Synthesis, crystal structure and luminescence of [Ag(PPh3) 2(H2TMT)]

Article abstract of DOI:10.1002/zaac.200400524

The silver complex Ag(PPh₃)₂(H₂TMT) (1)(H₃TMT = 2,4,6-trimercapto-1,3,5-triazine) has been synthesized and characterized. The ligand trimercaptotriazine exhibits a novel coordination mode and the complex shows a special hydrogen bonding linkage in the crystal packing. The colorless crystals of 1 exhibit broad emission in the visible region at room temperature. TDDFT calculation indicated that the π-π attraction is crucial for fluorescence of the title complex.

Full text of DOI:10.1002/zaac.200400524

Synthesis, Crystal Structure and Luminescence of [Ag(PPh3)2(H2TMT)]
Yong-Qin Wei, Ke-Chen Wu, Bo-Tao Zhuang, Zhang-Feng Zhou, Ming-Xin Zhang, and Cai-Ping Liu
Fuzhou, Fujian / P. R. China, State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter,
the Chinese Academy of Sciences
Received December 15th, 2004.
Abstract. The silver complex Ag(PPh3)2(H2TMT) (1)(H3TMT ϭ
2,4,6-trimercapto-1,3,5-triazine) has been synthesized and charac-
terized. The ligand trimercaptotriazine exhibits a novel coordi-
nation mode and the complex shows a special hydrogen bonding
linkage in the crystal packing. The colorless crystals of 1 exhibit
broad emission in the visible region at room temperature. TDDFT
calculation indicated that the π-π attraction is crucial for fluor-
escence of the title complex.
Keywords: Silver; Trimercaptotriazine; Crystal structure; Lumi-
nescence spectra; π-π imteraction
Introduction
Synthesis
Preparation of [Ag(PPh3)2(H2TMT)] (1): 1 mmol of H3TMT re-
acted with 3 mmol of CH3ONa in 10 mL of CH3OH for half an
hour. After 3 mmol of [Ag(PPh3)2]NO3in 20 mL of CH3CN was
added, the resulting mixture was refluxed for one hour. After cool-
ing, the precipitate was removed by filtration. The filtrate was then
put aside affording the colorless crystals of 1. Yield 0.72 g.
In the view of the strong coordination ability and versatile
bonding modes, the sodium salt (Na3TMT) of 2,4,6-trimer-
captotriazine (S3C3N3 ϭ TMT) can be used to remove uni-
valent (Agϩ) and divalent heavy metal (Hg2ϩ, Cd2ϩ, Pb2ϩ
and Cu2ϩ) from wastewaters.[1] Some metal complexes and
metal clusters with novel structures have been synthesized,
in which the TMT ligand adopts sixfold coordination donor
atoms (three N and three S) bonding to metal ions. Such
examples include Ba(H2TMT)2·4.5H2O, [2], (AuL)3TMT
(L ϭ PPh3, t-BuNC, P(OMe)3, P(OPh)3, PCy3) [3],
(HgMe)3TMT, [4], [(AuL)2(AuTMT)]2 (L ϭ t-BuNC,
PPhMe2,) [3, 5], [(CuPPh3)6(μ6-TMT)2]Cl3 [6], and (Os3H-
(CO)10)3TMT. [7] The common coordination mode of TMT
is either to use its N and S donor atoms or to bond to the
metal ions via its S donor atoms. In this article, we report
a new silver complex [Ag(PPh3)2(H2TMT)] (1), in which the
TMT unit exhibits a new coordination mode and only uses
one nitrogen atom to coordinate to the univalent silver. To
our knowledge, this is the first example of such coordi-
nation mode of TMT.
Elemental analysis [found (Calcd)] for C39H32N3P2S3Ag : C 57.38 (57.93); H
4.23 (3.99); N 5.55 (5.20) %.
Infrared spectrum (KBr, cmϪ1): ν (TMT-H) 3434s; ν (CϭC, phenyl) 1615s,
1475m, 1454s; ν (P-C) 1089m; γ (C-H phenyl) 742s, 696s.
X-ray crystallographic study
A
suitable single crystal of complex 1 with dimension of
0.50ϫ0.20ϫ0.12 mm was carefully selected and glued to thin glass
fibers with epoxy resin. Intensity data for single crystal was col-
lected at 293 K on a Bruker SMART CCD detector with graphite-
˚
monochromatized MoKͰ radiation (λ ϭ 0.71073 A). An empirical
absorption correction was applied using SADABS program [9]. The
structures were solved by direct methods and refined on F2 by full-
matrix least-squares technique using the SHELX97 program pack-
age [10, 11]. Anisotropic thermal parameters were applied to all
non-hydrogen atoms. The crystallographic data are listed in table 1.
Calculational details: TDDFT calculation on the excited states of
1 was performed with the Gaussian 03 suite of programs [12] at the
B3LYP/CEP-121G level. The contour plots of MOs were obtained
with the GaussianView program. The model was obtained directly
from the crystal structure of complex 1.
Experimental Section
General remarks: H3TMT was commercially available.
[Ag(PPh3)2]NO3 was synthesized by the procedure described in lit-
erature [8]. Elemental analyses were performed on a Vario EL III
CHNOS Elemental Analyzer. The Infrared spectrum of KBr pellets
was made on a Perkin Elmer Spectrum One FT-IR Spectrometer.
The emission spectrum was recorded on a FLS920 fluorescence
spectrophotometer.
Results and Discussion
Synthesis and crystal structure
All the three hydrogen atoms of H3TMT are expected to be
removed so as to all the six S and N donor atoms of TMT
bound to the metal ions. However, complex 1 was isolated
unexpectedly from the filtrate, in which two of hydrogen
atoms are still remain (as shown in fig. 1). When
[Ag(PPh3)3]NO3 was utilized in place of [Ag(PPh3)2]NO3,
crystals of 1 were still obtained from the filtrated solution.
* Prof. Dr. Kechen Wu
Fujian Institute of Resarch on the structure of matter,
the Chinese Academy of Sciences,
Fuzhou, Fujian, 350002 / P. R. China
Tel.: ϩ86-591-83792600
Fax: ϩ86-591-83714946
E-mail address: wkc@ms.fjirsm.ac.cn
1532
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
DOI: 10.1002/zaac.200400524
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Synthesis, Crystal Structure and Luminescence of [Ag(PPh3)2(H2TMT)]
Table 1 Crystallographic data for [Ag(PPh3)2(H2TMT)]
Formula
C39 H32 N3 P2 S3Ag
808.67
0.50 ϫ 0.20 ϫ 0.12
colorless
monoclinic
P21/c
11.2956(6)
17.9990(8)
18.9604(10)
105.4490(10)
3715.5(3)
4
Formula weight
Crystal size /mm
Crystal color
Crystal System
Space group
˚
a /A
˚
b /A
˚
c /A
β /°
3
˚
V /A
Z
Dcalc /(g·cmϪ3
F(000)
)
1.446
1648
0.829
μ /(mmϪ1
)
θ for data collection /°
Reflections collected
Unique reflections
Refined parameters
R1, wR2 [I > 2σ(I)]
R1, wR2(all data)
1.59 to 25.03
6473
4712
Fig. 2 Hydrogn bonding in the packing arrangement of 1 (the phe-
nyl groups of PPh3 were omitted for clearity)
433
0.0528, 0.0937
0.0871, 0.1095
0.395/Ϫ0.437
Ϫ3
˚
Largest/smallest peaks /eA
Fig. 3 Excitation (left, upon emission at 450 nm) and emission
(right, upon excitation at 350 nm) spectra of 1 at ambient tempera-
ture in solid state.
Fig. 1 The coordination environment of 1. Selected bond distances /
A and angles /°.
Ag(1)-P(1) 2.511(1), Ag(1)-P(2) 2.417(1), Ag(1)-N(71) 2.311(1), P(1)-Ag(1)-
P(2) 128.74(2), P(1)-Ag(1)-N(71) 97.41(4), P(2)-Ag(1)-N(71) 128.34(4).
Anionic H2TMTϪ also exists in the complexes
Ca(H2TMT)2·11H2O and Sr(H2TMT)2·11H2O [2], but
H2TMTϪ is not bound directly to Ca2ϩ and Sr2ϩ octahy-
drate units. To our knowledge, complex 1 is the first ex-
ample that TMT only uses one nitrogen atom to coordinate
to a metal ion.
˚
Figure 1 shows the molecular structure of 1. One phenyl
group in the PPh3 is nearly coplanar with H2TMTϪ group
Another important crystal feature is a nearly planar stack
of H2TMTϪ groups and they are connected by an extensive
array of hydrogen-bonding contacts between the NHϩ
groups and S atoms. Figure 2 shows the crystal packing of
1. Each one H2TMTϪ1 group uses two sulfur atoms (S(1)
and S(2), as shown in the figure 1) to form hydrogen bonds.
˚
with ring centroid distance of about 3.5 A. This distance is
in the range expected for π-π attractions [13]. Univalent sil-
ver is nearly localized at a nearly trigonal-planar environ-
ment and torsion angle of P(2)-Ag(1)-N(71)-P(1) is
155.14(4)°. H2TMTϪ only uses one nitrogen atom to coor-
dinate to univalent silver. There is no bond to exist between
the S atom and the Ag atom because Ag(1)···S(1) distance
˚
The S(1)···H and S(2)···H distances are 2.417(2) A and
˚
2.585(0) A, respectively.
˚
(3.688(2) A) is longer than the sum of van der Waals radii
˚
for Ag and
S
(3.52 A). The Ag(1)···S(3) distance
Luminescence
The singlet excited states of AgI complexes are easily
changed to triplet excited states by the intense spin-obital
˚
(3.086(1) A) is longer than common Ag-S bond distance
(about 2.5 A). The remaining two hydrogen atoms on the
˚
TMT ligand protonate the uncoordinated nitrogen atoms.
Z. Anorg. Allg. Chem. 2005, 631, 1532Ϫ1535
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© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
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Y.-Q. Wei, K.-C. Wu, B.-T. Zhuang, Z.-F. Zhou, M.-X. Zhang, C.-P. Liu
Fig. 4 Comparison of theoretical and experimental excitation spec-
trum for 1
coupling of AgI, which causes the luminescenent qenching
of AgI complexes. Most of luminescent AgI complexs exhi-
bit emission at low temperature [14Ϫ16] and AgI complexs
which exhibit luminescence at room temperature are few
[17Ϫ22]. Interestingly, complex 1 is luminescent at ambient
temperature. As shown in figure 3, there are two excitation
peaks (276 nm and 346 nm) in ultraviolet region. With exci-
tion at 350 nm, complex 1 shows broad emission in visible
region with maximum at 453 nm. The emission of 1 belongs
to fluorescence since the emission lifetime is 6.7 ns. Obvi-
ously the emission of 1 does not originate from triplet ex-
cited states and spin-obital coupling of AgI may be has no
effect on the lowest singlet excited state of complex 1.
Fig. 5 Frontier molecular orbitals for 1 (the value of isosurface
is 0.01)
Table 2 TD/B3LYP excitation energy (λ, nm), the corresponding
oscillator strength (f) and composition for the lowest excited states
of 1
State
λ
f
Compositon
11A
21A
386.62
354.67
0.0002
0.0006
0.65 (125aǞ126a) ϩ 0.20 (125aǞ127a)
0.16 (121aǞ126a) Ϫ 0.20 (122aǞ126a)
ϩ0.57 (123aǞ126a) ϩ 0.26 (125aǞ127a)
31A
340.04
319.69
0.0002
0.0727
Ϫ0.18 (121aǞ126a) ϩ 0.15 (121aǞ127a)
ϩ0.20 (122aǞ127a) Ϫ 0.26 (123aǞ126a)
Ϫ0.16 (125aǞ126a) ϩ 0.54 (125aǞ127a)
41A
0.10 (121aǞ126a) Ϫ 0.40 (122aǞ126a)
Ϫ0.12 (123aǞ126a) ϩ 0.40 (124aǞ126a)
Ϫ0.28 (124aǞ127a) Ϫ 0.10 (125aǞ127a)
TDDFT calculation
With an objective to understand the origin of photolumi-
nescence of the title complex, 20 singlet excited states of 1
were calculated at the level of B3LYP/ECP-121G. In the
case of metal complexes of such large size, the TDDFT ap-
proach [23] is one of the most suitable choices to calculate
accurately the excited energy because of its lower compu-
tational cost compared with other high-level ab initio tech-
niques and including the effects of electron correlation at
some reasonable level. For excitation energy studies on
small molecules, the basis sets with diffuse functions need
to be used to describe the outer molecular region. However,
for the system of such large size under study, the main ef-
fects are related to ordinary bound orbitals, which are well
described with the used basis set CEP-121G including rela-
tivistic effects. 694 basis functions and 125 occupied orbitals
were involved in the calculation.
ter, which brings difficulty for assignment of charge-transfer
in the excited states. But the LUMO (126a) and LUMOϩ1
(127a) are always relative to the multitransition of the low-
est excited states from 11A to 71A. We perform a visual
analysis of frontier molecular obitals. In the highest occu-
pied obitals from 121a to 125a (HOMO), there has no π-π
attraction in the two coplanar rings of TMT and phenyl
groups. As shown in figure 5, the two lowest unoccupied
orbitals 126a and 127a are mainly localized on the two co-
planar rings which exhibit obvious π-π attraction character.
The π-π attraction is stronger in the lowest excited states
compared to the ground state.
The basic conclusion is that the excitation has the com-
plicated multitransition character, whereby the two co-
planar rings of TMT and phenyl with π-π attraction charac-
ter act as fluorophores.
The TDDFT method gives a satisfactory result. As
shown in figure 4, two excited states with high oscillator
strength, 41A : 319.69 nm f ϭ 0.0727 and 171A: 277.57 nm
f ϭ 0.0672, are close in energy to the experimental exci-
tation peaks (346 nm and 276 nm). Unfortunately, every of
excited states exhibits complicated multitransition charac-
Acknowledgement. We gratefully acknowledge the financial support
of Natural Science Foundation of China (No. 20173064 and
90203017)
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Synthesis, Crystal Structure and Luminescence of [Ag(PPh3)2(H2TMT)]
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