Synthesis, properties, and theoretical studies of new stepwise layered lodoplumbate: [ni(opd)2(acn)2]n[pb 4i10]n

Article abstract of DOI:10.1021/ic8012624

A novel 2D layered iodoplumbate, [Ni(opd)₂(acn) ₂]_n[Pb₄l₁₀]_n (1), yellow-green in color, has been synthesized. The anionic [Pb₄l ₁₀^2-]_n layer is

Full text of DOI:10.1021/ic8012624

Inorg. Chem. 2009, 48, 1260-1262
Synthesis, Properties, and Theoretical Studies of New Stepwise Layered
†
Iodoplumbate: [Ni(opd) (acn) ] [Pb I ]
2
2 n
4 10 n
‡
,§
‡,§
Jin-Peng Li, Long-Hua Li, Li-Ming Wu, and Ling Chen*
‡
,‡
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of
Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, People’s Republic of China, and
Graduate School of Chinese Academy of Sciences, Beijing 100039, People’s Republic of China
Received July 6, 2008
4
c,5
6
A novel 2D layered iodoplumbate, [Ni(opd)
yellow-green in color, has been synthesized. The anionic [Pb
layer is comparable to the hexagonal PbI sheet but in a lower
2
(acn)
2
]
n
[Pb
4
I
10
]
n
(1),
of the 2D layer
and 3D framework are relatively rare.
2-
4 10 n
I ]
Few heterometallic layered hybrids are also reported, such
2
-
7
as [Bi
Most of the layered iodoplumbates belong to the perovskite
type, in which the packing motif of the vertex-sharing [PbI
Ag I
4 2 16
n
] .
2
symmetry. Although the intercalated cations contribute negligibly
to the electron transition, they induce the reconstruction of the
inorganic moiety, which leads to a band-gap blue shift with respect
6
]
4
a,8
octahedra is looser than that of PbI
2
.
Such a density
decrease is because the involvement of cations requires
negative charges on the inorganic moiety. On the other hand,
the packing density of the Pb/I moiety usually reflects the
band gap of the compound. The Pb:r ratio is an empirical
parameter to indicate the packing density of the Pb/I moiety,
2
to that of PbI .
2 2
Layered binary PbI (CdI type), a direct wide-band-gap
semiconductor, has attracted continuous interest for several
decades because of its application as a photocell, X-ray and
where r is defined as r ) ∑(Nµ
n
n
-I)/n, n ) 1-6; Nµ -I means
9
the number of n-fold-coordinated I atoms per building unit.
The lower and upper Pb:r limits are 0.167 and 1.5,
respectively. The lower limit is calculated from the loosest
1
γ-ray detectors, etc. The closely related iodoplumbate can
be understood as a Pb/I hybrid generated by the introduction
4-
1
0
of suitable organic molecules/ions into PbI
2
, which exhibits
example, a discrete [PbI
from PbI , the most condensed example. The perovskite
iodoplumbate has a Pb:r ratio between 0.333 and 0.667.
A big challenge in the synthetic chemistry is how to increase
such a ratio to generate more condensed structures. Here we
report a novel layered iodoplumbate [Ni(opd)
Pb (1), with the highest Pb:r ratio (0.8) among the
anionic layered iodoplumates, in which the [PbI ] connection
is comparable to that in hexagonal PbI sheet but of lower
symmetry. The single-crystal structure, optical band gap,
thermal stability, and electronic structure are reported.
Compound 1 (Figure 1) crystallizes in the monoclinic
6
]
cluster, and the upper limit,
great structural diversity and a combination of the beneficial
2
2
4
a,8
properties of both moieties. The majority of the iodoplum-
3
4
bates are isolated clusters, 1D chains, while the derivatives
†
Dedicated to Prof. Xin-Tao Wu on the occasion of his 70th birthday.
2 2 n
(acn) ] -
*
To whom correspondence should be addressed. E-mail: chenl@
[
4 10 n
I ]
fjirsm.ac.cn. Tel.: (011)86-591-83704947. Fax: (011)86-591-83704947.
‡
Chinese Academy of Sciences.
Graduate School of Chinese Academy of Sciences.
6
§
2
(
1) (a) Kasi, G. K.; Dollahon, N. R.; Ahmadi, T. S. J. Phys. D: Appl.
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space group P2
1
/c and features a novel infinite 2D stepwise
2-
2+
[Pb
4
I
10
]
n
anionic layer with [Ni(opd)
lated cations (opd ) o-phenylenediamine; acn ) acetonitrile).
2
(acn)
2
]
as interca-
(
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(
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1
(
4) (a) Guloy, A. M.; Tang, Z.; Miranda, P. B.; Srdanov, V. I. AdV.
Mater. 2001, 13, 833. (b) Zhang, Z.-J.; Xiang, S.-C.; Zhang, Y.-F.;
Wu, A.-Q.; Cai, L.-Z.; Guo, G.-C.; Huang, J.-S. Inorg. Chem. 2006,
(8) Billing, D. G.; Lemmerer, A. CrystEngComm 2007, 9, 236.
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4
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333.
1260 Inorganic Chemistry, Vol. 48, No. 4, 2009
10.1021/ic8012624 CCC: $40.75  2009 American Chemical Society
Published on Web 01/16/2009

COMMUNICATION
Figure 1. (010) view of 1.
2 2
Figure 3. Imaginary parts ꢀ (ω) of the dielectric functions of 1 and PbI .
Figure 2. Cation effect leading to symmetry breaking. Left: single hcp
2-
2
layer in PbI . Right: single [Pb
I
4 10
n
] anionic layer in 1. The blue rhombus
2
Figure 4. Total and partial density of states of (a) PbI and (b) 1.
confines the 2 × 2 subunit.
Different from the vertex sharing in perovskite iodoplum-
bates, the [PbI ] octahedra are edge-shared in 1 (Figure 1).
The 2 × 2 subunit [Pb
shared [PbI ] octahedra, extends along the c axis in a zigzag
motif via sharing of the I3-I3 edges and propagates along
the b axis via the common I3-I4 and I4-I4 edges (Figures
which is coordinated with one µ
atoms, and from 84.45 to 93.67 and from 174.28° to 177.10°
for Pb2, which is coordinated by one µ -I and five µ -I atoms
see details in the Supporting Information, Table S2). The
t
-I, one µ
2
-I, and four µ
3
-I
6
2
-
4
I10] , which is made of four edge-
2
3
6
(
angles in PbI
coordinate to six µ
2
are nearly 90° or 180°, in which all Pb atoms
-I atoms.
The diffuse-reflectance spectra of 1 and PbI
3
1
and 2 and Supporting Information, Figure S7). Similar 2
2 subunits could be abstracted from PbI with a different
] . Two more I anions per subunit are
2
have been
×
2
measured, and the band gaps have been evaluated by the
extrapolation method (Supporting Information, Figure S1).
0
-
formula: [Pb
4
I
8
involved in 1 because of the occurrence of the less coor-
Their optical band gaps are 2.67 and 2.34 eV, respectively
dinated µ
while the I anions in PbI
t
-I1 (terminal I, one-fold coordination) and µ
2
-I2,
-I).
-I atoms are responsible for the loose packing
] octahedra (Figure 2). The anionic layer in 1 also
distinguishes it from that in ꢀ-(EDT-TTF-I
in which the charge balance has been achieved differently
12
(
2
the latter is comparable to the reported 2.27 eV for PbI ).
-
2
are all 3-fold-coordinated (µ
3
The linear absorption optical properties were described
in terms of the imaginary part ꢀ (ω) of the dielectric function
t
The µ - and µ
2
2
of [PbI
6
and calculated with the CASTEP code (Supporting Informa-
tion). As shown in Figure 3, the onset of the transition edges
of 1 and the Pb/I anionic moiety is nearly identical.
Therefore, the organic complex cations have minor contribu-
2 2 1/6 2 3
) [Pb5/60 I ] ,
2
+
5
via the Pb defects. The formation of the stepwise anionic
layers in 1 may be attributed to the cation effect because
tions to the electron transition, similar to that previously
the smaller cation in [Me
2
HN-(CH
2
)
2
-NMe
2
H][Sn
3
I
8
] induces
4b
2
reported. The electronic structures of 1 and PbI have been
2- n
11
a stepwise [Sn I ] anionic layer but with a narrower step.
3 8
calculated (Figures 4 and 5). For the sake of a clear
comparison, the cations in 1 have not been considered. As
The Pb-I bonds in 1 are quite distorted in the range of
.001(1)-3.529(9) Å, with 3.22 Å as the average (the Pb-I
3
shown in Figure 5a, PbI
2
has a direct band gap, and the
bond is 3.22 Å in PbI
2
), and the I-Pb-I angles range from
highest occupied crystal orbitals (HOCOs) are mainly the
8
1.63° to 104.15° and from 164.56° to 172.25° for Pb1,
(
12) Zhu, X.-H.; Wei, Z.-R.; Jin, Y.-R.; Xiang, A.-P. Cryst. Res. Technol.
2007, 42, 456.
(
11) Krautscheid, H.; Lode, C. Z. Anorg. Allg. Chem. 2001, 627, 1454.
Inorganic Chemistry, Vol. 48, No. 4, 2009 1261

COMMUNICATION
2
Figure 5. Electronic band structures of (a) PbI and (b) 1. The arrows
indicate the direct and indirect band gaps.
antibonding states of Pb 6s and I 5p (p
x y
/p ) at A (k ) 0.0,
0.0, 0.5) and the lowest unoccupied crystal orbitals (LUCOs)
z
are mostly Pb 6p orbitals (Supporting Information, Figures
S2 and S3). The HOCO antibonding interactions are along
the z axis (parallel to the crystallographic c axis), and p
Figure 6. TG/DTA curves of compound 1.
z
orbitals of LUCOs show σ interactions between neighboring
layers. The maximum destabilization is at A (k ) 0.0, 0.0,
(
calcd 3.37%) above 210 °C, because of the loss of CH
molecules, and then 8.39% weight (calcd 8.90%) above 290
C, because of the loss of opd molecules. Finally, 1 has been
completely decomposed to PbI , which melts at 400 °C.
In summary, a novel type of stepwise Pb/I inorganic layer
has been found in compound [Ni(opd) (acn) [Pb with
3
CN
1
3
0
.5), while the lowest energy of the conducting band is
°
also observed at A, which therefore indicates the direct band-
gap character. Both HOCOs and LUCOs of 1 have similar
components but with larger degrees of distortion (Supporting
Information, Figures S4 and S5). The interlayer orbital
interactions are slightly off the x direction (parallel to the
crystallographic a axis); the flat band structures from Y
2
2
]
2 n
4 10 n
I ]
the highest Pb:r ratio (0.8) among the anionic layered
iodoplumbates. The inorganic layer is more condensed than
that in the perovskite type but less symmetric than the
hexagonal PbI sheet. The linear absorption optical property
2
calculation indicates a minor contribution of the cations to
the transition edge. However, the cation template effect leads
to such a novel packing motif of the [PbI
with PbI , 1 has a 0.33 eV wider band gap and less thermal
stability. New layered iodometalates are expected via the
choice of suitable intercalate species and a new combination
of inorganic building units.
(
-
k ) 0.0, 0.5, 0.0) to A (k ) -0.5, 0.5, 0.0) and E (k )
0.5, 0.5, 0.5) to C (k) 0.0, 0.5, 0.5) indicate that there is
only a very weak interaction along the a axis because of
intercalation of the cations. So, nearly no electron transition
would occur along such an axis, and the electron transition
should be confined to the Pb/I layer. This may be in response
6
] unit. Compared
2
2
to the band-gap blue shift observed between 1 and PbI . On
the other hand, the orbital distortion may affect the transition
direction of the electrons and lead to an indirect band gap
for 1 (Figure 5b). These simple correlations suggest that,
although the intercalated cations between Pb/I layers con-
tribute negligibly to the electronic transition, the template
effect of the cations causes the reconstruction of the Pb/I
inorganic moiety and thus leads to different properties.
The thermal stability of 1 has been studied by thermo-
gravimetric/differential thermal analysis (TG/DTA) on hand-
picked crystals, of which the phase purity has been confirmed
by the X-ray diffraction pattern (Supporting Information,
Figure S6). As shown in Figure 6, 1 first loses 3.13% weight
Acknowledgment. This work was supported by the
National Natural Science Foundation of China under Projects
2
FIRSM” (Projects SZD08002 and SZD07004), and the “Key
Project from CAS” (Project KJCX2-YW-H01).
0773130, 20733003, and 20821061, the “Key Project from
Supporting Information Available: Crystallographic data in
the form of a CIF file, details of synthesis methods, experimental
measurements of compound 1, theoretical calculation details, and
other supporting tables and figures. This material is available free
of charge via the Internet at http://pubs.acs.org.
(13) Bradley, C. J.; Cracknell, A. P. The Mathematical Theory of Symmetry
in Solids; Clarendon Press: Oxford, U.K., 1972.
IC8012624
1262 Inorganic Chemistry, Vol. 48, No. 4, 2009