Synthesis and structures of vanadium-cerium trinuclear complexes with schiff-base ligands

Article abstract of DOI:10.1246/bcsj.79.1393

A vanadium(V)-cerium(IV) trinuclear complex, [{V^VO ₂(L₁)}₂Ce^IV] (1) (H ₃L₁: N,N′-bis-3-ethoxysalicylidene-2-hydroxy-1,3- propanediamine), was prepared by the reaction of [V^I

Full text of DOI:10.1246/bcsj.79.1393

ꢀ 2006 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 79, No. 9, 1393–1397 (2006) 1393
Synthesis and Structures of Vanadium–Cerium Trinuclear
Complexes with Schiff-Base Ligands
ꢀ1
Masanobu Tsuchimoto, Toshio Ishii,2 Takane Imaoka,3 Kimihisa Yamamoto,3
Naoki Yoshioka,4 and Yukinari Sunatsuki5
1Department of Life and Environmental Sciences, Chiba Institute of Technology,
2-1-1 Shibazono, Narashino 275-0023
2Department of Chemistry, Faculty of Engineering, Chiba Institute of Technology,
2-1-1 Shibazono, Narashino 275-0023
3Department of Chemistry, Faculty of Science and Technology, Keio University,
3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522
4Department of Applied Chemistry, Faculty of Science and Technology, Keio University,
3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522
5Department of Chemistry, Faculty of Science, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530
Received February 27, 2006; E-mail: tmoto@sea.it-chiba.ac.jp
A vanadium(V)–cerium(IV) trinuclear complex, [{VVO2(L1)}2CeIV] (1) (H3L1: N,N0-bis-3-ethoxysalicylidene-2-
hydroxy-1,3-propanediamine), was prepared by the reaction of [VIVO(acac)2] and [CeIII(acac)3] 3H2O with H3L1 in
ꢁ
CH3CN, followed by oxidation of the product in air. The structure of complex 1 was determined by X-ray crystal struc-
ture analysis. The complex has a VV–CeIV–VV trinuclear structure with two dioxovanadium(V) moieties on each side
of the cerium(IV) moiety. Complex 1 has two L1 ligands to form a trinuclear structure. The basal oxo atoms of the
˚
dioxovanadium(V) moieties are coordinated to the cerium atom with Ce–O distances of 2.322(3) and 2.343(3) A. The
apical two non-coordinating oxo atoms are oriented to the same direction to form an endo structure. IR data of complex
1 show V=O stretching bands at 975 cmꢂ1 for the apical non-coordinated oxo atoms and 802 cmꢂ1 for the basal coor-
dinated oxo atoms. The cyclic voltammogram of complex 1 in CH3CN shows a quasi-reversible two-electron redox
couple with E1=2 ¼ ꢂ0:60 V vs Fc/Fcþ.
Recently, heteronuclear metal complexes with transition
But
OH
OC2H5 C2H5O
OH HO
But
HO
metal and lanthanide ions have been extensively studied be-
cause of their magnetic1–3 and fluorescence4 properties. For
3d–4f mixed-metal complexes with the Schiff-base ligands,
like 3-MeOsalen (H23-MeOsalen: N,N0-bis-3-methoxysalicyli-
dene-1,2-ethanediamine), preparation and magnetic properties
of dinuclear VIV–GdIII,5 CuII–LnIII {LnIII = GdIII, CeIII, and
YbIII},6–8 NiII–LnIII {LnIII = GdIII and DyIII}8,9 complexes
have been reported. In these complexes, two phenolate oxygen
and two methoxy oxygen atoms of the [M(L)] (M ¼ VO, Cu,
and Ni; L: Schiff-base ligand) moiety are coordinated to a
Ln3þ ion to form a [M(L)Ln]3þ dinuclear structure. However,
different structures and properties are expected for 3d–4f
mixed-metal complexes with the Schiff-base ligands that have
another alcohol group (Fig. 1). This study reports the prepara-
tion and structures of new vanadium(V)–cerium(IV) hetero-
nuclear complexes, [{VVO2(L1)}2CeIV] (1) (H3L1: N,N0-
bis-3-ethoxysalicylidene-2-hydroxy-1,3-propanediamine) and
[{VVO2(L2)}2CeIV] (2) (H3L2: N,N0-bis-3,5-tert-butylsalicyli-
dene-2-hydroxy-1,3-propanediamine). As vanadium and ceri-
um complexes often have more than one oxidation state, sev-
eral oxidation states are also expected for the heteronuclear
complexes. Electrochemical properties for the complexes are
also discussed.
But
But
N
N
N
N
OH
OH
H L
3 1
H L
3 2
Fig. 1. H3L1 and H3L2.
Results and Discussion
Synthesis and Structures.
Brown vanadium(V)–ceri-
um(IV) heteronuclear complexes, [{VVO2(L1)}2CeIV] (1) and
[{VVO2(L2)}2CeIV] (2) were prepared by the reaction of
[VIVO(acac)2] and [CeIII(acac)3] 3H2O with the Schiff-base
ligand in CH3CN, followed by oxidation of the product in air.
ꢁ
Complex 1 was also obtained by the reaction of [VIVO(HL1)]
with [CeIII(acac)3] 3H2O in CH3CN, followed by oxidation of
ꢁ
the product in air.10,11
The structure of complex 1 was determined by X-ray crystal
structure analysis (Fig. 2). The complex has a VV–CeIV–VV
trinuclear structure with two dioxovanadium(V) moieties
Published on the web September 5, 2006; doi:10.1246/bcsj.79.1393

1394 Bull. Chem. Soc. Jpn. Vol. 79, No. 9 (2006)
Vanadium–Cerium Trinuclear Complexes
(a)
* *
(a)
(b)
*
*
(b)
Fig. 2. (a) ORTEP drawing and (b) side view of complex 1
with 30% probability ellipsoids. Water and DMSO mole-
˚
cules are eliminated. Selected bond lengths (A): Ce1–O5
(c)
*
2.322(3), Ce1–O7 2.399(2), Ce1–O8 2.178(3), Ce1–O10
2.343(3), Ce1–O12 2.400(3), Ce1–O13 2.176(3), Ce1–
N19 2.548(3), Ce1–N21 2.525(3), V2–O4 1.599(3), V2–
O5 1.709(3), V2–O6 1.851(3), V2–O7 1.949(2), V2–N18
2.135(3), V3–O9 1.587(3), V3–O10 1.712(3), V3–O11
1.859(3), V3–O12 1.944(3), V3–N20 2.115(3).
2000
1600
1200
800
400
Wavenumber / cm−1
Fig. 4. IR spectra of (a) complex 1, (b) 18O-labelled com-
plex 1, (c) complex 1Red. The V=O stretching bands are
shown in the figures with asterisks.
EtO
EtO
O
O
V
N
O
O
N
Ce
N
O
N
O
O
N
Ce
N
OEt
OEt
V
O
V
O
V
those of monomeric dioxovanadium(V) complexes (1.607(1)–
13
O
O
O
O
O
O
O
˚
1.621(5) A). Two apical non-coordinated oxo atoms (O4
EtO
EtO
OEt
O
O
N
O
N
O
OEt
and O9) are oriented to the same direction to form an endo
structure (Fig. 3). The Ce1 V2 and Ce1 V3 distances are
ꢁꢁꢁ
ꢁꢁꢁ
˚
3.274(1) and 3.292(1) A, respectively, and the V2 V3 distance
ꢁꢁꢁ
endo
exo
˚
is 5.800(1) A.
To assign the V=O stretching bands, 18O-labelled complex
1 was prepared by the reaction of the complex with H218O in
dry acetonitrile.14–16 The oxygen atom exchange reaction be-
tween the oxo ligands of complex 1 and H218O proceeded very
slowly. The 18O-labelled complex 1 was obtained after stirring
the reaction mixture for 10 days at 30 ꢃC.17 Figure 4 shows the
IR spectra of complex 1 and 18O-labelled complex 1. The
spectrum of the 18O-labelled complex 1 in Fig. 4b shows
two new strong broad bands at 934 and 771 cmꢂ1 with a large
decrease in intensity of the strong bands at 975 and 802 cmꢂ1
in the spectrum of complex 1 in Fig. 4a. Thus, the strong bands
at 975 and 802 cmꢂ1 in the spectrum of complex 1 are assigned
to the V=O (apical) and V=O (basal) stretching bands, respec-
tively. The frequency of the V=O (apical) stretching band of
complex 1 is higher than those of monomeric dioxovana-
dium(V) complexes with a tridentate Schiff-base ligand
(920–960 cmꢂ1), and the frequency of V=O (basal) stretching
band of complex 1 is lower than those of monomeric dioxova-
nadium(V) complexes (850–880 cmꢂ1).13 The oxygen atom
exchange reaction did not proceed for complex 2, which has
bulky hydrophobic tert-butyl groups.
Fig. 3. Two possible isomers for 1.
on each side of the cerium(IV) moiety. Two L1 ligands are
coordinated to the cerium atom with phenolate oxygen (O8
and O13), imine nitrogen (N19 and N21), and alcoholate oxy-
gen (O7 and O12) atoms. Coordination of two Schiff-base
ligands to a central cerium(IV) ion is also observed for
[Ce(5-Clsalen)2] (H25-Clsalen: N,N0-bis-5-chlorosalicylidene-
1,2-ethanediamine) and other cerium(IV) complexes with
tetradentate Schiff-base ligands.12 The central cerium(IV) moi-
ety has an eight-coordinate square-antiprismatic structure, and
both of the dioxovanadium(V) moieties have a five-coordinate
square-pyramidal structure. Basal oxo atoms of the dioxovana-
dium(V) moieties (O5 and O10) are coordinated to the cerium
atom with Ce1–O5 and Ce1–O10 distances of 2.322(3) and
˚
2.343(3) A, respectively. The vanadium–basal oxo atom dis-
˚
˚
tances of complex 1 (V2–O5: 1.709(3) A, V3–O10: 1.712(3) A)
are longer than those of monomeric dioxovanadium(V) com-
plexes with a tridentate Schiff-base ligand (1.659(1)–1.675(3)
˚
A), and the vanadium–apical oxo atom distances of complex
˚
˚
1 (V2–O4 1.599(3) A, V3–O9 1.587(3) A) are shorter than

M. Tsuchimoto et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 9 (2006) 1395
The VV–CeIV–VV trinuclear complexes with a d0–f0–d0
electron configuration are diamagnetic. The 13C NMR spec-
trum of complex 1 in DMSO-d6 shows 21 signals at ꢀ 166.2,
164.7, 156.9, 153.9, 147.3, 144.9, 124.3, 123.5, 122.4, 121.2,
118.5, 118.2, 117.0, 113.9 (Ar and N=CH–C), 80.4 (–OCH-
(CH2–)2), 64.3, 64.1 (O–CH2–C), 63.9, 62.4 (N–CH2–C), 14.8,
14.6 (CH3). The structure of complex 1 in the solution is con-
sidered to be an endo structure (C2 symmetry), similar to the
structure in crystals. However, the 13C NMR spectrum of com-
plex 2 in CDCl3 is complicated. More than 60 carbon signals
were observed in the 13C NMR spectrum of complex 2. All the
signals could not be assigned because of weak intensities and
overlapping signals.18 However, two strong and four weak N–
CH2–C carbon signals (ꢀ 64.9, 65.2, 65.4, 65.8, 66.2, 67.4)
with a relative intensity ca. 2:1, and one strong and two weak
–OCH(CH2–)2 carbon signals (ꢀ 80.6, 80.9, 84.3) with a rela-
tive intensity ca. 2:1 in the spectrum of complex 2 suggest two
possible structures for 2: (1) a mixture of the endo (C2 symme-
try) and exo (C1 symmetry) isomers (Fig. 3) in the ratio of ca.
1:1; (2) another heteronuclear structure different from the tri-
nuclear structure of complex 1. Unfortunately, structure of
complex 2 could not be determined by X-ray structure analysis
because single crystals were not obtained. Steric repulsions
between the tert-butyl groups in the ligand L2 may cause the
structural difference between complexes 1 and 2.
to that of [VVO(L1)], which shows a quasi-reversible VV/VIV
redox couple with E1=2 ¼ ꢂ0:83 V.10 The current peak values
for the redox couple of complex 1 is about two times larger
than those for the redox couple of [VVO(L1)]. This result
would indicate a two-electron redox reaction for the redox
process of complex 1. The cyclic voltammogram of complex 2
shows an irreversible redox couple with a reduction wave at
ꢂ0:99 V and an oxidation wave at ꢂ0:41 V.18 Chemically re-
duced products of complexes 1 and 2 (abbreviated as 1Red and
2Red) were prepared by the reaction of complexes 1 and 2 with
equimolar amounts of ascorbic acid in methanol, respectively.
The brown reduced complexes 1Red and 2Red were rather un-
stable. When complexes 1 and 2 were reacted with excess as-
corbic acid in methanol, respectively, the trinuclear complexes
decomposed to yield yellow monomeric oxovanadium(IV)
complexes. Moreover, complexes 1Red and 2Red were air-
unstable, and gradually oxidized in air to give complexes 1
and 2, respectively, even in the solid state. IR spectrum of
complex 1Red is shown in Fig. 4c. In the spectrum of complex
1Red, there is no V=O (basal) stretching band, and only the
V=O (apical) stretching band at 982 cmꢂ1 is observed. Similar
tendency is also observed in the IR spectrum of complex
18
2Red
.
Disappearance of the V=O (basal) stretching band
for the two-electron reduced complex 1Red may suggest that
complex 1Red is a hydroxo-bridged (V–OH–Ce) trinuclear
complex (Fig. 6). The reduced complex may have a VIV–
CeIV–VIV trinuclear structure with a d1–f0–d1 electron config-
uration. Further investigations will be necessary to elucidate
the electronic structure of the reduced complexes.19
Electrochemistry. Cyclic voltammograms of complex 1
and [VVO(L1)] with 1 mM concentrations in acetonitrile are
shown in Fig. 5. The voltammogram of complex 1 shows a
quasi-reversible redox couple with E1=2 ¼ ꢂ0:60 V vs Fc/Fcþ.
Peak separation of the redox couple is 226 mV. The redox
potential of complex 1 is shifted positive by 230 mV compared
Experimental
Preparation of the Ligands. The ligand H3L1 was prepared
by the literature method.10 The ligand H3L2 was prepared by the
reaction of 2-hydroxy-1,3-propanediamine with 2 equiv amounts
of 3,5-tert-butyl-2-hydroxybenzaldehyde in ethanol. The reaction
mixture was evaporated to dryness to yield a yellow oily product.
The oily product was poured into water, and the mixture was stir-
red for 1 day. The resulting yellow powder was collected by filtra-
tion and used for further reactions without purification. 13C NMR
(CDCl3) ꢀ 168.4, 158.0, 140.2, 136.7, 127.2, 126.2, 117.8 (Ar and
N=CH–C), 70.6 (–OCH(CH2–)2), 63.3 (N–CH2–C), 35.0, 34.1
(C–C–(CH3)3), 31.5, 29.4 (CH3).
4.0
3.0
(a)
2.0
1.0
0.0
-1.0
-2.0
-3.0
-4.0
-5.0
-6.0
(b)
[{VVO2(L1)}2CeIV] 0.5H O (1). Method 1: The ligand
Á
2
H3L1 (1.93 g, 5 mmol), [VIVO(acac)2] (1.33 g, 5 mmol), and
[CeIII(acac)3] H2O (1.23 g, 2.5 mmol) were added to 1 dm3 of
-2.0
-1.5
-1.0
-0.5
0.0
0.5
ꢁ
CH3CN, and the reaction mixture was vigorously stirred in air
for 3 h at 70 ꢃC. The brown reaction mixture was filtered, and
the filtrate was evaporated to dryness. The resulting brown residue
was dissolved in 600 cm3 of dichloromethane–ethanol solution
(1:1 v/v), and the solution was left for two days in air. The result-
Potential / V vs. Fc/Fc+
Fig. 5. Cyclic voltammograms of (a) complex 1 and (b)
[VVO(L1)] in CH3CN with a scan rate of 100 mV sꢂ1
.
OEt
EtO
OEt
EtO
O
O
+ 2H
O
O
N
O
O
H
O
N
O
O
N
Ce
N
N
Ce
N
V
V
O
O
O
H
O
O
O
O
V
V
OEt
OEt
O
N
O
N
O
O
EtO
EtO
1/2 O2
H2O
Fig. 6. Proposed mechanism for the redox reaction of complex 1.

1396 Bull. Chem. Soc. Jpn. Vol. 79, No. 9 (2006)
Vanadium–Cerium Trinuclear Complexes
ing brown crystals were collected by filtration. Yield: 3.77 g
(70%). Found: C, 46.32; H, 4.39; N, 5.11%. Calcd for C42H47Ce1-
N4O14:5V2: C, 46.62; H, 4.37; N, 5.14%. IR (KBr, cmꢂ1): 802,
975 [ꢁ(V=O)].
I > 2ꢆðIÞ. Crystallographic data have been deposited with Cam-
bridge Crystallographic Data Centre: Deposition number CCDC-
606023 for compound [{VO2(L1)}2Ce] 2H2O 2DMSO. Copies
ꢁ
ꢁ
of the data can be obtained free of charge via http://www.ccdc.
cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystal-
lographic Data Centre, 12, Union Road, Cambridge, CB2 1EZ,
UK; Fax: +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk).
Electrochemical Measurements. Cyclic voltammetric mea-
surements were carried out using a ALS 600 electrochemical ana-
lyzer at 25 ꢃC (1 mM complex, 0.1 M N(C4H9)4BF4). A platinum
electrode, an Ag/Agþ electrode (Ag/0.01 M AgNO3), and a plat-
inum wire were employed as the working, reference, and auxiliary
electrodes.
Magnetic Measurements. Magnetic susceptibility measure-
ments were carried out using a Quantum Design MPMS XL5
magnetometer in the temperature range of 1.9–300 K using a mag-
netic field of 0.1 T. The susceptibilities of complex 2Red have been
corrected for the diamagnetic contribution of ꢇdia ¼ ꢂ766:6 ꢄ
10ꢂ6 cm3 molꢂ1, calculated by Pascal’s method.
Method 2: [CeIII(acac)3] H2O (0.49 g, 1 mmol) was added to
ꢁ
an acetonitrile solution (300 cm3) of [VIVO(HL)] H2O (0.938 g,
ꢁ
2 mmol),10 and the reaction mixture was vigorously stirred in air
for 3 h at 70 ꢃC. The reaction product was treated by the method
similar to that for Method 1. Yield: 1.32 g (81%).
[{VVO2(L2)}2CeIV] 4CH CN (2). The complex was prepared
Á
3
by the method similar to that for [{VVO2(L1)}2CeIV] 0.5H2O
ꢁ
(Method 1). For complex 2, the product was recrystallized from
acetonitrile in air. Yield: 3.51 g (93%). Found: C, 58.69; H, 7.00;
N, 7.48%. Calcd for C74H106Ce1N8O10V2: C, 58.86, H, 7.07; N,
7.42%. IR (KBr, cmꢂ1): 812, 974 [ꢁ(V=O)].
Oxygen Atom Exchange Reaction for 1. To a dry acetoni-
trile solution (10 cm3) of complex 1 (0.005 mmol) was added
0.04 cm3 (ca. 2 mmol) of H218O (97 > atom%). The solution
was stirred at 30 ꢃC under an argon atmosphere for 10 days and
then evaporated to dryness.
Reduction of the Vanadium(V)–Cerium(IV) Trinuclear
Complexes. The reaction was carried out under a nitrogen atmo-
sphere. Ascorbic acid (0.035 g, 0.2 mmol) was added to a metha-
nol solution of complexes 1 or 2 (400 cm3 for 0.2 mmol of com-
plex 1, 100 cm3 for 0.2 mmol of complex 2), and the mixture
was stirred for 30 min at 10 ꢃC. The mixture was evaporated to
dryness below 20 ꢃC, and washed with water. Yield: 80–90%.
The brown reduced products were rather unstable and gradually
oxidized in air even in the solid state. IR data (KBr, cmꢂ1): 982
Other Measurements. IR spectra were recorded on a JASCO
A-202 spectrophotometer. The ESR spectrum in benzene at room
temperature was recorded on a JEOL JES-RE3X spectrometer
with a 100 kHz field modulation. The 13C NMR spectra were
recorded on a Bruker AVANCE 400 spectrometer with a TMS
reference.
The present work was supported in part by Grants-in-Aid
for Scientific Research No. 15550055 from the Ministry of
Education, Culture, Sports, Science and Technology, Japan.
[ꢁ(V=O)] for 1Red; 980, 998 [ꢁ(V=O)] for 2Red
.
Crystal Structure Determination of [{VVO2(L1)}2CeIV
]
2H O 2DMSO. Crystals suitable for X-ray crystal structure
Supporting Information
Á
analysis were obtained by recrystallization of complex 1 from
The 13C NMR spectrum of complex 2 (Fig. S1), IR spectra of
complexes 2 and 2Red (Fig. S2), cyclic voltammogram of complex
2 (Fig. S3), ꢇmT–T plots of complex 2Red (Fig. S4), and ESR
spectrum of complex 2Red (Fig. S5) in PDF files. This material
is available free of charge on the web at: http://www.csj.jp/
journals/bcsj/.
Á
DMSO. Crystal data of [{VO2(L1)}2Ce] 2H2O 2DMSO: Ce1V2-
2
ꢁ
ꢁ
S2O18N4C46H62, M = 1265.13, crystal size: 0:43 ꢄ 0:40 ꢄ 0:30
mm3, orthorhombic, space group Pbca (No. 61), a ¼ 18:286ð3Þ,
3
˚
˚
b ¼ 32:985ð8Þ, c ¼ 17:887ð3Þ A, V ¼ 10789ð3Þ A , Z ¼ 8,
ꢂ(Mo Kꢃ) = 1.319 mmꢂ1, 13411 reflections measured, 12356 in-
dependent reflections. The intensity data were collected at 298 K
on a Rigaku AFC-7R diffractometer with graphite-monocꢃhromat-
References
˚
ized Mo Kꢃ radiation (ꢄ ¼ 0:71073 A) up to 2ꢅ ¼ 55 by !
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Graphics O2 workstation with the program system teXsan,21 and
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atoms of the DMSO molecule were disordered, and two positions
were assigned for these atoms. Site occupancy factors for the
S65A, O67A atoms and the S65B, O67B atoms were 60 and
40%, respectively. Non-hydrogen atoms were treated anisotropi-
cally. All H-atom positions attached to the carbon atoms of the
complex and C70 and C71 atoms of the DMSO molecule were ca-
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of the disordered DMSO molecule were not introduced. H-atom
positions attatched to the O68 atom of the water molecule were
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be found by difference synthesis. The refinement was based on
2
3
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5
a) J. P. Costes, A. Dupuis, J. P. Laurent, J. Chem. Soc.,
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2
2
1=2
2
2
2
2
F2 with Rw ¼ ½ꢁwðFo ꢂ Fc Þ =ꢁwðFo Þ ꢅ , wꢂ1 ¼ ꢆ2ðFo Þ þ
J. P. Costes, F. Dahan, A. Dupuis, J. P. Laurent, Chem.
2
2
2
ð0:0603PÞ þ 8:3885P, where P ¼ ðFo þ 2Fc Þ=3 against all of
the 12356 reflections. The Rw value was 0.118. The R value
2
9
4284.
J. P. Costes, F. Dahan, A. Dupuis, Inorg. Chem. 1997, 36,
2
(ꢁjFo ꢂ Fc j=ꢁFo2) was 0.038 for the 8477 reflections with

M. Tsuchimoto et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 9 (2006) 1397
10 M. Tsuchimoto, T. Ishii, T. Imaoka, K. Yamamoto, Bull.
Chem. Soc. Jpn. 2004, 77, 1849.
11 Complex 1 was also prepared by the reaction of a mono-
19 As complex 1Red was too unstable to obtain magnetic data,
complex 2Red was used for the magnetic and ESR measurements.
Elemental anlysis for complex 2Red; Found: C, 58.05; H, 7.26; N,
oxovanadium(V) complex [VVO(L)] with [CeIII(acac)3] 3H2O
3.97%. Calcd for [{VO(OH)(L2)}2Ce] H2O (2Red) C66H98N4-
ꢁ
ꢁ
in CH3CN followed by oxidation of the product in air. Yield:
74%.
O11Ce1V2: C, 58.04; H, 7.23; N, 4.10%. Magnetic moment of
complex 2Red at 300 K is 2.36 mB, which is a little smaller than
the calculated spin-only magnetic moment value for two S ¼
12 K. Kubono, N. Hirayama, H. Kokusen, K. Yokoi, Anal.
Sci. 2001, 17, 193.
13 G. Asgedom, A. Sreedhara, J. Kivikoski, J. Valkonen, C. P.
Rao, J. Chem. Soc., Dalton Trans. 1995, 2459.
14 M. Tsuchimoto, E. Yasuda, S. Ohba, Chem. Lett. 2000,
562.
15 M. Tsuchimoto, G. Hoshina, R. Uemura, K. Nakajima,
M. Kojima, S. Ohba, Bull. Chem. Soc. Jpn. 2000, 73, 2317.
16 M. Tsuchimoto, Bull. Chem. Soc. Jpn. 2001, 74, 2101.
17 Clear difference between the reactivity of the basal and
apical oxo atoms of complex 1 with H218O was not observed.
18 The 13C NMR spectrum of complex 2, IR spectrum of
complexes 2 and 2Red, and cyclic voltammogram of complex 2
are part of the supporting material.
1=2 centers with no interaction, fð1ð1 þ 2Þ þ 1ð1 þ 2ÞÞg1=2mB
¼
2:45 mB. However, the ꢇmT–T plots of complex 2Red show a
complicated behavior. Complex 2Red was ESR-silent in a benzene
solution at 298 K, but showed an ESR signal at giso ¼ 1:957 in the
solid state at 298 K. The ꢇmT–T plots and ESR spectrum of com-
plex 2Red are deposited.
20 A. C. T. North, D. C. Phillips, F. S. Mathews, Acta
Crystallogr., Sect. A 1968, 24, 351.
21 teXsan, Version 1.11, Single Crystal Structure Analysis
Software, MSC, 9009 New Trial Drive, The Woodlands, TX
77381, U.S.A. Rigaku, 3-9-12 Akishima, Tokyo 196-8666, Japan.
22 G. M. Sheldrick, SHELXL97: Program for the Refinement
of Crystal Structures, University of Gottingen, Germany, 1997.
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