Anion controlled structural variation of silver(I) coordination polymers with a new donor-π-acceptor ligand

Article abstract of DOI:10.1016/j.ica.2011.03.003

A new ligand with D-π-A symmetry has been synthesized in high yield by Knoevenagel condensation of 4-(dimethylamino)benzaldehyde with malononitrile. The ligand forms coordination polymers with Ag(I) salts at room temperature where the ultimate structure i

Full text of DOI:10.1016/j.ica.2011.03.003

Inorganica Chimica Acta 372 (2011) 425–428
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Note
Anion controlled structural variation of silver(I) coordination polymers
with a new donor–
p
–acceptor ligand
⇑
Sanjib Das, Susan Sen, Parimal K. Bharadwaj
Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 13 March 2011
A new ligand with D–p–A symmetry has been synthesized in high yield by Knoevenagel condensation of
4
-(dimethylamino)benzaldehyde with malononitrile. The ligand forms coordination polymers with Ag(I)
salts at room temperature where the ultimate structure is dependent upon the counter anion. With
AgNO , a 2D tubular structure is formed where the nitrate anions bridge two Ag(I) centers. When AgBF
Dedicated to Prof. S.S. Krishnamurthy
3
4
is used, a 1D grid structure results but with AgOTf, a 1D zigzag structure is formed. Thus, anions control
the structure of the coordination polymers formed. Each coordination polymer affords high TPA activity
that can be correlated with the structure of the polymer.
Keywords:
Coordination polymer
Ag complexes
Ó 2011 Elsevier B.V. All rights reserved.
Role of anions
Optical nonlinearity
1
. Introduction
The design and synthesis of coordination polymers have re-
that the counter anion controls the ultimate polymeric structure
thereby varying the possible charge transfer symmetry as well as
dimensionality and associated
2
r value. Materials exhibiting large
ceived enormous attention in recent years due to their potential
applications [1] in diverse areas. Formation of these structures de-
pend on several factors: (i) stereoelectronic molecular information
encoded in the ligand(s), (ii) reading-out this information by metal
ions with preferences for coordination numbers as well as stereo-
chemistry, and (iii) the conditions used for the synthesis. The coun-
ter anions can also control the ultimate structure [2] of the
coordination polymer. Efforts have been directed towards the syn-
thesis of coordination polymers exhibiting large second order bulk
optical nonlinearity [3]. However, polymers that exhibit large third
order optical nonlinearity are still very rare. Recent studies show
that metal clusters and polymers in DMF/DMSO solution exhibit
third-order NLO responses by measuring the effective third-order
two-photon absorption cross-section are important for their
potential use in several areas of bio-photonics and materials
science [7].
2
. Experimental
2.1. Materials
Reagent grade 4-(dimethylamino)benzaldehyde, malononitrile,
piperidine and the silver salts were from Aldrich while the solvents
were from SD Fine Chemicals, India. All solvents were purified
prior to use while the rest of the chemicals were used as received.
2 2
NLO absorption coefficient (a ) and refractive index (g ) with
nanosecond laser pulses [4]. Third order optical nonlinearity can
be evaluated in terms of two photon absorption (TPA) cross-
section (
symmetrical charge transfer and increased dimensionality (1D to
D) are expected [6] to have significant TPA cross-section. Herein,
we report a ligand with donor– –acceptor structural motif that it-
self shows a low value but on making coordination polymers
with Ag-salts exhibit significantly large values measured by
femtosecond open-aperture Z-scan technique at 880 nm. We show
r
2
) [5]. Molecules having extended
p
-conjugation with
2.2. Physical measurements
3
Spectroscopic data were collected as follows: IR (KBr disk,
ꢀ1
p
400–4000 cm ) Perkin–Elmer Model 1320. Microanalyses for the
compounds were obtained from the Central Drug Research Insti-
tute, Lucknow, India. ESI-MS data were acquired on a MICROMASS
r
2
r
2
1
QUATTRO Quadruple Mass Spectrometer. H NMR spectra recorded
on a JEOL JNM-LA400 FT (400 MHz) instrument in CDCl
3
with
Me Si as internal standard. Melting points were recorded with
4
⇑
Corresponding author.
E-mail address: pkb@iitk.ac.in (P.K. Bharadwaj).
an electrical melting point apparatus by PERFIT, India and are
uncorrected.
0
020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.03.003

4
26
S. Das et al. / Inorganica Chimica Acta 372 (2011) 425–428
2
2
.3. Synthesis
2 4 n
2.3.3. Synthesis of {Ag(L) BF }
This complex is synthesized following the above procedure
replacing AgNO by AgBF . Yellow rectangular single crystals are
isolated after standing for a week at room temperature. Yield
43%. Anal. Calc. for C24 Ag: C, 48.93; H, 3.76; N, 14.26.
Found: C, 48.99; H, 3.87; N, 14.35%.
.3.1. Ligand L
3
4
The ligand L is synthesized in ꢁ90% yield as a yellow solid by
Knoevenagel condensation of 4-(dimethylamino)benzaldehyde
with malononitrile in dry ethanol. To a solution containing 0.15 g
4 6
H22BF N
(
1 mmol) of 4-(dimethylamino)benzaldehyde and 0.1 g (1.5 mmol)
of malononitrile in 10 ml dry ethanol, two drops of piperidine are
added. After 30 min of stirring at room temperature, a deep yellow
solid formed that is collected by filtration, washed with ethanol
2
.3.4. Synthesis of {Ag(L)CF
3 3 n
SO }
A solution of CF SO Ag (0.26 g; 1 mmol) in benzene (10 ml) is
3
3
added slowly and carefully on the top of a 10 ml dichloromethane
solution of L (0.2 g; 1 mmol) in a crystallization tube. After stand-
ing at room temperature for 7 days, orange rectangular crystals of
the title compound can be isolated in 47% yield. Anal. Calc. for
C
2
1
and finally dried under vacuum. Yield 92%. M.pt. 150 °C. H NMR
(
7
400 MHz, CDCl
.44 (s, 1H), 7.79 (d, 2H). ESI-mass m/z (%): 196 (80). Anal. Calc.
for C12 : C, 73.07; H, 5.62; N, 21.30. Found: C, 73.12; H,
.73; N, 21.41%.
3
, TMS, 25 °C): d (ppm) 3.12 (s, 6H), 6.68 (d, 2H),
11 3
H N
H
13 11
N
3
O
3
SF
3
Ag: C, 34.38; H, 2.44; N, 9.26. Found: C, 34.35; H,
5
.55; N, 9.32%.
2
.3.2. Synthesis of {Ag(L)NO
A solution of AgNO (0.17 g; 1 mmol) in ethanol (5 ml) is added
slowly and carefully on the top of the layer of a solution of L (0.2 g;
mmol) in dichloromethane (10 ml) in a crystallization tube. Sin-
gle crystals in the form of red blocks are obtained after standing for
3
}
n
2.3.5. X-ray structural studies
Single crystal X-ray data on 1–3 were collected at 100 K
on a Bruker SMART APEX CCD diffractometer using graphite-
3
1
monochromated Mo Ka radiation (k = 0.71073 Å) and the struc-
tures were solved and refined as described earlier [8]. The crystal
and refinement data are collected in Table 1 while selective bond
distances and angles are given in Table 2. Several non-bonding
interactions are shown in Table 3.
2
C
3
days at room temperature. Yield 52%. Anal. Calc. for
Ag: C, 39.26; H, 3.02; N, 15.26. Found: C, 39.34; H,
.16; N, 15.38%.
12
11 4 3
H N O
Table 1
Crystallographic data and details of the refinement procedure for 1–3.
Compound
1
2
3
Empirical formula
C
12
H
11AgN
4
O
3
C
24
H22AgBF
N
4 6
13 3 3 3
C H11AgF N O S
Formula weight
Radiation, wavelength (Å)
Crystal system
Space group
a (Å)
367.12
Mo K , 0.71073
monoclinic
P2 /n
8.831(5)
7.911(5)
19.094(5)
97.70
1321.9(1)
4
1.845
0.18 ꢂ 0.16 ꢂ 0.14
100(2)
1.537
589.16
Mo K , 0.71073
monoclinic
454.18
Mo K , 0.71073
monoclinic
P2 /n
6.745(5)
14.702(5)
16.022(5)
101.68(5)
1555.9(1)
4
a
a
a
1
C2/c
1
19.772(5)
8.047(5)
15.202(5)
99.22(5)
2387.5(2)
4
b (Å)
c (Å)
b (°)
V (Åꢀ3)
Z
D
calc (g cmꢀ3)
3
1.450
1.939
Size (mm )
0.15 ꢂ 0.13 ꢂ 0.11
0.17 ꢂ 0.15 ꢂ 0.13
100(2)
1.481
T (K)
l
100(2)
(mm 1
ꢀ
)
0.888
Reflections measured
Reflections used [I P 2
Parameters
3243
2934
185
1.019
2939
2316
169
1.307
3844
3304
221
1.030
r
(I)]
Goodness-of-fit (GOF) on F2
Final R indices [I P 2
r
(I)]
R
R
1
= 0.0308, wR
= 0.0351, wR
2
= 0.0723
= 0.0741
R
R
1
= 0.0812, wR
= 0.1051, wR
2
2
= 0.1827
= 0.2307
R
R
1
= 0.0322, wR
= 0.0402, wR
2
= 0.0756
= 0.0786
R indices (all data)
1
2
1
1
2
Maximum/minimum residual (e Åꢀ3)
Refinement method
1.172/ꢀ0.492
1.439/ꢀ1.812
0.818/ꢀ0.371
full-matrix least-squares on F2
full-matrix least-squares on F2
full-matrix least-squares on F2
Table 2
Selected bond distances (Å) and bond angles (°) for 1–3.
1
Ag1ꢃ ꢃ ꢃN2
Ag1ꢃ ꢃ ꢃN3
Ag1ꢃ ꢃ ꢃO1
Ag1ꢃ ꢃ ꢃO2
Ag1ꢃ ꢃ ꢃO3
2.373(2)
2.289(2)
2.500(2)
2.607(2)
2.444(2)
Ag1ꢃ ꢃ ꢃAg1
7.024(3)
94.72(5)
75.17(7)
120.19(9)
100.75(8)
O2ꢃ ꢃ ꢃAg1ꢃ ꢃ ꢃO3
50.78(3)
N2ꢃ ꢃ ꢃAg1ꢃ ꢃ ꢃO2
N2ꢃ ꢃ ꢃAg1ꢃ ꢃ ꢃO1
N3ꢃ ꢃ ꢃAg1ꢃ ꢃ ꢃO1
N3ꢃ ꢃ ꢃAg1ꢃ ꢃ ꢃO3
O2ꢃ ꢃ ꢃAg1ꢃ ꢃ ꢃO1
94.83(9)
128.20(7)
94.97(8)
O1ꢃ ꢃ ꢃAg1ꢃ ꢃ ꢃO3
N2ꢃ ꢃ ꢃAg1ꢃ ꢃ ꢃN3
2
Ag1ꢃ ꢃ ꢃN1
2.139(5)
2.833(2)
Ag1ꢃ ꢃ ꢃAg1
8.047(3)
100.05(5)
N1ꢃ ꢃ ꢃAg1ꢃ ꢃ ꢃN20
N3ꢃ ꢃ ꢃAg1ꢃ ꢃ ꢃO3
79.95(5)
Ag1ꢃ ꢃ ꢃN2
N1ꢃ ꢃ ꢃAg1ꢃ ꢃ ꢃN2
3
Ag1ꢃ ꢃ ꢃN1
Ag1ꢃ ꢃ ꢃN3
Ag1ꢃ ꢃ ꢃO3
2.196(2)
2.169(2)
2.3791(19)
N1ꢃ ꢃ ꢃAg1ꢃ ꢃ ꢃN3
N1ꢃ ꢃ ꢃAg1ꢃ ꢃ ꢃO3
138.95(8)
97.63(7)
113.45(7)

S. Das et al. / Inorganica Chimica Acta 372 (2011) 425–428
427
ꢀ
Table 3
The BF4 anions occupy the space between two 1D polymeric
6
Geometrical parameters for various noncovalent interactions found in 2 and 3.
3
2
chains joining them via C(sp )–Hꢃ ꢃ ꢃF and C(sp )–Hꢃ ꢃ ꢃF hydrogen
bonding interactions (Table 3) to form a 2D hydrogen bonded net-
work structure. Each 2D network is packed on top of another via
Interaction
Da (Å)
db (Å)
hc (°)
2
2
C(Ar)–Hꢃ ꢃ ꢃF
F2ꢃ ꢃ ꢃH3
3.385(3)
3.089(3)
3.385(5)
3.748(5)
3.387(4)
3.249(5)
3.055(4)
2.461(4)
2.315(4)
2.470(3)
2.883(2)
2.816(3)
172.41(2)
131.58(5)
159.30(4)
150.36(7)
118.98(4)
Ag–C(arene) interactions (3.055, 3.249 Å) and C(sp )–Hꢃ ꢃ ꢃF hydro-
2
C(sp )–Hꢃ ꢃ ꢃF
F3ꢃ ꢃ ꢃH9
gen bonding interactions (Table 3). The Ag–C interactions are con-
siderably greater than the limits (2.47–2.76 Å) commonly observed
in Ag(I)–aromatic complexes [14].
3
C(sp )–Hꢃ ꢃ ꢃF
F3ꢃ ꢃ ꢃH15A
F2ꢃ ꢃ ꢃH1A
F2ꢃ ꢃ ꢃH1C
Ag1ꢃ ꢃ ꢃC3
Ag1ꢃ ꢃ ꢃC4
In 3, each Ag(I) ion is tri-coordinated with ligation from two CN
donors belonging to two different ligands and one O atom of the
Agꢃ ꢃ ꢃC(arene)
ꢀ
CF
3
SO3 counter anion. The two CN groups of each ligand bind
3
C(Ar)–Hꢃ ꢃ ꢃO
O2ꢃ ꢃ ꢃH3
O2ꢃ ꢃ ꢃH5
O1ꢃ ꢃ ꢃH9
O1ꢃ ꢃ ꢃH8A
F2ꢃ ꢃ ꢃH9
3.486(5)
3.460(7)
3.282(2)
3.332(6)
3.412(3)
3.468(7)
2.746(5)
2.871(6)
2.696(3)
2.535(4)
2.616(2)
2.415(3)
2.621(3)
2.570(4)
143.39(2)
173.16(3)
130.48(5)
159.78(4)
145.44(3)
155.74(2)
two metal ions thereby propagating the 1D coordination polymeric
chain along the crystallographic c axis in a zigzag fashion (Fig. 3).
2
C(sp )–Hꢃ ꢃ ꢃO
0
The N,N -dimethylbenzene moieties are oriented perpendicular to
3
C(sp )–Hꢃ ꢃ ꢃO
2
this chain on either side of the polymeric chain in an alternate
fashion. These 1D chains are arranged parallel to one another with
considerable Ag–C(arene) and C–Hꢃ ꢃ ꢃF interactions (Table 3). There
C(sp )–Hꢃ ꢃ ꢃF
3
C(sp )–Hꢃ ꢃ ꢃF
F3ꢃ ꢃ ꢃH7C
Ag1ꢃ ꢃ ꢃC2
Ag1ꢃ ꢃ ꢃC2
Agꢃ ꢃ ꢃC(arene)
are also considerable interlayer C–Hꢃ ꢃ ꢃO interactions involving O
a
b
c
atom of CF
SO anion and the ligand. The Ag–C contacts (2.746,
ꢀ
D is the distance between C and the acceptor (C, O or F atom).
d is the distance between H and the acceptor (C, O or F atom).
h is the angle at H in C–Hꢃ ꢃ ꢃX (X = C, O or F atom).
3
3
2.871 Å) are slightly greater than the limits (2.47–2.76 Å) com-
monly observed in Ag(I)–aromatic complexes. Thus, the benzene
2
ring in 3 coordinates to the Ag(I) ion with an
g
bonding mode,
which is normally observed in arene–metal complexes [14].
2.3.6. TPA cross-section measurements
The TPA cross-section ( ) values are measured by using a stan-
r
2
dard open aperture z-scan technique [9] for 1 cm long quartz sam-
ple cells. We have used 150 fs pulses at 880 nm with 76 MHz
repetition rate from mode-locked tunable Coherent Mira titanium:
sapphire laser (Model 900) which is pumped by Coherent Verdi
frequency doubled Nd: vanadate laser. The experimental proce-
dure followed as described earlier [10]. All of the compounds were
ꢀ4
measured at 5 ꢂ 10 M solution in DMF solvent. The solvent itself
does not show any TPA activity under experimental conditions. The
open-aperture traces for the polymers are given as Supporting
information. We have taken Rhodamine 6G for which the
2
r value
is known in the literature [11] as the reference for calibrating our
measurement technique. The low solubility of the complexes in
THF and their insolubility in low boiling organic solvents do not al-
low for making thin films of the polymers for solid-state TPA
measurements.
3
. Results and discussion
All the coordination polymers possess high stability towards
Fig. 1. A perspective view of the 2D network in 1.
light and air. They are moderately soluble in DMF, DMSO and
slightly soluble in THF.
Single crystal X-ray diffraction studies reveal that structure of 1
2 2
consists of planar dimeric [Ag L ] units where each metal is coor-
dinated to two CN groups from two ligands and three O atoms from
ꢀ
two NO3 ions in a distorted square-pyramidal geometry. The di-
meric units are repeated via bridging nitrates forming a 2D net-
0
work (Fig. 1). The N,N -dimethylbenzene moieties align
perpendicularly on both side of the crystallographic bc plane at
an approximate distance of 7.911 Å from each other signifying ab-
sence of any significant interactions. All Ag–N bond distances
found in 1 are within the normal range observed in other –CN do-
nor ligands complexed with Ag(I) [12]. The two Ag–Onitrate bond
lengths (2.607 and 2.501 Å) are slightly longer than those observed
in other nitrate bridged Ag(I) complexes [13]. The Agꢃ ꢃ ꢃAg separa-
tion in the dimeric unit is 7.024 Å.
ꢀ
Due to non-coordinating nature of BF4 counter anion, each
Ag(I) ion in 2 is tetra-coordinated in a square planar geometry with
coordination from four CN groups belonging to four different li-
gands propagating the polymeric chain along the crystallographic
b axis. While viewing down the crystallographic a axis, it looks like
a grid structure (Fig. 2).
Fig. 2. A perspective view of the grid structure in 2.

4
28
S. Das et al. / Inorganica Chimica Acta 372 (2011) 425–428
the counter anion of the Ag(I) salt. Further studies are in progress
on other systems in our laboratory.
Acknowledgments
Financial support received from DRDO and DST, New Delhi,
India (to P.K.B.) is gratefully acknowledged. S.S. thanks the CSIR,
India for Senior Research Fellowship. We thank Professor D.
Goswami for the NLO data.
Appendix A. Supplementary material
CCDC 617604, 617605 and 617606 contain the supplementary
crystallographic data for 1–3. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2011.03.003.
Fig. 3. A perspective view of the zigzag structure of 3.
N
Symmetric
charge transfer
Asymmetric
charge transfer
D
References
π
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AgX
Ag
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