A Bis-Polydentate Oxamate-Based Achiral Ligand That Can Stabilize a Macrocyclic Mixed Valence Compound or Induce a 1D Helical Chain

Article abstract of DOI:10.1002/ejic.202000490

The reaction of the N-(2-hydroxyphenyl)oxamate ligand (ohpma) has been investigated with cobalt(II) and copper(II) ions. It has led to two coordination compounds, (TMA)₃[{Co^III(ohpma)₂Co^II(MeOH)₂}

Full text of DOI:10.1002/ejic.202000490

European Journal of Inorganic Chemistry
Accepted Article
Title: A bis-polydentate oxamate-based achiral ligand able to stabilize
a macrocyclic mixed valence compound or induce a 1D helical
chain
Authors: Ang Li, Yanling Li, Lise-Marie Chamoreau, Christophe
Desmarets, laurent lisnard, and Yves Journaux
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202000490
Link to VoR: https://doi.org/10.1002/ejic.202000490
01/2020

10.1002/ejic.202000490
European Journal of Inorganic Chemistry
FULL PAPER
A bis-polydentate oxamate-based achiral ligand able to stabilize a
macrocyclic mixed valence compound or induce a 1D helical
chain
Ang Li,[a] Yanling Li,[a] Lise-Marie Chamoreau,[a] Christophe Desmarets,[a] Laurent Lisnard,*[a] and Yves
Journaux*[a]
Abstract: The reaction of the N-(2-hydroxyphenyl)oxamate ligand
prepared and used to coordinate metal ions.[17–26] Nevertheless,
their study has either been focused on the metalloligand
formation or been limited by deprotonation issues, preventing
the “full” coordination of such multi-polydentate ligands. So far,
only two ligands have been observed to display a coordination
mode where all donor atoms participate at least in one
coordination bond: the 2-(oxamato)benzoic acid and the
2,6-pyridinebis(oxamic acid).[18,23]
(ohpma) has been investigated with cobalt(II) and copper(II) ions. It
has
led
to
two
coordination
compounds,
(1) and
(TMA)3[{CoIII(ohpma)2CoII(MeOH)2}3]·10H2O·5MeOH
(HNEt3)[Cu(ohpma)] (2). Both compounds have been characterized
by single-crystal X-ray diffraction and magnetometry. The X-ray
diffraction studies have revealed atypical structures that are not
commonly observed in oxamate coordination chemistry with
a
macrocyclic arrangement for the mixed-valence cobalt-based
complex 1, and a helical chiral chain for compound 2. In the latter,
the bis-polydentate nature of the (ohpma)3- ligand with distinct
tridentate and bidentate coordination sites creates a chirogenic
center on the copper ion. The investigation of the magnetic
properties shows for complex 1 a single-molecule magnet behavior
detectable under static field, while antiferromagnetic interactions
dominate the behavior of 2.
Seeking to explore the reactivity of these multi-polydentate
oxamate-based ligands, we have been investigating the ethyl
N-(2-hydroxyphenyl)oxamate ligand (H2Et-ohpma, Figure 1) and
we present here two coordination compounds obtained by its
reaction with Co(II) or Cu(II) ions: the macrocyclic complex
(TMA)3[{CoIII(ohpma)2CoII(MeOH)2}3]·10H2O·5MeOH (1) and the
chiral one-dimensional polymer (HNEt3)[Cu(ohpma)] (2). The
compounds have been obtained in non-aqueous media starting
from the ester oxamate ligand or its acid, and while a chloride
salt of the copper(II) ions was used to prepare 2, a carboxylate
cobalt(II) starting materials was necessary to isolate complex 1.
Both compounds display uncommon structural types for
oxamate-based systems. The characterization of the magnetic
properties also revealed that 1 behaves as a single-molecule
magnet.
Introduction
Oxamate ligands have largely proven their efficiency for the
design of metalloligands and the rational multi-step preparation
of attractive molecular materials, from sensors, sieves and
chemical nanoreactors to magnets and spintronic candidates.[1–6]
This is undoubtedly related to their chemical flexibility and the
wide range of organic substrates that can yield oxamate ligands.
Considerable work has been devoted so far to phenyl-based
oxamate ligands, and more recently, amino acid-based oxamate
ligands have also shown strong appeal.[7–13] In the case of
phenyl derivatives, the role of alkyl substituents and their steric
hindrance has also been probed to investigate the effect on the
magnetic interactions and on the dimensionality of the
compounds.[14–16] The introduction on the phenyl ring of
additional coordinating groups to afford multi-polydentate ligands
is, however, less investigated. Some phenyloxamate-based
ligands bearing additional carboxylato or hydroxo groups, or else
pyridine-based oxamate ligands, have been successfully
OH
O
O
NH
O
Figure 1. Representation of the H2Et-ohpma ligand.
Results and Discussion
Crystal structures. Complex 1 crystalizes in the monoclinic
P21/c space group and consists of an anionic hexametallic
mixed-valence {CoIII3CoII } macrocyclic ring-like complex (Figure
3
[a]
Dr. A. Li, Dr. Y. Li, L.-M. Chamoreau, Dr. C. Desmarets, Dr. L.
Lisnard, Dr. Y. Journaux
2). In the ring, three CoII ions are bridged by three bis-bidentate
[CoIII(ohpma)2]3- complexes. In the [CoIII(ohpma)2]3- complex, the
CoIII ion is coordinated to two (ohpma)3- ligands, via their
tridentate sides involving the nitrogen and oxygen atoms of the
oxamato groups, and the oxygen atoms of the phenolato group.
The CoIII ion is thus six-coordinate in an octahedral geometry.
Sorbonne Université, CNRS, Institut Parisien de Chimie Moléculaire,
IPCM, F-75252, Paris, France
E-mail: laurent.lisnard@sorbonne-universite.fr
Homepage: www.ipcm.fr
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/ejic.202000490
European Journal of Inorganic Chemistry
FULL PAPER
CoIII-N/O bond lengths vary from 1.870(6) to 1.967(4) Å (av.
1.907 Å). Angles in the octahedral geometry around the metal
center vary from 83 to 98° (average deviation from orthogonality
of 4°) and the O-Co-O angles indicative of the ligands’ constraint
vary from 169 to 171°. The CoII ions are six-coordinate in
distorted octahedral environments (two of the CoII atoms are
disordered, see experimental section). Each ion is coordinated
to two [CoIII(ohpma)2]3- complexes via their remaining carbonyl
oxygen atoms, and to two methanol solvent molecules. CoII-O
distances vary from 2.041(6) to 2.181(5) Å (av. 2.095 Å), and the
O-Co-O angles from 80 to 100° (av. deviation to orthogonality of
5°). BVS calculations support the presence as well as the
localisation within the ring of both CoII and CoIII ions (see
supporting information). The oxidation of the cobalt ions must
result from the coordination by the (ohpma)3- ligand in basic
medium and in air.
oxidation states.[29–32] As this Co(III) complex will be inert, its
formation should constitute the first step in the building of the
hexagonal ring. It places the two uncoordinated bidentate parts
of the two oxamato ligands at 120° from each other. This
arrangement makes the formation of hexagonal cycles or zigzag
chains highly probable when [CoIII(ohpma)2]3 complexes
coordinate with Co(II) ions.
Compound 2 consists of an anionic oxamato-bridged CuII helical
chain with triethylammonium counter-cations. It crystallizes in
the trigonal P32 chiral space group. In the chain, the CuII ion is
five-coordinate and adopts a square-based pyramid geometry.
The base is defined by one nitrogen and two oxygen atoms
coming from the phenolato and oxamato groups of the ligand
(N1, O1, O4), and one oxygen atom (O3) from a second
oxamate function belonging to bidentate side of an adjacent
ligand. The latter has its remaining carbonyl oxygen atom (O2)
occupying the apical position of the CuII complex (Figure 3). The
bond lengths around the copper atom (in Å: Cu-N1 = 1.914(2),
Cu-O3 = 1.965(2), Cu-O4 = 1.969(1), Cu1-O1 = 1.983(1), Cu1-
O2 = 2.243(1)) are rather short looking at the Cu-N(amide) and
Cu-O(carboxylate) bonds formed with the oxamato group. It
resembles that of more constrained oxamate-based complexes,
such as those obtained with bis-oxamate ligand (from 1.887 Å to
1.931 Å),[33–38] in opposition to bis(mono-oxamate) CuII
complexes.[39–41] The O1-Cu-O4 angle from the phenolate to the
oxamate group is a good indicator of the constraint coming from
the tridentate side of the ligand, with a value here of 162°.
Figure 2. Structure representation of 1. Solvent molecules, TMA+ cations and
H atoms have been omitted for clarity.
Figure 3. Structure representation of 2 with atom labels. HNEt3+ cations and H
atoms have been omitted for clarity.
In the solid, the TMA+ cations are located between the rings, and
relatively strong H-bonds (O···O < 2.6 Å) between coordinated
methanol molecules and oxygen atoms from the phenolato
groups generate chains of macrocycles along the
crystallographic b axis (Figure S1 in the supporting information).
The shortest intermolecular metal-metal distance is actually
situated along the H-bond between CoII and CoIII ions, and is of
5.73 Å. Considering paramagnetic ions, the shortest
intermolecular distance is also found between two adjacent rings
in the chain, and it is equal to 6.76 Å.
Complex
coordination ring. The other two examples being
hexametallic wheel, which is based on an amino-acid-based
oxamate ligand,[27] and decametallic {MnII CuII } wheel
1
is only the third example of oxamate-based
a
CuII
a
5
5
obtained from a bis-oxamate ligand.[28] If the hexagonal ring
structure was unexpected, it seems, in hindsight, a logical
outcome. From a thermodynamic point of view, an octahedral
cobalt complex with two tridentate ligands should be more stable
and form preferentially. The presence of two deprotonated
amide functions in the coordination sphere of the cobalt ion also
makes this complex easier to oxidize. It is well established that
deprotonated amide function stabilize metal ions in high
Figure 4. Representation of the helices in the packing of 2, through the
intrachain Cu—Cu bonds (orange). HNEt3 cations and H atoms have been
omitted for clarity.
+
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10.1002/ejic.202000490
European Journal of Inorganic Chemistry
FULL PAPER
Interestingly, this 1D chain has a helical configuration (Figure 4),
which is rarely observed in oxamate chemistry.[42,43] The two
other examples of helical chains have been observed both with
copper ions, and with an amino-acid-based oxamate ligand,
helical structure and pitch of the helix are then induced by
interchain interactions. These are difficult to control and it is
almost impossible to predict whether a helical structure will be
obtained. It is worthy of note that the (ohpma)3- ligand is not
atropisomeric, and that the existence of a helical structure
cannot come from the ligand. In fact, it is the bis-polydentate
nature of the (ohpma)3- ligand associated to the 4+1
coordination of the copper ions that induce the helicity in
compound 2. The bis-polydentate (ohpma)3- ligand acts as a
tridentate ligand on one side and as a bidentate ligand on the
other. The base of the square pyramidal coordination of the
Cu(II) ions in 2 is determined by the tridendate side of the
(ohpma)3- ligand with the remaining corner being occupied by
one oxygen atom from the bidentate side of an adjacent
(ohpma)3- ligand. This means that the oxamate group of the
tridentate part of the ligand occupies one edge of the square
(R)-N-(ethyloxoacetate)phenylglycine,
or
the
2-dimethylaminoethyl(oxamate) ligand. Indeed, these ligands
have very similar tridentate coordination modes with donor
atoms on the β-carbon of the N-substituted oxamato group.
Compound 2 grows parallel to the crystallographic c axis and the
chains are rather well separated from each other (Figure 4, and
Figures S2-S3 in the supporting information). The helical
configuration along with the peripheral phenyl groups from the
ligands and the bulky triethylammonium cations afford an
effective spacing between the metal ions of neighboring chains.
The shortest interchain Cu···Cu distance is 9.66 Å.
This 1D chain adopts a left-handed configuration. None of the
tested crystals crystallize in the enantiomorphic P31 space group. base while the two oxygen atoms of the bidentate part of the
The solid state circular dichroism (CD) and absorption spectra of
2 are shown in Figure 5. The CD spectrum of 2 exhibits a pair of
weak positive peaks at 280 nm and 314 nm, and a negative
Cotton effect around 280 (strong), 386 (strong) and 775 nm
(weak). The investigation of several batches of compound 2 with
CD measurements in the solid state indicates that the left-
handed helicity is the only configuration we observe, while the
synthesis solution gives no dichroic signal (see supporting
information, Figures S4-S6).
neighboring oxamate ligand occupy one edge on the opposite
triangular face of the pyramid (Figure 6). For a pyramid whose
height is equal to one half of the square diagonal, there is a 120°
angle between the two directions described by these edges. As
the copper-copper directions are perpendicular to these edges,
this configuration determines the 120° angle formed by three
successive copper ions (Figure 6).
3
2
1
0
Figure 6. Representation of the 4+1 coordination sphere of the copper ions,
with the 120° “right edge” (see text) linking between successive copper ions
(blue copper ions, red oxygen atoms, light blue nitrogen atom). The
polyhedron edges in red symbolize the position of the oxamate groups in the
coordination sphere.
400
600
800
Wavelength (nm)
10
0
In fact, the asymmetric nature of the chelation in this ligand,
tridentate on one side and bidentate on the other, creates a
chirogenic center on the Cu(II) ion with no inversion center or
mirror. In 2, the connection between adjacent copper ions is
always made via the right edge of the triangular face that sits
opposite the oxamate group lying in the square base of a
complex. This confers a SPY-5-14(A) absolute configuration for
the Cu ions,[46] and the chaining results in a left-handed helicity.
The angle of 120° determines a pitch of three for the helical
structure (the c axis value). A chaining through the left edge of
the pyramid triangular face would lead to a right-handed helical
structure and to the P31 space group. The other possible and
simple arrangement would be a regular alternation of “left edge”
(SPY-5-14(C) configuration) and “right edge” (SPY-5-14(A)
configuration) connectivities in the pyramid triangular face,
resulting in a cyclic hexagonal structure (Figure S7 in the
supporting information). Less simple sequences of connections
would lead to other types of structures that are more difficult to
anticipate.
-10
-20
-30
-40
-50
400
600
800
Wavelength (nm)
Figure 5. UV-Vis and CD spectra of compound 2 in the solid state (pellet;
0.25 % in KBr).
Spontaneous resolution is not a frequent phenomenon.[44] It is
even less common when the reactants are achiral. For
coordination polymers, the helical structure is generally obtained
with flexible or atropisomeric ligands able to induce a pitch angle
due to ligand torsion or the rotation around a C-C bond.[45] The
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10.1002/ejic.202000490
European Journal of Inorganic Chemistry
FULL PAPER
Compound 2 is not the first example of a helical chain with
magnetic ions obtained from non-chiral reactants. The most
emblematic examples are the metal nitronyl nitroxyde chains
which include the first reported single-chain magnet.[47–49]
However, the use of copper ions and substituted oxamate
ligands that offer a tridentate side at either end of the oxamate
bridge seems to make the preparation of helical chains almost
controllable. As explained above, the number of likely structures
is reduced, with the most probable ones being the hexagonal
macrocycle and the helical chain. This is well illustrated by the
work of Pardo et al. with oxamate ligands that are substituted
with chiral amino acid.[27,43]. With R or S-valine substituted
oxamate ligands, they have obtained hexametallic copper(II)
wheels where the copper ions alternate the left edge (SPY-5-
12(C) configuration) and right edge (SPY-5-12(A) configuration)
connectivities on the pyramid triangular face.[27] Whereas the
use of the D-phenyl-glycine substituted oxamate ligand yields a
right-handed helical chain crystallizing in the P31 space group. In
this structure, it is always the left edge of the pyramid’s
triangular face that links neighboring copper ions (SPY-5-12(C)
configuration).[43] The structure of compound 2 and the results
non stoichiometric hydrated cobalt hydroxide impurity which is
commonly seen around 10−15 K in CoII complexes when
performing low field measurements (Figure 7).[55]
Figure 7. Temperature dependence of cMT for 1 under an applied magnetic
field of 500 Oe from 3 to 200K. The solid black line is the best obtained fit.
The interaction between the CoII ions through the diamagnetic
CoIII metalloligands within the ring is expected to be very small
and the magnetic data can be modeled as three isolated CoII
ions using the following Hamiltonian and the T≡P
isomorphism:[56–58]
obtained by Pardo et al. show that the use of
a
bidentate/tridentate double-sided oxamate-based ligand and the
4+1 coordination of Cu(II) ions can induce helical or cyclic
structure. This is supported by the early work of Kachi-Terajima
et al. They have obtained with the achiral 2-
dimethylaminoethyl(oxamato) ligand and Cu(II) ions a left-
handed helical chain. As in compound 2, the chain forms
through the right edge connectivity of the pyramid’s triangular
face, leading to an absolute SPY-5-13(C) configuration.[42]
However, it is puzzling that all the tested crystals give the same
left-handed helicity whereas, with an achiral ligand in a case of
spontaneous resolution, a conglomerate with the same amount
of crystals of both enantiomers is expected. Kachi-Terajima et al.
describe the same phenomenon with equally no satisfactory
explanation.[42] This enantiomeric excess has also been
observed by other authors in the case of spontaneous
resolution.[50] It has been shown that an enantiomeric excess
can be induced by various means such as agitation[51] or a
competitive reaction.[52] Similarly, it can be suppressed in some
cases by sonication of the reagents.[50] A possible explanation
for compound 2 could be the existence of a very fast equilibrium
in solution between the two enantiomers which favors the
crystallization of an enantiomer as soon as it starts to
crystallize.[53] In this case, however, the enantiomer obtained
should vary from one crystallization to the other and this is not
what we observe. At this stage, we thus lack a satisfactory
explanation for obtaining only the left-handed helicity.
3
(
*
)
+
-
,
"
%
2
"
%
3
2
1
3
3α
2
zCoi
Η υ
=
−
αλLCo SCo + Δ L
−
LCo + −
LυCo + geSυCo β.H
'
i i
$
'
$
∑
i
i
i
2
#
&
#
&
i=1
with υ = x, y, z
λ
is the spin-orbit coupling constant, α the orbital reduction
factor and Δ the axial distortion parameter. L and S are
respectively the orbital and spin operators with L = 1 in the T-P
isomorphism approach and S = 3/2. The least square fit of the
magnetic data in the 200-13 K temperature range gave λ = -132
cm-1, α = 0.84, Δ = -378 cm-1, with an agreement factor F =
2.6*10-5 calculated as follows:
2
"
#
%
χ T
− χ T
∑
(
)
(
)
$
M
M
'
&
calc.
exp
F =
2
"
%
&
χ T
∑
(
)
$
M
'
#
exp
The dynamic properties of 1 were explored by alternating-
current measurements (AC). At zero DC magnetic field, there
were neither frequency-dependent χM′ nor χM″ signals observed
and it may come from the fast quantum tunneling effect reported
in other single-ion or single-molecule magnets (SIMs and
SMMs).[59,60] However, when DC magnetic field is applied, both
the χM′ and χM″ gave strong frequency dependent signals typical
of SMMs. The measurements shown in Figure 8 were performed
under a 1800 Oe DC field that was determined to maximize
relaxation time. Nevertheless, the blocking temperature is quite
low and the maxima of χM′ and χM″ are only visible at high
frequency.
The magnetic properties of complex 1 were studied under a field
of 500 Oe and in a 3-200 K temperature range, shown by the
χMT versus T plot in Figure 7. At 200 K, the χMT value is 9.71
cm3 mol−1 K and it sits in the expected range for three isolated
CoII ions (2.7 < χMT < 3.4 cm3mol−1K for one Co(II),[54] so 8.1 <
χMT < 10.2). Upon cooling, χMT steadily decreases to reach a
value of 5.64 cm3 mol−1 K at 13 K. The product then goes up
before finally decreasing to 5.18 cm3 mol−1 K at 3 K. Down to 13
K, this behavior is typical of Co(II) ions in octahedral
4
To extract the relaxation times, the generalized Debye model,
which considers a distribution of relaxation times, has been
used.[61]
environment with a T1g ground state and first order spin-orbit
coupling. The bump of χMT curve around 12 K is caused by the
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10.1002/ejic.202000490
European Journal of Inorganic Chemistry
FULL PAPER
The values of τ, η, χadia and χiso at the studied temperatures are
given in Table S2 in the supporting information. The small η
values (η = 0.07−0.13), with respect to that expected for a
Debye model (η = 0), indicate a small dispersion of relaxation
times.[63]
2.0
1.5
1.0
χ
0.5
0.8
0.6
0.0
2
4
6
8
10
T(K)
0.4
″
Frequency
279 Hz
0.8
0.6
0.4
0.2
0.0
1882 Hz
2389 Hz
3032 Hz
3850 Hz
4887 Hz
6205 Hz
7877 Hz
10000 Hz
0.2
χ
354 Hz
449 Hz
571 Hz
724 Hz
920 Hz
1167 Hz
1482 Hz
0.0
101
102
103
104
ν(Hz
)
5.0 K
3.5 K
4.8 K
3.3 K
4.5 K
3.0 K
4.3 K
4.0 K
3.8 K
○
●
▼
▽
△
◇
□
■
2.8 K
2.5 K
●
▲
◆
1.0
2
4
6
8
10
T(K)
0.8
0.6
0.4
0.2
0.0
Figure 8. Temperature dependence of χM’ (a) and χM’’ (b) in 1 under an
applied DC field of 1800 Oe and in the 10−10000Hz frequency range. The
solid lines are only eye-guides.
″
χ
The frequency dependence of χM″ and Cole-Cole plot of 1 are
shown in Figure 9. As suggested by Dekker et al.,[62] two steps
procedures were used to extract the relaxation time τ at each
temperature. First a fit to the locus of χ in the Cole-Cole plot was
performed to extract the values of χadia, χiso and η, using the
following equation, independent of τ and of the frequency:
0.5
1.0
1.5
cm3.mol-1
2.0
2.5
′
χM
(
)
Figure 9. (top) Out-of-phase component, χM″, of the magnetic susceptibility of
1 under a 1.8 kOe magnetic field and for frequencies comprised between 10
Hz and 10 kHz. (bottom) Cole–Cole plot of 1 measured from 2.5 to 5 K under
1.8 kOe. The solid lines are the least-squares fitting of the data using a
generalized Debye model.
!
#
#
"
$
&
&
%
!
#
"
$
2
2
$
!
1
πη
χ,,
=
2
cos2
−cos πη
(
χ
adia + χiso − 2χ, + 4χ,
χ
adia + χiso −6χadia χiso + χa2dia + χi2so − 4 χ, + sin πη
χ
adia − χiso
&#
&
)
(
)
(
)(
)
(
)
(
)
!
$
"
%
%
2
πη
4cos2
#
&
The spin relaxation can occur by several mechanisms,[64,65]
namely quantum tunneling, direct, Raman and Orbach
processes. The thermal and magnetic field variation of these
mechanisms are given in the following equation:
2
"
%
where χadia and χiso stand for adiabatic and isothermal
susceptibilities respectively and η characterizes the spreading of
the relaxation time.
In a second step τ is obtained by the fit of χ' and χ’’ using the
values of χadia, χiso and η determined in the first step:
"
$
#
%
'
&
B
−Ueff
τ −1 = AH4T +
+CTn +τ0−1 exp
1
1+ B2T
kT
"
%
'
&
"
$
#
%
'
&
2π 1−η sin
υτ 1−η +1
πη
χ
iso − χ
$
(
adia ) (
)
(
)
2
#
χ, =
where n is the Raman exponent, τ0 is the pre-exponential factor
and Ueff is the effective energy barrier to reverse the
"
%
'
&
2−2η
υτ 2−2η + 22−η π1−η sin
υτ 1−η +1
πη
2π
$
(
)
(
)
(
)
2
#
magnetization.[65] For Kramer's doublet the theoretical
n
exponent is equal to 9,[66] and the direct process varies with the
power 4 of the magnetic field.[64,66]
!
#
"
$
1−η
πη
2
χ
iso − χ
2π 1−η cos
υτ
&
(
adia )(
)
(
)
%
χ,, =
!
$
&
%
2−2η
2π
υτ 2−2η + 22−η π1−η sin
υτ 1−η +1
πη
#
(
)
(
)
(
)
2
"
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10.1002/ejic.202000490
European Journal of Inorganic Chemistry
FULL PAPER
caution because only the Orbach relaxation mechanism has
been taken into account.
150
100
50
The magnetic properties of 2 were investigated in the 2 – 300 K
temperature range. Two applied field, 1000 Oe and 1 T, were
used at low and high temperature, respectively. Its χM versus T
plot is shown in Figure 11. At room temperature, χMT is equal to
0.376 cm3 mol−1 K, a smaller value than the calculated one for
II
an isolated CuII ion (SCu = ½, χMT = 0.413 cm3 mol−1 K with gCu
0
=
2.1 (inset Figure 11)). This value is typical of an
2
3
4
5
antiferromagnetic behavior arising from an antiferromagnetic
interaction between two adjacent Cu(II) ions through the
oxamato bridge. A broad maximum of χM is observed at 70 K,
followed by a minimum and a sharp increase at low temperature.
This last feature is due to a small amount of a Cu(II) uncoupled
impurity.
T(K)
-10
-11
-12
0.004
0.4
0.3
0.2
0.003
0.1
0.0
χ
0
100
200
250
300
0.2
0.3
T-1(K-1
0.4
T(K)
0.002
0.001
χ
)
Figure 10. (top) Relaxation Time 1/τ v. T for complex 1; (bottom) Log(τ) v. 1/T
for compound 1. The solid black lines are the best fitting curves.
0
50
100
150
200
300
T/K
Obviously, the determination of 6 parameters with a single data
set is extremely delicate and almost meaningless due to over-
parameterization. In favorable cases, it is possible to determine
the three parameters for magnetic field-dependent relaxation
mechanisms at low temperatures by measuring the relaxation
time as a function of the magnetic field. For this to happen, the
Raman and Orbach mechanisms must be negligible at these
temperatures. This is the case for the Raman mechanism, which
varies according to the power of 9 of the temperature, but for the
Orbach one, the energy barrier must be large to fulfill this
condition. In the case of 1, these favorable conditions are not
met due to the low blocking temperature, which implies a
probable small energy barrier. The determination of the
parameters by modeling the 1/τ curve as a function of the
temperature is therefore rather unreliable. Nevertheless,
considering that the Log(τ) curve as a function of 1/T is almost
linear (Figure 10), we have assumed that the Orbach
mechanism is dominant and the equation we have used to fit the
data is:
Figure 11. Experimental and best fitting curve of χM vs. T for 2 under an
applied magnetic field of 1 T (T≥ 40 K) and 1000 Oe (T ＜40 K). Inset shows
the temperature dependence of χMT for 2. The solid black lines are the best
obtained fit.
To model the magnetic data of 2, the Bonner Fisher's empirical
law for a S = 1/2 1D regular chain has been used,[67] to which we
have added
a TIP contribution (temperature independent
paramagnetism) of 60*10-6 cm3 mol-1 per CuII ion. Furthermore, to
take into account the small amount of impurity a Curie law term
was added:
2
2
Ng2β2
0.25 +0.074975x +0.075235x2
1.0 +0.9931x +0.172135x2 +0.757825x3
Ng β
!
#
"
$
&
%
χM
=
1− ρ +
ρ +TIP
(
)
kT
4kT
with:
J
x =
kT
"
%
'
&
Ueff
kT
τ −1 = τ0−1 exp −
N being Avogadro’s number, β being the electronic Bohr
magneton, k is the Boltzmann constant, J is magnetic coupling
constant and g is the gyromagnetic Lande factor. ρ is the mass
proportion of uncoupled impurity. The best fit parameters
obtained are J = -84.1 cm-1, g = 2.176, ρ = 0.0033 (Figure 11),
with F = 9.14 × 10-8.
$
#
The best fit parameters are Ueff = 8.5 cm-1 and τ0 = 4.6*10-7
(Figure 10), with F = 2.5 × 10-3. The deviation from linearity at
low temperature for the experimental points in the curve of
Log(τ) versus 1/T probably comes from the effect of relaxation
mechanisms not considered in the modeling (Figure 10 bottom).
The Ueff and τ0 values are in the expected range for SMM
compounds. However, these values should be taken with
In comparison to other oxamate-bridged CuII homometallic
compounds, the result shows
a weaker antiferromagnetic
interaction in 2.[68,69] This is due to the particular coordination of
the copper ion inside this chain which presents the so-called
orbital reversal phenomenon.[70–72] Because of the helical
This article is protected by copyright. All rights reserved.

10.1002/ejic.202000490
European Journal of Inorganic Chemistry
FULL PAPER
N-(2-hydoxyphenyl)oxamic acid hydrate, mixed sodium salt
(H2.5Na0.5-ohpma·0.5H2O). To 6.25 g of H2Et-ohpma (M = 209.2 gmol-1;
29.9 mmol) suspended in 400 mL of water were slowly added 45 mL of
2M NaOH (3eq.). The solution was stirred for 30 min and filtered on
paper. Under stirring, 23 mL of 4M HCl (3eq.) were added dropwise to
the filtrate and stirring was maintained for 1 hr in an ice bath. The
precipitate that formed was collected on a sintered glass filter. Further
washing was done with cold 96% ethanol and the resulting white solid
was dried with ether and then in air. (Yield: 5.66 g, 94% based on H2Et-
ohpma; M=201.1 gmol-1). 1H-NMR (400 MHz, DMSO) δ (ppm): 10.36 (s,
1H), 9.81 (s, 1H), 8.09 (d, J = 7.9 Hz, 1H), 6.87 (m, 2H), 6.80 (t, J = 7.7
Hz, 1H). 13C-NMR (101 MHz, DMSO) δ (ppm): 162.18 (s, -COO-),
158.86 (s, -CONH-), 146.72 (s, Ph), 125.61 (s, Ph), 124.48 (s, Ph),
119.32 (s, Ph), 119.04 (s,Ph), 114.88 (s, Ph). FTIR (cm-1): 3488 (w),
3381 (w), 3076 (s), 1771 (m), 1676 (s), 1612 (m), 1594 (w), 1540 (s),
1469 (s), 1357 (m), 1278 (m), 1192 (w), 1103 (w), 930 (w), 805 (m), 749
(s), 692 (m), 599 (m), 504 (s), 452 (m), 317 (m). Elemental analysis (%):
calc. for C8H7.5NNa0.5O4.5. C, 47.77; H, 3.76; N, 6.96. Found: C, 47.94; H,
3.68; N, 6.95.
structure and the 4+1 copper(II) coordination, the Cu-O2 bond
length is the largest. This means that the delocalized spin
density onto the O2 oxygen atom is very weak. In fact, the high
spin densities are localized on the O1, O3, O4 and N1 atoms, to
where the dx2-y2 orbital containing the single electron of the CuII
ion points. As such, when compared to the systems where the
magnetic dx2-y2 orbitals of neighboring copper ions share the
same plane with the oxamato bridge, the interaction through the
oxamate bridge is much weaker here. It only occurs on the
amide function side. This considerably reduces the overlap
between the magnetic orbitals of the neighboring magnetic
centers. The interaction being approximately proportional to the
square of the overlap between magnetic orbitals,[73] a lower
overlap results in a lower interaction, as observed in compound
2. In the helical copper chain obtained with the 2-
dimethylaminoethyl(oxamato) ligand, the interaction is equal
to -74.1 cm-1,[42] close to the value determined for 2.
[Co2(H2O)(O2CCMe3)4(HO2CCMe3)4], {Co2piv}, was prepared according
to the literature procedure.[76] Elemental analysis (%) calculated for
C40H78Co2O17 (Mr=948.9 g mol-1): C 50.63, H 8.29. Found: C 50.46, H
8.25.
Conclusions
The use of the heterotopic hydroxyphenyloxamic ligand in non-
aqueous media has led to the formation of two homometallic
compounds, a mixed-valence cobalt-based macrocycle and a
copper-based chiral 1D polymer. The atypical structures we
have obtained with this type of bis-polydentate ligands open up
new prospects. An a posteriori analysis of the structures of the
two compounds shows that they are not as serendipitous as we
originally thought. We will use these findings to investigate both
the nature of the additional coordinating group and its position
on the phenyloxamate platform.
(TMA)3[{CoIII(ohpma)2CoII(MeOH)2}3]·10H2O·5MeOH (1). To a 15 mL
MeOH solution of H2.5Na0.5-ohpma·0.5(H2O) (0.100 g, 0.5 mmol) was
added 690 µL of TMAOH (tetramethylammonium hydroxide 25% w/w in
MeOH, 1.5 mmol) and the resulting solution was stirred for 15 min.
{Co2Piv} (0.474 g, 0.5 mmol, M=948.9 gmol-1, 1eq.) was then added
directly into the solution. The solid {Co2Piv} dissolved immediately with
the apparition of a light precipitate that quickly disappears; giving a red-
brown solution. Stirring was maintained for 2 h and the solution was
filtered and left to crystallize by slow evaporation at room temperature.
Dark
brown
block
crystals
of
(TMA)3[{CoIII(ohpma)2CoII(MeOH)2}3]·10H2O·5MeOH (1) were obtained
overnight (Yield: 0.100 g, 58% based on the ligand; M=2071.1 gmol-1).
Elemental analysis (%): calc. for C63H100Co6N10O45: C, 36.53; H, 4.87; N,
6.76. Found: C, 36.37; H, 4.81; N, 6.54. Selected IR data (cm–1):
3185(sh), 2929(w), 1602(m), 1465(m), 1421 (w), 1338(m), 1301(w),
1273(s), 1241(m), 1151(w), 1105(w), 1025(w), 962(m), 950(w), 892(m),
844(s), 745(m), 645(w), 607(m), 451(w), 403(m), 329(m), 235(w).
Experimental Section
All reagents were used as purchased with no further purification. The
ester form of the ligand, ethyl N-(2-hydroxyphenyl)oxamate, was
prepared according the general procedure for oxamate ligand,[74] which
differs from the previously reported synthesis.[75]
(HNEt3)[Cu(ohpma)] (2). To a 15 mL acetonitrile solution of H2Etohpma
(0.104 g, 0.5 mmol) was added 210 µL of NEt3 (1.5 mmol). A 5 mL
aqueous solution of CuCl2.2H2O (0.084 g, 0.5 mmol) was then added
dropwise. The resulting green solution was kept under stirring for 2 h and
then filtered. Green block crystals of (HNEt3)[Cu(ohpma)] (2) were
obtained after two days by slow evaporation of the solution and washed
with acetonitrile (Yield: 0.134 g, 78% based on the ligand; M=343.8 gmol-
1). Elemental analysis (%): calc. for C14H20CuN2O4: C, 48.90; H, 5.86; N,
8.15. Found: C, 48.37; H, 5.75; N, 7.90. Selected IR data (cm–1): 2992(w),
1647(m), 1605(s), 1576(m), 1465(s), 1405(m), 1326(m), 1305(m),
1290(m), 1265(s), 1240(s), 1182(m), 1148(m), 1103(w), 1026(w), 878(s),
780(s), 594(m), 557(m), 493(w), 456(w), 336(m).
Ligands
preparation.
Ethyl
N-(2-hydroxyphenyl)oxamate
(H2Etohpma). To 5.00 g of 2-aminophenol (M=109.1 gmol-1, 45.8 mmol)
in 150 mL of THF were added dropwise 5.2 mL of ethyloxalyl chloride
(98%; 1eq.) under strong stirring. The mixture was refluxed for 90 min.
The resulting dark red solution was left to cool down and filtered on paper.
Removal of the solvent under reduced pressure yielded a grey powder.
The powder was washed with 400 mL of H2O under stirring for 30 min
and then collected on a sintered glass filter. Further washing was
performed rapidly with cold 96% ethanol and the solid was dried with
ether and then in air. The final product was collected as a white powder
(Yield: 6.36 g, 66% based on the 2-aminophenol; M=209.2 gmol-1). 1H-
NMR (300 MHz, DMSO) δ (ppm): 10.19 (s, 1H), 9.60 (s, 1H), 7.94 (d, J =
8.0 Hz, 1H), 7.02 (t, J = 7.4 Hz, 1H), 6.92 (d, J = 8.1 Hz, 1H), 6.83 (d, J =
7.7 Hz, 1H), 4.29 (q, J = 7.1 Hz, 2H), 1.30 (t, J = 7.1 Hz, 3H). 13C-NMR
(75 MHz, DMSO) δ (ppm): 160.97 (s, -COO-), 154.85 (s, -CONH-),
148.02 (s, Ph), 126.08 (s, Ph), 125.17 (s, Ph), 121.35 (s, Ph), 119.65 (s,
Ph), 115.29 (s, Ph), 63.09 (s, -CH2-), 14.29 (s, -CH3). FTIR (cm-1): 3361
(m), 3241 (m), 1723 (m), 1682 (s), 1595 (s), 1540 (s), 1507 (m), 1462 (s),
1397 (s), 1369 (m), 1347 (m), 1326 (m), 1266 (s), 1227 (m), 1188 (m),
1103 (m), 1022 (m), 947 (m), 877 (s), 834 (s), 743 (m), 703 (m), 652 (m),
571 (m), 453 (m), 350 (s). Elemental analysis (%): calc. for C10H11NO4. C,
57.41; H, 5.30; N, 6.70. Found: C, 57.12; H, 5.26; N, 6.71.
Magnetic measurements. Magnetic measurements in dc mode were
performed on polycrystalline samples of 1 and 2 restrained within a
capsule with a Quantum Design MPMS SQUID. Magnetic susceptibility
data were corrected for the diamagnetism of the constituent atoms using
the Pascal’s constants. The diamagnetism of the sample holder was
measured and subtracted from the raw data.
Elemental analysis were performed in the “service de microanalyse” at
ICSN (CNRS, Gif/Yvette).
This article is protected by copyright. All rights reserved.

10.1002/ejic.202000490
European Journal of Inorganic Chemistry
FULL PAPER
FT-IR, TGA, NMR. ATR/FT-IR spectra were collected on a Bruker
TENSOR 27 equipped with a simple reflexion ATR diamond plate of the
Harrick MPV2 series. The thermogravimetric analysis (TGA) was
performed on a TA Instruments SDTQ600 under air or nitrogen with a
heating rate of 5 °C/min. 1H and 13C NMR spectra were collected on 300
and 400 MHz Bruker Avance spectrometers at 298 K.
Armentano, Y. Journaux, F. Lloret, M. Julve, Coord. Chem. Rev. 2015,
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F. R. Fortea-Pérez, M. Mon, J. Ferrando-Soria, M. Boronat, A. Leyva-
Pérez, A. Corma, J. M. Herrera, D. Osadchii, J. Gascon, D. Armentano,
E. Pardo, Nat. Mater. 2017, 16, 760–766.
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CD, UV-Vis spectra. Circular dichroism spectra were collected on a
JASCO J-815 spectropolarimeter at room temperature, in the solid state
using KBr pellets or in solution (MeCN:H2O). UV-Vis spectra were
collected on a Agilent Cary-5000 spectrometer, at room temperature, in
the solid state using KBr pellets or in solution (MeCN:H2O).
[6]
[7]
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M. Viciano-Chumillas, M. Mon, J. Ferrando-Soria, A. Corma, A. Leyva-
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Crystallography. Crystal data for 1 (C74H118.50Co6N9O39): dark blocks,
monoclinic, P21/c, a = 9.9479(3) Å, b = 28.8849(10) Å, c = 32.8203(10) Å,
β = 97.123(2), V = 9357.9(5) Å3, Z = 4, T = 200(2) K, ρ = 1.502 g cm-3,
F(000) = 4406, µ = 1.130 mm-1. Crystal data for 2 (C14H20CuN2O4): green
hexagons, trigonal, P32, a = 9.6625(2) Å, c = 13.9393(4) Å, V =
1127.07(6) Å3, Z = 3, T = 200(2) K, ρ = 1.520 g cm-3, F(000) = 537, µ =
1.470 mm-1. The data collections for 1 and 2 were carried out on a Bruker
Kappa-APEX II CCD diffractometer (MoKα, λ = 0.71073 Å). Crystals
were mounted on a cryoloop using Parabar oil and placed in the cold flow
produced with an Oxford Cryosystems device. Data collection strategies
were generated with the APEX2 suite of programs (BRUKER).[77] The
refinement of the unit cell parameters and data reduction were carried
out with SAINT (BRUKER),[77] and absorptions were corrected with
SADABS.[77,78] The structures were solved with SHELXT-14[79] and
refined with the SHELXL-2014/7 program[79] (WinGX or Olex 2 software
packages[80,81]). Data refinement for 1 gave (using 1237 parameters and
14 restraint) wR2 = 0.2039 (18383 unique reflections), R1 = 0.0898 [14569
reflections with I > 2σ(I)], and GOF = 1.186. A disorder model (with a
ratio of 0.9/0.1) was introduced for the Co2 and Co6 atoms as well as
some atoms in their coordination spheres to take into account the
residual density in these regions. However, this model is only partial.
Further disorder modelling leads unfortunately to either a diverging model
or an incomplete one, since the residual density is mostly observed for
the Co atoms. Data refinement for 2 gave (using 194 parameters and 1
restraint) wR2 = 0.0527 (4906 unique reflections), R1 = 0.0198 [4748
reflections with I > 2σ(I)], GOF = 1.060, and a Flack parameter of -
0.021(3). CCDC-1985070 and 1985071 contain the supplementary
crystallographic data for this article. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/structures.
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This work was supported by the Ministère de la Recherche et de
l’Enseignement Supérieur (MRES), the Centre National de la
Recherche Scientifique (CNRS) and the China Scholarship
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European Journal of Inorganic Chemistry
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10.1002/ejic.202000490
European Journal of Inorganic Chemistry
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The reaction of a double-sided bis-
polydentate oxamate-based ligand
with transition metal ions has led to a
cobalt-based hexametallic and
macrocyclic complex and a copper-
based chiral chain compound. Both
structural types are not commonly
seen in oxamate chemistry and
result from the alternative choice of
ligand.
Oxamate chemistry
Ang Li, Yanling Li, Lise-Marie
Chamoreau, Christophe Desmarets,
Laurent Lisnard* and Yves Journaux*
Page No. – Page No.
A bis-polydentate oxamate-based
achiral ligand able to stabilize a
macrocyclic mixed valence
compound or induce a 1D helical
chain
This article is protected by copyright. All rights reserved.