A lanthanide salen "square prism" and a wrapped exo-lanthanide salen "double decker"

Article abstract of DOI:10.1039/c4dt03959a

An erbium(iii) salen "square prism" and a supramolecular aggregate of exo-erbium(iii) salen "double-decker" cations wrapped by an anionic cuprous cyanide network were prepared from N,N′-ethylene bis[4-(diethylamino)salicylideneimine. Both erbium(iii) edif

Full text of DOI:10.1039/c4dt03959a

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Succeeded in building lanthanide salen “square prism” and in wrapping labile exo-lanthanide salen “double
decker” by cuprous cyanide netting. Both lanthanide edifices show near-infrared (NIR) luminescence.
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Lanthanide Salen “Square Prism” and Wrapped Exo-
Lanthanide Salen “Double Decker”
Cite this: DOI: 10.1039/x0xx00000x
YuꢀBo Shua and WeiꢀSheng Liu*a
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
www.rsc.org/
An erbium(III) salen “square prism” and a supramolecular of a chemically modified salen ligand, N,N'ꢀethylene bis[4ꢀ
aggregate of exo-erbium(III) salen “double-decker” cation (diethylamino)salicylideneimine] (H2L, Scheme 1), here we
wrapped by anionic cuprous cyanide network were prepared report a quadrupleꢀstranded dinuclear lanthanide molecular
from N,N’-ethylene bis[4-(diethylamino)salicylideneimine. “square prism” of Er(III) with octahedral metal centers. Two
Both erbium(III) edifices show fine-structure near-infrared previous examples of structurally characterized quadruplyꢀ
(NIR) luminescence under the excitation at visible light area
.
stranded dinuclear lanthanide edifices have been reported, one
Here provides a novel and efficient method for stabilizing is molecular “helicate” of Dy(III) with squareꢀantiprismatic
non-isolable lanthanide edifice in the solid state.
metal centers,8 and another one is molecular “lanterns” of light
and medium lanthanides with monocapped squareꢀantiprismatic
metal centers.9
Lanthanideꢀcontaining monoꢀ and polymetallic complexes have
received extensive attention because of their beautiful
architectures and highly desirable properties in optics and
magnetism.1 Recently, great interest has been focused on
polynuclear Nd, Er, and Yb(III) lanthanide complexes with
nearꢀinfrared (NIR) emission around 0.9 to 1.6 µm, due to their
potential applications in many advanced technologies such as
telecommunication, laser, as well as bioꢀanalysis and imaging.2
However, the design and assembly of emissive NIR lanthanide
edifices remains a real challenge for synthetic chemists, caused
by the fact that: (i) most organic ligands (chromophores) are
poor sensitizer for NIR lanthanides especially for Er(III) with
the smallest energy gap between its excited and groundꢀstate
levels that easily matched by the C–H vibrational oscillator,3
and (ii) lanthanide coordination spheres display high kinetic
lability and weak stereochemical preference.4
Schiff base or salen ligands are well known for their versatility
in the construction of functional metal complexes.5 The
emerging field of study on salenꢀbased complexes is the
exploitation of their photophysical properties.5c Che and Yersin
have reported phosphorescent platinum(II) salen complexes and
the application in highꢀperformance organic lightꢀemitting
devices (OLEDs).6 From a series of salen ligands with varying
flexible backbones, Yang and Jones has synthesized many
visibleꢀ and NIRꢀemissive 4f and d–4f complexes.7 By design
Scheme 1. The H2L ligand.
An issue often encountered in structural characterization and
study on properties is the low stability of lanthanideꢀcontaining
molecular edifices in the solid state,4b,10 manifesting as the loss
of single crystallinity or even the dissociation of molecule. It is
necessary to develop an efficient method for stabilizing and
observing valuable edifice molecules. Fujita has succeeded in
direct crystallographic observation of extremely labile organic
and organometallic species trapped in confined cavities.11 In
our experience, most of polynuclear lanthanide complexes are
positively charged. Therefore, we consider wrapping the huge
body of lanthanide edifice with cuprous cyanide netting,12
which is negatively charged due to the necessitation of 3 or 4ꢀ
connected Cu(I) sites. Then, a supramolecular aggregate of exoꢀ
erbium(III) “doubleꢀdecker” cation caught by anionic cuprous
cyanide network is presented.
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Figure 1. The quadruple-stranded dinuclear “square prism” of complex 1. Color
scheme: Er(III), purple; Cl-, dark green.
Figure 2. The asymmetric unit of complex
2
. Color scheme: Er(III), purple; Cl-,
dark green; Cu(II), pink; Cu(I), pale yellow; C and N of CN-, pale grey.
Solvothermal reaction of H2L with ErCl3ꢁ6H2O in methanol
solution at 65 °C results in the formation of yellowishꢀbrown
polyhedral crystals of [Er2(H2L)4Cl4ꢁ(MeOH)2Cl2] (
1). Singleꢀ
crystal Xꢀray analysis of at 80 K reveals that it crystallizes in
1
triclinic space group Pꢀ1. The asymmetric unit contains only
one crystallographically independent Er(III) ion. Each Er(III)
ion is sixꢀcoordinate and adopts Oh octahedron geometry
(Figure S4a). In addition to two terminal chlorine anions [Er–
Cl1 2.683 Å, Er–Cl2 2.624 Å] at the axial location, the Er(III)
ion is equatorially bound to four oxygen atoms [Er–O in the
range of 2.200–2.221 Å] from four different H2L ligands. The
four H2L ligands in turn serve to bridge two adjacent Er(III)
ions forming a quadrupleꢀstranded dinuclear molecular “square
prism” with the Er···Er separation being ca. 8.9 Å (Figure 1).
This “square prism” edifice has molecular S2 symmetry about
its center. It should be noted that the ligands (H2L) remain
neutral in the complex through protons migrate from the phenol
oxygen atoms to the nitrogen atoms of imine. The valence
requirements of the “square prism” molecule are satisfied by
the presence of two uncoordinated chloride ions. Each “square
prism” interacts with eight neighboring ones through
intermolecular π–π stacking and van der Waals force (Figure S5)
Figure 3. View of the supramolecular aggregate of complex 2 along b direction.
Color scheme: Er(III), purple; Cl-, dark green; Cu(II), pink; Cu(I), pale yellow; C and
N of CN-, pale grey.
to generate
a 3ꢀD supramolecular framework with the
interstices occupied by chlorine counter ions and methanol CuIIL unit approachs another one from the side to compose a
guest molecules.
boatꢀshape O2O2 donor set, which is coordinated to the Er(III)
Solvothermal reaction of H2L with ErCl3ꢁ6H2O and CuICN in ion [Er–O in the range of 2.277–2.318 Å] (Figure 2). The lastly
methanolꢀacetonitrile solution at 65 °C affords brownꢀblack distorted octahedron coordination geometry of Er(III) is
rectangular block crystals of [CuI4(CN)5(CH3CN)4ꢁErCuII L2Cl2] completed by two terminal chlorine anions [Er–Cl1 2.530 Å,
2
(2). Singleꢀcrystal Xꢀray analysis of 2 at room temperature Er–Cl2 2.529 Å] (Figure S4b). The formed electropositive
reveals that it crystallizes in triclinic space group Pꢀ1. The [ErCuII L2Cl2] unit can be described as exoꢀlanthanide “doubleꢀ
2
asymmetric unit contains four independent Cu(I) ions, two decker” cation, which seems hard to exist alone because of the
Cu(II) ions, and one Er(III) ion. The Cu(II) ion is generated in weak µꢀO donor. These cations are confined in 1ꢀD rectangular
situ to fit the square planar N2O2 donor set of the L ligand,13 channels that constructed between adjacent 2ꢀD anionic
forming a CuIIL metalloligand with potential
µ
ꢀO donors. The
[CuI4(CN)5(CH3CN)4]∞ networks bearing terminal acetonitrile
2 | J. Name., 2012, 00, 1-3
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ligands (Figure 3). In the 1ꢀD array, the neighboring cations are
oriented antiparallel to each other (Figure S6). The cuprous
cyanide network exhibits hcb (6,3) topology through treating 3ꢀ
connected Cu(I) ions (trigonal planar coordinated) as nodes and
thinking of both CNꢀ groups and 2ꢀconnected Cu(I) ions (linear
coordinated) as linkers.
The single crystal of complex
1 is unstable both in mother
liquor and in air at room temperature. Inꢀsitu powder Xꢀray
diffraction (PXRD) analysis of bulk crystals in air at room
temperature shows the fast weathering, but without the change
of molecular structure (Figure S2). Thermogravimetric analysis
(TG) of weathered sample of
shows that the “square prism” molecule can be stable up to
~290 °C (Figure S7). Thus, the low stability of complex is
1 under nitrogen atmosphere
1
merely the easy loss of single crystallinity due to intraꢀ and
intermolecular rearrangement in the crystals (e.g., rotation,
bending, swinging, sliding, shrinking, or swelling).14 The single
Figure 4. Solid-state reflectance spectra of
1 and 2 at room temperature.
crystal of complex
2 is quite stable at room temperature, and
the content of Er(III) ion in bulk crystals can be further
confirmed by inductively coupled plasmaꢀatomic emission
spectrometry (ICPꢀAES). TG analysis of complex
2 under
nitrogen atmosphere shows that the supramolecular framework
is stable up to ~250 °C (Figure S8). As a consequence, we
characterized the photophysical properties of both complexes in
bulk crystals at room temperature.
The reflectance spectra of complex
Figure 4. The absorption band of
1
and
2 are presented in
1
contains two peaks at 305
and 444 nm in regard to π→π* and intraꢀligand charge transfer
(ILCT) transitions respectively. The ILCT transition originates
from the movement of electron density from the diethylamino
group to the imine group in the process of absorption.6,15
Moreover, weak f→f transitions of Er(III) (4I15/2→4F7/2,488 nm;
4
4
4I15/2→2H11/2, 521 nm; I15/2→4S3/2, 546 nm; I15/2→4F9/2, 655
nm; I15/2→4I9/2, 800 nm; I15/2→4I11/2, 978 nm) are observed.
The absorption band of consists of π→π* transition at 323 nm,
ILCT transition at 443, and an additional d→d transition of
Cu(II) at 678 nm. The excitation spectra of complex and
(Figure 5a and 5b) are in good agreement with their reflectance
spectra. Complex
than 300 nm and another one at 446 nm. Complex
4
4
2
1
2
1
shows two excitation peaks with one lower Figure 5. Solid-state excitation and emission spectra of
(slit width 12 nm) at room temperature. (a) Excitation of
emission of , and (d) emission of
1
(slit width 9 nm) and
2
2
, (b) excitation of , (c)
1
2
also
1
2.
exhibits two excitation peaks at 350 and 424 nm. The strong
visibleꢀlight excitation is more desirable as visible light is less
likely to damage organic and biological materials.15,16
to the characteristically weak emission of Er(III),3a we still
identify the stronger luminescence of than that of through
comparing their spectral intensities. The weak luminescence of
is attributed to the presence of Er(III)→Cu(II) (4f→3d)
energy transfer, shown in the hardly observable Er(III) f→f
transitions in reflectance spectrum of 2 7
1
2
As presented in Figure 5c and 5d, both complex
1
and
2
1
exhibit
is split
4
fineꢀstructure emission. The I13/2→4I15/2 transition in
2
into three components at 1425, 1478, and 1543 nm with a
dominant one at the minimum wavenumber (1543 nm), and in
2
.
the split is at 1425, 1479, and 1549 nm with the maximum at
medium wavenumber (1479 nm). These three components
Conclusions
4
reflect the ligandꢀfield splitting of the ground state F15/2 level
under Oh symmetry.17 The energy barycentre of Er(III) ion
In summary, from a chemically modified salen ligand, we built
an erbium(III) molecular "square prism", and thereafter
assembled a supramolecular aggregate of exoꢀerbium(III)
"doubleꢀdecker" cation wrapped by anionic cuprous cyanide
network. This is the first attempt of the fabrication of cuprous
cyanide network around unstable lanthanide edifice. The fineꢀ
shifts toward high wavenumber because of the enhanced Cl–Er
(III) ionic bond, and also the increased electrovalence of µꢀO–
Er(III) bond resulted from the decreased orientation in distorted
octahedron coordination environment.18 Although it is failing to
determine the luminescence lifetimes and quantum yields due
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structure NIR emissions of both Er(III) edifices were detected 14.8845(9),
b
= 15.6342(8),
= 61.857(6)º,
The final refinement converges to final
611 parameters from 11712 independent reflections (
goodness of fit on F2 was 0.945. Crystal data for
: C55H67Cl2Cu6ErN14O4,
= 1607.69, triclinic, space group Pꢀ1 = 15.091(5),
15.948(6) Å, = 112.308(3)º, = 98.746(4)º, = 108.033(3)º,
3161.5(19) Å3,
to final = 0.0240 and wR = 0.0589 with 748 parameters from 11115
independent reflections ( >2
)). The goodness of fit on F2 was 0.973.
CCDC reference numbers 1006240 and 1025686.
c
= 15.6534(11) Å,
= 2954.4(4) Å3, = 1, Dc = 1.267 g cmꢀ3.
= 0.0792 and wR = 0.2044 with
>2 )). The
α = 69.359(5)º, β =
by visible light excitation.
89.180(5)º,
γ
V
Z
R
I
σ(I
Acknowledgements
2
The authors acknowledge financial support from the National
Natural Science Foundation of China (NSFC) (grant numbers
21431002, and 91122007) and the Specialized Research Fund
for the Doctoral Program of Higher Education (grant number
20110211130002).
M
,
a
b
= 15.687(5),
c
=
=
α
β
γ
V
Z
= 2, Dc = 1.689 g cmꢀ3. The final refinement converges
R
I
σ(I
Notes and references
1
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Utilization of Gansu Province and State Key Laboratory of Applied
Organic Chemistry, College of Chemistry and Chemical Engineering,
Lanzhou University, Lanzhou 730000, P. R. China. Eꢀmail:
liuws@lzu.edu.cn
†
Electronic Supplementary Information (ESI) available: [IR spectra,
PXRD patterns, TG curves, and additional diagrams]. See DOI:
10.1039/c000000x/
2
3
Experimental
Synthesis of 1: H2L (0.010 g, 0.025 mmol) and ErCl3·6H2O (0.0095 g,
0.025 mmol) were dissolved in MeOH solvent (2 mL). This solution was
sealed and heated at 65 °C for 1 day, and then cooled to room
temperature. The resulting yellowishꢀbrown crystals were filtered off and
dried in air. Yield (based on H2L): 81%. IR (KBr, cm−1): 3389 (w), 3178
(w), 2970 (w), 2929 (w), 1616 (vs), 1516 (vs), 1387 (m), 1347 (s), 1272
(s), 1241 (s), 1147 (s), 1079 (m), 1014 (m), 968 (w), 848 (m), 779 (m),
703 (m), 587 (m). Elemental analysis (%): calcd for C98H144Cl6Er2N16O10
(2253.52): C 51.19, H 6.39, and N 9.94; found: C 52.01, H 6.36, and N
9.35.
4
5
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6
7
8
9
Synthesis of 2: CuCN (0.0086g, 0.009 mmol) was added to a solution of
H2L (0.010 g, 0.025 mmol) and ErCl3·6H2O (0.0057 g, 0.015 mmol) in
mixed MeOH–MeCN solvent (2/2 mL). After stirring for 5 min, this
slurry was sealed and heated at 65 °C for 6 days, and then cooled to room
temperature. The resulting brownꢀblack crystals were filtered off and
dried in air. Yield (based on H2L): 75%. IR (KBr, cm−1): 3428 (w), 2968
(w), 2925 (w), 2123 (m), 1596 (vs), 1523 (vs), 1409 (m), 1354 (s), 1327
(m), 1243 (s), 1139 (s), 1075(m), 1015 (w), 974 (w), 829 (m), 792 (m),
705 (m), 644 (m), 587 (w), 563 (w). Elemental analysis (%): calcd for
C55H67Cl2Cu6ErN14O4 (1607.69): C 41.05, H 4.17, and N 12.19; found: C
40.79, H 4.03, and N 11.82. ICPꢀAES analysis (%): Er 10.54.
X.ꢀP. Yang, R. A. Jones, S.ꢀM. Huang, Coord. Chem. Rev., 2014, 273
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63.
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Crystallography analyses: Singleꢀcrystal Xꢀray diffraction data of
collected on an Agilent Technologies Gemini A System (Cu Kα,
1.54178 Å) at 80 K. The data was processed using CrysAlis. Data
collection of was performed on a Bruker APEXꢀII CCD diffractometer
(Mo Kα, = 0.71073 Å) at 293 K. An empirical absorption correction
1 was
λ
=
12 a) X.ꢀP. Zhou, W.ꢀX. Ni, S.ꢀZ. Zhan, J. Ni, D. Li, Y.ꢀG. Yin, Inorg.
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2
λ
based on a comparison of redundant and equivalent reflections was
applied using SADABS. Both structures were solved by direct methods
and refined by fullꢀmatrix leastꢀsquares cycles on F2. The Olex2,
SHELXS97, and SHELXL97 programs were used for all the
calculations.19 The SQUEEZE program was used to remove the
contributions of disordered methanol guest molecules.20 Crystal data for
13 X.ꢀM. Chen, M.ꢀL. Tong, Acc. Chem. Res., 2007, 40, 162.
14 M. H. Mir, L. L. Koh, G. K. Tan, J. J. Vittal, Angew. Chem. Int. Ed.
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,
1: C98H144Cl6Er2N16O10, M = 2253.52, triclinic, space group Pꢀ1, a =
5
4 | J. Name., 2012, 00, 1-3
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17 J. C. G. Bünzli, S. V. Eliseeva, Basics of Lanthanide Photophysics, In
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