Synthesis, spectroscopic characterization and redox reactivity of some transition metal complexes with salicylaldimines bearing 2,6-di-phenylphenol.

Article abstract of DOI:10.1016/S1386-1425(03)00217-8

New bidentate N-(2,6-di-phenyl-1-hydroxyphenyl) salicylaldimines bearing X=H and 3,5-di-t-butyl substituents on the salicylaldehyde ring, L(x)H, and their copper(II) complexes, M(Lx)2, (M=Cu(II), Co(II), Pd(II), Ni(II) and Zn(II)) have been synthesized an

Full text of DOI:10.1016/S1386-1425(03)00217-8

Spectrochimica Acta Part A 60 (2004) 31–39
Synthesis, spectroscopic characterization and redox reactivity of some
transition metal complexes with salicylaldimines bearing
2,6-di-phenylphenol
V.T. Kasumova,∗, Fevzi Köksalb
a
Department of Chemistry, Faculty of Arts and Sciences, Harran University, Sanliurfa, Turkey
b
Physics Department, Faculty of Arts and Sciences, Ondokuz Mayıs University, Samsun, Turkey
Received 6 January 2003; accepted 4 March 2003
Abstract
New bidentate N-(2,6-di-phenyl-1-hydroxyphenyl) salicylaldimines bearing X = H and 3,5-di-t-butyl substituents on the salicylaldehyde
ring, LxH, and their copper(II) complexes, M(Lx)2, (M = Cu(II), Co(II), Pd(II), Ni(II) and Zn(II)) have been synthesized and characterized
1
by IR, UV/vis, H NMR, 13C NMR, ESR spectroscopy, magnetic susceptibility measurements, as well as their oxidation with PbO2 and
reduction (for Cu(Lx)2) with PPh3 were investigated. ESR studies indicate that oxidation of M(Lx)2 produces ligand-centered MII-phenoxyl
radical species. The Cu(Lx)2 complexes, unlike others M(Lx)2, are readily reduced by PPh3 via intramolecular electron transfer from ligand to
copper(II) to give unstable radical intermediates which are converted to another stable secondary radical species. The analysis of ESR spectra
of Cu(Lx)2, Co(L1)2 and generated phenoxyl radicals are presented.
© 2003 Elsevier B.V. All rights reserved.
Keywords: Transition metal complexes; Spectroscopy; Redox-activiy; 2,6-di-Phenylphenol; MII-phenoxyl radicals
1. Introduction
groups on the phenolates which were used for generation
of MII,III-phenoxyl radical complexes [4–8].
Electron transfer reactivity of the coordination compounds
has become an area of extensive research in recent years be-
cause of transition metal complexes containing oxidized or
reduced ligands were frequently found as crucial intermedi-
ates or as reaction products in metal–metal or metal–ligand
electron transfer reactions [1], in redox-catalytic processes
[2] and play a central role in biological redox metalloen-
zymes like plastocyanin, hemocyanin, azurin and other
multimetal oxidases [3]. The discovery of coordinated
and uncoordinated tyrosyl radical in the active form of
the copper(II)-containing enzymes (galactose and glyoxal
oxidases) [2–4] and in the active site of diiron enzyme ri-
bonucleotide reductase [5c] has stimulated the development
of structural and functional model complexes of transi-
tion metals with ligands having bulky t-butyl protecting
The coordination chemistry of phenoxyl radicals bound
to transition metal ions is not well developed [1c], despite
the fact that there are some intriguing problems concerning
electronic structure. In principle, a one-electron oxidation
of a transition metal phenolato complex can be either metal
or ligand centered. The question then arises whether the
above two formulations are merely resonance structures of
the same electronic ground state, or whether we are dealing
with two distinct chemical species with different ground
states and different physical and chemical properties [8].
Previously we reported on the chemistry of the transition
metal complexes with redox-active ligands bearing steri-
cally hindered 2,6-di-t-butylphenol, 2,4-di-t-butylphenol,
2,5-di-t-butylaniline residues [9]. Interest in these com-
pounds derives from their ability that facilely undergo one-
or two-electron transfer in their treatment with PbO2 and
triarylphosphines (for Cu(II) and Pd(II) complexes) to gen-
erate persistent metal–phenoxyl radical species, in which
it is possible to examine intramolecular metal–radical or
radical–radical magnetic interactions as well as their ability
∗
Corresponding author. Tel.: +90-414-312-8456;
fax: +90-414-315-1998.
E-mail address: vkasumov@harran.edu.tr (V.T. Kasumov).
1386-1425/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S1386-1425(03)00217-8

32
V.T. Kasumov, F. Köksal / Spectrochimica Acta Part A 60 (2004) 31–39
condensation between 2,6-di-Ph-1-hydroxyaniline and ap-
propriate salicylaldehydes in methanol in equimolecular
quantities. HL1: To a stirred warm solution of salicylalde-
hyde (0.47 g, 3.83 mmol) in methanol (25 cm3) was added
2,6-di-Ph-1-hydroxy-aniline (1 g, 3.83 mmol). The solution
was heated at reflux for 2 h, and then allowed to cool to room
temperature and the volume of mixture reduced by evapora-
tion of solvent to approximately 5 ml. The precipitated solid
was collected, washed with a minimal amount of cooled
methanol (2 cm3) and air-dried. : Yield 94%. M.p. 124 ◦C.
UV/vis (C2H5OH): λmax (log ε) = 208(4.78), 267(4.53),
350(sh), 355(4.36), 440 nm (2.44). IR (KBr pellet): ν = 1618
Scheme 1.
to undergo intramolecular electron transfer between metal
and coordinated radical ligand or oxidative C–C cou-
pling of the coordinated radical ligands in these systems
[9a,b,c]. Although the synthesis and some aspects of the
chemistry a series of salicylaldimine complexes contain-
ing 2,6-di-t-butylphenolic residues were reported [9], their
structural analogs bearing 2,6-di-phenylphenolic arms are
not reported. It is of interest to explore the changes which
can occur in redox reactivity of LxH and Cu(Lx)2 when the
t-butyl groups on 2,6-positions in the phenolic moiety of sal-
icylaldimine ligands were replaced by Ph rings (Scheme 1).
In this paper we describe the synthesis, spectroscopic,
magnetochemical characterization and electron transfer be-
haviors of copper(II), cobalt(II), nickel(II), palladium(II) and
zinc(II) complexes, M(Lx)2, on the basis of the redox-active
N-(2,6-di-phenyl-1-hydroxyphenyl)-salicylaldimine (HL1)
and N-(2,6-di-phenyl-1-hydroxyphenyl)-3,5-di-t-butylsali-
cylaldimine (HL2) ligands, respectively.
=
(CH N), 2550–3000 (intramolecular H-bonding), 3532
cm−1 (free OH). 1H-NMR. (200 MHz, CDCl3): δ = 5.49 (br
s, 1H, OH), 6.87–7.03 (m, 2 H, meta-coupled multiplet ring
protons on the phenol), 7.26–7.61 (m, 14 H, Ph), 8.65, 8.66
(d, 1H, CH N), 13.40 (s, 1H, OH/NH). 13C{H}-NMR(200
=
=
MHz, CDCl3): δ = 160.89, 160.74 (CH N), 148.51, 141.11,
136.86, 132.71, 131.95, 129.55, 129.19, 128.89, 127.94,
122.49, 119.23, 118.94, 117.09 (all aromatic C). C25H19NO2
(365.4): calcd. C 82.16, H 5.25, N 3.83; found C 83,11,
H 5.74, N 3.56. HL2 : Yield 78%. M.p. 169 ◦C. UV/vis
(C2H5OH): λmax (log ε) = 230(4.76), 271(4.60), 336(4.38),
=
361(4.40), 480 nm (sh). IR (KBr pellet): ν = 1615 (CH N),
2450–2800 (intramolecular H-bonding), 2868–2959 (C–H
of –C(Me)3), 3535 cm−1 (free OH). H-NMR (200 MHz,
1
CDCl3): δ = 1.32, 1.49 (s, 18H, C(Me)3), 5.45 (br, s, 1H,
OH), 7.20, 7.21 (d, 2H, ring protons on salicylic moiety),
=
7.28–7.58 (m, 12H, Ph), 8.71 (s, 1H, CH N), 13.72 (br s,
1H, OH/NH). 13C{H}-NMR(200 MHz, CDCl3): δ = 161.77
2. Experimental
=
(CH N), 158.11, 148.26, 141.30, 140.41, 136.99, 136.82,
129.63, 129.22, 128.90, 127.91, 127.62, 126.60, 122.52,
118.36 (all aromatic C), 35.06 (C(CH3)3), 34.14 (C(CH3)3),
31.46 (C(CH3)3), 29.41(C(CH3)3). C35H35NO2 (477.6):
calcd. C 82.98, H 7.38, N 3.54; found. C 81.78, H 7.56, N
2.98.
2.1. Physical property measurements
The experimental procedures and instruments used for
the physical property measurements were as previously
described [9g,h]. The ESR spectra of polycrystalline pow-
der and solution samples of Cu(Lx)2 were recorded at
300 and 133 K. Prior to oxidation or reduction, the solu-
tions of the compounds were degassed thoroughly by the
freeze-pump–thaw technique. The oxidation of HLx and
M(Lx)2 were carried out with a 3–4 fold excess of lead
dioxide in a degassed system as described previously [9].
The reduction of Cu(Lx)2 and Pd(Lx)2 with an excess of
PPh3 was carried out by mixing their degassed solutions
under vacuum as described previously [9d–h]. The spectra
were calibrated with the diphenylpicrylhydrazyl free radical
(DPPH) (g = 2.0036). The errors for g- and A-parameters
of radicals are 0.0005 and 0.005 G, respectively.
Cu(L1)2·H2O. A solution of Cu(ac)2·H2O (0.5 mmol)
in methanol (5 ml) was added to a stirred solution of HL1
(0.365 g, 1.0 mmol) in ethanol (40 ml) at approximately
50 ◦C. The dark green reaction mixture was refluxed for
approximately 1 h, during which the green crystalline com-
pound precipitated. The volume of the solution was then
reduced to approximately 10 ml by slow evaporation, al-
lowed to cool to room temperature and precipitated green
solid was filtered off, washed with cold methanol and dried
in air. Yield: 0.312 g (78.6%). Cu(L2)2. This compound
was prepared in a manner similar to that for Cu(L1)2·H2O.
Yield: 75.6%. M.p.>270 ◦C. The analogous complexes of
Co(II), Ni(II) and Zn(II) metal ions were prepared in a sim-
ilar procedure using M(ac)2·4H2O (M = Co(II), Ni(II)) and
Zn(ac)2·2H2O instead of Cu(ac)2·H2O.
2.2. Preparation of the compounds
The Pd(Lx)2 complexes were prepared by addition solid
Pd(ac)2 (0.5 mmol) to a hot methanol solutions (50 ml) of
ligands (1 mmol) and the mixtures were heated at 40–45 ◦C
with stirring for approximately 1 h. The resulting solution
was allowed to evaporate slowly at room temperature to
All chemicals from commercial sources were reagent
grade and used as received. The reagent 3,5-di-t-butylsalicyl-
aldeyde was synthesized according to published procedure
[10]. The ligands HL1 and HL2 were obtained via the

V.T. Kasumov, F. Köksal / Spectrochimica Acta Part A 60 (2004) 31–39
33
Table 1
Physical properties the M2L2 complexes
Compond
Color
M.p. (dec.)
Empirical formula
µeff (␮B)
Found(Calcd.) (%)
C
H
N
Cu(L1)2·H2O
Cu(L2)2
Co(L1)2
Co(L2)2
Ni(L1)2
Pd(L1)2
Pd(L2)2
Zn(L1)2
Green
Green
Orange
Red
Green
Green
Green
Yellow
248
(234)
(150)
180
(165)
>270
>270
192
C50
66H68N2O4Cu
C50 36N2O4Co
H
38N2O5Cu
1.87
1.78
3.48
3.95
2.89
Dia
74.89(74.11)
77.79(77.96)
75.12(76.04)
79.11(78.32)
76.67(76.07)
71.34(71.73)
75.26(74.81)
76.84(76.38)
4.38(4.73)
6.54(6.74)
5.21(4.86)
6.23(6.77)
5.19(4.85)
4.89(4.57)
6.87(6.47)
5.08(4.81)
3.16(3.46)
2.68(2.75)
4.98(3.55)
3.19(2.77)
3.24(3.55)
3.78(3.34)
2.45(2.64)
3.14(3.52)
C
H
C
C
66H68N2O4Co
50H36N2O4Ni
C50H36N2O4Pd
C
C
66H68N2O4Pd
50H36N2O4Zn
Dia
Dia
approximately 10 ml and the precipitated green solid was
filtered off, washed with cold methanol recrystallized from
CH2Cl2 and dried in air. The analytical data are collected in
Table 1.
that coordination has taken place through the azomethine
nitrogen atom of the ligands. The νOH of phenolic moiety
of HLx and M(Lx)2 appears in the 3514–3539 cm−1 region.
A broad intense band observed in the spectrum of Cu(L1)2
at 3368 cm−1 is indicative to ν(OH) of the coordinated
H2O molecule. A strong intense bands in the 2868–2957
cm−1 region of HL2 and M(L2)2 compounds are assigned
to νC–H stretching modes of the t-Bu groups.
3. Results and discussion
The ligands L1H and L2H were obtained as yellow to or-
ange solids and are not air sensitive. As supported by the
ESR and IR spectral studies in the complexation of Cu(II)
with HLx in polar solvents and under air, unlike their salicy-
laldimine analogous bearing 2,6-di-tert-butyl groups [9,11],
the oxidative C–C coupling of the coordinated ligand did not
takes place and the samples of Cu(Lx)2 did not show any ev-
idence of the formation of radical species during synthesis.
5. Ligands
In the electronic spectra of these ligands along with bands
in the 208–361 nm region which are due to intraligand
␲→␲* and n→␲* transitions involving molecular orbitals
=
of the C N chromofore and benzene ring, a broad shoulder
at approximately 480 nm (L2H) and a maxima at 440 nm
(L1H) were observed. The latter bands are attributed to a
n(oxygen)→␲* transition of the dipolar zwitterionic struc-
ture or keto-amine tautomer of HLx [12]. The oxidation of
HL1 with PbO2 at 300 K in deoxygenated toluene/CHCl3
mixtures under vacuum leads to the formation of poorly re-
solved phenoxyl radical signals centered at g = 2.0045 with
a line width of 5.5 G. One-electron oxidation of HL2 under
similar conditions immediately leads to the formation of the
phenoxyl radical species displaying well-resolved ESR spec-
4. Infrared spectra
1
The electronic, infrared, H NMR and 13C NMR char-
acteristics of the HL1 and HL2 are presented in Section 2.
The strong sharp bands at 1618 and 1615 cm−1 due to
=
ν(C N) stretch of the free HL1 and HL2 ligands, respec-
tively, are shifted towards lower frequencies (1606–1608
cm−1) in the spectra of the complexes (Table 2), indicating
Table 2
IR and electronic spectral data for LxH and M(Lx)2 compounds
Compound
IR spectra (cm−1
)
Electronic spectra, ␭/nm (log ε M−1 l−1
)
νCH = N
νOH
L1H
L2H
1618
1615
1606
1610
1696
1610
1609
1605
1606
1605
3532
3535
3527
3533
3524
3539
3529
3514
3538
3523
208(4.78), 267(4.53), 350a, 355(4.36), 440 nm (2.44)
230(4.76), 271(4.60), 336(4.38), 361(4.40), 480a
b255(4.8), 320a, 360(4.2), 500a, 690(2.2)
Cu(L1)2.H2O
Cu(L2)2
Co(L1)2
Co(L2)2
Ni(L1)2
Pd(L1)2
Pd(L2)2
Zn(L1)2
210(4.9), 237(4.8), 290a, 313(4.5), 416(4.3), 500a, 700(2.6)
212(4.9), 236(4.9), 250a, 300a, 390a, 402(4.1), 650(2.4)
208(4.9), 236(4.7), 316(4.6), 408(4.4), 500a, 712(2.1)
209(4.9), 230a,260a, 329(4.3), 510a, 711(1.9)
b290, 350a, 380a, 417(4.5)
208(4.9), 246(4.8), 260a, 307(4.4), 406(4.1)
207(4.93), 233(4.84), 267(3.98), 352(4.49), 460a
a
Shoulder.
In CHCl3.
b

34
V.T. Kasumov, F. Köksal / Spectrochimica Acta Part A 60 (2004) 31–39
Fig. 1. ESR spectrum of radical generated from L1H in toluene at 300 K. Experimental conditions: frequency, 9.52 GHz; microwave power, 5 dB;
modulation amplitude, 0.8 G; gain, 630; scan range, 100 G.
trum (g = 2.0045) with hyperfine splitting constants (hfsc) of
1.125 G on the central part of the spectrum (Fig. 1). At both
sides of this spectrum low intense a broad satellite lines spac-
Cu(Lx)2 show G<4, suggesting the presence of an exchange
coupling between two adjacent Cu(II) centers in solid state
[15].
ing of approximately 4 G, probably, due to coupling to 13
C
The room temperature solutions spectra of Cu(L1)2
(giso = 2.125, Aiso = 64 G) and Cu(L2)2 (giso = 2.124,
Aiso = 60 G) in CHCl3 exhibit so broad low-field pattern
that the low-field MI = −3/2 and −1/2 components of the
four-line copper pattern cannot be resolved even very diluted
toluene solutions. The observed anizotropically broadened
behavior can be explained by a slower rate of the molec-
ular tumbling in solution of these too bulky complexes.
The frozen glass ESR spectra of Cu(L1)2 (gII = 2.229,
(I = 1/2) isotopes in natural abundance have been observed.
6. Cu(II) complexes
The Cu(Lx)2 complexes showing a pairs band appearing
as shoulders in the region 500–700 nm, are attributed to
dx2−y2 →dxy, dx2−y2 →dxz,yz transitions in a distorted square
planar ligand field, respectively [13]. An intense bands in the
range 360–420 nm can be assigned to the MLCT transition
(CuII→phenolate, CT band from filled d(dxz, dyz) orbitals
of copper(II) to the antibonding ␲* orbital of the phenolic
residue) [14].
g = 2.067, AII = 165 G, A = 19.5 G) and Cu(L2)2
⊥
(gII = 2.242, g = 2.065, AII =⊥150 G, A = 15 G exhibit an
⊥
⊥
axial symmetry (gII>g >ge and a d
ground state) [16]
x2−y2
⊥
without resolved shf structures due to coupling to 14N and 1H
nuclei in the perpendicular region of the spectra. The gII/AII
ratio, which is a good measure of the degree of tetrahedral
distortion [17], are 145 and 160 cm for Cu(L1)2 and Cu(L2)2,
respectively, and correlate well with the tetrahedral distorted
arrangement around copper center (for square-planar struc-
tures the gII/AII ratio falls within the range 105–135 cm).
The room temperature effective magnetic moments of
Cu(L1)2 (1.93 B.M.) and Cu(L2)2 (1.88 B.M.) are typical
for tetrahedrally distorted mononuclear CuII complexes.
6.1. ESR spectra of Cu(Lx)2
X-Band ESR spectra of the Cu(Lx)2 compounds were
run at 298 and 133 K, both as powders and in toluene or
CHCl3 solution. None of the solid state spectra show resolv-
able copper hyperfine coupling or any detectable half-field
absorption associated with a ꢀMs = 2 forbidden transi-
tions. The solid state spectrum of Cu(L1)2 displays a single
slightly asymmetric broad line at gav = 2.054 (gII = 2.092,
6.2. Reduction of Cu(Lx)2 with PPh3
In our early works [9,18] it has been demonstrated
that the copper(II) complexes with salicylideneimine,
2-hydroxy-benzylamine, 2-hydroxy-arylazo and β-ketoa-
minate ligands bearing sterically hindered 2,6-di-t-butyl-
and 2,4-di-t-butyl phenolic arms as well as 2,5-di-t-butyl
anilinic residue on treatment with PPh3 at 300 K, unlike their
non butylated analogous, without any signs of the adduct
formation, along with reduction of Cu(II)–Cu(I) the gener-
ation of various radical intermediates also were observed.
g = 2.026, G = 3.78), but Cu(L2)2 exhibits spectral fea-
⊥
ture with resolved gz and gx,y components at g = 2.048,
⊥
gII = 2.103 and G = 2.19, respectively. The exchange in-
teraction parameter, G = (gII−2.0023/g −2.0023), for
⊥

V.T. Kasumov, F. Köksal / Spectrochimica Acta Part A 60 (2004) 31–39
35
Fig. 2. The initial stage ESR spectrum Cu(L1)2+PPh3 system recorded immediately after mixing of deoxygenated toluene/CHCl3 (1:3) solutions of
Cu(L1)2 and PPh3 under vacuum at modulation, 4 G, and scan, 800 G (a); the radical part of (a) recorded in the scan range of 200 G (b, c); the radical
spectrum of the reaction mixture Cu(L2)2 with PPh3 in toluene (d).
When Cu(Lx)2 was treated with an excess of PPh3 in
toluene or CHCl3 solutions under vacuum along with a
color changes from green to yellow–brown, the decreasing
of the intensities of copper hyperfine lines and immedi-
ately appearance of radical signals centered at g = 2.0049
and g = 2.0063 for the reduced Cu(L1)2 and Cu(L2)2 com-
plexes, respectively, were observed (Fig. 2a). The spectrum
of reduced Cu(L1)2 shows complicated pattern having a
low intense broad line on both sides of the central intense
quartet lines spacing of 2.5 G (Fig. 2b and c). The radical
signal observed for reduced samples of Cu(L2)2 in PhMe
(Fig. 2d) displays a narrowed 1:2:1 triplet pattern spacing
of 1.25 G and low intense broad lines on the both wings of
the spectrum. After keeping this sample of approximately
1 h under vacuum, a broad lines on wings are disappeared
and remains a 1:2:1 triplet signal at g = 2.0041 with hfsc
of 1.25 G. Not that these spectral patterns are quite differ-
ent from those observed for the radical species generated
from bis[N-2,6-di-t-butyl-1-hydroxyphenyl)-salicylaldimi-
nato] copper(II) [18b] and di-2,5-t-butylated bis(salicylaldi-
minate)copper(II) [18c] complexes by PPh3.
of phenoxyl radicals [9a,b]. The spectral features, g-factors
and hfsc values of these radical species are quite different
from those observed for radicals generated from HLx. As
seen from Fig. 3a and 3b, the values of g-factor and copper
hyperfine coupling constant of oxidized Cu(L1)2 complex
are a slightly changed (g = 2.113, ACu = 68 G). The spec-
trum of radical species generated from Cu(L1)2 consist of a
7-line components centered at g = 2.0036 with hfsc of 2.5
G and exhibits an additional a less resolved shf splitting of
0.5 G (Fig. 3c). A broad line patterns at high field and low
field sides of the spectrum, probably, originate from Cu(II)
containing paramagnetic products. A similar 7-line radical
spectrum (g = 1.999) with hfsc of 2 G and an additional
splitting of approximately 0.5 G on some components was
also observed for the oxidized Cu(L2)2 samples (Fig. 3d).
Unfortunately, the anisotropically broadening and alternat-
ing line width character of the hyperfine structure compli-
cate the spectral interpretation. But general spectral patterns
are similar to those observed for biradical M(II)-stabilized
phenoxyls [9,11,18], in which ESR signal appeared as a
superposition of two non-interacting monoradical centers
with S = 1/2. It is interesting to note that in the one-electron
oxidation with PbO2 or O2 of 2,6-di-t-butyl substituted sali-
cylaldiminte analogs of Cu(Lx)2 [9a,b,18a], as supported by
IR, ESR and X-ray crystallography analysis, the formation
of tetradentate salicylaldiminate copper(II) complexes as a
result of the oxidative C–C coupling of phenolic moieties
of the coordinated salicylaldimine ligands were observed.
6.3. Oxidation of Cu(Lx)2 with PbO2
The one-electron oxidation of the Cu(Lx)2 with PbO2 in
toluene/CHCl3 mixtures or in CHCl3 at 300 K, unlike their
copper(II) salicylaldiminate analogs bearing 2,6-di-t-butyl
groups on phenolic moiety, easily leads to the formation

36
V.T. Kasumov, F. Köksal / Spectrochimica Acta Part A 60 (2004) 31–39
Fig. 3. ESR spectrum of Cu(L1)2 in toluene/CHCl3 mixture (a); initial sage spectrum of Cu(L1)2+PbO2 system in toluene/CHCl3 under vacuum (b); the
spectrum of radical part of (b) recorded in the scan range of 200 G (c); the radical spectrum observed in the oxidation of Cu(L2)2 with PbO2 in toluene
in the scan range of 100 G (d).
7. Co(II) and Ni(II) complexes
390–408, ∼500, 650–712 nm ranges (Table 2). The bands
at ∼500 and 650–712 nm can be assigned to 4A2→ T2
4
4
4
The room temperature magnetic susceptibility data reveal
that the Co(L1)2 and Co(L2)2 (Table 1) have effective mag-
netic moments of 3.48 and 3.95 ␮B, respectively, indicating
an S = 3/2 ground state for a tetrahedral Co(II) complexes
[19]. A lowered µeff (3.48 B.M) founded for Co(L1)2 may
be arises from existence of high spin Co(II) (s = 3/2) and
low spin Co(II) (s = 1/2) states or from a tetrahedral square
planar transition in the solid state. The electronic spectrum
of these complexes shows new absorption bands in the
and A2→ T1(P) transitions in Td symmetry, respectively
[20]. The solid state ESR spectrum of Co(L1)2 exhibits
spectral pattern with gII = 2.105 and g = 2.0305 (Fig. 4a).
⊥
The samples of Co(L1)2 oxidized with PbO2 in degassed
toluene solutions leads to the formation of Co(II)-stabilized
phenoxyl radical species. Its ESR spectrum exhibits a nar-
row 1:2:1 triplet pattern (g = 2.0061) spacing of 1.25 G
(Fig. 4b) due to couplings of the unpaired electron to two
equivalent m-protons of phenolic arms and is superimposed

V.T. Kasumov, F. Köksal / Spectrochimica Acta Part A 60 (2004) 31–39
37
Fig. 4. ESR spectrum of powder Co(L1)2 at 300 K (a); the radical spectra observed in the oxidation of Co(L1)2 (b), Ni (L1)2 (c), Pd(L1)2 (d) and
Zn(L1)2 (e) with PbO2 in toluene solutions at 300 K.
on the broad weak signal. The similar triplet with hfsc of
1.25 G (g = 2.0057), overlapped with a broad unresolved
singlet (ꢀH = 10 G), at g = 2.006 was also observed for
the oxidized Co(L2)2 samples.
8. Pd(II) and Zn(II) complexes
In the electronic spectra of Pd(Lx)2 along with intraligand
bands arising from ␲→␲* and n→␲* transitions, a new
intense bands at approximately 310 and 410 nm also were
observed (Table 2). According to their very higher molar
coefficient extinctions we assigned these bands to MLCT
transitions from metal filled dxz,yz orbitals to phenolic and
The room-temperature µeff value (2.89 B.M./NiII) of
Ni(L1)2 is slightly lower than normal ‘octahedral’ values
(3.0-3.3 B.M.) for uncoupled nickel(II) complexes [21],
possible suggesting the presence of a weak intermolecular
antiferromagnetic exchange interactions or the existence
of diamagnetic square-planar configuration impurity in the
solid state. The bands observed at 510 and 711 nm in the
electronic spectrum of Ni(L1)2 according to the values of
coefficient extinction (82 M−1 cm−1) can be assigned to
=
–CH N– groups unfilled ␲* orbitals. One-electron oxidized
samples of Pd(Lx)2 in degassed CHCl3/toluene (1:1) mix-
tures show spectral feature consisting of the superposition
of a 1:2:1 triplet (g = 2.0041) spacing of 1.1878 G and
low intensity broader 7-line pattern centered at g = 2.0029
with hfsc of 2.125 G (Fig. 4d). The central triplet signal
3T1→ A2 and T1→ T(P) transitions in tetrahedral sym-
metry [21]. One-electron oxidized samples of Ni(L1)2 in
degassed toluene solution and under vacuum exhibits an
isotropic radical signal at g∼2.0041 with a peak-to-peak
line width of ∼5 G and no hyperfine structure at 300 K
(Fig. 4c).
3
3
3
•
is very similar to that observed for [Co(L1 )2] species and
more probably arises from ligand centered Pd(II)–phenoxyl
radical species. It is thought that the low intense rela-
tively broad signal is associated with a dipole–dipole cou-
pled biradical species. The observed spectral pattern is

38
V.T. Kasumov, F. Köksal / Spectrochimica Acta Part A 60 (2004) 31–39
(c) P.F. Knowles, N. Ito, Perspectives in Bioinorganic Chemistry,
vol. 2, Jai Press Ltd, London, 1994, pp. 207–244.
[3] (a) C. Stevens, Z.B. Orgel, J.N. Keen, K.D.S. Yadav, P.F. Knowles,
Nature 350 (1991) 87;
subsequently differs from that obtained for analogous oxi-
dized bis[N-(2,6-di-t-butyl-1-hydroxyphenyl)salicyilaldimi-
nato]palladium(II) complexes [22]. Another interesting
behavior of Pd(Lx)2, in contrast to their bis[N-(2,6-
di-t-butyl-1-hydroxyphenyl)salicyilaldiminato]palladium(II)
analogs [22], were their unreactivity towards PPh3 in
CHCl3/toluene solutions. We have found that on treatment
of Pd(Lx)2 with PPh3 in toluene or CHCl3/toluene mixtures
nether color changes nor formation of radical species did
not take place.
Unfortunately, our attempts to prepare of Zn(L2)2 com-
plex were unsuccessful. The electronic absorption spec-
trum of Zn(L1)2 in ethanol solution along with intense
ligand centered bands also shows a new maxima at 233
nm and a shoulder at approximately 460 nm. The last
absorption according to its very higher molar coefficient
extinctions has been assigned to MLCT transition. The
ESR spectrum of the lead dioxide oxidized Zn(L1)2 can
be considered as two superimposed signals (Fig. 4e). More
intense central 1:2:1 triplet spacing of 1.25 G centered at
2.0031 and can be is assigned to Zn(II)–phenoxyl species
in which spin density localized on phenoxyl rings. Un-
fortunately, the second low intense complex multipilet
feature with various hfsc (4.0 and 1.5 G), non binomial
intensities of hyperfine components, as well as some of
unresolved hfsc pattern complicate its interpretation. Note
that these spectral features are quietly different from those
observed for oxidized bis(salicylaldimine)zinc(II) bearing
2,6-di-tert-butyl-1-hydroxyphenyl groups [9a,22c].
(b) N. Ito, S.E. Phllipps, K.D.S. Yadav, P.F. Knowles, J. Mol. Biol.
238 (1994) 794;
(c) M.M. Wittaker, P.J. Kersten, N. Nakamura, J. Sanders-Loehr,
E.S. Schwezer, J.W. Wittaker, J. Biol. Chem. 271 (1996) 681.
[4] (a) S. Itoh, M. Taki, S. Fukuzumi, Coord. Chem. Rev. 198 (2000) 3;
(b) J.A. Halfen, Y.G. Yong, W.B. Tolman, Angew. Chem. Int. Ed.
Engl. 35 (1996) 1687;
(c) J.A. Halfen, B.A. Jazdzevski, S. Mahapatra, L.M. Berreau, E.C.
Wilkinson, L. Que Jr., W.B. Tolman, J. Am. Chem. Soc. 119 (1997)
8217.
[5] (a) A. Sokolwski, H. Leitbecher, T. Weyhermüller, R. Schnepf, E.
Bothe, E. Bill, K. Wieghardt, J. Biol. Inorg. Chem. 2 (1997) 1407;
(b) J. Müller, T. Weyhermüller, E. Bill, P. Hildebrandt, L. Ould-
Moussa, T. Glaser, K. Wieghardt, Angew. Chem. Int. Ed. Engl. 37
(1998) 616;
(c) J. Stubbe, H. Eklund, P. Reichard, Adv. Enzymol. 65 (1992) 147.
[6] (a) D. Zurita, I. Gautier-Luneau, S. Menage, J.-L. Pierre, E. Saint-
Aman, J. Biol. Inorg. Chem. 2 (1997) 46;
(b) S. Itoh, S. Takayama, R. Arakawa, A. Furuta, M. Komatsu, A.
Ishida, S. Takamuku, S. Fukuzumi, Inorg. Chem. 46 (1997) 1407.
[7] (a) J.-L. Pierre, Chem. Soc. Rev. 29 (2000) 251;
(b) B.A. Jazdewski, W.B. Tolmen, Coord. Chem. Rev. 200–202
(2000) 833;
(c) F. Thomas, G. Gellon, I. Gautier-Luneau, E. Saint-Aman, J.-L.
Pierre, Angew. Chem. Int. Ed. 41 (2002) 3047.
[8] (a) P. Chaudhuri, M. Hess, U. Flörke, K. Wieghardt, Angew. Chem.
Int. Ed. 37 (1998) 2217;
(b) P. Chaudhuri, M. Hess, T. Weyhermüller, K. Wieghardt, Angew.
Chem. Int. Ed. (1999) 1095;
(c) P. Chaudhuri, M. Hess, J. Müller, K. Hildebrand, E. Bill, T.
Weyhermüller, K. Wieghardt, J. Am. Chem. Soc. 121 (1999) 9599;
(d) B. Adam, E. Bill, E. Bothe, A. Sokolowski, S. Steenken, T.
Weyhermüller, K. Wieghardt, Chem. Eur. J. 3 (1997) 308.
[9] (a) A.A. Medjidov, V.T. Kasumov, H.S. Mamedov, Koord. Khim. 7
(1981) 66;
9. Concluding remarks
(b) M.K. Guseyinova, A.A. Medjidov, V.T. Kasumov, J. Struct. Chem.
23 (1982) 114;
(c) V.T. Kasumov, A.A. Medjidov, Rus. J. Coord. Chem. 16 (1990)
1355;
(d) V.T. Kasumov, S.N. Lyubchenko, A.A. Medjidov, V.A. Kogan,
Rus. J. Coord. Chem. 16 (1990) 1633;
(e) V.T. Kasumov, A.A. Medjidov, R.D. Kasumov, Rus. J. Coord.
Chem. 22 (1996) 938;
This work demonstrates that the replacement of t-butyl
groups in the 2,6-positions of the phenolic arms of the sal-
icylaldimine ligands by Ph ring significantly alters of their
redox-reactivity towards PbO2 and PPh3. The ESR spectra
of the generated phenoxyl radicals were also substantially
different from those obtained for their t-Bu analogous. The
oxidative C–C coupling of the coordinated di-t-butylated
salicylaldimine ligands in the synthesis of copper(II) com-
plexes in polar solvents in present copper(II) complexes are
not observed.
(f) V.T. Kasumov, A.A. Medjidov, Rus. J. Coord. Chem. 21 (1995)
210;
(g) V.T. Kasumov, J. Coord. Chem. 52 (2001) 57;
(h) V.T. Kasumov, Z. Naturforsh. 56b (2001) 778.
[10] J.F. Larrow, E.N. Jacobsen, Y. Gao, Y. Hong, X. Nie, C.M. Zepp, J.
Org. Chem. 59 (1994) 1939.
[11] (a) V.T. Kasumov, F. Köksal, Zeit. Anorg. Allg. Chem. 627 (2001)
2553;
References
(b) V.T. Kasumov, Spectrochim. Acta A 57 (2001) 1649.
[12] (a) G.O. Dudek, E.P. Dudek, J. Am. Chem. Soc. 88 (1966) 2407;
(b) P.W. Alexander, R.J. Sleet, Aust. J. Chem. 23 (1970) 1183;
(c) G.L. Estiu, A.H. Jubert, J. Costamagna, J. Vargas, J. Molec.
Struct. (Theochem) 367 (1996) 97.
[13] (a) B. Bosnich, J. Am. Chem. Soc. 90 (1968) 627;
(b) R. Bhafta, M. Hellrwell, M. Garner, Inorg. Chem. 36 (1997)
2944.
[14] A.R. Amundsen, J. Whelan, B. Bosnich, J. Am. Chem. Soc. 99
(1977) 6730.
[15] B.J. Hathaway, A.A.G. Tomlinson, Coord. Chem. Rew. 5 (1970) 1.
[16] (a) B.J. Hathaway, in: G. Wilkinson R.D. Gillard J.A. McCleaverty
[1] (a) W. Kaim, Coord. Chem. Rev. 76 (1987) 187;
(b) T.J. Meyer, Progr. Inorg. Chem. 30 (1993) 389;
(c) E.I. Solomon, M.J. Baldwin, M.D. Lowery, Chem. Rev. 92 (1992)
521;
(d) D.P. Goldberg, S.J. Lippard, Adv. Chem. Ser. 246, H.H. Thorp,
V.L. Pecoraro (Eds.), ACS, Washington, DC, 1995.
[2] (a) J.W. Wittaker, in: K.D. Karlin Z. Tyeklar (Eds.), Bioinorganic
Chemistry of Copper, Chapman Hall, New York, 1993;
(b) M.M. Wittaker, Y.-Y. Chuang, J.W. Wittaker, J. Am. Chem. Soc.
115 (1993) 10029;

V.T. Kasumov, F. Köksal / Spectrochimica Acta Part A 60 (2004) 31–39
39
(Eds.), Comprehensive Coordination Chemistry, vol. 5, Pergmon,
Oxford, 1987, pp. 533–594;
[19] F.A. Cotton, R.H. Holm, J. Am. Chem. Soc. 82 (1960) 2979.
[20] (a) L. Sacconi, M. Ciampolini, F. Maffio, F.P. Cavasino, J. Am.
(b) G.A. McLachlan, G.D. Fallon, R.L. Martin, L. Spiccia, Inorg.
Chem. 34 (1995) 254.
Chem. Soc. 83 (1962) 3245;
(b) B. Diamantis, H. Weigold, B.O. West, J. Chem. Soc. (A) (1967)
[17] (a) U. Sakaguchi, A.W. Addison, J. Chem. Soc., Dalton Trans. (1979)
600;
1281.
[21] L. Sacconi, M. Ciampolini, N.J. Nardi, J. Am. Chem. Soc. 86 (1964)
(b) H. Yokoi, A.W. Addison, Inorg. Chem. 16 (1977) 1341.
[18] (a) V.T. Kasumov, A.A. Medjidov, R.Z. Rzaev, I.A. Golubeva, Rus.
J. Coord. Chem. 19 (1993) 933;
819.
[22] (a) V.T. Kasumov, A.A. Medjidov, Koord. Khim. 15 (1989)
1404;
(b) V.T. Kasumov, Spectrochim. Acta A 57 (2001) 2337;
(c) V.T. Kasumov, F. Koksal, Spectrochim. Acta 8 (2002) 2199;
(d) V.T. Kasumov, Trans. Met. Chem. 27 (2002) 228.
(b) V.T. Kasumov, B. Karabulut, I. Kartal, F. Köksal, Trans. Met.
Chem. 26 (2001) 64;
(c) V.T. Kasumov, Spectrochim. Acta Part A 57 (2001) 2337.