Polymeric polymorphs and a monomer of pseudohalide incorporated Cu(II) complexes of 2,4-dichlorido-6-((2-(dimethylamino)ethylimino)methyl)phenol]: Crystal structures and spectroscopic behavior

Article abstract of DOI:10.1016/j.ica.2016.01.008

In the present investigation, copper(II) complexes of tridentate 2,4-dichlorido-6-((2-(dimethylamino)ethylimino)methyl)phenol] (HL) Schiff base system incorporating azido [Cu(L)(N₃)]_n(1a and 1b) and cyanato groups [Cu(L)(NCO)] (2) are prepared and characterized by elemental analysis, IR, UV–Vis and single crystal X-ray diffraction studies. While the polymeric polymorphs, 1a and 1b have a square-pyramidal geometry for the basic unit, complex 2 exhibits square planar topology. The polymorphs are one-dimensional helical coordination polymers with azido group in single asymmetric equatorial–axial end-on bridging mode. The interestingly different combinations of intermolecular interactions have resulted in polymorphs 1a and 1b. Based on the angular preference, intermolecular distance and the size of Cl atom, type I halogen interactions which is rather rarely observed is also discussed. Solvent effect on the charge-transfer bands and d–d bands were analyzed and the former exhibits negative solvatochromic effect while latter a positive effect with increasing polarity of solvents. Solid and solution state optical emission properties are analyzed. All the copper complexes emit in the blue region. Thermal analyses have been performed in order to understand the thermal decomposition pattern of the complexes. Spin Hamiltonian and bonding parameters have been calculated from EPR analysis. The g values, calculated for the complexes 1a, 1b in frozen DMF, indicate the presence of the unpaired electron in the d_x²-y²orbital consistent with a square pyramidal topology whereas that of complex 2 corresponds to a rhombic symmetry.

Full text of DOI:10.1016/j.ica.2016.01.008

Inorganica Chimica Acta 443 (2016) 251–266
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Polymeric polymorphs and a monomer of pseudohalide incorporated
Cu(II) complexes of 2,4-dichlorido-6-((2-(dimethylamino)ethylimino)
methyl)phenol]: Crystal structures and spectroscopic behavior
N. Aiswarya a, M. Sithambaresan b, S.S. Sreejith a, Seik Weng Ng c, M.R. Prathapachandra Kurup a,
⇑
a Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682 022, Kerala, India
b Department of Chemistry, Faculty of Science, Eastern University, Sri Lanka, Chenkalady, Sri Lanka
c Chemistry Department, King Abdulaziz University, PO Box 80203, Jeddah, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present investigation, copper(II) complexes of tridentate 2,4-dichlorido-6-((2-(dimethylamino)
ethylimino)methyl)phenol] (HL) Schiff base system incorporating azido [Cu(L)(N3)]n (1a and 1b) and cya-
nato groups [Cu(L)(NCO)] (2) are prepared and characterized by elemental analysis, IR, UV–Vis and single
crystal X-ray diffraction studies. While the polymeric polymorphs, 1a and 1b have a square-pyramidal
geometry for the basic unit, complex 2 exhibits square planar topology. The polymorphs are one-
dimensional helical coordination polymers with azido group in single asymmetric equatorial–axial
end-on bridging mode. The interestingly different combinations of intermolecular interactions have
resulted in polymorphs 1a and 1b. Based on the angular preference, intermolecular distance and the size
of Cl atom, type I halogen interactions which is rather rarely observed is also discussed. Solvent effect on
the charge-transfer bands and d–d bands were analyzed and the former exhibits negative solvatochromic
effect while latter a positive effect with increasing polarity of solvents.
Received 26 October 2015
Received in revised form 21 December 2015
Accepted 6 January 2016
Available online 11 January 2016
Keywords:
Polymeric polymorphs
Azido bridges
Crystal structures
Halogen interaction
Solvatochromism
Solid and solution state optical emission properties are analyzed. All the copper complexes emit in the
blue region. Thermal analyses have been performed in order to understand the thermal decomposition
pattern of the complexes. Spin Hamiltonian and bonding parameters have been calculated from EPR
analysis. The g values, calculated for the complexes 1a, 1b in frozen DMF, indicate the presence of the
unpaired electron in the dx2
orbital consistent with a square pyramidal topology whereas that of
ꢀy2
complex 2 corresponds to a rhombic symmetry.
Ó 2016 Elsevier B.V. All rights reserved.
1. Introduction
N2O donor tridentate Schiff bases (N-substituted diamines with
salicylaldehyde or its derivatives), coligands are employed to gen-
erate structures of variable composition apart from satisfying the
coordination number [8,9]. Among the various coligands known,
pseudohalides (azido, cyanato, thiocyanato, dicyanamido) deserve
special attention on account of their versatile modes of binding.
Of them, azido group is the most widely studied because of its flex-
ible coordinating ability. The family of reported metal-azido sys-
tems consist of discrete mono-/di-/oligonuclear complexes as well
as 1-D, 2-D and 3-D coordination polymers [10–16]. Of the various
transition metals, the chemistry of polynuclear copper(II) com-
plexes is getting more importance now-a-days because of its rele-
vance to various metallo-proteins and metallo-enzymes [17–21].
Structure–property correlation studies are found to be interest-
ing in case of metallo-pseudohalide systems. For example, some of
the factors governing the magnetic properties of such exchange-
coupled systems are (a) type of bridge, metrical parameters like
The current scenario of coordination chemistry is witnessing the
exploitation of coordination bonds and noncovalent interactions to
generate self-assemblies of various dimensions having not only
esthetic values but also countless applications and that paved
way for supramolecular chemistry/crystal engineering. The struc-
tural variety, interesting properties and potential applications in
the fields of catalysis [1], luminescence [2], gas adsorption [3],
and magnetic materials [4,5] attracts researchers to this area. Most
of such fascinating work employs Schiff bases obtained by the con-
densation of an amine and a carbonyl compound. The use of diami-
nes in the synthesis of high-nuclearity complexes utilizes the
bridging capacity of phenoxo atoms [6,7]. Whereas in the case of
⇑
Corresponding author. Tel.: +91 484 2862423; fax: +91 484 2575804.
E-mail addresses: mrpcusat@gmail.com, mrp_k@yahoo.com (M.R.P. Kurup).
http://dx.doi.org/10.1016/j.ica.2016.01.008
0020-1693/Ó 2016 Elsevier B.V. All rights reserved.

252
N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
the (b) metal–N–metal bridge angle (c) metal–N–N–metal torsion
angle, metal–N–N angle and metal–N distance [13–17,22–24]. On
the other hand, even the prediction of the nature and magnitude
of the exchange interaction for some types of systems, e.g., com-
plexes having an equatorial–axial l1,1-azido bridge [25–29] is dif-
ficult and that makes the field evergreen.
2.2.2. Synthesis of [Cu(L)(N3)]n (1b) [HL = 2,4-dichloro-6-((2-
(dimethylamino)ethylimino)methyl)phenol]
Complex 1b was prepared by a method similar to that of com-
plex 1a except that copper(II) sulfate pentahydrate (0.249 g,
1 mmol) was added to the hot reaction mixture instead of copper
(II) chloride dihydrate. To the resulting deep green solution,
sodium azide (0.130 g, 2 mmol) in a MeOH/H2O (1:9) mixture
was added dropwise with continuous stirring and filtered. Suitable
single crystals for structure determination by X-ray diffraction
were obtained by slow evaporation of the mother liquor in air.
Complex 1b was found to be a polymorph of 1a. M.P. 234.5 °C.
Yield: 0.2123 g (66%). Anal. Calc. for C11H13Cl2CuN5O (365.70):
C, 36.13; H, 3.58; N, 19.15. Found: C, 36.09; H, 3.55; N, 19.10%.
Though several factors like the nature of metal ion, solvent,
blocking organic ligand, metal:pseudohalide ratios etc. can be sta-
ted as those that control the nature of the final product, no gener-
alization can be arrived at and therefore in many cases called
‘Serendipitous self assembly’ [30]. Although voluminous research
work has been done in this arena, still researchers find it difficult
to control the composition and nuclearity of the final product
and this ambiguity intrigues us to pursue more.
Since not much of experimental work highlighting the halogen
interaction is known, our group employed halogen substituted
salicylaldehydes to explore more on halogen interactions [31], a
new tool for crystal engineers and to discuss the role of various
other weak interactions in stabilizing a specific crystal system.
Herein, we have used the N2O tridentate Schiff base derived from
refluxing N,N-substituted ethylene diamine and 3,5-dichlorosalicy-
laldehyde along with azido and cyanato ligands. We have
UV–Vis, kmax/nm (
237 (31.27).
Magnetic moment:
e
max/103 Mꢀ1 cmꢀ1) (acetonitrile): 376 (8.12),
l
= 1.85 B.M.
2.2.3. Synthesis of [Cu(L)(NCO)] (2) [HL = 2,4-dichloro-6-((2-
(dimethylamino)ethylimino)methyl)phenol]
Complex 2 was prepared by a similar method except for the
pseudohalide used. Here, sodium cyanate (0.130 g, 2 mmol) in a
MeOH/H2O mixture was added dropwise and the resulting solution
further stirred for ca. 2 h and filtered. Diffraction quality single
crystals for structure determination were obtained by slow evapo-
ration of this mother liquor in air. M.P. 240 °C.
obtained two azido linked polymeric polymorphs and
a
monomeric cyanato complex of 2,4-dichlorido-6-((2-(dimethy-
lamino)ethylimino)methyl)phenol. Only azido ligand produced
polymeric complexes revealing its greater ability to bridge over
the other. The synthesis, spectral characterization, crystal
structures, packing interactions (supramolecular assemblies
including halogen interactions), photophysical studies and EPR
studies are discussed here.
Yield: 0.2081 g (54%). Anal. Calc. for C11H13Cl2CuN5O (365.70):
C, 39.41; H, 3.58; N, 11.49. Found: C, 39.20; H, 3.50; N, 11.52%.
UV–Vis, kmax/nm (
238 (25.16).
Magnetic moment:
e
max/103 Mꢀ1 cmꢀ1) (acetonitrile): 389 (5.16),
l
= 1.75 B.M.
2.3. Physical measurements
2. Experimental
Carbon, hydrogen and nitrogen analyses were carried out using
a Vario EL III CHNS analyzer. Infrared spectra were recorded on a
JASCO FT-IR-5300 Spectrometer in the range 4000–400 cmꢀ1 using
KBr pellets. Electronic spectra were recorded on Ocean Optics USB
4000 UV–Vis Fiber Optic Spectrometer in the 200–1000 nm range
using solutions in various solvents. Molar conductivities of the
complexes in DMF solutions (10ꢀ3 M) at room temperature were
measured using a Systronic model 303 direct reading conductivity
meter. Magnetic susceptibility measurements were made in the
polycrystalline state on a Vibrating Sample Magnetometer using
Hg[Co(SCN)4] as calibrant at room temperature. TG-DTG analyses
of the complexes were carried out in a Perkin Elmer Pyris Diamond
analyser under nitrogen at a heating rate of 10 °C minꢀ1 in the 50–
700 °C range. The solid state photoluminescence measurements
were carried out using a Schimadzu Scientific spectrofluorometer
(Model No: RF-5301PC) at room-temperature and the solution
state studies were done in Thermo Fischer Variaskan Flash spec-
trofluorometer. The EPR spectra were recorded in a Varian E-112
X-band spectrometer using TCNE (g = 2.00277) as standard.
2.1. Materials
All chemicals were of reagent grade and purchased from com-
mercial sources. The solvents were purified according to standard
procedures. 3,5-Dichlorosalicylaldehyde (Aldrich), N,N-dimethyl-
1,2-diaminoethane (Aldrich), CuCl2ꢁ2H2O, CuSO4ꢁ5H2O, NaN3,
NaCNO (all are BDH, AR quality) were used as received.
The Schiff bases were formed in situ.
Caution! Azido compounds are potentially explosive. Although
no problems were encountered in the present study, it should be
prepared only in small quantities and handled with care.
2.2. Synthesis of copper(II) complexes
2.2.1. Synthesis of [Cu(L)(N3)]n (1a) [HL = 2,4-dichloro-6-((2-
(dimethylamino)ethylimino)methyl)phenol]
3,5-Dichlorosalicylaldehyde (0.191 g, 1 mmol) and N,N-
dimethyl-1,2-diaminoethane (0.088 g, 1 mmol) were dissolved in
10 mL methanol and refluxed for about an hour. A methanolic solu-
tion (10 mL) of copper(II) chloride dihydrate (0.170 g, 1 mmol) was
added to the hot reaction mixture. To the resulting deep green
solution, sodium azide (0.130 g, 2 mmol) in a MeOH/H2O (1:9)
mixture was added dropwise with continuous stirring and filtered.
Suitable single crystals for structure determination by X-ray
diffraction were obtained by slow evaporation of the mother liquor
in air. M.P. 231 °C.
2.4. X-ray crystallography
Single crystals of compounds [Cu(L)(N3)]n (1a), [Cu(L)(N3)]n
(1b), [Cu(L)(NCO)] (2) suitable for X-ray diffraction studies were
grown from their methanol solutions by slow evaporation at room
temperature. Single crystals were selected and mounted on a Bru-
ker SMART APEX diffractometer, equipped with a graphite crystal,
incident-beam monochromator, and a fine focus sealed tube with
Yield: 0.297 g (81%). Anal. Calc. for C11H13Cl2CuN5O (365.70): C,
Mo Ka (k = 0.71073 Å) as the X-ray source. The crystallographic
36.13; H, 3.58; N, 19.15. Found: C, 36.09; H, 3.55; N, 19.10%.
data along with details of structure solution refinements are given
in Tables 1 and 2. The unit cell dimensions were measured and the
data collection was performed at 293(2) K. Bruker SMART software
was used for data acquisition and Bruker SAINT software for data
UV–Vis, kmax/nm (
238 (28.54).
Magnetic moment:
e
max/103 Mꢀ1 cmꢀ1) (acetonitrile): 376 (7.60),
l
= 1.89 B.M.

N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
253
Table 1
integration [32]. Absorption corrections were carried out using SAD-
Crystal data and refinement details of complexes 1a and 1b.
ABS based on Laue symmetry using equivalent reflections [33]. The
structure was solved by direct methods and refined by full-matrix
least-squares calculations with the WINGX software package [34a]
and the SHELXL-97 software package [34b]. The molecular and
crystal structures were plotted using DIAMOND version 3.2 g [35a]
and ORTEP-3 for Windows [34a]. All non-hydrogen atoms were
refined anisotropically, and all H atoms on C and N were placed
in calculated positions, guided by difference maps and refined
isotropically, with C–H and N–H bond distances of 0.93 Å and
0.86 Å respectively.
The crystal of 1a is a non-merohedral twin, and the diffraction
intensities were separated into two sets by using PLATON [35b].
The minor component refined to 17.8(2)%. Complex 2 possess a
crystallographic mirror symmetry with all the atoms lying on a
mirror plane and hence enjoys an occupancy factor of 0.50
(special position constraint). The occupation site of atoms in
disorder refinement is 50:50.
Parameters
1a
1b
Empirical formula
Formula weight
T (K)
C
11H13Cl2CuN5O
C22H26Cl4Cu2N10O2
731.43
296(2)
0.71073
monoclinic
P21/n
a = 6.9187(2) Å
a = 90°
b = 19.2758(7) Å
b = 97.682(2)°
c = 21.3470(7) Å
c = 90°
2821.36(16)
4
1.722
1.928
1480
365.71
293(2)
0.71073
monoclinic
P21/c
k (Å)
Crystal system
Space group
Unit cell dimensions
a = 11.0792(5) Å
a
= 90°
b = 6.8477(3) Å
b = 101.826(2)°
c = 19.5346(8) Å
c
= 90°
V (Å3)
1450.58(11)
4
1.675
1.875
Z
Dcalc (Mg mꢀ3
)
Absorption coefficient (mmꢀ1
F(000)
)
740
Crystal size (mm)
h range for data collection (°)
Limiting indices
0.41 ꢂ 0.13 ꢂ 0.10
3.12–27.77
ꢀ14 6 h 6 14,
0 6 k 6 8,
0 6 l 6 25
10989
0.40 ꢂ 0.35 ꢂ 0.35
1.43–26.50
ꢀ8 6 h 6 8,
ꢀ24 6 k 6 20,
ꢀ26 6 l 6 26
18807
3. Results and discussion
Reflections collected
Unique reflections
Refinement method
6794 [Rint = 0.0000] 5861 [Rint = 0.0307]
3.1. Synthetic protocol of ligand and its copper(II) complexes
full-matrix least-
squares on F2
3356/0/182
1.084
R1 = 0.0538,
full-matrix least-
squares on F2
5853/0/366
Facile condensation of 3,5-dichlorosalicylaldehyde with N,N-
dimethyl-1,2-diaminoethane in equimolar ratio (1:1) resulted in
the formation of the tridentate Schiff base ligand (Scheme 1). Since
the isolation of the Schiff base was difficult, one-pot synthetic
strategy was adopted for the preparation of all complexes.
The Schiff-base on reaction with copper(II) chloride dihydrate
and copper(II) sulfate pentahydrate, followed by the addition of
sodium azide in the ratio 1:1:2 yielded the polymeric polymorphs
1a and 1b respectively whereas the monomeric complex 2 was
obtained by adding sodium cyanate in the same ratio (Scheme 2).
The polymorphic complexes show only marginal variation in the
cell parameters.
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.014
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0299,
wR2 = 0.0790
R1 = 0.0444,
wR2 = 0.0901
0.341 and ꢀ0.480
wR2 = 0.1172
R1 = 0.0937,
wR2 = 0.1354
Largest difference in peak and
hole (e Aꢀ3
0.764 and ꢀ0.5913
)
R1
=
R
||Fo| ꢀ |Fc||/
R|Fo|.
wR2 = [
R
w(F2o ꢀ F2c)2/
R .
w(F2o)2]1/2
All the complexes are analytically pure as confirmed from their
elemental analysis. They are soluble in polar solvents like metha-
nol, DMF and DMSO. The conductivity measurements were made
in DMF solution and all complexes are found to be non-electrolytic
in nature [36]. According to Boudreaux, theoretically calculated
value for the magnetic moment of square-pyramidal copper(II)
complexes lies in the range 2.11–2.21 B.M. at room temperature
[37,38], though experimental measurements usually give a slightly
lesser value (1.88 B.M.). Room temperature magnetic moment val-
ues of the polymorphs 1a and 1b are 1.89 and 1.85 B.M. respec-
tively [39], thus confirming the square pyramidal environment of
Cu(II). While the magnetic moment of complex 2 has a value very
close to the expected spin only value of 1.73 B.M. for a d9 copper
system.
Table 2
Crystal data and refinement details of complex 2.
Parameters
2
Empirical formula
Formula weight
T (K)
C
12H18Cl2CuN3O2
366.71
296(2)
0.71073
orthorhombic
Pnma
a = 18.5526(12) Å
b = 6.8128(3) Å b = 90°
c = 11.1901(6) Å
1414.37(13)
4
1.722
1.925
k (Å)
Crystal system
Space group
Unit cell dimensions
a = 90°
c = 90°
V (Å3)
Z
Dcalc (Mg mꢀ3
)
Absorption coefficient (mmꢀ1
F(000)
)
744.0
3.2. Description of crystal structures
Crystal size (mm3)
h range for data collection (°)
Limiting indices
0.35 ꢂ 0.25 ꢂ 0.20
2.85–28.25
3.2.1. [Cu(L)(N3)]n (1a)
ꢀ24 6 h 6 24,
ꢀ8 6 k 6 9,
ꢀ14 6 l 6 14
10832
1892 [Rint = 0.0342]
full-matrix least-squares on F2
1882/2/145
Compound crystallizes in monoclinic P21/c space group. A per-
spective view of the complex with atom labeling scheme is shown
in Fig. 1. Selected bond lengths and angles are given in Table S1.
The single crystal X-ray analysis reveals the asymmetric unit as a
crystallographically distinct square planar Cu(II) center with its
plane accommodated by amino nitrogen (N2), imine nitrogen
(N1), phenoxo oxygen (O1) and the N3 of the azido group (Fig. 2)
although in the entire polymeric structure, each unit has pentaco-
ordinated (4+1) geometry, with the fifth coordination site being
satisfied by the nitrogen of the azido group of the adjacent unit
Reflections collected
Unique reflections
Refinement method
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.044
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0300, wR2 = 0.0715
R1 = 0.0407, wR2 = 0.0774
0.544 and ꢀ0.450
Largest difference in peak and hole (e Aꢀ3
)
R1
wR2 = [
=
R
||Fo| ꢀ |Fc||/
R|Fo|.
R
w(F2o ꢀ F2c)2/
R .
w(F2o)2]1/2
via l1,1-bridging. In brief, the coordination modes are satisfied by

254
N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
Scheme 1. Formation of tridentate Schiff base ligand.
Scheme 2. Synthetic route to the complexes.
Fig. 1. Perspective view of complex 1a. Only relevant atoms are labeled. Symmetry
element: * = x, 5.5 ꢀ y, ꢀ0.5 + z.
Fig. 2. ORTEP plot showing the atom labeling of the asymmetric unit of the
complex 1a (drawn with 50% thermal ellipsoid).

N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
255
tridentate monoanionic Schiff base system and two azido ions,
both of which are involved in end-on bridging (Fig. 1).
The pattern of propagation of the chain is in such a manner that
each azido group exhibits dual nature – while it is axially disposed
with respect to one metal ion, the same Nꢀ3 is equatorially aligned
with respect to the adjacent metal ion. Bridging Cu–N bond lengths
are significantly different with values 1.975(4)/2.694(5) for
basal/axial bonds. Therefore the mode of end-on azido bridging is
asymmetric in terms of the type of the coordination position it
occupies [40].
The extent of distortion of the pentacoordinated geometry can
be conveniently measured by Addison parameter, given by the
equation
onal bipyramidal geometries the values of
respectively). The value of – the angular structural parameter,
s
= (b ꢀ
a
)/60 [41] (for perfect square pyramidal and trig-
s
are zero and unity
s
an index of degree of trigonality is 0.051, suggestive of an almost
square pyramidal geometry. Also the metal center deviates from
the least squares plane by a distance of 0.0442 Å towards apical
donor atom and among the other donor atoms, the imino nitrogen
deviates the most (0.0533 Å) from the plane.
The trans-l1,1 bridging mode of azido group constructs the
whole molecule into a one-dimensional polymeric structure along
‘b’ axis. Also, each monomeric unit is related to its adjacent one by
a 21 screw axis. This translational element of symmetry coupled
with the trans bridging mode of Nꢀ3 generates a helical chain
(Fig. 3).
Fig. 4. The two adjacent chains of complex 1a fit to form a zipper-like structure
It is interesting to note that although several
l1,3-N3 bridged
with teeth tilted.
helical chains have been reported, there are very few examples
reported for helical trans-l1,1 chains with Cu(II) [42a,b,c]. The
N3–Cu1–N3 bond angle emerges to 99.09(18)°. The bond distances
in the azido complex follow the order: metal-axial azido nitrogen
(2.694(5) Å) > metal-amino nitrogen (2.071(4) Å) > metal-equato-
rial azido nitrogen (1.975(4) Å) > metal-imino nitrogen (1.951
(4) Å) > metal-phenoxo oxygen (1.924(3) Å). The Cu–N distance in
apical position is longer than the basal distance, which is an obvi-
ous consequence of Jahn–Teller distortion in a d9 copper(II) system
(Table S1). Also the metal-imine bond distance is shorter than
metal-amino nitrogen, as seen in many other similar systems
[43a,b]. The five membered chelate ring incorporating the amino
fragment i.e.: Cg(1) adopts an envelope conformation with C(9)
as the flap atom of the envelope, with a puckering amplitude of
trans
l1,1-azido ligand packs the succeeding units in such a
fashion that the alternate units can be stacked one over the other
with a dihedral angle of 0° between them, further evidencing the
piling of the units. Two adjacent 1-D strands fit into a zipper-like
structure where the alternate teeth are spaced at a distance of
6.8477(3) Å (Fig. 4).
The Cuꢁ ꢁ ꢁCu non-bonded distance along a chain is 4.2548(10) Å
and the interchain Cuꢁ ꢁ ꢁCu distance is 10.1471(10) Å. The bridging
pseudo-halide is quasi-linear as revealed by the N–N–N bond angle
of 177.0(6)°.
The metrical parameters like metal–N–metal bridge angle
(Cu1–N3–Cu1) in this metal-azido complex is 130.8(2)° and the
Fig. 3. Helical propagation of polymeric complex 1a.

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N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
Q = 0.422(6) Å and u = 108.8(6)° [44]. The puckering of the metal-
locycle is also calculated in terms of pseudorotation parameters P
and sm [45] and the envelope conformation was confirmed with
unveils the fact that the higher value of Addison parameter is
due to variation in the non-linear trans angle value involving azido
nitrogen atoms (N1–Cu1–N3, 169.73(9)°/N6–Cu2–N8, 167.39(9)°
over N1–Cu1–N3, 173.8(2)° of former crystal). A measure of the
relative strength of bonding follows the same order as that of 1a
i.e.: metal-phenoxo oxygen > metal-imino nitrogen > metal-equa-
torial azido nitrogen > metal-amino nitrogen > metal-axial azido
nitrogen although slight variations do exist in the bonding dis-
tances (Table S2).
P = 264.6(3)° and
s = 47.3(3)° for reference bond Cu(1)–N(1). The
six membered chelate ring formed by the aldehydic moiety, Cg
(2) also assumes an envelope conformation with puckering ampli-
tude, Q = 0.163(4) Å and u = 182(2)°.
3.2.2. [Cu(L)(N3)]n (1b)
In complex 1b, the five membered ring involving amine is
twisted on C9–N2 bond with puckering parameters, Q = 0.443
(3) Å and u = 120.9(3)°. The metallocycle (Cu2–N6–C19–C20–N7)
assumes an envelope conformation with C20 as the flap atom of
the envelope with parameters Q = 0.419(3) Å and u = 113.2(3)°.
Puckering of both metallocycles is further confirmed by the pseu-
The polymorphic counterpart crystallizes in monoclinic P21/n
space group. The asymmetric unit of this polymeric polymorph
houses two crystallographically distinct molecules, with both the
Cu(II) centers, (Cu1 and Cu2) disposing in square planar topology
(Fig. 5) and the polymeric one dimensional chain constituting both
Cu1 and Cu2 (Fig. 6) units are built by the end-on bridging of azido
group in axial-equatorial fashion along ‘a’ axis (Fig. S1).
The asymmetric alignment of the pseudohalide is further evi-
denced by the metrical parameters like metal-nitrogen distance,
metal–N–N bond angle, metal–N–metal bridge angle etc.
dorotation parameters – i.e.; P = 274.5(2)° and
erence bond Cu(1)–N(1) in Cg(1) and P = 267.9(2)° and
s
m = 47.2(2)° for ref-
m = 46.3
s
(2)° for reference bond Cu(2)–N(6) in Cg(2). No puckering was
Metrical parameters
With respect to Cu1
With respect to Cu2
Metal-nitrogen distance (Å)
Cu1–N3a basal
Cu1–N8b axial
Cu1–N3–N4
Cu1–N8–N9
Cu1–N3–Cu2
1.980(2)
2.629(2)
120.1(1)
110.29(16)
132.01(10)
Cu2–N3c axial
Cu2–N8b basal
Cu2–N3–N4
Cu2–N8–N9
Cu1–N8–Cu2
2.713(2)
1.967(2)
106.97(16)
117.7(1)
131.93(10)
Metal–N–N bond angle (°)
Metal–N–metal bridge angle (°)
a = 1.5 ꢀ x, ꢀ0.5 + y, 0.5 ꢀ z; b = ꢀ1 + x, ꢀ1 + y, ꢀ1 + z; c = 0.5 ꢀ x, ꢀ0.5 + y, 0.5 ꢀ z.
The azido groups in the crystallographically distinct units are
quasi-linear with N–N–N bond angle of 177.3(3)°. The non-bonded
distances of Cu1 with the symmetrically related copper centers
[Cu2 (x, ꢀ1 + y, ꢀ1 + z)] along this chain are 4.2061(5) and
4.2965(5) Å respectively. This complex is much more closely
packed as revealed by the comparatively lower interchain Cuꢁ ꢁ ꢁCu
distances of 9.7985(6) and 9.8565(6) Å, with respect to 1a. The
polymorphic form also exhibits a zipper like structure with a spac-
ing of 6.9187(2) Å between alternate teeth (Fig. 7).
The central metal atoms, Cu1 and Cu2 deviate by 0.0720 and
0.0724 Å from the respective least square planes. Though both
forms have axially elongated pentacoordinated environment, this
crystallographic form with two different copper centers exhibits
a greater distortion as revealed by a trigonality index value of
0.11 and 0.1565 respectively, which is almost and more than twice
of its counterpart. A closer examination of the transoid angles
found for the six membered ring unlike seen in its polymorphic
counterpart.
3.2.2.1. Comparison of the polymorphic structures. An overall com-
parison brings out that the strongest axial bond and the strongest
equatorial bonds are seen in complex 1b (Table 3). The value of
Addison parameter,
s and the deviation of metal center from the
least squares plane are taken as indicators of the relative extent
of distortion of a square-pyramidal environment [45]. In the case
of polymorphic compounds we obtained, the s/d (Å) values are
0.051/0.0442 (1a), 0.11/0.0720 (Cu1 of 1b), 0.1565/0.0724 (Cu2
of 1b) from which the extent of distortion follows the order: Cu2
Fig. 5. ORTEP plot showing the atom labeling of asymmetric unit of complex 1b
(drawn with 50% thermal ellipsoid).
Fig. 6. Perspective view of complex 1b. Only relevant atoms are labeled. Symmetry
element: * = 4 ꢀ x, 2 ꢀ y, 2 ꢀ z.

N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
257
Fig. 7. The two adjacent chains of complex 1b fit to form a zipper-like structure.
Table 3
Comparative analysis of metal-donor atom bond distances in the polymorphic forms.
Crystallographic
Two distinct crystallographic
distinct form (1a)
entities (1b)
Metal-axial azido nitrogen
Metal-amino nitrogen
Metal-equatorial azido nitrogen
Metal-imino nitrogen
Cu1–N31a
Cu1–N2
Cu1–N31b
Cu1–N1
Cu1–O1
2.694(5)
2.071(4)
1.975(4)
1.951(4)
1.924(3)
Cu1–N82b
Cu1–N2
Cu1–N32a
Cu1–N1
Cu1–O1
2.629(2)
2.053(2)
1.980(2)
1.943(2)
1.9069(17)
Cu2–N32c
Cu2–N7
Cu2–N82b
Cu2–N6
Cu2–O2
2.713(2)
2.051(1)
1.967(2)
1.931(2)
Metal-phenoxo oxygen
1.9067(17)
1a = 1 ꢀ x, 1 ꢀ y, 1 ꢀ z; 1b = x, 0.5 ꢀ y, ꢀ0.5 + z.
2a = 1.5 ꢀ x, ꢀ0.5 + y, 0.5 ꢀ z; 2b = ꢀ1 + x, ꢀ1 + y, ꢀ1 + z; 2c = 0.5 ꢀ x, ꢀ0.5 + y, 0.5 – z.
(1b) > Cu1 (1b) > Cu1 (1a). Coupled to the above values, the wide
variation in transoid bond angle values [(176.72(8)°/167.39(9)°]
also contribute to the greater distortion of Cu2 environment of
complex 1b.
3.2.3. [Cu(L)(NCO)] (2)
Complex 2 crystallizes in the orthorhombic space group Pnma.
The complex assumes a square planar geometry, with the tetraco-
ordination of Cu(II) being satisfied by the imino nitrogen (N1),
amino nitrogen (N2), phenoxo oxygen (O1) of the tridentate Schiff
base ligand (L1) and N3 atom of the cyanato group (Fig. 8). The
extent of deformation in a tetracoordinated complex is given by
the s4 index, a measure of the extent of distortion between a per-
fect tetrahedron (
4 = 0), given by the formula:
being the two largest angles around the central metal atom in
the complex [46]. The 4 value of 0.1084, for this complex confirms
s
4 = 1) and perfect square planar geometry
(s
s
4 = [360° ꢀ ( + b)]/141°, and b
a
a
s
a slightly distorted square planar geometry. Moreover, the differ-
ent angles around the copper metal summate to 359.36° indicating
negligible deviation from the coordination polyhedron. Of the var-
ious coordinating atoms O1, N1, N2 and N3, imino nitrogen (N1)
and amino nitrogen (N2) shows 0.2081 and 0.2299 Å deviation
from the least square mean plane whereas O1 and N3 lies exactly
in the plane. No deviation was found for Cu(II) from the reference
plane. The metal-donor bond strength follows the order Cu1–N3
(cyanato nitrogen) > Cu1–O1 (phenoxo oxygen) > Cu1–N1 (amino
nitrogen) > Cu1–N2 (imino nitrogen) which in turn reflects the
reverse order of the metal-donor bond distances (Table S3). The
pseudolinearity of the cyanato ligand is evidenced by the bond
Fig. 8. ORTEP plot showing the atom labeling of asymmetric unit of complex 2
(drawn with 50% thermal ellipsoid).
angle value of 179.6(4)° for N(3)–C(12)–O(2). The tridentate ligand
forms six and five membered metallocycles with chelate bite
angles of 91.59(6)° and 83.13(11)° for the rings respectively.
Ring puckering analyses and least square plane calculations
shows that the five membered metallocycle, Cg(1) is twisted on
C(8)–C(9) bond with puckering amplitude, Q = 0.400(6) Å and

258
N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
u = 97.8(7)°. A boat conformation is found for the six membered
metallocycle, Cu1–N1–C7–C6–C7a–N1a [C7a, N1a stands for the
disordered atoms] with puckering parameters Q = 1.524(8) Å, and
u = 180.0(5)°. Another six membered metallocycle, Cg(3) is also
puckered with an amplitude of Q = 0.106(6) Å and u = 165(5)°.
The H bonding between H(5) atom on C(5) with that of the N(5)
of the azido group of a similar molecule in the adjacent chain
stitches the neighboring one-dimensional polymeric chains in such
a manner that the molecules pack in ‘bc’ plane (Table S4, Fig. S2).
No significant ring interactions are found in the complex.
In the polymorphic form, the three intermolecular interactions,
namely C(7)–H(7)ꢁ ꢁ ꢁN(5), C(16)–H(16)ꢁ ꢁ ꢁN(10) and C(18)–H(18)ꢁ ꢁ ꢁ
N(10) sews together adjacent one-dimensional chains and pack the
molecules in ‘ab’ plane (Fig. S3).
3.2.4. Supramolecular features as structural adhesives
While one of the hydrogen atoms, H(11B) borne by the C(11)
atom of the methyl group forms an (intermolecular) intrachain
hydrogen bonding interaction with the deprotonated phenoxy
oxygen atom (O1), the other hydrogen atom H(11C) of the same
carbon is involved in two intramolecular interactions with N(3)
and N(4) of the azido group, thus forming a bifurcated, three center
H bonding interaction (Fig. 9), leading to S(3) ring motif. Due to the
involvement of azido nitrogens in H bonding, S(5) and S(6) motifs
are also formed.
A trifurcated H bonding interaction is established by H(10C), H
(18) and H(16) with a common acceptor, N(10) (Fig. 10). A R12ð6Þ
pattern is generated considering only the H bond interaction of H
(18) and H(16) with the common acceptor, N(10) (bifurcated inter-
action, Fig. 10).
One of the phenoxy oxygens, O(1) is engaged in an intermolec-
ular H bonding with the hydrogen [H(21A)] of the methyl carbon C
Fig. 9. Intrachain intermolecular and intramolecular H bonding interactions in complex 1a.
Fig. 10. Plot highlighting the trifurcated and bifurcated hydrogen bonding interaction in complex 1b.

N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
259
Table 4
(21). The other phenoxy oxygen O(2), is involved in an intrachain
intermolecular H bonding with the hydrogens (H10B & H11A) of
methyl carbons, C(10) and C(11) of two different adjacent units,
Type I halogen contacts in complex 1b.
Interaction h1 (°)
h2 (°)
(h1 ꢀ h2) Xꢁ ꢁ ꢁX
(Å)
creating
a bifurcated interaction and bringing them closer
together. Apart from this, an intramolecular H bond is formed by
the nitrogen of azido functional group, N(4) with the hydrogen
[H(11B)] borne by the methyl carbon, C(11) thus forming a S(6)
ring motif (Fig. S4). The two interactions arising from H(10B) & H
Cl1ꢁ ꢁ ꢁCl1
Cl2ꢁ ꢁ ꢁCl3
C2–Cl1ꢁ ꢁ ꢁCl1
162.66(9)
Cl1ꢁ ꢁ ꢁCl1–C2
162.66(9)
0
3.266
3.622
C4–Cl2ꢁ ꢁ ꢁCl3
C13–Cl3ꢁ ꢁ ꢁCl2
4.5
165.57(11)
170.07(11)
(10C) of C(10) to O(2) & N(10) forms a R22(8) pattern (Table S5).
No classic hydrogen bonds are present in the complexes.
In form 1b, the halogen bearing aromatic ring of one copper unit
is involved in a face to face p–p [Cg(5)–Cg(6)] interaction [3.7106
(15) Å] with a similar ring of the adjacent unit in the nearby poly-
1.722 Mg mꢀ3 for 1 and 2 respectively), is supportive of the greater
close packing of molecules in form 1b as compared to that of 1a.
Apart from the Cgꢁ ꢁ ꢁCg stacking interaction between rings and
the hydrogen bonding interactions, these polymorphs are charac-
terized by a difference in the halogen bonding interactions.
In the cyanato complex (2), an intramolecular H bonding
between the nitrogen (N3) of the cyanato group and the methyl
carbon, C(10) generates a S(5) ring motif. A bifurcated, 3c-2 elec-
tron bond is seen between the phenoxy oxygen, O(2) [acceptor]
and H(7) & H(8B) of the donor atoms C(7) [azomethine carbon]
meric chain (Table S6, Fig. S5).
The azido nitrogens, N(5) and N(10) establishes a non-covalent
interaction with the six membered metallocycles, Cg(4) and Cg(3)
respectively. Also the halogen atom, Cl(4) establishes a contact
with the halogen bearing aromatic ring, [Cg(5)] of the nearby one
dimensional chain (Table S7, Fig. S6).
Complex 1a doesn’t have any halogenꢁ ꢁ ꢁhalogen interaction
whereas two intermolecular halogen interactions are seen in its
polymorphic counterpart. Halogen–halogen interaction is seen
between Cl1ꢁ ꢁ ꢁCl1 and Cl2ꢁ ꢁ ꢁCl3 atoms with distances, 3.266 and
3.6222(11) Å respectively between them which is definitely less
than the sum of their van der Waals radii (Fig. 11). According to
Desiraju and co-workers [47,48], halogen interactions are classified
as type I and II based on bond angles ‘h1’ and ‘h2’ made at the halo-
gen atoms and the intermolecular distances. So considering the
angular preference, intermolecular distance and the size of Cl atom
[48], we conclude these to be Type 1 halogen interaction where
0° 6 |h1 ꢀ h2| 6 15° (Table 4). Type 1 interaction is geometry based
contact that arises from close packing and this is most effective in
Cl due to its small polarisability over other halogens.
An intramolecular interaction C(2)–Cl1ꢁ ꢁ ꢁO1 is seen in the com-
plex 1a with a donor–acceptor distance of 2.912(4) Å (Fig. S7). Sim-
ilar interactions, C(2)–Cl(1)ꢁ ꢁ ꢁO(1) and C(13)–Cl(3)ꢁ ꢁ ꢁO(2) with
Xꢁ ꢁ ꢁB distances of 2.889(1) and 2.906(1) Å respectively are seen
in the complex 1b (Fig. S8). Still they cannot be categorized as
halogen bonding since the halogen in both cases are bonded to a
less electronegative carbon and hence chances for chlorine to
become electrophilic is meagre [49].
and C(8) respectively which creates a R12ð6Þ pattern (Table S8,
Fig. 12) and interconnects the molecules along ‘c’ axis.
Ring interactions exist between the halogen bearing ring, Cg(6)
and metallocycles Cg(3) & Cg(4). Also aromatic rings, Cg(6) interact
face to face with each other (Table S9, Fig. 13).
There is the presence of Y–Xꢁ ꢁ ꢁCg interaction between the halo-
gen, Cl(2) and aromatic rings Cg(3) and Cg(4) (Table S10, Fig. S9).
3.3. Spectral characterization
3.3.1. IR and electronic spectra
The C@N stretching vibrations for all the four complexes lie in
the region 1625–1634 cmꢀ1 [43a]. The polymorphic pair shows a
single band consistent with the presence of only one type of
azido bridge in the structures and this characteristic strong band
at 2045 cmꢀ1 can be ascribed to the presence of asymmetric
bridging [51a,b]. Moreover, the IR spectra also exhibits peaks at
1319 and 758 cmꢀ1 corresponding to symmetric stretching,
m
s(N3) and bending mode d(N3) of the pseudohalide present [52].
One sharp and strong band at 2234 cmꢀ1 in the IR spectrum of
complex 2 indicates the presence of N bonded cyanato group
[43a]. The IR band in the region 2918–2930 cmꢀ1 seen in
complexes is assignable to alkyl C–H stretching vibrations [53].
The electronic spectra of all the three complexes were recorded
in acetonitrile in the 200–1000 nm region at room temperature.
The difference in the intermolecular interactions present in
complexes enabled a variation in the packing motifs, thus resulting
in packing polymorphism [50]; polymorph 1a and 1b. The various
packing interactions and the calculated density values (1.675 and
Fig. 11. Intermolecular Cl1ꢁ ꢁ ꢁCl1 (pink) and Cl2ꢁ ꢁ ꢁCl3 (green) interaction in 1b. (For interpretation of the references to color in this figure legend, the reader is referred to the
web version of this article.)

260
N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
Fig. 12. Hydrogen bonding interactions in 2 (The C10 and H10C atoms are disordered and treated).
Fig. 13. Ring interactions in complex 2 (disordered atoms are omitted for clarity).
Table 5
The kmax (nm) values along with their
e
(Mꢀ1 cmꢀ1) in various solvents.
Polarity index*
5.1
Solvents (decreasing
order of polarity)
Complex 1a kmax (nm)
* 103 (Mꢀ1 cmꢀ1
Complex 1b kmax (nm)
* 103 (Mꢀ1 cmꢀ1
Complex 2 kmax (nm)
* 103 (Mꢀ1 cmꢀ1
e
)
e
)
e
)
Methanol
384
235
5.32
27.56
385
235
7.29
30.32
389
238
209
5.12
23.61
24.32
5.8
Acetonitrile
376
238
7.60
28.54
376
237
8.12
31.27
389
238
5.16
25.16
5.1
4.4
4.0
4.1
Acetone
378
384
385
8.73
8.27
8.39
378
385
385
8.80
8.35
9.09
388
395
398
5.73
4.58
4.43
Ethylacetate
Tetrahydrofuran
Chloroform
387
245
7.39
22.52
387
245
8.89
26.44
404
273
4.33
14.75
2.4
Toluene
390
8.66
390
9.62
402
5.45
*
Relative measure of degree of interaction of the solvents with various polar test solutes.
The electronic spectra of all complexes show broad bands in the
high energy 370–390 nm region consistent with the LMCT bands
comprising of transitions from the coordinating atoms of
respective pseudohalides to the metal center [51b,54] apart from
O ? Cu, N ? Cu transitions. The bands ca. 235 nm correspond to
(Table 5). The absorption at low energy region, 590–650 nm
corresponds to d–d transition. For complexes 1a and 1b, peak at
593 nm typical of a square pyramidal environment of the Cu(II)
2
center is seen, enclosing A1g 2B1g
,
2B2g 2B1g, and 2Eg 2B1g
transitions [28,56a,b] and peak ca. 630 nm can be assigned to a
intraligand transitions [55a,b]. The high
e
values for these bands
square-planar environment with transitions 2B2g 2B1g
,
is supportive of the charge transfer and intraligand transitions
2A1g 2B1g and 2Eg 2B1g [56a]. It is difficult to interpret the

N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
261
electronic spectra of Cu(II) complexes as they possess flexible
stereochemistry due to Jahn–Tellar distortion [57].
solvatochromism will result [58]. This is due to a solvent-induced
change of the electronic ground-state structure from a less dipolar
(in non-polar solvents) to a more dipolar chromophore (in polar
solvents) with increasing solvent polarity. The kmax (nm) along
with their
(Table 5).
The solvents apart from influencing the chromophoric groups
also affects the coordination environment of the metal center
which is reflected as a shift in the d–d absorption band. The color
change of the complexes can be attributed to this shift. Pseudo-
halogeno complexes appear in various shades of green [59]
(Fig. S11).
3.3.2. Solvatochromism and photo-physical studies
e
(Mꢀ1 cmꢀ1) values in various solvents are tabulated
The electronic spectra of all the three complexes were recorded
in different solvents of varying polarity to investigate the effect of
solvents on the absorption bands (CT and dd) of the copper com-
plexes. Solvents chosen for the study included polar protic (metha-
nol), polar aprotic (tetrahydrofuran, ethyl acetate, acetone and
acetonitrile) and non-polar solvents (toluene, chloroform). All the
three complexes exhibited interesting solvatochromic behavior.
All the complexes are soluble in a wide range of organic sol-
vents that make their solvatochromic study easy. Both charge
transfer bands and d–d bands exhibited solvatochromism although
significant shift in energy was seen for the d–d bands.
The charge-transfer and intraligand transitions exhibited nega-
tive solvatochromism (Figs. 14 and S10), though the variation
occurs within a narrow range. With increasing solvent polarity,
within each classification of solvents (polar protic, polar aprotic
and non-polar), hypsochromic (or blue) shift of these bands are
observed. This is called ‘‘negative solvatochromism” and this
occurs due to differential solvation of the ground and first excited
state of the light-absorbing molecule (or its chromophore): if, with
increasing solvent polarity, the ground-state molecule is better sta-
bilized by solvation than the molecule in the excited state, negative
The influence of the donor power of the solvent on the mmax val-
ues of the d–d bands of the complexes have been investigated by
means of visible spectroscopy. Four solvents of varying donor pow-
ers – DMSO, MeOH, CH3CN and DCM were chosen for the study and
it was found that the d–d band shifts to red with increasing donor
number of the solvent. Observed shift in this region as a function of
donor power of chosen solvents was significant and a positive sol-
vatochromism was noted (Figs. 14 and S12, Table 6).
The d–d band spectra of all the three complexes show almost a
broad band in the visible region assignable to the promotion of
2
2
electron in the low energy orbitals to the hole in dxꢀy orbital of
the copper(II) ion (d9). The position of this band is shifted to longer
wavelengths as the DN (donor number) of the solvent increases. As
Fig. 14. The spectra showing solvatochromic behavior of LMCT, intraligand transitions (top row, con: 1 * 10ꢀ3 M) and d–d transitions (bottom, con: 2 * 10ꢀ3 M) of complex 1a
in various solvents.

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N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
Table 6
The kmax (nm) values along with their
e
(Mꢀ1 cmꢀ1) of d–d bands in various solvents.
Solvents
Donor number of
solvents (DN)
Complex 1a kmax (nm)
(Mꢀ1 cmꢀ1
Complex 1b kmax (nm)
(Mꢀ1 cmꢀ1
Complex 2 kmax (nm)
(Mꢀ1 cmꢀ1
e
)
e
)
e
)
DMSO
29.8
19.0
14.1
0.0
639
613
593
583
535
509
164
142
213
250
259
262
639
619
591
583
535
509
128
151
195
214
223
225
656
640
633
632
152
204
162
151
Methanol
Acetonitrile
DCM
the solvent molecules approach along the z axis of the complex the
ligands in the x, y plane move out and the interactions become more
with orbitals that have z characters (dz2, dxz, and dyz). These orbitals
are thus destabilized, while the other orbitals energetically
decreases and eventually a typical octahedral d orbital splitting is
formed and in this process the d–d bands shift to red region. The
change in the color of the complex with solvent molecules is because
of weak coordination of the solvent molecules which is attributable
to a strong Jahn–Teller effect of the Cu(II) center with a d9 configu-
ration [60a,b].
Among the three complexes, greatest solvatochromic effect was
seen for the azido pair and there is a difference of 1500 cmꢀ1 as we
move from DCM to DMSO whereas for 2 that difference is only
around 580 cmꢀ1. It was observed that in solvent with the highest
donor number (DMSO), the absorption maxima for the complexes
is hardly noticeable (406 cmꢀ1) and in weakly coordinating solvent
like DCM, there is considerable difference (1330 cmꢀ1).
Spectral analysis of the optical emission of all the three com-
plexes were investigated in acetonitrile solution and in solid state
at room temperature. The fluorescent emission spectra are shown
in Fig. 15. The luminescent data of the complexes are summarized
in Table 7. All copper(II) complexes showed fluorescence behavior.
Complexes 1a, 1b and 2 on photoexcitation in the range 386–
400 nm in their solid state, showed almost same behavior with
an emission in the blue region (ca. 465 nm). The solution state
emission of the same complexes showed only violet luminescence
(ca. 420 nm) when excited at 345 nm. There is a red shift in the
major emissive peak in solid state when compared with that of
solution state. The possibility of greater stacking due to the pres-
ence of stronger non-covalent interactions between molecules
may be responsible for the larger red shifts of the solid state emis-
sion bands compared to their respective counterparts in solution
[61]. The coordination of a metal ion with the ligand produces
metallocycles which increases the conjugation length and confor-
mational coplanarity thereby reducing transition energy of intrali-
gand charge transfer [62].
3.3.3. Thermal analysis
The thermogravimetric analysis of complex 1a shows a single
weight loss of 25.50% (calcd. 23.70%) in the temperature range of
230–260 °C corresponding to the loss of amine part. The process
is exothermic as seen in DSC curves (Fig. 16-1a). Beyond 400 °C a
gradual weight loss occurs due to the thermal degradation of the
remaining part of the complex and the decomposition is not com-
pleted even at 700 °C. While its polymorphic counterpart exhibits
three stage decomposition – an initial weight loss of 7.45% (calcd.
7.65%) corresponding to the loss of nitrogen from the amine por-
tion in the range 220–240 °C, then the decomposition of azide
group as N3H coinciding with a mass loss of 13.99% (calcd.
12.43%) in the 240–271 °C range and finally there is a loss of chlo-
ride ion as HCl in 320–360 °C fitting to a 12.66% (calcd. 12.72%)
mass loss. Unlike seen in complex 1a, here a plateau like formation
is observed at higher temperatures indicating the formation of a
stable metal oxide. The DSC curves show exothermic peaks for all
the three stages (Fig. 16-1b).
The thermogram of complex 2 shows a 29.54% (calcd. 30.89%)
weight loss (230–263 °C), exothermically corresponding to the loss
Table 7
Photophysical data of complexes.
Complex Excitation (nm) Solid state
emission (nm)
Solution state emission (nm)
at excitation of 345 nm
1a
1b
2
386
386
399
466
465
464
424
424
428
Fig. 15. Solid state (left) and solution state (right) [acetonitrile, 1 * 10ꢀ3 M concentration] fluorescence spectra of the complexes.

N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
263
Fig. 16. Thermogram of complexes 1a and 1b.
of HCN and Cl2O (Fig. S13) after which a stable metal oxide is
formed.
consistent with the X-ray structural analysis and rules out the pos-
sibility of a trigonal bipyramidal structure, which would be
expected to have g\ > g .
k
Complex 2 also presents a typical axial spectra in the polycrys-
3.3.4. EPR studies
talline state with well-defined g and g\ values. The spectra is
k
The EPR spectra of the copper(II) complexes in polycrystalline
state at 298 K and in DMF at 77 K were recorded in the X-band,
using 100-kHz modulation frequency and 9.1 GHz microwave fre-
quency and g factors were quoted relative to the standard marker
TCNE (g = 2.00277). All the EPR spectra are simulated using EASYSPIN
54.0.2 package [63] and the experimental (red) and simulated
(blue) best fits are included (Figs. 17 and S14). EPR parameters of
the copper(II) complexes are presented in Table 8 .
broad because of the fast spin lattice relaxation and exchange cou-
pling. Eventhough axial features are displayed, since it is magnet-
ically concentrated, hyperfine splitting was not clear both in
parallel and perpendicular regions. Calculated G values for complex
2 is slightly greater than 4 ruling out the possibility of an exchange
interaction. The spectrum of compound 2 in DMF gave three g val-
ues, viz. g1 = 2.056, g2 = 2.180 and g3 = 2.293, indicating a rhombic
distortion in the geometry.
The EPR spectra of the polycrystalline polymeric complexes 1a
and 1b at room temperature are of axial type giving rise to two g
The bonding parameters
sure of the covalency of in-plane
out-of-plane -bonds respectively are evaluated using the EPR
a
2, b2 and
c
2, considered to be the mea-
-bonds and
r
-bonds, in-plane
p
values, g and g\ with g > g\ > ge (2.0023), with no hyperfine lines
k
k
p
in the parallel and perpendicular region. The variation in the g and
k
parameters g , g\, gav, A (Cu) and A\ (Cu) along with the energies
k
k
g\ values indicate that in the solid state, the geometry of the com-
pounds is affected by the nature of coordinating ligands.
The g-values in axial symmetry are correlated by the
expression,
of d–d transition.
The value of in-plane sigma bonding parameter a2 was esti-
mated from the expression [66]
a2 ¼ ꢀA =0:036 þ ðg ꢀ 2:0023Þ þ 3=7ðg? ꢀ 2:0023Þ þ 0:04
G ¼ ðgk ꢀ 2:0023Þ=ðg? ꢀ 2:0023Þ ½64ꢃ
k
k
The following simplified expression were used to calculate the
bonding parameters
which reflects the exchange interaction between Cu(II) centers in
the solid polycrystalline complexes. Accordingly, if G is greater than
4, the exchange interaction may be negligible; however, if G is less
than 4, a considerable exchange interaction is indicated in the solid
complex [65]. The G values for the polymer complexes were found
to be less than 4.0, indicative of considerable exchange interaction
between the copper centers in the solid.
K2k ¼ ðg ꢀ 2:0023ÞEdꢀd=8ko
k
K2? ¼ ðg? ꢀ 2:0023ÞEdꢀd=2ko
Kk2
¼
¼
a
2b2
The EPR spectra of the complexes recorded in frozen state at
77 K gives more information on the geometry of the complexes.
K?2
a2c2
Both the complexes, 1a and 1b display axial features [(g = 2.232,
k
g\ = 2.085) and (g = 2.202, g\ = 2.120)] with well resolved hyper-
k
fine splittings in parallel and perpendicular region due to the inter-
action of the odd electron with the nuclear spin (63,65Cu, I = 3/2).
Although expected superhyperfine splittings are not seen for com-
plex 1a, its polymorphic counterpart shows quintet splittings in
the perpendicular region due to the coupling of electron spin with
the nuclear spin of the two nitrogen atoms (I = 1) with super
exchange splitting constant, A – N\ = 15.83 * 10ꢀ4 cmꢀ1. However,
the superhyperfine splittings are not visible in the parallel region.
where K and K\ are orbital reduction factors and k0 represents the
k
one electron spin orbit coupling constant which equals ꢀ828 cmꢀ1
.
Hathaway [58a] has pointed out that for pure sigma bonding
K ꢄ K\ ꢄ 0.77, for in plane
p-bonding K < K\ and for out-of-plane
-bonding, K\ < K . For complexes 1a, 1b and 2, it is observed that
k
p
k
k
K < K\ which indicates the presence of significant in-plane
k
p
-bonding. The nature of metal–ligand bond is evaluated by
comparing the value of in-plane sigma bonding parameter a2 i.e.,
if the M–L bond is purely ionic, the value of a2 is unity and it is
For these pentacoordinate complexes 1a and 1b, the fact that g
k
is greater than g\ suggests a distorted square-pyramidal structure
completely covalent, if a
2 = 0.5 [56a]. Here a2 values calculated

264
N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
Fig. 17. EPR spectra of complexes (1a and 1b) in polycrystalline (left) and frozen DMF at 77 K (right).
Table 8
Spin Hamiltonian and bonding parameters of copper(II) complexes.
Compounds
Polycrystalline state (298 K)
DMF solution (77 K)
k/g3 \/g1, g2
giso
g
g\
G
g
g
gav
A
A\
Aav a2
0.8602
b2
c2
K
k
K\
f
k
k
[Cu(L1)(N3)]n (1a)
[Cu(L1)(N3)]n (1b)
[Cu(L1)(NCO)] (2)
–
–
–
2.20
2.195
2.22
2.056
2.06
2.056
3.6816
3.3397
4.054
2.232
2.202
2.293
2.085
2.120
2.056,
2.180
2.1337
2.1471
2.1384
200
214
208
36
39
34
0.889
0.8058
0.3985
1.0668
1.2373
1.4496
0.7647
0.7142
0.3579
0.9177
1.0966
1.3020
111.60
102.48
110.10
–
–
0.8863
0.8982
A values in 10ꢀ4 cmꢀ1
.
for all the complexes lie in between 0.5 and 1, which means that
the metal–ligand bonds in the complexes under study are
partially ionic and partially covalent in nature.
4. Conclusions
In the present work, we have discussed the pseudohalide incor-
The g values also provide information regarding the nature of
porated
2,4-dichloro-6-((2-(dimethylamino)ethylimino)methyl)
phenol] Schiff base system. Of these, the azido ligand forms a poly-
meric polymorph, formed by varying the copper salt used for syn-
thesis and the cyanato forms a simple square planar monomeric
k
metal–ligand bond [67]. The g value is normally 2.3 or larger for
k
ionic and less than 2.3 for covalent metal–ligand bonds. The g val-
k
ues obtained for our complexes indicate a significant degree of
covalency in the metal–ligand bonds [68]. The index of tetragonal
distortion f is calculated as f = g /A , whose value may vary from
form. Both the polymers involve l1,1-azido linkage which is rather
rare. The role of various weak interactions responsible for packing
polymorphism and stability of a particular crystalline structure are
discussed. It was a deliberate attempt of our group to introduce
halogen substituted carbonyl compounds so as to experimentally
k
k
105 to 135 for small to medium distortion and depends on the nat-
ure of the coordinated atom [69]. In all complexes distortion is
medium and is found to be in the range 105–115 cm [70].

N. Aiswarya et al. / Inorganica Chimica Acta 443 (2016) 251–266
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N. Aiswarya gratefully acknowledges the UGC, New Delhi, India
for financial support in the form of a Senior Research Fellowship. S.
S. Sreejith is thankful to Cochin University of Science and Technol-
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to the Sophisticated Analytical Instrumentation Facility (SAIF),
Kochi India for single crystal X-ray diffraction measurements, TG-
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thank School of Pure and Applied Physics, M.G. University and
Department of Chemical Oceanography, Cochin University of
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Appendix A. Supplementary material
CCDC 1407849, 1407850 and 1407851 contain the supplemen-
tary crystallographic data for compounds [Cu(L1)(N3)]n (1a), [Cu
(L1)(N3)]n (1b) and [Cu(L1)(NCO)] (2), respectively. These data can
be obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplemen-
tary data associated with this article can be found, in the online
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