Trinuclear CuIIMIICuII complexes of an oxamide/dioxime ligand and extension to a bimetallic magnetic compound

Article abstract of DOI:10.1039/b006613n

N,N′-Bis[2-(hydroxyiminomethyl)phenyl]oxamide (H₄L) provided trinuclear Cu^IIM^IICu^II complexes [M{Cu(HL)-(DMF)}₂(DMF)₂] (M^II = Mn 1, Co 2, Ni 3 or Zn 4). The crystal structures of 1-4 have been determined by X-ray crystallography. They are isomorphous and have an oxamidate-bridged trinuclear Cu^IIM^IICu^II structure. The Cu^II resides in a pseudo-macrocyclic framework of (HL)^3- comprised of an oxamidate and a hydrogen-bonded dioximate (=N-O...H...O-N=) groups to form a square-pyramidal structure {Cu(HL)(DMF)} together with a DMF molecule. Two {Cu(HL)(DMF)} entities co-ordinate to a Mn^II through the oxamidate oxygens to afford a cis octahedral environment about the metal together with two DMF oxygens. The Cu^II...M^II intermetallic distance separated by the oxamidate bridge is 5.33-5.49 A. In the case of 1 and 3 a significant antiferromagnetic interaction operates between the adjacent Cu^II and M^II. The reaction of 1 with Mn^II in acetonitrile in the presence of KOH and 18-crown-6 formed Mn{Cu(L)}(H₂O)₄ that has a polymeric structure extended by the dioximate-Mn^II-dioximate linkage. It is a weak ferromagnet (T_C = 5.5 K) exhibiting a weak antiferromagnetic interaction between the ferrimagnetic chains. The Royal Society of Chemistry 2001.

Full text of DOI:10.1039/b006613n

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Trinuclear CuIIMIICuII complexes of an oxamide/dioxime ligand
and extension to a bimetallic magnetic compound
—
Nobuo Fukita,a Masaaki Ohba,a Takuya Shiga,a Hisashi Okawa*a and Yoshitami Ajirob
a Department of Chemistry, Faculty of Sciences, Kyushu University, Hakozaki 6-10-1,
Higashiku, Fukuoka 812-8581, Japan
b Department of Physics, Faculty of Sciences, Kyushu University, Hakozaki 6-10-1, Higashiku,
Fukuoka 812-8581, Japan
Received 14th August 2000, Accepted 10th October 2000
First published as an Advance Article on the web 7th December 2000
N,NЈ-Bis[2-(hydroxyiminomethyl)phenyl]oxamide (H4L) provided trinuclear CuIIMIICuII complexes [M{Cu(HL)-
(DMF)}2(DMF)2] (MII = Mn 1, Co 2, Ni 3 or Zn 4). The crystal structures of 1–4 have been determined by X-ray
crystallography. They are isomorphous and have an oxamidate-bridged trinuclear CuIIMIICuII structure. The CuII
resides in a pseudo-macrocyclic framework of (HL)3Ϫ comprised of an oxamidate and a hydrogen-bonded dioximate
(᎐N–O ؒ ؒ ؒ H ؒ ؒ ؒ O–N᎐) groups to form a square-pyramidal structure {Cu(HL)(DMF)} together with a DMF
᎐
᎐
molecule. Two {Cu(HL)(DMF)} entities co-ordinate to a MnII through the oxamidate oxygens to afford a cis
octahedral environment about the metal together with two DMF oxygens. The CuII ؒ ؒ ؒ MII intermetallic distance
separated by the oxamidate bridge is 5.33–5.49 Å. In the case of 1 and 3 a significant antiferromagnetic interaction
operates between the adjacent CuII and MII. The reaction of 1 with MnII in acetonitrile in the presence of KOH and
18-crown-6 formed Mn{Cu(L)}(H2O)4 that has a polymeric structure extended by the dioximate–MnII–dioximate
linkage. It is a weak ferromagnet (TC = 5.5 K) exhibiting a weak antiferromagnetic interaction between the
ferrimagnetic chains.
Introduction
The design of molecular-based magnetic materials is a current
subject of many studies.1–4 The use of paramagnetic metal
complexes as the constituents has great advantages over organic
radical constituents because electron spin can be reserved
to each metal center, 1-D to 3-D network structures can be
constructed based on versatile stereochemistries of metal com-
plexes, and the magnetic nature of complex-based magnets
can be tuned by choice of metal ion and bridging group.5,6 For
constructing complex-based network structures, ‘complex
Fig. 1 Chemical structure of H4L.
bridges’ are generally used that have two or more sites capable
of acting as bridges to outer metal ions.
The bridging function of oxamidate groups is well known.7–12
One of the present authors used N,N-bis(3-aminopropyl)-
oxamidatocopper() as a ‘complex ligand’ to obtain triangular
Ni 3 or Zn 4) have been prepared and characterized by X-ray
crystallography and cryomagnetic studies. An extension of
1 into a polymeric compound Mn{Cu(L)}(H2O)4 exhibiting
a magnetic phase transition at Tc = 5.5 K is reported.
tetranuclear MIICuII complexes with the MII at the center
3
and CuII at the corners of the triangle.7 These and related
complexes9 showed a significant antiferromagnetic interaction
between the adjacent CuII and MII through the oxamidate
bridge in cis arrangement. Oxamidate bridges in trans arrange-
ment are similarly good magnetic mediators and have been used
for providing bimetallic magnetic materials.9–12 The oximate
Experimental
Physical measurements
Elemental analyses of C, H and N were obtained at the Service
Center of Elemental Analysis of Kyushu University, metal
analyses using a Shimadzu A-A 680 Atomic Absorption/Flame
Emission Spectrophotometer. Infrared spectra were measured
on KBr disks with a Perkin-Elmer Spectrum BX FT-IR system,
Reflectance spectra on powdered samples with a Shimadzu
UV-3100PC spectrophotometer using an integrating sphere
attachment. Magnetic susceptibilities were measured using a
Quantum Design MPMS 5XL or MPMS2 SQUID suscepto-
meter in the temperature range 2–300 K. Calibrations were
made with the standard Pd. Data were corrected for magnetiz-
ation of the sample holder and capsule used. Diamagnetic
corrections were made using Pascal’s constants.23 Magnetiz-
ation studies were carried out with the same apparatus.
group (᎐N–OϪ) is another magnetic mediator between metal
᎐
ions.13–22 In a trinuclear copper() complex derived from
bis(dimethylglyoximato)cuprate() complete spin coupling
occurs at room temperature through the dioximate bridge
in cis arrangement.18 Significant antiferromagnetic interaction
between dissimilar ions of CuII and MII through a dioximate
bridge has been reported.19,22
In the context mentioned above, N,NЈ-bis[2-(hydroxyimino-
methyl)phenyl]oxamide (Fig. 1), abbreviated as H4L, has been
prepared in this work. Its mononuclear copper() complex
[Cu(HL)]Ϫ is expected to act as a ‘complex bridge’ with its
oxamidate and dioximate termini. Trinuclear CuIIMIICuII
complexes [M{Cu(HL)(DMF)}2(DMF)2] (MII = Mn 1, Co 2,
64
J. Chem. Soc., Dalton Trans., 2001, 64–70
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b006613n

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Preparations
ether and dried in vacuo over P2O5. The yield was 82 mg (80%).
Calc. for C16H18CuMnN4O8: C, 37.48; H, 3.54; Cu, 12.39; Mn,
10.71; N, 10.93%. Found: C, 37.48; H, 3.89; Cu, 12.86; Mn,
10.93; N, 10.42%. Selected FT-IR using KBr: ν/cmϪ1 1615,
1562, 1333, 916 and 754. Visible spectrum on powdered sample:
λ/nm 500 and 590.
N,NЈ-Bis(2-formylphenyl)oxamide was prepared by the liter-
ature method.24 All chemicals were of reagent grade used as
purchased.
N,NЈ-Bis[2-(hydroxyiminomethyl)phenyl]oxamide
(H4L).
N,NЈ-Bis(2-formylphenyl)oxamide (2.96 g, 10 mmol) and
hydroxylammonium chloride (1.39 g, 20 mmol) were added to
ethanol–water (1:1 in volume, 500 ml) and the mixture was
refluxed for 3 hours. N,NЈ-Bis(2-formylphenyl)oxamide itself
was insoluble in the mixed solvent but gradually dissolved to
form a clear yellow solution. It was evaporated to dryness, and
the resulting yellow residue treated with a saturated NaHCO3
solution (300 ml) and washed with water. Crystallization from
hot ethanol gave pale yellow needles melting at 284 ЊC. The
yield was 2.31 g (71%). Calc. for C8H7N2O2: C, 58.89; H, 4.32;
N, 17.17%. Found: C, 58.91; H, 4.37; N, 17.12%. 1H NMR [d6-
DMF]: δ 7.32 (t(2H), ring proton), 7.51(t(2H), ring proton),
Crystal structural analyses
Each single crystal of complexes 1–4 was mounted on a
glass fiber and coated with epoxy resin. Intensities and lattice
parameters were obtained on a Rigaku AFC-5S automated
four-circle diffractometer with graphite-monochromated
Mo-Kα radiation (λ = 0.71069 Å) for 2 and a Rigaku AFC-
7R automated four-circle diffractometer with graphite-
monochromated MoKα radiation (λ = 0.71069 Å) and 12 kW
rotating anode generator for 1, 3 and 4. Cell constants and
the orientation matrix for the data collection were obtained
from 25 reflections and the ω–2θ scan mode was used for the
intensity collections at 23 1 ЊC. Pertinent crystallographic
parameters are summarized in Table 1.
Three standard reflections were monitored every 150
measurements. A linear correction factor was applied to the
data to account for decay. Intensity data were corrected for
Lorentz and polarization effects.
The structures were solved by the direct method and
expanded using Fourier techniques. Non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were included in the
structure analysis but not refined. Computation were carried
out on an IRIS O2 computer using TEXSAN.25
7.61(d(4H), ring proton), 8.45(s(2H), ArCH᎐N), 8.68(d(2H),
᎐
ArNHC) and 12.46(s(2H), NOH). Selected FT-IR using KBr:
ν/cmϪ1 3540, 3272, 1691, 1578, 1315, 1293, 1007 and 750.
[Mn{Cu(HL)(DMF)}2(DMF)2] 1. H4L (163 mg, 0.5 mmol)
was dissolved in DMF (N,N-dimethylformamide) (50 ml) and
an aqueous solution of NaOH (80 mg, 2 mmol) added. A DMF
solution of copper() acetate monohydrate (100 mg, 0.5 mmol)
was added dropwise and the mixture stirred for 30 minutes.
A DMF solution of manganese() acetate tetrahydrate (61 mg,
0.25 mmol) was then added, and the mixture diffused with
diethyl ether to form dark green crystals. The yield was 182 mg
(65%). Calc. for C44H50Cu2MnN12O12: C, 47.14; H, 4.50; Cu,
11.34; Mn, 4.9; N, 14.99%. Found: C, 47.06; H, 4.63; Cu, 10.90;
Mn, 4.6; N, 14.62%. Selected FT-IR using KBr: ν/cmϪ1 1664,
1639, 1603, 1569, 1558, 1337, 920 and 756. Visible spectrum
on powdered sample: λ/nm 525 and 600.
CCDC reference number 186/2228.
See http://www.rsc.org/suppdata/dt/b0/b006613n/ for crystal-
lographic files in .cif format.
Results and discussion
Synthesis and general properties
[Co{Cu(HL)(DMF)}2(DMF)2] 2. This complex was obtained
as dark green crystals similarly to 1, using cobalt() acetate
tetrahydrate. The yield was 196 mg (70%). Calc. for C44H50-
CoCu2N12O12: C, 46.98; H, 4.48; Co, 5.2; Cu, 11.30; N, 14.94%.
Found: C, 46.71; H, 4.65; Co, 5.0; Cu, 10.83; N, 14.62%.
Selected FT-IR using KBr: ν/cmϪ1 2928, 1664, 1640, 1557,
1336, 920 and 756. Visible spectrum on powdered sample:
λ/nm 515 and 600.
In spite of many efforts, all attempts to isolate a mononuclear
copper() precursor complex of H4L were in vain. Thus, this
was prepared in solution and treated with a second metal()
ion to provide the trinuclear complexes [M{Cu(HL)(DMF)}2-
(DMF)2
] 1–4. They show complicated IR bands in the region
2300–3000 cmϪ1, which are characteristic of the hydrogen-
bonded –O–H ؒ ؒ ؒ O– linkage of the dioximate group.26,27 The
ν(C᎐O) band of the oxamidate group is seen around 1635–1640
᎐
cmϪ1, which is low relative to that of H4L (1691 cmϪ1). This is in
accord with the bridging function of the group as discussed
[Ni{Cu(HL)(DMF)}2(DMF)2] 3. This complex was obtained
as dark green crystals similarly to 1, using nickel() acetate
tetrahydrate. The yield was 168 mg (60%). Calc. for C44H50-
Cu2N12NiO12: C, 46.99; H, 4.48; Cu, 11.30; Ni, 5.2; N, 14.94%.
Found: C, 47.07; H, 4.71; Cu, 11.03; Ni, 5.5; N, 14.41%.
Selected FT-IR using KBr: ν/cmϪ1 2928, 1663, 1636, 1555,
1341, 920 and 756. Visible spectrum on powdered sample:
λ/nm 515, 600 and 965.
below. An IR band around 1663 cmϪ1 is assigned to the ν(C᎐O)
᎐
mode of the co-ordinating DMF.
The reflectance spectrum of compound 1 (CuIIMnIICuII)
shows two visible bands at 525 and 600 nm which are attributed
to the d–d components of CuII: MnII in a high-spin state has no
spin-allowed d–d band. Compound 4 (CuIIZnIICuII) also shows
two visible bands at 515 and 600 nm. A similar visible spectrum
was obtained for 2 (CuIICoIICuII). It is considered that the
d–d bands of octahedral CoII are weak and concealed by those
of CuII. In the case of 3 (CuIINiIICuII) an additional band
is observed at 965 nm that is assigned to a d–d component
of NiII.
[Zn{Cu(HL)(DMF)}2(DMF)2] 4. This complex was obtained
as dark green crystals similarly to 1, using zinc() acetate tetra-
hydrate. The yield was 170 mg (60%). Calc. for C44H50Cu2-
N12O12Zn: C, 46.71; H, 4.45; Cu, 11.23; N, 14.86; Zn, 5.8%.
Found: C, 46.80; H, 4.45; Cu, 11.43; N, 14.86; Zn, 6.3%.
Selected FT-IR using KBr: ν/cmϪ1 2928, 1663, 1637, 1604,
1557, 1339, 920 and 756. Visible spectrum on powdered sample:
λ/nm 515 and 600.
Crystal structures
Complexes 1–4 are isostructural. An ORTEP28 drawing of 1
with the atom numbering scheme is given in Fig. 2. Selected
bond distances and angles for 1–4 are summarized in Table 2.
The asymmetric unit consists of half of the [Mn{Cu(HL)-
(DMF)}2(DMF)2]: the Mn exists on the mirror plane. The
Cu resides in the N4 cavity of the ligand with two oxamidate
nitrogens and two oxime nitrogens. The geometry about the Cu
is square pyramidal with N(1), N(2), N(3) and N(4) of (HL)3Ϫ
Mn{Cu(L)}(H2O)4 5. To a solution of complex 1 (224 mg, 0.2
mmol) in CH3CN–water (1:1 in volume, 50 ml) were added
KOH (22 mg, 0.4 mmol) and 18-crown-6 (105 mg, 0.4 mmol).
To the resulting solution was added manganese() perchlorate
hexahydrate (72 mg, 0.2 mmol) and the mixture stirred to give a
brown crystalline powder. It was collected, washed with diethyl
J. Chem. Soc., Dalton Trans., 2001, 64–70
65

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Table 1 Crystal parameters for complexes 1–4
1
2
3
4
Formula
Formula weight
Crystal system
Space group
a/Å
b/Å
c/Å
C44H50Cu2MnN12O12
C44H50CoCu2N12O12
1124.98
Monoclinic
C2/c (no. 15)
24.903(5)
10.222(4)
19.569(6)
103.87(2)
4836(2)
C44H50Cu2N12NiO12
1124.74
Monoclinic
C2/c (no. 15)
24.86(1)
10.279(3)
19.373(5)
104.86(3)
4784(2)
C44H50Cu2N12O12Zn
1131.42
Monoclinic
C2/c (no. 15)
24.910(4)
10.245(3)
19.459(3)
104.72(1)
4802(1)
1120.98
Monoclinic
C2/c (no. 15)
24.904(4)
10.229(2)
19.581(2)
103.93(1)
4841(1)
4
β/Њ
V/Å3
Z
4
4
4
µ(Mo-Kα)/cmϪ1
12.12
12.85
13.45
14.48
No. observations (I > 3.00σ(I))
R
2996
0.043
2831
0.049
1537
0.063
2082
0.049
Rw
0.051
0.058
0.068
0.050
Table 2 Selected bond distances (Å) and angles (Њ) for complexes 1–4
M = Mn (1)
Co (2)
Ni (3)
Zn (4)
Cu–N(1)
Cu–N(2)
Cu–N(3)
Cu–N(4)
Cu–O(5)
M–O(1)
M–O(2)
M–O(6)
1.991(4)
1.998(4)
2.014(4)
1.976(4)
2.378(4)
2.174(4)
2.167(3)
2.159(4)
1.988(4)
1.999(4)
2.007(5)
1.989(5)
2.375(4)
2.173(4)
2.163(3)
2.159(5)
1.99(1)
1.99(1)
2.01(1)
1.99(1)
2.38(1)
2.052(9)
2.022(9)
2.04(1)
1.991(6)
2.009(6)
2.012(7)
1.987(6)
2.376(6)
2.103(5)
2.064(5)
2.089(6)
N(1)–Cu–N(2)
N(1)–Cu–N(3)
N(1)–Cu–N(4)
N(2)–Cu–N(3)
N(2)–Cu–N(4)
N(3)–Cu–N(4)
O(1)–M–O(1)*
O(1)–M–O(2)
O(1)–M–O(2)*
O(1)–M–O(6)
O(1)–M–O(6)*
O(2)–M–O(2)*
O(2)–M–O(6)
O(2)–M–O(6)*
O(6)–M–O(6)*
84.2(1)
89.0(2)
172.7(1)
164.1(1)
90.7(1)
94.6(2)
93.6(2)
74.3(1)
97.7(1)
91.3(1)
163.8(1)
168.6(2)
98.5(1)
89.7(1)
88.3(2)
83.8(2)
89.0(2)
172.7(2)
164.1(2)
91.1(2)
94.7(2)
93.5(2)
74.5(1)
97.7(1)
91.2(2)
163.8(2)
168.8(2)
98.4(2)
89.6(2)
88.5(3)
84.0(5)
89.5(5)
171.0(5)
164.6(4)
90.4(5)
94.1(5)
94.4(5)
79.7(3)
96.0(3)
90.8(4)
170.8(4)
173.6(6)
92.3(4)
92.4(4)
85.1(7)
84.0(2)
89.2(3)
171.7(3)
164.7(3)
90.3(3)
94.9(3)
94.5(3)
78.1(2)
95.8(2)
90.7(2)
168.4(2)
171.2(3)
95.4(2)
91.1(2)
86.1(4)
1
–
Symmetry operation: (*) Ϫx, y, 2 Ϫ z.
N(4)–O(4)–H(6) and O(3)–H(6)–O(4) angles are 98.4, 102.0
and 156.9Њ, respectively. The O(3) ؒ ؒ ؒ O(4) separation is short
(2.381(6) Å), suggesting that the hydrogen bond is very strong.
The oxamidatomanganese entity forms a good coplane, but the
[Cu(HL)]Ϫ molecule is not coplanar. The least-squares plane
defined by Cu, N(1), N(2), N(3) and N(4) and that defined by
N(1), N(2), C(15), C(16), O(1), O(2) and Mn are bent at the
N(1) ؒ ؒ ؒ N(2) edge with a dihedral angle of 21.02Њ (see Fig. 2).
The MnII has a cis-octahedral geometry with four oxamidate
oxygens, O(1), O(2), O(1)* and O(2)*, and two DMF oxygens,
O(6) and O(6)* (* indicates the symmetry operation of Ϫx, y,
¹ Ϫ z). The Mn–O bond distances range from 2.159(4) to
¯
²
2.174(4) Å. The CuII ؒ ؒ ؒ MnII separation is 5.491(1) Å.
The {Cu(HL)}Ϫ parts in complexes 1–4 are essentially
similar. Some noticeable differences in the structures are
seen in the geometry around the MII. The average M–O bond
distance decreases in the order: 1 (2.167) ≈ 2 (2.165) > 4
(2.085) > 3 (2.038 Å). Notably, 1 and 2 have the same
M–O bond distance in spite of the markedly differing ionic
radius between MnII (0.97) and CoII (0.89 Å).29 The M–O
bond distance of 2–4 decreases with decreasing ionic radius
of the MII. The M ؒ ؒ ؒ Cu intermetallic distances separated by
the oxamidate bridge are in a similar order: 1 (5.491(1)) ≈ 2
(5.490(2)) > 4 (5.385(1)) > 3 (5.334(3) Å).
Fig. 2 An ORTEP view of [Mn{Cu(HL)(DMF)}2(DMF)2] 1 with the
atom numbering scheme.
on the basal plane and O(5) of DMF at the apex. The Cu–N
bond distances range from 1.976(4) to 2.014(4) Å. The axial
Cu–O(5) bond distance is 2.378(4) Å which is elongated due to
the Jahn–Teller effect of the d9 electronic configuration. The
Cu is displaced by 0.179 Å from the basal least-squares plane
toward O(5). One proton of the oxime group is deprotonated to
form a N–O–H ؒ ؒ ؒ O–N hydrogen bond. The N(3)–O(3)–H(6),
66
J. Chem. Soc., Dalton Trans., 2001, 64–70

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Fig. 4 χm vs. T plots for [Co{Cu(HL)(DMF)}2(DMF)2] 2 and χm vs. T
Fig. 3 χm vs. T and µeff vs. T plots for [Mn{Cu(HL)(DMF)}2-
(DMF)2] 1.
and µeff vs. T plots for [Ni{Cu(HL)(DMF)}2(DMF)2] 3.
of CoII.34 An antiferromagnetic interaction may operate
between the adjacent CuII and CoII, but the exchange integral
could not be evaluated because of the orbital contribution from
the CoII.
The µeff vs. T and χm vs. T curves of complex 3 are shown
in Fig. 4. The effective magnetic moment at room temperature
is 3.38 µB, which is small relative to the spin-only value (3.74 µB)
expected for two CuII (S = 1/2) and one NiII (S = 1). The
magnetic moment decreased with decreasing temperature to
0.82 µB at 2 K. The magnetic behavior indicates significant
antiferromagnetic interaction between the adjacent CuII and
NiII through the oxamidate bridge. The magnetic susceptibility
expression for the CuII–NiII–CuII system is given by eqn. (2),30
Magnetic properties
The room-temperature magnetic moment of complex 1 is
6.20 µB (per molecule) that is slightly smaller than the spin-
only value (6.40 µB) expected for two CuII (S = 1/2) and one
MnII (S = 5/2). The effective magnetic moment decreased
with decreasing temperature to a near plateau value of 3.90 µB
below 20 K (Fig. 3). The plateau moment is close to the
spin-only value for ST = 3/2 (3.87 µB) resulting from the anti-
ferromagnetic spin coupling in the CuII–MnII–CuII system. The
interaction between the terminal CuII can be ignored because
complex 4 (CuZnCu) shows little temperature dependence
of magnetic moment (1.78 µB at 300 K and 1.76 µB at 10 K).
Based on the spin Hamiltonian H = Ϫ2JSMn(SCu1 ϩ SCu2),
the magnetic susceptibility expression for the CuII–MnII–CuII
system is given by eqn. (1),30 where N is Avogadro’s number,
χm = {2Ng2β2/kT}[5exp(4J/kT) ϩ 1 ϩ
exp(2J/kT)]/[5exp(4J/kT) ϩ 3 ϩ
exp(Ϫ2J/kT) ϩ 3exp(2J/kT)] ϩ Nα (2)
χm = {Ng2β2/4k(T Ϫ θ)}[84exp(5J/kT) ϩ
based on the Heisenberg model H = Ϫ2JSNi(SCu1 ϩ SCu2).
Magnetic simulations with this equation gave a poor fitting
in the low temperature region below 60 K. A sharp increase
in χm below 10 K suggests a secondary contribution such as
an intermolecular interaction or contamination with a para-
magnetic impurity. Thus, magnetic simulations were carried
out using the modified expression (2Ј), where ρ is the fraction
35exp(Ϫ2J/kT) ϩ 10exp(Ϫ7J/kT) ϩ 35]/[4exp(5J/kT) ϩ
3exp(Ϫ2J/kT) ϩ 2exp(Ϫ7J/kT) ϩ 3] ϩ Nα (1)
g the Lande g factor, β the Bohr magneton, k the Boltzmann
constant, J the exchange integral, T the absolute temperature,
θ the Weiss constant and Nα the temperature-independent
paramagnetism. The same g factor is applied for four different
spin states, (S = 7/2, SЈ = 1), (S = 5/2, SЈ = 1), (S = 3/2, SЈ = 1)
and (S = 5/2, SЈ = 0), defined by S = SMn ϩ SCu1 ϩ SCu2 and
SЈ = SCu1 ϩ SCu2. A good magnetic simulation is obtained by
eqn. (1), using the best-fit parameters J = Ϫ14 cmϪ1, g = 2.07,
and Nα = 120 × 10Ϫ6 cm3 molϪ1 and θ = Ϫ0.1 K (see Fig. 3). The
discrepancy factor defined as R(χ) = [∑(χobs Ϫ χcalc)2/∑(χobs)2]1/2
χm = (1 Ϫ ρ){2Ng2β2/k(T Ϫ θ))}[5exp(4J/kT) ϩ 1 ϩ
exp(2J/kT)]/[5exp(4J/kT) ϩ 3 ϩ exp(Ϫ2J/kT) ϩ
3exp(2J/kT)] ϩ (2Ng2β2ρ/3kT) ϩ Nα (2Ј)
of paramagnetic impurity. The paramagnetic impurity is
presumed to be a nickel() species because no copper()
complex was isolated from H4L. As seen in Fig. 4, a tolerable
magnetic simulation is achieved using J = Ϫ48 cmϪ1, g = 2.06,
Nα = 400 × 10Ϫ6 cm3 molϪ1, and ρ = 0.08. The discrepancy
was 2.99 × 10Ϫ3
.
Oxamato-bridged CuIIMnIICuII complexes with a similar
trinuclear core structure are known.31 It is noted that their
exchange integrals (Ϫ14.7 to Ϫ16.9 cmϪ1) are comparable to
that observed for 1 (J = Ϫ14 cmϪ1). Comparable exchange
integrals (Ϫ11.7 to Ϫ18.3 cmϪ1) have also been reported for
other complexes with CuII and MnII combined by oxamido or
oxamato bridges.10,32,33
factor R(χ) was 6.98 × 10Ϫ2
.
Extension to an ordered network
The trinuclear complexes 1–4 are expected to combine another
metal ion through the dioximate bridge to give a polymeric
compound. This is possible only when the trinuclear CuMCu
core does not cause metal scrambling in the reaction with a
third metal ion. In order to avoid such a problem, in this work
1 (CuMnCu) was treated with MnII. It is considered that
The µeff vs. T curve of complex 2 is given in Fig. 4. The
effective magnetic moment at room temperature is 5.78 µB
that is larger than the spin-only value (4.24 µB) expected for two
CuII (S = 1/2) and one CoII (S = 3/2). The magnetic moment
slightly increased with decreasing temperature to a maximum
of 5.88 µB near 245 K and then continuously decreased to
1.52 µB at 2 K. Such magnetic behavior is probably due to a
MnII prefers the dioximate oxygens to the N4 cavity of L4Ϫ
.
In our first attempt using LiOH as the base in CH3CN, com-
plex 1 formed a stable dilithium salt that had little reactivity
4
large orbital contribution arising from the T1g ground term
J. Chem. Soc., Dalton Trans., 2001, 64–70
67

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Scheme 1 Synthesis of Mn{Cu(L)}(H2O)4 5 from complex 1.
toward MnII. Thus, KOH was used fully to deprotonate the
dioxime proton and 18-crown-6 added to eliminate potassium
ion by complexation. To the resulting solution was added
manganese() perchlorate hexahydrate, precipitating crystalline
Mn{Cu(L)}(H2O)4 5. The synthesis is shown in Scheme 1.
Compound 5 shows no IR vibration in the region 2300–3000
cmϪ1, indicating that the dioxime part is fully deprotonated
and involved in polymeric structure formation. Another not-
able feature is the lack of the ν(C᎐O) vibration of DMF and the
᎐
appearance of a ν(OH) mode around 3500 cmϪ1. This means
that the DMF molecules in 1 are replaced with water molecules
in 5. In fact, analytical data for 5 indicate the presence of four
water molecules instead of DMF. The reflectance spectrum of
5 resembles that of 1 and shows two visible bands at 500 and
590 nm. Together with the crystallographic result for 1, the
most likely structure of 5 is as in Scheme 1.
The cryomagnetic properties of complex 5 were studied in
the temperature range 2–300 K. The χm vs. T and µeff vs. T plots
are given in Fig. 5. The effective magnetic moment at room
temperature is 5.99 µB, which is slightly smaller than the spin-
only value (6.16 µB) expected for uncoupled CuII (S = 1/2) and
MnII (S = 5/2) ions. The magnetic moment decreased with
decreasing temperature to a minimum value of 5.04 µB near
60 K. This is close to the spin-only value for ST = 2 (4.90 µB)
arising from antiferromagnetic spin coupling between CuII
(S = 1/2) and MnII (S = 5/2). This fact implies a strong anti-
ferromangetic interaction between CuII and MnII through the
cis dioximate bridge in spite of a large intermetallic distance
(ca. 3.65–3.75 Å18). With further decrease in temperature,
the magnetic moment of 5 increased to a maximum value of
17.80 µB at 5 K and then decreased below this temperature. The
cryomagnetic behavior suggests that 5 is a weak ferromagnet
exhibiting a weak antiferromagnetic interaction between the
ferrimagnetic chains.
Fig. 5 χm vs. T and µeff vs. T plots for Mn{Cu(L)}(H2O)4 5.
The field-cooled magnetization (FCM) under an applied field
of 5 G increased rapidly below 9 K to a maximum at 5.2 K,
decreased to a minimum at 4.2 K, and then increased to 67 cm3
G molϪ1 at 2.0 K (Fig. 6). When the applied field was switched
off at 2 K a remnant magnetization of 34 cm3 G molϪ1
remained that decreased upon warming and vanished at ≈8 K.
The zero-field-cooled magnetization (ZFCM) under an applied
field of 5 G showed a maximum at 5.5 K. From these studies the
magnetic phase transition temperature (TC) was determined to
be 5.5 K. The ZFCM curve shows another phase transition at
3.6 K, but its origin was not studied.
Fig. 6 Field-cooled magnetization (FCM) (᭹) under 5 G, zero-field-
cooled magnetization (ZFCM) (᭺), and remnant magnetization
(RM) (᭝) for Mn{Cu(L)}(H2O)4 5.
68
J. Chem. Soc., Dalton Trans., 2001, 64–70

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Fig. 9 M vs. T curves of Mn{Cu(L)}(H2O)4 5 under different applied
fields (measured at 2 K): (1) 50, (2) 100, (3) 200, (4) 250, (5) 300 G.
Fig. 7 Field dependences of magnetization for Mn{Cu(L)}(H2O)4
5 (determined at 2 K).
Acknowledgements
This work was supported by Grants-in-Aid for Scientific
Research (No. 09440231), Scientific Research on Priority
Area ‘Metal-assembled Complexes’ (No. 10149106) and an
International Scientific Research Program (No. 09044093)
from the Ministry of Education, Science and Culture, Japan.
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