–C(16)–C(17), respectively.
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SYNTHESIS AND CRYSTAL STRUCTURES
335
(a)
O(1A)
C(2A)
C(9)
C(5)
C(1A)
N(1A)
C(3A)
C(4A)
C(7)
C(8)
C(6)
C(4)
C(8A)
C(6A)
C(7A)
N(1)
C(5A)
C(1)
C(3)
C(9A)
C(2)
O(1)
(b)
C(7)
C(6)
Cu(2B)
C(19)
N(4)
Br(1)
C(8)
C(1)
C(5)
Cu(1B)
C(4)
C(3)
C(2)
C(9)
N(1)
C(10)
N(3)
O(1)
N(2)
Cu(1)
Cu(2)
O(2)
N(5)
C(11)
C(20)
C(12)
C(14)
C(13)
Br(1A)
Cu(1A)
C(17)
C(16)
C(15)
C(18)
Cu(2A)
Fig. 1. A perspective view of the molecular structures: H L (a), I (b) with the atom labeling scheme. Thermal ellipsoids are drawn
2
at the 30% probability level. The symmetry positions: (A) 1 – x, –y, 1 – z for H L and (A) –x, 1 – y, 1 – z; (B) –1/2 + x, 1/2 –
2
y, 1 – z for I. Hydrogen bonds for H L are shown as dashed lines.
2
H(1)···N(1) hydrogen bonds (O(1)–H(1) 0.82, has a separation of 7.121(3) Å. The distance between
H(1)···N(1) 1.88, O(1)···N(1) 2.610(2) Å, O(1)–
H(1)···N(1) 148°) in the Schiff base molecule make
S(6) ring motifs [26]. Moreover, there exists π···π
interactions (Table 3) in the crystal packing (Fig. 2a).
The molecular structure of complex I is shown in
Fig. 1b. The Schiff base ligand coordinates to the Cu
atoms through the phenolate O and imino N atoms.
The phenolate O atoms act as bridging groups, coordi-
nating to two different Cu atoms. The dihedral angle
between the two benzene rings is 15.9(3)°. The small-
est repeat unit of complex I is a dicyanamide bridged
Cu(1) and Cu(2) atoms is 2.955(1) Å. The Cu(1) atom
is in a square pyramidal coordination with the basal
plane defined by two phenolate O and two imino N
atoms of the Schiff base ligand and with the apical
position occupied by a Br atom. The square pyramidal
geometry is slightly distorted, as evidenced by the
bond lengths and angles related to Cu(1) atom. The
bond lengths in the basal plane are within 1.90–
1.91 Å, and the bond angles within the basal plane are
in the range 80.25(9)°–95.91(9)°. The deviation of the
basal angles from the ideal value of 90° is mainly
caused by the strain created by the four-membered
tetranuclear
copper(II)
complex
moiety,
{Cu2LBr[N(CN)2]}2, in which there exists a crystallo- chelate ring Cu(1)–O(1)–Cu(2)–O(2) and the five-
membered chelate ring Cu(1)–N(1)–C(9)–C(10)–
N(2). The bond angles among the apical and the basal
graphic inversion symmetry. The inversion center is
located at the midpoint of the Cu(2) and Cu(2A)
atoms (symmetry code for A: –x, 1 – y, 1 – z) which donor atoms are range from 94.14(7)° to 96.83(7)°.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 43 No. 5 2017

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QIU et al.
(a)
x
z
0
y
(b)
0
z
y
x
Fig. 2. Molecular packing diagrams: H L along the x axis (a), I along the z axis (b). Hydrogen bonds for H L are shown as dashed
2
2
lines. Hydrogen atoms for I and hydrogen atoms unrelated to hydrogen bonding for H L are omitted for clarity.
2
The Cu(1) atom deviates from the least-squares plane coordinate bond lengths in complex I are comparable
defined by the four basal donor atoms by 0.172(2) Å.
The Cu(2) atom is also in a square pyramidal coordi-
nation with the basal plane defined by two phenolate
O atoms of the Schiff base ligand and two N atoms of
the dicyanamide ligands and with the apical position
occupied by a Br atom. The square pyramidal geome-
try is somewhat distorted, as evidenced by the bond
lengths and angles related to the Cu(2) atom. The
bond lengths in the basal plane are within 1.97–
2.05 Å, and the bond angles within the basal plane are
in the range 75.00(8)°–93.85(10)°. The deviation of
the basal angles from the ideal value of 90° is mainly
caused by the strain created by the four-membered
chelate ring Cu(1)–O(1)–Cu(2)–O(2). The bond
angles among the apical and the basal donor atoms are
range from 98.04(9)° to 104.65(9)°. The Cu(2) atom
deviates from the least-squares plane defined by the
to those observed in the copper(II) complexes with
Schiff bases [27–29].
The tetranuclear moieties are further linked
through Br bridging atoms, forming a zigzag chain.
The bromido-bridged Cu···Cu distance is 4.823(2) Å.
The chains are further linked by dicyanamide ligands,
forming a two-dimensional network (Fig. 2b). In
addition, crystal of the complex is stabilized by π···π
interactions (Table 3).
ACKNOWLEDGMENTS
This work was financially supported by K.C. Wong
Magna Fund in Ningbo University, and the Open
Laboratory Program of Liaoning Normal University
four basal donor atoms by 0.410(2) Å. In general, the (project no. cx20160102).
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SYNTHESIS AND CRYSTAL STRUCTURES
337
15. Tsui, E.Y., Day, M.W., and Agapie, T., Angew. Chem.
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