Intramolecular magnetic interaction of phenylene-linked bis-β-diketone metal complexes

Article abstract of DOI:10.1246/cl.2000.812

Dinuclear metal complexes of phenylene-linked bis-β-diketone ligands were prepared and the magnetic interactions between the complex units along the π-conjugated linkers were investigated. Both ferro-and antiferromagnetic interactions were observed for th

Full text of DOI:10.1246/cl.2000.812

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Chemistry Letters 2000
Intramolecular Magnetic Interaction of Phenylene-Linked
Bis-β-diketone Metal Complexes
Michio M. Matsushita,†,†† Tomohiro Yasuda, Ryuji Kawano, Tadashi Kawai, and Tomokazu Iyoda*
†
†
†
†
†
Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397
†
†
PRESTO21, JST, Hachioji, Tokyo 192-0397
(Received April 24, 2000; CL-000388)
Dinuclear metal complexes of phenylene-linked bis-β-di-
ketone ligands were prepared and the magnetic interactions
between the complex units along the π-conjugated linkers were
investigated. Both ferro- and antiferromagnetic interactions were
observed for the m- and p-phenylene-linked dimers, respectively.
Recently, a wide variety of supramolecular structures have
been constructed by self-assembling technique of molecular
building blocks with hydrogen bonding and coordination bond-
1
ing. These kinds of structures are still more responsible for the
design of molecular magnetism, because the dimensionality and
the topology of the assembly structures delicately affect their
whole electronic structures. β-Diketone is one of the best versa-
2
8
angular prism structure with three twisted ligands can be con-
tile building blocks to construct coordination-based assemblies as
multi-nuclear metal complexes with strong interaction through
the pseudo-aromatic six-membered ring consisting of the enolate
and the coordinated metal ion. When plural β-diketones are
linked by an appropriate π-conjugated linker, inter-metal, π−π,
and metal-π interactions should be considered. Here, the spin
exchange interaction between the paramagnetic metal ions was
investigated in a series of dinuclear metal complexes consisting
of m- and p-phenylene-linked bis-β-diketone ligands 1 and 2 as
cluded as common structures of the divalent and trivalent metal
complexes, respectively (Figure 1). The same metal-to-ligand
compositions with 1:1 and 2:3 for divalent and trivalent metal
ions, respectively, were found in case of the ligand 2, although
the possibility of polymeric structures was not excluded yet.
The magnetic susceptibilities of all the dinuclear complexes
in a high temperature range were consistent with the expected
spin multiplicities. As lowering temperature, an increasing and a
decreasing χT values were observed for m- and p-phenylene-
linked Cu(II) complexes, respectively, whereas the mononuclear
3,4
the smallest models for the extended coordination polymers.
3
·Cu complex showed paramagnetic behavior in a wide temper-
2
ature range (Figure 2). The temperature-dependent susceptibili-
Considerable red-shifts of the UV absorption bands of the
bis-β-diketone ligands 1 were observed at 356 nm and 2 at 375
5
nm, compared with 1,3-diphenyl-1,3-propanedione 3 at 343 nm.
These spectra suggest an extended π-conjugation due to the
phenylene linkers connecting two β-diketones. The metal com-
plexes were prepared by mixing the ligands with metal acetate or
perchlorate in the 1:1 mixed solution of methanol and
dichloromethane. The divalent metal ions, Zn(II), Cu(II) and
Ni(II), afforded 1:1 complexes with 1 and 2, while trivalent metal
ions, Mn(III) and Fe(III), afforded 2:3 complexes, based on CHN
ties (Figure 3) of several metal complexes of 1 were well fitted
by the dinuclear model (eq. (1), solid lines). The evaluated
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elemental analysis and ICP measurement. All the FT-IR spectra
indicated complete coordination of two enolate anions of the lig-
intra- and intermolecular magnetic interactions, J and J’, are list-
ed in Table 1. All the intramolecular J values of the complexes
of 1 were positive. Direct through-space interaction should be
negligible because of too long intramolecular metal-to-metal dis-
tance (approximately 7 Å). The consistent positive values of
the spin exchange interaction strongly suggests that the m-
ands.7 The H-NMR spectra of 1 ·Zn suggested the rotation-
1
2
2
pinning of the m-phenylene linker and the formation of a large
cyclic structure, shown as a dotted circle in Figure 1(a). The di-
nuclear metal complexes of 1 gave consistent parent peaks in the
FAB mass spectra. A planar structure with a large ring and a tri-
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
813
This work was partially supported by Grant-in-Aid for
Scientific Research (A) (No. 11305061), and Scientific Research
on Priority Area (B) of “Development of Molecular Conductors
and Magnets by Spin-Control” (No.730/11224207) from the
Ministry of Education, Science, Sports, and Culture, Japan.
References and Notes
1
2
3
J.-M. Lehn, “Supramolecular Chemistry”, VCH Publishers, Inc.,
Weinhelm (1995).
“Magnetic Properties of Organic Materials”, ed. by P. M. Lahti,
Marcel Dekker, Inc., New York (1999).
The β-diketone dimers, 1 and 2, were prepared from dimethylphtha-
late isomers and acetophenone by Claisen condensation: D. F. Martin,
M. Shamma, and W. C. Fernelius, J. Am. Chem. Soc., 80, 4891 (1958).
A few crystallographic studies on a series of dinuclear metal com-
plexes based on the identical bis-β-diketone ligands have been report-
ed, but no information on the electronic interaction was given: V. A.
Grillo, E. J. Seddon, C. M. Grant, G. Aromí, J. C. Bollinger, K.
Folting, and G. Christou, J. Chem. Soc., Chem. Commun., 1997, 1561.
Only enol-type tautomer exists in benzene solution.
4
5
6
1 ·Zn ·H O: white solid, Found: C, 64.76; H, 3.60; Zn, 14.47%. Calcd
2
2
2
−
1
for C H O Zn: C, 65.10; H, 3.87; Zn, 14.77%. ν : 1591 cm
,
4
8
34
9
COO
−
1
ν
: 236 cm . 1 ·Cu : green solid, Found: C, 66.24, H, 3.67%.
2 2
1
O–Zn
−
Calcd for C48H32Cu O : C, 66.74; H, 3.73%. ν
O–Cu
: 283 cm .
2
8
1
·Ni ·DMF : yellowish green crystal, Found: C, 60.50, H, 4.45%.
2 4
1
2
−
Calcd for C H N Ni O C, 60.38; H, 4.29%. ν : 1597 cm , ν :
52
44
4
2
12
C=O
O–Ni
−
1
+
2
61 cm
. MS(FAB): m/z 853 (M+1) . 1 ·Mn ·(CH Cl ) : dark
3 2 2 2 0.5
green crystals, Found: C, 69.36, H, 3.83%. Calcd for
−
1
C1 H Cl Mn O : C, 69.25; H, 3.93%. ν : 1593 cm , νO–Mn: 320
45
98
2
4
12
C=O
−
1
cm
. 1 ·Fe : red crystal, Found: C, 70.96, H, 3.96%. Calcd for
3 2
1
−
−1
C H Fe O : C, 71.07; H, 3.98%. ν : 1591 cm , ν
: 293 cm .
7
2
48
2
12
C=O
O–Fe
2
·Cu: green solid, Found: C, 66.97, H, 3.63%. Calcd for C H CuO :
24 16 4
–1
C, 66.74; H, 3.73%. ν
: 273 cm . 2·Ni·DMF : yellowish green
2
O–Cu
crystal, Found: C, 60.35, H, 4.50%. Calcd for C H N Ni O C,
5
2
44
4
2
12
−1
−1
6
0.38; H, 4.29%. ν : 1591 cm , ν
: 285 cm . 2 ·Mn ·CH Cl :
C=O
O–Ni 3 2 2 2
brown solid, Found: C, 66.58, H, 4.15%. Calcd for C H Cl Mn O :
7
3
50
2
2
12
−1
−1
C, 67.45; H, 3.88%. ν : 1593 cm , ν
: 321 cm .
C=O
O–Mn
7
8
The complete coordination of the complexes were confirmed by FT-
IR measurements: (1) The disappearance of the C–H bending of the
−
1
keto-type tautomer at 758 cm . (2) The red-shift of the C=O stretch-
ing band (3) The appearance of the Metal–O stretching band in a far-
infrared region.
Crystal data for 1 ·Fe : C H Fe O , molecular weight = 1216.18,
3
2
72 48
2
12
monoclinic, space group C2/c (No. 15), a=23.0620(8),
3
b=17.9239(12), c=18.2615(3) Å, β=127.244(5)°, V=6267.2(4) Å ,
3
Z=4, D
= 1.3013 g/cm , R (Rw) =0.048 (0.043) for 2406 unique
calcd
reflections with I > 3σ and 386 parameters. The ORTEP drawing of
the molecular structure is shown in the graphical abstract. Another
structure on the 1 ·Fe , was reported as one of polymorphism. The
Mn(III), Ti(III), and V(III) complexes were also reported: see Ref. 4.
The dinuclear model with isotropic antiferromagnetic intermolecular
interaction: O. Kahn, “Molecular Magnetism,” VCH Publishers, Inc.,
New York (1993).
N. Mataga, Theor. Chim. Acta, 10, 372 (1968); A. A. Ovchinnikov,
Theoret. Chim. Acta, 108, 368 (1986); A. Rajca, Chem. Rev., 94, 871
(1994).
phenylene linker carries ferromagnetic through-bond interaction
between two metal ions, whereas the p-phenylene does antifer-
romagnetic interaction. These results can be explained by the
spin polarization mechanism, well-established for the pheny-
3
2
9
1
1
0
lene-linked diradicals (Figure 4). The metal-dependence of
0
the observed J values is similar to a series of dinuclear metal
1
2
complexes consisting of 2,2'-bipyrimidine ligands, implying
1
3
11 The drawing in Figure 4 stands on the spin polarization mechanism,
well-established in the phenylene linkers. Although the spin alterna-
tion on the aromatic system might be influenced through intervening
heteroatoms, it dose not influence the whole metal–metal interaction
in these dinuclear complexes, because the structural symmetry found
in the dinuclear complexes gives the consistent result on the whole
metal-to-metal interaction.
that the d−π interaction at the coordination bonds also plays
an important role in the interaction path.14
12
G. De Munno, M. Julve, F. Lloret, J. Cano, and A. Caneschi, Inorg.
Chem., 34, 2048 (1995); E. Andrés, G. De Munno, M. Julve, J. A.
Real, and F. Lloret, J. Chem. Soc., Dalton Trans., 1993, 2169; J. A.
Real, J. Zarembowitch, O. Kahn, and X. Solans, Inorg. Chem., 26,
2
939 (1987); G. De Munno, R. Ruiz, F. Lloret, J. Faus, R. Sessoli,
and M. Julve, Inorg. Chem., 34, 408 (1995); G. De Munno, M. Julve,
F. Lloret, and A. Derory, J. Chem. Soc., Dalton Trans., 1993, 1179.
F. Lloret, M. Julve, J. Faus, X. Solans, Y. Journaux, and I.
Morgenstern-Badarau, Inorg. Chem. 29, 2232 (1990).
1
3
In conclusion, the present dinuclear metal complexes based
on the phenylene-linked bis-β-diketone ligands should become
the potential prototype for the coordination-based molecular
architecture with the manipulation of the path-specific electron-
ic interactions such as the spin polarization.
14 The spin polarization along the phenylene linker also varies as a func-
tion of the dihedral angle between the adjacent π-conjugated planes,
according to the Karplus’s relationship: A. Izuoka, M. Fukada, R.
Kumai, M. Itakura, S. Hikami, and T. Sugawara, J. Am. Chem. Soc.,
1
16, 2609 (1994).