Synthesis, characterisation and magnetic properties of cobalt (II) complexes with 3-hydroxypicolinic acid (HpicOH): [Co(picOH)2(H 2O)2] and mer-[N(CH3)4][Co(picOH) 3]·H2O

Article abstract of DOI:10.1016/j.poly.2005.01.002

Two complexes with Co²⁺ and 3-hydroxypicolinic acid, [Co(picOH)₂(H₂O)₂] (I) and mer-[N(CH ₃)₄][Co(picOH)₃]·H₂O (II), have been synthesised and characterised using single-crystal X-ray diffraction, elemental analysis, infrared spectroscopy, and thermoanalytical measurements. The 3-hydroxypicolinate ligands are coordinated to the Co²⁺ centres via its typical N,O-chelating coordination fashion. While in I the presence of two coordinated water molecules leads to the formation of a neutral [Co(picOH)₂(H₂O)₂] complex which is strongly hydrogen bonded to another four neighbouring complexes, in II the inclusion of a third picOH^- ligand leads to an anionic octahedral complex, [Co(picOH)₃]^-, in which all the N- and O-atoms are occupying mer positions. The properties of these two compounds were further investigated by measuring their magnetic behaviour.

Full text of DOI:10.1016/j.poly.2005.01.002

Polyhedron 24 (2005) 563–569
www.elsevier.com/locate/poly
Synthesis, characterisation and magnetic properties of cobalt (II)
complexes with 3-hydroxypicolinic acid (HpicOH):
[Co(picOH)2(H2O)2] and mer-[N(CH3)4][Co(picOH)3] Æ H2O
a
a
c
Penka I. Girginova , Filipe A. Almeida Paz a,b, Helena I.S. Nogueira , Nuno J.O. Silva ,
c
Vıtor S. Amaral , Jacek Klinowski , Tito Trindade
b
a,
*
´
a
Department of Chemistry, CICECO, University of Aveiro, Campus Santiago, 3810-193 Aveiro, Portugal
b
Department of Chemistry, University of Cambridge, Lensfield Road, CB2 1EW Cambridge, UK
c
Department of Physics, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal
Received 10 December 2004; accepted 24 January 2005
Abstract
Two complexes with Co2+ and 3-hydroxypicolinic acid, [Co(picOH)2(H2O)2] (I) and mer-[N(CH3)4][Co(picOH)3] Æ H2O (II), have
been synthesised and characterised using single-crystal X-ray diffraction, elemental analysis, infrared spectroscopy, and thermoan-
alytical measurements. The 3-hydroxypicolinate ligands are coordinated to the Co2+ centres via its typical N,O-chelating coordina-
tion fashion. While in I the presence of two coordinated water molecules leads to the formation of a neutral [Co(picOH)2(H2O)2]
complex which is strongly hydrogen bonded to another four neighbouring complexes, in II the inclusion of a third picOHꢀ ligand
leads to an anionic octahedral complex, [Co(picOH)3]ꢀ, in which all the N- and O-atoms are occupying mer positions. The prop-
erties of these two compounds were further investigated by measuring their magnetic behaviour.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Cobalt complexes; Crystal structures; 3-Hydroxypicolinic acid; Magnetic properties
1. Introduction
one report for single coordination through the pyridinic
nitrogen atom [6], and no examples are known of single
coordination via the (de)protonated hydroxyl group.
We have exploited the versatile chelating properties
of HpicOH to synthesise a series of lanthanide com-
plexes and investigate the role of this ligand in the pho-
toluminescence of the materials [1]. However, HpicOH
is more commonly used with second- and third-row
transition metal centres [5–8], and only a handful of
structures containing first-row transition cations are
found in the literature [2–4,9]. Other derivatives of picol-
inic acid are also known to form complexes with several
metal centres [10,11], particularly those of 2-hydroxyni-
cotinic acid which are of special interest [12,13]. Follow-
ing our interest in exploring the coordination chemistry
of HpicOH, we report on the synthesis, structural char-
acterisation and magnetic behaviour of two novel Co2+
3-Hydroxypicolinic acid (HpicOH) is a relatively sim-
ple organic molecule, which can act as a versatile ligand
with distinct coordination fashions. For example, depro-
tonation of the carboxylic acid and hydroxyl groups
makes O,O-chelation possible with the consequent for-
mation of a typical six-membered chelate ring [1–3].
The mono-deprotonated ligand (picOHꢀ) can also form
five-membered chelate rings through the pyridinic nitro-
gen atom and the carboxylate group (N,O-chelation)
with this coordination fashion being the most commonly
found in the literature [1–9]. Interestingly, there is only
*
Corresponding author. Tel.: +351 234 370 726; fax: +351 234 370
084.
E-mail address: ttrindade@dq.ua.pt (T. Trindade).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.01.002

564
P.I. Girginova et al. / Polyhedron 24 (2005) 563–569
complexes with this ligand: [Co(picOH)2(H2O)2] and
mer-[N(CH3)4][Co(picOH)3] Æ H2O.
on F2 using SHELXL-97 [23]. Non-hydrogen atoms were
directly located from difference Fourier maps and re-
fined with anisotropic displacement parameters. The
last difference Fourier map synthesis showed, for I,
ꢀ3
˚
˚
2. Experimental
the highest peak (0.354 e A ) located at 1.14 A from
O(2), and the deepest hole (ꢀ0.614 e Aꢀ3) located at
˚
˚
0.70 A from Co(1); for II, the highest peak
2.1. Syntheses
ꢀ3
˚
(0.389 e A ) located at 0.84 A from O(4), and the deep-
˚
ꢀ3
˚
˚
Chemicals were readily available from commercial
sources and were used as received without further puri-
fication. Syntheses were carried out in PTFE-lined stain-
less steel reaction vessels (ca. 40 cm3), under
autogeneous pressure and static conditions in a pre-
heated oven at 150 ꢁC. Reactions took place over a per-
iod of 48 h after which time the vessels were cooled
slowly to ambient temperature before opening.
In a typical synthesis, an aqueous solution of Co-
Cl2 Æ 6H2O (0.5 mmol) was added dropwise to an aque-
ous solution containing 3-hydroxypicolinic acid
(2 mmol) and [(CH3)4N]OH (2 mmol) and then the final
pH was adjusted to ca. 7 with 1 M CH3COOH. This mix-
ture was treated under hydrothermal conditions as de-
scribed above and then transferred into a covered
beaker. A pale orange powder of [Co(picOH)2(H2O)2]
was obtained (yield: 15.7%) and orange single-crystals
of the same compound were grown after 10 days from
the supernatant solution (m.p. 160 ꢁC). Red crystals of
mer-[N(CH3)4][Co(picOH)3] Æ H2O could be obtained
from the same mother solution after ca. 2 months
(m.p. 228 ꢁC).
est hole (ꢀ0.490 e A ) located at 0.67 A from Co(1).
Hydrogen atoms bound to carbon were placed in cal-
culated positions and refined using a riding model with
an isotropic displacement parameter fixed at x times
Ueq for the atom to which they are attached (x = 1.5
for –CH3 and –OH groups, x = 1.2 for the remaining
hydrogen atoms). Hydrogen atoms from water mole-
cules were directly located from successive difference
Fourier maps and refined with the O–H and Hꢁ ꢁ ꢁH dis-
˚
tances restrained to 0.95(1) and 1.55(1) A (for I), and
˚
0.85(1) and 1.39(1) A (for II), respectively (in order to
ensure a chemically reasonable geometry for these mol-
ecules), and using a riding model with an isotropic dis-
placement parameter fixed at 1.5 times Ueq of the
atom to which they are attached. Hydrogen atoms asso-
ciated with the –OH groups could also be directly lo-
cated in successive difference Fourier maps, but their
position was instead placed geometrically using HFIX
instructions in SHELXL.
Table 1
Crystal and structure refinement data for [Co(picOH)2(H2O)2] (I) and
mer-[N(CH3)4][Co(picOH)3] Æ H2O (II)
I
II
2.2. Single-crystal X-ray diffraction
Formula
C
371.17
12H12CoN2O8
C22H24CoN4O9 Æ H2O
565.40
180(2)
Formula weight
Temperature (K)
Crystal system
Space group
Suitable single-crystals of [Co(picOH)2(H2O)2] (I)
and mer-[N(CH3)4][Co(picOH)3] Æ H2O (II) were
mounted on a glass fibre using perfluoropolyether oil
[14]. Data for I were collected at 180(2) K on a Nonius
Kappa charge coupled device (CCD) area-detector dif-
fractometer (Mo Ka graphite-monochromated radia-
180(2)
monoclinic
P21/c
monoclinic
P21/n
˚
a (A)
11.491(2)
9.1413(18)
6.8357(14)
91.84(3)
717.7(2)
2
8.2794(20)
12.8360(32)
23.5421(57)
97.021(4)
2483.2(11)
4
˚
b (A)
˚
c (A)
˚
b (ꢁ)
Volume (A )
tion, k = 0.7107 A), equipped with an Oxford
3
˚
Cryosystems cryostream and controlled by the COLLECT
software package [15]. Images were processed using the
software packages of Denzo and Scalepack [16] and the
data were corrected for absorption by using the empir-
ical method employed in Sortav [17,18]. Data for II
were collected at ambient temperature (at the Unidade
de Raios-X, RIAIDT, University of Santiago de Com-
postela, Spain) on a Bruker SMART 1000 charge cou-
pled device (CCD) area-detector diffractometer (Mo
Z
Dc (g cmꢀ3
l (Mo Ka) (mmꢀ1
F(0 0 0)
)
1.718
1.241
378
1.512
0.754
1172
)
Crystal size (mm)
Crystal type
h Range
0.35 · 0.23 · 0.18
brown blocks
3.55–27.49
ꢀ14 6 h 6 14,
ꢀ11 6 k 6 11,
ꢀ8 6 l 6 8
5621
0.36 · 0.20 · 0.15
orange prisms
3.57–26.42
ꢀ10 6 h 6 10,
0 6 k 6 16,
0 6 l 6 29
21 304
Index ranges
˚
Reflections collected
Ka graphite-monochromated radiation, k = 0.7107 A),
Independent reflections 1638 (Rint = 0.0407) 5075 (Rint = 0.0555)
controlled by the SMART software package [19]. Images
were processed using the SAINTPlus software package
[20] and data were corrected for absorption by using
the semi-empirical method of SADABS [21]. The two
structures were solved by the direct methods of
SHELXS-97 [22] and refined by full-matrix least squares
Final R indices
[I > 2r(I)]
Final R indices
(all data)
R1 = 0.0277,
wR2 = 0.0711
R1 = 0.0347,
wR2 = 0.0736
R1 = 0.0383,
wR2 = 0.0905
R1 = 0.0775,
wR2 = 0.1127
0.389 and ꢀ0.490
Largest difference peak 0.354 and ꢀ0.614
ꢀ3
˚
and hole (e A
)

P.I. Girginova et al. / Polyhedron 24 (2005) 563–569
565
Information concerning crystallographic data collec-
2.3. Instrumentation
tion and structure refinement details are summarised
in Table 1. Selected bond lengths and angles for the
two structures are given in Tables 2 and 3. Hydrogen-
bonding geometry for the two structures is described
in Tables 4 and 5.
FT-IR spectra were measured from KBr disks (Al-
drich, 99%+, FT-IR grade) on a Matson 700 FTIR spec-
trometer. Elemental analyses for C, H and N were
performed in the Microanalysis Laboratory of the Uni-
versity of Aveiro. Thermogravimetric analyses (TGA)
were carried out using a Shimadzu TGA-50, with a heat-
ing rate of 10 ꢁC/min. Magnetic measurements were
performed using a Quantum Design SQUID (Supercon-
ducting Quantum Interference Device) magnetometer
MPMS at the University of Lisbon (Portugal).
Table 2
a
˚
Bond lengths (in A) and angles (in ꢁ) for [Co(picOH)2(H2O)2] (I)
Co(1)–O(1W)
Co(1)–O(1)
Co(1)–N(1)
2.0789(13)
2.1105(12)
2.1245(15)
O(1W)–Co(1)–O(1)
O(1W)–Co(1)–O(1)i
O(1W)–Co(1)–N(1)
O(1W)–Co(1)–N(1)i
O(1)–Co(1)–N(1)
93.07(5)
86.93(5)
89.15(6)
90.85(6)
78.23(5)
101.77(5)
O(1)–Co(1)–N(1)i
3. Results and discussion
a
Symmetry transformations used to generate equivalent atoms: (i)
ꢀx, 2ꢀy, ꢀz.
3.1. Crystal structure of [Co(picOH)2(H2O)2] (I)
The reaction under aqueous media between Co2+ and
3-hydroxypicolinic acid led to the formation of a highly
crystalline, air- and light-stable product which was for-
mulated as [Co(picOH)2(H2O)2] (I) on the basis of sin-
gle-crystal X-ray diffraction (Table 1) and elemental
analysis. This structure shares striking similarities with
those recently reported by Jin and co-workers [4],
[Zn(picOH)2(H2O)2] and [Mn(picOH)2(H2O)2], also
containing first-row transition metal cations.
Compound I is formed by neutral centrosymmetric
[Co(picOH)2(H2O)2] complexes (Fig. 1), in which the
Co2+ centre is located at an inversion centre and six-
coordinated to two N,O-chelating picOHꢀ anionic li-
gands [bite angle of 78.23(5)ꢁ] plus two water molecules,
{CoN2O4}, with the coordination geometry resembling
a slightly distorted octahedron (Fig. 1 and Table 2).
As found in the structures containing Zn2+ and Mn2+
[4], the water molecules are trans-coordinated (Fig. 1)
with the Owater–Co–Owater vector not being exactly per-
pendicular to the {N2O2} plane of the octahedron
formed by the two picOHꢀ anionic ligands (Table 2).
The vector is indeed tilted by a combination of ca.
Table 3
˚
Bond lengths (in A) and angles (in ꢁ) for mer-[N(CH3)4][Co(picO-
H)3] Æ H2O (II)
Bond lengths
Co(1)–O(1)
Co(1)–O(4)
Co(1)–O(7)
2.077(2)
2.066(2)
2.078(2)
Co(1)–N(1)
Co(1)–N(2)
Co(1)–N(3)
2.134(2)
2.149(2)
2.144(2)
Bond angles
O(1)–Co(1)–O(7)
O(1)–Co(1)–N(1)
O(1)–Co(1)–N(2)
O(1)–Co(1)–N(3)
O(4)–Co(1)–O(1)
O(4)–Co(1)–O(7)
O(4)–Co(1)–N(1)
O(4)–Co(1)–N(2)
97.70(8)
78.45(8)
90.52(9)
93.91(9)
164.80(8)
93.67(8)
91.98(9)
78.68(9)
O(4)–Co(1)–N(3)
O(7)–Co(1)–N(1)
O(7)–Co(1)–N(2)
O(7)–Co(1)–N(3)
N(1)–Co(1)–N(2)
N(1)–Co(1)–N(3)
N(3)–Co(1)–N(2)
98.16(9)
87.93(8)
171.45(9)
78.93(8)
96.08(9)
163.84(9)
98.22(9)
Table 4
˚
Hydrogen-bonding geometry (distances in A and angles in ꢁ) for
[Co(picOH)2(H2O)2] (I)a
D–Hꢁ ꢁ ꢁA
d(Dꢁ ꢁ ꢁA)
1.799(19)
1.841(10)
1.83
\(DHA)
O(1W)–H(1A)ꢁ ꢁ ꢁO(2)i
O(1W)–H(1B)ꢁ ꢁ ꢁO(1)ii
O(3)–H(3)ꢁ ꢁ ꢁO(2)
a
167(2)
168(2)
146
O(1W)
Symmetry transformations used to generate equivalent atoms: (i) x,
1.5 ꢀ y, 1/2 + z; (ii) ꢀx, 1/2 + y, 1/2ꢀz.
C(5)
C(6)
C(4)
N(1)
Co(1)
O(1)
C(1)
O(3)
Table 5
C(3)
C(2)
O(2)
˚
Hydrogen-bonding geometry (distances in A and angles in ꢁ) for mer-
[N(CH3)4][Co(picOH)3] Æ H2O (II)a
D–Hꢁ ꢁ ꢁA
d(Dꢁ ꢁ ꢁA)
\(DHA)
O(3)–H(4A)ꢁ ꢁ ꢁO(2)
O(6)–H(6A)ꢁ ꢁ ꢁO(5)
O(9)–H(9)ꢁ ꢁ ꢁO(8)
O(1W)–H(1A)ꢁ ꢁ ꢁO(1)
O(1W)–H(1B)ꢁ ꢁ ꢁO(8)i
a
2.577(3)
2.540(3)
2.547(3)
2.822(3)
2.766(3)
145.3
147.2
145.5
172(3)
169(4)
Fig. 1. Schematic representation of the neutral complex [Co(picOH)2 -
(H2O)2] of I, emphasising the slightly distorted octahedral coordina-
tion environment for the Co2+ metal centre. Non-hydrogen atoms
belonging to the asymmetric unit are represented with thermal
ellipsoids drawn at the 70% probability level. For selected bond
˚
Symmetry transformations used to generate equivalent atoms: (i) x,
1.5 ꢀ y, 1/2 + z.
lengths (in A) and angles (in ꢁ) see Table 2. For details on the
hydrogen-bonding geometry, see Table 4.

566
P.I. Girginova et al. / Polyhedron 24 (2005) 563–569
O(6)
O(5)
N(2)
O(4)
Co(1)
O(1)
Co
O
H
N(3)
O(2)
C
N
O(9)
N(1)
O(3)
O(7)
b
c
O(8)
Fig. 3. Schematic representation of the anionic mer-[Co(picOH)3]ꢀ
complex in II, showing the slightly distorted octahedral coordination
environment for the Co2+ metal centre and the labelling scheme for
selected atoms. Non-hydrogen atoms are represented with thermal
ellipsoids drawn at the 70% probability level. For selected bond lengths
Fig. 2. Crystal packing of I viewed in perspective along the a direction,
showing how the O–Hꢁ ꢁ ꢁO hydrogen bond interactions (represented as
dashed white-filled bonds) establish physical links between neighbour-
ing [Co(picOH)2(H2O)2] complexes. For details on the hydrogen-
bonding geometry, see Table 4.
˚
(in A) and angles (in ꢁ) see Table 3. For details on the hydrogen-
bonding geometry, see Table 5.
3.1ꢁ and 0.9ꢁ in both directions of the {N2O2} plane,
values comparable with those registered for [Zn(pi-
cOH)2(H2O)2] and [Mn(picOH)2(H2O)2] (ca. 2.9/0.8
and 2.5/1.2, respectively) [4]. Interestingly, this distor-
tion seems to be driven by the presence of extensive
hydrogen-bonding networks in the crystal structures of
these structures. In fact, apart from the homonuclear,
intra-molecular and strong O–Hꢁ ꢁ ꢁO hydrogen bond be-
tween the hydroxyl and the carboxylate groups (Fig. 1
and Table 4), each [Co(picOH)2(H2O)2] moiety is fur-
ther strongly hydrogen-bonded via the coordinated
water molecules to another four neighbouring com-
plexes, leading to a recurring R22ð10Þ graph set motif
[24] which expands the dimensionality of the structure
into the two dimensions (see Fig. 2).
ca. 78.7ꢁ which, although comparable with the analo-
gous value for I [78.23(5)ꢁ], imposes some strain in the
octahedral geometry; on the other, the presence of three
large substituent ligands within the first coordination
sphere leads to an inherent steric hindrance directly
affecting the global geometry of the complex. In fact,
these distortions are reflected in the ranges of the cis
and trans angles of the octahedron which can be found
within the 78.45(8)ꢁ–98.22(9)ꢁ and 163.84(9)ꢁ–171.45(9)ꢁ
ranges, respectively (Table 3). The average Co–O and
Co–N distances are almost identical (ca. 2.07 and
˚
2.14 A, respectively) and comparable with those found
in related compounds [25,26].
The hydrogen-bonding network present in the crys-
tal structure of II is not so extensive as that described
for I. However, physical bridges via homonuclear and
relatively strong O–Hꢁ ꢁ ꢁO hydrogen bonds between
neighbouring mer-[Co(picOH)3]ꢀ complex anions are
assured by the water molecules of crystallisation
(Table 5 and Fig. 4) which, along with interactions
of the intra-molecular nature, lead to the formation
of supramolecular hydrated {mer-[Co(picOH)3] Æ
H2O}ꢀ anionic tapes running along the a direction
(Fig. 4, perpendicular to the plane of the representa-
tion). This supramolecular arrangement is constructed
from a recurring C23ð7Þ graph set motif [24].
3.2. Crystal structure of mer-[N(CH3)4]
[Co(picOH)3] Æ H2O (II)
The substitution of the coordinated water molecules
from the coordination sphere of I by a third 3-hydroxyp-
icolinate ligand leads to the formation of an intriguing
mer-isomer [Co(picOH)3]ꢀ complex anion (Fig. 3) which
co-exists in the asymmetric unit of II with a tetramethyl-
ammonium cation plus a water molecule of crystallisa-
tion (not shown), corresponding to the empirical
formula mer-N(CH3)4][Co(picOH)3] Æ H2O (II).
As in the previous structure, the crystallographically
unique Co2+ centre appears six-coordinated, {CoN3O3}
(Fig. 3), with a geometry resembling a distorted octahe-
dron due to the geometrical constraints of the picOHꢀ
ligand: on the one hand, the chelating nature of
3-hydroxypicolinate leads to an average bite angle of
3.3. Magnetic measurements
Magnetisation (M) measurements were performed in
the 2–270 K temperature (T) range and in a constant
magnetic field of H = 100 Oe. No thermal irreversibility

P.I. Girginova et al. / Polyhedron 24 (2005) 563–569
567
C
H
N
b
O
Co
c
Fig. 4. Crystal packing of II viewed in perspective along the a direction, with the O–Hꢁ ꢁ ꢁO hydrogen-bonding interactions represented as dashed
white-filled bonds. The crystallisation water molecule establishes a physical link between neighbouring anionic mer-[Co(picOH)3]ꢀ complexes, leading
to the formation of supramolecular hydrated {mer-[Co(picOH)3] Æ H2O}ꢀ anionic tapes running along the a direction. For details on the hydrogen-
bonding geometry, see Table 5.
was observed since measurements taken with decreasing
temperature gave identical results, either after cooling
from ambient temperature to 2 K in zero applied mag-
netic field (zero field cooling), or after cooling under
the measurement field.
Fig. 5 represents the magnetic susceptibility multi-
plied by the temperature (vT, with v = M/H) for com-
of crystal field of I and II, just like it is also observed
in several mononuclear systems containing high-spin
Co2+ ions in an octahedral coordination geometry [27].
The lowest energy levels of the Co2+ cations are C6
and C7 doublets, and in a first approximation one can
consider that only these two are thermally populated.
Hence the total susceptibility, can be described by [27]:
pounds
I
and II. The temperature dependence
g2z vz þ 8g2xvx
indicates deviation from simple paramagnetic (Curie-
like) ion behaviour. Such is ascribed to the influence
v ¼ A
þ v0; with
and vx ¼
4T
À
Á
3T
4D
1 þ
1 ꢀ eꢀð2D=TÞ
1 þ 9eꢀð2D=TÞ
vz ¼
;
1 þ eꢀð2D=TÞ
1 þ eꢀð2D=TÞ
3.5
ð1Þ
I
where A ¼ Nl2B=3k; gz and gx are the Lande factors
associated with z and x directions, respectively, D is
the crystal field splitting and v0 is the residual temper-
ature independent which accounts for diamagnetic con-
tributions. Within this approximation, D includes the
C6 and C7 energy gap and the influence of the orbital
momentum [27]. Fitting the data to Eq. (1) (lines in
Fig. 5) we obtain D = 24 and 65 cmꢀ1 for samples I
and II, respectively, in good agreement with the values
expected for Co2+ cations (Ref. [27] and references
therein). From the fitting, it is also feasible to calculate
gx = 2.1, gz = 2.3 and gx = 1.8, gz = 1.7. Small varia-
tions of these parameters are not critical for the quality
of the fit and are subject to absolute errors of the order
of 0.1. Although at present we do not have a plausible
´
3.0
2.5
II
2.0
1.5
0
50
100
150
200
250
300
T (K)
Fig. 5. Temperature dependence of the magnetic susceptibility multi-
plied by temperature (vT vs. T)for compounds I and II. Solid lines are
fits to Eq. (1) (considering the influence of crystal field).

568
P.I. Girginova et al. / Polyhedron 24 (2005) 563–569
Table 6
Analytical and spectroscopic data for 3-hydroxypicolinic acid and compounds I and II
Compound
Elemental composition (%)a
Vibrational data (in cmꢀ1 b
)
C
N
H
masymð–CO2ꢀÞ
m(C–N)
msymð–CO2ꢀÞ
m(C–O)h
3 Hydroxypicolinic acid
I
1701s
1644s
1631s
1609s
1602s
1602s
1322s
1343s
1333s
1282s
1268s
1248s
38.05 (38.83)
46.31 (46.73)
7.38 (7.55)
9.93 (9.91)
3.55 (3.26)
4.83 (4.63)
II
a
Calculated values are in parentheses.
s: strong.
b
explanation for the difference between these values
for the two compounds, the ratio gz/gx is ca. 1.1, in
good agreement with the values reported for similar
compounds (1.06) [27]. The differences registered for
the crystal field splitting can be attributed to the influ-
ence of the donor atoms present in the Co2+ first coor-
dination shell. In fact, compound II has one more
pyridinic ring bound to the metal, which increases the
crystal field splitting, in agreement with the spectro-
chemical series.
water molecules (calculated weight loss of 9.7%). Be-
tween 180 and 500 ꢁC, a total weight loss of ca. 68.6%
(DTG peaks at 353, 409, 418 and 432 ꢁC) corresponds
to the release of the organic component.
The thermal decomposition of II between ambient
temperature and ca. 550 ꢁC is slightly more complex
than that of I with more overlapping decomposition
steps corresponding to the oxidation of the organic mol-
ecules. However, as for I, at ca. 550 ꢁC only the stoichi-
ometric CoO residue remains with a total weight loss of
ca. 88.6% (calculated 86.7%).
3.4. Vibrational spectroscopy
Acknowledgements
Selected and diagnostic FT-IR data for compounds I
and II are given in Table 6 (only bands of 3-hydroxypi-
colinic acid sensitive to metal coordination are
reported). Infrared spectroscopy confirms the coordina-
tion of picOHꢀ to the metal centres via the carboxylate
group, with the asymmetric stretching masymð–CO2ꢀÞ
mode showing shifts up to 70 cmꢀ1 to lower wavenum-
bers when compared with the values registered for the
free ligand. Furthermore, the measured values of
D½masymð–CO ꢀÞ ꢀ msymð–CO ꢀÞ] for I (301 cmꢀ1) and II
We are grateful to the Portuguese Foundation for
Science and Technology (FCT) for their general finan-
cial POCTI programme supported by FEDER and the
Ph.D. scholarships No. SFRH/BD/3024/2000 (to
F.A.A.P) and SFRH/BD/10383/2002 (to N.J.O.S.).
P.G. thanks CICECO for a research grant. We thank
Professor Margarida Godinho for allowing us to per-
form the magnetic measurements at the Faculty of Sci-
ences, University of Lisbon.
2
2
(298 cmꢀ1) are clear evidence of the presence of carbox-
ylate groups coordinated to the Co2+ centres in uniden-
tate fashion [28], in agreement with the N,O-chelation
described by the crystal structures (Figs. 1 and 3). The
m(C–O)h mode for I and II shows shifts up to ca. 14
and 34 cmꢀ1, respectively, possibly due to hydrogen-
bonding involving the carboxylate groups and the water
molecules (Tables 4 and 5). The typical stretching
m(C–N) vibrational mode of substituted pyridines ap-
pears for the uncoordinated ligand at 1609 cmꢀ1 and
shows small shifts (up to 7 cmꢀ1) for the two compounds
(Table 6), in good agreement with N,O-chelation involv-
ing the nitrogen atom of picOHꢀ.
Appendix A. Supplementary data
Crystallographic data (excluding structure factors)
for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-
241918 and -241919. Copies of the data can be obtained
free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 2EZ, U.K. (fax: (+44) 1223 336033;
e-mail: deposit@ccdc.cam.ac.uk, and http://www.ccdc.
cam.ac.uk).
Supplementary data associated with this article can
be found, in the online version at doi:10.1016/j.poly.
2005.01.002.
3.5. Thermal analysis
Thermal decomposition of compound I occurs in a
multi-step process between ambient temperature and
ca. 500 ꢁC leading to the formation of the stoichiometric
amount of CoO (total weight loss of 78.1%, calculated
79.8%). The first weight loss (ca. 9.5%) occurs in the
80–180 ꢁC temperature range (DTG peak at 150 ꢁC)
and is attributed to the release of the two coordinated
References
[1] P.C.R. Soares-Santos, H.I.S. Nogueira, V. Felix, M.G.B. Drew,
R.A.S. Ferreira, L.D. Carlos, T. Trindade, Chem. Mater. 15
(2003) 100.

P.I. Girginova et al. / Polyhedron 24 (2005) 563–569
569
[2] E. Kiss, A. Benyei, T. Kiss, Polyhedron 22 (2003) 27.
[3] S. Yano, M. Nakai, F. Sekiguchi, M. Obata, M. Kato, M. Shiro,
I. Kinoshita, M. Mikuriya, H. Sakurai, C. Orvig, Chem. Lett.
(2002) 916.
[14] T. Kottke, D. Stalke, J. Appl. Crystallogr. 26 (1993) 615.
[15] R. Hooft, COLLECT: Data Collection Software, Nonius B.V., Delft,
The Netherlands, 1998.
[16] Z. Otwinowski, W. Minor, in: C.W. CarterJr., R.M. Sweet (Eds.),
Methods in Enzymology, vol. 276, Academic Press, New York,
1997, p. 307.
[4] C.Y. Sun, X.J. Zheng, L.P. Jin, J. Mol. Struct. 646 (2003)
201.
[5] S.M.O. Quintal, H.I.S. Nogueira, H.M. Carapuca, V. Felix,
M.G.B. Drew, J. Chem. Soc., Dalton Trans. (2001) 3196.
[6] S.M.O. Quintal, H.I.S. Nogueira, V. Felix, M.G.B. Drew, New J.
Chem. 24 (2000) 511.
[17] R.H. Blessing, Acta Crystallogr., Sect. A 51 (1995) 33.
[18] R.H. Blessing, J. Appl. Crystallogr. 30 (1997) 421.
[19] SMART. Bruker Molecular Analysis Research Tool v. 5.054ꢀ
Bruker AXS, Madison, WI, USA, 1997–1998.
[20] SAINTPlus. Data Reduction and Correction Program v. 6.01ꢀ
Bruker AXS, Madison, WI, USA, 1997–98.
[7] A. Dar, K. Moss, S.M. Cottrill, R.V. Parish, C.A. McAuliffe,
R.G. Pritchard, B. Beagley, J. Sandbank, J. Chem. Soc., Dalton
Trans. (1992) 1907.
[21] G.M. Sheldrick. SADABS v. 2.01, Bruker/Siemens Area Detector
Absorption Correction Program Bruker AXS, Madison, WI,
USA, 1998.
[8] S. Gatto, T.I.A. Gerber, G. Bandoli, J. Perils, J.G.H. du Preez,
Inorg. Chim. Acta 269 (1998) 235.
[9] A. Shaver, J.B. Ng, D.A. Hall, B.S. Lum, B.I. Posner, Inorg.
Chem. 32 (1993) 3109.
[22] G.M. Sheldrick, SHELXS-97, Program for Crystal Structure Solu-
tion, University of Go¨ttingen, 1997.
[10] R. March, W. Clegg, R.A. Coxall, L. Cucurull-Sanchez, L.
Lezama, T. Rojo, P. Gonzalez-Duarte, Inorg. Chim. Acta 353
(2003) 129.
[23] G.M. Sheldrick, SHELXL-97, Program for Crystal Structure
Refinement, University of Go¨ttingen, 1997.
[24] J. Bernstein, R.E. Davis, L. Shimoni, N.L. Chang, Angew. Chem.
Int. Ed. 34 (1995) 1555.
[11] P.C.R. Soares-Santos, H.I.S. Nogueira, V. Felix, M.G.B. Drew,
R.A.S. Ferreira, L.D. Carlos, T. Trindade, Inorg. Chem. Com-
mun. 6 (2003) 1234.
[25] K. Abe, K. Matsufuji, M. Ohba, H. Okawa, Inorg. Chem. 41
(2002) 4461.
[12] P.C.R. Soares-Santos, H.I.S. Nogueira, J. Rocha, V. Felix,
M.G.B. Drew, R.A.S. Ferreira, L.D. Carlos, T. Trindade,
Polyhedron 22 (2003) 3529.
[26] Y.C. Liang, M.C. Hong, J.C. Liu, R. Cao, Inorg. Chim. Acta 328
(2002) 152.
[27] O. Kahn, Molecular Magnetism, Wiley-VCH, New York, 1993.
[28] G.B. Deacon, R.J. Phillips, Coord. Chem. Rev. 33 (1980)
227.
[13] S.M.O. Quintal, H.I.S. Nogueira, V. Felix, M.G.B. Drew,
Polyhedron 21 (2002) 2783.