Co-existence of ferro- and antiferromagnetic interactions in a hexanuclear mixed-valence Co III 2 Mn II 2 Mn IV 2 cluster sustained by a multidentate Schiff base ligand

Article abstract of DOI:10.1039/c9dt02503k

The successful utilization of the direct synthesis approach yielded the unprecedented hexanuclear complex of formula [Co₂MnII2MnIV2(L¹)₄Cl₂(μ₃-O)₂(dmf)₄]·2dmf (1) (H₃L is the Schiff base derived from the condensation of salicylaldehyde and 3-aminopropane-1,2-diol). Single crystal X-ray analysis revealed that 1 crystallizes in the monoclinic system P2₁/c and it contains a rare mixed-valence {CoIII2MnII2MnIV2(μ₂-O)₈(μ₃-O)₂} core where all metal ions are linked through the phenolato and alkoxo groups of the L^3- ligand. Besides the charge balance resulting from the X-ray structure, the oxidation state of the metal ions has been confirmed by XPS spectroscopy. Cryomagnetic studies indicate the coexistence of ferro- (Mn^IV-Mn^II, J₂ = +1.10(3) cm^-1, J₃ = +2.19(3) cm^-1; Mn^II-Mn^II, j = +0.283(3) cm^-1) and antiferromagnetic interactions (Mn^IV-Mn^IV, J₁ = -17.31(4) cm^-1), with the six-coordinate Co^III ions being diamagnetic. DFT type calculations were carried out to substantiate these values. The energy diagram for the different spin states using the best-fit parameters shows the occurrence of six low-lying spin states (S = 0-5) which are close in energy but clearly separated from the remaining ones, with the ground spin state being S = 5. Complex 1 is found to be the first example where weak ferromagnetic exchange between Mn^II ions through the long -O-Mn^IV-O- pathway takes place.

Full text of DOI:10.1039/c9dt02503k

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An international journal of inorganic chemistry
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Synytsia, S. R. Petrusenko, V. Kokozay, A. El-Ghayoury, J. Cano, F. Lloret, M. Julve, B. Fleury and N.
Avarvari, Dalton Trans., 2019, DOI: 10.1039/C9DT02503K.
Volume 46
Number 10
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March 2017
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ISSN 0306-0012
COMMUNICATION
Douglas W. Stephen et al.
N-Heterocyclic carbene stabilized parent sulfenyl, selenenyl,
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Page 1 of 22
Dalton Transactions
Co-existence of ferro- and antiferromagnetic interactions in a hexVaienw AurticcleleOnalinre
DOI: 10.1039/C9DT02503K
mixed-valence CoIII
MnII
MnIV
cluster sustained by a multidentate Schiff base
2
2
2
ligand†
ab
b
b
b
Oleh Stetsiuk, Valentyn Synytsia, Svitlana R. Petrusenko, Vladimir N. Kokozay, Abdelkrim
El-Ghayoury,a Joan Cano,*c Francesc Lloret,c Miguel Julve,c Benoit Fleury,de and
Narcis Avarvari*a
Abstract
The successful utilization of the “direct synthesis” approach yielded the unprecedented
hexanuclear complex of formula [Co
Schiff base derived from the condensation of salicylaldehyde and 3-aminopropane-1,2-diol).
Single crystal X-ray analysis revealed that 1 crystallizes in the monoclinic system P2 and it
contains a rare mixed-valence {CoIII MnII MnIV
(μ -O) (μ -O) } core where all metal ions are
2
MnII
2
MnIV
2
(L1)
4
Cl
2
(μ
3
-O)
2
(dmf)
4
]∙2dmf (1) (H
3
L is the
/
1 c
2
2
2
2
8
3
2
3
-
linked through the phenolato and alkoxo groups of the L ligand. Besides the charge balance
resulting from the X-ray structure, the oxidation state of the metal ions has been confirmed by XPS
IV
II
spectroscopy. Cryomagnetic studies indicate the coexistence of ferro- (Mn –Mn , J
2
= +2.19(1)
–
1
–1
II
II
–1
cm , J
3
= +1.10(1) cm ; Mn –Mn , j = +0.283(3) cm ) and antiferromagnetic interactions
IV
IV
-1
III
(
Mn –Mn , J
1
= –17.31(4) cm ), the six-coordinate Co ions being diamagnetic. DFT type
calculations were carried out to substantiate these values. The energy diagram for the different
spin states using the best-fit parameters show the occurrence of six low-lying spin sates (S = 0-5)
which are close in energy but clearly separated from the remaining ones, the ground spin stae being
S = 5. Complex 1 is found to be the first example where weak ferromagnetic exchange between
II
IV
Mn ions through the long –O–Mn –O– pathway takes place.
_
___________________
a
MOLTECH-Anjou, UMR 6200, CNRS, UNIV Angers, 2 bd Lavoisier, 49045 ANGERS Cedex
(France). E-mail: narcis.avarvari@univ-angers.fr
b
Department of Inorganic Chemistry, Taras Shevchenko National University of Kyiv,
Volodymyrska str. 64/13, Kyiv 01601 (Ukraine).
c
Instituto de Ciencia Molecular (ICMol)/Departament de Química Inorgànica, Universitat de
València, C/Catedrático José Beltrán 2, 46980 Paterna (Valencia) (Spain). E-mail:
Joan.Cano@uv.es

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Page 2 of 22
d
Sorbonne Université, CNRS. Institut Parisien de Chimie Moléculaire, UMR 8232, F-75005
View Article Online
DOI: 10.1039/C9DT02503K
Paris (France)
e
CNRS, UMR 8232, Institut Parisien de Chimie Moléculaire, F-75005 Paris (France)
†
Electronic supplementary information (ESI) available: Infrared spectrum (Fig. S1), XPS spectra
(Figs. S2-S4), hydrogen bonding (Fig. S5), bond valence sum calculations (Table S1) and spin
configuration of the manganese atoms (Table S2). CCDC reference number 1819913. For ESI
and crystallographic data in CIF or other electronic format see DOI : 10.1039/xxxxx.
Introduction
High nuclearity heterometallic clusters are among the most promising investigation objects of
modern coordination chemistry. On the one hand, the presence of several metals in one complex
makes such compounds a perspective platform for developing materials possessing magnetic1-2
and catalytic properties.3-6 On the other hand, the abundance of 3d metals in nature can be a fertile
field for modelling the active sites of enzymes. In this respect, the Mn/Co pair is among the most
interesting combinations for developing polymetallic complexes. Thus, besides the opportunity to
exist in several oxidation states and to form polynuclear architectures, heterometallic Mn/Co active
sites are found in enzymes that catalyse vital processes such as nitrogen fixation and carbon
dioxide reduction.7-9 Recent series of Mn/Co cubane complexes described by Tilley and coll.10-11
have been used as water oxidation catalysts (WOCs). Moreover, the quantitative addition of
cobalt(II) acetate to the heterometallic cubane complex [MnCo
3
O
4
(OAc)
5
(py)
3
] (HOAc = acetic
acid and py = pyridine) afforded the pentametallic “dangler” compound of formula
1
2
[
MnCo
centre which generates dioxygen from water. The oxygen-evolving complex (OEC) is a peculiar
cofactor consisting of a [Mn CaO
] cubane core appended with a “dangling” Mn centre,14-16 in
4
O
4
(OAc)
6
(NO
3
)(py)
3
], which is reminiscent of the photosystem II’s oxygen-evolving
1
3
3
4
1
7
which the manganese ions present variable oxidation states, and for which several synthetic
model systems have been reported.18-20
It is therefore of utmost importance to access polynuclear heterometallic mixed-valence
manganese-based clusters as they can constitute valuable models for the manganese clusters
occurring in the living systems, and to clearly demonstrate the co-existence of several manganese
ions in different oxidation states along with the investigation of their magnetic properties. From
structural and magnetic points of view, the Mn/Co heterometallic complexes show a large diversity
2
,3
ranging from simple binuclear antiferromagnetic complexes such as [CoMn(L )(AcO)]ClO
4
∙dmf,
(L and L are derived from the condensation of 2,6-diformyl-4-
methylphenol, ethylenediamine, and 1,3-trimethylenediamine or 1,4-tetramethylenediamine),21
2
,4
2,3
2,4
[
CoMn(L )(AcO)]ClO
4

Page 3 of 22
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[
CoMnL(OAc)]ClO
4
and [CoMnL(NCS)]ClO
4
(L is a macrocycle derived by the 2:1:1
View Article Online
2
2
DOI: 10.1039/C9DT02503K
condensation of 2,6-diformyl-4-methylphenol, ethylenediamine, and diethylenetriamine), to
polynuclear
mixed-valence
tea)(acac) ](NO ·3CH
(acac) ](NO ·2MeOH (H tea = triethanolamine and Hacac =
compounds
MnII
MnII
Mn Co
III
III
(OH)(Htea)
CoIII
(Htea) (OMe)
(H
)
2
Cl
and
[
[
2
2
3
2
3
3
2
2
MnIII
)
2
2
2
2
4
2
4
3
3
2
3
acetylacetone) exhibiting intramolecular ferromagnetic exchange and single molecule magnet
behaviour, respectively.
Most of the polynuclear complexes reported in literature so far have been obtained by
2
4
applying the “serendipitous assembly” approach described by Winpenny. A particular case of this
2
5
approach consists of the “direct synthesis of complexes”, based on the use of zero-valent metals
as reagents for the generation of heterometallic aggregates. Recent application of the “direct
26
27
synthesis” strategy has been successful for the preparation of heterobimetallic Mn/Cu, Cu/Fe,
Co/Fe,28 mixed-valent Co/Cu29 and as well as heterotrimetallic complexes,30-31 possessing a
diversity of sophisticated crystal structures and properties. Herein we report the direct synthesis of
the heterometallic complex [CoIII
MnII
MnIV
(μ
(L1)
-O)
Cl
(μ
-O)
(dmf) ]∙2dmf (1), containing a very
2
2
2
4
2
3
2
4
rare hexanuclear {CoIII MnII MnIV
(μ-O)
} core with co-existence of Mn and Mn
II
IV
2
2
2
8
3
2
centres, showing intriguing magnetic properties.
Results and discussion
Synthesis and infrared spectroscopy
The open air reaction of cobalt powder and manganese chloride tetrahydrate in the presence of the
multidentate Schiff base ligand N-(propylene-2,3-diol)salicylideneimine (H
L1), derived from
3
salicylaldehyde and 3-aminopropane-1,2-diol (Scheme 1), affords a heterometallic complex
possessing an extremely rare heterometallic Mn/Co cluster with a dicubane-like core (see below).
Its formation can be explained if one considers the following reaction scheme:
2
Co + 4MnCl
2
∙4H
2
O + 4H
3
L1 + 2.5O
MnII MnIV
2
+ 6Et
3
N + 6dmf →
[
CoIII
2
2
2
(L1)
4
Cl (μ -O) (dmf)
2
3
2
4
]∙2dmf (1) + 6Et
3
N∙HCl + 19H O.
2
N
OH
OH
H3L1
OH
1
Scheme 1. The polydentate Schiff base ligand H
3
L .
The lack of O-H stretching vibrations in the high-frequency region of the infrared spectrum
1
3-
of 1 supports the presence of the fully deprotonated Schiff base (L ) as ligand (Fig. S1, ESI). The

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Page 4 of 22
-1
occurrence of a strong absorption centred at ca. 1632 сm is tentatively assigned to the ν(C=O)
View Article Online
3
2
DOI: 10.1039/C9DT02503K
stretching vibration of dmf molecules while the weak intense broad bands at 3100–2975 and
-1
2
975–2840 сm attributed to ν(C–H) of the aromatic ring and aliphatic C–H bonds, respectively.
Crystal structure
Single crystal X-Ray analysis reveals that compound 1 crystallizes in the monoclinic system, space
group P2
is based on the heterometallic hexanuclear core {CoIII
metal ions are linked through μ- and μ -O atoms from the deprotonated O-H groups of the Schiff
base ligand (Fig. 1b). According to CSD, a hexanuclear core {М (μ-Х) (μ -Х) }, similar to that of
, was firstly described in 1993 for metal-antimony ethoxides of general formula [M Sb
M = Mn, Mg, Ni),33-34 and later on for 3d metals it has been described only for the homometallic
1
/c (Table 1) with half of the complex in the asymmetric unit (Fig. 1a). The structure of
1
2
MnII MnIV
2
2
(μ-O) (μ -O) }, where all the
8
3
2
3
6
8
3
2
1
2
4
(OEt)16]
(
Ni complex (HNEt
3
)
2
[Ni
6
(ntba)
4
(μ
3
-OH)
2
(μ-OH
2
)
2
]·5CH
3
CN·2.6H
2
O
(H
3
ntba = 2,2′,2′′-
3
5
III
LnIII
(Ln
nitrilotribenzoic acid). Recently, this core was also observed for a series of 3d-4f Mn
4
2
=
Sm, Gd and Dy) complexes with a Schiff base ligand derived from of o-vanillin and
3
6
3
-aminopropane-1,2-diol. Thereby, complex 1 is found to be the first example of heterometallic
3
d metal complex possessing hexanuclear mixed-valence dicubane-like core with a rare co-
II
IV
existence of Mn and Mn oxidation states.
a
b
Fig. 1 (a) View of the crystal structure of 1 with atom labelling (the hydrogen atoms and the crystallization dmf
molecules were omitted for clarity). (b) Ball-and-stick representation of the {CoIII
MnII MnIV
(μ-O) (μ -O) }
2 2 8 3 2
2
molecular core.

Page 5 of 22
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Table 1 Summary of the crystal data and structure refinement for 1
View Article Online
DOI: 10.1039/C9DT02503K
Formula
58 2 2 4 10 20
C H82Cl Co Mn N O
–
1
M [g·mol ]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
1647.86
monoclinic
P2 /c
1
8.5730(2)
21.4804(4)
18.9257(4)
91.632(2)
3483.78(13)
2
1.571
10.722
1696
β [ ͦ ]
V [Å
3
]
Z
3
]
Ρ
calcd. [g/cm
–
1
µ [mm ]
F(000)
Goodness-of-fit on F
Т [К]
2
1.042
150
2
Θ
max
140
R
int
0.0214
final R
/wR
Largest difference peak/hole (e∙Å )
1
/wR
2
(all data)
2
[I > 2σ(I)]
0.0284/ 0.0337
0.0738/ 0.0771
0.646/-0.391
R
1
3
о
Table 2 Selected geometrical parameters (distances/Å and angles/ ) for 1*
Mn1—O3
Mn1—O4
Mn1—O5
Mn1—O6
Mn1—O7
Mn1—O7i
Mn2—O5
Mn2—O6i
Mn2—O8
Mn2—O9
Mn2—Cl1
1.9825(14)
1.9580(13)
1.9117(13)
1.9051(13)
1.8442(13)
1.8379(14)
2.1358(13)
2.1007(14)
2.1505(17)
2.1645(15)
2.4079(6)
N1—Co1
N2—Co1
O1—Co1
O2—Co1
O3—Co1
O4—Co1
1.9461(17)
1.9455(16)
1.8760(15)
1.8858(14)
1.9389(14)
1.9263(13)
i
O7 —Mn1—O7
85.21(6)
97.30(6)
87.17(6)
86.33(6)
99.37(6)
172.80(6)
168.46(6)
95.53(6)
94.24(6)
82.18(6)
99.03(6)
168.24(6)
81.43(6)
91.88(6)
82.52(6)
O1—Co1—O2
O1—Co1—O4
O2—Co1—O4
O1—Co1—O3
O2—Co1—O3
O4—Co1—O3
O1—Co1—N2
O2—Co1—N2
O4—Co1—N2
O3—Co1—N2
O1—Co1—N1
O2—Co1—N1
O4—Co1—N1
O3—Co1—N1
N2—Co1—N1
93.80(7)
91.14(6)
169.57(6)
168.53(6)
92.27(6)
84.49(6)
86.42(7)
93.73(7)
95.74(6)
83.48(6)
94.21(7)
87.29(7)
83.19(6)
95.79(6)
178.77(7)
i
O7 —Mn1—O6
O7—Mn1—O6
i
O7 —Mn1—O5
O7—Mn1—O5
O6—Mn1—O5
i
O7 —Mn1—O4
O7—Mn1—O4
O6—Mn1—O4
O5—Mn1—O4
i
O7 —Mn1—O3
O7—Mn1—O3
O6—Mn1—O3
O5—Mn1—O3
O4—Mn1—O3

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Page 6 of 22
i
O6 —Mn2—O5
87.89(5)
86.64(6)
164.70(7)
152.50(6)
96.17(6)
82.37(6)
103.39(4)
97.68(4)
97.48(6)
103.00(4)
i
View Article Online
DOI: 10.1039/C9DT02503K
O6 —Mn2—O8
O5—Mn2—O8
i
O6 —Mn2—O9
O5—Mn2—O9
O8—Mn2—O9
i
O6 —Mn2—Cl1
O5—Mn2—Cl1
O8—Mn2—Cl1
O9—Mn2—Cl1
*Symmetry code: (i) = 1–x, 1–y, 1–z.
Each cobalt(II) ion in 1 has a distorted octahedral surrounding CoN
2
O
4
which is formed by
the donor atoms of two Schiff bases (CoN O unit). The NOO donor set of each Schiff base
2
4
exhibits a fac-arrangement with the two nitrogen atoms in a trans disposition. The values of the
Co-(O)N bond lengths are in the range 1.8775(14)–1.9478(16) Å and those of the cis-/trans-angles
are 83.505(60)–95.736(62)˚ and 168.547(59)–178.742(67)˚, respectively (Table 2). Analysis of
the bond lengths with further bond valence sum (BVS)37-39 calculation for Co (Table S1) ion allows
us to consider its oxidation state as +3, a conclusion which is in agreement with other examples of
4
0
cobalt-containing complexes described in literature. The above-mentioned oxidation state was
also confirmed by X-ray photoelectron spectroscopy (XPS), a technique that has been widely used
for the determination of the elements and the oxidation states of metal ions thanks to spin-multiplet
splitting features of their core level peaks. Multiplet splitting of a photoelectron peak occurs when
the photoelectron interacts with unpaired valence electrons and is observed for Mn 3s and Co 2p3/2
4
1
levels. The Co2p XPS spectrum displays the characteristic spin-orbit 2p3/2 and 2p1/2 peaks split
by 15 eV at 780.5 eV and 795.5 eV respectively (Fig. S2), a value in accordance with trivalent Co
ions.42-44 More convincing, the 2p3/2 level does not show any spin-multiplet satellite, proving the
diamagnetic trivalent oxidation state for the cobalt centres.
The oxidation states of both types of Mn ions (Mn1 and Mn2) were established to be +II
(
Mn2) and +IV (Mn1), which was further confirmed by the BVS calculation (Table S1), magnetic
and XPS measurements. Regarding the determination of the average oxidation state (AOS) by
XPS, the closest analogy of this complex can be made with the tetranuclear MnII MnIV
mixed-
2
2
4
5
valence clusters, described by Tong et al. where the oxidation states have been proved by
considering the Mn2p XPS spectrum. Indeed, analysis of the Mn2p XPS data for complex 1 gives
the values 641.8 and 635.4 eV of the binding energies (Fig. S3), which are indicative of the
IV
presence of Mn ions. Considering spin multiplet splitting of the Mn3s edge, examples of XPS
spectra of molecular compounds are scarce and the best analogy we could find is the one with the
[
Mn12
O12(O
2
CCH
2
C(CH
3
)
3
)
8
(O
2
CCHCl
2
)
8
(H
2
O) ] (Mn12) complex in which the AOS is +3.3 and
4

Page 7 of 22
Dalton Transactions
4
6
for which the Mn3s splitting is 5.50 eV. The Mn3s XPS spectrum of 1 (Fig. S4) reveals a spin
View Article Online
multiplet with an energy splitting of 5.57 eV. The slightly higher value of thiDsOsI:p1l0i.t1t0i3n9/gC9fDoTr02150i3nK
comparison to the one of Mn12 is in good agreement with the slightly lower AOS of +3 in complex
1
; indeed, the lower the AOS, the larger the splitting.
The coordination environment of the manganese ions of 1 is formed by oxygen (Mn1) and
oxygen and chlorine (Mn2) donor atoms, resulting in distorted Mn1O
6
and Mn2O Cl octahedral
5
surroundings. The Mn1–O bond lengths are in the range 1.8380(14)–1.9823(14) Å, values which
are shorter than those at Mn2 [2.1006(14)–2.5533(13) Å] as expected due to the lower oxidation
state of this last metal atom. The remaining Mn2–Cl bond distance is equal to 2.4079(6) Å. It
III
should be noted that the absence of Jahn-Teller distortion, which is typical for Mn -containing
mixed-valence complexes,47-51 may be also the aside statement of the oxidation state +IV for the
Mn1 ions.
The values of the intermetallic metal-metal distances within the heterometallic core are
2
.9115(6) (Co1∙∙∙Mn1), 2.7103(6) (Mn1∙∙∙Mn1) and 3.2936(5) Å (Mn1∙∙∙Mn2). In the crystal
packing numerous intermolecular van der Waals interactions between coordinated and
uncoordinated DMF molecules and chloride anions were found [C–Н∙∙∙Cl: d(C27∙∙∙Cl1) = 3,75 Å,
∠
(C27–H27–Cl1) = 167˚; d(C22∙∙∙Cl1) = 3,66 Å, ∠(C22–H22C–Cl1) = 152˚; d(C26∙∙∙Cl1) = 3,64
Å, ∠(C26–H26B–Cl1) = 158˚]. This allows us to consider complex 1 as a supramolecular 1D
coordination polymer (Fig. S5).
The peculiarity of the crystal structure of 1 induced us to try to understand the possible ways
for its formation. The analysis of some of the previous reports where the self-assembly of
polynuclear compounds was described,28,52,53 prompted us to propose a rational pathway for its
formation (see Fig. 2).

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Page 8 of 22
View Article Online
DOI: 10.1039/C9DT02503K
Fig. 2 Proposed pathway for the formation of 1.
At the beginning, the coordination of the deprotonated Schiff base in the open air would lead to
III
1
]3− unit, possessing a typical N
the formation of the [Co (L )
2
2
O
4
coordination environment for
cobalt(III). The subsequent coordination of this unit to manganese ions through the alkoxo-groups
III
IV
1
]+ species. The self-
(L1) ]2– fragment.
of the ligand would allow the formation of the heterometallic [Co Mn (L )
2
assembly of these two blocks would lead to the tetranuclear [Co
2
IIIMn IV(µ-O)
2
2
4
The presence of the oxo groups can be explained by the formation of water molecules during the
Schiff base condensation. Then there are two possible routes of further self-assembly. The first
one is the interaction of [Co
2
IIIMn
2
IV(µ-O)
2
(L1) ]2–, possessing the vacant coordination positions
4
III
IV
1
]+ species. As a result of such assembly
of unsaturated oxygen atoms, with the [Co Mn (L )
2
process, the octanuclear [Co
4
IIIMn
4
IV(µ-O)
2
(L1)
8
] complex would have been obtained. Most likely,
the steric hindrance of the bulky benzene rings prevents the formation of the octanuclear complex.
II
Moreover, an excess of Mn ions in the reaction mixture, which are solvated by the dmf molecules,
forces the interaction of the [Co
2
IIIMn
2
IV(µ-O)
2
(L1) ]2– fragment with the less bulky
4
2
+
[
MnCl(dmf)
x
] units to yield 1.
Magnetic properties and DFT type calculations
The magnetic properties of 1 in the form of χ
per CoIII MnII MnIV
unit] are shown in Fig. 3. At room temperature, χ
mol K, a value which is as expected for a set of two manganese(II) and two manganese(IV) ions
M
T against T plot [χ
M
is the magnetic susceptibility
T is equal to 12.45 cm3
2
2
2
M
-1
3
-1
magnetically isolated, (χ
M
T = 2 (4.375 + 1.875) = 12.5 cm mol K with SMn(II) = 5/2, SMn(IV) = 3/2
T steadily
and gMn(II) = gMn(IV) = 2.0), the cobalt(III) ions being diamagnetic. Upon cooling, χ
M

Page 9 of 22
Dalton Transactions
3
-1
3
decreases to reach a minimum of 10.27 cm mol K at 5.0 K and it further increases to 11.20 cm
View Article Online
DOI: 10.1039/C9DT02503K
-1
mol K at 1.9 K. The shape of this curve in the high temperature domain indicates the occurrence
of a dominant antiferromagnetic interaction between some of the paramagnetic centres. The
increase of χ T after the minimum at low temperatures could be the result of the co-existence of
M
ferro- and antiferromagnetic interactions (see below) and/or to the non-compensation of the
average Landé factors of the interacting manganese cations. This last assumption has to be
discarded because of the practically identical values of the g factors of Mn(II) and Mn(IV) cations.
Neither in-phase nor out-of-phase signals were observed for 1 under zero or non-zero applied dc
magnetic fields down to 1.9 K.
__
_ _
…
M
Fig. 3 Temperature dependence of χ T: (o) experimental; ( ), ( ) and ( ) best-fit curves through eq (1) (see text).
An inspection of the crystal structure of 1, reveals the presence of several intramolecular
i
exchange pathways: (i) the double oxo bridge for Mn1/Mn1 (J
1
); (ii) the alkoxo and oxo bridges
i
i
i
i
for Mn1/Mn2 (and Mn1 /Mn2 ) (J
2
) and Mn1/Mn2 (and Mn1 /Mn2) (J ); and (iii) the multiatom
3
i
second-neighbour for Mn2/Mn2 (j) (see Scheme 2). Consequently, the appropriate spin
Hamiltonian to analyse the magnetic data of 1 would be given by eq (1):
�
ꢀ
̂ ̂
̂ ̂
̂ ̂
̂ ̂
̂ ̂
̂ ̂
̂
̂
̂
̂
2i
= −ꢁ ꢂ ꢂ − ꢁ ꢃꢂ ꢂ + ꢂ ꢂ ꢄ − ꢁ ꢃꢂ ꢂ + ꢂ ꢂ ꢄ − ꢅꢂ ꢂ + ꢆꢇꢀ(ꢂ + ꢂ + ꢂ + ꢂ )
1
1 1i
2
1 2
1i 2i
3
1 2i
1i 2
2 2i
1
1i
2
where g is the average Landé factor which is assumed to be identical for the manganese(II) and
manganese(IV) ions.

Dalton Transactions
Page 10 of 22
View Article Online
DOI: 10.1039/C9DT02503K
Scheme 2. Exchange coupling pattern in 1.
Nevertheless, prior to perform this analysis, and having in mind the uncommon tetranuclear
mixed-valence MnII MnIV motif in 1 where each oxo bridge connects one Mn(II) (Mn2 or Mn2i)
with two Mn(IV) (Mn1 or Mn1 ) ions,
MnIII MnII
cluster where the two oxo bridges would be hydroxo groups and each Mn(IV) becomes
Mn(III). DFT type calculations on the two structural possibilities were carried out. Focusing first
on the MnII MnIV
model, the results displayed in Table 3 indicate the co-existence of the ferro-
and antiferromagnetic couplings. The fact that the antiferromagnetic interaction is the dominant
one accounts for the shape of the χ T plot in the high temperature domain. However, the standard
2
2
i
45, 54-56
we have considered another structural alternative: a
2
2
2
2
M
deviations of the J1-3 parameters are relatively high, a feature that can be due to the presence of the
2nd neighbour interactions. The inclusion of the j coupling causes a significant decrease of these
deviations and, even though they are larger than usual (most likely because of a partial charge
transfer between the MnIV ions and the oxo bridges), they can be considered correct. This
additional magnetic coupling (j) is weak (as expected) and ferromagnetic. Dealing with the second
model (MnIII
MnII
), the standard deviation for the magnetic coupling constants, independently on
2
2
the incorporation of the j parameter, are uncommonly large, even greater than the calculated J
i
values. Therefore, this model should be ruled out.
Once the possibility of the MnIII
of the MnIV MnII
motif through eq (1) by the VPMAG program was carried out considering first
j = 0 and fixing g = 2.0. The best-fit parameters are J
MnII
model is discarded, the treatment of the magnetic data
2
2
57
2
2
–
1
–1
1
= –17.23(4) cm , J
2
= +2.14(1) cm , J =
3
–
1
+
2.04(1) cm (set a). This model (dotted line in Fig. 3) matches well the magnetic data until 10

Page 11 of 22
Dalton Transactions
K, but it is unable to reproduce the minimum and the further increase of χ T at very low
M
View Article Online
temperatures. The second approach incorporating j as variable parameter reprodDuOcI:e1s0.1v0e3r9y/C9wDeT0l2l5t0h3eK
magnetic data in the whole temperature range explored (solid line in Fig. 3), the best-fit parameters
–
1
–1
–1
–1
being J
1
= –17.31(4) cm , J
2
= +2.19(1) cm , J
3
= +1.10(1) cm , and j = +0.283(3) cm (set b).
These results together with those from theoretical calculations give support to the reliability of the
nd
II
occurrence of the weak 2 neighbour magnetic interaction between Mn ions. Finally, in order to
illustrate the influence of the j parameter on the shape of the χ
M
T plot, we performed the last
–
1
–1
= +1.10(1) cm–1,
simulation of the magnetic data with J
1
= –17.31(4) cm , J
2
= +2.19(1) cm , J
3
–
1
and fixing j = 0 cm (set c). The calculated χ
M
T plot (dashed line in Fig. 3) follows the shape of
the magnetic data in the high temperature domain being always below them, and it sharply
decreases at low temperatures, being unable to reproduce the minimum and the further increase of
M
χ T below 10 K. This feature reveals the determinant character of the weak ferromagnetic
coupling j to simulate the magnetic data of 1.
In order to illustrate the influence of the spin coupling pattern on the energy of the different
spin states, and indirectly on the magnetic behaviour, the energy diagram for the different spin
states using the best-fit parameters from set (b) is shown in Fig. 4a. One can see in this picture that
six low-lying spin states (S = 0–5) are clearly separated from the remaining ones, the ground spin
state being S = 5. These low-lying states are very close in energy as shown the magnification
shown in Fig. 4b. This fact reveals that small variations of certain magnetic couplings can modify
the nature of the ground spin state. Fig. 5 is very illustrative in this respect. In such a case, any of
the six low-lying spin states could be the ground state through a small variation of j in the range
–
1
of 0.06 to 0.14 cm .

Dalton Transactions
Page 12 of 22
Table 3 Selected magneto-structural data for 1
Magnetic Coupling Bridges
–
1
J
exp (cm–1)
ꢋ
ꢈꢉꢊꢈꢉ (deg)
Centres
d
Mn–Mn (Å)
J
calc (cm )
µ
µ
3
-O
-O
94.37
94.87
110.57
97.52
110.52
95.86
Mn 1I V − Mn1
IV
2.710
–19.2(4)
–17.31(4)
+1.10(1)
+2.10(1)
+0.283(3)
J
J
J
1
2
3
ꢌ
3
µ-OR
-O
µ-OR
-O
IV
ꢌ
II
Mn 1I V − Mn /Mn
II
− Mn2
2
ꢌ
3.329
3.294
6.043
+4.07(13)
+6.93(13)
+0.29(15)
1
µ
3
IV
II
2
IV
II
ꢌ
Mn1
ꢌ
− Mn /Mn − Mn2
1
µ
3
IV
µ-(OMn O)
µ-(OMn O)
II
II
2
j
Mn − Mn
2
ꢌ
-----
IV

Page 13 of 22
Dalton Transactions
View Article Online
DOI: 10.1039/C9DT02503K
Fig. 4 (Top) Energy levels for the spin states of 1 by using the isotropic exchange parameters of the set (b). (Bottom)
A detail of the energy levels of the low-lying S = 0–5 spin states for 1.
Fig. 5 Energy of the low-lying S = 0–5 spin states of 1 as a function of the j parameter. Data obtained through the
1 2 3
values of J , J and J of the set (b).

Dalton Transactions
Page 14 of 22
Let us to finish this interpretation by discussing the nature and magnitude of the magnetic
View Article Online
couplings in 1. The antiferromagnetic coupling between the Mn(IV) ions throuDgOhI:t1h0.e10d39o/Cu9bDlTe0-2o50x3oK
bridges (J
1
)
is comparable to the value obtained for this coupling in the
(heed) (EtOH) Br ]Br [H heed = N,N-bis(2-hydroxyethyl)ethylene diamine] (J =
[
MnII MnIV
2
2
O
2
2
6
2
2
2
–
1
56
–
23.8 cm ), where with this type of exchange pathway occurs. In such a case, the values of the
angle at the bridgehead oxo atom [Mn-O-Mn = 96.18(8)º] and the intramolecular MnIV…MnIV
distance (96.2º and 2.71 Å) are comparable to those in 1 (94.6º and 2.71 Å). However, there are
–
1
also examples with stronger magnetic couplings (–J values in the range 96–164 cm ) for similar
5
8
systems but having shorter intramolecular intermetallic distances. In this respect, theoretical
calculations demonstrated that this kind of magnetic coupling is very sensitive to the value of the
intermetallic MnIV…Mn metal distance and, consequently, to the Mn–Ooxo–Mn angle. Moreover,
other factors as geometrical distortions of the coordination sphere or the electronic nature of the
peripheral ligands can play a significant role. Anyway, the relatively strong antiferromagnetic
IV
IV
II
coupling found for J
concerned, a µ -oxo and one alkoxo atoms act as bridges between these two cations. Given that
magneto-structural studies on the Mn –Mn pair are very scarce
1
in 1 is within normal expectations. As far as the Mn –Mn couple in 1 is
3
IV
II
45,54-56
the unambiguous
determination of the magnetic coupling between these ions remains an open question. The closer
example in the literature to this fragment in 1 is represented by the compound of formula
[
MnII
hydroxyethyl)ethylenediamine and H
alkoxo group acts as bridge.45 The magnetic coupling through this pathway in such a compound
2
MnIV
2
(µ
4
-Hedte)
2
(thme)
2
].2MeOH
thme = 1,1,1-tris(hydroxymethyl)ethane] where a double
[H
4
edte
=
N,N,N’,N’-tetrakis(2-
3
-1
is J = +2.91 cm , a value which is of the same nature and comparable size to those found in 1 for
IV
II
–1
–1
the Mn –Mn pair (J
2
= +1.10 cm and J
3
= +2.10 cm ). The electronic configurations of the
six-coordinate Mn and Mn ions are t2g3e
IV
II
0
and t2g3e 2
respectively. Then, the contributions
g
g
involving the t2g magnetic orbitals of both metal ions are mostly antiferromagnetic and those
IV
II
entailing the t2g from Mn and e
between the interacting magnetic orbitals. The larger spin delocalization of the e
orbitals provokes that the last contributions are dominant and a weak ferromagnetic net coupling
for J and J is expected. Finally, as far as we are aware, no examples are reported dealing with
g
from Mn are ferromagnetic because of the strict orthogonality
g
against t2g
2
3
II
IV
magnetic interactions between Mn ions through the long –O–-Mn –O– pathway (j). However, a
very weak magnetic coupling is what one could predict for this pathway given the multiatom set
involved, but a clear-cut answer to the origin of its ferromagnetic nature is precluded.

Page 15 of 22
Dalton Transactions
Conclusions
The open air reaction of cobalt powder, manganese(II) chloride in a DMF solutDioOIn: 10c.o10n3t9a/Cin9DinT0g25t0h3eK
polydentate Schiff base ligand H
L1 allowed us to obtain the unprecedented hexanuclear Co/Mn
complex 1. It is the first example of heterometallic 3d-metal complexes possessing the mixed-
View Article Online
3
valence core {CoIII
MnII
MnIV
(μ-O)
(μ
-O) } with a rare co-existence of Mn and Mn centres.
II
IV
2
2
2
8
3
2
The presence of several metal ions in different oxidation states has a paramount importance in
many chemistry areas ranging from bioinorganic, as possible models for metalla-enzymes such as
the oxygen evolving centre (OEC), to molecular magnetism in the search for tunable spin state
complexes. The proposed pathway of the formation of 1 may be a small piece of the jigsaw of the
self-assembly approach towards heterometallic compounds. The cryomagnetic study of 1 shows
the co-existence of ferro- and antiferromagnetic interactions and reveal that the complex herein is
II
the first example where magnetic interactions between Mn ions can be mediated through the long
IV
-
O-Mn -O- bridge.
Experimental section
General procedures
Reactions were carried out under air using HPLC solvents. IR spectra were recorded on ATR
Bruker Vertex 70 spectrophotometer in the 4000−400 cm−1 range. Elemental analyses were
recorded using a Flash 2000 Fisher Scientific Thermo Electron analyzer and the metals
determination was performed by atomic absorption spectroscopy at the Department of Chemistry,
Taras Shevchenko National University of Kyiv.
Synthesis of [CoIII
mmol), 3-aminopropane-1,2-diol (0.09 g, 1.0 mmol) and triethylamine (0.28 mL, 2.0 mmol) were
dissolved in DMF (20 mL), forming a yellow solution of H
L1 which was stirred at 100–120 °C
during 10-15 min. Then, cobalt powder (0.06 g, 1.0 mmol) and manganese(II) chloride tetrahydrate
0.2 g, 1.0 mmol) were added to the hot yellow solution of the ligand and stirred until the total
MnII
MnIV
(L1)
Cl
(μ
-O)
(dmf) ]∙2dmf (1). Salicylaldehyde (0.1 mL, 1.0
2
2
2
4
2
3
2
4
3
(
dissolution of the cobalt(II) powder was observed (2 h). Dark brown crystals of 1 suitable for X-
ray analysis were obtained from the reaction mixture upon diffusion of diethyl ether after few days.
Yield: 0.25 g in pure crystalline state, 15% (per Mn). Anal. calc. for C58
H82Cl
2
Co
2
Mn
4
N
10
O20: C,
4
7
2.27; H, 5.02; N, 8.50; Mn, 13.34; Co, 7.15. Found: C, 42.05; H, 5.00; N, 8.40; Mn, 13.25; Co,
−
1
.06%. IR (KBr, cm ): 2930 (w), 2870 (w), 1635 (s), 1533 (s), 1445 (s), 1399 (m), 1290 (s), 1190
(m), 1140 (s), 1040 (s), 935 (m), 900 (m), 755 (s), 656 (s), 590 (m), 530 (w), 467 (m), 435 (m).
Compound 1 is soluble in dmso and dmf, sparingly soluble in MeOH and MeCN and insoluble in
water.

Dalton Transactions
Page 16 of 22
Physical measurements
View Article Online
Variable-temperature (1.9-290 K) direct current (dc) magnetic susceptibility meDaOsI:u10re.10m39e/nC9tsDTu0n25d0e3Kr
applied dc fields of 0.5 T (T ≥ 50 K) and 250 G (T < 50 K) and variable field (0-5 T) were carried
out on crushed crystals of 1 with a Quantum Design SQUID magnetometer. Alternating current
(ac) magnetic susceptibility measurements in the temperature range 2.0 -12 K) under different
applied static fields in the range 0–2.5 kG were performed on a Quantum Design Physical Property
Measurement System (PPMS). The experimental magnetic susceptibility an magnetization data
were corrected for the diamagnetic contributions of the constituent atoms and the sample holder
(a plastic bag).
Computational details
DFT calculations were carried out through the Gaussian 09 package to estimate the magnitude of
5
9
the magnetic coupling between the magnetic centres in 1. These calculations were performed
with the B3LYP hybrid functional, the quadratic convergence approach and a guess function
generated with the fragment tool from the same program.60-62 Triple-ζ and double-ζ all-electron
basis sets proposed by Ahlrichs et al. were employed for the metal atoms and the rest,
respectively.63,64 The magnetic coupling states were obtained from the relative energies of the
broken-symmetry (BS) singlet spin states from the high-spin state with parallel local spin moments
(
see Table S2). More details about the use of the broken-symmetry approach to evaluate the
magnetic coupling constants can be found in the literature.65-67 A polarizable continuum model
PCM) was introduced in the calculations with the parameters corresponding to the acetonitrile.68
(
X-ray crystallography
Single crystal X-ray diffraction data were collected on an Agilent Technologies SuperNova
diffractometer equipped with AtlasCCD detector and micro-focus Cu-Kα radiation (λ = 1.54184
2
Å). The structures were solved by direct methods and refined on F by full matrix least-squares
6
9
techniques using SHELX97 package. All non-hydrogen atoms were refined anisotropically and
7
0
multiscan empirical absorption was applied using CrysAlisPro program. The hydrogen atoms
were included in the geometrically calculated position and refined riding on the corresponding
atom. Crystallographic data andrefinement statistics are given in Table 1 whereas main bond
lengths and angles are listed in Table 2. The crystallographic drawings were performed by means
7
1
of the Diamond program. CCDC 1819913 contains the supplementary crystallographic data for
this paper. This data can be obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.

Page 17 of 22
Dalton Transactions
ORCID
View Article Online
DOI: 10.1039/C9DT02503K
Vladimir Kokozay: 0000-0003-1834-3020
Joan Cano: 0000-0002-7382-7135
Francesc Lloret: 0000-0003-2959-0879
Miguel Julve: 0000-0001-9006-8268
Narcis Avarvari: 0000-0001-9970-4494
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
This work was supported in France by the CNRS, the University of Angers, in Ukraine by the
Ministry of Education and Science, the Taras Shevchenko National University of Kyiv and the
French Embassy in Kyiv (grant to O.S.), and in Spain by the Ministerio Español de Economía y
Competitividad (Projects CTQ2016-75068P and CTQ2016-75671P) and the Unidad de Excelencia
María de Maetzu (Project MDM2015-0538). Marion Giraud (University of Paris Diderot) is
gratefully acknowledged for her assistance with the XPS measurements.
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Table of contents
Co-existence of ferro- and antiferromagnetic interactions in a hexanuclear mixed-valence
III
II
IV
Co Mn Mn cluster sustained by a multidentate Schiff base ligand:
2
2
2
III
II
IV
An unprecedented hexanuclear mixed-valence Co Mn Mn cluster has been synthesized
2
2
2
and structurally characterized. In depth magnetochemical investigations combined with DFT
calculations demonstrate the co-existence of antiferro- and ferromagnetic interactions within
IV
II
the Mn Mn core.
2
2
1