Synthesis, structure, spectroscopic and redox properties of copper(II)-N-3,5-Bu2tphenylsalicylaldinine complexes: Crystal and molecular structure of bis(N-3,5-Bu2t- phenylsalicylaldininato)copper(II)

Article abstract of DOI:10.1016/j.poly.2005.08.048

New bulky bis(N-3,5-Bu2tphenyl-R-salicyaldiminato)copper(II) complexes X were synthesized and characterized by analytical, spectroscopic (IR, UV/Vis, EPR), electrochemical methods, and their chemical redox reactivity were studied. X-ray structural analysis of 1 revealed that the CuN₂O₂ coordination core forms a distorted square-planar geometry with a cis-N ₂O₂ donor set which is not expected for analogous complexes. The UV/Vis and EPR results indicate that X complexes have a tetrahedrally distorted square-planar structure in the solid state and in solution. In the chemical oxidation of X by (NH₄) ₂Ce(NO₃)₆ along with disappearance of their EPR spectra, the appearance of new Cu(II) patterns at g = 2.169-2.189 for all X and radical signals in the cases of 5 and 6 were detected. The chemical reduction of some X complexes was accompanied by the disappearance of their EPR signals. The separation in peak potentials (ΔE_p) for complexes X are in order 4 < 3 < 2 < 1 < 6. The electrochemical results suggested that the complex 4 has the highest electrochemical rate assuming both the Cu(II) and Cu(I) forms appear in a similar geometrical configuration, so the electron transfer does not require larger reorganization of the complex in complex 4.

Full text of DOI:10.1016/j.poly.2005.08.048

Polyhedron 25 (2006) 1133–1141
www.elsevier.com/locate/poly
Synthesis, structure, spectroscopic and redox properties
of copperðIIÞ-N-3; 5-But2phenylsalicylaldinine complexes:
Crystal and molecular structure of
bisðN-3; 5-But2-phenylsalicylaldininatoÞcopperðIIÞ
a,
b
b
a
*
ˇ
Veli T. Kasumov , Ahmet Bulut , Fevzi Ko¨ksal , Mehmet Aslanoglu ,
b
b
_
Ibrahim Uc¸ar , Canan Kazak
a
Department of Chemistry, Harran University, Osmanbey, 63300 Sßanlıurfa, Turkey
Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayıs University, 55139 Kurupelit, Samsun, Turkey
b
Received 22 June 2005; accepted 15 August 2005
Available online 18 October 2005
Abstract
New bulky bisðN-3; 5-But2phenyl-R-salicyaldiminatoÞcopperðIIÞ complexes X were synthesized and characterized by analytical, spec-
troscopic (IR, UV/Vis, EPR), electrochemical methods, and their chemical redox reactivity were studied. X-ray structural analysis of 1
revealed that the CuN2O2 coordination core forms a distorted square-planar geometry with a cis-N2O2 donor set which is not expected
for analogous complexes. The UV/Vis and EPR results indicate that X complexes have a tetrahedrally distorted square-planar structure
in the solid state and in solution. In the chemical oxidation of X by (NH4)2Ce(NO3)6 along with disappearance of their EPR spectra, the
appearance of new Cu(II) patterns at g = 2.169–2.189 for all X and radical signals in the cases of 5 and 6 were detected. The chemical
reduction of some X complexes was accompanied by the disappearance of their EPR signals. The separation in peak potentials (DEp) for
complexes X are in order 4 < 3 < 2 < 1 < 6. The electrochemical results suggested that the complex 4 has the highest electrochemical rate
assuming both the Cu(II) and Cu(I) forms appear in a similar geometrical configuration, so the electron transfer does not require larger
reorganization of the complex in complex 4.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Bulky salicylaldiminato-Cu(II) complexes; X-ray crystal structure; Spectroscopy; Electrochemistry; Chemical redox behaviors
1. Introduction
them to produce peripherally bounded stable phenoxyl
radical complexes and in some cases affords dramatically
changing in the chemical properties of some bisðN-Bu2t
phenyl-X-salÞMðIIÞ complexes [4,5]. For example, we have
found that in the complexations of Cu(II) with
N-2; 6-But2-1-hydroxyphenyl-R-sal (I) in polar solvents in-
stead of the expected bisðN-2; 6-But2-1-hydroxyphenyl-
R-salÞCuðIIÞ, as founded by X-ray structural analysis, the
formation of copper(II) complexes having oxidative C–C
coupled tetradentate-sal ligand were observed [4b]. In addi-
tion, bisð2-oxy-3; 5-Bu2t phenyl-arylazoÞCuII [5c] and some
bisðN-But2phenyl-R-salÞCuII chelates depending on the
positions of tert-butyl groups on the phenyl rings possesses
The design, synthesis and structural characterization of
salicylaldimine (sal) complexes are a subject of current
interest due to their interesting structural, magnetic, spec-
tral, catalytic and redox properties, use as models for en-
zymes and various theoretical interests [1–3]. During our
systematic studies on these systems, we have established
that introduction of two bulky tert-butyl substituents into
phenoloate groups on the ortho- and para-positions, enable
*
Corresponding author. Tel.: +904143440020; fax: +903440051.
E-mail address: vkasumov@harran.edu.tr (V.T. Kasumov).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.08.048

1134
V.T. Kasumov et al. / Polyhedron 25 (2006) 1133–1141
strikingly different reactivity behaviors towards triaryl-
phosphines [5]. In order to further examination of the effect
of tert-butyl groups on the structural properties and redox
reactivity of the Cu(II) salicylaldiminates we have carried
out the synthesis of bisðN-3; 5-But2-phenyl-R-salÞcopperðIIÞ
complexes, where R = H, OH, OCH3, t-Bu, and their spec-
troscopic, structural and redox reactivity properties were
studied.
In the present work, the preparation, spectroscopy, electro-
chemical and chemicalredox properties of bisðN-3;5-But2phenyl-
R-salÞcopperðIIÞ complexes, (X), derived from 3;5-But2aniline
and salicylaldehyde derivatives, i.e.: bisðN-3;5-But2phenyl-
salÞcopperðIIÞ (1), bisðN-3;5-But2phenyl-3-methoxy-salÞ-
copperðIIÞ (2), bisðN-3;5-But2phenyl-4-methoxy-salÞcopperðIIÞ
(3), bisðN-3;5-But2phenyl-3-hydroxy-salÞcopperðIIÞ (4),
bisðN-3;5-But2phenyl-4-hydroxy-salÞcopperðIIÞ (5), bisðN-3;5-
But2phenyl-3;5-But2-salÞcopperðIIÞ (6) and crystal structural
analysis of 1 are reported.
(d, J = 8.0 Hz., 1H ArH), 1.37 (s, 18H, t-Bu); 13C NMR
(50 MHz, CDCl3): d 161.3 (CH@N), 152.4, 146.3, 145.5,
122.8, 121.4, 118.5, 117.2, 115.2, 35.1, 31.5; UV/Vis
(EtOH):
k
(loge, cmꢀ1 Mꢀ1) = 222(4.45), 280(4.22),
318(4.19), 461(2.60) nm 1 cmꢀ1 Mꢀ1; Anal. Calc. for
C22H29NO2: C, 77.84; H, 8.61; N, 4.12. Found: C, 78.58;
H, 9.09; N, 4.26%. Compound L4H: Yield % 75; m.p.
163 ꢁC; Selected IR (cmꢀ1, KBr): 1620 (CH@N), 3452
(OH), 2902–2964 (C–H, But); 1H NMR (200 MHz,
CDCl3): d 13,46 (s, 1H), 8.6 (s, 1H, CH@N), 7.39 (s, 1H,
ArH), 7.06–6.95 (m, 4H, ArH), 6.82 (d, J = 8.0 Hz., 1H,
ArH), 1.37 (s, 18 H, t-Bu); 13C NMR (50 MHz, CDCl3):
d 161.3 (CH@N), 152.4, 146.3, 145.5, 122.8, 121.4, 118.5,
117.2, 115.2, 35.1, 31.5; UV/Vis (EtOH):
k (loge,
1 cmꢀ1 Mꢀ1) = 222(4.45), 280(4.22), 318(4.19), 461(2.60)
nm cmꢀ1 Mꢀ1; Anal. Calc. for C21H27NO2: C, 77.50; H,
8.36; N, 4.30. Found: C, 78.12; H, 8.43; N, 4.37%. Com-
pound L5H: yield % 81; m.p. 192 ꢁC; Selected IR (cmꢀ1
,
KBr): 1622(CH@N), 3259 (bs, OH), 2902–2964 (C–H,
1
2. Experimental
But); H NMR (200 MHz, CDCl3): d 13,75 (s, 1H), 8.4
(s, 1H, CH@N), 7.35 (t, 1H, Ar), 7.19 (d, J = 8.8 Hz, 1H
Ar), 7.1 (d, J = 1.6 Hz, 3H, Ar), 6.9 (bs, 1H, Ar), 6.5 (s,
1H, OH), 6.4 (d, J = 8.4 Hz, 2H, CH)); 13C NMR
(50 MHz, CDCl3): d 159.1 (CH@N), 152.9, 134.8, 120.9,
114.6, 113.9, 110.3, 108.6, 104.1, 31.9 (d, J = 1.2 Hz, C-
But); UV/Vis (EtOH): k (loge cmꢀ1 Mꢀ1): 214(3.95),
239(4.56), 290(sh), 341(4.51), 416(3.88); Anal. Calc. for
C22H29NO2: C, 77.50; H, 8.36; N, 4.30. Found: C, 77.68;
H, 8.17; N, 4.43%. Compound L6H: yield % 85; m.p.
119 ꢁC; Selected IR (cmꢀ1, KBr): 1619 (CH@N), 2902–
2.1. Chemicals
All solvents, Cu(ac)2 Æ H2O, (NH4)2Ce(NO3)6, n-Bu4N-
ClO4, PPh3, 3,5-di-tert-butylaniline, salicylaldehyde and
its 3-HO, 4-HO, 3-OCH3, 4-OCH3 derivatives were pur-
chased from Aldrich Chemical Co. and were used without
further purification. 3,5-di-tert-butylsalicylaldehyde was
prepared according to the procedure described by Jacobsen
and his co-workers [3d].
1
2964 (C–H, But); H NMR (200 MHz, CDCl3): d 13.97
2.2. Ligands
(s, 1H, OH), 8.60 (d, J = 6.0 Hz, 1H, CH@N), 7.49–7.15
(m, 4H, ArH), 1.54–1.37 (m, 36 H, t-Bu); 13C NMR
(50 MHz, CDCl3): d 163.2 (CH@N), 158.3, 152.1, 148.2,
140.5, 136.9, 127.8, 126.7, 120.8, 118.5, 115.5, 35.1, 34.2,
31.6, 29.5; UV/Vis (EtOH): k (loge 1 cmꢀ1 Mꢀ1): 210(sh),
230(4.40), 268(4.25), 341(4.26), 438(2.36) nm; Anal. Calc.
for C29H43NO: C, 82.61; H, 10.28; N, 3.32. Found: C,
82.42; H, 9.87; N, 3.42%.
N-3,5-di-tert-butylphenyl-R-sal (LxH) were prepared in
good yields by the condensation of 3,5-di-tert-butylaniline
and appropriate salicylaldehydes in refluxing methanol.
The yellow imines were recrystallized from methanol.
Yields of the LxH are in the range 75–88%. Compound
L1H: yield % 78; m.p. 114 ꢁC; selected IR (cmꢀ1, KBr):
1618 (CH@N), 2902–2964 (C–H, But); 1H NMR
(200 MHz, CDCl3): d 13.47 (s, 1H, OH), 8.64 (s, 1H,
CH@N), 7.44–7.34 (m, 3H, ArH), 7.13–6.91 (m, 4H
ArH), 1.37 (s, 18 H, t-Bu); 13C NMR (50 MHz, CDCl3):
d 162.1 (CH@N), 152.2, 132.9, 132.2, 121.1, 118.9, 117.3,
115.4, 35.1, 31.5; UV/Vis (EtOH): k (loge l cmꢀ1 Mꢀ1):
210(sh), 230(4.40), 268(4.25), 341(4.26), 438(2.36) nm;
Anal. Calc. for C21H27NO: C, 77.50; H, 8.36; N, 4.30.
Found: C, 7.71; H, 8.24; N, 4.48%. Compound L2H:
yield % 82; m.p. 144 ꢁC; selected IR (cmꢀ1, KBr): 1624
(CH@N), 2902–2960 (C–H, But); UV/Vis (EtOH): k (loge
cmꢀ1 Mꢀ1): 214(3.95), 239(4.56), 290*, 341(4.51),
416(3.88)1620. Anal. Calc. for C22H29NO2: C, 77.84; H,
8.61; N, 4.12. Found: C, 77.68; H, 8.37; N, 4.23%. Com-
2.3. Complexes
The complexes X were prepared by refluxing methanolic
solutions of Cu(ac)2 Æ H2O (0.25 mmol) and LxH (0.5 mmol)
in a 1:2 molar ratio for 1.0–1.5 h. The volume of the result-
ing solution was reduced to one half and left at room tem-
perature without stirring. The precipitate microcrystals
were collected by filtration, washed with a small amount
of cold methanol and dried on air (yields 68–85%). Recrys-
tallization of 1 from methanol afforded X-ray suitable
crystals. Yield: 76%. M.p. 196 ꢁC. leff = 1.76lB; UV/Vis
(CHCl3): k (loge) = 294(4.79), 400(4.41), 500(sh), 670-
(2.43); IR (KBr, cmꢀ1): m = 1608 (CH@N), 2864–2956
(C–H in But). C42H52N2O2Cu: Calc.: C, 74.2; H, 7.7; N,
4.1. Found: C, 74.3; H, 7.6; N, 4.2%. Elemental analysis,
physico-chemical, electronic spectral and IR data of X com-
plexes are summarized in Table 1.
pound L3H: Yield % 85; m.p. 102 ꢁC; Selected IR (cmꢀ1
,
KBr): 1626 (CH@N), 3452, 2902–2964 (C–H, But); 1H
NMR (200 MHz, CDCl3): d 14.04 (s, OH), 8.5 (s, 1H,
CH@N), 7.39 (s, 1H, ArH), 7.06–6.95 (m, 4H, ArH), 6.82

V.T. Kasumov et al. / Polyhedron 25 (2006) 1133–1141
1135
Table 1
Elemental analysis, physico-chemical, electronic spectral and IR data of X compounds
Compound
M.p. (ꢁC)
Yield (%)
Electronic spectra, k/nm (loge, cmꢀ1 Mꢀ1
)
IR spectra,
cmꢀ1
Found (Calc.) (%)
mC@N
mOH
C
H
N
1
2
3
4
5
6
196
262
196
245
236
76
78
82
68
75
85
294(4.8), 400(4.4), 500a, 660(2.2)
306(4.6), 408(4.4), 500a (3.2), 700a
255, 305, 379, 480a, 673(2.25)
293, 387, 500a, 700a (2.28)
308, 376, 450a, 500a, 700a
1608
1603
1612
1616
1603
1598
74.3(74.2)
71.2(71.4)
71.2(71.4)
71.7(70.8)
70.6(70.8)
86.3(86.5)
7.6(7.7)
7.7(7.6)
7.8(7.6)
7.5(7.4)
7.2(7.4)
9.5(9.5)
4.2(4.1)
3.9(3.8)
3.7(3.8)
4.1(3.9)
3.7(3.9)
3.2(3.1)
3488
3438
3432b
3286b
>275
295, 416, 500, 710a (2.36)
a
Shoulder.
Strong narrow band.
b
2.4. Physical measurements
Table 2
Crystallographic data for the compound 1
Elemental analyses were carried out using a LECO
CHNS 932 elemental analyzer. The magnetic susceptibili-
ties of powdered samples were measured in a Sherwood
Scientific Magnetic Susceptibility Balance (Model MK 1)
magnetometer at r.t. Electronic spectra were measured on
a Shimadzu 1601 UV–Vis spectrophotometer in various
solvents. The IR spectra were recorded on a Perkin–Elmer
Formula
Molecular weight
Temperature (K)
C42H52CuN2O2
680.40
293(2)
0.71069
monoclinic
C2/c
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions
˚
a (A)
13.943(5)
16.413(5)
16.781(5)
99.602
3786(2)
4
1.194
0.613
1452
0.42 · 0.28 · 0.19
1.93–29.38
ꢀ19 6 h 6 19, ꢀ22 6 k
6 22, ꢀ21 6 l 6 23
35857
5183
3111
1
FTIR spectrometer using KBr discs. H and 13C NMR
˚
b (A)
˚
c (A)
spectra were recorded on a Bruker Spectro spin Avance
DPX-400 Ultra Shield Model NMR or on a BRUKER
AC 200 using TMS as an internal standard in CDCl3.
The ESR spectra were recorded on a Varian E-109 C model
X-band spectrometer with 100 kHz modulations. The X-
band EPR spectra at 300 and 113–133 K were recorded
on a Varian E109 C model EPR spectrometer with
100 kHz frequency modulation using DPPH (g = 2.0036)
as standard. Errors in giso, gi and g^ are 0.0005; errors
in Aiso, Ai and A^ are 0.5, 1.0 and 1.0 G, respectively.
An EcoChemie Autolab-12 potentiostat with the elec-
trochemical software package GPES 4.9 (Utrecht, The
Netherlands) was used for voltammetric measurements. A
three electrode system was used: a Pt counter electrode,
an Ag/AgCl reference electrode and a 2-mm sized Pt disc
as working electrode. The potentiostat/galvanostat has an
IR-compensation option. Therefore, the resistance due to
the electrode surface was compensated throughout the
measurements. Oxygen-free nitrogen was bubbled through
the solution before each experiment. All experiments were
carried out at room temperature.
b (ꢁ)
Volume
Z
Calculated density (Mg mꢀ3
l (mmꢀ1
F(000)
Crystal size (mm)
h Range
Index ranges
)
)
Reflections collected
Independent reflections
Reflections observed (>2r)
Absorption correction
Maximum and minimum
transmission
integration
0.7065–0.8637
Refinement method
full-matrix least-squares on F2
3111/0/224
Data/restrains/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
0.945
R1 = 0.0462, wR2 = 0.1213
R1 = 0.0772, wR2 = 0.1331
0.62 and ꢀ0.54
ꢀ3
˚
Largest difference in peak and hole (A
)
2.5. X-ray crystallography
plied to non-hydrogen atoms in a full-matrix least-squares
refinement based on F2 using SHELXL-97 [9]. All hydrogen
atoms were positioned geometrically and refined by a rid-
ing model with Uiso 1.2 times that of attached atoms.
Molecular drawings were obtained using ORTEP-III [10].
A suitable single crystal was mounted on a glass fiber
and data collections were performed on a STOE IPDSII
image plate detector using Mo Ka radiation
˚
(k = 0.710690 A). Intensity data were collected in the h
range 1.93–29.38ꢁ at 298 (2) K. Crystallographic data are
listed in Table 2. Data collection: Stoe X-AREA [7]. Cell
refinement: Stoe X-AREA [7]. Data reduction: Stoe X-
RED [7]. The structure was solved by direct-methods using
SIR97 [8] and anisotropic displacement parameters were ap-
3. Results and discussion
Except 5 (R = 4-OH) all X complexes are soluble in
chloroform, dichloromethane, but less soluble in solvents
such as alcohols, tetrahydrofuran and DMSO. The elemen-

1136
V.T. Kasumov et al. / Polyhedron 25 (2006) 1133–1141
Table 3
tal analyses were satisfactory, indicating that the complexes
have a ligand-to-metal ratio of 2:1.
˚
Selected bond lengths (A) and angles (ꢁ) for complex 1
Bond lengths
Cu1–O1
Cu1–N1
N1–C1
N1–C8
O1–C7
C2–C3
C2–C7
C3–C4
C4–C5
It is well known that tetra coordinated copper(II)-Schiff
base complexes derived from bidentate N-aryl(alkyl)-R-sal
ligands with CuN2O2 coordination sphere usually display
trans square planar, distorted square planar or tetrahedral
arrangement [2–4c,11]. At the same time, recently reported
X-ray structural studies of the solvated Cu(N-Ph-5-Cl-
sal)2 Æ 1/2CH2Cl2 [3a] and Cu(N-p-CH3Ph-sal)2 Æ DMF
[12] revealed that in these complexes the ligands are coor-
dinated in a cis-N2O2 planar configuration. Interestingly,
in the present unsolvated complex 1 the copper atom has
a tetrahedrally distorted square planar geometry with two
3; 5-di-But2phenyl-sal ligands in a cis-N2O2 arrangement.
1.8850(16)
1.9706(16)
1.293(3)
1.437(2)
1.293(3)
1.409(3)
1.411(3)
1.364(3)
1.388(4)
1.350(4)
C5–C6
Bond angles
O1Cu1N1
O1Cu1O10
N1Cu1N10
O10Cu1N10
O1Cu1N10
N1C8C9
N1C1C2
C1N1C8
C1C2C7
C2C7O1
93.73(7)
87.70(10)
97.13(9)
93.73(10)
152.81(8)
118.56(16)
127.40(19)
117.7(2)
3.1. Description of the structure of 1
The molecular structure of complex 1 is illustrated in
Fig. 1. Details of the crystal and data collection are out-
lined in Table 2. The selected bond lengths and bond angles
are listed in Table 3. The X-ray diffraction analysis of 1
show that the copper ion is bonded to the oxygen and
nitrogen donor atoms of the two bidentate ligand mole-
cules in the unusual a cis-N2O2 arrangement. The geometry
of 1 is distorted square planar where the dihedral angle be-
tween the two coordination planes defined by O10Cu1N10
and O1CuN1 is 36.91(6)ꢁ (Fig. 1). The compound has crys-
tallographic C2 2-fold axes passing through the copper
122.5(3)
123.81(18)
122.20(13)
127.93(13)
120.00(13)
Cu1N1C1
Cu1O1C7
Cu1N1C8
atom. The crystal structure of 1 is built from pairs of mol-
ecules orientated in the trans position respect to each other
and the two salicylidene groups of the neighboring mole-
Fig. 1. An ORTER diagram of 1. Displacement ellipsoids are drawn at the 40% probability level. H atoms are omitted for clarity.

V.T. Kasumov et al. / Polyhedron 25 (2006) 1133–1141
1137
Fig. 2. View of the packing in 1 along the a-axis showing the possible pꢁ ꢁ ꢁp and C–Hꢁ ꢁ ꢁp contacts at 10% probability displacement ellipsoids.
cules are oriented nearly parallel to each other as shown in
Fig. 2. Although the centroids of the two di-tertbutylphe-
nyl rings are indeed too far apart for any p–p interactions
[the distances between the centroids of the aromatic rings
of the neighboring SA molecules are 4.791(2) and
the most significant aspect of the present structure is that
it demonstrates the possibility coordination of the biden-
tate N-aryl-SA ligands to copper atom in the sterically
unfavorable a cis-N2O2 arrangement configuration. The
reasons that the cis-configuration is preferred for complex
1 are not clear.
˚
4.568(2) A, a distances that are longer than the sum of
˚
the van der Vaals radii of two carbon atoms (3.4–3.6 A)],
1
the rings are not parallel, and C8ꢁ ꢁ ꢁC90 and C9ꢁ ꢁ ꢁC80 are
3.2. IR, H NMR and 13C NMR spectra
˚
only 3.413(3) A, indicating quite strong interactions be-
tween these two carbons in both rings [11]. The Cu–Cu dis-
tance between the neighboring complexes units is so large
(8.392 A) that intermolecular interaction can be excluded.
In the IR spectra of the ligands along with character-
istic bands in the 1619–1626 and 2550–2800 cmꢀ1 regions
(Section 2.2) due to m(C@N) and intramolecularly
H-bonded m(OH), respectively, a strong narrow peak at
˚
The copper center in 1 is in a distorted square planar envi-
ronment with O1–Cu1–N1i, N1–Cu1–N1i, and O1–Cu1–
O1i (symmetry code: (i) x, y, ꢀz + 0.5), angles of
152.81(8)ꢁ, 97.13(9)ꢁ and 87.70(10)ꢁ, respectively. The dihe-
dral angles between two phenyl rings and between the two
salicylidene benzene rings are 27.40(9)ꢁ and 28.49(8)ꢁ,
respectively. The Cu1–N1 and Cu1–O1 bond distances of
3452 cmꢀ1 in L4H and
a
broad strong peak
at 3259 cmꢀ1 in L5H attributed to m(OH) stretching of
3-OH group and intermolecularly H-bonded 4-OH,
respectively, were observed.
In the spectra of X complexes the m(C@N) band of the
ligands undergoes small shift to lower frequencies (1598–
1616 cmꢀ1), indicating that the ligands are coordinated
through the imine nitrogen atoms. The disappearance of
the broad band at 2600–2800 cmꢀ1 and the appearance of
new medium intensity bands in the region 450–600 and a
strong band centered at 1523–1552 cmꢀ1 which appeared
only in the spectra of X can be assigned to mCu–N, mCu–O
and mC@C (Table 1), respectively, as described in similar
complexes [14]. The medium intensity bands detected at
3488 and 3438 cmꢀ1 in the spectra of 2 and 3, respectively,
assigned to mOH of lattice water molecules.
˚
1.9706(16) and 1.8850(16) A, respectively, agree well with
the corresponding distances founded in bis(N-phenyl-
˚
SA)copper(II) [Cu1–N1 (1.99) and Cu1–O1 (1.88) A [6a],
bis(N-p-methylphenyl-SA)copper(II) [Cu1–N1 1.965 (3)
˚
and Cu1–O1 1.895(2) A] [13b] and bis[N-p-(CH3)2N-phe-
˚
nyl-SA]copper(II) [Cu–N 1.996 (6) and Cu–O 1.885(5) A]
[6b] and in many N-alkyl substituted bis-SA and bis-naph-
thaldimine–CuII complexes [13,15,16]. Surprisingly, although,
the present complex 1 differs from bisðN-3; 5-But2-4-
OCH3-phenyl-SAÞCuII (II) complexes [4c] only with the
absence of a OCH3 group in the 4-position of aniline ring
of 1, the latter complex has practically undistorted a
trans-N2O2 square-planar geometry around Cu(II) center
with Cu1–N1 and Cu1–O1 distances of 2.029 and
1
The H NMR and 13C NMR spectral results obtained
for LxH ligands in CDCl3, with their assignments are given
in Section 2. 1H NMR signals were assigned on the basis of
their integral intensity, spin–spin coupling patterns and
chemical shift values.
˚
1.900 A, respectively [4c]. From a chemical point of view

1138
V.T. Kasumov et al. / Polyhedron 25 (2006) 1133–1141
3.3. Electronic spectra
The solution EPR spectra except 5 of all X in CHCl3 at
300 K display the expected typical 4-line pattern from cou-
pling to nuclei of 65Cu (I = 3/2) isotopes, without 14N-shfs
resolutions on the high-field mI = 3/2 line component.
Complex 4 displays a five-line superhyperfine structure on
high field copper component with ANiso ¼ 8:8 G due to cou-
pling with two 14N (I = 1) nuclei. The resonances show mI
dependent line widths with the high field line being nar-
rower and more intense than the low field line. According
to spectral parameters obtained from frozen glass spectra
of X (Table 4) at 133 K the complexes exhibit axial symme-
try feature with gi > g^ > 2.03 indicating a dx2ꢀy2 or dxy
ground state in a tetragonal copper centers [18b]. The quo-
tient gi/Ai value of 146–167 cm for X, lying between 140
and 250 cm again indicates a slightly distorted environment
for Cu(II) centers [22]. It is interesting that according to
gi/Ai value (Table 4) complex 1 prepared from unsubsti-
tuted salicylaldehyde exhibits significantly more tetrahedral
distortion than 6 prepared from sterically bulky 3; 5-
But2salicylaldehyde. Another interesting feature consist of
significant difference between gi/Ai ratio for 6 determined
from its powdered spectrum (192 cm) and frozen glass
spectrum (146 cm), indicating changes its geometry from
strongly distorted tetrahedral to a slightly distorted planar
in solution.
Electronic spectral data of the LxH ligands in EtOH
solution are presented in the Experimental Section. The
electronic spectra of X in CHCl3 solutions (Table 1) along
with intraligand absorptions originated from p ! p* and
n ! p* transitions also exhibited three visible bands at
400–450, 500(sh) and 660–710 nm which are assigned to
the following transitions in order of decreasing energy the
MLCT transition (CT band from filled dp orbitals of CuII
to the antibonding p* orbitals of phenoate), dxy ! dx2ꢀy2
,
and dz2 ! dx2ꢀy2 , respectively, in a distorted square planar
geometry around copper(II) ion [17,18a].
3.4. EPR and magnetic properties
The room temperature effective magnetic moments of 1,
5, and 6 (1.73, 1.76 and 1.70lB) (Table 4) are close to the
spin only value of 1.73lB expected for 3d9 systems. The
similar magnetic behaviors are noticed in the magnetically
dilute systems; therefore this indicates the absence of any
coupling in the solid state [18a]. Indeed, our present X-
ray study revealed that the nearest Cuꢁ ꢁ ꢁCu distance in 1
˚
is 8.386 A. The complexes 2, 4 and 3 exhibit magnetic mo-
ments (1.83 and 1.97lB) typical for square planar or pseu-
do-tetrahedral mononuclear copper(II) complexes with a
S = 1/2 spin state [19,20].
3.5. Reduction of X complexes with PPh3
The spin Hamiltonian parameters of X complexes is
listed in Table 4. The EPR spectra of powder of all X at
300 and 113 K exhibit an axial signal with copper-hyperfine
splitting with gi > g^ > ge pattern typical for a slightly dis-
torted square planar or square planar geometries with a
dx2ꢀy2 ground state [18]. Selected spectra are shown in
Fig. 3. Spectral features for 1, 4, 5, were significantly differ-
ent from those for 2, 3 and 6 for which in gi region two
[(Ai = 172 G (for 2), 164 G (for 3)] and three components
(Ai = 119 for 6) of the four parallel copper hyperfine fea-
tures were resolved (Fig. 3). When EPR spectra of 2, 3
and 5 were scanned from 293 to 113 K without any changes
in the line widths and g-factors, the linearly increasing in
intensity of the high field doublet spectrum which follows
the Curie law (I = C/T) were detected. The similar behav-
ior is consistent with J > 0 (ferromagnetic coupling) or
J = 0 [21].
In our early works, it has been demonstrated that some
copper(II) complexes with salicylaldimine, 2-hydroxy-
benzylamine and b-ketoamine ligands bearing sterically
hindered 2,6-di-tert-butylphenyl fragment unlike their
unhindered analogs, undergo one-electron transfer reac-
tions in the interactions with triarylphosphines giving
corresponding metal-stabilized radical intermediates
[5a,5b,5c,5d,5e]. When some copper(II) bis-chelates with
N-2; 5-di-But2pheny-R-sal, structural isomers of the present
complexes, was treated with a 2–3-fold excess of PPh3 in
various solvents the decreasing of the intensity of copper
EPR signals and immediate appearance of radical signals
with g = 2.005–2.0082 for R = 3-OH, 3-OCH3, and 5-OH
complexes were detected [23]. At the same time, no reduc-
tion process were observed for similar II complexes even in
the interaction with 10-fold excess of PPh3. Similar treat-
Table 4
EPR and magnetic moment data of X complexes
Compound
EPR parametersa
Solid
Solution (CHCl3)
X
leff (lB)
gi
g^
giso
gi
g^
Aiso
Ai
A^
gi/Ai (cm)
1
2
3
4
5
6
a
1.73
1.83
1.97
1.83
1.76
1.70
2.202
2.186
2.227
2.142
2.189
2.236
2.051
2.063
2.073
2.046
2.059
2.047
2.111
2.129
2.121
2.127
2.242
2.245
2.242
2.217
2.046
2.071
2.061
2.082
66
68
68
80
144
156
160
192
27
24
22
24
167
155
150
124
2.118
2.232
2.063
63
164
11
146
Aiso, Ai and A^ values are given in units of G (Gauss).

V.T. Kasumov et al. / Polyhedron 25 (2006) 1133–1141
1139
Fig. 3. ESR spectra of some X complexes: microcrystalline solids (a) 1 and (b) 5 at r.t., (c) powdered solid 4 at 293 K and (d) at 113 K; (e) powdered 6 at
293 K; (f) solution spectrum 6 in CHCl3 and (g) oxidized 6 at r.t. under identical scanning conditions.
ment of the present X complexes revealed that upon addi-
tion of 3–4-fold excess of PPh3 to CHCl3 solution of 1, 2, 4
and 6 complexes at r.t., during 3–6 h their black color chan-
ged to orange-yellow and their absorption peaks within
the range of 450–700 nm were disappeared. Under similar
conditions the dark brown color of 3, during even 3 days
has not changed practically [(340, 390(sh), 420(sh).
500(sh) and 670 nm(sh) (3 + PPh3)]. In the EPR monitor-
ing of X + PPh3 (X = 1,2,4,6) systems during reaction pro-
cess in air or in vacuum only slowly decreasing in the
intensity of their spectra without appearance of any radical
signals were detected.
g = 2.0052 were observed (Figs. 3(f) and (g)). The decreas-
ing of the signal intensity of X + CAN system suggest that
one-electron oxidation results in the generation of a CuII-
phenoxyl radical complex and there is antiferromagnetic
coupling between an S = 1/2CuII and an S = 1/2 phenoxyl
radical. We suggest that the detected radical signals more
ꢀ
probably originate from CuðLxÞ2 type diradical species in
which one radical center is fully antiferromagnetically cou-
pled with Cu(II).
The spectral changes for X + CAN systems were also
monitored by UV–Vis spectroscopy during the progress
of the oxidation of X complexes with ACN in CHCl3. Since
the oxidant is insoluble in CHCl3 the reaction system was
heterogeneous. However, the solution X + CAN system
was mixed using a spatula for 5–6 s prior to each scanning.
When three to five excess of CAN was added to the solu-
tion of X in CHCl3 at r.t., the black solution turns to
brown or light yellow with the disappearance of the origi-
nal bands of visible bands at 450–700 nm.
3.6. Chemical oxidation of the complexes
Our recent studies demonstrated that in the chemical
oxidation of bis½N-alkylðarylÞ-3; 5-But2salꢂcopperðIIÞ com-
plexes with one-electron oxidant (NH4)2[Ce(NO3)6]
(CAN) in CHCl3, along with decreasing of the Cu(II) sig-
nal intensity, the generation of directly coordinated phe-
noxyl radical complexes are also detected [23]. The
present investigation of the oxidative behavior of X com-
plexes at r.t. and in air conditions, revealed that when they
are treated with of three to 5-fold excess amount of CAN
along with color change from black or dark brown to light
brown or light yellow, the disappearance of the EPR spec-
tra of X and appearance new broad lines (peak-to-peak
about DH = 92–108 G) at g = 2.169–2.189 were detected.
For complexes 5 and 6 besides broad singlets at 2.169
and 2.189 the strong radical signals at g = 2.0055 and
3.7. Electrochemistry
Electrochemical properties of the complexes X except 5
due to its poor solubility were studied on a Pt disc electrode
in dimethylsulfoxide containing 0.05 M n-Bu4NClO4 as the
supporting electrolyte. Table 5 summarizes the electrode
potentials for all complexes in dimethylsulfoxide. A cyclic
voltammogram of 1 is given in Fig. 4. This complex dis-
plays a reduction peak at E1pc ¼ 0:14 V with a correspond-
ing oxidation peak at E1pa ¼ 0:26 V. The peak separation of

1140
V.T. Kasumov et al. / Polyhedron 25 (2006) 1133–1141
Table 5
Voltammetric data for Cu(II) complexes
X
E1pa
E1pc
DEp
E2pa
E3pa
E2pc
DEp
E4pa
E3pc
DEp
E4pc
1
2
3
4
5
0.26
0.26
0.24
0.29
0.37
0.14
0.17
0.14
0.21
0.20
0.12
0.11
0.10
0.08
0.17
0.65
1.08
1.04
0.92
ꢀ0.45
ꢀ0.11
ꢀ0.16
0.01
ꢀ0.59
ꢀ0.24
ꢀ0.22
ꢀ0.09
0.14
0.13
0.06
0.10
ꢀ0.28
ꢀ0.59
ꢀ0.67
ꢀ0.48
ꢀ0.96
ꢀ1.58
ꢀ0.44
ꢀ0.53
ꢀ0.35
0.15
0.14
0.13
ꢀ0.47
Supporting electrolyte = 0.05 M n-Bu4NClO4, scan rate = 100 mV/s.
Potentials are presented in volts.
25000
8000
6000
4000
2000
0
20000
15000
10000
5000
-2
-1.5
-1
-0.5
0
0.5
1
1.5
-2000
-4000
-6000
-8000
0
-1.5
-1
-0.5
0
0.5
1
1.5
E (V) vs . Ag/AgCl
-5000
-10000
-15000
E (V) vs. Ag/AgCl
Fig. 4. A cyclic voltammogram of 1 in dimethylsulfoxide containing
0.05 M n-Bu4NClO4 as supporting electrolyte. Scan rate = 100 mV/s.
Fig. 5. A cyclic voltammogram of 4 in dimethylsulfoxide containing
0.05 M n-Bu4NClO4 as supporting electrolyte. Scan rate = 100 mV/s.
this couple (DEp) is 0.12 V at 0.1 V/s and increases with
scan rate. The most significant feature of this redox couple
is the 1e-transfer electrochemical process of the formation
of Cu(II)/Cu(I). The difference between forward and back-
ward peak potentials can provide a rough evaluation of the
degree of the reversibility of one electron transfer reaction.
The analysis of cyclic voltammetric responses with the scan
rate varying 50–300 mV/s gives the evidence for a quasi-
reversible one electron oxidation. The ratio of cathodic to
anodic peak height was less than one. However, the peak
current increases with the increase of the square root of
the scan rate. The Ip/v1/2 value is almost constant for all
scan rates. This establishes the electrode process as diffu-
sion controlled [24]. The separation in peak potentials in-
creases at higher scan rates. These characteristic features
are consistent with the quasi-reversibility of Cu(II)/Cu(I)
couple. The other oxidation or reduction peaks are listed
in the Table 5 and are probably due to the ligand moiety
of complex. The electrode potentials of the rest of the cop-
per(II) complexes are given in Table 5.
trode process is controlled by diffusion. The separation in
peak potentails (DEp) for complexes are in order
4 < 3 < 2 < 1 < 6. The difference between forward and
backward peak potentials can provide a rough evaluation
of the degree of the reversibility. This shows that the elec-
trochemical process of complex 4 is faster than that of the
other complexes. This behavior may suggest that in com-
plex 4, both the Cu(II) and Cu(I) forms appear in a similar
geometrical configuration, so the electron transfer does not
require larger reorganization of the complex coordination
geometry.
In conclusion, the present work indicates that a small
changes of the substituents on the ligands of the
bisðN-3; 5-But2phenyl-R-salÞcopperðIIÞ type complexes re-
sults in striking changes both in the molecular structure of
the complexes and their chemical redox reactivity. Surpris-
ingly, in complex 1 with R = H unlike its structurally char-
acterized bis(N-aryl(alkyl)-sal) analogs copper center
exhibits a tetrahedrally distorted cis-N2O2 square planar
geometry. Chemical oxidation of some complexes leads to
the formation of the coordinated Cu(II)-phenoxyl radical
complexes. As supported by EPR and electronic spectral
studies their reduction with PPh3 proceeded slowly without
generation any radical species. The electrochemical mea-
surements have indicated that complexes showed quasi-
reversible 1e-electron transfer reduction to Cu(I) along with
the reduction and oxidation of the ligand moiety of the
complexes. The results also indicated that 4 has the highest
A cyclic voltammogram of the complex 4 is given in
Fig. 5. The complex 4 exhibits a reduction peak at
E1pc ¼ 0:21 V with
a
directly re-oxidation peak at
E1pa ¼ 0:29 V corresponding to the formation of Cu(II)/
Cu(I) couple. The peak separation of this couple (DEp) is
0.08 V. This redox couple also have quasi-reversible char-
acter as the separation in peak potentials are higher than
59 mV and the peak currents rises with increasing v1/2
.
Diagnostic test for the complex 4 indicated that the elec-

V.T. Kasumov et al. / Polyhedron 25 (2006) 1133–1141
1141
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does not require larger reorganization of the complex.
[7] Stoe & Cie, X-AREA (Version 1.18) and X-RED32 (Version 1.04),
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4. Supplementary data
[8] A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C. Giaco-
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Crystallographic data (excluding structure factors) for
the structure in this paper have been deposited with the
Cambridge Crystallographic Data Centre as the Supple-
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data can be obtained, free of charge, on application to
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK, fax:
+44 1223 366 033, e-mail: deposit@ccdc.ac.uk or on the
web www: http://www.ccdc.cam.ac.uk.
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