5,5′-Dibenzoimidazole as building block for a new 3D Co(II) coordination polymer: A combined EPR and DFT study using UB3LYP model

Article abstract of DOI:10.1016/j.poly.2019.07.029

A new Co(II) three-dimensional coordination polymer, [Co(L)(L′)]_n (1) [where L = 5,5′-dibenzoimidazole, and L′ = doubly deprotonated terephthalic acid] has been synthesized hydro(solvo)thermally and its molecular and crystal structure have been elucidated through single crystal X-ray diffraction analysis. Each Co(II) ion displays a slightly distorted trigonal bipyramidal geometry, the apical positions being occupied by the nitrogen atoms of two symmetry-related dibenzoimidazole ligands, while the oxygen atoms from three distinct terephthalic acids are in the equatorial plane. Considering the Co₂C₂O₆ dimeric moieties as nodes, and the ancillary ligands as connectors, the structure can be simplified as a 8-c uninodal net of the type bcu, body centered cubic, with point symbol {4²⁴·6⁴} and vertex symbol [4·4·4·4·4·4·4·4·4·4·4·4·4(3)·4(3)·4(3)·4(3)·4(3)·4(3)·4(3)·4(3)·4(3)·4(3)·4(3)·4(3)·*·*·*·*]. The EPR spectra for 1 have been reported, showing g_|| = 2.176 and g_⊥ = 2.052 at RT (room temperature), and g_|| = 2.172 and g_⊥ = 2.060 at LNT (liquid nitrogen temperature). Finally, the electronic nature of the molecular geometry of 1 has been explored by DFT computation applying the UB3LYP/def2-TZVP level of theory, showing the energy difference between the high spin and low spin configurations.

Full text of DOI:10.1016/j.poly.2019.07.029

Journal Pre-Proof
5,5'-Dibenzoimidazole as Building Block for a New 3D Co(II) Coordination
Polymer: A Combined EPR and DFT Study Using UB3LYP Model
Amitabha Datta, Chiara Massera, Eugenio Garribba, Antonio Frontera
PII:
S0277-5387(19)30507-8
https://doi.org/10.1016/j.poly.2019.07.029
POLY 14079
DOI:
Reference:
Polyhedron
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Revised Date:
Accepted Date:
11 May 2019
15 July 2019
21 July 2019
Please cite this article as: A. Datta, C. Massera, E. Garribba, A. Frontera, 5,5'-Dibenzoimidazole as Building Block
for a New 3D Co(II) Coordination Polymer: A Combined EPR and DFT Study Using UB3LYP Model,
Polyhedron (2019), doi: https://doi.org/10.1016/j.poly.2019.07.029
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JOURNAL PRE-PROOF
5,5'-Dibenzoimidazole as Building Block for a New 3D Co(II)
Coordination Polymer: A Combined EPR and DFT Study Using
UB3LYP Model
Amitabha Datta,*a Chiara Massera,b Eugenio Garribba,c Antonio Frontera,d
a Institute of Chemistry, Academia Sinica, Nankang, Taipei – 115, Taiwan
b Dipartimento di Scienze Chimiche, della Vita e della Sostenibilità Ambientale,
Università degli Studi di Parma, Viale delle Scienze 17/A, 43124 Parma, Italy
c Dipartimento di Chimica e Farmacia, Università di Sassari, Via Vienna 2, I-07100
Sassari, Italy
d Departament de Química, Universitat de les Illes Balears, Crta de Valldemossa km
7.5, 07122 Palma de Mallorca (Baleares), Spain
*Corresponding authors. amitd_ju@yahoo.co.in (A. Datta)
Keywords: Co(II) 3D coordination polymer; Crystal structure; Topology; EPR; DFT

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A B S T R A C T
A new Co(II) three-dimensional coordination polymer, [Co(L)(L′)]n (1) [where L =
5,5'-dibenzoimidazole, and L′ = doubly deprotonated terephthalic acid] has been
synthesized hydro(solvo)thermally and its molecular and crystal structure have been
elucidated through single crystal X-ray diffraction analysis. Each Co(II) ion displays a
slightly distorted trigonal bipyramidal geometry, the apical positions being occupied
by the nitrogen atoms of two symmetry-related dibenzoimidazole ligands, while the
oxygen atoms from three distinct terephthalic acids are in the equatorial plane..
Considering the Co2C2O6 dimeric moieties as nodes, and the ancillary ligands as
connectors, the structure can be simplified as a 8-c uninodal net of the type bcu, body
centered cubic, with point symbol {424.64} and vertex symbol
[4.4.4.4.4.4.4.4.4.4.4.4.4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).*.*.*.
*]. The EPR spectra for 1 have been reported, showing g|| = 2.176 and g = 2.052 at
RT (room temperature), and g|| = 2.172 and g = 2.060 at LNT (liquid nitrogen
temperature). Finally, the electronic nature of the molecular geometry of 1 has been
explored by DFT computation applying the UB3LYP/def2-TZVP level of theory,
showing the energy difference between the high spin and low spin configurations.

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1. Introduction
The main strategy for the preparation of novel multifunctional materials is still based
on self-assembly methods which employ polydentate organic ligands containing N- or
O-donor as building blocks. In this context, those ligands containing imidazole or
carboxylate groups are of special interest due to their good coordination ability and
diverse coordination modes [1-4]. Up to now, however, there are still few studies
reporting the use of ligands containing both imidazole and carboxylate moieties as
building blocks for the construction of functional MOFs [5-9]. Moreover, in the case
of metal–organic complexes, not only the organic ligands, but also the choice of the
metal ion employed is very important to determine the functionality of the resulting
compounds [10]. It is well known that Co(II) is a good candidate for the construction
of magnetic or luminescent metal–organic materials [11-18] because it can adopt
diverse coordination modes in combination with N- or O-donor ligands. Recently, a
few CPs and MOFs with intriguing topologies have been reported, containing
different aromatic carboxylates and bis(imidazole) as precursors [19-21]. Moreover,
inspired by the use of some flexible bis(imidazole) ligands [22-24], Lee et. al. have
used 9,10-di(1H-imidazol-1-yl)anthracene (dia) possessing a flat anthracenyl ring to
exploit its ability in exploiting two different coordination sites [25]. Thus, inspired by
recent research paths which exploit flexible ligands to get enthralling metal organic

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frameworks endowed with interesting topologies [19-21], in the present contribution
we have decided to use the symmetrical terephthalic acid (H2L’) as bifunctional
bridging organic tecton in combination with 5,5'-dibenzoimidazole (L) as N-donor
connector (see Scheme 1). The hydro(solvo)thermal reaction of cobalt chloride
hexahydrate as metal salt with L′ and L has produced the new three dimensional CP
[Co(L)(L′)]n (1) in moderate yield. Its solid-state structure, topological analysis and
solid state EPR spectra are here described. DFT computation has been also employed
to evaluate the energy differences between its high spin and low spin configurations
and to interpret the EPR spectra both in solution and in the solid state.
N
HO
O
H
N
N
H
O
OH
N
L
H2L′
Scheme 1. Molecular sketch of the ligands employed to generate the coordination
polymer (1): 5,5'-dibenzoimidazole (L, left) and terephthalic acid (H2L′, right)..
2. Results and discussion
2.1. Structural description
The crystal structure of compound 1 was elucidated through X-ray diffraction analysis
on single crystals. It consists of a coordination polymer of general formula

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[Co(L)(L’)]n, where L is 5,5'-dibenzoimidazole, and L’ = C8H4O4 is the doubly
deprotonated terephthalic acid. The complex crystallizes in the monoclinic space
group P21/c and its asymmetric unit comprises one Co(II) cation, one 5,5'-
dibenzoimidazole ligand, and two half molecules of doubly deprotonated terephtalic
acid. Figure 1 highlights the coordination environment around the metal center. Co(II)
displays a slightly distorted trigonal bipyramidal geometry, with the two nitrogen
atoms N1 and N4iv from two symmetry-related dibenzoimidazole ligands in the apical
positions, and the oxygen atoms O1, O3 and O4ii from three distinct molecules of
terephthalic acids in the equatorial plane. Bond distances and angles are in the normal
range for this type of compounds (see Table 1 for selected geometrical parameters).
As can be seen from Figure S1, there are two types of terephthalic acids
Figure 1. Coordination environment around the metal in 1. Symmetry codes: i = 2-x,
1-y, 1-z; ii = 1-x, 1-y, -z; iii = 1+x, y, z.; iv = 2-x, -1/2+y, 1/2-z; v = -x, 1-y, -z.

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in the structure, coloured in green and magenta, respectively. In the first one, only one
oxygen atom (O1) of each carboxylic group is involved in the coordination, thus
connecting two metal centers at the time. On the contrary, the second ligand employs
all four oxygen atoms (O3, O4 and the symmetry-related ones) to bridge four different
cobalt ions.
Table 1. Selected bond lengths [Å] and angles [o] for 1.
Co1-N1
Co1-N3iv
Co1-O1
Co1-O3
Co1-O4ii
2.116(2)
2.137(2)
2.007(2)
2.010(2)
2.004(2)
N1-Co1-N3iv
O3-Co1-O1
O3-Co1-O4ii
O1-Co1-O4ii
177.13(8)
115.24(9)
130.29(9)
114.45(7)
This combination forms a sheet parallel to the ac plane of the unit cell. These sheets
are connected by the dibenzoimidazole ligands along the b-axis direction of the unit
cell, yielding the three-dimensional structure shown in Figure 2. Each ligand, which
is roughly planar [the angle between the two mean planes passing through the
benzimidazole motieties is of 12.93(8)°] bridges two metal centers through the
nitrogen atoms N1 and N3.

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Figure 2. View along the a-axis direction of the sheets formed by the terephtalic acids
coordinated to the cobalt ions, connected through dibenzoimidazole ligands acting as
pillars. H atoms have been omitted for clarity. The two types of terephtalic acids are
represented in magenta and green, respectively.
In the crystal structure, two sets of strong H-bonds are present, involving the N-H
groups of the imidazole rings which act as donors towards the oxygen atoms of the
carboxylic moieties (Figure 3 and Table 2).
Table 2. Relevant geometrical parameters (Å, °) for the hydrogen binding network in
1.
D-H···A
N2-H2N∙∙∙O1(-
D-H
H···A
2.01(5)
D···A
D-H···A
0.85(5)
2.882(3)
172.6(9)
x+1,+y+1/2,z+1/2)
N4-H4N∙∙∙O2(x+1,+y,+z)
0.88(4)
1.84(5)
2.691(3)
162.6(9)

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Figure 3. View of the N-H∙∙∙O hydrogen bonds (cyan dotted lines) present in the
structure of 1.
The tridimensional structure of 1 can be also analyzed and described with the program
ToposPro [26]. In the left part of Figure 4, the simplification used for the analysis is
shown: the Co2C2O6 dimer is considered node of the net, while the ligand
benzoimidazole and the carbon skeleton of the two types of terephtalic acids are the
connectors. The resulting structure can therefore be seen as a 8-c uninodal net of the
type bcu, body centered cubic, with point symbol {424.64} and vertex symbol
[4.4.4.4.4.4.4.4.4.4.4.4.4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).*.*.*.
*] [27] (Figure 4, right).

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Figure 4. Left: simplification used to create the net. Right: view of the of the 8-c
uninodal net of the type bcu.
The 5,5’-bibenzo[d]imidazole ligand used in this work can be generally found in four
different isomeric configurations (I–IV) taking into consideration the tautomeric
forms of the imidazole ring (I and III) and the rotation around the bis-arene C–C
bond (II and IV), as indicated in Scheme 2. The form I is observed in compound 1
(with an anti-conformation of the Co metal centers and, concomitantly, of the NH
groups (Scheme 2 and Figures 1 and 2). As described above, the imidazole ligand in
this form acts as pillar connecting the 2-D Co/terephtalic acids sheets along the b-axis
direction, thus adding the third dimension to the polymer.

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M
N
H
N
H
N
N
H
NH
N
N
N
M
I
II
M
M
M
H
N
H
N
H
N
N
M
N
HN
M
N
N
M
III
IV
Scheme 2. Structural diagram of the four configurations of 5,5’-
bibenzo[d]imidazole.
A search in the Cambridge Structural Database (CSD, Version 5.38, update August
2018) [28] for complexes containing the 5,5'-dibenzoimidazole backbone yielded only
two hits, none of them coordination polymers, and never featuring the ligand in forms
II and IV. In particular, Yin and coworkers used different derivatives of 5,5’-
bibenxo[d]imidazole (fully deprotonated) to obtain multinuclear ruthenium complexes
with bypiridine (see for instance LIMBIT) [29]. In this structure the imidazole ligands
coordinates four distinct Ru centers all showing an octahedral geometry. Moreover, a
pyridine derivative of the ligand in its form I [bis(2-pyridyl)-5,5'-bi-benzimidazole]
was used to synthesize a copper-based pseudorotaxane (RAKLEW) [30] featuring two
penta-cooridinated copper(II) ions showing a square-pyramidal geometry. In both

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cases, the bibenzoimidazole scaffold has proved to be a very robust and stable ligand,
providing rigidity to the resulting compound. Finally, a theoretical DFT study has
been recently carried out [31], to investigate the effect of different configurations of
bibenzoimidazole, namely 2,2’-bibenzo[d]imidazole, 2,5’-bibenzo[d]imidazole, and
5,5’-bibenzo[d]imidazole in forming H-bonding networks with phosphporic acid. This
proves the versatility of this molecule towards the rational design of 3-dimensional
architectures, both as ligand in metal complexes and as synthon in supramolecular
self-assembly.
A search in the CSD for cobalt, terephtalic acid and benzimidazole-containing
ligands gave 17 hits, but only in 11 of them the benzimidazole was coordinated to the
metal center through its N atom and in 3 of them cobalt was also coordinating other
ligands such as water or methanol molecules, or chloride ions. Of the 8 structures
remaining, compounds SITVEZ [32] and XAVKEL [33] are those in which the cobalt
ions are penta-coordinated like in the title compound. In particular, in the case of
SITVEZ, two different cobalt centers are present, with Co1 being the one surrounded
by three different terephthalic acid ligands, one chelating and two bridging, and by a
benzoimidazole ligand, giving rise to a very distorted squared pyramidal coordination
of the tipe CoO4N (one of the oxygen atoms of the chelating ligand is at the much
longer distance of 2.445(3) with respect to the other oxygen atoms). In the compound

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indicated with refcode XAVKEL the Co ion shows a distorted trigonal–bipyramidal
coordination geometry of the type CoO3N2: each tertephtalic acid behaves as
chelating (with one carboxylate unit) and monodentate (with the other one) ligand,
thus forming 1-D polymeric chains, while two benzimidazole ligands simply occupy
the two left coordinating positions around the metal center.
2.2. EPR spectra
Cobalt(II) has a 3d7 configuration and can form both high-spin (S = 3/2 with three
unpaired electrons) and low-spin (S = 1/2 with only one unpaired electron) complexes.
For high-spin states, the fast spin-lattice relaxation time precludes the possibility to
obtain resolved EPR spectra at room temperature (RT) and liquid nitrogen
temperature (LNT) and very low temperatures are needed to detect any signal [34-37].
In contrast, species with a low-spin state give a resolved spectrum both at 298 and 77
K. The EPR spectra recorded on the polycrystalline powder of 1 are well resolved at
RT and LNT (Figure 5). This suggests a low-spin state at both the temperatures. The
two spectra are characterized by g|| = 2.176 and g = 2.052 at RT, and g|| = 2.172 and
2
2
g = 2.060 at LNT. These data indicate a ground state based on the cobalt dxy or dx –y
orbitals [38,39].

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Figure 5. X-band EPR spectra of the polycrystalline powder of 1: (a) at RT and (b) at
LNT. With the asterisk the "forbidden" MS = ±2 resonance at half-field is indicated.
In fact, for five-coordinate Co(II) complexes with trigonal bipyramidal geometry and
2
2
a symmetry close to D3h, such as 1, the electron configuration is (dxz)2 (dyz)2 (dx –y
)
2
1
(dxy)1 or (dxz)2 (dyz)2 (dxy)2 (dx –y ) [40]. For this situation, the EPR theory predicts a
value of g|| larger than g, which – in its turn – is larger than ge (2.0023), in agreement
with what was experimentally observed (see Table 3). Overall, the spectral pattern
closely resembles that of other trigonal bipyramidal Co(II) species [41]. The weak
resonances at half-field at g ~ 4.3 can be attributed to the "forbidden" MS = ±2
resonance, often observed in the case of dinuclear metal complexes (for example, with
2
2

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copper(II)) in a doublet spin state [42]. The small distance between the two Co(II)
ions would support an interaction between the two paramagnetic centers.
Table 3. Values of g measured for 1 in the solid state and in organic solutions.
Temperature
RT
g||
g at half-field
4.294
g
Solid state
2.176
2.172
2.184
2.180
2.179
2.052
2.060
2.046
2.040
2.046
Solid state
LNT
4.278
Solid dissolved in DMSO
Solid dissolved in DMF
Solid dissolved in MeOH
LNT
4.289
LNT
4.284
LNT
4.287
When compound 1 is dissolved in an organic solvent, no significant changes in the
EPR spectra – compared to those recorded in the solid state – are observed (Figure
6): two resonances in the magnetic field range 3000-3500 Gauss are revealed plus the
transition at half-field at ca. 1570 Gauss. This suggest that, unlike other dinuclear
complexes [43-53], the structure of 1 is retained in the organic solution. The values of
g measured in DMF, DMSO and MeOH are reported in Table 3.

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Figure 6. X-band EPR spectra recorded at LNT on the polycrystalline powder of 1
dissolved in: (a) DMSO, (b) DMF and (c) MeOH. With the asterisk the "forbidden"
MS = ±2 resonance at half-field is indicated.
2.3. DFT computation
We have used DFT calculations to shed light on the spin state and electronic
configuration of compound 1. Due to the polymeric nature of the X-ray structure, we
have used a theoretical model, which is shown in Figure 7. It is composed of two
metal centers, two bridging terephthalic acid ligands, two additional terephthalic acid
monodentate ligands and four 5,5'-dibenzoimidazole ligands occupying the apical
positions. We have first computed the energy difference between the high spin (S =
3/2) and low-spin (S = 1/2) configuration at the UB3LYP/def2-TZVP level of theory
for the model shown in Figure 7.

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Figure 7. Theoretical model of 1. H-atoms have been omitted for clarity.
The low spin complex is 22.0 kcal/mol more stable than the high spin per cobalt unit,
in agreement with the experimental findings. The calculated values of the g-tensor
components at the B3LYP/def2-TZVP level of theory for the theoretical model of 1
are g|| = 2.164 and g = 2.076, which correlate reasonably well with the experimental
values. Moreover, in order to investigate the electronic configuration of the Co(II)
metal center, we have represented one of both single-occupied molecular orbitals
(SOMO) and the spin density plot of the model of compound 1 in Figure 8. The spin
density plot shows that the unpaired electrons are located on the Co metal centers with
some spin delocalized into the ligands. Both spin density and SOMO plots confirm
2
2
the presence of the unpaired electron in the dx y orbital.

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Figure 8. Spin density plot (a) and SOMO (b) of the theoretical model of 1 at the
B3LYP/def2-TZVP level of theory.
3. Conclusion
In summary, we have described the rational design of a thermally stable Co(II) three-
dimensional coordination polymer, generated by employing a carboxylate precursor,
terephthalic acid, and 5,5'-dibenzoimidazole as N-donor ancillary co-ligand. Single
crystal X-ray diffraction analysis has elucidated the molecular and crystal structure of
the coordination polymer, highlighting the role of 5,5'-dibenzoimidazole in producing
a 3D, 8-c uninodal network of the type bcu. EPR measurements have been carried out
both in the solid state (at RT and LNT) and in organic solution to outline the
electronic configuration of Co(II) on the spin-lattice location in the molecular unit.

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Furthermore, DFT has been employed to interpret the molecular alignment of the 3-D
polymeric chain. Further work is underway, focusing on the capacitance
measurements and sensor activities of MOFs and CPs incorporating
dibenzoimidazole-type ligands in combination with different metal centers.
4. Experimental section
4.1. Materials
Terephthalic acid was purchased from Acros Organics. Co(NO3)2·6H2O, 2,4-
dinitroaniline and hydrazine monohydrate were purchased from Aldrich Chemicals.
All the reagents were used as received for synthesis without further purification.
4.2. Physical measurements
Microanalytical data (C, H, and N) were collected on a Perkin–Elmer 2400 CHNS/O
elemental analyzer. EPR spectra were recorded from 0 to 8000 Gauss at liquid
nitrogen temperature (LNT, 77 K) or room temperature (RT, 298 K) with an X-band
Bruker EMX spectrometer equipped with a HP 53150A microwave frequency counter.
The microwave frequency was in the range 9.40-9.41 GHz, microwave power was 20
mW (which is, with the ER4119 HS resonator, below the saturation limit), time
constant was 81.92 ms, modulation frequency 100 kHz, modulation amplitude 0.4 mT,

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resolution 8192 points.
4.3. Synthesis of 5,5'-dibenzoimidazole
Heating of 2,4-dinitroaniline (0.183 g, 1 mmol) with N2H4·H2O (0.100 g, 2 mmol) at
110°C in presence of Pd/C first yielded 4-nitro-o-phenylenediamine (V) from which
5-nitrobenzimidazole was prepared in 70% yield. Then, refluxing of 5-
nitrobenzimidazole (1 mmol) with N2H4·H2O (0.100 g, 2 mmol) at 110°C in presence
of Pd/C in 30 mL of amyl alcohol afforded 5-aminobenzimidazole in 77% yield. Later
reduction of diazotized 5-aminobenzimidazole generated the desired derivative (5,5'-
dibenzoimidazole) in 69% yield.
4.4. Synthesis of compound (1)
A mixture of terephthalic acid (0.0996 g, 0.60 mmol), 5,5'-dibenzoimidazole (0.0936
g, 0.40 mmol) and Co(NO3)2·6H2O (0.5822 g, 2.0 mmol) in water (8 mL) was placed
in a 25 mL stainless steel reactor with Teflon liner and heated to 140 C for 72 h; then
it was cooled down to room temperature at the rate 6C/h. Orange rectangular-
shaped crystals were separated by filtration, washed with deionized water and dried in
air. Yield: 0.071 g. Anal. Calc. for C22H14O4N4Co: C, 57.73; H, 3.09; N, 12.25. Found:
C, 58.03; H, 3.29; N, 12.03%.

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4.5. X-ray crystallography
The crystal structure of compound 1 was determined by X-ray diffraction methods.
Intensity data and cell parameters were recorded at 190(2) K on a Bruker ApexII
diffractometer (MoK radiation  = 0.71073 Å) equipped with a CCD area detector
and a graphite monochromator. The raw frame data were processed using the
programs SAINT and SADABS to yield the reflection data files [54]. The structure
2
was solved by Direct Methods using the SIR97 program [55] and refined on Fo by
full-matrix least-squares procedures, using the SHELXL-2014/7 program [56] in the
WinGX suite v.2014.1 [57]. The structure of the title compound was refined as a two-
component twin. All non-hydrogen atoms were refined with anisotropic atomic
displacements, while the hydrogen atoms were found in the difference Fourier map
and refined freely. The weighting scheme used in the last cycle of refinement was w =
2
2
1/ [2Fo + (0.0513P)2 + 5.1777P], where P = (Fo + 2Fc2)/3. Crystal data and
experimental details for data collection and structure refinement are reported in Table
4. Crystallographic data for the structure reported have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publication no. CCDC
1898073 and can be obtained free of charge on application to the CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-336-033; e-mail

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deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
Table 4. Crystallographic data of compound 1.
Empirical formula
Formula weight
Temperature
Wavelength (Å)
Crystal system
Space group
a, Å
C22H14O4N4Co
457.30
190(2)
0.71073
Monoclinic
P21/c
10.544(2)
13.995(3)
13.434(2)
111.569(4)
1843.5(6)
4
b, Å
c, Å
, deg
Volume, Å3
Z
Dcalc (mg m-3)
 (Mo K) (mm-1)
F(000)
1.648
0.972
932
Total reflections
Observed reflections
[Fo>4σ(Fo)]
GOF on F2a
R indices [Fo>4σ(Fo)]bR1,
wR2
5623
4428
1.002
0.0506, 0.1228

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Largest diff. peak and
0.517, -0.622
hole, e.Å-3
2
aGoodness-of-fit S = [w(Fo -Fc2)2/ (n-p)]1/2, where n is the number of reflections
b
2
and p the number of parameters. R1 = Σ║Fo│-│Fc║/Σ│Fo│, wR2 = [Σ[w(Fo -
2 2
Fc2)2]/Σ[w(Fo ) ]]1/2.
4.6. Theoretical methods
The calculation of the EPR g-tensor has been performed using the Gaussian-09
program [58] and the B3LYP/def2-TZVP level of theory. For the calculation in the
solid state, the crystallographic coordinates have been used, where the positions of the
H atoms have been optimized.
Acknowledgements
AD expresses his appreciation to the Ministry of Science & Technology (MOST),
Taiwan, for financial assistance. We also thank Prof. Chen-Hsiung Hung for his
valuable suggestions in crystallography.
Conflict of interest
We wish to assure that our manuscript does not contain any potential interest or "no
conflict of interest”.

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