Self-organized three dimensional architectures based on non-covalent interactions in square planar Cu(II) thiosemicarbazone: Solvent mediated crystallization and EPR based correlation study

Article abstract of DOI:10.1016/j.ica.2018.01.005

A series of copper complexes of 2-acetylpyridine-N⁴-methylthiosemicarbazone (HL4M) were synthesized and characterized by elemental analyses, UV–Vis, FT-IR, conductivity and EPR studies. The molecular structures of [Cu(L4M)Cl] (1), [Cu(L4M)I] (2), [Cu(L4M)OAc]·H₂O (3) and [Cu(μ-S-L4M)(NCS)]₂·DMSO (4) were confirmed by single crystal X-ray crystallography. Complexes 1, 2 and 3 have square planar geometry constituted by NNS donor sites from deprotonated thiosemicarbazone ligand and the fourth site is occupied by anionic group/atom. Complex 4 is a centrosymmetric dimer. The XRD results revealed that the solvents play a decisive role in the crystallization of products. These four complexes exhibit strong hydrogen bonding interactions in the solid state and are self-assembled into infinite 3D supramolecular structure via π?π stacking interactions. The g_|| and A_|| of complexes were analyzed by Peisach–Blumberg plot which proves an inverse correlation among NNS and ONS thiosemicarbazone complexes.

Full text of DOI:10.1016/j.ica.2018.01.005

Accepted Manuscript
Research paper
Self-organized three dimensional architectures based on non-covalent interac-
tions in square planar Cu(II) thiosemicarbazone: Solvent mediated crystalliza-
tion and EPR based correlation study
Lincy Tom, N. Aiswarya, S.S. Sreejith, M.R. Prathapachandra Kurup
PII:
S0020-1693(17)31286-0
https://doi.org/10.1016/j.ica.2018.01.005
ICA 18079
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
14 August 2017
1 January 2018
4 January 2018
Please cite this article as: L. Tom, N. Aiswarya, S.S. Sreejith, M.R.P. Kurup, Self-organized three dimensional
architectures based on non-covalent interactions in square planar Cu(II) thiosemicarbazone: Solvent mediated
crystallization and EPR based correlation study, Inorganica Chimica Acta (2018), doi: https://doi.org/10.1016/j.ica.
2
018.01.005
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Self-organized three dimensional architectures based on non-covalent
interactions in square planar Cu(II) thiosemicarbazone: Solvent mediated
crystallization and EPR based correlation study
a
Lincy Tom , N. Aiswarya , S.S. Sreejith , M. R. Prathapachandra Kurup
a
a
a,b*
a
Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682 022,
b
Kerala, India, Department of Chemistry School of Physical Sciences, Central University of Kerala,
Nileshwar-671314
Abstract
4
A series of copper complexes of 2-acetylpyridine-N -methylthiosemicarbazone (HL4M) were
synthesized and characterized by elemental analyses, UV–Vis, FT-IR, conductivity and EPR studies.
The molecular structures of [Cu(L4M)Cl] (1), [Cu(L4M)I] (2), [Cu(L4M)OAc]·H
2
O (3) and [Cu(ꢀ-S-
L4M)(NCS)] ·DMSO (4) were confirmed by single crystal X-ray crystallography. Complexes 1, 2
2
and 3 have square planar geometry constituted by NNS donor sites from deprotonated
thiosemicarbazone ligand and the fourth site is occupied by anionic group/atom. Complex 4 is a
centrosymmetric dimer. The XRD results revealed that the solvents play a decisive role in the
crystallization of products. These four complexes exhibit strong hydrogen bonding interactions in the
solid state and are self-assembled into infinite 3D supramolecular structure via ꢁ···ꢁ stacking
interactions. The g|| and A|| of complexes were analyzed by Peisach–Blumberg plot which proves an
inverse correlation among NNS and ONS thiosemicarbazone complexes.
Keywords: Copper complexes, X-ray crystal structure, Solvent effect, Hydrogen bonding,
Supramolecular structures, A|| - g|| correlation
1
. Introduction
Thiosemicarbazones, an important class of N–S donor ligands, have shown wide range of
coordination modes, flexible coordination fashions, structural diversity and outstanding
supramolecular binding with most of the transition or rare earth metal ions. Cu(II) thiosemicarbazone
chemistry remains an area of unabated attention due to their catalytical, analytical and biological
applications. [1-3] Among these, N-heterocyclic thiosemicarbazones have attracted more attention,
because many of them displayed promising anticancer activity [4].
*
Corresponding author
E mail address: mrpcusat@gmail.com, mrp_k@yahoo.com (M.R. Prathapachandra Kurup)
Phone: +91-9895226115
Fax: +91-484-2575804
Cu(II) complexes of the type [CuLX], where L is an anionic tridentate thiosemicarbazone and X is a
monoanionic donor like Cl, I, OAc etc. and its binuclear complexes are especially attractive due to
1

their different coordination chemistry. Cu(II) atoms can be bridge through thiolato sulfur atom or by
the X atoms giving rise to a centrosymmetric dimer or a non-centrosymmetric box dimer [5-7]. The
underlying reasons that govern the nature of the bridging atom (i.e. thiolato bridged versus X-bridged
dimers) are not clear to date. The structural motifs of complex molecules are determined by several
factors and the changes in the crystallization conditions often leads to structural diversities [8]. In
particular, solvents have significant impact on crystallization process and on the coordination trend of
the metal centres. They generally affect the crystal structures of coordination complexes in the
following ways: (i) solvents participating in coordination highly influence the coordination
environment and geometry of the metal ions; (ii) solvents are not coordinated to the metal ions, but
they exist in the crystal lattice as guest molecules; and (iii) solvents are not found in the final
products, but they have great impact on crystal growth and induce different structural aggregations
[9]. However, the exact reasons for these solvent-induced behavior are still under investigation.
In the present work, we have used four different monoanions to prepare copper(II) complexes and
except in the case of thiocyanate co-ligand we obtained mono-nuclear complexes. In recent years,
self-assembly directed by non-covalent interactions are increasingly used as a powerful tool for the
bottom up fabrication of supramolecular architectures.
Herein, we report the synthesis,
characterization, crystal structures, spectral studies and the role of secondary interactions in the
creation of molecular architectures. Interestingly, the use of different solvent systems directly
influenced the competitive coordination among components and crystallization of the products. An
attempt is made to correlate the hyperfine splitting (A||) and g factor (g||) in copper(II) complexes of
ONS and NNS donor ligands.
2
. Experimental
2
.1. Materials and techniques
The solvents were purchased from Merck and the reactants for syntheses were procured from Aldrich
Sigma Ltd. The elemental analysis of carbon, hydrogen, nitrogen and sulfur were carried out using an
elementar model Vario EL III elemental analyzer. The IR absorption spectra were performed with a
-1
JASCO FT-IR-5300 Spectrometer in the 4000-400 cm region by making their KBr discs. The
electronic spectra were taken on a Spectro UV-vis Double beam UVD-3500 spectrometer in the 200-
9
00 nm range. The EPR spectra were recorded on a Varian E-112 X-band spectrometer using TCNE
g = 2.00277) as standard. Systronic model 303 direct reading conductivity bridge was employed for
molar conductivity measurements.
(
2

2
2
.2. Synthesis
4
.2.1. Synthesis of 2-acetylpyridine-N -methylthiosemicarbazone (HL4M)
4
N -methylthiosemicarbazide (0.1051 g, 1mmol) dissolved in 10 mL hot 10% acetic acid solution was
slowly mixed with 2-acetylpyridine (0.121g, 1 mmol) in the same solution with stirring. The
complete mixture was then stirred for additional 30 min. The resulting pale yellow solid was filtered
off, washed with hot water, ethanol and dried. Crude product was recrystallized from dichloromethane
to yield X-ray quality single crystals by slow evaporation at room temperature. The crystal structure
has been already published [10].
The ligand was obtained with 50% yield, M.P.158 °C. Anal.Calc. for C
9
H
12
4
N S (208.288): C, 51.90;
-1
4–
H, 5.81; N, 26.90; S, 15.39. Found: C, 51.49; H, 5.33; N, 27.35; S, 14.74%. IR (KBr, cm ): υ(N H)
3
3
290s; υ(N –H) 3240s; υ(C=N) 1534vs; υ(N–N) 1116w; υ(C=S) 832w; ν(ꢂ(ip)) 616. Mass to charge
+
ratio (m/z): 208.2 (M ).
2
.2.2. Synthesis of [Cu(L4M)Cl] (1)
A suspension of the HL4M (0.104 g, 0.5 mmol,) in 10ꢃmL of EtOH was heated to boiling and 0.5
mmol (0.0852 g) of CuCl ·H O dissolved in minimum amount of water was then added. The mixture
2
2
on stirring for about 30 minutes afforded green precipitate and single crystals suitable for study was
obtained by redissolving the product in DMSO and slowly evaporating the solvent. Yield, 38%.
Anal. Calc. for C
9
H
11CuClN S (306.27): C, 35.29; H, 3.62; N, 18.29; S, 10.47. Found: C, 35.04; H,
4
-
1
2
-1
-1
4–
3
1
.91; N, 17.89; S, 10.06%. Λ (ohm cm mol , DMF): 4.8. IR (KBr, cm ): ꢄ (N H) 3303s; ꢄ(C=N)
518vs; ꢄ(N–N) 1079w; ꢄ(C=S) 773w; ν(ꢂ(ip)) 626m.
2
.2.3. Synthesis of [Cu(L4M)I] (2)
An acetonitrile solution containing cuprous iodide (0.0955 g, 0.5 mmol) was added with constant
stirring to HL4M (0.104 g, 0.5 mmol) in EtOH (CH CN:EtOH, 1:3) and refluxed. A dark brown
3
shinning residue started to form and refluxing continued for 1 hour. The product was filtered and
dried. Dark green crystals were obtained by slow evaporation of its DMSO solution. Yield, 40%.
9 4
Anal. Calc. for C H11CuIN S (397.74): C, 27.18; H, 2.79; N, 14.09; S, 8.06. Found: C, 27.42; H,
-
1
2
-1
-1
4–
2
1
.91; N, 14.18; S, 7.51%. Λ (ohm cm mol , DMF): 30. IR (KBr, cm ): ꢄ(N H) 3319s; ꢄ(C=N)
515vs; ꢄ(N–N) 1075w; ꢄ(C=S) 763w; ν(ꢂ(ip)) 640m.
2
2
.2.4. Synthesis of [Cu(L4M)OAc]·H O (3)
To a solution of HL4M (0.104 g, 0.5 mmol) in hot ethanol was added a solution of Cu(OAc)
2 2
·H O
(0.0995 g, 0.5 mmol) in water. The resultant deep green solution was stirred with refluxing for 1
hour, cooled and the solution was left to stand at room temperature. Few days later, dark green
3

shining crystals that formed was filtered, washed and dried. Yield, 64%. Anal. Calc. for
S (347.90): C, 37.98; H, 4.64; N, 16.11; S, 9.22. Found: C, 37.54; H, 4.27; N, 15.85;
C
11
H16CuN
4
O
3
-1
2
-1
-1
4–
S, 8.69%. Λ (ohm cm mol , DMF): 26. IR (KBr, cm ): ꢄ(N H) 3265s; ꢄ(C=N) 1534vs; ꢄ(N–N)
1
022w; ꢄ(C=S) 773w; ν(ꢂ(ip)) 617m. ꢄ(C–O)as 1587; ꢄ(C–O)sym 1338.
2
.2.5. Synthesis of [Cu(µ-S-L4M)(NCS)] · DMSO (4)
2
An ethanolic solution of HL4M (0.104 g, 0.5 mmol) is slowly added to aqueous solution of KSCN
0.0485 g, 0.5 mmol) and stirred for 10 min. The mixture was then refluxed by adding solution of
Cu(OAc) ·H O (0.0995 g, 0.5 mmol) in water. The resultant green precipitate was washed, dried and
recrystallized from DMSO. Yield, 32%. Anal. Calc. for [Cu(ꢀ-S-L4M)(NCS)] · C OS (655.95): C,
6.52; H, 3.37; N, 21.29; S, 19.50. Found: C, 36.93; H, 3.28; N, 20.85; S, 19.69%. Λ (ohm cm mol
(
2
2
2
2
H
6
-
1
2
-
3
1
-1
4–
,
DMF): 32. IR (KBr, cm ): (N H) 3325s; ꢄ(C=N) 1590vs; ꢄ(N–N) 1082w; ꢄ(C=S) 783w; ν(ꢂ(ip))
6
75m,
2
.3. X-ray data collection, structure solution and refinement
Crystallographic data were collected with a Bruker SMART APEX diffractometer with graphite
monochromated Mo Kꢅ (ꢆ = 0.71073 Å) X-ray source. Bruker SMART software was used for data
acquisition and Bruker SAINT Software for data integration [11]. Absorption corrections were
carried out using SADABS based on Laue symmetry using equivalent reflections [12]. The structure
was solved by direct methods and refined by full-matrix least-squares calculations with the SHELXL-
9
7 software package [13]. All non-hydrogen atoms were refined with anisotropic displacement
parameters and positions of hydrogen atoms were located in the difference Fourier maps and were
placed in calculated positions and refined as riding atoms: C–H = 0.93 Å (heteroaromatic), 0.96 Å
(
CH
3
) and
N–H = 0.86-0.87 Å with Uiso (H) = 1.2 Ueq (C,N). Bond lengths and angles were
restrained to ensure proper geometry using DFIX and DANG instructions. All the graphical plots
were made using ORTEP 3 and MERCURY 3.8 programs [14].
In complex 4 the non-coordinating DMSO molecule is disordered over two conformations with
refined occupancies of 0.719(7) and 0.281(7) respectively. For these atoms, SIMU/ISOR/SADI
restraints were applied [15].
4

3
. Results and discussion
3
.1. Comments on synthesis – An insight into solvent effects on crystallization
3
Reactions of copper salts with neutral thiosemicarbazone involved deprotonation at N position and
coordination to Cu(II) center as anion. The structural motifs of the complexes lie on several factors,
such as metal-ligand ratio, coordinated anions, pH, experimental conditions, solvent systems etc.
Complexes 1, 2, and 3 have the same stoichiometry [Cu(L4M)X] (X = Cl, I, OCOCH
3
) with four
coordinate square planar structure (structure I) and complex 4 has a dimeric structure (structure III).
Figure 1. Coordination modes in NNS donor Cu(II) thiosemicarbazone complexes.
In order to investigate the effect of solvents on crystallization, we used different solvent conditions for
the synthesis. The product was isolated as precipitate in all cases except for 3. No other solvent
system (water/EtOH/acetonitrile) yielded good quality single crystals for analysis. Dissolving either
the ligand or copper salt in methanol, DMF, dichloromethane and CHCl did not lead to the formation
3
of good quality crystals and no X-ray structure could be established. In order to further investigate
the effect of solvents, we made a brief survey on different thiosemicarbazones complexes and its
crystallization conditions. The final structures primarily rely on the polarity of the solvent used for
recrystallization.
4
Table 1. Color, molar conductivity and partial elemental analyses of 2-acetylpyridine-N -methyl-3-
thiosemicarbazone and its copper(II) complexes
Found (Calc.) %
Compound
HL4M
Colour
Λm
C
H
N
S
Colourless
Dark green
Dark green
Dark green
Dark green
51.49 (51.90)
35.04 (35.29)
27.42 (27.18)
37.54 (37.98)
36.93 (36.52)
5.33 (5.81)
3.91 (3.62)
2.91 (2.79)
4.27 (4.64)
3.28 (3.37)
27.35(26.90)
17.89(18.29)
14.18(14.09)
15.85(16.11)
20.85 (21.29)
14.74(15.39)
10.06(10.47)
7.51(8.06)
8.69(9.22)
19.69 (19.50)
[
Cu(L4M)Cl] (1)
Cu(L4M)I] (2)
Cu(L4M)OAc]·H2O (3)
Cu(L4M)NCS]2·C2H6OS (4)
4.8
30
26
15
[
[
[
Reactions of copper halides/acetate with thiosemicarbazones (NNS) either produce mononuclear
(structure I and II) or binuclear (structure III and IV, with bridging halogen/sulfur atoms) edifices
5

(Figure 1). Structural analysis reveal that complexes 1, 2 and 3 exist as a discrete mononuclear
structure (structure I). Correlating the preparation methods and structural features, such a
presupposition could be reached: in the Cu(II) thiosemicarbazone systems introduction of different
solvent systems can yield complexes with different stoichiometries and structural features.
Table 2. Effect of solvents on structural diversity of Cu(II) complexes
Ligand system
NNS
Mother liquor
Structure
Ref
[
[
[
[
[
[
[
[
[
[
[
[
CuL
CuL
CuL
CuL
CuL
CuL
CuL
CuL
CuL
1
1
1
2
3
4
1
5
6
Br]
Cl]
I]
C1]
DMSO
DMSO
DMSO
DMSO/ether
[17]
*
*
[18]
[19]
[20]
*
Cl]
3 3
DMSO/CH COCH
(OAc)]
(OAc)]
NNS
NNS
NNS
EtOH
EtOH/H O
2
ꢀ-Cl]
ꢀ-Cl]
2
CH
CH
CH
CH
3
3
3
3
OH
OH/CH
OH/CCl
OH/CH
[21]
[22]
[23]
[24]
[25]
2
3
Cl
Cu(HL
CuL (ꢀ-N
Cu (ꢀ-OAc)
7
) ꢀ-Cl
2
]
2
4
8
3
)]
3
Cl/DCM
OH
2
L
9
2
]
NNO
DMF/CH
3
[
[
[
[
Cu(ꢀ-SL10)NCS)]
2
NNS
NNS
NNO
NNO
DMSO
DMSO
DMF/EtOH
DMF/EtOH
[26]
*
[27]
[27]
Cu(ꢀ-SL )NCS)]
1
2
Cu(ꢀ-SL11)Cl]
Cu(ꢀ-SL12)Cl]
2
2
·2 DMF
·2 DMF
*
Present work
HL = 2-Acetylpyridine N4-methyl thiosemicarbazone
HL
HL
HL
HL
HL
HL
HL
HL
1
2
= 2-BenzoylpyridineN4-azepanethiosemicarbazone
= 2-Acetylpyridine N4-tolyl thiosemicarbazone
3
4
= 2-Pyridineformamide N4-dimethylthiosemicarbazone
= Pyridine-2-carbaldehyde-4-methyl-4-phenyl-3-thiosemicarbazone
= 2-Benzoylpyridine N4,N4-(butane-1,4-diyl)thiosemicarbazone
= 2-Pyridineformamide thiosemicarbazone
5
6
7
8
= Di-2-pyridyl ketoneN4-methyl, N(4)-phenylthiosemicarbazone
= 2-Benzoylpyridine-N(4)-phenylsemicarbazone
9
HL10 = Pyridine-2-carbaldehyde thiosemicarbazone
HL11 = 5-Methyl-2-oxoindolin-3-ylidene)-N-phenylhydrazinecarbothioamide
HL12 = 5-Fluoro-2-oxoindolin-3-ylidene)-N-phenylhydrazinecarbothioamide
-
-
-
-
Nucleophilicity of halogens in polar protic solvents follows the order F < Cl < Br < I and their
reactivities are greatly influenced by solvation via hydrogen bonding interactions. These solvated
species are more stable and less reactive compared to unsolvated "naked" anions. As a result, the
electrophilic copper center devoid of electrons forced to form halogen/sulfur bridges to partially
balance the electron deficiency. Polar, aprotic solvents such as DMSO and DMF do not solvate
anions. This decreased solvation is enough to balance the electrophilic Cu(II) center. Consequently,
most of the nucleophiles react more rapidly in solutions prepared from these solvents. Thus, for
reaction in DMSO solution, reactivity order of halogens get reversed. Dissolution of dimeric
complexes in DMSO can lead to partial dissociation and form different structural aggregates with
readily available halogen ions and achieve greater structural stability than in protic solvents.
Therefore, we can infer that, in aforementioned systems solvent plays a crucial role in crystallization
which sequentially influence the geometry of the complexes. Ligands forming hydrogen bonds are
6

well solvated by protic solvents and the complex formation with such ligands in protic solvents will
therefore be weaker than in aprotic solvents [16]. An exhaustive review of the literature [17-27]
shows that, these facts are in agreement with studies on analogous NNO and NNS donor copper(II)
complexes, which is shown in Table 2.
Presence of powerful sigma-donor groups (pyridyl and azomethine nitrogen) very effectively
stabilizes the higher oxidation state of copper. Accordingly, strong electron donation by the ligand
facilitates the ready oxidation of Cu(I). Cu(II) is a borderline acid and anionic ligand coordinates
through relatively harder nitrogen ends and soft sulfur end on the basis of HSAB theory.
We employed copper(I) iodide salt for the synthesis of complex 2 due to the reducing nature of the
II
bulky iodide ion. Eventhough, the formation of Cu -I bond was a challenging task, attempts made to
crystallize the complex were finally successful. Shikha et al suggested a probable pathway that
paved the way for the synthesis of complex 2 (Scheme 1). The neutral ligand reacts with Cu–I to
form an adduct (A) by coordination through the S donor atom and undergoes a rearrangement to form
an intermediate species B. The formation of complex 2 (C) is achieved by a rapid proton-coupled
electron transfer (PCET). PCET occurs only via the presence an additional coordinating functionality
in the proximity of the donating centers, such as pyridyl group, and no similar reaction occurs if the
groups at C2 are Ph, H or Ph, Ph. Thus, the presence of pyridyl group at the C2 atom appears to assist
the simultaneous tautomeric transformation and electron transfer from the CuI center. Thus, the
thiosemicarbazone ligands with pyridyl rings at the aldehydic/ketonic fragment are capable of
II
forming stable Cu –I complexes by coordinating in a tridentate manner. The possibility of aerobic
oxidation at the copper(I) center is ruled out because the reactions for the formation of the complexes
2
gave identical products under a N atmosphere [28].
Scheme 1. PCET process in the formation of complex 2.
3
The presence of acidic N–H allows ligand to remain either as the thione tautomer or the thiol
tautomer or as a mixture of both tautomers. Earlier studies [29, 30] have shown that, in the solid state
7

as well as in solution, thiosemicarbazones remain in their thione tautomeric form. It can coordinate
with metal ions in both the protonated thione and deprotonated thiolato form [31]. Complexes
containing the neutral ligand only result from reactions in weakly acidic aqueous media or non-
aqueous solvents of low polarity [32]. The molar conductivity values of the complexes show that they
are non-electrolytes and the analytical data of the complexes are listed in Table 1.
3
.2. Structural commentary
Table 3. Crystal and structure refinement data for complexes 1-4
Parameters
[Cu(L4M)Cl] (1)
[Cu(L4M)I] (2)
[Cu(L4M)OAc]·H
2
O (3)
2 2 6
[Cu(ꢀ-S-L4M)(NCS)] · C H OS (4)
Empirical formula
Formula weight
C
9
H
11ClCuN
4
S
C
9
H
11CuIN
397.74
293(2) K
0.71073 Å
Monoclinic
P2 /n
4
S
C
11
H
16CuN
347.90
293(2) K
4
O
3
S
22 2 5
C H28Cu N10OS
306.27
735.94
Temperature
Wavelength
Crystal system
Space group
296(2) K
293(2) K
0.71073 Å
Triclinic
P
0.71073 Å
Monoclinic
0.71073 Å
Monoclinic
P2
1
/n
1
1
P2 /c
Unit cell dimensions
a (Å)
8
.0660(16)
8.1465(9)
7.0284(5
9.418(2)
b (Å)
15.994(4)
9.193(2)
90.00
16.3888(19)
11.1368(9)
13.556(3)
c (Å)
9.5084(12)
90.00
19.3407(16)
90.00
13.883(3)
61.581(6)
87.597(6)
80.474(7)
ꢅ (°)
ꢇ (°)
92.356(7)
90.00
96.199(3)
90.00
99.338(3)
90.00
ꢈ (°)
3
3
3
3
Volume
1185.0(5) A
1262.1(3) A
1493.8(2) A
1536.0(6) A
Z
4
4
4
2
3
3
3
3
Calculated density
Absorption coefficient
F(000)
1.717 Mg/m
2.093 Mg/m
1.547 Mg/m
1.591Mg/m
-
1
-1
-1
-1
2.221 mm
4.320 mm
1.613 mm
1.760 mm
620
764
716
764
Crystal size
0.50 x 0.30 x 0.30 mm
2.55° to 25.99°
-9 ꢊ h ꢊ 9
0.30 x 0.11 x 0.09 mm
0.31 x 0.19 x 0.17
mm
2.81° to 27.50°
0.30 x 0.11 x 0.09
mm
2.63° to 24.99°
ꢉ range for data
collection
Limiting indices
2.49° to 25.50°
-9 ꢊ h ꢊ 9
-19 ꢊ k ꢊ 19
-9 ꢊ h ꢊ 9
-14 ꢊ k ꢊ 13
-21 ꢊ l ꢊ 25
10766
-11 ꢊ h ꢊ 10
-16 ꢊ k ꢊ 15
-13 ꢊ l ꢊ 16
6345
-
19 ꢊ k ꢊ 19
-11 ꢊ l ꢊ 11
-11 ꢊ l ꢊ 11
Reflections collected
Unique reflections
6230
7634
2306 [R(int) = 0.0694]
2346 [R(int) = 0.0338]
3431 [R(int) =
5402 [R(int) =
0.0329]
0
.0324]
Refinement method
Full-matrix least-squares
Full-matrix least-squares on
Full-matrix least-squares
Full-matrix least-
squares on F
2
2
2
2
on F
1.052
F
on F
1.012
2
Goodness-of-fit on F
1.112
1.007
Final R indices [I >2ꢋ(I)]
R
1
1
= 0.0446, wR
.1009
= 0.0667, wR
.1085
0.938 and
2
=
=
R
1
1
= 0.0307, wR
2
2
= 0.0694
= 0.0776
R
1
1
= 0.0304, wR
0.0812
2
=
=
R
1
1
= 0.0547, wR
0.1377
2
=
=
0
R indices (all data)
R
2
R
= 0.0388, wR
R
= 0.0383, wR
0.0865
2
R
= 0.0833, wR
0.1572
2
0
Largest diff. peak and
hole
0.621 and
-0.653 e.A
0.368 and
1.122 and
-3
-3
-3
-3
-1.011 e.A
-0.402 e.A
-0.810 e.A
Complexes 1, 2 and 3 crystallizes in non-centrosymmetric polar monoclinic crystal system with space
group P2 /n for complexes 1 and 2 while P2 /c for complex 3, with four molecules per unit cell. The
1
1
lattice nature of complex 4 is triclinic with space group symmetry P . Figs. 2-5 show the molecular
8

structures and Table 3 represent the crystallographic details. Selected bond distances and angles for
the proligand in the structures are compiled in Table 4 and those involving metal atom in
supplementary (Table S1) for the sake of comparison.
In complexes [Cu(L4M)Cl] (1), [Cu(L4M)I] (2) and [Cu(L4M)OAc]·H
2
O (3), the central copper(II)
cation coordinates in a square planar fashion satisfied by tridentate thiosemicarbazone moiety and the
-
-
-
coordination number is made up to four by binding with anionic group or atom (Cl , I and CH
The square plane in each case suffers slight tetrahedral distortion as indicated by the ꢌ values 0.0847,
.0644 and 0.1018 respectively for complexes 1, 2 and 3 [33], which means the coordination
3
COO ).
4
0
environment is more biased to ideal square planar extreme. Coordination results in structural
reorientation of the ligand about C5–C6, N2–C6, N3–C8 bonds and changes its configuration from E,
Z, E to Z, E, Z. This suggests that a possible rotation about the azomethine double bond occurs on
coordination and pyridyl N and thiocarbonyl S atom are cis aligned to coordinate in NNS manner. In
the complexes, the central atom deviates negligibly (0.07 Å) from the least squares plane through the
Table 4. Selected bond lengths (Å) and bond angles (°) of HL4M and the complexes 1-3
HL4M
(1)
(2)
(3)
C(8)–S(1)
1.680(2)
1.366(3)
1.372(3)
1.326(3)
1.286(3)
118.3(2)
116.3(2)
119.8(2)
119.0(2)
1.744(3)
1.325(4)
1.369(3)
1.349(4)
1.281(4)
119.2(2)
116.7(3)
125.9(2)
111.5(2)
1.751(5)
1.305(5)
1.365(5)
1.351(6)
1.288(5)
118.7(4)
117.3(4)
125.8(3)
111.8(4)
1.747(2)
1.319(3)
1.359(2)
1.325(3)
1.290(3)
119.12(16)
117.7(2)
125.08(16)
111.46(16)
C(8)–N(3)
N(2 –N(3)
C(8)–N(4)
C(6)–N(2)
C(6)–N(2)–N(3)
N(3)–C(8)–N(4)
N(3)–C(8)–S(1)
C(8)–N(3)–N(2)
donor atoms and the trans angles, N(1)–Cu(1)–S(1) and N(2)–Cu(1)–X(1) are similar and deviate less
from linearity. The coordinated ligand have longer N2–N3 bonds, shorter N3–C8 bond, and longer
C8–S1 bonds compared to the parent thiosemicarbazone as reported in the literature [10] and reflects
the ꢁ delocalization. The Cu–N bond lengths exactly fall in the normal ranges, 1.9476(16) to
2
.027(3) Å. The other geometric parameters associated with the complexes are also as expected. The
comparison of Cu–pyridine N, N(1) and Cu–azomethine N, N(2) distances in the complexes show
that the bond with the azomethine nitrogen atom is stronger, doubtless due to the greater basicity of
this nitrogen atom and possibly, the trans effect [10].
Table 5. Intermolecular hydrogen bonds in the complexes 1, 2, 3 and 4.
9

Symmetry transformations used to generate equivalent atoms:
D-H···A (Å)
d (D-H) (Å)
d (H···A) (Å)
2.57
d (D···A) (Å)
3.431(3)
∠DHA (°)
Complex (1)
a
N(4)-H(4A) ···Cl
0.86
177.9
Complex (2)
b
N(4)-H(4A)···I(1)
Complex (3)
0.875(10)
2.894(12)
3.766(4)
174(5)
c
N(4)-H(4')···O(1W)
0.872(10)
0.845(10)
0.846(10)
2.106(13)
2.029(10)
1.975(14)
2.936(3)
2.869(2)
2.779(2)
159(2)
173(2)
158(3)
d
O(1W)-H(1A)···O(1)
O(1W)-H(1B)···O(2)
Complex (4)
e
f
N(4)-H(4')...O(1)
0.873(10)
2.23(5)
2.938(10)
138(6)
a = x-1/2, -y+1/2, z-1/2; b = x+1/2, -y+5/2, z+1/2; c = x, y-1, z; d = -x+1, y+1/2, -z+3/2; e = -x+2, y+1/2, -z+3/2; f = x+1,y,z
Figure 2. ORTEP diagram of complex 1. Displacement ellipsoids are drawn with 30% probability.
Figure 3. ORTEP diagram of complex 2. Displacement ellipsoids are drawn with 30% probability.
1
0

Quasi-planar [Cu(L4M)NCS] entity forms the crystal structure of complex 4 [Cu
L4M) (NCS) ]·DMSO (4) stacked through thiolate atom, which leads to dinuclear centrosymmetric
species. The unequal Cu–S distances of its central Cu(ꢀ-S) Cu core, forms a parallelogram. Each
2
(ꢀ-S-
2
2
2
copper atom is further coordinated to a terminal N of thiocyanate, imine nitrogen and pyridine
nitrogen making the Cu1 and Cu2 coordination environments square pyramidal (ꢌ = 0.08 and 0.04
respectively) and the DMSO molecule present in the lattice completes the asymmetric unit. The
square pyramids are oriented in such a manner that basal-apical edges are shared with parallel basal
planes [5]. The fragments are related to each other by a C
2
axis passing through the thiolate bridged
corners of the Cu core. Copper(II) dimers with same core and similar arrangement of square
2 2
S
pyramids are rare among thiosemicarbazone complexes, the related dimeric complexes [34-37] being
other examples. A perspective view of the dimer is shown in Fig. 5 and bond parameters and core
angles are given in supplementary table S2. The intradimeric and the minimum interdimeric Cu···Cu
distances are 3.499(1) and 4.7145(14) Å respectively.
Figure 4. ORTEP diagram of complex 3. Displacement ellipsoids are drawn with 30% probability. (H
2
O
molecule has been omitted for clarity).
1
1

2 2 2 2 6
Figure 5. ORTEP diagram of complex [Cu (ꢀ-S-L4M) (NCS) ] ·C H OS (4). Displacement ellipsoids are
drawn with 30% probability. (DMSO molecule has been omitted for clarity).
Supramolecular features. The molecular structures of complexes [Cu(L4M)Cl] (1) and [Cu(L4M)I]
2) reveal their nearly planarity and only methyl groups are out of the plane. On probing into the
(
crystal packing, it was deduced that complexes 1 and 2 are associated into 1D supramolecular
network sustained by N–H···X hydrogen bonding interactions. Hydrogen bonding parameters are
presented in Table 5. Each unit cell comprises four chains of this type. The halogen atom and
uncoordinated nitrogen have significant impact on packing and adopts an edge to face ‘herringbone’
arrangement with an interplanar distance of 4.7607(8) and 4.5314(10) Å respectively for complexes 1
and 2. Crystal packing is also augmented by weakly attractive chelate ring-chelate ring interactions
and chelate ring-pyridine ring interactions. The unique propagation of the supramolecular chains is
an important structural feature of these complexes and these propagation modes have been unknown
in the literature so far. Viewed along the ‘c’ axis, the zipper-like chains in complex 1 propagates by
intercepting the ‘c’ axis and complex 2 is characterized by propagation perpendicular to the ‘b’ axis.
Usually supramolecular chains are aligned along/parallel to any of the three crystallographic axes.
The 1D motif interact in turn through further ꢁ···ꢁ interactions which expand the supramolecular
aggregation to three-dimensional framework.
Pairs of such chains related to one another by
inversion symmetry and hence running antiparallel, are linked by ꢁ···ꢁ stacking interactions. Thus
the formation of framework can be most simply analyzed in terms of two substructures, one of them
one-dimensional and involving N–H···X hydrogen bond, while the other is two dimensional and
involves five stacking interactions [38]. Combination of two interactions generates parallel sheets
and the successive layers are interconnected by utilizing the other three interactions. Owing to the
1
2

isostructural behavior of complexes 1 and 2, we only restrict our discussion to the supramolecular
aggregation of complex 2.
Figure 6. Formation of 1D ‘zipper like’ chain in complex 1 intercepting ‘c’ axis
Figure. 7. Herring bone packing arrangement in complex 2.
Figure 8. 3D network drawing for complex 2 (H atoms have been omitted for clarity).
1
3

-
In the first substructure, the nitrogen atom at (x, y, z) acts as a hydrogen bond donor to I at (x+1/2, -
y+5/2, z+1/2) forming a chain. In the second substructure, parallel layers are formed by the
stacking interactions between rings Cu1, S1, C8, N3, N2 at (x, y, z) with Cu1, S1, C8, N3, N2 at their
closest approach with centroid-to-centroid distance of 3.584(2) Å and the ring-centroid separation
3
.245(13) Å , corresponding to a ring offset of 1.520 Å and Cu1, N1, C5, C6, N2 at (2-x, 2-y, -z)
(
centroid-to-centroid distance is 3.431(2) and ring-centroid separation is 3.3231(15)). The propagating
chains interact each other through five membered chelate rings and pyridine ring. The rings Cu1, S1,
C8, N3, N2 and Cu1, N1, C5, C6, N2 at (x, y, z) act as donors respectively to N1, C1-C5; Cu1, S1,
C8, N3, N2 (symmetry code: 1-x, 2-y, z) and Cu1, N1, C5, C6, N2 act as donor to N1, C1-C5
(symmetry code: 1-x, 2-y, z). Thus the combination of moderately strong ring interactions links the
sheet aggregates to three dimensional framework. The fragments of supramolecular architecture are
depicted in Figs. 7 and 8.
Figure 9. Water molecules (shown in space filling model) sandwiched between two symmetry-related layers of
complex 3.
The supramolecular array in complex 3 shows that the solvent molecule in the lattice has a key role in
the self-assembly of molecules into a two dimensional structure. The water molecules are sandwiched
by two symmetry-related layers of complex molecules as shown in Fig. 9. The solvent molecules are
held in place by interaction with three complex molecules through three hydrogen bonds. The O1 and
O2 acceptor positions of acetate moiety establish strong O–H···O hydrogen bonds [symmetry codes: -
x+1,y+1/2,-z+3/2; -x+2,y+1/2,-z+3/2,] and these chains are further cross-linked by means of N(4)–
(H4’)···O(1W) hydrogen bonds [symmetry code: x,y-1,z], resulting in an extended bidimensional
assembly parallel to the crystallographic ab (110) plane. The most attractive aspect is that, the two
dimensional sheets resembles a seamless tribal pattern with men holding hands (Fig. 10). The layers
are further linked via combination of ꢁ···ꢁ and C–H··· ꢁ interactions along ‘c’ axis to generate a three
dimensional framework. The molecules are ꢁ stacked in two nonequivalent layers which are nearly
1
4

vertical to each other due to the occurrence of C–H··· ꢁ intermolecular contacts. The ring centroid
separation between metallocycle Cu1 N1, C5, C6, N2 and the pyridyl ring [at (x, y, z) and (1-x, -y, 1-
z), respectively] is 3.7488(12) Å with dihedral angle 1.89(9)°. Moreover the supramolecular
aggregation is reinforced by ꢁ···ꢁ stacking interaction between metallocycles Cu1 N1, C5, C6, N2 at
(x, y, z) and (1-x, -y, 1-z): the ring centroid separation is 3.5391(11) Å , corresponding to a ring offset
of 1.077 Å . The three dimensional packing of the layers in the crystal building of the compound is
shown in Fig. 11.
Figure 10. A view of the 2D supramolecular architecture in the crystal structure of complex 3 extending in the
ab plane (resembles a seamless tribal pattern with men holding hands).
Figure 11. 3D Supramolecular array in 3 showing ꢁ-ꢁ interaction.
1
5

In complex 4, the supramolecular structure is comparatively less complex than that in the case of
other three complexes. The structure contains two intermolecular N(4)–H(4')···O(1) and C(14)–
H(14)···S(2) hydrogen bonds running parallel to the ‘a’ axis. But these interactions cannot be
regarded as structurally important, because the N–H···O and C–H···S angles are very close to 140°
[39]. Nevertheless, the combination of graphitic ꢁ···ꢁ stacking and ring-metal interactions, rendering
low dimensional supramolecular aggregation running parallel to ‘b’ axis has great impact on the
overall stability of the complex (Fig.12).
Figure 12. Graphitic ꢁ···ꢁ stacking interactions in complex 4.
3
3
.3. Spectral investigation
.3.1. Infrared spectra and coordination mode
-
1
Absorptions between 3200 and 3350 cm correspond to the stretching modes of N–H groups. The
-1
3
band at 3240 cm in the spectrum of free ligand due to N –H vibration disappears in the spectra of all
complexes, thus proving the ligand coordination around Cu(II) ion in the deprotonated thiolate form.
The occurrence of the ꢄ(N–N) band at higher frequencies in the IR spectra of the complexes, compared
to that observed for the ligand, confirms coordination through the azomethine nitrogen atom. The
thioamido band, which contains considerable ꢄ(CS) character, is less intense in complexes and is
found at lower wavenumbers [40]. Two absorption bands in the imine region are consistent with the
formation of a new imine bond upon coordination of copper to sulfur in the thiolato form. The acetate
-1
complex 3 has an additional broad band at 3453 cm corresponds to the O–H stretching of water. In
-1
addition to this, a strong peak is observed near 1300 cm , characteristic of C–O vibration. The
antisymmetric (νasym) and symmetric (νsym) O–C–O vibrations, together with the difference ∆νasym-sym
is indicative of the strength of coordination, and the mode of binding, which can be monodentate or
,
-1
-1
-1
bidentate. The νasym at 1587 cm and νsym at 1338 cm with a difference of 249 cm confirms the
-1
monodentate coordination of acetate [41-43]. Complex 4 exhibits a strong band at 2058 cm , a
1
6

-1
-1
medium band at 735 cm and a weak band at 479 cm , attributable to ꢄ(CN), ꢄ(CS) and ꢄ(NCS)
respectively of a typical N-bonded thiocyanate complex [44].
3
.3.2. Electronic spectra
The data obtained for the complexes in DMF solutions are indicative of square planar geometry and
are dominated by intense intraligand and charge transfer bands. However, possible d-d bands
2B1g→ A1g, B1g→ B2g and B1g→ E
2
2
2
2
2
] corresponding to the energy levels dx -y ꢍꢍ dxy ꢍ d ꢍ dxz, dyz
2
2
2
[
g
z
have been hidden within a single broad band with maxima in the range 589-598 nm, as expected. The
intense bands in the range 408-412 nm are assignable to a combination of SꢎCu(II) and NꢎCu(II)
charge transfer transitions. The ligand showed absorption band around 310 nm and this transition are
shifted in the spectra of all the complexes by appropriate amounts. The relative intensity and
frequency of absorption varies with ꢁ donor properties of ligand. The d-d transitions of ꢁ acceptor
ligands to be of a higher frequency than the ꢁ donor.
3
.3.3. EPR studies
In order to obtain further information concerning the electronic structure of the metal and its
immediate surroundings, EPR spectra were recorded in the polycrystalline state and in frozen DMSO
solution. The magnetically non-diluted solid state spectra are not self-explanatory with regard to the
hyperfine structure, which indicate the existence of anisotropy caused by g factors and strong dipolar
interaction between the Cu centres. Transmission of hydrophobic interactions through weak non-
negligible exchange interaction also contribute to the lack of hyperfine structure in the solid epr
spectra [45]. In order to exclude unwanted effects, spectra were recorded in DMSO solution at 77 K.
The spectra were paired with simulation using Easyspin 4.0.0 package [46]. The effort to get virtuous
fit failed due to the asymmetric nature of superhyperfine structure. In frozen solution the complexes
show hyperfine splitting into four lines, characteristic of monomeric Cu(II) complexes corresponding
to -3/2, -1/2, 1/2 and 3/2 transitions (ꢏMs = ±1). The EPR spectral parameters of the title complexes
in the polycrystalline state at 298 and in DMSO solution at 77 K are presented in Table 6 and 7.
It is seen that complexes 2 and 3 display isotropic spectra and 1, 4 show typical axial behavior in the
polycrystalline state (Figure S3 and S4). All the solution spectra are axial in nature with tensor values
2
2
2
g
|| > g
⊥
> 2.002, which are consistent with a dx -y ( B1g) ground state indicating the presence of the
unpaired electron. The existence of exchange coupling between copper centers in a polycrystalline
state is quantified by geometric parameter G = (g|| -2.0023)/( g -2.0023), G < 4 [47]. The exchange
⊥
interactions are ensued via the N(4)–H(4)···X (Cl / O) hydrogen bonding which relates the nearest
Cu(II) ions at distances 4.7607(8) and 3.499(3) Å for 1 and 4 respectively. Larger Cu···Cu
1
7

interatomic distances in complex 2, 5.4752(11) Å and 3, 5.3468(4) Å may result in weak exchange
coupling between Cu(II) paramagnetic centres [48].
The complexes 2 and 3 recorded in 77 K show quartet hyperfine structure in the low field range,
characteristic of square planar or square pyramidal coordination environment around copper centers.
⊥
The high field g component is well resolved with superhyperfine lines due to interaction of two
nitrogens with Cu(II) xy plane. Complex 4 displays an axial spectrum with four hyperfine lines.
There is no half field signal corresponding to the forbidden magnetic dipolar transition for complex 4
(
Figure S2), confirming the absence of dimeric structure. It proves that dimeric structure existing in
solid state was destroyed by DMSO. Low temperature spectra of complex 2 and 3 are depicted in Fig
3. Low temperature spectrum of Complex 1 shown in Figure S1.
1
Table 6. EPR spectral parameters of the complexes in the polycrystalline state.
Polycrystalline state (273 K)
Compound
g
||
g
⊥
g
iso
G
Complex 1
Complex 2
2.236
-
2.06
-
4.05
-
2.11
2.09
Complex 3
Complex 4
-
-
-
2.24
2.07
3.51
Table 7. EPR spectral parameters of the complexes in DMSO solution.
Compound
DMSO solution (77 K)
Cu
a
||
Cu
a
Cu
a
N1
a
N2
a
2
2
2
b
g
||
g
⊥
g
av
A
A
⊥
A
0
A
0
A
0
ꢅ
ꢇ
ꢈ
K
||
K
⊥
f
Complex 1
Complex 2
Complex 3
Complex 4
2.16
2.09
2.113 186
2.091 203
0
62
83
87
62
0.752 0.838 1.249 0.630 0.941 115
0.808 0.848 0.794 0.686 0.642 107
0.819 0.836 0.786 0.686 0.645 106
0.734 0.865 0.911 0.635 0.669 115
2.188
2.191
2.16
2.043
2.044
2.046
24
27
0
5.95
10.17 7.19
4.73
2.09
206
2.084 186
a
-1
-4
Expressed in units of cm multiplied by a factor of 10
expressed in units of cm
b
In a tetragonal (D4h) crystal field the effective spin-Hamiltonian [49] of the EPR spectra of copper(II)
complexes can be described as,
Cu
Cu
N
H = ꢇ[g||HzSz + g
⊥
(HxSx + HyS
y
)] +
A||SzIz(Cu) +
A
⊥
[SxIx(Cu) + Sy Iy(Cu)] + [ A||SzI (N) +
z
N
⊥
A {SxIx(N) + SyIy(N)}]
The degree of distortion, f factor (g||/A||) is regarded as an empirical index of deviation from idealized
geometry [50]. For square planar complexes, f = 105-135 and increases with increasing tetrahedral
distortion. Values from 106 to 115 cm for the present series of complexes suggest structures close to
planarity. Since the superhyperfine structure is well resolved, the ligating system (NNS) appears to be
⊥
coplanar with the two chelate rings, thus corroborating the nearly planar geometry (g||>g ) [51].
1
8

Figure 13. Low-temperature (77 K) EPR spectrum of complexes 2 (a) and 3 (b) in DMSO solution paired with
its simulation (blue line).
Table 8. Comparison of epr parameters A|| and g|| for complexes 1-4 with other reported ONS and NNS donor
Cu(II) thiosemicarbazone complexes
NNS donor thiosemicarbazone complexes
ONS donor thiosemicarbazone complexes
Complex
Complex
g
||
A
||
Ref.
*
g
||
A
||
Ref.
A
[Cu(L4M)Cl]
2.16
186
206
186
F
[(CuL
4
)
2
]
2.177
2.167
2.17
182.3 [57]
[
[
[
Cu(L4M)I]
2.191
2.16
*
*
*
[CuL
4
dmbipy]
190.5 [57]
175 [58]
Cu(L4M)OAc]·H
2
O
G
[Cu(L
5
)(bpy)]
Cu(ꢀ-S-L4M)(NCS)]
OS
[Cu(L)NCS]_H
Cu(L)I]
2
·
C
2
H
6
2.188
2.192
2.204
203
208
205
[Cu(L
[Cu(L
5
5
)(phen)]
)(dmp)]
2.17
2.17
175 [58]
175 [58]
181 [59]
188 [59]
188 [59]
185 [59]
116 [59]
176 [60]
177.3 [60]
160 [60]
170 [61]
172 [61]
170 [61]
170 [61]
166.7 [61]
173.3 [61]
B
C
2
O
[56]
[56]
[21]
[21]
[21]
[21]
[21]
[21]
[21]
[6]
[
H
I
[Cu(HL
6
)Br
2
]
2.21
[CuL
1
1
1
1
2
2
Cl]
2.1607
2.1787
2.1544
2.1787
2.1625
2.1563
2.1697
2.175
186.6
195
[Cu(L
[Cu(L
[Cu(L
[Cu(L
6
6
6
6
)
2
]
2.22
[CuL
[CuL
[CuL
NO
3
]
2
)(OAc)(H
)(ClO4)(H
)(NO )(H O)
N)
O)
2
O)]
2.195
2.205
2.4
N
3
]2·2/3H
]2(ClO4)2·2H
Cl]
2
O
187.75
194.9
188.5
187.92
192.5
192
2
O)]
2
O
3
2
2
]
D
E
[CuL
2
[Cu
2
(L
7
)
2
(Et
3
2
(H
2
O)
4
](NO
3
)
2
2.228
2.236
2.370
2.193
2.19
[CuL
N
3
]
[Cu(L
[Cu(L
[Cu(L
[Cu(L
[Cu(L
[Cu(L
7
7
8
8
9
9
)
2
(H
2
2
]
[Cu(HL
2
)
2
](ClO
)(SO )]·H
Br]_1/2H
(NCS)]
4
)
2
·1/2EtOH
)(OAc)(H
2
O) ]
2
[Cu(HL
3
4
2
O
J
)(2,20-bipy)]
[
[
[
[
CuL
3
2
O
2.16
193
[6]
)(1,10-phen)]
)(2,20-bipy)]
)(1,10-phen)]
CuL
3
2.178
209
[6]
K
L
2.194
2.19
Cu
Cu
2
L
L
3
(OAc)
2
]·H
2
O
2.184
193
[6]
2
3
I
2
]
2.194
204
[6]
[Cu(L10)(2,20-bipy)]
Cu(L10)(1,10-phen)]
2.19
[
2.174
*
Present work
B =
E =
F =
H =
K =
C =
I =
L =
1
9

D =
G =
J =
Kivelson and Neiman [52] reported that, g|| values less than 2.3 is an indication of significant covalent
character. From the spectral data we can infer that the g|| values are nearly same for all the four
complexes (< 2.3) and show appreciable covalent character. The EPR parameters and d–d transition
energies were used in the evaluation of other spectral parameters.
2
The bonding parameter ꢅ is considered as measure of the covalency of the in-plane ꢋ- bonding
2
2
between the 3d-metal orbital and the ligand orbital. ꢇ and γ are in-plane ꢁ bonds and out-of-plane ꢁ
2
2
2
2
2 2
bonds respectively. K|| = ꢅ ꢇ and K
⊥
= ꢅ ꢈ are the orbital reduction factors.
Hathaway [53] has pointed out that for pure sigma bonding K|| ꢐ K
and for out-of plane ꢁ-bonding, K < K|| . For complexes 1 and 4, it is observed that K|| < K
indicates significant in plane ꢁ-bonding. For other complexes out of plane ꢁ-bonding is important.
⊥
ꢐ 0.77, for in plane ꢁ-bonding K||
<
K
⊥
⊥
⊥
The stronger covalency should result in smaller hyperfine interaction. In the case of 100% ionic
2
character, ꢅ values are expected to be 1.0 and becomes smaller with increasing covalent bonding. It is
inferred that the in-plane-bonding of investigated Cu(II) complexes have partial ionic and partial
2
covalent character with the ꢅ values 0.75, 0.80, 0.81 and 0.73 respectively. These values indicate that
2
2
approximately 70-80% of the spin population is in the copper dx -y orbital of all the Cu(II) species
concerned [54].
A|| - g|| correlation analysis: The A|| - g|| ratios reflect the degree of tetrahedral distortion.
Nevertheless the Peisach – Blumberg correlation diagram [55] suggest the nature of the coordinated
atoms to the Cu(II). Presently, we are analyzing trends in A|| - g|| relations of ONS donor Cu(II)
complexes with NNS donor Cu(II) complexes from collected experimental data (Table 8) [56-61].
2
2
According to molecular orbital theory [62] Cu(II) complexes having dx -y ground state, hyperfine
splitting(A||) and g-factor(g||) is related as
-1
where P characterizes average radius r
d
of the ground state d-orbital and is equal to 0.036 cm for free
2
+
2+
Cu ion, is the Fermi contact hyperfine interaction parameter which is equal to 0.43 for free Cu
2
2+
i
ion, ꢏg = g - 2.0023 and ꢅ is unpaired electron density in Cu ground state reflecting the degree of
coordination bond covalency. Plot of A|| vs. g|| is a straight line and the slope of the line is determined
2
by the P-value and line is shifted to the left when covalency grows (ꢅ decreases) [63].
2
0

Figure 14. Peisach – Blumberg correlation diagram for NNS donor thiosemicarbazone Cu(II) complexes
Figure 15. Peisach – Blumberg correlation diagram for ONS donor thiosemicarbazone Cu(II) complexes.
For ONS donor complexes it has been observed that g|| increases with concomitant decrease in A||
component, which means the parameters have a negative linear correlation. Versatility and more
flexibility in coordination can be introduced by varying the heterocyclic group. Nonetheless, the
additional donor site impart a surprising inverse relation between these parameters. The correlation
line gives a negative slope with smaller range of g|| factors and A|| splitting. The g|| value decreases
and hyperfine splitting A|| grows as nitrogen replaces oxygen of thiosemicarbazones (NNS donor).
Peisach – Blumberg plot of selected complexes are depicted in Figs. 14 and Fig. 15.
A correlationship of A|| and f (Fig. 16) is investigated and suggests that A|| linearly decreases with f as
a consequence of the deformation of the square planar geometry. Moreover, it results in
2
1

unsymmetrical electron delocalization which in turn influences the copper hyperfine structure. From
the results we can infer that the magnetic and physicochemical properties of the complexes differ as
chromophoric group varies.
Figure. 16. Correlationship of A|| and f for ONS and NNS donor thiosemicarbazone Cu(II) complexes from
Table 7.
4
. Concluding remarks
In summary, we have solvent-dependently synthesized four Cu-based thiosemicarbazone complexes
where Cu(II) is in a (3+1) coordination environment for complexes 1-3. For complex 4, Cu(II)
formed thiolate bridged dinuclear complex. The physico-chemical analyses confirmed the structures
of all the new products. Structural analysis indicates the importance of solvent for different geometry
and coordination mode enables an understanding of the crucial role of solvents in the assembly,
crystallization and stability of the supramolecular architectures. Substitution of different anions alter
the hydrogen bonding patterns and hence the intermolecular interactions, as well as supramolecular
2
2
2
patterns. The evaluated values of ꢅ , ꢇ and ꢈ of the complexes are consistent with strong in-plane ꢁ
bonding and out-of-plane ꢁ bonding. Ligands, capable of forming extended networks through
hydrogen bonding can act as a channel for transferring magnetic exchange interactions. The
correlation between g-factor and hyperfine splitting factor for ONS and NNS donor
thiosemicarbazone complexes is depicted using Peisach-Blumberg diagram and we found that the A||
vs g|| correlation is a straight line and are inversely related as it is suggested by a collection of
experimental data.
2
2

Acknowledgements
Lincy Tom acknowledges CSIR for the award of a Junior Research Fellowship. N. Aiswarya
gratefully acknowledges the UGC, New Delhi, India for financial support in the form of Senior
Research Fellowship and S.S. Sreejith is thankful to the Cochin University of Science and
Technology, Kochi, India for financial assistance in the form of Junior Research Fellowship. The
authors are indebted to SAIF, Cochin University of Science and Technology, Kochi, Kerala, India for
elemental analysis and Single Crystal X-ray diffraction studies. We are thankful to IIT, Bombay and
Madras for providing EPR and magnetic susceptibility results. We gratefully acknowledge Dr.
Mathias Zeller Department of Chemistry, Purdue University for his help in Single crystal XRD
refinement.
Appendix A. Supplementary data
CCDC 1527237 – 38 and 1527240 - 41 contains the supplementary crystallographic data for
compounds 1, 2 and 3, 4 respectively. Copies of this information may be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html or from the Director, CCDC, 12 Union Road, Cambridge,
CB2, IEZ, UK (fax: +44-1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
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2
5

Self-organized three dimensional architectures based on non-covalent
interactions in square planar Cu(II) thiosemicarbazone: Solvent mediated
crystallization and EPR based correlation study
a
Lincy Tom , N. Aiswarya , S.S. Sreejith , M. R. Prathapachandra Kurup
a
a
a,b*
Highlights
4
•
•
Four copper (II) complexes of 2-acetylpyridine-N -methyl thiosemicarbazone were prepared.
Stability of complexes in polar protic and aprotic solvents were investigated and the effects of
solvents were studied.
•
•
EPR parameters g|| and A|| of complexes were analyzed by Peisach–Blumberg plot and
established an inverse correlation among NNS and ONS thiosemicarbazone complexes.
The detailed crystal structures and supramolecular interactions of all the prepared complexes
showed the role of secondary interactions in the creation of molecular architectures.
2
6

Self-organized Three Dimensional Architectures based on Non-covalent
Interactions in Square planar Cu(II) Thiosemicarbazone: Solvent mediated
crystallization and EPR based Correlation Study
a
Lincy Tom , N. Aiswarya , S.S. Sreejith , M. R. Prathapachandra Kurup
a
a
a,b
Graphical Abstract
2
7