Impact of the Schiff base ligand substituents on the solid state and solution properties of eleven iron(III) complexes

Article abstract of DOI:10.1039/c9nj03087e

Investigations on a series of mononuclear iron(iii) Schiff base complexes of the general formula [Fe(L)Cl]·S (where L^2- is a Schiff base ligand anion, S is a solvent molecule) are reported. Derivatives of salicylaldehyde or 2-hydroxy-1-naphthal

Full text of DOI:10.1039/c9nj03087e

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DOI: 10.1039/C9NJ03087E
Impact of the Schiff Base Ligand Substituents on the Solid State
and Solution Properties in Eleven Iron(III) Complexes
Lukáš Pogány,a Barbora Brachňaková,a Petra Masárová,a Ján Moncol,a Ján Pavlik,a Miroslav
Gál,b Milan Mazúr,c Radovan Herchel,d Ivan Nemec,d Ivan Šalitroš,a,d*
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a) Department of Inorganic Chemistry, Faculty of Chemical and Food Technology,
Slovak University of Technology in Bratislava, Bratislava SK-81237, Slovakia,
*e-mail: ivan.salitros@stuba.sk
b) Department of Inorganic Technology, Faculty of Chemical and Food Technology,
Slovak University of Technology, Bratislava-81237, Slovakia
c) Department of Physical Chemistry, Faculty of Chemical and Food Technology,
Slovak University of Technology in Bratislava, Bratislava SK-81237, Slovakia
d) Department of Inorganic Chemistry, Faculty of Science, Palacký University, 17.
listopadu 12, 771 46 Olomouc, Czech Republic
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Abstract:
Investigations on a series of mononuclear iron(III) Schiff base complexes of general
formula [Fe(L)Cl]·S (where L2- is Schiff base ligand anion, S is a solvent molecule) are
reported. Derivatives of salicylaldehyde or 2-hydroxy-1-naphtaldehyde were used in
combination with a linear either symmetrical or non-symmetrical aliphatic triamines to
synthesize the Schiff base ligands and the consecutive reactions with iron(III) chloride
afforded various [Fe(L)Cl] complexes. Compounds were characterized by conventional
techniques and the crystal structures of all complexes have been determined as well.
Structural study has revealed relationship between the spatial arrangement of N3O2-donor
atom set and length of the aliphatic part of Schiff base ligand. Magnetic and EPR
investigation confirmed the high spin state behaviour in all reported compounds and their
analysis allowed to quantify the parameters of spin Hamiltonian. Formation of hydrogen-
bonded pseudodimers with antiferromagnetic exchange coupling was found in the
complexes with the shortest aliphatic part of Schiff base ligands. Experimental exchange
coupling constants are in good agreement with those obtained from DFT calculation and
correlate with the strength of the hydrogen bonds. Cyclic and square wave voltammetry
were employed to investigate the redox properties of reported compounds and the
experimental redox potentials were compared with those obtained from the DFT calculations.
..................
Keywords: Iron(III) complexes, Schiff base ligand, Crystal structure, EPR spectroscopy,
DFT, Electrochemistry
Introduction
Schiff base (SB) ligands play an important role in the coordination chemistry. The low prices
and good availability of the starting chemicals, the simple preparation or variety of
coordination possibilities of SB ligands provide many research opportunities in inorganic and
organic chemistry. The SB condensation between carbonyls and primary amines results into
formation of imines which offer participation in binding with metal ions via nitrogen lone
pair electrons. If the starting materials contain additional functional groups with potential
donor atoms, the corresponding SBs might become polydentate ligands capable to stabilize

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metal ions in various oxidation states, controlling the performance of metals in a lDaOrgI: e10.v10a3Vr9iie/ewCt9AyrNtiJcl0e3O0n8li7nEe
of useful catalytic transformations,1 in microbiological process simulations,2 or their
luminescence properties.3 Special attention is paid on coordination compounds containing
polydentate chelating SB ligands exhibiting magnetic activity. Miscellaneous examples of SB
metal complexes were reported to date in which magnetic ordering,4 spin crossover
properties,5 single molecule magnetism6 or magnetocaloric effect7 were investigated.
Multiple denticity and chelating effect of SBs allow the formation of stable coordination
compounds8 whose magnetic properties can be tuned by the counter anion variation or by
goal-directed introduction of substituents on the ligand skeleton. 9
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Iron(III) complexes with salen (N,N′-bis(salicylidene)ethylenediamine) or saldien (N,N′-
bis(salicylidene)diethylenetriamine) type of ligands present well-established family of
coordination compounds in which two or one coordination site, respectively, are still
available for other bridging ligands.10 Such strategy of synthesis might end up with the
formation of discrete oligo/polynuclear complex compounds11 or with the coordination
polymers with 1D,12 2D,13 or 3D14 supramolecular structures. Our group has already explored
a wide pallet of ferric complexes with N3O2-pentadentate SB ligands H2L, prepared by the
condensation of aliphatic triamines and aromatic 2-hydroxycarbaldehyde derivatives. The
iron(III) complexation with H2L results in to the formation of high spin [Fe(L)Cl] complexes
in the first step, and consecutive chlorido ligand replacement allows to prepare mononuclear
-
complexes with pseudohalido terminal ligands [Fe(L)X] (X- = CN-, NCS-, N3 , NCSe-, NCO-
etc.).15-17 Depending on the nature of used pseudohalides, one can tune the ligand field of
iron(III) central atom and prepare low spin,15 high spin16 or spin crossover16b,17 compounds.
Another synthetic approach involves hydroxido, cyanido, metallocyanido or bipyridine N-
donor bridging ligands capable to merge two or more {Fe(L)}+ moieties into the
oligomeric/polynuclear complex compounds.18 Based on our thorough research in this field,
there is apparent that substituents introduced on the aromatic ring as well as the length and/or
symmetry of the aliphatic triamine part of H2L pentadentate ligands have a significant impact
on the structural and magnetic properties of resulted coordination compounds. For instance,
magnetism of six similar heptanuclear mixed-valence complexes [{(L)FeIIINC}6-FeII]Cl2
prepared from corresponding ferric precursors [Fe(L)Cl] and potassium ferrocyanide strongly
depends on the molecular architecture of used pentadentate ligand H2L.19 In general, the
structure of [{(L)FeIIINC}6-FeII]2+ contains six ferric centres bonded with N3N’O2 donor atom
set supporting the spin crossover event. However, only one heptanuclear analogue exhibits
thermally induced low spin ↔ high spin bistability.19a Another five heptanuclear compounds
contain permanently high spin iron(III) centres, but, again the nature of the intramolecular
magnetic exchange interaction strongly depends on the type of the used (L)2- ligand.19b-e
In order to understand how the substituent variation in pentadentate SB ligands affect the
structural and other physical properties in corresponding iron(III) complexes, we decided to
investigate a wide family of mononuclear ferric complexes of [Fe(L)Cl] type. N3O2-donor
atoms of (L)2- ligand anion can be arranged in four possible configurations (Figure 1) which
have a significant impact on the degree of angular distortion of coordination polyhedra.
Moreover, particular alignment of N3O2-donor atoms can influence the spectral properties,
intermolecular interactions, magnetic anisotropy and magnetic exchange coupling. Herein we
report on the synthesis, structural, spectral and magnetic properties of numerous mononuclear
complexes with pentadentate SB ligands and chlorido terminal ligand. Altogether, we
prepared and characterized eleven novel compounds [Fe(L)Cl] where pentadentate SB ligand
dianions (L)2- contain variously substituted aromatic rings. Four aliphatic triamines have been
chosen for the SB condensation and their different length and symmetry control the
configuration of donor atoms, degree of angular distortion of coordination polyhedra or type

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of the intermolecular interactions. Magnetic and EPR investigation confirmed high spin VsietwatAerticle Online
DOI: 10.1039/C9NJ03087E
behaviour in all reported compounds. Parameters of magnetic anisotropy and exchange
coupling interaction were extracted from experimental data, compared with theoretical ones
obtained from DFT calculations and related to the structural features. Electrochemistry
investigation in the solution has been performed and experimental as well as calculated redox
potential have been related with the corresponding molecular structures of reported
complexes.
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a)
b)
Nim
Nam
c)
d)
Nam
O
Nim
Nim
Nam
Nim
Nim
Nim
Nam
O
Fe
Fe
Fe
Fe
O
O
O
O
Nim
Nim
O
O
Cl
Cl
Cl
Cl
Figure 1 Four possible configurations of pentadentate SB ligand in octahedral [Fe(L)Cl] coordination
compounds. Two phenolic oxygen atoms and three nitrogen donor atoms (two imino and one amino) gain chiral
cis-O2/fac-N3 when axial position occupied by one of imino nitrogen atom (a), cis-O2/fac-N3 with axial position
occupied by amino nitrogen atom (b, so far not reported, thus hypothetical configuration, chiral only if SB
ligand is asymmetric), chiral trans-O2/mer-N3 (c) and chiral cis-O2/mer-N3 (d).
Results and discussion
Synthesis, spectral properties and solid-state structures
The pentadentate ligands H2Ln (n=1-10) (Figure 2) were synthesized by a SB condensation
between corresponding aliphatic triamines and 1-(2-hydroxyphenyl)ethan-1-one, derivatives
of the 2-hydroxybenzaldehyde or 2-hydroxynaphthaldehyde, respectively (see Experimental
part S1 in electronic supporting information (ESI)). Complexation with iron(III) chloride
afforded formation of mononuclear complexes of the general formula [Fe(Ln)Cl] and their
single crystals were obtained after the recrystallization of polycrystalline powders from
acetone (1, 6, 8, 7c, 9, 10), methanol (2, 3 and 5) or from methanol-acetonitrile mixture (4,
7t) in 67-92 % yield. Infrared spectroscopy supports the structural characterization of 1-10
(see Experimental part S1 in ESI). N-H vibrations were detected in the expected region 3270-
3130 cm-1 for complexes containing secondary amino groups (1-8) and those of them which
involve amino groups in H-bonding (vide infra) exhibit vibrations shifted below 3210 cm-1.
Aromatic and aliphatic C-H vibrations have been detected for all reported complexes in the
region 3100–3000 cm-1 and 3000–2800 cm-1, respectively. The most intense vibrational
bands are assigned to imino C=N and Car-Car located between 1635–1500 cm-1. In addition,
signals of co-crystallized water (8, 10), methanol (4) and acetone (1) solvent molecules have
been identified as well. Generally, UV-VIS absorption spectra of the high-spin iron(III)
complexes provide information about their electronic structures and in the case of solution
spectra of 1-10, three major absorption bands can be distinguished. The d-d transitions of the
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high-spin iron(III) complexes with the ground state A1 are banned by formal spin and
Laporte rule and often overlapped by intense metal-to-ligand (MLCT) charge transfer bands
in the visible light region (≈ 500 nm). The next two bands are located in the UV region and
most probably present intraligand n→π* (≈ 300 nm) and π→π* (≈ 230 nm) electronic
transitions.

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Figure 2 Molecular structures of ligands H2Ln which are used for the preparation of
complexes 1-10. Ligands and compounds prepared from DET amine are in blue, PET in red
and DPT or DPTM in black colour.
Molecular structures of reported complexes have been confirmed by single-crystal X-ray
diffraction analysis and selected crystallographic parameters are listed in

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Table 1. X-ray diffraction experiments have been carried out at 293 K (for 3, 5(P21/c), 6, 7t,
8, 9, and 10), 150 K (4, 5(P-1), 7c) and at 100 K (1, 2, 10). Temperature variation did not
cause any symmetry change of 10 which maintain the same monoclinic P21/c space group at
both temperatures, but the position of acetone solvent molecule was not possible to localize at
293 K. However, the room temperature monoclinic structure of 5(P21/c) has reversibly
changed upon the cooling to lower triclinic P-1 symmetry (denoted as 5(P-1)). Complex 7t
crystallizes in non-centrosymmetric orthorhombic space group Pna21. Crystal structure of
four complexes contain co-crystallized lattice solvent molecules (complex 1 -
[Fe(L1)Cl]·CH3COCH3; complex 4 - [Fe(L4)Cl]·CH3OH; complex 8 - [Fe(L8)Cl]·H2O;
complex 10 - [Fe(L10)Cl]2·2H2O·CH3COCH3) and the other seven crystal structures (2, 3, 5,
6, 7t, 7c, 9) are solvent-free. Nine structures contain one complex molecule [Fe(Ln)Cl] and
corresponding lattice solvent molecules in their asymmetric unit (complexes 1 -
[Fe(L1)Cl]·CH3COCH3, 2 - [Fe(L2)Cl], 3 - [Fe(L3)Cl], 5(P21/c) - [Fe(L5)Cl], 6 - [Fe(L6)Cl],
7t and 7c - [Fe(L7)Cl], 8 - [Fe(L8)Cl]·H2O and 9 - [Fe(L9)Cl]), while two complex
molecules with corresponding solvents in the asymmetric unit have been found in the crystal
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structure of
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({[Fe(L4)Cl]2·(CH3OH)2}), 5(P-1) ({[Fe(L5)Cl]2}) and 10
({[Fe(L10)Cl]2·(H2O)2}·CH3COCH3).
In general, all reported compounds exhibit similar structural motif. The iron(III) central atom
is coordinated by N3O2-donor atoms of the SB ligand and the sixth coordination site is
occupied by chlorido terminal ligand (Figure 1). Despite the seemingly uneventful structural
variability, the shape and arrangement of {FeN3O2Cl} coordination chromophore depends
strongly on the gentle variation of the SB ligand molecular design. In particular, the
configuration of three nitrogen donor atoms strongly depends on the length of its aliphatic
part. Two imino and one amino nitrogen donor atoms are placed in the facial fashion (fac-N3;
Figure 1a) when corresponding SB ligand contains the shortest “N,N-bis(ethylene)amino”
aliphatic bridging part (derived from N-(2-aminoethyl)ethane-1,2-diamine, abr. DET;
compounds 14; Figure 3a and Table S3.1 in ESI). The meridional (mer-N3) arrangement has
been found in the structures 510 (Figure 3b-e and Table S3.1 in ESI)) with longer either
asymmetric “N,N-ethylene-propyleneamino” (derived from N-(2-aminoethyl)propane-1,3-
diamine, abbr. PET) or symmetric “N-bis(1,3-propylene)amino” (derived from N-(3-
aminopropyl)propane-1,3-diamine, abbr. DPT) and “N-methyl-N-bis(1,3-propylene)amino”
(derived from N-(3-aminopropyl)-N-methylpropane-1,3-diamine, abbr. DPTM) aliphatic
bridges of SB ligands. The trans configuration of phenolato oxygen donor atoms is observed
only in the case of compound 7t (trans-O2/mer-N3; Figure 3c and Table S3.1 in ESI)), while
all other complexes 510 show cis-O2/mer-N3 arrangement.
Table S3.1 (see ESI) contains full list of bond distances and angles of coordination polyhedra.
Average values of FeNim and FeNam distances are typical for high spin iron(III)
coordination centres and vary in the ranges 2.072.16 Å and 2.152.30 Å, respectively
(Table 2). In accordance with structures of the previously reported complexes,15-19 the
shortest FeO and the longest FeCl bond distances of coordination polyhedra obey typical
average values in the ranges 1.901.97 Å and 2.31 Å  2.41 Å, respectively (Table 2).
Deviation of {FeN3O2Cl} coordination chromophore from ideal octahedron can be
quantitatively expressed by  and Θ structural parameters (Table 2, Table S3.1, Figure S3.1
see ESI).20 Both distortion parameters reflect the angular deviation of cis and torsion angles
from ideal octahedral geometry of coordination polyhedra, respectively, and their values
divide reported compounds into three groups sorted according to the symmetry and the length
of aliphatic parts of SB ligands. Complexes 1-4 with the shortest DET aliphatic moiety and
cis-O2/fac-N3 configuration exhibit the most distorted coordination polyhedra and their Σ and
Θ parameters range in 80°93° and 181°231°, respectively. The lowest distortion has been

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noticed for compounds containing DPT and DPTM aliphatic parts where those with the cis-
O2/mer-N3 configuration (7c and 8-10) acquire Σ and Θ values in the range °° ( and
°° (Θ), while compound 7t with the trans-O2/mer-N3 configuration exhibits the highest
distortion in this group (  ° and (Θ = 105°).  and Θ intermediate values of 5(P-1),
5(P21/c) and 6 with asymmetric PET derived SB ligands present a crossing region between
the DPT/DPTM and DET group of complexes. In addition, linear correlation between  and
Θ has been observed and one can conclude that the lowest and the highest angular distortion
of coordination polyhedron have been noticed for 7c and 3, respectively (Figure S3.1a,c, see
ESI). Distortion from reference polyhedron can be expressed also by symmetry measure
parameter proposed by Avnir.21 Continuous shape measurement and derived symmetry
parameters describe a degree of deformation from the shape of ideal polyhedron (Table 2;
Table S3.2, see ESI). For instance, symmetry measures S(Oh) and S(D3h) introduced by
Alvarez et al. can quantify degree of Bailar twisting between regular octahedron (Oh;
S(Oh)=0) and trigonal prism (D3h; S(Oh)=16.737), but they are also sensible to further types
of distortions or to the spin state variation of central atom.22 All herein reported structures
contain coordination polyhedra with shapes close to the regular octahedron, since the range of
S(Oh) spans from 0.56 to 2.50 and because the next lowest parameter S(D3h) acquires already
too high values indicating the major deviation from trigonal prism symmetry. It is also
interesting to point out, that variation of temperature in the case of complex 10 or phase
transition in complex 5 does not have significant influence on the values of symmetry
measure parameters.
The previously reported halido/pseudohalido iron(III) complexes with pentadentate SB
ligands exhibited two basic types of supramolecular contacts: 1) centrosymmetric
supramolecular dimers held by two NH···O hydrogen bonds between the amine group
hydrogen and phenolate oxygen atoms, which is typical for mononuclear complexes with
DET aliphatic bridge of SB ligand.16,19e 2) 1D zig-zag chain substructure held by NH···X or
NH···S···X contacts (X = halido or atom from pseudohalido terminal ligand, S = solvent
molecule). Both types of synthons can be found in the presented series of compounds, too
(Figure S3.2, Table S3.3, see ESI). The supramolecular dimerization via NH···O hydrogen
bonds was observed in compounds 1, 2, 3 and 4 (d(N···O) = 3.245(3) for 1, 3.003(2) for 2,
2.906(4) for 3 and 2.846(2) Å for 4; Figure 3a). In 1 the NH···O hydrogen bonds are
bifurcated by another acceptor – coordinated chloride ligand (d(N···Cl) = 3.474(2) Å). The
NH···Cl chain is observed in 5(P-1) (d(N···Cl) = 3.248(3) and 3.345(3) Å) and this motif
survives the phase transition to 5(P21/c) (d(N···Cl) = 3.399(18) Å). However, the
supramolecular chains held by hydrogen bonding are found also in other compounds from the
present series. In 6, such chain substructure is formed by the NH···O hydrogen bonds
(d(N···O) = 3.061(4) Å) between the amine group hydrogen and methoxy oxygen atoms
(Figure 3b). In other compounds, the “bridging” function between the complex molecules in
chain substructures is held by the solvent molecules. In 8 the supportive role is taken by the
water molecule which interconnects two [Fe(L8)Cl] molecules by NH···O (amine
group···water molecule. d(N···O) = 2.960(8) Å) hydrogen bonding and two OH···O
hydrogen bonds (water molecule···phenolate/methoxy oxygen atom. d(O···O) =
2.888(8)/2.970(8) Å). In 10, two lattice water molecules interconnect two [Fe(L10)Cl]
molecules but without propagation of this motif to the chain substructure. Both water
molecules form bifurcated OH···O hydrogen bonds with phenolate and methoxy oxygen
atoms (acceptors) from adjacent complex molecules and they both are linked together by
OH···O hydrogen bond of moderate strength (d(O···O) = 2.899(3) Å, structure measured at
100 K; Figure 3e). Furthermore, the water molecule which is acceptor of water···water
hydrogen bond forms relatively long OH···Cl non-covalent contact with coordinated
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chlorido ligand (d(O···Cl) = 3.522(2) Å). The compounds 7c, 7t and 9 do not possess any
significant hydrogen bonds.
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Table 1 Selected crystallographic data for 1 – 10
5
6
7
8
Compound
1 K
2 K
3 K
4 K
C19H21Br2ClFeN3O3
5 K
5 K
6 K
Empirical formula
Formula weight
Crystal system
Space group
T [K]
C29H29ClFeN3O3
558.85
C28H27ClFeN3O2
528.82
C20H23ClFeN3O4
460.71
C23H29ClFeN3O4
502.79
C23H29ClFeN3O4
502.79
C21H23Br2ClFeN3O4
632.54
590.51
Monoclinic
P21/n
Monoclinic
P21/n
Monoclinic
P21/n
Triclinic
Monoclinic
P21/c
Triclinic
Monoclinic
P21/n
9
P
P
1
150(1)
1
10
11
12
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16
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100(1)
100(1)
293(1)
150(1)
293(1)
293(1)
a [Å]
16.0970(15)
7.0994(4)
24.040(2)
90
18.021(3)
7.448(5)
18.822(2)
90
10.8572(4)
10.4047(3)
18.9387(7)
90
11.5360(4)
12.6730(4)
16.2456(5)
94.651(2)
101.474(3)
106.584(3)
2206.59(13)
4
9.9944(2)
22.3122(5)
10.9698(2)
90
9.8897(6)
10.8138(6)
22.2761(13)
90.162(5)
91.327(5)
107.242(5)
2274.5(2)
4
12.185(1)
16.5136(9)
13.1192(9)
90
b [Å]
c [Å]
α [°]
β [°]
104.105(7)
90
96.64(1)
90
101.464(4)
90
107.526(2)
90
114.409(9)
90
γ [°]
V [Å3]
2664.4(4)
4
2509.5(18)
4
2096.75(13)
4
2332.68(9)
4
2403.9(3)
4
Z
ρcalc [g.cm–3
µ [mm−1
]
1.393
1.400
1.459
1.778
1.432
1.468
1.748
]
5.749
0.738
0.878
4.451
6.527
0.816
4.096
Crystal size [mm]
Data/restrains/parameters
S
0.22 x 0.08 x 0.06
5135/0/336
0.834
0.16 x 0.16 x 0.12
5108/0/318
1.032
0.26 x 0.26 x 0.08
4145/0/265
1.240
0.45 x 0.30 x 0.23
9005/0/527
0.940
0.50 x 0.16 x 0.05
4496/524/345
0.801
0.31 x 0.22 x 0.20
9274/433/584
0.988
0.40 x 0.14 x 0.06
4904/0/294
1.019
R1 [I>2σ(I)]
wR2 (all data)
CCDC
0.03863
0.0882
0.0387
0.0665
0.0290
0.0339
0.0500
0.0478
0.0855
0.1006
0.0596
0.0799
0.1258
0.0922
1062787
1062788
1062789
1062791
1507222
1062792
1062793
Compound
7c K
7t K
8 K
9 K
10 K
Empirical formula
Formula weight
Crystal system
Space group
T [K]
C20H21Br2ClFeN3O2
586.52
C20H21Br2ClFeN3O2
586.52
C20H27Br2ClFeN3O5 C29H29ClFeN3O2
C46H54Br4Cl2Fe2N6O8.2H2O
1357.18
C49H65Br4Cl2Fe2N6O11
1416.31
664.58
542.85
Monoclinic
P21/c
Orthorhombic
Pna21
Monoclinic
P21/n
Monoclinic
P21/c
Monoclinic
P21/c
Monoclinic
P21/c
293(1)
150(1)
293(1)
293(1)
293(1)
100(1)
a [Å]
7.6216(5)
12.2155(7)
23.4460(10)
90
15.733(5)
15.024(5)
10.024(5)
90
12.0070(10)
16.9410(10)
13.6630(10)
90
7.5539(4)
23.432(1)
14.244(1)
90
18.8416(3)
27.6317(4)
11.0612(2)
90
18.7064(8)
27.4015(14)
10.9938(3)
90
b [Å]
c [Å]
α [°]

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2
3
4
5
6
7
8
β [°]
98.896(5)
90
90
112.820(10)
90
95.577(5)
99.7690(10)
90
104.105(7)
90
γ [°]
V [Å3]
90
90
2156.6(2)
4
2369.4(16)
4
2561.7(4)
4
2509.3(2)
4
5675.24(16)
4
5675.24(16)
4
Z
ρcalc [g.cm–3
µ [mm−1
]
1.806
1.644
1.723
1.437
1.588
1.694
]
4.551
4.142
3.850
0.740
3.478
3.559
Crystal size [mm]
Data/restrains/parameters
S
0.50 x 0.20 x 0.08
4404/0/262
1.022
0.45 x 0.22 x 0.11
2980/1/263
0.961
0.50 x 0.12 x 0.04
5134/11/308
1.088
0.20 x 0.12 x 0.08
5042/0/325
1.138
0.55 x 0.46 x 0.11
11592/0/637
1.062
0.55 x 0.46 x 0.11
11341/0/673
1.051
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
R1 [I>2σ(I)]
wR2 (all data)
CCDC
0.0353
0.0381
0.0954
1062794
0.0939
0.0728
0.1045
1062796
0.0391
0.0221
0.0832
0.1843
0.0908
0.0564
1063388
1062795
1062798
1062799

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a)
b)
c)
d)

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9
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23
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42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
e)
Figure 3 Molecular structures and hydrogen bonds (black dashed lines) for complex 4 (a) with DET aliphatic
part of SB ligand; 6 (b) with PET type of SB ligand; 7t (c) and 7c (d) polymorphs with DPT type of SB ligands
and compound 10 (e) with DPTM type of SB ligands. Colour code: orange-Fe; blue-N; red-O; grey-C; white- H;
brown-yellow - Br.
Table 2. Summary of selected bond distances and distortion parameters of coordination polyhedra in 1 – 10
(Fe1 and Fe2 are denoted as two independent metal centres. A and B symbols are used for the characterization
of disordered coordination polyhedra with occupancy)
5(P21/c) (293 K)
4 (150 K)
1 (100 K) 2 (100 K) 3 (293 K)
(0.35)*
1.94
2.11
2.21
2.40
78
A(0.65)*
1.94
2.11
2.21
2.40
54
Fe1
1.94
2.15
2.20
2.31
93
Fe2
1.95
2.15
2.20
2.31
92
(Fe-O)avg
(Fe-Nim)avg
Fe-Nam
Fe-Cl
Σ20 / °
Θ20/ °
1.95
2.12
2.24
2.32
87
1.95
2.14
2.21
2.32
80
1.93
2.14
2.23
2.33
92
199
199
211
181
249
2.73
9.08
231
221
1.50
S(Oh)
2.06
11.13
1.67
11.72
2.50
10.45
2.35
10.40
11.27
S(D3h)
7t (150 K)
7c
(293K)
5(P-1) (150 K)
Fe2A*
6
Fe2B*
(0.52)
(293 K)
Fe1
1.94
2.10
2.20
2.40
54
(0.48)
(Fe-O)avg
(Fe-Nim)avg
Fe-Nam
1.90
2.07
2.29
2.39
84
1.97
2.13
2.29
2.39
58
1.93
2.11
2.19
2.35
57
1.93
2.06
2.20
2.40
41
1.95
2.11
2.25
2.33
36
Fe-Cl

20 / °
Θ20/ °
159
213
167
169
105
52
S(Oh)
S(D3h)
1.34
11.62
1.71
10.90
1.47
11.75
1.29
14.90
0.561
16.406
10 (293 K)
10 (100K)
8 (293 K) 9 (293 K)
Fe1
Fe2
Fe1
Fe2

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(Fe-O)avg
(Fe-Nim)avg
Fe-Nam
1.95
2.10
2.20
2.34
40
1.94
2.10
2.30
2.36
42
1.96
2.10
2.27
2.33
41
1.95
2.10
2.26
2.36
37
1.95
2.11
2.25
2.34
43
1.96
2.11
2.26
2.36
35
Fe-Cl

20 / °
Θ20 / °
S(Oh)
S(D3h)
86
86
88
92
93
93
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
0.73
15.38
0.79
15.31
0.79
14.97
0.79
14.72
0.76
15.22
0.80
14.66
*occupancy factor of disordered structures
Magnetic properties
The temperature and field dependent magnetism of 1-10 was studied in detail. At temperature
range above 50 K all eleven complexes possess the value of effective magnetic moment close
to 5.9 μB per centre and their magnetisation converges to value close to 5.0 μB per centre at
low temperature and high magnetic field. Such limiting behaviour indicates permanent high
spin state with total spin per centre S = 5/2.
As a rule, in octahedral high spin iron(III) complexes a weak zero-field splitting (ZFS) is
present.23 Further, based on the structural analysis (vide supra), the oligomeric and polymeric
supramolecular motifs can be recognized in each of systems 1-10 which motivate
introduction of weak magnetic exchange interactions.24 Weak interactions of polymeric
topology can be usually well approximated by a mean-field interaction, called in this context
molecular field.25 On top of it, magnetic exchange interaction of dimeric topology transmitted
through H-bonds can be assumed for systems 1-4. In this spirit, a spin Hamiltonian
normalized to one centre was postulated as follows
r
1
r
1
1
2
1z
2
2z
ˆ
ˆ
ˆ
ˆ
2a
ˆ
H  J(S  S )  D(S  S ) 
(S1a  S )  gB  (zj) S
(1)





2
B
a
a
T
2
2 ax, y,z
Here J is the parameter of isotropic magnetic exchange interaction between neighbouring
centres, D is the parameter of axial ZFS parameter and Ba is the a-th component of the vector
of magnetic field. The g-tensor was considered isotropic and represented thus by only one
quantity g. The molecular field is quantified by the renormalized parameter (zj). The
calculated susceptibility is corrected by empirical temperature independent magnetism25 as
follows
corr  mol  TIM
(2)
For systems 1-4 a decrease of magnetic moment below 4 μB (or, equivalently, a maximum at
the susceptibility curve) at low temperature is apparent (Figure 4a, Figure S4.1-S4.4), which
indicates presence of dominant antiferromagnetic exchange interaction. Less dramatic
decrease of magnetic moment for compounds 5-10 (Figure 4b-e, Figure S4.5-S4.11) can be
well explained by weak antiferromagnetic molecular field and/or weak ZFS. The apparent
deflection of the curve of magnetization vs. magnetic field from the Brillouin-like shape,
which is well visible for systems 3, 7t and 9, indicates ZFS with absolute value of D
parameter higher than 0.5 cm-1. The sign of this parameter cannot be reliably extracted from
magnetic functions if its value is lower than ≈1.0 cm-1.26
The fitted optimum values of spin Hamiltonian parameters for the alternative with negative
ZFS are collected in Table S4.1 and for the alternative with positive value of D in Table S4.2
(see ESI) along with the corresponding fitting residuals (R(χ) and R(M)). The reconstructed

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curves for the former alternative are displayed in Figure 4 (compounds 4, 6, 7t,DO7Ic: 10a.1n0d39/1C09N)J03087E
and both alternatives are viewed in Figure S4.1-S4.11for all reported compounds (see ESI).
All optimum values of parameters span the range expected for this family of high spin
[Fe(L)X] complexes (where X= Cl- or pseudhalido terminal ligands), as is obvious from the
Table S4.4 (see ESI) presenting the magnetic parameters observed for the similar reported
systems.16a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
6.00
6.00
6.0
5.0
4.0
3.0
2.0
1.0
0.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
2.0 K
5.00
4.00
3.00
2.00
1.00
0.00
5.00
4.00
3.00
2.00
1.00
0.00
B = 0.1 T
B = 0.1 T
2.0 K
20
15
10
5
20
15
10
5


4.6 K
4.6 K




0
0
0
10
20
T/K
30
40
50
0
10
20
T/K
30
40
50
0
50
100
150
200
250
300
0
2
4
6
8
0
50
100
150
200
250
300
0
2
4
6
8
T/K
B/T
T/K
B/T
a)
b)
6.00
5.00
4.00
3.00
2.00
1.00
0.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
6.0
5.0
4.0
3.0
2.0
1.0
0.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
B = 0.1 T
2.0 K
B = 0.1 T
2.0 K
20
15
10
5
20
15
10
5

4.6 K



4.6 K


0
0
0
10
20
30
40
50
0
10
20
30
40
50
T/K
T/K
0
50
100
150
200
250
300
0
2
4
6
8
0
50
100
150
200
250
300
0
2
4
6
8
T/K
B/T
T/K
B/T
c)
d)
6.00
5.00
4.00
3.00
2.00
1.00
0.00
6.0
5.0
4.0
3.0
2.0
1.0
0.0
B = 0.1 T
2.0 K
20
15
10
5

4.6 K


0
0
10
20
30
40
50
T/K
0
50
100
150
200
250
300
0
2
4
6
8
T/K
B/T
e)
Figure 4 Magnetic functions for compounds 4 (a), 6 (b), 7t (c), 7c (d) and 10 (e): effective magnetic moment
vs. temperature (left), magnetization vs. magnetic field (right), magnetic susceptibility vs. temperature (inset);
grey circles: experimental data, solid line: fitted data for negative D alternative.
As it was shown elsewhere,27 the miscellaneous structural features of coordination polyhedra
might influence the magnetic anisotropy of the complex compounds containing the
hexacoordinated 3d transition metal ions. In order to bring more light to the evolution of ZFS
within the series of reported compounds 1-10, the obtained values of D parameters were
correlated with the angular distortion parameters Σ and Θ. From all four dependencies (both
D- negative or positive D+ variants vs Σ and Θ, respectively; Figure 5a and Figure S4.12, see
ESI) is evident that the lowest absolute values of D were found for compounds with

New Journal of Chemistry
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2
3
4
5
6
7
8
9
asymmetric SB ligands prepared from PET amines (compound 5 and 6) aDnOdI: 1f0o.10r3V9ite/wwC9AorNtiJcl0e3O0n8li7nEe
complexes 2 and 4 with the shortest DET type of ligands. As it was already emphasised (vide
supra), those four compounds contain the intermediate (5 and 6) and high degree (2 and 4) of
angular distortion in the 1-10, respectively. On the other hand, the highest values of |D| were
obtained for next two complexes with DET type of SB ligands (1 and 3) which show high
angular distortion as well as for whole group of complexes containing the DPT and DPTM
type of SB ligands (7-10) exhibiting the lowest angular distortion. This leads to the
conclusion that angular deviation of coordination polyhedra is only one of the several effects
which influence the magnetic anisotropy in the hexacoordinated iron(III) complexes.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Magnetic exchange coupling parameters can be easily assessed with the help of density
functional theory (DFT) by employing the strategy of broken symmetry.28 In this approach the
value of parameter J is estimated from comparison of the energy of broken symmetry state
EBS and high spin state EHS of a system. Since from the magnetic measurements it was
concluded that all couplings are very weak (coupling constants lower than 1.0 cm-1),
following variant of the formula was adopted.29
2 E  E

HS 
BS
S2
J 
(3)
where S is the value of the total spin of the HS state, i.e. in all studied systems S = 5. The
hybrid exchange-correlation functional X3LYP was selected for calculation of energy as it
was designed for study of H-bonds and weak interactions30 and has proven its reliability
previously.16a,31 The resulting calculated values of magnetic exchange coupling are collected
in Table S4.3 (see ESI) along with the optimum fitted values. Somehow lower values were
obtained from DFT calculation for systems 1 and 4, while excellent mutual agreement with
fitted values can be concluded for systems 2 and 3. Both, the calculated and experimental
exchange coupling constants J, correlate with the strength of the hydrogen bonds of
supramolecular dimers in 1-4 (Figure 5b). Thus, the hypothesis of magnetic exchange
interaction transmitted through H-bonds leading to the formation of supramolecular magnetic
dimers can be considered legitimate.
-0,1
0,0
1
5
-0,2
-0,3
-0,4
-0,5
-0,6
-0,7
-0,8
6
2
-0,2
-0,4
-0,6
-0,8
-1,0
4
2
8
1
4
7t
10
3
9
7c
3
J calc
J(-)
J(+)
2,8
2,9
3,0
3,1
3,2
3,3
30
40
50
60
70
80
90
100
lenght of H-bond / A
 / o
b)
a)
Figure 5 Magnetostructural correlation of reported compounds 1-10: (a) Evolution of axial zero-field splitting
parameter D (negative alternative) upon the variation of Σ distortion parameter. Datapoints of compounds
containing the shortest DET aliphatic part are marked with blue, PET with red and DPT or DPTM with black
colour. (b) Correlation of calculated and experimentally obtained exchange coupling constants J with the N···O
hydrogen bond distances of complexes 1- 4.

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EPR spectroscopy
6
7
8
9
Figure S5.1 shows the X-band EPR spectra of powder iron(III) complexes 1 - 6 and 8 - 10
recorded at temperature of 293 K and 98 K. It is obvious that no significant differences in the
spectral features were found comparing the corresponding EPR spectra recorded at 293 and
98 K, except that the EPR signal intensity slightly increased at 98 K. In addition, at low
temperature, the resonance lines in the EPR spectra of samples 1 and 2 are better resolved.
Hence, we can describe the EPR spectra obtained at both temperatures jointly.
In the EPR spectra of the complexes 3, 4, 6 and 10, the dominant resonance line is a
broad signal down field near the effective g-value of geff ≈ 4.3. Comparing to this, spectra of
8 contain the relative less broad, dominant resonance appeared down field near geff ≈ 6.0 and
in the case of 4, the additional resonance of much lower intensity down field near geff ≈ 2.0
was detected. Unfortunately, in the EPR spectra of sample 5, the above-mentioned
resonances are not very well resolved which is caused by the very broad line width of the
individual signals. Finally, in the case of complex 9, the signal intensity of wide resonance up
field near geff ≈ 2.0 significantly decreased at 98 K.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 3 collects the geff values of the dominant resonances, which were refined by computer
simulation. The geff values of complexes 3, 4, 6 and 10 (the first group) hit the relatively
narrow range of 3.53 – 4.16. Furthermore, the corresponding geff values were temperature
independent (within experimental error).
Table 3 The effective g-factor (geff) values of the dominant resonance EPR signals obtained for the first (3, 4, 6,
10) and the second (5, 8, 9) group of the complexes. The geff - values, which were evaluated from the
experimental EPR spectra recorded at temperature of 293 K and 98 K, were further refined by computer
simulation.
Iron(III)
Complexes
The first group
The second group
8
3
4
6
10
5
9
geff
at 293 K
at 98 K
3.80(3) 3.53(3) 3.96(3) 4.16(3) 3.30(3) 6.13(3)
3.81(3) 3.55(3) 3.96(3) 4.16(3) 3.30(3) 6.10(3)
3.86(3); 2.11(3)
3.85(3); 2.14(3)
In the case of complex 1 and mainly complex 2, the line shape of the EPR spectra is
substantially different than those obtained for the other iron(III) complexes 3 - 10. Therefore,
the EPR spectral features are discussed separately. In the EPR spectra of complex 1, the
dominant resonance is again a broad signal down field near geff ≈ 4.3, but with the addition of
a broad shoulder up field near geff ≈ 6.0 and a wide resonance up field near geff ≈ 2.0. The
dominant resonances in the EPR spectra of complex 2 are two broad signals, the first one up
field near geff ≈ 2.0 at both temperatures, and the second one up field near geff ≈ 4.3 at 293 K
and down field near geff ≈ 4.3 at 98 K. Additionally, the relatively sharp resonance line
appeared down field near geff ≈ 10.0 at both temperatures. However, such simple analysis
does not describe satisfactorily the experimental EPR spectra of complexes 1 and 2.
Therefore, the computer simulation of the EPR line shape was performed by the original
program “Spin”,32 which was created for the high spin systems (S > 1/2). The following spin
Hamiltonian parameter values were obtained from the best computer fit to the experimental
EPR spectral line: (i) In the case of complex 1, geff = 2.19(3) and the axial zero field splitting
parameter, D = 0.061(3) cm-1 at 293 K; and geff = 2.28(3) and D = 0.062(3) cm-1 at 98 K. We
note that the calculated D-values are relatively very small. (ii) In the case of complex 2, geff =
4.33(3) and D = 0.290(3) cm-1 at 293 K; and geff = 4.15(3) and D = 0.290(3) cm-1 at 98 K. For
both complexes, the rhombic zero field splitting parameter (E) was estimated to span the

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range 0.001 cm-1 or less. It is clear that, for the given complex, the D values were DteOmI: 1p0.e10r3a9t/uCr9eNJ03087E
independent (within experimental error). All the zero field splitting parameters are presented
in their absolute values, since the resulting line shape of computed EPR spectrum is almost
sign independent.
In Figure S5.2, the EPR spectra of complexes 7c and 7t measured at 293 and 98 K are
compared. The resonance lines of the given complex are very similar at both temperatures,
except that the better signal intensity was obtained at low temperature. However, the
significant differences are seen in the line shape of complex 7c vs. 7t. Using the computer
simulation of the line shape, the best fit to the experimental EPR spectra was obtained for the
effective g-values as follows: (i) In the case of complexes 7c and 7t, geff = 2.01(3), at both
temperatures. (ii) In the case of complex 7c (for relative narrow, downfield signal of small
intensity), geff = 4.25(3) at 293 K and geff = 4.27(3) at 98 K. (iii) In the case of complex 7t
(for broad downfield signal), geff = 4.46(3) at 293 K and geff = 4.48(3) at 98 K.
The small, sharp line that is present in the EPR spectra in the Figures S4.1 and S4.2
(*-marked) at geff ≈ 2.00 and superimposed on the broad resonance lines located in this
region, is due to a low concentration of irremovable impurity present on the microwave
cavity walls and is not connected with the iron(III) EPR spectra.
It is obvious, that the first derivative X-band EPR spectra of powder complexes 1 - 10
recorded at 293 K and 98 K exhibited the broad resonance signals near the effective g-values
of 2.0, 4.3 and 6.4. However, the line shape seen in the EPR spectra of complex 1 and mainly
complex 2 is essentially different compared with those of complexes 3 - 10. Additionally,
comparing the line shape of the corresponding EPR spectra of complexes 1 – 10, which were
recorded at high and low temperature indicates, that no spin-crossover transition (S = 5/2 ↔
1/2) was detected in the temperature interval from 293 K to 98 K.
8
9
10
11
12
13
14
15
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18
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54
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59
60
In accordance with the literature,33 all the resonance signals detected in the EPR
spectra of powdered complexes 1 – 10 are attributed to the high spin (S = 5/2) magnetically
active iron(III) state. The inhomogeneous broad line width could be caused by the combined
effect of the g- and D- strain. The above mentioned effective g-factor values and zero field
splitting values are in good accordance with those found for the similar high spin iron(III)
complexes (S = 5/2) presented in the literature.34
Electrochemistry
The redox behaviour of iron(III) complexes was studied by cyclic and square wave
voltammetry in 0.1 M LiCl solution in dry ethanol. Both cyclic voltammetry and square wave
voltammetry confirmed a quasi-reversible one-electron transfer reaction which is in good
agreement with previous studies.35 The expected direct relationship between both, the
electron withdrawing and electron donating character of the individual substituents and its
reduction potential, was recorded. Therefore, proceeding from compound 10 to compound 1,
the reduction increases in power from Ep/2 = -669 to -830 mV vs. ferrocenium/ferrocene
(Fc+/Fc) couple (Table 6, column Ep/2-Ep/2(Fc),Figure S6.1 and Figure S6.3 see ESI).
Compounds 6, 7, 8 and 10 containing bromo-substituted benzene rings in the SB ligands
show the highest redox potential (from -669 to -732 mV vs. Fc+/Fc). Apparently, naphthalene
rings in 9 might have the similar impact on the redox potential as 5-Br or 6-Br substituents of
6, 7, 8 and 10. Two couples (6-8 and 7-4) with the same substituents introduced on the
benzene rings exhibit notable difference in their reduction power which was therefore
tentatively attributed to the different length of aliphatic parts of their SB ligands. Thus, the
prolongation of aliphatic part from PET to DPT in case of 6 and 8 with 3-methoxy and 6-
bromo substituted benzenes, or the shortening from DPT to DET in 7 and 4 with 5-bromo
substituents decreases the redox potential from -669 mV to -732 mV vs. Fc+/Fc in the first

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couple and from -680 mV to -793 mV vs. Fc+/Fc in the second couple (Table 4). On the other
hand, the compounds with DET aliphatic spacer (1-4) are reduced at more negative potentials
than those with longer aliphatic substituents introduced in their SB ligands. The most
negative redox potential was detected in the case of the compounds 1 and 2 containing the
naphthalene aromatic moieties. Thus, if the reduction potentials of compounds 1 with DET
aliphatic part on one side, and compounds 10 with DPTM aliphatic part on the second side
are compared, the effect of spacer length on the redox properties of the respective compounds
seems to be also important. Figure S6.1 suggests a trend in which compounds with shortest
DET spacer have more negative Ep/2 and the complexes with the longest DPT and DPTM
moieties show the weakest reduction power.
5
6
7
8
9
10
11
12
13
14
15
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The redox properties were studied also by DFT method, where the thermodynamic cycle
shown in Figure S6.2 (see ESI) was employed. In accord with this Born-Haber cycle, the
standard Gibbs free energy of a redox half reaction in solution, Gsolv, was obtained by
calculating the change in free energy of redox reaction in gas phase, Gg, and solvation free
energies of each of the species, Gsolv(Ox) and Gsolv(Red), by employing this equation
Gsoolv  Ggo  Gsoolv (Red)  Gsoolv (Ox)
(4)
In next step, the reduction potential was calculated with Nernst equation assuming transfer of
one electron as
EOox/Red  Gsoolv / F
(5)
where F is Faraday constant. With the aim to acquire reliable reduction potential for
the iron(III) complexes under study, we used an internal reference system to minimize the
error between calculated and experimental values.36 Thus, the ferrocenium/ferrocene (Fc+/Fc)
redox pair was selected as internal reference, as suggested also by IUPAC for the
experimental work.37 The ωB97X-D3 range-separated hybrid GGA functional with empirical
dispersion correction38 was chosen, because it provided accurate results for other iron-based
complexes.39 The molecular geometries of iron(III) and iron(II) complexes 1-10 were
optimized in vacuo followed by calculations of the molecular vibrations. Then, gas-phase
zero-point energies, thermal corrections, and entropic corrections were calculated using the
standard formulas for the statistical thermodynamics of an ideal gas under the harmonic
oscillator approximation for T = 298.15 K resulting in the respective Gibbs free energies. The
respective solvation Gibbs free energies were calculated with the SMD solvation model40
setting solvent to ethanol according to the experimental conditions. The computational results
are listed in Table 4 and calculated and experimental redox potentials relative to Fc+/Fc redox
couple are compared in Figure 6. Sufficiently good linear correlation (except of compounds 2
and 7t) between the calculated and experimental redox potentials was found. Large deviation
of 7t from this trend might suggest that compound 7 is present as cis-isomer (see the position
of 7c in Figure 6) in ethanol solution. The deviation of the compound 2 from the overall trend
can be explained by the fact that this is the only compound within the series, which possess
methyl group on imine bond. Since, the computation of the solvation Gibbs free energy is in
general problematic, we also computed the electron affinity Eea of the complexes following
IUPAC convention as energy required to detach an electron from the singly charged negative
ion
[Fe(퐿5)Cl] ― (푔)→[Fe(퐿5)Cl](푔 ) + 푒 ―
(7)
and the results are listed in Table 4 and depicted in Figure 7. Evidently, the electron affinity
nicely correlate with the experimental redox potentials, only the value for complex 4 slightly

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deviates. Thus, such simplified calculations are also suitable to predict trends in the reduction
potential for similar type of the coordination compounds.
6
7
8
Table 4 Calculated Gibbs free energies, electron affinities and redox potentials compared to the experimental
redox potentials
Ep/2-
Ep/2(Fc)
9
Gsoolv (Red)
Gsoolv
EOox/Red
EOox/Red  EFoc+/Fc
Gsoolv (Ox)
kcal/mol
-34.346
-33.984
-30.069
-30.011
-31.861
-25.065
-26.860
-26.323
-25.005
-30.074
-25.162
-54.450
g
Eea
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
kcal/mol
-49.713
-48.199
-47.512
-54.241
-50.315
-57.061
-53.348
-56.350
-52.888
-52.559
-53.770
-166.219
kcal/mol
-71.665
-68.997
-68.454
-63.905
-68.748
-58.433
-58.280
-58.232
-60.517
-65.258
-59.665
-9.353
kcal/mol
-87.035
-83.214
-85.898
-88.137
-87.204
-90.431
-84.770
-88.262
-88.403
-87.746
-88.275
-121.126
V
mV
mV
eV
1
3.774
3.609
3.725
3.822
3.782
3.922
3.676
3.827
3.834
3.805
3.828
5.253
-1478
-830
2.010
1.903
1.922
2.217
2.037
2.348
2.162
2.306
2.142
2.136
2.186
7.225
2
-1644
-1528
-1431
-1471
-1331
-1577
-1425
-1419
-1448
-1425
0
-802
-822
-793
-768
-669
-680
-680
-732
-726
-690
0
3
4
5
6
7t
7c
8
9
10
Fc+/Fc
Figure 6 The correlation plot calculated vs. experimental relative redox potentials of the respective compounds.
The red line corresponds to linear equation y = -922 + 0.694x. Compounds 2 and 7t were excluded from the
linear fit.

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Figure 7 The correlation plot for calculated electron affinity vs. experimental relative redox potentials of the
respective compounds.
Summary
A series of novel iron(III) SB complexes was structurally, spectrally and magnetically
characterized. Eleven mononuclear compounds of general formula [Fe(L)Cl] contain
pentadentate ligand anion L prepared by SB condensation between miscellaneous derivatives
of salicylaldehyde and linear aliphatic triamines. Thus, each central atom is surrounded by
N3O2Cl donor atom set which supports the high spin state electronic configuration.
Structural investigation revealed interesting impact of the length and symmetry of SB ligands
on the stereochemistry of coordination polyhedra. In the line with our previous findings,15-17
compounds containing the shortest aliphatic bridge derived from DET amine adopt the cis-
O2/mer-N3 configuration. Such arrangement of SB ligand donor atoms causes the highest
angular distortion of coordination polyhedra among the reported compounds and promote the
formation of antiferromagnetically coupled hydrogen bonded pseudodimers within the crystal
lattice. It is interesting to note that experimental and DFT calculated magnetic exchange
coupling constants are in good agreement to each other.
Compounds with the longer either asymmetric PET or symmetric DPT and DPTM aliphatic
bridges introduced on the SB ligand skeleton prefer the cis-O2/mer-N3 arrangement of donor
atoms and their angular distortion of coordination polyhedra decreases in the order PET >
DPT, DPTM. Complex 7 with DPT type of ligand exists in two isomeric forms adopting
either cis-O2/mer-N3 or trans-O2/mer-N3 configuration and complex 5 with PET asymmetric
SB ligand exhibits reversible monoclinic-triclinic phase transition upon the temperature
variation. Interestingly, neither the isomerism nor phase transition has significant impact on
their physical properties.
Magnetic and EPR study confirmed the high spin behaviour of the iron(III) central atoms in
all cases, too, with indication of weak zero-field splitting with a small absolute value (|D| <1
cm-1); however, its sign cannot be determined with the employed methods. The first
derivative EPR spectra of powdered complexes 1 - 10 measured at two temperatures confirm
the high spin (S = 5/2) magnetically active iron(III) state as well.
Redox properties of reported compounds in the solution are also significantly dependent on
the molecular design of SB ligand. One can conclude that reduction power increases with the

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shortening of the aliphatic spacer in order DPT, DPTM < PET < DET and decreaDsOeIs: 1w0.1i0t3h9/tCh9eNJ03087E
introduction of bromo substituents on the aromatic part of chelating ligands. Redox potentials
were also calculated by DFT method employing the Born-Haber cycle to consider solvation
effects which resulted in the good agreement between the experimental and theoretical
values.
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Acknowledgements
We are very grateful to Mrs. Kristína Tatár for the powder X-ray diffraction analysis of the
compound 7 at room temperature to confirm the purity of the prepared trans isomer. Grant
Agencies (Slovakia: APVV-18-0197, APVV-18-0016, APVV-15-0053, APVV-17-0183,
VEGA 1/0125/18) are acknowledged for the financial support. This article was created with
the support of the MŠVVaŠ of the Slovak Republic within the Research and Development
Operational Programme for the project "University Science Park of STU Bratislava" (ITMS
project no. 26240220084) co-funded by the European Regional Development Fund. We are
also grateful to the HPC centre at the Slovak University of Technology in Bratislava, which is
a part of the Slovak Infrastructure of High Performance Computing (SIVVP project, ITMS
code 26230120002, funded by the European region development funds, ERDF). R.H., I.N.
and I.Š acknowledges the financial support from institutional sources of the Department of
Inorganic Chemistry, Palacký University Olomouc, Czech Republic. I.N. acknowledges the
financial support from the National Programme of Sustainability I (LO1305) of the Ministry
of Education, Youth and Sports of the Czech Republic. I.Š. and R.H. also wish to
acknowledge the COST Action CM1305 ECOSTBio (Explicit Control Over Spin-States in
Technology and Biochemistry).
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Σ  12  90
20 (a)
; where φ represents values of twelve cis angles in DoOcI:ta10h.1e0d39r/oCn9N.J03087E
i1 

i
i
Adapted from the reference: P. Guionneau, M. Marchivie, G. Bravic, J. F. Létard, D.
Θ  24   60
Chasseau, Top. Curr. Chem. 2004, 234, 97-128. (b)
; where are
θi
i1 

i
24 angles measured on the projection of two triangular faces of the octahedron along
with their common pseudo-threefold axis. Adapted from the reference M. A. Halcrow,
Chem. Soc. Rev. 2011, 40, 4119–4142.
10
11
12
13
14
15
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DOI: 10.1039/C9NJ03087E
Graphical abstract
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A series of novel iron(III)–Schiff base complexes has been prepared and structuraly
characterised. The stereochemical, magnetic and redox properties were corelated with the
molecular design of the corresponding N3O2-pentadentate Schiff base ligand.