Alkoxo-bridged dinuclear and tetranuclear copper(II) complexes with Schiff-bases derived from benzoylacetone and 1,n-diamino-n′-hydroxyalkanes (n, n′ = 3, 2; 4, 2; and 5, 3)

Article abstract of DOI:10.1246/bcsj.75.2595

Alkoxo-bridged copper(II) complexes with N,N′-bis(1-methyl-3-hydroxy-3-phenyl-2-propen-1-ylidene)-1, 3-diamino-2-propanol (H₃bzacpro), N,N′-bis(1-methyl-3-hydroxy-3-phenyl-2-propen-l-ylidene)-1, 4-diamino-2-butanol (H₃bzacbu), and N,N′-bis(1-methyl-3-hydroxy-3-phenyl-2-propen-l-ylidene)-1, 5-diamino-3-pentanol (H₃bzacpen), [Cu₂(bzacpro)(CH₃CO₂)] (1), [Cu₄(bzacpro)₂(C₂H₅ O)₂] (2), [Cu₂(bzacbu)(CH₃CO₂)] (3), [Cu₄(bzacbu)₂(CH₃O)₂] (4), [Cu₄(bzacpen)₂(CH₃ CO₂)₂] (5), and [Cu₄(bzacpen)₂O]·H₂O (6) have been synthesized and characterized by measurements of the infrared and electronic spectra, and the magnetic susceptibilities. Single-crystal X-ray analyses revealed that 1 and 3 are dinuclear copper(II) complexes having a dinuclear core bridged by an alkoxo-oxygen atom of bzacpro or bzacbu and acetato-oxygen atoms, whereas 2, 4, 5, and 6 are tetranuclear copper(II) complexes composed of μ-alkoxo(bzacpro)-μ-ethoxo-, μ-alkoxo(bzacbu)-μ-methoxo-, μ-alkoxo(bzacpen)- μ-acetato-, and μ-alkoxo(bzacpen)-μ-oxo-bridged units, respectively. Magnetic-susceptibility data show that an antiferromagnetic interaction is operative within the dinuclear or tetranuclear core in 1-3, 5 and 6, whereas a ferromagnetic coupling is operative in 4. The crystal structures of the three Schiff-base ligands have also been elucidated.

Full text of DOI:10.1246/bcsj.75.2595

c. Jpn.
© 2002 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 75, 2595–2607 (2002) 2595
e Chemical
ciety of Ja-
n
e Chemical
ciety of Ja-
n
Alkoxo-Bridged Dinuclear and Tetranuclear Copper(Ⅱ) Complexes
with Schiff-Bases Derived from Benzoylacetone and 1,n-Diamino-nꢀ-
hydroxyalkanes (n, nꢀ = 3, 2; 4, 2; and 5, 3)
Dinuclear and Tetranuclear Copper(Ⅱ) Complexes
M. Mikuriya et al.
02
95
Masahiro Mikuriya,* Kenichi Minowa, and Ryoji Nukada
07
Department of Chemistry, School of Science and Technology, Kwansei Gakuin University, Gakuen 2-1, Sanda 669-1337
(Received April 8, 2002)
SJA8
09-2673
089
Alkoxo-bridged copper(Ⅱ) complexes with N,Nꢀ-bis(1-methyl-3-hydroxy-3-phenyl-2-propen-1-ylidene)-1,3-
diamino-2-propanol (H3bzacpro), N,Nꢀ-bis(1-methyl-3-hydroxy-3-phenyl-2-propen-1-ylidene)-1,4-diamino-2-butanol
(H3bzacbu), and N,Nꢀ-bis(1-methyl-3-hydroxy-3-phenyl-2-propen-1-ylidene)-1,5-diamino-3-pentanol (H3bzacpen),
[Cu2(bzacpro)(CH3CO2)] (1), [Cu4(bzacpro)2(C2H5O)2] (2), [Cu2(bzacbu)(CH3CO2)] (3), [Cu4(bzacbu)2(CH3O)2] (4),
[Cu4(bzacpen)2(CH3CO2)2] (5), and [Cu4(bzacpen)2O]•H2O (6) have been synthesized and characterized by measure-
ments of the infrared and electronic spectra, and the magnetic susceptibilities. Single-crystal X-ray analyses revealed
that 1 and 3 are dinuclear copper(Ⅱ) complexes having a dinuclear core bridged by an alkoxo-oxygen atom of bzacpro or
bzacbu and acetato-oxygen atoms, whereas 2, 4, 5, and 6 are tetranuclear copper(Ⅱ) complexes composed of µ-
alkoxo(bzacpro)-µ-ethoxo-, µ-alkoxo(bzacbu)-µ-methoxo-, µ-alkoxo(bzacpen)-µ-acetato-, and µ-alkoxo(bzacpen)-µ-
oxo-bridged units, respectively. Magnetic-susceptibility data show that an antiferromagnetic interaction is operative
within the dinuclear or tetranuclear core in 1–3, 5 and 6, whereas a ferromagnetic coupling is operative in 4. The crystal
structures of the three Schiff-base ligands have also been elucidated.
02
02
There has been much interest in the past years in alkoxo-
bridged copper(Ⅱ) complexes, with particular interest directed
towards the magnetostructural correlation between the magnet-
ic properties and the crystal structures, especially the relation-
ship between the magnetic coupling constant (2J) and the Cu–
O–Cu angle.1–12 The alkoxo-bridged dinuclear copper(Ⅱ) com-
plexes have also been studied in the context of modeling bio-
logical systems, because dinuclear copper centers have impor-
tant functional roles in the active sites of copper-containing
proteins, such as hemocyanin, tyrosinase, and catecol oxi-
dase.13–20 An example of such a model is an alkoxo-bridged
dinuclear complex with N,N,Nꢀ,Nꢀ-tetrakis[2-(1-ethylbenzimi-
dazolyl)methyl]-1,3-diamino-2-propanol, reported by Reed et
al.16 They utilized a dinucleating ligand having 1,3-diamino-2-
propanolate as a bridging skelton. This kind of polydentate
ligand which has an alcoholic group is useful to design the
synthesis of endogenous-alkoxo-bridged dinuclear metal com-
plexes.16–36 Among these dinucleating ligands, N,Nꢀ-bis(1-
methyl-3-hydroxy-3-phenyl-2-propen-1-ylidene)-1,3-propane-
diamino-2-propanol (abbreviated as H3bzacpro, Scheme 1) is
unique, because the Schiff-base ligand possesses a dinucleat-
ing functionality that can serve as a bridging alkoxo group in
addition to keto-oxygen and imino-nitrogen atoms, and also
give oligonuclear metal species with interesting physicochemi-
cal properties. So far, a variety of oligonuclear structures have
been elucidated for complexes of manganese, iron, cobalt,
nickel, and zinc ions by the X-ray crystallography.36 However,
no oligonuclear structures have been found in a copper system,
although some alkoxo-bridged dinuclear copper(Ⅱ) structures
were reported.32 We have therefore made a detailed and fur-
ther study to extend this copper system by using analogous
Schiff-base ligands additionally. Herein we report on the syn-
thesis, crystal structures, and magnetic properties of alkoxo-
bridged copper(Ⅱ) complexes with N,Nꢀ-bis(1-methyl-3-hy-
droxy-3-phenyl-2-propen-1-ylidene)-1,3-diamino-2-propanol
(H3bzacpro), N,Nꢀ-bis(1-methyl-3-hydroxy-3-phenyl-2-propen-
1-ylidene)-1,4-diamino-2-butanol (H3bzacbu), and N,Nꢀ-bis(1-
methyl-3-hydroxy-3-phenyl-2-propen-1-ylidene)-1,5-diamino-
3-pentanol (H3bzacpen) as well as the crystal structures of the
free Schiff-base ligands (Scheme 1).
Experimental
Synthesis of the Schiff-Base Ligands.
1,3-Diamino-2-pro-
panol was obtained from Tokyo Kasei Kogyo Co., Ltd. 1,4-Di-
amino-2-butanol and 1,5-diamino-3-pentanol were synthesized
according to a method reported elsewhere.28
N,Nꢀ-Bis(1-methyl-3-hydroxy-3-phenyl-2-propen-1-ylidene)-
1,3-diamino-2-propanol (H3bzacpro).
1,3-Diamino-2-pro-
panol (1.80 g, 20.0 mmol) was dissolved in methanol (25 cm3) and
added to a solution of benzoylacetone (6.49 g, 40.0 mmol) in
methanol (25 cm3). The mixed solution was refluxed for 0.5 h and
then allowed to stand overnight at 5 °C. The resulting white crys-
tals were filtered, washed with diethyl ether and dried in vacuo
over P2O5. Yield, 5.47 g (72.0%). Found: C, 72.68; H, 6.89; N,
7.57%. Calcd for C23H26N2O3: C, 72.99; H, 6.92; N, 7.40%. IR
(KBr) ν(CwO) 1598 (s), ν(CwC) 1578 (s), 1535 (s), 1437, 1317,
1289 cm−1
N,Nꢀ-Bis(1-methyl-3-hydroxy-3-phenyl-2-propen-1-ylidene)-
.
1,4-diamino-2-butanol (H3bzacbu).
1,4-Diamino-2-butanol
(0.52 g, 5.0 mmol) was dissolved in methanol (7 cm3) and added
to a solution of benzoylacetone (1.62 g, 10.0 mmol) in methanol

2596 Bull. Chem. Soc. Jpn., 75, No. 12 (2002)
Dinuclear and Tetranuclear Copper(ꢀ) Complexes
[Cu4(bzacpro)2(C2H5O)2] (2). After H3bzacpro (19 mg, 0.05
mmol) and copper(Ⅱ) chloride dihydrate (17 mg, 0.10 mmol) were
dissolved in ethanol (2.5 cm3)–acetonitrile (7.5 cm3), triethyl-
amine (65 mg, 0.64 mmol) was added. After the mixed solution
was allowed to stand for several days at room temperature, dark-
green plates resulted, which were filtered and dried in vacuo over
P2O5: Yield, 15 mg (55%). Found: C, 54.67; H, 5.24; N, 5.36%.
Calcd for C50H56Cu4N4O8: C, 54.83; H, 5.15; N, 5.12%. IR (KBr)
ν(CwC) 1595, 1571, ν(CwN) 1506 (s), 1481 (s), 1455 (s), 1410
cm−1 (s). µeff (300 K) per Cu4 tetramer/µB 3.66. λM (CH2Cl2) 0
S mol−1 cm2. Diffuse reflectance spectrum: λmax/nm 235, 287,
318, 404, 650. Electronic spectrum in CH2Cl2: λmax/nm (ε per Cu
/dm3 mol−1 cm−1) 242 (14700), 297 (7970), 348 (13100), 658
(163).
[Cu2(bzacbu)(CH3CO2)] (3). After H3bzacbu (20 mg, 0.05
mmol) was dissolved in acetonitrile (5 cm3), a solution of cop-
per(Ⅱ) acetate monohydrate (18 mg, 0.10 mmol) in acetonitrile
(5 cm3) was added. After the mixed solution was allowed to stand
for several days at room temperature, dark-green plates resulted,
which were filtered and dried in vacuo over P2O5: Yield, 20 mg
(69%). Found: C, 54.33; H, 4.95; N, 4.94%. Calcd for C26H28Cu2-
N2O5: C, 54.25; H, 4.90; N, 4.87%. IR (KBr) ν(CwC) 1593, 1565
(s), νas(COO−) 1570 (s), ν(CwN) 1501 (s), 1482 (s), 1452 (s),
νs(COO−) 1413 cm−1 (s). µeff (300 K) per Cu2 dimer/µB 2.17. λM
(CH2Cl2) 0 S mol−1 cm2. Diffuse reflectance spectrum: λmax/nm
233, 275, 317, 385sh, 618. Electronic spectrum in CH2Cl2: λmax
/
nm (ε per Cu/dm3 mol−1 cm−1) 244 (16600), 280 (8150), 347
(15000), 618 (153).
Scheme 1.
[Cu4(bzacbu)2(CH3O)2] (4). After H3bzacbu (20 mg, 0.05
mmol) was dissolved in methanol (5 cm3), a solution of copper(Ⅱ)
perchlorate hexahydrate (37 mg, 0.10 mmol) in methanol (5 cm3)
was added, followed by triethylamine (35 mg, 0.10 mmol) with
stirring. After the solution had been filtered, the filtrate was
placed at room temperature for several days to give dark-green
plates. Yield, 15 mg (55%). Found: C, 55.18; H, 4.94; N, 5.15%.
Calcd for C50H56Cu4N4O8: C, 54.83; H, 5.15; N, 5.12%. IR (KBr)
ν(CwC) 1595, 1571, ν(CwN) 1507 (s), 1481 (s), 1455 (s), 1413
cm−1 (s). µeff (300 K) per Cu4 tetramer/µB 3.20. λM (CH2Cl2) 0 S
mol−1 cm2. Diffuse reflectance spectrum: λmax/nm 232, 285sh,
322, 385sh, 655. Electronic spectrum in CH2Cl2: λmax/nm (ε per
Cu/dm3 mol−1 cm−1) 245 (14600), 275 (6350), 350 (20600), 642
(79).
[Cu4(bzacpen)2(CH3CO2)2] (5). After H3bzacpen (10 mg,
0.03 mmol) was dissolved in acetonitrile (9 cm3), a solution of
copper(Ⅱ) acetate monohydrate (18 mg, 0.10 mmol) in acetonitrile
(9 cm3) was added. The mixed solution was left standing for sev-
eral days at room temperature to give dark-green plates. These
were collected by filtration and dried in vacuo over P2O5:Yield, 10
mg (68%). Found: C, 54.90; H, 5.12; N, 4.92%. Calcd for C54H60-
Cu4N4O10: C, 55.00; H, 5.13; N, 4.75%. IR (KBr) νas(COO−)
1675 (s), ν(CwC) 1588 (s), 1564 (s), ν(CwN) 1510 (s), 1483 (s),
1458 (s), 1412 (s), νs(COO−) 1354 cm−1 (s). µeff (300 K) per Cu4
tetramer/µB 2.52. λM (CH2Cl2) 0 S mol−1 cm2. Diffuse reflectance
spectrum: λmax/nm 318, 400sh, 655. Electronic spectrum in
CH2Cl2 λmax/nm (ε per Cu/dm3 mol−1 cm−1) 247 (18300), 351
(16900), 566 (99).
(8 cm3). The mixed solution was refluxed for 2 h, and then al-
lowed to stand overnight at 5 °C. The resulting pale-brown crys-
tals were filtered, washed with diethyl ether and dried in vacuo
over P2O5. Yield, 0.91 g (46%). Found: C, 73.30; H, 7.35; N,
7.40%. Calcd for C24H28N2O3: C, 73.44; H, 7.19; N, 7.14%. IR
(KBr) ν(CwO) 1595 (s), ν(CwC) 1575 (s), 1537 (s), 1433, 1323,
1288 cm−1
.
N,Nꢀ-Bis(1-methyl-3-hydroxy-3-phenyl-2-propen-1-ylidene)-
1,5-diamino-3-pentanol (H3bzacpen). 1,5-Diamino-3-pentanol
(2.37 g, 20.0 mmol) was dissolved in methanol (10 cm3) and add-
ed to a solution of benzoylacetone (6.49 g, 40.0 mmol) in metha-
nol (10 cm3). The mixed solution was refluxed for 2 h and then al-
lowed to stand overnight at 5 °C. The resulting white crystals
were filtered, washed with diethyl ether and dried in vacuo over
P2O5. Yield, 1.30 g (15.0%). Found: C, 73.60; H, 7.60; N, 7.03%.
Calcd for C25H30N2O3: C, 73.86; H, 7.44; N, 6.89%. IR (KBr)
ν(CwO) 1595 (s), ν(CwC) 1575 (s), 1538 (s), 1431, 1376, 1321,
1289 cm−1
.
Synthesis of the Complexes. [Cu2(bzacpro)(CH3CO2)] (1).
After H3bzacpro (19 mg, 0.05 mmol) was dissolved in acetonitrile
(5 cm3), a solution of copper(Ⅱ) acetate monohydrate (18 mg, 0.10
mmol) in acetonitrile (5 cm3) was added. After the mixed solution
was allowed to stand for several days at room temperature, deep-
blue plates resulted, which were filtered and dried in vacuo over
P2O5: Yield, 16 mg (57%). Found: C, 53.33; H, 4.59; N, 5.36%.
Calcd for C25H26Cu2N2O5: C, 53.47; H, 4.67; N, 4.99%. IR (KBr)
ν(CwC) 1590 (s), νas(COO−) 1574 (s), ν(CwN) 1503 (s), 1480 (s),
1460 (s), 1420 (s), νs(COO−) 1412 cm−1 (s). µeff (300 K) per Cu2
dimer/µB 2.14. λM (CH2Cl2) 0 S mol−1 cm2. Diffuse reflectance
spectrum: λmax/nm 243, 275, 332, 609. Electronic spectrum in
CH2Cl2 λmax/nm (ε per Cu/dm3 mol−1 cm−1) 241 (14300), 278
(8340), 347 (14900), 612 (215).
[Cu4(bzacpen)2O]•H2O (6). After H3bzacpen (10 mg, 0.03
mmol) and copper(Ⅱ) chloride dihydrate (9 mg, 0.05 mmol) were
dissolved in acetonitrile (10 cm3), triethylamine (39 mg, 0.38
mmol) was added. After the mixed solution was allowed to stand
for several days at room temperature, dark-greenish-brown plates

M. Mikuriya et al.
Bull. Chem. Soc. Jpn., 75, No. 12 (2002) 2597
bridged metal complexes,32,36 little information is available on
the structure of the free ligand H3bzacpro. To elucidate the
structures of the free Schiff-base ligands, a crystal-structure
determination was performed not only for H3bzacpro, but also
for H3bzacbu and H3bzacpen. The crystal structure of the
H3bzacpro ligand is shown in Fig. 1. In the crystal, the ligand
does not take a planar structure, but an extended form, showing
a twisting of the two side arms around the central alkoxy
group. The C–O bands [O1–C7 1.237(9), O2–C17 1.243(9)
Å] are in the normal observed bond lengths of CwO bonds; the
CwN imine bonds [N1–C9 1.335(9) and N2–C15 1.308(1) Å]
are a little longer than the normal CwN imine bond lengths, al-
though these distances are significantly shorter than the C–N
bond lengths [N1–C11 1.445(10), N2–C13 1.457(9) Å].
Moreover, hydrogen atoms are attached to the N1 and N2 at-
oms. These facts show that the Schiff-base is in a keto-amine
tautomer. There are intramolecular hydrogen bonds between
them [O1≥H(N1) 1.644 Å, O1≥H(N1)–N1 141.5°, O2≥
H(N2) 2.043 Å, O2≥H(N2)–N2 134.4°]. One of the two keto
groups of H3bzacpro is hydrogen-bonded to the alkoxy group
of the neighboring Schiff-base ligand [O2≥H(O3)ꢀ 1.707 Å,
O2≥H(O3)ꢀ–O3ꢀ 168.5°], forming a dimer of H3bzacpro in the
crystal.
The crystal structure of H3bzacbu is shown in Fig. 2. The
molecule has an extended trans form having a crystallographic
inversion center at the midpoint of C12–C12ꢀ. The alkoxy
group is disordered and distributed into the two positions O2
and O2ꢀ with an occupancy factor of 0.5, respectively. The
O1–C7 and N–C9 distances are 1.267(3) and 1.328(4) Å, re-
spectively, which are consistent with the keto-amine tau-
tomer. There is an intramolecular hydrogen bond [O1≥H(N)
1.793 Å, O1≥H(N)–N 135.9°] and an intermolecular hydro-
gen bond between the keto and the alkoxy group of the
resulted, which were filtered and dried in vacuo over P2O5: Yield,
8 mg (58%). Found: C, 54.73; H, 5.01; N, 5.23%. Calcd for
C50H56Cu4N4O8: C, 54.83; H, 5.15; N, 5.12%. IR (KBr) ν(CwC)
1589, 1566, ν(CwN) 1507 (s), 1482 (s), 1458 (s), 1410 cm−1 (s).
µeff (300 K) per Cu4 tetramer/µB 2.98. λM (CH2Cl2) 0 S mol−1
cm2. Diffuse reflectance spectrum: λmax/nm 232, 317, 380sh, 575.
Electronic spectrum in CH2Cl2: λmax/nm (ε per Cu/dm3 mol−1
cm−1) 247 (16600), 352 (14900), 570 (80).
Measurements. Carbon, hydrogen, and nitrogen analyses
were carried out using a Perkin-Elmer 2400 Series Ⅱ CHNS/O
Analyzer. Infrared spectra were measured with a JASCO Infrared
Spectrophotometer model IR700 in the 4000–400 cm−1 region on
a KBr disk. The electronic conductivities were measured on a
Horiba conductivity meter (DS-14). Electronic spectra were mea-
sured with a Shimadzu UV-vis-NIR Recording Spectrophotometer
(Model UV-3100). The temperature dependence of the magnetic
susceptibilities was measured with a Quantum Design MPMS-5S
SQUID susceptometer operating at a magnetic field of 0.5 T
between 4 and 300 K. The susceptibilities were corrected for the
diamagnetism of the constituent atoms using Pascal’s con-
stants.37 The effective magnetic moments were calculated from
the equation µeff = 2.828
ceptibility per mole.
, where χ is the magnetic sus-
χMT
M
X-ray Crystal Structure Analysis. Diffraction data were
collected on an Enraf-Nonius CAD4 diffractometer using graph-
ite-monochromated Mo-Kα radiation at 25 1 °C. Crystal data
and details of the data collection are given in Table 1. The unit-
cell parameters were determined by a least-squares refinement
based on 25 reflections with 20 ꢀ 2θ ꢀ 30°. Intensity data were
corrected for Lorentz-polarization effects. The structures were
solved by direct methods and refined by full-matrix least-squares
methods. All of the non-hydrogen atoms were refined with aniso-
tropic thermal parameters. In the case of H3bzacpro, hydrogen at-
oms attached to the alkoxy-oxygen and amino-nitrogen atoms
were located from a difference Fourier map, and the other hydro-
gen atoms were inserted at their calculated positions. These hy-
drogen atoms were fixed at their positions. Hydrogen atoms of
H3bzacbu and H3bzacpen were located from the difference Fourier
maps and fixed at their positions. For 1–6, hydrogen atoms were
inserted at their calculated positions and fixed at their positions.
The final discrepancy factors, R = Σ||Fo| − |Fc|| / Σ|Fo|, Rw =
2
[Σw(|Fo| − |Fc|)2/ Σw|Fo| ]1/2, are listed in Table 1. The weight-
ing scheme, w = 1/[σ2(|Fo|) + (0.02|Fo|)2 + 1.0], was employed.
All of the calculations were carried out on a VAX station 4000
90A computer using a MolEN program package.38 The atomic co-
ordinates and thermal parameters of the atoms and the anisotropic
thermal parameters of the non-hydrogen atoms have been deposit-
ed as Document No. 75050 at the Office of the Editor of Bull.
Chem. Soc. Jpn. Crystallographic data have been deposited at the
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK and copies can
be obtained on request, free of charge, by quoting the publication
citation and the deposition numbers 193370–193378.
Fig. 1. ORTEP drawing of the structure of H3bzacpro, show-
ing the atom-labeling scheme. Thermal ellipsoids are at
the 50% probability.
Results and Discussion
The present Schiff-base ligands were synthesized by a one-
pot reaction from benzoylacetone under a condition [reflux
with half amount of diamine (1,3-diamino-2-propanol, 1,4-
diamino-2-butanol, and 1,5-diamino-3-pentanol) in methanol
for several hours] similar to those we previously reported for
the corresponding salicylideneaminate ligands.28 Although
bzacpro3− is commonly found as a constituent of alkoxo-
Fig. 2. ORTEP drawing of the structure of H3bzacbu, show-
ing the atom-labeling scheme. Thermal ellipsoids are at
the 50% probability.

2598 Bull. Chem. Soc. Jpn., 75, No. 12 (2002)
Dinuclear and Tetranuclear Copper(ꢀ) Complexes
α
σ
θ
α
β
γ
µ

M. Mikuriya et al.
Bull. Chem. Soc. Jpn., 75, No. 12 (2002) 2599
Fig. 3. ORTEP drawing of the structure of H3bzacpen, show-
ing the atom-labeling scheme. Thermal ellipsoids are at
the 50% probability.
Fig. 4. ORTEP drawing of the structure of [Cu2(bzacpro)-
(CH3CO2)] (1) showing the 35% probability thermal ellip-
soids and atom labeling scheme. Hydrogen atoms are
omitted for clarity.
neighboring Schiff-base ligand [O1≥H(O2)ꢁ 1.468 Å, O1≥
H(O2)ꢁ–O2ꢁ 156.5°].
As shown in Fig. 3, the Schiff-base ligand H3bzacpen con-
sists of discrete molecules in the keto-amine tautomer [O1–C7
1.263(6), O2–C19 1.247(8), N1–C9 1.319(7), N2–C17
1.321(9) Å] with intramolecular hydrogen bonds [O1≥H(N1)
2.000, O2≥H(N2) 1.740 Å, O1≥H(N1)–N1 126.0, O2≥
H(N2)–N2 130.0°] The two side arms have a severely twisted
conformation. The molecule is associated with the neighbor-
ing molecule by intermolecular hydrogen bondings
[O1≥H(O3ꢀ) 1.814 Å, O1≥H(O3)ꢀ–O3ꢀ 159.7°].
Fig. 5.
(CH3CO2)] (1).
View of the stacking feature of [Cu2(bzacpro)-
The present Schiff-base ligands show ν(CwO) and ν(CwC)
bands of the benzoylacetonato moiety at 1598–1595 and
1578–1535 cm−1, respectively, in the infrared spectra, which
are consistent with the keto-amine tautomer of the benzoylace-
toneimine moiety.
in the literature.22,24,31 Contrary to the structure of the free
ligand, the 1,3-diamino-propane backbone of bzacpro in 1
takes a planar structure, resulting in a coplanar structure of the
two coordination spheres. The dihedral angle of the two coor-
dination planes is 174.5°. In the crystal, the two planar dinu-
clear molecules are stacked on each other with a close Cu2–
Cu2ꢀ distance of 3.570(2) Å (Fig. 5).
The crystal structure of 3 consists of crystallographically in-
dependent dinuclear molecules, which are similar to that of 1
(Fig. 6). In these dinuclear molecules, the aliphatic backbones
of bzacpro are not planar, and the dihedral angles of the two
coordination planes within the dinuclear molecules are both
136.5°. The Cu1–Cu2 and Cu3–Cu4 distances are both
3.393(1) Å. The Cu1–O3–Cu2 and Cu3–O8–Cu4 angles are
125.1(4) and 125.3(3)°, respectively. In the infrared spectra of
1 and 3, the antisymmetric and symmetric C–O stretching
bands of the acetate ions are found at around 1570 and 1410
cm−1, respectively. This feature is in harmony with the syn–
syn bridging mode of the acetate group.39
The crystal structure of 5 is shown in Fig. 7. The tetranucle-
ar molecule is crystallographically centrosymmetric. The two
Cu atoms are bridged by an alkoxo-oxygen atom (O3) of the
Schiff-base ligand bzacpen and an oxygen atom (O4) of an ac-
etate group with a monatomic bridging mode. The Cu1–Cu2
distance and Cu1–O3–Cu2 angle are 3.049(1) Å and
106.6(1)°, respectively. The shortening of the Cu–Cu distance
and the acute Cu–O–Cu angle compared with those of 1 and 3
may be caused by the steric requirement of the adjacent 6-6-
membered chelate rings of the ligand backbone of bzacpen3−.
The various bridging modes of acetate ion in 1, 3, and 5 means
the flexible coordinating properties of the acetate ion.40 The
two alkoxo-bridged dinuclear units are held together by further
bridging of the monatomic bridging acetate ion (O4 and O4ꢀ)
The present complexes were prepared via the one-pot syn-
thesis describing in the Experimental Section. In previous
papers, we reported that the H3bzacpro ligand affords the
mononuclear species [Pd(Hbzacpro)],36d dinuclear species
[(VO)2-(bzacpro)(pz)] (Hpz = pyrazol),36e trinuclear species
[Mn3-(bzacpro)2(CH3O)2(CH3OH)(C2H5OH)](ClO4),36a tetra-
nuclear species [Co4(bzacpro)2(CH3O)4],36b [Co4(bzacpro)2-
(C2H5O)4],36b [Zn4(Hbzacpro)4],36c [Ni4(bzacpro)2(CH3O)2-
(CH3OH)2],36f [Ni2Zn2(bzacpro)2(CH3O)2(CH3OH)2]36c and oc-
tanuclear species [Zn8(bzacpro)4(OH)4].36c In the present cas-
es, the reaction of the Schiff-base ligand with copper(Ⅱ) gave
dinuclear and tetranuclear species [Cu2(bzacpro)(CH3CO2)]
(1) and [Cu4(bzacpro)2(C2H5O)2] (2), depending on the exoge-
nous ligand, which comes from the metal source or solvent.
The H3bzacbu ligand also affords similar dinuclear and tetra-
nuclear species [Cu2(bzacbu)(CH3CO2)] (3) and [Cu4-
(bzacbu)2(CH3O)2] (4). On the other hand, the H3bzacpen
ligand affords only the tetranuclear species [Cu4(bzacpen)2-
(CH3CO2)2] (5) and [Cu4(bzacpen)2O]•H2O (6).
The X-ray crystallography of 1 reveals a dinuclear structure
where two copper(Ⅱ) ions are bridged by the alkoxo-oxygen
atom of the Schiff-base ligand bzacpro and the exogenous ace-
tate ion in a syn–syn configuration. A perspective view of the
molecule is shown in Fig. 4. Selected bond distances and an-
gles are listed in Table 2. Each copper atom takes a planar ge-
ometry with keto-oxygen, amino-nitrogen, and alkoxo-oxygen
donor atoms of bzacpro and acetate ion. The Cu1–Cu2 dis-
tance and Cu1–O3–Cu2 angle are 3.498(1) Å and 131.8(3)°,
respectively. A similar dinuclear structure was already known

2600 Bull. Chem. Soc. Jpn., 75, No. 12 (2002)
Dinuclear and Tetranuclear Copper(ꢀ) Complexes

M. Mikuriya et al.
Bull. Chem. Soc. Jpn., 75, No. 12 (2002) 2601

2602 Bull. Chem. Soc. Jpn., 75, No. 12 (2002)
Dinuclear and Tetranuclear Copper(ꢀ) Complexes
Fig. 6. ORTEP drawing of the structure of [Cu2(bzacbu)(CH3CO2)] (3) showing the 35% probability thermal ellipsoids and atom
labeling scheme. Hydrogen atoms are omitted for clarity.
Fig. 7. ORTEP drawing of the structure of [Cu4(bzacpen)2-
(CH3CO2)2] (5) showing the 50% probability thermal ellip-
soids and atom labeling scheme. Hydrogen atoms are
omitted for clarity.
Fig. 8. Core structure of [Cu4(bzacpen)2(CH3CO2)2] (5).
and keto-oxygen (O2 and O2ꢀ) to form a step-like tetranuclear
core, as shown in Fig. 8. Each copper atom takes a distorted
tetragonal-pyramidal geometry with an elongated axial Cu–O
bond [Cu1–O2ꢀ 2.588(3), Cu2–O4ꢀ 2.339(3) Å]. The equatori-
al Cu–O bond lengths of Cu1–O3 [1.891(3) Å], Cu2–O3
[1.913(3) Å], Cu1–O4 [2.057(3) Å], and Cu2–O4 [2.114(2) Å]
are significantly shorter than those of the axial Cu–O bonds.
Therefore, the magnetic exchange interaction via Cu1–O3–
Cu2 and Cu1–O4–Cu2 may be expected to contribute to the
magnetic property of 5 predominantly. Only a few examples
of structurally characterized copper(Ⅱ) complexes with mona-
tomic bridging of the acetate ion are known.41
The crystal structure of 2 is shown in Fig. 9. The tetranucle-
ar molecule is crystallographically centrosymmetric. The Cu1
and Cu2 atoms are bridged by an alkoxo-oxygen atom (O3) of
the Schiff-base ligand bzacpro and ethoxo ion (O4ꢀ). The two
dinuclear units are associated into a step-to-step tetranuclear
core (Fig. 10) by further bridging of keto-oxygen atoms (O1
Fig. 9. ORTEP drawing of the structure of [Cu4(bzacpro)2-
(C2H5O)2] (2) showing the 35% probability thermal ellip-
soids and atom labeling scheme. Hydrogen atoms are
omitted for clarity.
and O1ꢀ) and ethoxo ions (O4 and O4ꢀ). The Cu1–O4ꢀ and
Cu2–O1ꢀ lengths are 2.443(5) and 2.666(6) Å, respectively,

M. Mikuriya et al.
Bull. Chem. Soc. Jpn., 75, No. 12 (2002) 2603
Fig. 10. Core structure of [Cu4(bzacpro)2(C2H5O)2] (2).
Fig. 12. Core structure of [Cu4(bzacbu)2(CH3O)2] (4).
Fig. 11. ORTEP drawing of the structure (molecule b) of
[Cu4(bzacbu)2(CH3O)2] (4) showing the 35% probability
thermal ellipsoids and atom labeling scheme. Hydrogen
atoms are omitted for clarity. Primed and unprimed atoms
are related by the inversion.
Fig. 13.
ORTEP drawing of the structure of [Cu4-
(bzacpen)2O]•H2O (6) showing the 35% probability ther-
mal ellipsoids and atom labeling scheme. Hydrogen atoms
and solvent molecule are omitted for clarity. Primed and
unprimed atoms are related by the C2 axis.
pyramidal NO4 donor set. From this structural feature, the
Cu1–O3–Cu2 [99.6(3)°], Cu1–O4–Cu2 [100.5(3)°], Cu3–O7–
Cu4 [101.1(3)°], and Cu3–O8–Cu4 [100.6(4)°] angles may be
considered to be important in the magnetic exchange property
of 4.
which are significantly longer than the Cu1–O3 [1.961(6) Å],
Cu2–O3 [1.959(5) Å], Cu1–O4 [1.967(5) Å], and Cu2–O4ꢀ
[1.949(5) Å] lengths. Thus, the magnetic exchange coupling
via Cu1–O3–Cu2 and Cu1–O4–Cu2ꢀ may be important in this
tetranuclear core. The Cu1–O3–Cu2 and Cu1–O4–Cu2ꢀ an-
gles are 103.3(2) and 112.9(3)°, respectively.
The crystal structure of 6 is shown in Fig. 13. The molecule
has a unique tetranuclear structure, where the four copper at-
oms are arranged in a tetrahedral array around the central oxo
atom (O4), which is located at the crystallographic C2 axis.
The tetrahedron around the oxo atom shows considerable dis-
tortion. The bond angles vary from 96.6(10)° for Cu1–O4–
Cu2 to 148.0(6)° for Cu2–O4–Cu2ꢀ with Cu–O distances of
1.942(3) and 1.950(5) Å. The Cu1 and Cu2 atoms are bridged
by the alkoxo-oxygen atom (O3) of bzacpen and the oxo atom.
Each copper atom takes a planar arrangement with the keto-
oxygen, amino-nitrogen, and alkoxo-oxygen atoms of bzacpen
and the oxo atom. The tetranuclear core found here is different
from the previously reported similar tetranuclear copper(Ⅱ)
species in which the central oxygen atom is surrounded tetra-
hedrally by four octahedral copper atoms.42 The planar ar-
rangement of each copper atom of 6 may be caused by the ster-
ic hindrance of the benzoyl group of the other bzacpro3−,
The crystal structure of 4 contains two crystallographically
independent tetranuclear molecules, which have a crystallo-
graphic inversion center; they are abbreviated as a and b. Fig.
11 shows the structure of molecule b. Both comprise a similar
centrosymmetric tetranuclear molecule, and no significant dif-
ference in the geometries can be recognized between mole-
cules a and b. The tetranuclear core is shown in Fig. 12. The
two µ-methoxo-µ-alkoxo(bzacbu)-bridged dinuclear units are
associated by further bridging of the µ-alkoxo-oxygen atom of
bzacbu3− with distances of 2.532(8) Å [Cu2–O3ꢁ] and
2.535(7) Å [Cu4–O7ꢀ], resulting in different coordination
spheres of the copper atoms. The coordination geometries of
the Cu1 and Cu3 atoms can be regarded as a planar NO3 envi-
ronment because of the long distances of Cu1≥N2ꢁ [3.329(12)
Å] and Cu3≥N4ꢀ [3.334(10) Å], whereas the coordination
spheres of the Cu2 and Cu4 atoms have a distorted square-

2604 Bull. Chem. Soc. Jpn., 75, No. 12 (2002)
Dinuclear and Tetranuclear Copper(ꢀ) Complexes
Bleaney–Bowers equation based on an isotropic Heisenberg
model,43 H = −2JS1•S2,
2
χM = (1 − p){(2Ng2µB /3kT)[1 + (1/3)exp(−2J/kT)]−1}
2
+ pNg2µB /2kT + 2Nα,
(1)
where J is an exchange integral for the two copper atoms and
Nα represents the temperature-independent paramagnetism,
which was set to 60 × 10−6 cm3 mol−1 for each copper atom;
the other symbols have their usual meanings. A correction for
a small amount (p) of paramagnetic impurity (S = 1/2) was
taken into account. The best-fitting parameters obtained were
g = 2.01, 2J = −168 cm−1, and p = 0.0061 for 1 and g =
2.11, 2J = −238 cm−1, and p = 0.0078 for 3. For di-µ-
hydroxo-bridged dinuclear copper(Ⅱ) complexes, a linear rela-
tionship was found between the magnetic exchange coupling
(2J) and the Cu–O–Cu angle.44 The exchange coupling is anti-
ferromagnetic for Cu–O–Cu angles greater than 97.5°, and an
increase of the bridging angle leads to an increase in the anti-
ferromagnetic coupling. A similar correlation exists for
alkoxo-bridged dinuclear copper(Ⅱ) complexes.1,2 Judging
from the fact that the Cu–O–Cu angles are 131.8(3)° for 1 and
125.1(4) and 125.3(3)° for 3, the magneto-structural correla-
tion would indicate strong antiferromagnetism. However, the
observed antiferromagnetic coupling seems to become weak in
the present µ-alkoxo-µ-acetato-bridged dinuclear complexes.
The 2J values are comparable to those (2J = −95– −207 cm−1)
observed for analogous µ-acetato-µ-alkoxo-bridged dinuclear
copper(Ⅱ) complexes, which show depressed antiferromagnet-
ic coupling due to a “countercomplementary effect” of the ace-
tato-bridge.22,31 On the other hand, the room-temperature mag-
netic moments of tetranuclear complexes [2, 3.66 µB (300 K);
4, 3.20 µB (300 K); 5, 2.52 µB (300 K); 6, 2.98 µB (300 K)] are
comparable to, or lower than, the spin-only value (3.46 µB) for
four non-interacting d9 ions. The profiles of the temperature
dependence of the magnetic moments of complexes 2, 5, and 6
show that an antiferromagnetic interaction is mainly operative,
as illustrated in Fig. 16. In the case of 4, the magnetic moment
gradually increases to 3.87 µB at 4 K with lowering of the tem-
perature, as shown in Fig. 17, suggesting that the magnetic in-
teraction between the metal ions is ferromagnetic. The mag-
netic-susceptibility data may be analyzed under a first approxi-
mation by using a modified Bleaney–Bowers equation with the
Weiss temperature (θ) corrected for an interdimer interaction,
Fig. 14.
(CH3CO2)] (1).
Diffuse reflectance spectrum of [Cu2(bzacpro)-
which excludes the axial ligation.
The diffuse reflectance spectra of the present complexes are
similar, and are characterized by an intense absorption at near-
UV and an absorption band at 570–660 nm. The diffuse reflec-
tance spectrum of 1 is shown in Fig. 14 as a representative
example. The shoulder band around 332–404 nm can be as-
signed as a charge-transfer transition from bridging alkoxo-
oxygen to copper(Ⅱ), although the band is not a distinctive
one.7–9 The absorption spectra in CH2Cl2 for the complexes
show a d–d transition band at 566–658 nm, depending on the
coordination geometries of the copper ions, followed by a
charge-transfer transition band at about 350 nm.
The magnetic susceptibilities were measured over the tem-
perature range 4–300 K. The magnetic moments of dinuclear
complexes, 1 and 3, are 2.14 and 2.17 µB, respectively, at room
temperature, which are lower than the spin-only value, 2.45 µB,
for two non-interacting S = 1/2 copper(Ⅱ) ions. As shown in
Fig. 15, the magnetic moments of both complexes decrease to
ca. 0.12 and 0.13 µB, respectively, at 4 K. The temperature de-
pendence of the magnetic susceptibilities was analyzed by the
2
χM = (1 − p){[4Ng2µB /3k(T − θ)][1 + (1/3)exp(−2J/kT)]−1}
2
+ pNg2µB /kT + 4Nα,
(2)
in order to compensate for the tetranuclear cores. Fitting of the
magnetic data to this modified Bleaney-Bowers equation was
performed for complexes, 2, 4, and 5, which have similar step-
like-tetranuclear cores. The values for parameters g, J, θ, and
p, determined by the fitting procedure, are as follows: g =
2.12, 2J = −52 cm−1, θ = 7.6 K, and p = 0.022 for 2, g =
1.80, 2J = 36 cm−1, θ = 0.5 K, and p = 0 for 4, and g = 1.74,
2J = −219 cm−1, θ = −24 K, and p = 0.0087 for 5. It can be
assumed that complexes 2 and 5 are antiferromagnetic in na-
ture and complex 4 is ferromagnetic, although the fitting re-
sults contain some unrealistic g values for 4 and 5, and do not
Fig. 15. Magnetic susceptibility data (ꢀ, ꢁ) and effective
magnetic moments (ꢂ, ꢃ) of [Cu2(bzacpro)(CH3CO2)]
(1)) and [Cu2(bzacbu)(CH3CO2)] (3). The solid lines show
the best fit obtained (see text).

M. Mikuriya et al.
Bull. Chem. Soc. Jpn., 75, No. 12 (2002) 2605
Fig. 16. Magnetic susceptibility data (ꢁ, ꢄ, ꢀ) and effective
magnetic moments (ꢃ, ꢅ, ꢂ) of [Cu4(bzacpro)2-
(C2H5O)2)] (2) [Cu4(bzacpen)2(CH3CO2)2] (5) and [Cu4-
(bzacpen)2O]•H2O (6). The solid lines show the best fit ob-
tained (see text).
Fig. 18. Field dependence of the magnetization: experimen-
tal data for [Cu4(bzacbu)2(CH3O)2] (4) at 4 (ꢅ), 4.5 (ꢂ),
and 10 K (ꢃ); theoretical curves for S = 3/2 (—) and S =
1 (- - -) spin states (g = 2.0).
H = −2[J1(Scu1•Scu2 + Scu1ꢀ•Scu2ꢀ) +
J2(Scu1ꢀ•Scu2 + Scu1•Scu2ꢀ + Scu1•Scu1ꢀ + Scu2•Scu2ꢀ)], (3)
where J1 refers to the exchange interaction, Cu1–Cu2 and
Cu1ꢀ–Cu2ꢀ, and J2 to the other copper-copper interactions. The
susceptibility can be expressed by Eq. 4, with x = J1/kT and y
= J2/kT.42
χM = (1 − p)(Ng2µB /kT){[10exp(2x) + 2exp(−2x)
2
+ 4exp(−2y)]/[5exp(2x)+ 3exp(−2x) + exp(−4x)
2
+ 6exp(−2y) + exp(−4y)]} + p(Ng2µB /kT) + 4Nα (4)
The best-fit parameters were g = 2.07, J1 = −74 cm−1, J2 =
−73 cm−1, p = 0.049 (Fig. 16). The Cu–O–Cu angles con-
cerning to J1 are 98.9(3)° (Cu1–O3–Cu2) and 96.6(10)° (Cu1–
O4–Cu2) for the µ-alkoxo-µ-oxo Cu2 moieties, whereas the
Cu–O–Cu angles concerning to J2 are 97.4(10)° (Cu1–O4–
Cu2ꢀ), 127.8(6)° (Cu1–O4–Cu1ꢀ), and 148.0(6)° (Cu2–O4–
Cu2ꢀ) for the mono-µ-oxo Cu2 moieties. From this feature, it
was expected that the J1 and J2 interactions could be ferromag-
netic and antiferromagnetic, respectively. However, the fitting
result does not support this expectation. It is not easy to give a
clear explanation of the magnetic properties in terms of the
magneto-structural correlation for 6, although a moderate anti-
ferromagnetic coupling can be expected overall in this system.
Fig. 17. Magnetic susceptibility data (ꢁ) and effective mag-
netic moment (ꢃ) of [Cu4(bzacbu)2(CH3O)2] (4). The sol-
id lines show the best fit obtained (see text).
perfectly reproduce the increase in µeff at low temperature for
4. Considering the relationship between the 2J and the Cu–O–
Cu bridging angle, an antiferromagnetic behavior may be ex-
pected for 2 and 5, since most of the important Cu–O–Cu an-
gles are greater than 97.5° [Cu1–O3–Cu2 103.3(2)°, Cu1–O4–
Cu2ꢀ 112.7(3)° for 2, Cu1–O3–Cu2 106.6(1)°, Cu1–O4–Cu2
93.9(1)° for 5]. On the other hand, the Cu–O–Cu angles of 4
become closer to 97.5° [Cu1–O3–Cu2 99.6(3)°, Cu1–O4–Cu2
100.5(3)°, Cu3–O7–Cu4 101.1(3)°, Cu3–O8–Cu4 100.6(4)°
for 4]. The different magnetic behavior of 4 from the other
compounds may be attributed to the small Cu–O–Cu angles.
To confirm the ferromagnetic behavior of 4, the magnetization
of 4 versus the applied field was measured (Fig. 18). The mag-
netization curve of 4 lies above the curve of the Brillouin func-
tion for the S = 1 state, further supporting the presence of in-
tramolecular ferromagnetic coupling.
Conclusion
Alcoholic-oxygen-containing pentadentate ligands, N,Nꢀ-
bis(1-methyl-3-hydroxy-3-phenyl-2-propen-1-ylidene)-1,3-di-
amino-2-propanol (H3bzacpro), N,Nꢀ-bis(1-methyl-3-hydroxy-
3-phenyl-2-propen-1-ylidene)-1,4-diamino-2-butanol (H3bz-
acbu), and N,Nꢀ-bis(1-methyl-3-hydroxy-3-phenyl-2-propen-1-
ylidene)-1,5-diamino-3-pentanol (H3bzacpen) were synthe-
sized and proved to be useful ligands for the synthesis alkoxo-
bridged dinuclear and tetranuclear copper(Ⅱ) complexes which
exhibit a diversity of structural types and different magnetic
exchange properties as well as oligonuclear complexes of man-
ganese, iron, cobalt, nickel, and zinc ions.
In the case of 6, the data could not be fitted by the modified
Bleaney–Bowers equation, and consequently fitted to a more
accurate model. The spin Hamiltonian for complex 6, assum-
ing, an interaction in each pair, can be described in terms of the
Heisenberg model,

2606 Bull. Chem. Soc. Jpn., 75, No. 12 (2002)
Dinuclear and Tetranuclear Copper(ꢀ) Complexes
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