AgI/VV heterobimetallic frameworks generated from novel-type {Ag2(VO2F2)2(triazole) 4} secondary building blocks: A new aspect in the design of SVOF hybrids

Article abstract of DOI:10.1021/ic3000894

A series of new silver(I)-containing MOFs [Ag₂(tr ₂ad)₂](ClO₄)₂ (1), [Ag ₂(VO₂F₂)₂(tr₂ad) ₂]·H₂O (2), [Ag₂(VO₂F ₂)₂(tr₂eth)₂(H₂O) ₂] (3), and [Ag₂(VO₂F₂) ₂(tr₂cy)₂]·4H₂O (4) supported by 4-substituted bifunctional 1,2,4-triazole ligands (tr₂ad = 1,3-bis(1,2,4-triazol-4-yl)adamantane, tr₂eth = 1,2-bis(1,2,4- triazol-4-yl)ethane, tr₂cy = trans-1,4-bis(1,2,4-triazol-4-yl) cyclohexane) were hydrothermally synthesized and structurally characterized. In these complexes, the triazole heterocycle as an N¹,N ²-bridge links either two adjacent Ag-Ag or Ag-V centers at short distances forming polynuclear clusters. The crystal structure of compound 1 is based on cationic {Ag₂(tr)₄}²⁺ fragments connected in a 2D rhombohedral grid network with (4,4) topology. The neighboring layers are tightly packed into a 3D array by means of argentophilic interactions (Ag···Ag 3.28 A). Bridging between different metal atoms through the triazole groups assists formation of heterobimetallic Ag^I/V^V secondary building blocks in a linear V-Ag-Ag-V sequence that is observed in complexes 2-4. These unprecedented tetranuclear {Ag₂(VO₂F₂)₂(tr) ₄} units (the intermetal Ag-Ag and Ag-V distances are 4.24-4.36 and 3.74-3.81 A, respectively), in which vanadium(V) oxofluoride units possess distorted trigonal bipyramidal environment {VO₂F₂N}, are incorporated into 1D ribbon (2) or 2D square nets (3, 4) using bitopic μ₄-triazole ligands. The valence bond calculation for vanadium atoms shows +V oxidation state in the corresponding compounds. Thermal stability and photoluminescence properties were studied for all reported coordination polymers.

Full text of DOI:10.1021/ic3000894

Article
pubs.acs.org/IC
I
V
Ag /V Heterobimetallic Frameworks Generated from Novel-Type
Ag (VO F ) (triazole) } Secondary Building Blocks: A New Aspect in
{
2
2 2 2
4
the Design of SVOF Hybrids
†
§
†
,†
‡
Ganna A. Senchyk, Valeriy O. Bukhan’ko, Andrey B. Lysenko,* Harald Krautscheid,
Eduard B. Rusanov, Alexandr N. Chernega, Miroslaw Karbowiak, and Konstantin V. Domasevitch
§
∥
†
†
Inorganic Chemistry Department, National Taras Shevchenko University of Kyiv, Volodimirska Street 64, Kyiv 01033, Ukraine
‡
§
∥
̈
̈
Institut fur Anorganische Chemie, Universitat Leipzig, Johannisallee 29, D-04103 Leipzig, Germany
Institute of Organic Chemistry, Murmanska Street 5, Kyiv, 02660, Ukraine
Faculty of Chemistry, University of Wroclaw, 14 Joliot-Curie Street, 50-383 Wroclaw, Poland
*
S Supporting Information
ABSTRACT: A series of new silver(I)-containing MOFs
[
[
[
Ag (tr ad) ](ClO ) (1), [Ag (VO F ) (tr ad) ]·H O (2),
2 2 2 4 2 2 2 2 2 2 2 2
A g ( V O F ) ( t r e t h ) ( H O ) ] ( 3 ) , a n d
2
2
2
2
2
2
2
2
Ag (VO F ) (tr cy) ]·4H O (4) supported by 4-substituted
2
2
2 2
2
2
2
bifunctional 1,2,4-triazole ligands (tr ad = 1,3-bis(1,2,4-triazol-
2
4
-yl)adamantane, tr eth = 1,2-bis(1,2,4-triazol-4-yl)ethane,
2
tr2cy = trans-1,4-bis(1,2,4-triazol-4-yl)cyclohexane) were hy-
drothermally synthesized and structurally characterized. In
1
2
these complexes, the triazole heterocycle as an N ,N -bridge
links either two adjacent Ag−Ag or Ag−V centers at short distances forming polynuclear clusters. The crystal structure of
2
+
compound 1 is based on cationic {Ag (tr) } fragments connected in a 2D rhombohedral grid network with (4,4) topology. The
2
4
neighboring layers are tightly packed into a 3D array by means of argentophilic interactions (Ag···Ag 3.28 Å). Bridging between
I
V
different metal atoms through the triazole groups assists formation of heterobimetallic Ag /V secondary building blocks in a
linear V−Ag−Ag−V sequence that is observed in complexes 2−4. These unprecedented tetranuclear {Ag (VO F ) (tr) } units
2
2
2 2
4
(
the intermetal Ag−Ag and Ag−V distances are 4.24−4.36 and 3.74−3.81 Å, respectively), in which vanadium(V) oxofluoride
units possess distorted trigonal bipyramidal environment {VO F N}¯, are incorporated into 1D ribbon (2) or 2D square nets (3,
4
2
2
) using bitopic μ -triazole ligands. The valence bond calculation for vanadium atoms shows +V oxidation state in the
4
corresponding compounds. Thermal stability and photoluminescence properties were studied for all reported coordination
polymers.
INTRODUCTION
active phases for solid-state battery applications. At the same
■
I
V
time, mixed-metal Ag /V hybrids show photocatalytic activity
in the light-driven production of H and/or O in aqueous
Heterobimetallic secondary building units (SBUs), where two
different metal centers are connected through a short bridge,
have great potential for construction of metal−organic
2
2
solutions arising from a metal-to-metal charge transfer
1
0
0
28
1
(MMCT) between the d and the d electron configurations.
However, only a few VOF examples with direct ligation of
polymers with nontrivial magnetic, optical, luminescent, and
2
catalytic behavior. In this context, simultaneous incorporation
22−25
organic N-donor chelates have been reported so far
Table 1).
(see
of early and late transition metal ions into the framework
develops a highly fascinating trend toward solid materials.
Among them, organic−inorganic hybrid solids containing a
vanadium oxofluoride (VOF) matrix are of particular interest
presenting an enormous diversity of types and structural
Azole heterocycles with two neighboring N-donor atoms
(
pyrazole, triazole, tetrazole) offer many attractive opportu-
nities in bridging of metal centers into polynuclear fragments.
Such functional groups show high affinity not only toward late
transition metals (Cu, Ag, etc.) but also to early transition metal
3
−25
motifs.
In spite of considerable efforts made in this field the
main success was achieved in synthesis of simple VOF salts
with organic charge-compensating cations
Integration of VOF anions into coordination polymers, where
they play a bridging role or are a structurally important part of
the framework, represents an impressive advantage. For
4
−18,20,21
oxide/oxofluoride species (MoO , etc.). It suggests the
(Table 1).
3
possibility to form heterometallic compounds by means of
N,N-bridging. However, this idea is confirmed only by several
26
instance, silver(I)-containing VOFs (SVOFs, Ag V O F
Received: January 13, 2012
4
2
6 2
2
7
and Ag VO F ) received much attention as electrochemically
3
2 4
©
XXXX American Chemical Society
A
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Inorganic Chemistry
Article
Table 1. Vanadium Oxo−Fluoride (VOF) Compounds Previously Reported and Structurally Characterized
B
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Inorganic Chemistry
Article
Table 1. continued
*
Abreviations: mono (py = pyridine), di (en = ethylenediamine; 4,4′-bipy = 4,4′-bipyridine; dabco = 1,4-diazabicyclo[2.2.2]octane; pip = piperazine;
bpe = trans-1,2-bis(4-pyridyl)ethylene; 1,5-dap = 1,5-diaminopentane; 1,6-dah = 1,6-diaminohexane), tri (deta = diethylenetriamine; tren = tris(2-
aminoethyl)amine; adap = N-(3-aminopropyl)-1,3 diaminopropane); tetraprotonated species (teta = triethylenetetramine or 1,4,7,10-
tetraazadecane); im = imidazole; 1,10-phen = 1,10-phenantroline; 2,2′-bipy = 2,2′-bipyridine.
−
metal−organic hybrids where acido−tetrazolate derivatives
connect d-element atoms with the molybdenum−oxide
and two charge-compensating VO F (H O) acceptors affords
2
2
2
the tetranuclear unit {Ag (VO F ) } supported by four triazole
2
2 2 2
2
9
matrix. In the case of neutral 1,2,4-triazole ligands, the
bridges.
assembly of metal oxide− or oxo−fluoride−organic frameworks
In the present article we introduce the design principles
toward novel Ag /VOF heterobimetallic complexes based on
I
(
MOOFs) is the result of strong cooperation between N,N-
30
azole and short covalent oxo bridges.
the {Ag (VO F ) (tr) } SBUs, which are integrated into MOFs
2
2
2 2
4
At first glance, it is surprising that a symmetrical triazole ring,
having two equivalent donor sites (N1 and N2), can
simultaneously and selectively interact with different metal
types. The situation essentially changes in metal clusters with
free donor centers, that is often observed in silver−triazole
systems. From Scheme 1 it becomes evident that the simplest
employing bitopic 1,2,4-triazole ligands with aliphatic linkers:
flexible 1,2-ethanediyl, semirigid linear trans-1,4-cyclohexane-
diyl, and rigid angular 1,3-adamantanediyl (Scheme 2).
Following this strategy, the compounds were successfully
prepared in high yields by a simple ‘one-pot’ hydrothermal
methodology.
2
2+
{
Ag (η -tr) (tr) } binuclear cationic fragment is unsaturated
2 2 2
(
two N atoms remain noncoordinating) and has a potential for
EXPERIMENTAL SECTION
■
further interactions as a Lewis base. On the other hand, a big
Synthesis of Organic Ligands. All chemicals were of reagent
grade and used as received without further purification. 1,2,4-Triazole
ligands were prepared in yields up to 60% by the general synthetic
procedure: refluxing of the corresponding diamines (ethane-1,2-
diamine, trans-cyclohexane-1,4-diamine, adamantane-1,3-diamine)
with N,N-dimethylformamide azine in xylene/toluene in the presence
variety of vanadium oxo−fluoride anions (mononuclear
{
{
coordinated water molecule, very labile toward N-donor ligand
substitution, and can behave as Lewis acids. Thus, the rational
combination between the dicationic {Ag (η -tr) (tr) } donor
5
−7
8,9
VOF (H O)},
binuclear {V O F (H O) }
and
4
2
2
2
6
2
2
1
2
14,15
V O F (H O)}, or polymeric
) contain a weakly
2
2
8
2
2
2+
30,31
of p-toluenesulfonic acid monohydrate as the catalyst.
2
2
2
C
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Inorganic Chemistry
Article
H, 3.80; N, 17.59. Found: C, 35.25; H, 3.68; N, 17.47. IR (KBr discs,
selected bands, cm ): 624s, 640s, 666m, 728m, 850m, 884m, 986s,
Scheme 1. New Approach to ‘One-Pot’ Synthesis of
Heterometallic Ag/VOF Coordination Polymers That
Promotes Formation of Novel Tetranuclear SBUs Supported
by 1,2,4-Triazole Bridges
−
1
1
094s, 1196s, 1238m, 1290m, 1326s, 1340m, 1370m, 1456m, 1520s,
2
868m, 2916m, 2948m, 3128s.
[
Ag (VO F ) (tr ad) ]·H O (2). A mixture of AgOAc (13.6 mg, 0.074
2 2 2 2 2 2 2
mmol), tr ad (10.0 mg, 0.037 mmol), and V O (6.7 mg, 0.037 mmol)
2
2
5
was added to 5 mL of water with aqueous HF (50%, 100 μL, 2.89
mmol) in a Teflon vessel. The sealed reactor was kept at 165 °C for 24
h and then slowly cooled to room temperature during 50 h, yielding
1
6.2 mg (87%) of big light-yellow prismatic crystals. Anal. Calcd for
C H Ag F N O V : C, 33.09; H, 3.77; N, 16.54. Found: C, 32.98;
H, 3.80; N, 16.51. IR (KBr discs, selected bands, cm ): 532s, 590s,
28
38
2
4
12
5 2
−1
6
1
58s, 734m, 854m, 918s, 1030m, 1072s, 1200s, 1324m, 1366m,
464m, 1526s, 2858m, 2924s, 2986m, 3028m, 3080s, 3116m, 3434m.
[
Ag (VO F ) (tr eth) (H O) ] (3). A mixture of AgOAc (16.7 mg,
2 2 2 2 2 2 2 2
0
.100 mmol), tr eth (16.4 mg, 0.100 mmol), V O (9.1 mg, 0.050
2
2
5
mmol), and 5 mL of water with aqueous HF (50%, 150 μL, 4.33
mmol) was placed in a Teflon vessel. The reactor was heated at 150 °C
for 24 h and cooled to room temperature during 50 h, leading to
yellowish crystalline product in 27.2 mg yield (73%). Anal. Calcd for
C H Ag F N O V : C, 17.53; H, 2.45; N, 20.45. Found: C, 17.61;
1
2
20
2
4
12
6 2
−1
H, 2.42; N, 20.37. IR (Nujol, selected bands, cm ): 570w, 640s,
6
1
3
84m, 722m, 878s, 910s, 964s, 998m, 1036m, 1082s, 1172s, 1200s,
332m, 1378s, 1462s, 1540s, 1668m, 2674m, 2724m, 3112m, 3154m,
228m.
[
Ag (VO F ) (tr cy) ]·4H O (4). A mixture of AgOAc (16.7 mg,
2 2 2 2 2 2 2
0
.100 mmol), tr cy (10.9 mg, 0.050 mmol), V O (9.1 mg, 0.050
2
2
5
mmol), and 5 mL of water with aqueous HF (50%, 150 μL, 4.33
mmol) was added into a Teflon vessel. Then the components were
heated at 150 °C for 24 h and slowly cooled to room temperature
during 50 h, yielding 20.3 mg (84%) of light-yellow prismatic crystals.
Anal. Calcd for C H Ag F N O V : C, 24.86; H, 3.76; N, 17.40.
20
36
2
4
12
8 2
−1
Found: C, 24.79; H, 3.85; N, 17.25. IR (Nujol, selected bands, cm ):
5
1
1
3
76m, 652s, 722m, 802m, 916s, 950s, 978m, 992m, 1014m, 1028m,
046s, 1088s, 1190s, 1216s, 1238m, 1306m, 1352s, 1376s, 1406m,
444s, 1470s, 1540s, 1634m, 2672m, 2724m, 2832s, 2988s, 3094s,
180m, 3444m.
Measurements. Elemental analysis was carried out with a Vario
EL-Heraeus microanalyzer.
Scheme 2. Bitopic 1,2,4-Triazole Ligands with Aliphatic
−1
IR spectra (400−4000 cm ) were collected using a Perkin-Elmer
FTIR spectrometer on KBr discs and Nujol for all compounds. IR
spectra recorded as Nujol mulls were identical to those recorded in
KBr, except for the Nujol absorptions.
Spacers, Flexible Linear (tr eth), Semi-Rigid Linear (tr cy),
2
2
and Rigid Angular (tr ad) Platform, Utilized in the
2
Presented Study
X-ray powder diffraction was carried out on a Shimadzu XRD-6000
(
Cu Kα radiation) and Stoe STADIP (Cu Kα ) using a linear PSD
1
detector. Temperature-dependent X-ray measurements were carried
out on a Stoe STADIP with a high-temperature attachment and image
plate detector system.
Diffuse reflectance spectra were recorded in the 800−200 nm range
at 298 K on a Cary-500 UV−vis−NIR spectrophotometer. Corrected
emission and excitation spectra were recorded at 298 and 77 K on an
Edinburgh Instruments FLSP 920 spectrofluorometer using the
Optistat DN liquid nitrogen cryostat (Oxford Instrument).
X-ray Crystallography. Diffraction data were collected at 213 K
using a Stoe Imaging Plate Diffraction System for 2 (numerical
absorption correction) and at 100 K on a Bruker APEXII CCD area-
detector diffractometer (φ scans) for 1, 3, and 4 (graphite-
monochromated Mo Kα radiation, λ = 0.71073 Å). Data were
corrected for Lorentz-polarization effects and the effects of absorption
(multiscans method). Structures were determined by direct methods
Synthesis of Coordination Compounds. Caution: HF (50%) is
toxic and corrosive and must be handled in a well-ventilated fume hood
with extreme caution using appropriate protective gear!
All complexes were prepared under hydrothermal conditions as
follows. A mixture of the components and distilled water was placed
into a 20 mL Teflon-lined steel autoclave, stirred for 30 min, and
heated in an oven at the temperature range of 150−180 °C for 24−40
h, with further cooling to room temperature (cooling rate 2−2.5 °C/
h). Crystalline products were collected, washed with water and
methanol, and dried in air.
2
and refined by full-matrix least-squares on F using the SHELX-97
3
2
package. CH hydrogen atoms were placed in calculated positions
and refined as fixed contributions with Uiso = 1.2Ueq(C), while OH
hydrogen atoms were located and then fixed at O−H = 0.85 Å and
−
with U = 1.5U (O). In 1, the oxygen atoms of ClO are unequally
iso
eq
4
[
Ag (tr ad) ](ClO ) (1). A mixture of AgClO4 (15.4 mg, 0.074
disordered with partial occupancy factors 0.7 and 0.3. Disorder was
resolved with restrained geometry for both contributions, while atoms
of the minor component were left isotropic and refined with equal
atomic displacement parameters. In 3, the organic ligands adopt two
closely separated orientations and are equally disordered. The
2
2
2
4 2
mmol), tr ad (10.0 mg, 0.037 mmol), and 5 mL of water was placed in
2
a Teflon reactor and heated at 180 °C for 40 h. Cooling to room
temperature during the next 60 h led to colorless prisms of the product
in 24.7 mg yield (70%). Anal. Calcd for C H Ag Cl N O : C, 35.20;
28
36
2
2
12
8
D
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Inorganic Chemistry
Article
disordered portion was refined anisotropically without restraints in
geometry, and hydrogen atoms were added with partial occupancies of
SBUs. In the IR spectra of the obtained compounds it is
−
1
possible to ascribe the bands at 910−920 cm to the
0
.5. Crystallographic data and experimental details for structural
symmetric and asymmetric VO stretches, while the stretches
analyses are summarized in Table S1, Supporting Information.
Crystallographic material can also be obtained from the CCDC, the
deposition numbers being CCDC 862508−862511.
−1
of terminal V−F bonds are observed at ca. 590 cm (according
t o r e f 8 a ) . I n t h e c r y s t a l s t r u c t u r e o f
[
Ag (VO F ) (tr ad) ]·H O (2) the silver atoms adopt the
2 2 2 2 2 2 2
distorted tetrahedral environment AgN O and are associated
with the vanadium oxo−fluoride anions {VO F } through the
triazole and oxo bridges (Figure 2). The bis-triazole ligands are
RESULTS AND DISCUSSION
In silver−triazole complexes, bi- and tetranuclear clusters
are the most widespread structural motifs. For the studied
3
■
−
33
34
2 2
2
+
compounds (1−4) the first type {Ag (tr) } is clearly
2
4
represented in the complex [Ag (tr ad) ](ClO ) (1). Every
2
2
2
4 2
silver ion of the centrosymmetric binuclear cluster adopts a
triangular AgN environment completed by two μ and one
3
2
monocoordinating triazole ring. Within the pseudo-planar
2
+
{
Ag (tr) } fragment the metal centers are separated by
2 4
1
2
means of the N ,N -bridge at a distance of 4.0375(9) Å. The
organic ligands (tr ad) link neighboring clusters into a 2D
2
rhombohedral grid network (dimensions of the grid are 13.71
×
13.71 Å, and diagonal-to-diagonal distances between the
disilver nodes are 18.88 × 19.88 Å, Figure 1). In this case only
Figure 2. Tetranuclear mixed-metal SBU in complex 2. 1,2,4-Triazole,
as a short N,N-bridge, connects two metal ions, forming disilver
fragments with further vanadium coordination.
μ4 coordinating: one functional group links two adjacent silver
ions (Ag···Ag 4.3633(7) Å), while another one combines silver
and vanadium ions at a distance of 3.7997(6) Å. Thereby the
vanadium centers possess a five-coordinated environment as a
distorted trigonal bipyramid VO F N (principal geometric
2
2
parameters are given in Table 2). Such polyhedra can be more
precisely described by Reedijk’s factor τ of ca. 0.74 (τ = 0 for
36
square pyramid and τ = 1 for trigonal bipyramid ). The
angular geometry of the bitopic ligand tr ad facilitates
2
catenation of the SBUs at 12.6 Å (distance between the
centers of binuclear silver fragments) by double organic bridges
into a 1D coordination polymer (Figure 3). The anionic parts
of heterobimetallic clusters are involved in hydrogen bonding
with triazoles and solvate water molecules leading to close
packing in the crystal.
The structural motif in compound [Ag (VO F ) (tr eth) -
H O) ] (3) is slightly different. The tetrahedral environment
2 2
2
2
2 2
2
2
(
of the silver atoms AgN O is supplemented with a weakly
3
bonded water molecule (Ag−O 2.595(3) Å) while being
Figure 1. Square net of compound 1: dinuclear silver units act as
nodes of the framework, where uncoordinated perchlorate anions
occupy the cavities.
connected with the anionic fragment {VO F }¯ only through a
2
2
triazole bridge. The IR spectrum of 3 is clearly representative,
−1
showing two strong bands at 910 and 878 cm from terminal
VO stretches. Assuming a linear geometry in the crystal
three N-donor atoms are used in coordination, while the last
one remains uncoordinating, forming the hydrogen bond with
the C−H (triazole) group (distance N2−C3 is 3.17 Å). Such
networks are tightly packed, leading to hydrophilic channels
with a van der Waals cross section of 2 × 3 Å running along the
a axis (see Figure S1, Supporting Information). The closest
lattice, the bitopic organic ligand (tr eth), as a μ -linker,
2
4
organizes the heterobimetallic SBUs into a square net (the
shortest distance between the centers of tetranuclear units
within the sheet is 13.2 Å) (Figure 4). Between the layers, the
inorganic clusters are located close to one another at a distance
δ+
δ−
of 4.05 Å, which causes the distant double V −F interaction
of 2.842(4) Å between two anionic parts (Figure S5,
Supporting Information). The coordination environment of
the vanadium atoms can be described as a distorted tetragonal
bipyramid (τ = 0.44) with one elongated bond. The hydrogen
bonding between the coordinated water molecule and the
I
distance between Ag ions of the nearest layers is 3.2827(9) Å ,
which can be interpreted as a sufficiently strong argentophilic
interaction, by a comparison with known Ag−triazole
3
5
complexes. The channel space is occupied with non-
−
coordinating ClO4 anions that are involved in hydrogen-
bonding and anion···π(tr) interactions. In the IR spectrum of
vanadium oxo−fluoride unit (O −O
is 2.76 Å) promotes
w
anion
−1
compound 1 two bands at 1094 and 624 cm can be assigned
tight parallel packing of planar nets.
−
to stretches of the ClO4 anions.
The same principle is realized with 1,4-bis(1,2,4-triazol-4-
y l ) c y c l o h e x a n e i n c o o r d i n a t i o n p o l y m e r
[Ag (VO F ) (tr cy) ]·4H O (4). Similarly to complex 2, the
I
While investigating the Ag /V O /HF/tr-ligand systems
2
5
under hydrothermal conditions we found formation of novel
,2,4-triazole-supported mixed-metal {Ag (VO F ) (tr) }
2
2
2 2
2
2
2
1
coordination environment AgN O is completed with vanadium
2
2
2
2
4
3
E
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Table 2. Principal Geometric Parameters (Angstroms, degrees) of Heterobimetallic Fragments in Compounds 2−4
[
Ag (VO F ) (tr ad) ]·H O (2)
[Ag (VO F ) (tr eth) (H O) ] (3)
[Ag (VO F ) (tr cy) ]·4H O (4)
2 2 2 2 2 2 2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
VO
1.6390(15), 1.669(2)
1.8365(15), 1.8400(15)
2.1826(17)
1.639(3), 1.650(4)
1.866(3), 1.890(3)
2.147(3)
1.616(3), 1.639(2)
V−F
1.841(2), 1.8837(19)
2.133(2)
V−Ntr
Ag−Ntr
Ag − O
Ag···V
2.2088(16)−2.464(2)
2.5578(16)
2.212(3)−2.445(3)
2.595(3)
2.178(2)−2.520(3)
2.667(3)
3.7997(6)
3.8132(8)
3.7400(6)
Ag···Ag (dimer)
OVO
OV−F
4.3633(7)
4.2745(6)
4.2384(5)
110.59(9)
107.54(17)
109.95(15)
ax
97.8(2), 99.33(16)ax
96.85(11), 99.69(11)ax
99.37(8), 100.08(10)
eq
111.00(17), 139.69(16)eq
121.80(13), 126.81(14)eq
1
20.93(8), 125.69(9)
F−V−F
88.07(7)
86.87(12)
86.31(10)
OV−N
F−V−N
N−Ag−N
86.65(7), 87.45(8)
79.91(7), 167.90(8)
88.60(13), 90.33(15)
79.90(11), 166.28(14)
103.45(10)−145.03(11)
89.44(11), 89.80(12)
79.78(10), 166.06(10)
92.12(9)−161.37(9)
100.23(6)−142.35(6)
cm− from VO stretching vibration. The value of Reedijk’s
factor (ca. 0.65) reveals a distorted trigonal bipyramidal
geometry for the five-coordinated vanadium ions (O F N).
1
2
2
The trans-1,4-disubstituted cyclohexane derivative adopts the
most profitable chair configuration that supports the
equatorial−equatorial (e,e) disposition of the triazole hetero-
cycles rather than an alternative axial−axial (a,a) conforma-
37
Figure 3. Catenation of Ag/VOF SBUs into 1D coordination polymer
by means of double organic bridge tr ad.
tion. At the same time, the tr rings are orthogonally arranged
2
2
to the aliphatic core. As a linear connector, tr cy bridges
2
heterobimetallic fragments into 2D square nets at a distance of
1
4.43 Å (Figure 5), which are closely packed at the expense of
hydrogen bonding.
+V
In hydrothermal reactions the V forms can be easily
reduced to V+ and even V . According to valence bond
calculations, in 2−4 the oxidation state +V is realized (Table 3).
Comparing the crystal structure data with the results of such
IV
+III
5
Figure 4. Heterobimetallic Ag/VOF unit with additionally coordinated
water molecule in complex 3 that is connected with linear triazole
ligands tr eth into a 2D square net.
2
Figure 5. Ag/VOF building fragment as a node of the ‘square grid’
framework topology with linear triazolyl linkers in the crystal structure
of 4.
oxo−fluoride anions as a distant bonding contact Ag−O
anion
2
.667(3) Å. The IR spectrum shows one strong band at 916
F
dx.doi.org/10.1021/ic3000894 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
a
Table 3. Bond Valence Sums for {VO F N}¯ Units in the Heterobimetallic Complexes
2
2
[
Ag (VO F ) (tr ad) ]·H O (2)
[Ag (VO F ) (tr eth) (H O) ] (3)
[Ag (VO F ) (tr cy) ]·4H O (4)
2 2 2 2 2 2 2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
Ri, Å
Si
V − Si
Ri, Å
Si
V − S
Ri, Å
Si
V − Si
i
b
c
b
V−O1
V−O2
V−F1
V−F2
V−Ntr
1.6390(15)
1.669(2)
1.55
1.43
0.71
0.71
0.45
0.45
1.650(4)
1.639(3)
1.866(3)
1.890(3)
2.147(3)
1.51
1.56
0.66
0.62
0.50
0.49
1.616(3)
1.639(2)
1.66
1.55
0.63
0.70
0.52
0.34
c
c
c
0.57
0.44
0.45
c
1.8400(15)
1.8365(15)
2.1826(17)
0.29
0.29
0.34
1.8837(19)
1.841(2)
2.133(2)
0.37
d
c
0.38
0.30
∑
S = 4.85
∑S = 4.85
∑S = 5.06
a
Valence sums were calculated with the formula S = exp[(R − R )/B] (S , bond valence of bond “i”; R , constant dependent on the bonded element;
i
0
i
i
0
R , length of bond “i”; B = 0.370. ∑S, bond valence sum for vanadium. V, predicted valence for a site. R (V−O) = 1.803 Å, R (V−F) = 1.710 Å, R
i
0
0
0
b
+
c
d
(
V−N) = 1.889 Å. Bond to Ag . H-bond acceptor. Elongated contact V−F.
calculations there are some correlations between the bond
lengths in vanadium oxo−fluoride anions and their hydrogen
bonding in the crystal. Atoms with the highest partial negative
charges (V − S ) have a tendency either for coordination to
i
metal centers or for H-bond accepting, as is clearly observed in
compound 2. Thus, two oxygen atoms O1 and O2 have partial
negative charges of 0.45 and 0.57, respectively, which is a result
of their higher nucleophilic ability, leading to distal bonds to
silver ions and hydrogen bonds with C−H groups of triazole
heterocycles (O−C = 3.08−3.12 Å). In compounds 3 and 4 the
hydrogen-bond network is more complicated, including solvate
water molecules and triazole moieties; therefore, almost all O
and F atoms of VOF anions are involved in H-bonding patterns
as reflected in the partial negative charge calculations (Table 3).
Thermal Stability. The thermal behavior of complexes 1, 2,
and 4 was studied using temperature-dependent powder X-ray
diffractometry (TD PXRD) in a capillary under argon
atmosphere (Figures S15 and S16, Supporting Information).
According to the diffraction patterns, compounds 1 and 2
remain stable up to 300 °C. In the case of compound 4 the
thermal behavior is more complicated. The structure is
invariable until 160 °C; then the reflection angles are shifted
caused by removal of the solvate water molecules located
between the metal−organic layers. The Guinier−Simon
diagram reveals three phase transitions in the temperature
range up to 280 °C. Total decomposition of substances occurs
at 300 °C accompanied by crystallization of silver in the face-
centered cubic lattice.
Figure 6. Diffuse reflectance spectra of free ligands and complexes 1−
4
.
quenched by the thermal rotations of triazole rings around the
C−C and C−N bonds. The intraligand fluorescence was
observed for tr eth after its immobilization in a coordination
2
3
8
network, which stops rotation and freezes a single
conformation. It seems that a similar effect is responsible for
Photoluminescence Properties. The synthesized com-
pounds show an extended absorption in the UV−vis range. The
room-temperature diffuse reflectance spectra of free ligands are
shown in Figure 6, curves a−c. Spectra are very similar with two
maxima at ca. 320 and ca. 250 nm and a strong UV absorption
band starting at ca. 220 nm. Curves d−g in Figure 6 present the
observed tr ad emission. The 1,2,4-triazole rings are connected
2
by rigid angular 1,3-adamantanediyl, which increases the ligand
conformational stiffness, thereby reducing the nonradiative
decay of the intraligand (π−π*) excited state. This is not the
case for the tr eth ligand with a flexible 1,2-ethanediyl linker.
2
Figure 7 presents the emission and excitation spectra
reflectance spectra recorded for compounds 1−4. Spectra of 2−
recorded for tr ad and compound 1. Emission of 1 at 77 K is
2
−
4
are dominated by the strong absorption band of VO F ,
more intense than at 298 K, and the bands are a little better
resolved. Both the emission and the excitation bands are very
2
2
responsible for the yellowish color of these AgVOFs. The
compound [Ag (tr ad)](ClO ) ] (1) has no absorption band
similar for the free tr ad ligand and compound 1, and only the
2
2
4 2
2
in a visible range. The most striking feature of its spectrum is
small shift of the band positions toward longer wavelengths can
be noticed for the latter. The maximum of the excitation band
the absence of the absorption band observed for the free tr ad
2
ligand at 320 nm. Moreover, the absorption bands of 1 seem to
be slightly red shifted as compared to those of free ligand.
The solid state luminescence spectra of free ligands and
is observed at 285 nm for tr ad and 290 nm for 1. Emission
spectra show vibronic structure with maxima at 412, 438, and
2
460 nm for tr ad and at 418, 442, 463, and 486 nm for 1. The
2
complexes 1−4 were examined at 298 and 77 K. The tr ad
observed vibrational progressional spacings of ca. 1100−1440
2
−1
−1
ligand and compound 1 are luminescent at room temperature,
cm for tr ad and ca. 1020−1300 cm for 1 suggest that the
2
while for tr cy a weak luminescence could be noticed only at 77
emission of complex 1 arises from a ligand-centered transitions.
2
K. In contrast, the tr eth ligand as well as compounds 2−4 are
The inset in Figure 7 shows the emission decay curves recorded
2
not luminescent even after cooling them to liquid nitrogen
at 77 K for tr ad ligand and compound 1. In both cases the
2
temperature. The possible tr eth fluorescence is apparently
decay curves are biexponential with the major contribution
2
G
dx.doi.org/10.1021/ic3000894 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
for nonradiative relaxation (e.g., through intersystem crossing,
ISC). A similar effect of oxovanadium VO2+ cation on emission
quenching of pyridyl/pyrimidyl−pyrazole-derived ditopic li-
41
gands has been reported recently.
CONCLUSION
■
In the present study we demonstrated a rational design
approach for construction of heterobimetallic AgVOF frame-
works utilizing the unique coordination potential of bifunc-
tional 1,2,4-triazoles. Unprecedentedly, in the discrete
[
Ag (VO F ) (tr) ] cluster architecture four triazole hetero-
2 2 2 2 4
cycles elegantly connect two diverse metal centers in pairs
Ag···V 3.74−3.81 Å), affording the zigzag V−Ag−Ag−V
(
sequence. The design principle opens an efficient pathway to
the mixed-metal AgVOF materials with high thermal stability
and interesting photochemical properties. Apparently, the
approach can also be applied to other heterocyclic systems
(
1,2,3-triazoles, tetrazoles, etc.). Photoluminescence of the tr ad
2
ligand originates from n−π* or π−π* transitions, while
luminescence of [Ag (tr ad)](ClO ) ] is due to ligand-centered
2
2
4 2
Figure 7. Excitation (I) (λem = 440 nm) and emission (II) (λex = 290
π−π* transitions. Such intraligand emission is quenched,
nm) spectra recorded for tr ad at 77 K (a), compound 1 at 77 K (b),
2
−
however, if the {VO F } anion is incorporated into the
and compound 1 at 298 K (c). (Inset) Emission decay curves recorded
2 2
complex structure.
for tr ad (a) and 1 (b) at 77 K.
2
ASSOCIATED CONTENT
Supporting Information
X-ray crystallographic data of 1−4 in CIF format, crystallo-
graphic data and experimental details for X-ray structural
analyses, spectral characterization data, XRPD, thermo-XRPD
diffractograms, and DFT computations. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
from the longer component. The determined time constants
*
S
are t = 2.5 ns, t = 8.3 ns for tr ad and t = 4.8 ns, t = 14.6 ns
1
2
2
1
2
for 1. The almost two times increase in the decay times
observed for 1 may result from the less efficient nonradiative
relaxation process due to the larger rigidity of the ligand
surrounding in the coordination frameworks.
The emission bands of tr ad should be assigned as n−π* or
2
π−π* transitions. On the basis of MO calculations (see
Supporting Information, density functional theory (DFT)
computations) and the observed similarity of the excitation
and emission bands of the free ligand and the complex, the
emission of compound 1 may be assigned to originate from
intraligand π−π* transitions.
AUTHOR INFORMATION
Corresponding Author
E-mail address: ab_lysenko@univ.kiev.ua.
■
*
Notes
The authors declare no competing financial interest.
For d10 metal complexes besides the ligand-centered π−π*
transitions the ligand-to-metal or metal-to-ligand (LMCT or
ACKNOWLEDGMENTS
39
■
MLCT) charge-transfer transitions are possible. Furthermore,
Financial support by Deutsche Forschungsgemeinschaft is
gratefully acknowledged.
+
the Ag ion can exert a heavy-atom effect on the ligand, leading
40
to the intraligand phosphorescence. The emission originating
3
from the [π−π*] excited state of the Ag(I) complex with 3,5-
3
5
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dx.doi.org/10.1021/ic3000894 | Inorg. Chem. XXXX, XXX, XXX−XXX