Synthesis, X-ray single crystal and magnetic study of new heteroleptic late transition metal alkoxides with tetranuclear square planar metal core, Co4Cl2(OC2H4OEt)6, Co4(OMe)2(ac

Article abstract of DOI:10.1016/S0277-5387(03)00349-8

Interaction of 4 equiv. CoCl₂ with 6 equiv. of NaOC₂H₄OEt in toluene/HOC₂H₄OEt medium provided Co₄Cl₂(OC₂H₄OEt)₆ (1) with practically quantitativ

Full text of DOI:10.1016/S0277-5387(03)00349-8

Polyhedron 22 (2003) 2581ꢀ2586
/
www.elsevier.com/locate/poly
Synthesis, X-ray single crystal and magnetic study of new heteroleptic
late transition metal alkoxides with tetranuclear square planar metal
core, Co4Cl2(OC2H4OEt)6, Co4(OMe)2(acac)6(MeOH)2 and
Zn4(OMe)2(acac)6(C7H8)
Gulaim A. Seisenbaeva a, Mikael Kritikos b, Vadim G. Kessler a,*
a Department of Chemistry, SLU, P.O. Box 7015, SE-75007 Uppsala, Sweden
b Department of Structural Chemistry, Arrhenius Laboratory, Stockholm University, SE-10691 Stockholm, Sweden
Received 20 January 2003; accepted 11 April 2003
Abstract
Interaction of 4 equiv. CoCl2 with 6 equiv. of NaOC2H4OEt in toluene/HOC2H4OEt medium provided Co4Cl2(OC2H4OEt)6 (1)
with practically quantitative yield. Reaction of Co(acac)2 with Ti(OMe)4 in 1:1 ratio in toluene gave Co4(OMe)2(acac)6(MeOH)2 (2)
with moderate yields. The same reaction for Zn(acac)2 resulted in formation of Zn4(OMe)2(acac)6(C7H8) (3). The structures of 1ꢀ3
/
contain planar tetranuclear cores of M4(m3-OR)2(m2-OR)4 type ([Ti(OMe)4]4 type structure), where the metal atoms are
pentacoordinated in 1, hexacoordinated in 2, and both penta- and hexacoordinated in 3. The magnetic measurements have
revealed competing ferromagnetic and antiferromagnetic interactions between the 4 Co(II) atoms in 1, but only ferromagnetic in 2.
# 2003 Elsevier Ltd. All rights reserved.
Keywords: Antiferromagnetic interaction; Alkoxide; Late transition metal; X-ray; Molecular structure
1. Introduction
magnetic coupling on both intramolecular and
intermolecular level. In the present contribution we
report the synthesis, structural characterization and
magnetic properties of two new heteroleptic Co(II)
alkoxides, Co4Cl2(OC2H4OEt)6 (1) and Co4(OMe)2(a-
cac)6(MeOH)2 (2), and also the synthesis and structural
characterization of a zinc analog of the latter, Zn4(O-
Me)2(acac)6(C7H8) (3).
Oligo- and polynuclear complexes of late transition
metals, particularly carboxylates and b-diketonates,
have recently, attracted attention of researchers as
prospective molecular magnetic materials [1]. Alkoxide
groups have been recognized as extremely attractive
bridging ligands in such aggregates and a number of
molecular magnets*derivatives of Co(II) with methox-
/
ide bridges, such as Co4(OMe)4(acac)4(MeOH)4 [2], and
di-2-pyridylketone bridges in the gem-diol form such as
[Co4(N3)2(O2CPh)2{(py)2C(OH)O}4]2DMF [3], [Co4-
(N3)2(N3)2{(py)2C(OH)O}2{(py)2C(OMe)O}2]2H2O [4],
and [Co4(N3)2(H2O)2{(py)2C(OH)O}2{(py)2C(OMe)O-
2. Experimental
All manipulations were carried out in a dry nitrogen
atmosphere using Schlenk techniques or a glove box.
Waterfree CoCl2 was purchased from Aldrich Chemical
Company Inc. and used without further purification.
Waterfree Co(acac)2 was obtained by sublimation of the
commercial anhydrous Co(acac)2 (Aldrich Chemical
}2](BF4)2×/4H2O [5], have been obtained and structurally
characterized. The magnetic behavior of all these com-
plexes could be explained using the concept of ferro-
Company Inc.) at 110ꢀ
Zn(acac)2 was obtained by refluxing Zn(acac)2×
(Aldrich Chemical Company Inc.) with dry toluene with
/
145 8C and 1 mmHg. Waterfree
* Corresponding author. Tel.: ꢁ
3476.
/
46-18-67-1541; fax: ꢁ46-18-67-
/
/xH2O
E-mail address: vadim.kessler@kemi.slu.se (V.G. Kessler).
0277-5387/03/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0277-5387(03)00349-8

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G.A. Seisenbaeva et al. / Polyhedron 22 (2003) 2581ꢀ2586
/
subsequent evaporation, repeated twice. Ti(OMe)4 was
obtained by dissolution of about 2.0 g of Ti(OiPr)4 in 30
ml MeOH and 30 ml toluene with subsequent evapora-
tion to dryness. This operation was repeated trice
leaving a light yellow glassy solid. Toluene (Merck,
2.3. Zn4(OMe)2(acac)6(C7H8)(3)
Zn(acac)2 (0.321 g, 1.2 mmol) and Ti(OMe)4 (0.210 g,
1.2 mmol) were dissolved by refluxing in 4 ml toluene
and the colorless solution was left for crystallization
PA) was purified by distillation over LiAlH4. UVꢀ
spectra were registered for 0.025ꢀ0.05 M solutions in
toluene using an Hitachi U-2001 spectrophotometer. IR
/
Vis
overnight at ꢂ30 8C. The colorless precipitate was
/
/
separated by decantation from the light yellow solution
and dried in vacuo. Yield: 0.11 g (40%). IR (cmꢂ1): 1603
s br, 1377 s br, 1256 s, 1194 w, 1144 sh, 1093 s br, 1042 s,
1015 s, 925 s, 793 w, 782 w, 770 m, 696 w, 667 w, 649 w,
spectra of nujol mulls were registered with a Perkinꢀ
/
Elmer FT-IR spectrometer 1720X. 1H NMR spectra
were recorded for the CDCl3 solutions on a Bruker 400
MHz spectrometer at 300 K. Satisfactory results of
microanalysis (C, H) were obtained for all the reported
compounds by Mikrokemi AB, Uppsala, Sweden using
the combustion technique.
1
630 m, 564 s, 552 sh, 439 m, 408 m. H NMR, ppm:
7.25ꢀ7.15 (phenyl-CH toluene, 5H), 5.39 (singlet, CH
/
acac, 6H), 3.54 (singlet, CH3 OMe, 6H), 2.34 (singlet,
CH3 toluene, 3H), 1.99 (singlet, CH3 acac, 36H).
The AC magnetic susceptibility on polycrystalline
samples of 1 and 2 were measured (at 500 Hz, 125 A
mꢂ1 and at 500 Hz, 500 A mꢂ1) in the temperature
2.4. Crystallography
For details of data collection and refinement experi-
range 12ꢀ320 K using a Lake Shore Inc. AC Suscept-
/
ments see Table 1. The air sensitive crystals of 1ꢀ3 were
/
ometer, Model 7130, equipped with a helium cryostat.
Diamagnetic corrections of raw data were made using
Pascal’s constants [6,7].
chosen under nitrogen and vacuum-sealed into Linde-
man tubes. All structures were solved by standard direct
methods, the majority of non-hydrogen atoms being
located already from the initial solution. The missing
non-hydrogen atoms were then found in subsequent
difference Fourier syntheses. All non-hydrogen atoms
(except for the disordered carbon atoms of the clathrate
toluene molecule in 3 refined only isotropically) were
refined in isotropic and then anisotropic approxima-
tions. Hydrogen atom positions (except for the OH-
proton in 2, located in the difference Fourier syntheses
and refined isotropically) were calculated geometrically
and included into the final refinement in isotropic
approximation riding on the correspondent carbon
2.1. Co4Cl2(OC2H4OEt)6 (1)
Sodium metal (1.325 g, 57.6 mmol) was dissolved in
the mixture of 2-ethoxyethanol (10.4 ml) and toluene (50
ml). CoCl2 (5.001 g, 38.5 mmol) was added to the
obtained clear solution with vigorous stirring. The dark
greyish blue mixture thus formed was subjected to reflux
for 40 min, left to precipitate for 30 min at room
temperature and then the dark blue solvent was
separated from the greyish precipitate by decantation
atoms with Uꢃ/1.2Uiso for the methyne- and methyl-
and left for crystallization overnight at ꢂ30 8C. Dark
/
ene-, and Uꢃ1.5Uiso for methyl groups, respectively.
/
blue crystals formed were separated from the weakly
colored violet solution by decantation and dried in
vacuo. Yield: 11.621 g (96%). IR (cmꢂ1): 1482 s, 1412
m, 1346 s, 1295 w, 1264 w, 1241 m, 1163 sh, 1124 s, 1101
s, 1070 s, 933 s, 910 s, 844 sh, 828 s, 801 w, 610 s, 598 s,
3. Results and discussion
3.1. Synthetic approaches and molecular structures
478 s, 427 m, 380 s. UVꢀ
/
Vis, l, nm o): 632(113),
614(118), 589(120), 524(93).
Continuing the systematic search for the alkoxide
precursors of late transition metal based oxide materials,
we investigated the possibility to obtain cobalt(II)
alkoxy-alkoxides using the metathesis of cobalt(II)
chloride with alkali alkoxy-alkoxides:
2.2. Co4(OMe)2(acac)6(MeOH)2 (2)
Co(acac)2 (0.179 g, 0.7 mmol) and Ti(OMe)4 (0.150 g,
0.9 mmol) were dissolved by refluxing in 3 ml toluene
and the pinkish violet solution was left for crystal-
CoCl2(s)ꢁ2NaOC2H4OR Toluene=HOC H OR
Co(OC2H4OR)2 ꢁ2NaCl; R ꢃ Me; Et
2
4
lization overnight at ꢂ30 8C. The pinkish violet pre-
/
cipitate was separated by decantation and dried in
vacuo. Yield: 0.071 g (42%). IR (cmꢂ1): 1604 s, 1520
s, 1496 s, 1477 sh, 1408 s br, 1363 m, 1256 m, 1195 w,
1123 w, 1082 w, 1043 w, 1016 m, 924 m, 768 m, 729 s,
These reactions tended to lead to viscous dark blue
solutions extraordinarily sensitive to the ambient atmo-
sphere due, supposedly, to easily occurring oxidation of
Co(II) to Co(III), which was indicated by formation of a
voluminous precipitate possessing the greenish brown
695 s, 659 w, 562 m, 464 m, 419 m. UVꢀ
/
Vis, l, nm o):
500 (38).
color characteristic of Co(II)ꢀ/Co(III) mixed-valence

G.A. Seisenbaeva et al. / Polyhedron 22 (2003) 2581ꢀ
/
2586
2583
Table 1
Crystal data and the diffraction experiments details for compounds 1ꢀ
/
3
1
2
3
Chemical formula
Formula weight
Temperature (K)
Crystal system
Space group
C
24H54Cl2Co4O12
C34H56Co4O16
956.51
295(2)
C32H48O14Zn4
918.18
295(2)
841.29
295(2)
monoclinic
P21/c
monoclinic
P21/n
triclinic
¯
P1
/
˚
a (A)
9.2988(11)
19.048(2)
10.9380(13)
90
10.387(3)
20.246(4)
11.005
9.8561(13)
10.5271(15)
11.4424(16)
93.946(2)
100.463(3)
103.504(2)
1127.5(3)
1
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
90
111.053(15)
90
111.393(2)
90
3
˚
V (A )
Z
1803.9(4)
2
2.006
2159.7(9)
2
1.573
m (mmꢂ1
)
2.155
Number of independent reflections
Number of observed reflections
4187 [Rint
ꢃ
2s(I)]
/
0.0502]
3768 [Rint
ꢃ
2s(I)]
/
0.0740]
3864 [Rint
ꢃ0.0315]
/
2291 [I ꢀ
/
1827 [I ꢀ
/
2046[Iꢀ2s(I)]
/
R1
0.0513
0.1216
0.0586
0.1017
0.0564
0.1332
wR2
derivatives [8]. In the case of RꢃEt in one of the
/
syntheses we have observed also the formation of a
small crop of bluish violet prismatic single crystals. X-
ray single crystal study showed them to be an alkoxide
chloride*compound 1. Carrying out the metathesis
/
reaction with the proper stoichiometry offered 1 in
practically quantitative yield:
4CoCl2(s)ꢁ6NaOC2H4OEt Toluene=HOC H OEt
Co4Cl2(OC2H4OEt)6(1)ꢁ2NaCl
2
4
Compound 1 is poorly soluble in any organic solvent
at room temperature, but dissolves readily on heating in
the parent alcohol, toluene or mixtures of these two.
The molecular structure of
1 belongs to the
[Ti(OMe)4]4 structure type [9], based on the M4(m3-
O)2(m2-O)4-core. The specific feature of 1 is that all the
four metal atoms in it are pentacoordinated (see Fig. 1,
Table 2). The coordination around the Co atoms is
distorted tetragonal pyramidal with the bond lengths
dependent clearly on the structural function of the
Fig. 1. Molecular structure of Co4Cl2(OC2H4OEt)6 (1).
commonly observed in the oligonuclear complexes of
Co(II) [2ꢀ5].
/
It appeared interesting to compare the structure and
properties of 1 with those of compound 2, discovered
earlier as the product of the interaction of Co(acac)2
with Ta(OMe)5 in the presence of traces of MeOH [10]:
oxygen atoms: the shortest ones are those to the m2-O
˚
2.019(3) A),
atoms of the alkoxide bridges (1.871(3)ꢀ
/
those to the m3-O atoms of the alkoxide bridges are
Toluene
˚
2.206(3) A) and the longest
noticeably longer (2.098(3)ꢀ
in average (2.173(3)ꢀ2.281(4) A) are the bonds to the
ether functions of the alkoxy-alkoxide groups. The
/
4Co(acac)2 ꢁ2Ta(OMe)5 ꢁ4MeOH
˚
/
Co4(OMe)2(acac)6(MeOH)2 ꢁ2Ta(OMe)4(acac)
˚
˚
Co(2)ꢀ
longer than the Coꢀ
the chloride ligand. It is also important to note the
remarkably short Co(1)ꢀCo(1A) bond length of
2.7238(12) A, indicating the possibility of metalꢀmetal
bonding interactions (alternatively*the antiferromag-
netic spin coupling) in this structure. The other CoꢀCo
Co(2) 3.235(1) A) is very close to those
/
Cl(1) bond length 2.6938(18) A is ca. 0.5 A
The triclinic modification of 2, described in literature
/
O bonds due to the bigger radius of
was obtained at ꢁ4 8C. The yield of 2 in the reaction
/
above was very low and we considered an alternative
approach with a medium introducing small amounts of
MeOH in this reaction. The interaction of Co(acac)2
with the glassy product of the Ti(OMe)4 preparation
(via the alcohol interchange reaction) permitted the
increase of yields to moderate ones (about 40%). The
/
˚
/
/
/
˚
distance (Co(1)ꢀ
/

2584
G.A. Seisenbaeva et al. / Polyhedron 22 (2003) 2581ꢀ2586
/
Table 2
Table 3
˚
˚
Selected bond distances (A) and angles (8) in the structure of 1
Selected bond distances (A) and angles (8) in the structure of 2
Bond lengths
Bond lengths
Co(1)ꢀ
Co(1)ꢀ
Co(1)ꢀ
Co(1)ꢀ
Co(1)ꢀ
Co(1)ꢀ
/
O(3)
1.975(4)
2.019(3)
2.098(3)
2.173(3)
2.206(3)
2.7238(12)
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
/
O(2)
O(3)
O(1)
O(5)
Cl(1)
1.871(3)
1.904(4)
2.105(3)
2.281(4)
2.6938(18)
Co(1)ꢀ
Co(1)ꢀ
Co(1)ꢀ
Co(1)ꢀ
Co(1)ꢀ
Co(1)ꢀ
/
O(5)
O(4)
O(2)
O(1)#1
O(3)
O(1)
2.020(4)
2.054(4)
2.081(4)
2.084(3)
2.084(3)
2.091(3)
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
/
O(7)
O(6)
O(1)
O(3)#1
O(8)
O(2)
2.000(4)
2.012(4)
2.037(3)
2.157(4)
2.202(5)
2.242(4)
/O(2)#1
/
/
/
/O(1)
/
/
/
/O(4)
/
/
/
/O(1)#1
/
/
/
/Co(1)#1
/
/
Bond angles
O(3)ꢀCo(1)ꢀ
O(3)ꢀCo(1)ꢀ
O(2)#1ꢀ
O(3)ꢀCo(1)ꢀ
O(2)#1ꢀCo(1)ꢀ
O(1)ꢀCo(1)ꢀ
O(3)ꢀCo(1)ꢀ
O(2)#1ꢀ
O(1)ꢀCo(1)ꢀ
O(4)ꢀCo(1)ꢀ
Bond angles
O(5)ꢀCo(1)ꢀ
O(5)ꢀCo(1)ꢀ
O(4)ꢀCo(1)ꢀ
O(5)ꢀCo(1)ꢀ
O(4)ꢀCo(1)ꢀ
O(2)ꢀCo(1)ꢀ
O(5)ꢀCo(1)ꢀ
O(4)ꢀCo(1)ꢀ
O(2)ꢀCo(1)ꢀ
/
/
O(2)#1
173.96(15) O(2)ꢀ
71.90(13) O(2)ꢀ
114.07(13) O(3)ꢀ
87.36(14) O(2)ꢀ
86.64(14) O(3)ꢀ
159.19(13) O(1)ꢀ
99.79(14) O(2)ꢀ
78.44(13) O(3)ꢀ
101.53(12) O(1)ꢀ
79.90(12) O(5)ꢀ
/
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
/
O(3)
O(1)
O(1)
O(5)
O(5)
97.37(16)
84.34(13)
73.11(13)
73.23(14)
99.02(15)
/
/
O(4)
O(2)
O(2)
91.74(16) O(7)ꢀ
89.30(15) O(7)ꢀ
89.75(15) O(6)ꢀ
/
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
Co(2)ꢀ
/
O(6)
O(1)
O(1)
88.85(18)
179.01(17)
90.40(16)
/
/
O(1)
/
/
/
/
/
/
/
Co(1)ꢀ
O(4)
O(4)
/O(1)
/
/
/
/
/
/
/
/
/
/
/
/
O(1)#1 171.45(14) O(7)ꢀ
/
/O(3)#1 100.93(16)
/
/
/
/
/
/
O(1)#1
O(1)#1
O(3)
89.14(15) O(6)ꢀ
99.21(14) O(1)ꢀ
90.92(15) O(7)ꢀ
93.47(15) O(6)ꢀ
176.76(15)
/
/O(3)#1 168.67(16)
/
/
O(4)
/
/
O(5) 155.23(14)
Cl(1) 129.99(11)
Cl(1) 132.54(13)
Cl(1) 104.75(10)
/
/
/
/O(3)#1
79.88(13)
88.78(18)
94.44(18)
/
/
O(1)#1
/
/
/
/
/
/O(8)
/
Co(1)ꢀ
/O(1)#1
/
/
/
/O(3)
/
/O(8)
/
/
O(1)#1
O(1)#1
/
/
/
/O(3)
/
/
/
/Cl(1)
97.80(11)
IR spectrum of the Ti(OMe)4 prepared by this route
contains always a broad band at 3460 cmꢂ1 indicating
presence of residual MeOH that cannot be removed
completely even by a prolonged drying in vacuum at
room temperature. The data of elementary microana-
lysis permit to formulate the reactant thus obtained as
the first one with shorter distances of 2.000(4)ꢀ
/
2.091(3)
includes both the bonds to terminal O-atoms of the
acac-ligands and to the m3-O atoms of the alkoxide
bridges and the second one with longer ones, 2.157(4)ꢀ
/
˚
2.242(4) A, *
acac-ligands and to the terminal O-atoms of the solvat-
O bond angles are
/
those to the bridging m2-O atoms of the
Ti(OMe)4×
from the reaction mixture as a new monoclinic mod-
ification at ꢂ30 8C that remained, however, stable
/
xMeOH, where x #
/
0.15ꢀ0.20. 2 crystallized
/
ing MeOH molecules). The Oꢀ
/
Coꢀ
/
fairly close to either 908 or 1808, manifesting that only
minor distortion of the octahedra takes place in this
/
indefinitely at room temperature. It has rather high
solubility in toluene at room temperature and can be
recrystallized from it. Its dissolution in MeOH leads to
crystallization of Co(acac)2(MeOH)2, described earlier
by us [10].
The molecular structure of 2 (Fig. 2, Table 3) also
belongs to the [Ti(OMe)4]4 structure type, but all cobalt
atoms in it are octahedrally coordinated. The bond
length distribution is much less pronounced in 2
compared to 1 (two groups can be distinguished, where
case. The Coꢀ
to each other (3.139(1) and 3.212(1) A) and to those
commonly observed [2ꢀ5].
/
Co distances in the structure of 2 are close
˚
/
We attempted also in this work the preparation of a
non-magnetic analog of 2 in order to try to follow its
molecular structure in solution using the NMR techni-
que. The reaction of Zn(acac)2 with the glassy Ti(OMe)4
provided 3 with moderate yields. 3 is readily soluble in
toluene at room temperature. Its molecular structure
(Fig. 3, Table 4) is close to that of 2, with the only
difference being the absence of the solvating alcohol
molecules, which results in distorted trigonal bipyrami-
dal coordination for half of the zinc atoms (Zn(2) having
an octahedron with a missing vertex). The distribution
in the bond lengths is analogous to that observed in 2
with the only exception that the bonds to the m3-O atoms
of the alkoxide bridges are rather asymmetric in this
˚
case (1.980(4), 2.065(4) and 2.178(4) A), indicating more
covalent character of bonding in case of the zinc
1
derivative. The H NMR spectrum indicated the pre-
sence of only one type of alkoxide and acetylacetonate
ligands in the structure of 3 in solution, permitting to
suppose that its molecule is preserved on dissolution but
undergoes a quick exchange of the acac-ligands, facili-
tated obviously by the presence of structurally unsatu-
rated pentacoordinated zinc atoms.
Fig. 2. Molecular structure of Co4(OMe)2(acac)6(MeOH)2 (2).

G.A. Seisenbaeva et al. / Polyhedron 22 (2003) 2581ꢀ
/
2586
2585
Fig. 4. Experimental xMT versus T for Co4Cl2(OC2H4OEt)6 (1) (open
squares) and Co4(OMe)2(acac)6(MeOH)2 (2) (filled squares).
Fig. 3. Molecular structure of Zn4(OMe)2(acac)6(C7H8) (3).
(90.58) would be consistent with a ferromagnetic ex-
change pathway.
Table 4
˚
Selected bond distances (A) and angles (8) in the structure of 3
For 2 xMT reaches approximately the same value
(10.8 cm3 K molꢂ1) as for 1 in the high temperature
limit and decreases continuously as the temperature is
decreased down to 12 K. Clearly, 2 shows a different
magnetic behavior compared to 1. This xMT versus T
curve is a typical indication of antiferromagnetic inter-
actions between the Co atoms. Although 2 exhibits the
same Co4(m2-O)4(m3-O)2 core structure as 1, the two
Bond lengths
Zn(1)ꢀ
Zn(1)ꢀ
Zn(1)ꢀ
Zn(1)ꢀ
Zn(1)ꢀ
Zn(1)ꢀ
/
O(3)
O(6)
O(1)#1
O(2)
O(4)
O(1)
2.019(5)
2.058(5)
2.065(4)
2.086(5)
2.126(4)
2.178(4)
Zn(2)ꢀ
Zn(2)ꢀ
Zn(2)ꢀ
Zn(2)ꢀ
Zn(2)ꢀ
Zn(2)ꢀ
/
O(7)
O(1)
1.944(5)
1.980(4)
2.018(5)
2.035(5)
2.204(5)
3.1187(12)
/
/
/
/
O(4)
/
/
O(5)
/
/
O(2)#1
Zn(1)
/
/
Bond angles
O(3)ꢀZn(1)ꢀ
O(3)ꢀZn(1)ꢀ
O(6)ꢀZn(1)ꢀ
O(3)ꢀZn(1)ꢀ
O(6)ꢀZn(1)ꢀ
O(1)#1ꢀ
O(3)ꢀZn(1)ꢀ
O(6)ꢀZn(1)ꢀ
O(1)#1ꢀ
O(2)ꢀZn(1)ꢀ
/
/
O(6)
93.8(2)
O(7)ꢀ
/
Zn(2)ꢀ
Zn(2)ꢀ
Zn(2)ꢀ
Zn(2)ꢀ
Zn(2)ꢀ
Zn(2)ꢀ
Zn(2)ꢀ
Zn(2)ꢀ
Zn(2)ꢀ
Zn(2)ꢀ
/
O(1)
O(4)
136.9(2)
135.0(2)
86.05(18)
91.3(2)
complexes differ in their values of the Coꢀ
/
Oꢀ/Co angles.
/
/
O(1)#1 166.98(19) O(7)ꢀ
/
/
For 2, they range between 95.98 and 102.28, these values
also support a model where intramolecular antiferro-
magnetic couplings dominate in the temperature region
investigated.
/
/O(1)#1
92.23(19) O(1)ꢀ
87.31(19) O(7)ꢀ
102.27(19) O(1)ꢀ
80.13(18) O(4)ꢀ
94.2(2)
O(7)ꢀ
85.93(19) O(1)ꢀ
97.71(18) O(4)ꢀ
171.55(18) O(5)ꢀ
/
/
O(4)
O(5)
/
/O(2)
/
/
/
/O(2)
/
/
O(5)
98.7(2)
/
Zn(1)ꢀ
/
O(2)
/
/
O(5)
94.8(2)
87.7(2)
/
/O(4)
/
/
O(2)#1
O(2)#1
O(2)#1
The disagreement between the measured data and the
simple spin-only model is what can be expected for
systems such as 1 and 2. Moreover, the actual g values
have not been measured and are probably underesti-
mated [11,12]. These susceptibility measurements are
not sufficient in order to make a more thorough analysis
of the spin behavior in these complicated tetranuclear
Co4 systems. They have, however, showed that, two
systems with the same core topology, but with different
coordination environments can exhibit different mag-
netic behavior.
/
/O(4)
/
/
79.18(17)
88.81(19)
/
Zn(1)ꢀ
/
O(4)
/
/
/
/O(4)
/
/
O(2)#1 175.7(2)
3.2. Magnetic properties
The xMT versus T curves of 1 and 2 are shown in Fig.
4. The molar magnetic susceptibility, xM is given per
tetranuclear unit. For 1, a minimum in the xMT curve is
observed at 32 K. Below this temperature xMT increases
It is interesting to note, that from alkoxide chemistry
the well known, M4(m2-O)4(m3-O)2 structure unit
(Ti4(OMe)16 [9]) is also well represented among the
Co4 complexes exhibiting ferromagnetic behavior. Some
of these tetramers are based on the ligands di-2-pyridyl
ketone and azide anions and the core is described as a
double cubane with two missing metal atom vertices.
Two of the bridging ligand atoms connecting the
rhombic Co4 unit are nitrogen instead of oxygen atoms.
Examples with this specific core geometry and composi-
tion are the compounds [Co4(N3)2(O2CPh)2{(py)2C(O-
H)O}4]2DMF [3], [Co4(N3)2(N3)2{(py)2C(OH)O}2-
{(py)2C (OMe)O}2]2H2O [4] and [Co4(N3)2(H2O)2-
monotonically down to 12 K. Above Tꢃ200 K, xMT
/
flattens out at a value of 10.8 cm3 K molꢂ1. The
observed value is significantly higher than the spin-only
value 7.50 cm3 K molꢂ1 expected for a completely
uncoupled Co(II)4 cluster with the assumptions of Sꢃ3/
/
2 and a g value of 2 for high spin Co2ꢁ. Looking at the
molecular structure of 1, it is possible to interpret these
results as the result of competing antiferromagnetic and
ferromagnetic exchange interactions. In the molecule,
the Coꢀ
larger angles would allow for antiferromagnetic ex-
change pathways and the angle Co(1)ꢀO(1)ꢀCo(2)
/
Oꢀ
/
Co angles range between 78.58 and 1138. The
/
/

2586
G.A. Seisenbaeva et al. / Polyhedron 22 (2003) 2581ꢀ2586
/
{(py)2C(OH)O}2{(py)2C(OMe)O}2](BF4)2×
/
4H2O [5]. As
deposition numbers 201520ꢀ
tively.
/
201522 for 1ꢀ3, respec-
/
pointed out previously it is not possible to analyze
polynuclear Co complexes with effective Hamiltonians
based on pairwise spin only interactions [5]. Hence, the
variable temperature magnetic susceptibility behavior of
these complexes was only analyzed in a qualitative way.
The magnetic susceptibility measurements on complexes
1 and 2 give the same xMT value (10.8 cm3 K molꢂ1) at
room temperature as that found for the DMF derivative
above [3]. However, while 1 exhibits a possible mixture
of ferromagnetic and antiferromagnetic behavior the
DMF derivative is purely ferromagnetic. Although the
compounds have the same core topology this work
shows that the nature of the ligands and the specific
coordination geometry around each cobalt center play a
decisive role in the magnetic properties of these tetra-
nuclear complexes.
References
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Brechin, A. Yamaguchi, E.M. Rumberger, S.M.J. Aubin, Z.M.
Sun, G. Aromi, Mol. Cryst. Liquid Cryst. 376 (2002) 301.
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4. Supplementary material
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[11] R.L. Carlin, Magnetochemistry, Springer, Berlin, 1986.
Supplementary data are available from the CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: ꢁ44-
/
[12] H. Andres, J.M. Clemente-Juan, M. Aebersold, H.U. Gudel, E.
¨
Coronado, H. Buttner, G. Kearly, J. Melero, R. Burriel, J. Am.
¨
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk) on request, quoting the
Chem. Soc. 121 (1999) 10028.