Two new silver(I) complexes with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz): Preparation, characterization, crystal structure and alcohol oxidation activity in the presence of oxone

Article abstract of DOI:10.1016/j.poly.2010.07.005

Two new silver(I) complexes ((tptz)Ag₂(NO₃) ₂ and [Ag₅(tptz)₄](NO₃)₅) with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) have been synthesized and characterized by X-ray diffraction, elemental analysis, ¹H NMR, IR, fluorescence, UV-Vis spectroscopy and electrochemistry. Oxidation of alcohols to their corresponding aldehydes and ketones was conducted with one of the Ag complexes as a catalyst, soluble enough in organic solvent, using oxone (2KHSO₅·KHSO₄·K₂SO₄) as an oxidant under biphasic reaction conditions (CH₂Cl ₂/H₂O) and tetra-n-butylammonium bromide as phase transfer agent under air at room temperature.

Full text of DOI:10.1016/j.poly.2010.07.005

Polyhedron 29 (2010) 2837–2843
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Two new silver(I) complexes with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz):
Preparation, characterization, crystal structure and alcohol oxidation activity
in the presence of oxone
a,*
b,**
c
a
Mohammad Mahdi Najafpour , Małgorzata Hoły n´ ska
, Mojtaba Amini , Sayed Habib Kazemi ,
b
c
Tadeusz Lis , Mojtaba Bagherzadeh
a
Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
Department of Chemistry, University of Wrocław, 14 Joliot-Curie St, 50-383 Wrocław, Poland
Chemistry Department, Sharif University of Technology, P.O. Box 11155-3516, Tehran, Iran
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new silver(I) complexes ((tptz)Ag (NO ) and [Ag (tptz) ](NO ) ) with 2,4,6-tris(2-pyridyl)-1,3,5-tri-
2
3
2
5
4
3 5
Received 1 May 2010
Accepted 3 July 2010
Available online 8 July 2010
1
azine (tptz) have been synthesized and characterized by X-ray diffraction, elemental analysis, H NMR, IR,
fluorescence, UV–Vis spectroscopy and electrochemistry. Oxidation of alcohols to their corresponding
aldehydes and ketones was conducted with one of the Ag complexes as a catalyst, soluble enough in
organic solvent, using oxone (2KHSO
CH Cl /H O) and tetra-n-butylammonium bromide as phase transfer agent under air at room
temperature.
5
ÁKHSO
4
ÁK
2 4
SO ) as an oxidant under biphasic reaction conditions
Keywords:
(
2
2
2
Silver(I) complexes
Alcohol oxidation
Catalysis
Ó 2010 Elsevier Ltd. All rights reserved.
1
. Introduction
A combination of conjugated ligands and electron-rich metal
Both title compounds are silver(I) complexes of tptz, containing ni-
trate anions, which form part of the silver(I) atoms coordination
sphere only in case of 1 and in case of 2 part of the nitrate anions
is disordered. Moreover, 2 contains also water molecules of solva-
tion, part of which is disordered. There are twelve tptz complexes
of silver(I) deposited in the CCDC database [3–6]. Seven of these
compounds also contain phosphine ligands [3,6], one is a mixed sil-
ver(I)–ruthenium(II) complex (reported as a new DNA cleavage
agent) [4] and one contains also trifluoroacetate ligands bonded
to silver(I) atoms [5]. The possibility of obtaining 1 along with 2
from one system corresponds to the reported observation, accord-
ing to which it could be expected, that the product composition
may be not related to the molar ratio of reactants [3]. It is specu-
centers can produce low energy electronic interactions between
metal centers and ligands, resulting in a product with interesting
optical or electronic properties. Complexes of silver(I) and N-het-
erocyclic ligands lead to the formation of a variety of geometric
configurations and photophysical properties [1]. In recent years,
2
,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), which functions simulta-
neously as a tridentate and a bidentate ligand, has gained consid-
erable interest, because of its use as a spacer for designing
supramolecular complexes [2].
The reactions of tptz and silver(I) nitrate at ratio of 1:2 in aceto-
nitrile/water at many different ratios produce two different com-
pounds together. We could separate each compound by optimizing
the reaction conditions. In a mixture of acetonitrile/water at ratio
lated, that in these self-assembly processes the anion-p non-cova-
lent interactions play a crucial role [5]. In the here reported
particular case the presence of water in the used solvents seems
to be an important factor to be considered as affecting the self-
assembly processes route.
Some silver-based catalysts including electrolytic silver and
supported silver catalysts, have been recently demonstrated for
the selective oxidation of alcohols [7] but there are no reported
surveys on the use of silver(I) complexes as homogenous catalysts
in the alcohol oxidation reaction. The alcohol oxidation activity of 1
in the presence of oxone is considered with regard to the sufficient
of 9:1, 1 (catena-{[nitrato-
ver(I)][(dinitrato- -2,4,6-tris(2-pyridyl)-1,3,5-triazinesilver(I)]})
was formed and at the solvent ratio of 1:9, 2 (tetrakis(
-2,4,6-tris(2-pyridyl)-1,3,5-triazine)-
3
l -2,4,6-tris(2-pyridyl)-1,3,5-triazinesil-
l
2
l
2
,l ,
2
1 2 2 1 1 1 1 1 1 1
l :l ,l ,l :l ,l ,l :l ,l ,l
pentasilver(I) nitrate hydrate (1/7)) was formed. At other ratios
both compounds are formed together (see Section 4 for details).
*
Corresponding author.
solubility of 1 in CH
is an efficient catalyst for the oxidation of primary and secondary
alcohols. Although it is difficult to stop the oxidation of primary
2 2
Cl . The results have shown that the complex
*
* Corresponding author.
E-mail addresses: mmnajafpour@iasbs.ac.ir (M.M. Najafpour), mholynska@
1
gmail.com (M. Hoły n´ ska).
0
277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.07.005

2
838
M.M. Najafpour et al. / Polyhedron 29 (2010) 2837–2843
alcohols at the intermediate aldehyde stage, this system is very
useful in the transformation of primary alcohols into aldehydes
without over-oxidation to carboxylic acids (Table 2).
similarly to the previous results for the corresponding complexes
of tptz with Ni and Fe [10]. The midpoint potential values for these
peaks are: À0.15, À0.81 and À1.58 V, respectively. Also, an irre-
versible anodic wave is observed at around +0.5 V versus reference
electrode, which is attributed to the oxidation of silver ion in the
complex. It should be mentioned that the ligand has no redox peak
in the positive potential region of the voltammogram.
2
. Results and discussion
The results of catalytic studies (see Section 4) have shown that
The X-ray studies (Table 1) reveal, that in solid state in 1 there
are two symmetry-independent silver(I) atoms (Fig. 1a). Ag1 atom
is coordinated to pyridyl N12 and N13 atoms and to the triazine
N11 atom from the tptz ligand, as well as to the nitrate O15 atom
(Table 1S). Also a weaker bond to O25 atom from the same nitrate
anion could be distinguished (Table 1S). Thus the coordination
number of Ag1 atom could be given as 4 or 5. All ligands bonded
to Ag1 atom lie in one plane. In order to provide a quantitative
description of the coordination sphere also computations with
the use of SHAPE software [11,12] were carried out. Five possible
geometries were considered and the best fit was observed for PP-
5 pentagon geometry [11] (the calculated figure of merit was
2.25 for this geometry; for ideal fit zero value is obtained; in this
case the four remaining geometries yielded the analogous values
at about 30). If the weaker Ag1–O25 bond is disregarded, the
geometry of Ag1 atom coordination sphere could be described as
square-planar. The square-planar geometry around Ag(I) atom is
not unprecedented and there are well-characterized examples as
recently reviewed by Young & Hanton [13].
the complex 1 (catena-{[nitrato-
3
l -2,4,6-tris(2-pyridyl)-1,3,5-tri-
azinesilver(I)][(dinitrato- -2,4,6-tris(2-pyridyl)-1,3,5-triazinesil-
l
2
ver(I)]}) is an efficient catalyst for the oxidation of primary and
secondary alcohols. Although it is difficult to stop the oxidation
of primary alcohols at the intermediate aldehyde stage, this system
is very useful in the transformation of primary alcohols into alde-
hydes without over-oxidation to carboxylic acids (see Table 2, en-
tries 1–4). Benzyl alcohols were oxidized to give the corresponding
aldehydes with a 100% conversion yield (Table 2, entries 1–4). The
substrates bearing electron-donating and -withdrawing substitu-
ents bonded to the aromatic ring were compatible with this proto-
col. The change of nature of substituents (methyl, methoxy, and
nitro) in the aromatic ring of benzyl alcohol to probe electronic ef-
fects displayed no regular trends in the conversion. With the
exception of 1-indenol (Table 2, entry 8), aliphatic alcohols and
secondary alcohols were less reactive in comparison to aromatic
alcohols (Table 2, entries 5–10).
Both title complexes have been characterized by a number of
different techniques, both in solid state and in solution.
Silver(I) coordination number three and unusual in silver(I)
chemistry coordination number four seem to be characteristic for
silver(I) tptz complexes [3–6], along with severely distorted coordi-
nation polyhedra [4]. Similarly, in case of Ag2 atom the closest
coordination sphere consists of four atoms (pyridyl N14 atom
Electronic spectra of 1 in acetonitrile/water (9/1) and of 2 in
water/acetonitrile (9/1) solution were recorded and are very simi-
lar (Fig. 4S). The electronic spectra display two strong absorption
bands at about ꢀ205 and ꢀ250 nm. These are clearly charge trans-
fer in origin and the absorption band observed at ꢀ290 nm can be
assigned to the charge transfer from the coordinated ligand to the
Ag(I) centre [8].
i
and triazine N31 atom from the tptz ligand, as well as O16, O36
The IR spectrum recorded for 2 shows a broad band at ꢀ3200–
Table 1
À1
3
500 cm related to lattice water (antisymmetric and symmetric
Selected X-ray data for complex 1 and 2.
À1
O–H stretching) and at ꢀ1630 cm assigned to H–O–H bending
1
2
mode) [9]. Peaks revealing the presence of the tptz ligand in the
Formula
(C18
652.10
120(2)
H
12
6
N )Ag
2
(NO
)
3 2
5 12 6 4 3 5 2 7
[Ag (C18H N ) ](NO ) (H O)
À1
complex occur in the ranges 3100–2900 cm
(aromatic C–H
(C@C)
(C–N) vibrations], and
Formula weight
Temperature (K)
k (Å)
Crystal system
Space group
a (Å)
2224.86
100(2)
0.71073
orthorhombic
Pnna
24.384(5)
28.832(6)
11.083(4)
À1
stretching vibrations), 1600–1550 cm
[m(C@N) and m
À1
stretches], 1470–1020 cm
10–710 cm
[
m(C–C) +
m
0.71073
monoclinic
P2 /c
14.969(4)
6.593(3)
20.767(4)
108.42(3)
1944(2)
4, 2.227
2.08
À1
8
(aromatic C–H deformation vibrations) [9]. The
1
asymmetric stretch of the nitrate ion is split into a high-frequency
N–O asymmetric stretch and to a lower-frequency symmetric
b (Å)
c (Å)
À1
stretch upon coordination. These occur at 1480 and 1250 cm
,
b (°)3
respectively, for 1. The appearance of a broad band at 1380–
À1
V (Å )
7792(4)
4, 1.897
1.33
1
390 cm on the spectrum recorded for 2 is indicative of the pres-
À3
Z,
qcalc (g cm
)
ence of uncoordinated nitrate ions [10].
À1
l
(mm
)
Fluorescence emission spectra of complex 1 or 2 in DMSO
F(0 0 0)
1272
4432
(
Fig. 3S) are similar. The peaks at around 543.97 nm may be attrib-
Crystal size (mm)
h Range (°)
Reflections: total/
unique
0.14 Â 0.06 Â 0.05
0.14 Â 0.11 Â 0.06
4.7–38.6
4.2–35.0
uted to the intraligand emission ( *) from the tptz ligand. The
p
? p
19592/10118
80161/17127
fluorescence intensity for the complex 1 and 2 is larger than that
for the free tptz ligand, probably due to the rigidity of the coordi-
nated ligand in the complex in comparison to the free ligand. On
the other hand, the fluorescence intensity enhancement may be
due to the coordination of the free ligand to Ag(I) centre, reducing
the non-radiative decay of the intraligand excited state.
R
int
0.059
analytical
0.053
analytical
Absorption
corrections
Minimum,
maximum
transmission
factors
0.796, 0.908
0.832, 0.933
3
Ag(II) ion in water is obtained from oxidation of AgNO by
strong oxidizing agents but it is unstable due to its powerful oxi-
dizing nature in solution (standard redox potential: 1.98 V) and
must be stabilized by coordination with organic ligands, most
notably the nitrogen-containing heterocycles [1]. To test of the sta-
bilizing effect of tptz, electrochemical studies were performed.
From the electrochemical studies carried out for 1 (see Section 4
and Fig. 5S) it is concluded that the three ligand reduction pair
peaks appear in the negative potential region of voltammogram,
Data/restraints/
parameters
10118/0/307
0.683
17127/0/645
1.04
Goodness-of-fit
GOF) on F2
(
R
1
[I > 2r(I)]
0.036
0.042
1.55, À0.98
0.035
0.036
2.00, À1.01
wR (all data)
2
Maximum,
minimum
Dq
elect
À3
(
e Å
)

M.M. Najafpour et al. / Polyhedron 29 (2010) 2837–2843
2839
(
a)
i
i
(
b)
Fig. 1. Atom labeling scheme for the symmetry-independent part in complex 1 (a) and complex 2 (b). Only the closest coordination sphere (see text) of the Ag(I) atoms is
indicated (with open lines). For complex 2 (b) the nitrate anions and water molecules are omitted. Symmetry codes: [i] 2 À x, y À 0.5, Àz + 0.5, [ii] x, 0.5 À y, 1.5 À z.
atoms from two nitrate anions, Table 1S). These atoms lie in verti-
ces of a very distorted tetrahedron. Also weaker bonds to O26 and
O26 atoms from the same nitrate anions participating in Ag2 clos-
est coordination sphere could be distinguished. Thus geometry of
the whole coordination sphere of Ag2 atom is very irregular (Table
HP-6, 12.26 for pentagonal pyramid PPY-6, 18.58 for octahedron
OC-6, 13.18 for trigonal prism TPR-6, 14.01 for Johnson pentagonal
pyramid JPPY-57. In Table 2S the interplanar angles between
planes of the ligands for Ag1 and for Ag2 central atoms, as well
as deviations of the central atoms from the ligands planes are
given.
i
1
S). The analogous calculations as for Ag1 atom with the use of
SHAPE software [11,12], taking into consideration fitting to five ideal
polyhedra, yield the following figures of merit: 24.39 for hexagon
The tptz ligand is generally considered as a rigid ligand with an
extended
p system [3]. Both coplanar, as well as nearly coplanar

2
840
M.M. Najafpour et al. / Polyhedron 29 (2010) 2837–2843
(
with one pyridyl ring twisted with respect to the remaining mol-
(3.147(4)–3.472(5) Å), ring with N13 atom and ring with N12 atom
at 1 À x, y À 0.5, 0.5 À z (3.060(5)–3.384(5) Å), ring with N14 atom
and ring with N14 atom at 2 À x, 2 À y, 1 À z (3.208(4)–3.220(4) Å),
ring with N14 atom and ring with N14 atom at 2 À x, 1 À y, 1 À z
(3.039(4)–3.050(5) Å). Another kind of interaction involves the ring
with N11 atom and the nitrate anion with N15 atom at 1 À x,
0.5 + y, 0.5 À z (anion atoms are shifted from the interacting ring
plane at 3.240(4)–3.342(4) Å), as well as the ring with N11 atom
and the nitrate anion with N15 atom at 1 À x, y À 0.5, 0.5 À z (an-
ion atoms are shifted from the interacting ring plane at 3.203(4)–
ecule part) forms of this ligand have been reported for silver(I)
complexes [3]. In the tptz ligand in 1 the rings with N11 atom, with
N12 atom and with N13, respectively, are almost coplanar; the ring
with N14 atom is bent with respect to the plane of these rings (see
Table 2S for the corresponding interplanar angles). The tptz ligand
bonding mode could be described as
centres [3].
Thus defined units (comprising two tptz ligands, four silver(I)
atoms and five nitrate anions) are repeated along [0 1 0] direction
to form a one-dimensional coordination polymeric structure
3 2
l –l linking together Ag(I)
3.305(4) Å). This kind of
p
Á Á Áanion interaction has been considered
À À À
(Fig. 2a). The neighbouring units are linked by nitrate O36 atom,
by Zhou et al. for tptz ligands interacting with ClO
4
, BF
4
or PF
6
which further coordinates to Ag2 atom at [iv] 2 À x, 0.5 + y, 0.5 À z.
The adjacent polymeric chains (see Article text) are intercon-
nected via the following stacking interactions involving tptz
ligands rings (in brackets the range of the shifts of atoms of one
ring with respect to the plane of the interacting ring is given): ring
with N13 atom and ring with N12 atom at 1 À x, 0.5 + y, 0.5 À z
anions as a directing factor in formation of Ag(I) coordination net-
works [2]. In 1 numerous weak hydrogen bonds of C–HÁ Á ÁO type
and also C–HÁ Á ÁN(triazine ring from tptz ligand) (Table 3S) could
be distinguished.
In 2 there are four symmetry-independent silver(I) atoms
(Fig. 1Sb). Ag1 atom is bonded to four atoms from two tptz ligands:
Fig. 2. Formation of a one-dimensional polymeric structure in complex 1 (a) and a cationic unit in complex 2 (b). Symmetry codes: [ii] x, 0.5 À y, 1.5 À z; [iii] x, y À 1, z; [iv]
À x, 0.5 + y, 0.5 À z. In (a) the unit repeating along [0 1 0] (see text) is marked in black. Selected atoms are labeled. The continuation of the polymeric structure is denoted
with black dashed lines. In (b) the symmetry-independent part is marked in black.
2

M.M. Najafpour et al. / Polyhedron 29 (2010) 2837–2843
ii
2841
ii
triazine N111 and N111 atoms, pyridyl N131 and N131 atoms.
0.5 À y, 1.5 À z, 3.191(1)–3.664(4) Å; ring with N142 atom and ring
with N141 atom, 3.273(3)–3.466(5) Å; ring with N112 atom and
ring with N142 atom at x, 0.5 À y, 1.5 À z, 3.191(3)–3.664(4) Å;
ring with N122 atom and ring with N121 atom, 3.205(4)–
3.391(3) Å; ring with N121 atom and ring with N111 atom at x,
0.5 À y, 1.5 À z, 2.969(4)–3.358(3) Å), but also between the adja-
cent units (ring with N141 atom and ring with N122 atom at x,
0.5 À y, 0.5 À z, the shifts of atoms of one ring with respect to the
plane of the interacting ring are in the 3.265(3)–3.398(4) Å range).
When also weaker coordination of nitrate anions to the Ag(I) atom
is taken into account, it could be noted, that the pentameric units
are linked by these anions to form interlinked layers perpendicular
to [0 1 0].
In general, both in 1 and 2 a preference towards very distorted
tetrahedral geometry of Ag(I) centres closest coordination sphere
could be observed. However, as the distortion is extreme, hardly
available new coordination sites are created, making it possible
for weaker bonds to other ligands to occur, as Ag(I) is a d10 system
with no significant stereochemical preferences [13]. However, also
an important factor determining this coordination mode is some
degree of rigidity within the tptz ligand itself.
These N atoms are of very distorted tetrahedral arrangement. This
distortion creates another possible coordination site, which is
occupied by O25 and O25 atoms from two weakly monocoordi-
ii
nated nitrate anions. Thus, taking into account all these ligands,
the coordination environment of Ag1 is very irregular and could
be described as an extremely distorted octahedron (the calcula-
tions with the use of SHAPE software [11,12] lead to the following
figures of merit: 16.35 for hexagon HP-6, 19.25 for pentagonal pyr-
amid PPY-6, 10.20 for octahedron OC-6, 15.17 for trigonal prism
TPR-6, 20.37 for Johnson pentagonal pyramid JPPY-5). Similar mo-
tifs in silver(I) coordination chemistry have already been observed
and are generally interpreted as semi-coordination of the silver(I)
atoms by nitrate anions [12]. Ag2 closest coordination sphere com-
prises triazine N211, N212 atoms and pyridyl N122, N141 atoms,
forming a distorted octahedron. Also weak coordination of nitrate
iii
O16 and O15 atoms could be distinguished, which, if not ne-
glected, leads to the conclusion, that Ag2 coordination sphere is
very distorted octahedral, but not as extremely distorted as in case
of Ag1. The strongest coordination bonds to Ag3 atom are those
ii
involving N atoms from two tptz ligands: pyridyl N142 , N142,
ii
N121 , N121 atoms. These atoms lie in vertices of a distorted tet-
It is suggested that a structure in the solid-state is preserved in
solution, which may be likely to hold for most solvents with low
polarity. However, for polar solvents, such as water, able to pro-
mote ligand exchange, significant structural modifications may oc-
cur, which would drastically change the structure of the complex
in solid state, while promoting equilibria with other species stabi-
rahedron. Also a weaker coordination to other N atoms from the
ii
ii
two tptz ligands is observed: triazine N121 , N211, N211 , N212
atoms, also of distorted tetrahedral arrangement. When the two
tetrahedral, consisting of tptz N atoms, are taken together and
the possible coordination geometries are fitted with SHAPE software
the lowest figure of merit at 3.56 is obtained for dodecahedron DD-
1
13
lized by solvation [14–23]. H NMR and C NMR spectra recorded
1
13
8
geometry (also small values are obtained for square antiprism
SAPHR-8: 4.30; Johnson – biaugmented trigonal prism JBTP-8:
.56). The coordination environment of Ag4 atom is very similar
for 1 in Me
2 6
SO-d were investigated. H NMR and C NMR spectra
1
13
suggest that the ligand unit is dissociated in solution. H NMR,
C
4
NMR, COSY and HSQC spectra of the complex are consistent with
that of the ligand itself in solution. Four H NMR peaks in the range
of 7.9–9 ppm and six C NMR peaks in the range of 125–170 ppm
clearly signify that all tptz ligands are released. Such a fact indi-
cates that the Ag–N bonds are labile in solution, which is also re-
ported by others [24–26].
1
as in case of Ag1 atom. The closest coordinated atoms are N atoms
from two tptz ligands: triazine N312 , N312 atoms (two longer Ag–
N bonds) and pyridyl N132, N132 atoms (two shorter Ag–N
ii
13
ii
bonds), forming a distorted tetrahedron. The specific distortion of
this tetrahedron makes it possible for weak monodentate coordi-
iii
iv
nation of two nitrate anions (through O26 and O26 atoms,
respectively) to occur and the resulting coordination sphere is very
distorted octahedral.
3
. Conclusions
Characteristic pentameric units are formed in 2, comprising
four tptz ligands (two symmetry-independent ligand molecules
and the two symmetry-related ligand molecules at [ii] x, 0.5 À y,
Two different silver(I) complexes were isolated in the reaction
of tptz ligand with silver(I) nitrate. The complexes differ in struc-
ture: 1 comprises polymeric chains of [(C18
units, in 2 pentameric [Ag (C18 ](NO
H
12
N
6
)
2
Ag
units are
4 3 4
(NO ) ]
1
.5 À z) interconnected by five silver(I) atoms (four symmetry-
5
H
12
N
)
6 4
3
)
5
(H
2
O)
7
independent Ag1, Ag2, Ag3 and Ag4 atoms and the symmetry-re-
lated Ag2 atom at [ii] x, 0.5 À y, 1.5 À z; Fig. 2b). The shortest
AgÁ Á ÁAg distance in 2 is observed within a pentameric unit
present. It has been shown, that complex 1 exhibits catalytic prop-
erties in oxidation of alcohols. This study involves not only presen-
tation of a new catalytic system, but also may be useful in design of
new catalysts.
(
Ag2Á Á ÁAg3 of 3.496(2) Å). The formation of such units is connected
with considerable distortion of the tptz ligands and their unusual
conformation (see description of tptz ligand for 1), as illustrated
by the interplanar angles between the planes of the rings constitut-
ing these ligands, listed in Table 3S. The pentameric units are ar-
ranged in layers parallel to (1 0 1). Between the layers spaces are
formed, which contain disordered nitrate anions and water mole-
cules, as well as the ordered water molecules.
4. Experimental
4.1. Syntheses
2 3 2
Complex 1 ((tptz)Ag (NO ) ) was synthesized by adding of
In 2 water molecules participate as donors in O–HÁ Á ÁO hydrogen
bonds, in which other water molecules or nitrate anions act as
acceptors (Table 4S). Also numerous weak hydrogen bonds of C–
HÁ Á ÁO type, along with C–HÁ Á ÁN (triazine ring from tptz ligand),
could be found (Table 5S). The ordered nitrate anions are distrib-
uted within the layers of complex units participating in the con-
tacts described above. Also numerous stacking interactions
between rings constituting tptz ligands are observed, the majority
within the mentioned pentameric units (the following contacts of
this kind are observed, with the range of the shifts of atoms of
one ring with respect to the plane of the interacting ring, respec-
tively: ring with N112 atom and ring with N142 atom at x,
2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) (1 mmol, 0.312 g) to a
solution of silver nitrate (2 mmol, 0.34 g) in 20 ml of acetonitrile/
water (9/1). The mixture was stirred for about 1 h at room temper-
ature. The resulting yellow precipitate was filtered off and recrys-
tallized by using acetonitrile/water (9/1) to give yellow crystals.
After 4 days, yellow crystals of 1 were obtained that were suitable
for X-ray determination. Anal. Calc.: C, 33.15; H, 1.85; N, 17.18.
1
Found: C, 33.54; H, 1.97; N, 17.41%. H NMR for tptz in CDCl
3
(ppm): 8.99 (d, 1H), 8.88 (d, 1H), 7.99 (t, 1H), 7.57 (t, 1H). 13
NMR in CDCl (ppm): 172.10 (C1), 152.98 (C2), 150.41 (C3),
137.13 (C4), 126.56 (C5), 125.15 (C6). H NMR for 1 in DMSO
C
3
1
(ppm): 8.95 (d, 1H), 8.78 (d, 1H), 8.2 (t, 1H), 7.82 (t, 1H).

2
842
M.M. Najafpour et al. / Polyhedron 29 (2010) 2837–2843
Complex 2 ([Ag
5
(tptz)
4 3
](NO )
5
Á7H
2
O) was synthesized by add-
Table 2
Oxidation of alcohols catalyzed by complex 1.
ing of 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) in 2 mL of warm
acetonitrile (1 mmol, 0.312 g) to a solution of silver nitrate
2 mmol, 0.34 g) in 10 mL of water. The mixture was stirred for
about 10 h at 313 K in the dark. The resulting yellow precipitate
was filtered off and recrystallized by using water/acetonitrile (9/
) to give yellow crystals. After 10 days, orange crystals of 2 were
obtained that were suitable for X-ray determination. Anal. Calc.:
C, 38.87; H, 2.81; N, 18.26. Found: C, 38.03; H, 2.61; N, 18.01%.
H NMR for 2 in DMSO (ppm): 8.83 (d, 1H), 8.50 (d, 1H), 8.08(t,
Entry
1
Substratea
Conversion (%)b
100
TONc
50
(
CH
OH
2
2
3
4
CH3
100
100
100
50
50
50
1
CH OH
2
OMe
CH OH
1
2
1
H), 7.64 (t, 1H).
NO2
4.2. IR spectra
CH OH
2
5
6
88
93
44
À1
OH
IR spectra (4000–400 cm wavenumber range) were measured
on a FT-IR JASCO 460 spectrophotometer as KBr pellets.
CH3
OH
46.5
4
.3. Fluorescence emission spectra
7
8
90
45
50
H C
OH
3
Fluorescence emission spectra for solutions of 1 and 2 in DMSO
OH
100
were recorded with excitation wavelength of 200 nm at room tem-
perature on Cary Eclipse Fluorescence spectrophotometer
equipped with quartz cuvettes of 1 cm path length. The represen-
tative fluorescence emission spectrum is depicted in Fig. 3S.
9
OH
OH
73
66
36.5
33
10
4.4. UV–Vis spectra
a
The molar ratios for catalyst: phase transfer agent: substrate: oxidant are
1:10:50:50, respectively. The reactions were run for 2 h at room temperature in a
biphasic medium (CH Cl /H O).
Electronic spectra of 1 in acetonitrile/water (9/1) and of 2 in
water/acetonitrile (9/1) solution were recorded (Fig. 4S) on a Cary
00 Bio Varian UV–Vis spectrometer.
2
2
2
b
The GC conversion (%) are measured relative to the starting alcohol after 2 h.
TON = (mmol of products)/mmol of catalyst.
1
c
4.5. Catalytic reaction
4.8. X-ray studies
Based on the observed results from optimization of the reaction
4.8.1. X-ray measurement
conditions, the catalyst, tetra-n-butylammonium bromide, sub-
Both crystals of complex 1 and 2 were measured on Xcalibur PX
strate and oxone were used in the following molar ratio:
diffractometer with Mo Ka radiation (see Table 1S for selected X-
1
:10:50.50. Reactions were performed at room temperature under
ray data). The X-ray measurement for complex 1 was performed
air in a (1:5) mixture of CH Cl /H O.
2
2
2
at 120 K and for complex 2 at 100 K.
After optimization, the oxidations of wide variety of primary
and secondary aliphatic and benzylic alcohols to corresponding
aldehydes or ketones were investigated and the details of catalytic
activity with respect to oxidation of alcohols are recorded in
Table 2.
4
.9. Refinement
Both structures were solved by direct methods using SHELXS pro-
gram and refined using SHELXL [27].
For complex 1 all H atoms were generated based on the known
geometry and refined with Ueq = 1.2Ueq(parent atom).
4.6. Electrochemistry
For complex 2 the atoms constituting the complex symmetry-
independent part (2.5 silver(I) atoms, 2 ligand molecules), as well
as two ordered nitrate anions lying in special positions on twofold
axes, were easily found on the E-map. The remaining maxima were
interpreted as arising due to the presence of two symmetry-inde-
pendent water molecules (with O1W and O2W atoms, respec-
tively) and a disordered nitrate anion, covering 1.5 of the positive
charge. The disorder of the nitrate anion seems to be cooperative
with disorder of water molecules occupying very near sites. The
anion disorder was assumed to consist of three half-occupancy
components (with N17, N18 and N19 atoms, respectively), essen-
tially related by shifts along the c axis. The neighbouring compo-
nents would be very near, with short OÁ Á ÁO contacts, therefore
they cannot occupy these sites in the crystal structure simulta-
neously. Each of the anion half-occupancy components seems to
be cooperatively disordered with a half-occupancy water molecule
Electrochemical studies were carried out in a conventional
three electrode cell using Pt electrode as a counter electrode and
Ag wire quasi-reference electrode, and a 2 mm diameter glassy
carbon disk electrode as a working electrode. All potentials were
reported versus Ag/AgCl reference electrode. Prior to all measure-
ments the acetonitrile electrolyte was degassed at least for
1
0 min and throughout the measurement the cell was kept under
nitrogen gas atmosphere to avoid oxygen interference. Electro-
chemical measurements were run using Zahner-Zennium poten-
tiostat–galvanostat under ambient temperature.
Electrochemical studies for 1 in acetonitrile solvent containing
.05 M of supporting electrolyte were carried out and a typical vol-
0
tammogram is presented in Fig. 5S.
4
.7. NMR spectra
(
with O17W, O18W and O19W atoms, respectively) at a position
Nuclear magnetic resonance (NMR) spectra were recorded on a
very near to the anion N atom. The assumed model was first care-
fully refined with DFIX restraints setting the disordered anion
components N–O bond lengths at 1.20(2) Å with isotropic temper-
3
Bruker 400 MHz spectrometer, using CDCl or DMSO as a solvent at
2
98.5 K.

M.M. Najafpour et al. / Polyhedron 29 (2010) 2837–2843
2843
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[
(
(
[
[
[
[
[
0
.60(3) and 0.40(3) for O2W and O3W component, respectively).
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atom)) with O2W and O3W components coordinates constrained
at the same time. Subsequently, AFIX 3 constraints were used to
constrain the water H atoms parameters and constraints were re-
moved from O2W and O3W components coordinates (it was neces-
sary to use there constraints to prevent O2W/O3W components
shifts changing the O–H bond lengths during the refinement). All
remaining H atoms bonded to the ligand C atoms were generated
from the known geometry. On the final difference Fourier map
the highest peak of 1.55 e/Å3 was present at 0.08 Å from the Ag2
atom. All ten highest peaks on the final difference Fourier map
were located in the neighbourhood of Ag atoms.
(
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[
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[
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[
[
[
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Acknowledgments
[
[
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19] A.L. Rosen, G.M. Hieftje, Spectrochim. Acta B 59 (2004) 135.
MMN and SHK are grateful to Institute for Advanced Studies in
Basic Sciences in Zanjan.
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[
[
[
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1168.
Appendix A. Supplementary data
[
[
[
24] E.C. Plappert, D.M.P. Mingos, S.E. Lawrence, D.J. Williams, Dalton Trans. (1997)
2119.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2010.07.005.
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(2006) 1005.
26] NMR data are also consistent with the structure shown in Fig. 1S. In the
+
proposal structure a tptz ligand is coordinated to three Ag ions as a bidentate
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