Synthesis, structure and properties of hexacoordinated compounds of cadmium(II) halides/pseudohalides containing a pentadentate N-donor Schiff base

Article abstract of DOI:10.1016/j.molstruc.2011.03.039

Five hexacoordinated compounds of type [Cd(L)(X)]Y·nMeCN (1-5) [L = N,N′-(bis(pyridin-2-yl)benzylidene)diethylenetriamine; Y=PF6-, n = 1; X = Cl^- (1), Br^- (2), I^- (3) and Y=PF6-, n = 0, X=N3-, (4); Y=ClO4-, n = 0, X = NCO<

Full text of DOI:10.1016/j.molstruc.2011.03.039

Journal of Molecular Structure 994 (2011) 306–312
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structure and properties of hexacoordinated compounds of
cadmium(II) halides/pseudohalides containing a pentadentate N-donor Schiff base
Bhola Nath Sarkar a, Somnath Choubey a, Kishalay Bhar a, Soumi Chattopadhyay a, Partha Mitra b,
Barindra Kumar Ghosh a,
⇑
a Department of Chemistry, The University of Burdwan, Burdwan 713 104, 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
Five hexacoordinated compounds of type [Cd(L)(X)]YꢀnMeCN (1–5) [L = N,N0-(bis(pyridin-2-yl)benzyli-
dene)diethylenetriamine; Y ¼ PF6ꢁ, n = 1; X = Clꢁ (1), Brꢁ (2), Iꢁ (3) and Y ¼ PF6ꢁ, n = 0, X ¼ Nꢁ3 , (4);
Y ¼ ClOꢁ4 , n = 0, X = NCOꢁ, (5)] are synthesized and characterized. Structures of all the compounds are
solved by X-ray diffraction measurements. Structural analyses reveal that each cadmium(II) center
adopts a distorted octahedral geometry bound by five N atoms of L along with terminal halide in 1–3
and N atom of terminal pseudohalide in 4 and 5. Intermolecular NAHꢀ ꢀ ꢀO, CAHꢀ ꢀ ꢀO, NAHꢀ ꢀ ꢀF and
Article history:
Received 24 January 2011
Received in revised form 7 March 2011
Accepted 11 March 2011
Available online 22 March 2011
Keywords:
Cadmium(II)
Pentadentate Schiff base
Halides/Pseudohalides
X-ray structures
Luminescence
CAHꢀ ꢀ ꢀF hydrogen bondings and CAHꢀ ꢀ ꢀ
p interactions as is the case lead to different crystalline aggre-
1
gates in 1–5. The complexes display intraligand
(
pA
pꢂ) fluorescence in DMF solutions at room
temperature.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
and structurally characterized one heptacoordinated monomer
[Cd(L)(NCS)(OClO3)] and two 1D coordination polymers of the type
[Cd(L)(dca)]n(ClO4/PF6)n. This work stems from our interest to
make a thorough study on cadmium(II)-L chemistry in combina-
tion with halides like chloride, bromide and iodide and pseudoha-
lides such as azide and cyanate towards preparation of new
molecular and crystalline aggregates through covalent bonds and
non-covalent interactions. We have successfully isolated five hexa-
coordinated compounds of type [Cd(L)(X)]YꢀnMeCN (1–5) [Y ¼ PFꢁ6 ,
n = 1; Xꢁ= Clꢁ (1), Brꢁ (2), Iꢁ (3) and Y ¼ PF6ꢁ, n = 0, X ¼ N3ꢁ, (4);
Y ¼ ClO4 , n = 0, X = NCOꢁ, (5)]. The details of syntheses, character-
izations, X-ray structures and molecular properties of these new
compounds are described below.
Research on design and synthesis [1,2] of mono-, di- and poly-
nuclear coordination compounds of cadmium(II) [3–8] are of great
interest for the preparation of functional materials with specific
electronic and optoelectronic properties [9,10]. One-pot [11,12]
reactions in appropriate molar ratios of the building units held to-
gether by covalent [13] as well as non-covalent [14–17] bonds re-
sult in veritable molecular and crystalline architectures [17–20].
We are also interested in this field [21–25] to isolate different cad-
mium(II) compounds with interesting molecular properties using
multidentate N-donor Schiff bases in combination with halides/
pseudohalides. The coordination behaviors of Schiff bases [26,27]
are of great interest because of their ease of preparation, structural
variety, varied denticities and subtle steric and/or electronic effects
leading to complexes of different dimensionalities. Halides [28–31]
and pseudohalides [32–35] are suitable terminal/bridging units
which in combination with organic ligands result in different
mono-, di-, polynuclear coordination molecules and supramolecu-
lar entities. Recently, we examined coordination behavior of thio-
cyanate [21] and dicyanamide (dca) [25] towards cadmium(II) in
combination with a pentadentate N-donor Schiff base, N,N0-
(bis(pyridin-2-yl)benzylidene)diethylenetriamine (L, Scheme 1)
2. Experimental
2.1. General remarks and physical measurements
2.1.1. Materials
High purity diethylenetriamine (SRL, India), 2-benzoylpyridine
(Lancaster, UK), cadmium(II) chloride/bromide/iodide (SRL, India),
sodium azide (E. Merck, India), sodium cyanate (Lancaster, UK),
cadmium(II) acetate (E. Merck, India) and ammonium hexafluoro-
phosphate (Fluka, Germany) were purchased from respective con-
cerns and used as received. Cadmium(II) perchlorate hexahydrate
was prepared [36] by treatment of the corresponding cadmium(II)
⇑
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 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.03.039

B.N. Sarkar et al. / Journal of Molecular Structure 994 (2011) 306–312
307
2.2. General synthesis of complexes
Ni
Na
H
2.2.1. [Cd(L)(X)]PF6ꢀMeCN [X = Clꢁ (1), Brꢁ (2) and Iꢁ (3)]
Ni
pN
C
C
L (0.433 g, 1 mmol) in acetonitrile (10 mL) was added dropwise
to a solution of CdCl2ꢀH2O (0.201 g, 1 mmol) in methanol (10 mL).
To the resulting light yellow solution, a methanolic solution
(10 mL) of NH4PF6 (0.163 g, 1 mmol) was added slowly with con-
stant stirring. The final light yellow solution was filtered and left
for slow evaporation in air. After a week colorless crystals of 1 that
separated, were washed with hexane and dried in vacuo over silica
gel indicator. Yield: 0.614 g (80%). For preparations and isolations
of 2 and 3 in pure crystalline states, similar reaction condition
and reaction stoichiometry as used in 1 were followed except that
CdBr2ꢀ4H2O (0.344 g, 1 mmol) and CdI2 (0.366 g, 1 mmol) instead
of CdCl2ꢀH2O were used respectively. The light yellow solutions
were processed as in 1. Yield: 2, 0.617 g (76%) and 3, 0.644 g
(75%). Anal. Calc. for C30H30N6F6PClCd (1): C, 47.0; H, 3.9; N, 11.0.
Np
(L)
Scheme 1.
carbonate (E. Merck, India) with perchloric acid (E. Merck, India)
followed by slow evaporation on a steam-bath, filtration through
a fine glass-frit and preserved in a desiccator containing concen-
trated sulfuric acid (E. Merck, India) for subsequent uses. The Schiff
base, N,N0-(bis(pyridin-2-yl)benzylidene)diethylenetriamine (L),
was prepared by condensation of a 1:2 M ratio of diethylentri-
amine and 2-benzoylpyridine following a reported method [25].
All other chemicals and solvents used were AR grade. The synthetic
reactions and work-up were done in open air.
Caution! Azide and perchlorate compounds of metal ions are
potentially explosive [37] especially in the presence of organic li-
gands. Only a small amount of these materials should be prepared
and handled with care.
Found: C, 47.2; H, 4.1; N, 11.2%. IR (KBr, cmꢁ1):
3350, 3290; (CAH) 2955, 2935, 2873; (C@N) +
1592;
(PF6) 843, 800, 557. KM (MeCN, ohmꢁ1 cm2 molꢁ1): 130.
m
(NAH) 3447,
m
m
m(C@C) 1650,
m
UV–Vis (k, nm): 280. Anal. Calc. for C30H30N6F6PBrCd (2): C, 44.4;
H, 3.7; N, 10.4. Found: C, 44.5; H, 3.6; N, 10.2%. IR (KBr, cmꢁ1):
m(NAH) 3438, 3344, 3287;
m(CAH) 2954, 2929, 2871;
m
(C@N) + (C@C) 1649, 1591;
m
m(PF6) 839, 802, 558. KM (MeCN,
ohmꢁ1 cm2 molꢁ1): 125. UV–Vis (k, nm): 281. Anal. Calc. for
C
30H30N6F6PICd (3): C, 41.9; H, 3.5; N, 9.8. Found: C, 42.0; H, 3.4;
N, 10.0%. IR (KBr, cmꢁ1):
(NAH) 3430, 3340, 3279; (CAH)
(PF6) 842, 800,
m
m
2954, 2928, 2871; m(C@N) + m(C@C) 1647, 1590; m
556. KM (MeCN, ohmꢁ1 cm2 molꢁ1): 120. UV–Vis (k, nm): 283.
2.1.2. Physical measurements
Elemental analyses (carbon, hydrogen and nitrogen) were per-
formed on a Perkin–Elmer 2400 CHNS/O elemental analyzer. IR
spectra (KBr discs, 4000–300 cmꢁ1) were recorded using a Per-
kin–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 MeCN
was used as solvent. Ground state absorptions were measured with
a Jasco model V-530 UV–Vis spectrophotometer. Fluorescence
measurements were done using Hitachi Fluorescence Spectroflu-
rimeter F-4500.
2.2.2. [Cd(L)N3]PF6 (4)
To a methanolic solution (5 mL) of Cd(OAc)2ꢀ2H2O (0.088 g,
0.33 mmol), L (0.143 g, 0.33 mmol) in acetonitrile (10 mL) was
added dropwise followed by the addition of NaN3 (0.022 g,
0.33 mmol) and NH4PF6 (0.054 g, 0.33 mmol) in methanol
(15 mL), that results in a light yellow solution which was processed
as above in 1 to yield colorless block shaped crystals of 4. Yield:
0.181 g (75%). Anal. Calc. for C28H27N8F6PCd (4): C, 45.9; H, 3.7;
N, 15.4. Found: C, 46.0; H, 3.6; N, 15.5%. IR (KBr, cmꢁ1):
m(NAH)
Table 1
Crystallographic data and structure refinement parameters for 1–5.
Compounds
Formula
Weight
Crystal system
Space group
a (Å)
1
C
2
3
4
5
30H30N6F6PClCd
C30H30N6F6PBrCd
811.88
Monoclinic
P21/c
8.5438(4)
18.6590(8)
19.8207(9)
100.3040(10)
3108.8(2)
0.71073
C30H30N6F6PICd
858.88
Monoclinic
P21/c
8.6908(5)
18.6748(10)
19.9198(12)
98.3350(10)
3198.8(3)
0.71073
C28H27N8F6PCd
732.95
Monoclinic
P21/n
11.8900(13)
17.944(2)
14.3585(17)
104.454(2)
2966.5(6)
0.71073
C29H27N6O5ClCd
687.42
Monoclinic
P21/c
14.7391(12)
9.0415(8)
21.4359(17)
100.601(2)
2807.9(4)
0.71073
1.626
767.42
Monoclinic
P21/c
8.6090(4)
18.9603(8)
19.8041(9)
102.0670(10)
3161.2(2)
0.71073
b (Å)
c (Å)
b (°)
V (Å3)
k (Å)
qcalcd (gm cmꢁ3
Z
)
1.612
4
1.735
4
1.783
4
1.641
4
4
T (K)
l
120(2)
0.893
120(2)
2.031
120(2)
1.764
100(2)
0.862
305(2)
0.924
(mmꢁ1
)
F (0 0 0)
1544
691
1688
1472
1392
h ranges (°)
h/k/l
Reflections collected
1.50–25.00
ꢁ10, 9/ꢁ22, 22/ꢁ23, 23
5581
1.51–25.16
ꢁ10, 10/ꢁ22, 22/ꢁ23, 23
5553
1.50–23.70
ꢁ9, 9/ꢁ21, 21/ꢁ22, 22
4846
1.85 to 25.00
ꢁ16,17/ꢁ21,21/ꢁ16,17
5226
1.41–25.00
ꢁ17, 17/ꢁ10, 10/ꢁ25, 25
30,757
Independent reflections (Rint
Data/restraints/parameters
Goodness-of-fit on F2
)
4624(0.044)
4624/0/407
1.144
4314 (0.066)
4314/0/407
1.045
3720 (0.074)
3720/0/407
1.040
4350 (0.074)
4350/0/401
1.018
4952 (0.036)
4952/0/379
1.090
Final R indices [I > 2
R indices (all data)
r
(I)]
R = 0.0366, wR = 0.1045
R = 0.0462, wR = 0.1109
0.817 and ꢁ0.531
R = 0.0352, wR = 0.0777
R = 0.0527, wR = 0.0849
0.807 and ꢁ0.588
R = 0.0356, wR = 0.0658
R = 0.0566, wR = 0.0731
0.0632 and ꢁ0.536
R = 0.0344, wR = 0.0823
R = 0.0444, wR = 0.0880
0.912 and ꢁ0.659
R = 0.0231, wR = 0.0578
R = 0.0209, wR = 0.0565
0.343 and ꢁ0.417
Largest peak and hole (eÅꢁ3
)
h
i
Weighting scheme: R ¼ kjFoj ꢁ jFcjj= jFoj, wR ¼
wðF2o ꢁ Fc2Þ = wðFo2Þ 1=2, calcd w ¼ 1=½r2ðF2oÞ þ ðxPÞ þ yPꢃ; x = 0.0609 (for 1), 0.0375 (for 2), 0.0209 (for 3), 0.0386
P
P
P
P
2
2
2
(for 4), 0.0311 (for 5), and y = 3.577 (for 1), 1.4643 (for 2), 5.3544 (for 3), 2.1211 (for 4), 1.1029 (for 5); where P ¼ ðF2o þ 2Fc2Þ=3.

308
B.N. Sarkar et al. / Journal of Molecular Structure 994 (2011) 306–312
3430, 3353, 3295;
m(CAH) 2945, 2922, 2879;
m
(N@N@N) 2035;
sulfoxide but are insoluble in water. In MeCN solutions, 1–5 behave
m(C@N) +
m
(C@C) 1648, 1593;
m
(PF6) 842, 802, 557. KM (MeCN,
as 1:1 electrolytes [45] as reflected in their respective conductivity
values (vide Section 2). In IR spectra, the complexes show m(NAH)
ohmꢁ1 cm2 molꢁ1): 110. UV–Vis (kmax, nm): 280.
stretching frequencies of
L lying within the range 3450–
3270 cmꢁ1. Several weak bands in the range 2960–2870 cmꢁ1
2.2.3. [Cd(L)(NCO)]ClO4 (5)
assignable to aliphatic CAH stretching vibration [46] are seen in
An acetonitrilic solution (10 mL) of L (0.143 g, 0.33 mmol) was
added dropwise to a solution containing a mixture of Cd(ClO4)2.6-
H2O (0.139 g, 0.33 mmol) and NaNCO (0.022 g, 0.33 mmol) in
methanol (20 mL). The reaction mixture was processed as above
all the compounds.
m(C@N) plus m(C@C) stretching vibrations of
the metal-bound Schiff base (L) are observed within 1650–
1590 cmꢁ1 range. In 4, asymmetric azide stretch appears as a strong
band at 2035 cmꢁ1. Compound 5 shows characteristic asymmetric
cyanate stretching vibration at 2205 cmꢁ1; this is substantially
higher than free ion value (ꢄ2155 cmꢁ1) [46,47] and is consistent
[48] with N-bonding rather than O-coordination. Additionally,
hexafluorophosphate stretches in 1–4 and perchlorate bands in 5
(vide Section 2) [46] exhibit splittings which is attributed to some
kind of hydrogen bondings with the counter anions. X-ray study
corroborates this hypothesis.
in
29H27N6O5ClCd (5): C, 50.7; H, 4.0; N, 12.3. Found: C, 50.8; H,
4.1; N, 12.4%. IR (KBr, cmꢁ1):
(NAH) 3450, 3342, 3293; (CAH)
2950, 2935, 2882; (NCO) 2205; (C@N) + (C@C) 1648, 1590;
(ClO4) 1111, 1087, 622. KM (MeCN, ohmꢁ1 cm2 molꢁ1): 115.
1 to get pure 5. Yield: 0.163 g (72%). Anal. Calc. for
C
m
m
m
m
m
m
UV–Vis (kmax, nm): 282.
2.3. X-ray crystallographic study
Colorless DMF solutions of compounds 1–5 show ligand-based
transitions at ꢄ280 nm presumably due to nApꢂ
/pA
pꢂ transition
Diffraction data of the single crystals of 1–5 were collected at
120(2) K (for 1–3), 100(2) K (for 4) and 305(2) K (for 5) on a Bruker
AXS SMART APEX-II CCD area-detector diffractometer using graph-
[49,50].
3.2. Description of the structures of the complexes (1–5)
ite monochromated Mo K
a radiation. The unit cell parameters
were obtained from SAINT [38] and absorption corrections were
performed with SADABS [39]. The structures were solved by direct
methods and refined by full-matrix least-squares method based on
F2 using SHELXL-97 [40] for 1, 4 and 5 and SHELXTL [40] for 2 and
3. All non-hydrogen atoms were refined with anisotropic displace-
ment parameters. The hydrogen atoms were fixed geometrically
and refined using a riding model. All calculations were carried
out using SHELXL-97, SHELXTL, CAMERON [41], PARST [42], Mer-
cury 2.3 [43] and ORTEP-3 [44] programs. A summary of the crys-
tallographic data and structure determination parameters is given
in Table 1.
Single crystal X-ray structure analyses show that compounds
1–5 consist of mononuclear (0D) units which are further engaged
in different kinds of cooperative hydrogen bondings like NAHꢀ ꢀ ꢀF,
CAHꢀ ꢀ ꢀF, NAHꢀ ꢀ ꢀO and CAHꢀ ꢀ ꢀO and CAHꢀ ꢀ ꢀ
p interactions as is the
case among themselves resulting in different supramolecular
architectures. ORTEP diagrams with atom numbering schemes
and perspective views of the crystalline architectures in 1 and 4
are shown in Figs. 1–4 and for 2, 3 and 5 in Figs. S1–S7. Selected
bond distances and bond angles relevant to the metal coordination
spheres and the non-covalent bonding parameters are set in
Tables 2 and 3.
3. Results and discussion
3.2.1. [Cd(L)(Cl)]PF6ꢀMeCN (1), [Cd(L)(Br)]PF6ꢀMeCN (2) and
[Cd(L)(I)]PF6ꢀMeCN (3)
3.1. Synthesis and formulation
The structures (Figs. 1, S1 and S3) of 1–3 are made up of
[Cd(L)(X)]+ cation [X = Clꢁ, 1; Brꢁ, 2; Iꢁ, 3], PFꢁ6 counter anion and
a solvent molecule, MeCN. The overall geometry at the cadmium(II)
center is best described as a distorted octahedron with a CdN5X
chromophore ligated by five N (N1, N2, N3, N4 and N5) atoms of L
and one terminal halide (Clꢁ for 1, Brꢁ for 2 and Iꢁ for 3). Two Np
(N4, N5 for 1, N1, N4 for 2 and N1, N3 for 3), one Ni (N3 for 1 and
2 and N4 for 3) and one Na (N2 for 1 and N5 for 2 and 3) atoms
[Np = N(pyridine); Ni = N(imine) and Na = N(amine)] of L define the
equatorial plane and the remaining Ni (N1 for 1, N2 for 2 and 3) atom
of L and one terminal halide (Clꢁ for 1, Brꢁ for 2 and Iꢁ for 3) occupy
the axial sites. The cisoid and transoid angles (Table 2) around the
metal center are in line with strong distortion from an idealized
octahedral geometry due to the asymmetric nature of the bound
Schiff base. The CdACl bond distance [2.4890(11) Å] in 1 is compa-
rable with the CdAN bond distances, but larger ionic radii of bro-
mide and iodide in 2 and 3, respectively result in longer CdAX
distances [2.6247(5) Å in 2 and 2.7997(5) Å in 3] over CdAN bond
lengths (Table 2). The differences among the CdACl (in 1), CdABr
(in 2) and CdAI (in 3) (vide Table 2) bond distances correspond
approximately to the differences of the ionic radii of the halides
[31]. Each metal center in 1–3 has four 5-membered chelate loops
with bite angles N(3)ACd(1)AN(4) 68.35(10)°, N(1)ACd(1)AN(5)
68.43(9)°, N(3)ACd(1)AN(2) 70.89(10)° and N(1)ACd(1)AN(2)
70.20(10)° for 1; N2ACd1AN1 68.51(11)°, N2ACd1AN5
70.38(10)°, N3ACd1AN5 71.10(11)° and N3ACd1AN4 68.52(11)°
The hexacoordinated mononuclear compounds of the type
[Cd(L)(Cl/Br/I)]PF6ꢀMeCN (1/2/3) were isolated as colorless crystals
through one-pot synthesis of 1:1:1 M ratio of the respective
cadmium(II) halide salts, pentadentate Schiff base (L) and NH4PF6
from methanol–acetonitrile (2:1) solution mixtures at room tem-
perature. Use of 1:1:1:1 M ratio of Cd(OAc)2ꢀ2H2O, L, NaN3 and
NH4PF6 in the same solvent mixture results in 4. Compound 5
was obtained in good yield through self-assembly of 1:1:1 M ratio
of Cd(ClO4)2ꢀ6H2O, L and NaNCO. The reactions are summarized in
Eqs. (1)–(3):
MeOH—MeCN
CdX2 ꢀ nH2O þ L þ NH4PF6
½CdðLÞðXÞꢃPF6 ꢀ MeCN
ð1Þ
ꢀꢀꢀꢀ!
Clꢁð1Þ=Brꢁð2Þ=Iꢁð3Þ
298K
ðn ¼ 1; X ¼ Cl;
n ¼ 4; X ¼ Br and
n ¼ 0; X ¼ IÞ
X
¼
MeOH—MeCN
ꢀꢀꢀꢀ!
298K
CdðOAcÞ2 ꢀ 2H2O þ L þ NaN3 þ NH4PF6
½CdðLÞðN3ÞꢃPF6
ð4Þ
ð2Þ
ð3Þ
CdðClO4Þ ꢀ 6H2O þ L þ NaNCO MeOH—MeCN ½CdðLÞðNCOÞꢃClO4
ꢀꢀꢀꢀ!
2
298K
ð5Þ
The new complexes were characterized by microanalytical (C, H
and N), spectroscopic, thermal and other physicochemical results.
The microanalytical data are in good conformity with the formula-
tions 1–5. The moisture-insensitive complexes are stable over long
periods of time in powdery and crystalline states and are soluble in
methanol, ethanol, acetonitrile, dimethylformamide and dimethyl-
for
2 and N4ACd1AN1 68.62(15)°, N4ACd1AN5 70.96(14)°,
N2ACd1AN5 70.80(14) ° and N2ACd1AN3 68.62(14)° for 3. The
ethylenic arms of the Schiff base in 1–3 are to some extent puckered

B.N. Sarkar et al. / Journal of Molecular Structure 994 (2011) 306–312
309
Fig. 1. An ORTEP diagram of [Cd(L)Cl]PF6.MeCN (1) with atom numbering scheme (30% probability ellipsoids for all non-hydrogen atoms).
Fig. 2. A perspective view of 2D sheet structure in 1 formed by cooperative double NAHꢀ ꢀ ꢀF and CAHꢀ ꢀ ꢀF hydrogen bonds and CAHꢀ ꢀ ꢀ
p interaction in bc-plane.
due to sp3 hybridization of the saturated fragment of the chelating L
and bond angles deviate (vide Table 2) from the ideal value (109.5°).
The metal(II) center in 1–3 departs 0.251 Å, 0.214 Å and 0.197 Å,
respectively from the corresponding mean plane (N2, N3, N4, N5
for 1, N1, N3, N4, N5 for 2 and 3) towards the axial halide. Among
the four equatorial nitrogens N3, N5 in 1, N1, N3 in 2 and N3, N4
in 3 shift (N3, 0.199 Å, N5, 0.095 Å in 1; N1, 0.086 Å and N3,
0.180 Å in 2, and N3, 0.083 Å and N4, 0.175 Å in 3) towards the axial
halide whereas N2, N4 in 1, N4, N5 in 2 and N1, N5 in 3 show con-
siderable deviation (N2, 0.123 Å and N4, 0.171 Å in 1, N4, 0.155 Å
and N5, 0.112 Å in 2, and N1, 0.150 Å and N5, 0.108 Å in 3) towards
the axial Ni atom from the mean plane.
In the crystal packing of 1, the [Cd(L)Cl]+ cations are associated
by double NAHꢀ ꢀ ꢀF and CAHꢀ ꢀ ꢀF hydrogen bonds (Table 3) into 1D
chain along b-axis. These chains are further interconnected along c-
axis by single CAHꢀ ꢀ ꢀ
p
interaction (Table 3) involving H (H6) atom
-cloud of one of the benzene [Cg7:
of the ligand framework and
p
C(11)AC(12)AC(26)AC(25)AC(24)AC(13)] rings into a 2D sheet
structure parallel to the bc-plane (Fig. 2). The monomeric 0D units
of 2 are packed through NAHꢀ ꢀ ꢀF and CAHꢀ ꢀ ꢀF hydrogen bonds

310
B.N. Sarkar et al. / Journal of Molecular Structure 994 (2011) 306–312
Fig. 3. An ORTEP representation of [Cd(L)(N3)]PF6 (4) with atom labeling scheme. Thermal ellipsoids are drawn at the 20% probability level.
Fig. 4. 2D sheet structure in (4) formed by multiple CAHꢀ ꢀ ꢀF hydrogen bonds.
involving H atoms of L and F atoms of interstitial hexafluorophos-
phate ions coupled with single CAHꢀ ꢀ ꢀ interaction (Table 3)
involving H atoms of L and -cloud of one of the pyridine rings
[Cg(5): N(1)AC(1)AC(2)AC(3)AC(4)AC(5)] leading to a 2D supra-
molecular architecture parallel to the bc-plane. This is further sta-
polyhedron around each metal center in 4/5 (Fig. 3/Fig. S5) is best
described as a distorted octahedron with a CdN6 chromophore. The
coordination includes the chelated pentadentate Schiff base ligated
by two Np (N1 and N5 in 4; N3 and N6 in 5), two Ni (N2 and N4 in 4
and 5), one Na (N3 for 4 and N1 for 5) atoms of L and the sixth po-
sition is occupied by terminal azide N (N6) atom in 4 and cyanate N
(N5) atom in 5. The basal planes of 4 and 5 consist of two Np (N1,
N5 for 4 and N6, N3 for 5), one Ni (N4 for both 4 and 5) and one Na
(N3 for 4 and N1 for 5) atoms of L, whereas the axial positions are
occupied by the terminal pseudohalide N (N6 for 4 and N5 for 5)
and the remaining Ni (N2 for both 4 and 5) atom of L. The equato-
rial CdAN distances are in the range 2.378(3)–2.567(3) Å and
2.3417(15)–2.4603(15) Å in 4 and 5, respectively and the axial
CdAN distances are lying between 2.264(3)–2.319(3) Å (in 4) and
2.2010(17)–2.3196(15) Å (in 5). The degrees of distortion from an
ideal octahedral geometry are reflected in the equatorial
[65.76(9)–133.76(8)° in 4 and 68.93(5)–130.98(5)° in 5] and the
axial [152.26(9)° in 4 and 141.26(6)° in 5] bond angles. The two
p
p
bilized by another CAHꢀ ꢀ ꢀ
the solvent molecule and
N(4)AC(24)AC(25)AC(26)AC(27)AC(28)] ring (Fig. S2). The
p
interaction involving H (H33B) atom of
p
-cloud of another pyridine [Cg(6):
F
atoms of the interstitial hexafluorophosphate ions and H atoms
of the Schiff base and the solvent molecule in 3 are engaged in
NAHꢀ ꢀ ꢀF and CAHꢀ ꢀ ꢀF hydrogen bonds interlocking the mononu-
clear units into a 1D chain along b-axis which are further con-
nected through CAHꢀ ꢀ ꢀ
p interaction (Table 3) along a-axis
resulting in a 2D sheet (Fig. S4) parallel to the ab-plane.
3.2.2. [Cd(L)(N3)]PF6 (4) and [Cd(L)(NCO)]ClO4 (5)
The crystal lattices of 4 and 5 consist of mononuclear (0D) units
[Cd(L)(N3)]PF6 and [Cd(L)(NCO)]ClO4, respectively. The coordination

B.N. Sarkar et al. / Journal of Molecular Structure 994 (2011) 306–312
311
Table 2
Table 3
Selected bond distances (Å) and angles (o) for 1–5.
Hydrogen bond distances (Å) and angles (°) for 1–5 and CAHꢀ ꢀ ꢀ
p
interactions (Å, °) for
1–3.
Bond distances
Bond angles
Compound
DAHꢀ ꢀ ꢀA
DAH
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
DAHꢀ ꢀ ꢀA
Compound 1
Cd1AN1
Cd1AN3
Cd1AN5
Cd1AN4
Cd1AN2
Cd1ACl2
1
2
3
4
5
N2AH2ꢀ ꢀ ꢀF1a
N2AH2ꢀ ꢀ ꢀF2a
C6AH6ꢀ ꢀ ꢀF4b
C22AH22Bꢀ ꢀ ꢀF2a
0.91
0.91
0.93
0.97
2.42
2.51
2.54
2.50
3.268(5)
3.262(5)
3.252(7)
3.279(5)
155
140
134
137
2.320(3)
2.337(3)
2.425(3)
2.430(3)
2.541(3)
2.4890(11)
N1ACd1ACl2
N1ACd1AN5
N3ACd1AN4
N5ACd1AN4
N1ACd1AN2
N3ACd1AN2
133.28(7)
68.43(9)
68.35(10)
88.72(10)
70.20(10)
70.89(10)
N5AH5ꢀ ꢀ ꢀF1c
N5AH5ꢀ ꢀ ꢀF4c
C2AH2ꢀ ꢀ ꢀF2d
C30AH30Aꢀ ꢀ ꢀF1c
0.91
0.91
0.93
0.97
2.54
2.33
2.50
2.47
3.284(4)
3.175(5)
3.227(6)
3.256(5)
139
154
135
139
Compound 2
Cd1AN2
Cd1AN4
Cd1AN5
Cd1AN3
Cd1AN1
Cd1ABr2
2.314(3)
2.411(3)
2.527(3)
2.339(3)
2.431(3)
2.6247(5)
N2ACd1ABr2
N2ACd1AN1
N2ACd1AN5
N3ACd1AN5
N3ACd1AN4
N4ACd1AN1
132.68(8)
68.51(11)
70.38(10)
71.10(11)
68.52(11)
89.17(10)
N5AH5ꢀ ꢀ ꢀF6a
0.91
0.97
0.93
0.96
2.29
2.50
2.54
2.55
3.111(5)
3.291(7)
3.229(7)
3.083(10)
150
138
131
115
C13AH13Bꢀ ꢀ ꢀF4a
C27AH27ꢀ ꢀ ꢀF3b
C30AH30Bꢀ ꢀ ꢀF5e
C1AH1ꢀ ꢀ ꢀF4i
C2AH2ꢀ ꢀ ꢀF6i
C3AH3ꢀ ꢀ ꢀF6j
C11AH11ꢀ ꢀ ꢀF2k
0.93
0.93
0.93
0.93
2.52
2.50
2.36
2.55
3.287(4)
3.358(4)
3.254(5)
3.467(4)
140
154
162
171
Compound 3
Cd1AN2
Cd1AN4
Cd1AN1
Cd1AN3
Cd1AN5
I1ACd1
2.298(4)
2.337(4)
2.392(4)
2.448(4)
2.526(4)
2.7997(5)
N2ACd1AI1
N2ACd1AN3
N4ACd1AN5
N2ACd1AN5
N4ACd1AN1
N1ACd1AN3
133.54(10)
68.62(14)
70.96(14)
70.80(14)
68.62(15)
89.33(14)
N1AH1ꢀ ꢀ ꢀO4d
0.91
0.93
0.93
0.93
0.93
2.29
2.58
2.48
2.56
2.50
3.129(2)
3.509(2)
3.388(3)
3.468(3)
3.334(3)
152
174
164
167
149
C9AH9ꢀ ꢀ ꢀꢀ ꢀ ꢀO5a
C10AH10ꢀ ꢀ ꢀO2l
C14AH14. . .O3
C23AH23ꢀ ꢀ ꢀO4m
Compound 4
Cd1AN1
Cd1AN2
Cd1AN3
Cd1AN4
Cd1AN5
Cd1AN6
N7AN8
2.415(3)
2.319(3)
2.470(3)
2.378(3)
2.567(3)
2.264(3)
1.160(4)
1.199(4)
N2ACd1AN6
N4ACd1AN5
N4ACd1AN3
N3ACd1AN2
N2ACd1AN1
N1ACd1AN5
N7AN6ACd1
N6AN7AN8
152.26(9)
65.76(9)
70.70(9)
71.91(9)
68.44(8)
83.87(9)
117.9(2)
178.2(3)
1
2
C6AH6ꢀ ꢀ ꢀCg7f
0.93
0.93
0.93
0.93
3.00
2.84
2.97
2.90
3.629(4)
3.627(4)
3.538(6)
3.555(6)
127
143
119
129
C9AH9ꢀ ꢀ ꢀCg5g
C33AH33Bꢀ ꢀ ꢀCg6h
C27AH27ꢀ ꢀ ꢀCg8f
3
Symmetry codes: a = 1 ꢁ x, 1/2 + y, 3/2 ꢁ z; b = ꢁ1 + x, 1 + y, z; c = 1 ꢁ x, ꢁ1/2 + y, 1/
2 ꢁ z; d = x, ꢁ1 + y, z; e = x, 1 + y, z; f = ꢁ1 + x, y, z; g = ꢁx, ꢁy, ꢁz; h = x, y, z; i = 1/
2 ꢁ x, ꢁ1/2 + y, 3/2 ꢁ z; j = ꢁ1/2 + x, 1/2 ꢁ y, ꢁ1/2 + z; k = 1 + x, y, z; l = x, 3/2 ꢁ y, 1/
2 + z; m = 2 ꢁ x, ꢁ1/2 + y, 3/2 ꢁ z.
N7AN6
Compound 5
Cd1AN1
Cd1AN2
Cd1AN3
Cd1AN4
Cd1AN5
Cd1AN6
N5AC6
2.4364(15)
2.3196(15)
2.4603(15)
2.3417(15)
2.2010(17)
2.4099(15)
1.162(2)
N2ACd1AN5
N1ACd1AN4
N4ACd1AN6
N3ACd1AN2
N2ACd1AN1
N6ACd1AN3
C6AN5ACd1
N5AC6AO5
141.26(6)
72.83(5)
68.93(5)
67.78(5)
72.84(5)
84.02(5)
164.96(15)
178.0(2)
a 2D sheet structure (Fig. 4). Mononuclear units of 5 pack through
three kinds of CAHꢀ ꢀ ꢀO hydrogen bonds involving H atoms of the
ligand backbone and O atoms of the perchlorate counter ions (Ta-
ble 3) into a 2D sheet structure (Fig. S6) parallel to the ab-plane.
These sheets are further involved in NAHꢀ ꢀ ꢀO and CAHꢀ ꢀ ꢀO hydro-
gen bonds along c-axis resulting in a 3D network structure
(Fig. S7).
C6AO5
1.208(2)
subsequent CdAN distances: Cd1AN6 2.264(3) Å in 4 and Cd1AN5
2.2010(17) Å in 5 indicate stronger coordination through anionic
cyanate in 5 over azide in 4. The ethylenic arms of the Schiff base
are to some extent puckered as is evident from the respective bond
angle values (vide Table 2). The cadmium(II) centers have four five-
membered chelate loops with bite angles N2ACd1AN1 68.44(8)°,
N4ACd1AN5 65.76(9)°, N2ACd1AN3 71.91(9)° and N4ACd1AN3
3.3. Luminescence behaviors
In DMF solutions, the compounds, 1–5, show band maxima cen-
tered at ꢄ280 nm (see Section 2). Upon photo excitations at the
corresponding absorption bands in DMF solutions at 298 K com-
pounds 1–3 show weak emission bands centered at ꢄ400 nm
whereas complexes 4 and 5 exhibit intense emission bands at
70.70(9)° in
4
and N2ACd1AN3 67.78(5)°, N2ACd1AN1
72.84(5)°, N4ACd1AN1 72.83(5)° and N4ACd1AN6 68.93(5)° in
5. The metal center is deviated 0.374 Å in 4 and 0.353 Å in 5 to-
wards the axial pseudohalide N atom. The deviation of equatorial
atoms in 5 (N1, 0.186 Å; N3, 0.157 Å; N4, 0.303 Å and N6,
0.274 Å) is larger than that (N1, 0.074 Å; N3, 0.096 Å; N4, 0.154 Å
and N5, 0.132 Å) in 4. The azide is more bent in 4 than the cyanate,
in 5 as reflected in the respective bond angle values (vide Table 2).
In 4, the N7AN6 [1.199(4) Å] distance is larger than N7AN8
[1.160(4) Å] indicating coordination of the N6 over N8, and the
length is larger than the reported [51] ones. The N5AC6
[1.162(2) Å] distance is larger and C6AO5 [1.208(2) Å] length is
smaller than the expected one [52] which is in consonance with
the N-coordination of terminal cyanate in 5. The bond angle values
N6AN7AN8 178.2(3)° in 4 and N5AC6AO5 178.0(2)° in 5 indicate
the quasi-linearity of the terminal pseudohalides.
In the crystalline state, 0D mononuclear units of 4 are associ-
ated by multiple CAHꢀ ꢀ ꢀF hydrogen bonds (Table 3) involving H
atoms of the ligand framework and F atoms of the hexafluorophos-
phate ions embedded among these mononuclear units resulting in
Fig. 5. Emission spectra of complexes 3 and 5 in DMF solution at 298 K.

312
B.N. Sarkar et al. / Journal of Molecular Structure 994 (2011) 306–312
1
(pA
pꢂ) fluores-
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