Self-organized metallo-helicates and -ladder with 2,2′-biphenyldicarboxylate (C14H8O4)2-: Synthesis, crystal structures, and magnetic properties

Article abstract of DOI:10.1246/bcsj.75.1283

We report on the hydrothermal synthesis, single-crystal structures and magnetic properties of three one-dimensional coordination polymers employing the 2,2′-biphenyldicarboxylate dianion, (C₁₄H₈O₄)^2-, as the bridging component. [M^II(H₂O)₄(C₁₄H₈ O₄)], where M = Co (1) and Ni (2), consist of helical chains of square-planar M^II(H₂O)₄ bridged by C₁₄H₈O₄ with each carboxylate group acting as a mono-dentate ligand. The magnetic properties are those of paramagnets (1:C = 3.34(1) cm³K/mol, μ_eff= 5.17 μ_B, θ = -51(1) K;2: C = 0.985(9) cm³K/mol, μ_eff = 2.81 μ_B, θ = +27(2) K) with an antiferromagnetic exchange for 1 and a ferromagnetic exchange for 2. Cu₂(C₁₄H₈O₄) (H₂O)₂ (3) is composed of tetracarboxylato-dimeric units bridged into ladders by biphenyl units. The ladders are packed parallel to each other, and narrow channels are present due to insufficient space filling of the biphenyl rings. Its magnetic behavior follows that of a Bleaney-Bowers singlet-triplet model with a gap of 470(10) K.

Full text of DOI:10.1246/bcsj.75.1283

c. Jpn.
© 2002 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 75, 1283–1289 (2002) 1283
e Chemical
ciety of Ja-
n
e Chemical
ciety of Ja-
n
Self-Organized Metallo-Helicates and -Ladder with 2,2ꢀ-Biphenyldicar-
boxylate (C14H8O4)2−: Synthesis, Crystal Structures, and Magnetic
Properties
Self-Organizaed Metallo-Helicates and -Ladder
H. Kumagai et al.
02
83
Hitoshi Kumagai,* Katsuya Inoue, and Mohamedally Kurmoo†
89
Applied Molecular Science, Institute for Molecular Science, Nishigounaka 38, Myoudaiji, Okazaki 444-8585
†Institut de Physique et Chimie des Matériaux de Strasbourg, 23 rue du Loess, F-67037 Strasbourg Cedex, France
SJA8
09-2673
425
(Received November 28, 2001)
01
02
We report on the hydrothermal synthesis, single-crystal structures and magnetic properties of three one-dimension-
al coordination polymers employing the 2,2ꢀ-biphenyldicarboxylate dianion, (C14H8O4)2−, as the bridging component.
Ⅱ
Ⅱ
[M (H2O)4(C14H8O4)], where M = Co (1) and Ni (2), consist of helical chains of square-planar M (H2O)4 bridged by
C14H8O4 with each carboxylate group acting as a mono-dentate ligand. The magnetic properties are those of paramag-
nets (1: C = 3.34(1) cm3 K/mol, µeff = 5.17 µB, θ = −51(1) K; 2: C = 0.985(9) cm3 K/mol, µeff = 2.81 µB, θ = +27(2)
K) with an antiferromagnetic exchange for 1 and a ferromagnetic exchange for 2. Cu2(C14H8O4)(H2O)2 (3) is composed
of tetracarboxylato-dimeric units bridged into ladders by biphenyl units. The ladders are packed parallel to each other,
and narrow channels are present due to insufficient space filling of the biphenyl rings. Its magnetic behavior follows that
of a Bleaney–Bowers singlet-triplet model with a gap of 470(10) K.
.1
.2
Coordination polymers are attracting much interest due to
the strength and rigidity of the extended lattices for gas sorp-
tion and intercalation and for the connectivity between mag-
netic ions in designing molecular magnets.1–5 They belong to a
subset of organic–inorganic hybrid materials, and usually em-
ploy a central metal ion and a multitopic organic ligand or a
coordination complex having ambidentate ligands, such as cy-
anide and oxalate.6–9 In some cases, other organic ligands are
used to control the dimensionality or structure.10,11 The choice
of the metals and of the ligands depends on the desired proper-
ties. On the one hand, there is strong interest by scientists
studying catalysis and the adsorption of gases originating from
the possibility of creating structures with cavities, channels or
pores and, consequently, large surface areas.12–15 On the other
hand, there is increasing interest from magneto-chemists due
principally to the realization of organizing the magnetic orbit-
als of the moment carriers to favor a particular magnetic
ground state.3,4,6–8,16 One good and simple example of the lat-
ed.27,28 Over the last decade the choice of ligands has evolved
from the traditional simple cyanide, thiocyanate, nitrate, ni-
trite, and oxalate to more unconventional, complex and large
ligands, such as the poly-pyridines, poly-amines and polycya-
nides, which have structure-directive properties through their
geometry and stereochemistry.5,10,11,29–31 The polycyanides pro-
vide another factor in complexity, that of electrical conductivi-
ty. A very good example, which has been thoroughly studied,
is Cu(DCNQI)2 and its analogues, because they exhibit a range
of interesting cooperative phenomena, such as charge redistri-
bution, π–d interaction, electronic conduction, metal–insulator
transition, superconductivity, and weak ferromagnetism.32 The
use of functionalized TTF is also being developed. Several ex-
amples of poly-phosphates, -phosphinates and carboxy-phos-
phonates are known. Poly-carboxylates have so far been prin-
cipally used by those interested in gas sorption.1,13,15 Follow-
ing the disappointing, though very interesting, early work on
using poly-carboxylate to propagate magnetic exchange, we
recently found some interesting magnetic properties from
compounds containing mono-carboxylates, di-carboxylates,
tri-carboxylates, and a tetracarboxylate.26,33 Their magnetic
properties range from ferrimagnetic with Curie temperatures
of up to 60 K and a coercivity of 20 kOe to metamagnetic with
remanance and coercivity in excess of 50 kOe at 2 K.26 In the
present study we used 2, 2ꢀ-biphenyldicarboxylic acid (also
known as diphenic acid, and abbreviated here as DPhA, ) be-
cause it contains two sterically hindered carboxylate groups
and adopts two optically active geometries (Scheme 1). Here,
we report on the hydrothermal synthesis and structures of co-
balt and nickel complexes that consist of helical chains, and of
a copper complex that consists of copper dimers bridged into
parallel ladders. We also report on their magnetic properties.
−
ter is the use of the dicyanamide (N(CN)2 ) ion to organize di-
valent transition metals into a 3-dimensional coordination
polymer having a Rutile-like structure.17–19 The ligand does
not have to be diamagnetic, as in the case of dicyanamide. The
field of coordination polymers based on organic radicals is a
very active area, indeed.20–24 Several ground states have been
established and a clear molecular-orbital picture to explain the
observations is emerging.3,4,25 Our present interest in the field
of molecular magnetism resides in the use of small diamagnet-
ic ligands; recently, we are making use of the coordination
properties of the carboxylate ion.26
The key to designing polymeric structures is, in general, that
employed in the field of supra-molecular chemistry; further, all
of the rules of covalent and hydrogen bonding are also adopt-

1284 Bull. Chem. Soc. Jpn., 75, No. 6 (2002)
Self-Organizaed Metallo-Helicates and -Ladder
Found: C, 45.04; H, 4.33; Co, 15.84%.
Calcd for 2: C14H16NiO8; C, 45.33; H, 4.35; Ni, 15.83%;
Found: C, 45.05; H, 4.34; Ni, 15.52%.
Ⅱ
Preparation of [Cu 2 (DPhA)2(H2O)2].
Copper(Ⅱ) nitrate
trihydrate (1 g) and diphenic acid (0.5 g) were dissolved in dis-
tilled water (30 mL). The mixtures were placed in the Teflon liner
of autoclaves, sealed and heated to 120 °C for 1 day. The bomb
was allowed to cool to room temperature in a water bath. Blue
crystals were obtained from a clear solution (yield 65%). The
crystals were washed with water and acetone, and dried in air.
Calcd for 3: C28H20Cu2O10; C, 52.26; H, 3.13%; Found: C,
53.28; H, 3.18%.
Scheme 1. Molecular structure of the P and M forms of
diphenic acid.
X-ray Crystallography and Structure Solution.
Selected
Experimental
single crystals were glued on the tip of glass fibers. Diffraction
data for the complexes were collected on a Bruker SMART APEX
CCD area detector employing the ω-scan mode at room tempera-
ture. The diffractometer was equipped with graphite-monochro-
mated Mo-Kα (0.7107 A) radiation. The data were corrected for
Lorentz and polarization effects. The structure was solved by di-
rect methods and expanded using Fourier techniques.34 The non-
hydrogen atoms were refined anisotropically. The final cycle of a
full-matrix least-squares refinement was based on the number of
observed reflections and n variable parameters. They converged (a
The syntheses were carried out in home-built teflon-lined cylin-
drical stainless-steel pressure bombs having a maximum capacity
of 120 mL. X-ray powder diffraction data were collected using a
Bragg–Bretano geometry on a Seimens D-500 with Co-Kα (1.789
Å) radiation at room temperature. Thermogravimetric analyses
(20 °C to 900 °C) were performed on a SETARAM TG-DTA sys-
tem at a warming rate of 5 °C/minute in a constant flow of air. In-
frared spectra were recorded by transmission through fine parti-
cles of the compounds dispersed on a KBr plate. The temperature
and field dependence of the magnetization of the complexes were
determined on a Quantum Design MPMS-XL SQUID operating in
the temperature range 2 – 300 K and fields of up to 5 T.
large parameter shift was σ times its e.s.d.) with agreement factors
of R = ΣꢀFo| − |Fcꢀ / Σ|Fo|, Rw = [Σw(|Fo| − |Fc|)2 / Σw |Fo| ]
.
2 1/2
No extinction corrections were applied. Details of the crystallo-
graphic data are given in Table 1. The CIF data for the two crys-
tals are deposited as Document No. 75028 at the Office of the Ed-
itor of Bull. Chem. Soc. Jpn. Crystallographic data hae been de-
posited 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 number CCDC 178288
– 178290.
All chemicals were obtained from Aldrich and Fluka, and were
used without purification.
Preparation of [M (DPhA)(H2O)4], M = Co or Ni.
Ⅱ
Me-
tal(Ⅱ) nitrate hexahydrate (1 g), diphenic acid (0.5 g), and NaOH
(0.34 g) were dissolved in distilled water (30 mL). The mixtures
were placed in the Teflon liner of autoclaves, sealed and heated to
120 °C for 1 day. They were allowed to cool to room temperature
in a water bath. In the case of cobalt, a black residue of cobalt ox-
ide was formed together with red block crystals (yield 60%). The
crystals were separated by decantation. For nickel, pale blue-
green crystals were obtained from a clear solution. The crystals
were washed with water and acetone and dried in air.
Results and Discussion
Biphenyls containing large groups in the ortho-positions
cannot freely rotate about the central bond because of a steric
hindrance. This restricted rotation gives rise to perpendicular
disymmetric planes and, consequently, two forms (M and P)
Calcd for 1: C14H16CoO8; C, 45.30; H, 4.34; Co, 15.88%;
Table 1. Summary of Crystallographic Data for 1, 2, and 3
1
2
3
Formula
C14H16CoO8
371.21
C14H16NiO8
370.98
C28H20Cu2O10
643.55
orthorhombic
Cmca (64)
21.224(3)
7.045(1)
Molecular weight
Crystal system
Space group
a/Å
b/Å
c/Å
monoclinic
P21/n (14)
14.347(1)
7.5253(6)
15.578(1)
115.382(1)
1519.6(2)
4
monoclinic
P21/n (14)
14.304(1)
7.4861(6)
15.570(1)
115.756(1)
1501.6(2)
4
17.720(3)
β/°
V/Å3
2649.4(7)
4
Z
Dc/g cm−3
µ(Mo Kα)/cm−1
No. unique
Reflections
No. observations
R (Rw)
1.622
11.69
3752
1.641
13.32
3678
1.613
16.64
1584
2326 (I > 3.0σ(I))
0.035 (0.032)
+0.47
2296 (I > 3.0σ(I))
0.034 (0.031)
+0.52
1584 (all data)
0.043 (2.0σ(I))
+0.64
Residual (e−/Å3)
−0.46
−0.36
−0.75

H. Kumagai et al.
Bull. Chem. Soc. Jpn., 75, No. 6 (2002) 1285
(Scheme 1). An example is biphenyl 2,2ꢀ-disulfonic acid.35
The case of hexahelicene is similar, in which one side must lie
above the other because of crowding.36 A literature search for
biphenyldicarboxylate and binaphtyldicarboxylate revealed
several examples of clathrates but, surprisingly, no crystal-
lograhically characterized known examples of metal complex-
es.37
Synthesis. For the synthesis we employed a commercially
available racemic mixture of two enantiomers of 2, 2ꢀ-biphen-
yldicarboxylic acid. Consequently, the resulting compounds
consisted of equal amounts of the two forms. In 1 and 2, we
find that the structure consists of segregated helices (M and P),
where each helix contains one form of the acid. Further details
are given below. Hydrothermal reactions with transition met-
als in mild alkaline solutions with carboxylic acid usually give
several phases, depending on the pH, the temperature, the con-
centration and sometimes the period of the reaction. Here, we
repeatedly found good-quality crystals having a maximum size
of 5 mm of only one phase under the conditions described
above, while non-characterized forms were obtained as pow-
ders at higher pH and higher temperatures.
Structures of 1 and 2. X-ray crystal structure analyses of
1 and 2 revealed that the complexes are isostructural (Table 1)
and show the expected lattice contraction on going from diva-
lent cobalt with an ionic radius of 0.89 Å to nickel with 0.83 Å.
The crystals belong to the monoclinic system, P21/n, a =
14.347(1), b = 7.5253(6), c = 15.578(1) Å, β = 115.382(1)°,
V = 1519.6(2) Å3 and Z = 4 for 1 and a = 14.304(1), b =
7.4861(6), c = 15.570(1) Å, b = 115.756(1)°, V = 1501.6(2)
Å3 and Z = 4 for 2. Since the two compounds are isostructur-
al, we restrict our description to only the cobalt compound, and
only mention the pertinent points for nickel when appropri-
ate. Figure 1 shows the asymmetric unit which contains one
metal ion, one acid and four water molecules together with the
atomic numbering scheme; selected bond distances and angles
are given in Table 2. The key feature of the structure is one-di-
mensional helices consisting of pseudo square-planar M(H2O)4
units bridged by the dicarboxylate (Figs. 2 and 3). This struc-
tural feature is basically the same as those of other M(H2O)4-
dicarboxylate, where the dicarboxylate is succinate, fumarate,
or adipate.38–40 The main difference is that in the alkane or alk-
ene backbone the chains are linear, but in the present case of
diphenic acid the chains are helical as a consequence of a re-
stricted rotation of the acid mentioned above.
Fig. 1. Structure of 1 with atomic numbering scheme. Hy-
drogen atoms are omitted for clarity. Atoms are represent-
ed by thermal ellipsoids at the 50% probability level.
Same numbering is adopted for 2.
Table 2. SelectedBondDistances(Å)andAngles(°)in1and2
Co(1)–O(1)
Co(1)–O(5)
Co(1)–O(7)
2.042(2)
2.168(3)
2.115(2)
Co(1)–O(3)
Co(1)–O(6)
Co(1)–O(8)
2.063(2)
2.096(2)
2.097(2)
O(1)–Co(1)–O(3) 176.98(8) O(1)–Co(1)–O(5) 88.0(1)
O(1)–Co(1)–O(6) 90.14(9)
O(1)–Co(1)–O(8) 91.71(9)
O(3)–Co(1)–O(6) 87.56(9)
O(3)–Co(1)–O(8) 90.62(9)
O(5)–Co(1)–O(7) 178.2(1)
O(6)–Co(1)–O(7) 87.36(8)
O(7)–Co(1)–O(8) 91.7(1)
O(1)–Co(1)–O(7) 90.26(9)
O(3)–Co(1)–O(5) 90.20(9)
O(3)–Co(1)–O(7) 91.59(8)
O(5)–Co(1)–O(6) 92.6(1)
O(5)–Co(1)–O(8) 88.4(1)
O(6)–Co(1)–O(8) 177.9(1)
Ni(1)–O(1)
Ni(1)–O(5)
Ni(1)–O(7)
2.021(2)
2.111(3)
2.065(2)
Ni(1)–O(3)
Ni(1)–O(6)
Ni(1)–O(8)
2.037(2)
2.071(2)
2.055(3)
The geometry of the dianion in the present compounds is
similar to those found in the pure acid.41 The two phenyl rings
are arranged in a near-orthogonal way, and appear like the
wings of a butterfly. The carboxylate groups are slightly out of
the plane of the phenyl rings. The average dihedral angles of
the two CO2 groups and the C6 rings are 40° and 26°. The di-
hedral angle between the two carboxylate groups is 49°. The
O≥O distances within the CO2 group are 2.19 and 2.235 Å.
The distances (O≥O) between the two CO2 groups are 3.425,
3.772, 5.228 and 5.425 Å.
O(1)–Ni(1)–O(3) 176.09(9) O(1)–Ni(1)–O(5) 87.0(1)
O(1)–Ni(1)–O(6) 89.23(9)
O(1)–Ni(1)–O(8) 93.0(1)
O(3)–Ni(1)–O(6) 88.03(9)
O(3)–Ni(1)–O(8) 89.7(1)
O(5)–Ni(1)–O(7) 177.4(1)
O(6)–Ni(1)–O(7) 87.13(9)
O(7)–Ni(1)–O(8) 91.8(1)
O(1)–Ni(1)–O(7) 90.35(9)
O(3)–Ni(1)–O(5) 90.31(9)
O(3)–Ni(1)–O(7) 92.30(9)
O(5)–Ni(1)–O(6) 92.5(1)
O(5)–Ni(1)–O(8) 88.6(1)
O(6)–Ni(1)–O(8) 177.5(1)
The metal centers adopt a distorted octahedral geometry
with a pseudo square-planar M(H2O)4 and two carboxylate ox-
ygen atoms at the trans-positions. The M–OH2 distances lie in
the range of 2.096(2)–2.168(3) Å and have angles of 91.7(1)–
92.6(1)°. The M–O(carboxylate) distances are 2.042(2) and
2.063(2) Å. The latter suggests a slightly compressed octahe-
dron. The O–Co–O angle is 177°. The Co≥Co distance with-
in a chain is 4.990 Å with M–OC6O–M connectivity; and the
next nearest Co–Co is 7.5 Å. The latter defines the pitch of the
helix and corresponds to two formula units. The nearest

1286 Bull. Chem. Soc. Jpn., 75, No. 6 (2002)
Self-Organizaed Metallo-Helicates and -Ladder
Fig. 4. Structure of a ladder in 3. Hydrogen atoms are omit-
ted for clarity. Atoms are represented by thermal ellipsoids
at the 50% probability level.
Fig. 2. Helical structure of two adjacent chains in 1 running
clockwise (left) and anticlockwise (right).
Table 3. Selected Bond Distances (Å) and Angles (°) in 3
Cu(1)–O(1)
Cu(1)–O(2)
Cu(1)–O(3)
1.949(4) Cu(1)–O(1ꢀ)
1.952(4) Cu(1)–O(2ꢀ)
2.225(6)
1.949(4)
1.952(4)
O(1)–Cu(1)–O(1)
O(1)–Cu(1)–O(2ꢀ) 90.6(2)
O(1)–Cu(1)–O(3ꢀ) 99.2(2)
88.6(3)
O(1)–Cu(1)–O(2)
O(1)–Cu(1)–O(3)
O(2)–Cu(1)–O(2ꢀ) 88.4(2)
O(2)–Cu(1)–O(3ꢀ) 91.0(2)
169.8(2)
99.2(2)
O(2)–Cu(1)–O(3)
91.0(2)
Fig. 3. Packing of the helices in 1 viewed down the chain.
Fig. 5. Structure of a single ladder of 3. The water mole-
cules and the hydrogen atoms are omitted for clarity.
Co≥Co distances between adjacent chains are 5.746, 6.404
and 8.032 Å; those between layers are 12.66–14.45 Å.
This particular structure contains an equal number of M-
and P-helices (Figs. 2 and 3). Therefore, no optical activity is
expected. The helices are parallel to the y-axis, and alternate
within the xz-plane. The helices are knitted together by several
hydrogen bonds between the oxygen atoms of the carboxylates
and the hydrogen atoms of the coordinated water molecules.
Several hydrogen bonds are found not only within the chains,
but also between the chains. The interchain bond distance be-
tween O(7) and O(2) is 2.638(2) Å. The intrachain bond is
found between a coordinated water molecule and uncoordinat-
ed carboxylate oxygen atoms (O(8)–O(2), 2.604 Å).
in contrast to the layered structure of Co(H2O)2(terephthalate),
which is composed of layers of octahedral CoO6 bridged by
the terephthalate dianion.26
Structure of 3. The structure of 3 consists of a Cu(Ⅱ),
DPhA ligand and a water molecule. Figure 4 shows an
ORTEP drawing of the dimer motif of 3 with the atomic-num-
bering scheme. Selected bond distances and angles with their
estimated standard deviations are listed in Table 3. The repeat-
ing structural motif is a propeller dicopper-tetracarboxylate
dimer (Fig. 5). The structure is composed of one-dimensional
chains of these dimers, parallel to the b-axis (Fig. 6). Because
the copper atoms within a dimer are symmetry related, all cop-
per atoms in the chain are equivalent. Each copper atom has
These hydrogen bonds create a 2D-network with all the
metals aligned in planes separated by the phenyl groups. The
two carboxylate groups are both coordinated to the same layer,

H. Kumagai et al.
Bull. Chem. Soc. Jpn., 75, No. 6 (2002) 1287
Fig. 6. Packing of the ladders in 3 viewed along the b-axis.
Fig. 7. Thermogravimetry and heat flow for 1 (dashed lines)
and 2 (solid lines).
two short Cu–O bonds (1.949(4) and 1.952(4) Å) with the
DPhA ligands and one long with the oxygen atom of the water
molecule (2.225(6) Å). The Cu≥Cu distance within the dimer
is 2.58 Å, which lies within the range found in previously re-
ported dicopper-tetracarboxylate dimers. The Cu≥Cu distanc-
es in the coper carboxylate dimers span the narrow range of
2.57 – 2.63 Å, and no dependence of the length on the substit-
uent R of the carboxylate ligand has been found.42
The geometry of the dianion in the present compounds is
similar to those found in the pure acid and in 1 and 2. The two
phenyl rings are arranged in a near-orthogonal geometry. The
carboxylate groups are slightly out of the plane of the phenyl
rings. The dihedral angle between the CO2 groups and the C6
ring is about 14°, which is smaller than that of 1. The copper
dimers are bridged by both the P and M forms of the ligand.
Thus, two enantiomers are present within the same chain, in
contrast to segregation of P and M forms in different chains for
1 and 2. Another point of difference is the hydrogen-bonding
interactions. The coordinated water molecules act as hydrogen
donors to generate a two-dimensional layer structure in 1 and
2; however, the water molecules of 3 show no hydrogen-bond-
ing interactions between the ladders. One of the possible rea-
sons is the coordination mode of the DPhA ligand. The DPhA
ligand acts as a monodentate ligand to bind a metal ion, and
the other oxygen atom of the acid becomes the hydrogen ac-
ceptor site in 1 and 2. Because the DPhA ligand acts as a bi-
dentate ligand to bridge two metal centers in 3, no more hydro-
gen bonding sites are provided. The packing of the ladders is
not very efficient due to the orientation and bulkiness of the
diphenyl groups. Some narrow cavities appear between the
ladders that may be appropriate for gas sorption.43
Fig. 8. Temperature dependence of the χT and 1/χ for 1 and
2.
ature in a fixed magnetic field and the isothermal magnetiza-
tion in a field of up to 5 T at 2 K. The results for 1 and 2 are
shown in Figs. 8 and 9. The moment of 1, presented as the
product of the susceptibility and temperature, shows a gradual
decrease upon lowering the temperature; the data above 150 K
fit the Curie-Weiss function with C = 3.34(1) cm3 K/mol, θ =
−51(1) K. The calculated moment is µeff = 5.17 µB, which is
on a higher side of the expected value for an octahedral coordi-
nated cobalt(Ⅱ). This may be the effect of a distortion of the
octahedron, and the consequent, dark-red coloration. The neg-
ative Weiss temperature suggests an antiferromagnetic ex-
change between near neighbors. However, the Weiss tempera-
ture derived from the fit also reflects the effect of spin-orbit
coupling, which is of the order of −20 K in the case of a free
ion assuming a spin orbit coupling of 170 cm−1.44 A similar
analysis for 2 gives C = 0.985(9) cm3 K/mol and θ = +27(2)
K. The effective moment (µeff = 2.81 µB) is as expected for oc-
tahedral Ni(Ⅱ). The positive Weiss temperature suggests a
considerable ferromagnetic exchange. However, at low tem-
Thermogravimetry. The thermal analysis of 1 and 2 and
the associated heat flow are shown in Fig. 7. Both compounds
are stable up to 85 °C. They lose a total of four molecules of
water endo-thermically upon heating up to 165 °C. There is a
difference of 25 °C between the cobalt and nickel complexes,
suggesting a slightly stronger M–OH2 bond for 2. The second
step is the exothermic decomposition of the organic moiety,
which spans 280–350 °C. The resulting products are the ex-
pected oxides, Co3O4 and NiO.
Magnetic Properties. The magnetic susceptibilities of
the three compounds were studied as a function of the temper-

1288 Bull. Chem. Soc. Jpn., 75, No. 6 (2002)
Self-Organizaed Metallo-Helicates and -Ladder
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This work was funded by a Grant-in-Aid for scientific re-
search from the Ministry of Education, Science, Sports, and
Culture and the CNRS, France. MK thanks the Royal Society
of Chemistry (UK) for a travel grant and HK thanks the Japan
Society for the Promotion of Science for his postdoctoral fel-
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