Dinuclear copper(II) complexes of a novel 3-(aminomethyl)naphthoquinone Mannich base: Synthesis, structural, magnetic and electrochemical studies

Article abstract of DOI:10.1016/j.poly.2010.07.011

A novel versatile tridentate 3-(aminomethyl)naphthoquinone proligand, 3-[N-(2-pyridylmethyl)aminobenzyl]-2-hydroxy-1,4-naphthoquinone (HL), was obtained from the Mannich reaction of 2-hydroxy-1,4-naphthoquinone (Lawsone) with 2-aminomethylpyridine (amp) a

Full text of DOI:10.1016/j.poly.2010.07.011

Polyhedron 29 (2010) 2884–2891
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Dinuclear copper(II) complexes of a novel 3-(aminomethyl)naphthoquinone
Mannich base: Synthesis, structural, magnetic and electrochemical studies
b
a
Amanda P. Neves a, Kelly C.B. Maia a, Maria D. Vargas a, , Lorenzo C. Visentin , Annelise Casellato ,
*
Miguel A. Novak c, Antônio S. Mangrich d
a Instituto de Química, Universidade Federal Fluminense, Campus do Valonguinho, Centro, CEP 24020-150, Niterói, RJ, Brazil
b Instituto de Química, Universidade Federal do Rio de Janeiro, Ilha do Fundão, CEP 21945-970, Rio de Janeiro, RJ, Brazil
c Instituto de Física, Universidade Federal do Rio de Janeiro, Ilha do Fundão, CEP 21945-970, Rio de Janeiro, RJ, Brazil
d Departamento de Química, Centro Politécnico, Universidade Federal do Paraná, CEP 81531-970, Curitiba, PR, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel versatile tridentate 3-(aminomethyl)naphthoquinone proligand, 3-[N-(2-pyridylmethyl)amino-
benzyl]-2-hydroxy-1,4-naphthoquinone (HL), was obtained from the Mannich reaction of 2-hydroxy-
1,4-naphthoquinone (Lawsone) with 2-aminomethylpyridine (amp) and benzaldehyde. The reactions
Received 30 March 2010
Accepted 13 July 2010
Available online 21 July 2010
of HL with CuCl2ꢀ2H2O yielded two novel dinuclear copper(II) complexes, [Cu(L)(H2O)(
l-Cl)Cu(L)Cl]
(1b), [CuCl(L)( -Cl)Cu(amp)Cl] (2) and a polymeric compound, [Cu(L)Cl)]n (1a), whose relative yields
l
Keywords:
were sensitive to temperature, reagents concentration and presence of base. The crystalline structures
of 1b and 2 were determined by X-ray diffraction studies. The two copper atoms in complex 1b are con-
nected by a single chloro bridge with a Cuꢀ ꢀ ꢀCu separation of 4.1342(8) Å and Cu(1)–Cl(1)–Cu(2) angle of
109.31(4)°. In complex 2 the two copper atoms are held together by a chloro and a naphthalen-2-olate
bridges [Cu(1)–Cl(2)–Cu(2) and Cu(1)–O(1)–Cu(2) angles being 83.31(3) and 109.70(9)°, respectively,
and the Cuꢀ ꢀ ꢀCu separation, 3.3476(9) Å]. As expected, variable-temperature magnetic susceptibility
measurements of complex 1b showed weak antiferromagnetic intramolecular coupling between the cop-
per(II) centers, with J = ꢁ5.7 cmꢁ1, and evidenced for complex 2 strong antiferromagnetic coupling, with
J ꢂ ꢁ120 cmꢁ1. Furthermore, the magnetic behaviour of compound 1a suggested an infinite 1D coordina-
tion polymeric structure in which the copper(II) centers are connected by Cl–Cu–Cl bridges. Solution data
(UV–Vis spectroscopy and cyclic voltammetry) indicated structural changes of 2 and 1a in CH3CN, and
evidenced conversion of polymer 1a into dimer 1b.
Dinuclear copper(II) complexes
Naphthoquinone ligands
X-Ray diffraction
Magnetic properties
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
with the chelating deprotonated ligands resulted only in formation
of mononuclear square planar complexes. Herein we report the
Quinones are known for their pharmacologic properties [1] and
for taking part in many biological processes, such as respiration and
photosynthesis [2]. Due to their binding ability, the coordination of
these chelating compounds to transition metal ions has also been
the subject of growing interest [3]. The main motivations for the
synthesis of novel naphthoquinone metal complexes are the study
of their biological applications [4,5] and the investigation of their
magnetic properties [6–9]. Ligands which contain potentially bridg-
ing phenoxo oxygen and nitrogen donor atoms have been widely
used in the synthesis of dinuclear copper complexes [10,11].
As the result of our ongoing investigations of biologically active
3-(aminomethyl)naphthoquinone transition metal complexes we
described recently the synthesis and antimicrobial activities of no-
vel Mannich bases 3-[N-(2-phenyl)aminoalkyl]-2-hydroxy-1,4-
naphthoquinones and of their copper(II) [4] complexes. Interaction
synthesis of the aminomethylpyridine derivative, 3-[N-(2-pyri-
dylmethyl)aminobenzyl]-2-hydroxy-1,4-naphthoquinone (HL),
a
potentially tridentate ligand, and the analogous complexation
reactions, that yielded a polymeric compound and novel copper(II)
dimers, whose solid state structures have been established by
X-ray diffraction studies. Magnetic studies evidenced antiferro-
magnetic interaction in all cases, whose strength was found to
depend on the type of bridge and the Cu–Cu separation [12]; a
possible structure was proposed for the polymer, based on these
studies and other spectroscopic data. This is the first report of
3-(aminomethyl)naphthoquinone dinuclear copper(II) complexes.
2. Experimental
2.1. Materials and physical measurements
Solvents (Vetec), 2-hydroxy-1,4-naphthoquinone, CuCl2ꢀ2H2O
* Corresponding author. Tel.: +55 21 26292225; fax: +55 21 26292236.
E-mail address: mdvargas@vm.uff.br (M.D. Vargas).
(Aldrich) and 2-aminomethylpyridine (Acros) were used as supplied.
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.07.011

A.P. Neves et al. / Polyhedron 29 (2010) 2884–2891
2885
Table 1
Benzaldehyde (control) was washed with NaOH 1 mol/L and
Crystal data and structure refinement for 1b and 2.
distilled; triethylamine (Tedia Brazil) was distilled prior to use.
Microanalyses were performed using a Perkin–Elmer CHN 2400
microanalyser at Central Analítica – Instituto de Química, Univer-
sidade Federal de São Paulo, Brazil. Melting points were obtained
with use of a Mel-Temp II, Laboratory Devices – USA apparatus
and were uncorrected. Conductivity measurements were carried
out at 25 °C in acetonitrile using a Schott conductometer. IR spec-
tra (KBr pellets) were recorded on a FT-IR spectrum One (Perkin–
Elmer) spectrophotometer. 1H and 13C NMR spectra were recorded
with a Varian Unit Plus 300 MHz spectrometer in deuterated
CDCl3; chemical shifts were reported in parts per million (ppm)
relative to an internal standard of Me4Si. The hydrogen signals
1b
2
Empirical formula
Formula weight
T (K)
C
46H36N4O7Cl2Cu2
C29H25N4O3Cl3Cu2, H2O
724.98, 18.02
295(2)
0.71073
Monoclinic, P21/c
954.77
295(2)
Radiation, k (Å)
Crystal system, space
group
0.71073
Monoclinic, P21/c
Unit cell dimensions
a (Å)
b (Å)
A = 7.5917(15)
24.551(5)
25.041(5)
98.25(3)
4618.9(16)
4, 1.373
A = 13.256(3)
10.807(2)
21.623(4)
94.53(3)
3088.0(11)
4, 1.598
c (Å)
b (°)
V (Å3)
1
were attributed through coupling constant values and 1H ꢃ H –
Z, calculated density
(g cmꢁ3
)
COSY experiments. Electronic spectra were taken on a Cary 50
(Varian) spectrophotometer using spectroscopic grade solvents
(Tedia Brazil) in 10ꢁ3 and 10ꢁ4 mol/L solutions. Electron paramag-
netic resonance (EPR) spectra of the solid samples were obtained
at liquid nitrogen temperature (77 K), on a Bruker ESP300E equip-
ment with modulation frequency of 100 kHz, operating at 9.5 GHz
(X-band). Variable temperature magnetic susceptibility measure-
ments were carried out using samples of a few mg of compounds
1a, 1b and 2 using a Cryogenic Sx600 SQUID magnetometer oper-
ating at temperatures from 1.8 to 300 K. The susceptometer was
calibrated with YFeGarnet NIST standard. Cyclic voltammetry
experiments were carried out with a BAS Epsilon potentiostat–gal-
vanostat system controlled by software using spectroscopic aceto-
nitrile (Tedia Brazil) in 10ꢁ3 mol/L solutions. The electrochemical
cell was a conventional one with three electrodes: Ag/AgCl was
used as reference electrode, a platinum wire as the auxiliary elec-
trode and glassy carbon as the working electrode. Tetrabutylam-
monium hexafluorophosphate (Bu4NPF6) in acetonitrile was used
as supporting electrolyte at 0.1 mol/L, and the whole cell was
deoxygenated by argon. The ferrocene/ferrocenium (FcH/FcH+)
couple was used as an internal reference (E1/2 372 mV versus Ag/
Ag+; E1/2 0.40 V versus NHE) [13].
Absorption coefficient
(mmꢁ1
F(0 0 0)
Crystal size (mm)
Theta range (°)
Index range
1.089
1.679
)
1952
1512
0.50 ꢃ 0.20 ꢃ 0.08
2.84–25.00
ꢁ9 6 h 6 8,
ꢁ28 6 k 6 29,
ꢁ29 6 l 6 29
68 633
0.11 ꢃ 0.06 ꢃ 0.06
3.01–25.50
ꢁ16 6 h 6 16,
ꢁ13 6 k 6 13,
ꢁ26 6 l 6 26
64 394
Reflections collected
Independent reflections 8093 [0.0593]
[R(int)
5739 [0.0993]
]
Completeness to theta
maximum
Maximum and
minimum
transmission
Refinement method
99.7
99.8
0.9179 and 0.6120
0.9016 and 0.8407
Full-matrix least-
squares on F2
8093/0/574
full-matrix least-squares
on F2
5739/0/390
Data/restraints/
parameters
Goodness-of-fit (GOF)
1.017
1.040
on F2
Final R indices
[I > 2r(I)]
R1 = 0.0453
R1 = 0.0377
wR2 = 0.0948
R1 = 0.0746
wR2 = 0.0678
R1 = 0.0669
R indices (all data)
wR2 = 0.1048
0.455 and ꢁ0.441
wR2 = 0.0745
0.294 and ꢁ0.293
Largest difference peak
and hole (e Åꢁ3
)
2.2. X-ray crystallography
Singles crystals were fixed on a glass fiber for the X-ray data col-
lection. Crystal data and structure refinement for complexes 1b
and 2 are show in Table 1.
Fourier difference map and refined freely with an isotropic dis-
placement parameter.
X-ray diffraction data of complexes were collected from a Bru-
The solution and refinement of 1b revealed the presence of four
water molecules as crystallization solvates. The hydrogen atom
coordinates corresponding to those water molecules could not be
located experimentally in the Fourier map. For this reason, the
SQUEEZE procedure contained in the PLATON program [21] was car-
ried out to exclude the electronic density contributions relative to
the water molecules. This is valid because the water molecules are
not part of the assembly of the organized network. Before the
SQUEEZE procedure, these water molecules occupied 707.6 Å3 in
the unit cell; after this procedure, which involved the exclusion
of 69 electrons per unit cell, this space is void.
ker KAPPA CCD diffractometer [14], at 295 K and Mo Ka monochro-
matic-graphite radiation. Cell parameters for 1b and 2 were
obtained using PHICHI [15] and refined by DIRAX [16]. The collected
reflections were reduced with EVALCCD [17] and corrected by Lorentz
polarization and absorption with SADABS [18]. Both molecular struc-
tures were solved by SHELXS-97 [19], via Patterson method and re-
fined on F2 with anisotropic temperature parameters for all non
H atoms used SHELXL-97 [20].
For 1b and 2 the positional parameters of the H atoms bonded
to C atoms in the aromatic rings were obtained geometrically, with
the C–H distances fixed in 0.93 Å for Csp2, and refined as riding on
their respective C atoms, with Uiso(H) = ꢁ1.2 Ueq(Csp3). H atoms
bonded to C atoms in the methylene moiety were obtained geo-
metrically with C–H distances fixed in 0.97 Å for Csp3 and with
Uiso(H) = ꢁ1.2 Ueq(Csp3). H atom bonded to C atoms in the meth-
yne moiety were obtained geometrically with C–H distances fixed
in 0.98 Å for Csp3 and with Uiso(H) = ꢁ1.2Ueq(Csp3). The positional
parameters of H atoms bonded to nitrogen atoms were obtained
from a Fourier difference map and refined freely with an isotropic
displacement parameter.
2.3. Synthesis of the compounds
2.3.1. Preparation of the ligand 3-[N-(2-pyridylmethyl)aminobenzyl]-
2-hydroxy-1,4-naphthoquinone (HL)
The Mannich base HL was synthesized according to methodol-
ogy recently described in the literature [4]. To a suspension of
2-hydroxy-1,4-naphthoquinone (Lawsone) (870 mg, 5 mmol) in
ethanol (15 mL), kept under stirring at 22 °C, were added the 2-
aminomethylpyridine (5.6 mL, 5.5 mmol) and, after about 5 min,
the benzaldehyde (6.6 mL, 6 mmol). The mixture was stirred at this
For 2 the positional parameters of H1, H3a and H3b atoms
bonded to N1 and N3 atoms, respectively, were obtained from a

2886
A.P. Neves et al. / Polyhedron 29 (2010) 2884–2891
temperature for 5 h, the bright orange solid was filtered, washed
with ethanol and water and dried under vacuum. Yield: 1.253 g
(68%); m.p. 133–134 °C (with dec.). 1H NMR (CDCl3, 300 MHz,
ppm): d (ppm) 8.62 (ddd, J = 4.9, 1.7, 0.9 Hz, 1H, H22); 7.88 (dd,
J = 7.7, 1.3 Hz, 1H, H5 or H8); 7.78 (dd, J = 7.7, 1.4 Hz, 1H, H8 or
H5); 7.70 (td, J = 7.7, 7.7, 1.7 Hz, 1H, H24); 7.65–7.61 (m, 2H,
H25/H23); 7.52 (td, J = 7.7, 7.5, 1.4 Hz, 1H, H6 or H7); 7.40 (td,
J = 7.7, 7.5, 1.3 Hz, 1H, H7 or H6); 7.34–7.23 (m, 5H, Ph); 5.73 (s,
1H, H11); 4.48 (d, J = 14.7 Hz, 1H, H19); 4.24 (d, J = 14.7 Hz, 1H,
H190). 13C NMR (CDCl3, 75 MHz) d (ppm) 185.1, 181.9, 174.2,
151.8, 149.3, 137.1, 137.0, 133.8, 133.5, 131.1, 131.0, 128.8,
128.4, 128.0, 125.9, 125.4, 123.3, 122.7, 113.2, 60.7, 49.7. IR (KBr,
2 in similar yields. Yield 48 mg (67%). m.p. 150 °C (with dec.). IR
(KBr,
max/cmꢁ1): 3448 (O–H), 3152 (N–H), 3034 (C–H), 1677
(C@O), 1662 (C@O), 1610 (C@N), 1591 (C@C), 1553 (d N–H),
1277 (C–O/C–N), 1221 (C–O/C–N). UV–Vis [CHCl3; k/nm (log )]:
279 (4.33), 322 (3.81), 428 (3.52), 654 (2.38). UV–Vis [CH3CN; k/
nm (log )]: 263 (4.64), 316 (3.78), 411 (3.46), 687 (2.40). Anal.
Calc. for C29H25N4O3Cl3Cu2.CH3OH: C, 48.49; H, 3.93; N, 7.54.
Found: C, 48.45; H, 3.91; N, 7.58%. Complex 2 could also be
obtained from decomposition of HL: to a suspension of HL
(0.25 mmol; 92 mg) in methanol (15 mL) was added a solution of
CuCl2ꢀ2H2O (0.25 mmol; 43 mg) in 2 mL of methanol, resulting in
a clear dark green solution. The solution was left stirring at 30 °C
for 1 h. The green 1a precipitate was filtered off (yield 30 mg,
24%). Slow evaporation of the solvent yielded green hexagonal
crystals of complex 2 which were adequate for X-ray analysis
(Yield: 10 mg, 6%).
m
e
e
m
max/cmꢁ1): 3435 (O–H), 3062 (C–H), 2967 (C–H), 1679 (C@O),
1591 (C@N/C@C), 1570 (C@C), 1527 (d N–H), 1476 (C@C), 1278
(C–O/C–N), 1229 (C–O/C–N). UV–Vis [CHCl3; k/nm (log )]: 267
e
(4.05), 329 (3.12), 431 (2.96). Anal. Calc. for C23H18N2O3.0.5 H2O:
C, 72.74; H, 5.00; N, 7.38. Found C, 72.68; H, 5.07; N, 7.79%.
3. Results and discussion
2.3.2. Preparation of the complexes [Cu(L)Cl)]n (1a) and
[Cu(L)(H2O)(l-Cl)Cu(L)Cl] (1b)
3.1. Synthesis
To a suspension of HL (92 mg; 0.25 mmol) in methanol (15 mL)
was added a solution of CuCl2ꢀ2H2O (43 mg; 0.25 mmol) in 2 mL of
methanol at 30 °C, resulting in a clear dark green solution. A few
minutes after the addition of Et3N (0.035 mL; 0.25 mmol) precipi-
tation of a green solid was observed. This compound was filtered
off, washed with cold methanol and dried under vacuum. Elemen-
tal analysis suggested the following composition: [Cu(L)Cl)].2H2O
The Mannich base HL is synthesized by the one-pot Mannich
condensation between 2-hydroxy-1,4-naphthoquinone (Lawsone),
2-aminomethylpyridine and benzaldehyde (HL, 68%) (Scheme 1).
The resulting bright orange powder is soluble in CHCl3, CH2Cl2,
DMSO and slightly soluble in alcohols. HL undergoes decomposi-
tion in solution, but is stable is the solid state. Rapid recrystalliza-
tion from ethanol gave analytically pure samples which were
characterized by elemental analysis, IR, UV–Vis, 1H NMR, and 13C
NMR spectroscopy.
The reaction of 3-[N-(2-pyridylmethyl)aminobenzyl]-2-hydro-
xy-1,4-naphthoquinone HL with CuCl2ꢀ2H2O and Et3N (1:1:1), in
methanol (0.017 mol/L final concentrations of HL and Cu2+) at
30 °C results in the immediate precipitation of a light green solid
1a (57%) which analyses as [Cu(L)Cl)].2H2O. If the reaction mixture
is left stirring for a further 5 h darkening is observed and the dark
green solid 1b isolated by filtration (55%) analyses as [Cu(L)Cl]ꢀ
0.5H2O. Compound 1b is obtained in up to 75% yield when the reac-
tion is carried out under higher concentration of the reagents
(0.044 mol/L). Recrystallization of 1a and 1b from methanol gives
identical dark green prismatic crystals of same composition as 1b.
X-ray diffraction analysis, revealed a di-copper(II) compound,
1a. Yield: 71 mg (57%). m.p. (with dec.) 207 °C. IR (KBr, mmax
/
cmꢁ1): 3445 (O–H), 3154 (N–H), 2941 (C–H), 1677 (C@O), 1611
(C@N), 1591 (C@C), 1547 (d N–H), 1487 (C@C), 1479 (C@C), 1277
(C–O/C–N). UV–Vis [CHCl3; k/nm (log
426 (3.59), 667 (2.47). UV–Vis [CH3CN; k/nm (log
e
)]: 265 (4.77), 314 (4.00),
)]: 265 (4.70),
e
319 (3.91), 423 (3.65), 655 (2.54). Anal. Calc. for C23H17ClCuN2O3.2-
H2O: C, 54.76; H, 4.20; N, 5.55. Found: C, 54.00; H, 4.18; N, 5.44%.
When the reaction mixture was left stirring under the same condi-
tions for over 5 h darkening was observed. Elemental analysis of
the dark green solid 1b isolated after 24 h as described above sug-
gested the following composition: [Cu(L)Cl]ꢀ0.5H2O. Yield: 65 mg
(55%). m.p. 194 °C (with dec). IR (KBr, m
max/cmꢁ1): 3453 (O–H),
3135 (N–H), 2904 (C–H), 1674 (C@O), 1617 (C@N), 1588 (C@C),
1543 (d N–H), 1273 (C–O/C–N). UV–Vis [CHCl3; k/nm (log )]:
269 (4.79), 313 (4.07), 431 (3.73), 651 (2.52). UV–Vis [CH3CN; k/
nm (log )]: 265 (4.70), 319 (3.91), 423 (3.61), 655 (2.53). Anal.
e
e
[Cu(L)(H2O)(l-Cl)Cu(L)Cl] 1b (Scheme 2).
Calc. for C23H17ClCuN2O3ꢀ0.5H2O: C, 57.86; H, 3.80; N, 5.87. Found:
C, 58.65; H, 3.94; N, 6.03%. Best yields of compound 1b were ob-
tained when the reaction is scaled up and carried out under more
concentrated conditions: HL (740 mg; 2 mmol) and 45 mL total
volume of methanol (yield: 713 mg, 75%). Recrystallization of 1a
and 1b from methanol gave identical dark green prismatic crystals
When the reaction of HL with CuCl2ꢀ2H2O is carried out under
dilute conditions (0.017 mol/L), and in the absence of Et3N, at
30 °C, precipitation of some green 1a (24%) is observed after about
an hour. Slow evaporation of the mother liquor yields hexago-
nal shaped light green crystals of compound 2 and a greenish
yellow solution. X-ray diffraction analysis showed that complex
of same composition as 1b. m.p. 181 °C (with dec.). IR (KBr, mmax
/
[CuCl(L)(l-Cl)Cu(amp)Cl] (2), obtained in 6% yield, is a di-copper
cmꢁ1): 3428 (O–H), 3309 (N–H), 3170 (N–H), 2908 (C–H), 1666
species stabilized by one Lꢁ and one aminomethylpyridine (amp)
ligands. The latter ligand is formed as the result of hydrolysis of
HL, possibly catalyzed by Cu2+. Attempts at isolating the expected
hydrolysis product by column chromatography of the greenish yel-
low mother liquor on silica gel, with ethyl acetate as eluent, gave a
mixture of products, according to NMR spectroscopy. Under the
(C@O), 1615 (C@N), 1589 (C@C), 1550 (d N–H), 1481 (C@C), 1280
(C–O/C–N), 1226 (C–O/C–N). UV–Vis [CHCl3; k/nm (log
(4.75), 312 (4.03), 431 (3.69), 655 (2.49). UV–Vis [CH3CN; k/nm
(log )]: 265 (4.75), 319 (3.95), 423 (3.67), 655 (2.49). Anal. Calc.
e)]: 272
e
for C46H36Cl2Cu2N4O7: C, 57.86; H, 3.80; N, 5.87. Found: C, 58.00;
H, 3.77; N, 5.76%.
2.3.3. Preparation of the complex [CuCl(L)(l-Cl)Cu(amp)Cl] (2)
To a solution of CuCl2ꢀ2H2O (0.2 mmol; 34 mg) and 2-amino-
methylpyridine (0.2 mmol; 0.02 mL) in 5 mL of methanol was
added a suspension of complex 1b (0.05 mmol; 48 mg) in 10 mL
of methanol. After stirring for 16 h at 30 °C, the green precipitate
was filtered and washed with methanol. Crystals of complex 2
were obtained by slow evaporation of solution of the precipitate
in methanol. Furthermore, replacing 1b with 1a also gave complex
Scheme 1. Synthesis of proligand HL.

A.P. Neves et al. / Polyhedron 29 (2010) 2884–2891
2887
Scheme 2. Formation of complexes 1a and 1b.
same conditions but in the absence of Cu2+ HL also undergoes
decomposition to unidentified products. Best yield (30%) of com-
plex 2 is obtained when the reaction is carried out at 20 °C.
Complex 2 is best synthesized by addition of 1b to a solution
of amp and CuCl2ꢀ2H2O in methanol, the yields depending on
the temperature, concentration and proportion of the reagents.
At 30 °C, with 1b:aminomethylpyridine:CuCl2ꢀ2H2O = 1:2:2, com-
pound 2 is obtained in 40% yield. With a twofold excess of amp
and CuCl2ꢀ2H2O, however, the product is isolated in 67%. Further-
more, replacing 1b with 1a also gives complex 2 in similar yields.
These reactions are summarized in Scheme 3.
Fig. 1. View of the ORTEP-3 [24] projection of [Cu(L)(H2O)(
l
-Cl)Cu(L)Cl] (1b)
showing the
50% level.
p stacking of the naphthoquinone rings. Displacement ellipsoids at the
labelling scheme used. Selected bond distances and angles with
estimated standard deviations are listed in Table 2 and hydrogen
bond parameters are reported in Table S1 (Supporting infor-
mation).
The structure of compound 1b reveals two copper(II) centers
bridged by a chloro ligand and bonded to two chelating Lꢁ via
the naphthalen-2-olate oxygen, a pyridine and an amine nitrogens.
Both metal centers exhibit approximate square-pyramidal (spy)
geometry, with the apical positions occupied by Cl(1). The value of
3.2. Crystal structures of [Cu(L)(H2O)(l-Cl)Cu(L)Cl] (1b) and
[CuCl(L)( -Cl)Cu(amp)Cl] (2)
l
the trigonality index
and = one, to a trigonal bipyramidal (tbp) structure) is 0.033 for
Cu(1) [where b represents the angle N(1)–Cu(1)–O(1) and
s [22] (s = zero corresponds to a spy geometry
Complexes 1b and 2 were studied by X-ray diffraction. Com-
pound 1b crystallizes from methanol as bright-green prisms. The
molecular structure of 1b is shown in Fig. 1 together with the
s
a
,
Scheme 3. Synthesis of complex 2 from 1b (A) and hydrolysis of HL with formation of complex 2 (B).

2888
A.P. Neves et al. / Polyhedron 29 (2010) 2884–2891
Table 2
Table 3
Selected bond lengths (Å) and angles (°) for complex 1b.
Selected bond lengths (Å) and angles (°) for complex 2.
Cu(1)–O(1)
Cu(1)–N(2)
Cu(1)–N(1)
Cu(1)–O(1W)
Cu(1)–Cl(1)
Cu(2)–O(4)
Cu(2)–N(4)
Cu(2)–N(3)
Cu(2)–Cl(2)
Cu(2)–Cl(1)
Cu(1)ꢀ ꢀ ꢀCu(2)
1.950(2)
1.997(3)
2.005(3)
2.016(2)
2.4982(10)
1.988(2)
2.018(3)
2.031(3)
2.2782(11)
2.5698(10)
4.1342(8)
N(2)–Cu(1)–O(1W)
O(1)–Cu(1)–N(1)
N(2)–Cu(1)–N(1)
O(1)–Cu(1)–N(2)
N(4)–Cu(2)–N(3)
O(4)–Cu(2)–N(4)
O(4)–Cu(2)–N(3)
N(4)–Cu(2)–Cl(2)
Cu(1)–Cl(1)–Cu(2)
162.61(12)
164.61(9)
83.04(11)
88.12(10)
83.24(12)
85.86(9)
161.87(10)
165.05(9)
109.31(4)
Cu(1)–N(2)
Cu(1)–N(1)
Cu(1)–O(1)
Cu(1)–Cl(2)
Cu(1)–Cl(3)
Cu(2)–N(3)
Cu(2)–N(4)
Cu(2)–O(1)
Cu(2)–Cl(1)
Cu(2)–Cl(2)
Cu(2)–O(2)
Cu(1)–Cu(2)
Cu(1)ꢀ ꢀ ꢀCu(2)
2.009(2)
2.012(2)
2.0308(19)
2.2820(10)
2.5402(10)
2.009(3)
N(4)–Cu(2)–O(1)
N(3)–Cu(2)–Cl(1)
O(1)-Cu(2)–Cl(2)
N(2)–Cu(1)–O(1)
N(1)–Cu(1)–Cl(2)
O(1)–Cu(1)–Cl(2)
Cu(1)–Cl(2)–Cu(2)
Cu(1)–O(1)–Cu(2)
167.70(9)
173.53(8)
76.78(6)
160.76(9)
173.46(8)
88.76(6)
83.31(3)
109.70(9)
2.018(3)
2.063(2)
2.2684(10)
2.7295(9)
2.470(2)
3.3476(9)
3.3476(9)
N(2)–Cu(1)–O(1W)] and 0.053, for Cu(2) [where b represents the
angle Cl(2)–Cu(2)–N(4) and , O(4)–Cu(2)–N(3)]. The coordination
a
The structural motif exhibited in this complex is uncommon,
although there are four other structurally characterized copper(II)
complexes of nitrogen donor-based ligands containing both a
bridging phenolate anion and a chloride anion in which similar
Cu(II)–Cu(II) distances were encountered [27]. Both metal centers
spheres of Cu(1) and Cu(2) are completed with a water molecule
and a chlorine atom, respectively. The Cu(1) and Cu(2) centers
deviate from their mean equatorial planes O(1)/N(2)/N(1)/O(1w)
and O(4)/N(4)/N(3)/Cl(2) by 0.0323 and 0.0006 Å, respectively,
and the dihedral angle between the two equatorial planes is
70.01(8)°. To our knowledge this is the first dinuclear copper (II)
structure with this structural motif, although an analogous di-
exhibit approximate square-pyramidal geometry, with
Cu(1) of 0.045 [where b represents the N(1)–Cu(1)–Cl(2) angle
and , N(2)–Cu(1)–O(1)] and of 0.097, for Cu(2) [where b repre-
sents the Cl(1)–Cu(2)–N(3) angle and , O(1)–Cu(2)–N(4)].
ꢁ interacts further with Cu(1) via the pyridine and amine nitro-
s, for
a
l-chloro-di-l-imidazolato-tetracopper(II) complex has been de-
a
scribed in the literature [23].
L
The packing contains molecules connected by classical and non
classical hydrogen bonds, building an infinite 3D network via
intermolecular weak directional forces along the [1 0 0], [0 1 0]
and [0 0 1] crystallography directions, see Fig. S2 and Table S1
(Supporting information).
Compound 2 crystallizes from methanol as dark-green hexa-
gons. The molecular structure of 2 is presented in Fig. 2 together
with the labelling scheme used. Selected bond distances and angles
with estimated standard deviations are presented in Table 3 and
hydrogen bond parameters, in Table S2 (Supporting information).
The molecular structure of compound 2 contains two copper(II)
atoms bridged asymmetrically by a chloride and by the Lꢁ naph-
thalen-2-olate oxygen. The Cu–Cl distance values are similar to
those found in other pentacoordinate copper(II) complexes that
contain bridging phenoxy oxygen atoms [11,25,26]. The two cop-
per(II) centers are separated by 3.3476(9) Å.
gens forming a five membered chelate ring N(2)/C(19)/C(18)/N(1)/
Cu(1) that deviates from the plane of fitted atoms (r.m.s) by
0.0807 Å. All amine–Cu(II) and pyridine–Cu(II) bond distances are
within the normal range observed in other copper(II) complexes
of aminomethylpyridine and analogous ligands. The coordination
sphere of Cu(1) is completed by Cl(3) located in the apical position
of the square based pyramid. Cu(2) also contains a chloride in the
apical position and is bonded to an aminomethylpyridine ligand,
the chelate ring N(4)/C(28)/C(29)/N(3)/Cu(2) deviating from the
plane of fitted atoms by 0.1351 Å. Finally, Cu(2) also interacts
weakly with the carbonyl oxygen of Lꢁ [Cu(2)–O(2) 2.470(2) Å];
this interaction does not lead to lengthening of the carbonyl bond
[O(2)–C(2) 1.229(3) Å], compared with that of the carbonyl in the
para position [O(3)–C(9) 1.231(4) Å]. The Cu(1) and Cu(2) centers
deviate from their mean equatorial planes (O(1)/Cl(2)/N(2)/N(1))
and (Cl(1)/N(4)/N(3)/O(1)) by 0.1000 and 0.1234 Å, respectively,
and the dihedral angle between the two equatorial planes is
89.56(6)°.
The crystal structure contains molecules related by the axial
c-glide plane and 21 screw axis, building an infinite 2D network
via intermolecular weak directional forces along of (0 0 1) plane
(Fig. S3 Supporting information).
3.3. Conductivity measurements
The molar conductivity values for complexes 1a, 1b and 2 in
acetonitrile are 31.3, 10.7 and 17.2
X
ꢁ1 cm2 molꢁ1, respectively,
indicative of neutral complexes, according to the literature [28].
3.4. Electronic spectra
The UV–Vis spectra for complexes 1a, 1b and 2, in chloroform
and acetonitrile solutions at 10ꢁ4 mol/L (Figs. S5–S7 Supporting
information) exhibit three absorptions around 270, 310 and
430 nm. The intense band at 270 nm is assigned to ligand
p ?
p*
transitions. The other two bands between 310 and 430 nm are typ-
ical of ligand-to-metal charge transfer (LMCT) of the naphthoquin-
onate moiety to the metal ion. The d–d transition band can be
visualized in concentrated chloroform solutions at 10ꢁ3 mol/L,
around 650 nm, for the dinuclear complexes 1b and 2 and at 667
for 1a. These absorptions are consistent with a square-pyramidal
Fig. 2. View of an ORTEP-3 [24] projection of [CuCl(L)(l-Cl)Cu(amp)Cl] (2)
evidencing the asymmetrically bridged chloride and the chelate coordination.
Displacement ellipsoids at the 50% level.

A.P. Neves et al. / Polyhedron 29 (2010) 2884–2891
2889
geometry of the Cu(II) centres in these complexes [25,29,30].
When the spectrum of 1a is recorded in acetonitrile the d–d
transition band appears at 655 nm i.e. the spectrum is identical
to that of 1b thus indicating conversion of 1a into 1b in this sol-
vent. In the case of complex 2, the slight shift of the maximum of
655 nm in CHCl3 to 687 nm in acetonitrile may suggest distortion
of the geometry of the Cu(II) centers possibly by coordination of
the solvent to the metal ions and cleavage of the bridges.
tively, indicating that in both cases, in solution the two copper ions
exhibit different coordination environments, like in the solid state.
In addition, an extra sharp anodic peak around = ꢁ0.68 V versus
FcH/FcH+ is seen on the CV curve of complexes 1b and 2 which is
characteristic of a redissolution process of copper(0) on the elec-
trode surface [32]. The CV of complex 1a (Fig. S10, Supporting
information) is similar to that of 1b thus confirming the conversion
of 1a into 1b in acetonitrile solution, as observed in the electronic
spectra.
3.5. Electrochemical studies
3.6. Magnetic susceptibility studies and EPR
The redox behaviour of complexes 1a, 1b and 2 and of Mannich
base HL was evaluated by cyclic voltammetry (CV), at room tem-
perature, in acetonitrile/Bu4NPF6. The CVs, depicted in Fig. 3 (and
Figs. S8–S10 Supporting information), were obtained versus ferro-
cene/ferrocenium (FcH/FcH+).
The magnetization properties of all compounds have been stud-
ied to evaluate the magnetic interactions between the two copper
ions in 1b and 2 and specially the existence of Cu–Cu interactions
in compound 1a whose structure is unknown.
Variable temperature magnetic susceptibility measurements in
the 1.8–300 K temperature range, under a constant magnetic field
of 1 kOe were carried out and the results are presented in Figs. 4
The CV of Mannich base HL (Fig. S8, Supporting information) in
acetonitrile shows four quasi-reversible processes attributed to the
quinone groups of HL and of its deprotonated form L1ꢁ (E1/2(1)
=
and 5 and Fig. S13 Supporting information in the form of
v
mT versus
ꢁ0.385, E1/2(2) = ꢁ1.07, E1/2(3) = ꢁ1.01, E1/2(4) = ꢁ1.74 V). The irre-
versible waves at the positive range of the voltammogram can be
assigned to the self-protonation processes of the species in
solution as described in the literature [31]. The data obtained for
complexes 1a, 1b and 2 are summarized in Table 4.
T plots where
vm is the molar susceptibility. Data were corrected for
The voltammograms of the three complexes show only one
characteristic wave for the quinone portion of Lꢁ (Ep1/2(3) around
ꢁ1.60 V), thus confirming, in solution, interaction via the naphtha-
len-2-olate oxygen in the three cases. In the voltammograms of
complexes 1b and 2 (Fig. S9, Supporting information and Fig. 3,
respectively) two irreversible peaks are observed and assigned to
the CuII,CuII ? CuII,CuI and CuII,CuI ? CuI,CuI processes, respec-
Fig. 4. Plot of
vmT vs. T per mol of crystalline sample of [Cu(L)(H2O)(l-Cl)Cu(L)Cl]
(1b). Full line is the best fit with Bleaney Bowers equation and 17% paramagnetic
contribution, from which J = ꢁ5.7 cmꢁ1
.
Fig. 3. Cyclic voltammogram of 2 in 0.1 mol/L Bu4NPF6/CH3CN obtained at 0.1 V/s
with a glassy carbon electrode, the potentials being referred to the ferrocene/
ferrocenium (FcH/FcH+) pair internal standard.
Table 4
Electrochemical data for 1b, 1a and 2, determined by cyclic voltammetry in
acetonitrile at a glassy carbon electrode; scan rate 0.1 V/s; E vs. ferrocene/ferroce-
nium (FcH/FcH+) pair internal standard.
Compound
Ep1c (V)
Ep2c (V)
Ep1/2(3) (V)
1a
1b
2
ꢁ0.67
ꢁ0.63
ꢁ0.83
ꢁ1.13
ꢁ1.09
ꢁ1.21
ꢁ1.55
ꢁ1.54
ꢁ1.60
Fig. 5. Plot of
v vs. T per mol of crystalline sample of [CuCl(L)(l-Cl)Cu(amp)Cl] (2).
Inset: mT vs. T plot, with a maximum at 105 K.
v

2890
A.P. Neves et al. / Polyhedron 29 (2010) 2884–2891
Table 5
gelatine capsule sample holder as well as for diamagnetic and tem-
perature independent paramagnetism contributions.
EPR parameters for complexes 1a, 1b and 2.
Complex
A\ (ꢃ10ꢁ4 cmꢁ1
)
A// (ꢃ10ꢁ4 cmꢁ1
)
g\
g//
The data for a crystalline sample of 1b from which a crystal was
selected for the X-ray diffraction study show that
vmT remains
1a
1b
2
2.0635
2.0700
2.0450
2.1880
2.1250
2.2050
constant over most of the temperature range, at its 300 K value
25
65
of 0.83 cm3 K molꢁ1, consistent with two magnetically isolated CuII
(S = ½) centers in the molecule (Fig. 4). Below 50 K, the
vmT prod-
uct decreases to reach a value of 0.2 cm3 K molꢁ1 at 2 K. This
behaviour is typical of an antiferromagnetically weakly coupled
copper pair. The coupling constant, J = ꢁ5.7 cmꢁ1, was estimated
Values for g\ larger than those observed for g// are consistent
with a tetragonally elongated square-pyramidal geometry around
the copper(II) ions in the three complexes, in agreement with the
X-ray structures of 1b and 2 [25,29,37]. The very low parallel com-
ponent of the hyperfine coupling constant (not resolved in the
spectra of the 1a and 2) has been explained by considering a mix-
from a fit of
v
ꢃ T data with the Bleaney Bowers equation and a
monomer or impurity term (see Supporting information). The data
obtained for a sample of 1b before recrystallization is identical to
that described above for the crystalline sample of 1b. To our
knowledge, there is no report in the literature of a dinuclear copper
complex linked by only one chloro bridge. Dinuclear complexes
containing two chloro bridges have been described [25,33] and in
all cases magnetic couplings were found weaker than for the anal-
ogous complexes containing phenolate bridges, as the result of
weaker overlap between the copper(II) orbitals.
ture of the dz2 and dx2
orbitals as the ground state [38].
ꢁy2
4. Conclusions
Three novel copper(II) complexes of the Mannich base 3-[N-(2-
pyridylmethyl)aminobenzyl]-2-hydroxy-1,4-naphthoquinone HL
were synthesized and fully characterized both in the solid state
and in solution. The complexation reactions were found to depend
on the reaction conditions, in part because of the facile decompo-
sition of HL upon standing in solution. Marked differences in prod-
ucts solubility were also responsible for drastic changes in product
distribution and yields upon varying the reagents concentration. In
spite of the lability of this proligand, the monoanion Lꢁ acted as a
versatile tridentate donor allowing formation of interesting com-
plexes with different structural arrangements. By careful choice
and monitoring of the reaction conditions reasonable yields of each
of the products could be obtained. The X-ray diffraction studies re-
vealed two dinuclear copper(II) complexes 1b and 2 with approx-
imate square-pyramidal geometries around the metal ions,
complex 1b presenting an uncommon structural motif with a sin-
gle chloro- bridge. Both complexes 1b and 2 presented antiferro-
magnetic interactions, but as expected on the basis of their solid
state structures, significant differences in coupling constants, J
were observed. As for other systems, both the nature of the bridge
and the Cuꢀ ꢀ ꢀCu distance in these dimers exert significant influence
on the J values. Based on the magnetic susceptibility data a possi-
ble structural arrangement consisting of a polymeric structure con-
nected by Cu–Cl–Cu bridges was proposed for complex 1a.
As expected the
cates strong antiferromagnetic coupling between the copper ions
and exhibits a maximum of around 105 K (Fig. 4). Below 10 K a
Curie tail is observed which is frequently ascribed to paramagnetic
impurity [34]. A rough estimate of the coupling constant was ob-
vmT versus T curve obtained for complex 2 indi-
v
tained from the maximum of
v
ꢃ T, J ꢂ ꢁ120 cmꢁ1, which is much
larger than for complex 1b, due to the presence of both naphtha-
len-2-olate and chloride bridges which maintain the two copper
ions at closer proximity [3.3476(9) ꢃ 4.1342(8) Å]. Studies have
shown that short Cu–O bonds and large Cu–O–Cu angles in
square-pyramidal phenolate-bridged Cu dimers result in strong
overlap of dx2
orbitals and thus produce strong antiferromag-
ꢁy2
netic couplings [25,29,35]. Copper(II) dimers with both halide
and phenolate bridges have been shown to exhibit strong antifer-
romagnetic coupling constants around ꢁ100 cmꢁ1 [34]. The short
Cu–O bonds relative to the long Cu–X bonds point at a dominant
coupling through the phenolate bridge [34] which explains the
stronger coupling constant observed for complex 2 as compared
to 1b that contains only one chloro bridge.
The
sor of dimer 1b), illustrated in Fig. S11 Supporting information,
shows a
mT of 0.44 cm3 K molꢁ1 around room temperature, which
vmT versus T curve obtained for compound 1a (the precur-
v
increases as T is lowered, indicating ferromagnetic interaction. A
good fit to the Bleaney Bowers equations with J/kB = 10.5 K could
be obtained above the maximum at 5 K. Below this maximum,
Acknowledgements
vmT starts to decrease, suggesting weaker antiferromagnetic inter-
dimer interactions. Such behaviour could be explained by two dif-
ferent models. Either this compound exhibits an infinite 1D
coordination polymeric structure in which the copper(II) centers
are connected by Cl–Cuꢀ ꢀ ꢀCl bridges, similar to those found for
The authors thank the Brazilian agencies ‘Conselho Nacional de
Desenvolvimento Científico e Tecnológico’ (CNPq), ‘Coordenação
de Aperfeiçoamento de Pessoal de Nível Superior’ (CAPES) and
‘Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro’ (FA-
PERJ) for financial support. Pronex-FAPERJ (Grant Number E-26/
171.512/2006) is acknowledged. M.D. Vargas and A.P. Neves are
recipients of CNPq research fellowships. A. Casellato was benefited
with CAPES fellowships. We also thank the X-ray diffraction labo-
ratory (LDRX) of Universidade Federal Fluminense for data
collection.
N-(2-pyridylmethyl)-L-glycine (Hpgly) and N-(2-pyridylmethyl)-L-
alanine (Hpala) copper(II) complexes, namely [Cu(pgly)Cl]ꢀH2O
and [Cu(pala)Cl]ꢀH2O, respectively, for which no magnetic data
have been reported [36]. The Cl–Cuꢀ ꢀ ꢀCl-chain would present
predominant ferromagnetic interactions increasing the effective
moment, and a weak antiferromagnetic interaction forming an
alternating linear chain. The other possibility is the presence of
antiferromagnetic interchain interactions between ferromagnetic
chains which would be responsible for the decrease of
vmT below
Appendix A. Supplementary data
4 K. Unfortunately, crystals of 1a suitable for an X-ray diffraction
study could not be obtained to prove either model, since this com-
pound rearranges into 1b in solution.
Powder X-Band (9.5 GHz) EPR spectra of powdered samples of
1a, 1b and 2 were collected at 77 K. Table 5 presents the EPR
parameters for the three complexes.
CCDC 726553 and 726554 contain the supplementary crystallo-
graphic data for 2 and 1b. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with this

A.P. Neves et al. / Polyhedron 29 (2010) 2884–2891
2891
[17] A.J.M. Duisenberg, L.M.J. Kroon-Batenburg, A.M.M. Schreurs, J. Appl.
Crystallogr. 36 (2003) 220.
[18] G.M. Sheldrick, SADABS, Program for Empirical Absorption Correction of Area
Detector Data, University of Göttingen, Germany, 1996.
[19] G.M. Sheldrick, SHELXS97, Program for Crystal Structure Solution, University of
Göttingen, Germany, 1997.
article can be found, in the online version, at doi:10.1016/
j.poly.2010.07.011.
References
[20] G.M. Sheldrick, SHELXL97, Program for Crystal Structure Refinement, University
of Göttingen, Germany, 1997.
[21] A.L. Spek, J. Appl. Crystallogr. 36 (2003) 7.
[22] A.W. Addison, T.N. Rao, J. Reedjik, J. Van Rijn, G.C. Vershcoor, J. Chem. Soc.,
Dalton Trans. (1984) 1349.
[23] H.-L. Zhu, L.-M. Zheng, D.-G. Fu, P. Huang, W.-M. Bu, W.-X. Tang, Inorg. Chim.
Acta 287 (1999) 52.
[24] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[25] X.H. Bu, M. Du, L. Zhang, Z.L. Shang, R.H. Zang, H. Shionoya, J. Chem. Soc.,
Dalton Trans. (2001) 729.
[26] (a) M. Vaidyanathan, M. Palaniandavar, R.S. Gopalan, Inorg. Chim. Acta 324
(2001) 241;
(b) D. Kong, J. Mao, A.E. Martell, A. Clearfield, Inorg. Chim. Acta 342 (2003)
260;
(c) Y. Xie, Q. Liu, H. Jiang, J. Ni, Eur. J. Inorg. Chem. (2003) 4010.
[27] (a) S.P. Foxon, D. Utz, J. Astner, S. Schindler, F. Thaler, F.W. Heinemann, G.
Liehr, J. Mukherjee, V. Balamurugan, D. Ghoshc, R. Mukherjee, Dalton Trans.
(2004) 2321;
[1] R.H. Thompson, Naturally Occurring Quinones IV: Recent Advances,
Champman & Hall, London, 1997.
[2] T.W. Goodwin, E.I. Mercer, Introduction to Plant Biochemistry, Pergamon Press,
New York, 1972.
[3] (a) C.G. Pierpont, Coord. Chem. Rev. 216–217 (2001) 99;
(b) K. Yamada, H. Tanaka, S. Yagishita, K. Adachi, T. Uemura, S. Kitagawa, S.
Kawata, Inorg. Chem. Commun. 45 (2006) 4322.
[4] A.P. Neves, C.C. Barbosa, S.J. Greco, M.D. Vargas, L.C. Visentin, C.B. Pinheiro, A.S.
Mangrich, J.P. Barbosa, G.L. da Costa, J. Braz. Chem. Soc. 20 (2009) 712.
[5] (a) N.H. Gokhale, K. Shirisha, S.B. Padhye, S.L. Croft, H.D. Kendrick, V. Mckee,
Bioorg. Med. Chem. Lett. 16 (2006) 430;
(b) N.H. Gokhale, K. Shirisha, S.B. Padhye, S.L. Croft, H.D. Kendrick, W. Davies,
C.E. Anson, A.K. Powell, J. Inorg. Biochem. 95 (2003) 249;
(c) J. Chen, Y. Huang, G. Liu, Z. Afrasiabi, E. Sinn, S. Padhye, Y. Ma, Toxicol. Appl.
Pharmacol. 197 (2004) 40;
(d) A.I. Francisco, M.D. Vargas, T.P. Fragoso, J.W.M. Carneiro, A. Casellato, F.C.
Silva, V.F. Ferreira, J.P. Barbosa, C. Pessoa, L.V. Costa-Lotufo, J.D.B. Marinho
Filho, M.O. Moraes, A.S. Mangrich, J. Braz. Chem. Soc. 21 (2010) 1293;
(e) A.P. Neves, G.B. Silva, M.D. Vargas, C.B. Pinheiro, L.C. Visentin, J.D.B.
Marinho Filho, A.J. Araújo, L.V. Costa-Lotufo, C. Pessoa, M.O. Moraes, Dalton
Trans., doi:10.1039/C0DT00572J.
(b) P. Kamaras, M.C. Cajulis, M. Rapta, G. Brewer, G.B. Jameson, J. Am. Chem.
Soc. 116 (1994) 10334;
(c) K.D. Karlin, A. Farooq, J.C. Hayes, B.I. Cohen, T.M. Rowe, E. Sinn, J. Zubieta,
Inorg. Chem. 26 (1987) 1271;
[6] S.Y. Salunke-Gawali, V.G. Rane, C. Puranik, Guyard-Duhayon, F. Varret,
Polyhedron 23 (2004) 2541.
[7] P. Garge, R. Chikate, S. Padhye, J. Savariault, P. de Loth, J. Tuchagues, Inorg.
Chem. 29 (1990) 3315.
[8] S. Salunke-Gawali, R. Dalvi, K. Ah, S. Rane, J. Therm. Anal. Calorim. 76 (2004)
801.
[9] (a) S. Rane, S. Gawali, S. Padhye, Indian J. Chem. 42A (2003) 255;
(b) S.Y. Rane, E.M. Khan, D.R. Thube, S.B. Padhye, S.K. Date, P.P. Bakare, Indian J.
Chem. 39A (2000) 1117.
[10] R. Gupta, S. Mukherjee, R. Mukherjee, J. Chem. Soc., Dalton Trans. (1999)
4025.
[11] L. Rodríguez, E. Labisbal, A. Sousa-Pedrares, J.A. García-Vázquez, J. Romero,
M.L. Durán, J.A. Real, A. Sousa, Inorg. Chem. 45 (2006) 7903.
[12] (a) V.H. Crawford, H.W. Richardson, J.R. Wasson, D.J. Hodgson, W.E. Hatfield,
Inorg. Chem. 15 (1976) 2107;
(b) A. Asokan, B. Varghese, P.T. Manoharan, Inorg. Chem. 38 (1999) 4393.
[13] R.R. Gagne, C.A. Koval, G.C. Lisensky, Inorg. Chem. 19 (1980) 2854.
[14] Nonius, COLLECT, Nonius BV, Delft, The Netherlands, 1998.
[15] A.J.M. Duisenberg, R.W.W. Hooft, A.M.M. Schreurs, J. Kroon, J. Appl. Crystallogr.
33 (2000) 893.
(d) R.J. Majeste, C.L. Klein, E.D. Stevens, Acta Crystallogr., Sect. C 39 (1983) 52.
[28] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[29] S. Torelli, C. Belle, I. Gautier-Luneau, J.L. Pierre, E. Saint-Aman, J.M. Latour, L.L.
Pape, D. Luneau, Inorg. Chem. 39 (2000) 3526.
[30] S.J. Brudenell, L. Spiccia, E.R.T. Tiekink, Inorg. Chem. 35 (1996) 1974.
[31] C. Frontana, I. Gonzalez, J. Electroanal. Chem. 603 (2007) 155.
[32] D. Zurita, C. Scheer, J.L. Pierre, E. Saint-Aman, J. Chem. Soc., Dalton Trans.
(1996) 4331.
[33] M. Rodríguez, A. Llobet, M. Corbella, A.E. Martell, J. Reibenspies, Inorg. Chem.
38 (1999) 2328.
[34] I.A. Koval, M. Huisman, A.F. Stassen, P. Gamez, O. Roubeau, C. Belle, J.L. Pierre,
E. Saint-Aman, M. Lüken, B. Krebs, M. Lutz, A.L. Spek, J. Reedijk, Eur. J. Inorg.
Chem. (2004) 4036.
[35] (a) L. Merz, W. Haase, J. Chem. Soc., Dalton Trans. (1980) 875;
(b) W.E. Marsh, W.E. Hatfield, D.J. Hodgson, Inorg. Chem. 21 (1982) 2679.
[36] X. Wang, J.D. Ranford, J.D. Jagadese, J. Vittal, J. Mol. Struct. 796 (2006) 28.
[37] E. Guimarães, A.S. Mangrich, V.G. Machado, D.G. Traghetta, M.A. Lobo, J. Braz.
Chem. Soc. 12 (2001) 734.
[38] I.C. Mendes, J.P. Moreira, N.L. Speziali, A.S. Mangrich, J.A. Takahashi, H. Beraldo,
J. Braz. Chem. Soc. 17 (2006) 1571.
[16] A.J.M. Duisenberg, J. Appl. Crystallogr. 25 (1992) 92.