M. Gaber et al. / Journal of Molecular Structure 1180 (2019) 318e329
323
G* ¼
D
H* ꢁ T
D
S*
meff ¼ spin onlyð1 ꢁ al=10DqÞ
D
h
i.
where
tion entropy (Jmolꢁ1Kꢁ1),
D DS* is the activa-
H* is the activation enthalpy (KJmolꢁ1),
B ¼ 4ðn3 ꢁ 15DqÞ2 ꢁ 10Dq2
n1 ¼ 10 Dq
½60ðn3 ꢁ 15DqÞ ꢁ 180Dqꢃ
D
G* is the Gibbs activation free energy
(KJmolꢁ1), h is the Plank constant, KB is the Boltzmann constant and
T is the observed peak temperature, universal gas constant,A the
pre-exponential factor (sꢁ1
)
According to the data obtained, the following remarks can be
pointed out:
b
¼ BðcomplexÞ=Bðfree ionÞ
For Co(II),B (free ion) is 963 cmꢁ1 and
a
is 4. The 10Dq, B and b
values are 2983, 614 cmꢁ1 and 0.63, respectively. These results
show that the interelectronic repulsion of the d electrons in a
complex is less than in the free ion. The value of B in a Co(II)
complex is 63% of the free-ion value. The
to covalence, the reduction of B by complex formation is caused by
delocalization of the d-electron.
Cloud on the ligand, which is in turn caused by the formation of
covalent bond. The data show the Co(II) complex has covalent
character [61].
1 The high values of the energy of activation of the complexes
E*) reflect the high stability of the investigating complexes
(D
due to their covalent character [48].
b value is related directly
2 For Co(II) complex, the kinetic and thermodynamic parameters
increase with increasing the heating rate. For Cu(II) complex,
these values decrease with increasing the heating rate. For the
other complexes, the results show that the calculated values are
independent on the heating rate.
3 The positive sign of
DG* for the complexes under investigation
The ligand field parameter B (interelectronic repulsion of the
revealed that the free energy of the final residue is higher than
that of the initial compound and all the decomposition steps are
non-spontaneous processes [49,50].
d electrons in complex),
Ni(II)complex are calculated according to the equations [62].
b (The Nephelauxetic effect) and 10Dq for
4 The negative values of
complex than reactant and/or the reaction was slow [51].
5 The positive values of H* means that the decomposition pro-
cesses were endothermic [52].
6 The values of the kinetic parameters obtained by the three
mentioned methods are in good agreement.
DS* indicated a more order activated
340Dq2 ꢁ 18ðn2
þ n3 ÞDq þ n2n3 ¼ 0
D
n2
þ
n3 ꢁ 30Dq
B ¼
15
where B (free ion) for Ni(II) is 1041 cmꢁ1. The 10Dq and B are 4256
and 739 cmꢁ1 respectively and
value is 0.76. These results show
b
that the interelectronic repulsion of the d electrons in a complex is
less than in the free ion. The value of B in a complex is 70% of the
free-ion value. The data show the Ni(II) complex has covalent
character.
Based on the data of IR, UVeVis spectra and magnetic moment
values as well as the conductance values together with the data of
elemental analysis, ICP and thermal analyses, the complexes can be
formulated as follows:
3.2.3. Electronic absorption and magnetic moment measurements
As the result of failure to obtain a single crystal for x-ray ana-
lyses, the electronic and magnetic measurements can be used to
confirm the geometry of the investigated complexes.
The electronic absorption spectrum of Cr(III) complex displayed
two bands at 14290, 18180 cmꢁ1 due to the 4A2(F)/4T1 (F) and4A2
(F)/4T1 (p) transitions, respectively. This indicates the octahedral
configuration around Cr(III) ion which was further deduced from
the meff value (4.02 BM) [53]. Mn(II) complex exhibited two bands
at19607 and 17857 cmꢁ1assigned as 6A1g /4T1g and 6A1g/4Eg
transition, respectively, assuming the square planar geometry for
this complex [54]. The meff value of Mn(II) complex is 4.4 BM indi-
cating the presense of 3 unpaired electrons. The higher value may
be due to orbital contribution [55]. Co(II) complex showed two
bands at 14492 and 19492 cmꢁ1 which may be assigned to 4A2
(F)/4T1 (F) and4A2(F)/4T1 (p), respectively, assuming the tetra-
hedral geometry around the Co(II) ion. The meff value (4.81 BM) of
complex verified the geometry of Co(II) complex [53]. The Nujol
mull spectrum of Ni(II) complex displayed two bands at 14285 and
19607 cmꢁ1due to the4A2(F)/4T1(F) and4A2(F)/4T1(p) transi-
tions, respectively. This indicates the octahedral configuration
around Ni(II) ion. The meff value (3.25 BM) of Ni(II) complex lies in
the normal range (2.9e3.3 BM) observed for octahedral Ni(II)
complexes [56]. The spectrum of Cu(II) complex displayed a band at
15384 cmꢁ1 (2B1g/2E1gtransition) assuming square planar geom-
etry around the central Cu(II) ion. The value of the magnetic
moment (1.84 BM) of this complex confirmed the square planar
geometry [57,58]. This meff value is a typical for Cu(II) complexes
supporting the exclusion of any perceivable spin-spin coupling
between unpaired electrons of the various molecules [22,59].
The ligand field parameter B (interelectronic repulsion of the
3.2.4. Molecular modeling
Since our trials to obtain a single crystals of the metal complexes
were unsuccessful so far, and in order to gain a better under-
standing of geometrical structures of the investigated complexes,
molecular modeling studies have been done by means of Hyper-
chem program package. The molecular modeling of the ligand and
all complexes were carried out for the proposed structures are
given in Figs. 2e7. These values are obtained as a result of mini-
mization of energy through MM2 method in Chem 3D Ultra 8.0.7.
Some selected bond lengths of ligand and its complexes are listed in
Table 7. The cis angles around Cr(III) ion are 92.95, 62.63, 90.26 and
137.00ꢀ but the trans angle is 136.06ꢀ. The values of bond angle
confirmed the octahedral geometry around the Cr(III) ion. For
Mn(II) and Cu(II) complexes, the copper and manganese atoms are
situated almost exactly on the average plane defined by the donor
atoms of the ligand and water molecule. The cis angles around the
ꢀ
Mn(II) and Cu(II) ions in the range 86e98 and 84e94ꢀfor Mn(II)
and Cu(II) complexes, respectively; the trans angles ranging from
159 to 174ꢀ and from 173 to 170ꢀfor Mn(II) and Cu(II) complexes,
respectively, indicating square planar geometry with almost no
tetrahedral distortion. For Co(II) complex, the angles around the
Co(II) ion are 116.63, 116.23, 110.63 and 116.47ꢀ indicating tetra-
hedral geometry. For Ni(II) complex, the cis angle around Ni(II) ion
are 104.60, 76.06, 76.72 and 103.70ꢀ but the trans angle is 160.95ꢀ.
The values of the bond angle confirmed the octahedral geometry
d electrons in complex),
b (The Nephelauxetic effect) and 10Dq for
Ni(II) complex are calculated according to the equations [60].