Trigonal-bipyramidal geometry in a cobalt(II) complex with an unsymmetrical tripodal ligand

Article abstract of DOI:10.1246/bcsj.74.2131

A cobalt(II) complex with bis[2-(3,5-dimethylpyrazol-1-yl)ethyl][(pyrazol-1-yl)methyl]amine (bppa), [CoCl(bppa)][B(C₆H₅)₄]· C₂H₅OH, was synthesized and characterized by measurements of the magnetic moment and the electronic spectra. The X-ray crystal structure shows that the compound has a distorted trigonal bipyramid with a N₄Cl coordination environment.

Full text of DOI:10.1246/bcsj.74.2131

c. Jpn.
Bull. Chem. Soc. Jpn., 74, 2131–2132 (2001) 2131
e Chemical
ciety of Ja-
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Short Articles
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Trigonal-Bipyramidal Geometry in a
Cobalt(Ⅱ) Complex with an Unsym-
metrical Tripodal Ligand
J. W. Lim
01
31
32
Jong-Wan Lim, # Masahiro Mikuriya,*
and Hiroshi Sakiyama†
SJA8
09-2673
1019
Department of Chemistry, School of Science,
Kwansei Gakuin University, Uegahara,
Nishinomiya 662-8501
†Department of Chemistry, Faculty of Science,
Yamagata University, Yamagata 990-8560
01
(Received May 28, 2001)
01
.2
Fig. 1. Perspective view of the structure of 1 showing the
atom labeling scheme. Selected bond distances (Å) and
angles (°): Co(1)–N(11) 2.036(11), Co(1)–N(13) 2.032(9),
Co(1)–N(15) 2.096(11), Co(1)–Cl(1) 2.302(4), Co(1)–
N(17) 2.524(10), Co(2)–N(21) 2.005(11), Co(2)–N(23)
2.003(12), Co(2)–N(25) 1.914(11), Co(2)–Cl(2) 2.285(5),
Co(2)–N(27) 2.482(12); N(11)–Co(1)–N(13) 121.6(5),
N(11)–Co(1)–N(15)108.2(5), N(13)–Co(1)–N(15)119.8(4),
N(11)–Co(1)–Cl(1) 106.6(4), N(13)–Co(1)–Cl(1) 99.3(3),
N(15)–Co(1)–Cl(1) 96.6(4), N(11)–Co(1)–N(17) 81.1(4),
N(13)–Co(1)–N(17) 81.5(4), N(15)–Co(1)–N(17) 74.6(4),
Cl(1)–Co(1)–N(17) 169.9(3), N(21)–Co(2)–N(23) 119.6(5),
N(21)–Co(2)–N(25)110.3(5), N(23)–Co(2)–N(25) 118.2(4),
N(21)–Co(2)–Cl(2) 105.7(3), N(23)–Co(2)–Cl(2) 99.4(4),
N(25)–Co(2)–Cl(2) 99.7(4), N(21)–Co(2)–N(27) 83.2(4),
N(23)–Co(2)–N(27) 78.4(5), N(25)–Co(2)–N(27) 73.37(4),
Cl(2)–Co(2)–N(27) 170.6(3).
A cobalt(Ⅱ) complex with bis[2-(3,5-dimethylpyrazol-
1-yl)ethyl][(pyrazol-1-yl)methyl]amine (bppa), [CoCl(bp-
pa)][B(C6H5)4]•C2H5OH, was synthesized and characterized
by measurements of the magnetic moment and the electronic
spectra. The X-ray crystal structure shows that the compound
has a distorted trigonal bipyramid with a N4Cl coordination
environment.
Metal complexes of tripodal ligands have drawn much at-
tention over the last three decades due to a recognition of their
utility as model compounds for understanding biological metal
systems.1 The most common tripodal ligands have three iden-
tical pendant donor groups, such as amines, pyridyl, imida-
zolyl, and pyrazolyl groups, and have been utilized to make a
trigonal-bipyramidal coordination geometry. On the other
hand, tripodal ligands having different pendant groups are not
well developed. Such unsymmetrical tripodal ligands may af-
ford a new aspect in coordination geometries and molecular
structures. Thus, while pursuing our interest in coordination
chemistry with unsymmetrical tripodal ligands, we synthe-
sized a new tripodal ligand, bis[2-(3,5-dimethylpyrazol-1-
yl)ethyl][(pyrazol-1-yl)methyl]amine (bppa), and obtained a
of bppa are in the equatorial positions with the amino nitrogen
in one of the axial sites.
An unsymmetrical feature can be
found in the small bond angle of N(15)–Co(1)–N(17) com-
pared with the N(11)–Co(1)–N(17) and N(13)–Co(1)–N(17)
angles.
The equatorial Co–N(pyrazolyl) distances are
1.914(11)–2.096(11) Å. The axail Co–N and Co–Cl distances
are 2.524(10) or 2.482(12) Å and 2.302(4) or 2.285(5) Å, re-
spectively. Most tripodal ligands have been used to make a
trigonal bipyramidal coordination geometry. Mani et al. re-
ported that the tripodal ligand tris[2-(3,5-dimethylpyrazol-1-
yl)ethyl]amine (metpea) forms an unusual four-coordinate
complex, [Co(metpea)][B(C6H5)4]2, contrary to the case for the
unmethylated ligand tris[2-(pyrazolyl-1-yl)ethyl]amine (tpea),
cobalt(Ⅱ)
complex
with
bppa,
[CoCl(bppa)][B-
(C6H5)4]•C2H5OH (1). Here, we report on the synthesis and
structural characterization of 1.
The treatment of
a reaction mixture of bppa and
CoCl2•6H2O with Na[B(C6H5)4] in ethanol afforded a purple
precipitate. Recrystallization from acetone–ethanol gave crys-
tals of 1. An X-ray crystallographic study revealed that the
bppa ligand is coordinated to the metal center with a N4 donor
set, giving a distorted trigonal-bipyramidal coordination envi-
ronment with chloride ion (Fig. 1). The crystal structure con-
tains two crystallographically independent complex cations,
[CoCl(bppa)]+, of which the molecular structures are essen-
tially similar. The nitrogen atoms of the three pyrazolyl arms
which affords
a trigonal bipyramidal environment in
[CoI(tpea)][B(C6H5)4].2,3 They attributed this to a screening
effect of bulky 3-methyl substituents at the pyrazole rings. In
the present case, the bppa ligand forms a distorted trigonal bi-
pyramidal coordination for Co(Ⅱ), picking up a fifth donor at-
om. This result suggests that the effective steric hindrances
hold for only the tris methylated ligand.
The magnetic moment of 1 is 4.50 BM at 300 K, and de-
creases slightly upon lowering the temperature (3.68 BM at 2
K). We introduced the Curie–Weiss law, χA = 5Ng2β2/[4k(T −
# Visiting Research Fellow from Kyungpook National University,
Korea

2132 Bull. Chem. Soc. Jpn., 74, No. 11 (2001)
© 2001 The Chemical Society of Japan
Synthesis of 1. To a solution of bppa (29 mg, 0.085 mmol) in
10 cm3 of ethanol was added 20 mg (0.084 mmol) of cobalt(Ⅱ)
chloride hexahydrate. The reaction mixture was heated at 70 °C
for 10 min and then sodium tetraphenylborate (29 mg, 0.085
mmol) was added. A purple precipitate was collected, washed
with ethanol, and air-dried. Recrystallization was performed from
acetone–ethanol: Yield, 42 mg (65%). Found: C, 65.99; H, 6.63;
N,12.46%. Calcd for C42H47BClCoN7•C2H5OH: C, 65.97; H, 6.67;
N, 12.24%.
Measurements. Carbon, hydrogen, and nitrogen analyses
were carried out using a Perkin-Elmer 2400 Series Ⅱ CHNS/O
Analyzer. The magnetic susceptibilities were measured on a
Quantum Design MPMS-5S SQUID susceptometer operating at a
magnetic field of 0.5 T. The susceptibilities were corrected for the
diamagnetism of the constituent atoms using Pascal’s constants.
The effective magnetic moments were calculated from the equa-
tion µeff = 2.828
tibility.
, where χ is the atomic magnetic suscep-
χAT
A
Fig. 2. Temperature dependence of magnetic susceptibility
(ꢀ) and magnetic moment (ꢁ) of 1.
X-ray Crystal Structure Analysis. A purple crystal of 1 was
mounted on a glass fiber with epoxy cement at room temperature.
A preliminary examination was made and data were collected on a
Bruker CCD X-ray diffractometer using graphite-monochromated
Mo-Kα radiation. The structure was solved by direct methods and
refined by full-matrix least-squares. All non-hydrogen atoms
were refined with anisotropic thermal parameters, except for the
carbon atoms and the ethanol molecule. The hydrogen atoms
were inserted at their calculated positions and fixed there. All of
the calculations were carried out on a Pentium Ⅲ Windows NT
computer utilizing the SHELXTL software package.
Crystallographic data: for 1; C44H53BClCoN7O, FW = 801.12,
monoclinic, space group Pc, a = 13.9808(7), b = 14.1777(7), c =
22.2725(11) Å, β = 106.456(1)°, V = 4233.9(4) Å3, Z = 4, Dc =
1.257 g cm−3, µ(Mo Kα) = 0.510 mm−1, crystal dimensions 0.11
× 0.16 × 0.35 mm, 19132 reflections collected, 9683 independent
reflections, R1 [I > 2σ(I)] = 0.0645, wR2 [I > 2σ(I)] = 0.1623.
The X-ray analysis data have been deposited as Document No.
74051 at the Office of the Editor of Bull. Chem. Soc. Jpn. Crystal-
lographic data have been deposited 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 deposi-
tion number 167874.
Fig. 3. Diffuse reflectance spectrum of 1.
θ)] + Nα for an analysis of the magnetic data. The best fitting
parameters are θ = −0.82 K, g = 2.26, and Nα = 600 × 10−6
cm3 mol−1, as shown by the solid line in Fig. 2. The observed
and calculated moments agree well with reasonable g and Nα
4
values, in agreement with the A2ꢀ state being the lowest as a
first approximation.4 This result indicates that the magnetic in-
teraction between the cobalt ions is very weak. This is under-
standable, since the closest metal-metal separation is a
Co1≥Co2 (x, y − 1, z) distance of 7.699(3) Å in the crystal.
The diffuse reflectance spectrum of 1 shows several absorp-
tions in the visible and near-infrared region, as shown in Fig. 3.
These absorptions (572, 1080, 1350, and 1690 nm) can be as-
We are grateful to Dr. Kenji Yoza (Bruker Japan Co., Ltd.)
for his helpful assistance in the X-ray crystal structure analy-
sis.
References
1
2
3
4
S. Trofimenko, Prog. Inorg. Chem., 34, 115 (1986).
4
4
signed to d–d transitions (4A2ꢀ → Eꢁ(P) + 4A2ꢀ(P), 4A2ꢀ → Eꢀ,
F. Mani and C. Mealli, Inorg. Chim. Acta, 54, L77 (1981).
M. D. Vaira and F. Mani, Inorg. Chim. Acta, 70, 99 (1983).
L. Banci, A. Bencini, C. Benelti, D. Gatteschi, and C.
4
4
4
4
4A2ꢀ → Eꢁ, and A2ꢀ → A1ꢁ + A2ꢁ respectively) due to the
Ⅱ
trigonal-bipyramidal high-spin Co irrespective of the distort-
ed structure.
Zanchini, Struct. Bonding, 52, 37 (1982).
T. N. Sorrel and M. R. Malachowski, Inorg. Chem., 22,
1883 (1983).
5
Experimental
The ligand, bppa, was synthesized by a condensation reaction
of bis[2-(3,5-dimethylpyrazol-1-yl)ethyl]amine5 with N-hydro-
xymethylpyrazole6 using 1,2-dichloroethane as a solvent.
6
W. L. Driessen, Recl. Trav. Chim. Pays-Bas, 101, 441
(1982).