Inorganic-organic hybrid compounds based on face-sharing octahedral [PbI3]∞ chains: Self-assemblies, crystal structures, and ferroelectric, photoluminescence properties

Article abstract of DOI:10.1039/c0dt00875c

Eight inorganic-organic hybrid compounds with a formula of [R-Bz-1-APy][PbI₃] (R-Bz-1-APy⁺ = mono-substituted benzylidene-1-aminopyridinium Schiff base derivative; R = m-CN (1), m-CH ₃ (2), H (3), p-F (4), p-Cl (5), p-Br (6), o-Cl (7), o-Br (8)) have been synthesized and characterized structurally. The common characteristic of the crystal structures of 1-8 is that the inorganic components form straight and face-sharing octahedral [PbI₃]_∞ chains and the Schiff base cations surround the [PbI₃]_∞ chains to form molecular stacks. The substituent (R) on the phenyl ring of the Schiff base cation clearly influences the packing structures of 1-8, and the hybrid compound crystallizes in the space group P6₃ when R = CN (1) in the meta-position of the phenyl ring, and in a central symmetric space group when R is in the ortho- or para-position of the phenyl ring. The conformation of the Schiff base cation is related to the R position, and the dihedral angle between the phenyl and pyridyl rings increases in the order of para- < meta- < ortho-position substitution of the phenyl ring. The long molecular axis of the Schiff base cation adopts a manner approximately parallel to the straight inorganic [PbI₃]_∞ chain in the para-substituted hybrid compounds, and perpendicular to the straight inorganic [PbI ₃]_∞ chain in the ortho-substituted hybrid compounds. 1 is second harmonic generation (SHG) active with a comparable response as that of urea and also exhibits ferroelectricity with larger P_s and P _r values; 1-8 emit multi-band luminescence in the 300-650 nm regions under the excitation of ultraviolet light.

Full text of DOI:10.1039/c0dt00875c

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PAPER
Inorganic–organic hybrid compounds based on face-sharing octahedral
[PbI3]• chains: self-assemblies, crystal structures, and ferroelectric,
photoluminescence properties†
Hai-Bao Duan,a,b Hai-Rong Zhao,a,b Xiao-Ming Ren,*a,b,c Hong Zhou,d Zheng-Fang Tiana,b and Wan-Qin Jina
Received 20th July 2010, Accepted 23rd November 2010
DOI: 10.1039/c0dt00875c
Eight inorganic–organic hybrid compounds with a formula of [R-Bz-1-APy][PbI3] (R-Bz-1-APy+ =
mono-substituted benzylidene-1-aminopyridinium Schiff base derivative; R = m-CN (1), m-CH3 (2), H
(3), p-F (4), p-Cl (5), p-Br (6), o-Cl (7), o-Br (8)) have been synthesized and characterized structurally.
The common characteristic of the crystal structures of 1–8 is that the inorganic components form
straight and face-sharing octahedral [PbI3]• chains and the Schiff base cations surround the [PbI3]•
chains to form molecular stacks. The substituent (R) on the phenyl ring of the Schiff base cation clearly
influences the packing structures of 1–8, and the hybrid compound crystallizes in the space group P63
when R = CN (1) in the meta-position of the phenyl ring, and in a central symmetric space group when
R is in the ortho- or para-position of the phenyl ring. The conformation of the Schiff base cation is
related to the R position, and the dihedral angle between the phenyl and pyridyl rings increases in the
order of para- < meta- < ortho-position substitution of the phenyl ring. The long molecular axis of the
Schiff base cation adopts a manner approximately parallel to the straight inorganic [PbI3]• chain in the
para-substituted hybrid compounds, and perpendicular to the straight inorganic [PbI3]• chain in the
ortho-substituted hybrid compounds. 1 is second harmonic generation (SHG) active with a comparable
response as that of urea and also exhibits ferroelectricity with larger Ps and Pr values; 1–8 emit
multi-band luminescence in the 300–650 nm regions under the excitation of ultraviolet light.
struction of functional molecular solids from molecules and ions,
are powerful tool for the assembly of designed functional materials
Introduction
over the past three decades.1,5 Despite a great deal of progress
that has been made in the syntheses of acentric structures,6
challenges still remain in the synthesis of non-centrosymmetric
polar packing arrangements, especially, the assembly from the
non-chiral molecular or ionic building architectures. Therefore, it
is necessary to explore new molecular self-assembly for functional
materials and to better understand the relationship between the
crystal packing structure and the properties of the molecular
architecture (for example, the shape, size, polarity, local charge
distribution, types and location of functional groups of molecules)
at the molecular level.
Inorganic–organic hybrids and polar solid-state materials are
two fertile topics of research; the former are able to merge the
advantages of the organic components (straightforward synthetic
approach, easily tailored molecular structure and functional prop-
erties) to those of an inorganic network (chemical, thermal and
mechanical stabilities); the later possess the technologically impor-
tant physical properties from optics to electronics, such as second-
order nonlinear optical (NLO) properties,1 pyroelectricity,2
ferroelectricity3 and triboluminescence.4 Supramolecular chem-
istry and molecular crystal engineering, which is the planning and
utilization of crystal-oriented syntheses for the bottom-up con-
The inorganic building-block of metal-halide with the formula
of MX6
(M = Sn2+, Pb2+, Bi3+, Sb3+; X- = F-, Cl-, Br-, I-)
4-/3-
aState Key Laboratory of Materials-Oriented Chemical Engineering, Nan-
jing University of Technology, Nanjing 210009, P. R. China
has received special attention in the aspect of the construction of
inorganic–organichybridmaterials,7,8 among whichtheoctahedral
building block of lead halides, PbX64-, occupy an important
position for their versatile topology structures and enthralling
properties, and have been used for creating versatile crystal struc-
tures from a one-dimensional (1D) chain to a three-dimensional
(3D) framework through corner-, edge- or face-sharing mode.9
It has been reported that the negatively charged inorganic chain
probably induce positive-charged organic components packed into
bCollege of Science, Nanjing University of Technology, Nanjing 210009,
P. R. China
cState Key Lab & Coordination Chemistry Institute, Nanjing University,
Nanjing 210093, P. R. China
dDepartment of Chemistry, Nanjing Xiaozhuang University, Nanjing 210017,
PR China. E-mail: xmren@njut.edu.cn; Fax: +86 25 83587438; Tel: +86
25 83587820
† Electronic supplementary information (ESI) available. CCDC reference
numbers 780403–780411. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt00875c
1672 | Dalton Trans., 2011, 40, 1672–1683
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The Royal Society of Chemistry 2011
©

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a polar and highly anisotropic array under Coulomb forces,10 and
in our previous studies, the octahedral [PbI6]4- building blocks
were chosen for self-assembly with the Schiff base derivatives of 3-
R-benzylidene-1-aminopyridinium (3-R-Bz-1-APy+) to give four
inorganic–organic hybrid compounds with a formula of [3-R-
benzylidene-1-aminopyridinium][PbI3] (R = m-NO2, m-F, m-Cl,
m-Br), which are isostructural and crystallize in the polar space
group P63; the inorganic components assemble into face-sharing
octahedral [PbI3]• chains and the organic Schiff base cations
surround the [PbI3]• chains to align into tubular architectures
in the crystals.11b Those inorganic–organic hybrid compounds
show the arresting ferroelectric property with larger remnant
polarization and the saturation of the spontaneous polarization.
These findings prompted us to further investigate the series of [R-
benzylidene-1-aminopyridinium][PbI3] inorganic–organic hybrid
compounds via modifying the nature of the substituent R, hoping
to gain some useful information which could guide the assembly
of such a type functional inorganic–organic hybrids.
In this paper, we presented the crystal structures and photolumi-
nescence properties in solid state for eight new hybrid compounds,
[R-Bz-1-APy][PbI3] (R = m-CN (1), m-CH3 (2), H (3), p-F (4), p-Cl
(5), p-Br (6), o-Cl (7), o-Br (8)) (Scheme 1), among which 1 has a
polar crystal structure, and its second NLO as well as ferroelectric
properties were investigated. The effect of the substituent feature
in the phenyl ring of the Schiff base cation on the conformation of
the Schiff base cation as well as on the crystal packing structure
of the hybrid compound were explored.
Cu-Ka radiation (l = 1.5418 A). FT-IR spectra were recorded on
an IF66V FT-IR (4000–400 cm-1) spectrophotometer with KBr
pellets. UV-Vis absorption spectra in the solid state were taken
using a Cary 5000 UV-Vis spectrometer at room temperature. The
measurements for solid-state fluorescence were performed at room
temperature on a Perkin-Elmer LS 50B spectrofluorimeter. TGA
experiments were performed with a TA2000/2960 thermogravi-
metric analyzer from 20 to 800 ◦C at a warming rate of 10 ◦C min-1
under a nitrogen atmosphere, and the polycrystalline samples were
placed in an aluminium crucible.
˚
A pulsed Q-switched Nd:YAG laser with l = 1064 nm was used
to generate a SHG signal from the sample of 1 (which was prepared
into a powder pellet with ca. 0.150 mm diameters and ca. 0.8 mm
thickness under 300 MPa pressure). The backward scattered SHG
light was collected using a spherical concave mirror and passed
through a filter which transmits only 532 nm radiation. The SHG
efficiency of 1 was estimated according to the principle proposed
by Kurtz and Perry.13 The P-E hysteresis loop on a ferroelectric
tester (Radient Technology), with electrodes made of Cu wire with
about 150 mm diameter covered by Ag-conducting glue on the
approximate crystallographic face (001).
Preparation of compounds 1–8
[m-CNBz-1-APy][PbI3] (1). A mixture of PbI2 and [m-CNBz-
1-APy]I with a molar ratio of 1 : 1 in DMF was placed in an
oven and slowly evaporated at 40 ◦C for 8–10 days to produce
light yellow needle-shaped crystals in ca. 70% yield. Anal. calc. for
C13H10N3I3Pb: C, 19.61; H, 1.27; N, 5.28. Found: C, 19.67; H, 1.22;
N, 5.18. IR spectrum (cm-1): 3057 s (nC–H of phenyl and pyridyl
ring), 2233 s (nC N) and 1622 m (nC N).
A similar procedure to the preparation of 1, with the [m-CNBz-
1-APy]I replaced with the corresponding Schiff base iodide, was
employed to produce 2–8.
[m-CH3Bz-1-APy][PbI3] (2). Light yellow needle-shaped crys-
tals in ca. 80% yield. Anal. calc. for C13H13N2I3Pb: C, 19.89; H,
1.67; N, 3.57. Found: C, 19.98; H, 1.54; N, 3.66. IR spectrum
(cm-1): 3052 s (nC–H of benzene and pyridine rings); 2924 s and
as
s
2857 s (n
C–H and n C–H of -CH3); 1618 m (nC of Schiff
C–H
N
base).
[Bz-1-APy][PbI3] (3). Orange needle-shaped crystals in ca.
57% yield. Anal. calc. for C12H11N2I3Pb: C, 18.69; H, 1.44; N,
3.63. Found: C, 18.73; H, 1.38; N, 3.56. IR (KBr cm-1): 3061 s
Scheme 1 The molecular structures of the Schiff base cations in the hybrid
compounds 1–8.
(nC–H of phenyl and pyridyl rings); 1655 s (nC of pyridyl rings
N
and nC phenyl ring); 1626 m (nC of Schiff base).
C
N
Experimental
[p-FBz-1-APy][PbI3] (4). Light yellow needle-shaped crystals
in ca. 75% yield. The sample, dried under vacuum at 120 ◦C for 6 h,
was used for elemental analysis. Anal. calc. for C12H10N2FI3Pb: C,
18.26; H, 1.28; N, 3.55. Found: C, 18.34; H, 1.24; N, 3.45. IR
spectrum (cm-1): 3061 s (nC–H of phenyl and pyridyl rings); 1620 m
(nC N).
Chemicals and materials
All chemicals and solvents were reagent grade, and used without
further purification. 1-Aminopyridinium iodide ([1-APyI])12 and
Schiff base derivatives [RBz-1-Apy]I were prepared using a similar
method reported in our previous studies.11
[p-ClBz-1-APy][PbI3] (5). Orange needle-shaped crystals in ca.
86% yield. Anal. calc. for C12H10N2ClI3Pb: C, 17.89; H, 1.25; N,
3.48. Found: C, 17.93; H, 1.24; N, 3.35. IR spectrum (cm-1): 3063 s
(nC–H of phenyl and pyridine rings); 1655 s and 1647 s (phenyl and
pyridyl rings); 1625 m (nC N).
Physical measurements
Elemental analyses for C, H and N were performed with an Ele-
mentar Vario EL III analytic instrument. Power X-ray diffraction
(PXRD) data were collected on a Bruker D8 diffractometer with
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Table 1 Crystal and structural refinement data of 1–4
Compound
1
2
3
4
Chemical formula
CCDC no.
C13H10N3I3Pb
780405
796.13
296(2)
0.71073
Hexagonal
P63
20.114(2)
20.114(2)
7.9255(18)
90.00
90.00
120.00
2776.9(8)/6
2.856
14.110
C13H13N2I3Pb
780404
785.14
C12H11N2I3Pb
780403
771.12
296(2)
0.71073
Monoclinic
P21/c
10.1409(19)
22.136(4)
8.0822(15)
90.00
100.913(2)
90.00
1781.4(6)/4
2.875
14.656
1352.0
1.84–27.70
-13 £ h £ 13
-26 £ k £ 28
-10 £ l £ 10
15604
C12H10N2FI3Pb
780411
789.11
Formula weight
T/K
293(2)
293(2)
˚
Wavelength (A)
1.54178
Monoclinic
P21/c
11.8306(7)
20.2084(14)
7.9333(5)
90.00
98.925(6)
90.00
1873.7(2)/4
2.783
56.236
1384.0
3.78–62.93
-13 £ h £ 13
-23 £ k £ 20
-9 £ l £ 9
9950
0.71073
Monoclinic
C2/c
13.693(2)
22.527(4)
15.988(3)
90.00
126.139(16)
90.00
3982.8(12)/8
2.632
13.121
2768
1.81–26.00
-16 £ h £ 16
-24 £ k £ 27
-19 £ l £ 19
11043
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V(A )/Z
Density (g cm-3)
m/mm-1
F(000)
2100
Data collect q range
Index range
2.02–27.50
-25 £ h £ 25
-25 £ k £ 25
-10 £ l £ 10
23426
Reflns collected
Independent reflns
Rint
4223
0.0666
2988
0.0624
4156
0.0358
3876
0.2221
Refinement method on F2
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2d(I)]
Full-matrix least-squares
4223/1/181
1.106
R1 = 0.0584
wR2 = 0.1045
R1 = 0.1193,
wR2 = 0.1412
2988/1/172
1.065
R1 = 0.1015,
wR2 = 0.3441
R1 = 0.1136
wR2 = 0.3591
4156/0/163
1.027
R1 = 0.0301,
wR2 = 0.0557
R1 = 0.0511
wR2 = 0.0617
3876/0/164
0.862
R1 = 0.0608,
wR2 = 0.1561
R1 = 0.0826,
wR2 = 0.1657
R indices (all data)
ꢀ
ꢀ
ꢀ
ꢀ
R1 = (ꢀF0|-|Fcꢀ)/ |F0|, wR2 = w(|F0|2-|Fc|2)2/ w(|F0|2)2]1/2
[p-BrBz-1-APy][PbI3] (6). Orange needle-shaped crystals in
ca. 85% yield. Anal. calc. for C12H10N2BrI3Pb: C, 16.96; H, 1.19;
N, 3.30. Found: C, 17.05; H, 1.10; N, 3.40. IR spectrum (cm-1):
3064 s (nC–H of phenyl and pyridine rings); 1651 s (phenyl and
pyridyl rings); 1625 m (nC N).
the full-matrix least-squares procedure on F2 using SHELXL-97
program.16 The non-Hydrogen atoms were anisotropically refined
using the full-matrix least-squares method on F2. The crystal of
1 belongs to a chiral space group, the absolute structure and
its invert structure were refined, which gives a flack parameter
of 0.109(16) and 0.88(2), respectively; in accordance with the
suggestion of SHELXL-97 program, the keyword ‘twin’ was used
in the procedure of refinement, which leads to a flack parameter
being 0.00 and no ‘esd’. The restraints of special position, Uij
and sof were used for Pb(1), Pb(2) and Pb(3) atoms during
refinement of 1; and a ‘rigid bond’ restraint of ‘delu’was used
for C(11) and C(13) of 2; N(1) and N(2) of 6 as well as Pb(1) and
I(1) atoms of 8 during refinements, respectively. The crystal of 4
contains disordered solvent molecules, which is further confirmed
by TGA analysis (~5.1% weight loss corresponds to the solvent
molecular releasing; see Fig. 10b), and the structure of both
inorganic and organic components are defined even if the solvent
molecule is badly defined. During the refinement, the disorder
solvent molecules were removed and Platon SQUEEZE was used
for smoothing the electron density; the details from the Platon
SQUEEZE run in a sqf file were appended to the cif of 4. For 1–8,
the crystallographic details about data collection and structural
refinement are summarized in Table 1 and Table 2; the selected
bond lengths and angles together with their estimated standard
deviations are listed in Table S1 and Table S2†.
[o-ClBz-1-APy][PbI3] (7). Light yellow block-shaped crystals
in ca. 78% yield. Anal. calc. for C12H10N2ClI3Pb: C, 17.89; H, 1.25;
N, 3.48. Found: C, 17.97; H, 1.18; N, 3.42. IR spectrum (cm-1):
3052 s (nC–H of phenyl and pyridyl rings); 1615 m (nC N).
[o-BrBz-1-APy][PbI3] (8). Light yellow block-shaped crystals
in ca. 82% yield. Anal. calc. for C12H10N2BrI3Pb: C, 16.96; H, 1.19;
N, 3.30. Found: C, 16.88; H, 1.37; N, 3.18. IR spectrum (cm-1):
3052 s (nC–H of phenyl and pyridyl rings); 1614 m (nC of Schiff
N
base).
X-Ray crystallography. The single crystal X-ray diffraction
data for 1, 3–8 were collected at room temperature with graphite
˚
monochromated Mo-Ka (l = 0.71073 A) on a CCD area
detector (Bruker-SMART). Data reductions and absorption cor-
rections were performed with the SAINT and SADABS soft-
ware packages,14 respectively. The single crystal X-ray diffraction
data for 2 were collected on an Oxford Diffraction Xcalibur
diffractometer equipped with a Sapphire 3 CCD detector and a
˚
mirror monochromated Cu-Ka radiation (l = 1.54184 A) at room
temperature. The data collection routine, unit cell refinement, and
data processing were carried out with the program CrysAlis.15
Structures were solved by the direct method and refined by
DFT calculation details. All calculations were carried out with
the Gaussian 98 program17 by density functional theory (DFT).18
1674 | Dalton Trans., 2011, 40, 1672–1683
This journal is
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Table 2 Crystal and structural refinement data of 5–8
Compound
Chemical formula
CCDC no.
5
6
7
8
C12H10N2ClI3Pb
780410
C12H10N2BrI3Pb
780408
C12H10N2ClI3Pb
780407
C12H10N2BrI3Pb
780406
Formula weight
T/K
805.56
296(2)
0.71073
Monoclinic
P21/c
13.8862(16)
16.3785(19)
7.8922(9)
90.00
90.884(2)
90.00
1794.7(4)/4
2.981
14.699
850.02
293(2)
805.56
293(2)
850.02
293(2)
˚
Wavelength (A)
0.71073
Monoclinic
P21/c
13.8838(5)
16.4673(6)
7.8911(3)
90.00
90.357(3)
90.00
1804.10(12)/4
3.130
16.689
1488
2.86–26.00
-17 £ h £ 17
-20 k £ 17
-9 £ l £ 9
11042
0.71073
Monoclinic
P21/c
12.0905(5)
8.2004(3)
19.9568(10)
90.00
112.369(4)
90.00
1829.77(14)/4
2.924
14.417
1416
3.03–26.00
-14 £ h £ 14
-10 £ k £ 10
-23 £ l £ 24
10910
0.71073
Monoclinic
P21/c
12.2054(9)
8.1916(5)
20.1750(11)
90.00
113.115(3)
90.00
1855.2(2)/4
3.043
16.230
1488
1.81–26.00
-14 £ h £ 15
-9 £ k £ 10
-19 £ l £ 24
10292
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V(A )/Z
Density (g cm-3)
m/mm-1
F(000)
1416
Data collect q range
Index range
1.47–25.50
-16 £ h £ 16
-18 £ k £ 19
-9 £ l £ 9
13303
Reflns collected
Independent reflns
Rint
3330
0.0382
3523
0.0614
3567
0.0316
3629
0.1199
Refinement method on F2
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2d(I)]
Full-matrix least-squares
3330/0/172
0.998
R1 = 0.0279,
wR2 = 0.0625
R1 = 0.0463,
wR2 = 0.0681
3523/1/169
1.162
R1 = 0.0931,
wR2 = 0.2537
R1 = 0.1065,
wR2 = 0.2571
3567/0/173
1.097
R1 = 0.0308,
wR2 = 0.0831
R1 = 0.0395,
wR2 = 0.0849
3629/1/172
0.837
R1 = 0.0534,
wR2 = 0.1235
R1 = 0.0867,
wR2 = 0.1333
R indices (all data)
ꢀ
ꢀ
ꢀ
ꢀ
R1 = (ꢀF0|-|Fcꢀ)/ |F0|, wR2 = w(|F0|2-|Fc|2)2/ w(|F0|2)2]1/2
Becke’s three-parameter functional combined with Lee–Yang–
Parr’s correlation functional (B3LYP)19 were employed as well
as the basis set of 6-31+G(d,p)20 which were used for C, H and
N atoms, while Lanl2DZ21 for Pb and I atoms. The calculations
for the dipole moments of the Schiff base cations and the [PbI3]•
chains in a unit cell were performed at the single crystal X-ray
experimental structure and the SCF convergence criterion is 10-8.
the c-axis direction. The Pb–I bond lengths are in the range of
3.1894(17)–3.2581(17) A within the chain 1, and in the range of
˚
˚
3.2151(18)–3.2458(18) A within the chain 2; the Pb–I distances
with the I–Pb–I bond angles in three types of PbI6 coordination
octahedra are summarized in Table S1† and comparable to the
reported [PbI3]• compounds.11b
The Schiff base cation shows a non-planar conformation with
a dihedral angle of 45.3(9)◦ between the phenyl and pyridyl rings.
Two types of [PbI3]• chains, coupled to the Schiff base cations by
Coulomb and van der Waals forces, direct the Schiff base cations
to adopt tubular architectures (Fig. 1) that are collinear with the
[PbI3]• chains. The supramolecular tubes are present in chiral
forms, namely, the hexagonal supramolecular tube, occupied by
[PbI3]• chain 1, is built from the Schiff base cation with a 9-
fold helix; the trigonal supramolecular tube, occupied by [PbI3]•
chain 2, is built from the Schiff base cations with a 3-fold
helix. In the supramolecular tube, there exists a p . . . p stacking
interaction between the phenyl ring and the pyridyl ring of two
neighboring Schiff base cations with the dihedral angle of 6.85◦,
Results and discussion
Crystal structure descriptions
Compound 1 crystallizes in the hexagonal space group P63
(no. 173), which belongs to the polar point group C6, and an
asymmetric unit contains three different Pb2+ ions and three
different I- anions together with one Schiff base cation (as depicted
in Fig. 1). The Pb(1) ion occupies the Wyckoff position a, its
coordination octahedron, with the symmetry of C3 point group, is
built from six I(1)-type iodide ions, the neighboring coordination
octahedra are linked together via face-sharing mode to form a
uniform [PbI3]• chain along the c-axis direction (labeled as chain
1). The Pb(2) and Pb(3) ions occupy the Wyckoff position b,
and such two types of Pb2+ ions are respectively surrounded by
three I(2)- and three I(3)-type iodide ions to form an octahedral
coordination environment; the Pb(2)- and Pb(3)-type coordination
octahedra, with the symmetry of C3 point group, are connected
with each other via face-sharing mode into a regular [PbI3]• chain
( . . . Pb(2)I3Pb(3)I3 . . . , which is labeled as chain 2) running along
˚
the phenyl plane-to-pyridyl plane distance of 3.644 A and centroid-
˚
to-centroid distance of 3.820 A as well as a shorter interatomic
˚
distance of dC(2) . . . C(12A) = 3.521 A (symmetric code: A = y, -x + y,
-0.5 + z; Figure S2†).
Compounds 2 and 3 are isostructural and the two hybrid
compounds crystallize in the monoclinic space group P21/c with
similar cell parameters and packing structures. As shown in Fig. 2,
the asymmetric unit in the crystals of 2 and 3 contain one Pb2+
cation and three distinct I- anions with one corresponding Schiff
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172.24(6)–176.97(6)◦ in 2 versus 174.356(14)–177.973(14)◦ in 3,
which are normal. The distorted PbI6 octahedra are constructed
into straight and regular [PbI3]• chains along the c-axis direction
via a face-sharing model in 2 and 3, which are similar to the case
of 1.
The Schiff base cations in 2 and 3 show the twist molecular
conformations with similar dihedral angles between the pyridyl
and phenyl rings (18.3(9)◦ in 2 and 22.1(2)◦ in 3), respectively,
these dihedral angles are much smaller than that in 1. The cations
assemble into an irregular stack, as illustrated in Fig. 3 for 2
(and Figure S4 for 3†), and there are longer centroid-to-centroid
distances between the phenyl and pyridyl rings of the neighboring
˚
cations within a stack (alternate as d1 = 3.922 and d2 = 4.868 A in
˚
2 versus d1 = 4.114 and d2 = 4.805 A in 3), since the neighboring
cations align in a manner of anti-parallel arrangement along the
long molecular axis as well as the existence of slippage along the
short molecular axis. The straight inorganic [PbI3]• chains are
Fig. 1 (a) The view of an asymmetric unit of compound 1 with non-H
atomic labeling and the thermal ellipsoids at the 20% probability (H atoms
in the cation omitted for clarity; and the symmetric codes: 1A = 1 - y, 2 +
x - y, z; 1B = -1 -x + y, 1 - y, z; 1 C = -x, 2 - y, 0.5 + z; 1D = -1 + y,
-x + y, 0.5 + z; 1E = 1 + x - y, 1 + x, 0.5 + z; 2A = 3A = 1 - y, 1 + x
- y, z; 2B = 3B = 1 + x - y, 1 - x, z); and (b) space-filling representation
of channels projected along the c-axis direction as well as supramolecular
tubes surrounding the [PbI3]• chain 1 with 9-fold stranded helix and the
[PbI3]• chain 2 with 3-fold stranded helix in the crystal 1.
base cation. The Pb2+ ion occupies a general position (Wyckoff
site e) and is coordinated with six iodides to form a distorted
octahedron coordination geometry, the Pb–I lengths range from
˚
˚
3.1300(19) to 3.354(2) A in 2 versus 3.1005(6) to 3.2846(6) A in
3; the I–Pb–I bond angles between two cis-model iodides and
lead ion are distributed in the range 84.39(5)-97.33(5)◦ in 2 versus
84.871(16)-97.332(15)◦ in 3, and the I–Pb–I bond angles between
two trans-model iodides and lead ion are distributed in the range
Fig. 3 The alignment of the inorganic and organic components in the
crystals of 2.
Fig. 2 The view of the asymmetric units with non-H atomic labeling and the thermal ellipsoids at the 20% probability (H atoms in the cation omitted
for clarity) for (a) 2 (symmetric codes: 1A = 3A = x, 0.5 - y, -0.5 + z; 2A = x, 0.5 - y, 0.5 + z) and (b) 3 (symmetric codes: 1A = x, 0.5 - y, -0.5 + z; 2A =
3A = x, 0.5 - y, 0.5 + z), respectively.
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embedded in the cation stacks, and there exist only weak van
der Waals forces between the inorganic and organic components
besides the Coulomb attractions.
center, as well as between two cis-model iodides and lead ion,
are distributed in the range 84.88(3)–95.12(3)◦ for the Pb(1) ion;
the corresponding angles are in the range of 176.30(4)–176.94(2)◦
and 85.68(3)–96.82(3)◦ for the Pb(2) ion. Pb(1)- and Pb(2)-type
ions form straight and regular [PbI3]• chains in a pattern of
. . . Pb(1)I3Pb(2)I3 . . . along the c-axis direction.
The Schiff base cation shows a non-planar conformation with
dihedral angles of 16.7(5)◦ between the phenyl and pyridyl rings.
Comparing the packing structure of 4 with 2 and 3, the striking
distinction is that the stacks of the Schiff base cations align into
a layer in 4, which is parallel to the crystallographic (101) plane
(Fig. 4b and Figure S5†), and the inorganic [PbI3]• chains with the
solvent molecules are filled in the interlayer spaces of the Schiff
base cations. In a cationic layer, the stack of Schiff base cations is
irregular and the neighboring cations shows two types of overlap
fashions, namely, two adjacent cations align in an anti-parallel
Crystal of 4 belongs to the monoclinic system with the space
group C2/c. An asymmetric unit consists of two crystallographi-
cally inequivalent Pb2+ ions, three distinct I- anions, and one Schiff
base cation together with an undefined solvent molecule, which
is probably DMF molecule. The potential molecule-accessible
area in the guest-depleted structure of 4 was further calculated
3
22
˚
as 582.2 A or 14.6% of the unit-cell volume, and this has to
3
˚
be compared to an expected volume for H2O of 40 A or a small
molecule such as toluene of 100–300 A . The Pb(1) ion is located on
3
˚
a centre of inversion and the Pb(2) ion coincides with a 2-fold screw
axis; two crystallographically different Pb2+ ions are octahedrally
coordinated with six iodides, and the Pb–I bond lengths are in the
˚
range 3.1931(8) to 3.2670(15) A for the Pb(1) ion and 3.1945(11)
˚
˚
to 3.2631(10) A for the Pb(2) ion, respectively. The I–Pb–I bond
model with the centroid-to-centroid distance of 3.762 A, the plane-
˚
to-plane distance of 3.255 A, the shorter interatomic separations
angles, between two trans-model iodides and lead ion, are exactly
equal to 180◦ due to the symmetric constraint of an inversion
of dC(7) . . . C(5A) = 3.386 A, dC(12) . . . C(5A) = 3.420 A (symmetric code:
˚
˚
Fig. 4 (a) The view of the asymmetric unit of 4 with non-H atomic labeling and the thermal ellipsoids at the 20% probability (H atoms in the cation as
well as the undefined solvent molecule omitted for clarity; symmetric codes: A = 1 - x, 1 - y, -z; B = 1 - x, y, 0.5 - z) (b) the arrangement of inorganic
and organic components in the crystals of 4.
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Fig. 5 The view of the asymmetric units with non-H atomic labeling and the thermal ellipsoids at the 20% probability (H atoms in the cation omitted for
clarity) for (a) 5 (symmetric codes: 1A = 2A = 3A = x, 1.5 - y, 0.5 + z) and (b) 6 (symmetric codes: 1A = 2A = x, 1.5 - y, -0.5 + z; 3A = x, 1.5 - y, 0.5 + z).
A = 0.5 - x, 0.5 - y, -z) and dihedral angle of 17.29◦ as well as in a
˚
rotation manner with the centroid-to-centroid distance of 3.575 A
˚
the plane-to-plane distance of 3.392 A, the shorter interatomic
˚
˚
separations of dC(9) . . . C(5B) = 3.428 A, dC(10) . . . C(4B) = 3.457 A (symmetric
code: B = -x, 1 + y, 0.5 - z) and dihedral angle of 3.87◦ between
the phenyl and pyridyl rings, respectively.
Compounds 5 and 6 are isostructural with similar cell parame-
ters as well as the packing structures. Two compounds crystallize
in the monoclinic space group P21/c, and an asymmetric unit con-
tains one Pb2+ ion, three different I- ions with one corresponding
Schiff base cation (Fig. 5). It is similar to those of crystals 1–4, the
inorganic components form straight and regular chains via face-
sharing of coordination octahedra along the c-axis direction; in a
chain the Pb–I distances and I–Pb–I bond angles are in agreement
with those in 1–4 (Table S2†). It is noticeable that the Schiff base
cations in 5 and 6 exhibit an approximately planar conformation
of the molecule (with a dihedral angle of 5.6(2)◦ for 5 and 5.5(9)◦
for 6 between the pyridyl and phenyl rings), and this is different
from 1–4. The Schiff base cations form into a regular stack along
the c-axis direction owing to the existence of one corresponding
Schiff base cation per repeat unit (as displayed in Fig. 6 and Figure
S6†). Within a cationic stack, the Schiff base cations possess the
same orientation and two adjacent Schiff base cations arrange
with a slippage along the long molecular axis as well as the short
molecular axis, and this leads to the phenyl ring of one Schiff
base cation incompletely superimposed on the pyridyl ring of the
neighboring Schiff base cation (ref. Fig. 6) with a shorter inter-
Fig. 6 The arrangement of inorganic [PbI3]• chains and Schiff base cation
stacks in the crystals of 5.
[PbI3]• chain is regular and the corresponding Schiff base cation
stacks are also regular.
Compared the structures of 7 and 8 with 1–6, two particular
differences are arresting; (1) the corresponding Schiff base cation
shows a heavily twisted conformation with a dihedral angle of
64.9(2)◦ in 7 versus 62.3(5)◦ in 8 between the phenyl and pyridyl
rings; (2) the long molecular axis of the corresponding Schiff base
cation is almost perpendicular to the inorganic [PbI3]• chain.
˚
plane separation between the phenyl and pyridyl rings of 3.307 A
˚
for 5 and 3.504 A for 6.
Compound 7 is isostructural with 8, and crystals of two the
hybrid compounds belong to the monoclinic system with space
group P21/c. Fig. 7a and Fig. 7b show the asymmetric units of 7
and 8, which consist of one Pb2+ ion, three different I- ions with
one corresponding Schiff base cation, and is similar to 2, 3 and 5,
6. The coordination octahedra of PbI6 form a 1D chain via face-
sharing model along the b-axis direction. The Pb–I lengths as well
as the I–Pb–I bond angles in the PbI6 coordination octahedra are
normal and in agreement with those in 1–6 (Table S1 and Table
S2†). The crystals of 7 and 8 have a similar packing structure,
as demonstrated in Fig. 8 and Figure S7, the straight inorganic
Features of the substituents, conformations of the Schiff base
cations and the packing structures of hybrid compounds
Combined with previous studies,11b we have achieved a series of
hybrid compounds with a formula of [Cation]PbI3, where the
cation represents the mono-valence Schiff base cation of the sub-
stituted benzylidene-1-aminopyridinium. From our studies, some
significant observations (which correspond to the relationship of
the features of substituents attached to the phenyl ring of the
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Fig. 7 The view of the asymmetric units with non-H atomic labeling and the thermal ellipsoids at the 20% probability (H atoms in the cation omitted
for clarity) for (a) 7 (symmetric codes: 1A = 2A = 1 - x, 0.5 + y, 1.5 - z; 3A = 1 - x, -0.5 + y, 1.5 - z) and (b) 8 (symmetric codes: 1A = 2A = 3A = 2 - x,
0.5 + y, 1.5 - z).
Table 3 The dihedral angle (◦) between the pyridyl and the phenyl rings
in the series of hybrid compounds
Hybrid compounds
Dihedral angle/◦
References
[p-ClBz-1-APy][PbI3] (5)
[p-BrBz-1-APy][PbI3] (6)
[p-FBz-1-APy][PbI3] (4)
[Bz-1-APy][PbI3] (3)
[m-CH3Bz-1-APy][PbI3] (2)
[m-FBz-1-APy][PbI3]
[m-ClBz-1-APy][PbI3]
[m-BrBz-1-APy][PbI3]
[m-NO2Bz-1-APy][PbI3]
[m-CNBz-1-APy][PbI3] (1)
[o-ClBz-1-APy][PbI3] (7)
[o-BrBz-1-APy][PbI3] (8)
5.6(2)
5.5(9)
this work
this work
this work
this work
16.7(5)
22.1(2)
18.3(9)
48.6(4)
45.3(7)
44.9(5)
51.3(2)
45.3(9)
64.9(2)
62.3(5)
this work
Reference 11b
Reference 11b
Reference 11b
Reference 11b
this work
this work
this work
the position of substitution; the long molecular axis of the cation
adopts a manner approximately parallel to the straight inorganic
[PbI3]• chain in the para-substituted hybrid compounds, while
perpendicular to the straight inorganic [PbI3]• chain in the ortho-
substituted hybrid compounds (as an example, Fig. 9 shows the
relative orientation of the long molecular axis of the cation and
the straight [PbI3]• chain for the hybrid compounds [p-ClBz-1-
APy][PbI3] (5) and [o-ClBz-1-APy][PbI3] (7)).
Fig. 8 The arrangement of inorganic [PbI3]• chains and Schiff base cation
stacks in the crystals of 7.
Schiff base cation, the conformations of Schiff base cation and
the packing structures of the related hybrid compounds) could
be outlined below: (1) the inorganic components in these hybrid
compounds are favorable to the formation of a straight and face-
sharing octahedral [PbI3]• chain. (2) A substituent attached to the
phenyl ring of the Schiff base cation clearly influences the packing
structure of the hybrid compound. The hybrid compounds are
isostructural when the substituent group R = F, Cl, Br, NO2 and
CN (besides CH3) is in the meta-position of the phenyl ring, and in
which crystal the Schiff base cations surround the straight [PbI3]•
chains to align into polar arrangements (space group P63), whereas
the inorganic components and the Schiff base cations are packed
in a central symmetric space group when the substituent group is
attached to the ortho- or para-position of the phenyl ring. (3) The
conformation of the Schiff base cation is related to the position
of the substituent group, and the distortion of the Schiff base
cation, reflected by the dihedral angle between the phenyl and
pyridyl rings (Table 3), becomes much more serious in the order
of para- < meta- < ortho-position substitution in the phenyl ring.
(4) The relative orientation of the long molecular axis of the Schiff
base cation and the straight inorganic [PbI3]• chain depends on
Fig. 9 The relative orientation of the long molecular axis of the Schiff
base cation and the straight [PbI3]• chain in the hybrid compounds (a)
[p-ClBz-1-APy][PbI3] and (b) [o-ClBz-1-APy][PbI3].
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The crystal packing modes of inorganic salts depend mostly
upon the Madelung energy (ionic lattice energy), while the
arrangements of ions in the organic or the inorganic–organic
hybrid crystals are determined by not only the Madelung energy,
but also Lennard-Jones potential (which depend on the molecular
properties, such as shape, size, polarity, local charge distribution,
types and location of functional groups of molecules; and
generally, is less important than the Madelung energy).23 For
the series of [R-Bz-1-APy][PbI3] hybrid compounds, the common
crystal-structural characteristic is that the inorganic components
form the straight face-sharing octahedral [PbI3]• chains and the
mono-valence Schiff base cations surround the inorganic chains,
this fact indicates that the Madelung energy of an ionic crystal
probably plays an important role in the formation of such a type
of crystal packing structure; on the other hand, the nature of
the substituent group attached to the phenyl ring of the Schiff
base cation can finely tune the arrangements of the Schiff base
cations in each hybrid compound, however, it is not exactly clear
which properties of the substituent group play an key role in
tuning the alignments of the Schiff base cation. For instance, the
CH3 is a typical electron-pushing group, while F, Cl, Br, NO2
and CN are typical electron-withdrawing groups, so the hybrid
compounds [m-RBz-1-APy][PbI3] (R = F, Cl, Br, NO2 and CN)
are isostructural with each other but are different from the hybrid
compound [m-CH3Bz-1-APy][PbI3]; it is also noted that the hybrid
compounds, [p-RBz-1-APy][PbI3] (R = Cl, Br and CH3,24 and the
crystal structure are refered to in Figure S8†), are isostructural. In
order to gain insight into understanding the effect of the nature
of the substituent group on the arrangements of the Schiff base
cations, obviously it is necessary to combine the experimental
(such as systematically changing the properties of the substituent
group to assemble the new series of [RBz-1-APy][PbI3] hybrid
compounds) and theoretical investigations, and these studies are
in progress.
iodide, for example, the weight loss is about 42.7% in the 200–
320 ◦C range for 1, which corresponds to losing [m-CNBz-1-APy]I
(the calculated value is 42.2%) and PbI2 remaining; (3) above
600 ◦C, there is no residual which is in agreement with the fact
◦
PbI2 sublimates in the 450–600 C under N2 atmosphere (150 to
600 mmHg).25 For 4, since its lattice contains solvent molecules,
the first procedure of weight loss occurs in the temperature range
of 78–226 ◦C corresponds to losing the solvent molecules, and
the subsequent two weight loss processes are related to losing [p-
FBz-1-APy]I in the temperature range of 226–297 ◦C and PbI2
sublimation above 600 ◦C, respectively.
Second-order NLO and ferroelectric properties for 1
The second-order nonlinear optical and ferroelectric properties
for 1 were examined since this hybrid compound crystallizes in a
polar space group (P63). The study of a powdered sample indicated
1 is SHG active with a comparable response as that of urea.
The ferroelectric behavior was tested for the selected single
crystals, as illustrated in Fig. 11a, and the typical hysteresis loops
are observed in the polarization vs. electric field (P-E) curves of
1 under various AC electric fields at room temperature, which
show the remnant polarization (Pr) of ca. 2.3–10.8 mC cm-2,
the saturation of the spontaneous polarization (Ps) of ca. 15.1–
33.2 mC cm-2 and the coercive field (Ec) of ca. 1.6–4.7 kV cm-1.
Furthermore, the extremely low leakage currents (less than
10-8A cm-2, Fig. 11b) demonstrate the observed hysteresis loops
are clearly due to ferroelectricity.26 It is noticeable that the Ps
and Pr values of 1 are comparable with those of typical inorganic
ferroelectric compounds BaTiO3 (Ps ª 25 mC cm-2) and KNbO3
(Ps ª 37 mC cm-2).27,28
DFT calculation
Generally, the polarization of a dielectric material can be expressed
as eqn (1),
Thermogravimetric (TG) analyses for 1–8
(1)
P = Pe + Pi + Porien
TG plots for the hybrid compounds 1–8 are displayed in Fig. 10,
which shows three common features for 1–3 and 5–8; (1) the
seven compounds are thermally stable up to 200 C; (2) the first
where Pe represents the polarization due to displacement of
electrons, Pi is the polarization due to displacement of ions
and Porien is the orientation polarization contributed from the
permanent dipole moments. For 1, the p-electron delocalization
◦
procedure of weight loss corresponds to losing the Schiff base
Fig. 10 TG curves of (a) 1–3, 5–8 and (b) 4 in the temperature region from room temperature to 800 ◦C, respectively.
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Fig. 11 (a) P-E loops under various AC electric fields at room temperature and (b) leakage currents versus electric fields for 1.
can appear in the phenyl and pyridyl ring moieties as well as in
Pb2+ and I- ions which are far more polarizable, and as a result,
the displacement of electrons under electric field could give rise
to higher Pe value. On the other hand, the displacement of ions
within a [PbI3]• chain and between the negative charge of the
[PbI3]• chains and the Schiff base cations are not too difficult
to achieved under an electric field in such a molecular crystal
because of the weakly intermolecular interactions, which probably
provide higher contributions of polarization. The most important
contribution to the polarization in a ferroelectric compound is the
orientation polarization from the permanent dipole moments of
the molecules.
To better understand the observation of 1 having larger Pr
and Ps values, the theoretical investigation is necessary and
the energy band theory is the better approach because the
calculations for the dipole contributions between the nearest-
neighbor molecules as well as the next-nearest-neighbor molecules
are considered under the periodic boundary conditions; however,
such a kind of calculation is too complicated to be easily performed
because this hybrid compound contains lots of atoms. As an
approximation, only the dipole contributions between the nearest-
neighbor molecules are taken into account and the dipoles in
per unit cell were calculated by a DFT theoretical approach. From
the view point of crystal structure of 1, a unit cell contains six
crystallographically equivalent Schiff base cations together with
one Pb(1)I3-type [PbI3]• chain, which localizes at the c-axis; two
Pb(2)I3Pb(3)I3-type [PbI3]• chains, which localize inside of the cell,
and the repeat unit of each [PbI3]• chain along c-axis direction is
the fragment of [Pb2I6]2- (see Fig. 12).
DFT calculations gave rise to the dipole moment = 12.7247
D for one m-CNBz-1-APy+ cation, and 47.6571 D (with three
components X = -0.0021, Y = 0.0034 and Z = 47.6571 D) for the
total six Schiff base cations, 20.7906 (X = -0.0002, Y = 0.0003
and Z = 20.7906) D and 20.1869 (X = 0.0101, Y = -0.0086 and
Z = 20.1869) D for the [Pb2I6]2- fragments in the chain 1 and
chain 2, respectively, thus the total dipole moment of the hybrid
compound 1 in a unit cell = 47.6571 + 20.1869 ¥ 2 + 20.7906 =
101.8215 D = 12.24 mC cm-2, and the P value (under zero applied
electric field) is approximately equal to one third of Ps value from
P-E measurement.
Fig. 12 The illustration of a unit cell for 1, which contains six Schiff
base cations together with one Pb(1)I3-type and two Pb(2)I3Pb(3)I3-type
[PbI3]• chains (up) and the repeat unit of each [PbI3]• chain along the
c-axis direction, which contains the fragment of [Pb2I6]2- (down).
dipole moment; (2) the p-electrons delocalizing in the phenyl and
pyridyl ring moieties as well as both Pb2+ and I- ions are far
more polarizable; and (3) the displacements of ions being easily
achieved under an electric field in a molecular crystal. Therefore,
it is reasonable to understand the observation of 1 having a higher
polarization.
UV-vis absorption and photoluminescence spectroscopes
UV-Vis spectra of 1–8 in solid state are shown in Fig. 13, and their
commonly spectroscopic characters could be described below: (1)
there are 2–4 absorption bands in 200–320 nm regions and the
corresponding absorption band positions are similar to each other
but the relative intensities are different for each hybrid compound,
compared with our previous studies,11a and these absorption bands
could be assigned to the p–p* transitions within the cation; (2)
a broad absorption band centered around 400 nm appears in the
Based on the analysis above, it is found that the hybrid
compound 1 possesses the natures below: (1) a larger permanent
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Table 4 the main emission bands for the hybrid compounds 1–8
Compound (lex = 220 nm)
Emission bands/nm
1
2
3
4
5
6
7
8
393, 417, 437, 480, 527
393, 419, 437, 483, 525
397, 420, 458, 483, 525
393, 421, 439, 483, 529
391, 418, 440, 483, 528
399, 419, 439, 481, 523
395, 423, 444, 481, 525
400, 420, 450, 478, 526
Conclusions and remarks
In summary, eight inorganic–organic hybrid compounds with the
formula of [cation][PbI3] have been synthesized and characterized
structurally, where the cation is the mono-substituted benzylidene-
1-aminopyridinium derivative. In crystals of the eight hybrid
compounds, the inorganic components form straight and face-
sharing octahedral [PbI3]• chains and stacks of the Schiff base
cations surround the [PbI3]• chains. Combined with our previous
studies, it has been found that the Madelung energy of an ionic
crystal probably plays an important role in the formation of
such type of crystal packing structure; in addition, the nature
of the substituent group attached to the phenyl ring in the Schiff
base cation can finely tune the arrangements of the Schiff base
cations in the hybrid compounds. However, it is not exactly clear
which properties of the substituent group (such as the shape, size,
polarity, local charge distribution, types and location of functional
groups of molecules) play a key role in the tuning of the Schiff base
cation alignments.
The hybrid compounds of [R-benzylidene-1-aminopyridi-
nium][PbI3] with a typical electron-withdrawing group (Such as F,
Cl, Br, NO2 and CN) attached to the phenyl ring are isostructural
and crystallize in the polar space group P63; the corresponding
hybrid compounds are SHG active with a comparable response as
that of urea and exhibit ferroelectricity. Since the Schiff base cation
possesses a larger permanent dipole moment, the p-electrons
delocalize in the phenyl and pyridyl ring moieties of a Schiff base
cation, both the Pb2+ and I- ions are far more polarizable and
the displacements of ions are easily achieved under an electric
field in such types of molecular crystals, the hybrid ferroelectric
compounds show larger Ps and Pr values. Additionally, eight
hybrid compounds emit multi-band luminescence in the 300–
650 nm region under the excitation of ultraviolet light.
Fig. 13 UV-Vis absorption spectra in solid state for 1–8.
spectrums of 1–8, which originates from one-dimensional excitons
of the [PbI3]• chains;29 (3) there are 1–2 weak and broad absorption
bands in the l > 450 nm regions, which are probably contributed
to the charger-transfer transitions between [PbI3]• chains and the
Schiff base cations.
Fig. 14 shows the emission spectra of 1–8 in solid state at
room temperature. Upon a single-wavelength photo-excitation
at 220 nm, the eight hybrid compounds exhibit multiple band
emissions in the 300–650 nm regions, and the lmax values of the
emission bands for each hybrid compounds are summarized in
Table 4. By comparing the emission spectra, from the features of
the spectra it can be concluded that: (1) each hybrid compound
shows more than five overlaping emission bands in 300–650 nm,
the peak position of the corresponding emission band for each
hybrid compoundis similar to each other butthe relative intensities
are distinct; (2) the lmax for the most intense emission band is less
400 nm for 1 and 5; around 450 nm for 2, 4, 6, 7 and 8 as well as
in the range of 450–500 nm for 3.
There has been considerable interest in the molecular system
with technologically important physical properties for the purpose
of its application to molecular devices. Our results suggest the
possibility of ferroelectric and multiple emissions in the reasonably
designed inorganic–organic hybrid compounds.
Acknowledgements
Authors thank State Key Laboratory of Materials Oriented
Chemical Engineering, Nanjing University of Technology and
the National Natural Science Foundation of China (KL08-3,
20871068 and 20901039) for financial support.
Fig. 14 The photoluminescence spectra of 1–8 under excitation of lex
220 nm in solid state at room temperature.
=
1682 | Dalton Trans., 2011, 40, 1672–1683
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17 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
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24 Notes: the single crystal X-ray diffraction data for the hybrid com-
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˚
monochromated Mo-Ka (l = 0.71073 A) on a CCD area detector
(Bruker-SMART) and the crystallographic data are given below,
˚
˚
˚
C13H13N2I3Pb, a = 13.819(10◦) A, b = 16.772(12) A, c = 7.911(6) A, a =
◦
◦
3
˚
90.00 , b = 90.00 , g = 90.00 , 1834(2) A , Z = 4. The crystal structure
data are not good for this hybrid compound owing to the bad quality
of the single crystal, so the crystal structure for [p-CH3Bz-1-APy][PbI3]
was not discussed in this paper with other eight compounds. This hybrid
compound is isostructural with 5 and 6; the three compounds show
similar crystal packing structures (Figure S8†).
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