Towards a better understanding of magnetic exchange mediated by hydrogen bonds in Mn(iii)/Fe(iii) salen-type supramolecular dimers

Article abstract of DOI:10.1039/c4dt02025a

A thorough study of structural and magnetic properties was performed on a series of trinuclear and dinuclear Mn(iii)/Fe(iii) complexes consisting of [M(L4)(Solv)]⁺ and [Fe(CN)₅(NO)]^2- moieties (M = Fe(iii) or Mn(iii), Solv

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ARTICLE TYPE
Towards better understanding of magnetic exchange mediated by
hydrogen bonds in Mn(III)/Fe(III) salenꢀtype supramolecular dimers
Ivan Nemec, Radovan Herchel, Tomáš Šilha, and Zdeněk Trávníček*
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
The thorough study of structural and magnetic properties were performed on a series of trinuclear and
dinuclear M(III)/Fe(III) complexes consisting of [M(L4)(Solv)]+ and [Fe(CN)5(NO)]2ꢀ moieties (M =
Fe(III) or Mn(III), Solv = H2O or CH3OH, L4 = tetradentate salenꢀtype ligands), in which dominant
magnetic exchange is mediated by OS–H···OPh hydrogen bonds in [M(L4)(Solv)]+···[M(L4)(Solv)]+
10 supramolecular dimers. As deduced from magnetic analysis involving also determination of zeroꢀfield
splitting (ZFS) parameters for Mn(III) and Fe(III) ion as well as from comprehensive DFT calculations
and modelling, it may be concluded that the strength of magnetic exchange is correlated with a number of
hydrogen bonds and with the OPh⋅⋅⋅OS distance between the phenolic oxygen of salenꢀtype ligand (OPh)
and oxygen of the solvent coordinated to the adjacent metal atom (OS)
a transitional metal, x = a number of cyanido ligands, m = charge
of M), and b) heteroleptic cyanido complexes [M(L)(CN)x](x+lꢀm)ꢀ
(L = an organic ligand different from CN, l = charge of L). Such
50 cyanidometallates can be left further to react with the
coordinatively unsaturated complexes (or with labile complexes
from the kinetic point of view) forming thus compounds
exhibiting a wide variability in their structures and magnetic
properties.
15 Introduction
In recent years, significant amount of the research work has been
devoted to the study of molecular magnetic materials due to their
potential applications as molecular switches or highꢀdensity
memory materials.1 There is an unceasing effort to correlate
20 magnetic properties of such materials to their structures in order
to establish the rational design methods for preparation of
molecule based magnetic materials. The most of the correlations
dealt with the strength of the isotropic magnetic interactions
mediated through the covalent bonds between two paramagnetic
25 metal atoms,2 or with the magnetic anisotropy defined by the
zeroꢀfield splitting (ZFS) parameters – the prerequisite for
observation of the slowꢀrelaxation of magnetisation. However,
there is another magnetic exchange coupling phenomenon
emerging especially in the study of the organicꢀbased molecular
30 magnets and that is magnetic exchange mediated by nonꢀcovalent
contacts such as hydrogen bonding or π−π stacking of the
aromatic rings. This kind of exchange might play important role
also in the coordination compounds with interesting magnetic
properties, e.g. in mediating intrachain exchange interaction thus
35 giving rise to singleꢀchain magnets,3 in magnetic sponges,4 in
occurrence of slowꢀmagnetic relaxation in polynuclear
compounds5 or in magnetic properties of simple paramagnetic
compounds.6
55 The objective of this article was to prepare and characterize a
series of trinuclear nitroprusside bridged Mn(III)/Fe(III)
complexes containing Schiff base ligands11, more concretelly,
salenꢀtype ligands (L42ꢀ
=
salen2ꢀ
=
N,N'ꢀethaneꢀ
bis(salicylideneiminate) dianion, other abbreviations of the
60 ligands used or mentioned in this work can be found in the
reference12) and therefore, such type of polynuclear salenꢀtype
compounds bridged by metallocyanate will be discussed below
briefly.
The cationic part in the presented complexes consists of the
65 tetradentate salenꢀlike dianion ligand (L42ꢀ) coordinated to the
transition metal creating thus the [M(L4)](mꢀ2)ꢀ moiety with the L4
ligand forming the equatorial plane of the complex. Two axial
positions are potentially available for the coordination and
therefore, the [M(L4)](mꢀ2)ꢀ moiety can be considered as a perfect
70 building block for the preparation of low dimensional
coordination compounds but also variously dimensional (1D, 2D
or 3D) coordination polymers can be prepared. In general, three
basic structural types can be distinguished where the [M(L4)](mꢀ2)ꢀ
moiety is coordinated by:
The big group of the magnetically interesting coordination
40 compounds are the cyanidoꢀbridged complexes (so called
Prussian blue analogues and related compounds) 7,8 which are of
interest due to their structural and magnetic properties9 or their
potential use as optical devices and catalyst.10 As a bridging unit
a wide variety of the cyanido complexes can be used and these
45 can be generally divided into two subgroups: a) homoleptic
cyanido complexes with the general formula [M(CN)x](xꢀm)ꢀ (M =
75 a) One Nꢀcyanido ligand from the cyanidometallate and the
second axial position is occupied by the solvent molecule (most
usually water or methanol). The resulting complex structure is
lowꢀdimensional and polynuclear due to the terminal function of
the solvent ligand (further abbreviated as Solv). However, the
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Solv molecules often extend the dimensionality (usually to 1D
atom. In order to explore this phenomenon thoroughly we have
arrays) of the crystal structure by the hydrogen bonding formed 35 decided to study another system with diamagnetic bridging
with suitable acceptor atoms from the neighbouring molecules
(Scheme 1A, vide infra).
cyanidometallate, i.e. nitroprusside [Fe(CN)5(NO)]2ꢀ and further,
we have focused our attention not only to its MnIII complexes but
also to the FeIII ones.
From the literature survey aimed on the above mentioned
40 compounds it is apparent that the nitropusside–[MIII(L4)]+
compounds (MIII = FeIII, MnIII), which belong to group (A,
Scheme 1A) involve only MnIII complexes (the explanation of the
ligand abbreviations can be found in Scheme 2):
5
b) Two Nꢀcyanido ligands, each from different adjacent
cyanidometallate molecules and therefore, the resulting complex
structure is polymeric in most cases (Scheme 1B, vide infra).
c) One Nꢀcyanido ligand from the cyanidometallate whereas the
second position is occupied by the phenolic oxygen atom from
10 the adjacent [M(L4)](mꢀ2)ꢀ molecule forming thus the dimeric unit.
It must be stressed that this kind of the dimer is not unique for the
[{Mn(L4i)(H2O)}2{
ꢀ
ꢀ
ꢀFe(CN)5(NO)}]
ꢀFe (CN)5NO}]·2CH3OH
[{Mn(L4m)(CH3OH)}2{ ꢀFe(CN)5 NO}]
[{Mn(L4k)(H2O)}2{ ꢀFe(CN)5NO}]·2H2O (7d)
[{Mn(L4l)(H2O)}2{
ꢀFe(CN)5NO}] (7e).25
(7a),22
(7b),
(7c),23
and
MnIII complexes only, but it can be also found in other transition 45 [{Mn(L4b)(H2O)}2{
metal complexes (Co
NiII 19, Scheme 1C).
,
II/III 13 FeIII,14 RuIII,15 TiIII,16 ZnII,17 CuII 18 and
ꢀ
24
ꢀ
ꢀ
The compounds of the group (B) are polymeric with twoꢀ
50 dimensional crystal structure (Scheme 1B). The nitroprusside
anion acts as a moiety bridging four [MIII(L4)]+ entities in all the
reported cases, and creating thus the gridꢀlike sheets built from
the [{M(L4)}2{ꢀ4ꢀFe(CN)5NO}]n units. This group contains six
26
coordination polymers: [{Mn(L4j)}2{
ꢀ
4ꢀFe(CN)5(NO)}] (7f)
,
55 [{Mn(L4f)}2{
(NO)}]n (7h)
ꢀ
4ꢀFe(CN)5(NO)}] (7g) 24, [{Fe(L4f)}2{
ꢀ
4ꢀFe(CN)5
27
28
,
[{Fe(L4g)}2{
ꢀ
4ꢀFe(CN)5(NO)}] (7i)
(7j)
4ꢀFe(CN)5(NO)}]·2H2O (7k) 23
,
[{Mn(L4f)}2{
[{Mn(L4f)}2{
ꢀ
ꢀ
4ꢀFe(CN)5(NO)}]·2H2O
2
and
.
The group (C), depicted in Scheme 1C, is represented by one
60 example only: [{Mn(L4h)}2{
4ꢀFe(CN)5(NO)}] (7l).24 This
ꢀ
compound is polymeric with four [{Mn(L4h)}2]2+ dimers bridged
by one nitroprusside anion thus creating twoꢀdimensional
network. In this article the great deal of attention is devoted to the
study of seven novel trinuclear nitroprusside complexes with
65 salenꢀtype Schiff base ligands having the general formula
[{MIII(L4)(H2O)}2{
= Fe or Mn.
ꢀꢀFe(CN)5(NO)}]·xCH3OH, x = 0 or 1 and M
15
Scheme 1. Schematic representations of three structural types of the
[M(L4)](mꢀ2)ꢀ complexes with cyanidometallates
In our previous works we have reported on the coordination
compounds built from various [MnIII(L4)]+ moieties bridged by
20 the [Pt(SCN)4]2ꢀ or [Pt(SCN)6]2ꢀ complex anions.20,21 Almost all
of the prepared compounds were trinuclear with the general
formula [{Mn(L4)(Solv)}2{ꢀꢀPt(SCN)x}], where x = 4 or 6, and
thus they belong to the group (a). It was shown that the exchange
interactions mediated by the diamagnetic bridging anion are
25 negligible and it was proved that the dominant magnetic
exchange pathway is included by nonꢀcovalent interactions, i.e.
hydrogen bonding within the supramolecular dimer
[Mn(L4)(Solv)]+···[Mn(L4)(Solv)]+. Therefore, this kind of
supramolecular system represents an ideal object of study for
30 investigation of the magnetic exchange mediation through
hydrogen bonding. Furthermore, it was observed that there is a
significant difference in the strength of the magnetic exchange
depending from the type of the Solv molecule bonded to the MnIII
70 Scheme 2. Schematic representations of H2L4 tetradentate Schiff base
ligands used in this work and their abbreviations.
The crystal structures of the complexes [{Fe(L4b)(H2O)}2{
Fe(CN)5(NO)}]·2CH3OH (3a), [{Fe(L4c)(H2O)}2{ ꢀFe(CN)5
(NO)}] (4a), [{Mn(L4c)(H2O)}2{ ꢀFe(CN)5(NO)}] (4b) and
75 [{Fe(L4d)(H2O)}2{ ꢀFe(CN)5(NO)}] (5a) have been determined
ꢀꢀ
ꢀ
ꢀ
ꢀ
by a single Xꢀray diffraction. The magnetic measurements were
performed for all the prepared compounds including two
2
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compounds
[{Fe(L4a)(H2O)}2{
[{Mn(L4a)(H2O)}2{
Furthermore, we report on novel type of the nitroprusside
without
ꢀFe(CN)5(NO)}]·CH3OH
ꢀFe(CN)5(NO)}]·CH3OH
determined
crystal
structures:
4b and 10.173(4) in 5a. The coordination polyhedrons of the
ꢀ
ꢀ
(2a), 40 [M(L4)(H2O)]+ subunits can be described as axially elongated
(2b).
octahedrons and the distortion is more obvious for the Mn(III)
derivatives due to the JahnꢀTeller effect. In general, it can be
concluded, as for herein and previously reported salenꢀtype
complexes, that the Mn(III) compounds show significantly longer
45 axial (usually MꢀNCN and MꢀOS bonds, NCN stands for nitrogen
atom of the nitroprusside cyanido group, OS is oxygen atom from
coordinated solvent molecule) bond lengths (ca. d(MnꢀNCN) =
2.30 Å, d(FeꢀNCN) = 2.17 Å, d(MnꢀOS) = 2.27 Å, d(FeꢀOS) = 2.10
Å, Table 1) in comparison with Fe(III) ones. On the contrary, the
5
complex with ionic structure where the [{Mn(L4e)(H2O)}{ꢀꢀ
Fe(CN)5(NO)}]ꢀ anion is charge balanced by the
[{Mn(L4e)(H2O)(CH3OH)]+ cation (6b).
With the aim to elucidate the magnetic exchange and magnetic
anisotropy in herein reported compounds, temperature and field
10 dependent magnetic data were simultaneously fitted to provide
trustworthy values of isotropic exchange constants (J) and singleꢀ
ion zeroꢀfield splitting parameters (D). Furthermore, thorough 50 MꢀNim bond lengths are longer in the case of the Fe(III)
DFT study was undertaken to determine dominant superꢀ
exchange pathways and the role of minor changes in crystal
15 structures on overall magnetic exchange. Ultimate goal of our
investigations is to build up a magnetoꢀstructural correlation
complexes (ca. d(MnꢀNim) = 1.99 Å, d(FeꢀNim) = 2.11 Å, Nim
stands for nitrogen atom from imino group of L4). The length of
the MꢀOPh bonds is roughly the same for both central ions (Table
1, OPh stands for the phenolate oxygen atoms). The angular
between the isotropic magnetic exchange constant
J
and 55 distortions from the ideal octahedron Σ 30 are obviously smaller
structural parameters in the group of compounds containing
[M(L4)(Solv)]+···[M(L4)(Solv)]+ supramolecular dimers. So far
20 several studies devoted to magnetic exchange mediated by
O−H···O hydrogen bonds were published,29 but mainly for
for the Mn(III) compounds (Table 1).
As it was mentioned in the introduction these trinuclear
complexes belong to the group (a) in which the nonꢀcovalent
connections between the polynuclear species are provided by the
copper(II) complexes, in which only the isotropic exchange is 60 hydrogen bonding between the coordinated Solv molecules and
present. In our study, the situation is complicated by zeroꢀfield
splitting of Fe(III) and Mn(III) atoms, and thus, advanced
25 magnetic analysis had to be employed.
phenolate oxygen atoms and thus, the roughly linear arrays of the
centrosymmetric and supramolecular
[Mn(L4)(Solv)]+·····[Mn(L4)(Solv)]+ dimers “separated” by the
nitroprusside anions are formed. In the crystal structure of the
65 compounds 3a, 4a, 4b and 5a the Solv molecules (Solv = H2O)
form two basic types of the interconnections: i) simple
OS−H···OS hydrogen bond (in 3a), ii) bifurcated hydrogen bond
where two Hꢀatoms from the water molecule interact with four
oxygen atom acceptors (two alkoxy (OA) and two phenolate
Results and Discussion
Crystal structures of trinuclear complexes 3a, 4a, 4b and 5a
The selected bond lengths for herein and already reported salenꢀ
type complexes are summarized in Table 1. The crystal data and
30 structure refinements for compounds reported in this article are 70 oxygen atoms, in 4a, 4b and 5a). The hydrogen bonding
given in Table 2.
bifurcation prolongs the donor···acceptor lengths in the case of
OS···OPh contacts (in Å): d(OS···OPh) = 2.690(3) in 3a vs.
2.792(2) and 2.927(2) in 4a, 2.851(3) and 2.934(3) in 4b,
2.814(2) and 2.866(2) in 5a. The OS···OA hydrogen bonds are
The molecular structures of these complexes are very similar
consisting of the trinuclear [{MIII(L4)(H2O)}2{
ꢀ
ꢀFe(CN)5(NO)}]
moieties (MIII = FeIII or MnIII, Fig. S1ꢀS4 in Electronic
35 Supplementary Information (ESI)), which have slightly bent 75 longer in general, however, in crystal structure of 4b we observe
{H2OꢀMIIIꢀNCꢀFeꢀCNꢀMIIIꢀH2O} arrangement, (Fig. 1ꢀ3). The
MIII···MIII separations within the trinuclear complexes are very
similar (in Å): 10.1621(6) in 3a, 10.1532(5) in 4a, 10.225(2) in
one relatively short contact (in Å): d(OS···OA) = 3.024(2) and
3.248(2) in 4a, 2.866(3) and 3.115(4) in 4b, 3.064(2) and
3.279(2) in 5a.
80
Fig. 1 Fragments of the crystal structures of the complexes 4a (up) and 4b (down). The hydrogen atoms are omitted for clarity, except for the atoms
responsible for the formation of “supramolecular dimer” of 4a and 4b due to hydrogen bonds (dashed lines). Selected bond lengths and angles are shown
in Figs. S2 and S3 in ESI.
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Fig. 2 Left: Fragments of the crystal structures of the complexes 3a (left up) and 5a (left down). The hydrogen atoms and methanol molecules (3a) are
omitted for clarity, except for the atoms responsible for the formation of “supramolecular dimer” of 3a and 5a due to hydrogen bonds (dashed lines).
Selected bond lengths and angles are shown in Figs S1 and S4 in ESI. Right: A perspective view on the 2D supramolecular structure in 3a.
5
The MIII···MIII separations within the supramolecular dimer are
from relatively narrow range (in Å): 4.8728(5) in 3a, 4.5608(4) in
Table 1 Selected structural parameters for nitroprusside complexes. Bond
lengths are given in Å.
4a, 4.7132(9) in 4b and 4.594(2) in 5a. The crystal structure of 3a
differs significantly from the structures of 4a, 4b and 5a due to a
10 presence of the coꢀcrystallized molecule of methanol. This
extends the structural dimensionality of the compound to 2D by
[a]
[a]
[b]
MꢀNim
MꢀOPh
MꢀNCN
2.151(2)
2.1512(14)
2.343(3)
2.163(2)
MꢀOS
Σ/
°
3a
4a
4b
5a
2.109
2.085
1.973
2.084
1.896
1.897
1.878
1.889
2.0548(16)
2.1309(12)
2.256(2)
37.7
56.4
44.4
53.9
2.143(2)
linking
supramolecular
chains
[{Fe(L4b)(H2O)}2{ꢀꢀ
6b
mol1
6b
mol2
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
Fe(CN)5(NO)}]n together by hydrogen bonding between
coordinated water molecule and methanol and further, methanol
15 is hydrogen bonded to nonꢀcoordinated nitrogen atom from the
neighbouring nitroprusside bridging complex (Fig. 2).
1.962
1.953
1.882
1.868
2.245(3)
2.292(2)
22.4
29.5
2.309(2)
2.256(2)
2.271(5)
2.223(5)
2.358(3)
2.224(5)
2.258(2)
−
1.970
1.986
1.962
2.036
1.981
1.989
1.985
2.109
2.111
1.987
1.969
1.978
1.863
1.872
1.881
1.900
1.880
1.863
1.888
1.898
1.898
1.888
1.881
1.885
2.355(6)
2.304(6)
2.288(4)
2.263(6)
2.394(2)
2.378(2)
2.305(3)
2.173(6)
2.175(5)
2.304(4)
2.326(3)
2.246(4)
49.6
27.2
53.8
35.4
46.3
54.1
34.1
57.0
55.3
33.8
35.9
57.7
Crystal structure of complex 6b
−
−
−
−
−
−
−
The crystal structure of 6b is depicted in Fig. 3. It consists of the
dimeric [{Mn(L4e)(H2O)}{ꢀꢀFe(CN)5NO}] (6b mol1) and
20 [{Mn(L4e)(H2O)(CH3OH)] (6b mol2) moieties, where both
manganese atoms are hexacoordinated with four donor atoms
(N2O2) coming from the L4e2ꢀ ligand. The remaining
coordination sites (axial positions) are occupied by two oxygen
7k
7l
atoms coming from the coordinated water and methanol in 6b 40 a The average values calculated from two bond length values. b Distortion
parameter defined as sum of deviations from 90° of the twelve cis angles
25 mol1, on the other hand, the axial positions in 6b mol2 are
occupied by the oxygen atom from the water molecule and by the
in the coordination sphere.30
Both complex molecules with an assistance of the coꢀcrystallized
water and methanol molecules create rich 2D network of
45 hydrogen bonds (Fig. 3). As a main building block of the crystal
nitrogen atom from the bridging cyanido group of nitroprusside.
The average bond lengths are (mol1, mol2; in Å): d(Mn–Nim) =
1.961, 1.953, d(Mn–OPh) = 1.882, 1.868. The axial bond lengths
30 differ in the length due to the different solvent molecule
coordinated to the Mn(III) atom (in Å): d(MnꢀOS) = 2.292(3)
(H2O) in mol1, 2.256(3) (CH3OH) and 2.309(3) (H2O) in mol2. It
must be noted that the crystal structure of 6b exhibits
substitutional disorder on mol2, where the methanol molecule
35 (the main part, the occupation factor of 0.68) is partially
substituted by the water molecule and this is further hydrogen
bonded to another disordered water molecule (Fig. S5 in ESI).
structure
the
[{Mn(L4e)(H2O)}{
ꢀꢀ
Fe(CN)5NO}][{Mn(L4e)(H2O)(CH3OH)]
assembly
(mol1···mol2) can be considered, in which the interconnection
between the mol1 and mol2 parts is provided by hydrogen
50 bonding between the coordinated water molecules and
complementary phenolate oxygen atoms, similarly to compounds
3a−5a. The mol1···mol2 assembly is further propagated to linear
1D chain by a series of hydrogen bonds between the coordinated
methanol molecule from mol2 and coꢀcrystallized water molecule
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and further by hydrogen bonding to coꢀcrystallized methanol,
which is in a close contact with the adjacent cyanido group (the
trans position with respect to the cyanido group coordinating the
the neighbouring cyanido group (the cis position with respect to
the cyanido group coordinating the Mn atom) and also by
hydrogen bonds between the coꢀcrystallized water molecule and
Mn atom) from the other mol1···mol2 assembly. Linear 10 cyanido group from the neighbouring mol1 moiety.
supramolecular chains are interconnected via hydrogen bonding
5
between the coordinated water molecule from the mol1 part and
Fig. 3. Fragment of the crystal structure of the complex 6b. The hydrogen atoms are omitted for clarity, except for the atoms responsible for the formation
of “supramolecular dimer” of 6b due to hydrogen bonds and highlight several πꢀπ stacking in the complex (dashed lines). Selected bond lengths (Å) and
angles (°) are shown in Fig. S5 in ESI.
15
maximum on susceptibility (T < 10 K) is a fingerprint of the
antiferromagnetically coupled homospin dimer. This results in
Infrared spectroscopy
The presence of the Schiff base in the complexes was indicated
by FTꢀIR spectra measured in the range of 400ꢀ4000 cmꢀ1. The
spectra of all the compounds exhibit two weak intensity bands at
50 decrease of ꢀeff/ꢀB on cooling. Moreover, the interplay of the
zeroꢀfield splitting on magnetic properties cannot be neglected,
especially for Mn(III) atoms.
20 3115ꢀ3132 and 3025ꢀ3037 cm−1 corresponding to asymmetric and
symmetric stretching vibrations of the aromatic C–H groups. The
characteristic bands assignable to the C=N and (C–C)ar vibrations
were observed in the 1625ꢀ1613 cmꢀ1, and 1595ꢀ1437 cmꢀ1 region,
respectively, in all complexes. Formations of the cyanidoꢀbridges
25 in all the nitroprusside complexes are evidenced by the C≡N
vibration stretching bands in the 2000ꢀ2200 cmꢀ1 region. The
maximum at 2143 cmꢀ1 may be assigned to the vibration of the
cyanido group in sodium nitroprusside dihydrate, while the
maxima associated with the vibration in the case of complexes
30 2aꢀ6b were observed in the range of 2138ꢀ2163 cmꢀ1.31 The
strong peaks in the region of 1906ꢀ1922 cmꢀ1 are assignable to the
N=O stretching vibration, which is lower than that found in the
complex Na2[Fe(CN)5NO]·2H2O (1936 cmꢀ1).
Therefore the following spin Hamiltonian was postulated
2
r
r
2
2
2
ˆ
ˆ
ˆ
ˆ
ˆ
ˆ
H = −J S ⋅S
+
D (Si,z − Si / 3) + ꢀBBgiSi,a − zj Si,a Si,a
i
(
)
∑
1
i=1
(1)
55 The first term stands for the isotropic exchange (J), the second
part is due to the zeroꢀfield splitting (D – an axial singleꢀion ZFS
parameter), the third part is the Zeeman term and the last
expression represented with the zj variable is the common
molecularꢀfield correction parameter, which is due to small
60 intra/interꢀchain molecular interactions. The <Sa> is a thermal
average of the molecular spin projection in a direction of
magnetic field defined as Ba = Bꢁ(sinθcosϕ, sinθsinϕ, cosθ) with
the help of the polar coordinates. Then, the molar magnetization
in aꢀdirection of magnetic field can be numerically calculated as


C+
Z
C
exp −εa,i / kT
(
)
(
)
∑∑∑ ik
a
li


kl
Magnetic properties
i
k
l
Ma = −NA
exp −εa,i / kT
35 In all the presented compounds, we can observe the formation of
quasiꢀdimers among [{MnIII(L4)(H2O)}]+ or [{FeIII(L4)(H2O)}]+
subunits held by hydrogen bonds between the coordinated solvent
molecules and phenolic oxygen atoms. Within these quasiꢀ
dimers, the Mn⋅⋅⋅Mn and Fe⋅⋅⋅Fe separations vary between 4.71ꢀ
40 5.06 Å, and 4.59ꢀ4.87 Å, respectively, in contrast to large
interatomic distances (more than 10 Å) through covalent bonds
formed by diamagnetic nitroprusside bridges.
These structural aspects strongly suggest that the superꢀexchange
mechanism is mainly active through hydrogen bonds. The nature
45 of the magnetic exchange can be estimated by inspecting the
temperature dependence of susceptibility and the effective
magnetic moment of these compounds. The presence of the
(
)
∑
i
65
(2)
where Za is the matrix element of the Zeeman term for the aꢀ
direction of the magnetic field and C are the eigenvectors
resulting from the diagonalization of the complete spin
Hamiltonian matrix. Then, the averaged molar magnetization of
70 the powder sample was calculated as integral (orientational)
average
2
π
Mmol =1/ 4
π Ma sin
θdθdϕ
π ∫0 ∫0
(3)
With the aim to bring more insight in general properties of the
antiferomagnetically coupled dimer with ZFS, the shift of
75 temperature of maximum of the susceptibility (Tmax
) was
inspected for varying ratios of D/J either for S1 = S2 = 2 or S1 = S2
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= 5/2 (Fig. 4). There is a simple formula, which interconnects the
strength of the antiferromagnetic exchange with Tmax, but it is
available only for the isotropic case: |J|/kTmax = 0.462 for S1 = S2
= 2 and |J|/kTmax = 0.347 for S1 = S2 = 5/2. In both cases, the
equal to 7.1 µB, which is very close to theoretical value of 6.93 ꢀB
for two paramagnetic nonꢀinteracting centres with S = 2 (g = 2.0).
The susceptibility is increasing on cooling and is reaching its
maximum at 6.5 K, which is also accompanied by decrease of ꢀeff
5
introducing the nonꢀzero zeroꢀfield splitting results in increase of 40 below 50 K down to 2.1 µB at 1.9 K. The isothermal
Tmax, and this change is more emphasized for D < 0 (Fig. 4).
As both antiferromagnetic exchange and ZFS have similar effects
magnetization at 2 K is not saturated even at B = 7 T and has
value of Mmol/NAµB = 6.2, which is below the saturation limit of
Mmol/NAµB = 8 (2 x S = 2 and g = 2.0). By applying equations 1ꢀ3
to both temperature and field dependent magnetic data, we
on magnetic properties, the decrease of the ꢀeff/ꢀB, the both
temperature and field dependent magnetization data were
10 experimentally acquired and concurrently used in finding the 45 obtained J = −0.72(1) cmꢀ1, g = 2.048(1), D = −3.65(9) cmꢀ1 and
bestꢀfit parameters of the above introduced spin Hamiltonian
(eq.1). Furthermore, the standard deviations of varied parameters
were calculated with 95% probability confidence limits.32
zj = –0.06(1) cmꢀ1 (Fig. 5). The negative and large value of Dꢀ
parameter are in agreement with the elongated octahedrons of
Mn(III) centres due to the JahnꢀTeller effect. However, the
chromophores of the respective Mn(III) centres differ in one
50 apical position – {MnO3N3} for Mn1 and {MnO4N2} for Mn2
(Fig. 3) and because of that the calculated Dꢀvalue serves as an
average value of both distinct Mn(III) centers. The most
important outcome is that considerably large magnetic exchange
is mediated by hydrogen bonds between Mn(III) centers.
55
Trinuclear
complexes 4b and 2b
[{Mn(L4)(H2O)}2{ꢀꢀFe(CN)5NO}]·xCH3OH
The compound 4b shows very similar magnetic properties to
compound 6b (Fig. 5), which justifies the presumption that
60 dominant magnetic exchange is mediated through hydrogen
bonds (d(Mn⋅⋅⋅Mn)
= 4.7132(9) Å) and not through the
diamagnetic nitroprusside anion (d(Mn⋅⋅⋅Mn) = 10.225(2) Å).
Thus, the magnetic data of 4b were treated using the same
procedure as for 6b under the condition that D1 = D2, because
65 there is only one Mn atom in the asymmetric unit. The resulting
parameters are J = −0.79(1) cmꢀ1, g = 1.981(2), D = −3.7(1) cmꢀ1
and zj = +0.12(2) cmꢀ1 (Fig. 5). The last reported Mn(III)
compound is complex 2b, which exhibits comparable properties
to compounds 4b and 6b (Fig. 5) Thus, we used the same model
70 despite the lack of its Xꢀray crystal structure. The best fit was
obtained with the following parameters: J = −0.55(1) cmꢀ1, g =
1.987(2), D = −3.5(2) cmꢀ1 and zj = –0.10(2) cmꢀ1 (Fig. 5).
15
Fig. 4 Top: the modelling of the interplay of the antiferromagnetic
exchange (J) and the singleꢀion zeroꢀfield splitting (D) on the temperature
of the maximum of the molar magnetization (or the mean susceptibility)
Tmax for a dinuclear systems. The line’s labels correspond to J’s values.
Trinuclear
75 complexes 2a, 3a, 4a and 5a
[{Fe(L4)(H2O)}2{ꢀꢀFe(CN)5NO}]·xCH3OH
20 The Dꢀparameter was varied from ꢀ10 to +10 cmꢀ1. Bottom: the variation
of magnetic properties for S1 = S2 = 2 dimer, with the fixed parameters J =
ꢀ1 cmꢀ1 and g = 2.0, while D was varied: D = 0 (black full line), D = ꢀ2
cmꢀ1 (blue dashed line) and D = ꢀ4 cmꢀ1 (red dotted line).
The magnetic behaviour of trinuclear Fe(III)ꢀnitroprusside
complexes 2a, 3a, 4a and 5a was found to be very similar (Fig.
6). The room temperature values of the effective magnetic
moment are in the range of 8.42–8.57
80 theoretical value of 8.37 ꢀB for two paramagnetic nonꢀinteracting
centres with S = 5/2 (g = 2.0). Upon cooling, the ꢀeff ꢀB
ꢀB, which is very close to
25 Dinuclear complex 6b
/
dependences are almost constant down to 50 K and then they start
to decrease to values of 3.33, 3.46, 2.68 and 2.73 at T = 1.9 K for
2a, 3a, 4a, and 5a, respectively.
The unique molecular and crystal structure of 6b results in
forming quasi linear and discrete trimers of MnIIIꢀMnIIIꢀFeII type
in which paramagnetic manganese atoms are connected through
hydrogen bonds (d(Mn⋅⋅⋅Mn) = 5.0575(7) Å) and the diamagnetic
30 nitroprusside anion serves as a terminal entity. This give us an
opportunity to study the magnetic exchange of the MnIIIꢀMnIII
type mediated by waterꢀhydrogen bonds unaffected by bridging
through nitroprusside, which is found in the remaining reported
complexes. The experimental magnetic data are presented in Fig.
35 5. The room temperature effective magnetic moment of 6b is
6
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15 presence of the antiferromagnetic exchange between Fe(III)
mediated by hydrogen bonds and/or also the zeroꢀfield splitting
of Fe(III) centers. Moreover, the isothermal magnetization
measurements at liquid helium temperatures (2.0 and 4.6 K)
support this presumption, because the experimental values of
20 Mmol/NAꢀB are below the theoretical saturation value Mmol/NAꢀB =
gꢁSꢁ2 = 10 (g = 2.0, S = 5/2), Fig. 6. Therefore, the same spin
Hamiltonian was used as in the equation 1, but in this case S1 = S2
= 5/2 holds. It must be stressed that including the ZFS term has
been essential to responsibly fit all experimental data together.
25 We have found that slightly better fits could be obtained for
positive than negative sign of Dꢀparameters and both sets are
tabulated for each of the presented compound in Table 3 (see also
Fig.
6
and Figs. S9ꢀ12, ESI). Evidently, the weak
antiferromagnetic exchange was found in the range from ꢀ0.52 to
30 ꢀ1.05 cmꢀ1. In the case of positive Dꢀparameter, the |D/J| ratios
vary between 1.70 and 2.45, but in the case of negative Dꢀ
parameter, the |D/J| ratios vary between 0.50 and 1.15. To
summarize, the values of the antiferromagnetic exchange in
Mn(III) and Fe(III) compounds 2aꢀ6b were found to be in narrow
35 interval between –0.52 cmꢀ1 and –1.05 cmꢀ1, but the ZFS is much
larger in case of Mn(III) complexes. This is expected feature for
Mn(III) atom due to the JahnꢀTeller effect and larger distortion of
coordination polyhedral.33
Furthermore, we strived to find clear magnetoꢀstructural
40 correlation either for isotropic exchange (J) or magnetic
anisotropy (D) in the reported series of compounds taking into
account various structural parameters. However, the Dꢀparameter
does not simply correlate with geometric deformation of
coordination chromophore (Σ), which can be explained by
45 complexity and variedness of donor atoms. Conversely, there are
some remarks concerning the isotropic exchange, which must be
taken into account: our previous results20 predicted weaker
exchange interactions within the supramolecular dimer
[M(L4)(Solv)]+···[M(L4)(Solv)]+. when Solv = CH3OH and
50 stronger ones for compounds with Solv = H2O. As can be seen
from Table
3 this prediction holds true; the compounds
containing [M(L4)(CH3OH)]+ fragments possess weaker
exchange interactions with J values ranging from ꢀ0.3 to ꢀ0.6 cmꢀ1
while the [M(L4)(H2O)]+ compounds have J values lower from ꢀ
55 0.7 to ꢀ1.3 (when not including most probably overestimated J
values due to the omitting of the ZFS term in the magnetic data
analysis, for details see Table 3). From the collected data it seems
to be apparent that difference in the quality of the exchange
interactions mediation between coordinated methanol and water
60 molecules is not caused by the intrinsic difference found between
these two solvents, but it is most probably caused just by the
different number of the hydrogen bonds formed by each
particular solvent molecule: CH3OH (2 hydrogen bonds within
the dimer), H2O (usually 4 hydrogen bonds). This can be
65 supported by two examples from the present series of the
nitroprusside bridged compounds.
Fig. 5 Magnetic properties of 2b, 4b and 6b. Each plot shows the
5
temperature dependence of the effective magnetic moment (calculated
from the temperature dependence of magnetization at B = 0.1 T; inset)
and the isothermal magnetizations measured at T = 2.0 (◊) and 4.6 K (□).
Experimental data – empty symbols, full lines ꢀ the best fit calculated
with J = −0.55(1) cmꢀ1, g = 1.987(2), D = −3.5(2) cmꢀ1 and zj = –0.10(2)
10 cmꢀ1 for 2b, J = −0.79(1) cmꢀ1, g = 1.981(2), D = −3.7(1) cmꢀ1 and zj =
+0.12(2) cmꢀ1 for 4b and J = −0.72(1) cmꢀ1, g = 2.048(1), D = −3.65(9)
cmꢀ1 and zj = –0.06(1) cmꢀ1 for 6b
.
Also, the maxima of the molar magnetization (or mean molar
susceptibility) ranged from 3.5 to 6.5 K. This fact indicates the
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ARTICLE TYPE
Table 2 Crystallographic data and structure refinement details for the complexes 3a
,
4a
,
4b, 5 and 6b
3a·2CH3OH
C47H40N10O9Fe3
1056.44
4a
C45H48N10O11Fe3
1072.48
4b
5a
C47H52N10O11Fe3
1100.54
6b·H2O·CH3OH
C62.5H50N10O10.5Fe1Mn2
1274.85
Formula
Mr
C45H48N10O11Fe1Mn2
1070.66
T / K
150(2)
150(2)
150(2)
150(2)
150(2)
Crystal system
a / Å
Triclinic, Pꢀ1
10.8773(4)
11.0243(4)
11.6197(4)
99.960(3)
116.960(4)
105.062(3)
1128.77(10)
1
Monoclinic, C2/c
23.0051(7)
13.7936(4)
14.7860(4)
90.00
Monoclinic, P21/c
13.2000(11)
13.1797(8)
14.860(2)
90.00
Monoclinic, P21/c
13.651(5)
13.387(5)
15.434(4)
90.00
Triclinic Pꢀ1
10.6373(3)
15.3822(4)
18.2505(5)
78.980(2)
79.305(2)
73.460(2)
2782.45(13)
2
b / Å
c / Å
α
β
γ
/ °
/ °
/ °
96.407(3)
90.00
4662.6(2)
4
116.958(8)
90.00
2304.3(4)
2
120.29(2)
90.00
2435.5(14)
2
V / Å3
Z
Dc / gꢁcmꢀ3
1.554
1.528
1.543
1.501
1.520
1.021
542
0.993
2216
0.923
1104
0.952
1140
0.778
1310
ꢀ
/ mmꢀ1
F (0 0 0)
Reflections collected/unique
Data/restraints/parameters
Goodnessꢀofꢀfit (GOF) on F2
10554/3948
3948/3/320
1.110
16257/4091
4091/3/322
1.043
18371/4058
4058/0/315
0.875
19415/4240
4240/5/364
1.052
24066/9726
9726/13/815
1.009
0.0350/0.0912
0.0415/0.0928
0.0238/0.0625
0.0295/0.0638
0.0469/0.0890
0.0972/0.0965
0.0303/0.0837
0.0417/0.0861
0.0426/0.0946
0.0735/0.1000
R1, wR2 (I> 2
R1, wR2 (all data)
σ(I))
5
Fig. 6 Magnetic properties of 2a, 3, 4a and 5a. Each plot shows the temperature dependence of the effective magnetic moment (calculated from the
temperature dependence of magnetization at B = 0.1 T; inset) and the isothermal magnetizations measured at T = 2.0 (◊) and 4.6 K (□). Experimental data
– empty symbols, full lines ꢀ the best fit calculated with: J = −0.64(2) cmꢀ1, g = 2.031(2), D = +1.1(2) cmꢀ1 and zj = –0.09(2) cmꢀ1 for 2a, J = −0.53(2) cmꢀ1,
g = 2.042(3), D = +1.3(2) cmꢀ1 and zj = –0.24(3) cmꢀ1 for 3a, J = −1.01(4) cmꢀ1, g = 2.064(3), D = +1.9(3) cmꢀ1 and zj = +0.03(3) cmꢀ1 for 4a, J = −0.94(2)
10
cmꢀ1, g = 2.033(1), D = +1.6(2) cmꢀ1 and zj = –0.026(4) cmꢀ1 for 5a
.
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The compound 3a represents a novel structural type of the
[M(L4)(H2O)]+···[M(L4)(H2O)]+ supramolecular dimer which is
held by two hydrogen bonds whereas two other remaining
aminodiethylenesalicylideneiminate) dianion, L4o2ꢀ = N,N´ꢀ3ꢀ
methylbenzeneꢀbis(3ꢀethoxysalicylideneiminate) dianion, L4p2ꢀ
N,N´ꢀethyleneꢀbis(naphthylidenebenzeneiminate) dianion, were
=
hydrogen atoms point to the lattice solvent molecules (Fig. 2, Fig. 45 also included in Table 3.
5
7). Noticeably, the value of the coupling constant (J = −0.52 cmꢀ
1) is very similar to those observed for the compounds with Solv
= CH3OH (Table 3). Furthermore, the compound 6b has another
unique asymetric dimeric synthon with three supportive hydrogen
bonds (Fig. 3, Fig. 7). The strength of the exchange interaction is
The isotropic exchange analysis was based on the following
Heisenberg spin Hamiltonian
r
r
ˆ
H = −J S ⋅ S
(
)
1
2
(4)
and evaluation of energy difference between highꢀspin (HS) and
50 brokenꢀsymmetry (BS) spin states, ꢁ = EBS – EHS, using quantumꢀ
chemical computational software ORCA. The final Jꢀvalues were
calculated by the Ruiz’s
10 in between the values typical for CH3OH and H2O with J = 0.72
cmꢀ1.
J Ruiz = ꢁ / 2S S + S
(
)
1
2
1
(5)
and Yamaguchi’s
JYam = 2ꢁ / S2 − S2
(
)
HS
BS
55
(6)
approaches and are tabulated for [{MIII(Li)(H2O)(NC)}2]
fragments in Table 3. HS spin states had small spin
contamination, which is manifested by the calculated <S2>HS
values that are close to the theoretical values <S2>HS = S(S + 1)
60 where S = 5 for M = Fe and S = 4 for M = Mn (SHS is the total
spin value for the HS state), while BS spin states’s <S2>LS values
are close to MS2 + SHS (MS is spin projection of the BS spin state).
First, the DFT calculation for [{FeIII(L3)(H2O)}2{ꢀꢀ
FeII(CN)5NO}] molecular fragment of 4a resulted in trifling
65 magnetic exchange, JYam = +0.031 cmꢀ1 (JRuiz = +0.026 cmꢀ1),
thus supporting our presumption that this superexchange path is
very inefficient in promoting magnetic exchange.
Fig. 7 A detailed view on novel types of the “supramolecular dimers” in
3a (left) and 6b (right). The hydrogen atoms are omitted for clarity,
15 except for the atoms involved in hydrogen bonding (black dashed lines).
DFT calculations
In order to support our conclusions from magnetochemical
analyses of the experimental data, we performed the isotropic
Next, the calculation performed for Hꢀbonded dimers
[{MIII(L4)(H2O)(NC)}2] (M = Fe, Mn) resulted in the Jꢀvalues
exchange parameters’ calculations using the DFT method for Hꢀ 70 tabulated in Table 3. The JYamꢀvalues were found in the range
20 bond
bridged
dinuclear
molecular
fragments
from –0.54 to –0.60 cmꢀ1 for [{FeIII(L4)(H2O)(NC)}2] (3a, 4a and
5a), and in the range from –0.56 to –0.94 cmꢀ1 for
[{MnIII(L4)(H2O)(NC)}2] and [{MnIII(L4)(H2O)(NCS)}2] (2bꢀ6b
and 7bꢀ11). The good congruence between Jꢀvalues derived from
[{MIII(L4)(H2O)(NC)}2] (M = Fe, Mn) for compounds reported
here 3a–6b, and also for similar compounds reported in literature,
7aꢀ7e. Moreover, we investigated also the role of the diamagnetic
nitroprusside anion in mediation of magnetic exchange for 75 magnetochemical analysis of the experimental data and DFT
25 compound 4a using the [{FeIII(L4c)(H2O)}2{
molecular fragment.
ꢀ
ꢀFeII(CN)5NO}]
calculations was obtained for compounds 3a, 4b, 6b and 7b,
when taking into account the JYam values. However, the larger
discrepancies were observed for the remaining compounds, e.g.
in case of 4a magnetic analyses resulted in Jmag ≈ –1.0 cmꢀ1,
All the calculations were based on experimental Xꢀray geometries
except for 7a, where some hydrogen atoms were missing in CSD
deposited data (CCDC IGAKEG), and their atomic positions 80 which is in contrast to the values of JRuiz = –0.48 cmꢀ1 or JYam = –
30 were optimized with the BP86 functional and def2ꢀTZVP(ꢀf)
basis set.
0.57 cmꢀ1 (Table 3). The question then arises: why the same used
DFT method resulted in so unequal results in comparison to
magnetic analysis? We can speculate that these discrepancies are
due to small changes in the crystal structures, which may occur at
As this work extend our research of magnetic exchange in
transition metal complexes containing diamagnetic bridging
polythiocyanidoplatinate,20,21 the same hybrid functional B3LYP 85 lower temperature than that used for Xꢀray analysis. To testify
35 together with def2ꢀTZVP basis set and the scalar relativistic
secondꢀorder Douglas–Kroll–Hess Hamiltonian were used.
Therefore, the results of relevant hydrogen bonds bridged
this possibility, we performed constrained geometry optimization
for [{FeIII(L4c)(H2O)(NC)}2] molecular fragment of 4a, where
the Fe⋅⋅⋅Fe distance was varied between 4.4 and 4.9 Å. The
geometry was optimized using the BP86 functional with def2ꢀ
compounds,
[{Mn(L4o)(H2O)}2{ꢀꢀPt(SCN)6}]
(8)
and
[{Mn(L4n)(H2O)}2{ꢂꢀPt(SCN)4}] (9), [{Mn(L4b)(CH3OH)}2{ꢂꢀ 90 TZVP(ꢀf) basis set together with conductorꢀlike screening model
40 Pt(SCN)4}] (10), [{Mn(L4p)(CH3OH)}2{ꢂꢀPt(SCN)4}] (11),
where N,N´ꢀbenzeneꢀbis(4ꢀ
L4n2ꢀ
(COSMO), van der Waals corrections (VDW10) and the
relativistic effects with the scalar relativistic secondꢀorder
=
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Douglas–Kroll–Hess Hamiltonian (DKH2). Afterwards, the Jꢀ
values were calculated at the B3LYP+DKH2/def2ꢀTZVP level of
theory for each of the optimized molecular structures to ensure
the same condition as that used for molecular fragments of 3aꢀ11
based on their Xꢀray structures.
5
Fig. 9 Molecular fragment [{Fe(L4c)(H2O)(NC)}2] of 4a: the comparison
of hydrogen atom positions based on Xꢀray structure (light gray balls) and
based on geometry optimized using BP86/def2ꢀTZVP(ꢀf) (dark gray
balls). The rest of hydrogen atoms not involved into the formation of
supramolecular dimer were omitted for clarity.
45
The Hꢀatoms geometry optimization procedure for molecular
fragments 4a, 5a, 4b, 7a, 7e and 8ꢀ11 generally resulted in the
increase of the O–H bonds, which can be demonstrated for O–H
50 distances of water molecules in 4a: d(O–H)Xꢀray = 0.831 and
0.837 Å and d(O–H)DFT = 0.989 and 0.994 Å (Fig. 9). In next
step, the Jꢀvalues were calculated using B3LYP+DKH2/def2ꢀ
TZVP and resulted in much larger antiferromagnetic exchange
constants (Table 3), which can be exemplified again for 4a: JRuiz
55 = –0.81 cmꢀ1 or JYam = –0.98 cmꢀ1 and especially the latter value
is almost identical to Jmag ≈ –1.0 cmꢀ1 determined from magnetic
analysis.
Fig. 8 The calculated isotropic exchange JRuiz (circles) and JYam (squares)
as a function of the Fe⋅⋅⋅Fe distance (left) and the OPh⋅⋅⋅OS (right) in the
molecular fragment [{Fe(L4c)(H2O)(NC)}2] of 4a calculated using
B3LYP+DKH2/def2ꢀTZVP, while the molecular geometries were
optimized using BP86+COSMO+VDW10+DKH2/def2ꢀTZVP(ꢀf).
10
This resulted in magnetoꢀstructural correlation depicted in Fig. 8
from which we can conclude that the antiferromagnetic exchange
is increasing with decreasing the Fe⋅⋅⋅Fe separation. However, the
15 approximate change of ꢁ(JDFT)/ꢁ(dFeꢀFe) ≈ 0.5–1.0 cmꢀ1/Å cannot
explain itself large discrepancies between JDFT and Jmag in the
case of possibly small changes in crystal structure induced by
cooling to very low temperature.
Thus, we also tested another hypothesis related to positions of
20 hydrogen atoms in molecular/crystal structure. It is well known
that the determination of the hydrogen atom positions from the Xꢀ
ray analysis can be potentially inaccurate, especially when the
hydrogen atoms are bonded to atoms with high electronegativity
such as oxygen or nitrogen atoms. This was pointed out also in
25 several DFT studies devoted to problematic of magnetic
exchange mediated by hydrogen bonds in other transition metal
complexes.29 Due to these reasons we have to strive out how the
position of hydrogen atoms influences the magnetic exchange
interactions. Therefore, the positions of hydrogen atoms involved
30 in magnetic exchange pathway (in Hꢀbond bridged dinuclear
molecular fragments [{MIII(L4)(H2O)(NC)}2] (M = Fe, Mn) (4a,
5a, 4b, 7a, and 7e) and also for [{Mn(L4)(H2O)(NCS)}2] (8 and
9), while keeping all other atoms in the same positions as
determined from their Xꢀray structures) were optimized using the
35 BP86/defꢀTZVP(ꢀf). The situation for other complexes, namely
3a, 6b, 7b and 7d is more complex, because water molecules are
not only involved in hydrogen bonds between closest metal
atoms, but also form hydrogen bonds to methanol molecules (3a
and 7b) or to cyanido ligands of the nitroprusside anions from
40 other supramolecular chains (6b and 7d), so they were excluded.
Fig. 10 The isotropic exchange Jꢀvalues as a function of the average
60 OPh···OS distance in Mn(III) compounds molecular compounds 4b
, 7a, 7e,
8
and , either derived from magnetic analysis (left) or calculated by DFT
9
using B3LYP+DKH2/def2ꢀTZVP on geometries in which only the
hydrogen atoms were optimized using BP86/def2ꢀTZVP(ꢀf).
65 These results demonstrate much larger sensitivity of magnetic
exchange to position of hydrogen atom within the O–H⋅⋅⋅O
hydrogen bond than to the M⋅⋅⋅M distance, which can explain
some discrepancies observed between Jꢀvalues derived from
magnetic analysis and DFT calculations based on Xꢀray
70 molecular structures. Furthermore, there is a clear evidence that
10 | Journal Name, [year], [vol], 00–00
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DOI: 10.1039/C4DT02025A
Jꢀvalue correlates with averaged OPh···OS distance both in Fe(III)
and Mn(III) complexes as demonstrated in Figure 8 and Figure
10,
respectively.
Table 3 Summary of structural details, results from magnetic analysis and DFT calculations for iron(III) and manganese(III)
5
nitroprusside/polythiocyanidoplatinateꢀbridged complexes.
Selected structural data[a]
Magnetic analysis data[b]
DFT calculated data
<S2>HS
/
JRuiz/JYam
Compo
und
zj
J
D
M⋅⋅⋅M*
(Å)
M⋅⋅⋅M
OPh⋅⋅⋅OPh*
OPh⋅⋅⋅OS*
(Å)
g
(cmꢀ1)
(cmꢀ1)
(cmꢀ1)
<S2>BS
(cmꢀ1)
(Å)
(Å)
−0.64(2)
−0.67(5)
−0.53(2)
–0.52(6)
−1.01(4)
−1.00(5)
−0.94(2)
−1.05(4)
−0.55(1)
2.031(2)
2.033(3)
2.042(3)
2.044(3)
2.064(3)
2.070(3)
2.033(1)
2.036(2)
1.987(2)
+1.1(2)
−0.48(7)
+1.3(2)
−0.6(1)
+1.9(3)
–0.69(7)
+1.6(2)
–0.53(5)
−3.5(2)
–0.09(2)
–0.13(5)
–0.24(3)
–0.29(5)
+0.03(3)
–0.12(6)
–0.026(4)
–0.02(4)
–0.10(2)
2a
3a
4a
−
−
−
−
3.459(2)
2.690(3)
2.927(2)
2.792(2)
2.865(2)
2.814(2)
s
30.02/5.02
30.02/5.02
30.02/5.02
30.02/5.02
30.02/5.02
30.02/5.02
–0.45/–0.54
4.8728(5)
4.5608(4)
4.593(2)
10.1621(6)
10.1532(5)
10.173(4)
3.682(2)
3.263(2)
3.338(2)
–0.48/–0.57
–0.81/–0.98f
–0.50/–0.60
–0.86/–1.04 f
5a
2b
4b
2.934(3)
2.851(3)
3.243(3)
3.022(3)
2.907(6)
2.830(7)
3.338(4)
2.790(6)
3.089(6)
2.910(6)
2.913(2)
2.858(2)
2.882(4)
2.930(5)
2.707(8),
2.806(8)
2.779(8),
2.834(8)
2.728(3)
2.777(2)
20.07/4.07
20.07/4.07
–0.59/–0.74
–0.94/–1.16f
4.7132(9)
5.0575(7)
4.690(2)
5.152(3)
5.067(2)
4.694(1)
4.7007(9)
10.225(2)
–
3.296(3)
−0.79(1)
−0.72(1)
–0.88c
1.981(2)
2.048(1)
2.05
−3.7(1)
−3.65(9)
–2.62
–2.46
–
+0.12(2)
3.534(3)
3.579(3)
6b
7a
7b
7d
7e
8
–0.06(1)
20.07/4.07
20.06/4.06
20.07/4.07
20.08/4.08
–0.55/–0.68
–0.98/–1.24f
–0.71/–0.89
–0.61/–0.76
10.358(3)
10.288(3)
10.400(2)
10.388(3)
12.5840(8)
3.339(5)
3.803(5)
–
–0.90d
2.02
–
–
3.496(6)
3.748(6)
–1.90e
2.0
20.07/4.07
20.07/4.07
20.09/4.09
20.08/4.08
–0.50/–0.62
–0.82/–1.04f
–0.45/–0.56
–0.82/–1.02f
3.303(2)
3.242(4)
–
–
–
–
–0.88
2.09
ꢀ3.06
+0.21
3.365(8)
3.550(8)
20.07/4.07
20.07/4.07
–0.76/–0.94
–1.40/–1.74f
9
4.858(2)
12.017(2)
–1.31(6)
1.848(2)
–2.2(1)
–0.41(5)
10
11
5.004(2)
5.0682(2)
12.044(2)
11.749(3)
3.469(3)
3.764(2)
ꢀ0.53(1)
ꢀ0.47(1)
1.879(2)
1.889(2)
ꢀ4.6(2)
ꢀ3.6(1)
+0.23(2)
+0.03(1)
20.08/4.08
20.08/4.08
–0.54/–0.68
–0.33/–0.42
[a] M⋅⋅⋅M* is shortest distance between metal atoms bridged through water mediated hydrogen bonds; M⋅⋅⋅M is shortest distance between metal atoms
bridged by nitroprusside or polythiocyanidoplatinate; OPh⋅⋅⋅OPh* and OPh⋅⋅⋅OS* are distances between oxygen atoms of phenol groups or phenol group and
oxygen atom of water/methanol molecule attached to different metal atoms M and M*. [b] Jꢀvalues reported in literature were scaled according to spin
Hamiltonian in equation 1. [c] ref 22., [d] ref 23.[e] ref 24, comment: Jꢀvalue is most probably overestimated due to omitting ZFS term. [f] results based
10 on DFT calculations performed on molecular fragments, in which hydrogen atoms were optimized with BP86/def2ꢀTZVP(ꢀf).
30 H2L4e), ethaneꢀ1,2ꢀdiamine (H2L4c) or propaneꢀ1,2ꢀdiamine
(H2L4d). Reaction mixture of 20 mL of methanol solutions of
respective derivatives of benzaldehyde (5 mmol) and diamine
(2.5 mmol) in 10 mL of methanol was stirred under reflux at 40
°C for 2 hours, and it resulted in yellow powder material after the
Experimental Section
Materials.
All the starting chemicals were of analytical reagent grade and 35 solvent evaporation. The solid powdered substance was washed
15 were
used
as
received.
FeCl3·6H2O,
MnCl2·4H2O,
with diethyl ether and dried in a vacuum; yield was higher than
97 %.
Na2[Fe(CN)5NO]·2H2O and solvents were obtained from the
commercial sources and the organic compounds 1,2ꢀ
diaminocyclohexane, 1,2ꢀdiaminoꢀbenzene, ethaneꢀ1,2ꢀdiamine,
propaneꢀ1,2ꢀdiamine, 2ꢀhydroxyꢀbenzaldehyde, 4ꢀhydroxyꢀ1ꢀ
Synthesis of the precursors [Fe(L4a)Cl] (1a) [Mn(L4a)Cl]
(1b), [Fe(L4b)Cl] (1c), [Fe(L4c)Cl] (1d), [Mn(L4c)Cl] (1e),
40 [Fe(L4d)Cl] (1f) and [Mn(L4e)Cl] (1g)
20 naphthaldehyde,
triethylamine (Et3N), (SigmaꢀAldrich Co., Acros Organics Co.,
Lachema Co. and Fluka Co.).
3ꢀethoxyꢀ2ꢀhydroxybenzaldehyde
and
The solution of 10 mmol of FeCl3·6H2O or MnCl2·4H2O in 10
mL of methanol was added to a solution of 10 mmol of H2L4aꢀ
H2L4e in 20mL of ethanol. The mixture was stirred for 10 min,
and then 20mmol of triethylamine in ethanol (10 mL) was added.
45 The resulting solution was refluxed for 2 h, then after cooling
diethyl ether was added which resulted in precipitation of black
or brown powder. The solid was filtered off, washed with diethyl
ether and dried in a vacuum yield was higher than 90 %.
Synthesis of the tetradentate Schiff base H2L4aꢀ H2L4e
These organic compounds where prepared by the Schiff base
25 condensation between the following derivatives, i.e. 2ꢀ
hydroxybenzaldehyde (H2L4a or H2L4c), 4ꢀhydroxyꢀ1ꢀ
naphthaldehyde (H2L4e) or 3ꢀethoxyꢀ2ꢀhydroxybenzaldehyde
(H2L4b or H2L4d) and the corresponding diamines, i.e. 1,2ꢀ
diaminocyclohexane (H2L4a), 1,2ꢀdiaminobenzene (H2L4b or
Synthesis of the complexes 2aꢀ6b
50 The darkꢀbrown crystals or dark powder of complexes 2aꢀ6b
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have been obtained from a methanol solution (40 mL) of the
complexes 1aꢀ1g (0.2 mmol) combined with a methanol/water 60 953w; 894w; 843w; 779w; 763w; 732m; 690w; 603m.
mixture (1:1) of Na2[Fe(CN)5NO]·2H2O (0.1 mmol). The [{Fe(L4d)(H2O)}2{ ꢀFe(CN)5(NO)}] (5a). Yield: 70% Anal.
solution was stirred at room temperature for h. slow
1254m; 1216w; 1178w; 1153w; 1108w; 1083m; 1050w; 1018w;
ꢀ
4
Calcd. for C47H52N10O11Fe3: C, 51.29; H, 4.76; N, 12.72. Found:
C, 50.91; H, 4.55; N, 12.54%. ΛM (DMF, S·cm2·molꢀ1): 14.2. FTꢀ
IR (Nujol, cmꢀ1): 518m; 489m; 452m; 449m; 431w; 354s; 303m;
5
evaporation of the resulting solution at room temperature
afforded black single crystals suitable for Xꢀray diffraction of the
complexes after a week. Black crystals were filtered off, washed 65 284m ν(Fe−N); 276w; 246w ν(Fe−O); 241m. FTꢀIR (KBr, cmꢀ1):
twice with water, diethyl ether and dried in a vacuum.
3348w; 3268w; 3061w ν(C−H)ar; 2981w ν(C−H)alip; 2930w
ν(C−H)alip; 2880w; 2149s ν(C≡N); 1882vs ν(N=O); 1616vs
ν(C=N); 1594s; 1552m; 1463m ν(C=C)ar; 1443vs ν(C=C)ar;
1391m; 1345w; 1322w; 1295m; 1250m; 1218m; 1180w; 1110w;
[{Fe(L4a)(H2O)}2{ ꢀFe(CN)5(NO)}]·CH3OH (2a). Yield: 76%,
ꢀ
10 Anal. Calcd. for C46H48N10O8Fe3: C, 53.30; H, 4.66; N, 13.51.
Found: C, 53.52; H, 4.53; N, 13.70%. ΛM (DMF, S·cm2·molꢀ1):
5.2. FTꢀIR (Nujol, cmꢀ1): 517m; 486m; 474m; 444m; 431w; 369s; 70 1076w; 1037w; 1014w; 895w; 850w; 762w; 731m; 605w.
342m; 329m; 296m ν(Fe−N); 275w; 245w ν(Fe−O); 236m;
185w; 174w. FTꢀIR (KBr, cmꢀ1): 3115w; 3037w ν(C−H)ar;
15 2872w; 2987w ν(C−H)alip; 2939w ν(C−H)alip; 2152m ν(C≡N);
1917m ν(N=O); 1625vs ν(C=N)ar; 1595m; 1541m; 1472m
[{Mn(L4e)(H2O)(CH3OH)][{Mn(L4e)(H2O)}{ꢀꢀFe(CN)5
(NO)}]·H2O·CH3OH (6b). Yield: 63% Anal. Calcd. for
C63H49N10O10Mn2Fe1: C, 59.44; H, 3.95; N, 11.00. Found: C,
59.58; H, 3.66; N, 11.27%. ΛM (DMF, S·cm2·molꢀ1): 91.2. FTꢀ
ν(C=C)ar; 1452vs ν(C=C)ar; 1357w; 1274w; 1222w; 1193w; 75 FTꢀIR (Nujol, cmꢀ1): 525m; 492m; 453m; 447m; 434w; 355s;
1157w; 1114w; 1110w; 1039w; 1018w; 945w; 858w; 752m.
351m; 305m 278m ν(Mn−N); 248w; 233m ν(Mn−O); 213w. FTꢀ
IR (KBr, cmꢀ1): 3457m; 3398w; 3074w ν(C−H)ar; 2987w
ν(C−H)alip; 2978w ν(C−H)alip; 2875w; 2152s ν(C≡N); 1886vs
ν(N=O); 1614vs ν(C=N); 1587s; 1549m; 1474m ν(C=C)ar;
[{Mn(L4a)(H2O)}2{ ꢀFe(CN)5(NO)}]·CH3OH (2b). Yield:
ꢀ
20 75%, Anal. Calcd. for C46H48N10O8Mn2Fe1: C, 53.39; H, 4.67; N,
13.53. Found: C, 53.54; H, 4.57; N, 13.74%. ΛM (DMF,
S·cm2·molꢀ1): 11.5. FTꢀIR (Nujol, cmꢀ1): 572w; 539w; 510w; 80 1454vs ν(C=C)ar; 1387m; 1332w; 1319w; 1287m; 1245m;
468m; 455w; 438w; 419w; 379m; 333w; 322w; 286m ν(Mn−N);
259w ν(Mn−O); 209w. FTꢀIR (KBr, cmꢀ1): 3132w; 3021w
25 ν(C−H)ar; 2931w ν(C−H)alip; 2859w; 2163m ν(C≡N); 1922m
ν(N=O); 1618vs ν(C=N)ar; 1596m; 1544m; 1468m ν(C=C)ar;
1443m ν(C=C)ar; 1395w; 1307w; 1286w; 1268w; 1233w; 1196w;
1148w; 1052w; 1006w; 995w; 907w; 851w; 753m; 677w.
1217m; 1184w; 1122w; 1097w; 1017w; 889w; 867w; 787w;
745m; 645w.
General methods
Elemental analysis (CHNS) was performed on an FLASH 2000
85 CHNS Analyzer (ThermoFisher Scientific). Infrared spectra of
the complexes were recorded on a ThermoNicolet NEXUS 670
FTꢀIR spectrometer using the KBr technique on the diamond
plate in the range of 400–4000 cmꢀ1 and Nujol techniques in the
range of 150–600 cmꢀ1. Thermogravimetric (TG) and differential
90 thermal analyses (DTA) were measured on an Exstar TG/DTA
6200 thermal analyzer (Seiko Instruments Inc.). TG/DTA studies
were performed in ceramic pans from laboratory temperature to
850 °C with a 2.5 °C minꢀ1 temperature gradient in dynamic air
atmosphere (100 mL minꢀ1).
[{Fe(L4b)(H2O)}2{ꢀꢀFe(CN)5(NO)}]·2CH3OH (3a). Yield:
30 71%, Anal. Calcd. for C47H40N10O9Fe3: C, 53.43; H, 3.81; N,
13.25. Found: C, 53.56; H, 3.52; N, 13.71%. ΛM (DMF,
S·cm2·molꢀ1): 15.2. FTꢀIR (Nujol, cmꢀ1): 568w; 554w; 515w;
491w; 460m; 426w; 390w; 352m; 332w; 306w; 285m ν(Fe−N);
267w; 241m ν(Fe−O); 217w; 198w. FTꢀIR (KBr, cmꢀ1): 3372w;
35 3299w; 3217w; 3118w; 3025w ν(C−H)ar; 2932w ν(C−H)alip
;
2139m ν(C≡N); 1906m ν(N=O); 1613vs ν(C=N)ar; 1539m;
1467m ν(C=C)ar; 1446m ν(C=C)ar; 1398w; 1314m; 1268w;
1230w; 1023w; 997w; 904w; 809w; 753m; 661w.
95 Singleꢀcrystal Xꢀray analysis details
[{Fe(L4c)(H2O)}2{ꢀꢀFe(CN)5(NO)}] (4a). Yield: 72% Anal.
Xꢀray measurements on the selected crystals of 3aꢀ6b were
performed on an Oxford Diffraction XcaliburTM2 equipped with a
Sapphire2 CCD detector using the MoꢀKα radiation at 100 K.
The CrysAlis program package (version 1.171.33.52, Oxford
100 Diffraction) was used for data collection and reduction.34 The
molecular structures were solved by direct methods SHELXꢀ97
and all nonꢀhydrogen atoms were refined anisotropically on F2
using fullꢀmatrix leastꢀsquares procedure SHELXSꢀ9735. All the
hydrogen atoms were found in differential Fourier maps and their
105 parameters were refined using a riding model with Uiso(H) = 1.2
(CH, CH2, OH) or 1.5Ueq (CH3). Nonꢀroutine aspects of the
structure refinement are as follows: in the compounds 3a, 4a, 5a
and 6b the Fe atom of nitroprusside lies at the inversion center
with disorder of the nitrosyl and cyanido groups in two trans
110 positions. Occupation factors for both disordered parts were set to
0.5.
40 Calcd. for C45H48N10O11Fe3: C, 50.39; H, 4.51; N, 13.06. Found:
C, 50.52; H, 4.69; N, 13.33%. ΛM (DMF, S·cm2·molꢀ1): 21.8. FTꢀ
IR (Nujol, cmꢀ1): 508m; 492m; 475m; 446w; 437w; 372vs; 344m;
318m; 288w ν(Fe−N); 248m ν(Fe−O); 224w; 170w. FTꢀIR (KBr,
cmꢀ1): 3445w; 3414w; 3047w ν(C−H)ar; 2992w ν(C−H)alip
;
45 2942w ν(C−H)alip; 2882w; 2141m ν(C≡N); 1882vs ν(N=O);
1616vs ν(C=N); 1581m; 1552m; 1468m ν(C=C)ar; 1437m
ν(C=C)ar; 1395w; 1347w; 1295m; 1250m; 1211w; 1174w;
1141w; 1112w; 1074m; 1055w; 1021w; 947w; 857w; 841w;
774w; 732w; 692w.
50 [{Mn(L4c)(H2O)}2{ꢀꢀFe(CN)5(NO)}] (4b). Yield: 65% Anal.
Calcd. for C45H48N10O11Mn2Fe1: C, 50.48; H, 4.51; N, 13.08.
Found: C, 50.55; H, 4.64; N, 13.27%. ΛM (DMF, S·cm2·molꢀ1):
16.5. FTꢀIR (Nujol, cmꢀ1): 515m; 491m; 469m; 452m; 429w;
378s; 351m; 311m ν(Mn−N); 254w ν(Mn−O); 239m; 170w. FTꢀ
55 IR (KBr, cmꢀ1): 3443w; 3412w; 3072w ν(C−H)ar; 3056w
ν(C−H)ar; 2996w ν(C−H)alip; 2926w ν(C−H)alip; 2877w; 2138m
ν(C≡N); 1874vs ν(N=O); 1614vs ν(C=N); 1579m; 1550m;
1465m ν(C=C)ar; 1438m ν(C=C)ar; 1393w; 1346w; 1298m;
DFT calculations
The theoretical calculations were done with the ORCA 2.9.1
computational package. The magnetic exchange (J) was
12 | Journal Name, [year], [vol], 00–00
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DOI: 10.1039/C4DT02025A
calculated using the hybrid B3LYP functional.36 The brokenꢀ
symmetry (BS) spin state was generated by “FlipꢀSpin” feature of
[MIII(L4)(Solv)]+···[MIII(L4)(Solv)]+ dimers and they might be
useful for estimations of the strength of such interactions in more
the ORCA program and the isotropic exchange constants J were 60 magnetically complicated systems (e.g. with paramagnetic
calculated both by the Ruiz’s formula37 and Yamaguchi
approach.38 The polarized tripleꢀζ quality basis set (def2ꢀTZVP)
proposed by Ahlrichs and coꢀworkers has been used for all
atoms.39 The relativistic effects were dealt with the scalar
bridging complex, systems possessing magnetic ordering or slowꢀ
relaxation of magnetization).
5
Acknowledgements
relativistic secondꢀorder Douglas‐Kroll‐Hess Hamiltonian 65 We acknowledge the financial support from the Czech Science
(DKH2) together with relativistically recontracted version of the
Foundation (GAČR P207/11/0841), the Operational Program
Research and Development for Innovations ꢀ European Regional
Development Fund (CZ.1.05/2.1.00/03.0058) of the Ministry of
Education, Youth and Sports of the Czech Republic, and Palacký
10 def2ꢀTZVP basis set.40 The calculations utilized the RI
approximation with the decontracted auxiliary def2ꢀTZVP/J
Coulomb fitting basis set and the chainꢀofꢀspheres (RIJCOSX)
approximation to exact exchange41 as implemented in ORCA. 70 University (PrF_2013_015 a 2014009.). The authors would like
Increased integration grids (Grid5 and Gridx5 in ORCA
15 convention) and tight SCF convergence criteria were used in all
calculations. The geometry optimization of molecular fragment
[{Fe(L3)(H2O)(NC)}2] (4a) were done using the BP86
functional42 with the def2ꢀTZVP(ꢀf) basis set together with
conductorꢀlike screening model (COSMO),43 van der Waals
20 corrections (VDW10)44 and DKH2. The positions of hydrogen
atoms in Hꢀbond bridged dinuclear molecular fragments
[{MIII(L4)(H2O)(NC)}2] (M = Fe, Mn) (4a, 5a, 4b, 7a, and 7e)
and also for [{Mn(L4)(H2O)(NCS)}2] (8 and 9) were performed
again with BP86/de2ꢀTZVP(ꢀf).
to thank Dr. Radka Křikavová for infrared spectroscopy
measurements.
Notes and references
a
Regional Centre of Advanced Technologies and Materials &
75 Department of Inorganic Chemistry, Faculty of Science, Palacký
University, 17. listopadu 12,771 46, Olomouc, Czech Republic.
Fax: +420585 634 954, Eꢀmail: zdenek.travnicek@upol.cz.
† Footnotes should appear here. These might include comments relevant
to but not central to the matter under discussion, limited experimental and
80 spectral data, and crystallographic data.
Electronic Supplementary Information (ESI) available: []. See
DOI: 10.1039/b000000x
25 Conclusions
We have reported the synthesis of trinuclear iron(III) and
manganese(III) (2aꢀ5a) and dinuclear manganese(III) (6b) Schiff
[1] (a) C. Chappert, A. Fert, F. N. Van Dau, Nat. Mater., 2007,
(b) L. Bogani, W. Wernsdorfer, Nat. Mater., 2008, , 179. (c) C.
Felser, G. H. Fecher, B. Balke, Angew. Chem., Int. Ed., 2007, 46
668. (d) W. Wernsdorfer, Nat. Nano, 2009, , 145.
[2] (a) V. H. Crawford, H. W. Richardson, J. R. Wasson, D. J. Hodgson,
W. E. Hatfield, Inorg. Chem., 1976, 15, 2107. (b) J. Glerup, D. J.
Hodgson, E. Pedersen, Acta. Chem. Scand., 1983, 37, 161. (c) S. M.
Gorun, S. J. Lippard, Inorg. Chem., 1991, 30, 1625. (d) N. A. Law, J.
W. Kampf, V. L. Pecoraro, Inorg. Chim., Acta 2000, 297, 252.
[3] M. Ding, B. Wang, Z. Wang, J. Zhang, O. Fuhr, D. Fenske, S. Gao,
Chem. Eur. J., 2012, 18, 915.
6, 813.
7
base complexes
utilizing the nitroprusside anion,
,
[FeII(CN)5NO]2ꢀ, as a building block. The compounds were
30 characterized by various physical methods (elemental analysis,
FTꢀIR, TG/DTA, singleꢀcrystal Xꢀray analysis), which clearly
confirmed their compositions and molecular/crystal structures. It
was observed that coordinated water molecules are responsible
for formation of supramolecular 1D chains (3aꢀ5a) or
35 supramolecular dimers (6b) through hydrogen bonds of the type
O–H⋅⋅⋅O. The thorough magnetic analysis, which consisted in the
concurrent fitting of temperature and field dependent powder
magnetic data, played an important role in proper identifying
values of the isotropic exchange Jꢀparameters and zeroꢀfield
40 splitting Dꢀparameters.
4
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45 the nitroprusside anion was found negligible. Moreover, the
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50 within the O–H⋅⋅⋅O hydrogen bond forming superꢀexchange
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55 of solvent (water, methanol) coordinated to next metal atom (OS).
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benzeneꢀbis(salicylideneiminate), H2L4c N,N’ꢀethyleneꢀbis(3ꢀ
=
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ethoxysalicylideneiminate), H2L4e = N,N'ꢀbenzeneꢀbis(naphthylide
neiminate), H2L4f = N,N’ꢀethyleneꢀbis(salicylideneiminate), H2L4g =
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=
N,N′ꢀ
1506.
1,1,2,2ꢀtetramethyl etyleneꢀbis(salicylideneiminate), H2L4i = N,N’ꢀ
ethyleneꢀbis(3ꢀmethoxysalicylideneiminate), H2L4j = N,N’ꢀethyleneꢀ
bis(5ꢀbromosalicylideneiminate), H2L4k = N,N'ꢀ1,3ꢀpropyleneꢀbis(5ꢀ
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bromo salicylideneiminate), H2L4l
methoxy salicylideneiminate),
tetramethylethyleneꢀbis(naphthylideneiminate), H2L4n
benzeneꢀbis(4ꢀaminodiethylenesalicylideneiminate), H2L4 o = N,N´ꢀ
=
N,N’ꢀ1,3ꢀpropylene ꢀbis(3ꢀ
H2L4m N,N′ꢀ1,1,2,2ꢀ
N,N´ꢀ
=
=
[32]The standard deviations were calculated as σi = (Piiꢀ1·S/(N–k))ꢀ1/2
,
3ꢀmethylbenzeneꢀbis(3ꢀethoxysalicylideneiminate) and H2L4p
=
where Pij = Σ(δꢀn/δai·δꢀn/δaj) and S = Σ(ꢀn –
ꢀnexp)2 with n = 1 to N;
N,N'ꢀethyleneꢀbis(salicylidenebenzeneiminate).
ai and aj are fitted parameters, N is number of experimental points
(sum of temperature and field dependent data), ꢀn and ꢀn are the
calculated and experimental effective magnetic moments for given
temperature and magnetic field. The σi was then multiplied by
exp
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DOI: 10.1039/C4DT02025A
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DOI: 10.1039/C4DT02025A
The detailed investigations of the magnetic coupling and magnetic anisotropy in a series of Schiff base salen-like Fe(III)
and Mn(III) complexes, based on SQUID experiments and DFT calculations, are reported.