[Dichlorido (2-(2-(1H-benzo[d]thiazol-2-yl)hydrazono)propan-1-ol) Cu(II)]: Crystal structure, Hirshfeld surface analysis and correlation of its ESI-MS behavior with [Dichlorido 3-(hydroxyimino)-2-butanone-2-(1H-benzo[d]thiazol-2-yl)hydrazone Cu(II)]

Article abstract of DOI:10.1016/j.molstruc.2017.07.109

In the present work, Cu(II) complexes of 2-(2-benzo[d]thiazol-2-yl)hydrazono)propan-1-ol (L¹) and 3-(hydroxyimino)-2-butanone-2-(1H-benzo[d]thiazol-2-yl)hydrazone (L²) are synthesized and characterized by various spectro-analytical techniques. The structure of Cu(II) complex of L¹ i.e., [CuL¹Cl₂], is unambiguously determined by single crystal X-ray diffraction method. While similar efforts were unsuccessful in the case of Cu(II) complex of L² i.e., [CuL²Cl₂]. Hence, to avail the structural facts, various cationic/anionic fragments or adducts formed during positive/negative mode electrospray ionization (ESI) of CuL¹Cl₂ and CuL²Cl₂ have been identified with the help of their charge, monoisotopic masses and isotopic distributions. The similarity in the ESI behavior of two complexes has inferred their structural resemblance, which is further supported by DFT optimized structures, EPR spectral studies and analytical measurements. The EPR spectral behavior (g_|| > g_⊥ > 2.02) of the complexes are attributed to an axial symmetry with the d_x²?y² ground state having square pyramidal Cu(II) ion. CuL¹Cl₂ has crystallized in monoclinic crystal system in P2₁/c space group. The molecular complex has ring-metal (Cg-Me) interactions of the type Cg···>Cu, which contributes to the crystal packing. The Cl?H (30.6%) interactions have the major contribution among all intermolecular contacts and have played a vital role in the stabilization of the molecular structure, which is extended to 3D network through C–H···Cg and Cg-Cg interactions.

Full text of DOI:10.1016/j.molstruc.2017.07.109

Accepted Manuscript
[Dichlorido (2-(2-(1H-benzo[d]thiazol-2-yl)hydrazono)propan-1-ol) Cu(II)]: Crystal
structure, Hirshfeld surface analysis and correlation of its ESI-MS behavior with
[Dichlorido 3-(hydroxyimino)-2-butanone-2-(1H-benzothiazol-2-yl)hydrazone Cu(II)]
Vinayak Kamat, Karthik Kumara, Krishna Naik, Avinash Kotian, Priya Netalkar,
Naveen Shivalingegowda, Neratur Krishnappagowda Lokanath, Vidyanand Revankar
PII:
S0022-2860(17)31053-0
10.1016/j.molstruc.2017.07.109
MOLSTR 24136
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 19 May 2017
Revised Date: 30 July 2017
Accepted Date: 31 July 2017
Please cite this article as: V. Kamat, K. Kumara, K. Naik, A. Kotian, P. Netalkar, N. Shivalingegowda,
N.K. Lokanath, V. Revankar, [Dichlorido (2-(2-(1H-benzo[d]thiazol-2-yl)hydrazono)propan-1-ol) Cu(II)]:
Crystal structure, Hirshfeld surface analysis and correlation of its ESI-MS behavior with [Dichlorido 3-
(hydroxyimino)-2-butanone-2-(1H-benzothiazol-2-yl)hydrazone Cu(II)], Journal of Molecular Structure
(2017), doi: 10.1016/j.molstruc.2017.07.109.
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ACCEPTED MANUSCRIPT
[Dichlorido (2-(2-(1H-benzo[d]thiazol-2-yl)hydrazono)propan-1-ol) Cu(II)]: Crystal
structure, Hirshfeld surface analysis and correlation of its ESI-MS behavior with
[Dichlorido 3-(hydroxyimino)-2-butanone-2-(1H-benzothiazol-2-yl)hydrazone Cu(II)]
Vinayak Kamata, Karthik Kumarab, Krishna Naika, Avinash Kotiana, Priya Netalkarc, Naveen
Shivalingegowdad, Neratur Krishnappagowda Lokanathb and Vidyanand Revankara.
a Department of Chemistry, Karnatak University, Dharwad-580003, India.
b Department of Studies in Physics, University of Mysore, Manasagangotri, Mysuru-570 006, India.
c Department of Chemistry, Karnatak Science College, Dharwad-580001, India.
d Institution of Excellence, Vijnana Bhavan, University of Mysore, Manasagangotri, Mysuru- 570 006,
India.
Contact email: vkrevankar@rediffmail.com
Abstract
In the present work, Cu(II) complexes of 2-(2-benzo[d]thiazol-2-yl)hydrazono)propan-1-ol (L1)
and 3-(hydroxyimino)-2-butanone-2-(1H-benzothiazol-2-yl)hydrazone (L2) are synthesized and
characterized by various spectro-analytical techniques. The structure of Cu(II) complex of L1 i.e.,
[CuL1Cl2], is unambiguously determined by single crystal X-ray diffraction method. While similar efforts
were unsuccessful in the case of Cu(II) complex of L2 i.e., [CuL2Cl2]. Hence, to avail the structural facts,
various cationic/anionic fragments or adducts formed during positive/negative mode electrospray
ionization (ESI) of CuL1Cl2 and CuL2Cl2 have been identified with the help of their charge, monoisotopic
masses and isotopic distributions. The similarity in the ESI behavior of two complexes has inferred their
structural resemblance, which is further supported by DFT optimized structures, EPR spectral studies
and analytical measurements. The EPR spectral behavior (g|| > g⊥ > 2.02) of the complexes are
attributed to an axial symmetry with the dx2-y2 ground state having square pyramidal Cu(II) ion. CuL1Cl2
has crystallized in monoclinic crystal system in P21/c space group. The molecular complex has ring-metal
(Cg-Me) interactions of the type Cg···>Cu, which contributes to the crystal packing. The Cl···H (30.6%)
interactions have the major contribution among all intermolecular contacts and have played a vital role
in the stabilization of the molecular structure, which is extended to 3D network through C—H···Cg and
Cg-Cg interactions.
Keywords
Copper complexes of benzothiazol hydrazone, Crystal structure of the copper complex, Hirshfeld
analysis of metal complex, ESI-MS of a coordination complex.
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Highlights
•
Two complexes, [Dichlorido (2-(2-(1H-benzo[d]thiazol-2-yl)hydrazono)propan-1-ol) Cu(II)] and
[Dichlorido 3-(hydroxyimino)-2-butanone-2-(1H-benzothiazol-2-yl)hydrazone Cu(II)] are
synthesized.
•
•
X-ray structure, intermolecular interactions and Hirshfeld surface analysis of [Dichlorido (2-(2-
(1H-benzo[d]thiazol-2-yl)hydrazono)propan-1-ol) Cu(II)] are explored.
Various cationic/anionic fragments or adducts formed during positive/negative mode
electrospray ionization of the complexes have been identified with the help of their charge,
monoisotopic masses and isotopic distributions.
Graphical abstract
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1. Introduction
Polydentate heterocyclic ligands containing both sulfur and nitrogen atoms possess versatile
coordination ability toward various transition metal ions. Hence, polyfunctional benzothiazole-based
derivatives assume an exceptional importance in the construction of metal complexes of different types
[1]. Due to this fact, a wide variety of copper (II) complexes derived from benzothiazole core have been
reported in the literature [2-4].
X-ray crystallography remains the method of choice for definitive determination of the structure
of a new coordination complex, despite the tremendous advances in spectroscopic methods for
structure elucidation [5]. Hence, X-ray crystallography is often touted as the ultimate technique for
substance characterization. While this is often true, limitations in growing the single crystals suitable for
diffraction need to be recognized.
Recent developments of new soft ionization methods have made possible the application of
mass spectrometry in various fields of analytical chemistry. Electrospray Ionization (ESI) is one such soft
ionization method, that keeps any weakly bound ligands intact to the metal ion in a coordination
complex. Because of this advantage of ESI, it has become increasingly popular as an analytical tool in
inorganic and organometallic chemistry [6, 7]. Hence electrospray ionization mass spectrometry (ESI-
MS) can be used as a complementary tool in the characterization of coordination species. However, due
to susceptibility to thermal decomposition, ESI-MS may not always detect molecular ions in most of the
cases [8, 9]. This makes it extremely important to identify the various species formed during ESI of
coordination complexes.
Considering these facts, herein we have tried to correctly establish the structure of two copper
complexes derived from benzothiazole moiety, through detailed comparative analysis of their ESI-MS
behavior. Further, the structures have been correlated with the structure obtained from X-ray
crystallography of one of the complex. In addition, to explore the packing modes and intermolecular
interactions in molecular crystal, Hirshfeld surface(HS) analysis of the complex is also carried out.
2. Experimental
2.1. Materials and physical measurements
In the present studies, hydroxyacetone obtained from Sigma-Aldrich and diacetyl monoxime
obtained from Thomas-Baker were used as supplied. The other reagents were obtained from SD-Fine
Chemicals. Solvents were purified and dried according to the standard procedures. The metal salt used
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was in its hydrated form, CuCl2.2H2O. The reaction progresses were maintained through silica gel thin
layer chromatographic technique.
The CHN analysis was performed on a Thermo quest elemental analyzer. The 1H NMR spectra of
the ligands were recorded on AGILENT VNMRS-400 spectrometer, in a DMSO-d6 solvent. The EI mass
spectrum of the ligands was obtained with a Shimadzu GCMS-QP2010S spectrometer. Infrared spectra
were recorded in KBr discs in the region 4000–400 cm−1 on a Nicolet-6700 FT-IR spectrometer. The
solution state UV–Vis spectra of all the compounds in DMF were recorded on a JASCO V-670 UV-Vis
spectrophotometer. The room temperature electron paramagnetic resonance (EPR) spectrum of the
complexes was recorded on the polycrystalline samples with an X-band JEOL-JES-200 spectrometer.
2.2. Synthesis
[Dichlorido (2-(2-(1H-benzo[d]thiazol-2-yl)hydrazono)propan-1-ol) Cu(II)] ([CuL1Cl2]) and [Dichlorido
3-(hydroxyimino)-2-butanone-2-(1H-benzothiazol-2-yl)hydrazone Cu(II)] ([CuL2Cl2])
As depicted in scheme 1, the complexes were synthesized in two steps. First, the free ligands (L1
and L2) were synthesized according to the previous reports [10, 11]. In the next step, 10 mmol of ligands
(2.21g of L1 or 2.48g of L2) were refluxed with 10 mmol of CuCl2.2H2O (1.70g) in ethanol/methanol for 4
hours. The obtained brown colored precipitates were filtered off and air dried. Single crystals of
[CuL1Cl2] suitable for X-ray diffraction were obtained from the slow evaporation of its ethanolic filtrate.
L1: Isolated yield: 75%. m.p. 150 0C. Anal. Calc. for C11H12N4OS (%): C, 54.28; H, 5.01; N, 18.99. Found for
L1: C, 54.03; H, 5.10; N, 18.63. 1H NMR (400 MHz, DMSO- d6): δ ppm: 11.10 (s, 1H, NH), 7.60 (d, 1H, J =7.7
Hz, aromatic H), 7.36 (d, 1H, J =7.7 Hz, aromatic H), 7.23 (dd, 1H, J = 7.6 Hz, J = 7.6 Hz, aromatic H), 7.04
(dd, 1H, J = 7.6 Hz, J = 7.6 Hz, aromatic H), 5.08 (t, 1H, OH, J = 5.9Hz), 3.97 (d, 2H, methylene H, J = 5.9
Hz), 2.01 (s, 3H, methyl H). EI-MS (m/z): 221 (M+). IR (KBr, υ, cm−1): 3346, 1602, 1549, 1020, 755. λmax
(nm): 250 (π→π∗), 295 (n→π∗ ).
L2: Isolated yield: 83%. m.p.: 280°C. Anal. Calc. for C11H12N4OS (%): C, 53.21; H, 4.87; N, 22.56. Found for
L2 (%): C, 53.53; H, 5.01; N, 22.32. 1H NMR (400 MHz, DMSO- d6): δ (ppm) 11.66 (s, 1H, OH), 11.46 (s, 1H,
NH), 7.70 (s, 1H, aromatic H), 7.37 (s, 1H, aromatic H), 7.76 (m, 1H, aromatic H) 7.07 (m, 1H, aromatic H),
2.11 (s, 3H, C1H), 2.01 (s, 3H, C4H). EI-MS (m/z): 248 (M+). IR (KBr, v, cm−1): 3442, 1612, 1571, 1545, 750.
λmax (nm): 231 (π→π∗), 313 (n→π∗ ).
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[CuL1Cl2]: Isolated yield: 2.10g, (59%). m.p. >3000C. Anal. Calc. for C10H11Cl2CuN3OS (%): C, 35.43; H, 3.47;
N, 13.15. Found for [CuL1Cl2] (%): C, 35.28; H, 3.58; N, 12.92. IR (KBr, υ, cm−1): 3446, 1540, 1449, 1051,
753. λmax (nm): 250 (π→π∗), 338 (n→π∗ ), 500 (d-d transition).
[CuL2Cl2]: Isolated yield: 1.95g, (51%). m.p. >3000C. Anal. Calc. for C11H12Cl2CuN4OS (%): C, 34.52; H, 3.16;
N, 14.64. Found for [CuL2Cl2] (%): C, 34.28; H, 3.38; N, 14.82. IR (KBr, υ, cm−1): 3439, 1560, 1521, 1494,
760. λmax (nm): 271 (π→π∗), 317 (n→π∗ ), 454 (d-d transition).
H
S
N
S
H
N
N
CuCl2.2H2
O
N
N
Cu
OH
N
Ethanol, Reflux 4h
Cl
Cl
HO
e
n
o
t
,
h
4
e
c
x
a
u
l
y
f
x
e
o
r
R
d
l
y
o
H
n
a
h
t
e
M
S
N
S
N
Reflux 10h
SH
NH
NH2-NH2.H2O (80%)
NH2
D
i
a
c
e
t
y
l
M
m
e
o
t
n
x
h
o
a
x
n
i
o
m
e
l
,
H
R
e
S
N
f
l
u
S
H
4
N
N
h
N
CuCl2.2H2
O
N
N
Cu
N
Ethanol, Reflux 4h
OH
Cl
Cl
N
OH
Scheme 1. Synthesis of complexes.
2.3. SC-XRD Data collection and refinement of [CuL1Cl2]
A single crystal of dimensions 0.29×0.27×0.26 was mounted on a glass fiber. The X-ray intensity
data were collected at a temperature of 130 K on a Bruker Proteum2 CCD diffractometer with X-ray
generator operating at 45 kV and 10 mA, using Cu-Kα radiation of wavelength 1.54178 Å. Data were
collected for 24 frames per set with different settings of φ(0° and 90°), keeping the scan width of 0.5°,
exposure time of 5 s, the sample to detector distance of 45.10 mm and 2θ value at 46.6°. A complete
data set was processed using SAINT PLUS [12]. All the frames were indexed using a primitive monoclinic
lattice.The structure was solved on Olex2 [13] with ShelXT [14] structure solution program using intrinsic
phasing and refined with the XL [15] refinement package using least squares minimization. All non-
hydrogen atoms were identified in the first difference Fourier map and were refined anisotropically.
Further, all the hydrogen atoms were geometrically positioned. After several cycles of refinement, the
final difference Fourier map showed peaks of no chemical significance and the residual was saturated to
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0.048. The mercury-3.8 package was used to generate molecular graphics [16]. The crystal data and the
structure refinement details are given in Table 1.
Table 1. Crystal data and the structure refinement details.
Crystal data
CCDC 1532568
Chemical formula
C10H11Cl2CuN3OS
Mr
355.72
Crystal system, space group
Monoclinic, P21/c
Temperature (K)
a, b, c (Å)
β (°)
296
8.0596 (3), 19.9590 (7), 9.0924 (3)
115.285 (1)
1322.49 (8)
4
V (Å3)
Z
Radiation type
Cu Kα
µ (mm-1)
7.46
Crystal size (mm)
Data collection
Diffractometer
Absorption correction
Tmin, Tmax
0.29 × 0.26 × 0.22
Bruker X8 Proteum
Multi-scan SADABS
0.221, 0.291
No. of measured, independent and
10513, 2062, 1848
observed [I > 2σ(I)] reflections
Rint
0.042
0.584
(sin θ/λ)max (Å-1)
Refinement
R[F2 > 2σ(F2)], wR(F2), S
No. of reflections
No. of parameters
H-atom treatment
0.048, 0.168, 1.19
2062
164
H-atom parameters constrained
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∆〉max, ∆〉min (e Å-3)
0.83, -0.89
2.4. Computational methods
The geometry of the molecules, [CuL1Cl2] and [CuL2Cl2]were optimized using density functional
theory. ORCA program package (version 3.0.3) was used for DFT calculations. Tight convergence criteria
were chosen for all calculations. All calculations were performed using the hybrid functional BP in
combination with Ahlrichs split-valence double-ξ basis set def2-SVP [17] for all atoms. ORCA calculation
times were minimized using the RI approximation [18] [19] using SVP/J auxiliary basis sets [18] from the
TurboMole basis set library II. The outputs were visualized using molecular visualizer tool Avogadro 1.1.1
[20] and Mercury-3.8 package [16].
2.5. Hirshfeld surface analysis of [CuL1Cl2]
The molecular HS in the crystal structure was created based on the electron distribution
calculated as the sum of spherical atom electron densities. The normalized contact distance (dnorm
)
based on both de, di and the van Der Waals radii enables identification of the regions of particular
interest to intermolecular interactions. The HSs and 2D fingerprint plots(FP) presented here were
plotted using the software Crystal Explorer 3.0 [21]. The dnorm plots were mapped with color scale in
between −0.491 au (blue) and 1.541 au (red). The FPs [22, 23] were displayed by using the expanded
0.6–2.8 Å view with the de and di distance scales displayed on the graph axes. Shape-index and
Curvedness surfaces are specified on the basis of local curvature of the Hirshfeld surface [24].
2.6. ESI-MS analysis
The positive and negative mode ESI measurements were performed in DMF solvent, on Waters
Q-TOF Premier-HAB213 mass spectrometer in the mass range 0-1300 Da. The Sample was dissolved in
DMF to form a 10-5M solution. The resulting solution was directly infused into the instrument's ESI
source at a flow rate of 0.2 mL min−1. The data was acquired at a capillary voltage of 3.5 kV, sampling
cone voltage of 10 V, and a source temperature of 100 °C.
3. Results and discussion
3.1. Spectral characterization
The IR spectrum of ligand L1 has shown υ(O-H) band at 3346 cm-1. The sharp intense bands at
1597 cm-1 and 1549 cm-1 in L1 are assigned to azomethine and benzothiazole ring υ(C=N) vibrations. In
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the complex, these bands have broadened and intensified due to the coupling of the exo-azomethine
band with azomethine of benzothiazole ring with a low energy shift. This suggests the coordination of
the benzothiazole ring nitrogen and azomethine nitrogen to the Cu(II) ion [25]. A sharp intense band at
1020 cm-1 in the ligand L1, is assigned to υ(C-O), which has shifted to 1051 cm-1 in the complex indicating
the coordination of –OH to the metal ion upon complexation.
In the free ligand L2 the υ(O-H) of oxime functionality, has given stretching vibrations at 3442
cm-1. This has shifted to 3439cm-1 in the complex. The low energy shift of this band in the complex is due
to the coordination of oxime nitrogen[26]. The sharp intense bands observed at 1612, 1571 and 1545
cm-1 in L2 are assigned to azomethine, oxime and ring υ(C=N) vibrations respectively [27, 28]. In the
complex, these bands have suffered from low energy as well as significant low-intensity shifts, indicating
the coordination azomethine, oxime and ring nitrogens [29].
In the Uv-Vis spectrum of L2, it has exhibited broad bands in the UV region at a λmax of 231 and
313 nm respectively. These bands are assigned to the intra ligand π→π∗ and n→π∗ transitions
respectively. L1 has shown these transitions at 250 and 295 nm. These bands have appeared in
complexes with a slight shift in their λmax. This shift is attributed to the change in π conjugation and
coordination of azomethine nitrogens upon complexation [30]. The absorption spectrum of [CuL1Cl2]
and [CuL2Cl2] have given a d–d electronic bands at 500 and 454 nm respectively.
The singlet at 11.10 ppm in L1 is ascribed to the hydrazine NH, while it is observed at 11.46 in L2.
A triplet is observed at 5.08 ppm in L1, due to the OH proton. The oxime proton in L2 has given a broad
singlet at 11.66 ppm. Methylene protons of L1, have resonated as a doublet at 3.97 ppm. The methyl
protons in L1 have resonated as a singlet at 2.01 ppm, while in L2, they are observed at 2.01 and 2.11
ppm. The proton signals in the aromatic region are discussed in the syntheses section.
3.2. Crystal structure data and description of [CuL1Cl2]
The title compound C10H11Cl2CuN3OS has crystallized in the monoclinic crystal system with the
space group P21/c. The unit cell dimensions a, b and c are 8.0596 (3) Å, 19.9590 (7) Å and 9.0924 (3) Å
respectively. β = 115.2850 (1), Z = 4 and V = 1322.49 (8) Å3 for the unit cell. Mercury rendered ORTEP of
the molecule with displacement ellipsoids drawn at 50 % probability level is shown in Fig.1. The bond
lengths and bond angles given in Table 1 and Table 2 of supplementary information (SI) are in good
agreement with the standard values.
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Figure 1. ORTEP diagram of the title molecule with 50 % probability displacement thermal ellipsoids.
The asymmetric unit contains a neutral complex molecule with no crystal held solvent or water
molecules. The ligand is coordinated to the central metal ion in an NNO tridentate fashion with the
benzothiazole-N (N1), imine-N (N3) and hydroxyl-O (O1) as donor atoms. In addition, two coordinated
chlorides have given a penta coordinated tetragonally distorted square pyramidal complex. The ligand
has formed two five-membered chelate rings with the metal center. The deviation of metal centered
bond angles from 90° indicates the deviation from ideal square pyramidal geometry. In the structure,
the axial chloride-metal distance (Cu1-Cl1) 2.56 Å is considerably longer than the basal distance (Cu1-
Cl2) 2.21 Å as ascertained by geometry index (τ5) of 0.198. (τ = 0 for a square pyramid, and τ = 1 for a
trigonal bipyramid)[25].
The ligand has adopted + syn-periplanar conformation at both the chelate rings Cu(1)-->O(1)--
>C(1)-->C(2)-->N(3) (ring A, torsion angle + 8.41°) and Cu(1)-->N(1)-->C(4)-->N(2)-->N(3) (ring B, torsion
angle +7.12°). The nine membered benzothiazole ring (S(1)-->C(4)-->N(1)-->C(10)-->C(9)-->C(8)-->C(7)--
>C(6)-->C(5)) has accepted +anti-clinal conformation with the ring average torsion angle of +105.52°.
The ring puckering analysis of two chelate rings can be carried out with the help of pseudo
rotation parameters, P and τ [31]. The values of P (phase angle of pseudorotation) and τ (amplitude of
puckering) signify the variations in endocyclic bond angles [32]. The chelate ring A is characterized by P =
193.9(14)° and τ = 11.9(2)°. This substantiates the twisted conformation on Cu(1)--O(1) on ring A. While
ring B has adopted envelope conformation on Cu(1), as ascertained by P = 334.2(19)° and τ = 9.4(3)°.
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The molecular complex exhibits C—H···Cg interaction; C(1)—H(1B)···Cg4 (Cg4 is the centroid of
the ring C5/C6/C7/C8/C9/C10) with a C—Cg distance of 3.406(5) Å, H···Cg distance of 2.61Å, C—H···Cg
angle of 139° with the symmetry code 1-x,1-y,1-z. The C—H···Cg interaction; C(3)—H(3A)···Cg3 (Cg3 is
the centroid of the ring S1/C4/N1/C10/C5) is with a C—Cg distance of 3.648(6) Å, H···Cg distance of 2.77
Å, C—H···Cg angle of 153° with the symmetry code -x,1-y,1-z. The complex shows ring-metal (Cg-Me)
interactions of the type Cg(2)···>Cu(1) and Cg(3)···>Cu(1) with the ring to metal distance of 3.637 Å and
3.849 Å respectively. These interactions contribute to the crystal packing.
The molecule also exhibits Cg···Cg interaction; Cg1···Cg3 (Cg1 is the centroid of the ring
Cu1/O1/C1/C2/N3) and Cg3 is the centroid of the ring S1/C4/N1/C10/C5) with a Cg—Cg distance of
3.555(2) Å, α = 4.08(19)°, β = 18.7°, γ = 19.3°, a perpendicular distance of Cg1 on ring S1/C4/N1/C10/C5
= 3.3553(16) Å, a perpendicular distance of Cg3 on ring Cu1/O1/C1/C2/N3 = 3.3680(17) Å with the
symmetry code 1-x,1-y,1-z.
The molecules are further connected through inter and intra molecular O—H···Cl, N—H···Cl and
C—H···Cl hydrogen bond interactions [33], which helps to stabilize the molecular structure by forming a
three-dimensional network. The hydrogen bonding geometry is listed in Table 2. The hydrogen bonding
interactions arising from axial chloride(Cl1), are depicted in Fig.2. The packing of molecules along 'c' axis
(Fig.3) shows that the molecules form layered stacking along (0 0 1) plane.
Table 2. Geometric parameters for hydrogen bond interactions (Å, o).
D—H...A
D—H H...A D...A
D—H...A
C(9)---H(9)...Cl(2)* 0.93 2.76 3.536(5) 142
O(1)---H(1)...Cl(1)i 0.93 2.26 2.991(3) 134
N(2)---H(2)...Cl(1)ii 0.86
2.25 3.040(4) 153
*Intra; i:1-x,1-y,2-z; ii:-x,1-y,1-z.
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Figure 2. Hydrogen bonding interactions.
Figure 3. The packing of molecules along 'c' axis.
3.3. DFT optimized structures
Repeated attempts to grow the single crystals of [CuL2Cl2]suitable for X-ray diffraction were not
fruitful. Hence the structure of [CuL2Cl2] is obtained from DFT calculations. The DFT optimized
structures of [CuL1Cl2]and [CuL2Cl2] are given in Fig.4. These structures are quite close to the structure of
[CuL1Cl2] obtained from the single crystal. The calculated single point energies (SPE) for [CuL1Cl2]and
[CuL2Cl2] are found to be -3679.27 and -3585.91 kJ/mol respectively. SPE calculates the wave function
and charge density, and hence the energy, of a particular arrangement of nuclei [34].
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Figure 4. DFT optimized structures of [CuL1Cl2]and [CuL2Cl2]
The optimized structures were used to calculate the energies of the molecular orbitals (MOs).
Besides the HOMO and LUMO, HOMO-1 and LUMO+1 are also considered for both the structures. The
contributions of each atom in the molecular orbital are reflected in the molecular density distribution
through the MO. The localization of the density for the orbitals and energies of [CuL1Cl2]and [CuL2Cl2]are
depicted in Fig.5. The highest contribution for the HOMO for all the structures is attributed to the
chloride ligands. In the LUMO orbital, in addition to the localized density from the benzene ring, there is
some contribution from other atoms as shown in Fig.5.
Figure 5. The localization of the density for the orbitals and energies of [CuL1Cl2]and [CuL2Cl2].
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3.3. Hirshfeld Surface studies of [CuL1Cl2]
HS analysis provides surface features characteristic of different types of intermolecular
interactions. These features can be revealed by color coding distances from the surface to the nearest
atom exterior (de plots) or interior (di plots) to the surface. This gives a visual picture of different types of
interactions present and also reflects their relative contributions from molecule to molecule. FPs, in
particular, the breakdown of these plots into specific atom…atom contacts in a crystal can provide a
quantitative idea of the types of intermolecular contacts experienced by molecules in the bulk [22, 35,
36].
HSs comprising dnorm surface and FPs were generated and analyzed for [CuL1Cl2] in order to
explore the packing modes and intermolecular interactions. Fig.6 illustrates the two-dimensional FPs
from HS analysis. This shows the difference between the intermolecular interaction patterns and the
relative contributions to the HS for the major intermolecular contacts associated [35]. Importantly, H...Cl
(30.6%) bonding appears to be a major contributor in the crystal packing, whereas the H...H (30.0%),
C...H/H...C (17.1%), S...H/H...S (7.1%), S...Cl/Cl...S(3.0%) being the other contributors. Fig.7 shows the
intermolecular contacts which are highlighted by the conventional mapping of dnorm on molecular HSs.
The red spots over the HS indicate the intercontacts involved in a hydrogen bond. The dark-red spots on
the dnorm surface arise as a result of the short interatomic contacts [35, 37, 38], i.e., strong hydrogen
bonds, while the other intermolecular interactions appear as light-red spots.
Fig.8 shows the shape index and curvedness mapped on HS. The shape index shows a red
concave region on the surface around the acceptor atom and a blue region around the donor H-atom.
The adjacent red and blue triangles on the shape index surface shows that the π-π stacking interaction is
almost identical in the total crystal structures [39]. Curvedness on the Hirshfeld surface has divided the
surface into contact patches with each neighboring molecules. On the curvedness surface, the flat
region towards the bottom of the molecule indicates π-π stacking interactions.
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Figure 6. Two-dimensional Fingerprint plots of the showing Cl...H, H...H, C…H, S...H and S...Cl
interactions. (di is the closest internal distance from a given point on the Hirshfeld surface and de is the
closest external contacts).
Figure 7. dnorm mapped on Hirshfeld surface for visualizing the molecular interactions.
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Figure 8. Hirshfeld surface mapped with (a) shape index and (b) curvedness.
3.4. ESI-MS analysis
Electrospray technique is a powerful tool in the study of coordination complexes, due to its
ability to sample various molecular species in solution systems. The ESI-MS of the complexes has shown
several peaks due to the molecular species (cation/anion) of the various fragments formed during ESI.
Only singly charged complex ions were identified, presenting various metal to ligand stoichiometries.
Table 3 and 4 of SI presents the assignments for all the peaks observed in positive and negative mode
ESI-MS of both the complexes. The corresponding spectra are depicted in Fig.1-4 of SI. The assignment
of every peak in ESI-MS has been further supported by calculated isotopic distribution for the moiety
formula. For [CuL1Cl2], the expanded portions of positive mode ESI-M spectrum and calculated isotopic
mass distributions of various species are provided in SI.
In the positive mode ESI, the title compounds have shown very close fragmentation pattern.
Complexes have lost 2 chloride ligands, generating two mono-positive cations (Scheme 2). This is
evident in the intense peaks observed at an m/z of 318.96, 282.98 for [CuL1Cl2] and 345.97, 309.99 for
[CuL2Cl2]. These peaks support the structure obtained from X-ray crystallography for [CuL1Cl2]. The base
peaks at an m/z of 222.06 and 249.08 are due to the protonated ligands. Complexes have shown peaks
at an m/z of 356.04 and 383.06, which closely resembles the mass of whole molecules. But from
calculated isotopic distributions, these peaks are more precisely assigned to [Cu+L+4(H2O)]+ type aqua
adducts of the complexes. Peaks at 504.04 and 558.07 exactly correspond to in situ generated ML2 type
species [Cu+2L-H]+. The complex [CuL1Cl2] has shown an additional peak at 473.03, which accounts for
the mass of [Cu+2L-CH2OH-H]+species formed by the loss of methanol fragment from the ML2 species
[25]. In the case of [CuL2Cl2], this peak is not expected due to its structure. Additional less intense peaks
at a higher m/z are assigned to various mono-positive cations, as identified in Table 3 of SI.
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In the negative mode ESI of complexes, molecular ion peaks are expected at an m/z of 354.92
and 316.94 for the species [Cu+L+2Cl-H]-. However, due to the presence of labile chloride ligands, these
peaks are observed with very less intensity. But the peaks due to [Cu+L+Cl-2H]- at an m/z of 381.93 and
343.96 are sufficiently intense to index the presence of MLCl2 complex. Spectra have even detected the
formation of M2L2 type species [2Cu+2L+Cl-4H]-, in the form of intense peaks at an m/z of 600.92 and
654.94. The base peaks at an m/z of 134.86 in these spectra, exactly correspond to in situ generated
[CuCl2]- species. Additional less intense peaks at a higher m/z are assigned to various mono-negative
anions varying from M4L4 to M2L2 type species, as identified in Table 4 of SI. Most of the coordination
entities formed here have maintained 1:1 metal to ligand ratio. Overall, in all the peaks of negative
mode ESI, spectrum has shown a maximum of 2 ionizable hydrogens per ligand and 2 ionizable
chlorides per metal ion for both the complexes. In conclusion, comparative account of ESI behavior of
the complexes strongly suggest the structural similarities.
S
NH
N
N
Cu
l
C
O
H
-
m/z = 282.98
S
N
S
NH
NH
-Cl
N
N
N
Cu
Cu
Cl
Cl
Cl
O
O
H
-
H
S
m/z = 318.96
NH
N
N
Cu
(H2O)4
O
H
m/z = 356.04
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S
N
NH
N
Cu
N
O-
S
m/z = 309.99
S
NH
NH
-Cl
N
N
N
N
Cu
Cu
Cl
Cl
Cl
N
N
S
OH
-
m/z = 345.97
OH
NH
2
4
N
N
Cu
N
(H2O)4
OH
m/z = 383.06
Scheme 2.Positive mode ESI-fragmentation of the complexes.
3.5. EPR spectral analysis
The room temperature EPR spectrum of [CuL1Cl2] and [CuL2Cl2] was recorded on polycrystalline
samples, to get the insights into the geometry of complexes. Corresponding spectra are given in Fig.5
and Fig.6 of SI. The g|| and g⊥ values observed for the complexes are 2.28, 2.09 (for [CuL1Cl2]) and 2.24,
2.09 (for [CuL2Cl2]) respectively. This spectral behavior (g|| > g⊥ > 2.02) of the complexes are attributed
to an axial symmetry with the dx2-y2 ground state having elongated octahedral, square pyramidal or
square planar coordination geometry around the Cu(II) ion [40]. This observation is clearly in support of
observed square pyramidal X-ray structure of [CuL1Cl2]. When the geometry is compressed octahedral or
trigonal bipyramidal, an EPR spectrum will be characterized by g⊥ > g|| = 2.0023 [41]. Hence the present
trend (g|| > g⊥ > 2.02) rules out the possibility of trigonal bipyramidal geometry around the
pentacoordinated Cu(II). In both the complexes, g|| values (2.28, 2.24) are less than 2.3, indicating a
larger percentage of covalency of metal–ligand bonding [42].
4. Conclusions
In the present studies, two new transition metal complexes, [Dichlorido (2-(2-(1H-
benzo[d]thiazol-2-yl)hydrazono)propan-1-ol)
Cu(II)]
and
3-(hydroxyimino)-2-butanone-2-(1H-
benzothiazol-2-yl)hydrazone are synthesized and characterized by various spectro-analytical techniques.
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The structure of [CuL1Cl2] is determinedby single crystal X-Ray diffraction method. In [CuL1Cl2], the ligand
is coordinating to the central metal ion Cu(II), in an N, N, O-tridentate fashion. Along with the two
chloride ligands, the organic moiety has produced a penta-coordinated tetragonally distorted square
pyramidal complex. The molecular complex involves ring-metal (Cg-Me) interactions of the type
Cg···>Cu. The molecular and crystal structure of the molecule is stabilized by hydrogen bond interactions
arising from axial chloride ligand, which is visualized with the help of dark red spots on the Hirshfeld
surface of the molecule. 2D fingerprint plots reveal that H...Cl (30.6%) interaction to be a major
contributor in the crystal packing, which extends to the 3D network through C—H···Cg and Cg-Cg
interactions. EPR spectral behavior (g|| > g⊥ > 2.02) of the complexes are attributed to an axial symmetry
with the dx2-y2 ground state having square pyramidal geometry around the Cu(II) ion. In the positive
mode, ESI of both the complexes, along with the mono-cationic molecular fragments, various adducts of
M2L2 and ML2 type species have been identified. Most of the coordination entities formed in the
negative mode ESI have maintained 1:1 metal to ligand ratio. This observation strongly supports the
crystal structure. M2L2, M3L3 and M4L4 type anionic molecular adducts of higher m/z have been generated
during ESI. Comparative account of ESI behavior of the complexes, EPR analysis and DFT optimized
structures strongly suggest the structural similarities in the synthesized complexes.
Acknowledgements
The authors gratefully acknowledge the Institution of Excellence, Vignana Bhavana, University of
Mysore, Mysuru, for providing single crystal X-ray diffractometer facility to collect the X-ray intensity
data. Recording of ESI-MS at Dept. of Chemistry, IIT-Kanpur, Kanpur is greatly acknowledged. Authors
sincerely thank Mr. P. Kadigachalam for his cooperation in collecting ESI-MS. One of the authors
(Vinayak Kamat) is thankful to UGC-New Delhi for providing financial assistance under UGC-SRF
(101864/June 2013).
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References
[1] L.M.T. Frija, A.J.L. Pombeiro, M.N. Kopylovich, Coordination chemistry of thiazoles, isothiazoles and
thiadiazoles, Coordination Chemistry Reviews, 308, Part 1 (2016) 32-55.
[2] S.M. Annigeri, A.D. Naik, U.B. Gangadharmath, V.K. Revankar, V.B. Mahale, Symmetric binuclear
complexes with an ‘end-off’ compartmental Schiff base ligand, Transition Metal Chemistry, 27 (2002)
316-320.
[3] V.H. Arali, V.K. Revankar, V.B. Mahale, Synthesis, characterization and biological studies of 2-(3,5-
dimethylpyrazol-1-yl)benzothiazole complexes of cobalt(II), nickel(II) and copper(II), Transition Metal
Chemistry, 18 (1993) 158-162.
[4] E.K. Beloglazkina, I.V. Yudin, A.G. Majouga, A.A. Moiseeva, A.I. Tursina, N.V. Zyk, Synthesis and
electrochemical study of 2-(2-pyridyl)benzothiazole complexes with transition metals (CoII, NiII, and
CuII). Molecular structure of aquabis[2-(2-pyridyl)benzothiazole]copper(II) diperchlorate, Russian
Chemical Bulletin, 55 (2006) 1803-1809.
[5] J.E. Penner-Hahn, X-ray absorption spectroscopy in coordination chemistry, Coordination Chemistry
Reviews, 190–192 (1999) 1101-1123.
[6] G. Bhaskar, M.A. Chary, M.K. Kumar, K. Syamasundar, M. Vairamani, S. Prabhakar, Electrospray
ionization studies of transition-metal complexes of 2-acetylbenzimidazolethiosemicarbazone using
collision-induced dissociation and ion-molecule reactions, Rapid Communications in Mass Spectrometry,
19 (2005) 1536-1544.
[7] W. Henderson, B.K. Nickleson, L.J. McCaffrey, Applications of electrospray mass spectrometry
inorganometallic chemistry, Polyhedron, 17 (1998) 4291-4313.
[8] W. Henderson, J.S. McIndoe, The ESI MS Behaviour of Coordination Complexes, Mass Spectrometry
of Inorganic, Coordination and Organometallic Compounds, John Wiley & Sons, Ltd2005, pp. 127-173.
[9] K. Yamaguchi, Cold-Spray Ionization Mass Spectrometry: Applications in Structural Coordination
Chemistry, Mass Spectrometry, 2 (2013) S0012.
[10] P.P. Netalkar, S.P. Netalkar, S. Budagumpi, V.K. Revankar, Synthesis, crystal structures and
characterization of late first row transition metal complexes derived from benzothiazole core: Anti-
tuberculosis activity and special emphasis on DNA binding and cleavage property, European Journal of
Medicinal Chemistry, 79 (2014) 47-56.
[11] V. Kamat, A. Kotian, A. Nevarekar, K. Naik, D. Kokare, V.K. Revankar, In situ oxidation triggered
heteroleptically deprotonated Cobalt(III) and homoleptic Nickel(II) complexes of diacetyl monoxime
derived tri-nitrogen chelators; Synthesis, molecular structures and Biological assay, Inorganica Chimica
Acta, DOI https://doi.org/10.1016/j.ica.2017.07.036.
[12] S.P. Bruker, Bruker AXS Inc., Madison, Wisconsin, USA., DOI.
[13] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann, OLEX2: a complete
structure solution, refinement and analysis program, Journal of Applied Crystallography, 42 (2009) 339-
341.
[14] G. Sheldrick, SHELXT - Integrated space-group and crystal-structure determination, Acta
Crystallographica Section A, 71 (2015) 3-8.
[15] G. Sheldrick, Crystal structure refinement with SHELXL, Acta Crystallographica Section C, 71 (2015)
3-8.
[16] C.F. Macrae, I.J. Bruno, J.A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock, L. Rodriguez-Monge, R.
Taylor, J. van de Streek, P.A. Wood, Mercury CSD 2.0 - new features for the visualization and
investigation of crystal structures, Journal of Applied Crystallography, 41 (2008) 466-470.
[17] A. Schäfer, C. Huber, R. Ahlrichs, Fully optimized contracted Gaussian basis sets of triple zeta
valence quality for atoms Li to Kr, The Journal of Chemical Physics, 100 (1994) 5829-5835.
19

ACCEPTED MANUSCRIPT
[18] K. Eichkorn, O. Treutler, H. Öhm, M. Häser, R. Ahlrichs, Auxiliary basis sets to approximate Coulomb
potentials, Chemical Physics Letters, 240 (1995) 283-290.
[19] F. Neese, G. Olbrich, Efficient use of the resolution of the identity approximation in time-dependent
density functional calculations with hybrid density functionals, Chemical Physics Letters, 362 (2002) 170-
178.
[20] M.D. Hanwell, D.E. Curtis, D.C. Lonie, T. Vandermeersch, E. Zurek, G.R. Hutchison, Avogadro: an
advanced semantic chemical editor, visualization, and analysis platform, Journal of Cheminformatics, 4
(2012) 17.
[21] D.J.G. S.K. Wolff, J.J. McKinnon, M.J. Turner, D. Jayatilaka, M.A. Spackman, CrystalExplorer (Version
3.1), 2012.
[22] S.K. Seth, Tuning the formation of MOFs by pH influence: X-ray structural variations and Hirshfeld
surface analyses of 2-amino-5-nitropyridine with cadmium chloride, CrystEngComm, 15 (2013) 1772-
1781.
[23] S.K. Seth, Structural elucidation and contribution of intermolecular interactions in O-hydroxy acyl
aromatics: Insights from X-ray and Hirshfeld surface analysis, Journal of Molecular Structure, 1064
(2014) 70-75.
[24] J.J. Koenderink, A.J. van Doorn, Surface shape and curvature scales, Image and Vision Computing, 10
(1992) 557-564.
[25] V. Kamat, D. Kokare, K. Naik, A. Kotian, S. Naveen, S.R. Dixit, N.K. Lokanath, S.D. Joshi, V.K.
Revankar, Transition metal complexes of 2-(2-(1H-benzo[d]imidazol-2-yl)hydrazono)propan-1-ol:
Synthesis, characterization, crystal structures and anti-tuberculosis assay with docking studies,
Polyhedron, 127 (2017) 225-237.
[26] M.M. Al-Ne’aimi, M.M. Al-Khuder, Synthesis, characterization and extraction studies of some metal
(II) complexes containing (hydrazoneoxime and bis-acylhydrazone) moieties, Spectrochimica Acta Part A:
Molecular and Biomolecular Spectroscopy, 105 (2013) 365-373.
[27] S.P. Netalkar, P.P. Netalkar, A.A. Nevrekar, V.K. Revankar, Pd(II) complexes of N(4)-substituted
phenylaminoacetohydrazone and biacetylmonooxime: synthesis, characterization, structures and
catalytic behaviour towards Suzuki–Miyaura coupling reactions, Applied Organometallic Chemistry, 30
(2016) 170-180.
[28] A. Kamath, S.P. Netalkar, D. Gangaram Kokare, K. Naik, V.K. Revankar, Phenoxide bridged
tetranuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes: Syntheses, characterization and fluorescence
studies, Journal of Luminescence, 132 (2012) 2763-2768.
[29] A. Sreekanth, U.L. Kala, C.R. Nayar, M.R. Prathapachandra Kurup, Cobalt(III) complexes of 2-
hydroxyacetophenone N(4)-phenyl semicarbazone containing heterocyclic coligands: syntheses,
structure and spectral studies, Polyhedron, 23 (2004) 41-47.
[30] D.G. Kokare, V. Kamat, K. Naik, A. Nevrekar, A. Kotian, V.K. Revankar, Evaluation of DNA cleavage,
antimicrobial and anti-tubercular activities of potentially active transition metal complexes derived from
2,6-di(benzofuran-2-carbohydrazono)-4-methylphenol, Journal of Molecular Structure, DOI
http://dx.doi.org/10.1016/j.molstruc.2016.07.072.
[31] D. Cremer, J.A. Pople, General definition of ring puckering coordinates, Journal of the American
Chemical Society, 97 (1975) 1354-1358.
[32] E. Westhof, M. Sundaralingam, Interrelationships between the pseudorotation parameters P and
.tau.m and the geometry of the furanose ring, Journal of the American Chemical Society, 102 (1980)
1493-1500.
[33] J. Bernstein, R.E. Davis, L. Shimoni, N.-L. Chang, Patterns in Hydrogen Bonding: Functionality and
Graph Set Analysis in Crystals, Angewandte Chemie International Edition in English, 34 (1995) 1555-
1573.
20

ACCEPTED MANUSCRIPT
[34] V. Kamat, K. Naik, V.K. Revankar, Effect of acetate and nitrate anions on the molecular structure of
3-(hydroxyimino)-2-butanone-2-(1H-benzimidazol-2-yl)hydrazone, Journal of Molecular Structure, 1133
(2017) 546-556.
[35] M.A. Spackman, D. Jayatilaka, Hirshfeld surface analysis, CrystEngComm, 11 (2009) 19-32.
[36] R. Soman, S. Sujatha, C. Arunkumar, Quantitative crystal structure analysis of fluorinated
porphyrins, Journal of Fluorine Chemistry, 163 (2014) 16-22.
[37] K. Kumara, N. Shivalingegowda, L.D. Mahadevaswamy, A.K. Kariyappa, N.K. Lokanath, Crystal
Structure Studies and Hirshfeld Surface Analysis of 5-(4-methoxyphenyl)-3-(thiophen-2-yl)-4,5-dihydro-
1H-pyrazole-1-carbothioamide, Chemical Data Collections, DOI
http://dx.doi.org/10.1016/j.cdc.2016.11.006.
[38] C. Feng, D. Zhang, Z.-J. Chu, H. Zhao, Dimeric complexes of transition metal based on azole
nucleating ligands involving hydrogen bonding interactions, Polyhedron, 115 (2016) 288-296.
[39] S.K. Seth, D. Sarkar, A.D. Jana, T. Kar, On the Possibility of Tuning Molecular Edges To Direct
Supramolecular Self-Assembly in Coumarin Derivatives through Cooperative Weak Forces:
Crystallographic and Hirshfeld Surface Analyses, Crystal Growth & Design, 11 (2011) 4837-4849.
[40] E. Garribba, G. Micera, The determination of the geometry of Cu (II) complexes: an EPR
spectroscopy experiment, J. Chem. Educ, 83 (2006) 1229.
[41] W. Henke, S. Kremer, D. Reinen, Copper(2+) in five-coordination: a case of a pseudo-Jahn-Teller
effect. 1. Structure and spectroscopy of the compounds Cu(terpy)X2.nH2O, Inorganic Chemistry, 22
(1983) 2858-2863.
[42] D. Kivelson, R. Neiman, ESR Studies on the Bonding in Copper Complexes, The Journal of Chemical
Physics, 35 (1961) 149-155.
21