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M.S. El-Shahawi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 459–465
of the absorption bands of the complexes in DMF and in solid state
at ambient temperature are not significantly different, showing no
electronic or geometric changes and the compositions of the chro-
mophores of the complexes are the same in DMF and in solid state
and are stable [34]. The spectra of the complexes in DMF with their
probable assignments and ligand field parameters (10Dq, b, B and
LFSE) [34] are given in Table 3.
protons, respectively [29] indicating participation of OH and the
CH@N groups. Thus, the two peaks at 20,449 and 21,929 cmꢁ1
were assigned to spin allowed transitions 1A2g ? 1Bg and
1A1g ? 1Eg in square planar-geometry [34]. Bands at 24,043 and
26,666 cmꢁ1 are assigned to CT or ligand bands [34].
The spectrum of [Cu(BTS)Cl H2O] showed three bands around
12,820 (br.), 25,440 and 34,366 cmꢁ1 (Table 3). leff was 1.8 B.M
concluding formation of paramagnetic copper complex. Thus,
broad band at 12,820 cmꢁ1 was assigned to 2E2g ? 2T2g transition
in Oh symmetry [34]. The band at 25,440 cmꢁ1 was assigned to
S ? Cu (II) LMCT, whereas the band at 34,366 cmꢁ1 was assigned
to O ? Cu (II) LMCT and intraligand (n ? pꢂ) charge transfer [34].
Thermal analysis of the complex showed well defined peak at
160 °C due to loss of water molecule suggesting water coordination
to central copper (II).
In the spectrum of [Rh(BTS)2]Cl, three absorption bands at
m
1 = 16,790, m2 = 28,620 and m
3 = 39,420 cmꢁ1 were observed with
low molar extinction coefficients (Table 3). The complex was dia-
magnetic and it is consistent with Oh symmetry of N and S atoms
producing strong field. 1H NMR spectrum in d6-DMSO showed sig-
nals at d 7.07, 8.6, and 7.94 ppm assigned to NH, NH2 and benzyli-
denimin protons, respectively [29]. The azomethine proton
(CH@N) signal showed downfield shift at d 8.16–8.7 ppm indicat-
ing involvement of azomethine in coordination. Thus, the first
Based upon the 10Dq values (Table 3) of the aformentioned Oh
BTS complexes, the stability of the complexes followed the order
[28]:
5
two bands were assigned to spin-allowed transitions for t2 e1
g
g
state in Oh symmetry around Rh. Hence, the two peaks were as-
signed to 1A1g ? 1T1g
,
and 1A1g ? 1T2g and charge transfer
1
1A1g ? b, T1u transitions, respectively.
½RuðBTSÞ2ꢅCl > ½RhðBTSÞ2ꢅCl > ½Cu2ðBTSÞ2Cl2 ꢃ 2H2Oꢅ
In the spectrum of [Cu(B2ED)], the broad bands at 14,700 cmꢁ1
The interelectronic repulsion parameter B of [Rh(BTS)2]Cl was
about 59% of the free ion (B = 720 cmꢁ1) (Table 3) indicating con-
siderable orbital overlap with a strongly covalent metal–ligand
bond character [34]. The low value of B is associated with a reduc-
tion in the effective nuclear charge (Zꢂ) on Rh3+ ion [34]. The vari-
ation of B of 4 d metal ions with ionic charge (Zꢂ), and the number
of d-electrons in the partially filled d-state (q) is given by the
equation:
(log
e
= 1.6) and 16,650 cmꢁ1 were assigned to spin allowed
2B1g ? 2A1g
(m1)
ðdX2
! dZ2
Þ
(10Dq) and 2B1g ? 2Eg
(m3)
ꢁY2
ðdX2
! dXZ; dXZÞ transitions in square-planar geometry [34]. leff
ꢁY2
of the complex was 1.76 B.M. and close to the spin moment for
one un-unpaired electron confirming the proposed structure. The
spectrum of [Ni(B2ED)] showed two bands at 21,270, 27,170 and
33,120(sh) cmꢁ1. The complex was diamagnetic and its 1H NMR
spectrum showed signals at d 7.02, 7.54, 7.66, 8.54 and 8.8 ppm
confirming deprotonation of OH group upon coordination. The
bands at 21,270, 27,170 and 33,120 (sh) cmꢁ1 are assigned to
B ¼ 742 þ 28q ¼ 50ðZꢂ þ 1Þ ꢁ 500=ðZꢂ þ 1Þ
ð2Þ
The value of Zꢂ of Rh in [Rh(BTS)2]Cl complex was 0.75 below
the formal value of trivalent metal ions. The nephelauxetic param-
eter b (0.58) of the complex indicated that, the ligand BTS lies is in
the middle of the nephelauxetic of other nitrogen donor series
indicating participation of BTS in a tridentate fashion (SNO) to
1A1g ? 1A2g 3) and 1A1g ? 1B2g
(m (m2) and a CT transitions in a
square-planar geometry [34], respectively.
Redox behavior of metal complexes
Rh3+
.
The CV data of selected complexes vs. Ag/AgCl electrode at
The spectrum of [Ru(BTS)2]Cl displayed three bands at
50 mV sꢁ1 sweep rate (
m) are summarized in Table 4. Representative
m
1 = 13,700, 2 = 21,320 and
m
m
3 = 23,600 cmꢁ1. The leff of the com-
CV of [Rh(BTS)2]Cl complex in DMF-TBA+Clꢁ is shown in Fig. 3. In the
CV of [Rh(BTS)2]Cl, one cathodic peak (Ep,c) at ꢁ0.86 V coupled with
one anodic peak (Ep,a) at ꢁ0.2 V with potential–potential separation
plex was 1.94 BM, indicating a one electron paramagnetic of a low
spin t52g (S = 1/2) Oh symmetry around Ru (III) ion. Hence, the
2
ground state T1g of Ru (III) in an Oh environment is arising from
(
D
Ep = Ep,a ꢁ Ep,c) of 0.66 V were observed The number of electron
t52g configuration [34]. The order of increasing energy of the first ex-
transfer was calculated from charge–time curve of controlled poten-
tial coulometry (CPC) at the potential of the limiting current plateau
of cathodic peak under N2 atmosphere at Pt net electrode under the
same experimental conditions. The complex was reduced by a po-
tential step from ꢁ0.2 V to ꢁ0.9 V and the number of electron trans-
fer was calculated using the equation:
2
2
cited doublet levels is A2g and T1g arising from t52g eg1 configura-
tion. Hence, the first (m1) and third (m3) bands are assigned to the
spin forbidden 2T1g ? 2E2g and 2T1g ? 2A1g whereas, the band at
21,320 cmꢁ1 is due to the spin allowed transitions 2T2g ? 2A2g of
low spin d5 Ru3+ in Oh geometry, t25g [27–29]. B value was about
443 cmꢁ1 and 70% of the free ion (B = 630 cmꢁ1) indicating consid-
erable orbital overlap with a strongly covalent metal–ligand bond
character [25]. The low values of 10Dq and B for Rh3+ and Ru3+
complexes (Table 3) may be attributed to participation of S in coor-
dination [25]. The nephelauxetic parameter, b35 of Rh3+ and Ru3+
BTS complexes was 0.58 and 0.64, respectively. The 10Dq values
(Table 3) are close to the range for RuN2O2S2 [25]. Thus, the ligand
BTS lies in middle range of the spectrochemical series. The de-
crease in B values of the two complexes compared to the free ions
suggests strong covalent bonding between the donor site and the
metal ions. The increase in the 10Dq, was associated with consid-
erable electron delocalization in the complex [29–31]. A represen-
tative structure of Rh3+ or Ru3+ complex is proposed in Fig. 2.
The electronic spectrum of [Pd(BTS)Cl] showed peaks at 20,449,
21,929 cm 24,043 and 26,666 cmꢁ1 (Table 3) with low extinction
coefficient. The complex was diamagnetic and its 1H NMR spec-
trum in d6-DMSO showed proton signals at d 7.07, 8.6, 7.94; 8.4–
8.9 ppm and were assigned to NH, NH2, benzylidenimin and CH@N
QF ¼ QT ꢁ QB ¼ nFVc
ð3Þ
where Q is the charge in coulomb, QF the faradic charge required for
complete electrolysis of the complex in solution, QT the faradic
charge required for complete electrolysis of the test solution which
was measured by extrapolating the linear of the curve to zero time,
QB the faradic charge required for complete electrolysis of the sup-
porting electrolyte only, V the volume of the test solution in the cell
in liter, C the concentration of the test solution, mol Lꢁ1 and F is the
Faraday’s number, 96,485 C/equiv. A value of one electron transfer
was computed from charge–time curve. One electron nature of this
couple was also established by comparing the displayed current
height with similar analogous of Rh (III) complexes [24]. The irre-
versible nature of the couple was confirmed from the observed in-
crease in
The product of the number of electron transfer involved in the
reduction step (n ) and the corresponding charge transfer coeffi-
DEp on rising scan rate.
a
El-Shahawi
