Anion effects on the formation of silver(I) complexes with the flexible ligand 4,4′-Bis(1,2,4-triazol-1-ylmethyl)biphenyl

Article abstract of DOI:10.1002/zaac.201000433

The reaction of 4,4′-bis(1,2,4-triazol-1-ylmethyl)biphenyl (btmb) with silver(I) salts of BF₄^-, NO₃^- and N₃^- led to the formation of four new silver(I) coordination polymers {[Ag(btmb)]BF₄}_n (1), {[Ag ₂(btmb)₃](NO₃)₂(H₂O) ₅}_n (2), [Ag₂(btmb)(N₃) ₂]_n (3), and [Ag(btmb)(N₃)]_n (4). Their coordination number varies from 2 (in 1) to 3 (in 2), 4 (in 3), and 5 (in 4). Different from the single chain structure of 1, complex 2 displays a 1D ladder-like double chain framework, whereas complex 3 exhibits a 2D layered architecture. Complex 4 has the same anion as complex 3 but shows a different metal-to-ligand ratio and a 1D double-zigzag chain structure. Both 3 and 4 have Ag...Ag argentophilic interactions. The ligand btmb adopts both cis or trans configuration in the studied complexes. A trans- or cis-btmb ligand link silver ions with Ag...Ag distances of ≈18 and 13 A, respectively. BF₄^- and NO₃^- are non-coordinating anions in 1 and 2. N₃^- is the bridging anion in 3 (1,3-bridging fashion) and 4 (1,1-bridging fashion). These findings suggest that the coordination numbers around the Ag^I ion correlate to the coordination abilities of anions and the btmb to silver ratio. In addition, the influence of anions on thermal stability were also investigated. This work is a good example that nicely supports the less explored field of anion-dependent structures of complexes with non-pyridyl ligands.

Full text of DOI:10.1002/zaac.201000433

ARTICLE
DOI: 10.1002/zaac.201000433
Anion Effects on the Formation of Silver(I) Complexes with the Flexible
Ligand 4,4'-Bis(1,2,4-triazol-1-ylmethyl)biphenyl
Tianjun Ni,[a,b] Yongmei Zhao,[a] Min Shao,[c] Shourong Zhu,*[a] Feifei Xing,[a] and
Mingxing Li[a]
Keywords: Silver; 4,4'-Bis(1,2,4-triazole-1-ylmethyl)biphenyl; Crystal structure; Anion effect; Metal-organic frameworks
Abstract. The reaction of 4,4'-bis(1,2,4-triazol-1-ylmethyl)biphenyl trans configuration in the studied complexes. A trans- or cis-btmb
–
–
–
(btmb) with silver(I) salts of BF4 , NO3 and N3 led to the formation ligand link silver ions with Ag···Ag distances of ≈18 and 13 Å, respec-
–
–
–
of four new silver(I) coordination polymers {[Ag(btmb)]BF4}n (1), tively. BF4 and NO3 are non-coordinating anions in 1 and 2. N3 is
{[Ag2(btmb)3](NO3)2(H2O)5}n (2), [Ag2(btmb)(N3)2]n (3), and the bridging anion in 3 (1,3-bridging fashion) and 4 (1,1-bridging fash-
[Ag(btmb)(N3)]n (4). Their coordination number varies from 2 (in 1) ion). These findings suggest that the coordination numbers around the
to 3 (in 2), 4 (in 3), and 5 (in 4). Different from the single chain AgI ion correlate to the coordination abilities of anions and the btmb
structure of 1, complex 2 displays a 1D ladder-like double chain frame- to silver ratio. In addition, the influence of anions on thermal stability
work, whereas complex 3 exhibits a 2D layered architecture. Complex were also investigated. This work is a good example that nicely sup-
4 has the same anion as complex 3 but shows a different metal-to- ports the less explored field of anion-dependent structures of com-
ligand ratio and a 1D double-zigzag chain structure. Both 3 and 4 have plexes with non-pyridyl ligands.
Ag···Ag argentophilic interactions. The ligand btmb adopts both cis or
ease to vary the coordination number.[8–13] Several studies of
1. Introduction
the structural dependence on anions were reported by Klaus-
In recent years, the rational design, synthesis, and characteri-
meyer et al.,[6,14] which concentrated on silver(I) complexes
zation of novel well-defined metal-organic frameworks
with ligands containing a coordinating pyridyl function. A re-
(MOFs) have found great research interest. Much of their ap-
lated area of this research that proved lacking, however, was
peal comes from their intriguing variety of architectures and
the one that concerned ligands, which involved other coordina-
topologies as well as their tremendous potential applications
tion groups. As it is known, ligands containing triazole groups
such as electronic, magnetic, optical, absorbent, and catalytic
are another class of N-heterocyclic building blocks, which are
materials.[1–4] Currently, one of the greatest challenges in this
used extensively in crystal engineering. The triazole group has
area is the assembly of novel supramolecular entities with de-
different coordination modes that could result in different
sired structures and properties and there are still lots of re-
solid-state architectures when reacting with metal ions com-
search to be done.[5] It was proved that some factors such as
pared to the pyridyl function.
anion control, metal-to-ligand ratio, and the coordination ar-
For a better understanding of the silver(I) network topology
rangement of metal atoms have a profound effect upon the
constructed from ligands different from those with a pyridyl
resulting network topology.[6,7] Among them, the study of the
function under anion control, the ligand 4,4'-bis(1,2,4-triazol-
silver(I) coordination architectures is particularly interesting
1-ylmethyl)biphenyl (btmb, Scheme 1) was synthesized, in
because of the flexibility of its coordination sphere and the
which the two triazole groups are linked by a biphenylmethyl
group. Another reason of adopting btmb was because that the
rigid biphenyl group could provide thermal stability for the
framework, whereas the flexible methylene group could induce
* Prof. Dr. S. Zhu
Fax: +86-21-60947570
E-Mail: shourongzhu@shu.edu.cn
[a] Department of Chemistry
College of Science
Shanghai University
Shanghai 200444, P. R. China
[b] Department of Chemistry
Xinxiang Medical University
East of Jinsui Road
Xinxiang, Henan 453003, P. R. China
[c] Instrumental Analysis and Research Center
Shanghai University
Shanghai 200444, P. R. China
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201000433 or from the
author.
Scheme 1. The “cis” and “trans” conformations of btmb.
Z. Anorg. Allg. Chem. 2011, 637, 689–697
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
689

T. Ni, Y. Zhao, M. Shao, S. Zhu, F. Xing, M. Li
ARTICLE
Scheme 2. Effect of counterions and reaction ratio on the structure of silver(I) coordination polymers.
a Nicolet A370 FT–IR spectrometer as KBr pellets in the range 400–
subtle environmental changes that may modify the resulting
structures.[15–21] Additionally, to the best of our knowledge, the
coordination chemistry of the ligand btmb is less studied and
there exist only one CuII polymer reported by Su Zhong-Min[22]
and two polymers involving ZnII and CoII ions investigated by
our group hitherto.[23]
4000 cm–1. Thermogravimetric analyses were completed with
a
Netzsch STA–409PC thermal analyzer at a heating rate of 10 °C·min–1
in air. Fluorescent spectra were recorded with a Shimadzu RF-5301
spectrophotometer. All of the silver complexes reported herein were
stable in air and at room temperature with little sign of decomposition
within several hours upon exposure to light. In solution, the complexes
tend to undergo decomposition to form an oily black product.
In light of the above mentioned, in this work, we select three
anions, which have different size, arrangement, and coordina-
–
tion abilities [i.e. the tetrahedral BF4 , the planar NO3– and the
CAUTION: Although not encountered in our experiments, azido com-
pounds of metal ions are potentially explosive. Only a small amount
of the materials should be prepared, and it should be handled with
care.
–
–
–
–
linear N3 (size: BF4 > NO3 > N3 ; coordination abilities:
–
–
–
BF4 < NO3 < N3 )] to synthesize four new silver(I) com-
plexes, namely,
4,4'-bis(1,2,4-triazol-1κN4,1'κN4'-1-yl-
methyl)biphenyl-silver(I) tetrafluoroborate {[Ag(btmb)]BF4}n
(1), tris(4,4'-bis(1,2,4-triazol-1κN4,2κN4'-1-ylmethyl)biphenyl-
disilver(I) nitrate pentahydrate {[Ag2(btmb)3](NO3)2(H2O)5}n
(2), bis(μ2-azide-1κN1,2κN3)4,4'-bis(1,2,4-triazol-1κN4,2κN4'-
1-ylmethyl)biphenyl-disilver(I) [Ag2(btmb) (N3)2]n (3), and μ2-
azide-1:1'κ2N1-4,4'-bis(1,2,4-triazol-1κN4,1'κN4'-1-ylmethyl)-
biphenyl-silver(I) [Ag(btmb)(N3)]n (4). The influence of the
counterion on the composition, dimensionality, conforma-
tional, coordination number around the silver ion and the ther-
mal stabilities of complexes were investigated. The relation-
ship between the counterions and metal-to-ligand ratio and the
resulting crystal structures are summarized in Scheme 2.
2.2. Synthesis of the Complexes
2.2.1 {[Ag(btmb)]BF4}n (1)
A solution of btmb (31.6 mg, 0.1 mmol) in acetone (10 mL) was
added to an aqueous solution of freshly prepared [Ag(NH3)2]BF4 (0.05
mol·L–1, 2 mL) and was stirred for 15 minutes. After filtration, the
mixture was allowed to stand at room temperature for a week. Color-
less crystals of 1 were obtained with yield 68 % based on btmb. Anal.
for C18H16AgN6BF4: calcd. C 42.31, H 3.16, N 16.45 %; found: C
42.27, H 3.21, N 16.55 %. FT-IR (KBr): ν = 3446 m, 3141 m, 1634
˜
m, 1516 s, 1440 m, 1405 w, 1370 w, 1345 m, 1276 s, 1214 s, 1139 s,
1082 s, 880 m, 842 m, 808 m, 750 s, 732 s, 675 s, 649 s, 520 w, 483
w cm–1.
2. Experimental Section
2.2.2 {[Ag2(btmb)3](NO3)2(H2O)5}n (2)
2.1. Materials and Measurements
The flexible ligand 4,4'-bis(1,2,4-triazol-1-ylmethyl)biphenyl (btmb) A solution of btmb (31.6 mg, 0.1 mmol) in acetone (10 mL) was
was synthesized according to the literature method.[24] [Ag(NH3)2]N3, added to an aqueous solution of freshly prepared [Ag(NH3)2]NO3 (0.05
[Ag(NH3)2]BF4, and [Ag(NH3)2]NO3 were prepared as described mol·L–1, 4 mL) and was stirred for 15 minutes. Colorless crystals of 2
elsewhere.[25] Other chemicals of reagent grade were used as received were obtained with a yield of 37 % based on btmb after the filtrate
without further purification. Elemental analyses were performed with was allowed to stand for three weeks. Anal. for C54H58Ag2N20O11:
a Vario EL III elemental analyzer. Infrared spectra were recorded with calcd. C 47.04, H 4.24, N 20.32 %; found: C 47.21, H 4.18, N
690
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© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 689–697

Silver(I) Complexes with the Ligand bmtb
Table 1. Crystallographic data for complexes 1–4.
Complexes
1
2
3
4
Empirical formula
Formula weight
T /K
C18H16AgBF4N6
511.05
298(2)
Monoclinic
C2/c
C54H58Ag2N20O11
1378.94
298(2)
C9H8AgN6
308.08
298(2)
C18H16AgN9
466.27
298(2)
Crystal system
Space group
a /Å
Orthorhombic
Pccn
Monoclinic
P21/c
Triclinic
¯
P1
29.358(4)
4.2576(5)
17.341(2)
90
16.6439(16)
17.6983(16)
19.7571(18)
90
14.752(3)
5.5035(10)
12.324(2)
90
7.6537(8)
8.3467(9)
15.1008(16)
96.4400(10)
103.9040(10)
102.3680(10)
900.96(17)
2
b /Å
c /Å
α /°
β /°
113.605
90
90
90
91.713(2)
90
γ /°
V /Å3
1986.2(4)
4
5819.8(9)
4
1000.1(3)
4
Z
Dc /Mg·m–3
μ /mm–1
F (000)
R(int)
1.709
1.574
2.046
1.719
1.069
0.751
1.994
1.144
1016
2816
604
468
0.0155
0.0742
0.0254
1772 / 0 / 145
0.0158
Data / restraints / pa- 1745 / 0 / 151
rameters
5154 / 3 / 389
3120 / 0 / 253
GOF on F2
1.073
0.0409, 0.1244
0.0454, 0.1290
1.039
1.084
1.080
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
0.1027,0.2540
0.1856,0.3012
1.372, –0.775
0.0260, 0.0611
0.0286, 0.0627
0.321, –0.442
0.0243, 0.0607
0.0260, 0.0619
0.217, –0.546
largest diff peak and 0.943, –0.422
hole /e·A–3
20.39 %. FT-IR (KBr): ν = 3445 br, 3109 m, 1517 s, 1381 vs, 1277 absorption corrections were applied using SADABS program. The
˜
s, 1212 m, 1184 m, 1135 s, 1075 w, 1017 w, 1006 w, 982 w, 844 w, structures were solved by direct method with SHELXS-97[26] and re-
826 w, 805 w, 754 s, 675 m, 648 m, 634 m, 581 w, 507 w cm–1.
fined by full-matrix least-squares on F2 with SHELXL-97.[27] All non-
hydrogen atoms were refined anisotropically and hydrogen atoms were
placed geometrically. Molecular graphics were drawn with using XP,
and Diamond software.[28] The crystal data and refinement results are
given in Table 1. Selected bond lengths and angles are presented in
Table 2.
2.2.3 [Ag2(btmb) (N3)2]n (3)
A solution of btmb (31.6 mg, 0.1 mmol) in acetone (10 mL) was
added to an aqueous solution of freshly prepared [Ag(NH3)2]N3 (0.05
mol·L–1, 4 mL). Afterwards, the mixture was stirred for 15 minutes
and filtered. Colorless crystals of 3 were obtained with a yield of 63 %
based on btmb after the filtrate was allowed to stand for a week. Anal.
for C18H16Ag2N12: calcd. C 35.09, H 2.62, N 27.28 %; found: C 35.16,
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ. Copies of
the data can be obtained free of charge on quoting the depository num-
bers CCDC-767426 (1), -767427 (2), -767428 (3), and -767429 (4).
(http://www.ccdc.cam.ac.uk/conts/retrieving.html, Fax: +44-1223-336-
033; E-Mail: deposit@ccdc.cam.ac.uk).
H 2.53, N 27.37 %. FT-IR (KBr): ν = 3448 m, 3116 m, 2035 s, 1997
˜
s, 1512 s, 1429 w, 1321 w, 1270 s, 1214 w, 1131 s, 1011 s, 978 m,
875 m, 834 m, 801 s, 756 s, 674 m, 648 m, 469 m cm–1.
2.2.4 [Ag(btmb)(N3)]n (4)
Supporting Information (see footnote on the first page of this article):
TG and DSC curves, IR and fluorescence spectra of the complexes
under discussion.
Complex 4 was obtained by a procedure similar to the one reported
for complex
3 with the exception that a greater amount of
[Ag(NH3)2]N3 was added (2 mL, 0.05 mol·L–1). The Ag/btmb ratio
was 1:1, not 2:1 as in complex 3. Colorless crystals were obtained
with a yield of 41 % based on btmb after the filtrate was allowed to
stand for three weeks. Anal. for C18H16AgN9 : calcd. C 46.37, H 3.46,
3. Results and Discussion
3.1. Description of Crystal Structures
3.1.1. {[Ag(btmb)]BF4}n (1)
N 27.04 %; found: C 46.25, H 3.32, N 27.16 %. FT-IR (KBr): ν =
˜
3297 w, 3111 w, 3078 m, 2015 s, 1607 w, 1514 s, 1433 m, 1369 m,
1341 m, 1278 s, 1210 m, 1168 w, 1132 s, 1013 s, 983 m, 920 m, 842
m, 802 m, 752 s, 700 s, 673 m, 651 m, 633 m, 583 w, 497 m cm–1.
The composition of 1 is identical to the synthesis reactants.
The asymmetric unit is made up by half a btmb ligand, half a
silver atom, and half a BF4– anion. The structure of 1 is shown
in Figure 1. Each silver atom is coordinated by two nitrogen
atoms of btmb ligands in a linear arrangement with the bond
2.3. X-ray Crystallography
Single crystal diffraction data for complexes 1–4 were collected with
a Bruker Smart Apex-II CCD diffractometer with graphite monochro-
matic Mo-Ka radiation (λ = 0.71073 Å) at room temperature. Empirical N1 of 2.139(3) Å. It is noteworthy that the BF4 anion in 1
angle of N1–Ag1–N1B being 180° and a bond length of Ag1–
–
Z. Anorg. Allg. Chem. 2011, 689–697
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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691

T. Ni, Y. Zhao, M. Shao, S. Zhu, F. Xing, M. Li
ARTICLE
Table 2. Selected bond lengths /Å and angles /° for complexes 1–4.
Complex 1
Ag(1)–N(1)
2.139(3)
Complex 2
Ag(1)–N(6)#1
Ag(1)–N(1)
N(6)#1–Ag(1)–N(1)
2.23(1)
2.25(1)
127.9(5)
Ag(1)–N(7)
N(6)#1–Ag(1)–N(7)
N(1)–Ag(1)–N(7)
2.32(1)
113.9(5)
118.0(5)
Complex 3
Ag(1)–N(4)
2.166(3)
2.211(2)
82.46(6)
122.21(7)
64.16(6)
Ag(1)–N(6)#1
2.604(3)
3.2745(6)
161.1(1)
105.7(1)
92.61(9)
Ag(1)–N(1)
Ag(1)–Ag(1)#2
N(6)#1–Ag(1)–Ag(1)#2
N(4)–Ag(1)–Ag(1)#2
N(1)–Ag(1)–Ag(1)#2
N(4)–Ag(1)–N(1)
N(4)–Ag(1)–N(6)#1
N(1)–Ag(1)–N(6)#1
Complex 4
Ag(1)–N(6)#1
2.221(2)
2.227(2)
2.508(2)
104.08(6)
105.99(8)
91.59(7)
99.69(7)
87.78(7)
Ag(1)–Ag(1)#2
Ag(1)–N(7)#2
3.1332(5)
2.584(2)
Ag(1)–N(1)
Ag(1)–N(7)
N(7)–Ag(1)–N(7)#2
N(6)#1–Ag(1)–N(7)
N(1)–Ag(1)–N(7)
N(6)#1–Ag(1)–N(7)#2
N(1)–Ag(1)–N(7)#2
N(6)#1–Ag(1)–N(1)
N(6)#1–Ag(1)–Ag(1)#2
N(1)–Ag(1)–Ag(1)#2
N(7)–Ag(1)–Ag(1)#2
N(7)#2–Ag(1)–Ag(1)#2
158.38(8)
111.06(5)
89.44(5)
53.14(5)
50.94(5)
Symmetry codes: 1 #1–x, –y+2, –z. 2 #1 x, y–1, z; #3 x, y+1, z. 3 #1 x, y–1, z; #2 –x, –y+2, –z+1; #4 x, y+1, z. 4 #1 x+2, y+1, z+1; #2 –
x+3, –y+1, –z+2; #3 x–2, y–1, z–1.
does not participate in the coordination with AgI. The BF4
–
anions are disordered and have two positions as shown in Fig-
ure 1a. Except the F3 atom, the occupancies of all other atoms
–
in BF4 are 0.5. The centrosymmetric btmb unit in 1 adopts a
trans conformation. The two benzene rings are exactly co-
planar due to central symmetry. However, the dihedral angle
between the phenyl ring and the adjacent triazole ring is
66.52°. There exists C–H···F H bonding as shown in Figure 1.
Each btmb ligand connects two different silver ions through its
two triazole nitrogen atoms to form a one–dimensional chain
structure. The Ag···Ag separation across the bridging btmb is
17.80 Å (Figure 1b), which is similar to all other Ag···Ag dis-
tances that are linked by trans-btmb (17.657 Å in 3 and
18.383 Å in 4). The nearest Ag···Ag distance between adjacent
chains is 4.258 Å. No Ag–Ag interaction exist in 1 due to the
fact that the nearest Ag···Ag distance is longer than the sum of
the van der Waals radii of 3.44 Å. From the b axis, the 1D
chains are linked through C–H···F H bonds[29–32] (Figure 1b).
3.1.2 {[Ag2(btmb)3](NO3)2(H2O)5}n (2)
Figure 1. Crystal structure of [Ag(btmb)]BF4}n (1). (a) Coordination
environments and (b) packing from b axis. Dotted lines are hydrogen
bonds. Symmetry codes: #1 –x, –y+2, –z; #2 –x+1/2, –y+3/2, –z+1.
–
–
The replacement of BF4 with NO3 and an increase in the
Ag:btmb ratio afforded complex 2. The structure of 2 is shown
in Figure 2. The asymmetric unit is made up of one silver ion,
one nitrate anion, 1.5 btmb ligands, and 2.5 crystalline water
molecules. Different from complex 1, there are two different close to 120° (Table 2). The Ag–N distances are in the range
btmb ligands in 2, only one of them is centrosymmetric. Each 2.229 to 2.316 Å (Table 2), which are similar to those ob-
AgI atom is tricoordinated to three nitrogen atoms (N1, N6 served for complex 1 and agree well with the reported
from the asymmetric btmb, and N7 from the symmetric btmb) values.[33–35] NO3 is a very weak ligand and does not partici-
–
from three different btmb ligands to form a triangular coordi- pate in the coordination with AgI in 2, similar to the uncoordi-
–
nation environment since the three N–Ag–N angles are all nated BF4 ion in 1.
692
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Z. Anorg. Allg. Chem. 2011, 689–697

Silver(I) Complexes with the Ligand bmtb
dark films and ligand precipitates. The crystals we could obtain
in a series of reactions with different ratio were either 1 or 2.
3.1.3. [Ag2(btmb) (N3)2]n (3)
X-ray crystallographic analysis shows that the asymmetric
unit in 3 contains the basic building block of one AgI ion, half
a btmb ligand, and one azide anion. The ligand btmb is located
at an inversion center. Each AgI ion is bound to one nitrogen
atom from a btmb triazole group, two nitrogen atoms from two
azide molecules, and one silver ion to form tetracoordinated
environments as illustrated in Figure 3. Four atoms in the
AgN3 unit are essentially located in the same plane (Figure
S2). The distances Ag1–N4 (2.166(3) Å) and Ag1–N1
(2.211(2) Å) are similar to those of other AgI triazole
complexes.[33–35] The distance between the Ag1 and N6 atom
of the azide anion is longer (2.603(3) Å), which indicates that
only weak bonding is present.[42] The AgIN3 unit shows a dis-
torted Y-shaped coordination arrangement with N1–Ag1–
N6A = 92.6°, N1–Ag1–N4 = 161.1°, and N6A–Ag1–N4 =
105.7°. The Ag1–Ag1 distance of 3.275 Å is shorter than the
sum of the van der Waals radii of two silver atoms
(3.44 Å).[43–45]
Figure 2. Crystal structure of {[Ag2(btmb)3](NO3)2(H2O)5}n (2). (a)
–
Coordination environments; H2O and NO3 are omitted for clarity. (b)
Double-strand 1D ladder viewed from a axis. (c) The 1D ladder viewed
from b axis (left) and crystal packing from b axis (right). Red thin
–
lines represent NO3 anions. Symmetry codes: #1: x, y–1, z; #2: –x–1/
2, –y+1/2, z.
In contrast to the trans configuration of the ligand btmb in
1, in complex 2 the ligand exhibits trans and cis configuration
for the asymmetrical and symmetrical btmb, respectively. In
complex 2, the dihedral angle between the two benzene rings
of the biphenyl group in the asymmetric trans-configured btmb
ligand is 8.84°, whereas in the cis-configured symmetric btmb
ligand, the dihedral angle between two benzene rings is
22.752° (Figure S1, Supporting Information). The trans-btmb
ligand links adjacent AgI ions to form an infinite non-interpen-
etrated molecular chain (Figure 2b). Two chains are linked
through a symmetric btmb ligand to form a double chain lad-
der. The Ag···Ag distance within trans-btmb links is 17.70 Å
along the side chain, whereas the Ag···Ag distance of cis-btmb
links is 13.05 Å. Furthermore, the centroid–centroid distances
and the dihedral angles between two triazole rings A and B in
neighboring btmb ligands are 3.884 Å and 13.100°, respec-
tively. For B and C planes, the distances and angles are
4.235 Å and 7.488°, respectively (Figure 2b). This indicates
the presence of T-type edge-to-face π–π interactions
(Figure 2b).[36–41] The complex is packed alternatingly up and Figure 3. Crystal structure of [Ag2(btmb) (N3)2]n (3). (a) Coordination
environments of 3. Hydrogen atoms were omitted for clarity. (b) Struc-
down into a 3D framework as shown in Figure 2c.
ture of coordination sheet by Ag–Ag bonds. The red and green sticks
Complexes 1 and 2 have different coordination environments
are Ag+–N3– coordination chains in left and right–hand helix. (c) Crys-
due to the different anions and different ligand to metal ratios.
tal packing from b axis. Symmetry codes: #1 x, y–1, z; #2 –x, –y+2, –
To highlight the anion effects at the same reaction ratio, we
tried the same reaction ratio in syntheses of 1 and 2, but all
reactions other than those reported for the syntheses of 1 and
z+1.
As a comparison, the distances of Ag···Ag argentophilic in-
2 have very low yield with considerable light reaction to form teractions in many coordination complexes are in the range
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T. Ni, Y. Zhao, M. Shao, S. Zhu, F. Xing, M. Li
ARTICLE
of 3.0–3.4 Å.[46–49] We hypothesize that Ag–Ag argentophilic four or higher are scarce.[50–54] A CCDC search was conducted
interactions exist in complex 3. The unusual feature of this and revealed about pentacoordinated 40 silver complexes with
structure is due to the fact that the 1D ladder chains are con- Ag–Ag bonds.[55–59]
nected to each other by interchain Ag–Ag interactions, which
result in a 2D grid sheet structure shown in Figure 3b.
[Ag2(btmb)(N3)2]n (3) is one of a few silver coordination net-
works with a 2D grid structure built by weak Ag···Ag argento-
philic interactions between the 1D ladder chains (Scheme 2).
Taken Ag–Ag argentophilic interactions into consideration, the
AgI ion is tetracoordinated to form an AgN3Ag chromophore.
It was noted that btmb in complex 3 adopts trans conforma-
tion, in which the two triazole rings are on the opposite direc-
tion of the central phenyl ring. The dihedral angle between the
phenyl ring and the adjacent triazole rings amounts 78.6° and
the two triazole rings are parallel to each other. Each btmb
ligand bridges two silver atoms by two exodentate nitrogen
atoms at the 4-position of the triazole rings, which are identical
to those in 1 and 2. The Ag···Ag separations across the bridg-
ing btmb ligand and the 1,3-bridging azide molecule are
17.656(1) and 5.5034(5) Å, respectively (Figure 3b). The 1,3-
bridging azide molecule and the silver atom connect alternat-
ingly to form 10-membered rings. The bidentate btmb ligand
and the silver atom are bound alternatingly to form a 42-mem-
bered macrocycle (Figure 3b). In each macrocycle, the phenyl
or triazole rings between the two adjacent ligands are found to
be strictly coplanar and the intermetallic distance between the
two silver(I) atoms in the ladder square is
5.503 Å × 17.656 Å. The metallamacrocyclic unit and the 10-
membered Ag–azide rings link the complex into a 2D grid
polymer as shown in Figure 3b. It is noteworthy that the Ag–
Figure 4. Crystal structure of [Ag(btmb)(N3)]n (4). (a) Coordination
N3 chains are in both left and right-hand helix (Figure 3b). The
length of a repeating Ag–N3 chain is 5.50 Å. From b axis, the
2D sheets overlap to pack into a 3D structure (Figure 3c).
environment. (b) Double strand 1D coordination chain with Ag–Ag
bond. (c) Packing from a axis. Symmetry codes: #1 x+2, y+1, z+1;
#2 –x+3, –y+1, –z+2.
This complex is a good example of high coordinated silver
complexes. The Ag–N(triazole) distances fall in the range
3.1.4. [Ag(btmb)(N3)]n (4)
Complex 4 is synthesized by the same procedure as reported 2.221–2.227 Å, which are similar to those observed in com-
for 3 with the exception that less silver ions are employed. The plex 3, whereas the Ag–N(azide) distances (2.508–2.584 Å)
reaction of [Ag(NH3)2]N3 with btmb is carried out in 1:1 ratio are shorter than those in complex 3. The btmb ligand in 4
and complex 4 can be isolated. X-ray structural analysis re- exhibits an asymmetric trans configuration, which is similar to
veals that the fundamental unit of 4 contains one AgI atom, the symmetric trans-btmb configuration in 3. Each btmb ligand
one btmb ligand, and one azide anion, which is in agreement connects to two silver atoms to form a 1D zigzag polymeric
with the reaction ratio of the starting materials. In comparison structure as shown in Figure 4b. The dihedral angles between
to 3, complex 4 contains more btmb ligand molecules and only the two triazole rings and the two phenyl rings in the btmb
one btmb ligand is located in the asymmetric unit of 4. The ligand are 18.26° and 31.83°, respectively. The dihedral angles
composition of 4 is identical to that of complex 1 with the between the phenyl ring and the adjacent triazole rings are
–
exception that BF4– is replaced by N3 . Different from the sym- slightly different in complexes 3 and 4. The Ag···Ag separation
metric trans configuration in 1, the btmb ligand in 4 is in the across the bridging btmb ligand is 18.383 Å, which is longer
asymmetric trans configuration. Each AgI ion is coordinated than the Ag···Ag separation of 17.656 Å in 3. The azide mole-
to two nitrogen atoms (N1 and N6) from two different btmb cule in 4 rather acts as a 1,1-bridging ligand, than as a 1,3-
ligands and two nitrogen atoms (N7) from two azide anions bridging ligand as reported for 3. In this configuration, two
(Figure 4). The adjacent silver ions are also weakly coordi- metal atoms and two nitrogen atoms from azide anions form
nated at 3.1332(4) Å, which is slightly stronger than the Ag– four-membered [M2(azide)2] metallacyclic rings, which are
Ag bond in 3. Thus, silver is pentacoordinated with τ = 0.79. further connected through btmb ligands to form a 1D
It can be described that silver is in a trigonal bipyramidal envi- chain.(Figure 4b). This is quite different from the 2D structure
ronment, in which triazole–Ag–triazole has the largest angle reported for complex 3. The Ag–Ag distance in 4 is with
of 159.4°. Silver complexes with a coordination number of 3.1332(4) Å obviously shorter than the corresponding distance
694
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Silver(I) Complexes with the Ligand bmtb
in 3 (3.275 Å) and similar to those reported by Chen et al.[60] the adjacent phenyl rings are much larger at 60–85°. The
However, this is still considered a weak interaction in compari- Ag···Ag distances of ions linked by trans- and cis-btmb are
son to shorter Ag–Ag bonds (2.8–3.0 Å).[61–65] The composi- about 18 and 13 Å, respectively. These data demonstrate that
tion of 4 is quite similar to that of 1. However, the coordination btmb is a flexible ligand.
number greatly differs from two in 1 to five in 4. The coordi-
–
nating ligand N3 greatly increases the coordination number
around the silver ions.
3.3. Thermal Analysis, IR and Fluorescent Spectra
The IR spectra of the free ligand btmb and complexes 1–4
are shown in Figure S4. Compared with the strong absorption
3.2. Conformational Analysis
band of the triazole ring at 1267 cm–1 in free btmb this signal
In order to understand the influence of the flexibility of the is shifted to 1278, 1277, 1271, and 1276 cm–1 in complexes
btmb ligand on the topologies of the motifs, the configuration 1–4, respectively. The 1510 cm–1 absorption band in btmb is
of btmb, N···N distance between two donor atoms of btmb, shifted to slightly higher amplitudes (1516, 1516, 1514,
Ag···Ag separation through btmb, and the torsion angles (de- 1514 cm–1 in complexes 1–4, respectively, Figure S4). For
grees) in 1–4 are listed in Table 3. The btmb ligands in 1, 3, complex 1, the absorption band at 1082 cm–1 corresponds to
–
–
and 4 adopt trans conformation, whereas the btmb ligands in the free BF4 anion. The absorption band for the free NO3
2 adopt trans configuration for the asymmetric btmb molecule anion is observed at 1382 cm–1 in 2. The IR data of the com-
and cis configuration for the symmetric btmb molecule. Thus, plexes agree well with their crystal structures. The strong ab-
btmb tends to adopt trans configuration in silver complexes. sorption bands at 2034 and 1998 cm–1 are assigned to the N3
–
The trans- and cis-btmb ligands adopt a “Z” and “C” shape, anion in 3, whereas the band of the 1,1-bridging azide in com-
respectively. Consequently, the distances between the metal at- plex 4 is observed at 2015 cm–1, which is similar to the data
oms separated by trans-btmb are about 4.6–5.3 Å longer than reported for other azide complexes (bands in the range of
those separated by cis-btmb. The intramolecular distances be- 2000–2200 cm–1).[66] The thermal stabilities of coordination
tween the two donor nitrogen atoms N···N in trans-btmb in 1, polymers 1–4 were investigated by thermogravimetric analysis
2, 3, and 4 are 14.627, 14.469, 14.859, and 14.752 Å respec- (Figure S5–Figure S8, Supporting Information). The analyses
tively, which suggest similarity. It is interesting that the coordi- showed that complex 1 is stable up to 300 °C. Compound 2
nating N···N distances in 4 are slightly shorter than those in 3, lost five lattice water molecules (found 6.28 %, calcd. 6.53 %)
whereas the Ag···Ag separation in 4 is obviously longer than from 44 to 125 °C. At a temperature of 245 °C the compound
the corresponding distance in 3 (Table 3). This is due to the began to decompose. A residue of Ag2O remained (found
fact that the silver ion in 3 lies away from the triazole plane 17.2 %, calcd. 16.8 %) at 694 °C. Complex 3 is stable up to
towards the symmetry center, whereas the silver ion in 4 is 219 °C, and subsequently displays a consecutive decomposi-
coplanar with the triazole molecule (Figure S3). The dihedral tion in the range of 220–350 °C with an exothermic peak at
angles between two triazole rings in trans-configured btmb are 216 °C. Compound 4 is stable up to 240 °C and also under-
0° for btmb in 1 and 3, 13.43° in 2, and 18.26° in 4. Therefore, goes a consecutive decomposition in the temperature range
the two triazole planes in a trans-btmb ligand are essentially 240–400 °C with an exothermic peak at 190 °C. Finally, com-
parallel to each other. The dihedral angle between the two ben- plex 1 is the most stable of all four complexes. This can be
–
zene ring planes are 0° for btmb in 1 and 3, 8.34° in 2 and explained by the fact that the BF4 ion is more stable than the
31.79° in 4, which means a great difference. The dihedral an- azide and nitrate anions.
gles between the phenyl and triazole rings, and the torsion an-
The fluorescence properties of the Inorganic-organic hybrid
gles (Table 3) indicate that the change of the spacer conforma- coordination polymers and their potential applications as lumi-
tion and the relative orientation of the triazole rings are nescent materials were investigated. The emission spectra of
responsible for the N···N distance. From Table 3 it can be seen, complexes 1–4 and of the free ligand in the solid state at room
that the ligand in trans configuration has dimensions of 14.5– temperature were investigated. All the four complexes have
14.8 Å, whereas the cis configured btmb is with at 12.87 Å similar emission peaks at ≈428 nm when excited at 360 nm
much shorter. The two phenyl rings have dihedral angles of 0– (Figure 5). An emission of free ligand btmb is observed at
32°, whereas the dihedral angles between the triazole units and 428 nm when excited at 360 nm. These data are similar to free
Table 3. Structural data of complex 1–4.
complex chromo
anion
μ2-btmb
d(N···N) /Å d(M···M) /Å
Dihedral angle /° of
configuration
two triazole rings two phenyl rings phenyl and
triazole rings
–
1
2
AgN2
AgN3
BF4
trans-symm
trans-asymm
cis-symm
trans-symm
trans-asymm
14.627
14.469
12.873
14.859
14.752
17.800
17.698
13.048
17.657
18.383
0
0
66.52
–
NO3
13.43
22.10
0
8.34
22.78
0
71.22, 74.90
84.45
–
3
4
AgN3Ag
AgN4Ag
1,3-N3–
1,1-N3
78.64
18.26
31.79
79.08, 59.40
Z. Anorg. Allg. Chem. 2011, 689–697
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695

T. Ni, Y. Zhao, M. Shao, S. Zhu, F. Xing, M. Li
ARTICLE
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coordinates to two silver ions to form coordination polymers
1–4. The coordination environments around the silver(I) ion as
well as the structures differ greatly amongst the four com-
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Acknowledgement
The project was supported by the National Natural Science Foundation
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