Synthesis, crystal structure, and electroluminescent properties of zinc and cadmium tetradentate azomethine complexes

Article abstract of DOI:10.1134/S0036023614070031

Chemical and electrochemical syntheses of zinc(II) and cadmium(II) complexes based on tetradentate Schiff bases (H₂L¹ and H₂L²) resulting from condensation of 2- tosylaminobenzaldehyde with 3,6-dioxa-1,8-octanediamine or 4,9-dioxa-1,12- dodecanediamine were performed. The structure, composition, and properties of the complexes were studied by elemental analysis, IR, ¹H NMR, and UV spectroscopy, X-ray absorption spectroscopy, and X-ray diffraction. The zinc(II) and cadmium(II) complexes luminesce in a DMF solution in the blue spectral region (λ_PL = 425-433 nm), the photoluminescence quantum yield φ being 0.25-0.30. Multilayer zinc(II)- and cadmium(II)-based electroluminescent structures with green-blue emission of the exciplex nature were fabricated.

Full text of DOI:10.1134/S0036023614070031

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2014, Vol. 59, No. 7, pp. 721–732. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © A.S. Burlov, V.G. Vlasenko, D.A. Garnovskii, N.V. Polosareva, A.S. Antsyshkina, G.G. Sadikov, V.S. Sergienko, A.V. Churakov, Ya.V. Zubavichus,
E.I. Mal’tsev, A.V. Dmitriev, D.A. Lypenko, A.S. Cheprasov, G.S. Borodkin, A.V. Metelitsa, 2014, published in Zhurnal Neorganicheskoi Khimii, 2014, Vol. 59, No. 7, pp. 934–946.
Synthesis, Crystal Structure, and Electroluminescent Properties
of Zinc and Cadmium Tetradentate Azomethine Complexes
A. S. Burlova, V. G. Vlasenkob, D. A. Garnovskiia, c, N. V. Polosarevaa, A. S. Antsyshkinad,
G. G. Sadikovd, V. S. Sergienkod, A. V. Churakovd, Ya. V. Zubavichuse, E. I. Mal’tsevf,
A. V. Dmitrievf, D. A. Lypenkof, A. S. Cheprasova, G. S. Borodkina, and A. V. Metelitsaa
a Research Institute of Physical and Organic Chemistry, Southern Federal University,
pr. Stachki 194/2, RostovꢀonꢀDon, 344090 Russia
b Research Institute of Physics, Southern Federal University, pr. Stachki 194, RostovꢀonꢀDon, 344090 Russia
c Southern Scientific Center, Russian Academy of Sciences, ul. Chekhova 41, RostovꢀonꢀDon, 344006 Russia
d Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 117907 Russia
e National Research Centre “Kurchatov Institute”, pl. Akademika Kurchatova 1, Moscow, 123182 Russia
f Frumkin Institute of Electrochemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow, 117071 Russia
eꢀmail: anatoly.burlov@yandex.ru
Received February 17, 2014
Abstract—Chemical and electrochemical syntheses of zinc(II) and cadmium(II) complexes based on tetꢀ
radentate Schiff bases (H2L1 and H2L2) resulting from condensation of 2ꢀtosylaminobenzaldehyde with
3,6ꢀdioxaꢀ1,8ꢀoctanediamine or 4,9ꢀdioxaꢀ1,12ꢀdodecanediamine were performed. The structure, compoꢀ
sition, and properties of the complexes were studied by elemental analysis, IR, 1H NMR, and UV spectrosꢀ
copy, Xꢀray absorption spectroscopy, and Xꢀray diffraction. The zinc(II) and cadmium(II) complexes lumiꢀ
nesce in a DMF solution in the blue spectral region (λPL = 425–433 nm), the photoluminescence quantum
yield
ϕ being 0.25–0.30. Multilayer zinc(II)ꢀ and cadmium(II)ꢀbased electroluminescent structures with
greenꢀblue emission of the exciplex nature were fabricated.
DOI: 10.1134/S0036023614070031
Since in 1987, Tang and van Slyke [1] designed the compound show brightness of >750 cd/m2 and a turnꢀ
first bilayer organic lightꢀemitting diodes (OLED) on threshold voltage of 4.5 V.
using tris(8ꢀhydroxyquinolinato)aluminum as the
This study is devoted to the synthesis of new
emitting layer, the interest in the synthesis and studies
zinc(II) and cadmium(II) complexes with tetradenꢀ
of metal complexes as electroluminescent organic
tate azomethine ligands formed upon condensation of
materials has not declined [1, 2]. Zinc(II) and cadꢀ
2ꢀtosylaminobenzaldehyde with 3,6ꢀdioxaꢀ1,8ꢀ
mium(II) complexes with tetradentate azomethine
octanediamine or 4,9ꢀdioxaꢀ1,12ꢀdodecanediamine
ligands based on 2ꢀhydroxybenzaldehyde belong to
(
H2L1, H2L2, see the scheme). These complexes have
this type of electroactive metalꢀcontaining luminoꢀ
phores [3–14]. They are synthetically accessible, have
suitable photoluminescent (PL) and electroluminesꢀ
cent (EL) properties, can be readily modified for optiꢀ
mization of characteristics, and form homogeneous
thin films upon thermal vacuum evaporation. The
OLED devices containing zinc chelates with tetradenꢀ
tate Schiff bases as the luminescence centers emit in
the shortꢀwavelength region (λPL = 440–510 nm) and
show brightness of >1400 cd/m2 at a 16 V voltage [3].
high fluorescence quantum yields and may serve as
lightꢀemitting materials for OLED devices. The
replacement of the hydroxy group by a 2ꢀtosylamino
group in the azomethine molecule results in the forꢀ
mation of metal chelates of these ligands with the MN4
coordination unit, which is expected to affect their
structure and PL and EL properties [13–15].
EXPERIMENTAL
[N,N'ꢀbis(salicylidene)ꢀ3,6ꢀdioxaꢀ1,8ꢀdiaminoctanꢀ
ate monohydrate]zinc(II) with the ZnN2O2 coordinaꢀ
tion unit with blue emission was synthesized and charꢀ
acterized by Xꢀray diffraction [10, 11]. The OLED
2ꢀTosylaminobenzaldehyde was prepared by a
reported procedure [16]; 3,6ꢀdioxaꢀ1,8ꢀoctanediꢀ
amine and 4,9ꢀdioxaꢀ1,12ꢀdodecanediamine were
devices with electroluminescent layer based on this commercial chemicals (Alfa Aesar).
721

722
BURLOV et al.
CH3
CH3
H3C
H3C
SO2
SO2
N
O2S
O2S
N
NH HN
M
N
N
N
N
n(CH2)
n(CH2)
(CH2)n
(CH2)n
O
O
O
O
(CH2)m
(CH2)m
= 2 (III
= 4 (IV
n
n
=
= 3,
m
)
n
n
=
m
= 2 H2L1 (
I)
m
)
= 3, m = 4 H2L2 (II
)
M = Zn(II) (
a
), Cd(II) (b)
Scheme.
Azomethines
I and II were prepared by condensaꢀ tion of I or II (0.5 mmol) in 20 mL of acetonitrile and
tion of 2ꢀtosylaminobenzaldehyde and the appropriꢀ [Et4N]ClO4 (0.01 g) as the supporting electrolyte.
ate amines.
'ꢀbis(2ꢀtosylaminobenzal)ꢀ3,6ꢀdioxaꢀl,8ꢀoctaneꢀ
Electrosynthesis was conducted at a current of 40 mA
and a voltage of 20 V for 1 h at room temperature. The
precipitated complexes were filtered off and recrystalꢀ
lized from a methanol–chloroform mixture (2 : 1).
N,N
diamine (I). 1,8ꢀDiaminoꢀ3,6ꢀdioxaoctane (0.148 g,
1 mmol) in 10 mL of anhydrous toluene was added to
a solution of 2ꢀtosylaminobenzaldehyde (0.55 g, 2 mmol)
in 30 mL of anhydrous toluene. The mixture was
refluxed for 2 h, and the precipitate was filtered off
and recrystallized from an ethanol–chloroform mixꢀ
ture (2 : 1).
N,N'ꢀbis(2ꢀtosylaminobenzal)ꢀ4,9ꢀdioxaꢀ1,12ꢀdodeꢀ
canediamine (II) was prepared in a similar way from
2ꢀtosylaminobenzaldehyde (0.55 g, 2 mmol) and
4,9ꢀdioxaꢀ1,12ꢀdodecaneamine (0.298 g, 1 mmol).
Cathode (Pt): LH2 + 2e
Anode: (Zn0 or Cd0) M– 2e
Solution: L2– + M2+
ML· solvent
The elemental analysis data for compounds
IIIa IIIb, and IV are summarized in Table 1.
→
L–2 + H2
M2+ (M is Zn, Cd).
.
→
→
I, II,
,
C,H,N elemental analysis was carried out on a
TCM 480 Carlo Erba instrument.
The IR spectra of samples as KBr pellets were
recorded on a Varian 3100ꢀFTIR Excalibur instruꢀ
ment in the 4000–400 cm–1 range by the frustrated
total internal reflection method.
1H NMR spectra were run on a Varian Unity 300
spectrometer operating at 300 MHz in the internal staꢀ
bilization mode at the 2H polar line in DMSOꢀd6 at
The (a) Zn(II) and (b) Cd(II) complexes (IIIa
,
IIIb, and IV) were prepared by chemical and electroꢀ
chemical procedures.
Chemical Synthesis
20°С.
Zinc and cadmium
N,N'ꢀbis(2ꢀtosylaminobenzal)ꢀ
Electronic absorption (UV/Vis) spectra were meaꢀ
sured on Varian Cary 100 and Varian Cary 50 spectroꢀ
photometers in acetonitrile.
3,6ꢀdioxaꢀl,8ꢀoctanediaminates (IIIa, IIIb). A soluꢀ
tion of zinc acetate dihydrate (0.11 g, 0.5 mmol) or
cadmium acetate dihydrate (0.13 g, 0.5 mmol),
respectively, in 5 mL of methanol was added to a soluꢀ
Xꢀray absorption spectroscopy. The Zn
Kꢀedge
tion of I (0.33 g, 0.5 mmol) in 20 mL of ethanol. The
absorption spectra of solid complexes IIIa and IV were
recorded in the transmission mode on a EXAFS specꢀ
trometer at the “Structural Material Science” station
of the Kurchatov Synchrotron Center (Moscow) [17].
The energy of the electron beam used as the source of
synchrotron Xꢀray radiation was 2.5 GeV at a current
of 80–100 mA. The Xꢀray radiation was monochroꢀ
matized using a double crystal Si(111) monochromaꢀ
tor. The spectra were treated by standard background
mixture was refluxed for 2 h. The precipitate that
formed on cooling was filtered off, washed two times
with 2 mL of methanol, and recrystallized from a
methanol : chloroform mixture (2 : 1).
Zinc
1,12ꢀdodecanediaminate (IV) was prepared from II
similarly to complexes IIIa and IIIb
N,N'ꢀbis(2ꢀtosylaminobenzal)ꢀ4,9ꢀdioxaꢀ
.
subtraction procedures, normalization to the
jump, and subtraction of the atomic absorption µ0 folꢀ
An electrochemical cell with a platinum cathode lowed by Fourier Transformation of the resulting
and a zinc (cadmium) anode was charged with a soluꢀ EXAFS ( )ꢀspectra in the photoelectron wave vector
Kꢀedge
Electrochemical Synthesis
χ
k
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 7 2014

SYNTHESIS, CRYSTAL STRUCTURE, AND ELECTROLUMINESCENT PROPERTIES
Table 1. Data of elemental analysis and some physicochemical properties of IIIb and IV
Content found/calculated, %
723
Compound
Molecular formula
mp, °C
Yield, %
C
H
N
M
H2L1,
H2L2, II
I
C34H38N4O6S2
C38H46N4O6S2
C35H40N4O7S2Zn
61.82/61.61 5.64/5.78 8.32/8.45
63.52/63.49 6.32/6.45 7.82/7.79
–
–
134–135
89–90
>300
80
96
ZnL1
⋅
CH3OH, III
a
55.52/55.44 5.43/5.32 7.41/7.39 8.57/8.62
85
95
CdL1
⋅
CHCl3, III
b
C35H37Cl3N4O6S2Cd 47.24/47.10 4.15/4.18 6.34/6.28 12.32/12.59 >300
C38H44N4O6S2Zn 58.42/58.34 5.70/5.67 7.26/7.16 8.40/8.36 >300
70
82
ZnL2, IV
a
85
90
range of 3.0–13.0 Å–1 with the weight function k3. The
Xꢀray diffraction. The structures were calculated
resulting Fourier Transform moduli (FTM) repreꢀ using the SHELXLꢀ97 program package [24]. The key
sented pseudoradial distribution of atoms of the nearꢀ data collection details and crystallographic parameters
est coordination shells (CS) around the absorbing of complexes IIIa and IIIb are summarized in Table 2.
metal atom, the radii of the CS being determined to an The compounds are deposited with the CCDC as
accuracy of phase corrections. The threshold ionizaꢀ No. 984137 (IIIa) and No. 984138 (IIIb).
tion energy E0 was chosen based on the maximum of
the first derivative of the ꢀedge spectra and was subꢀ
Fabrication and study of the OLED structures. The
OLED structures were formed and studied under inert
atmosphere (Ar) in a closed laboratory complex of the
Frumkin Institute of Electrochemistry, which comꢀ
prised equipment for manufacture of multilayer lightꢀ
emitting diode structures and measuring instrumentaꢀ
tion to record the spectral and electric characteristics.
The successive deposition of functional layers made use
of the cast technique on a centrifuge (1500–6000 rpm)
K
sequently varied during fitting. The accurate values of
the structural parameters of the local environment of
zinc ions were determined by nonꢀlinear fitting of the
CS parameters by comparing the calculated EXAFS
signal and the FTM isolated from the full EXAFS
spectrum by Fourier filtration. This nonꢀlinear fitting
was carried out using the IFFEFITꢀ1.2.11 program
package [18]. The scattering phase and amplitude of
the photoelectron wave needed to construct the model
spectrum were calculated using the FEFF7 program
[19] and atomic coordinates of compounds with simiꢀ
and thermal vacuum evaporation (2 ×
10–6 mbar) with
a precision control of the deposition rate (up to 1 Å/s)
and thickness. The transparent electrode surfaces
(
In2O3/SnO2 on glass as the anode) were prepared by
lar atomic structure. The goodnessꢀofꢀfit function Q,
standard purification procedures: successive ultraꢀ
sonic treatment in acetone, isopropyl alcohol, and
deionized water. At the final stage, the surface was
treated with oxygen plasma. The voltammetric characꢀ
teristics were measured using a SoursMeter Keithley 260
measuring source.
which was minimized to find the structural parameters
of the local environment, was calculated from the forꢀ
mula:
2
kχ (k) − kχ (k)
[
]
exp
th
∑
Q(%) =
×100.
2
Electroluminescence spectra were recorded on an
AvaSpec 2048 spectrofluorimeter (spectral range 200–
1100 nm, optical resolution from 0.04 nm).
kχ (k)
[
]
exp
∑
The quantum chemical calculations for the molecuꢀ
lar geometry of IIIa and IIIb in the ground state were
Fluorescence spectra were recorded on a Varian
performed using GAUSSIANꢀ03 program package Cary Eclipse spectrofluorimeter (spectral range 200–
[20] in the density functional theory (DFT) approxiꢀ 900 nm). The fluorescence quantum yields were deterꢀ
mation. The B3LYP threeꢀparameter hybrid funcꢀ mined using quinine sulfate luminophore standard
tional [21, 22] and the 6ꢀ31G(d) standard splitꢀ (0.1 N H2SO4,
ϕ = 0.55).
valence polarized basis set [23] were chosen.
The thicknesses were verified by interference
(MIIꢀ4M) and atomic force microscopes (Nanoꢀ
scopeꢀIV).
The UV/Vis absorption spectra for the molecules
were calculated by timeꢀdependent DFT (TDꢀDFT)
method using optimized atomic structure parameters
taking into account the solvent effect. The functional
and the basis set for the calculation of the UV/Vis
spectra were the same as used for the calculation of the
molecular geometry.
RESULTS AND DISCUSSION
Tetradentate azomethine compounds
prepared by condensation of 2ꢀtosylaminobenzaldeꢀ
I and II were
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 7 2014

724
BURLOV et al.
Table 2. Crystallogrphic parameters and Xꢀray experiment details for IIIa and IIIb
Compound IIIa
Chemical formula CH3OH
758.23
IIIb
CdL1
CHCl3
892.59
ZnL1
⋅
⋅
FW
color, habit
crystal dimensions
Temperature, K
System
colorless plates
0.40
×
0.40
×
0.30
0.35 × 0.35 × 0.10
150
Triclinic
Space group
Pꢀ1
a
b
, Å
, Å
11.3173(5)
12.4725(6)
12.9171(6)
79.780(1)
75.634(1)
81.581(1)
1728.2(2)
2
11.5989(5)
12.5302(6)
14.4530(8)
66.548(1)
85.773(1)
78.151(1)
1885.9(1)
2
c
α
β
γ
, Å
, deg
, deg
, deg
V
Z
, Å3
ρcalcd, g/cm3
1.451
0.886
786
1.572
1.141
908
μ
F
, cm–1
(000)
Diffractometer
Radiation
Bruker ApexꢀI I CCD
MoKα (0.71073), graphite monochromator
1.65/30.52 1.54/30.57
θ
, deg
The ranges of indices
–16
–16
–18
≤
≤
≤
h
k
l
≤
≤
≤
16
17
18
–16
–17
–20
≤
≤
≤
h
k
l
≤
≤
≤
16
17
20
The number of measured reflections
The number of independent reflections
The number of reflections with I > 2σ(I)
The number of refined parameters
GOOF on F2
18695
10055
8411
590
20473
11013
8984
608
1.000
0.836
R
[
I
> 2
σ
(
I
]
R
1 = 0.0408
wR2 = 0.1285
1 = 0.0502
R
1 = 0.0395
wR2 = 0.1096
1 = 0.0511
R
(for all reflections)
R
R
wR2 = 0.1537
0.283, 0.013
wR2 = 0.1244
0.857, 0.026
Δρmax and Δρmin, e/Å3
hyde and the corresponding diamines in toluene.
ν
(CH=N) absorption frequencies of the ligands (1638
Metal complexes IIIa,
IIIb, and IV were synthesized and 1634 cm–1) slightly decrease upon complexation
by two procedures: chemical synthesis using metal (to 1629–1636 cm–1) and the νasSO2 and νsSO2 freꢀ
acetates and electrochemical synthesis with sacrificial quencies also decrease. The H NMR spectra of zinc
1
metal anode in an acetonitrile solution of azomethines
and II
I
and cadmium complexes IIIa, IIIb, and IV in DMSOꢀ
.
d6 no longer contain NH proton signals, while the
CH=N proton signals slightly (by 0.1 ppm) shift
downfield (Table 3). This spectral behavior indicates
that the ligands are doubly deprotonated and form
chelates.
The IR spectra of
I
and II (Table 3) exhibit a broad
absorption band at 2700–3150 cm–1 corresponding to
stretching vibrations of the NH groups linked by a
1
strong intramolecular hydrogen bond. The H NMR
spectra (DMSOꢀd6) of compounds
broadened signals for NH protons at 13.06 (
13.25 (II) ppm, and the CH=N proton signals occur at
8.36 ( ) and 8.44 (II) ppm.
I
and II show
The atomic structure of complexes IIIa and IIIb
I
) and was determined by Xꢀray diffraction.
The local atomic structure of complexes IIIa and
IV was studied by Xꢀray absorption spectroscopy
I
According to elemental analysis data, complexes IIIa (XANES and EXAFS techniques). Quantum chemiꢀ
and IIIb have the composition ML · solvent, and the cal calculations in the density functional theory
composition of IV is ML (Table 1). The IR spectra of approximation made it possible to compare the experꢀ
the complexes no longer exhibit the ν(NH) bands. The imentally determined atomic structure characteristics
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 7 2014

SYNTHESIS, CRYSTAL STRUCTURE, AND ELECTROLUMINESCENT PROPERTIES
725
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 7 2014

726
BURLOV et al.
(а)
(b)
C(35)
C(31)
C(31)
O(5)
C(32)
O(6)
O(7)
C(32)
O(6)
O(5)
C(30)
C(29)
C(30)
C(29)
C(33)
C(34)
C(3)
C(16)
C(33)
C(7)
C(4)
C(34)
N(2)
C(2)
C(17)
C(15)
N(2)
N(3)
Cd(1)
C(14)
C(15)
C(16)
C(7)
C(14)
C(3)
C(17)
C(2)
N(3)
C(18)
C(4)
C(20)
C(5)
C(1)
C(19)
O(2)
C(18)
C(20)
C(19)
C(6)
O(4)
C(8)
Zn(1)
N(1)
S(1)
N(4)
N(1)
C(1)
N(1)
C(5)
S(1)
O(2)
C(6)
O(4)
C(6)
C(35)
Cl(2)
O(3)
S(2)
C(9)
O(1)
S(2)
C(21)
O(1)
C(21)
Cl(1)
Cl(3)
O(3)
C(22)
C(23)
C(24)
C(27)
C(9)
C(26)
C(25)
C(26)
C(13)
C(12)
C(28)
C(22)
C(13)
C(10)
C(11)
C(25)
C(24)
C(10)
C(11)
C(28)
C(23)
C(27)
C(12)
(c)
0
C(27)
C(24)
a
C(16)
C(34)
C(33)
O(3)
C(
O(4)
O(6)
C(17)
C(23)
C(18)
S(1)
C(15)
C(20)
C(26)
C(13)
C(32)
Cd(1)
C(21)
C(22)
S(2)
C(8)
C(12)
C(19)
N(4)
O(1)
C(1) C(6)
C(31)
N(1)
C(9)
C(11)
C(10)
C(30)
O(5)
N(2)
C(29)
C(5)
C(4)
O(2)
C(28)
C(2)
C(7)
b
C(3)
Cl(3)
C(35)
Cl(1)
Cl(2)
c
Cd(1B)
Fig. 1. Configuration of molecules (a) IIIa and (b) IIIb and (c) packing of the CdL and CHCl solvent molecules in the unit cell
3
of IIIb
.
of the molecules with the theoretically calculated virtually no influence on the structure of the complexes
parameters of the molecules in the equilibrium state.
but affect the packing of molecules in the unit cell.
According to Xꢀray diffraction data, the complex
molecules ML in IIIa and IIIb are constructed in the
same way. The configurations of the molecules are
shown in Figs. 1a and 1b. The packing of CdL and
CHCl3 solvent molecules in the unit cell of IIIb is
depicted in Fig. 1c.
In molecules IIIa and IIIb, the macrocyclic ligand
is coordinated to the metal atom in the tetradentate
chelating fashion by four nitrogen atoms to give a
coordination tetrahedron (the dihedral angles formed
by the planar N(1)ZnN(2) and N(3)CdN(4) fragꢀ
ments are 77.5° in IIIa and 82.0 in IIIb). Two sixꢀ
The Zn–N bond lengths in IIIa are 1.982(2), membered rings coupled at the M–N(3) bond and an
2.034(2), 2.031(2), and 1.992 Å. In IIIb, the correꢀ elevenꢀmembered metal ring are closed upon coordiꢀ
sponding bonds are much longer (2.217(2), 2.249(2), nation. Each sixꢀmembered chelate ring is conjuꢀ
2.259(2), 2.195(2) Å) in accordance with the increase gated with the corresponding benzene ring to form a
in the metal atomic radius:
1.99 Å. The solvent molecules incorporated in the group forms a dihedral angle of 57.6° with the “own”
compounds, СН3ОН IIIa) and НССl3 IIIb), have metal ring Zn(1)N(3)C(14)C(15)C(20)N(4) and a
r(Zn) is 1.83 Å and r(Cd) is nearly planar system. The triangular O(1)S(1)O(2)
(
(
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 7 2014

SYNTHESIS, CRYSTAL STRUCTURE, AND ELECTROLUMINESCENT PROPERTIES
727
C(31)
N(2)
C(32)
O(5)
C(32)
O(6)
C(33)
C(30)
O(5)
C(33)
C(29)
C(31)
Cd(1)
O(6)
C(29)
C(34)
C(34)
N(2)
C(30)
N(3)
Cd(1)
N(3)
Fig. 2. View of the elevenꢀmembered fragments in the structures of IIIa and IIIb
.
(a)
Zn
(b)
0.3
0.2
0.1
0
Kꢀedge
1.0
0.5
0
9650
9670
9690
E, eV
9710
9730
9660 9680 9700 9720 9740 9760
, eV
E
Fig. 3. (a) Zn
Kꢀedge Xꢀray absorption spectra, (b) first derivatives of the Kꢀedge spectra for complexes: (continuous line) IIIa
and (dashed line) IV
.
dihedral angle of 91.6° with the toluene ring
C(21)C(22)C(23)C(24)C(25)C(26). A similar fragꢀ
ment, O(3)SO(4), forms a dihedral angle of 31.8° with
the Zn(1)N(2)C(7)C(2)C(1)N(1) metal ring and
69.4° with the C(8)C(9)C(10)C(11)C(12)C(13) toluꢀ
ene ring.
Quantum chemical calculations of the molecular
geometry in the equilibrium state gave the bond
lengths and bond angles that were in good agreement
with Xꢀray diffraction data. The optimized parameters
(selected bond lengths and bond angles) of molecules IIIa
and IIIb are given in Table 4 in comparison with the Xꢀ
ray diffraction data. As can be seen in Table 4, the calꢀ
culated distances for IIIa differ from the experimental
crystallographic data by not more than 1%.
The elevenꢀmembered metal rings of the dioxadiꢀ
amine fragment incorporated in complex molecules IIIa
and IIIb have nonꢀplanar conformation and contain
no multiple bonds. Two orthogonal projections of the
ring are shown in Fig. 2. The metal rings are pseudoꢀ
centrosymmetrical provided that the C(31)–C(32)
group is opposed by the metal atom. The presence of
the metal brings about considerable ring deformation.
The torsion angles involving the metal occur in the
Meanwhile, for complex IIIb, the DFTꢀcalculated
values are somewhat greater than the data from Xꢀray
crystallography (by about 0.08 Å). This result can be
attributed to the fact that the basis set used was not
adjusted to cadmium ion. The theoretical and experiꢀ
mental bond angles and dihedral angles for IIIa and
IIIb differ by not more than 1° to 3°.
gauche
–
gauche
–
gauche conformation, while the
trans–gauche and
Analysis of the Zn Kꢀedge Xꢀray absorption spectra
other angles are in the gauche
–
(XANES and EXAFS) for complexes IIIa and IV (for
the latter, we did not manage to grow single crystals
suitable for Xꢀray diffraction) provided data on the
local atomic structures of zinc in these compounds.
gauche–gauche–trans conformations.
In both structures, the complexes form planar layꢀ
ers, the solvent molecules being located between the
layers. The replacement of methanol by a larger chloꢀ
roform molecule does not change fundamentally the
structural parameters, only some increase in the interꢀ
layer spacing being observed.
Figure 3 shows the Zn
tra and the first derivatives of the
K
ꢀedge Xꢀray absorption specꢀ
Kꢀedge spectra for
complexes IIIa and IV. The form of XANES and espeꢀ
cially of the first derivatives of XANES consisting of
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 7 2014

728
BURLOV et al.
Table 4. Optimized parameters of the structures of zinc and cadmium complexes IIIa and IIIb
Complexes
method
IIIa, M = Zn
IIIb, M = Cd
DFT
Xꢀray diffraction
DFT
Xꢀray diffraction
Bond lengths, Å
2.006(2)
2.044(4)
2.052(1)
2.006(6)
2.673(5)
2.659(4)
Bond angles, deg
92.6(2)
M(1)–N(1)
M(1)–N(2)
M(1)–N(3)
M(1)–N(4)
M(1)–O(1)
M(1)–O(3)
1.984(2)
2.030(2)
2.036(2)
1.991(2)
2.622(2)
2.756(2)
2.303(8)
2.334(8)
2.353(5)
2.298(7)
2.473(5)
2.465(4)
2.218(2)
2.248(2)
2.258(2)
2.195(2)
2.665(2)
2.653(2)
N(1)M(1)N(2)
N(2)M(1)N(3)
N(3)M(1)N(4)
N(1)M(1)N(4)
N(1)S(2)C(8)
N(4)S(1)C(2)(1)
N(2)C(34)C(33)
C(33)O(6)C(32)
C(32)C(31)O(5)
O(5)C(30)C(29)
C(30)C(29)N(2)
93.6(2)
111.2(2)
92.9(2)
80.3(9)
110.7(7)
79.5(4)
84.4(8)
111.4(4)
84.1(8)
114.5(6)
92.4(7)
143.4(3)
107.6(9)
107.0(2)
112.1(4)
114.1(1)
112.2(2)
108.1(1)
111.3(1)
143.1(2)
104.1(1)
109.6(3)
111.0(1)
113.7(1)
110.9(1)
107.1(1)
109.8(1)
157.5(8)
108.4(8)
107.4(9)
111.9(3)
114.0(7)
112.9(7)
108.0(3)
111.0(9)
147.5(7)
107.8(1)
106.7(1)
111.7(1)
112.2(1)
111.0(1)
107.7(1)
110.3(1)
Dihedral angles, deg
N(1)C(1)C(2)C(7)N(2)–N(3)C(14)C(15)C(20)N(4)
N(3)C(14)C(15)C(20)N(4)–C(15–20)
N(1)C(1)C(2)C(7)N(2)–C(1–6)
75.9
2.2
4.3
77.9
8.9
3.7
80.1
6.1
2.6
82.7
11.1
2.7
two broadened maxima is typical of complexes with a ilar structural parameters of the local environment in
tetrahedral environment of the absorbing atom. In Zn these complexes. The zinc ion is surrounded by four
K
ꢀedge XANES spectra of IIIa and IV, preꢀedge nitrogen atoms located an average distance of 2.02
structure A is virtually missing due to the fully occuꢀ IIIa) and 2.05 Å (IV). These distances are in good
pied shell of zinc(II).
Å
(
3d
agreement with Xꢀray diffraction data for IIIa (Zn–N,
2.01 Å) and DFT data (Zn–N, 2.03 Å). The Debye–
Waller factors for the nearest CS are somewhat greater
than the typical values but this increase can be attribꢀ
uted to averaging of the Zn–N bonds in singleꢀshell
fitting.
The quantitative characteristics of the local atomic
environment of IIIa and IV were derived from analysis
of the Zn Kꢀedge EXAFS spectra of these compounds.
It can be seen from Fig. 4 that all EXAFS FTM consist
of a principal peak of about = 1.60 Å, which unamꢀ
r
biguously corresponds to scattering in the nearest CS
consisting of ligand nitrogen atoms, and peaks at
greater distances corresponding to scattering on the
subsequent CS.
The parameters of zinc atomic environment in IIIa bathochromically with respect to those of azomethines
and IV calculated for selection of the appropriate and II
models of the coordination unit (Table 5) attest to simꢀ
The UV/Vis and PL spectra of azomethines
zinc and cadmium complexes IIIa IIIb, and IV were
studied (Table 3). The UV/Vis absorption bands of
complexes IIIa IIIb, and IV in acetonitrile are shifted
I, II,
,
,
I
.
To interpret the UV/Vis absorption bands of zinc
and cadmium complexes IIIa and IIIb, quantum
chemical calculations were carried out for the excited
states of these molecules. Figure 5 showed the simuꢀ
lated UV/Vis spectra in comparison with the experiꢀ
mental data. The experimental UV/Vis spectra exhibit,
in the 200–400 nm range, a broad absorption band with
a maximum at 350 nm (the halfꢀwidth is ~50 nm) and a
more intense absorption band at 234 nm. Also, relatively
lowꢀintensity peaks at 270–280 nm are present. The
longꢀwavelength band is due to singlet–singlet elecꢀ
tron transitions (Table 6) the major of which are the
Table 5. Local atomic structure data for IIIa and IV obꢀ
tained by singleꢀshell fitting of the EXAFS data ( are interꢀ
atomic distances,
is the coordination number, σ2 is the
Debye–Waller factor, is the goodnessꢀofꢀfit function, the
R
N
Q
note indicates the approximation area)
Comꢀ
pound
N
R
, Å
σ
2, Å2
Atom
Q*, %
IIIa
IV
4
4
2.02
2.05
0.0053
0.0043
N
N
0.6
1.2
intense transitions HOMO
→ LUMO, HOMOꢀ1 →
* rꢀspace, Δr = 1.0–1.9 Å.
LUMO, and HOMO → LUMO+1 having the highest
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SYNTHESIS, CRYSTAL STRUCTURE, AND ELECTROLUMINESCENT PROPERTIES
729
N
6
IIIa
4
2
0
1
2
3
4
5
6
r
, Å
6
4
IV
2
0
1
2
3
4
5
6
r, Å
Fig. 4. Zn Kꢀedge FTM for complexes IIIa and IV (continuous line is experiment, light circles are the theory).
(а)
(b)
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
0
180 200 220 240 260 280 300 320 340 360 380 400
, nm
200 220 240 260 280 300 320 340 360 380 400
, nm
λ
λ
Fig. 5. UV/Vis spectra for complexes: (a) IIIa and (b) IIIb; continuous line is experiment and dashed line is the theory.
oscillator strength (f). The TDꢀDFT calculation adeꢀ HOMO and LUMO of the molecules. The key differꢀ
quately reproduces the energy position of this absorpꢀ ence between the UV/Vis spectra of the zinc and cadꢀ
tion band, which additionally validates the optimized mium complexes is the fact that in the former case, the
strictures of molecules IIIa and IIIb. As has been HOMO and the LUMO involve to the same extent
repeatedly established in analyses of the UV/Vis specꢀ both azomethine moieties of the ligand, whereas each
tra of analogous zinc complexes, the nature of this of the frontier MO of cadmium complex IIIb involves
band is determined by transitions from the
orbital (HOMO) to antibonding orbital (LUMO) 234 nm is due to a set of electron transitions (Table 6),
of the ligands. This interpretation is valid not only for the principal ones being HOMOꢀ11 LUMO+1,
the corresponding metal complexes but also for the HOMO LUMO+7, HOMOꢀ LUMO+6, and
LUMO+6. For this band, too, the simulaꢀ
π bonding one moiety (different ones). The absorption band at
π*
→
→
1 →
initial ligands.
HOMO →
tion of the UV spectra also provides good agreement
with experimental results to within several nm.
As can be seen from Fig. 6, which depicts the
HOMO and the LUMO for molecules IIIa,b, the
HOMO makes the highest contribution to the
ponent of the MO of the phenyl group of the ligand
azomethine moiety, the same is true for the
bonding part of the LUMO. The tosylamine and is observed, as opposed to azomethine compounds
π
ꢀcomꢀ
Upon photoexcitation of the complexes IIIa, IIIb
(λexcit = 320 nm), a fluorescence emission band with
antiꢀ maxima at λPL = 425 nm (IIIa) and λPL = 433 nm (IIIb
π*
)
I
octanediamine moieties do not contribute to the and II. The fluorescence excitation spectra closely
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 7 2014

730
BURLOV et al.
), energies (E), oscillator strengths (f), assignments of
Table 6. Wavelengths of the principal vertical electron transitions (
the absorption bands to definite electron transitions, and TDꢀDFTꢀcalculated contributions of the electron transitions for
λ
IIIa and IIIb
IIIa, M = Zn
IIIb, M = Cd
electron transitions and their
contributions, %**
electron transitions and their
contributions, %
λ, nm
f
λ
, nm
f
356.15
(350)*
HOMO
→
LUMO (87.0%)
0.12
0.11
348.74
(350)*
HOMOꢀ1
→
LUMO (64%)
0.18
0.15
HOMO
→ LUMO (14%)
350.32
(350)*
HOMOꢀ1
HOMO
→
→
LUMO (73%)
LUMO+1 (15%)
346.53
(350)*
HOMOꢀ1
→
LUMO (11%)
HOMO
HOMO
→ LUMO (13%)
→
LUMO+1 (61%)
340.45
HOMOꢀ1
→
LUMO+1 (89%)
0.05
0.07
295.29
HOMOꢀ1
HOMOꢀ1
→
→
LUMO+2 (37%)
LUMO+3 (50%)
0.06
0.18
265.47
(277–270)* HOMOꢀ3
HOMOꢀ2
HOMOꢀ4
→
→
→
LUMO+1 (25%)
LUMO (24%)
LUMO (19%)
259.32
(277–270)* HOMOꢀ2
HOMOꢀ2
HOMOꢀ3
→
→
→
LUMO+1 (14%)
LUMO (14%)
LUMO+1 (21%)
257.45
HOMOꢀ9
HOMOꢀ6
→
→
LUMO (20%)
LUMO (25%)
0.14
0.12
0.30
0.24
0.12
257.72
HOMOꢀ7
HOMOꢀ4
HOMOꢀ1
→
→
→
LUMO (17%)
LUMO (34%)
LUMO+5 (12%)
0.07
0.08
0.38
0.31
0.31
HOMO
→
LUMO+4 (10%)
256.43
HOMOꢀ1
→
LUMO+4 (37%)
251.65
HOMOꢀ6
→
LUMO (75%)
HOMO
→ LUMO+5 (30%)
HOMOꢀ6
→
LUMO (13%)
233.57
(234)*
HOMO
HOMOꢀ11
HOMOꢀ11
→
LUMO+6 (34%)
→
→
234.14
(234)*
HOMO → LUMO+6 (25%)
HOMOꢀ11
HOMOꢀ11
LUMO+1 (35%)
LUMO (12%)
→
→
LUMO+1 (29%)
LUMO (17%)
232.23
(234)*
HOMO
HOMO
HOMOꢀ11
→
LUMO+7 (32%)
LUMO+6 (19%)
LUMO+1 (27%)
232.88
(234)*
HOMOꢀ11
HOMOꢀ1 → LUMO+5 (12%)
→
LUMO (60%)
→
→
231.9
(234)*
HOMOꢀ1
HOMO
HOMO
→
LUMO+6 (37%)
LUMO+6 (17%)
LUMO+7 (34%)
231.93
(234)*
HOMOꢀ11
HOMOꢀ11 →
→
LUMO (14%)
LUMO+1 (29%)
LUMO+5 (20%)
LUMO+5 (13%)
→
→
HOMOꢀ1
HOMO
→
→
* Experimental values; ** Electron transitions with contributions of >10% are presented.
coincide with the corresponding absorption spectra,
which supports the assignment of the fluorescence
bands of complexes IIIa and IIIb. The fluorescence of
ITO /CuPc(5 nm)/2ꢀTNATA(35 nm)/spiroꢀ
TPD(7 nm)/(20 nm)/BCP(5 nm)/IIIa or IIIb/
Bphen(20 nm)/LiF(1 nm)/AL(100 nm).
the complexes shows high efficiency, quantum yields
being 0.25–0.30.
ϕ
The names of compounds are given as standard
international abbreviations. The brightness of devices
with greenꢀblue emission and with the chromaticity
In view of high thermal stability of up to >300°C and
high fluorescence quantum yields of compounds IIIa
and IIIb, they were used to fabricate multilayer lightꢀ
emitting diode (OLED) structures by thermal vacuum
evaporation.
coordinates
x = 0.215; y = 0.276 (IIIa) and x = 0.199;
y
= 0.236 (IIIb) (the insets in Figs. 7 and 8) did not
exceed 500 cd/m2 at 12 V. Note the crucial difference
in the shapes and positions of PL and EL bands of the
two complexes. The EL spectrum of IIIb is a broad
single band, whereas in the case of IIIa, several peaks
are present corresponding to different excited states in
the system. The nature of these EL states was not studꢀ
ied. Judging by the shape and position of the broad
longꢀwavelength band, which is present in both cases,
it is related to the wellꢀknown formation of exciplexes
between excited complexes and molecules of the adjaꢀ
In the case of IIIa, evaporation was carried out at
207°C and for IIIb it was at 217°C. In both cases, the
process was virtually not accompanied by vacuum
deterioration. The spraying rates were 0.38 and 0.35 Å
per s, respectively. During heating, the color of comꢀ
pounds did not change. Two OLED structures conꢀ
taining each six functional layers were fabricated; their
composition was as follows:
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 7 2014

SYNTHESIS, CRYSTAL STRUCTURE, AND ELECTROLUMINESCENT PROPERTIES
731
IIIa, M = Zn
IIIb, M = Сd
LUMO
LUMO
HOMO
HOMO
Fig. 6. View of the frontier MO of complexes IIIa and IIIb
.
I, rel. units
y
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
2
0.7
0.6
0.5
0.4
0.3
1
0 0.1 0.3 0.5 0.7
x
0.2
0.1
0
350
400
450
500
, nm
550
600
650
λ
Fig. 7. Emission spectra of complex IIIa and chromaticity coordinates of the OLED device based on this complex. (
excitation at = 320 nm, ( ) EL. The inset shows the color diagram of the OLED device.
1) PL on
λ
2
excit
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 7 2014

732
BURLOV et al.
I, rel. units
y
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.7
0.6
0.5
0.4
0.3
0.2
0.1
2
0
0.1 0.3 0.5 0.7
x
1
380
430
480
λ
530
580
, nm
Fig. 8. Emission spectra of complex IIIb and chromaticity coordinates of the OLED device based on this complex. (
1) PL on exciꢀ
tation at = 320 nm, ( ) EL. The inset shows the color diagram of the OLED device.
λ
2
excit
9. N. Chantarasiri, V. Ruangpornvisuti, N. Muangsin,
cent functional layers (in this case, spiroꢀTPD or
BCP) at the interlayer boundary.
et al., J. Mol. Struct. 701, 93 (2004).
10. T. Yu, W. Su, W. Li, et al., Inorg. Chim. Acta 359, 2246
(2006).
ACKNOWLEDGMENTS
11. T. Yu, K. Zhang, Y. Zhao, et al., Inorg. Chim. Acta 361
233 (2008).
,
This work was supported by RF President grants
NSh 274.2014.3 and by the Russian Foundation for
Basic Research (12ꢀ03ꢀ00462a, 13ꢀ03ꢀ00171a). The
experimental IR and NMR spectra were recorded
using the equipment of the Collective Use Center of
the Southern Federal University “Molecular Specꢀ
troscopy.”
12. P. Wang, Z. Hong, Z. Xie, et al., Chem. Commun.,
1664 (2003).
13. M. R. Bermejo, M. Vazquez, J. Sanmartin, et al., New
J. Chem. 26, 1365 (2002).
14. A. V. Metelitsa, A. S. Burlov, S. O. Bezuglyi, et al., RF
Patent No. 2295527 (2007).
15. A. V. Metelitsa, A. S. Burlov, S. O. Bezuglyi, et al., Russ.
J. Coord. Chem. 32, 858 (2006).
16. N. I. Chernova, Yu. S. Ryabokobylko, V. G. Brudz’,
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