Synthesis, structure and luminescence behaviour of heptacoordinated one-dimensional coordination polymers of the type [Cd(L)(dca)]n(X)n (L = a pentadentate Schiff base; dca = dicyanamide; X =ClO4-, PF6-)

Article abstract of DOI:10.1016/j.molstruc.2009.09.043

Two heptacoordinated one-dimensional coordination polymers of the type [Cd(L)(dca)]_n(X)_n (1 and 2) [L = N,N′-(bis-(pyridin-2-yl)benzylidene)diethylenetriamine; dca = dicyanamide; X =ClO₄^- (1), PF₆^- (2)] have been prepared and characterized on the basis of microanalytical, spectroscopic and other physicochemical properties. Structures of 1 and 2 are solved by single crystal X-ray diffraction measurements. Structural study reveals that in both compounds each cadmium(II) center adopts a distorted pentagonal bipyramidal geometry with a CdN₇ chromophore coordinated by five N atoms of the pentadentate Schiff base and two nitrile N atoms of single bridged dca in μ_1,5 fashion. The polynuclear units in 1 are engaged in weak N-H...O and C-H...O hydrogen bondings with perchlorate ions embedded among the chains to give a 2D sheet structure. In the long-range form, the 1D polymeric chains of 2 pack through N-H...F and C-H...F hydrogen bonds with hexafluorophosphate placed in between chains resulting a 2D continuum. The complexes display intraligand ¹(π-π*) fluorescence in DMF solutions at room temperature.

Full text of DOI:10.1016/j.molstruc.2009.09.043

Journal of Molecular Structure 963 (2010) 35–40
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structure and luminescence behaviour of heptacoordinated
one-dimensional coordination polymers of the type [Cd(L)(dca)]n(X)n
(L = a pentadentate Schiff base; dca = dicyanamide; X = ClOꢀ4 , PF6ꢀ)
Bhola Nath Sarkar a, Kishalay Bhar a, Soumi Chattopadhyay a, Sumitra Das a, Partha Mitra b,
Barindra Kumar Ghosh a,
*
a Department of Chemistry, The University of Burdwan, Burdwan 713104, India
b Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700 032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Two heptacoordinated one-dimensional coordination polymers of the type [Cd(L)(dca)]n(X)n (1 and 2)
[L = N,N0-(bis-(pyridin-2-yl)benzylidene)diethylenetriamine; dca = dicyanamide; X = ClO4ꢀ (1), PFꢀ6 (2)]
have been prepared and characterized on the basis of microanalytical, spectroscopic and other physico-
chemical properties. Structures of 1 and 2 are solved by single crystal X-ray diffraction measurements.
Structural study reveals that in both compounds each cadmium(II) center adopts a distorted pentagonal
bipyramidal geometry with a CdN7 chromophore coordinated by five N atoms of the pentadentate Schiff
Received 4 August 2009
Received in revised form 22 September
2009
Accepted 25 September 2009
Available online 30 September 2009
base and two nitrile N atoms of single bridged dca in l1,5 fashion. The polynuclear units in 1 are engaged
Keywords:
in weak N–H. . .O and C–H. . .O hydrogen bondings with perchlorate ions embedded among the chains to
give a 2D sheet structure. In the long-range form, the 1D polymeric chains of 2 pack through N–H. . .F and
C–H. . .F hydrogen bonds with hexafluorophosphate placed in between chains resulting a 2D continuum.
Cadmium(II)dicyanamides
N-donor Schiff base
Synthesis
Superstructure
Luminescence
1
*
The complexes display intraligand
(p
–
p
) fluorescence in DMF solutions at room temperature.
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
towards cadmium(II) in combination with a neutral N-donor Schiff
base, N,N0-(bis-(pyridin-2-yl)benzylidene)diethylenetriamine (L).
Successfully, two heptacoordinated one-dimensional coordination
polymers of the type [Cd(L)(dca)]n(X)n (1 and 2) [dca = dicyanamide;
X = ClOꢀ4 (1), PFꢀ6 (2)] have been prepared through reaction of a
1:1:1 M ratio of cadmium(II) salt, L and dca in MeOH at room tem-
perature using appropriate counter anions. Structures of 1 and 2
are solved by single crystal X-ray diffraction measurements. In this
paper we report the synthesis, structures, characterization and
luminescence behaviour of these new complexes.
Polynuclear Group 12 metal ion complexes have witnessed a
great interest in search of functional materials [1–5] specially with
electronic [3] and optoelectronic [4] properties. The essential pre-
requisites for such research are the judicious choice [6] of organic
spacers and inorganic/organic bridges that may lead to directed
properties. Self-assembly [7] of the building units is an efficient ap-
proach towards preparation of such materials. Exploiting the variety
of coordination geometries around these metal ions, diverse molec-
ular and crystalline architectures [8,9] of different shapes and sizes
[10] may be accessed through strong metal–ligand covalent bonds
and multiple non-covalent bonds like hydrogen bonding [11,12]
2. Experimental
p. . .p [13], C–H. . .p [14,15] etc. interactions. Recently, we are active
[16–18] to prepare different mono-, di- and polynuclear complexes
of cadmium(II) in combination with multiple N-donor Schiff bases
[19] and related ligands, and pseudohalides [20–22] like azide and
thiocyanate towards preparation of luminous materials. To extend
this work with other larger pseudohalide like dicyanamide (dca)
[23,24] which is recently being studied by the coordination chemists
round the world, we have examined its coordination behaviour
2.1. General remarks and physical measurements
2.1.1. Materials
High purity 2-benzoylpyridine (Lancaster, UK), dicyanamide
(Lancaster, UK), potassium hexaflurophosphate (Fluka, Germany),
diethylenetriamine (SRL, India) and cadmium(II) acetate (SRL,
India) were purchased from respective concerns and used as re-
ceived. Cadmium(II) perchlorate hexahydrate was prepared [25]
on treatment of cadmium(II) carbonate (E. Merck, India) with per-
chloric acid (E. Merck, India) followed by slow evaporation on
* Corresponding author. Tel.: +91 342 2533913; fax: +91 342 2530452.
E-mail address: barin_1@yahoo.co.uk (B.K. Ghosh).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.09.043

36
B.N. Sarkar et al. / Journal of Molecular Structure 963 (2010) 35–40
steam-bath, filtration through fine glass-frit, and was preserved in
a desiccator containing concentrated sulphuric acid (E. Merck, In-
dia) for subsequent use. All other chemicals and solvents were
AR grade and were used as received.
Caution! Perchlorate compounds of metal ions are potentially
explosive [26] especially in presence of organic ligands. Only small
amount of the material should be prepared and handled with care.
solution was filtered and left in air for slow evaporation. Colourless
shining microcrystals of 2 were obtained in almost quantitative
yield.
The microanalytical and spectroscopic results of 2 obtained
from both the methods (A and B) are similar. Anal. Calc. for
C30H27N8F6PCd (2): C, 47.6; H, 3.6; N, 14.9. Found: C, 47.4; H,
3.4; N, 14.9%. IR (KBr, cm–1):
2868; mas s(C„N) 2275;
(C@N) 1618, 1593; as(C–N) 1318;
m
(NH) 3315, 3269;
as(C„N) 2220; s(C„N) 2148;
s(C–N) 954; (PF6) 846,
m(CH) 2948,
+
m
m
m
2.1.2. Physical measurements
m
m
m
m
Elemental analyses (carbon, hydrogen and nitrogen) were per-
formed on a Perkin-Elmer 2400 CHNS/O elemental analyzer. IR
spectra (KBr discs, 4000–300 cm–1) were recorded using a Perkin-
Elmer FTIR model RX1 spectrometer. Molar conductances were
measured using a Systronics conductivity meter where the cell
constant was calibrated with 0.01 M KCl solution and dry MeOH
and DMF were used as solvents. Ground state absorption was mea-
sured with a Jasco model V-530 UV–vis spectrophotometer. Fluo-
rescence measurements were done using Hitachi Fluorescence
Spectroflurimeter F-4500. Time-resolved fluorescence measure-
ments were carried out using a time-correlated single photon
counting (TCSPC) spectrometer Edinburgh Instruments, model
199; a hydrogen filled coaxial flash lamp with a pulse width of
1.2 ns at FWHM and a Philips XP-2020Q photomultiplier tube were
used as the excitation source and the fluorescence detector.
542. UV–vis (k, nm): 281.
2.4. X-ray crystallographic study
Single crystals of 1 and 2 suitable for X-ray analyses were se-
lected from those obtained by slow evaporation of methanolic
solutions of the reaction mixtures at 298 K. Diffraction data were
collected at 296 K on a Bruker AXS SMART APEX-II CCD area-detec-
tor diffractometer using graphite monochromated Mo-K
a radia-
tion. The unit cell parameters were obtained from SAINT;
absorption corrections were performed with SADABS [27]. A sum-
mary of the crystallographic data and structure determination
parameters are given in Table 1. The unique reflections were re-
corded using the
x scan technique and structures were solved by
direct methods using SHELX-97 [28]. All hydrogen atoms were
fixed geometrically and refined using a riding model and the calcu-
lations were carried out using PLATON [29] and ORTEP-32 [30].
2.2. Synthesis of the Schiff base
2.2.1. N,N0-(bis-(pyridin-2-yl)benzylidene)diethylenetriamine (L)
2-Benzoylpyridine (0.366 g, 2 mmol) was refluxed (10 h) with
diethylenetriamine (0.103 g, 1 mmol) in dehydrated alcohol. The
solution was evaporated under reduced pressure to yield a yellow
gummy mass that was dried and stored in vacuo over CaCl2 for sub-
sequent use. Yield: 0.368 g (85%). Anal. Calc. for C28H27N5 (L): C,
77.5; H, 6.3; N, 16.2; Found: C, 77.4; H, 6.2; N, 16.4%; IR (KBr,
3. Results and discussion
3.1. Synthesis and formulation
The ligand (L, Scheme 1) was synthesized by refluxing a 1:2 M
ratio of diethylenetriamine and 2-benzoylpyridine in boiling alco-
hol. Colourless powders of heptacoordinated one-dimensional
coordination polymers of the type [Cd(L)(dca)]n(X)n (1 and 2)
[X = ClOꢀ4 (1), PFꢀ6 (2)] were obtained in good yields through reac-
tion of a 1:1:1 M ratio of metal (II) perchlorate or acetate, Schiff
base ligand and pseudohalide molecular ion rod, dicyanamide.
For preparation of 2, two equivalents of potassium hexaflurophos-
phate was added to the reaction mixture containing 1:1:1 M ratio
of cadmium(II) acetate, L and dca; 2 was also isolated by metathe-
sis of 1 in methanol using potassium hexaflurophosphate. The
reactions are summarized in Eqs. (1)–(3):
cm–1):
m(C@N) 1624, 1595. UV–vis (k, nm): 368, 273.
2.3. General synthesis of the complexes
2.3.1. [Cd(L)(dca)]n(ClO4)n (1)
Cd(ClO4)2ꢁ6H2O (0.419 g, 1 mmol) and L (0.433 g, 1 mmol) were
taken in methanol (each with 5 mL) and mixed together slowly. To
the resulting light yellow solution, a methanolic solution (5 mL) of
sodium dicyanamide (0.089 g, 1 mmol) was added dropwise. The
light yellow solution was left undisturbed in air for slow evapora-
tion. After a few days colourless single crystals of 1 that separated,
were washed with water and dried in vacuo over silica gel indica-
tor. Yield: 0.569 g (80%). Anal. Calc. for C30H27N8O4ClCd (1): C, 50.6;
H, 3.8; N, 15.8. Found: C, 50.4; H, 3.6; N, 15.6%. IR (KBr, cm–1):
CdðClO4Þ ꢁ 6H2O þ L þ dca M!eOH ½CdðLÞðdcaÞꢂ ðClO4Þ
ð1Þ
ð2Þ
ð3Þ
2
n
n
298 K
ð1Þ
CdðOAcÞ ꢁ 2H2O þ L þ dca M!eOH ½CdðLÞðdcaÞꢂ ðPF6Þ
2
n
n
KPF6
ð2Þ
m
m
(NH) 3328, 3279;
as(C„N) 2226; s(C„N) 2141;
s(C–N) 927; (ClO4) 1104, 623. UV–vis (k, nm): 281.
m
(CH) 2965, 2878; mas
+
m
s(C„N) 2272;
MeOH
!
½CdðLÞðdcaÞꢂnðClO4Þn
½CdðLÞðdcaÞꢂnðPF6Þn
m
m
(C@N) 1620, 1592;
mas(C–N)
KPF6
ð1Þ
ð2Þ
1322;
m
m
The new complexes were characterized by elemental analyses,
spectroscopic studies and other physicochemical results. Microana-
lytical data are consistent with the formulations 1 and 2. The mois-
ture-insensitive complexes are stable over long period of time in
powdery or crystalline states and are soluble in a wide range of com-
mon organic solvents such as methanol, ethanol, acetonitrile, dime-
thyformamide and dimethylsulphoxide but are insoluble in water.
Conductance measurements in MeOH and DMF solutions show
low conductivity values (KM for 1, ꢃ50 and for 2, ꢃ40 ohm–1
cm2 mol–1) reflecting [31] association of the counter ions with the
metalated cationic organic frameworks in solid state as well as in
solution. In IR spectra, three bands at 2272, 2226 and 2141 cm–1
for 1 and at 2275, 2220 and 2148 cm–1 for 2 are indicative of
2.3.2. [Cd(L)(dca)]n(PF6)n (2)
2.3.2.1. Method A. A methanolic solution (5 mL) of L (0.433 g,
1 mmol) was added slowly to a solution (5 mL) of Cd(OAc)2ꢁ2H2O
(0.267 g, 1 mmol) in the same solvent. Sodium dicyanamide
(0.089 g, 1 mmol) in methanol (5 mL) followed by KPF6 (0.368 g,
2 mmol) solution (5 mL) in the same solvent were added to this
solution mixture. The resulting light yellow solution was filtered
and left undisturbed in an air for slow evaporation. On the next
day colourless crystals of 2 were produced that were collected in
pure form as described in 1. Yield: 0.644 (85%).
2.3.2.2. Method B. Complex 2 was prepared by metathesis of 1 with
KPF6 in 1:2 M ratio from an methanolic solution with constant stir-
ring for 45 min at room temperature. The resulting light yellow
l
1,5-dicyanamide bridging [32,33]. The results are confirmed by X-
ray structure determinations. Bands in the range 1620–1590 cm–1

B.N. Sarkar et al. / Journal of Molecular Structure 963 (2010) 35–40
37
Table 1
Crystallographic data for 1 and 2.
Complex
1
2
Formula
Formula weight
Crystal system
Space group
a (Å)
C30H27N8O4ClCd
711.45
Monoclinic
Cc
10.7523(3)
22.9551(7)
12.2789(3)
93.4070(10)
3025.32(15)
0.71073
C30H27N8F6PCd
756.97
Monoclinic
Cc
10.8987(11)
23.385(3)
12.4357(12)
91.741(2)
b (Å)
c (Å)
b (°)
V (Å3)
3168.0(6)
0.71073
1.587
k (Å)
qcalcd (gm cmꢀ3
)
1.562
Z
4
4
T (K)
l
296(2)
0.860
296(2)
0.810
(mmꢀ1
)
F (0 0 0)
1440
1520
Crystal size
h ranges (°)
h/k/l
0.22 ꢄ 0.17 ꢄ 0.13
1.77 to 32.90
ꢀ16,16/ꢀ34,31/ꢀ18,18
29,693
0.30 ꢄ 0.21 ꢄ 0.12
1.74 and 21.69
ꢀ11,11/ꢀ24,24/ꢀ12,12
10,971
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
9938
9938/2/397
1.021
3715
3715/418/415
1.050
Final R indices [I > 2
R indices (all data)
r
(I)]
R = 0.0352 and wR = 0.0746
R = 0.0489 and wR = 0.0807
0.608 and ꢀ0.458
R = 0.0375 and wR = 0.0765
R = 0.0435 and wR = 0.0798
0.585 and ꢀ0.381
Largest peak and hole (eÅꢀ3
)
ꢃ
ꢂ
ꢄ
1=2
ꢀ
ꢁ
ꢀ
ꢁ
.h
ꢀ
ꢁ
i
.h
ꢀ
ꢁ
2
P
P
P
P
2
2
Weighting scheme: R = |Fo| ꢀ |Fc||/ |Fo, wR2
2, where P = F2o þ 2Fc2 3.
=
w
F2o ꢀ F2c
w
Fo2
, Calc. w = 1 r2 Fo2 þ ð0:0412PÞ þ 0:3828P 1 and w = 1 r2 F2o þ ð0:0260PÞ þ5:1125Pꢂ:
2
ꢀ
ꢁ.
assignable to
are routinely observed. The stretches [34] corresponding to the
(ClO4) at 1104 and 623 cm–1 in 1 and (PF6) at 846 and 542 cm–1
m(C@N) + m(C@C)stretchingvibrationof theSchiff base
H
N
m
m
in 2 are also seen as expected. Reflectance spectra (281 nm for 1
and 282 nm for 2) in Nujol and electronic spectra in DMF solutions
are akin reflecting similar gross geometric and electronic structure
in solid state and in solution. The transition is assignable to ligand-
based charge transfer [35] as expected for d10 cadmium(II) com-
plexes containing organic ligand with unsaturation on its
framework.
N
N
Ph
Ph
N
N
3.2. Descriptions of the structures of [Cd(L)(dca)]n(ClO4)n (1) and
[Cd(L)(dca)]n(PF6)n (2)
The structural analyses show that 1 and 2 are isomorphous and
consist of 1D covalent chains running along the [1 0 1] direction.
Cooperative intermolecular N–H. . .O and C–H. . .O in 1 and N–
Scheme 1.
n+
Fig. 1. An ORTEP diagram of [Cd(L)(dca)]n with atom labeling scheme and 20% probability ellipsoids for all non-hydrogen atoms.

38
B.N. Sarkar et al. / Journal of Molecular Structure 963 (2010) 35–40
Table 2
Table 4
Selected bond distances (Å) and bond angles (°) for 1.
Hydrogen bond distances (Å) and angles (°) for 1.
Bond distances (Å)
Cd1–N4
Cd1–N6
Cd1–N8
Cd1–N3
Cd1–N1
Cd1–N2
Cd1–N5
N6–C29
D–H. . .A
D–H
H. . .A
D. . .A
D–H. . .A
2.369(2)
2.372(3)
2.380(3)
2.381(2)
2.408(2)
2.426(2)
2.470(2)
1.159(4)
1.287(5)
1.312(4)
1.169(4)
1.169(4)
N3–H3A. . .O3i
C2–H2. . .O2ii
0.91
0.93
2.09
2.51
2.980(5)
3.150(7)
165
127
Symmetry code: i = ꢀ1/2 + x, 3/2 ꢀ y, ½ + z; ii = x, 1 ꢀ y, 1/2 + z.
Table 5
N7–C30
Hydrogen bond distances (Å) and angles (°) for 2.
N7–C29
N8–C30a
C30–N8b
D–H. . .A
D–H
H. . .A
D. . .A
D–H. . .A
N3–H3A. . .F4i
C3–H3. . .F1ii
C9–H9. . .F3iii
C27–H27. . .F4iv
0.91
0.93
0.93
0.93
2.04
2.44
2.46
2.44
2.947(8)
3.041(8)
3.249(12)
3.165(9)
176
123
143
135
Bond angles (°)
N6–Cd1–N8
N4–Cd1–N3
N4–Cd1–N1
N3–Cd1–N1
N4–Cd1–N2
N3–Cd1–N2
N1–Cd1–N2
N4–Cd1–N5
N3–Cd1–N5
N1–Cd1–N5
N2–Cd1–N5
C29–N6–Cd1
C30–N7–C29
N6–C29–N7
C30a–N8–Cd1
N8b–C30–N7
171.36(10)
72.57(9)
149.62(9)
135.33(8)
142.03(8)
69.51(8)
67.47(8)
67.04(8)
136.86(9)
87.62(8)
147.68(9)
127.7(3)
116.1(3)
174.4(4)
145.3(3)
174.6(3)
Symmetry code: i = 1 + x, y, z; ii = 1/2 + x, ꢀ1/2 + y, z; iii = 3/2 + x, 3/2 ꢀ y, 1/2 + z;
iv = 1/2 + x, 3/2 ꢀ y, 1/2 + z.
parameters are set in Tables 4 and 5. Each cadmium(II) center has a
distorted pentagonal bipyramidal geometry (pbp) with a CdN7
chromophore. Two pyridine nitrogens (N1 and N5), two imine
nitrogens (N2 and N4), one amine nitrogen (N3) of L occupy the
equatorial plane; two nitrile nitrogens (N6 and N8) of two different
l
1,5-bridged dca complete the heptacoordination and connect
other neighboring cadmium(II) centers in a non-ending fashion
producing the 1D chain. Distortion from the ideal geometry is
due to the asymmetric nature of the bound Schiff base and the
deviations of the refine angles formed at the metal center. The de-
grees of distortion from ideal pbp geometry are also reflected in the
equatorial [67.04(8)_87.62(8)° in 1 and 66.9(2)–88.92(18)° in 2]
and axial [171.36(10)° in 1 and 168.6(2)° in 2] bond angles. The
cadmium(II) center deviates 0.056 Å from the mean plane towards
N6 in both 1 and 2. Among the five equatorial nitrogens, N1 and N4
in 1 and N2 and N5 in 2 deviate (N1, 0.355 Å and N4, 0.259 Å; N2,
0.231 Å and N5 0.334 Å) towards N8 whereas N2 and N5 in 1 and
N1 and N4 in 2 show considerable deviation (N2, 0.260 Å and N5,
0.353 Å; N1, 0.322 Å and N4, 0.268 Å) towards N6 from the mean
plane. The remaining nitrogen (N3) is almost on the mean plane
compared to other atoms with maximum deviations 0.001 Å in 1
and 0.020 Å in 2. The intrachain Cd. . .Cd separation in 1 (8.157 Å)
is shorter than that in 2(8.368 Å). Dicyanamide coordinates to
the metal centers via l1,5 bridge in a bending fashion as reflected
in the bond angles C29–N6–Cd1 [127.7(3)° in 1 and 150.5(6)° in
2] and C30–N8–Cd1 [145.3(3)° in 1 and 134.2(6)° in 2]. The skeletal
bond angles of dca are N6–C29–N7 [174.4(4)° in 1 and 175.0(8)° in
Symmetry code: a = ꢀ1/2 + x, 3/2 – y, ꢀ1/2 + z; b = 1/2 + x, 3/2 – y, 1/2 + z.
Table 3
Selected bond distances (Å) and bond angles (°) for 2.
Bond distances (Å)
Cd1–N4
Cd1–N8
Cd1–N6
Cd1–N3
Cd1–N1
Cd1–N2
Cd1–N5
N7–C29
N7–C30a
C29–N6
N8–C30
C30–N7b
2.361(6)
2.373(6)
2.382(6)
2.391(6)
2.412(5)
2.439(6)
2.494(6)
1.306(10)
1.318(9)
1.137(8)
1.139(9)
1.318(9)
Bond angles (°)
N8–Cd1–N6
N4–Cd1–N3
N4–Cd1–N1
N3–Cd1–N1
N4–Cd1–N2
N3–Cd1–N2
N1–Cd1–N2
N4–Cd1–N5
N3–Cd1–N5
N1–Cd1–N5
N2–Cd1–N5
C29–N7–C30a
N6–C29–N7
C29–N6–Cd1
C30–N8–Cd1
N8–C30–N7b
168.6(2)
71.7(2)
151.3(2)
134.90(19)
140.1(2)
68.4(2)
67.64(18)
66.9(2)
135.91(19)
88.92(18)
150.0(2)
120.0(6)
175.0(8)
150.5(6)
134.2(6)
175.1(8)
Symmetry code: a = 1/2 + x, 3/2 – y, 1/2 + z; b = ꢀ1/2 + x, 3/2 – y, ꢀ1/2 + z.
H. . .F and C–H. . .F in 2 hydrogen bondings link these covalent
chains into 2D supramolecular sheet structures parallel to the bc
plane. ORTEP diagram with atom numbering scheme of a typical
1D polymer viz. 1 is shown in Fig. 1. Selected bond distances and
bond angles relevant to the metal coordination spheres of 1 and
2 are given in Tables 2 and 3, respectively. The hydrogen bonding
Fig. 2. Packing diagram of 2D sheet structure in 1 containing cooperative N–H. . .O
and C–H. . .O hydrogen bondings along bc-plane.

B.N. Sarkar et al. / Journal of Molecular Structure 963 (2010) 35–40
39
2], C30–N7–C29 [116.1(3)° in 1 and 120.0(6)° in 2] and N8–C30–
N7 [174.6(3)° in 1 and 175.1(8)° in 2] that reflects non-linearity
of the larger pseudohalide rod.
rings. Excitation at 368 or 273 nm, L does not show any emission
band. The absorption spectra of the complexes 1 and 2 show band
maxima at 281 nm. Although dicyanamide, free Schiff base (L) and
common cadmium(II) salts used as building units are not lumines-
cent, interestingly the cadmium(II) complexes with this pentaden-
tate Schiff base containing the pyridine moiety show intense
fluorescence band at 570 nm (for 1) and at 566 nm (for 2) upon
excitation at the corresponding absorption band of the complexes
in DMF solutions at room temperature. The lifetimes are in the
range 2.65–2.70 ns. The appearance of the fluorescence [36] upon
complex formation could be inferred to the change in MO structure
in the complexes compared to that in the free L. The HOMO–LUMO
In the crystal packing of 1, 1D polymeric chains running along
the direction [1 0 1] are engaged in single N–H. . .O and single C–
H...O hydrogen bondings with the perchlorate ions embedded
among the chains leading to a 2D sheet parallel to the bc plane
(Fig. 2) with interchian Cd...Cd separation 12.674 Å. Similarly, 1D
polymeric chains of 2 running in the direction [1 0 1] pack through
involvement of single N–H...F and weak multiple C–H. . .F hydrogen
bondings with the hexafluorophosphate ions located between the
polymeric chains resulting once again in a 2D sheet parallel to
the bc plane (Fig. 3) but with greater (12.900 Å) interchain Cd...Cd
separation as compared to 1.
*
*
n–p type of forbidden transition of the free L changes to p–p type
of HOMO–LUMO transition in the metal complexes. Therefore
upon complexation the non-fluorescent free ligand favours fluores-
cence characteristic of the simple coordinated aromatic chromo-
phore. Spectral results are set in Table 6 and a representative
spectral pattern is shown in Fig. 4.
3.3. Absorption and luminescence properties
In DMF solution, the Schiff base L shows absorption bands at
*
368 and 273 nm assignable to n–p of transition of the aromatic
4. Conclusion
Successfully we have prepared two new luminous 1D coordina-
tion polymers of cadmium(II) in combination with a Schiff base li-
gand and dicyanamide bridge through a single-pot reaction of the
molecular building components in preassigned ratios. The interest-
ing feature is the enhanced coordination of the 4d metal ion. The
use of pentadentate ligand and larger-sized bridging unit ensures
such a conformation in the coordination frames that different
kinds of hydrogen bonds result in and lead to different crystalline
architectures. Structures of 1 and 2 represent the reliability of com-
bination of strong covalent bonds and weak non-covalent interac-
tions in crystal engineering for rational designing of functional
materials at molecular level.
Fig. 3. Packing diagram of 2D sheet structure in 2 formed by cooperative N–H. . .F
and C–H. . .F hydrogen bondings along bc-plane.
Acknowledgements
Financial support from the DST, CSIR and UGC, New Delhi, India
is gratefully acknowledged. The authors also acknowledge the use
of DST-funded National Single Crystal X-ray Diffraction Facility at
the Department of Inorganic Chemistry, IACS, Kolkata, India for
crystallographic studies. The authors K.B., S.C. and S.D. thank,
respectively, to the CSIR and UGC, New Delhi, India for fellowships.
Table 6
Photophysical data.
Sample
Absorption (k/nm)
Emission (k/nm)
Lifetime (ns)
Fluorescencea
1
2
281
281
570
566
2.66
2.68
a
In DMF at room temperature (298 K).
Appendix A. Supplementary data
Crystallographic data for the structural analyses (excluding
structure factors) have been deposited with the Cambridge Crystal-
lographic data center (CCDC Nos. 742990 for 1 and 742991 for 2).
Copies of this information can be had free of charge from The Direc-
tor, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44 1223
336033; e–mail: deposit@ccdc.cam.ac.uk or http://www. ccdc.ca-
m.ac.uk). Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2009.09.043.
1800
1600
1400
1200
1000
800
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