Synthesis, structure, and magnetic properties of dinuclear cobalt(II) complexes with a new phenol-based dinucleating ligand with four hydroxyethyl chelating arms

Article abstract of DOI:10.1021/ic0255297

A new end-off type acyclic ligand with four hydroxyethyl arms, 2,6-bis[bis(2-hydroxyethyl)aminomethyl]-4-methylphenol [H(bhmp)], formed dinuclear cobalt(II) complexes [Co₂(bhmp)(OAc)₂]BPh₄ (1) and [Co₂(bhmp)(OBz)₂]BPh₄ (2). The complex 1·2.5CH₃CN (C₅₀H_62.5BCo₂N_4.5O₉) crystallizes in the monoclinic space group C2/c with dimensions a = 25.424(5) A, b = 13.376(2) A, c = 29.913(6) A, β = 105.930(3)°, and V = 9781(3) A³ and with Z = 8. X-ray diffraction analysis revealed a μ-phenoxo-bis(μ-acetato)dicobalt(II) core structure containing two octahedral cobalt(II) ions. Electronic spectra were investigated for 1 and 2 in the range 400-1800 nm, and the data were typical for the octahedral high-spin cobalt(II) complexes. Magnetic susceptibility was measured for 1 and 2 over the temperature range 4.5-300 K, and the data were analyzed well using our theoretical method. The best fitting parameters were κ = 0.77, λ = -116 cm^-1, Δ = 572 cm^-1, and J = -0.44 cm^-1 for complex 1 and κ = 0.96, λ = -93 cm^-1, Δ = 616 cm^-1, and J = -0.33 cm^-1 for complex 2.

Full text of DOI:10.1021/ic0255297

Inorg. Chem. 2002, 41, 4058−4062
Synthesis, Structure, and Magnetic Properties of Dinuclear Cobalt(II)
Complexes with a New Phenol-Based Dinucleating Ligand with Four
Hydroxyethyl Chelating Arms
Md. Jamil Hossain,† Mikio Yamasaki,‡ Masahiro Mikuriya,§ Atsushi Kuribayashi,† and
,†
Hiroshi Sakiyama*
Department of Material and Biological Chemistry, Faculty of Science, Yamagata UniVersity,
Kojirakawa, Yamagata 990-8560, Japan, X-Ray Research Laboratory, Rigaku Corporation,
Matsubara 3-9-12, Akishima, Tokyo 196-8666, Japan, and Department of Chemistry, School of
Science and Technology, Kwansei Gakuin UniVersity, Gakuen 2-1, Sanda, 669-1337, Japan
Received February 5, 2002
A new end-off type acyclic ligand with four hydroxyethyl arms, 2,6-bis[bis(2-hydroxyethyl)aminomethyl]-4-methylphenol
[H(bhmp)], formed dinuclear cobalt(II) complexes [Co2(bhmp)(OAc)2]BPh4 (1) and [Co2(bhmp)(OBz)2]BPh4 (2). The
complex 1‚2.5CH CN (C H62.5BCo2N O ) crystallizes in the monoclinic space group C2/c with dimensions a )
3
50
4.5 9
3
25.424(5) Å, b ) 13.376(2) Å, c ) 29.913(6) Å, â ) 105.930(3)°, and V ) 9781(3) Å and with Z ) 8. X-ray
diffraction analysis revealed a µ-phenoxo−bis(µ-acetato)dicobalt(II) core structure containing two octahedral cobalt-
(II) ions. Electronic spectra were investigated for 1 and 2 in the range 400−1800 nm, and the data were typical for
the octahedral high-spin cobalt(II) complexes. Magnetic susceptibility was measured for 1 and 2 over the temperature
range 4.5−300 K, and the data were analyzed well using our theoretical method. The best fitting parameters were
κ ) 0.77, λ ) −116 cm-1, ∆ ) 572 cm-1, and J ) −0.44 cm-1 for complex 1 and κ ) 0.96, λ ) −93 cm-1,
∆ ) 616 cm-1, and J ) −0.33 cm-1 for complex 2.
Introduction
angular momentum; (2) a tetrahedral, square-planer, trigonal-
bipyramidal, or highly distorted octahedral case, in which a
ground term does not have an orbital angular momentum;
and (3) a highly distorted lower symmetric case, in which a
ground term has an orbital angular momentum. In group 1,
under an ideal Oh symmetry, the ground 4T1g term possesses
the orbital angular momentum. Thus, to analyze the magnetic
data, the effect of the orbital angular momentum should be
taken into account.1 In group 2, the ground term does not
have an orbital angular momentum; thus, a spin-only
treatment is valid for the complexes in this group. The effect
of the higher term possessing an orbital momentum can be
treated as a second-order Zeeman effect.2 In group 3, the
ground term possesses an orbital angular momentum due to
the admixture with higher states.2 At this stage, an appropriate
method should be selected to consider the symmetry around
the cobalt(II) ion for magnetic analysis.
The magnetism of dinuclear high-spin cobalt(II) complexes
is a challenging area because the orbital angular momentum
causes difficulties in the magnetic analysis.1 In general, the
orbital angular momentum is partially quenched in a ligand
field of a certain symmetry.2 For instance, in a ligand field
of Oh symmetry, only the orbital angular momenta of T terms
(T1g, T1u, T2g, and T2u) remain as a result of the quenching.
When the symmetry is decreased to D3h, only E terms (E′
and E′′) have orbital angular momenta. Thus, the effect of
the orbital angular momentum is highly dependent on the
symmetry around the metal ion. To our knowledge, the
magnetism of the high-spin cobalt(II) complexes is classified
into three groups: (1) an ideal octahedral or slightly distorted
octahedral case, in which a ground term possesses an orbital
* To whom correspondence should be addressed. E-mail: saki@sci.kj.
yamagata-u.ac.jp.
† Yamagata University.
In the magnetic analysis of homo dinuclear high-spin
cobalt(II) complexes, the classification above is also valuable.
It is not difficult to understand the magnetism of the dinuclear
complexes containing two cobalt(II) ions classified into group
‡ Rigaku Corporation.
§ Kwansei Gakuin University.
(1) Kahn, O. Molecular Magnetism; VCH Publishers: New York, 1993.
(2) Figgis, B. N.; Hitchman, M. A. Ligand Field Theory and its
Application; Wiley-VCH: New York, 2000.
4058 Inorganic Chemistry, Vol. 41, No. 15, 2002
10.1021/ic0255297 CCC: $22.00 © 2002 American Chemical Society
Published on Web 06/26/2002

PhOH-Based Dinucleating Ligand with Four Hydroxyethyl Arms
Chart 1. Chemical Structures of bhmp- (R ) H) and bomp- (R )
CH3)
new dinuclear cobalt(II) complexes [Co2(bhmp)(OAc)2]BPh4
(1) and [Co2(bhmp)(OBz)2]BPh4 (2) were synthesized.
Experimental Section
Measurements. Elemental analyses (C, H, and N) were obtained
at the Elemental Analysis Service Centre of Kyushu University.
1
IR spectra were recorded on a Hitachi 270-50 spectrometer. H
and 13C NMR spectra (400 MHz) were measured on a JEOL JNM-
R400 spectrometer in CDCl3 using SiMe4 as the internal standard.
Electronic spectra were measured in N,N-dimethylformamide
(DMF) on Jasco V-560 (400-900 nm) and Hitachi 330 (900-1800
nm). Molar conductances were measured in DMF on a DKK AOL-
10 conductivity meter at room temperature. The temperature
dependence of the magnetic susceptibilities was measured with a
Quantum Design MPMS-5S SQUID susceptometer operating at a
magnetic field of 0.5 T between 4.5 and 300 K. The susceptibilities
were corrected for the diamagnetism of the constituent atoms using
Pascal’s constant.1 The effective magnetic moments were calculated
from the equation µeff ) 2.828(øAT)1/2, where øA is the atomic
magnetic susceptibility. All the magnetic calculations were made
using the MagSaki9 magnetic software program of our laboratory.
Synthesis of Na(bhmp). To an aqueous solution (40 mL)
containing p-cresol (5.41 g, 50.0 mmol), NaOH (2.00 g, 50.0 mmol),
and bis(2-hydroxyethyl)amine (10.55 g, 100 mmol) were added
paraformaldehyde (3.00 g, 100 mmol) and ethanol (20 mL), and
the resulting solution was refluxed for 4 h. On cooling to 0 °C
Na(bhmp) was obtained as a white powder. Yield: 7.60 g (42%).
Selected IR data (ν/cm-1) using KBr disks: 3500-3200, 2980,
1658, 1608, 1444, 1366, 1300, 1146, 1052, 866 and 764. 1H NMR
(CDCl3: δ, ppm): 2.22 (s, 3H, CH3), 2.69 (t, 8H, NCH2R), 3.67
(t, 8H, OCH2), 3.73 (s, 4H, ArCH2N), 6.79 (s, 2H, ArH). 13C NMR
(CDCl3; δ, ppm): 20.40 (CH3), 55.63 (NCH2R), 57.12 (ArCH2N),
59.25 (OCH2), 123.48 (ArH), 128.04 (ArCH3), 130.13 (Ar), 153.71
(ArO).
2 because the spin-only treatment is possible. However, it
is much more difficult to elucidate the magnetism of the
dinuclear complexes containing two cobalt(II) ions classified
into group 1 because of the T ground term with an orbital
angular momentum, and there have been only a few
successful examples.3-6 In 1971, Lines reported a theory for
the analysis of the magnetic coupling between two high-
spin cobalt(II) ions of pure Oh symmetry using a temperature-
dependent Hamiltonian.3 This remarkable theory enabled the
analysis of the magnetic data of some dinuclear cobalt(II)
complexes,5 but it was limited to only highly symmetrical
cases. This limitation sometimes causes problems in the
magnetic analysis since the symmetry around the real
cobalt(II) ions is at best axial.1 Taking the anisotropy into
account, Drillon and co-workers made a successful low-
temperature study.4 In a whole-temperature-range magnetic
analysis for the dinuclear complexes classified into group
1, Lines’s theory3 had been the only efficient way until we
developed a new approximation method.6 In order to
introduce a distortion around the cobalt(II) ions, we adopted
the axial splitting parameter ∆, which was used by Lines7
and Figgis8 for mononuclear complexes to avoid over-
parametrization. In our approximation method, the magnetic
coupling between the two cobalt(II) ions is assumed to be
effective only between the lowest energy levels of each
cobalt(II) ion among the six energy levels generated from
[Co2(bhmp)(OAc)2]BPh4 (1). To a methanolic solution (15 mL)
of Na(bhmp) (0.19 g, 0.52 mmol) was added cobalt(II) acetate
tetrahydrate (0.25 g, 1.00 mmol), and the resulting solution was
refluxed for 1 h to give a deep violet solution. The addition of
sodium tetraphenylborate (0.17 g, 0.50 mmol) resulted the precipi-
tation of pink microcrystals. Yield: 0.32 g (67%). Anal. Found:
C, 60.16; H, 6.27; N, 3.36; Co, 13.5. Calcd for C45H55BCo2N2O9:
4
the T1g ground term by spin-orbit coupling. This ap-
proximation method gives a good result because the energy
gap between the lowest and the second-lowest energy levels
(∼300 cm-1) is, in general, much larger than the magnetic
coupling J (|J| < 5 cm-1). It should be emphasized that the
result obtained by our method is identical to that obtained
by Lines’s theory when the splitting parameter ∆ is zero.
In this study, a new acyclic end-off type dinucleating
ligand, 2,6-bis[bis(2-hydroxyethyl)aminomethyl]-4-meth-
ylphenol [H(bhmp)], was synthesized (Chart 1), and, with
the intention of revealing the relationship between the
structure and magnetism of dinuclear cobalt(II) complexes,
C, 60.28; H, 6.18; N, 3.12; Co, 13.15. Selected IR data (ν/cm-1
)
using KBr disks: 3600-3300, 3100, 2988, 1588, 1472, 1422, 1340,
1258, 1016, 866, 730, 702, 606. Molar conductance [Λ/S cm2
mol-1]: 37.
[Co2(bhmp)(OBz)2]BPh4 (2). This was prepared as pink mi-
crocrystals by a method similar to that of 1 using cobalt(II) benzoate
instead of cobalt(II) acetate tetrahydrate. Yield: 0.60 g (58%). Anal.
Found: C, 64.44; H, 5.82; N, 2.77; Co, 11.8. Calcd for C55H59-
BCo2N2O9: C, 64.72; H, 5.83; N, 2.74; Co, 11.63. Selected IR
data (ν/cm-1) using KBr disks: 3600-3300, 2988, 1600, 1562,
1474, 1390, 1258, 1046, 1128, 868, 704, 604. Molar conductance
[Λ/S cm2 mol-1]: 40.
Single-Crystal X-ray Analysis of Complex 1‚2.5CH3CN.
Experimental data were summarized in Table 1. All measurements
were made on a Rigaku/MSC Mercury CCD diffractometer with
graphite-monochromated Mo KR radiation. The data were collected
to a maximum 2θ value of 55.0°. Of the 45995 reflections, 11123
were unique (Rint ) 0.044). A symmetry-related absorption cor-
rection using the program REQAB10 was applied which resulted
(3) Lines, M. E. J. Chem. Phys. 1971, 55, 2977-2984.
(4) Coronado, E.; Drillon, M.; Nugteren, P. R.; de Jongh, L. J.; Beltran,
D. J. Am. Chem. Soc. 1988, 110, 3907-3913.
(5) De Munno, G.; Julve, M.; Lloret, F.; Faus, J.; Caneschi, A. J. Chem.
Soc., Dalton Trans. 1994, 1175-1183.
(6) Sakiyama, H.; Ito, R.; Kumagai, H.; Inoue, K.; Sakamoto, M.; Nishida,
Y.; Yamasaki, M. Eur. J. Inorg. Chem. 2001, 2027-2032. Sakiyama,
H.; Ito, R.; Kumagai, H.; Inoue, K.; Sakamoto, M.; Nishida, Y.;
Yamasaki, M. Eur. J. Inorg. Chem. 2001, 2705.
(7) Lines, M. E. Phys. ReV. 1963, 546-555.
(8) Figgis, B. N.; Gerloch, M.; Lewis, J.; Mabbs, F.; E. Web, G. A. J.
Chem. Soc. A 1967, 442-447.
(9) Sakiyama, H. J. Chem. Software 2001, 7, 171-178.
(10) Jacobson, R. Private communication, 1995-1998.
Inorganic Chemistry, Vol. 41, No. 15, 2002 4059

Hossain et al.
Table 1. Crystallographic Data for 1‚2.5CH3CN
empirical formula
C50H62.50BCo2N4.50O9
a/Å
b/Å
c/Å
â/deg
V/Å3
Z
25.424(5)
13.376(2)
29.913(6)
105.930(3)
9781(3)
8
fw
999.24
space group
T/°C
λ/Å
C2/c (No. 15)
-160 ( 1
0.71070
1.357
7.38
0.052
D
calcd/g cm-3
µ(Mo KR)/cm-1
2
R(Fo )a
2
Rw(Fo )b
0.081
a R ) ∑(Fo - Fc )/∑Fo . b Rw ) {∑w(Fo - Fc )2/∑w(Fo )2}1/2
.
2
2
2
2
2
2
in transmission factors ranging from 0.77 to 0.89. The data were
corrected for Lorentz and polarization effects.
The structure was solved by direct methods11 and expanded using
Fourier techniques.12 Most of the non-hydrogen atoms were refined
anisotropically, while the disordered atoms were refined isotropi-
cally. Hydrogen atoms were included but not refined. The final
cycle of full-matrix least-squares refinement was based on 11123
observed reflections. All calculations were performed using the
teXsan13 crystallographic software package of Molecular Structure
Corporation.
Figure 1. ORTEP14 view of the complex cation [Co2(bhmp)(OAc)2]+ in
1 with the atom-numbering scheme.
Table 2. Selected Distances (Å) and Angles (deg) for 1‚2.5CH3CN
Distances (Å)
Co(1)-O(1)
Co(1)-O(2)
Co(1)-O(3)
Co(1)-O(6)
Co(1)-O(8)
Co(1)-N(1)
Co(1)‚‚‚Co(2)
2.027(1)
2.178(1)
2.070(1)
2.090(1)
2.070(1)
2.178(2)
3.3563(5)
Co(2)-O(1)
Co(2)-O(4)
Co(2)-O(5)
Co(2)-O(7)
Co(2)-O(9)
Co(2)-N(2)
2.016(1)
2.158(2)
2.073(1)
2.093(1)
2.113(1)
2.163(2)
Results and Discussion
Crystal Structure of Complex 1‚2.5CH3CN. The crystal
structure consists of [Co2(bhmp)(OAc)2]+ complex cations,
tetraphenylborate anions, and acetonitrile molecules in a 1:1:
2.5 molar ratio. The structure of the complex cation is
depicted in Figure 1. Selected distances and angles with their
estimated standard deviations are listed in Table 2. The
complex cation consists of one dinucleating ligand bhmp-,
two cobalt(II) ions, and two acetate ions. The two cobalt(II)
ions are bridged by one phenolic oxygen of bhmp- and two
acetate ions, forming a µ-phenoxo-bis(µ-acetato)dico-
balt(II) core structure. The Co(1)‚‚‚Co(2) separation is
3.3563(5) Å. A similar separation [3.3360(3) Å] was found
in the related dinuclear cobalt(II) complex [Co2(bomp)-
(OAc)2]BPh4 (3) [H(bomp) ) 2,6-bis[bis(2-methoxyethyl)-
aminomethyl]-4-methylphenol].6 The bridging angle Co(1)-
O(1)-Co(2) is 112.21(6)°, and a similar bridging angle
[113.03(6)°] was found in complex 3.6
Angles (deg)
O(1)-Co(1)-O(2)
O(1)-Co(1)-O(3)
O(1)-Co(1)-O(6)
O(1)-Co(1)-O(8)
O(1)-Co(1)-N(1)
O(2)-Co(1)-O(3)
O(2)-Co(1)-O(6)
O(2)-Co(1)-O(8)
O(2)-Co(1)-N(1)
O(3)-Co(1)-O(6)
O(3)-Co(1)-O(8)
O(3)-Co(1)-N(1)
O(6)-Co(1)-O(8)
O(6)-Co(1)-N(1)
O(8)-Co(1)-N(1)
Co(1)-O(1)-Co(2)
164.62(5)
99.16(5)
89.93(5)
101.11(5)
90.42(5)
91.54(5)
78.36(5)
90.06(5)
81.17(5)
168.93(6)
88.77(5)
77.18(5)
95.70(5)
96.58(5)
163.14(5)
112.21(6)
O(1)-Co(2)-O(4)
O(1)-Co(2)-O(5)
O(1)-Co(2)-O(7)
O(1)-Co(2)-O(9)
O(1)-Co(2)-N(2)
O(4)-Co(2)-O(5)
O(4)-Co(2)-O(7)
O(4)-Co(2)-O(9)
O(4)-Co(2)-N(2)
O(5)-Co(2)-O(7)
O(5)-Co(2)-O(9)
O(5)-Co(2)-N(2)
O(7)-Co(2)-O(9)
O(7)-Co(2)-N(2)
O(9)-Co(2)-N(2)
162.39(6)
99.70(6)
101.57(5)
90.19(5)
91.21(5)
93.28(6)
90.73(5)
77.05(6)
79.62(6)
87.69(5)
170.11(6)
78.87(6)
90.31(5)
162.88(5)
101.10(5)
very similar to each other, and the complex cation has a
pseudo-C2 axis along C(12), C(4), C(1), and O(1). The least-
squares plane of the aromatic ring of bhmp- and the plane
defined by Co(1), Co(2), and O(1) are twisted with a dihedral
angle of 45°. This dihedral angle is similar to that of the
related cobalt(II) complex 3 (46°).
Atom Co(1) has a six-coordinate distorted octahedral
geometry with O(1), O(2), O(3), and N(1) of bhmp- and
O(6) and O(8) of the two acetate groups. The coordination
geometry around Co(2) is also distorted octahedral with O(1),
O(4), O(5), and N(2) of bhmp- and O(7) and O(9) of the
acetate groups. The geometries around Co(1) and Co(2) are
A characteristic feature in the structure of complex 1 is
the distortion around the cobalt atoms. The bond distances
between cobalt atoms and equatorial alcoholic oxygens
[2.178(1)-2.158(2) Å] are longer than those between cobalt
and axial alcoholic oxygens [2.070(1)-2.073(1) Å], whereas,
in the case of complex 3, the bond distances between cobalt
atoms and axial ether oxygens [2.200(1)-2.229(1) Å] are
longer than the equatorial ones [2.156(1)-2.160(1) Å]. Thus,
the distortion pattern around cobalts in complex 1 is different
from that in complex 3, presumably because of the less-
hindered hydroxy groups of bhmp-.
(11) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polodori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115-119.
(12) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de
Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF-94 program system;
Technical Report of the Crystallography Laboratory; University of
Nijmegen: Nijmegen, The Netherlands, 1994.
(13) Crystal Structure Analysis Package, Molecular Structure Corporation,
1985 and 1999.
(14) Johnson, C. K. ORTEP; Oak Ridge National Laboratory: Oak Ridge,
TN, 1976.
4060 Inorganic Chemistry, Vol. 41, No. 15, 2002

PhOH-Based Dinucleating Ligand with Four Hydroxyethyl Arms
Figure 3. Temperature dependencies of øA (O) and µeff (4) of the complex
1. Solid curves are drawn with the parameters κ ) 0.77, λ ) -116 cm-1
∆ ) 572 cm-1, and J ) -0.44 cm-1. Dashed curves are drawn with the
parameters κ ) 0.77, λ ) -116 cm-1, ∆ ) 572 cm-1, and J ) 0 cm-1
Figure 2. Electronic spectra for the complexes 1 (solid line) and 2 (shaded
line) in DMF.
,
Table 3. Electronic Spectral Components for 1 and 2 (cm-1
complex 1 complex 2
obsda obsda
calcd calcd
)
.
transition
4T1 f 2T2(2G), 2T1(2G) 21500(32) 20700, 22300 21200(46) 20400, 22000
4T1 f 4T1(4P)
4T1 f 4T2(4F)
19300(42) 19300
8300(10) 8300
19300(52) 19300
8400(14) 8400
a The ꢀ values are in parentheses.
Electronic Spectra of Complexes 1 and 2. Electronic
spectra for 1 and 2 are shown in Figure 2. The spectral
features of the complexes are very similar to each other, and
they are typical for the octahedral high-spin cobalt(II)
complexes,2 as shown by the X-ray analysis for complex 1.
However, the spectrum for 2 is slightly higher in intensity
than that for 1. This may indicate that the coordination
geometry around cobalt(II) ions in complex 2 is more
distorted than that in 1 and the Laporte forbidden rule is
thus much more relaxed. The peak positions of the spectral
components obtained by the Gaussian curve analysis are
summarized with their molar absorption coefficients in Table
3. The strongest absorption band around 19300 cm-1 was
assigned to 4T1 f 4T1(4P), the weak shoulder around 21500
cm-1 was assigned to 4T1 f 2T2(2G), 2T1(2G), and the broad
Figure 4. Temperature dependencies of øA (O) and µeff (4) of the complex
2. Solid curves are drawn with the parameters κ ) 0.96, λ ) -93 cm-1, ∆
) 616 cm-1, and J ) -0.33 cm-1. Dashed curves are drawn with the
parameters κ ) 0.96, λ ) -93 cm-1, ∆ ) 616 cm-1, and J ) 0 cm-1
.
Magnetic Properties of Complexes 1 and 2. Magnetic
susceptibility measurements for complexes 1 and 2 were
made on polycrystalline samples in the temperature range
4.5-300 K. The temperature dependencies of øA and µeff
per Co for 1 and 2 are shown in Figures 3 and 4. The µeff
values per Co of the complexes at room temperature are 4.58
and 4.83 µB, respectively. These values are larger than the
spin-only value of high-spin cobalt(II) (3.87 µB; µso ) [4S(S
4
4
band around 8300 cm-1 was assigned to T1 f T2(4F) for
complex 1. For complex 2, the spectral components were
assigned in the same way.
A spectral simulation was also made using calculations
from the angular overlap model (AOM). In this study, the
average value was used for eσ, and the π orbital contribution
was neglected. Optimization of the AOM parameter eσ and
Racha parameters B and C was performed using the AOMX2
program developed by Adamsky. The observed data were
well simulated by the calculation from the AOM with the
parameters eσ ) 3140 cm-1, B ) 810 cm-1, and C ) 2570
cm-1 for complex 1 and eσ ) 3170 cm-1, B ) 800 cm-1,
and C ) 2460 cm-1 for complex 2. The obtained parameters
are normal for octahedral high-spin cobalt(II) complexes with
the N and O donor atoms (eσ ) ∼4000 cm-1 for N and
∼3000 cm-1 for O).15
3
+ 1)]1/2; S ) /2) but close to the value expected when the
spin momentum and orbital momentum exist independently
3
[5.20 µB; µls ) [L(L + 1) + 4S(S + 1)]1/2; L ) 3, S ) /2].
This indicates a contribution of the orbital angular momen-
tum typical for the 4T1g ground term. The magnetic moments
decrease with decreasing temperature, and this can be
elucidated considering three factors: the contribution of the
(15) Bencini, A.; Benelli, C.; Gatteschi, D. Coord. Chem. ReV. 1984, 60,
131-169.
Inorganic Chemistry, Vol. 41, No. 15, 2002 4061

Hossain et al.
Table 4. Magnetic Data for Complexes 1-4
complex
κ
λ/cm-1
∆/cm-1
J/cm-1
gz
gx
D/cm-1
R(øΑ)
R(µeff
)
ref
1
2
3
4
0.77
0.96
0.98
0.84
-116
-93
-134
-138
572
616
749
440
-0.44
-0.33
-0.55
-0.70
2.11
2.09
2.18
2.45
4.73
4.91
4.99
4.84
74
69
120
144
3.6 × 10-5
1.6 × 10-4
1.2 × 10-4
1.7 × 10-3
3.6 × 10-6
5.9 × 10-5
8.9 × 10-5
1.6 × 10-4
this work
this work
6
6
orbital angular momentum, an intramolecular magnetic
coupling between two Co(II) ions, and an intermolecular
antiferromagnetic coupling. In order to evaluate them, the
experimental data were analyzed as described below.
First, the spin-only equation for the 3/2 spin system based
on the Heisenberg model (H ) -JS1‚S2) was used for the
analysis, but the data could not be explained. Next, Lines’s
theory3 was used, considering spin-orbit coupling, but the
cryomagnetic data could not be fitted well. Thus, our
approximation method6 was used to consider the distortion
around the cobalt(II) ions, and the data could be well
analyzed. The magnetic susceptibility øA was calculated with
the following equations:
cm-1).16 The orbital reduction factor κ corresponds to the
delocalization of unpaired electrons from metal ions to
ligand, but it also contains the admixture of the upper 4T1g-
(4P) state into the 4T1g(4F) ground state. The κ value is known
to be ∼0.93 for free cobalt(II) ion3,17 but is generally lower
than this when in the complexes.3 The κ value for complex
1 is quite normal for this kind of complex, but the value for
2 is slightly deviated from the normal value. This may be
due to the fact that the grade of the approximation decreases
when ∆ becomes larger. Thus, the quality of the magnetic
analysis for 2 was slightly worse than that for 1 because of
the larger distortion for 2. The same discussion can be made
for the obtained spin-orbit coupling constant λ. Theoreti-
cally, the expected λ value is -172 cm-1 for the free
cobalt(II) ion, and the deviation from this value increases
with increasing ∆.
øz + 2øx
øA )
3
In the best-fitting parameters, the J values were used since
the theoretically obtained cryomagnetic µeff curves assuming
J ) 0 were apparently different from the obtained data in
the low-temperature region, as shown in the insertions of
Figures 3 and 4. However, the obtained J values are small,
and the magnetic behavior can also be attributed to the
intermolecular interaction. Thus, it is impossible to separate
the intramolecular interactions from the intermolecular
interactions in the present cases, and we will conclude that
the intramolecular magnetic interactions between the two
cobalt(II) ions in complex cations are negligible for the both
complexes.
øz(x) ) N ×
25J
-E(n0)
+
(1)
z(x),n
2
(1)
2
-E(n0)
E
E
z(x),n
36
(2)
z(x),n
(2)
z(x),n
- 2E
exp
+
- 2E
exp
[
]
(
)
(
)
[
]
∑
∑
kT
kT
kT
kT
n)(1
n*(1
75J
25J
-E(n0)
-
-E(n0)
+
-E(n0)
1
36
3
36
exp
+
exp
+
exp
[
]
[
]
[
]
∑
∑
∑
4n)(1
kT
4n)(1
kT
kT
n*(1
where E(n0) is the energy of level n in the zero field (n ) (1
to (6), E(n1) and E(n2) were first- and second-order Zeeman
coefficients, respectively, and other symbols have their usual
meanings. The Zeeman coefficients E(n0), En(1), and En(2) were
calculated by equations reported previously.6 The best-fitting
parameters were κ ) 0.77, λ ) -116 cm-1, ∆ ) 572 cm-1,
and J ) -0.44 cm-1 for complex 1 and κ ) 0.96, λ ) -93
cm-1, ∆ ) 616 cm-1, and J ) -0.33 cm-1 for complex 2,
where κ was the orbital reduction factor and λ was a spin-
only coupling constant. The axial splitting parameter ∆ is
defined as the splitting of the orbital degeneracy of the 4T1g
term by the asymmetric ligand component, in the absence
of any spin-orbit coupling, and is taken to be positive when
the orbital singlet is lowest. The R(øA) values, defined as
R(øA) ) ∑[(øA,calc - øA,obs)2]/(øA,obs)2, were 3.6 × 10-5 and
1.66 × 10-4. The axial zero-field splitting parameter D is
defined as the energy gap between the two Kramers doublets
splitting of the lowest orbital singlet from the 4T1g term, and
is taken to be positive when the doublet referring to MS )
(1/2 is lowest. The D, gz, and gx values can be calculated by
our method and are summarized with the best-fitting
parameters in Table 4.
Conclusion
In this study, two dinuclear cobalt(II) complexes (1 and
2) were made using the dinucleating ligand, bhmp-, and the
crystal structure of complex 1 was determined. For the
purpose of analyzing the cryomagnetic data, our approxima-
tion method was used, and the experimental data were
successfully analyzed. This shows that the method we
developed is also suitable for the present complexes, which
have a different distortion pattern from previous complexes.
Acknowledgment. We thank Dr. Thomas Scho¨nherr and
Dr. Heribert Adamsky in Heinrich-Heine-Universita¨t Du¨s-
seldorf for providing a copy of the AOMX program.
Supporting Information Available: An X-ray crystallographic
file in CIF format, results of AOM calculations, cryomagnetic data,
and a set of magnetic equations. This material is available free of
charge via the Internet at http://pubs.acs.org.
The obtained axial splitting parameter ∆ for 2 is larger
than that for 1, and this is consistent with the fact that the
distortion around the cobalt(II) ion for 2 is larger than that
for 1, as discussed in the above section. The ∆ values are
normal for high-spin cobalt(II) complexes (∼200 to ∼800
IC0255297
(16) Figgis, B. N.; Gerloch, M.; Lewis, J.; Mabbs, F. E.; Webb, G. A. J.
Chem. Soc. A 1968, 2086-2093.
(17) Low, W. Phys. ReV. 1958, 109, 256-265.
4062 Inorganic Chemistry, Vol. 41, No. 15, 2002