2-Pyridinealdoxime [(py)CHNOH] in manganese(II) carboxylate chemistry: Mononuclear, dinuclear, tetranuclear and polymeric complexes, and partial transformation of (py)CHNOH to picolinate(-1)

Article abstract of DOI:10.1016/j.poly.2003.09.009

The preparation and crystal structures of four Mn^II carboxylate complexes containing 2-pyridinealdoxime, (py)CHNOH, are reported. The 1:1 reaction between Mn(O₂CPh)₂·2H₂O and (py)CHNOH in MeCN, followed by evaporation of the resulting solution, redissolution of the residue in CHCl₃ and precipitation with Et ₂O leads to isolation of [Mn₄(O₂CPh) ₆{(py)CO₂}₂{(py)CHNOH}₂]·0. 6CHCl₃ (1·0.6CHCl₃). The most interesting synthetic feature is the in situ formation of the picolinate(-1) ligand, (py)CO₂^-. The centrosymmetric tetranuclear cluster consists of an exactly planar zig-zag array of Mn^II ions and is held together by four syn,syn η¹:η²:μ₂ and two η¹:η²:μ₃ PhCO ₂^- groups, two η¹:η²: μ₂ (py)CO₂^- ligands and two N,N′-bidentate chelating (py)CHNOH molecules. The 1:4:7 [Mn ₃^{II,III, III}O(O₂CPh)₆(pyr) ₂(H₂O)]/Me₃SiCl/(py)CHNOH reaction mixture in MeCN (pyr=pyridine) yields the 1D coordination polymer [Mn(O₂CPh) {(py)CO₂}{(py)CHNOH}]_n (2), in which the partial (py)CHNOH→(py)CO₂^- transformation has again occurred. In each chain the Mn^II ions are bridged by syn,anti carboxylate groups of the η¹:η¹:η¹:μ ₂ (py)CO₂^- ligands, while the monodentate PhCO₂^- group and the N,N′-bidentate chelating (py)CHNOH molecule complete the octahedral coordination at each metal ion. The 1:3 reaction between Mn(O₂CMe)₂·4H₂O and (py)CHNOH in EtOH leads to the isolation of the dinuclear complex [Mn ₂(O₂CMe)₂{(py)CO₂} ₂{(py)CHNOH}₂] (3); crystallography reveals again the partial (py)CHNOH→(py)CO₂^- transformation. The dinuclear molecule is located at a centre of symmetry; the Mn^II ions are bridged by two oxygen atoms from the two symmetry-related η ¹:η¹:μ₂ (py)CO₂^- ligands, whose nitrogen atoms are ligated to different metal ions. Each Mn ^II ion is further coordinated by a monodentate MeCO₂ ^- group and a N,N′-bidentate chelating (py)CHNOH molecule. Reaction of Mn(hfac)₂·3H₂O (hfacH= hexafluoroacetylacetone) with 1 equivalent of (py)CHNOH in CH₂Cl ₂ yields complex [Mn(O₂CCF₃) ₂{(py)CHNOH}₂] (4); the CF₃CO₂ ^- ligand is one of the decomposition products of the hfac ^- ligand. The Mn^II ion in 4 is coordinated by two monodentate CF₃CO₂^- groups and two N,N′-bidentate chelating (py)CHNOH ligands in a cis-cis-trans fashion. The four complexes have been characterised by IR spectroscopy; characteristic bands are discussed in terms of the known structures and the coordination modes of the ligands. Variable-temperature magnetic susceptibility and EPR studies indicate weak antiferromagnetic exchange interactions in 1.

Full text of DOI:10.1016/j.poly.2003.09.009

Polyhedron 23 (2004) 83–95
www.elsevier.com/locate/poly
2-Pyridinealdoxime [(py)CHNOH] in manganese(II)
carboxylate chemistry: mononuclear, dinuclear, tetranuclear
and polymeric complexes, and partial transformation
of (py)CHNOH to picolinate()1) q
a
Constantinos J. Milios , Elena Kefalloniti , Catherine P. Raptopoulou , Aris Terzis ,
a
b
b
c
c,
a,
*
Albert Escuer , Ramon Vicente *, Spyros P. Perlepes
a
Department of Chemistry, University of Patras, GR 26504 Patras, Greece
b
Institute of Materials Science, NCSR ‘‘Demokritos’’, GR 15310 Aghia Paraskevi Attikis, Greece
c
Departament de Quimica Inorganica, Universitat de Barcelona, Diagonal 647, E-08028 Barcelona, Spain
Received 16 July 2003; accepted 10 September 2003
Abstract
The preparation and crystal structures of four MnII carboxylate complexes containing 2-pyridinealdoxime, (py)CHNOH, are
reported. The 1:1 reaction between Mn(O2CPh)2 ꢀ 2H2O and (py)CHNOH in MeCN, followed by evaporation of the resulting
solution, redissolution of the residue in CHCl3 and precipitation with Et2O leads to isolation of [Mn4(O2CPh)6{(py)CO2}2
{(py)CHNOH}2] ꢀ 0.6CHCl3 (1 ꢀ 0.6CHCl3). The most interesting synthetic feature is the in situ formation of the picolinate()1)
ligand, (py)CO2ꢁ. The centrosymmetric tetranuclear cluster consists of an exactly planar zig-zꢁag array of MnII ions and is held
ꢁ
together by four syn, syn g1:g2:l2 and two g1:g2:l3 PhCO2 groups, two g1:g2:l2 (py)CO2 ligands and two N,N0-bidentate
chelating (py)CHNOH molecules. The 1:4:7 [Mn3II;III; IIIO(O2CPh)6(pyr)2(H2O)]/Me3SiCl/(py)CHNOH reaction mixture in MeCN
(pyr ¼ pyridine) yields the 1D coordination polymer [Mn(O2CPh){(py)CO2}{(py)CHNOH}]n (2), in which the partial (py)CHNOH
ꢁ
! (py)CO2 transforꢁmation has again occurred. In each chain the MnII ions are bridged by syn, anti carboxylate groups of the
ꢁ
g1:g1:g1:l2 (py)CO2 ligands, while the monodentate PhCO2 group and the N,N0-bidentate chelating (py)CHNOH molecule
complete the octahedral coordination at each metal ion. The 1:3 reaction between Mn(O2CMe)2 ꢀ 4H2O and (py)CHNOH in EtOH
leads to the isolation of the dinꢁuclear complex [Mn2(O2CMe)2{(py)CO2}2{(py)CHNOH}2] (3); crystallography reveals again the
partial (py)CHNOH ! (py)CO2 transformation. The dinuclear molecule is located at a centre of symmetry; the MnII ions are
ꢁ
bridged by two oxygen atoms from the two symmetry-related g1:g1:l2 (py)CO2 liganꢁds, whose nitrogen atoms are ligated to
different metal ions. Each MnII ion is further coordinated by a monodentate MeCO2 group and a N,N0-bidentate chelating
(py)CHNOH molecule. Reaction of Mn(hfac)2 ꢀ 3H2O (hfacH ¼ hexafluoroacetylacetone) with 1 equivalent of (py)CHNOH in
ꢁ
CH2Cl2 yields complex [Mn(O2CCF3)2{(py)CHNOH}2] (4); the CF3CO2ꢁ ligand is one of the decomposition products of the hfacꢁ
ligand. The MnII ion in 4 is coordinated by two monodentate CF3CO2 groups and two N,N0-bidentate chelating (py)CHNOH
ligands in a cis–cis–trans fashion. The four complexes have been characterised by IR spectroscopy; characteristic bands are discussed
in terms of the known structures and the coordination modes of the ligands. Variable-temperature magnetic susceptibility and EPR
studies indicate weak antiferromagnetic exchange interactions in 1.
Ó 2003 Published by Elsevier Ltd.
Keywords: Crystal structures; Manganese(II) carboxylate chemistry; Magnetochemistry; Metal-assisted reactions; 2-Pyridinealdoxime complexes
q This work is dedicated to the memory of our young inorganic
chemistry colleague Spyridoula Kasselouri.
* Corresponding authors. Tel.: +34-3-402-1264; fax: +34-3-490-7725
(R. Vicente), Tel.: +30-2610-997146; fax: +30-2610-997118 (S.P.
Perlepes).
1. Introduction
Manganese carboxylate chemistry is of great current
interest from several viewpoints, including bioinorganic
chemistry and molecular magnetism. In the former area,
E-mail addresses: rvicente@kripto.qui.ub.es, ramon.vicente@
qi.ub.es (R. Vicente), perlepes@patreas.upatras.gr (S.P. Perlepes).
0277-5387/$ - see front matter Ó 2003 Published by Elsevier Ltd.
doi:10.1016/j.poly.2003.09.009

84
C.J. Milios et al. / Polyhedron 23 (2004) 83–95
small Mn carboxylate clusters are found at the active
sites of a variety of metallobiomolecules [1]; for exam-
ple, the water oxidising complex (WOC) of photosystem
II contains a tetranuclear Mn carboxylate cluster whose
structure and mechanism of function have not yet been
fully elucidated [2]. Thus, synthetic Mn4 molecular
clusters have been sought as models of the WOC [3–5].
Most of these have many structural/physical/spectro-
scopic properties similar to those of the WOC, but no
synthetic species currently seems to reproduce the
properties (especially the functional ones) of the cata-
lytic active site in all ways. In the molecular magnetism
arena, it has been discovered that some Mn carboxylates
clusters can function as single-domain nanomagnets at
very low temperatures [6–9]. These complexes have been
called single-molecule magnets (SMMs) to reflect the
fact that their magnetic properties are due to a combi-
nation of two intramolecular properties (and not to in-
termolecular exchange interactions and long-range
ordering), namely a high-spin ground state and a large
magnetoanisotropy, the latter reflected in a large and
negative value of the zero-field splitting parameter, D
[6,7]. Several groups, including our group [10–12], are
actively developing methods to high-nuclearity, high-
spin Mn molecular species that might be new SMMs.
There is currently a renewed interest in the coordi-
nation chemistry of oximes [13,14]. These efforts are
driven by a number of considerations, including the
solution of pure chemical problems [15–19], the desire to
provide useful bioinorganic models (oximes may be
considered to be reasonable models for the biologically
important imidazole donor group of the amino acid
histidine) [20], the development of new oxygen activa-
tion catalysts [21], the application of metal/oxime sys-
tems as simple and efficient catalysts for the hydrolysis
of organonitriles [22], the mechanistic study of corrosion
inhibition by Acorga P5000 (a modern corrosion in-
hibitor) on iron surfaces [23] and the employment of
oximate ligands in the synthesis of homometallic [10–
12,24] and heterometallic [25] clusters with interesting
magnetic properties. For example, the pure chemical
interest in the coordination chemistry of oximes arises
from the ability of the oximate()1) group (–C@N–Oꢁ)
to stabilise higher oxidation states of metals, e.g. NiIII or
NiIV [26,27], and the fact that the activation of oximes
by transition metal centres towards further reactions
seems to be an emergent area of modern synthetic
chemistry [13,14]. In contrast to the great number of
studies concerning metal complexes of simple oximes
and salicylaldoxime [12,15–19,23–25], very little is
known about complexes of pyridyloximes [28], although
this class of compounds could offer unique features in
terms of structural and physical properties.
cluster chemistry, in order to explore the influence of the
ligands on the cluster identity; the main objectives are the
access to new structural types of clusters with interesting
magnetic properties and the study of Mn-mediated re-
actions of the oxime group. Reaction schemes involving
di-2-pyridyl ketone oxime, (py)2CNOH (Fig. 1), and
various Mn carboxylate sources in the presence of Xꢁ led
[11] to the new family of valence-trapped, mixed-valent
III
complexes [Mn2IIMn2 (O2CR)2X2{(py)2CNO}2 {(py)2
2ꢁ
CO2}2](X ¼ Cl,Br;(py)2CO2 ¼ the gem-diolate()2) form
of di-2-pyridyl ketone); it has been of great interest that
an appreciable quantity of the oxime ligand undergoes
transformation to yield the coordinated dianion of the
gem-diol form of di-2-pyridyl ketone. The mechanism of
this transformation probably involves reaction(s) of the
electrophilically activated coordinated oxime group [11].
The use of phenyl 2-pyridyl ketone oxime, (ph)(py)C-
NOH (Fig. 1), in Mn carboxylate chemistry has yielded
[10] the novel clusters [Mn4IIMn4IIIO2 (OH)2(O2CR)10
{(ph)(py)CNO}4]; the core of these complexes has a
III
unique topology consisting of two linked {Mn2IIMn2
(l3-O)(l3-OH)}7þ units. The above prior results with
2-pyridyloximes encouraged us to proceed to the use of
2-pyridinealdoxime ((py)CHNOH, Fig. 1) to Mn car-
boxylate chemistry, and we have thus been exploring the
reactions of (py)CHNOH with suitable Mn starting
materials. The results of this investigation are reported
here. It is worth mentioning that (py)CHNOH has been
used only sparingly in Mn chemistry to date. The only
known compounds comprise two heterometallic com-
plexes and one homometallic coordination polymer.
The chain [Mn2III(saltmen)2 Ni{(py)CHNO}2 (pyr)2]n
(ClO4)2n (saltmen2ꢁ ¼ N,N0-(1,1,2,2-tetramethylethylene)
bis(salicylideneiminate)) shows evidence for single-chain
magnet behaviour; the 2-pyridinealdoximate()1) ligand
in this 1D complex bridges two adjacent MnIII and NiII
ions [29]. The dinuclear complex [LCrIII {(py)CHNO}3
MnII](ClO4)2, where L is 1,4,7-trimethyl-1,4,7-triaza-
cyclononane, is composed of two pseudooctahedral
H
C
C
C
N
N
N
N
N
OH
N
N
OH
OH
(py)CHNOH
(ph)(py)CNOH
(py)2CNOH
H
C
O
O
F3C
C
C
O
CF3
C
C
N
N
N
O
-O
O-
-
hfac
We have recently embarked on a programme aiming
at the amalgamation of the above two areas, namely the
use of pyridyloxime ligands in manganese carboxylate
2ꢁ
Fig. 1. Some of the ligands discussed in the text; note that (py) 2CO2
does not exist as a free species but exists only in its metal complexes.

C.J. Milios et al. / Polyhedron 23 (2004) 83–95
85
polyhedra which are joined by three oximato ( ¼ N–Oꢁ)
groups [30]. Complex [Mn(SO4){(py)CHN OH}(H2O)]n
is a double-chain polymer in which the MnII ions are
by filtration. The filtrate was treated with (py)CHNOH
(0.24 g, 2.0 mmol) under reflux. The dark brown–green
solution slowly faded to orange over the course of 1 h.
The homogeneous orange solution was layered with
Et2O (60 ml). Slow mixing yielded orange crystals of X-
ray quality, which were collected by filtration, washed
with Et2O and dried in air. Yield: 43% (based on total
Mn). Anal. Calc. for C19H15N3O5Mn: C, 54.3; H, 3.6; N,
10.0. Found: C, 54,1; H, 3.7; N, 10.2%. Selected IR data
(KBr pellet, cmꢁ1): 3442mb, 3064w, 1610m, 1588s,
1564m, 1474w, 1394s, 1332w, 1148w, 1092w, 1054m,
1012w, 918m, 892w, 830w, 782w, 766m, 714m, 674m,
490m.
2ꢁ
bridged by l3-SO4 ligands [31].
2. Experimental
2.1. General and physical measurements
All manipulations were performed under aerobic
conditions using materials (reagent grade) and solvents as
received. Mn(O2CPh)2 ꢀ 2H2O [32] and [Mn3O(O2CPh)6
(pyr)2(H2O)] [33] were prepared as described elsewhere.
Microanalyses (C, H, N) were performed by the
University of Ioannina (Greece) Microanalytical Labo-
ratory using an EA 1108 Carlo Erba analyser. IR spectra
(4000–450 cmꢁ1) were recorded on a Perkin–Elmer 16
PC FT spectrometer with samples prepared as KBr pel-
lets. Magnetic susceptibility measurements were carried
out for a polycrystalline sample of complex 1 (vide infra)
in the range 2–300 K using a SQUID susceptometer; the
applied magnetic field was 0.1 T. Diamagnetic correc-
tions were applied to the observed paramagnetic sus-
ceptibilities using PascalÕs constants. Solid-state EPR
spectra in the 77–300 K temperature range were recorded
on a Bruker ES200 spectrometer at X-band frequency.
2.2.3. [Mn2(O2CMe)2{(py)CO2}2{(py)CHNOH}2] (3)
Solid (py)CHNOH (0.09 g, 0.7 mmol) was added to a
stirred, colourless solution of Mn(O2CMe)2 ꢀ 4H2O (0.06
g, 0.25 mmol) in EtOH (20 ml). The resulting yellow
solution was allowed to stand undisturbed at 5 °C for
several days. Well-formed, X-ray quality yellow crystals
appeared, which were collected by filtration, washed
with Et2O and dried in vacuo over silica gel. Yields as
high as 75% were obtained. Anal. Calc. for
C28H26N6O10Mn2: C, 46.9; H, 3.7; N, 11.7%. Found: C,
46.5; H 3.7; N, 11.5%. Selected IR data (KBr pellet,
cmꢁ1): 3442mb, 1602m, 1548sb, 1478m, 1416s, 1330m,
1308w, 1258w, 1048s, 1010w, 924w, 888w, 782m, 678sh,
668m, 656s, 638w, 618w, 522w, 488w.
2.2. Compound preparation
2.2.4. [Mn(O2CCF3)2{(py)CHNOH}2] (4)
2.2.1.
[Mn4(O2CPh)6{(py)CO2}2{(py)CHNOH}2]ꢀ
To a pale yellow slurry of Mn(hfac)2 ꢀ 3H2O (0.47 g,
1.0 mmol) in CH2Cl2 (20 ml) was added dropwise a
colourless solution of (py)CHNOH (0.12 g, 1.0 mmol) in
the same solvent (10 ml). The reaction mixture colour
changed slightly from pale yellow to darker yellow. This
was stirred for about 10 min, a small quantity of un-
dissolved material removed by filtration and the filtrate
layered with n-hexane (60 ml). Slow mixing yielded
yellow crystals (some of them were of X-ray quality),
which were collected by filtration, washed with Et2O
and dried in air. The yield was typically 40%. Anal. Calc.
for C16H12N4O6F6Mn: C, 36.6; H, 2.3; N, 10.7. Found:
C, 36.9; H, 2.4; N, 10.5%. Selected IR data (KBr pellet,
cmꢁ1): 3428mb, 1668s, 1602m, 1508m, 1448m, 1328m,
1310m, 1206s, 1144s, 1038s, 890m, 840m, 780m, 678w,
640w.
0.6CHCl3 (1ꢀ 0.6CHCl3)
A colourless solution of Mn(O2CPh)2 ꢀ 2H2O (0.33 g,
1.0 mmol) in MeCN (20 ml) was treated with solid
(py)CHNOH (0.12 g, 1.0 mmol). The solid soon dis-
solved. The resulting yellow solution was evaporated
under reduced pressure, and the residue redissolved in
CHCl3 (20 ml) to give an orange solution. This was
layered with Et2O (40 ml). After several days, large
yellow prisms were formed; they were collected by fil-
tration, washed with Et2O and dried in air. Yield: 72%
(based on total Mn). The dried sample analysed as sol-
vent-free. Anal. Calc. for C66H50N6O18Mn4: C, 55.2; H,
3.5; N, 5.9. Found: C, 55.4; H, 3.4; N, 6.0%. Selected IR
data (KBr pellet, cmꢁ1): 3446mb, 3020w, 2926w, 1602s,
1555sh, 1544s, 1476w, 1404s, 1068w, 1024m, 776w, 720s,
674m.
2.2.2. [Mn(O2CPh){(py)CO2}{(py)CHNOH}]n (2)
To
2.3. X-ray crystallographic studies
a stirred deep brown solution of [Mn3O
(O2CPh)6(pyr)2(H2O)] (0.34 g, 0.3 mmol) in MeCN (30
ml) was added Me3SiCl (0.16 ml, 1.2 mmol) dropwise to
give a solution of essentially the same colour. No im-
mediate precipitate was observed, but slow formation of
a dark brown solid began soon after. When precipitation
was judged complete (2–3 h), the powder was removed
Crystals of complexes 2, 3 and 4 were mounted in air,
while a crystal of complex 1 ꢀ 0.6CHCl3 was mounted in
a capillary filled with drops of mother liquid. Diffrac-
tion measurements for 1 ꢀ 0.6CHCl3, 3 and 4 were made
on a Crystal Logic Dual goniometer diffractometer us-
ing graphite-monochromated Mo radiation. Data for

86
C.J. Milios et al. / Polyhedron 23 (2004) 83–95
complex 2 were collected on a P21 Nicolet diffractometer
upgraded by Crystal Logic using Ni-filtered Cu radia-
tion. Complete crystal data and parameters for data
collection and processing are reported in Table 1. Unit
cell dimensions were determined and refined by using
the angular settings of 25 automatically centred reflec-
tions in the ranges 11° < 2h < 23° (1 ꢀ 0.6CHCl3, 3 and
4) and 22° < 2h < 54° (2). In all cases, three standard
reflections, monitored every 97 reflections, showed less
than 3% fluctuation and no decay. Lorentz, polarisation
and W-scan absorption (except for 3) corrections were
applied using CRYSTAL LOGIC software.
hydrogen atoms were refined using anisotropic thermal
parameters, except those of the solvate CHCl3 molecule
in 1 ꢀ 0.6CHCl3 which were refined isotropically with
occupation factors fixed at 10.3; the fluorine atoms of
the –CF3 groups in 4 were found disordered and refined
anisotropically over two positions with occupation fac-
tors summing one.
3. Results and discussion
3.1. Syntheses
The structures were solved by direct methods using
SHELXS-86 [34] and refined by full-matrix least squares
techniques on F 2 with SHELXL-93 [35]. For 2, 3 and 4,
all hydrogen atoms – except those on the methyl carbon
(C(14)) in 3 which were introduced at calculated posi-
tions as riding on their bonded atom – were clearly visible
in subsequent Fourier maps and refined isotropically.
For 1 ꢀ 0.6CHCl3, all hydrogen atoms – except HO(11)
which was located by difference maps and refined iso-
tropically – were placed in ideal, calculated positions
riding on their respective carbon atoms. All non-
The reaction that we initially investigated was that
between Mn(O2CPh)2 ꢀ 2H2O and (py)CHNOH. Treat-
ment of a solution of Mn(O2CPh)2 ꢀ 2H2O with one
equivalent of (py)CHNOH in MeCN, followed by
evaporation of the resulting solution, redissolution of the
residue in CHCl3 and layering the solution with Et2O
allowed yellow crystals of the product to be obtained in a
form suitable for crystallography. The product was
identified as the interesting new tetranuclear cluster
[Mn4(O2CPh)6{(py)CO2}2{(py)CHNOH}2] ꢀ 0.6CHCl3
Table 1
Crystallographic data for complexes 1 ꢀ 0.6CHCl3, 2, 3 and 4
1 ꢀ 0.6CHCl3
66:6H50:6N6O18Cl1:8Mn4
1506.53
2
3
4
Formula
C
C19H15N3O5Mn
420.28
C28H26N6O10Mn2
716.42
C16H12N4O6F6Mn
525.24
Formula weight
Crystal colour, habit
Crystal dimensions (mm)
Crystal system
yellow, prism
0.16 ꢂ 0.20 ꢂ 0.50
monoclinic
P21=n
18.825(7)
17.012(7)
11.045(4)
yellow, prism
0.10 ꢂ 0.10 ꢂ 0.30
orthorhombic
Pcab
17.720(6)
21.869(7)
9.612(3)
orange, prism
0.15 ꢂ 0.28 ꢂ 0.50
monoclinic
P21=n
9.526(5)
8.761(4)
18.701(9)
yellow, prism
0.10 ꢂ 0.30 ꢂ 0.50
triclinic
ꢀ
Space group
ꢁ
P1
a (A)
ꢁ
9.439(7)
14.15(1)
9.291(8)
93.90(3)
118.82(3)
97.27(2)
1067(1)
2
b (A)
ꢁ
c (A)
a (°)
b (°)
c (°)
90.23(1)
99.61(2)
3
ꢁ
V (A )
3537(2)
2
1.415
3725(2)
8
1.499
1539(1)
2
1.546
Z
Dcalc (g cmꢁ3
)
1.635
0.711
l (mmꢁ1
)
0.837
Mo Ka (0.71073)
298
6.090
Cu Ka (1.54180)
298
0.886
Mo Ka (0.71073)
298
ꢁ
Radiation (k, A)
Temperature (K)
Scan mode/speed (°minꢁ1
2hmax (°)
Mo Ka (0.71073)
298
)
h ꢁ 2h=3:0
48.5
6020
h ꢁ 2h=1:5
124.8
2820
h ꢁ 2h=3:5
50.0
5222
h ꢁ 2h=3:6
50.0
3996
Reflections collected
Unique reflections (Rint
Data with I > 2rðIÞ
Parameters refined
½D=rꢃ
)
5698 (0.0131)
3865
450
2818 (0.0351)
2273
313
2663 (0.0361)
2062
250
3745 (0.0107)
3201
398
0.003
0.647, )0.290
1.019
0.002
0.256, )0.529
1.111
0.011
0.810, )0.386
1.145
0.016
ðDqÞmmaaxx; ðDqÞ (e A
)
0.272, )0.259
0.796
0.0322
ꢁ3
ꢁ
min
Goodness-of-fit (on F 2)
a
R1
0.0521
0.1376
0.0415
0.1034
0.0639
0.1578
b
wR2
0.0934
P
P
a R1 ¼ ðjFoj ꢁ jFcjÞ= jFoj.
P
P
2
2
1=2
2
b wR2 ¼ f ½wðFo2 ꢁ Fc2Þ ꢃ= ½wðFo2Þ ꢃg , w ¼ 1=½r2ðFo2Þ þ ðaPÞ þ bPꢃ, where P ¼ ½maxðFo2; 0Þ þ 2Fc2ꢃ=3.

C.J. Milios et al. / Polyhedron 23 (2004) 83–95
87
(1 ꢀ 0.6CHCl3). The most remarkable feature of this re-
action is the in situ formation of the picolinate()1) li-
gand, (py)CO2 (Fig. 2). The following experimental
among other reagents, microwave irradiation on clay
(Clayan), on wet sodium periodate impregnated silica
gel or in the presence of BiCl3, CuCl2 in MeCN, aque-
ous NaHSO3, KMnO4-aqueous MeCN, Amberlyst 15
and acetone, alkaline H2O2 and with Me3NHþCrO3Clꢁ
[38].
Oxidation of aldehydes to carboxylic acids is one of
the most common oxidation reactions in organic
chemistry [38] and has been carried out with manyꢁox-
idising agents, the most popular of which is MnO4 in
acidic, basic or neutral solution. Aldehydes are also
oxidised to carboxylic acids by atmospheric oxygen, but
the actual direct oxidation product is the peroxy acid
RCO3H ((py)CO3H in our case), which with another
molecule of aldehyde disproportionates to give two
molecules of acid ((py)COOH in our case).
ꢁ
points should be mentioned at this point: (a) the 1:1 re-
action between Mn(O2CPh)2 ꢀ 2H2O and (py)CHNOH
in MeOH under strictly anaerobic conditions affords a
solid, whose analytical data correspond to the formula
Mn(O2CPh)2{(py)CHNOH}2 and IR spectrum confirms
the absence of (py)CO2ꢁ. (b) No colour change, indica-
tive of oxidation of MnII to MnIII, was observed during
the preparation/crystalliꢁsation of 1. (c) The partial
(py)CHNOH ! (py)CO2 transformation noticed in 1
was also observed in the reactions of other Mn carbox-
ylate sources with (py)CHNOH (vide infra), and (d)
analogous reactions of CoII or NiII carboxylates and the
oxime did not give any evidence [36] for the formation of
picolinate()1). The above experimental facts do not
provide us with a clear mechanistic view. Without any
mechanistic implication, we suggest that the formation
of 1 is triggered by hydrolysis of an amount of
(py)CHNOH to the corresponding aldehyde, 2-pyri-
dinealdehyde ((py)CHO), followed by oxidation of the
latter to picolinic acid, (py)COOH, which is deproto-
nated by the excess of PhCO2ꢁs present in the reaction
mixture. This simplified transformation scheme is shown
in Fig. 2. The difference between regular and metal-
mediated conditions lead us to the belief that the trans-
formation is MnII-assisted and probably involves the
reaction of electrophilically activated coordinated oxime
group [14,37].
It has been demonstrated that direct hydrolysis of
oximes to carbonyl compounds proceeds slowly in low
yields and is subject to side reactions [13,14]. Attanasi et
al. [37] have proposed a facile method for this conver-
sion based on copper(II)-assisted hydrolysis, which is
not reductive or oxidative in nature but involves the
reaction of the electrophilically activated, coordinated
oxime group with water. In general, the conversion of
oximes into the parent carbonyl compounds requires
reductive or oxidative cleavages, strongly basic or acidic
media [13,14]. Oximes can be converted to the corre-
sponding aldehydes or ketones by treatment with,
Since single-crystal X-ray crystallography (vide infra)
revealed the existence of the interesting tꢁetranuclear
cluster 1 and the (py)CHNOH ! (py)CO2 transfor-
mation, we sought to prepare the acetate analogue of 1.
Our main goals were to determine whether this would be
isostructural with the benzoate species and (if they are
isostructural) to access any influence of the alkyl vs. aryl
difference on magnetochemical properties. A completely
analogous reaction scheme with that used for 1 was
initially employed, i.e., the 1:1 Mn(O2CMe)2 ꢀ 4H2O/
(py)CHNOH mixture in MeCN. This yielded a solid
with poor crystallinity. 1:1 reactions of (py)CHNOH
with Mn(O2CMe)2 ꢀ 4H2O in other solvents, including
alcohols, have also been carried out, but attempts to
crystallographically characterise the products have all
been unsuccessful to date. The isolation of the dinuclear
product [Mn2(O2CMe)2{(py)CO2}2{(py)CHNOH}2] (3)
came about from the employment of excess of
(py)CHNOH, i.e., MnII: (py)CHNOH ¼ 1:2.5–3.0, in
EtOH. X-ray crystallography revealed again the partial
ꢁ
(py)CHNOH ! (py)CO2 transformation! Since the
two systems that lead to 1 and 3 are clearly not analo-
gous, the difference in stoichiometry is not surprising;
the (py)CHNOH + (py)CO2ꢁ:MnII ratio in the formula
of 3 is 2:1 (whereas it is 1:1 in 1), and we attribute this to
the excess of (py)CHNOH used in the synthesis of the
acetate complex.
With the identity of 3 established, its benzoate ver-
sion was sought. Note that since only a dinuclear species
was being sought, excess of oxime was added. Several
1:2 and 1:3 Mn(O2CPh)2 ꢀ 2H2O/(py)CHNOH reaction
mixtures were studied using various conditions, but al-
most all led to a mixture of 1 and a yet unidentified
product. Since the RCO2ꢁ:MnII ratio in 1 is higher than
that in 3 (1.5:1 vs. 1:1), methods to reduce the benzoate
concentration were examined. Use of MnCl2 ꢀ 4H2O,
Mn(NO3)2 ꢀ 6H2O or Mn(ClO4)2 ꢀ 6H2O as starting
materials, followed by addition of one equivalent of
NaO2CPh, complicated the reaction mixtures. The car-
boxylate-abstraction reagent Me3SiCl [39,40] was our
H
N
H
O
H2O
MnII
O2
C
C
N
N
OH
(py)CHO
(py)CHNOH
OH
O
O
-
PhCO2
C
C
N
N
O
Fig. 2. A simplified view for the partial transformation of 2-pyr-
idinealdoximetopicolinate()1)duringthepreparationofcomplexes1–3.

88
C.J. Milios et al. / Polyhedron 23 (2004) 83–95
CF3COCH2COCH3 H2O=baseCF CO ꢁ þ CH3COCF3
ꢀꢀꢀꢀ!
next choice; this reagent forms the silyl ester as shown in
Eq. (1). Treatment of Mn(O2CPh)2 ꢀ 2H2O with 2–3
equivalents of
3
2
ð2Þ
Me3SiCl þ RCO ꢁ ! RCO2SiMe3 þ Clꢁ
ð1Þ
It has been previously suggested that hfacH reacts with
H2O to form initially a ‘‘dihydrate’’, i.e. hfacH ꢀ 2H2O
[43]; however, later rigorous studies by ChristouÕs group
demonstrated [44,45] that this reaction is far from simple.
These latter researchers have demonstrated that hfacH
reacts with H2O to yield the tetraol F3CC(OH)2CH2
C(OH)2CF3, which can act as ligand in transition metal
chemistry at various degrees of deprotonation. Ulti-
mately, the pH of the reaction solution seems to have a
profound effect on the nature of the product and how the
hfacꢁ ligand is cleaved [42].
2
Me3SiCl and 2–2.5 equivalents of (py)CHNOH in alco-
hols or MeCN gave orange powders whose analytical
data were consistent with the formulation Mn(O2CPh)
{(py)CO2}{(py)CHNOH}. The rather low solubility and
platelike crystallinity of the material precluded a crys-
tallographic investigation. Somewhat to our surprise, the
preparation and crystallisation of this orange compound
were achieved by the reaction of the mixed-valence
compound [Mn3II;III;IIIO(O2CPh)6 (pyr)2(H2O)] [33]
with 4 equivalents of Me3SiCl and ꢄ7 equivalents
of (py)CHNOH (Mn:oxime ꢅ1:2, in fact the actual
Mn:oxime ratio is lower, e.g. 1:3, because a small
quantity of a dark brown, Mn-containing solid was re-
moved prior to the addition of the oxime) in MeCN. The
advantage of the present procedure is its slow crystalli-
sation of product upon layering with Et2O and the well-
formed nature of the resulting crystals that have proven
excellent diffractors of X-rays. The product was crystal-
lographically identified as the coordination polymer
[Mn(O2CPh){(py)CO2}{(py)CHNOH}]n (2) rather than
the expected dinuclear species [Mn2(O2CPh)2 {(py)
CO2}2{(py)CHNOH}2]; note that the partial (py) CH
3.2. Description of structures
Selected interatomic distances and angles for com-
plexes 1 ꢀ 0.6CHCl3, 2, 3 and 4 are listed in Tables 2–5,
respectively.
Complex 1 ꢀ 0.6CHCl3 crystallises in monoclinic
space group P21=n. Its structure consists of the tetranu-
clear [Mn4(O2CPh)6{(py)CO2}2{(py)CHNOH}2] species
(Fig. 3) and lattice CHCl3 molecules; the latter will not
be further discussed. The tetranuclear molecule lies on a
crystallographic inversion centre, resulting in an exactly
planar zig-zag array of MnII atoms. The bꢁridging system
comprises four syn, syn g1:g1:l2 PhCO2 groups, two
g1:g2:l3 PhCO2ꢁ groups (those containing atoms O(41),
O(42) and O(410), O(420)) and two g1:g1:l2 picoli-
nate()1) ligands. Each outer metal ion (Mn(1), Mn(10))
is chelated by a single (py)CHNOH molecule bound in a
N,N0-bidentate fashion and forming a five-membered
ring. Atoms Mn(1) and Mn(2) are bridged by one
ꢁ
NOH ! (py)CO2 transformation again occurred. The
fading of the reaction solution after the addition of the
oxime and the MnII nature of 2 both require reduction
of MnIII to have occurred; the source of the reducing
equivalent is probably solvent, solvent impurities or ex-
cess ligand, facilitated by the strongly oxidising nature of
MnIII [32].
Complex [Mn(O2CCF3)2{(py)CHNOH}2] (4) was
not prepared from the reaction of a trifluoroacetate-
based Mn starting material and (py)CHNOH. How-
ever, we have incorporated this compound in the
present work because it does contain a carboxylate
ligand! Treatment of Mn(hfac)2 ꢀ 3H2O (hfac ¼ hexa-
fluoroacetylacetonate) with one equivalent of (py)CH-
NOH in CH2Cl2, followed by stirring of the slurry,
leads to a yellow solution that can be layered with n-
hexane to give 4 in 40% yield. Single-crystal X-ray
diffraction unambiguously established that this complex
ꢁ
g1:g1:l2 PhCO2 group, the ‘‘triatomic’’ part of ꢁone
ꢁ
g1:g2:l3 PhCO2 group and one g1:g2:l2 (py)CO2 li-
gand, while two oxygen atoms (O(42), O(420)) from the
ꢁ
g1:g2:l3 PhCO2 ligand and its symmetry partner
doubly bridge atoms Mn(2) and Mn(20). The
Mn(1) ꢀ ꢀ ꢀ Mn(20) pair is bridged by one g1:g1:l2
ꢁ
PhCO2 group and the ‘‘triatomic’’ part of the same l3
benzoate that bridges Mn(1) and Mn(2). The central
Mn(2)O(42)Mn(20)O(420) core is strictly planar due to
the presence of the inversion centre in the middle of the
core, with an Mn(2)–O(42)–Mn(20) angle of 103.1(1)°
ꢁ
contains monodentate CF3CO2 ligands. The origin of
the trifluoroacetate ligands is intriguing, and the
0
ꢁ
and a Mn(2) ꢀ ꢀ ꢀ Mn(2 ) separation of 3.460(2) A. This
separation is shorter than the Mn(1) ꢀ ꢀ ꢀ Mn(2) (3.557(2)
ꢁ
hfacꢁ ! CF3CO2 transformation has been cꢁonfirmed
0
ꢁ
ꢁ
in at least two cases [41,42]. The CF3CO2 ligand
should be one of the decomposition products of the
hfacꢁ ligand (Eq. (2)). b-Diketones have been known to
undergo the retro-Claisen condensation reaction to
produce a ketone and a carboxylate when strong bases
are present. The (py)CHNOH ligand could function as
the base to promote the decomposition of the hfacH
molecule [41].
A) and Mn(1) ꢀ ꢀ ꢀ Mn(2 ) (4.522(2) A) separations pre-
sumably due to the greater number (two) of mono-
atomic bridges.
The MnII atoms are octahedrally coordinated, their
chromophores being cis-Mn(1)N2O4 and Mn(2)NO5.
Both polyhedra are distorted; the main distortions arise
from the chelating rings with the narrow N(11)–Mn(1)–
N(12) (69.8(2)°) and O(1)–Mn(2)–N(1) (74.1(1)°) bond

C.J. Milios et al. / Polyhedron 23 (2004) 83–95
89
Table 2
Selected interatomic distances (A) and angles (°) for [Mn4(O2CPh)6{(py)CO2}2{(py)CHNOH}2] ꢀ 0.6CHCl3 (1 ꢀ 0.6CHCl3)a
Interatomic distances
ꢁ
Mn(1) ꢀ ꢀ ꢀ Mn(2)
Mn(1) ꢀ ꢀ ꢀ Mn(20)
Mn(1) ꢀ ꢀ ꢀ Mn(10)
Mn(2) ꢀ ꢀ ꢀ Mn(20)
Mn(1)–O(1)
3.557(2)
4.522(2)
7.364(3)
3.460(2)
2.224(3)
2.147(3)
2.129(3)
2.202(4)
Mn(1)–N(11)
Mn(1)–N(12)
Mn(2)–O(1)
Mn(2)–O(22)
Mn(2)–O(32)
Mn(2)–O(42)
Mn(2)–O(420)
Mn(2)–N(1)
2.302(5)
2.383(6)
2.233(3)
2.102(3)
2.050(3)
2.140(3)
2.278(3)
2.235(4)
Mn(1)–O(21)
Mn(1)–O(31)
Mn(1)–O(41)
Interatomic angles
Mn(1)–O(1)–Mn(2)
Mn(2)–O(42)–Mn(20)
O(1)–Mn(1)–O(21)
O(1)–Mn(1)–O(31)
O(1)–Mn(1)–O(41)
O(1)–Mn(1)–N(11)
O(1)–Mn(1)–N(12)
O(21)–Mn(1)–O(31)
O(21)–Mn(1)–O(41)
O(21)–Mn(1)–N(11)
O(21)–Mn(1)–N(12)
O(31)–Mn(1)–O(41)
O(31)–Mn(1)–N(11)
O(31)–Mn(1)–N(12)
O(41)–Mn(1)–N(11)
O(41)–Mn(1)–N(12)
105.9(1)
N(11)–Mn(1)–N(12)
O(1)–Mn(2)–O(22)
O(1)–Mn(2)–O(32)
O(1)–Mn(2)–O(42)
O(1)–Mn(2)–O(420)
O(1)–Mn(2)–N(1)
O(22)–Mn(2)–O(32)
O(22)–Mn(2)–O(42)
O(22)–Mn(2)–O(420)
O(22)–Mn(2)–N(1)
O(32)–Mn(2)–O(42)
O(32)–Mn(2)–O(420)
O(32)–Mn(2)–N(1)
O(42)–Mn(2)–O(420)
O(42)–Mn(2)–N(1)
O(420)–Mn(2)–N(1)
69.8(2)
89.0(1)
163.5(1)
96.4(1)
88.1(1)
74.1(1)
98.2(1)
92.1(1)
168.3(1)
100.1(1)
98.1(2)
87.6(1)
89.9(2)
77.0(1)
164.3(1)
90.0(1)
103.1(1)
83.3(1)
94.3(1)
111.6(1)
159.1(2)
95.3(2)
175.4(1)
83.1(1)
86.3(2)
104.1(2)
94.2(1)
97.2(2)
80.1(2)
84.9(2)
152.9(2)
a Symmetry transformations used to generate equivalent atoms: (0) ꢁx þ 1; ꢁy; ꢁz.
Table 3
Selected interatomic distances (A) and angles (°) for [Mn(O2CPh){(py)CO2}{(py)CHNOH}]n (2)a
ꢁ
Interatomic distances
Mn ꢀ ꢀ ꢀ Mn#1
Mn–O(1)
Mn–O(2)
5.855(2)
2.168(2)
2.092(3)
2.106(3)
Mn–N(1)
Mn–N(2)
Mn–N(3)
2.301(3)
2.324(3)
2.317(3)
Mn–O(4)
Interatomic angles
O(1)–Mn–O(2)
O(1)–Mn–O(4)
O(1)–Mn–N(1)
O(1)–Mn–N(2)
O(1)–Mn–N(3)
O(2)–Mn–O(4)
O(2)–Mn–N(1)
O(2)–Mn–N(2)
88.3(1)
97.3(1)
72.8(1)
94.1(1)
159.0(1)
97.8(1)
160.1(1)
89.4(1)
O(2)–Mn–N(3)
O(4)–Mn–N(1)
O(4)–Mn–N(2)
O(4)–Mn–N(3)
N(1)–Mn–N(2)
N(1)–Mn–N(3)
N(2)–Mn–N(3)
104.8(1)
90.9(1)
166.7(1)
97.1(1)
85.9(1)
91.8(1)
70.1(1)
a Symmetry transformations used to generate equivalent atoms: #1 ꢁx; ꢁy þ 1=2; z þ 1=2.
angles. The Mn–N and Mn–O bond lengths agree well
with values expected for high-spin MnII [30,31,46–50].
The bridging Mn–Opicolinate distances are symmetric
There is a rather small family of tetranuclear man-
ganese(II) clusters [51–62], which mainly adopt the cu-
bane, planar rhomboidal, zig-zag, adamantane-like and
pair-of-dimer topologies. Complex 1 joins a small family
of manganese(II) picolinate complexes [47–50] and it is
ꢁ
(2.224(3), 2.233(3) A), whereas the analogous Mn–
ꢁ
Obenzoate distances are asymmetric (2.140(3), 2.278(3) A).
ꢁ
The two bridging oxygens are essentially planar
(RoO(1) ¼ 357.5°, RoO(42) ¼ 355.7°). An intramolecular
hydrogen bond is present in 1 ꢀ 0.6CHCl3 with the oxime
oxygen, O(11), as donor and the uncoordinated picoli-
nate oxygen, O(2), as acceptor; its dimensions are
only the second such complex comprising the (py)CO2
ligand in the rare g1:g2:l2 coordination mode, the first
example being the 2D coordination polymer
[Mn(N3){(py)CO2}(H2O)]n [47].
Views of the structure of complex 2 are shown in Figs.
4 and 5. The compound contains zig-zag chains of re-
peating [Mn(O2CPh){(py)CO2}{(py)CHNOH}] units.
ꢁ
ꢁ
O(11) ꢀ ꢀ ꢀ O(2) 2.564 A, HO(11) ꢀ ꢀ ꢀ O(2) 1.382 A and
O(11)–HO(11) ꢀ ꢀ ꢀ O(2) 162.9°.

90
C.J. Milios et al. / Polyhedron 23 (2004) 83–95
Table 4
a
ꢁ
Selected interatomic distances (A) and angles (°) for [Mn2(O2CMe)2{(py)CO2}2{(py)CHNOH}2] (3)
Interatomic distances
Mn ꢀ ꢀ ꢀ Mn0
Mn–O(2)
Mn–O(20)
Mn–O(4)
3.633(2)
2.204(4)
2.210(4)
2.107(4)
Mn–N(1)
Mn–N(2)
Mn–N(30)
2.307(5)
2.298(5)
2.265(5)
Interatomic angles
Mn–O(2)–Mn0
O(2)–Mn–O(20)
O(2)–Mn–O(4)
O(2)–Mn–N(1)
O(2)–Mn–N(2)
O(2)–Mn–N(30)
O(20)–Mn–O(4)
O(20)–Mn–N(1)
110.8(2)
O(20)–Mn–N(2)
O(20)–Mn–N(30)
O(4)–Mn–N(1)
O(4)–Mn–N(2)
O(4)–Mn–N(30)
N(1)–Mn–N(2)
N(1)–Mn–N(30)
N(2)–Mn–N(30)
158.0(2)
69.2(2)
95.0(2)
90.4(2)
123.2(2)
142.3(2)
101.5(2)
92.5(2)
73.1(2)
166.0(2)
95.7(2)
91.8(2)
70.6(2)
91.9(2)
92.8(2)
a Symmetry transformations used to generate equivalent atoms: (0) ꢁx þ 1; ꢁy; ꢁz.
Table 5
ꢁ
Selected bond distances (A) and angles (°) for [Mn(O2CCF3)2{(py)CHNOH}2] (4)
Bond distances
Mn–O(3)
Mn–O(5)
Mn–N(1)
Mn–N(2)
Mn–N(3)
Mn–N(4)
2.147(2)
2.101(2)
2.287(2)
2.287(3)
2.289(2)
2.286(3)
C(13)–O(3)
C(13)–O(4)
C(15)–O(5)
C(15)–O(6)
N(2)–O(1)
N(4)–O(2)
1.232(3)
1.229(3)
1.225(3)
1.212(4)
1.380(2)
1.388(3)
Bond angles
O(3)–Mn–O(5)
O(3)–Mn–N(1)
O(3)–Mn–N(2)
O(3)–Mn–N(3)
O(3)–Mn–N(4)
O(5)–Mn–N(1)
O(5)–Mn–N(2)
O(5)–Mn–N(3)
90.6(1)
88.0(1)
96.9(1)
O(5)–Mn–N(4)
N(1)–Mn–N(2)
N(1)–Mn–N(3)
N(1)–Mn–N(4)
N(2)–Mn–N(3)
N(2)–Mn–N(4)
N(3)–Mn–N(4)
96.5(1)
71.4(1)
90.5(1)
91.5(1)
90.6(1)
155.3(1)
71.4(1)
171.4(1)
100.2(1)
172.0(1)
101.0(1)
92.1(1)
Fig. 3. An ORTEP plot at the 30% probability level of complex
1 ꢀ 0.6CHCl3. Primed and unprimed atoms are related by the crystal-
lographic inversion centre. Only the ipso carbon atoms of the phenyl
groups of the benzoate ligands are shown.
Fig. 4. A very small section of the polymeric chain of complex 2 em-
phasising the coordination sphere of the MnII atom.
The polymeric chain extends along the c axis of the Pcab
space group. In each chain the MnII atoms are bridged
by syn, anti carboxylato groups of the g1:g1:g1:l2 pico-
linate()1) ligands. The MnII atom is octahedrally coor-
dinated to one oxygen atom (O(4)) from the
ꢁ
monodentate PhCO2 group, two nitrogen atoms (N(2),

C.J. Milios et al. / Polyhedron 23 (2004) 83–95
91
An ORTEP plot of complex 3 is shown in Fig. 6. Its
structure consists of a dinuclear [Mn2(O2CMe)2 {(py)
CO2}2{(py)CHNOH}2] molecule located at a centre of
symmetry. The two MnII atoms are bridged by two
oxygen atoms (O(2), O(20)) from the two symmetry-
ꢁ
related g1:g2:l2 (py)CO2 ligands, the nitrogen atoms
of which are ligated to Mn and Mn0. Each MnII atom
is further coordinated by a monodentate acetate ion
and a N,N0-chelating (py)CHNOH ligand, completing
a distorted octahedral coordination at each metal. The
central MnO(2)Mn0O(20) core is strictly planar due to
the presence of the inversion centre in the middle of the
core. As for 1 ꢀ 0.6CHCl3, the bridging Mn–Opicolinate
ꢁ
distances are symmetric (2.204(4), 2.210(4) A). The
0
ꢁ
Mn ꢀ ꢀ ꢀ Mn distance of 3.633(2) A is somewhat longer
than the analogous Mn(2) ꢀ ꢀ ꢀ Mn(20) distance in
1 ꢀ 0.6CHCl3 (Fig. 3) reflecting the different nature of
the monoatomic bridge (picolinate versus benzoate); in
accord with this the corresponding Mn–O–Mn angle in
3 (110.8(2)°) is larger than that in 1 ꢀ 0.6CHCl3
(103.1(1)°). The Mn–N and Mn–O bond lengths are
normal [30,31,46–50]. The bridging oxygen is perfectly
planar (RoO(2) ¼ 360°).
An intramolecular hydrogen bond is present in 3 with
the oxime oxygen, O(1), as donor and the ‘‘free’’, i.e.,
uncoordinated, acetate oxygen, O(5), as acceptor; its
ꢁ
dimensions are O(1) ꢀ ꢀ ꢀ O(5) 2.479 A, HO(1) ꢀ ꢀ ꢀ O(5)
ꢁ
1.602 A and O(1)–HO(1) ꢀ ꢀ ꢀ O(5) 153.3°.
Fig. 5. Views of complex 2 along b axis (up) and c axis (down).
The structure of complex 4 consists of well-separated
[Mn(O2CCF3)2{(py)CHNOH}2] molecules (Fig. 7). The
MnII atom is coordinated by two monodentate trifluo-
roacetates and two N,N0-bidentate chelating (py)CH-
NOH molecules. The six-coordinate molecule is the
N(3)) from the chelating neutral 2-pyridinealdoxime
molecule, one nitrogen and one oxygen (N(1), O(1)) from
a picolinate()1) ligand and to one oxygen atom (O(2))
from a neighbouring picolinate()1) ligand; thus, the
chromophore is fac-MnN3O3. The Mn–O and Mn–N
bond lengths are in the narrow 2.092(3)–2.168(2) and
ꢁ
2.301(3)–2.324(3) A ranges, respectively. Inspection of
the bond angles listed in Table 3 shows that the octahe-
dral coordination sphere of Mn is distorted. The intra-
ꢁ
chain Mn ꢀ ꢀ ꢀ Mn distance is 5.855(1) A, slightly outside
ꢁ
the typical range (5.2–5.8 A) reported for singly syn, anti
carboxylate-bridged MnII atoms [63]. A strong intra-
chain hydrogen bond is present in 2 with the oxime ox-
ygen, O(3), as donor and the uncoordinated benzoate
oxygen, O(5), as acceptor; its dimensions are
ꢁ
ꢁ
O(3) ꢀ ꢀ ꢀ O(5) 2.489 A, HO(3) ꢀ ꢀ ꢀ O(5) 1.440 A, O(3)–
HO(3) ꢀ ꢀ ꢀ O(5) 175.9°.
Complex 2 joins a small family of structurally char-
acterised, neutral, 1D coordination polymers containing
six-coordinate MnII sites; representative examples are
described in [64–68]. It is also the first example in
manganese(II) picolinate chemistry in which the
(py)CO2 ion adopts the g1:g1:g1:l2 coordination
ꢁ
mode, i.e., chelating one MnII atom through its nitrogen
and one carboxylate oxygen, and bridging an adjacent
MnII atom through its second carboxylate oxygen.
Fig. 6. An ORTEP plot at the 30% probability level of complex 3.
Primed and unprimed atoms are related by the crystallographic in-
version centre. The carbon atoms are not labelled for clarity.

92
C.J. Milios et al. / Polyhedron 23 (2004) 83–95
ꢁ
range. Contributions from RCO2 (R ¼ Me, Ph, CF3)
and/or picolinate mas(CO2) and ms(CO2) would be ex-
pected in this region, but overlap with the stretching
vibrations of the aromatic rings renders assignments
difficult. It seems that the frequencies of the ms(CO2)
ꢁ
ꢁ
bands of PhCO2ꢁ/MeCO2 and (py)CO2 coincide in
the spectra of 1 (1404 cmꢁ1), 2 (1394 cmꢁ1) and 3
(1416 cmꢁ1). The bands at 1544, 1564 and 1548 cmꢁ1
in 1, 2 and 3, respectively, are assigned to the
PhCO2ꢁ= MeCO2ꢁ
mas(CO2Þ
vibration [72,73]. The difference
D (D ¼ mas(CO2) ) ms(CO2)) for 1 is 140 cmꢁ1, less than
that for NaO2CPh (184 cmꢁ1), as expected for the
bridging modes of benzoate ligation [72]. The value of
this parameter is 170 cmꢁ1 for 2 and 132 cmꢁ1 for 3,
less than the corresponding value for NaO2CPh (184
cmꢁ1) and NaO2CMe (164 cmꢁ1), respectively. These
low D values might be interpreted as indicating bid-
entate (bridging or chelating) benzoate/acetate groups
[72]; however, the crystal structures of both complexes
reveal the presence of monodentate carboxylate
groups. This disagreement with the spectroscopic cri-
terion of Deacon and Phillips [72] is presumably due
to the uncoordinated carboxylate oxygenÕs involve-
ment (O(5) in Figs. 4 and 6) in hydrogen-bonding
linkages [72,74] with the oxime group.
Fig. 7. ORTEP representation of the molecule of complex 4 at the 30%
probability level. The plot has derived considering the positions of the
F atoms with the larger occupation, i.e., 70% for F(1), F(2), F(3) and
60% for F(4), F(5), F(6).
In the IR spectrum of NaO2CF3, the mas(CO2) and
ms(CO2) bands appear at 1680 and 1457 cmꢁ1, respec-
tively, i.e., D ¼ 223 cmꢁ1 [72], while the corresponding
bands for KO2CCF3 are at 1678 and 1437 cmꢁ1
(D ¼ 241 cmꢁ1) [72]. In the spectrum of 4, the bands at
1668 and 1448 cmꢁ1 are assigned to mas(CO2) and
ms(CO2); the D value (220 cmꢁ1) is not as large as ex-
pected (D > 260 cmꢁ1) for monodentate trifluoroacetate
ligands [72]. This is again due to the fact that the car-
boxylate oxygens (O(4), O(6) in Fig. 7) not coordinated
to MnII are hydrogen bonded to the oxime groups,
giving what can be regarded as a ‘‘pseudo-bridging’’
arrangement [72]. In addition, the mas(CO2) and ms(CO2)
frequencies of 4 are sufficiently close to those of the al-
kali metal trifluoroacetates to raise the possibility of
anion (CF3CO2ꢁ/Brꢁ) exchange [72].
cis–cis–trans isomer considering the positions of the
oxygen, pyridyl nitrogen and oxime nitrogen atoms,
respectively. The molecule has no imposed symmetry,
although it approximates closely to C2 symmetry, the C2
axis bisecting the O(3)–Mn–O(5) angle. The four Mn–N
ꢁ
bond lengths are almost identical (2.286(3)–2.289(2) A).
Angular distortions from octahedral geometry are pri-
marily a consequence of the chelating oxime ligands and
their restricted bite angles. There are two intramolecular
hydrogen bonds with the uncoordinated oxime oxygens
as donors and the ‘‘free’’ carboxylate oxygens as ac-
ꢁ
ceptors. Their dimensions are: O(1) ꢀ ꢀ ꢀ O(6) 2.582 A,
ꢁ
HO(1) ꢀ ꢀ ꢀ O(6) 1.612 A, O(1)–OH(1) ꢀ ꢀ ꢀ O(6) 145.7° and
ꢁ
ꢁ
O(2) ꢀ ꢀ ꢀ O(4) 2.571 A, HO(2) ꢀ ꢀ ꢀ O(4) 1.697 A, O(2)–
HO(2) ꢀ ꢀ ꢀ O(4) 177.3°.
Complex 4 represents a new addition to the very
small family of MnII complexes possessing monodentate
CF3CO2 ligands [69,70]. Complex [Mn(O2CCF3)2
ꢁ
3.4. Magnetic properties and EPR spectra of 1
(bpy)2] [70] comes closest to reproduce the structural
features of 4; it has chelating 2,20-bipyridine molecules
instead of (py)CHNOH molecules.
Solid state variable-temperature (2–300 K) magnetic
susceptibility (vM) studies were performed on a poly-
crystalline sample of compound 1 in a 0.1 T field. The
data are plotted as vMT and vM versus T in Fig. 8. The
3.3. Characteristic IR bands
v
M versus T curve shows a maximum at approximately 5
A common, characteristic feature in the IR spectra
of 1–4 is the appearance of a medium broad band at
3446–3428 cmꢁ1 assignable [71] to m(OH) of the
(py)CHNOH ligand. The broadness and relatively low
frequency of this band are both indicative of hydrogen
bonding. Several bands appear in the 1670–1350 cmꢁ1
K, indicative of weak antiferromagnetic coupling [60].
The room-temperature vMT value is 16.1 cm3 molꢁ1 K,
somewhat lower than the expected value of vMT ¼ 17:5
cm3 molꢁ1 K for four S ¼ 5=2 uncoupled spins with
g ¼ 2. The vMT product decreases steadily with de-
creasing temperature and tends to zero at very low

C.J. Milios et al. / Polyhedron 23 (2004) 83–95
93
15
10
5
0,4
0,3
g = 2.02
J1 = -8.95; J2 = -0.60; J3: -3.37 cm-1
0,2
0,1
0,0
0
0
50
100
150
200
250
300
Fig. 8. Plots of vMT and vM vs. T for the tetranuclear complex 1.
temperatures, indicating an overall antiferromagnetic
behaviour. Since the spins carriers are all d5 MnII ions,
and therefore orbital singlet (S) ions, only the isotropic
part of the exchange interaction was considered and the
contribution of the zero-field splitting was neglected [60].
For a molecule such as 1 a total of five exchange
parameters Jij are required to cover each possible pair-
wise exchange interaction between MnII ions i and j; a
Fig. 9. Assignment of J values to Mn ꢀ ꢀ ꢀ Mn interactions for the
magnetic model used for 1. The numbering scheme used for the MnII
ions is the same with that used in Fig. 3. Atoms O(1) and O(10) are the
l2 picolinate()1) oxygens, while all the rest oxygen atoms belong to
benzoate ligands.
exhibit spin-orbit coupling [67]. The obtained J values
are in agreement with qualitative magnetostructural
correlations found in MnII complexes. J values reported
in the literature with only carboxylate groups as bridging
ligands are always small and negative, between approx-
imately )0.2 and )5 cmꢁ1 [67,76,77], indicating weak
antiferromagnetic coupling. The J2 value is well within
the reported range. The carboxylate group involving
O(41) and O(42) can be considered as poorly efficient to
transmit the superexchange interaction between Mn(1)
and Mn(20) due to the quasi orthogonal arrangement,
evidenced by the Mn(1)–O(41)–O(42)–Mn(20) dihedral
angle of 88.0°; this may explain the very low J2 value,
since only one syn, syn carboxylate bridge is operative
(the group involving O(31) and O(320)). DFT calcula-
tions on Mn–(OR)2–Mn systems indicate a strong de-
pendence of the antiferromagnetic coupling as function
of the Mn–O–Mn bond angle below 98° and weak, but
increasing, antiferromagnetic response for Mn–O–Mn
bond angles in the 98°–110° range [78]. Thus, on the basis
of the Mn(2)–O(42)–Mn(20) angle of 103.1(1)°, the weak
antiferromagnetic coupling J3 ()3.37 cmꢁ1) is under-
standable. The fact that the J1 value is outside the re-
ported range ()0.2 to )5 cmꢁ1) may be due to the
different carboxylate bridges involved (picolinate and
benzoate).
0
sixth parameter J11 (the numbering scheme is the same
as that shown in Fig. 3) is assumed to be zero, given the
large distance and superexchange pathway involved
0
ꢁ
(Mn(1) ꢀ ꢀ ꢀ Mn(1 ) ¼ 7.364(3) A). However, due to sym-
metry, a total of three exchange parameters are enough
to cover each possible pairwise interaction. The mag-
netic model that was used is shown graphically in Fig. 9.
Inspection of the molecular structure of 1 reveals that
the three exchange pathways can be described as fol-
lows: The first one, J1, refers to the interaction between
Mn(1) and Mn(2) (and their symmetry equivalents)
mediated by one monoatomic picolinate O-bridge, one
ꢁ
syn, syn bidentate bridging PhCO2 group and the
ꢁ
‘‘triatomic’’ part of one g1:g2:l3 PhCO2 group. The
second one, J2, refers to the interaction between Mn(1)
and Mn(20) (and their symmetry equivalenꢁts) mediated
by one syn, syn bidentate bridging PhCO2 group and
the ‘‘triatomic’’ part of the same l3 PhCO2ꢁ that bridges
Mn(1) and Mn(2). The third exchange pathway, repre-
sented by J3, refers to the Mn(2) ꢀ ꢀ ꢀ Mn(20) interaction
mediated by two monoatomic benzoate O-bridges. Best-
fit parameters, obtained by means of the full-matrix
diagonalisation program CLUMAG [75] and applying
the Hamiltonian given in Eq. (3) (where S1, S2, S3 and S4
correspond to Mn(1), Mn(2), Mn(20) and Mn(10), re-
spectively),
The X-band EPR spectrum of a polycrystalline
sample of 1 (Fig. 10) consists of an isotropic featureless
signal centred at g ¼ 2 (linewidth 390 G), and one weak
half-field signal centred at g ¼ ꢄ4. The spectrum remains
unchanged in the 77–300 K range. Such a spectrum is
typical for magnetically interacting MnII ions in the
solid state [61].
H ¼ ꢁJ1ðS1S2 þ S3S4Þ ꢁ J2ðS1S3 þ S2S4Þ ꢁ J3ðS2S3Þ ð3Þ
are J1 ¼ ꢁ8:95 cmꢁ1, J2 ¼ ꢁ0:60 cmꢁ1, J3 ¼ ꢁ3:37 cmꢁ1
and g ¼ 2:02 (R ¼ 5.1 ꢂ 10ꢁ5).
The g parameter presents a value very close to 2.0, in
accord with the presence of MnII ions which do not

94
C.J. Milios et al. / Polyhedron 23 (2004) 83–95
Acknowledgements
This research was supported by the Research Com-
mittee of the University of Patras (K. CARATHEOD-
ORY Program No. 1941 to S.P.P.) and by the Spanish
ꢂ
Ministerio de Ciencia y Tecnologıa, BQU2000/0791
project.
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