A study on copper(II)-Schiff base-azide coordination complexes: Synthesis, X-ray structure and luminescence properties of [Cu(L)(N3)]X (L = Schiff bases; X = ClO4, PF6)

Article abstract of DOI:10.1016/j.poly.2005.06.028

Two Schiff bases N,N′-(bis(pyridin-2-yl)benzylidene)propane-1,3- diamine (pbpd) and N,N′-(bis(pyridin-2-yl)formylidene)butane-1,4-diamine (pfbd) have been prepared and used to synthesize copper(II) complexes. Four complexes of the type [Cu(L)(N₃)]X (1-4) [L = pbpd; X = ClO ₄ (1); L = pbpd; X = PF₆ (2); L = pfbd; X = ClO ₄ (3); L = pfbd; X = PF₆ (4)] have been synthesized and characterized on the basis of microanalytical, spectroscopic, magnetic, electrochemical, luminescence and other physicochemical properties. Two representative complexes of the series, 2 and 3, have been characterized by single crystal X-ray diffraction measurements which reveal that in each complex the copper(II) ion assumes a distorted trigonal bipyramidal environment through coordination of the metal centre by two pyridine N atoms and two imine N atoms of the Schiff base with the fifth position occupied by a N atom of a terminal N3-. They display intraligand ¹(π-π*) fluorescence at room temperature and intraligand ³(π-π*) phosphorescence in glassy solutions (MeOH at 77 K). A band (492 nm) observed for the complexes in their solid-state emission spectra is an excimeric emission arising due to an aromatic π-π interaction. Electrochemical electron transfer study reveals Cu^II-Cu^I reduction in methanolic solutions.

Full text of DOI:10.1016/j.poly.2005.06.028

Polyhedron 24 (2005) 3091–3097
www.elsevier.com/locate/poly
A study on copper(II)-Schiff base-azide coordination
complexes: Synthesis, X-ray structure and luminescence properties
of [Cu(L)(N3)]X (L = Schiff bases; X = ClO4, PF6)
a,
b
a,
*
Sk Hafijur Rahaman *, Hoong-Kun Fun , Barindra Kumar Ghosh
a
Department of Chemistry, The University of Burdwan, Golapbag, Rajbati, Burdwan 713104, India
X-ray Crystallography Unit, School of Physics, University Sains Malaysia, 11800 USM, Penang, Malaysia
b
Received 6 April 2005; accepted 13 June 2005
Available online 15 August 2005
Abstract
Two Schiff bases N,N0-(bis(pyridin-2-yl)benzylidene)propane-1,3-diamine (pbpd) and N,N0-(bis(pyridin-2-yl)formylidene)butane-
1,4-diamine (pfbd) have been prepared and used to synthesize copper(II) complexes. Four complexes of the type [Cu(L)(N3)]X (1–4)
[L = pbpd; X = ClO4 (1); L = pbpd; X = PF6 (2); L = pfbd; X = ClO4 (3); L = pfbd; X = PF6 (4)] have been synthesized and char-
acterized on the basis of microanalytical, spectroscopic, magnetic, electrochemical, luminescence and other physicochemical prop-
erties. Two representative complexes of the series, 2 and 3, have been characterized by single crystal X-ray diffraction measurements
which reveal that in each complex the copper(II) ion assumes a distorted trigonal bipyramidal environment through coordination of
the metal centre by two pyridine N atoms and two imine N atoms of the Schiff base with the fifth position occupied by a N atom of a
1
3
ꢀ
terminal N3 . They display intraligand (p–p*) fluorescence at room temperature and intraligand (p–p*) phosphorescence in glassy
solutions (MeOH at 77 K). A band (492 nm) observed for the complexes in their solid-state emission spectra is an excimeric emission
arising due to an aromatic p–p interaction. Electrochemical electron transfer study reveals CuII–CuI reduction in methanolic
solutions.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Copper (II) azide; Schiff bases; X-ray structure; Luminescence spectra
1. Introduction
units may afford arrays of new architectures [6]. Pseud-
ohalides are versatile bridging ligands [7,8]; of them the
flexidentate azide [8] ion is the most important one. Dif-
ferent organic blockers with stereochemical control are
used to vary nuclearity through available coordination
sites in combination with suitable metal ions and
bridges. The chemistry of copper(II) azides is well docu-
mented [9–12] through structural and magneto-structural
characterization of a plethora of mono-, di- and polynu-
clear complexes of different dimensionalities. The main
focus is to prepare magnetic materials [12] and to model
natural copper proteins and their derivatives [13]. Schiff
bases have recently [14,15] been the focus of coordina-
tion chemists as versatile organic blockers because of
Stupendous progress has been made recently in pre-
paring inorganic–organic hybrid coordination polymers
with novel architectures [1] and with different functional
features [2]. Several synthetic strategies [3–5] are
adopted to make such polymers; of which self-assembly
[3] is the most important one. One-pot synthesis through
the use of metal ions, blocking ligands and bridging
*
Corresponding authors. 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.2005.06.028

3092
S.H. Rahaman et al. / Polyhedron 24 (2005) 3091–3097
used as received. The synthetic reactions and work-up
were done in the open air.
Caution! Perchlorate and azido compounds of metal
ions are potentially explosive especially in the presence
of organic ligands. Only a small amount of the material
should be prepared and it should be handled with care.
2.2. Physical measurements
Scheme 1.
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
made with a JASCO model V-530 UV–Vis spectropho-
tometer and Hitachi model F-4010 spectrofluorimeter,
respectively. Time-resolved fluorescence measurements
were carried out using a time-correlated single photon
counting (TCSPC) spectrometer, Edinburgh Instru-
ments, 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, respectively, used
as the excitation source and the fluorescence detector.
Magnetic susceptibilities were measured with a PAR
155 vibrating sample magnetometer. Electrochemical
measurements were carried out with the use of a com-
puter controlled EG&G PARC VersaStat model 270
electrochemical instrument using a platinum disk work-
ing electrode as described elsewhere [17]. The solutions
were IR compensated and the results were collected at
25 ꢁC. The following parameters and relations were
their preparative accessibilities, structural varieties and
varied denticities. Self-assembly [3] of a metal ion,
blocking ligand and bridging unit is the most important
way to make different sets of complexes. With the neu-
tral tetradentate N-donor Schiff bases L [L = N,N0-
(bis(pyridin-2-yl)benzylidene)propane-1,3-diamine-
(pbpd) or N,N0-(bis(pyridin-2-yl)formylidene)butane-
1,4-diamine (pfbd)] and using different mole ratios of
metal ion:Schiff base:azide, mono-, di- and polynuclear
complexes may be produced. A 1:1:2 molar ratio should
result in a mononuclear neutral compound [Cu(L)(N3)2]
and a 1:1:1 ratio should yield dicationic dinuclear
2þ
½CuðLÞðN3Þꢁ2
or polycationic polymer ½CuðLÞ-
nþ
ðN3Þꢁn compounds. However, with both ratios a pen-
tacoordinated mononuclear cationic complex of the type
[Cu(L)(N3)]+ is afforded. In this work, we report the
synthetic details and luminescence, magnetic and some
physicochemical properties of these mononuclear com-
plexes of the type [Cu(L)(N3)]X (1–4) [L = pbpd;
X = ClO4 (1); L = pbpd; X = PF6 (2); L = pfbd;
X = ClO4 (3); L = pfbd; X = PF6 (4)]. An X-ray crystal-
lographic study has been made for 2 and 3 to define the
coordination sphere (Scheme 1).
2. Experimental
used: scan rate (v), 50 mV sꢀ1
; formal potential
Eꢂ = 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.
2.1. Materials
High purity pyridine-2-carboxaldehyde (Lancester,
UK), 2-benzoylpyridine (Lancester, UK), propane-1,3-
diamine (Lancester, UK), butane-1,4-diamine (Lanc-
ester, UK), copper nitrate tetrahydrate (E. Merck, India),
sodium azide (Aldrich, USA) and potassium hexafluoro-
phosphate (Fluka, Germany) were purchased from the
respective concerns and were used as received. Copper
perchlorate hexahydrate was prepared by treatment of
copper 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 pres-
ervation in a desiccator containing concentrated sulfuric
acid (E. Merck, India) for subsequent use. Purification
of solvent (MeOH) and preparation of supporting elec-
trolyte ([Et4N][ClO4]) for electrochemical work were
executed following a published procedure [16]. All
other chemicals and solvents were AR grade and were
2.3. Preparation of ligands
The Schiff base blockers were prepared following a
reported [15] procedure. 2-Benzoyl-pyridine/pyridine-2-
carboxaldehyde was condensed with the respective
amine in a 2:1 molar ratio. Details are described below.
2.3.1. N,N0-(bis(pyridin-2-yl)benzylidene)propane-1,3-
diamine (pbpd)
Propane-1,3-diamine (0.074 g, 1 mmol) was refluxed
with 2-benzoyl pyridine (0.366 g, 2 mmol) in dehydrated
alcohol (25 cm3) for 12 h. The tetradentate ligand was
isolated after evaporating the solvent and purified from
alcohol. The product is isolated as a brown semi-solid

S.H. Rahaman et al. / Polyhedron 24 (2005) 3091–3097
3093
mass after being dried in vacuo over P4O10 for subse-
quent use. Yield, 0.425 g (78%). Anal. Calc. C27H24N4:
C, 80.16; H, 5.98; N, 13.85. Found: C, 80.09; H, 5.92;
1 mmol) in MeOH–H2O (2:1) mixture in a better yield
0.34 g (75%). Anal. Calc. for C27H24N7F6PCu (2): C,
49.51; H, 3.69; N, 14.96. Found: C, 49.51; H, 3.66; N,
14.98%. IR (KBr, cmꢀ1): m(C@N) 1635, 1593; (PF6)
820, 540; m(N3) 2073. KM (MeOH, Xꢀ1 cm2 molꢀ1):
120; UV–Vis (MeOH; k nm): 718, 404. Eꢂ298, V (DEp,
mV): 0.11 (100).
N, 13.92%. IR: m(C@N) 1590 cmꢀ1; UV–Vis, kmax
:
375 nm.
2.3.2. N,N0-(bis(pyridin-2-yl)formylidene)butane-1,4-
diamine (pfbd)
Pyridine-2-carboxaldehyde (0.214 g, 2 mmol) was re-
fluxed with butane-1,4-diamine (0.088 g, 1 mmol) in
dehydrated alcohol. After 10 h, the reaction solution
was evaporated under reduced pressure to give a gummy
mass, which was dried and stored in vacuo over CaCl2
for subsequent use. Yield, 0.242 g (80%). Anal. Calc.
C16H18N4: C, 72.2; H, 3.0; N, 21.0. Found: C, 72.4; H,
2.4.3. [Cu(pfbd)(N3)]ClO4 (3)
Solid pfbd (0.418 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. To this resulting solution,
a methanolic solution of sodium azide (0.065 g, 1 mmol)
was added. The mixture was filtered and the supernatant
liquid was kept in air for slow evaporation. After 7 days
3 was separated, washed with toluene and dried in vacuo
over silica gel indicator. Yield, 0.09 g (70%). Anal. Calc.
for C16H18N7O4ClCu (3): C, 40.77; H, 3.85; N,
20.80.Found: C, 40.75; H, 3.86; N, 20.85%. IR (KBr,
cmꢀ1): m(C@N) 1639, 1590; m(ClO4) 1082, 620; m(N3)
2072. KM (MeOH, Xꢀ1 cm2 molꢀ1): 120; UV–Vis
(MeOH; k nm): 720, 406. Eꢂ298, V (DEp, mV): 0.14 (110).
3.1; N, 21.3%. IR: m(C@N) 1590 cmꢀ1; UV–Vis, kmax
:
375 nm.
2.4. Preparation of the complexes
Mononuclear complexes 1and 3 were prepared from
the perchlorate salt of copper(II) using the same mole
ratio (1:1:1) of metal, pbpd/pfbd and azide. Complexes
2 and 4 were prepared using a 1:1:1:1 ratio of copper
(II) nitrate, pbpd/pfbd, sodium azide and potassium
hexafluorophosphate; these were also isolated by
metathesis of 1 and 3, respectively, with potassium hexa-
fluorophosphate. The quality of compound 2 was poor
compared to the other complexes. The typical syntheses
are described below.
2.4.4. [Cu(pfbd)(N3)]PF6 (4)
Complex 4 was prepared using the same procedure
and reaction stoichiometry as in 2 except that pfbd in-
stead of pbpd was used as the organic ligand. Yield,
0.16 g (73%).This was also prepared by metathesis of 3
(0.51 g, 1 mmol) with KPF6 (0.18 g, 1 mmol) in a
MeOH–H2O (2:1) mixture in a higher yield 0.87 g,
(80%). Anal. Calc. for C16H18N7F6PCu (4): C, 37.18;
H, 3.51; N, 18.97. Found: C, 37.19; H, 3.53; N,
18.95%. IR (KBr, cmꢀ1): m(C@N) 1637, 1595; m(PF6)
820, 542; m(N3) 2073. KM (MeOH, Xꢀ1 cm2 molꢀ1):
130; UV–Vis (MeOH; k nm): 717, 405. Eꢂ298, V (DEp,
mV): 0.13 (110).
2.4.1. [Cu(pbpd)(N3)]ClO4 (1)
A methanolic solution (5 ml) of pbpd (0.40 g,
1 mmol) was added dropwise to a solution of Cu-
(ClO4)2 Æ 6H2O (0.37 g, 1 mmol) in the same solvent
(10 cm3). NaN3 (0.065 g, 1 mmol) in warm MeOH
(5 cm3) was added slowly to it. The green solution was
filtered and the supernatant liquid was kept in air for
slow evaporation. After a few days the desired complex
that separated was washed with toluene and dried in va-
cuo over silica gel indicator. Yield, 0.12 g (70%). Anal.
Calc. for C27H24N7O4ClCu (1): C, 53.20; H, 3.97; N,
16.08. Found: C, 53.21; H, 3.95; N, 16.05%. IR (KBr,
cmꢀ1): m(C@N) 1637, 1592; m(ClO4) 1080, 622; m(N3)
2072. KM (MeOH, Xꢀ1 cm2 molꢀ1): 130; UV–Vis
(MeOH; k nm): 717, 406. Eꢂ298, V (DEp, mV): 0.11 (100).
2.5. X-ray diffraction study
Single crystals of the title complexes were obtained by
slow evaporation of a methanolic solution of the reac-
tion mixtures at room temperature (298 K). Suitable col-
ourless crystals were mounted on a Siemens SMART
CCD diffractometer equipped with a graphite-mono-
˚
chromator and Mo Ka (k = 0.71073 A) radiation. Dif-
fraction data were measured using the / and x-scan
method. Crystal data, data collection parameters and
the results of analyses can be found in Table 1. The
intensity data were corrected for Lorentz and polariza-
tion effects and an empirical absorption correction was
employed using the SAINT [18] and SADABS [19] program
for crystals 2and 3, respectively. The structures were
solved and refined used SHELXTL [20] and the refinement
is based on |F|2. All non-hydrogen atoms were refined
with anisotropic displacement parameters, whereas
hydrogen atoms were placed in calculated positions
2.4.2. [Cu(pbpd)(N3)]PF6 (2)
Cu(NO3)2 Æ 4H2O (0.24 g, 1 mmol) was dissolved in
MeOH (10 cm3). To this pbpd (0.40 g, 1 mmol) dis-
solved in same solvent (5 cm3) was added slowly, fol-
lowed by NaN3 (0.065 g, 1 mmol). KPF6 (0.18 g,
1 mmol) was added at a time. The final solution was fil-
tered, kept for slow evaporation and processed as in 1 to
yield pure 2. Yield, 0.20 g (72%). This was also prepared
by metathesis of 1 (0.60 g, 1 mmol) with KPF6 (0.18 g,

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S.H. Rahaman et al. / Polyhedron 24 (2005) 3091–3097
Table 1
Crystal data and structure refinement parameters for 2 and 3
2
3
Empirical formula
Formula weight
Temperature (K)
C27H24N7PF6Cu
655.04
213(2)
C16H18N7O4ClCu
471.36
213(2)
˚
Wavelength (A)
0.71073
0.71073
Crystal system, space group
monoclinic, Cc
22.3993(3)
12.2380(2)
monoclinic, P21/c
12.1272(4)
15.8851(6)
˚
a (A)
˚
b (A)
˚
c (A)
10.3083(1)
10.8302(4)
b (ꢁ)
V (A )
104.707(3)
2733.16(6)
4
1.592
0.931
1332
0.34 · 0.32 · 0.22
2.62–24.77
113.4780(10)
1913.63(12)
4
1.636
1.321
3
˚
Z
Dc (Mg mꢀ3
)
l (mmꢀ1
F(000)
)
964
Crystal size (mm3)
0.44 · 0.18 · 0.14
2.49–28.28
h ranges (ꢁ)
h/k/l
ꢀ26, 25/ꢀ14, 14/ꢀ12, 11
ꢀ9, 16/ꢀ16, 21/ꢀ14, 10
Reflections collected
Independent reflections
Completeness to theta
Absorption correction
Tmax and Tmin
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
6364
11371
3330 [Rint = 0.0624]
99.4% (24.77ꢁ)
numerical
0.8214 and 0.7425
3330/2/379
4647 [Rint = 0.0516]
97.7% (28.29ꢁ)
numerical
0.8366 and 0.5941
4647/0/262
0.984
0.916
R1 = 0.0643, wR2 = 0.1579
R1 = 0.0855, wR2 = 0.1824
0.657 and ꢀ1.365
R1 = 0.0469, wR2 = 0.1045
R1 = 0.0702, wR2 = 0.1118
1.037 and ꢀ1.070
ꢀ3
˚
Largest peak and hole (e A
)
where possible and given isotropic U values 1.2 times
that of the atom to which they are bonded. All crystal-
lographic calculations were conducted with SHELXL-97
[21], ORTEP-3 [22] and PLATON programs [23].
isolated. All the four complexes were characterized by
elemental analysis, solution electrical conductivity, mag-
netic susceptibility, IR, UV–Vis, reflectance spectra and
electrochemistry. The results are consistent with the pro-
posed mononuclear formulation. The air-stable mois-
ture-insensitive complexes are powders, soluble in a
range of common organic solvents such as methanol,
ethanol, dichloromethane, acetonitrile, but are insoluble
in water. In methanol solutions they behave [24] as 1:1
electrolytes as reflected in their KM values. Room-
temperature solid-phase magnetic susceptibility mea-
surements show that the copper (II) complexes have a
moment close to the spin-only value (S = 1/2),
1.73 BM, expected from discrete and a magnetically
non-coupled mononuclear 3d9 ion.
3. Results and discussion
3.1. Synthesis and formulation
The pentacoordinated mononuclear complex
[Cu(pbpd)(N3)]ClO4 (1) is initially formed in an MeOH
solution containing a 1:1:2 mixture of Cu(ClO4)2 Æ
6H2O, pbpd and NaN3, a reactant ratio expected to
yield
a mononuclear species of the composition
[Cu(pbpd)(N3)2]n. However, microanalyses showed a
1:1:1 ratio of metal, blocking ligand and the pseudoha-
lide, and in the IR spectrum the presence of perchlorate
bands was noticed. A reactant ratio corresponding to
the product stoichiometry afforded better yields of 1.
In an effort to prepare [Cu(pbpd)(N3)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 pseudohalide
produced a gummy mass of indefinite composition;
however, addition of KPF6 to the green reaction solu-
tion yielded shining microcrystalline powder of 2. The
latter was also obtainable from metathesis of 1 with
KPF6. A change of the ligand from pbpd to pfbd
showed similar behaviour and compounds 3 and 4 were
In the IR spectra, the point of interest is the band due
to azide at ꢃ2070 cmꢀ1. The presence of ionic perchlo-
rate bands at ꢃ1090 and ꢃ620 cmꢀ1 and ionic hexaflu-
orophosphate at ꢃ840 and ꢃ540 cmꢀ1 is routinely
noticed. The m(C@N) stretching vibrations of the metal
bound Schiff bases are seen at ꢃ1635 and ꢃ1590 cmꢀ1
[25]. All other characteristic ligand vibrations are seen
in the 1600–600 cmꢀ1 range. The solutions of 1–4 in
MeOH are dark green and exhibit absorption in the
400–720 range [1: k, 717, 406 nm; 2: k, 718, 404 nm; 3:
k, 720, 406 nm; 4: k, 717, 405 nm]. The transition
700 nm corresponds to a d-d transition of the copper(II)
moiety and the band around 400 nm for an intramolec-
ular (n ! p*/p ! p*) charge transfer transition [26].

S.H. Rahaman et al. / Polyhedron 24 (2005) 3091–3097
3095
Reflectance [1: k, 715, 400 nm; 2: k, 715, 408 nm; 3: k,
716, 404 nm; 4: k, 716, 402 nm] in nujol and electronic
spectra for each complex in MeOH solutions are akin
reflecting similar gross structure and electronic structure
in the solid state and in solution of each compound.
3.2. Electrochemistry
The 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 shown as follows:
1þ
½CuIIðLÞðN3Þꢁ þ e ! ½CuIðLÞðN3Þꢁ
ð1Þ
The electrode process in the CV is reproducible in the
potential range 0.08 to ꢀ0.08 V with no trace of decom-
position as reflected in a smooth cyclic voltammogram.
The one-electron stoichiometry of couple 1 was con-
firmed from the comparison of current height with that
of a standard [27] copper(II)–copper (I) couple, since at-
tempted coulometry at potentials more cathodic than
Epc gave a continuous coulomb count due to some
unidentified side reactions [28]. The similar pattern in
electron transfer behaviour of all the complexes at about
same potential once again corroborates the closely sim-
ilar structure of the cationic units.
Fig. 1. ORTEP representation of [Cu(pbpd)(N3)]PF6 (2) with the
atom labelling scheme and 50% probability ellipsoids for all non-
hydrogen atoms.
3.3. X-ray structure
In order to define the coordination sphere conclu-
sively, a single-crystal X-ray diffraction study was made.
An ORTEP diagram with the atom numbering
scheme of the mononuclear units in 2 and 3 are shown
in Figs. 1 and 2. Selected interatomic bond lengths
and bond angles are listed in Table 2. The crystal lattice
consists of [Cu(pbpd)(N3)]+ cations and PF anions for
ꢀ
6
2 and [Cu(pfbd)(N3)]+ cations and ClO4 anions for 3.
ꢀ
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 ligated by two pyridine nitro-
gens (N1, N4) and two imine nitrogens (N2, N3), and
one terminal azide nitrogen (N5). The equatorial posi-
tions are occupied by one imine nitrogen (N3), one pyr-
idine nitrogen (N1) and the azide nitrogen (N5) while
the axial positions are occupied by the remaining imine
(N2) 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 defining
angles (90degr/120ꢁ) formed at the metal centre. The
propylinic/butylenic part of the Schiff base N2–C13–
C14–C15–N3/N3–C10–C9–C8–C7–N2 is to some extent
puckered (Figs. 1 and 2). The equatorial Cu–N distances
Fig. 2. ORTEP diagram of [Cu(pfbd)(N3)]ClO4 (3) with the atom
labelling scheme and 50% probability ellipsoids for all non-hydrogen
atoms.
[101.57(10)–144.53(10) ꢁ] (3) show significant variations.
˚
The axial Cu–N distances [Cu1–N1 1.986(8) A, Cu1–N3
˚
˚
˚
1.977(8) A] in 2 and [Cu1–N1 1.997(2) A, Cu1–N3
1.991(2) A] in 3 are however close. The three bite angles
N4–Cu1–N3, N3–Cu1–N2 and N2–Cu1–N1 are
78.8(3)ꢁ, 91.4(3)ꢁ and 81.30(3)ꢁ in 2 and 79.16(9)ꢁ,
96.17(9)ꢁ and 81.33(9)ꢁ in 3. The larger bite in
N3–Cu1–N2 arises from the six- and seven-membered
puckered loop formed from the propylenic and buty-
lenic arm for 2 and 3, respectively, and it is of a similar
value to the non-bite angle [N1–Cu1–N4] 97.35(9)ꢁ for
complex 3, but there is significant variation
[101.00(3)ꢁ] for complex 2. The axial bond angle N1–
˚
˚
[2.003(7)–2.121(8) A] (2) and [1.992(2)–2.198(2) A] (3) as
well as the bond angles [95.1(3)–134.4(3)ꢁ] (2) and

3096
S.H. Rahaman et al. / Polyhedron 24 (2005) 3091–3097
Table 2
Table 3
˚
Selected bond distances (A) and angles (ꢁ) for 2 and 3
Photophysical data for 1–4
Sample Absorption, Emission, k (nm)
k (nm)
2
3
Lifetime
(ns)
˚
Bond distances (A)
Fluor-
Phosph-
Solid
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–N(3)
Cu(1)–N(4)
Cu(1)–N(5)
N(5)–N(6)
N(6)–N(7)
1.986(8)
2.003(7)
1.977(8)
2.121(8)
2.074(9)
1.198(13)
1.124(14)
1.997(2)
2.015(2)
1.991(2)
2.198(2)
1.992(2)
1.191(3)
1.160(3)
escencea orescenceb statec
Pbpd/pfbd 375
470
475
476
475
475
525
525
525
525
525
486
492
492
492
492
2.58
2.63
2.59
2.59
2.62
1
2
3
4
406
404
406
404
a
b
c
In MeOH at room temperature (298 K).
In MeOH at 77 K.
At room temperature.
Bond angles (ꢁ)
N(5)–Cu(1)–N(4)
N(5)–Cu(1)–N(2)
N(4)–Cu(1)–N(2)
N(2)–Cu(1)–N(l)
N(4)–Cu(1)–N(1)
N(5)–Cu(1)–N(3)
N(4)–Cu(1)–N(3)
N(2)–Cu(1)–N(3)
N(5)–Cu(1)–N(1)
N(3)–Cu(1)–N(1)
N(5)–N(6)–N(7)
95.10(3)
134.40(3)
130.40(3)
81.30(3)
101.00(3)
95.50(3)
78.80(3)
91.40(3)
94.20(3)
170.30(3)
179.00(13)
101.57(10)
144.53(10)
113.73(8)
81.33(9)
97.35(9)
93.64(9)
79.16(9)
96.17(9)
91.17(10)
174.54(9)
177.1(3)
Cu1–N3 [170.3(3)ꢁ] (2) and [174.54(9)ꢁ] (3) deviates
slightly from the ideal value (180ꢁ). The sum (359.9ꢁ/
359.83ꢁ) (2/3) of the equatorial angles are very close to
360.00ꢁ; so the atoms N2, N4, N5 and Cu1 are almost
in a same plane. In the terminal azide ligand, the N5–
˚
N6 distance 1.198(13) and 1.191(3) A is longer than
Fig. 3. Emission spectra of 2: UV in MeOH solution at 298 K
(ꢅ ꢅ ꢅ ꢅ ꢅ ꢅ ꢅ ꢅ ꢅ), fluorescence (——), phosphorescence in MeOH glassy
solution (ꢅ-ꢅ-ꢅ-ꢅ), solid state at 298 K (–––).
˚
the N6–N7 length [1.124(14) and 1.160(3) A for 2 and
3, respectively, and the values are very similar to the
ones previously reported [29]. The azide is coordinated
in a linear fashion as seen from its N5–N6–N7 angle
179.0(13)ꢁ and 177.1(3)ꢁ for 2 and 3, respectively.
The Director, CCDC, 12 Union Road, Cambridge, CB2
IEZ, UK (fax: +44 1223 336033; e-mail: deposit@ccdc.
cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
3.4. Luminescence studies
Acknowledgement
The spectroscopic data are listed in Table 3. The com-
plexes with pbpd and pfbd feature two intense absorp-
tions at ca. 405 nm which are assigned to intraligand
p–p* transitions. The emission energy of the complexes
in MeOH solutions at 298 K is almost same
(kmax ꢄ 475 nm) and is assignable to intraligand fluores-
cence [30,31]. The lifetimes of the fluorescence of 1, 2, 3
and 4 are 2.63, 2.59, 2.59 and 2.62 ns, respectively. In
glassy solutions (MeOH at 77 K) both fluorescence and
3(p–p*) phosphorescence is observed at 525 nm. In solid
state, they show a distinct emission band at 492 nm, dif-
fering from their fluorescence spectra in MeOH (Fig. 3).
Financial support from the DST and CSIR, New
Delhi, India is gratefully acknowledged.
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