Synthesis, Crystal Structures, and Magnetic Properties of New Hexanuclear MnIII2LnIII4 Complexes: SMM Behavior of the Terbium(III) Analogue

Article abstract of DOI:10.1002/ejic.201800792

This investigation reports the syntheses, crystal structures, and magnetic properties of a series of isomorphous hexanuclear Mn^III₂Ln^III₄ compounds of composition [Mn^III₂Ln^III₄L¹₂L²₂(μ₃-OH)₄(μ_1,3-Pivalate)₆(NO₃)₂]·2CH₃CN {Ln = Tb (1), Dy (2), Ho (3), Er (4)}, where H₂L¹ is the Schiff base ligand that is obtained by [1+1] condensation of 3-methoxysalicylaldehyde (HL²) with 2-amino-2-methyl-1-propanol. While the O(phenoxo)N(imine)O(alkoxo) pocket of the ligand [L¹]^2– binds a Mn^III ion, the other pocket, O(methoxy)O(phenoxo), remains noncoordinated. In contrast, each of the O(methoxy)O(phenoxo) and O(phenoxo)O(aldehyde) sites of [L²]^– is occupied by a Ln^III ion. Additionally, there are four μ₃-hydroxo, six μ_1,3-pivalate, and two chelating nitrate ligands, stabilizing the hexanuclear cores. Magnetic susceptibility (2–300 K) and magnetization (M) data reveal significant anisotropy in 1–4. Detailed ac susceptibility measurements have revealed single molecule magnet (SMM) behavior in the Tb^III analogue with U_eff = 11.12 cm^–1 and τ₀ = 1.04 × 10^–7 s under a 1000 Oe dc field and U_eff = 10.42 cm^–1 and τ₀ = 1.62 × 10^–7 s under a 3500 Oe dc field, while the other three analogues do not show slow relaxation of magnetization.

Full text of DOI:10.1002/ejic.201800792

A Journal of
Accepted Article
Title: Synthesis, Crystal Structures and Magnetic Properties of New
Hexanuclear MnIII2LnIII4 Complexes: SMM Behavior of the
Terbium(III) Analogue
Authors: Shuvayan Roy, Sagar Ghosh, Daniel O. T. A. Martins,
Floriana Tuna, and Sasankasekhar Mohanta
This manuscript has been accepted after peer review and appears as an
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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
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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.201800792
Link to VoR: http://dx.doi.org/10.1002/ejic.201800792

10.1002/ejic.201800792
European Journal of Inorganic Chemistry
1
Synthesis, Crystal Structures and Magnetic Properties of New Hexanuclear
MnIII LnIII4 Complexes: SMM Behavior of the Terbium(III) Analogue
2
Shuvayan Roy,[a] Sagar Ghosh,[a] Daniel O. T. A. Martins,[b] Floriana Tuna,[b] and
Sasankasekhar Mohanta*[a]
[a] S. Roy, S. Ghosh and Prof. S. Mohanta
Department of Chemistry, Inorganic Chemistry Section, University of Calcutta
92 A. P. C Road, Kolkata 700 009, India
E-mail: sm_cu_chem@yahoo.co.in.
Fax: 91-33-23519755
http://www.caluniv.ac.in/academic/department/Chemistry/Sasankasekhar-Mohanta.pdf
[b] Daniel O. T. A. Martins and Dr. F. Tuna
National EPR Facility, Photon Science Institute, University of Manchester
Oxford Road, Manchester, M13 9PL, United Kingdom.
https://www.research.manchester.ac.uk/portal/floriana.tuna.html
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejic.201800792R1
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
2
This investigation reports the syntheses, crystal structures and magnetic properties of a series
of isomorphous hexanuclear MnIII LnIII compounds of compositions [MnIII LnIII L1 L2 (µ3-
2
4
2
4
2
2
OH)4(µ1,3-Pivalate)6(NO3)2]·2CH3CN (Ln = Tb (1), Dy (2), Ho (3), Er (4)), where H2L1 is the
Schiff base ligand that is obtained by [1+1] condensation of 3-methoxysalicylaldehyde (HL2)
with 2-amino-2-methyl-1-propanol. While the O(phenoxo)N(imine)O(alkoxo) pocket of the
ligand [L1]2– binds a MnIII ion, the other pocket, O(methoxy)O(phenoxo), remains
noncoordinated.
In
contrast,
each
of
the
O(methoxy)O(phenoxo)
and
O(phenoxo)O(aldehyde)) sites of [L2]– is occupied by a LnIII ion. Additionally, there are four
µ3-hydroxo, six µ1,3-pivalate and two chelating nitrate ligands, stabilizing the hexanuclear
cores. Magnetic susceptibility (2–300 K) and magnetization (M) data reveal significant
anisotropy in 1–4. Detailed ac susceptibility measurements have revealed single molecule
magnet (SMM) behavior in the TbIII analogue with Ueff = 11.12 cm‒1 and τ0 =1.04 × 10‒7 s
under 1000 Oe dc field and Ueff = 10.42 cm‒1 and τ0 = 1.62 × 10‒7 s under 3500 Oe dc field
while the other three analogues do not show slow relaxation of magnetization.
Introduction
Single molecule magnets (SMMs) are molecules possessing one or more paramagnetic
centers that exhibit slow relaxation.[1‒5] The origin of slow relaxation of magnetization in
SMMs is the existence of an energy barrier (Ueff) that opposes the reversal of the
magnetization after the removal of the magnetic field. They may also exhibit a hysteresis
loop below a blocking temperature, TB.[4,5] In contrast to the conventional magnets where
magnetism arises from the bulk, the magnetic memory of SMMs arises solely from the
molecule itself and therefore SMMs have potential application in advanced technological
devices related to high-density data storage,[2a,6] quantum computing[7] and spintronics.[8] The
larger the Ueff and TB values of an SMM, the greater the feasibility of its application in
devices. The best reported Ueff and TB values for a SMM are 1223 cm–1 and 60 K,
respectively, and the concerned system is a mononuclear dysprosium(III) molecule,
dysprosocenium, which has been published very recently.[4a,b] Much efforts in this field are
directed toward the enhancement of Ueff and TB values with the aim of pushing the
applications of this class of materials. This requires synthesis of new molecules that show
slow magnetic relaxation and particularly metal complexes assembled from ligands that have
not been utilized in the area of SMMs. The later aspect is one focus of our investigation.
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
3
Gatteschi and co-workers have reported the first observation of SMM behaviour in a
molecular system, a dodecanuclear MnIII MnIV4 cluster (Mn12), in early 1990s.[1] The inherent
8
single-ion zero-field splitting of the Jahn-Teller MnIII ion was assumed to be the key
responsible factor for the overall uniaxial anisotropy (negative D value) and magnetic
bistability of the compound, and thus sufficient energy barrier is observed. Despite extensive
research on exchange-coupled 3d SMMs containing anisotropic MnIII, CoII or other 3d ions,
no much improvement in SMM properties was observed; the blocking temperature (TB) of
any 3d-SMM is below 5 K[9–11] and the best Ueff value obtained is only 63 cm–1.[10e] The
second milestone in the area of SMMs was laid by Ishikawa et al. who reported the first
lanthanide based SMM, [NBu4][Tb(phthalocyanine)2], with Ueff = 230 cm–1.[12] Since then,
numerous 4f[2e,3‒5,13‒21] and 3d-4f[22‒27] systems of different nuclearity and dimensionality
have been reported with the orientation to improve the key parameter values of the SMMs
and also to understand the underlying fundamental aspects. Theoretical models have been
proposed and ab initio calculations have been performed to rationalize the magnetic
phenomena of the lanthanide based systems.[4c,5b,c,13a‒c,15a,17,18a,c,21c,23a,b,25a‒c,26a] It has been
understood that high magnetic moment and inherent anisotropy associated with most
lanthanides (particularly heavier ones) as a result of strong spin-orbit coupling make these
metal ions alluring members to explore the area of SMMs.
Here we describe the results of our investigation focused on hexametallic systems that
comprise both anisotropic MnIII ions and anisotropic LnIII ions. It is worth mentioning that the
[1+1] condensation products of 3-methoxysalicylaldehyde and an aminoalcohol[18a,28,29] or an
aminophenol[27a,30] have previously been used to isolate 4f and 3d-4f compounds, with a
number of them being shown to be SMMs; in fact, it is not overwhelming to say that this
family of ligands have occupied a dominating position in 3d-4f and 4f molecular magnetic
systems. The interesting aspect of such ligands is that there are two types of pockets,
O(phenoxo)O(alkoxido)N(imine) (Pocket I; as in Scheme 1) that can bind with a 3d metal ion
more potentially, and O(phenoxo)O(methoxy) (Pocket II; as in Scheme 1) that preferentially
coordinates a 4f metal ion. It is also well known that different types of compounds with
different types of properties may be obtained through slight modification of the ligands. It is
worth noting that although several aminoalcohols and aminophenols have been utilized to
derive 4f or 3d-4f compounds from 3-methoxysalicylaldehyde–aminoalcohol/aminophenol
ligands, 2-amino-2-methyl-1-propanol has not been so far utilized in this area.
We have prepared a series of MnIII LnIII compounds of composition
2
4
[MnIII LnIII L1 L2 (µ3-OH)4(µ1,3-Pivalate)6(NO3)2]·2CH3CN (Ln = Tb (1), Dy (2), Ho (3), Er
2
4
2
2
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
4
(4)), where H2L1 is the Schiff base ligand (Scheme 1) obtained from [1+1] condensation of 3-
methoxysalicylaldehyde with 2-amino-2-methyl-1-propanol and is 3-
HL2
methoxysalicylaldehyde. Herein, we report the syntheses, crystal structures and dc and ac
magnetic properties of 1–4.
HL2
1
H L
2
Scheme 1. Chemical structures of the ligands.
Result and Discussion
Syntheses
H2L1 solution. A solution of 2-amino-2-methyl-1-propanol (0.09 g, 1 mmol) in 5 mL
methanol was added dropwise to a 10 mL methanol solution of 3-methoxy salicylaldehyde
(0.15 g, 1 mmol) under warming condition. The reaction mixture was refluxed for 2 h. After
cooling, the volume of the solution was diluted to 25 mL in a volumetric flask. The resulting
orange coloured ‘H2L1 solution’ was considered to contain 1 mmol of the ligand H2L1 and
was utilized for subsequent reactions without further purification.
Description of the crystal structures of 1–4.
All four compounds of general composition [MnIII LnIII L1 L2 (µ3-OH)4(µ1,3-
2
4
2
2
Pivalate)6(NO3)2]·2CH3CN (1, Ln = Tb; 2, Ln = Dy; 3, Ln = Ho; 4, Ln = Er) crystallize in the
same crystal system, monoclinic, and same space group, P21/n, with closely similar values of
unit cell parameters (Table 1), revealing that these four compounds are isomorphous. One
half of each structure is symmetry related to the another half due to the presence of inversion
center. The crystal structures of the four compounds are shown in Figures 1 (1), S1 (2), S2 (3)
and 2 (4). The structures show that these four compounds are isostructural as well; a
simplified and general schematic presentation of their structures is shown in Scheme 2.
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
5
Table 1. Crystallographic data for 1−4.
1
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
a[Å]
C74H108N6O34Mn2Tb4 C74H108N6O34Mn2Dy4 C74H108N6O34Mn2Ho4 C74H108N6O34Mn2Er4
2371.22
Monoclinic
P21/n
2385.54
Monoclinic
P21/n
2395.26
Monoclinic
P21/n
2404.58
Monoclinic
P21/n
13.0489(4)
20.7132(7)
17.3890(6)
90
13.0539(7)
20.7041(12)
17.3673(10)
90
12.9833(7)
20.6228(11)
17.2875(9)
90
12.9864(16)
20.648(2)
17.278(2)
90
b[Å]
c[Å]
α
β
γ
[°]
[°]
[°]
91.7740(10)
90
91.817(2)
90
91.883(2)
90
91.976(2)
90
V[Å3]
Z
4697.7(3)
2
4691.5(5)
2
4626.3(4)
2
4630.1(9)
2
T[K]
2θ[°]
[mm–1]
296(2)
3.058 − 73.396
3.311
296(2)
3.062 − 55.60
3.486
296(2)
3.076 − 55.99
3.726
296(2)
3.074 − 51.80
3.930
µ
ρcalcd[g cm–3]
F(000)
1.676
2352
1.689
2360
1.719
2368
1.725
2376
Absorption-correction
Index ranges
Multi-scan
−21 ≤ h ≤ 21
−34 ≤ k ≤ 33
−29 ≤ l ≤ 29
83444
Multi-scan
−16 ≤ h ≤ 16
−27 ≤ k ≤ 27
−22 ≤ l ≤ 21
59112
Multi-scan
−16 ≤ h ≤ 16
−27 ≤ k ≤ 27
−22 ≤ l ≤ 20
60066
Multi-scan
−15 ≤ h ≤ 15
−25 ≤ k ≤ 23
−21 ≤ l ≤ 20
33613
Reflections collected
Independent reflections
(Rint)
22901 (0.0399)
10871 (0.0682)
10938 (0.0541)
8818 (0.0689)
R1[a],wR2[b] [I > 2σ(I)]
0.0384, 0.0808
0.0758, 0.1001
1.027
0.0374, 0.0769
0.0784, 0.0928
1.004
0.0379, 0.0911
0.0634, 0.1048
0.0427, 0.0853
0.0780, 0.0989
1.002
2
R1[a],wR2[b] [for all Fo ]
Goodness-of-fit on F2, S
1.022
[a] R1 = [∑||Fo| – |Fc||/∑|Fo|]. [b] wR2 = [∑w(Fo – Fc2)2/∑wFo ]
2
4 1/2
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
6
Figure 1. Crystal structure of [MnIII TbIII L1 L2 (µ3-OH)4(µ1,3-Pivalate)6(NO3)2]·2CH3CN
2
4
2
2
(1). Hydrogen atoms, except those of the hydroxide ligands, and acetonitrile molecules of
crystallization have been omitted for clarity. Symmetry code: D = –x, 2–y, 2–z.
Figure 2. Crystal structure of [MnIII ErIII L1 L2 (µ3-OH)4(µ1,3-Pivalate)6(NO3)2]·2CH3CN
2
4
2
2
(4). Hydrogen atoms, except those of the hydroxide ligands, and acetonitrile molecules of
crystallization have been omitted for clarity. Symmetry code: D = –x, 2–y, –z.
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
7
O3
t
O17
N2
Bu
O6D
O4D
O5
O1
t
O16
Ln2
O11D
Bu
O12D
O15
O9D
Ln1D
O14
O2D
t
Mn1
N1
O10
O10D
N1D
O13D
Bu
O7D
O8D
O7
t
O8
Bu
O13
Mn1D
O2
O14D
Ln2D
O16D
O9
Ln1
O12
O15D
t
Bu
O11
O1D
O5D
O4
O6
N2D
t
O17D
Bu
O3D
Scheme 2. Simplified illustration of the hexanuclear core in 1–4.
It may be simpler to describe the structures by fragment analyses. Each structure
consists of the following species: (i) Two MnIII; (ii) Four LnIII; (iii) Two deprotonated
O(methoxy)O(phenoxo)N(imine)O(alkoxo) Schiff base ligands, [L1]2–, where both phenoxo
and alkoxo moieties of H2L1 are deprotonated; (iv) Two deprotonated
O(methoxy)O(phenoxo)O(aldehyde) ligands, [L2]–, where the phenoxo moiety of HL2 (3-
methoxysalicylaldehyde) is deprotonated; (v) Four µ3-hydroxo ligands; (vi) Six µ1,3-pivalate
ligands; (viii) Two chelating nitrate ligands. Of the two pockets of each of the two [L1]2–, the
O(phenoxo)N(imine)O(alkoxo) pocket is occupied by a MnIII ion (Mn1 in O1N1O2/Mn1D in
O1DN1DO2D), while the O(methoxy)O(phenoxo) pocket (O3O1/O3DO1D) remains
noncoordinated. In this way, the coordination of two [L1]2– with two MnIII produces two
mononuclear MnIII fragments. On the other hand, each of the two sites
(O(methoxy)O(phenoxo) and O(phenoxo)O(aldehyde)) of each of the two [L2]– ligand
fragments is occupied by a LnIII ion (Ln1 and Ln2D in one [L2]– and Ln1D and Ln2 in the
second [L2]–). Clearly, the two LnIII centers in one [L2]– ligand are phenoxo bridged. This
way, the coordination of two [L2]– with four LnIII produces two phenoxo-bridged dinuclear
LnIII fragments. The two mononuclear MnIII and two dinuclear LnIII fragments are
2
2
assembled by the two alkoxo oxygen atoms (O2/O2D) of two [L1]2– units and two aldehyde
oxygen atoms (O5/O5D) of two [L2]– units to generate a macrocycle; each alkoxo oxygen
atom (O2/O2D) coordinates to a LnIII ion (Dy1/Dy1D) in addition to a MnIII ion
(Mn1/Mn1D) and each aldehyde oxygen atom (O5/O5D) coordinates to a MnIII ion
(Mn1/Mn1D) in addition to a LnIII ion (Ln2/Ln2D). One can follow the so-said macrocycle in
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
8
Scheme 2 as the following shortest route (a part of blue coloured lines/curves): Mn1–
O2(alkoxo)–Ln1–O4(phenoxo)–Ln2D–O5D(aldehyde)–Mn1D–O2D(alkoxo)–Ln1D–
O4D(phenoxo)–Ln2–O5(aldehyde)–Mn1. The already mentioned four µ3-hydroxo ligands in
the structures of 1–4 are of two types: (i) The hydroxo oxygen atom (O7/O7D) of each of the
two first type hydroxo ligands that bridges one MnIII (Mn1/Mn1D) and two LnIII (Ln1 and
Ln2/Ln1D and Ln2D) ions; (ii) The hydroxo oxygen atom (O8/O8D) of each of the two
second type hydroxo ligands that bridges three LnIII ions (Ln1, Ln2 and Ln2D/Ln1D, Ln2 and
Ln2D). The already mentioned six µ1,3-pivalate ligands are of three types: (i) Two type 1 –
two oxygen atoms (O9 and O10/O9D and O10D) of this type bridge a 3d and a 4f metal ions
(Mn1 and Ln1/Mn1D and Ln1D), which are also bridged by an alkoxo oxygen atom
(O2/O2D); (ii) Two type 2 – two oxygen atoms (O11 and O112/O11D and O11D) of this
type bridge two phenoxo-bridged 4f metal ions (Ln1 and Ln2D/Ln1D and Ln2) in the said
dilanthanide(III) fragments; (iii) Two type 3 – two oxygen atoms (O13 and O14/O13D and
O14D) of this type bridge two 4f metal ions (Ln1 and Ln2/Ln1D and Ln2D), which are
symmetrically nonequivalent and evidently belong to two different said dilanthanide(III)
fragments. Finally, each of the two nitrates in
η2- mode through two of its oxygen atoms (O15 and O16/O15D and O16D).
The MnIII center (Mn1) in
is six-coordinated by one imine nitrogen atom (N1)
1–4
coordinates to a LnIII center, Ln2/Ln2D, in
1–4
and one phenoxo (O1), one µ-alkoxo (O2), one µ-aldehyde (O5), one µ3-hydroxo (O7) and
one µ1,3-pivalate (O10) oxygen atoms. As compared in Table 2, the values of corresponding
bond lengths and angles involving MnIII center in all the four compounds are very close in all
but the MnIII–O(aldehyde) bond distance; the maximum difference between the maximum
and minimum values of MnIII–O(aldehyde) bond distances is 0.05 Å, while the ranges of
differences between the maximum and minimum values of other MnIII–O/N bond distances
and O/N–MnIII–O/N bond angles are, respectively, 0.004–0.012 Å and 0.15–0.97º. The
MnIII–O/N bond distances follow a general trend, MnIII–O(aldehyde) (e. g., 2.642 Å in
MnIII–O(µ1,3-pivalate (e. g., 2.132 Å in ) > MnIII–N(imine) (e. g., 1.979 Å in ) > MnIII–O(µ-
) > MnIII–O(µ-phenoxo) (e. g., 1.863 Å in ) ≈ MnIII–O(µ-
). The values of MnIII–N/O bond distances involving imine,
1) >
1
1
hydroxo) (e. g., 1.937 Å in
alkoxo) (e. g., 1.873 Å in
1
1
1
phenoxo, hydroxo and alkoxo moieties clearly indicate that oxidation state of this metal ion is
+3, which is also supported by BVS calculations[31] (range of BVS values in
: 3.05–3.10,
Table S1). The MnIIIO5N coordination geometry is distorted octahedral as evident from the
ranges of the transoid angles (e. g., 162.54–172.21º in ) and cisoid angles (e. g., 72.83–
102.03º in ).
1–4
1
1
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
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Table 2. The values of bond lengths (Å) and angles (º) around the MnIII centers in 1–4.
Coordination
Bond Lengths (Å)
1
2
3
4
environment of Mn(III)
Mn1−N1
Mn1−O1
Mn1−O2/O2D
Mn1−O5/O5D
Mn1−O7
1.979(3)
1.863(2)
1.873(2)
2.6421
1.937(2)
2.132(2)
1.976(4)
1.869(4)
1.877(3)
2.6280
1.939(3)
2.133(4)
1.975(4)
1.864(4)
1.866(4)
2.6071
1.934(4)
2.121(4)
1.971(6)
1.866(5)
1.873(5)
2.5905
1.936(5)
2.123(5)
Mn1−O10
Bond Angles (º)
O1−Mn1−O2/O2D
O5/O5D−Mn1−O10
O7−Mn1−N1
O1−Mn1−N1
O1−Mn1−O5/O5D
O1−Mn1−O7
O1−Mn1−O10
O2/O2D −Mn1−N1
O2/O2D −Mn1− O5/O5D 88.326
O2/O2D−Mn1−O7
O2/O2D−Mn1−O10
O5/O5D−Mn1−N1
O5/O5D−Mn1−O7
O7−Mn1−O10
172.21(11)
164.482
162.54(10)
91.47(11)
87.004
98.27(10)
94.32(10)
82.59(10)
172.33(17)
164.203
162.38(17)
91.31(17)
87.246
98.67(16)
94.33(16)
82.65(16)
88.427
86.04(15)
91.57(15)
93.522
172.20(17)
163.815
162.48(17)
91.26(17)
86.962
98.96(16)
94.28(17)
82.61(17)
88.640
85.84(15)
91.75(16)
93.87
172.5(2)
163.67
162.5(2)
91.4(2)
87.437
99.1(2)
94.1(2)
82.5(2)
88.608
85.7(2)
91.5(2)
94.352
72.407
91.3(2)
101.9(2)
86.27(9)
91.85(10)
93.377
72.829
91.69(10)
102.03(11)
72.621
91.62(15)
102.12(17)
72.635
91.25(16)
102.21(17)
O10−Mn1−N1
162.54(10)−
172.21(11)
162.38(17)−
172.33(17)
162.48(17)−
172.20(17)
162.5(2)−
172.5(2)
Transoid angle ranges
Cisoid angle ranges
72.829−102.03 72.621−102.12 72.635−102.21 72.407−101.9
(11) (17) (17) (2)
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
10
The coordination number of the two types of LnIII centers in
1
–
4
is different. The Ln1
center is eight-coordinated by one µ-alkoxo (O2), one µ-phenoxo (O4), two µ3-hydroxo (O7
and O8), one methoxy (O6) and three µ1,3-pivalate (O9, O11 and O13) oxygen atoms. On the
other hand, the Ln2 center is nine-coordinated by one µ-phenoxo (O4D), one µ-aldehyde
(O5), three µ3-hydroxo (O7, O8 and O8D), two µ1,3-pivalate (O12D and O14) and two η2-
nitrate (O15 and O16) oxygen atoms. The selected bond distances and angles around the
lanthanide(III) centers, Ln1 and Ln2, are listed in Tables 3 and 4, respectively. As can be
seen from these Tables, the Ln–O bond distances gradually decrease from
1 (Ln = Tb) to 4
(Ln = Er) for both crystallographically different metal ions (Ln1 and Ln2) and for each of the
eight (for Ln1)/nine (for Ln2) bonds; such an order is expected due to lanthanide contraction.
The ranges of the Ln–O bond distances in the TbIII and ErIII analogues are, respectively,
2.304–2.529 Å and 2.267–2.493 Å for the Ln1 center and 2.309–2.511 Å and 2.269–2.534 Å
for the Ln2 center. The corresponding bond angles involving Ln1 center in all the four
compounds are not very different (the range of differences is 0.19–1.78º), as are those
involving Ln2 center (the range of differences is 0.06–2.76º); the ranges of the O–Ln–O bond
angles in the TbIII and ErIII analogues are, respectively, 63.86–147.88º and 65.00–147.17º for
the Ln1 center and 50.08–143.26º and 50.0–144.38º for the Ln2 center. SHAPE[32] analyses
(Tables S2 and S3) reveal that biaugmented trigonal prism (BTPR-8) and spherical capped
square antiprism (CSAPR-9) are the ‘most ideal’ geometries of the Ln1 and Ln2 centers,
respectively. The general illustrations of the BTPR-8 and CSAPR-9 geometries of Ln1 and
Ln2 centers, respectively, are shown in Figure 3. In the BTPR-8 case, two trigonal planes are
defined by O2, O9 and O11 atoms and O4/O4D, O8 and O13 atoms, while O6 and O7/O7D
are the augmented atoms; the dihedral angle between the two trigonal planes is 9.82º. In the
CSAPR-9 geometry, the two square planes are defined by O4/O4D, O5, O8D/O8 and
O8/O8D atoms and O7/O7D, O14, O12/O12D and O16 atoms, while O15 is the capping
atom; the dihedral angle between the two least-squares square planes is 23.23º.
One C–H hydrogen atom (C11–H11A / C11–H11C) of a methyl group
of the imino-alkoxo moiety of one of the two [L1]2– ligands of a hexanuclear moiety interacts
with an oxygen atom (O17E) of a nitrate ligand of a neighbouring hexanuclear unit. Due to
this single type of C–H····O hydrogen bond, one hexanuclear unit is interlinked with four
other symmetry related hexanuclear units to form a two-dimensional topology in all the
compounds 1–4 (Figures S3–S6 and Table S4).
This article is protected by copyright. All rights reserved.

10.1002/ejic.201800792
European Journal of Inorganic Chemistry
11
a)
b)
Figure 3. General illustration of the co-ordination environment showing biaugmented
trigonal prism (BTPR-8) geometry of each Ln1 center (a) and spherical capped square
antiprism (CSAPR-9) geometry of each Ln2 center (b) in
1–4.
Table 3. The values of bond lengths (Å) and bond angles (º) around the Ln1 centers in 1–4
.
1
2
3
4
Coordination
Bond Lengths (Å)
environment of Ln1
Ln1−O2
Ln1−O4/O4D
Ln1−O6
Ln1−O7/O7D
Ln1−O8
Ln1−O9
Ln1−O11
Ln1−O13
2.402(2)
2.400(2)
2.529(2)
2.486(2)
2.3040(19)
2.315(2)
2.341(2)
2.368(3)
2.391(3)
2.383(3)
2.518(4)
2.475(4)
2.290(3)
2.308(4)
2.328(4)
2.346(4)
2.369(3)
2.366(3)
2.498(4)
2.449(4)
2.272(3)
2.286(4)
2.306(4)
2.330(4)
2.359(4)
2.359(4)
2.493(5)
2.444(5)
2.267(5)
2.274(5)
2.293(5)
2.330(5)
Bond Angles (º)
O2−Ln1−O4/O4D
O2−Ln1−O6
O2−Ln1−O7/O7D
O2−Ln1−O8
136.80(7)
136.28(8)
64.40(7)
73.95(7)
75.34(8)
73.79(8)
137.37(8)
136.95(11)
136.05(12)
64.67(11)
74.28(12)
75.44(13)
73.81(12)
137.50(13)
137.02(12)
135.95(13)
64.94(12)
74.51(12)
75.71(13)
74.04(13)
137.30(13)
137.31(15)
135.50(16)
65.28(16)
74.49(16)
75.77(17)
74.19(17)
137.49(17)
O2−Ln1−O9
O2−Ln1−O11
O2−Ln1−O13
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
12
O4/O4D−Ln1−O6
O4/O4D−Ln1−O7/O7D
O4/O4D−Ln1−O8
O4/O4D−Ln1−O9
O4/O4D−Ln1−O11
O4/O4D−Ln1−O13
O6−Ln1−O7/O7D
O6−Ln1−O8
O6−Ln1−O9
O6−Ln1−O11
O6−Ln1−O13
O7/O7D−Ln1−O8
O7/O7D−Ln1−O9
O7/O7D−Ln1−O11
O7/O7D−Ln1−O13
O8−Ln1−O9
63.86(7)
122.02(7)
70.39(7)
144.39(8)
80.95(8)
78.72(8)
147.88(8)
132.51(7)
81.96(8)
73.90(9)
73.58(10)
70.03(7)
81.92(8)
136.35(8)
76.90(8)
145.04(8)
87.39(8)
109.85(8)
99.70(9)
82.48(9)
146.75(9)
64.35(11)
121.45(11)
70.17(11)
144.22(12)
81.36(12)
78.21(13)
147.64(13)
132.81(12)
81.35(12)
73.85(14)
73.66(14)
69.76(12)
82.41(13)
136.62(13)
76.69(13)
145.40(13)
87.93(13)
109.13(13)
99.35(14)
82.84(14)
146.68(14)
64.64(12)
121.22(12)
70.01(12)
143.90(13)
81.38(13)
78.15(13)
147.23(13)
133.01(12)
80.75(13)
73.68(14)
73.90(14)
69.80(12)
82.69(13)
137.16(13)
76.14(13)
145.85(13)
88.35(13)
108.60(13)
99.19(14)
82.86(14)
146.70(14)
65.00(15)
120.73(15)
70.19(15)
143.59(16)
81.56(17)
77.47(17)
147.17(17)
133.39(16)
80.18(17)
73.33(18)
74.25(18)
69.65(16)
83.17(17)
137.58(18)
75.88(17)
145.99(17)
88.41(17)
108.23(18)
99.03(18)
83.38(18)
146.54(18)
O8−Ln1−O11
O8−Ln1−O13
O9−Ln1−O11
O9−Ln1−O13
O11−Ln1−O13
63.86(7)−
147.88(8)
64.35(11)−
146.68(14)
64.64(12)−
146.70(14)
65.00(15)−
147.17(17)
Angle ranges
Table 4. The values of bond lengths (Å) and bond angles (º) around the Ln2 centers in 1–4.
Coordination
Bond Lengths (Å)
1
2
3
4
environment of Ln2
.
Ln2−O4/O4D
Ln2−O5
Ln2−O7/O7D
Ln2−O8/O8D
Ln2−O8D/O8
2.358(2)
2.511(2)
2.484(2)
2.347(3)
2.505(4)
2.467(3)
2.324(3)
2.488(4)
2.447(3)
2.367(3)
2.347(3)
2.311(4)
2.279(4)
2.520(4)
2.478(4)
2.320(4)
2.481(5)
2.434(5)
2.342(5)
2.363(5)
2.303(5)
2.269(5)
2.534(6)
2.464(6)
2.3777(19) 2.387(3)
2.394(2)
2.344(2)
2.309(2)
2.539(3)
2.500(3)
2.367(3)
2.334(4)
2.295(4)
2.538(4)
2.494(4)
Ln2−O12/O12D
Ln2−O14
Ln2−O15
Ln2−O16
Bond Angles (º)
O4/O4D−Ln2−O5
O4/O4D−Ln2−O7/O7D
O4/O4D−Ln2−O8/O8D
O4/O4D−Ln2−O8D/O8
70.94(7)
137.92(7)
69.89(7)
92.09(7)
71.18(12)
71.38(12)
71.59(16)
138.01(11) 138.25(12) 138.24(17)
69.50(11)
92.14(12)
79.90(13)
69.47(11)
92.21(12)
79.84(13)
69.59(15)
91.99(16)
79.90(17)
O4/O4D−Ln2−O12/O12D 80.27(9)
O4/O4D−Ln2−O14
O4/O4D−Ln2−O15
O4/O4D−Ln2−O16
O5−Ln2−O7/O7D
O5−Ln2−O8/O8D
O5−Ln2−O8D/O8
O5−Ln2−O12/O12D
O5−Ln2−O14
142.91(8)
127.33(9)
79.96(9)
67.56(7)
121.01(7)
71.60(7)
136.15(9)
137.74(9)
100.08(9)
68.82(9)
128.10(7)
68.68(7)
142.39(12) 142.18(12) 141.98(16)
127.36(14) 127.44(14) 127.43(18)
79.86(14)
67.47(12)
80.21(15)
67.55(12)
80.52(19)
67.35(16)
120.90(12) 121.17(12) 121.66(16)
71.60(12) 71.79(12) 71.53(16)
135.97(14) 135.61(14) 135.33(17)
138.57(13) 139.32(13) 139.88(17)
100.06(14) 100.01(14) 99.74(19)
O5−Ln2−O15
O5−Ln2−O16
O7/O7D−Ln2−O8/O8D
O7/O7D−Ln2−O8D/O8
O7/O7D−Ln2−O12/O12D 136.92(8)
68.40(14)
128.05(12) 127.93(12) 127.99(17)
68.39(11) 68.35(11) 68.31(17)
137.32(13) 137.08(13) 136.88(18)
68.20(15)
68.02(19)
O7/O7D−Ln2−O14
O7/O7D−Ln2−O15
O7/O7D−Ln2−O16
O8/O8D−Ln2−O8D/O8
72.87(8)
67.99(8)
91.36(9)
67.67(8)
73.55(12)
68.27(13)
91.47(13)
67.73(14)
76.00(13)
73.91(13)
68.32(13)
91.29(14)
67.77(14)
76.32(13)
74.44(17)
68.32(18)
90.97(19)
68.17(19)
76.55(17)
O8/O8D−Ln2−O12/O12D 76.02(8)
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
13
O8/O8D−Ln2−O14
O8/O8D−Ln2−O15
O8/O8D−Ln2−O16
73.80(8)
138.81(9)
140.52(9)
73.89(12)
73.93(12)
73.80(16)
138.93(14) 138.70(14) 138.48(19)
139.68(14) 139.63(14) 141.02(19)
143.31(13) 143.69(13) 144.38(17)
O8D/O8−Ln2−O12/O12D 143.26(8)
O8D/O8−Ln2−O14
O8D/O8−Ln2−O15
O8D/O8−Ln2−O16
O12/O12D−Ln2−O14
O12/O12D−Ln2−O15
O12/O12D−Ln2−O16
O14−Ln2−O15
80.87(9)
81.66(14)
82.52(13)
83.63(18)
135.60(8)
140.08(9)
84.00(10)
71.92(9)
74.23(10)
77.74(10)
135.59(13) 135.58(13) 135.64(17)
140.44(14) 140.75(14) 139.18(19)
83.32(15)
72.00(14)
74.47(15)
77.41(15)
82.64(15)
71.62(14)
74.24(16)
76.73(15)
82.05(19)
71.30(18)
74.0(2)
76.3(2)
O14−Ln2−O16
127.28(10) 127.18(15) 126.32(15) 125.6(2)
O15−Ln2−O16
Angle ranges
50.08(10)
50.08(10)
−143.26(8) −143.31(1
3)
50.38(15)
50.38(15)
50.25(16)
50.25(16)
−143.69(1
3)
50.0(2)
50.0(2)
−144.38(1
7)
Previously, two series of MnIII LnIII compounds were reported. The general
2
4
composition (excluding solvent of crystallization) of one series is [MnIII LnIII (µ4-O)2(2-
2
4
pyridinemethoxido)4(picolinate)2(pivalate)6(µ-azide)2] (Ln = Sm, Eu, Gd, Tb, Dy, Ho)[33]
.
The general composition (excluding solvent of crystallization) of the second series is
[MnIII LnIII L2(µ4-O)2(azide)2(methoxido)2(methanol)4(NO3)2] (Ln = Y, Gd, Tb, Dy)[34]. So,
2
4
in terms of the ligands and bridges, the three series are drastically different, i. e., the present
series represent a new type of hexanuclear MnIII LnIII4 compounds. Interestingly, the bridging
2
pattern observed in this series of compounds resembles to that of MnII LnIII compounds
2
4
derived from an aminohydrazide ligand.[35] As already discussed, an aldehyde oxygen atom
bridges one MnIII and one LnIII ions in
. The bridging ability of aldehyde oxygen atom is
1–4
generally weak and therefore metal complexes having µ-O(aldehyde) moiety (ies) are rare.[36]
In all of those very few examples, the aldehyde oxygen atom bridges one type of metal ions
(e. g. either of NaI [36a,b,c], MgII[36d],ZnII[36e], HgII[36f], CuII[36g], NiII[36e,h], CoII[36i], ZrIV[36j]
TbIII[36k] and HoIII[36l]). Hence, bridging of an aldehyde oxygen atom to two different ions (a
,
3d metal ion MnIII and a 4f metal ion TbIII–ErIII) in
1–4 is a new type of observation in
coordination chemistry.
Magnetic Properties
Variable-temperature (2–300 K) magnetic susceptibilities of powdered samples of
1–4 were
measured at an applied dc field of 0.1 T. The cryomagnetic behavior of the four MnIII LnIII
2
4
compounds
1 (Ln = Tb), 2 (Ln = Dy), 3 (Ln = Ho) and 4 (Ln = Er) are shown in Figure 4 in
terms of χMT versus T plots and the χMT values at the highest and lowest temperatures of
measurements along with theoretical values are listed in Table 5. The χMT values at 300 K for
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
14
1–4
are, respectively, 53.19, 61.80, 61.40 and 50.41 cm3 K mol–1. The theoretical values
(53.27, 62.68, 62.25 and 51.90 cm3 K mol–1, respectively) for a system with non interacting
two high spin MnIII (S = 2) and four LnIII ions are very close to the observed for all the four
compounds. The cryomagnetic features in 1–4 are similar. On lowering the temperature, χMT
values remain practically constant between 300 and 150 K, after which it decreases slowly to
a lower temperature (ca. 12 K, 30 K, 50 K and 40 K for, respectively, for TbIII, DyIII, HoIII
and ErIII analogues) and then more rapidly down to 2 K, reaching the values of 11.88, 28.76,
22.18 and 22.14 cm3 K mol–1, respectively. The decrease in χMT values on lowering the
temperature in 1–4 may take place due to three factors, namely, depopulation of the upper
Stark levels of LnIII ions, single-ion zero-field effect of MnIII or weak/very weak
antiferromagnetic MnIII····LnIII/LnIII····LnIII exchange interactions or two or more of these.
70
60
50
40
1,(MnIII TbIII )
2
4
30
20
10
2,(MnIII DyIII )
2
4
χ
χ
χ
χ
3,(MnIII HoIII )
2
4
4,(MnIII ErIII )
2
4
0
50
100
150
200
250
300
T
/ K
Figure 4. Temperature dependence of the dc magnetic susceptibility for
1
–
4
having
), Dy
composition [MnIII LnIII L1 L2 (µ3-OH)4(µ1,3-Pivalate)6(NO3)2]·2CH3CN (Ln = Tb (
1
2
4
2
2
(2), Ho (3), Er (4)).
Table 5. Summary of static magnetic properties of 1–4
.
1
,
2
,
3
,
4,
MnIII TbIII
MnIII DyIII
MnIII HoIII
MnIII ErIII
2
7F6
53.27
4
2
4
2
5I8
62.25
4
2
4
Ground state of Ln
Expected χT at 300 K,
cm3 K mol-1
6H15/2
62.68
4I15/2
51.90
Observed χT at 300 K,
cm3 K mol-1
53.19
61.80
61.40
50.41
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
15
Observed χT at 2 K,
cm3 K mol-1
Magnetization at 7 T,
2K, Nβ
11.88
25.22
44.00
28.76
29.28
47.90
22.18
30.41
48.00
22.14
26.37
44.00
Saturation
Magnetization, Nβa
aFormula used for (MnIII LnIII ) metallic core to calculate saturation magnetization,
2
4
Saturation Magnetization (Ms) = 4gLnJ + 2gMnSMn.
The magnetization (M) data up to 7 T at 2 and 4 K for 1–4 have been collected, which
are shown in Figures S7–S10. The magnetization curves of all four compounds do not reach
saturation even at 7 T. The magnetization values at 2 K and 7 T are in fact significantly
smaller than the theoretical saturation values (Table 5). Moreover, as shown in Figures 5, 6,
S11 and S12, the M versus H/T plots of each of the four compounds do not pass through a
master curve and extent of divergence is appreciable. All these indicate significant anisotropy
or low lying excited states in these systems. As all the four compounds 1–4 have significant
anisotropy, they may behave as single molecule magnets and exploration of that aspect is
discussed below.
25
20
µ
µ
µ
µ
15
10
5
2K
4K
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
H / T(TK-1)
Figure 5. Magnetizations versus field/temperature plots for [MnIII TbIII L1 L2 (µ3-OH)4(µ1,3-
2
4
2
2
Pivalate)6(NO3)2]·2CH3CN (1), collected at 2 K and 4 K (Solid lines are guide for eyes only).
This article is protected by copyright. All rights reserved.

10.1002/ejic.201800792
European Journal of Inorganic Chemistry
16
30
25
20
15
10
5
µ
µ
µ
µ
2K
4K
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
H / T(TK-1)
Figure 6. Magnetizations versus field/temperature plots for [MnIII DyIII L1 L2 (µ3-OH)4(µ1,3-
2
4
2
2
Pivalate)6(NO3)2]·2CH3CN (
2
), collected at 2 K and 4 K (Solid lines are guide for eyes only).
Variable-temperature (1.8–20 K) ac susceptibilities of the HoIII
(3
) and ErIII
(4)
analogues at three frequencies, 1, 10 and 956 Hz and under both zero dc field and applied dc
field of 0.1 T are shown in Figures S13 and S14. The out-of-phase susceptibilities under both
zero-field and 0.1 T dc field of these two compounds are practically non-detectable, revealing
that these two compounds do not show slow relaxation of magnetization. Variable-
temperature (1.8–20 K) ac susceptibilities of the DyIII (
and 956 Hz and under zero dc field are shown in Figure S15 which reveals that out-of-phase
susceptibilities of
(DyIII) under zero field are detectable but no maxima are observed above
1.8 K (which is the detection limit of the magnetometer used). For better understanding of the
possible SMM behavior of
(DyIII), the following measurements have been carried out: (i)
2) analogue at three frequencies, 1, 10
2
2
Temperature-dependent (1.8‒3.6 K) χM' and χM'' at frequencies ranging from 1 to 1399 Hz
under both 1000 Oe (Figure S16) and 3500 Oe (Figure S17) applied dc fields; (ii) Frequency-
dependent (10‒1399 Hz) χM' and χM'' under several dc fields (0‒4500 Oe) at 1.8 K (Figure
S18). As is obvious from these data in these three figures, compound
expected, no loop is observed in hysteresis data at 1.8 K between +6.5 T and –6.5 T field of
(Figure S15), (Figure S13) and (Figure S14).
Variable-temperature (1.8–20 K) ac susceptibilities of the TbIII (
2 is not an SMM. As
2
3
4
1
) analogue at three
frequencies, 1, 10 and 956 Hz and under zero dc field are shown in Figure S19. Although no
maxima appear in the χM'' versus T plots, the χM'' values are detectable well and a frequency-
dependent splitting takes place below around 4 K. Therefore, the following measurements
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
17
have been carried out for understanding the possible SMM properties of
1
(TbIII): (i)
Temperature-dependent (1.8‒3.6 K) χM' and χM'' at frequencies ranging from 1 to 1399 Hz
under both 1000 Oe (Figure S20) and 3500 Oe (Figure 7) applied dc fields; (ii) Frequency-
dependent (1‒1399 Hz) χM' and χM'' under several dc fields (0‒4500 Oe) at 1.8 K (Figure 8);
(iii) Frequency-dependent (1‒1399 Hz) χM' and χM'' at fixed temperatures between 1.8 and 2.4
K under both 1000 Oe (Figure S21) and 3500 Oe (Figure 9) applied dc fields. Clear splitting
of both χM' and χM'' in all these five figures (Figures 7, 8, 9, S20 and S21) along with either
indication (Figures 7 and S20) or clear appearance (Figures 8, 9 and S21) of maxima in the
χM'' plots confirm that the TbIII system is an SMM. The Cole-Cole plots corresponding to
Figures 8 (fixed temperature of 1.8 K), S21 (fixed field of 1000 Oe) and 9 (fixed field of
3500 Oe) are shown in Figures S22, S23 and 10, which could be simulated[37] with the
generalized Debye model[38] giving the values of relaxation time (
τ) and relaxation
distribution parameter (α), as listed in Tables S5, S6 and S7, respectively. The ranges of the α
values are almost similar (0.23‒0.31 (Table S5), 0.23‒0.26 (Table S6) and 0.23‒0.27 (Table
S7)) corresponding to the three Cole-Cole plots. Notably, the Cole-Cole plots could not be
fitted with modified Debye model,[39] revealing that single relaxation takes place in
larger value (> 0.1) of α arises most probably due to intermolecular interactions (hydrogen
bonds in
have already been discussed).[22c,40] The relaxation times (τ) at different
1; slightly
1
temperatures corresponding to the frequency-dependent and temperature-dependent out-of-
phase data at 1000 Oe (Figures S21 and S23 and Table S6) and at 3500 Oe (Figures 9 and 10
and Table S7) could be fitted well (as in Figures 11 and 12) with the Arrhenius equation (ln
= ln τ0 + Ueff/kBT), giving Ueff values of 11.12 cm‒1 and 10.42 cm‒1 and τ0 values of 1.04 ×
10‒7 s and 1.62 × 10‒7 s, respectively. As
is a weak SMM, no loop is observed in Hysteresis
data at 1.8 K between +6.5 T and –6.5 T field of (Figure S19).
τ
1
2
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10.1002/ejic.201800792
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18
χM
'
10
χ
Μ
8
6
4
2
0
2.0
3.5
4.0
4.5
2.5Tem3p.0erature (K)
Figure 7. Temperature dependence of the in-phase (χM') and out-of-phase (χM'') ac magnetic
susceptibility for [MnIII TbIII L1 L2 (µ3-OH)4(µ1,3-Pivalate)6(NO3)2]·2CH3CN (
) collected at
1
2
4
2
2
1.55 G ac field oscillating at frequencies between 1 and 1399 Hz, and under 3500 Oe dc field.
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
19
a)
b)
Figure 8. Frequency dependence of the in-phase ac molar susceptibility (χM') components (a)
and out-of-phase ac molar susceptibility (χM'') components (b) for [MnIII TbIII L1 L2 (µ3-
2
4
2
2
OH)4(µ1,3-Pivalate)6(NO3)2]·2CH3CN (1) at 1.8 K under different dc fields. Solid lines are
guide for eyes only.
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10.1002/ejic.201800792
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20
a)
b)
Figure 9. Frequency dependence of the in-phase ac molar susceptibility (χM') components (a)
and out-of-phase ac molar susceptibility (χM'') components (b) for [MnIII TbIII L1 L2 (µ3-
2
4
2
2
OH)4(µ1,3-Pivalate)6(NO3)2]·2CH3CN (1) under 3500 Oe dc field. Solid lines are guide for
eyes only.
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10.1002/ejic.201800792
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21
1.85 K
1.90 K
1.95 K
2.00 K
2.05 K
2.10 K
2.15 K
2.20 K
2.30 K
2.40 K
2.50 K
3.0
2.5
2.0
1.5
1.0
χ
χ
χ
χ
0.5
0.0
2
4
6
8
10
12
χΜ'/ cm3 mol-1
Figure 10. Cole-Cole plots for the frequency-dependent ac data (in Figure 9) at the indicated
temperatures under 3500 Oe dc field for [MnIII TbIII L1 L2 (µ3-OH)4(µ1,3-
2
4
2
2
Pivalate)6(NO3)2]·2CH3CN (1). The solid lines are the best fits to the experimental data
obtained with the generalized Debye model.
-7.2
Ueff
=
11.12 cm-1
-7.6
-8.0
-8.4
-8.8
0.46
0.48
0.50
0.54
0.56
-01.52
1/T (K )
Figure 11. Plot of ln(
dependent ac data (in Figures S21 and S23 and Table S6) at several temperatures under 1000
Oe dc field for [MnIII TbIII L1 L2 (µ3-OH)4(µ1,3-Pivalate)6(NO3)2]·2CH3CN (
). The red solid
τ) versus reciprocal temperature corresponding to the frequency-
1
2
4
2
2
line represents the linear fitting in the temperature range 1.80K‒2.15K.
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
22
-7.6
-8.0
-8.4
-8.8
Ueff = 10.42 cm-1
0.46
0.48
0.50
0.52
0.54
-1
1/T (K )
Figure 12. Plot of ln(
dependent ac data (in Figures 9 and 10 and Table S7) at several temperatures under 3500 Oe
dc field for [MnIII TbIII L1 L2 (µ3-OH)4(µ1,3-Pivalate)6(NO3)2]·2CH3CN (
). The red solid
τ) versus reciprocal temperature corresponding to the frequency-
1
2
4
2
2
line represents the linear fitting in the temperature range 1.80‒2.20 K.
A MAGELLAN[41] analysis (Figure 13) of the MnIII DyIII compound
2 reveals the
2
4
following: (i) The local anisotropic axes of the lanthanide centers are much deviated from
colinearity; (ii) The local anisotropic axis of any of the two lanthanide centers and the Jahn
Teller axis of the manganese(III) ion are far from being collinear. This actually reduces the
overall anisotropy of the molecule. As a result, compound
2 and other compounds herein
exhibit either no slow relaxation of magnetization or weak SMM property.
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10.1002/ejic.201800792
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23
Figure 13. The direction of the local anisotropy axes (green dotted lines) of DyIII ions and
Jahn-Teller axes (black solid lines) of MnIII ions in [MnIII DyIII L1 L2 (µ3-OH)4(µ1,3-
2
4
2
2
Pivalate)6(NO3)2]·2CH3CN (2).
It is relevant to compare the present series of compounds with those of the two
previously reported MnIII LnIII series. Of the six compounds of the [MnIII LnIII (µ4-O)2(2-
2
4
2
4
pyridinemethoxido)4(picolinate)2(pivalate)6(µ-azide)2] (Ln = Sm, Eu, Gd, Tb, Dy, Ho) series,
only TbIII analogue exhibit slow relaxation of magnetization under zero-field.[33] Of the four
compounds of the [MnIII LnIII L2(µ4-O)2(azide)2(methoxido)2(methanol)4(NO3)2] (Ln = Y,
2
4
Gd, Tb, Dy) series, the TbIII and DyIII analogues are SMMs under a applied dc field of 0.1
T.[34]
Conclusions
Although a number of aminoalcohol/aminophenol was previously utilized to derive either 4f
or 3d-4f compounds from 3-methoxysalicylaldehyde–aminoalcohol/aminophenol Schiff base
ligands, this investigation introduces 2-amino-2-methyl-1-propanol in this area and our aim
of getting new types of compounds has been fulfilled as the present series of four
isomorphous/isostructural, hexanuclear 3d-4f MnIII LnIII compounds (Ln = Tb, Dy, Ho, Er)
2
4
represent a new type of structure having these two types of metal ions. The bridging ability of
aldehyde oxygen atom is seldom observed. In those rare examples, aldehyde oxygen atom
bridges one type of metal ion. In contrast, interestingly, aldehyde oxygen atom acts as a
bridging ligand to two different types of metal ions (MnIII and LnIII) in the present series of
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10.1002/ejic.201800792
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24
compounds. The MnIII LnIII compounds in this investigation are also rare examples of
2
4
hexanuclear systems having two manganese(III) and four lanthanide(III) ions. Hopefully, 3d-
4f compounds with other 3d metal ions with H2L1 will stabilize new types of structures and so
this area may be further explored.
Detailed dc and ac magnetic studies reveal the following: (i) All compounds are
significantly anisotropic; (ii) The TbIII analogue is an SMM while the DyIII, HoIII and ErIII
analogues do not show slow relaxation of magnetization even under an applied dc field of
0.1/0.35 T. Some compounds (DyIII, HoIII and ErIII analogues) here do not show slow
relaxation of magnetization and only one (TbIII analogue; Ueff = ca. 11 cm‒1) is a weak SMM,
which are probably related to both the relative orientations of the anisotropic axes of
lanthanides and Jahn-Teller axes of manganese(III) as well as to intermolecular hydrogen
bonding interactions in these molecules.[22c]
Experimental section
Materials and physical measurements. All the reagents and solvents were purchased from
commercial sources and used as received. Elemental (C, H and N) analyses were performed
on a Perkin-Elmer 2400 II analyzer. IR spectra were recorded in the region 400–4000 cm–1 on
a Bruker-Optics Alpha–T spectrophotometer with samples as KBr disks. The magnetic
measurements were carried out with a SQUID magnetometer (MPMS, Quantum Design).
Syntheses of 1
[MnIII2LnIII4(L1)2(L2)2(µ3-OH)4(µ1,3-Pivalate)6(NO3)2]
Ln = Ho; , Ln = Er). All the four complexes were prepared by employing a general synthetic
–4:
·2CH3CN (1, Ln = Tb; 2, Ln = Dy; 3,
4
protocol, as follows: 5 mL ‘H2L1 solution’ consisting of 0.2 mmol H2L1 was taken and diluted
to 15 mL with acetonitrile. To it, triethylamine (0.056 mL, 0.4 mmol) and 2 mL methanol
solution of corresponding Ln(NO3)3·5H2O (0.2 mmol) were successively added and stirred
for 20 min. To the yellow coloured clear solution, a solution of MnCl2·4H2O (0.04 g, 0.2
mmol) in 2 mL methanol was added. Finally, a solution of pivalic acid (0.04 g, 0.4 mmol) and
triethylamine (0.056 g, 0.4 mmol) in 3 mL methanol was added and stirred for further 5 h.
The resulting brown coloured reaction mixture was filtered to remove any suspended
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10.1002/ejic.201800792
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25
particles and the filtrate was kept at ambient temperature for slow evaporation. After a few
days, dark brown crystalline compound was obtained, which was collected by filtration,
washed with cold methanol and dried in vacuum. Recrystallization from acetonitrile-
diethylether mixture (diffusion technique) produced dark brown crystalline compound
containing diffraction quality single crystals.
Data for
1. Yield: 0.067 g, 57% (based on lanthanide). C74H108N6O34Mn2Tb4
(2371.22): calcd. C 37.48, H 4.59, N 3.54; found: C 37.15, H 4.44, N 3.40. FT-IR (KBr):
–
1628 [vs, ν(C═N)], 1384, 1313 [s, m, ν(NO3 )], 1564, 1470 [(asym, s), (sym, m), ν(COO–)]
cm−1.
Data for 2. Yield: 0.073 g, 62% (based on lanthanide). C74H108N6O34Mn2Dy4
(2385.54): calcd. C 37.26, H 4.56, N 3.52; found: C 37.05, H 4.34, N 3.45. FT-IR (KBr):
–
1627 [vs, ν(C═N)], 1376, 1311 [s, m, ν(NO3 )], 1565, 1469 [(asym, s), (sym, m), ν(COO–)]
cm−1.
Data for
3. Yield: 0.076 g, 64% (based on lanthanide). C74H108N6O34Mn2Ho4
(2395.26): calcd. C 37.11, H 4.54, N 3.51; found: C 36.85, H 4.48, N 3.36. FT-IR (KBr):
–
1627 [vs, ν(C═N)], 1384, 1314 [s, m, ν(NO3 )], 1567, 1470 [(asym, s), (sym, m), ν(COO–)]
cm−1.
Data for
4. Yieid: 0.072 g, 60% (based on lanthanide). C74H108N6O34Mn2Er4
(2404.58): calcd. C 36.96, H 4.52, N 3.49; found: C 36.62, H 4.36, N 3.30. FT-IR (KBr):
–
1627 [vs, ν(C═N)], 1384, 1311 [s, m, ν(NO3 )], 1567, 1469 [(asym, s), (sym, m), ν(COO–)]
cm−1.
Crystal structure determination of 1–4.
The crystallographic data for 1−4 are summarized in Table 1. X-ray diffraction data were
collected on a Bruker-APEX II SMART CCD diffractometer at 296 K using graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å). The packages SAINT[42a] and
SADABS[42b] were used for data processing and absorption correction. The structures were
solved by direct and Fourier methods and refined by full-matrix least-squares based on F2
using SHELXS-97[42c] and SHELXL-2014/7[42d] packages.
During the refinement of the structures, two/three pivalate carbon atoms in
were found disordered over two sites. The disordered carbon atoms are as follows: C25 of
one pivalate and C33 of another pivalate in ; C24 of one pivalate and C33 of another
1/2/3/4
1
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10.1002/ejic.201800792
European Journal of Inorganic Chemistry
26
pivalate in
pivalate and C33 of another pivalate in
individual atom to refine freely. The final occupancy parameters were set as follows: 0.65
and 0.35 for C25 and 0.65 and 0.35 for C33 in ; 0.70 and 0.30 for C24 and 0.55 and 0.45 for
C33 in ; 0.80 and 0.20 for C24, 0.50 and 0.50 for C25 and 0.60 and 0.40 for C33 in ; 0.50
and 0.50 for C24, 0.55 and 0.45 for C25 and 0.55 and 0.45 for C33 in
2
; C24 and C25 of one pivalate and C33 of another pivalate in
3
; C24, C25 of one
4
. The disorder was fixed/treated allowing each
1
2
3
4
.
Each structure contains two acetonitrile (CH3CN) molecules as solvent of
crystallisation and those molecules have been properly assigned for each complex. All the
hydrogen atoms of 1–4 were inserted in geometrically calculated positions with fixed thermal
parameters. All non-hydrogen atoms were refined anisotropically, while all the hydrogen
atoms were refined isotropically. The final refinement converged at the R1/wR2 (I>2σ(I))
values of 0.0384/0.0808, 0.0374/0.0769, 0.0379/0.0911 and 0.0427/0.0853 for
respectively.
1–4,
CCDC 1841040–1841043 for
1–4, respectively, contains the supplementary
crystallographic data for this paper. These CIF data can also be obtained free of charge from
the Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif.
Supporting Information: Figures S1–S23 and Tables S1–S7.
Acknowledgments
Financial support for this work has been received from Government of India through Council
of Scientific and Industrial Research (fellowship to S. R. and S. G.) and University Grants
Commission (contingency from CAS-V project to S. M.), Crystallography was performed at
the DST-FIST-funded Single Crystal Diffractometer Facility at the Department of Chemistry,
University of Calcutta.
Keywords: SMM
/
Hexanuclear / Magnetic properties / Lanthanide(III) / Manganese(III)
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10.1002/ejic.201800792
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