Novel silver(I) compounds assembled from hybrid ligands based on linear or T-shaped coordination environment

Article abstract of DOI:10.1016/j.inoche.2009.05.004

Two novel 1D compounds {[Ag₃(Hbptc)(bpa)₂]·H₂O}_n (1) and [Ag₂(H₂bptc)(bpp)₂]_n (2) (H₄bptc = 3,3′,4,4′-benzophenonetetracarboxylic acid, bpa = 1,2-bis(4-pyr

Full text of DOI:10.1016/j.inoche.2009.05.004

Inorganic Chemistry Communications 12 (2009) 611–614
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Novel silver(I) compounds assembled from hybrid ligands based
on linear or T-shaped coordination environment
*
Ya-Nan Zhang, Hong Wang, Jian-Qiang Liu, Yao-Yu Wang , Ai-Yun Fu, Qi-Zhen Shi
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, Shaanxi Key Laboratory of Physico-Inorganic Chemistry,
Department of Chemistry, Northwest University, Xi’an 710069, China
a r t i c l e i n f o
a b s t r a c t
0
0
Article history:
Two novel 1D compounds {[Ag (Hbptc)(bpa) ]ꢁH O} (1) and [Ag (H bptc)(bpp) ] (2) (H bptc = 3,3 ,4,4 -
3
2
2
n
2
2
2 n
4
Received 13 January 2009
Accepted 4 May 2009
Available online 15 May 2009
benzophenonetetracarboxylic acid, bpa = 1,2-bis(4-pyridyl)ethane and bpp = 1,3-bis(4-pyridyl)propane)
were synthesized and structurally characterized. The crystal structures of compounds exhibit two kinds
of ladder-like chains based on linear or T-shaped coordination environment of Ag(I). Fluorescence spectra
of compounds 1 and 2 indicate the unusual intensity of fluorescent emission upon photoexcitation which
may be attributed to ligand-to-metal charge transfer and Ag–Ag interactions.
Keywords:
Coordination polymer
Crystal engineering
AgꢀAg contacts
Ó 2009 Elsevier B.V. All rights reserved.
Fluorescence spectrum
The rational design and assembly of metal-organic frameworks
MOFs) with well-regulated network structures have received
tion polymers formed [10]. Herein, we report the synthesis, crystal
structure and luminescent properties of two silver(I) coordination
(
remarkable attention in order to develop new functional materials
with potential applications [1]. In principle, the construction of
molecular architecture is based upon the sophisticated selection
and utilization of suitable metal ions and multifunctional organic
ligands. Among various organic ligands, multicarboxylate ligands
are often used as multifunctional organic ligands, not only because
of their various coordination modes to the metal ions, but also
because of their ability to act as H-bond acceptors and donors
assembling supramolecular structures [2]. For example, 1,2,4,5-
benzenetetracarboxylate, 3,3’,4,4’-biphenyltetracarboxylic acid
polymeric compounds {[Ag
[Ag (H bptc)(bpp) (2).
Compound 1 was synthesized hydrothermally by treating AgAc,
bpa and H bptc at 150 °C. The pH value of the reaction mixture was
3
(Hbptc)(bpa)
2
]ꢁH
2
O}
n
(1) and
2
2
2 n
]
4
adjusted to 4 by addition of triethylamine [11]. Compound 2 was
obtained at pH value 3 using the same procedure but with bpp in-
stead of bpa [11]. Single-crystal X-ray structural analysis reveals
that the structure of 1 contains three crystallographically indepen-
dent Ag(I) centers (Fig. 1a). The Ag1 ion is coordinated by two car-
boxylic oxygen atoms (AgꢀO 1.954(2) Å) from two different bptc
ligands. The Ag2 ion is three-coordinated with a T-shaped coordi-
nation geometry binding two nitrogen atoms from two different
bpa ligands (AgꢀN 2.010(3) and 2.038(3) Å) and one oxygen atom
of a carboxylate group from bptc ligand (AgꢀO 1.970(4) Å). Ag3 ion
coordinational sphere is similar to Ag2. Due to the partial deproto-
nation, bptc anion in 1 binds to three Ag(I) cations and exhibits a V-
shaped geometrical conformation. This can play a decisive role in
the formation of fascinating architectures and topologies and it
has been demonstrated by previous examples [8e].
[
3–5], 1,1’-biphenyl-2,3’,3,4’-tetracarboxylic acid [6] and methyl-
enediisophthalic acid [7] have been extensively used for the syn-
thesis of various coordination polymers. However, coordination
0
0
polymers built up from H
ophenonetetracarboxylic acid) have been rarely reported [8].
Therefore, we choose H bptc and auxiliary ligands (bpa and bpp)
4 4
bptc ligand (H bptc = 3,3 ,4,4 -benz-
4
to explore some intriguing architectures. The results show that
these ligands exhibit a special ability to formulate compounds
and play an important role in directing the final structures [8g].
On the other hand, silver(I) salt is often used in crystal engineering
because of its ability to form compounds with coordination num-
bers of 2, 3, or 4 and even more resulting in many different archi-
tectures development [9]. Moreover, the potential AgꢀAg
interactions also play a crucial role in the structures of coordina-
The most interesting feature of 1 is that the V-shaped bptc li-
gand and Ag1 ion are acting together as a bridge, linking the adja-
cent two chains to form a rare 1D double-ladder chain with a T-
2
shaped coordination geometry (AgN O). Although three-coordi-
nated Ag atom is not rare in the complexes [12–15], the structure
of 1 containing extended N-auxiliary ligands (bpa) is different from
the reported Ag complexes with bpy and carboxylate ligands [16].
Usually the carboxylate ligands are not coordinated with Ag ion
and Ag–bpy chains are linked into a 1D molecular ladder by
*
Corresponding author. Tel./fax: +86 029 88303798.
E-mail address: wyaoyu@nwu.edu.cn (Y.-Y. Wang).
1
387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2009.05.004

6
12
Y.-N. Zhang et al. / Inorganic Chemistry Communications 12 (2009) 611–614
double-ladder chains extend to a novel 3D supramolecular struc-
ture (Fig. S2).
The structure of compound 2 is based on AgꢀAg interaction, as
shown in Fig. 2a. It is an infinite ladder-like chain arrangement
+
with the [Ag(bpp)] unit. The distance of Agꢁ ꢁ ꢁAg in 2 is 3.176 Å,
which is also a weak AgꢀAg interaction. Due to partial deprotona-
tion of the bptc ligands in compound 2, they can act as medium H-
bond acceptors and donors, resulting in 3D supramolecular struc-
tures with channels (hydrogen-bonds: 2.334(2) and 2.509(1) Å).
These strong OꢀHꢁ ꢁ ꢁO hydrogen bonds can play an important role
for improving the stability of the 3D architecture (Fig. 2b). The lad-
der-like chains occupy these channels, and the whole structure is
additionally stabilized by the weak Agꢁ ꢁ ꢁO interactions (2.898(8)
and 2.928(1) Å).
Fig. 1a. ORTEP diagram showing the coordination environments for the Ag(I) ions
in 1.
Comparing known examples of Ag containing coordination
polymers [8] with the compounds 1 and 2, it is important to note
that the fascinating low dimension motifs rely on the following
contributions: silver(I) complexes act as bridges and exhibit close
AgꢀAg contacts with coordination numbers of 2 and 3 to form
general AgꢀAg interaction, and only weak Agꢁ ꢁ ꢁO interactions ex-
ist. In contrast, bptc carboxylate oxygen atoms of the compound
1
D chain architectures [9]; the one carboxyl coordinated bptc li-
1
are directly coordinated with Ag(I) forming a O
bridge. In addition, the Ag2ꢁ ꢁ ꢁAg3 distance within the chains is
.161 Å, which is shorter than the sum of the Van der Waals radii
2
CꢀCꢀCꢀCO
2
gands in 1 are protruding from the both sides of the 1D chain
and provide the stable links amongst them, as can be also found
in previous literature [8c]; finally, bptc ligands in 2 have sufficient
amount of supramolecular recognition sites for hydrogen bond
interactions to form unusual supramolecular structure.
3
of two silver atoms (3.44 Å) [17]. This is a clear indication of a weak
ligand-induced AgꢀAg interaction which could be found in many
other Ag(I) coordination polymers with AgꢀAg interatomic dis-
tance 3.0–3.3 Å [18]. Hence, ligand-induced AgꢀAg interaction
To study the thermal stabilities of these complexes, thermal
gravimetric analysis (TGA) of compounds 1ꢀ2 was carried out
and O
2
CꢀCꢀCꢀCO
2
bridge play a crucial role in the forming of
(Fig. S3). Compound 1 first loses its free water molecules below
the 1D double-ladder chain structure (Fig. S1).
1
60 °C; the weight loss found of 1.54% is consistent with that cal-
Furthermore, there are some other weak interactions between
the adjacent chains. The first are hydrogen bonds between the free
water molecules and the carboxylate groups (O10ꢀH10 Wꢁ ꢁ ꢁO6
culated (1.68%). When the temperature is in the 180–620 °C, the
product begins to decompose. The weight loss is owed to the re-
lease of ligands, the final residual weight is 30.74% (calc. 30.35%)
corresponding to Ag. For complex 2, TGA results show that the
weight loss in the range of 190–750 °C, which corresponds to the
release of ligands, the residual percentage weight (observed
2
.819(8) and O10ꢀH11 Wꢁ ꢁ ꢁO8 2.968(5) Å), which link the 1D dou-
ble-ladder chains into a 2D layer (Fig. 1b). The second are signifi-
cant interchain stacking interactions between the bpa
ligands. The face-to-face separation of the neighboring phenyl
pꢀp
2
0.23%) at the end of the decomposition of the complex is consis-
rings of bpa is 3.621 Å. As a result of these weak interactions, the
tent with the formation of Ag (expected 21.91%).
Fig. 1b. 1D double-ladder chains linked by hydrogen-bonding interactions into a 2D layer in 1. Hydrogen bonds are shown as dashed lines.

Y.-N. Zhang et al. / Inorganic Chemistry Communications 12 (2009) 611–614
613
+
Fig. 2a. Infinite ladder-like chains arrangement based on AgꢀAg contacts with the [Ag(bpp)] unit in 2.
Fig. 2b. bptc Ligands as medium H-bond acceptors and donors forming 3D supramolecular structure with channels along b axis in 2. Hydrogen bonds are shown as dashed
lines.
The solid-state emission spectra of compounds 1 and 2 have
been investigated at room-temperature (Fig. 3). The intense bands
in the emission spectra were observed at 398 nm and 460 nm
the literature [3,19], the luminescent properties of 1 (398 nm)
and 2 (415 nm) can be attributed to ligand-to-metal charge trans-
fer and AgꢀAg interactions. Compounds with AgꢀAg interactions
show emission with similar energy [20–23]. Experimental and the-
oretical results have proved that AgꢀAg interactions are significant
for the formation of luminescent species, which has been also dis-
(k
ex = 230 nm) for 1, 415 nm and 462 nm (kex = 260 nm) for 2. It
could be found that one weak emission at 462 nm (kex = 280 nm)
could be observed for free H bptc ligand (Fig. S5). According to
4
cussed in our previous work [24]. Moreover, the peak of 458 nm for
*
1
and 462 nm for 2 may be assigned to the intraligand (
p–p
)
fluorescence.
In order to confirm the phase purity of the bulk materials, X-ray
powder diffraction (XRPD) experiments were carried out on 1 and
2. The XRPD experimental and computer-simulated patterns of
them are shown in Fig. S4. Although minor differences can be seen
in the positions, intensities, and widths of some peaks, it can also
be considered that the as-synthesized materials are homogeneous
(
Fig. S4).
In conclusion, we have developed two novel luminescent sil-
ver(I) compounds with H bptc and extended N-auxiliary ligands.
4
Analysis of the silver compounds 1 and 2 crystal structures indi-
cates that ligand-induced and ordinary Ag–Ag interactions can link
Ag(I) ions into two kinds of ladder-like chains.
Acknowledgments
This work was supported by the National Natural Science Foun-
dation of China (No. 20771090) and TRAPOYT, and Specialized
Fig. 3. Solid-state emission spectra of compounds 1 and 2 at room temperature.

6
14
Y.-N. Zhang et al. / Inorganic Chemistry Communications 12 (2009) 611–614
Research Found for the Doctoral Program of Higher Education (No.
0050697005).
(c) W.H. Bi, R. Cao, D.F. Sun, D.Q. Yuan, X. Li, M.C. Hong, Inorg. Chem. Commun.
(2003) 1426;
d) F.Q. Liu, T.D. Tilley, Inorg. Chem. 36 (1997) 5090.
10] L. Pan, E.B. Woodlock, X.T. Wang, K.C. Lam, A.L. Rheingold, Chem. Commun.
2001) 1762.
11] Preparation of {[Ag
compound 1 was obtained by the reaction of AgAc, bpa and H
6
(
2
[
[
(
Appendix A. Supplementary material
3
(Hbptc)(bpa)
2
]ꢁH
2
O}
n
2
(1) and [Ag (H
2
bptc)(bpp)
2 n
] (2):
4
bptc in molar
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.inoche.2009.05.004.
ratio of 4:1:1 mixed with 15 mL of aqua and 1 mL of triethylamine under
hydrothermal conditions (at 150 °C for 6 days and cooled to room temperature
ꢀ
1
with a 5 °C h rate). Colorless crystals of 1 were collected in 55% yield. Anal.
Calcd. for C41 34Ag 10: C 46.18, H 3.21, N 5.25. Found C 46.48, H 3.31, N
5.16. IR data (KBr, cm ): 3407 s, 3213 s, 2927 m, 2821 w, 1653 w, 1551 vs,
414 vs, 1083 m, 980 w. Crystal data for compound 1: fw = 710.23, Triclinic,
H
3 4
N O
1
ꢀ
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