The effect of electronegativity upon the coordination sphere; heterodinuclear Ni(II) complexes with ONNO type Schiff bases, octahedral, square pyramidal and square planar coordination of Ni(II)

Article abstract of DOI:10.1016/j.molstruc.2020.128789

NiL.MX₂ heterodinuclear complexes with a nuclear structure of Ni^II-M^II (M = Zn, Cd, X = Cl, Br, I) were prepared in the dioxane medium by the use of an ONNO type ligand, Bis-N,N′(salicylidene)-1,3-propanediamine (LH₂). The complexes prepared were characterized by the use of infrared (IR) spectroscopy, thermogravimetry (TG), semi-micro nitrogen, metal and halogen analysis. The molecular structures and unit cell properties of the compounds were elucidated by the X-ray diffraction (XRD) method. In parallel to the literature, MX₂ group was observed to form μ? bridges with the phenolic oxygens of the organic ligand. The coordination sphere of NiL heterodinuclear complex in NiL group was observed to change depending upon the electronegativities of the atoms in MX₂ group. The electronegativities of the atoms in the MX₂ group affect the coordination sphere of NiL group of the heterodinuclear complex, and in parallel with the electronegativities of the atoms in MX₂ group, it was observed that NiL unit coordinated the solvent molecules and the coordination sphere changed. In addition to this, the coordination bonds get smaller as the number of donor atoms nearby NiL decreased. Using Gaussian 09 software, the theoretical bond lengths and bond angles were calculated and compared with the experimental data. With Gaussian 09 software, it was determined how the occupancy levels of d orbitals of the metal atoms changed by coordination of Ni(II) ion. Also, the change of the differences between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels of the complexes was monitored.

Full text of DOI:10.1016/j.molstruc.2020.128789

Journal Pre-proof
The effect of electronegativity upon the coordination sphere; heterodinuclear Ni(II)
complexes with ONNO type Schiff bases, octahedral, square pyramidal and square
planar coordination of Ni(II)
Yaprak Gürsoy Tuncer, Kübra Gürpınar, Nurcan Acar, Hasan Nazır, Ingrid Svoboda,
Orhan Atakol, Emine Kübra İnal
PII:
S0022-2860(20)31114-5
DOI:
https://doi.org/10.1016/j.molstruc.2020.128789
MOLSTR 128789
Reference:
To appear in: Journal of Molecular Structure
Received Date: 20 March 2020
Revised Date: 26 June 2020
Accepted Date: 27 June 2020
Please cite this article as: Y. Gürsoy Tuncer, Kü. Gürpınar, N. Acar, H. Nazır, I. Svoboda, O. Atakol,
Emine.Kü. İnal, The effect of electronegativity upon the coordination sphere; heterodinuclear Ni(II)
complexes with ONNO type Schiff bases, octahedral, square pyramidal and square planar coordination
of Ni(II), Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/j.molstruc.2020.128789.
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CRediT author statement
Yaprak Gürsoy Tuncer: Investigation. Kübra Gürpınar: Investigation. Nurcan Acar:
Visualization, Data curation. Hasan Nazır: Formal analysis, Software, Validation. Ingrid
Svoboda: Formal analysis, Resources. Orhan Atakol: Methodology, Supervision. Emine
Kübra İnal: Conceptualization, Writing - Review & Editing.

The effect of electronegativity upon the coordination sphere; heterodinuclear Ni(II)
complexes with ONNO type Schiff bases, octahedral, square pyramidal and square
planar coordination of Ni(II)
Yaprak Gürsoy Tuncera, Kübra Gürpınara, Nurcan Acara, Hasan Nazıra, Ingrid Svobodab,
Orhan Atakola, Emine Kübra İnala*
aAnkara University, Faculty of Science, Department of Chemistry, 06100, Ankara, Turkey
bTU-Darmstadt, Materialwissenschaft, Strukturforschung, Alarich-Weiss Strasse,
64287, Darmstadt, Germany
*e-mail: inal@science.ankara.edu.tr
ORCID:
Y. Gürsoy Tuncer: Not available
K. Gürpınar: 0000-0001-9307-7688
N. Acar: 0000-0003-3531-9073
H. Nazır: 0000-0002-8423-751X
I. Svoboda: Not available
O. Atakol: 0000-0003-0977-6588
E.K. İnal: 0000-0001-8334-2791
Abstract
NiL.MX2 heterodinuclear complexes with a nuclear structure of NiII-MII (M = Zn, Cd, X = Cl,
Br, I) were prepared in the dioxane medium by the use of an ONNO type ligand, Bis-
N,N'(salicylidene)-1,3-propanediamine (LH2). The complexes prepared were characterized by
the use of infrared (IR) spectroscopy, thermogravimetry (TG), semi-micro nitrogen, metal and
halogen analysis. The molecular structures and unit cell properties of the compounds were
elucidated by the X-ray diffraction (XRD) method. In parallel to the literature, MX2 group
was observed to form μ‒ bridges with the phenolic oxygens of the organic ligand. The
coordination sphere of NiL heterodinuclear complex in NiL group was observed to change
depending upon the electronegativities of the atoms in MX2 group. The electronegativities of
the atoms in the MX2 group affect the coordination sphere of NiL group of the
heterodinuclear complex, and in parallel with the electronegativities of the atoms in MX2
group, it was observed that NiL unit coordinated the solvent molecules and the coordination
sphere changed. In addition to this, the coordination bonds get smaller as the number of donor
atoms nearby NiL decreased. Using Gaussian 09 software, the theoretical bond lengths and
bond angles were calculated and compared with the experimental data. With the Gaussian 09
software, it was determined how the occupancy levels of d orbitals of the metal atoms
changed by coordination of Ni(II) ion. Also, the change of the differences between the highest
occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)
levels of the complexes was monitored.
Keywords: Salpn type Schiff base; Heteronuclear complexes; Thermogravimetry; Theoretical
calculation; DFT; NBO
1

1. Introduction
Bis-N,N'(salicylidene)-1,3-diaminopropane (LH2) is an O2N2 type tetradentate ligand known
since 1946 [1]. It has a very high tendency to give polynuclear complexes. The first dinuclear
complex prepared by the use of this ligand was reported in 1976 [2]. The magnetic anomaly
of Ni(II) and Cu(II) complexes of this ligand was noticed in the early 1960s. However, the
polynuclear complex formation of this ligand could not be verified due to the lack of X-ray
methods at that time [3]. The first trinuclear Ni(II) complex of LH2 ligand was reported
in1990 [4]. From that time today, there have been so many dinuclear [5-7], trinuclear [4,8-13],
tetranuclear [14-17] and polynuclear [18] complexes were and are still being reported in the
literature. The structures of the mononuclear of Ni(II) and Cu(II) complexes of LH2 has first
appeared in 1985 [19]. NiL complex was found to have a square planar coordination sphere.
NiL complex is dissolved in common organic solvents, attach the other coligands and solvent
molecules forming square pyramidal coordination spheres [20]. In the presence of other Lewis
acids result in the formation of dinuclear Ni(II) complexes with octahedral and occasionally
square pyramidal coordination sphere, dinuclear [NiL.ZnBr2.x(4-picoline)] complexes have
been previously reported using NiL, ZnBr2 and 4-methylpyridine (4-picoline) as coligand
[21]. In the reported study, depending on 4-picoline concentration, [NiL.ZnBr2.(4-picoline)2]
octahedral complex or at low 4-picoline concentration [NiL.ZnBr2.(4-picoline)] square
pyramidal coordination sphere was obtained. In this study, Ni‒picoline nitrogen distance in
square pyramidal coordination was found shorter than Ni–picoline nitrogen distance in the
octahedral complex. This is probably caused by ZnBr2 molecule. ZnBr2 attracts the electrons
of NiL unit through phenolic oxygen and attaches the coligand molecules to itself due to the
decreasing electron density of Ni(II) ion. If a single coligand is attached, Ni(II) ion will attract
more electrons, so the coordination bond will be shorter. If two coligands are attached, the
coordination bonds will be longer. Consequently, the electronegativity of Lewis acid bound to
the structure affects the coordination sphere of Ni(II) ion.
The aim of this study was to investigate the change of the coordination of Ni(II) in the
NiL group, depending on the electronegativity or hardness of the Lewis acid bound to NiL
group. In this study, dinuclear complexes were prepared by the use of ZnX2 (X = Br and I)
and CdI2 in DMF and dioxane media. In studies using ZnCl2 and CdCl2, the coordination
sphere has always been found to be an octahedral. It was determined by X-ray diffraction
where the Ni(II) ion was in an octahedral coordination sphere by binding two DMF
molecules. For this reason, iodides with lower electronegativity were used in this study. The
electronegativity of Cd atom is smaller than Zn atom, similarly, the electronegativity of I
atom is smaller than Br atom, in which case the coordination sphere of Ni(II) ion has been
investigated. The four coordination compounds obtained were characterized by element
analysis, IR spectroscopy and thermogravimetry method, then molecular models were
obtained by X-ray diffraction. The basic formula of the complexes prepared are given as
follows:
I
II
[NiL·ZnBr2·(DMF)2]
[(NiL)2 (ZnI2)2·(dioxane)3]
C23H30N4O6NiZnBr2
C46H56N4O10Ni2Zn2I4
III
IV
[(NiL)2 (ZnI2)2·(dioxane)].(dioxane)2 C46H56N4O10Ni2Zn2I4
[(NiL·CdI2)2] C34H32N4O4Ni2Cd2I2
2. Experimental
The reagents supplied from Sigma-Aldrich or Merck companies used without further
purification. In this study, Shimadzu IRAffinity-1 FTIR spectrometer equipped with three
2

reflectional ATR units was used for IR spectra with 4 cm-1 accuracy. The C, H, and N
analyses were performed on Eurovector 3018 CHNS analyzer. Metal analyses were carried
out on GBC Avanta PM Model atomic absorption spectrometer using FAAS mode. Complex
(2-3 mg) was dissolved in 1 mL HNO3 (63%) with heating, diluted to 100 mL and given to
nebulizer of atomic absorption spectrometer for metal analysis. Halogen analyses were
performed with classical gravimetrical methods. For the halogen analyses approximately 200
mg complex was digested in a Kjeldahl flask using 6 mL HNO3 (63%) and H2O2 (27%)
mixture (4:2, v/v) and after digestion was diluted in a 100 mL volumetric flask then was
precipitated as AgX using AgNO3. The mass spectra of the ligands were obtained by a
Shimadzu QP2010 Plus GCMS apparatus equipped with a direct inlet (DI) unit with an
electron impact ionizer. DI temperature was varied between 40-300 °C and ionization was
carried out with electrons with 70 eV energy. The NMR spectra were recorded on the Bruker
Ultrashield 300 MHz NMR spectrometer using d6-DMSO solution as the solvent. The
thermogravimetric analyses were carried out by Shimadzu DTG 60H in Pt pans between a
temperature range of 30-600 °C at a heating rate of 10 °C/min under N2 atmosphere. The
instrument was calibrated with metallic In and Zn.
2.1 X-ray crystallography
A single crystals of [NiL·ZnBr2·(DMF)2], [(NiL)2·(ZnBr2)2·(dioxane)3],
[(NiL)2·(ZnI2)2·(dioxane)].(dioxane)2 and [(NiL·CdI2)2] were analyzed on an Oxford
Diffraction Xcalibur Single Crystal X-ray Diffractometer with a sapphire CCD detector using
MoKα radiation (λ = 0.71073 A) operating in ω/2θ scan mode. The unit cell dimensions were
determined and refined by using the angular settings of 25 automatically centered reflections
in
2.778°≤θ≤27.779°
range
for
[NiL·ZnBr2·(DMF)2],
2.598°-27.933°
for
[(NiL)2·(ZnBr2)2·(dioxane)3], 2.547°-27.789° for [(NiL)2 (ZnI2)2·(dioxane)].(dioxane)2 and
2.608°-27.980° for [(NiL.CdI2)2]. The data for I, II and IV complexes were collected at 293(2)
K and for III was collected at 200(2) K. The empirical absorption corrections were applied by
the semi-empirical method via the CrysAlis CCD software [22]. The model was obtained
from the results of the cell refinement and the data reductions were carried out using the
solution software SHELXL97 [23]. The structure of the complexes was solved by direct
methods using the SHELXS 97 software implemented in the WinGX package [24].
Supplementary material for structure has been deposited to the Cambridge Crystallographic
Data Center as CCDC no: 1949378, 1949377, 1949379, and 1949376
(deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
2.2 Synthesis
2.2.1 Preparation of Bis-N,N'(salycilidene)-1,3-diaminopropane (LH2)
The ligand was prepared from salicylaldehyde and 1,3-propanediamine via a
condensation reaction in ethanol. 0.05 mole salicylaldehyde (6.1 g) was dissolved in 50 mL
EtOH under stirring and heating and was heated this solution up to the boiling point. Then
0.025 mole 1,3-propanediamine (1.85 g) was added dropwise to this solution and the final
mixture was left aside for 5-6 hours and the formed yellow crystals were filtered from
Buchner funnel and dried in the air.
Formula
C17H18N2O2
58
Melting Point (°C)
Yield (%)
90-95
3

Elemental Analysis
IR data (cm-1)
(Expected, %)
(Found, %)
C: 72.32 H: 6.43
C: 71.95 H: 6.33
N: 9.92
N: 10.09
νC=C(ring)
1608
νO-H
νC-H(Ar)
νC-H(Al)
2929-
2862
νC=N
1629
νC-O(Ph)
1274-
1151
δC-H(Ar)
762
2627
3021-
3019
λ
max (243 nm)
ε = 7045 dm3mol-1cm-1 in DMSO
ε = 7865 dm3mol-1cm-1 in MeOH
λmax (242 nm)
1HNMR (δ, ppm)
in d6-DMSO
13.51 (s) 8.60 (s)
(O‒H) (‒CH=)
7.43 (d)
(HAr)
7.32 (t)
(HAr)
6.88 (t)
(HAr)
3.68 (t)
(N‒CH2) (‒CH2‒)
2.01 (p)
13CNMR (δ, ppm)
in d6-DMSO
166.6 161.1 132.7 132.1 119.1 118.9 116.9 58.5 (N‒CH2) 31.9 (‒CH2‒)
282 [M]+ 161 [HO-C6H4-CH=N-CH2-CH2-CH2]+ 148 [HO-C6H4-CH=N-CH2-CH2]+
134 [HO-C6H4-CH=N-CH2]+ 120 [HO-C6H4-CH=N]+ 107 [HO-C6H4-CH2]+ 77
[C6H5]+
m/z
2.2.2 Preparation of mononuclear NiL complex
0.01 mole LH2 (2.86 g) prepared as described above was dissolved in 50 mL EtOH
under heating. 10 mL of concentrated ammonia and a solution of 0.01 mole NiCl2.6H2O (2.36
g) in 50 mL hot water were respectively added to this solution under stirring. The light green
bulky crystal of [(NiL)2.(NH3)3] complex was precipitated in a few minutes dried at 140 °C in
an oven for 4 hours. The resulting light brown material is NiL [20,21].
Formula
C17H16N2O2Ni
Melting Point (°C)
Yield (%)
311 (decomposed over 360 °C, DTA result)
73
Ni: 17.33
Ni: 17.19
Elemental Analysis
(Expected, %)
(Found, %)
C: 60.28 H: 4.76
C: 60.55 H: 3.17
N: 8.27
N: 7.93
νC-H(Ar)
3061-
3030
νC-H(Al)
2922-
2866
νC=N
1607
νC=C(ring)
1589-
1541
δC-H(Al)
1475
νC‒O(Ph)
1228-
1124
δC-H(Ar)
725-
744
IR data (cm-1)
m/z
340 (isotope peak) 338 (molecular peak) 219 [Ni-O-C6H4-CH=NH-CH2-CH2-CH2]+
205 [Ni-O-C6H4-CH=NH-CH2-CH2]+ 179 [Ni-O-C6H4-CH=NH]+ 134 [O-C6H4-
CH=NH-CH2]+ 107 [HO-C6H4-CH2]+ 58 [Ni]+
2.2.3 Preparation of [NiL·ZnBr2·(DMF)2] complex (I)
0.001 mole NiL (0.339 g), prepared as described above, was dissolved in 40 mL DMF
under stirring and heated up to 100-110 °C. A solution of anhydrous 0.001 mole ZnBr2 (0.226
g) in 20 mL hot MeOH was added to this solution. The mixture was rigorously stirred and left
at the bench for 2-3 days and the resulting granulated crystallized green complex was filtered
with a Buchner funnel and dried in air.
Formula
C23H30N4O6NiZnBr2
64-70
Yield (%)
Zn: 8.80
Zn: 8.75
Elemental Analysis
(Exp, %)
(Fnd, %)
C: 37.21
H: 4.07
H: 4.42
N: 7.54
N: 6.99
Ni: 7.90
Ni: 7.59
Br: 21.52
Br: 20.97
C: 36.86
νC-H(Ar)
3033-
3017
νC-H(Al)
2924-
2853
νC=N
1629
νC=C(ring)
1595-
1555
δC-H(Al)
1475
νC‒O(Ph)
1305-
1124
δC-H(Ar)
753-
735
IR data (cm-1)
4

2.2.4 Preparation of [(NiL)2 (ZnI2)2·(dioxane)3] complex (II)
0.002 mole NiL (0.678 g), prepared as described above, was dissolved in 50 mL
dioxane under stirring and heated up to the boiling point. A solution of 0.002 mole anhydrous
ZnI2 (0.638 g) in 30 mL hot MeOH was added to this solution. The resulting mixture was
stirred and left at the bench for 2-3 days. The green crystals of the complex were filtered by a
Buchner funnel and dried in air.
Formula
C46H56N4O10Ni2Zn2I4
42
Yield (%)
Elemental Analysis
(Exp, %)
(Fnd, %)
C: 34.94
C: 34.35
H: 3.57
H: 3.41
N: 3.54
N: 3.63
Ni: 7.42
Ni: 7.25
Zn: 8.27
Zn: 8.81
I: 32.11
I: 33.36
νC-H(Ar)
3021-
3008
νC-H(Al)
2924-
2850
νC=N
1618
νC=C(ring)
1595-
1558
δC-H(Al)
1473
νC‒O(Ph)
1301-
1195
δC-H(Ar)
752-
734
IR data (cm-1)
2.2.5 Preparation of [(NiL)2·(ZnI2)2 (dioxane)].(dioxane)2 complex (III)
This complex was synthesized using 0.002 mole NiL (0.678 g) and 0.002 mole
anhydrous ZnI2 (0.452 g) in 50 mL dioxane-MeOH mixture (1:1, v/v) as described above for
complex II.
Formula
C46H56N4O10Ni2Zn2I4
26
Yield (%)
Zn: 8.27
Zn: 8.55
Elemental Analysis
(Exp, %)
(Fnd, %)
C: 34.92
C: 35.86
H: 3.57
H: 3.81
N: 3.54
N: 3.40
Ni: 7.42
Ni: 7.31
I: 32.13
I: 33.57
νC-H(Ar)
3027-
3011
νC-H(Al)
2924-
2853
νC=N
1625
νC=C(ring)
1593-
1552
δC-H(Al)
1475
νC‒O(Ph)
1300-
1107
δC-H(Ar)
756-
734
IR data (cm-1)
Note: In the preparation of complex II and III, a mixture of both complexes are obtained. If
the solvent mixture contained a higher amount of MeOH, complex III dominates the total
complex formation. However, if dioxane is predominant in the solvent mixture then complex
II was formed in much higher quantities.
2.2.6 Preparation of [(NiL·CdI2)2] complex (IV)
This complex was synthesized using 0.002 mole NiL (0.678 g) and 0.002 mole
anhydrous CdI2 (0.736 g) in dioxane as described above for complex II.
Formula
C34H36N4O4Ni2Cd2I4
32
Yield (%)
Elemental Analysis
(Exp, %)
(Fnd, %)
C: 28.91
H: 2.28
H: 3.11
N: 3.96
N: 3.79
Ni: 8.31
Ni: 7.94
Cd: 15.91 I: 35.94
Cd: 15.55 I: 37.87
C: 28.04
νC-H(Ar)
3038-
3019
νC-H(Al)
2937-
2872
νC=N
1622
νC=C(ring)
1597-
1552
δC-H(Al)
1473
νC‒O(Ph)
1303-
1126
δC-H(Ar)
752-
734
IR data (cm-1)
5

3. Results and Discussion
3.1 X-ray diffraction
The Ortep drawings of the prepared complexes obtained from the X-ray diffraction studies are
given in Fig. 1. Data collection condition and crystal properties are listed in Table 1 and bond
lengths and bond angles in complex coordination spheres are shown in Table 2. Table 2 also
contains the bond lengths and angles determined by the use of Gaussian 09 software for
comparison purposes. There is almost no difference between the experimental results and the
corresponding values obtained from the theoretical results from the theoretical programs by
the use of X-ray data.
Fig. 1.
Table 1
Table 2
As seen from Fig. 1 Ni(II) ion has an octahedral coordination in complex I and II, a
square pyramidal structure in complex III and a square planar structure in complex IV. In
complex I, Ni(II) ion slightly deformed octahedral coordination sphere surrounded by two
phenolic oxygens and two iminic nitrogen donors of L2- and axially oriented two DMF
oxygens. The two phenolic oxygens also form a μ‒ bridge with Zn(II) ion of ZnBr2 molecule
resulting in a heterodinuclear complex. Zn(II) ion is in a distorted tetrahedral O2Br2
coordination sphere. There are so many examples of this structure in the literature. Many
mononuclear complexes prepared with LH2 ligand can coordinate Lewis acid via phenolic
oxygens resulting in dinuclear structures [5,6,25-27].
In complex II, a dioxane molecule stands between two NiL.ZnI2 units and the two
oxygen of this dioxane molecule coordinate the Ni(II) ion in separately NiL.ZnI2 units. In
addition to this case, each Ni(II) ion is coordinated one dioxane molecule from another side,
consequently is occurred each establishing an O4N2 octahedral coordination sphere around
Ni(II) ion. Additionally, the phenolic oxygens of Schiff base form μ‒ bridges with Zn(II) ions
of ZnI2 molecule constituting a distorted tetrahedral O2I2 coordination sphere. The situation
for complex III is different. Although it is formed by the same structural units (NiL, ZnI2, and
dioxane) the coordination is different. Complex II and III occur at the same medium as stated
in the experimental part.
Using equal amounts of NiL and ZnI2 in dioxane/MeOH mixture (50:50, v/v), a
mixture of complex II and complex III is formed. Since complex II has a blue and complex III
has a green color they can be mechanically separated. In complex III, one dioxane molecule
coordinated two Ni(II) ions with its two oxygens connecting to NiL units. However, in our
study NiL units are not coordinated with other dioxane molecules. Under these conditions,
Ni(II) ions in NiL units are located in an O3N2 square pyramidal coordination sphere. Square
pyramidal coordination is not a common coordination sphere for Ni(II) ions. There are some
examples of mononuclear and dinuclear complexes reported in the literature [20,21]. Again
Zn(II) ions in complex III are located in the distorted tetrahedral O2I2 coordination sphere.
Complex IV is entirely different since there are no solvent molecules coordinating NiL
units and Ni(II) ion is in a square planar coordination sphere. NiL units are coordinated Cd(II)
ion in CdI2 by μ‒ bridge through phenolic oxygens. Iodine atoms are coordinated to
neighboring Cd(II) by a different μ‒ bridge. Under these conditions, two [NiL·CdI2] are
connected forming a heterotetranuclear complex. Here Ni(II) ions of NiL units have
6

approximately square planar coordination sphere and Cd(II) ions are in the O2I3 distorted
square pyramidal coordination sphere. This shows the fact that the bond angles and bond
lengths displayed in Table 2, there is a very slight distortion in these parameters. On the other
hand, the tetrahedral coordination sphere of Zn(II) ions in complex I, II and III are highly
distorted. This fact is highly apparent from the decrease of halogen-zinc-halogen angles down
to 70°.
The degree of distortion of the coordination sphere can be estimated from bond
lengths and angles around the metal ion. The bond angles and the length of the complexes are
given in Table 2. There are two possibilities for the formation of pentadentate coordination in
complexes, namely square pyramidal and trigonal bipyramidal structures. The best method for
the determination of the coordination sphere is the determination of τ variable used since
1984 [28]. The parameter is calculated as τ = (α-β)/60. Here α and β are the largest angles in
the coordination sphere. If τ = 1 the structure of the coordination sphere is trigonal
bipyramidal and if τ = 0 the structure of the coordination sphere is square pyramidal. The
deviation from these values causes an increase in the distortion of the coordination sphere. τ
values for the coordination spheres of Ni(II) in complex III and Cd(II)in complex IV are
calculated taking the angles given in Table 2, it comes out to be 0.00167 for complex III and
0.45466 for complex IV. This shows the fact that the Ni(II) in complex III is located in a
slightly distorted square pyramidal and while Cd(II)ion in complex IV is in a highly deformed
square pyramidal coordination sphere.
The structure of NiL compound was explained in 1985. According to it, Ni(II) ions in
NiL mononuclear complex have a square planar coordination sphere [19]. However, the most
striking case in this study is when a Lewis acid such as MX2 (M = Zn(II) or Cd(II), X = Cl-,
Br- or I-) is coordinated to NiL complex via phenolic oxygens, the electronegativity of the
metal ion and halogen of Lewis acid effect the coordination around Ni(II) ion. In other words,
the coordination sphere and the bond lengths of the complexes apart are affected by the
electronegativity of the metal present in the complex. It also affects the magnetic
susceptibility. NiL is a diamagnetic complex but acts as paramagnetic if the coordination is a
square pyramidal or octahedral. This event, seen in complexes of ONNO type ligands and
occurring over oxygen bridges, is known as a super magnetic exchange [29]. As in complex I,
if the metal ion is in the case of halogen Cl- or Br-, this Lewis acid attracts some of the
electrons of phenolic oxygen, so phenolic oxygen cannot deliver electrons to Ni(II) ion as in
NiL mononuclear complex. In other words, the amount of electrons they offer to Ni(II)
decreases. Under these situations, Ni(II) ion coordinates the solvent around itself changing the
coordination sphere. If Ni(II) ion cannot find the electron donors to regain the decreasing
electron density, the dinuclear complex cannot occur [30]. Since ZnBr2 molecule attracts
some of the electrons of the phenolic oxygen in complex I, the amount of electrons that the
phenolic oxygen transfers to Ni(II) ion decrease in NiL unit. In this case, Ni(II) ion
coordinates the oxygen of two solvent molecules to itself to gain electron density. If the Lewis
acid used was ZnCl2, the result would be expected to be octahedral since Cl atom is more
electronegative than Br atom, indeed this complex has been reported in the literature and the
coordination of Ni(II) is octahedral. The difference in complex II and III is that instead of Br
atoms in Lewis acid, there are I atoms. The electronegativity of I is smaller, and therefore
ZnI2 unit attracts less electrons of phenolic oxygen and less electron is attracted from the
dioxane molecules bound to Ni(II) ion.
As seen from Table 2 the lengths of Ni(II)–N and Ni–O in NiL unit ranged as 2.013-
2.026 Å, the length of Ni(II)–O(DMF) changes between 2.134 and 2.135 Å in complex I. On
the other hand, while Ni(II)–N and Ni(II)–O bond lengths in NiL unit of complex II change
between 2.002 and 2.030 Å, Ni(II)–O(dioxane) distance is increased to 2.196 and 2.164 Å. It
is obvious that the lengths of NiL unit do not show a significant change but the distance
7

between the solvent molecules is increased because Ni(II) is less affected. In complex III,
Ni(II)–O and Ni(II)–N distances in NiL unit vary between 1.955 and 1.978 Å and Ni(II)–
O(dioxane) distance is increased to 2.371 Å. Coordinative dioxane is shared by two NiL in
this complex. That is why the increase in this distance is not surprising because the distances
in NiL unit are shortened. In complex IV, there is no solvent molecule participated in the
coordination, NiL unit seems to remain in mononuclear form. The Ni(II)–O and Ni(II)–N
distances in this complex ranged between 1.849 and 1.875 Å. These values were reported as
1.845 and 1.901 Å for NiL mononuclear complex in the literature. Bond lengths in NiL unit
relative to the mononuclear state were not affected by dinuclear complex formation. Because
the electronegativities of Cd(II) ion and I atoms are not high enough. The electrons they
attract from phenolic oxygens do not affect the coordination of NiL. For this reason, the
coordination of Ni(II) ion in NiL unit has not changed. There was no change in NiL unit, but
CdI2 unit of the complex formed the µ‒ bridge over I atoms and a tetranuclear complex was
formed. One I atom of each Cd(II) ion formed the µ‒ bridge with the other Cd(II) ion. In this
case, each Cd(II) ion had a 5-member coordination sphere and an over-deformed square
pyramidal coordination sphere was formed. It is possible to say that because the µ‒ bridge of I
atoms gives electrons to Cd(II) ion, Cd(II) ion does not receive too many electrons from
phenolic oxygen and does not affect NiL unit.
3.2 Thermal analysis
TG-DTA plots of the complexes for their thermal characterization are illustrated in Fig. 2a-d
and the resulting mass losses are listed in Table 3. DTA curves of four complexes are given in
Fig. 3 for comparison purposes.
Fig. 2.
Fig. 3.
Table 3
As seen in Fig. 2a and Table 3, complex I begins to decompose at 148 °C and a mass
loss of 21% is observed with an endothermic reaction. This mass loss corresponds to the mass
of DMF molecules coordinated. At 148 °C, DMF molecules are separated from the structure
and the complex is degraded. By separating DMF molecules, NiL and ZnBr2 remain in the
medium and the mixture endothermic decomposes at 400 °C. This degradation is the
disintegration of NiL unit. It has been previously reported that NiL molecule is broken down
by an endothermic reaction at 380-400 °C. Fig. 2b shows the degradation of complex II.
Complex II contains three molecules of dioxane and these dioxanes are coordinated according
to X-ray diffraction data. Two dioxane molecules coordinate two NiL units through one
oxygen and the other dioxane through two oxygen. An endothermic mass loss of 12.65% is
observed at 97 °C followed by a loss of endothermic mass of 6.32% at 126 °C. If calculated,
the first mass loss corresponds to about two dioxane molecules, the second mass loss
corresponds to a single dioxane molecule, the total mass loss at 97-126 °C corresponds to
three dioxane molecules. Possibly, single coordinated dioxane leaves the structure at 97 °C,
and the two coordinated dioxanes begin to separate at 126 °C. Fig. 2c shows the TG-DTA
curves of the complex III. X-ray results show that a dioxane molecule present in this molecule
as a solvate. This solvate molecule begins to detach from the structure at 92 °C and the initial
mass loss belongs to this solvate molecule and this is understood from the endothermic signal
at 92 °C. The fact that the separation temperature of the dioxane molecule is lower than that
8

of complex II indicates that the separated molecule is solvate. The second mass loss is again
endothermic and at a higher temperature, this mass loss again corresponds to a dioxane
molecule and is possibly the removal of coordinated dioxane. In Fig. 2d, TG-DTA curve of
complex IV is given. As it is seen, there is no mass loss up to 400 °C and the mass loss that
starts at this temperature belongs to the disintegration of NiL unit as in other complexes.
Thermal analysis contributed to the characterization of complexes in this study and
coordinative and solvate states of solvent molecules in complexes were determined by
thermogravimetry. Thermal analysis is particularly effective in determining complex
stoichiometry, especially in complexes containing solvate and coordinated solvent molecules
[31]. It is possible to determine the coordinated groups clearly from TG curves. In addition, it
is evident from TG curves whether the coordinated molecules are solvate or coordinative. The
fact that DTA curves are also endothermic is an expected condition for these decomposition
reactions. All complexes are degraded by an endothermic reaction with a curve of the same
form around 400 °C, and the form of this curve is almost the same as that of the single NiL
complex.
3.3 Computational calculations
The occupancy levels of d orbitals of metals were determined by the use of NBO (natural
bond orbital) algorithm embedded in Gaussian 09 software are listed in Table 4. ESP
(electrostatic potential) diagrams showing the electron density of the complexes and the
images of the HOMO and LUMO are illustrated in Fig. 4 and the energy difference between
these two orbitals and the dipole moments determined from ESP diagrams are tabulated in
Table 5.
Fig. 4.
3.3.1 NBO analysis
Table 4 lists the electron occupancy levels and relative energy levels of d orbitals of
Ni(II) and Zn(II) ion in complexes calculated by the use of NBO program, the electron
density values Ni(II) ion of octahedral complex I and complex II is as expected from the
classical field splitting theory [32]. The highest energy orbitals in both complexes are dyz and
dzx orbitals which are not totally occupied. On the other hand, dx2-y2, dxy and dz2 orbitals are
much more stable and almost totally occupied this situation is in good accordance with crystal
field theory for octahedral complexes. The d orbitals are split into three low and two high
energy orbitals.
Ni(II) ion is in a square pyramidal coordination sphere in complex III and a square planar
coordination sphere in complex IV. It is highly difficult to explain the crystal field splitting of
these complexes by the use of the data listed in Table 4. Table 4 also includes the data
calculated for NiL mononuclear complex. The occupancy values of d orbitals in the
mononuclear NiL complex is highly identically calculated. The highest energy orbital dxy is
practically empty and other orbitals carry two electrons. Under these conditions, NiL complex
expected to be diamagnetic. In fact, square planar Ni(II) complexes are diamagnetic [33].
According to the NBO data, d orbitals with at least one electron space in Ni(II) ion are
seen in complex I, II and III. In addition, NBO was theoretically calculated for NiL and four
orbitals were found to be full and one orbital was empty. In this case, complex I, II and III are
expected to be paramagnetic and NiL to be diamagnetic, and the coordination found proves
this. Only NBO results of complex IV are not fully explained. It is seen that almost two
orbitals contain two electrons, but the occupancy values of the other d orbitals are 1.41, 1.66
and 1.68 electrons. If Ni(II) ion was in the square planar coordination sphere, it would be
9

expected that four orbitals were filled and one orbital was empty. As a result, it can be said for
complex IV that the addition of CdI2 to the square planar NiL complex affects the electron
order of Ni(II) ion. The electronegativities of Cd and I atoms are relatively low, it does not
affect the coordination sphere of NiL complex, but it affects the electron distribution of Ni(II)
ion. It is probable that the electron order on phenolic µ‒ bridges is shared between Ni (II) and
Cd (II) ions.
Table 4
3.3.2 HOMO-LUMO analysis
Table 5 lists the calculated energies of HOMO and LUMO orbitals. The formation of
the dinuclear complex increases the stability of HOMO and LUMO energy levels. The
difference between HOMO and LUMO energies of the complex II and III are found to be
lower than expected.
ΔEHOMO-LUMO value in NiL complex was found as -4.949 eV. For all other
heteronuclear complexes, this value is less than -5.000. It was found that HOMO orbitals are
more stable in the formation of a heteronuclear complex. A similar situation was observed in
the energy levels of LUMO orbitals. LUMO orbitals of the heteronuclear complexes have
shifted to more negative values. But ΔEHOMO-LUMO value is different. This difference increased
in complex I, decreased in complex II and III, and did not change in complex IV. In complex
I, Lewis acid ZnBr2 is coordinated DMF solvent molecules. Due to its high electronegativity,
ZnBr2 withdraws more electrons from NiL unit. As a result, Ni(II) ion attracts more electrons
from DMF molecules and the overlaps between the orbitals are strengthened, in this case the
stability of HOMO orbitals increases. However, in complex II and III, ZnI2 is used as Lewis
acid and the coordinated solvent molecules are dioxane. Dioxane is a weaker ligand than
DMF. As a result, the energy of HOMO orbitals does not decrease too much and the energy of
LUMO orbitals does not increase and ΔEHOMO-LUMO value is low. In complex IV, Lewis acid
used is CdI2 and the solvent molecule is not coordinated because CdI2 has not drawn more
electrons from NiL units. The value of ΔEHOMO-LUMO remained approximately the same due to
the small impact of Ni(II).
Table 5
3.3.3 Theoretical structural analysis
Another parameter calculated from the theoretical programs is dipole moments of the
complexes. The dipole moments given in Table 5 were observed to change with the
electronegativity of the metal ion and geometry of the complexes. Fig. 4 shows the ESP maps
of the complexes. The red regions correspond to the electron-rich and blue regions correspond
to the electron-poor areas. It appears that the increase in the asymmetry of the molecules and
the electronegativities of the metal ions increases the dipole moment of the complexes.
Complex I is the most asymmetric complex among the complexes prepared in this study due
to the presence of Zn(II) and Br- ions having the largest dipole moment value. Complex IV
containing Cd(II) and I- has almost a symmetrical structure and the lowest dipole moment
value.
However, the theoretical dipole moment values given in Table 5 are quite identical. A
dipole moment parallel to the electronegativity of the atoms in Lewis acid was calculated.
While the dipole moment in the mononuclear NiL molecule was 5.618 Debye, it increased
parallel to the electronegativity of Lewis acid in complex I, II and III. In the mononuclear NiL
complex, it is expected to have a dipole moment due to two O and two N atoms in the cis
position. Because O atoms have higher electronegativity value than N atoms. As can be seen
10

in complex I, II and III, when a Lewis acid is bounded to the O atoms, the dipole moment
changes according to the electronegativity of the group that is bounded and this change can be
calculated theoretically. However, in complex IV, the molecule has become tetranuclear and
symmetrical due to the µ‒ bridges made by I atoms in CdI2 unit. In this case, as can be seen in
Fig. 4, the center of gravity of the positive and negative charges coincide, and therefore the
dipole moment is calculated low.
4. Conclusions
There were three different heteronuclear Ni(II) complexes with different coordination spheres
prepared by the attachment of mononuclear square planar NiL complex to different Lewis
acids in DMF, MeOH and dioxane mixtures. These prepared complexes were formed by
adding a Lewis acid and solvent molecules to the square planar NiL complex, and the
coordination of the solvent molecules affects the coordination sphere of Ni(II) ion. Thermal
analysis was very helpful in determining coordinated and solvated solvent molecules. The
structures of the complexes were enlightened by the X-ray diffraction method. Also, their
coordination sphere evaluated by the use of the algorithms embedded in Gaussian 09. If the
electronegativity of the atoms in Lewis acid increases, the square planar NiL unit turns the
coordination sphere into square pyramidal and octahedral by attracting electrons from the
solvent molecules. It was concluded that the electronegativity of Lewis acid used affects the
coordination sphere.
11

Acknowledgements
This research did not receive any specific grant from funding agencies. The authors declare
that there is no conflict of interest.
CRediT author contribution statement
Yaprak Gürsoy Tuncer: Investigation. Kübra Gürpınar: Investigation. Nurcan Acar:
Visualization, Data curation. Hasan Nazır: Formal analysis, Software, Validation. Ingrid
Svoboda: Formal analysis, Resources. Orhan Atakol: Methodology, Supervision. Emine
Kübra İnal: Conceptualization, Writing - Review & Editing.
12

References
1. A. Martell, M. Calvin, Die Chemie Der Metallchelat-Verbindungen, Verlag Chemie,
Weinheim, 1958.
2. R.J. Butcher, E. Sinn, Relation between magnetic, spectroscopic, and structural properties
of bis [chloro (N-isopropyl-2-hydroxybenzylidene) aminato-. mu.-O-copper (II)] and bis (N-
isopropyl-2-hydroxybenzylideneaminato) copper (II), Inorg. Chem. 15 (1976) 1604-1608.
3. M. Kato, Y. Muto, Factors affecting the magnetic properties of dimeric copper (II)
complexes, Coordin. Chem. Rev. 92 (1988) 45-83.
4. C. Fukuhara, K. Tsuneyoshi, N. Matsumoto, S. Kida, M. Mikuriya, M. Mori, Synthesis and
characterization of trinuclear Schiff-base complexes containing sulphur dioxide or
hydrogensulphite ions as bridging groups. Crystal structure of [Zn {(µ-CH 3 CO 2)(salpd-µ-
O, O′) Cu} 2][salpd= propane-1, 3-diylbis (salicylideneiminate)], Dalton T. 11 (1990) 3473-
3479.
5. M. Aksu, S. Durmuş, M. Sari, K. Emregül, I. Svoboda, H. Fuess, O. Atakol, Investigation
on the thermal decomposition some heterodinuclear NiII-MII complexes prepared from
ONNO type reduced Schiff base compounds (M II= ZnII, CdII), J. Therm. Anal. Calorim. 90
(2007) 541-547.
6. Y.N. Chen, Y.Y. Ge, W. Zhou, L.F. Ye, Z.G. Gu, G.Z. Ma, W.S. Li, H. Li, Y.P. Cai, The
first Mn–Zn heterometallic dinuclear compound based on Schiff base ligand N, N′-bis
(salicylidene)-1, 3-diaminopropane, Inorg. Chem. Commun. 14 (2011) 1228-1232.
7. P. Chakraborty, S. Mohanta, Mononuclear and heterometallic dinuclear, trinuclear and
dimer-of-dinuclear complexes derived from single-and double-compartment Schiff base
ligands having a less utilized diamine, Polyhedron 87 (2015) 98-108.
8. S. Öz, Ü. Ergun, M. Yakut, I. Svoboda, A. Atakol, E.K. İnal, N. Yılmaz, O. Atakol,
Synthesis, crystal structure, chromatographic seperation, and thermogravimetric investigation
of a ONNO type asymmetric Schiff base and its trinuclear complexes, Russ. J. Coord. Chem.
40 (2014) 571-582.
9. A. Hazari, A. Das, P. Mahapatra, A. Ghosh, Mixed valence trinuclear cobalt (II/III)
complexes: Synthesis, structural characterization and phenoxazinone synthase activity,
Polyhedron 134 (2017) 99-106.
10. A. Hazari, C.J. Gómez-García, M.G. Drew, A. Ghosh, Rare examples of diphenoxido-
bridged trinuclear NiII2FeIII complexes with a reduced salen type Schiff base ligand:
Structures and magnetic properties, Polyhedron 138 (2017) 145-153.
11. S. Ghosh, A. Ghosh, Coordination of metalloligand [NiL](H2L= salen type N2O2 Schiff
base ligand) to the f-block elements: Structural elucidation and spectrophotometric
investigation, Inorg. Chim. Acta. 442 (2016) 64-69.
12. P. Seth, A. Figuerola, J. Jover, E. Ruiz, A. Ghosh, Antiferro-to ferromagnetic crossover in
diphenoxido bridged NiII2MnII complexes derived from N2O2 donor Schiff base ligands,
Polyhedron 117 (2016) 57-63.
13. A. Hazari, S. Giri, C. Diaz, A. Ghosh, Unusual site selection of NCS− in trinuclear
complexes of Cu (II) and Ni (II) with a reduced N2O2 donor Schiff base: Structural,
theoretical and magnetic studies, Polyhedron 118 (2016) 70-80.
14. M. Mikuriya, S. Ikenoue, R. Nukada, J.W. Lim, Synthesis and structural characterization
of tetranuclear zinc (II) complexes with a linear array, B. Chem. Soc. Jpn. 74 (2001) 101-102.
15. R. Kurtaran, L.T. Yıldırım, A.D. Azaz, H. Namli, O. Atakol, Synthesis, characterization,
crystal structure and biological activity of a novel heterotetranuclear complex:[NiLPb (SCN)
2 (DMF)(H2O)] 2, bis-{[μ-N, N′-bis (salicylidene)-1, 3-propanediaminato-aqua-nickel
(II)](thiocyanato)(μ-thiocyanato)(μ-N, N′-dimethylformamide) lead (II)}, J. Inorg. Biochem.
99 (2005) 1937-1944.
13

16. A.D. Khalaji, H. Hadadzadeh, K. Fejfarova, M. Dusek, Metal-dependent assembly of a
tetranuclear copper (II) complex versus a 1D chain coordination polymer of cobalt (III)
complex with N2O2-chelating Schiff-base ligand: Synthesis, characterization and crystal
structures, Polyhedron 29 (2010) 807-812.
17. D. Bandyopadhyay, D. Karmakar, G. Pilet, M. Fleck, Synthesis and crystal structure of
two new heteropolynuclear [NiIICdIICdIINiII] and [NiIICdIINiII] Schiff base complexes
involving bridging chlorine and oxygen functions, Polyhedron 30 (2011) 2678-2683.
18. M. Mikuriya, N. Tsuru, S. Ikemi, S. Ikenoue, High nuclearity in a zinc (II) complex with
1, 3-bis (salicylamino)-2-propanol, Chem. Lett. 27 (1998) 879-880.
19. M.G. Drew, R.N. Prasad, R. Sharma, Structures of (N,N'-trimethylenedisalicylidene
aminato) nickel (II)(1) and (N, N'-trimethylenedisalicylideneaminato) copper (II)(2), Acta
Crystallogr. C. 41 (1985) 1755-1758.
20. Y. Elerman, M. Kabak, O. Atakol, An N, N'-bis (salicylidene)-1, 3-propanediamine–
nickel complex, Acta Crystallogr. C. 49 (1993) 1905-1906.
21. O. Atakol, H. Nazir, C. Arici, S. Durmus, I. Svoboda, H. Fuess, Some new Ni‒Zn
heterodinuclear complexes: square-pyramidal nickel (II) coordination, Inorg. Chim. Acta. 342
(2003) 295-300.
22. CrysAlis C. CrysAlis RED, version 1.171. Oxford Diffraction Ltd., Abdingdon, UK,
2002.
23. G.M. Sheldrick, SHELXS 97 and SHELXL 97, Program for Crystal Structure Solution
and Refinement, University of Göttingen, Germany, 1997.
24. L.J. Farrugia, WinGX suite for small-molecule single-crystal crystallography, J. Appl.
Crystallogr. 32 (1999) 837-838.
25. M.L. Colon, S.Y. Qian, D. Vanderveer, X.R. Bu, Chiral bimetallic complexes from chiral
salen metal complexes and mercury (II) halides and acetates: the anionic groups interact with
Cu (II) in apical position, Inorg. Chim. Acta. 357 (2004) 83-88.
26. L.K. Das, C.J. Gómez-García, M.G. Drew, A. Ghosh, Playing with different
metalloligands [NiL] and Hg to [NiL] ratios to tune the nuclearity of Ni (II)–Hg (II)
complexes: Formation of Di-, Tri-, Hexa-and nona-nuclear Ni–Hg clusters, Polyhedron 87
(2015) 311-320.
27. L. Tatar, O. Atakol, D. Ülkü, M. Aksu, {[μ-Bis (salicylidene)-1, 3-propanediaminato]-
copper (II)} dichlorozinc (II), Acta Crystallogr. C. 55 (1999) 923-925.
28. A.W. Addison, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor, Synthesis, structure,
and spectroscopic properties of copper (II) compounds containing nitrogen–sulphur donor
ligands; the crystal and molecular structure of aqua [1, 7-bis (N-methylbenzimidazol-2′-yl)-2,
6-dithiaheptane] copper (II) perchlorate, Dalton T. 7 (1984) 1349-1356.
29. C. Zeyrek, A. Elmali, Y. Elerman, Super-exchange interaction in a chair-piperazine
bridged dicopper (II/II) complex: synthesis, crystal structure, magnetic properties and
molecular orbital calculations, Z. Naturforsch. B. 61 (2006) 237-242.
30. A. Atakol, H. Nazir, I. Svoboda, M.L. Aksu, O. Atakol, Synthesis, crystal structure,
theoretical calculations and thermal characterization of two heterodinuclear Ni II–Zn II
complexes prepared from ONNO-type symmetrical Schiff base and its reduced derivative, J.
Therm. Anal. Calorim. 139 (2020) 1863-1882.
31. S. Durmuş, Ü. Ergun, J.C. Jaud, K.C. Emregül, H. Fuess, O. Atakol, Thermal
decomposition of some linear trinuclear schiff base complexes with acetate bridges, J. Therm.
Anal. Calorim. 86 (2006) 337-346.
32. J.R. Gispert, Coordination Chemistry, Wiley-VCH, Weinheim, 2008.
33. N.N. Greenwood, A. Earnshaw, Chemistry of the Elements, second ed., Elsevier, Oxford,
2012.
14

The List of Figures
Fig. 1. The Ortep drawings of the complexes prepared, a. [NiL·ZnBr2·(DMF)2] (I), b.
[(NiL)2·(ZnI2)2·(dioxane)3] (II), c. [(NiL)2·(ZnI2)2·(dioxane)].(dioxane)2 (III), d.
[(NiL·CdI2)2] (IV).
Fig. 2. TG-DTA curves a. [NiL·ZnBr2·(DMF)2] (I), b. [(NiL)2·(ZnI2)2·(dioxane)3] (II), c.
[(NiL)2·(ZnI2)2·(dioxane)].(dioxane)2 (III), d. [(NiL·CdI2)2] (IV), black: TG; red, blue, green,
pink: DTA curve.
Fig. 3. DTA curves of the complexes prepared in this study, red: complex I, blue: complex II,
green: complex III, purple: complex IV.
Fig. 4. The theoretically calculated ESP maps of the complexes prepared and their HOMO
and LUMO images.
15

Table 1
Data collection conditions and crystal data of the complexes.
Complexes
Parameters
Molar mass/ g mol-1 710.41
I
II
III
IV
1410.45
293(2)
red
triclinic
P-1
9.4637(10)
9.5815(6)
12.498(10)
94.171(8)
109.820(10)
112.316(9)
959.50(169
1
1580.70
293(2)
blue
monoclinic
P21/n
1404.88
200(2)
green
monoclinic
P21/n
T/ K
293(2)
Crystal color
Crystal system
Space group
a /Å
b /Å
c /Å
Alpha /°
Beta /°
Gamma /°
V /Å3
blue
monoclinic
Cc
10.5384(7)
15.1458(8)
17.5110(10)
90.00
98.763(8)
90.00
10.6740(10)
16.7230(2)
15.310(2)
90.00
10.6009(6)
12.4509(7)
20.8520(10)
90.00
91.689(9)
90.00
2731.7(5)
2
1.922
3.862
100.204(6)
90.00
2708.7(3)
2
1.938
3.895
2762.3(3)
4
Z
Calc. density/ g cm-3 1.708
2.441
5.319
µ /mm-1
4.478
F (000)
1424
1536
1536
660
Radiation
wavelength /Å
ϴ range /°
Index ranges
0.71073
0.71073
0.71073
0.71073
2.778 – 27.779
-13 ≤ h ≤ 11,
-17 ≤ k ≤ 18,
-21 ≤ l ≤ 21
2.598 – 27.933
-13 ≤ h ≤ 13,
-20 ≤ k ≤ 21,
-19 ≤ l ≤ 19
5883
2.547 – 27.789
-13 ≤ h ≤ 7,
-16 ≤ k ≤ 11,
-24 ≤ l ≤ 26
5763
2.608 – 27.980
-12 ≤ h ≤12,
-12 ≤ k ≤ 12
-14 ≤ l ≤ 16
4127
Reflections collected 4730
Reflections unique
R1, wR2 (2ó)
4122
3026
3275
3464
0.0434 ‒ 0.0548
0.0474 ‒ 0.1308 0.02045‒0.2224 0.065 ‒ 0.1101
R1, wR2 (all)
0.0443 – 0.1257 0.0984 – 0.2870 0.1360 – 0.1385 0.1253 ‒ 0.1338
Data / Parameters
4730/316
1.117
5883/307
1.053
5763/307
1.094
4127/226
1.088
GOOF of F2
Largest difference
peak hole /e Å-3
CCDC No
0.708 – (-1.193) 1.377 – (-1.231) 1.085 – (-1.021) 1.142 – (-2.230)
1949378
1949377
1949379
1949376
Crystal Dimensions
0.48×0.40×0.32 0.26×0.10×0.08 0.36×0.04×0.02 0.24×0.22×0.12
16

Table 2
The selected bond lengths and angles of the around coordination spheres of the complexes
and theoretical bond lengths and angles for comparison.
Experimentally
Complex measured
bond lengths
Theoretically
calculated
bond lengths
Experimentally
measured
bond angles
Theoretically
calculated
bond angles
I
Br1 Zn1 2.330(15) Br1 Zn1 2.330
Br2 Zn1 2.312(16) Br2 Zn1 2.312
Zn1 O2 Ni1 100.1(12)
N1 Ni1 O1 90.3(13)
N1 Ni1 O2 169.1(13)
O1 Ni1 O2 78.8(11)
N1 Ni1 N2 99.9(15)
O1 Ni1 N2 169.6(14)
O2 Ni1 N2 91.0(13)
N1 Ni1 O3 88.6(13)
O1 Ni1 O3 91.8(12)
O2 Ni1 O3 92.3(12)
N2 Ni1 O3 86.6(14)
N1 Ni1 O4 90.3(13)
O1 Ni1 O4 90.6(11)
O2 Ni1 O4 89.1(12)
N2 Ni1 O4 91.2(13)
O3 Ni1 O4 177.4(13)
O1 Zn1 O2 80.0(11)
O1 Zn1 Br2 112.2(10)
O2 Zn1 Br2 116.5(9)
O1 Zn1 Br1 111.6(9)
O2 Zn1 Br1 111.7(9)
Cl2 Zn1 Br1 118.6(6)
Ni1 O1 Zn1 100.5(4)
Ni1 O2 Zn1 100.2(4)
O1 Ni1 O2 79.7(4)
O1 Ni1 N2 169.9(5)
O2 Ni1 N2 90.5(5)
O1 Ni1 N1 90.4(4)
O2 Ni1 N1 169.5(4)
N2 Ni1 N1 99.5(6)
O1 Ni1 O4 91.2(4)
O2 Ni1 O4 91.3(4)
N2 Ni1 O4 86.5(5)
N1 Ni1 O4 92.6(4)
O1 Ni1 O3 91.8(3)
O2 Ni1 O3 87.1(3)
N2 Ni1 O3 90.2(4)
N1 Ni1 O3 89.6(4)
O26 Ni1 O3 176.3(3)
O1 Zn1 O2 79.5(4)
O1 Zn1 I2 116.5(3)
O2 Zn1 I2 113.7(2)
O1 Zn1 I1 112.1(3)
O2 Zn1 I1 114.8(3)
I2 Zn1 I1 115.4(8)
O1 Ni1 O2 77.9(2)
O1 Ni1 N1 91.7(3)
O2 Ni1 N1 169.2(2)
Zn1 O2 Ni1 100.1
N1 Ni1 O1 90.6
N1 Ni1 O2 169.7
O1 Ni1 O2 79.1
N1 Ni1 N2 100.1
O1 Ni1 N2 169.0
O2 Ni1 N2 91.2
N1 Ni1 O3 88.3
O1 Ni1 O3 91.8
O2 Ni1 O3 92.5
N2 Ni1 O3 86.2
N1 Ni1 O4 90.1
O1 Ni1 O4 90.9
O2 Ni1 O4 89.4
N2 Ni1 O4 91.2
O3 Ni1 O4 177.6
O1 Zn1 O2 80.2
O1 Zn1 Br2 112.8
O2 Zn1 Br2 116.3
O1 Zn1 Br1 111.4
O2 Zn1 Br1 111.8
Cl2 Zn1 Br1 118.3
Ni1 O1 Zn1 100.5
Ni1 O2 Zn1 100.2
O1 Ni1 O2 79.7
O1 Ni1 N2 169.9
O2 Ni1 N2 90.4
O1 Ni1 N1 90.5
O2 Ni1 N1 169.5
N2 Ni1 N1 99.6
O1 Ni1 O4 91.2
O2 Ni1 O4 91.3
N2 Ni1 O4 86.5
N1 Ni1 O4 92.5
O1 Ni1 O3 91.8
O2 Ni1 O3 87.1
N2 Ni1 O3 90.2
N1 Ni1 O3 89.6
O26 Ni1 O3 176.3
O1 Zn1 O2 79.5
O1 Zn1 I2 116.5
O2 Zn1 I2 113.7
O1 Zn1 I1 112.1
O2 Zn1 I1 114.8
I2 Zn1 I1 115.4
O1 Ni1 O2 77.9
O1 Ni1 N1 91.6
O2 Ni1 N1 169.2
Zn1 O1 1.984(6)
Zn1 O2 2.013(5)
Ni1 N1 2.017(7)
Ni1 O1 2.018(5)
Ni1 O2 2.026(6)
Ni1 N2 2.034(7)
Ni1 O5 2.134(5)
Ni1 O4 2.135(6)
Zn1 O1 1.984
Zn1 O2 2.013
Ni1 N1 2.018
Ni1 O1 2.018
Ni1 O2 2.026
Ni1 N2 2.035
Ni1 O5 2.134
Ni1 O4 2.135
II
N1 Ni1 2.030(11)
N2 Ni1 2.012(14)
O5 Ni1 2.196(8)
O6 Ni1 2.164(9)
O1 Ni1 2.002(9)
O1 Zn1 2.006(8)
O2 Ni1 2.005(9)
O2 Zn1 2.012(10)
Zn1 I2 2.519(2)
Zn1 I1 2.528(2)
N1 Ni1 2.030
N2 Ni1 2.012
O5 Ni1 2.196
O6 Ni1 2.164
O1 Ni1 2.002
O1 Zn1 2.006
O2 Ni1 2.006
O2 Zn1 2.013
Zn1 I2 2.519
Zn1 I1 2.528
III
N1 Ni1 1.972(7)
N2 Ni1 1.978(6)
O1 Ni1 1.955(5)
N1 Ni1 1.972
N2 Ni1 1.978
O1 Ni1 1.955
17

O1 Zn1 1.990(6)
O2 Ni1 1.965(6)
O2 Zn1 2.009(5)
O3 Ni1 2.372(5)
Zn1 I2 2.540(12)
Zn1 I1 2.555(12)
O1 Zn1 1.990
O2 Ni1 1.965
O2 Zn1 2.009
O3 Ni1 2.372
Zn1 I2 2.540
Zn1 I1 2.555
O1 Ni1 N2 169.1(3)
O2 Ni1 N2 91.6(3)
N1 Ni1 N2 98.7(3)
O1 Ni1 O3 91.7(2)
O2 Ni1 O3 92.4(2)
N1 Ni1 O3 90.6(2)
N2 Ni1 O3 91.8(2)
O1 Zn1 O2 76.0(2)
O1 Zn1 I2 113.3(17)
O2 Zn1 I2 115.6(16)
O1 Zn1 I1 115.0(17)
O2 Zn1 I1 113.5(17)
I2 Zn1 I1 116.9(4)
Ni1 O1 Cd1 100.7(2)
Ni1 O2 Cd1 107.3(2)
O1 Ni1 N1 95.1(2)
O1 Ni1 O2 83.6(2)
N1 Ni1 O2 170.6(2)
O1 Ni1 N2 168.1(2)
N1 Ni1 N2 92.6(3)
O2 Ni1 N2 90.3(2)
O2 Cd1 O1 63.9(17)
O2 Cd1 I1 117.3(14)
O1 Cd1 I1 99.6(12)
O2 Cd1 I2 110.4(14)
O1 Cd1 I2 91.8(12)
I1 Cd1 I2 131.2(3)
O2 Cd1 I2 96.2(13)
O1 Cd1 I2 158.5(11)
I1 Cd1 I2 97.0(3)
O1 Ni1 N2 169.1
O2 Ni1 N2 91.6
N1 Ni1 N2 98.7
O1 Ni1 O3 91.6
O2 Ni1 O3 92.4
N1 Ni1 O3 90.6
N2 Ni1 O3 91.6
O1 Zn1 O2 76.1
O1 Zn1 I2 113.3
O2 Zn1 I2 115.6
O1 Zn1 I1 115.0
O2 Zn1 I1 113.5
I2 Zn1 I1 116.9
Ni1 O1 Cd1 100.7
Ni1 O2 Cd1 107.3
O1 Ni1 N1 95.1
O1 Ni1 O2 83.6
N1 Ni1 O2 170.6
O1 Ni1 N2 168.0
N1 Ni1 N2 92.6
O2 Ni1 N2 90.3
O2 Cd1 O1 63.9
O2 Cd1 I1 117.3
O1 Cd1 I1 99.6
O2 Cd1 I2 110.4
O1 Cd1 I2 91.9
I1 Cd1 I2 131.2
O2 Cd1 I2 96.2
O1 Cd1 I2 158.5
I1 Cd1 I2 97.0
IV
N1 Ni1 1.857(6)
N2 Ni1 1.875(6)
O1 Ni1 1.849(5)
O1 Cd1 2.425(5)
O2 Ni1 1.865(5)
O2 Cd1 2.238(5)
Cd1 I1 2.697(8)
Cd1 I2 2.754(9)
Cd1 I2 3.065(10)
N1 Ni1 1.857
N2 Ni1 1.865
O1 Ni1 1.850
O1 Cd1 2.424
O2 Ni1 1.865
O2 Cd1 2.238
Cd1 I1 2.697
Cd1 I2 2.754
Cd1 I2 3.065
I2 Cd1 I2 87.3(2)
I2 Cd1 I2 87.3
Cd1 I2 Cd1 92.7(2)
Cd1 I2 Cd1 92.7
18

Table 3
The thermoanalytical data of the complexes prepared.
2nd Thermal Reaction
Thermal decomposition of NiL
Observed temperature Found
1st Thermal Reaction
Coordinative or solvated DMF or dioxane loss
Complex
Mass loss reaction
Observed temperature Expected
Found
range/ DTA peak/ °C mass loss/ %
mass loss/ %
range/ °C
mass loss/ %
I
Coordinative DMF loss 148.93 ‒ 235.62
20.56
21.22 ± 0.15
401.95 ‒ 438.20
/ 421.14
13.92 ± 0.31
/ 200.33
II
Coordinative first
dioxane loss
Coordinative dioxane
loss
97.41 ‒ 126.09
/ 116.69
126.09 ‒ 150.59
/ 140.82
92.90 ‒ 135.80
/ 113.69
178.98 ‒ 229.75
/ 211.89
6.32
6.37 ± 0.03
12.22 ± 0.14
10.23 ± 0.17
6.21 ± 0.12
402.37 ‒ 431.67
/ 419.80
13.54 ± 0.27
18.05 ± 1.96
24.35 ± 1.42
12.65
11.79
5.88
III
IV
Solvate dioxane loss
402.27 ‒ 440.49
/ 423.46
Coordinative dioxane
loss
400.5 ‒ 446.88
/ 419.47
This decomposition is the first thermal
reaction.
19

Table 4
Occupancy and relative energy levels of d orbitals of the metal ions in complexes.
Central Atoms
Complex
I
Orbital
Ni
Zn
Charge/ e Relative energy/ eV
1.97070 -0.28716
1.70502 -0.26950
1.07966 -0.23170
1.93698 -0.31654
1.95718 -0.28425
1.94755 -0.28936
1.69126 -0.27678
Charge/ e Relative energy/ eV
1.99635 -0.60960
1.99772 -0.61408
1.99655 -0.60844
1.99624 -0.60957
1.99575 -0.60905
1.99712 -0.61176
1.99795 -0.61253
1.99673 -0.61128
1.99723 -0.61212
1.99656 -0.61190
1.99722 -0.61270
1.99734 -0.61243
1.99670 -0.61277
1.99721 -0.61244
1.99734 -0.61302
1.99846 -0.62634
1.99935 -0.62708
1.99872 -0.62843
1.99888 -0.62807
1.99903 -0.62649
dxy
dzx
dyz
dz2
dx2-y2
dxy
dzx
dyz
dz2
dx2-y2
dxy
dzx
dyz
dz2
dx2-y2
dxy
dzx
dyz
dz2
II
1.1653
-0.24590
1.94958 -0.31721
1.90231 -0.28222
1.65517 -0.27116
1.65102 -0.28325
1.96345 -0.32043
1.90422 -0.27145
1.48519 -0.30237
1.93473 -0.31131
1.66494 -0.25805
1.98474 -0.32134
1.41303 -0.27529
1.68788 -0.25432
III
IV
NiL
dx2-y2
dxy
0.3286
-0.14287
dzx
dyz
dz2
dx2-y2
1.86985 -0.22360
1.90097 -0.22521
1.86360 -0.20962
1.96873 -0.27000
20

Table 5
Theoretically calculated HOMO and LUMO energy values and dipole moments of the
complexes.
Complex
I
II
III
IV
NiL
EHOMO / eV
-6.099
-5.755
-5.805
-5.862
-4.949
ELUMO / eV
-2.476
-2.809
-3.071
-2.326
-1.421
µ / D
9.177
8.081
8.299
1.495
5.618
∆E / eV
3.623
2.946
2.734
3.536
3.528
21

Highlights
•
•
•
•
•
Ni(II) complex of ONNO type LH2 ligand has a square planar coordination sphere.
Zn(II) and Cd(II) halides are coordinated to NiL by µ-bridge over phenolic oxygen.
The electronegativity of atom in the halide affects the coordination sphere of NiL.
If ZnCl2 or ZnBr2 is attached, the coordination sphere is inevitable octahedral.
If CdI2 is attached, the coordination sphere remains as a square pyramidal.

Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests: