Di- and trinuclear nickel(II) complexes containing tripodal hexadentate ligands

Article abstract of DOI:10.1246/cl.2001.842

The reaction of Ni²⁺ with a tripodal hexadentate ligand (H₃L = 1,1,1-tris(N-salicylideneaminomethyl)ethane) afforded the O-H...O bridged dinuclear [Ni₂(HL)₂] complex. When Ni²⁺ was allowed to react wi

Full text of DOI:10.1246/cl.2001.842

842
Chemistry Letters 2001
Di- and Trinuclear Nickel(II) Complexes Containing Tripodal Hexadentate Ligands
Hiromi Ohta, Kenji Harada, Koji Irie, Setsuo Kashino, Takashi Kambe,† Genta Sakane,†† Takashi Shibahara,††
Satoshi Takamizawa,††† Wasuke Mori,††† Matsuo Nonoyama,†††† Masakazu Hirotsu†††††, and Masaaki Kojima*
Department of Chemistry, Faculty of Science, Okayama University, Tsushima, Okayama 700-8530
†Department of Physics, Faculty of Science, Okayama University, Tsushima, Okayama 700-8530
††Department of Chemistry, Okayama University of Science, Ridai-cho, Okayama 700-0005
†††Department of Chemistry, Faculty of Science, Kanagawa University, Hiratsuka, Kanagawa 259-1293
††††Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602
†††††Department of Chemistry, Faculty of Engineering, Gunma University, Kiryu, Gunma 376-8515
(Received April 16, 2001; CL-010341)
The reaction of Ni2+ with a tripodal hexadentate ligand
molecules being linked by hydrogen bonding between phenol
and phenolate oxygen atoms. The distances between the hydro-
gen bonded oxygen atoms, O11···O22, 2.493(4); O12···O21,
2.490(4) Å, indicate a strong hydrogen bond. Each nickel atom
is in an approximately octahedral environment composed of
three facially coordinated imine nitrogen atoms and three phe-
nolic oxygen atoms.
(H3L = 1,1,1-tris(N-salicylideneaminomethyl)ethane) afforded
the O–H···O bridged dinuclear [Ni2(HL)2] complex. When Ni2+
was allowed to react with H3L in the presence of triethylamine
(3 : 2 : 6), the linear trinuclear [Ni3(L)2] complex formed,
where the central nickel(II) ion is bridged by six phenolate oxy-
gen atoms to the terminal nickel(II) ions.
Metal–metal interactions between paramagnetic metal cen-
ters through bridging atoms have been studied extensively in
order to understand fundamental factors controlling the exchange
interactions.1 Although both oxygen (hard base) and sulfur (soft
base) are Group 16 elements, their coordination abilities are quite
different. It is interesting to compare the properties of complexes
containing phenol groups with those of complexes containing
thiophenol groups. Here, we report the preparation, structures,
and magnetic properties of di- and trinuclear nickel(II) complex-
es containing tripodal hexadentate ligands, H3L and H3L5-MeO
(Figure 1). The synthesis of the NiII–MII–NiII type heterotrinu-
clear complexes is also reported.
Temperature-dependent molar susceptibility measurements
of powdered samples of the dinuclear complexes, 1 and 1',
were carried out in the temperature range 5–300 K. The two
complexes have very similar magnetic properties. The magnet-
ic moments are almost constant above 50 K and drop sharply
below 30 K. The magnetic data were analyzed using the
isotropic spin exchange coupling model. The spin Hamiltonian
in dinuclear complexes is expressed as H = –2JS1·S2 (S1 = S2 =
1). The best fits were obtained with J = –1.00 cm–1 (g = 2.02)
for 1; J = –1.02 cm–1 (g = 1.99) for 1'. The two Ni2+ are ca. 4.8
Å apart, and Ni–O–H···O–Ni superexchange pathways are pos-
sible. The small J values show that such pathways are not
effective. Auerbach et al.5 studied the magnetic properties of
dimeric [M2(HL')2](ClO4)2·2H2O (M = Cr, Fe; H3L' = 1,4,7-
tris(5-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane).
They reported spin exchange coupling constants similar to ours:
[Cr2(HL')2](ClO4)2·2H2O, J = –0.93 cm–1 (g = 1.98);
[Fe2(HL')2](ClO4)2·2H2O, J = –0.33 cm–1 (g = 1.98). It is to be
noted that the susceptibility data for in 1 and 1' can also be
accounted for by a single-ion zero-field splitting (D = 9.71 cm–1
and g = 1.93 for 1, D = 9.85 cm–1 and g = 1.90 for 1').
The bluish-green dinuclear complexes, [Ni2(HL)2] (1) and
[Ni2(HL5-MeO)2] (1'), were prepared in the same manner and have
very similar structures to each other; thus we describe only 1' as
a representative example. 1' was prepared by the reaction of Ni2+
with the H3L5-MeO ligand2 in methanol in a 1 : 1 molar ratio with-
out the addition of a base. Yield: 76%. The elemental analysis
indicated that there are no counter ions.3 Thus, one of the three
acidic hydrogen atoms of H3L5-MeO is not deprotonated and the
empirical formula, [Ni(HL5-MeO)] was suggested.
Figure 2 shows the X-ray structure of 1'.4 There are two
independent mononuclear molecules in the unit cell, the two
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
843
The fact that the ligands are not fully deprotonated in 1 and
1' indicates that the coordinated oxygen atoms still possess
basicity. This residual basicity can be used for the formation of
oxygen-bridged complexes. For the preparation of the trinuclear
complexes, Ni2+ was allowed to react with H3L or H3L5-MeO in a
3 : 2 molar ratio in the presence of triethylamine to deprotonate
the ligands. Orange complexes were obtained. Yield: 79% for
2 and 89% for 2'. The elemental analyses indicated that the
complexes have the trinuclear structure, [Ni3(L)2] (2) and
[Ni3(L5-MeO)2] (2').6 The trinuclear structures were confirmed
by X-ray crystallography.7
Figure 3 shows the molecular structure of 2' viewed down
the C2 axis. The complex is a doubly face-sharing, trinuclear
molecule. The coordination geometry around each Ni is
approximately octahedral. Two terminal nickel(II) ions are
coordinated by the hexadentate tripodal ligands, and the central
and the terminal nickel(II) ions are bridged by six phenolate
oxygen atoms (Nit···Nic 2.824(1) Å, Nit···Nit 5.648(3) Å). Thus,
the terminal mononuclear units function as a tridentate ligand.
Magnetic susceptibility data for powdered samples of the
trinuclear complexes were collected in the temperature range
The magnetic data were analyzed using the isotropic spin
exchange coupling model. The spin Hamiltonian in linear trin-
uclear complexes is expressed as H = –2(J12S1·S2 + J23S2·S3 +
J13S1·S3), where S1 = S2 = S3 = 1 for the S1–S2–S3 arrangement.
The terminal nickel(II) ions are crystallographically equivalent,
and thus the spin exchange coupling constant for the interac-
tions between the adjacent nickel(II) ions is expressed as J = J12
= J23. The best fits were obtained with J = 14.8 cm–1, J13
=
–1.77 cm–1, and g = 2.03 for 2; J = 15.8 cm–1, J13 = –2.61 cm–1,
and g = 2.19 for 2'. These complexes have the S = 3 ground
state. The structures and magnetic properties for 2 and 2' are
similar to those of [Ni3(acac)6] (acac = 2,4-pentanedionate
ion),8 although the magnitude of the magnetic interactions is
smaller for the present complexes. It should be noted that the
linear homotrinuclear nickel(II) complex with 1,4,7-tris(4-tert-
butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane shows anti-
ferromagnetic coupling between two adjacent nickel(II) ions (J
= –28 cm–1) and ferromagnetic coupling between terminal nick-
el(II) ions (J13 = 12 cm–1), and indicates the S = 1 ground state.9
The decrease in the magnetic moment of 2' below 7 K (Figure
4) may be accounted for by zero-field splitting.
2–300 K. In 2', the effective magnetic moment, µeff(Ni–Ni–Ni)
increases gradually on decreasing the temperature and reaches a
maximum at 7 K (7.63 µB), and then drops sharply (Figure 4).
,
We have prepared the phenolate-bridged heterotrinuclear
complexes, [M(NiL5-MeO)2] (M = Mn, Co)10 by the reaction of
[Ni2(HL5-MeO)2] (1’) and M2+ in the presence of triethylamine.
To avoid transmetallation, the reaction was carried out under
mild conditions (room temperature). Their magnetic properties
are under investigation.
References and Notes
1
See, for example, O. Kahn, “Molecular Magnetism,” VCH,
Weinheim (1993).
2
The H3L5-MeO ligand was prepared by condensation of 1,1,1-
tris(aminomethyl)ethane and 5-methoxysalicylaldehyde in ethanol
in a 1 : 3 molar ratio. Yield: 85%. Anal. Found: C, 66.86; H, 6.14;
N, 8.10%. Calcd for C29H33N3O6: C, 67.04; H, 6.40; N, 8.09%.
Anal. Found: C, 56.58; H, 5.64; N, 6.64%. Calcd for
C58H70N6Ni2O16 = [Ni2(HL5-MeO)2]·4H2O: C, 56.89; H, 5.76; N,
6.86%.
3
4
Bluish-green crystals of [Ni2(HL5-MeO)2]·10H2O were grown from a
methanol solution. Crystallographic data: formula weight 1332.69,
tetragonal, space group P4/nnc (No. 126), a = 36.617(1), c =
21.4647(5) Å, V = 28779(1) Å3, Z = 16, DC = 1.231 Mg m–3, µ(Mo
Kα) = 0.59 mm–1, 15872 unique reflections (2θmax = 54.2°), R1
(8449 reflections, I > 2.0σ(I)) = 0.070, Rw = 0.217.
5
6
U. Auerbach, T. Weyhermüller, K. Wieghardt, B. Nuber, E. Bill, C.
Butzlaff, and A. Trautwein, Inorg. Chem., 32, 508 (1993).
Anal. Found for 2: C, 55.58; H, 4.19; N, 7.24%. Calcd for
C53H49Cl3N6Ni3O6 = [Ni3(L)2]·CHCl3: C, 55.43; H, 4.30; N, 7.32%.
Found for 2': C, 52.30; H, 4.48; N, 5.91%. Calcd for
C60H64Cl4N6Ni3O12 = [Ni3(L5-MeO)2]·2CH2Cl2: C, 52.26; H, 4.68;
N, 6.09%.
7
Orange crystals of [Ni3(L5-MeO)2]·2CH2Cl2 were grown from a
dichloromethane–ethanol solution. Crystallographic data: formula
weight 1379.11, monoclinic, space group C2/c (No. 15), a =
19.886(7), b = 14.765(3), c = 23.211(7) Å, β = 115.08(2)°, V =
6172(3) Å3, Z = 4, DC = 1.48 Mg m–3, µ(Mo Kα) = 1.144 mm–1,
7347 unique reflections (2θmax = 55.0°), 5557 (I > 0.5σ(I)) used in
the refinement, R = 0.096, Rw = 0.140.
8
9
P. D. W. Boyd and R. L. Martin, J. Chem. Soc., Dalton Trans, 1979,
92.
T. Beissel, F. Birkelbach, E. Bill, T. Glaser, F. Kesting, C. Krebs, T.
Weyhermüller, K. Wieghardt, C. Butzlaff, and A. X. Trautwein, J.
Am. Chem. Soc., 118, 12376 (1996).
10 Anal. Found for the Mn complex: C, 53.60; H, 4.67; N, 6.34%.
Calcd for C59.5H63Cl3MnN6Ni2O12 = [Mn(NiL5-MeO)2]·1.5CH2Cl2:
C, 53.62; H, 4.76; N, 6.31%. Found for the Co complex: C, 52.80;
H, 4.66; N, 6.05%. Calcd for C60H64Cl4CoN6Ni2O12 = [Co(NiL5-
MeO)2]·2CH2Cl2: C, 52.25; H, 4.68; N, 6.09%.