L. Kong et al. / Polyhedron 29 (2010) 1575–1582
1581
Adjacent Cd2+ ions are linked by two bridging SCNꢁ anions and
two Hg2+ ions with the Cdꢀ ꢀ ꢀCd distance of 6.906 Å (Fig. 3b) and
Cdꢀ ꢀ ꢀHg distance ranging from 5.340 to 5.908 Å, which further
form 1D polymeric chain along the a axis.
that photoluminescence properties of the compounds can be chan-
ged by the frameworks and different center metals.
Owing to the excellent optical properties, these compounds
may be used as potential lighter-emitting materials, chemical sens-
ing and biological applications.
Cd2+ and Hg2+ ions are also linked by bridging SCNꢁ anions to
form 2D sheets in the ab plane, containing 24-membered
[Cd3Hg3(SCN)6] cycles as subunits, which adopt pseudo–chair con-
figuration, as shown in Fig. 3c. The 2D layers link each other
4. Conclusions
through C–Hꢀ ꢀ ꢀ
p
(ring C4, C5, C6, C7, C8, C9) interaction (Hꢀ ꢀ ꢀ
p dis-
Compounds 1–4 are synthesized by self-assembly of the flexible
ligand, trans-4-[40-(N-methyl-N-hydroxyethyl) amimo]styryl pyri-
dine) with M(SCN)x (M: Zn, Co, Cd, CdHg; x: 2, 4). By supramolec-
ular self-assembly of different metals with the same ligand,
different types of framework can be obtained. Compound 1 and 2
are only mononuclear compounds, while 3 is a polymer and 4 is
a heteropolymer. The result shows that the choice of metal ion is
critical in determining the architecture of the compound. O–
tance of 3.762 Å, C–Hꢀ ꢀ ꢀ
p
= 132.8°) to form 3D frameworks.
Comparing the four compounds, we have observed the differ-
ences in coordination mode, geometries and dimensions with var-
iation of the center metals. The SCNꢁ anion links the center metals
in various fashions to form different constructions. Compound 1
and 2 are mononuclear compounds, whose metal atom adopts dis-
torted tetrahedral coordination geometry. The adjacent molecules
are stacked through O–Hꢀ ꢀ ꢀ
p interactions to form ‘K’ type 1D
Hꢀ ꢀ ꢀN, C–Hꢀ ꢀ ꢀO, O–Hꢀ ꢀ ꢀ
p
and C–Hꢀ ꢀ ꢀ
p hydrogen bonds also play
structure. Compound 3 is an infinite coordination molecule. Cd2+
ions are linked by bridging SCNꢁ groups to create 1D zigzag poly-
meric chain comprising eight-membered (N–C–S–Cd)2 rings. The
structure displays ‘pupa’ type with two free ligands attached
through hydrogen bonds to enhance the stability of the whole
structure, which is just like a Chinese ‘dragon’ with two wings fly-
ing in the sky. For CdHg–L heteropolymer, each Cd2+ ion is in a dis-
torted octahedral environment and each Hg2+ ion is in a distorted
tetrahedral geometry. Cd2+ and Hg2+ ions are linked by bridging
SCNꢁ groups to form 1D polymer chain and 24-membered
[Cd3Hg3(SCN)6] cycles, which then create 2D polymeric plane. All
these further verify that the selection of metal cations can defi-
nitely adjust the topologies of coordination frameworks, even for
structures containing the same spacer ligand and anion.
significant roles in the final crystal structures. The emission wave-
length of the compounds can be changed by the frameworks and
introducing of different metals. These compounds have potential
usage as lighter-emitting materials, chemical sensing, and biologi-
cal applications.
Acknowledgments
This research was supported by the National Natural Science
Foundation of China (20771001, 50703001 and 50873001), Young
Teacher Foundation of Institution of High Education of Anhui Prov-
ince (2006jq1030), Education Committee of Anhui Province
(KJ2009A52) and Foundation for Scientific Innovation Team of An-
hui Province (2006KJ007TD).
Appendix A. Supplementary data
3.3. Optical properties
CCDC 741841, 737174, 707972 and 737173 contain the supple-
mentary crystallographic data for compound 1, 2, 3 and 4. These
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223–
336–033; or E–mail: deposit@ccdc.cam.au.uk. Supplementary data
associated with this article can be found, in the online version, at
The linear absorbance and photoluminescence properties for L
and four compounds in solid state have been studied at room tem-
perature. The electronic spectra of the compounds are very close to
that of free L. The longest wavelength UV absorption peaks are lo-
cated at about 375 nm for the compounds and 372 nm for free L
*
(Fig. S4), presumably arisen from
p–p
transitions [13]. Compared
to that of free L, there is a slight red shift in kabs-max when metals
are introduced. The detailed data are listed in Table 4.
Metal complexes are promising luminescent materials with po-
tential applications as light-emitting materials owing to their abil-
ity to enhance, quench, and shift luminescent emission of organic
ligands by metal coordination. Free L and the four compounds 1–
4 show emission in solid state at room temperature (Fig. S5). The
excitation spectra are very similar to their absorption spectra.
The nanosecond range of lifetime reveals that the emission is fluo-
rescent in nature. As shown in Fig. S5, the maxima emissions ob-
served in the four compounds are all red-shifted compared with
that of L. The maximum wavelengths of 1, 2 and 4 are red-shifted
by 33 nm, 30 nm and 46 nm from 501 nm to 534 nm, 531 nm and
547 nm, respectively. However, for 3, it is red-shifted by 15 nm
from 501 nm to 516 nm, which is closer to L than that of 1, 2
and 4. The outcome of synergy effect of compound and free ligand
may be responsible for the solid luminescence. The results indicate
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s
(ns)