Structure and magnetism of mono-, di-, and trinuclear benzoato cobalt(II) complexes

Article abstract of DOI:10.1016/j.poly.2011.02.047

Three cobalt(II) - benzoato (bz) complexes have been prepared and structurally characterized. In the mononuclear complex trans-[Co(bz) ₂(H₂O)₂(nca)₂] the benzoato ligand is unidentate (nca = nicotinamide). The dinuclear complex [(μ₂-bz) ₄{Co(qu)}₂] is a structural analog of the copper acetate (qu = quinoline) where four bidentate benzoato ligands link two cobalt(II) pentacoordinate centers. The trinuclear complex of the composition [Co ₃(bz)₆(inca)₆] contains a central hexacoordinate {(bz)₂Co(inca)₂(bz)₂} unit in which the bidentate benzoato ligands held the central and peripheral cobalt(II) centers (inca = iso-nicotinamide); the peripheral hexacoordinate {(bz)Co(inca)₂<} units contain the terminal benzoato ligand in its bidentate function. The magnetic susceptibility data down to T = 2 K and the magnetization data up to B = 7 T reveal a considerable magnetic anisotropy due to the single-ion zero-field splitting.

Full text of DOI:10.1016/j.poly.2011.02.047

Polyhedron 30 (2011) 1367–1373
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Structure and magnetism of mono-, di-, and trinuclear benzoato
cobalt(II) complexes
a
a,b,
c
b
ˇ b
ˇ
⇑
ˇ
ˇ
ˇ
J. Hudák , R. Boca
, L. Dlhán , J. Kozíšek , J. Moncol
a Department of Chemistry (FPV), University of SS. Cyril and Methodius, SK-91701 Trnava, Slovakia
b Institute of Inorganic Chemistry (FCHPT), Slovak University of Technology, SK-812 37 Bratislava, Slovakia
c Institute of Physical Chemistry (FCHPT), Slovak University of Technology, SK-812 37 Bratislava, Slovakia
a r t i c l e i n f o
a b s t r a c t
Article history:
Three cobalt(II) – benzoato (bz) complexes have been prepared and structurally characterized. In the
mononuclear complex trans-[Co(bz)2(H2O)2(nca)2] the benzoato ligand is unidentate (nca = nicotin-
amide). The dinuclear complex [(l2-bz)4{Co(qu)}2] is a structural analog of the copper acetate (qu = quin-
oline) where four bidentate benzoato ligands link two cobalt(II) pentacoordinate centers. The trinuclear
complex of the composition [Co3(bz)6(inca)6] contains a central hexacoordinate {(bz)2Co(inca)2(bz)2} unit
in which the bidentate benzoato ligands held the central and peripheral cobalt(II) centers (inca = iso-nic-
otinamide); the peripheral hexacoordinate {(bz)Co(inca)2<} units contain the terminal benzoato ligand in
its bidentate function. The magnetic susceptibility data down to T = 2 K and the magnetization data up to
B = 7 T reveal a considerable magnetic anisotropy due to the single-ion zero-field splitting.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 13 January 2011
Accepted 28 February 2011
Available online 6 March 2011
Keywords:
Co(II) complexes
Benzoato ligand
Structure
Magnetism
Zero-field splitting
1. Introduction
n-X-bz where n = 2, 3, and 4. Two aqua bridging ligands exist in
complexes with functionalized benzoato ligands: in [(
l
2-H2O)2-
2-H2O)2-
The cobalt(II) benzoates cover a wide-studied class of com-
plexes with a variety of structural motifs. The CCDC (Cambridge
Crystallographic Data Centre) offers information about existence
of mononuclear, dinuclear, trinuclear, and polynuclear complexes
containing Co(II) with benzoato ligands (bz = PhCOOꢀ).
{Co(bpy)(H2O)(4-CHO-bz)}2](4-CHO-bz)2 [2] and in [(
l
(
l
2-2,6-(pTol)2-bz)2{Co(2,6-(pTol)2-bz)L}2] [13].
Of trinuclear cobalt(II)–benzoato complexes let us mention
[Co3(bz)6(py)2] formulated as [(
2-bz-O,O,O0)2( 2-bz-O,O0)4-
l
l
Co3(py)2], where the central unit {(bz)3Co(bz)3} is hexacoordinate;
the peripheral units {(py)Co<<} are pentacoordinate [14]. An anal-
ogous structural motif exists in [Co3(bz)6(L)2]ꢁ2CH3CN, L = 4-(2-
(tetrathiafulvalenyl)ethenyl)-pyridine, [15]. In [Co3(bz)6(qu)2] the
central unit {(bz)3Co(bz)3} is hexacoordinate whereas the periphe-
ral units {(qu)Coꢂ} are tetracoordinate [16]. The complex with the
The mononuclear complexes are usually of the type trans-
[Co(bz)2(L2)(L0)2] where the central atom is hexacoordinate and
the benzoato ligand is unidentate. These complexes typically
0
contain {CoO2O4 }, {CoO2O02N2} and {Co2O2N4} chromophores.
This class is exemplified by [Co(bz)2(nca)(H2O)2] [1] and [Co(4-X-
bz)2(nca)(H2O)2]
[2–6]
(nca = nicotinamide,
3-CONH2-py).
refcode XOHLIQ consists of triangulo-[(l3-O)(l
2-bz)3CoIII3L3]+ and
However, bidentate benzoato ligands are also in the play in
cis-[Co(bz)2(Me2phen)] [7] and trans-[Co(4-X-bz)2(H2O)2] [8].
Among dinuclear complexes, one group covers the structural
analogs of the copper(II) acetate, i.e. four benzoato ligands link
two metal centers, [Co2(bz)4L2]; here the Co(II) atom is pentacoor-
catena-[CoII3(bz)6(bz)2]2ꢀ ions; in the latter, six benzoato ligands
bear a bridging function (two of them are tridentate) whereas
two additional are terminal-bidentate; all Co(II) centers are hexa-
coordinate [17].
Plenty of Co(II) benzoates are coordination polymers, for in-
dinate. This group is covered by [(
bz)4{Co(4-Me-qu)}2] where qu = quinoline [9,10]. Another group
with the composition [( 2-H2O),(
l2-bz)4{Co(qu)}2] and [(l2
-
stance catena-[{l l
3-(bz-O,O,O0,O0)( 2-bz-O,O0)Co}2] [18,19].
This short introduction points to a structural versatility of the
Co(II)–benzoato complexes. This will manifest itself in a versatility
of magnetic properties. Motivated by these considerations we pre-
pared mononuclear, dinuclear, and trinuclear Co(II) complexes
containing the benzoato ligands and heterocyclic pyridine-based
co-ligands (Fig. 1). Two of them have been reported previously
whereas the trinuclear complex is reported for the first time. For
all of these complexes the magnetic susceptibility data along with
the magnetization data have been recorded and analyzed in terms
of the spin Hamiltonian.
l
l
2-bz)2{Co(bz)(L)2}2]ꢁSol contains
one H2O bridging ligand where L = py and 4-Me-py, respectively. In
these complexes the metal centers are hexacoordinate [11,12]. The
above structural motifs are known also for substituted benzoates,
⇑
Corresponding author at: Institute of Inorganic Chemistry (FCHPT), Slovak
University of Technology, SK-812 37 Bratislava, Slovakia. Tel.: +421 259325610.
ˇ
E-mail address: roman.boca@stuba.sk (R. Boca).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.02.047

1368
J. Hudák et al. / Polyhedron 30 (2011) 1367–1373
washed with ethanol. The complexes 1 and 3 have been prepared
in a similar manner.
O
NH2
O
Anal. Calc. for (1) C26H26Co1N4O8 (M = 581.45): C, 53.7; H, 4.51;
N, 9.64. Found: C, 53.4; H, 4.35; N, 9.62%. Anal. Calc. for (2)
NH2
C
46H34Co2N2O8 (M = 860.61): C, 64.2; H, 3.98; N, 3.25. Found: C,
N
N
N
63.9; H, 4.00; N, 3.19%. Anal. Calc. for (3) 78H66Co3N12O18
C
(M = 1636.22): C, 57.3; H, 4.07; N, 10.3. Found: C, 57.6; H, 4.06;
N, 10.4%.
Fig. 1. Sketch of the nicotinamide, iso-nicotinamide, and quinoline (from left to
right).
2.2. Physical measurements
Table 1
Summary of X-ray crystallographic data.
Elemental analysis was carried out on FlashEA 1112, Thermo-
Finnigan. IR spectra were measured in KBr pellets (Magna FTIR
750, Nicolet) in the 4000–400 cmꢀ1 region. Electronic spectra were
measured in Nujol mull (Specord 200, Analytical Jena) in the range
Compound
1
2
3
Formula
C
26H26CoN4O8 C46H34Co2N2O8 C78H66Co3N12O18
Formula weight
Crystal system
Space group
Cell parameters
a (Å)
581.44
monoclinic
P21/n
860.61
orthorhombic
Pbca
1636.22
monoclinic
P21/c
9000–50 000 cmꢀ1
.
Single-crystal X-ray diffraction experiments for all complexes
have been performed using Gemini R CCD apparatus (Oxford Dif-
fraction). Data reduction and analytical absorption [20] corrections
were performed by CrysAlisPro package [21]. The structures were
solved by direct methods using SIR-97 [22] or SHELXS-97 [23] and re-
fined by the full-matrix least-squares procedure with SHELXL-97
[23]. Geometrical analyses were performed with SHELXL-97. The
structures were drawn with XP in SHELXTL [23] and MERCURY [24].
Crystal data and conditions of data collection and refinement are
reported in Table 1.
7.1638(2)
18.3028(4)
10.4052(3)
90
17.0960(4)
11.6428(3)
19.7266(6)
90
90
90
3926.5(2)
4
1.456
11.5241(2)
20.8012(3)
15.8270(2)
90
104.721(2)
90
3669.4(1)
2
1.481
b (Å)
c (Å)
a
(°)
b (°)
109.511(3)
90
1285.96(6)
2
c
(°)
V (Å3)
Z
Dcalc (g cmꢀ3
)
1.502
Absorption coefficient
(mmꢀ1
F(0 0 0)
0.725
0.904
0.752
)
Magnetic susceptibility and magnetization measurements were
done using a SQUID magnetometer (Quantum Design, MPMS-XL7)
between 2 and 300 K at B = 0.1 T. The magnetization data until
B = 7 T were taken at T = 2.0 and 4.6 K, respectively. Raw suscepti-
bility data were corrected for underlying diamagnetism using the
set of Pascal constants. The effective magnetic moment has been
602
1768
1.045
72 775
3983/0/262
1686
1.070
69 833
7275/0/503
S
1.069
Reflections collected
Data/restraints/
parameters
18 389
2619/4/179
R1[F2 > 2
r
(F2)], wR2(F2) 0.0276,
0.0909
0.356, ꢀ0.448 0.216, ꢀ0.218
0.0225, 0.0652 0.0446, 0.1181
qmin (e Åꢀ3
)
0.397, ꢀ0.367
calculated as usual: leff/l
B = 798(v0T)1/2 when SI units are
D
qmax
,
D
employed.
2. Experimental
3. Results and discussion
2.1. Synthesis
3.1. Molecular and crystal structure
Starting materials (nicotinamide, iso-nicotinamide, quinoline,
CoCl2ꢁ6H2O, PhCOONa and ethanol) were purchased from commer-
cial sources and used as received.
The crystal structure of trans-[Co(bz)2(H2O)2(nca)2] (1) has been
determined previously [1]. The description of molecular structure
of 1, according to the present redetermination, is contained in Sup-
plementary material – Fig. S1. The bond distances and bond angles
of 1 are comparable to other carboxylato trans-[Co(RCOO)2(-
H2O)2(nca)2] complexes [2–6,25–28]. The molecules of 1 are linked
via hydrogen bonds (N2–H2Aꢁ ꢁ ꢁO3iii [symmetry code: (iii) ꢀx + 2,
ꢀy, ꢀz]) of amide groups of nicotinamide through head-to-head
supramolecular synthons R22ð8Þ [29] into one-dimensional supra-
molecular chains (Fig. 2, Table 2). The one-dimensional supramo-
lecular chains are connected through hydrogen bonds between
Three complexes containing cobalt(II), benzoate and an organic
base B were prepared from cobalt chloride as follows. A suspension
of the quinoline (qu) in 10 cm3 of ethanol was combined with a
mixture of PhCOONa and CoCl2ꢁ6H2O in 10 cm3 of ethanol/water
(the molar ratio qu:PhCOONa:CoCl2ꢁ6H2O = 2:2:1). After stirring
for 1 h at 60 °C the insoluble solid precipitate was filtered off.
The filtrate was left for 2 days for a spontaneous evaporation.
The dark violet crystals were separated on Büchner funnel and
Fig. 2. Hydrogen bonding network through supramolecular synthons R22ð8Þ in crystal structure of 1. The hydrogen atoms and benzene rings of the bz ligands are omitted for
clarity. Symmetry codes: (ii) ꢀx + 2, ꢀy, ꢀz + 1; (iii) ꢀx + 2, ꢀy, ꢀz.

J. Hudák et al. / Polyhedron 30 (2011) 1367–1373
1369
benzoato ligands in a syn-anti arrangements (l2
-
g1
:g
1-bridging).
Table 2
Selected hydrogen bond parameters of 1 and 3 (Å, °)a.
One from three Co(II) atoms (Co1) lies in a special position of the
center of symmetry and octahedral coordination sphere of Co1
atom is built up by four carboxylato oxygen atoms of four bridging
benzoato anions [Co1–O4 = 2.1084(15) Å, Co1–O5 = 2.0661(14) Å]
and two pyridine nitrogen atom of two unidentate iso-nicotin-
amide ligands [Co1–N5 = 2.1842(17) Å]. The coordination environ-
ment of remaining Co2 atoms is a distorted octahedron and the
Co2 atoms are coordinated by two carboxylato oxygen atoms of
two bridging benzoato anions [Co2–O3 = 2.0128(15) Å, Co2–
O6 = 2.0055(15) Å], two carboxylato oxygen atoms of one chelating
benzoato anion [Co2–O1 = 2.2300(16) Å, Co2–O2 = 2.1997(15) Å],
and two pyridine nitrogen atoms of two unidentate iso-nicotin-
amide ligands [Co2–N1 = 2.1499(17) Å, Co2–N3 = 2.1739(17) Å].
Fig. 4 shows the hydrogen bonding networks in the crystal
structure of 3. The trinuclear molecular complexes of 3 are linked
via amide group head-to-head R22ð8Þ [29] N–Hꢁ ꢁ ꢁO hydrogen bonds
D–Hꢁ ꢁ ꢁA
1
O1W–H1Wꢁ ꢁ ꢁO2
O1W–H2Wꢁ ꢁ ꢁO3ii
N2–H2Aꢁ ꢁ ꢁO3iii
D–H
Hꢁ ꢁ ꢁA
Dꢁ ꢁ ꢁA
D–Hꢁ ꢁ ꢁA
0.82
0.82
0.86
1.80
2.16
2.14
2.585(2)
2.909(2)
2.973(2)
160
152
163
3
N2–H2Aꢁ ꢁ ꢁO8vi
N2–H2Bꢁ ꢁ ꢁO2vii
N4–H4Aꢁ ꢁ ꢁO7viii
N4–H4Bꢁ ꢁ ꢁO1ix
N6–H6Aꢁ ꢁ ꢁO9x
N6–H6Bꢁ ꢁ ꢁO8v
0.86
0.86
0.86
0.86
0.86
0.86
2.09
2.20
2.13
2.20
2.08
2.26
2.936(2)
3.040(3)
2.964(2)
3.038(3)
2.924(3)
3.067(3)
168
165
166
166
167
157
a
Symmetry codes: (ii) ꢀx + 2, ꢀy, ꢀz + 1; (iii) ꢀx + 2, ꢀy, ꢀz; (v) ꢀx, ꢀy, ꢀz; (vi)
x ꢀ 1, y, z ꢀ 1; (vii) x, ꢀy + 1/2, z ꢀ 1/2; (viii) x + 1, y, z + 1; (ix) x, ꢀy + 1/2, z + 1/2;
(x) ꢀx ꢀ 1, ꢀy, ꢀz + 1.
(N2–H2Aꢁ ꢁ ꢁO8vi, N4–H4Aꢁ ꢁ ꢁO7viii
,
N6–H6Aꢁ ꢁ ꢁO9x [symmetry
aqua ligands and amide oxygen atoms (O1W–H2Wꢁ ꢁ ꢁO3ii [symme-
try code: (ii) ꢀx + 2, ꢀy, ꢀz + 1]) into two-dimensional hydrogen-
bonding network.
codes: (vi) x ꢀ 1, y, z ꢀ 1; (viii) x + 1, y, z + 1; (x) ꢀx ꢀ 1, ꢀy, ꢀz +
1]) into infinite railroad-like band chains (Fig. 4A, Table 2). The
N–Hꢁ ꢁ ꢁO hydrogen bonds of supramolecular synthons R22ð8Þ inside
railroad-like band chains are also supplemented by N–Hꢁ ꢁ ꢁO
hydrogen bonds (N6–H6Bꢁ ꢁ ꢁO8v [symmetry code: (v) ꢀx, ꢀy, ꢀz])
between two parallel amide groups of iso-nicotinamide ligands.
The 3D hydrogen-bonding framework of 3 is created from the infi-
nite railroad-like band chains connected by N–Hꢁ ꢁ ꢁO hydrogen
bonds between amide groups of iso-nicotinamide ligands and
oxygen atoms of chelating coordinated benzoato anions
(N2–H2Bꢁ ꢁ ꢁO2vii, N4–H4Aꢁ ꢁ ꢁO1ix [symmetry codes: (vii) x, ꢀy + 1/
2, z ꢀ 1/2; (ix) x, ꢀy + 1/2, z + 1/2]) (Fig. 4B, Table 2).
The crystal structure of [Co2(l2-PhCOO)4(qu)2] (2) been solved
previously [9], but the present redetermination possesses much
better quality and significantly improves the set of bond distances
and bond angles. The description of molecular structure of 2 is con-
tained in Supplementary material ꢀ Fig. S2. The bond lengths and
angles are very similar to other Co(II) carboxylato complexes of the
formula [Co2(
The molecular structure of a centrosymmetric trinuclear com-
plex [Co3( 2-bz)4(bz)2(inca)6], hereafter 3, is drawn in Fig. 3. Two
Co(II) atoms are connected by four oxygen atoms of two bridging
l-RCOO)4(L)2] [10,30–34].
l
Fig. 3. View of the complex 3 with the atom numbering scheme and thermal ellipsoids drawn at the 30% probability level. Symmetry codes: (v) ꢀx, ꢀy, ꢀz. Selected
interatomic distances [Å] and angles [°]: Co1–O4 2.1084(15), Co1–O5 2.0661(14), Co1–N5 2.1842(17), Co2–O1 2.2300(16), Co2–O2 2.1997(15), Co2–O3 2.0128(15), Co2–O6
2.0055(15), Co2–N1 2.1499(17), Co2–N3 2.1739(17), O4–Co1–O5 94.83(6), O4–Co1–N5 92.88(6), O5–Co1–N5 87.15(7), O1–Co2–O2 59.09(6), O1–Co2–O3 88.97(6), O1–Co2–
O6 157.53(6), O1–Co2–N1 90.19(6), O1–Co2–N3 89.90(13), O2–Co2–O3 148.03(6), O2–Co2–O6 98.62(7), O2–Co2–N1 88.75(6), O2–Co2–N3 88.78(6), O3–Co2–O6 113.18(7),
O3–Co2–N1 90.14(7), O3–Co2–N3 92.44(7), O6–Co2–N1 86.17(6), O6–Co2–N3 93.31(7), N1–Co2–N3 177.37(7).

1370
J. Hudák et al. / Polyhedron 30 (2011) 1367–1373
Fig. 4. Hydrogen bonding network in complex 3. (a) 1D supramolecular band chain from molecules 3 through supramolecular synthons R22ð8Þ and (b) 3D hydrogen-bonding
network. The hydrogen atoms and benzene rings of the bz ligands are omitted for clarity. Symmetry codes: (v) ꢀx, ꢀy, ꢀz; (vi) x ꢀ 1, y, z ꢀ 1; (vii) x, ꢀy + 1/2, z ꢀ 1/2; (viii)
x + 1, y, z + 1; (ix) x, ꢀy + 1/2, z + 1/2; (x) ꢀx ꢀ 1, ꢀy, ꢀz + 1.
3.2. Electronic spectra
M1 ¼ Mmol=ðNAlBÞ ¼ 2:8. These data are consistent with a sizable
zero-field splitting.
The electronic spectra of studied complexes (Fig. 5) show a
number of spin-allowed d–d transitions followed by a charge-
transfer band. For the complexes 1 and 3 with the {CoO4N2} chro-
mophore they can be rationalized according to the crystal-field
term diagram.
Magnetic data for the complex 2 are shown in Fig. 7. The effec-
tive magnetic moment decreases gradually from its room temper-
ature
leff = 5.8 lB to the value of leff = 4.0 lB at T = 10 K; then it
drops down rapidly. The limiting value for two uncoupled spins
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
is leff lB ¼ giso 2 ꢁ sðs þ 1Þ and this gives an estimate giso = 2.12.
=
The first transition 4T2g
4T1g
(
D1 = 8Dq) occurs between 9000
The molar magnetic susceptibility on cooling reaches a maximum
at Tmax = 4.7 K. This feature is a fingerprint of the antiferromagnetic
exchange interaction. For the dinuclear systems the value of the
isotropic exchange coupling constant is directly related to the tem-
perature of the maximum, and in the case of genuine spins s = 3/2
the corresponding relationship is |J/k| = 0.648 Tmax [35]; this yields
estimates J/k = ꢀ3.04 K or J/hc = ꢀ2.12 cmꢀ1 (when only the isotro-
pic exchange contributes).
and 10 000 cmꢀ1, the second A2gðFÞ 4T1g
(D2 = 18Dq) is visible
4
at 16 000 cmꢀ1 as an arm, and the last T1gðPÞ 4T1g transition
4
(
D3) is formed by a broad band centered at 20 000 cmꢀ1. The last
transition in 3 is visibly split either owing to the presence of two
different coordination centers (central and terminal) or the tetrag-
4
4
onal splitting T1gðPÞ ! ð A2g; 4EgÞ.
The electronic spectrum for the dinuclear complex 2 is com-
pletely different, owing to the presence of a pentacoordinate chro-
mophore (Table 3).
The magnetization per formula unit at B = 7 T and T = 2.0 K
adopts a value of M1 = 3.2. This value is much lower than the the-
oretical limit Mm1 ax ¼ gisoSmax ¼ 6:4. Such a difference can be attrib-
uted to the combined effect of the antiferromagnetic coupling and
large zero-field splitting [36].
3.3. Magnetic data
Magnetic data for the complex 3 are shown in Fig. 8. The effec-
tive magnetic moment slowly decreases from its room tempera-
Magnetic data for the complex 1 are shown in Fig. 6. On cooling
the effective magnetic moment stays almost constant at its room
ture
eff = 3.8
is leff
leff = 8.1 lB until T = 100 K; then it drops down rapidly to
l
l
B at T = 2 K. The limiting value for three uncoupled spins
temperature
leff = 5.8 lB until 100 K when it gradually decreases
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
=
lB ¼ giso 3 ꢁ sðs þ 1Þ which yields an estimate giso = 2.42.
to
a value of leff = 4.5 lB at T = 2 K. The limiting value of
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
The magnetization per formula unit at B = 7 T and T = 2.0 K is
only M1 = 6.9 that is much lower than the theoretical limit
leff lB ¼ giso sðs þ 1Þ for s = 3/2 gives an estimate of giso = 3.0.
=
The magnetization at T = 2.0 K saturates to the value of

J. Hudák et al. / Polyhedron 30 (2011) 1367–1373
1371
4Eg
0.5
0.4
0.3
0.2
0.1
0.0
4T1g
CI
0.3
0.2
0.1
4P
1, 6-coodinate
2, 5-coordinate
3, 6-coordinate
4A2g
Δ3
15B
2G
4B+3C
4A2g
4B1g
Δ2
9
10 11 12 13 14 15 16 17 18 19 20
10Dq
4T2g
4F
4B2g
4Eg
1
Δ1
3
8Dq
4T1g
4Eg
4T2g
4T1g
4A2g
2
(4A2g,4Eg)
Δax > 0
4A2g
CT
26
(4B1g
)
(4Eg,4B2g
10
)
12
14
16
18
20
22
24
28
Wavenumber /103 cm−1
R3
Oh
D4h
Fig. 5. Electronic d–d spectrum of 1 through 3 in the visible region (left) and the corresponding term-diagram (right). Labels refer to the Oh group for 1 and 3; those in
parentheses refer to the D4h group.
Table 3
Electronic spectra for Co(II) complexes.
Complex
Chromophore
Spin allowed transition, (E/hc) (cmꢀ1), for Oh pattern
4T2g
4T1g ¼ 8Dq
4A2gðFÞ 4T1g ¼ 18Dq
4T1gðPÞ 4T1g
1
3
2
{CoO4N2}
{CoO4N2}
{CoO4N}
9500
10 500
<9000
(16 000)
16 000
13 500, 17 000, 18 500
20 000
19 500, 20 000, 21 000
22 500
3
6
T
= 2.0 K
B
= 0.1 T
5
4
3
2
1
0
T
= 4.6 K
2
1
0
20
15
10
5
μ
μ
N
μ
χ
0
0
5
10
15
250
20
300
0
1
2
3
4
5 6 7
0
50
100
150
200
B/T
T/K
Fig. 6. Temperature dependence of the effective magnetic moment (left) and field dependence of the magnetization (right) for 1. Lines – fitted data. Inset – molar magnetic
susceptibility.
Mm1 ax ¼ gisoSmax ¼ 10:9 owing to the combined effect of the antifer-
with the Zeeman term
romagnetic coupling and large zero-field splitting.
H ð#k; ulÞ ¼ lBBmꢀhꢀ1ðgA;x sin #k cos ulSA;x þ g sin #k
Z
A
^
^
The experimental data were fitted using the spin-Hamiltonian
accounting to the isotropic exchange (for 2 and 3) and the axial
zero-field splitting of the form
A;y
^
^
ꢃ sin ulSA;y þ gA;z cos #kSA;z
Þ
ð2Þ
N
N
N
N
X X
X
X
depending upon grids determined by polar angles #k and
experimental data-sets (M versus T at B0 = 0.1 T, and M versus B at
T0 = 2.0 and 4.6 K) have been processed simultaneously. The aver-
u
l. Two
ꢀhꢀ2JABðSA ꢁ SBÞ þ
ꢀhꢀ2DAðSA;z ꢀ SA=3Þ þ
HA ð1Þ
2
^
2
^
Z
^
^
~
~
H ¼ ꢀ
A
B<A
A¼1
A¼1

1372
J. Hudák et al. / Polyhedron 30 (2011) 1367–1373
4
7
6
5
4
3
2
1
0
B = 0.1 T
T = 2.0 K
3
4
3
2
1
0
μ
T = 4.6 K
μ
N
2
μ
1
χ
0
5
10
15
20
300
0
0
1
2
3
4
5 6 7
0
50
100
150
T/K
200
250
B/T
Fig. 7. Temperature dependence of the effective magnetic moment (left) and field dependence of the magnetization (right) for 2. Lines – fitted data. Inset – molar magnetic
susceptibility.
4
3
2
1
0
7
6
5
4
3
2
1
0
B = 0.1 T
T = 2.0 K
4
3
2
1
0
μ
T = 4.6 K
μ
N
μ
χ
0
5
10
15
20
300
0
1
2
3
4
5 6 7
0
50
100
150
T/K
200
250
B/T
Fig. 8. Temperature dependence of the effective magnetic moment (left) and field dependence of the magnetization (right) for 3. Lines – fitted data. Inset – molar magnetic
susceptibility.
age magnetization data have been calculated as a correct powder
average. The free parameters to be optimized are J(CoACo), gx(Co),
gz(Co), D(Co), and eventually aTIP (temperature-independent para-
magnetism). In accordance with the theoretical modeling for the
compressed tetragonal bipyramid, gz = 2.0 has been fixed for Co(II)
complexes [37].
the axial zero-field splitting parameter D. The spin-Hamiltonian
approach offers a constraint D ¼ ðk=2Þðgz ꢀ gxÞ where k stands for
the spin–orbit splitting parameter (k = ꢀ172 cmꢀ1 for Co(II) com-
plexes). Using this constraint, the estimated D-values are 94 and
50 cmꢀ1 that are in a remarkable agreement with the fitted data
for 1 and 3 where the tetragonal symmetry occurs.
The calculated magnetic parameters are listed in Table 4. It can
be seen that the complexes under study exhibit a considerable
magnetic anisotropy expressed by the g-values asymmetry and
High value of the D-parameter for the nearly-octahedral Co(II)
4
systems is given by the axial splitting of the T1gðOhÞ term into
the ground 4A2g and 4Eg terms (D4h). In the first approximation,
Table 4
Fitted magnetic parametersa.
Compound
J(CoACo)/hc (cmꢀ1
)
gx(Co)
gz(Co)
D(Co)/hc (cmꢀ1
)
a
TIP/10ꢀ9 (m3 molꢀ1
)
R(
v) [%]
R(M) [%]
1
2
3
none
3.09
2.14
2.58
[2.0]
[2.0]
[2.0]
94.1
67.2
54.7
10.0
7.9
3.0
1.9
0.8
3.3
5.1
6.3
ꢀ1.65
ꢀ1.51
a
Estimated errors: 0.01 for g-factors, 1.0 cmꢀ1 for the D-parameter.

J. Hudák et al. / Polyhedron 30 (2011) 1367–1373
1373
this energy gap Dax enters the formula D ¼ k2½A2j2
=
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4
4
Daxð A2g ! EgÞꢄ where the Figgis CI parameter in the weak crystal
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j
ꢅ 0.7–0.9 is the orbital reduction factor
[37]. Then the estimate for the axial crystal-field splitting parame-
ter is Dax ¼ A2
j
2k2=D, i.e. 453 and 789 cmꢀ1 for 1 and 3, respec-
4
tively. The value of Dax splits not only the ground T1gðFÞ term
but also the excited 4T1gðPÞ term. Thus the large value of Dax ratio-
nalizes the evident splitting of the D3 transition in the electronic
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Three Co(II) complexes containing benzoato ligands and pyri-
dine-type N-donor ligands (nicotinamide, quinoline, and iso-nico-
tinamide) have been prepared and structurally characterized. The
magnetic data (susceptibility and magnetization) were fitted using
the spin Hamiltonian that accounts to the spin Zeeman term, the
axial zero-field splitting and the isotropic exchange interaction
(for the dinuclear and trinuclear complex, respectively). It was
found that these complexes exhibit very large magnetic anisotropy
that manifests itself in the g-factor asymmetry (gx >> gz) and a siz-
able axial zero-field splitting parameter D (94, 67, and 57 cmꢀ1 for
1 through 3). This effect is caused by the tetragonal splitting Dax of
4
4
the ground crystal-field term 4T1gðOhÞ into f A2g þ EggðD4hÞ terms.
The spin–orbit coupling then yields the crystal-field multiplets
4A2gðD4hÞ ! fC6
þ
C7gðD0 Þ; these Kramers doublets are separated
4
just by the amount 2D. The spin Hamiltonian formalism offers a
4
4
relationship D ꢅ 1=Daxð A2g ! EgÞ which rationalizes why with
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Acknowledgments
Slovak grant agencies (VEGA 1/1005/09, 1/0052/11, APVV-
0202-10 and VVCE-0004-07) are acknowledged for the financial
support.
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Appendix A. Supplementary data
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Fabre, L. Ouahab, Inorg. Chem. 45 (2006) 10440.
CCDC 804191, 804192, and 804193 contain the supplementary
crystallographic data for 1, 2, and 3. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033;
or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found, in the online version, at doi:10.1016/
j.poly.2011.02.047.
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