Chelating N,N′-(bis(pyridin-2-yl)alkylidene)propane-1,3-diamine pseudohalide copper(II) and cadmium(II) coordination compounds: Synthesis, structure and luminescence properties of [M(bpap)(X)]ClO4 and [M(bpap)(X)2] [M = Cu, Cd; X = N3-, NCS -]

Article abstract of DOI:10.1016/j.poly.2005.04.023

Copper perchlorate hexahydrate on reaction with the chelating ligands, N,N′-(bis(pyridin-2-yl)alkylidene)propane-1,3-diamine (bpap) [(py)(R)CN-(CH₂)₃-NC(R)(py) where py = pyridine; R = H, (bpfp); R = Me, (bpmp); R = C₆H₅, (bpbp)] and NaN ₃/NH₄NCS in a 1:1:1 mole ratio forms the complexes [Cu(bpap)(N₃/NCS)]ClO₄ (1a-3b), while cadmium perchlorate hexahydrate/cadmium nitrate tetrahydrate in a 1:1:2 mole ratio produces [Cd(bpap)(N₃/NCS)₂] (4a-6b). Elemental, spectral, electrochemical and other physicochemical results characterize the complexes. Single crystal X-ray diffraction studies confirm the structure of two representative members, [Cu(bpbp)(N₃)]ClO₄ (3a) and [Cd(bpbp)(NCS)₂] (6b). The complexes of 1a-3b are reduced to [Cu(bpbp)₂]ClO₄ by ascorbic acid. However, air oxidation of [Cu(bpbp)₂]ClO₄ in the presence of N₃/NCS produces Cu(bpap)(N₃/NCS)]ClO₄. All the complexes display intraligand ¹(π-π*) fluorescence and intraligand ³(π-π*) phosphorescence in glassy solutions (MeOH at 77 K).

Full text of DOI:10.1016/j.poly.2005.04.023

Polyhedron 24 (2005) 1525–1532
www.elsevier.com/locate/poly
Chelating N,N0-(bis(pyridin-2-yl)alkylidene)propane-1,3-diamine
pseudohalide copper(II) and cadmium(II) coordination compounds:
Synthesis, structure and luminescence properties of
ꢀ
ꢀ
[M(bpap)(X)]ClO4 and [M(bpap)(X)2] [M = Cu, Cd; X ¼ N3 , NCS ]
Sk Hafijur Rahaman , Rajarshi Ghosh , Tian-Huey Lu , Barindra K. Ghosh
a
a
b
a,
*
a
Department of Chemistry, The University of Burdwan, Golapbag campus, Burdwan 713104, India
b
Department of Physics, National Tsing Hua University, Hsinchu, Taiwan 300, ROC
Received 24 December 2004; accepted 1 April 2005
Available online 27 June 2005
Abstract
Copper perchlorate hexahydrate on reaction with the chelating ligands, N,N0-(bis(pyridin-2-yl)alkylidene)propane-1,3-diamine
(bpap) [(py)(R)C@N–(CH2)3–N@C(R)(py) where py = pyridine; R = H, (bpfp); R = Me, (bpmp); R = C6H5, (bpbp)] and NaN3/
NH4NCS in a 1:1:1 mole ratio forms the complexes [Cu(bpap)(N3/NCS)]ClO4 (1a–3b), while cadmium perchlorate hexahydrate/
cadmium nitrate tetrahydrate in a 1:1:2 mole ratio produces [Cd(bpap)(N3/NCS)2] (4a–6b). Elemental, spectral, electrochemical
and other physicochemical results characterize the complexes. Single crystal X-ray diffraction studies confirm the structure
of two representative members, [Cu(bpbp)(N3)]ClO4 (3a) and [Cd(bpbp)(NCS)2] (6b). The complexes of 1a–3b are reduced
to [Cu(bpbp)2]ClO4 by ascorbic acid. However, air oxidation of [Cu(bpbp)2]ClO4 in the presence of N3/NCS produces
1
3
Cu(bpap)(N3/NCS)]ClO4. All the complexes display intraligand (p–p*) fluorescence and intraligand (p–p*) phosphorescence in
glassy solutions (MeOH at 77 K).
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Copper(II)/cadmium(II); Schiff base chelator; Cu(II)–Cu(I) interconversion; X-ray structure; Luminescence spectra
1. Introduction
metal ions like nickel(II), copper(II), zinc(II) and cad-
mium(II), coordination environment, organic ligands
and suitable bridging units [8–11]. Pseudohalides [8–
12], especially the azide and thiocyanate, have long been
known for their versatile coordination modes to give
monomeric, dimeric and polymeric complexes. Copper
complexes are of considerable interest mainly due to
their variety in coordination geometry, exquisite col-
ours, technical application, dependant molecular struc-
tures and spectroscopic properties, and their
biochemical significance [9,13]. Cadmium is well suited
[11,14,15] to this study as its d10 configuration permits
a wide range of symmetries and coordination numbers.
Reports on just a few copper(II) and cadmium(II)
Significant contemporary interests in inorganic–
organic hybrid materials [1] reflect their potential appli-
cations in areas such as catalysis, molecular electronics,
magnetism and photochemistry [2–5]. Schiff bases [6,7]
are useful chelators because of their preparational acces-
sibilities, structural varieties and varied denticities. We
are also interested in this field through variation of
*
Corresponding author. Tel.: +91 342 2558545; fax: +91 342
2530452.
E-mail addresses: hafijur_am@yahoo.co.in (S.H. Rahaman),
barin_1@yahoo.co.uk (B.K. Ghosh).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.04.023

1526
S.H. Rahaman et al. / Polyhedron 24 (2005) 1525–1532
complexes with the Schiff bases formed from propane-1,
3-diamine and different pyridine carboxyaldehyde or
-ketones [16,17] have prompted us to develop new coor-
dination compounds using azide and thiocyanate li-
gands. Successfully, we have prepared 12 mononuclear
complexes of the type [Cu(bpap)(N3/NCS)]ClO4 (1a–
3b) and [Cd(bpap)(N3/NCS)2] (4a–6b), characterized
on the basis of microanalytical, spectroscopic and other
physicochemical properties. X-ray crystallographic stud-
ies of [Cu(bpbp)(N3)]ClO4 (3a) and [Cd(bpbp)(NCS)2]
(6b) were made to define the coordination sphere. The
details of synthesis, structure and luminescence behav-
iour are described below.
made with a Shimadzu model UV-1601PC UV–Vis
spectrophotometer and Hitachi model F-4500 spectro-
fluorimeter equipped with polarization accessory and
low temperature unit (77 K). The temperature of the
solution was kept to within 0.1 K by circulating water
through a HETO HOLTEN system. Room-temperature
solid phase magnetic susceptibilities were measured at
298 K with a PAR 155 vibrating sample magnetometer
with Hg[Co(SCN)4] as the reference. Mass spectra were
obtained with a MAT 8200 (electron ionization, EIMS)
instrument. Electrochemical measurements (cyclic vol-
tammetry, CV) were carried out with the use of com-
puter controlled EG & G PARC VersaStat model 270
electrochemical instrument using a platinum disk work-
ing electrode as described elsewhere [19]. The solutions
were IR compensated and the results were collected at
298 K. The following parameters and relations were
used: scan rate (v), 50 mV sꢀ1; formal potential
E0 = 0.5(Epa + Epc) where Epa and Epc are anodic and
cathodic peak potentials, respectively; DEp is the peak-
to-peak separation. The potentials are referenced to a
saturated calomel electrode (SCE) and are uncorrected
for junction contributions.
2. Experimental
2.1. Materials
High purity pyridine-2-carboxyaldehyde (Lancaster,
UK), 2-acetylpyridine (Lancaster, UK), 2-benzoylpyri-
dine (Lancaster, UK), propane-1,3-diamine (Lancaster,
UK), sodium azide (Aldrich, USA), ammoniumthiocya-
nate (Aldrich, USA) potassium hexafluorophosphate
(Fluka, Germany), copper nitrate tetrahydrate
(E. Merck, India) and cadmium nitrate tetrahydrate
(E. Merck, India) were purchased from their respective
concerns and used as received. Copper perchlorate hexa-
hydrate and cadmium perchlorate hexahydrate were
prepared by treatment of copper carbonate and
cadmium carbonate (E. Merck, India) with perchloric
acid (E. Merck, India), respectively, followed by slow
evaporation on a steam-bath, filtration through a fine
glass-frit, and preservation in a desiccator containing
concentrated sulfuric acid (E. Merck, India) for subse-
quent use. Purification of MeOH (E. Merck, India)
and preparation of the supporting electrolyte ([Et4N]-
[ClO4]) for electrochemical work were executed follow-
ing a reported method [18]. All other chemicals and
solvents were AR grade and were used as received.
Caution! Perchlorate and azido compounds of metal
ions are potentially explosive, especially in the presence
of organic ligands. Only a small amount of material
should be prepared and it should be handled with care.
2.3. Preparation of the Schiff bases
The Schiff base chelators, bpfp, bpmp and bpbp, were
prepared following a reported [16] procedure with little
modification. The details for bpfp are described: Pyri-
dine-2-carboxyaldehyde (0.214 g, 2 mmol) was refluxed
with propane-1,3-diamine (0.074 g, 1 mmol) in dehy-
drated alcohol. After 10 h the reaction solution was evap-
orated under reduced pressure to yield a gummy mass,
which was dried and stored in vacuo over CaCl2 for
subsequent use [yield, 0.212 g (80%)]. Bpmp and bpbp
were prepared similarly by refluxing for with 10 h 2-acetyl
pyridine (0.242 g, 2 mmol) and 2-benzoylpyridine
(0.366 g, 2 mmol), respectively, instead of pyridine-2-car-
boxyaldehyde, with propane-1,3-diamine (0.088 g,
1 mmol) in a 2:1 molar ratio. Yield: (78–80%). Anal. calc.
for C15H16N4 (bpfp): C, 71.40; H, 6.39; N, 27.20. Found:
C, 71.41; H, 7.40; N, 27.23%. Mass spectrum (EI): m/z
252 (M+ = L+). IR (KBr, cmꢀ1): m(C@N) 1590. UV–Vis
(k, nm): 240, 370. Anal. calc. for C17H20N4(bpmp): C,
77.82; H, 7.19; N, 19.98. Found: C, 77.80; H, 7.20; N,
20.00%. Mass spectrum (EI): m/z 280 (M+ = L+). IR
(KBr, cmꢀ1): m(C@N) 1592 cmꢀ1. UV–Vis (k, nm): 243,
370. Anal. calc. for C27H24N4 (bpbp): C, 81.10; H, 5.98;
N, 13.85. Found: C, 80.05; H, 5.91; N, 13.80%. Mass spec-
trum (EI): m/z 404 (M+ = L+). IR (KBr, cmꢀ1): m(C@N)
1590. UV–Vis (k, nm): 245, 372.
2.2. Physical measurements
Elemental analyses (carbon, hydrogen and nitrogen)
were performed on a Perkin–Elmer 2400 CHNS/O Ele-
mental Analyzer. IR spectra (KBr discs, 4000–
300 cmꢀ1) were recorded using a JASCO FTIR model
420 spectrometer. Molar conductances were measured
using a Systronics conductivity meter where the cell con-
stant was calibrated with 0.01(M) KCl solution, and dry
MeOH was used as the solvent. Ground state absorp-
tion and steady-state fluorescence measurements were
2.4. Preparation of the complexes
Complexes 1a–3b were prepared from the perchlorate
salts of copper(II) using the same mole ratio (1:1:1) of

S.H. Rahaman et al. / Polyhedron 24 (2005) 1525–1532
1527
metal, bpfp/bpmp/bpbp and azide/thiocyanate; these
were also isolated using the nitrate salt by finally adding
one equivalent sodium perchlorate. 4a–6b were prepared
from both cadmium(II) nitrate and/or cadmium(II) per-
chlorate using a mole ratio of 1:1:2 with bpfp/bpmp/
bpbp and azide/thiocyanate. Typical syntheses are de-
scribed below.
N, 14.77%. IR (KBr, cmꢀ1): m(C@N) 1635, 1592;
m(NCS) 2092, 2078; m(ClO4) 1080, 622. KM (MeOH,
Xꢀ1 cm2 molꢀ1): 120; UV–Vis (k, nm): 717, 395. Anal.
Found: C, 43.12; H, 4.01; N, 13.93. Calc. for
C18H20N5SO4ClCu (2b): C, 43.11; H, 4.02; N, 13.96%.
IR (KBr, cmꢀ1): m(C@N) 1637, 1590; m(NCS) 2098,
2095; m(ClO4) 1080, 622. KM (MeOH, Xꢀ1 cm2 molꢀ1):
120; UV–Vis (k, nm): 720, 402.
2.4.1. Copper(II)azido complexes
Solid bpfp (0.252 g, 1 mmol) was added pinch by pinch
to a solution (10 cm3) of Cu(ClO4)2 Æ 6H2O (0.37 g;
1 mmol) in MeOH (15 cm3) followed by NaN3 (0.065 g,
1 mmol) with constant stirring. After 30 min the green
solution mixture was filtered and the supernatant liquid
was kept in air for slow evaporation. After 7 days 1a
was separated, washed with toluene and dried in vacuo
over silica gel indicator. Yield: 0.86 g (70%). 2a and 3a
were prepared by the same procedure using bpmp and
bpbp, respectively, instead of bpfp. Anal. calc. for
C15H16N7O4ClCu (1a): C, 39.39; H, 3.52; N, 21.44.
Found: C, 39.40; H, 3.54; N, 21.46%. IR (KBr, cmꢀ1):
m(C@N) 1637, 1592; m(N3) 2073; m(ClO4) 1080, 622. Mass
spectrum (FAB): m/z 357 (M+ = [Cu(bpfp)(N3)]+). KM
(MeOH, Xꢀ1 cm2 molꢀ1): 130; UV–Vis (k, nm): 715,
394. Anal. calc. for C17H20N7O4ClCu (2a): C, 42.06; H,
4.15; N, 20.20. Found: C, 42.08; H, 4.12; N, 20.22%. IR
(KBr, cmꢀ1): m(C@N) 1635, 1592; m(N3) 2072; m(ClO4)
1080, 622. Mass spectrum (FAB): m/z 385
(M+ = [Cu(bpmp) (N3)]+). KM (MeOH, Xꢀ1 cm2 molꢀ1):
130; UV–Vis (k, nm): 717, 395. Anal. calc. for
C27H24N7O4ClCu (3a): C, 53.20; H, 3.97; N, 16.08.
Found: C, 53.15; H, 4.21; N, 16.05%. IR (KBr, cmꢀ1):
m(C@N) 1637, 1590; m(N3) 2073; m(ClO4) 1080, 622. Mass
spectrum (FAB): m/z 510 (M+ = [Cu(bpbp)(N3)]+). KM
(MeOH, Xꢀ1 cm2 molꢀ1): 120; UV–Vis (k, nm): 720, 402.
2.4.3. Cadmium(II)azido complexes
A methanolic solution (5 cm3) of bpfp (0.252 g,
1 mmol) was added dropwise to
a solution of
Cd(ClO4)2 Æ 6H2O (0.311 g; 1 mmol) in the same solvent
(10 cm3) followed by NaN3 (0.13 g, 2 mmol) in warm
methanol (5 cm3). The green solution was filtered and
the supernatant liquid was kept in air for slow evapora-
tion. After a few days 4a was separated, washed with
toluene and dried in vacuo over silica gel indicator.
Yield: 0.113 g (70%). 5a and 6a were prepared by same
procedure using bpmp and bpbp, respectively, instead of
bpfp. Anal. calc. for C15H16N10Cd (4a): C, 40.18; H,
3.59; N, 31.24. Found: C, 40.14; H, 3.64; N, 31.26%.
IR (KBr, cmꢀ1): m(C@N) 1637,1592; m(N3) 2073, 2040.
KM (MeOH, Xꢀ1 cm2 molꢀ1): 5; UV–Vis (k, nm): 335.
Anal. calc. for C17H20N10Cd (5a): C, 42.85; H, 4.23;
N, 29.40. Found: C, 42.80; H, 4.22; N, 29.42% IR
(KBr, cmꢀ1): m(C@N) 1635, 1592; m(N3) 2072, 2045.
KM (MeOH, Xꢀ1 cm2 molꢀ1): 5; UV–Vis (k, nm): 336.
Anal. calc. for C27H24N10Cd (6a): C, 53.99; H, 4.02;
N, 23.32. Found: C, 53.95; H, 4.06; N, 23.35%. IR
(KBr, cmꢀ1): m(C@N) 1637, 1590; m(N3) 2073, 2040.
KM (MeOH, Xꢀ1 cm2 molꢀ1): 5. UV–Vis (k, nm): 335.
2.4.4. Cadmium(II)thiocyanato complexes
A methanolic solution (5 cm3) of bpbp (0.406 g,
1 mmol) was added dropwise to a solution of
Cd(ClO4)2 Æ 6H2O (0.311 g; 1 mmol) in the same solvent
(10 cm3) followed by NH4NCS (0.15 g, 2 mmol) in warm
methanol (5 cm3). The green solution was filtered and
the supernatant liquid was kept in air for slow evapora-
tion. After a few days 4b was separated, washed with
toluene and dried in vacuo over silica gel indicator.
Yield: 0.242 g (72%). 5b and 6b were prepared in the
same way using bpmp and bpbp. Anal. calc. for
C17H16N6S2Cd (4b): C, 42.48; H, 3.35; N, 17.48. Found:
C, 42.47; H, 3.39; N, 17.43%. IR (KBr, cmꢀ1): m(NCS)
2100, 2095; m(C@N) 1605. KM (MeOH, Xꢀ1 cm2 molꢀ1):
5; UV–Vis (MeOH; k, nm): 330. Anal. calc. for
C19H20N6S2Cd (5b): C, 44.88; H, 3.96; N, 16.53. Found:
C, 44.76; H, 3.92; N, 16.57%. IR (KBr, cmꢀ1): m(C@N)
1635, 1592; m(NCS) 2100, 2095. KM (MeOH,
Xꢀ1 cm2 molꢀ1): 5; UV–Vis (k, nm): 335. Anal. calc.
for C29H24N6Cd (6b): C, 55.06; H, 3.82; N, 13.28.
Found: C, 55.08; H, 3.86; N, 13.31%. IR (KBr, cmꢀ1):
m(C@N) 1637, 1590; m(NCS) 2100, 2095. KM (MeOH,
Xꢀ1 cm2 molꢀ1): 5; UV–Vis (k, nm): 332.
2.4.2. Copper(II)thiocyanato complexes
To copper(II) nitrate tetrahydrate (0.241 g, 1 mmol)
in methanolic solution (10 cm3), faint yellow bpbp
(0.406 g, 1 mmol) was added dropwise. An methanolic
solution (5 cm3) of ammoniumthiocyanate (0.076 g, 1
mmol) was added with constant stirring. To this solu-
tion one equivalent of sodium perchlorate was added
slowly drop by drop. The final deep green solution
was filtered and left for slow evaporation in air. After
a few days fine green crystals of 3b were separated
out, which were filtered, washed with methanol and
dried in vacuo over CaCl2. Yield: 0.125 g (74%). 1b
and 2b were prepared by the same procedure using bpfp
and bpmp respectively instead of bpbp. Anal. calc. for
C28H24N5SO4ClCu (3b): C, 53.76; H, 3.86; N, 11.19.
Found: C, 53.72; H, 3.88; N, 11.14%. IR (KBr, cmꢀ1):
m(C@N) 1637,1592; m(NCS) 2100, 2095; m(ClO4) 1080,
622. KM (MeOH, Xꢀ1 cm2 molꢀ1): 130; UV–Vis (k,
nm): 715, 394. Anal. calc. for C16H16N5SO4ClCu (1b):
C, 40.59; H, 3.40; N, 14.79. Found: C, 40.58; H, 3.42;

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S.H. Rahaman et al. / Polyhedron 24 (2005) 1525–1532
2.5. Copper(II)–copper(I) interconversion
[23]. The crystal data, data collection parameters and
the results of analyses of 3a and 6b can be found in
Table 1.
2.5.1. [Cu(bpap)(N3/NCS)]ClO4 ! [Cu(bpap)]ClO4
To a methanolic suspension (15 cm3) of the com-
plexes [Cu(bpap)(N3)]ClO4 (0.14 g, 0.25 mmol), ascorbic
acid (0.045 g, 0.25 mmol) in water (5 cm3) was added
with stirring. The brown suspension quickly changed
to deep red-brown and stirring was continued for 30
min, and the precipitated mass was filtered, washed with
water and cold methanol. The residue was dried over a
CaCl2 desiccator and subjected to column chromatogra-
phy on a silica gel column prepared in CHCl3. A brown-
ish-red band was eluted by CHCl3–MeOH (4:1, v/v)
mixture and dried in air. Crystals were obtained by dif-
fusion of a CH2Cl2 solution of the complex to a hexane
layer. Yield: 54–57%. The microanalytical data of the
complexes are as follows: Anal. calc. for [Cu(bpfp)]ClO4:
C, 43.43; H, 3.88; N, 13.50. Found: C, 43.40; H, 3.85; N,
13.49%. Anal. calc. for [Cu(bpmp)]ClO4: C, 46.10; H,
4.55; N, 12.65. Found: C, 46.09; H, 4.54; N, 12.63%.
Anal. calc. for [Cu(bpbp)]ClO4: C, 45.48; H, 5.38; N,
12.48. Found: C, 45.47; H, 5.37; N, 12.47%.
3. Results and discussion
3.1. Synthesis and formulation
In a one-pot reaction the chelators, the Schiff bases,
were prepared by the condensation of one equivalent of
propane-1,3-diamine and two equivalents of pyridine-2-
carboxyaldehyde/2-acetylpyridine/2-benzoylpyridine in
dry alcohol (Scheme 1). The pentacoordinated mononu-
clear complexes [Cu(bpap)(N3/NCS)]ClO4 (1a–3b) ini-
tially formed in an MeOH solution containing a 1:1:2
mixture of Cu(ClO4)2 Æ 6H2O, bpap and NaN3/
NH4NCS; a reactant ratio expected to yield a mononu-
clear species of the composition [Cu(pbpa)(N3/NCS)2].
However, microanalyses showed a 1:1:1 ratio of metal,
blocking ligand and the pseudohalide, and in the IR
spectra the presence of perchlorate bands was noticed.
A reactant ratio corresponding to the product stoichiom-
etry afforded better yields of [Cu(bpap)(N3/NCS)]ClO4
(1a–3b). In an effort to get [Cu(bpap)(N3/NCS)2], the
starting material was changed to Cu(NO3)2 Æ 4H2O, and
a 1:1:2 molar ratio of nitrate salt, ligand and the pseud-
ohalide produced a gummy mass of indefinite composi-
tion. The hexacoordinated mononuclear complexes
(4a–6b) were obtained starting with a 1:1:2 molar ratio
of cadmium perchlorate/metal nitrate, bpap and azide/
thiocyanate, and conformed in the IR spectra to the ab-
sence of perchlorate and/or nitrate bands. The air-stable
moisture-insensitive complex salts are highly soluble in
common organic solvents like methanol, ethanol, dichlo-
romethane, acetonitrile and dimethylformamide but are
insoluble in water. All the complexes were characterized
by elemental analysis, electrical conductivity, IR, UV–
Vis and reflectance spectra, luminescence behaviour
and also magnetic susceptibility, and electrochemistry
for the complexes 1a–3b. The results are consistent with
the proposed mononuclear formulation. In methanol
solutions 1a–3b behave as 1:1 electrolytes [24] as reflected
in their KM values (ca. 130 Xꢀ1 cm2 molꢀ1) but 4a–6b
behave as non-electrolytes as is evident from their low
conductivity values (ca. 5 Xꢀ1 cm2 molꢀ1). Room-
temperature solid-phase magnetic susceptibility mea-
surements show that the copper(II) complexes have
magnetic moments close to the spin-only value (S= 1/2),
1.73 BM, as expected from discrete and magnetically
non-coupled mononuclear 3d9 ions.
2.5.2. [Cu(bpap)]ClO4 ! [Cu(bpap)(N3/NCS)]ClO4
To a methanolic suspension of [Cu(bpap)]ClO4 (0.15 g,
0.25 mmol) an aqueous solution of NaN3 (0.015 g, 0.25
mmol) was added, air was passed for through the solution
for 30 min and from time to time methanol was added to
maintain the volume of the solution at 25 ml. The mixture
was filtered and kept in a freezer for 4 h. A brown precip-
itate was filtered and washed with water and cold metha-
nol. The compound was soluble in a mixture of 2-methoxy
ethanol and methanol (1:5, v/v) and crystallized by evap-
oration in air for aweek. Yield: 55–60%. The microanalyt-
ical data are consistent with complexes 1a–3b.
2.6. X-ray diffraction study
Suitable single crystals of compounds 3a and 6b were
mounted on a SMART CCD area detector equipped
with a graphite monochromotor and Mo Ka(k =
0.71073) radiation. The intensity data were corrected
for Lorentz and polarization effects for all the com-
plexes. Diffraction data for both 3a and 6b were mea-
sured using the / and x scan method. The structures
were solved by Patterson syntheses using SHELXS-97
[20] and followed by successive Fourier and difference
Fourier syntheses. Full-matrix least-squares refinements
on F2 were carried out using SHELXL-97 [21] with aniso-
tropic displacement parameters for all non-hydrogen
atoms for the complexes. The hydrogen atoms were
fixed geometrically and refined using a riding model.
In the final difference Fourier map the rꢀes3idual maxima
3.2. Spectral studies
˚
and minima were 0.395 and ꢀ0.262 e A for 3a, 0.812
ꢀ3
˚
and ꢀ0.395 e A for 6b, respectively. All calculations
In the IR spectra, the point of interest is the band
due to the azide and thiocyanate in the complexes.
were carried out using PLATON 99 [22] and ORTEP-32

S.H. Rahaman et al. / Polyhedron 24 (2005) 1525–1532
1529
Table 1
Crystal data and structure refinement parameters for 3a and 6b
3a
27H24N7O4ClCu
609.52
6b
Empirical formula
Formula weight
Temperature (K)
C
C29H24N6S2Cd
633.06
295(2)
296(2)
0.71073
˚
Wavelength (A)
0.71073
ꢀ
Crystal system, space group
˚
monoclinic, Cc
22.288(2)
triclinic, P1
a (A)
˚
7.8480(5)
13.7073(8)
14.7229(9)
62.9370(10)
75.9040(10)
83.8340(10)
1367.92(14)
2
b (A)
˚
c (A)
12.1157(12)
10.1279(10)
90
a (ꢁ)
b (ꢁ)
c (ꢁ)
102.636(2)
90
2668.6(5)
3
˚
V (A )
Z
4
1.517
Dcalc (Mg mꢀ3
)
1.537
0.981
l (mmꢀ1
F(000)
)
0.967
1252
640
0.38 · 0.30 · 0.25
1.59–28.27
Crystal size (mm3)
0.36 · 0.20 · 0.14
1.87–28.34
ꢀ29.22/ꢀ9.16/ꢀ11.12
7742
h ranges (ꢁ)
h/k/l
ꢀ10.10/ꢀ18.18/ꢀ18.19
14194
6395 [0.0310]
Reflections collected
Independent reflections [Rint
Completeness to h (%)
Tmax and Tmin
]
4844 [0.0242]
89.8
94.2
0.8693 and 0.7081
4844/2/361
0.995
0.783 and 0.709
6395/0/343
1.000
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
R1 = 0.0555, wR2 = 0.1727
R1 = 0.0639, wR2 = 0.1821
0.395 and ꢀ0.262
R1 = 0.0295, wR2 = 0.0734
R1 = 0.0347, wR2 = 0.0363
0.812 and ꢀ0.395
ꢀ3
˚
Largest peak and hole (e A
)
absorptions at ca. 330 nm. Reflectance spectra in nujol
and electronic spectra in MeOH solutions are akin in
each complex, reflecting similar gross structure and elec-
tronic structure in the solid state and in solution.
N
N
(CH2)3
R
R
C
C
N
N
R = H, bpfp; R = Me, bpmp; R = Ph, bpbp
3.3. Electrochemical studies for the copper(II) complexes
Scheme 1.
Electroactivity of the complexes was studied in
MeOH solutions using cyclic voltammetry and coulom-
etry at platinum working electrodes. A one-electron
reductive response is observed, presumably due to the
electrode reaction:
The spectra exhibit a very strong and sharp absorption
band at 2040–2080 cmꢀ1 due to asymmetric stretching
vibrations [25] of the terminal azide. The presence of io-
nic perchlorate bands at 1091 and 621 cmꢀ1 is noticed
for 1a–3b. The complexes 4a–6b show a characteristic
strong transmission at 2098–2105 cmꢀ1 along with a
weak band at 2090–2093 which correspond to
Â
Ã
Â
Ã
CuIIðLÞðN3Þ 1þ þ e ꢀ CuIðLÞðN3Þ
ð1Þ
The electrode process in the CV is reproducible in the
potential range of 0.08 to ꢀ0.08 V with no trace of
decomposition as reflected in smooth cyclic voltammo-
grams. The one-electron stoichiometry of couple 1 was
confirmed by a comparison of the current height with
that of a standard [27] copper(II)–copper(I) couple,
since attempted coulometry at potentials more catho-
dic than Epc gave a continuous coulomb count due
to some unidentified side reactions [28]. The similar
pattern in the electron transfer behaviour of all the
complexes at about the same potential once again cor-
roborates a similar structure of the cationic units.
m
asym(NCSꢀ). The stretching vibrations of the (C@N)
band of the Schiff base are seen at 1629 and 1589
cmꢀ1. All other characteristic ligand vibrations are seen
in the range 1600–600 cmꢀ1. The solutions of 1a–3b in
MeOH are dark green and exhibit absorptions at ca.
720, 400 nm. The transition >700 nm corresponds to a
d–d transition of the copper(II) moiety and the band
around 400 nm to intramolecular (n ! p*, p ! p*)
charge transfer transitions [26]. The solutions of the
complexes 4a–6b in MeOH are colourless and exhibit

1530
S.H. Rahaman et al. / Polyhedron 24 (2005) 1525–1532
Table 2
3.4. Luminescence properties
˚
Selected bond distances (A) and angles (ꢁ) for 3a
Bond distances
Cu–N(4)
Cu–N(5)
Complexes with bpap shows an intense absorption at
ca. 405 nm which is assigned to intraligand p–p* transi-
tions. The emission energy of the complexes in MeOH
solutions at 298 K is almost same (kmax ꢁ 475 nm) and
is assignable to intraligand fluorescence [11]. The life-
times of the complexes are in range 2.55–2.63 ns. In
glassy solutions (MeOH at 77 K) both fluorescence
and 3(p–p*) phosphorescence is observed at 525 nm.
In the solid state they show a distinct emission band at
492 nm, differing from their fluorescence spectra in
MeOH (Fig. 3).
1.978(4)
1.994(5)
2.101(5)
1.152(10)
2.005(5)
2.077(6)
1.170(9)
Cu–N(7)
N(2)–N(3)
Cu–N(6)
Cu–N(1)
N(1)–N(2)
Bond angles
N(4)–Cu–N(5)
N(4)–Cu–N(6)
N(5)–Cu–N(1)
N(5)–Cu–N(6)
N(4)–Cu–N(1)
N(6)–Cu–N(1)
N(4)–Cu–N(7)
N(5)–Cu–N(7)
N(6)–Cu–N(7)
N(1)–Cu–N(7)
N(2)–N(1)–Cu
N(3)–N(2)–N(1)
170.0(2)
92.14(19)
95.8(2)
80.3(2)
94.1(2)
3.5. X-ray crystal structure
132.7(2)
79.83(19)
100.6(2)
133.98(19)
93.2(2)
3.5.1. [Cu(bpbp)(N3)]ClO4 (3a)
In order to define the coordination sphere, a single-
crystal X-ray diffraction study was made in one case,
viz 3a. An ORTEP diagram with the atom numbering
scheme of the mononuclear unit in 3a is shown in
Fig. 1. Selected interatomic bond lengths and bond
angles are listed in Table 2. The crystalꢀlattice consists
of [Cu(bpbd)(N3)]+ cations and ClO4 anions. The
coordination polyhedron around the metal centre is
best described as distorted trigonal bipyramid (tbp)
with a CuN5 chromophore. The coordination includes
a tetradentate Schiff base (bpbp), a chelating blocker
ligated by two pyridine nitrogens (N5,N7) and two
imine nitrogens (N4,N6), and one terminal azide
nitrogen (N1). The equatorial positions are occupied
by one imine nitrogen (N6), one pyridine nitrogen
(N7) and the azide nitrogen (N1) while the axial
118.1(5)
179.0(8)
positions are occupied by the remaining imine (N5)
and pyridine (N4) nitrogen atoms. The distortion from
ideal tbp geometry is due to the asymmetric nature of
the Schiff base and the deviations of the refine angles
(90ꢁ/120ꢁ) formed at the metal centre. The propylenic
part of the Schiff base N4–C27–C26–C25–N6 is to
some extent puckered due to sp3 hybridization of
the saturated portion of the chelating ligand and devi-
ation [114.6(6)ꢁ] from the ideal bond C27–C26–C25
angle of 109ꢁ280 (Fig. 1). The equatorial Cu–N dis-
˚
tances [2.005(5)–2.101(5) A] as well as the bond angles
[93.2(2)–133.98(19)ꢁ] show significant variations. The
axial Cu–N distances [Cu–N4 1.978(4) A, Cu1–N5
˚
˚
1.994(5) A] are however close and these are the smaller
bond distances than the three equatorial bond distances
[9]. The three bite angles N4–Cu–N7, N4–Cu–N6 and
N6–Cu–N5 are 79.83(19)ꢁ, 92.14(19)ꢁ and 80.3(2)ꢁ,
respectively. The larger bite in N4–Cu–N6 arises due
to a six-membered puckered loop formed from the
propylenic arm and the lower value of the non-bite
angle N5–Cu–N7 [100.6(2)ꢁ]. The axial bond angle,
N4–Cu–N5 [170.0(2)ꢁ], deviates from the ideal value
(180ꢁ). The sum (359.88ꢁ) of the equatorial angles
N6–Cu–N7 [133.98(19)ꢁ], N1–Cu–N6 [132.7(2)ꢁ] and
N1–Cu–N7 [93.20(2)ꢁ are very close to 360.00ꢁ; so the
atoms N1, N6, N7 and Cu are almost the same plane.
In the terminal azide ligand the N1–N2 distance
˚
˚
[1.170(9) A] is longer than the N2–N3 length
[1.152(10) A] which indicates that the nitrogen (N1)
atom oꢀf N3 is coordinated to the copper(II) centre.
ꢀ
Fig. 1. ORTEP diagram of [Cu(bpbp)(N3)]ClO4 (3a) with the atom
numbering scheme and 40% probability ellipsoids for all non-hydrogen
atoms.
The N3 ion is coordinated in a linear fashion as seen
from its N1–N2–N3 angle [179.0(8)ꢁ] [8,10b].

S.H. Rahaman et al. / Polyhedron 24 (2005) 1525–1532
1531
Table 3
3.5.2. [Cd(bpbp)(NCS)2] (6b)
˚
Selected bond distances (A) and angles (ꢁ) for 6b
An ORTEP view with the atom numbering scheme of
the mononuclear unit in 6b is shown in Fig. 2. Selected
bond lengths and angles relevant to the coordination
sphere are listed in Table 3. The metal centre is best de-
scribed as a distorted octahedron with a CdN6 chromo-
phore. Distortion from the ideal octahedral geometry is
due to the asymmetric nature of the bound tetradentate
Schiff base and the deviations of the refine angles (90ꢁ/
180ꢁ) formed at the metal centre (Table 3). The coordi-
nation includes the Schiff base ligated by two pyridine
nitrogens (N3,N6) and two imine nitrogens (N4,N5),
and two nitrogens (N1,N2) of the thiocyanates. The
equatorial positions are occupied by the four nitrogen
atoms (N3, N4, N5 and N6) of the tetradentate ligand
while the nitrogens (N1,N2) of the isothiocyanato
groups are placed at the axial positions. The propylenic
part of the Schiff base N5–C17–C16–C5–N4 is to some
extent puckered due to sp3 hybridization of the satu-
rated portion of the chelating ligand and deviation
[119.1(2)ꢁ] from the ideal C15–C16–C17 bond angle of
109ꢁ280. The four N atoms of the ligand creates hard-
ness in the cadmium(II) centre; so it appears to be a ma-
jor reason to have preferential N-donation of the
ambidentate NCS through its electronegative hard cen-
tre. The degrees of distortion from an ideal octahedral
(90ꢁ) geometry are reflected in the cisoid [69.42(6)–
119.35(8)ꢁ] and the transoid angles [141.03(7)–
160.23(8)ꢁ]. Within the equatorial plane the Cd–N
Bond distances
Cd–N(3)
Cd–N(6)
2.3429(18)
2.4376(19)
2.271(2)
Cd–N(1)
Cd–N(4)
2.4486(18)
1.620(3)
2.301(2)
S(1)–C(1)
Cd–N(2)
Cd–N(5)
2.3157(19)
1.621(3)
1.161(3)
S(2)–C(2)
N(1)–C(1)
N(2)–C(2)
1.158(3)
Bond angles
N(3)–Cd–N(1)
N(5)–Cd–N(1)
N(3)–Cd–N(2)
N(5)–Cd–N(2)
N(1)–Cd–N(2)
N(5)–Cd–N(6)
N(3)–Cd–N(6)
N(1)–Cd–N(4)
N(6)–Cd–N(5)
N(3)–Cd–N(5)
N(2)–Cd–N(6)
N(2)–Cd–N(4)
N(5)–Cd–N(4)
N(3)–Cd–N(4)
N(6)–Cd–N(4)
N(1)–C(1)–S(1)
N(2)–C(2)–S(2)
94.37(8)
119.35(8)
100.70(8)
98.02(8)
90.63(9)
69.48(6)
98.44(6)
159.36(8)
82.97(7)
141.03(7)
160.23(8)
80.39(8)
80.53(6)
69.42(6)
111.25(6)
179.2(3)
179.2(3)
˚
distances are in the range [2.271(2)–2.4486(18) A], com-
parable to the corresponding values in similar systems
˚
[11]. Axial Cd–N distances [2.301(2)–2.4376(19) A] indi-
cate stronger coordination of the anionic isothiocyanate
over the neutral Schiff base [17]. The angles subtended
by the ligand around cadmium in the equatorial plane
shows a significant variation [69.42(6)–119.35(8)ꢁ] from
Fig. 3. Emission spectra of 3a: fluorescence (—), phosphorescence in
DMF glassy solution (Æ-Æ-Æ-Æ), solid state at 298 K (-----).
the ideal 90.00ꢁ. The trans N2–Cd–N6 angle has a value
[160.23(8)ꢁ], not close to the ideal value of 180.00ꢁ. The
angles N1–Cd–N3, N3–Cd–N4 and N4–Cd–N5 in the
equatorial plane with values 94.37(8)ꢁ, 69.42(6)ꢁ and
80.53(6)ꢁ are much less than the N1–Cd–N5 angle
[119.35(8)ꢁ], where N3, N6 belong to the two pyridine
ends of the Schiff base. Both the isothiocyanate ligands
Fig. 2. ORTEP plot of [Cd(bpbp)(NCS)2] (6b) with the atom
numbering scheme and 40% probability ellipsoids for all non-hydrogen
atoms.

1532
S.H. Rahaman et al. / Polyhedron 24 (2005) 1525–1532
(b) A.D. Garnovskii, A.L. Nivorozkin, V.L. Minkin, Coord.
Chem. Rev. 126 (1993) 1;
(c) V. Alexander, Chem. Rev. 95 (1995) 273.
are almost linear with exact 179.2(3)ꢁ angles. N–C
˚
˚
[1.158(3)–1.161(3) A] and C–S [1.620(3)–1.621(3) A]
bond lengths are as expected for N-coordination [11].
All the other bond lengths and angles on the ligand net-
work are close to the expected values [6a].
[7] (a) M.K. Saha, D.K. Dey, B. Samanta, A.J. Edwards, W. Clegg,
S. Mitra, J. Chem. Soc., Dalton Trans. (2003) 488;
(b) R. Paschke, S. Liebsch, C. Tschierske, M.A. Oakley, E. Sinn,
Inorg. Chem. 42 (2003) 8230.
[8] T.K. Karmakar, S.K. Chandra, J. Ribas, G. Mostafa, T.-H.
Lu, B.K. Ghosh, Chem. Commun. (2002) 2364, and references
therein.
4. Conclusion
[9] Sk.H. Rahaman, D. Bose, R. Ghosh, H.-K. Fun, B.K. Ghosh,
Indian J. Chem. A 43 (2004) 1901.
Twelve new complexes are prepared in combination
with tetradentate Schiff bases as blockers. In all cases
a chelation mode of the Schiff bases is noticeable. The
compounds are new example of luminous materials.
We are now investigating the congregation [8] behaviour
of related tetradentate N-donor Schiff bases with tailor-
ing on the propylenic arm as well as acidic proton(s) on
the ligand network towards the preparation of coordina-
tion polymers and supramers of varied molecular and
crystalline architectures, which may behave as better
luminous materials.
[10] (a) D. Bose, Sk.H. Rahaman, G. Mostafa, R.D. Bailey Walsh,
M.J. Zaworotko, B.K. Ghosh, Polyhedron 23 (2004) 545;
(b) J. Banerjee, D. Bose, Sk.H. Rahaman, M.J. Zaworotko, B.K.
Ghosh, Indian J. Chem. A 43 (2004) 1119.
[11] D. Bose, J. Banerjee, Sk.H. Rahaman, G. Mostafa, H.-K. Fun,
R.D. Bailey Walsh, M.J. Zaworotko, B.K. Ghosh, Polyhedron
23 (2004) 2045.
[12] (a) A.M. Golub, H. Kohler, V.V. Skopenko (Eds.), Chemistry of
Pseudohalides, Elsevier, Amsterdam, 1986;
(b) U. Ray, S. Jasimuddin, B.K. Ghosh, M. Monfort, J. Ribas,
G. Mostafa, T.-H. Lu, C. Sinha, Eur. J. Inorg. Chem. (2004) 250.
[13] (a) G. Wilkinson, Comprehensive Coordination Chemistry, vol. 5,
Pergamon Press, Oxford, 1987, p. 775;
(b) K.D. Karlin, J. Zubieta (Eds.), Copper Coordination Chem-
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Guilderland, NY, 1983.
5. Supplementary data
[14] (a) G. Mostafa, A. Mondal, A. Ghosh, I.R. Laskar, A.J. Welch,
N. Ray Chaudhuri, Acta Crystallogr., Sect. C 56 (2000) 146;
(b) B.G. Chand, U.S. Ray, G. Mostafa, T.-H. Lu, C.R. Sinha,
Polyhedron 23 (2004) 1669.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre Nos. 260089 for 3a and 260090 for 6b.
Copies of this information can be had free of charge
from The Director, CCDC, 12 Union Road, Cambridge,
CB2 IEZ, UK (fax: +44 1223 336 033; e-mail: deposit
@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
[15] (a) R. Wang, M. Hong, D. Yuan, Y. Sun, L. Xu, J. Luo, R. Cao,
A.S.C. Chan, Eur. J. Inorg. Chem. (2004) 37;
(b) X. Shi, G. Zhu, Q. Fang, G. Wu, G. Tian, R. Wang, D.
Zhang, M. Xue, S. Qiu, Eur. J. Inorg. Chem. (2004) 185.
[16] (a) C.-M. Liu, R.-G. Xiong, X.-Z. You, Y.-J. Liu, K.-K. Cheung,
Polyhedron 15 (1996) 4565;
(b) C.-M. Liu, R.-G. Xiong, X.-Z. You, H.-K. Fun, K. Sivaku-
mar, Polyhedron 16 (1997) 119;
Acknowledgement
(c) M.S. Ray, R. Bhattacharya, S. Chaudhuri, L. Righi, G.
Bocelli, G. Mukhopadhyay, A. Ghosh, Polyhedron 22 (2003)
617.
Financial support from the DST and CSIR, New
Delhi, India is gratefully acknowledged.
[17] A. Ja¨ntti, M. Wagner, M. Wagner, R. Suontamo, E. Kolehmai-
nen, K. Rissanen, Eur. J. Inorg. Chem. (1998) 1555.
[18] C.H. Hamann, A. Hammet, W. Vielstich, Electrochemistry,
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