Series of high spin mononuclear iron(III) complexes with Schiff base ligands derived from 2-hydroxybenzophenones

Article abstract of DOI:10.1039/c7nj00617a

The reaction of various phenols with benzoyl chloride afforded the derivatives of phenyl benzoate that subsequently underwent Fries rearrangement. The obtained 2-hydroxybenzophenone analogues were combined with linear aliphatic triamines, which afforded pentadentate Schiff base ligands. Moreover, nine new iron(iii) complexes with the general formula [Fe(L_n)X] (where, L_n is the dianion of the pentadentate Schiff base ligand, N,N′-bis((2-hydroxy-5-methylphenyl)phenyl)methylidene-1,5-diamino-3-azapentane = H₂L₁, N,N′-bis((2-hydroxy-3,5-dimethylphenyl)phenyl)methylidene-1,5-diamino-3-azapentane = H₂L₂, N,N′-bis((2-hydroxy-5-chlorophenyl)phenyl)methylidene-1,5-diamino-3-azapentane = H₂L₃, N,N′-bis((2-hydroxy-4-methylphenyl)phenyl)methylidene-1,5-diamino-3-azapentane = H₂L₄, N,N′-bis((2-hydroxy-5-bromophenyl)phenyl)methylidene-1,7-diamino-4-azaheptane = H₂L₅, N,N′-bis((2-hydroxy-5-bromophenyl)phenyl)methylidene-1,7-diamino-4-methyl-4-azaheptane = H₂L₆ and X is the chlorido, azido or isocyanato terminal ligand) were synthesized and characterized via elemental analysis, and IR and UV-VIS spectroscopy; in addition, the crystal structures of all the complexes were determined by X-ray diffraction. Magnetic investigation reveals high spin state behaviour in all the reported compounds. DFT calculations and analysis of the magnetic functions allowed to extract absolute values of the zero field splitting parameters and exchange coupling constants.

Full text of DOI:10.1039/c7nj00617a

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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
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Page 1 of 25
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Series of High Spin Mononuclear Iron(III) Complexes with Schiff Base ligands derived from 2-
DOI: 10.1039/C7NJ00617A
hydroxybenzophenones
a*
a
a
a
Lukáš Pogány, Ján Moncol, Ján Pavlik, and Ivan Šalitroš,
a) Department of Inorganic Chemistry, Faculty of Chemical and Food Technology, Slovak University
of Technology in Bratislava, Bratislava SK-81237, Slovakia, *e-mail: lukas.pogany@stuba.sk
Abstract
Reaction of various phenols with benzoyl chloride afforded derivatives of phenyl benzoate that
subsequently underwent Fries rearrangement. Obtained 2-hydroxybenzophenone analogues were
combined with linear aliphatic triamines which afforded formation of pentadentate Schiff base
ligands. Nine new iron(III) complexes of the general formula [Fe(L
n
)X] (where L
n
is dianion of
pentadentate Schiff base ligand N,N’-bis((2-hydroxy-5-methylphenyl)phenyl)methylidene-1,5-
diamino-3-azapentane=H
2 1
L ),
N,N’-bis((2-hydroxy-3,5-dimethylphenyl)phenyl)methylidene-1,5-
diamino-3-azapentane=H
2
L
2
), N,N’-bis((2-hydroxy-5-chlorophenyl)phenyl)methylidene-1,5-diamino-
N,N’-bis((2-hydroxy-4-methylphenyl)phenyl)methylidene-1,5-diamino-3-
N,N’-bis((2-hydroxy-5-bromophenyl)phenyl)methylidene-1,7-diamino-4-
3
-azapentane=H
2
L ),
3
azapentane=H
azaheptane=H
azaheptane=H
2
L
2
L
2
L
4
5
6
),
), N,N’-bis((2-hydroxy-5-bromophenyl)phenyl)methylidene-1,7-diamino-4-methyl-4-
and X is chlorido, azido or isocyanato terminal ligand) have been synthesized and
characterized by elemental analyses, IR, and UV–VIS and the crystal structures of all complexes have
been determined by X-ray diffraction. Magnetic investigation revealed high spin state behaviour in all
reported compounds. DFT calculations and analysis of magnetic functions allowed to extract absolute
values of zero field splitting parameters and exchange coupling constants.
Keywords: 2-hydroxybenzophenone derivative, Schiff base ligands; Iron(III) complexes; Exchange
coupling; DFT; SQUID magnetometry.

New Journal of Chemistry
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DOI: 10.1039/C7NJ00617A
1
.
Introduction
Spin-crossover (SCO) between the low-spin (LS) and high-spin (HS) state is a phenomenon that
4
7
occurs in complexes usually with 3d -3d electronic configuration of central atom wherein the spin
state transition of the metal centre can be activated by temperature, pressure, light irradiation,
magnetic field or their combination.1-3 Such case of molecular bistability triggered by external stimuli
4
5
6
opens the possibility of application in future memory devices, displays or sensors. The SCO is
essentially a single molecule phenomenon, however, interactions between switching moieties have
direct impact on the shape of thermal or photo-induced LS↔HS transition curves. With respect to
this, the interesting SCO behaviour is usually found in the complexes that create intermolecular
7
interactions, such as hydrogen bonding and π–π stacking within the crystal lattice. This brought a
motivation for investigation of compounds with increased potential for H-bonding and/or π–π
stacking interactions and impact of contacts on the magnetochemical behaviour.
When miscellaneous derivatives of salicylaldehyde react with symmetric aliphatic triamines (e.g.
N-(2-aminoethyl)ethane-1,2-diamine, N-(3-aminopropyl)propane-1,3-diamine, N-(3-aminopropyl)-N-
methylpropane-1,3-diamine), or asymmetric N-(2-aminoethyl)propane-1,3-diamine triamine one
arrives to a pentadentate N
3
O -donor Schiff-base ligands. The following complexation with ferric
2
chloride allows the formation of corresponding mononuclear complexes of general formula [Fe(L)Cl].
Thus, the rational design and synthesis of Schiff-base ligands present important steps in the bottom-
up synthesis of SCO compounds and series of corresponding [Fe(L)Cl] complexes can be prepared as
precursors for further modification of coordination sphere. The bond between iron(III) central atom
and terminal chlorido ligands is the weakest one and therefore allows systematic ligand replacement
10
11
either with pseudohalido ligands , with N-donor aromatic ligands (i.e. pyridine derivatives), or by
metalocyanates.12 Our group has already shown that the presence of chlorido terminal ligand in
[
Fe(L)Cl] complexes results always in the HS state behaviour,11,12 while the corresponding [Fe(L)CN]
complexes show LS behaviour.11,12 However, if the chlorido ligand is replaced by N-donor terminal
pseudohalide anions e.g. azide, cyanate, thiocyanate or selenocyanate, the iron(III) coordination
centre is then surrounded with N
4
O -donor set supporting the presence of SCO phenomenon.
2
-
-
-
-
The number of so far prepared [Fe(L)X] complexes (X=NCS , NCSe , N
3
, NCO ) allows us to
10
compare impact of ligand structure on the presence of SCO behaviour. When a Schiff bases were
prepared from salicylaldehyde or 3-ethoxysalicylaldehyde and symmetric triamines, appropriate
[
Fe(L)NCS] complexes revealed pure HS behaviour. 10a,12b,13 Compounds with Schiff bases containing
symmetric amines and azide or cyanate terminal ligands have not been reported yet. When 3-
methoxysalicylaldehyde, 3-ethoxysalicylaldehyde or 2-acetyl-1-hydroxynaphthalene were reacted
with asymmetric N-(2-aminoethyl)propane-1,3-diamine, the HS state was found in the corresponding
azido complexes.10a-d On the contrary, if the Schiff base ligand of azido iron(III) complexes started

Page 3 of 25
New Journal of Chemistry
Vie1w0Abr,dticle Online
DOI: 10.1039/C7NJ00617A
from 1-hydroxynaphthalene-2-carbaldehyde or 5-bromosalicylaldehyde, the SCO was present.
Similar trend has been noticed in the next example of isocyanato complexes [Fe(L)NCO], where L
contained aliphatic part derived from N-(2-aminoethyl)propane-1,3-diamine. If Schiff base ligands
contain an aromatic part originated from 3-methoxysalicylaldehyde or 5-chlorosalicylaldehyde, the
iron(III) central atom stays in the HS state.10c,d On the other hand, if naphthalenic carbaldehyde is
used in this sake, the SCO phenomenon does occur in the corresponding [Fe(L)NCO] compound.10d
It follows from previous observations that Schiff bases derived from symmetric triamines lead to
pure HS behaviour, while asymmetric triamine along with extended aromatic part of Schiff base
promotes the occurrence of SCO phenomenon. Therefore, the extension of „conventional“ aldehydes
to benzophenone analogues seemed to be promising way of rational design of Schiff base ligand. The
formal substitution of hydrogen atom of aldehyde group with phenyl or other aromatic unit was
motivated by the idea that potentially enhanced π-π interactions and cooperativeness can bring
about abrupt and hysteretic SCO. Furthermore, Schiff bases derived from the same amine can adopt
different configuration and appropriate complexes exhibit different magnetic behaviour, when 2-
14
hydroxybenzophenone derivative is used instead of substituted salicylaldehyde. This motivated us
to use such extended aromatic ketones with symmetric triamines and pseudohalides.
Despite from plenty of successful modifications discussed above, our assumptions were not
fulfilled and only pure HS compounds were obtained. Herein we report on the synthesis of nine
iron(III) complexes of general formula [Fe(L
ligand prepared by condensation of derivative of 2-hydroxybenzophenone and aliphatic triamine
where n=1-6, and X refers either to chlorido, azido or isocyanato terminal ligand, see Fig. 1.). All
n
)X], where L
n
is a deprotonated pentadentate Schiff base
(
prepared compounds have been characterized by elemental analyses, IR and UV–VIS spectroscopy
and the single crystal X-ray diffraction analysis confirmed their expected molecular structure. In
addition, the magnetic properties have been measured and interpreted using the spin Hamiltonian
approach and DFT calculations.
2
2
.
Experimental part
.1. Materials and physical measurements
All solvents and chemicals were purchased from commercial sources and used without further
purification. Elemental analysis was performed by using Eager 300 (Carlo Erba) elemental analyser.
UV-VIS spectra were obtained on a Specord 250 plus, Analytical Jena spectrophotometer. Infrared
1
spectra (ATR technique) were measured on a Magna FT- IR 750, Nicolet spectrophotometer. H NMR
13
and C spectrum was recorded with a Bruker DPX 500 (500 MHz). Chemical shifts are reported in
ppm relative to CDCl as an internal standard.
3

New Journal of Chemistry
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Data collection and cell refinement of C1-C9 were made by Stoe StadiVari diffractometer using
DOI: 10.1039/C7NJ00617A
Pilatus 300K HPAD detector and microfocus source Xenocs FOX3D with CuKα. The structures were
16
17
18
solved by direct or charge-flipping methods using SHELXT, SIR-2011, , or SUPERFLIP and refined
by the full-matrix least-squares procedure with SHELXL (version 2016/6).19 Geometrical analyses
20
were performed with SHELXL. The structures were drawn using the OLEX2 package. Crystal data
and conditions of data collection and refinement are reported in Tab. 1 The bispropyleneamine
group of 8 and N-methyl-bispropyleneamine group of 9 are disordered in two positions. The
occupancy factors of two parts of disordered groups are 0.507(3)/0.493(3) and 0.576(3)/0.424(3) for
8
and 9, respectively. The crystal structures of 2, 8 and 9 contain also disordered solvent molecules,
which have been modelled using solvent-masking in OLEX2 package. The all constrains and restrains
used for refinement of crystals structures are given in CIF file.

Page 5 of 25
New Journal of Chemistry
Tab. 1. Crystallographic data for the reported compounds.
Compound C1 C2 C3
Empirical formula C32
Formula weight 580.91
Temperature (K) 100(2)
C4
C5
C6
C7
C8
C9
H
31ClFeN
3
O
2
C
34
H
35ClFeN
3
O
2
C
34
H
35FeN
6
O
2
C
35
H
35FeN
4
O
3
C
30
H
2
25Cl FeN
6
O
2
C
31
H
2
25Cl FeN
4
O
3
C
32
H
31FeN
6
O
2
C
32
H
29Br
2
FeN
6
O
2
C
33
H
31Br
2
FeN
6
O
2
608.95
615.53
110(2)
615.52
110(2)
628.31
100(2)
628.30
100(2)
587.48
100(2)
745.28
110(2)
1.54186
triclinic
P-1
759.31
110(2)
1.54186
triclinic
P-1
110(2)
Wavelength (Å)
Crystal system
Space group
a (Å)
1.54186
1.54186
triclinic
1.54186
1.54186
1.54186
monoclinic
P2 /n
1.54186
monoclinic
P2 /n
1.54186
monoclinic
monoclinic
P2 /n
monoclinic
P2 /n
orthorhombic
Pbca
1
P2 /n
P-1
1
1
1
1
10.3034(3)
15.3208(4)
18.1489(6)
90
10.9490(3)
11.8076(3)
13.3882(3)
97.761(2)
104.537(2)
109.503(2)
1533.21(7)
2, 1.319
10.2617(3)
15.2514(3)
19.5057(5)
90
10.1275(3)
15.4288(4)
19.3778(6)
90
9.6274(3)
15.2106(3)
19.5026(7)
90
9.4543(3)
15.3791(4)
19.5339(5)
90
18.7577(5)
18.8838(6)
16.1938(4)
90
9.8877(2)
12.8918(2)
13.8494(2)
10.1152(3)
13.0131(3)
13.8985(4)
101.157(2)
96.653(2)
110.337(2)
1649.33(8)
2, 1.529
b (Å)
c (Å)
α (°)
102.1670(10)
97.8370(10)
109.2430(10)
1588.28(5)
2, 1.558
β(°)
101.693(3)
90
105.111(2)
90
103.679(2)
90
97.639(3)
90
95.402(2)
90
90
γ(°)
90
V (Å3)
Z, ρcalc g.cm-3
2805.46(15)
4, 1.373
2947.19(13)
4, 1.387
2942.00(15)
4, 1.390
2830.59(15)
4, 1.474
2827.59(14)
4, 1.476
5736.1(3)
8, 1.361
Radiation type
Cu-K
α
Cu-K
α
Cu-K
α
Cu-K
α
Cu-K
α
Cu-K
α
Cu-K
α
Cu-K
α
Cu-K
α
-
1
μ (mm )
5.456
5.015
638.0
4.442
4.456
6.336
6.350
4.539
7.070
750.0
6.819
766.0
F(000)
1212.0
1292.0
1292.0
1292.0
1292.0
2456.0
2
θ Ranges (°)
7.62 to 176.15 7.03 to 142.74 7.46 to 142.38 7.41 to 142.60 7.40 to 143.00 7.33 to 142.71 8.60 to 143.19 6.70 to 142.68 6.62 to 143.03
Reflections
collected
37250
34231
59381
35699
41976
43503
51484
57949
36401
Data/restrains/p
arameters
5
286/0/355
5745/0/374
5639/0/392
5477/0/392
5405/0/370
5378/0/370
5512/0/372
5978/483/410 6192/486/427
Final R indices
R
1
= 0.0404
wR = 0.1097
= 0.0458
wR = 0.1126
R
1
= 0.0288
wR = 0.0728
= 0.0328
wR = 0.0738
R
1
= 0.0268,
wR = 0.0651
= 0.0338, 2
wR = 0.0671
R
1
= 0.0258
wR = 0.0470
= 0.0395
wR = 0.0481
R
1
= 0.0458
wR = 0.1257
= 0.0555
wR = 0.1347
R
1
= 0.0328
wR = 0.0941
= 0.0362
wR = 0.0984
R
1
= 0.0307
wR = 0.0686
= 0.0468
wR = 0.0717
R
1
= 0.0329
wR
= 0.0352
wR = 0.0908
R
1
= 0.0303
= 0.0788
= 0.0348
= 0.0801
[
I > 2σ(I)]
R indices
all data)
2
2
2
2
2
2
2
2
= 0.08983 wR
2
R
1
R
1
R
1
R
1
R
1
R
1
R
1
R
1
R
1
(
2
2
2
2
2
2
2
2
wR
2
S
1.054
0.965
1.007
0.820
1.082
1.077
0.878
1.123
0.959
CCDC number
1525798
1525799
1525800
1525801
1525802
1525803
1525804
1525805
1525806

New Journal of Chemistry
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All herein reported magnetic measurements were performed on a SQUID magnetometer
DOI: 10.1039/C7NJ00617A
(Quantum Design, model MPMS-XL-7). In all cases, the temperature dependence of magnetization
was recorded at B = 0.1 T as an external magnetic field. The temperature sweeping rate was 1 K min-1
and was the same for cooling and heating mode. Gelatine capsules were used as sample containers
for the measurement in the temperature range 1.8 ↔ 300 K. The very small diamagnetic
contribution of the gelatine capsule and high-temperature sample holder had a negligible
contribution to the overall magnetization. The diamagnetic corrections of the molar magnetic
susceptibilities were applied using Pascal’s constants.21
The fitting of the magnetic susceptibility and magnetization was performed with the help of a
home-made program.
The DFT calculations of g-factors were carried out using the package ORCA 3.0.322 on the
23
geometries obtained from the X-ray analysis. The GGA functional PBE was selected and the scalar
relativistic correction was included applying the second order Douglass-Kroll-Hess approach (DKH).24
The relativistically recontracted Ahlrich’s def2-TZVP basis set was employed for all atoms.25 The
26
chain-of-spheres approximation (RIJCOSX) was set on using an automatically generated auxiliary
basis set.
Subsequently, the optimization of the positions of hydrogen atoms was performed for
supramolecular dimers using the basis set def2-SVP and the empirical dispersion correction D3BJ.27
28
The exchange coupling calculations were carried out using the package ADF 2016 on the geometries
with optimized hydrogen atoms. The hybrid functional X3LYP was selected29 and the Slater-type
orbital (STO) basis set of TZP quality was employed for the Fe atoms; while for other atoms DZP
quality was used.30 The “small core” option and increased integration quality (level 5 in ADF
convention) were set.
2
.2. Synthesis and spectral properties
The substituted phenyl benzoates (3a-e) were prepared by benzoylation of phenol derivatives
1
5
(
1a-e) with benzoyl chloride (2) in aqueous solution of sodium hydroxide. The derivatives of 2-
hydroxybenzophenone (4a-e) were prepared by Fries rearrangement of appropriate phenyl benzoate
3a-e) in molten and anhydrous aluminium chloride (Fig S1, top).15 Herein reported Schiff base
ligands H (n=1-6) have been synthesized without isolation, purification or characterisation. In situ
prepared ligands were reacted with iron(III) chloride in the presence of triethylamine as a base and
appropriate sodium salt of counteranion that leaded to complex of general composition [Fe(L )X]
Fig. 1, Fig. S1 bottom).
(
L
2 n
n
(

Page 7 of 25
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00617A
R4
R4
FeCl , Et N
(CH )
(CH )
2 n
(
CH2)n (CH2)n
3
3
2 n
N
N
N
N
N
N
2.3 eq. NaX (except C1,C2)
CH CN:CH OH (1:1, v/v)
3
3
O-
O-
R3
Fe
R3
R3
OH
HO
R3
rfx, 45 min
R2
R1
X-
R1
R2
R2
R1
R1
R2
H2L
n
C1 - C9
Fig. 1 Scheme of syntheses of complexes C1–C9. For C1 (and corresponding ligand H
H, R = CH , n = 2, X = Cl; for C2–C4 (and corresponding ligand H ) R = R = CH , R
and X = Cl (C2), N (C3) or NCO (C4); for C5 and C6 (and corresponding ligand H ) R
Cl, n = 2 and X = N (C5) or NCO (C6); for C7 (and corresponding ligand H ) R = R
CH , n = 2 and X = N ; for C8 (and corresponding ligand H ) R = R = R = H, R = Br, n = 3 and X = N
for C9 (and corresponding ligand H ) R = R = H, R = Br, R = CH , n = 3 and X = N
2
L
1
) R
1
= R
= H, n = 2
2
= R =
4
3
3
2
L
2
1
3
3
2
= R
= R
= R
4
3
2
L
3
1
2
= R
4
= H, R
3
=
3
2
L
4
1
3
4
= H, R
2
=
3
3
2
L
5
1
2
4
3
3
;
2
L
6
1
2
3
4
3
3
.
General procedure for phenyl benzoates preparation
The Erlenmeyer flask was charged with appropriate derivative of phenol (100 mmol), water (150 mL)
and 10 % sodium hydroxide solution (60 mL). Ice (ca. 150 g) was added to the solution and benzoyl
chloride (11.6 mL, 100 mmol) was poured in small portions while the reaction mixture was vigorously
stirred. The product that solidified upon stirring as off-white solid was filtered off and washed with
water (200 mL). Purification of product with activated charcoal and subsequent isothermal
crystallization from ethanol afforded products in white polycrystalline powder.
General procedure for 2-hydroxybenzophenone derivatives preparation
2
50 ml round-bottom flask was charged with derivative of phenyl benzoate (100 mmol, 1 eq.) and
anhydrous aluminium chloride (16.7 g, 125 mmol, 1.25 eq.). The melted reaction mixture was slowly
stirred at 160-180 °C for 3 hours, cooled down to room temperature and quenched with ice-cold
water (170 mL) and 10 % aqueous solution of hydrochloric acid (85 mL). Dichloromethane (200 mL)
was added and mixture was shaken well until it completely dissolved. The solution was transferred to
a separatory funnel, aqueous layer was separated from the organic one and extracted two more
times (2x200 mL). Combined organic layers were concentrated to ca. 150 mL under reduced
pressure, transferred back to separatory funnel and extracted with 2.5 % sodium hydroxide solution
(4x250 mL). Combined alkaline water layers were acidified with 10 % sulphuric acid (pH ≈1, ca 300
mL). When the product that precipitates as yellow crystalline solid, it was filtered off and dried in the
air. On the other hand, if product separates as yellow oil, it was extracted from water layer with
dichloromethane (3x500 mL). Combined organic layers were dried with anhydrous magnesium
sulphate and concentrated on rotary evaporator to dryness. The yellow oil or solid of product was

New Journal of Chemistry
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dissolved in methanol, purified with activated charcoal and the solution was set for isothermal
DOI: 10.1039/C7NJ00617A
crystallization that afforded product as yellow polycrystalline powder
Syntheses and spectral properties of complexes
C1 ([Fe(L
1
)Cl]): 4a (0.849 g, 4.0 mmol, 2 eq.) was combined with solution of N-(2-aminoethyl)ethane-
1
,2-diamine (0.206 g, 2 mmol, 1 eq.) in methanol:acetonitrile mixture (1:1 v/v, 25 mL) in Erlenmeyer
flask. The reaction mixture was refluxed for 45 minutes. In the second step, a solution of anhydrous
iron(III) chloride (0.324 g, 2.0 mmol, 1 eq.) in methanol:acetonitrile mixture (1:1 v/v, 25 mL) and
triethylamine (0.405 g, 4 mmol, 2 eq.) were added and the resulting mixture was refluxed for another
4
5 minutes. The solution was filtered and set for controlled crystallisation at laboratory temperature.
Single crystals suitable for X-Ray diffraction were collected after few days. Yield 55 %. FT−IR (ATR,
−
1
ṽ
max/cm ): 3121 (w, N-H), 2936 (w, C-Halif), 2899 (w, C-Halif), 1608 (s, C=N). UV-VIS (nujol, λmax/nm):
-
1
5
15, 464, 333, 247. Elemental analysis for C32
H31ClFeN
3
O (580.91 g.mol ): Found % (Calc. %): C 65.70
2
(66.16), H 5.53 (5.38), N 7.20 (7.23).
C2 ([Fe(L )Cl]): Complex C2 was prepared in the same manner as C1, however, 4b (0.905 g, 4.0 mmol,
2
−
1
2
eq.) was used instead of 4a. Yield 57 %. FT−IR (ATR, ṽmax/cm ): 3137 (w, N-H), 2932 (w, C-Halif), 2912
(w, C-Halif), 1607 (s, C=N). UV-VIS (nujol, λmax/nm): 541, 472, 334, 246. Elemental analysis for
-
1
34
C H
35ClFeN
3
O (608.95 g.mol ): Found % (Calc %): C 67.12 (67.06), H 6.05 (5.79), N 7.85 (6.90).
2
C3 ([Fe(L
with 4b (0.905 g, 4.0 mmol, 2 eq.) instead of 4a. After addition of triethylamine, the reaction mixture
was stirred for another 15 min and sodium azide NaN (0.300 g, 4.6 mmol, 2.3 eq.) was added. The
2
)N
3
]): Preparation of complex C3 departed in the same manner as C1, however, starting
3
final solution was refluxed for 45 minutes and filtered. Single crystals suitable for X-Ray diffraction
were collected after few days of controlled crystallisation at laboratory temperature. Yield 60 %.
−
1
FT−IR (ATR, ṽmax/cm ): 3154 (w, N-H), 2943 (w, C-Halif), 2915 (w, C-Halif), 2900 (w, C-Halif), 2052 (s, N
3
),
1
607(s, C=N). UV-VIS (nujol, λmax/nm): 521, 443, 326, 252. Elemental analysis for C34 35FeN
H
6
O
2
-
1
(
615.53 g.mol ): Found % (Calc %): C 66.90 (66.34), H 5.88 (5.73), N 13.79(13.65).
C4 ([Fe(L )NCO]): Complex C4 was prepared in the same manner as C1, however, starting with 4b
2
(0.905 g, 4.0 mmol, 2 eq.) instead of 4a and sodium cyanate NaNCO (0.300 g, 4.6 mmol, 2.3 eq.) was
−
1
used instead of sodium azide. Yield 64 %. FT−IR (ATR, ṽmax/cm ): 3184 (w, N-H), 2936 (w, C-Halif), 2899
(w, C-Halif), 2193 (s, NCO), 1607(s, C=N). UV-VIS (nujol, λmax/nm): 522, 471, 337, 251. Elemental
-
1
analysis for C35
H
35FeN
4
O (615.52 g.mol ): Found % (Calc %): C 67.51 (68.30), H 5.75 (5.73), N 9.05
3
(9.10).

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DOI: 10.1039/C7NJ00617A
C5 ([Fe(L
3
)N
3
]): Complex C5 was prepared in the same manner as C3, however, starting with 4c
−
1
(
0.931 g, 4.0 mmol, 2 eq.) instead of 4b. Yield 61 %. FT−IR (ATR, ṽmax/cm ): 3117 (w, N-H), 2940 (w, C-
3
Halif), 2903 (w, C-Halif), 2052 (s, N ), 1615 (s, C=N). UV-VIS (nujol, λmax/nm): 511, 441, 327, 251.
-
1
Elemental analysis for C30
H25Cl
2
FeN
6
O (628.31 g.mol ): Found % (Calc %): C 57.38 (57.35), H 4.04
2
(4.01), N 13.16 (13.38).
C6 ([Fe(L )NCO]): Complex C6 was prepared in the same manner as C4, however, 4c (0.931 g, 4.0
3
−
1
mmol, 2 eq.) was used instead of 4b. Yield 58 %. FT−IR (ATR, ṽmax/cm ): 3121 (w, N-H), 2936 (w, C-
Halif), 2903 (w, C-Halif), 2185 (s, NCO), 1606(s, C=N). UV-VIS (nujol, λmax/nm): 503, 457, 341, 246.
-
1
Elemental analysis for C31
H25Cl
2
FeN
4
O (628.30 g.mol ): Found % (Calc %): C 58.90 (59.26), H 3.99
3
(4.01), N 8.74 (8.92).
C7 ([Fe(L
4
)N
3
]): Complex C7 was prepared in the same manner as C3, however, starting with 4d
−
1
(
0.849 g, 4.0 mmol, 2 eq.) instead of 4b. Yield 40 %. FT−IR (ATR, ṽmax/cm ): 3244 (w, N-H), 3051 (w, C-
3
Har), 2936 (w, C-Halif), 2903 (w, C-Halif), 2051 (s, N ), 1600(s, C=N). UV-VIS (nujol, λmax/nm): 505, 436,
-
1
3
5
32, 247. Elemental analysis for C32
H
31FeN (587.48 g.mol ): Found % (Calc %): C 65.11 (65.42), H
6
O
2
.45 (5.32), N 14.40 (14.31).
C8 ([Fe(L
1.109 g, 4.0 mmol, 2 eq.) instead of 4b and N-(3-aminopropyl)propane-1,3-diamine (0.262 g, 2.0
mmol, 1 eq.) was used instead of N-(2-aminoethyl)ethane-1,2-diamine. Yield 52 %. FT−IR (ATR,
5
)N ]): Complex C8 was prepared in the same manner as C3, however, starting with 4e
3
(
−
1
ṽ
max/cm ): 3256 (w, N-H), 3059 (w, C-Har), 2953 (w, C-Halif), 2866 (w, C-Halif), 2046 (s, N
3
), 1578(sh,
C=N). UV-VIS (nujol, λmax/nm): 505, 454, 321, 245. Elemental analysis for C32
2 6
H29Br FeN O
2
-
1
(
745.28 g.mol ): Found % (Calc %): C 51.50 (51.57), H 3.92 (4.09), N 11.28 (11.63).
C9 ([Fe(L
1.109 g, 4.0 mmol, 2 eq.) instead of 4b and N,N-di-(3-aminopropyl)-N-methyl-amine (0.291 g, 2.0
mmol, 1 eq.) was used instead of N-(2-aminoethyl)ethane-1,2-diamine. Yield 56 %. FT−IR (ATR,
6
)N ]): Complex C9 was prepared in the same manner as C3, however, starting with 4e
3
(
−
1
ṽ
max/cm ): 3059 (w, C-Har), 2957 (w, C-Halif), 2928 (w, C-Halif), 2883 (w, C-Halif), 2043 (s, N
3
), 1601 (s,
C=N). UV-VIS (nujol, λmax/nm): 513, 456, 338, 244. Elemental analysis for C33
2 6
H31Br FeN O
2
-
1
(
759.31 g.mol ): Found % (Calc %): C 51.86 (52.20), H 4.22 (4.12), N 11.64 (11.07).
3
3
.
Results and discussion
.1. Syntheses and spectral characterisation
The synthesis of Schiff base ligands consisted of three steps. At first, the corresponding
derivative of phenol (1a-e) reacted with benzoyl chloride (2) in sodium hydroxide solution at lowered

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temperature. Substituted analogues of phenyl benzoate (3a-e) precipitated as off-white solids and
DOI: 10.1039/C7NJ00617A
isothermal crystallization from ethanol afforded pure products in the reasonable yield (72-85 %). In
the next, 3a-e were combined with powdered anhydrous aluminium chloride, the reaction mixture
was melted upon the heating which afforded formation of 2-hydroxybenzophenone derivatives (4a-
e) by Fries rearrangement. Products 4a-e were isolated by extraction with sodium hydroxide solution
and after the neutralisation they were isothermally crystallized from methanol as yellow solids and
the yields varied between 40-91 %. Schiff base ligands H
of 2-hydroxy-5-methylbenzophenone (4a, H ), 2-hydroxy-3,5-dimethylbenzophenone (4b, H
), 2-hydroxy-4-methylbenzophenone (4d, H ) or 5-bromo-
) with 1,5-diamino-3-azapentane (H , n=1-4), 1,7-diamino-4-
) in mixture of methanol and
2
L
1
-H
2
L
6
were prepared via the condensation
2
L
1
2 2
L ), 5-
chloro-2-hydroxybenzophenone (4c, H
-hydroxybenzophenone (4e, H , H
azaheptane (H
2
L
3
L
2 4
2
2
L
5
2
L
6
L
2 n
2
L
5
) or 1,7-diamino-4-methyl-4-azaheptane (H
L
2 6
acetonitrile (1:1, v/v). The yellow solutions of ligands were prepared in situ and used for the further
complexation without any purification and characterisation. Complexes C1-C9 of general formula
[
Fe(L )X] (where n=1 for C1, n=2 for C2-C4, n=3 for C5, C6, n=4 for C7, n=5 for C8 and n=6 for C9)
n
were prepared by complexation of Schiff bases with anhydrous iron(III) chloride in the presence of
triethyl amine as a base. In the case of C3-C9, chloride ligand anion was exchanged either with
sodium azide (C3, C5, C7-C9) or sodium cyanate (C4, C6). The dark violet crystals suitable for the
diffraction analysis were obtained after several days of controlled evaporation of solution at
laboratory temperature.
Newly prepared organic and coordination compounds were characterised by FTIR spectroscopy
(see supporting information Fig. S2-S4). In the case of 3a-e, vibrational bands of hydrogen atoms
-
1
attached to benzene ring Ar-H can be found in range 3072-3006 cm . Vibrational bands of aliphatic
-
1
C-H bonds are observed in range 2917-2924 cm in case of methylated esters 3a, 3b, and 3d. One can
-
1
also observe peaks of C=O bond from ester groups at 1724, 1727, 1731, 1730 and 1728 cm for 3a-e
respectively. Infrared spectra of 4a-e (see supporting information Fig. S4-S6) show vibrational bands
-
1
of Ar-H in the range 3070-3033 cm . Presence of methyl groups in 4a, 4b, and 4d leads to
-
1
observation of C-H bands in almost the same range 2917-2914 cm as for the corresponding
benzoates. Vibrational bands of C=O group of benzophenone unit are observed at 1626, 1614, 1623,
-
1
-1
1
622 and 1620 cm for 4a-e, respectively. N-H vibrational modes located in interval 3256-3117 cm
are identified for complexes C1-C9 (see supporting information Fig. S7-S11). Peaks of aromatic C-H
-
1
vibrations are observed at 3051, 3059 and 3059 cm for C7, C8 and C9, respectively, while in other
complexes these bands are combined with vibrations of N-H and aliphatic C-H groups. One can also
-
1
find symmetric and asymmetric vibrations of aliphatic C-H bonds in the ranges 2928-2957 cm and
-
1
2
2
866-2912 cm , respectively. Peaks corresponding to NCO terminal ligand are located at 2193 and
-
1
185 cm for C4 and C6, respectively. On the other hand, bands that can be assigned to azido

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-
1
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DOI: 10.1039/C7NJ00617A
terminal ligand are found at 2052, 2052, 2051, 2046 and 2043 cm in the IR spectra of C3, C5, C7, C8
-
1
and C9, respectively. Imino -C=N vibrations are found in the spectral region 1600-1615 cm for C1-C7
and C9, however, in case of complex C8 this band is combined with a band of skeletal vibrations of
-
1
aromatic rings and reaches a maximum at 1578 cm .
The solid state electronic absorption spectra of 3a-e exhibit very similar features (see supporting
information Fig. S12, left). One can observe a band at 232-234 nm that belongs to π→π* transition
with two shoulders in intervals 272-277 nm and 280-284 nm that correspond to another π→π* and
n→π* excitations. In case of 4a-e (see supporting information Fig. S12, right) bands at 218-226 nm
(blue shift in range 8-15 nm compared to 3a-e) and 259-273 nm (blue shift in range 3-15 nm
compared to 3a-e) are observed that belong both to π→π* transitions. Another band corresponding
to n→π* excitation is located at 339-362 nm (red shift in range 59-80 nm compared to 3a-e). The
solid state electronic absorption spectra of C1-C9 (see supporting information Fig. S13) exhibit four
bands: two of them that belong to π →π* transitions are found in intervals 244-252 nm and 321-341
nm, the third one is dedicated to a charge transfer appears in 436-472 nm region and band in the
visible region at 503-541 nm corresponding to charge transfer bands which obscure forbidden d-d
transition bands of iron(III) central atom (6A1g → 4T1g and6A1g → 4T2g).
1
In the H NMR spectra of compounds 3a-e (see supporting information Fig. S14-S18) hydrogen
atoms of benzoyl parts gain comparable values in ranges 8.26-8.18, 7.67-7.58 and 7.57-7.47 ppm for
those in ortho, para and meta positions, respectively. The aromatic protons signals of substituted
phenyl moiety differ due to the position and nature of substituents. In methylated 3a two well
separated doublets appear in ranges 7.21-7.20 ppm and 7.10-7.08 ppm. In chlorinated analogue 3c,
two multiplets in slightly higher regions 7.42-7.39 ppm and 7.20-7.17 ppm are found. In brominated
3
e, one of the signals is elevated even higher to the region 7.57-7.51 ppm such that it is combined
with the signal of protons from benzoyl unit. The other doublet at 7.14-7.11 ppm is detected in 3e. In
unsymmetrically methylated 3d a triplet at 7.36-7.33 ppm, a doublet at 7.13-7.11 ppm and a
multiplet at 7.08-7.05 ppm are observed. The signals are combined into one complex multiplet
appearing in lower region between 7.11 and 7.03 ppm in 3b with two methyl substituents.
Moreover, signals of aliphatic methyl groups are found at 2.36 ppm, at 2.36 and 2.22 ppm and at
2
.43 ppm in spectra of 3a, 3b and 3e, respectively.
1
In H NMR spectra of 4a-e (see supporting information Fig. S19-S23, upper) a singlet appears in
region 12.18-11.88 corresponding to OH phenyl group. Signals of benzoyl parts are found in regions
.77-7.65, 7.64-7.56 and 7.56-7.46 ppm for hydrogen atoms in ortho, para and meta positions,
7
respectively. These signals are slightly lowered compared with 3a-e. The aromatic protons of
substituted phenyl units appear in 4a at 7.37 ppm as singlet, and at 7.34-7.32 and 7.00-6.98 ppm as
doublets. In case of analogous compound 4c a signal of one proton is combined with a signal from

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protons of benzoyl moiety. Two doublets appear in region 7.47-7.44 and 7.05-7.03 ppm and obey
DOI: 10.1039/C7NJ00617A
values higher than those of 4a. Spectrum of brominated analogue 4e exhibits multiplet at 7.77-7.66
ppm with even higher value than 4c. One of the doublets appears in region 7.59-7.58 ppm that is
slightly higher than previous two compounds. The other doublet obeys values in range 7.00-6.98
ppm, comparable with 4a and 4c. In spectrum of 4d one can observe a multiplet in region 7.51-7.46
ppm, a singlet at 6.89 ppm and a doublet at 6.69-6.67 ppm that are the peaks with lowest observed
value. In 4b only one complex multiplet at 7.21-7.20 ppm is observed. Singlets of aliphatic methyl
groups gain values lower compared with 3a, 3b and 3d and were found at 2.26 ppm in 4a, at 2.30
and 2.22 ppm in 4b and at 2.38 ppm in 4d.
13
In C NMR spectra of compounds 3a-e (see supporting information Fig. S14-S18, bottom) peaks
of C=O carbon of ester group appear at 165.6, 165.4, 165.3, 165.5, 165.2 ppm for 3a-e, respectively.
Methyl groups are found at 21.2 ppm in 3a, at 21.2 and 16.5 ppm in 3b and at 21.6 ppm in 3d. The
13
other aromatic carbons are observed in region 151.2-118.9 ppm. Similarly, in C NMR spectra of
compounds 4a-e (see supporting information Fig. S19-S23, bottom) signals of carbon of C=O group
are found at 201.9, 202.2, 201, 201.4 and 200.9 ppm for 4a-e, respectively. Methyl groups exhibit
peaks at 20.8 ppm in 4a, at 20.8 and 15.9 ppm in 4b and at 22.3 ppm in 4d. Peaks in the region 163.7-
1
10.6 ppm are assigned to the aromatic carbons of two benzene rings.
.2. Description of crystal structures
3
Complexes C1 and C3-C6 crystallize in centrosymmetric monoclinic space group P2 /n, C2, C8
1
and C9 crystallize in triclinic P-1 space group and complex C7 in orthorhombic Pbca space group.
Within this series of compounds, three isomorphic groups can be recognised: the first includes
compounds C1, C3 and C4, the second C5 and C6, and the third one is C8 and C9. Selected
crystallographic parameters are listed in Tab. 1. Asymmetric unit in each crystal structure contains
one molecule of corresponding complex (Fig. 2 - Fig. 10) and the unit cell contains four asymmetric
units in case of monoclinic structures of C1, C3-C6, two asymmetric units for triclinic structures of C2,
C8-C9 and eight asymmetric units in the orthorhombic structure of C7. The iron(III) coordination
environment contains two imino (Nim) and one amino (Nam) nitrogen donor atoms, two oxygen donor
atoms and the sixth coordination place is occupied by terminal either chlorido (C1, C2) or nitrogen
donor atom (Nps) of pseudohalogenido ligand (C3-C9). Thus, the coordination chromophore can be
expressed as {Fe(Nim
)
2 am
N O
2
Cl} for C1 and C2 and {Fe(Nim
)
2 am
N N
ps
2
O } for C3-C9. In agreement with our
previous observations,10a,11a,12b compounds C1-C7 with short N,N-bis(ethylene)amine aliphatic part of
Schiff bases always adopt the facial configuration of three nitrogen and cis arrangement of two
oxygen donor atoms. In cis-O
2
and fac-N
3
configuration one of Nim atoms is always in axial position
with respect to the terminal ligand and all seven compounds C1-C7 contain Schiff base ligand

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wreathed around the iron(III) central atom in right hand ∆ configuration (see supporting information
DOI: 10.1039/C7NJ00617A
Fig. S33). We have also reported number of examples with cis-O
2
and mer-N configuration where
3
N,N-bis(propylene)amine or N-methyl-N,N-bis(propylene)amine aliphatic parts were included in the
molecular structure of corresponding Schiff base ligands. However, compounds C8 and C9 adopt very
scarce trans-O
2
and fac-N configuration where Nam donor atom are always in the axial position with
3
respect to the terminal pseudohalide anion.
The HS state is evident from values of iron-nitrogen bond distances which vary in the ranges
2
.17-2.35Å (Fe-Nam) and 2.10-2.22Å (Fe-Nim) (see Tab. 2). The Fe1-O1 and Fe1-O2 bonds lengths are
less sensitive to the spin state variation of central atom and are the shortest one within the
coordination chromophore with values in the range 1.88-2.01Å. The axial Fe-Cl bonds of C1 and C2
are the longest and weakest with values 2.25Å and 2.33Å, respectively. In the case of C3-C9 with
pseudohalido ligands, Fe-Nps bond distances acquire values from range 1.99Å-2.02Å (see Tab. 2)
typical for the HS state of central atom10,12a and apparently they are independent on the type of N -
3
-
and NCO terminal ligand anions.
Coordination polyhedra of reported compounds can be expressed as deformed tetragonal
bipyramid (for selected bond angles see Tab. S2). Σ and Θ distortion parameters are suitable
quantities for the detection of the spin state of central atom and for the recognition between various
32
isomeric configurations of coordination polyhedral. Values of both distortion parameters for C1-C7
are comparable with values for other similar HS mononuclear complexes with cis-O , fac-N
,10a and
for all seven compounds there is possible to observe good correlation between the Σ and Θ values
see supporting information Fig. S34). In this series of complexes, the lowest degree of deformation is
observed for complex C7 which contains Schiff base ligand with methyl substituent introduced in the
position 4 of benzene ring. Compounds C8 and C9 with trans-O and mer-N configuration of
coordination polyhedral acquire significantly lower values of Σ and Θ parameters.
2
3
(
2
3
In addition, crystal structures of C1-C7 contain similar hydrogen bonded interconnection of two
neighbouring complex molecules via Nam and oxygen donor atoms (for supramolecular dimers see Fig
S24 and Fig. S25, for whole packing see Fig. S26-Fig. S32) with distances from the range 2.84-3.02Å
(Tab. S3). Formation of hydrogen bonded pseudo-dimers allows communication between the
paramagnetic centres which results usually in the antiferromagnetic exchange coupling (vide infra).
The expected π-π interactions between aromatic parts of Schiff base ligand were thus suppressed
due to the edge to face (T-shaped) mutual orientation of benzene rings of two neighbouring
molecules of complex.

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DOI: 10.1039/C7NJ00617A
Tab. 2. Selected bond lengths and metric parameters of C1-C9
C1
C2
C3
C4
C5
Fe1-O1
Fe1-O2
1.8775(15)
2.0109(16)
2.1489(19)
2.349(2)
2.1650(18)
2.2460(6)
104
1.9428(11)
1.8977(11)
2.2177(11)
2.2166(13)
2.1973(13)
2.3315(4)
93
1.9595(10)
1.8987(10)
2.1817(12)
2.1960(12)
2.2016(12)
2.0206(13)
111
1.9605(11)
1.8988(11)
2.1715(13)
2.2093(14)
2.2165(13)
2.0078(14)
105
1.972(2)
1.907(2)
2.176(3)
2.172(3)
2.193(3)
2.017(3)
104
Fe1-N1(im)
Fe1-N2am
Fe1-N3
a
Fe1-X
1
5
Σ /°
15
Θ /°
226
243
262
244
241
C6
C7
C8A
C8B
C9
Fe1-O1
Fe1-O2
Fe1-N1
Fe1-N2
Fe1-N3
1.9718(14)
1.9025(14)
2.1781(16)
2.1717(17)
2.1999(17)
1.9926(19)
97
1.9436(12)
1.90812(12)
2.1434(14)
2.1967(15)
2.1616(15)
2.0207(15)
83
1.9610(16)
1.9389(17)
2.1066(19)
2.237(3)
2.1173(19)
2.010(2)
54
1.9610(16)
1.9389(17)
2.1066(19)
2.237(3)
2.1173(19)
2.010(2)
54
1.9561(15)
1.9362(16)
2.1039(19)
2.2949(19)
2.1104(19)
2.016(2)
48
a
Fe1-X
1
5
Σ /°
1
5
Θ /°
221
185
68
77
82
a
X is Cl1 for C1 and C2, N4 for C3-C9 respectively
Fig. 2 Asymmetric unit of complex C1.

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Fig. 3 Asymmetric unit of complex C2.
Fig. 4 Asymmetric unit of complex C3.
Fig. 5 Asymmetric unit of complex C4.

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Fig. 6 Asymmetric unit of complex C5.
Fig. 7 Asymmetric unit of complex C6.
Fig. 8 Asymmetric unit of complex C7.

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Fig. 9 Asymmetric unit of complex C8.
Fig. 10 Asymmetric unit of complex C9.
3
.3.
Magnetic properties
Magnetic behaviour of reported complexes C1-C9 was investigated in detail. The temperature
dependence of magnetic properties is presented as effective magnetic moment and the field
dependence as magnetization, both of them in units of Bohr magnetons per centre. In all nine
complexes, the effective magnetic moment acquires values about 5.9 μ
B
in the temperature range
5
0-300K and the molar magnetisation at 2 K and 7 T reaches almost 5 μ . Thus, both functions prove
B
permanent HS state behaviour of C1-C9. As discussed above, a supramolecular dimer motif can be
found in the structures of C1-C7 motivating thus a general anisotropic two-centre approach including
the magnetic exchange coupling. The postulated spin Hamiltonian reads21
J
2
1z
ˆ
ˆ
ˆ
1z
H   (S  S )  DS  S  gB
(1)
1
2
B
2
where J is the parameter of the isotropic exchange coupling interaction, D is the parameter of the
axial zero-field splitting, B is the absolute value of the magnetic field induction and g is the isotropic
gyromagnetic factor. The spin operators act on the neighbouring sites of the supramolecular dimer.
In cases C5-C9 the temperature independent magnetism was introduced as correction of the slope of
the high-temperature part of the curve. Regarding the sign of the axial zero-field splitting the

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magnetic properties of powder samples are inconclusive, especially in the case of small splitting
typical for iron(III) systems, therefore both, positive and negative values, were tested. The alternative
model where the small parameter of zero field splitting was replaced by the weak magnetic exchange
from surrounding molecules (i.e. molecular field) was tested, too, however, for system C2 where the
D parameter gains highest absolute value no better fits can be found with such model (see Fig S36).
To keep the consistency we use therefore the Hamiltonian (1) for all systems. The experimental
functions with their best fits are displayed in Fig. 11 and Fig. S35 and the resulting optimum
parameters along with the relative errors of fitting are presented in the Tables 3 and 4. All parameter
values span the range expected for this class of compounds. It is interesting to note, that both sets of
D parameters are apparently invariant upon the degree of angular deformation of coordination
polyhedral (see supplementary information, Fig. S37). It can be also seen, that the pairs C1-C2, C3-C4
and C5-C6 possess similar values of exchange coupling which correlates with their structural kinship.
Moreover, the pairs with stronger antiferromagnetic coupling show also lower dihedral angle Fe-N-
O-Fe and within all pairs the shorter is the Fe-Fe distance the stronger is the coupling. (see Tab. 5).
This is in accordance with expectation since both mentioned structural parameters enhance the
overlap of interacting orbitals along the superexchange pathway.33
Tab. 3. Summary of fitted magnetic parameters of systems C1-C9 and the corresponding relative
errors for the alternative with negative value of the D parameter.
J(-)/cm-1
g(-)
D(-)/cm-1
χ
TIM
[a]
R(χ)/R(M)
Complex
C1
C2
C3
C4
C5
C6
C7
C8
C9
-0.491
-0.707
-0.312
-0.312
-0.374
-0.370
-0.224
-
1.97
1.94
1.97
1.98
1.98
1.98
1.93
1.90
1.95
-0.57
-0.75
-0.67
-0.53
-0.37
-0.37
-0.56
-0.42
-0.60
0.00
0.00
0.00
0.00
0.030/0.021
0.005/0.024
0.016/0.022
0.023/0.027
15.94 0.011/0.027
15.48 0.005/0.019
13.60 0.025/0.014
-2.08
-2.53
0.041/0.030
0.027/0.053
-
[
a]
-9
3
-1
In units of 10 m mol .
Tab. 4. Summary of fitted magnetic parameters of systems C1-C9 and the corresponding relative
errors for the alternative with positive value of the D parameter.

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DOI: 10.1039/C7NJ00617A
J(+)/cm-1 g(+) D(+)/cm-1
χ
TIM
[a]
R(χ)/R(M)
Complex
C1
C2
C3
C4
C5
C6
C7
C8
C9
-0.522
-0.678
-0.371
-0.311
-0.423
-0.390
-0.276
-
1.96
1.96
2.00
1.98
2.00
2.00
1.96
1.90
1.95
0.65
0.95
0.81
0.58
0.33
0.48
0.73
0.44
0.70
0.00
0.00
0.00
0.00
9.92
0.022/0.018
0.040/0.025
0.027/0.021
0.001/0.027
0.023/0.035
10.16 0.012/0.024
4.66
-0.30
-4.74
0.003/0.17
0.041/0.027
0.032/0.045
-
[
a]
-9
3
-1
In units of 10 m mol .
Tab. 5. Dihedral angles Fe-N-O-Fe and distances Fe-Fe for systems C1-C7.
Complex
J(-)/cm-1
J(+)/cm-1
dihedral angle
d/Å
C1
C2
C3
C4
C5
C6
C7
-0.491
-0.707
-0.312
-0.312
-0.374
-0.370
-0.224
-0.522
-0.678
-0.371
-0.311
-0.423
-0.390
-0.276
40.8°
44.3°
50.4°
51.1°
45. 1°
47.3°
65.7°
5.12
5.09
5.04
5.10
4.99
5.03
4.95
6
5
.00
6.00
5.00
4.00
6
5
4
3
2
1
0
.0
.0
.0
.0
.0
.0
.0
6.0
5.0
2
.0
K
.00
B
=
0.1
T
B
=
0.1
T
2.0
K
3
2
2
1
1
0
5
0
5
0
5
0
4.00
3.00
2.00
1.00
0.00
30
25
20
15
10
5
4.0


4.6 K

4.6
K

3.00
3.0

2.00
1.00
2.0
1.0
0
0
10
20
30
40
50
0
10
20
30
40
50
T/K
T/K
0.0
0
0.00
0
0
50
100
150
T/K
200
250
300
0
2
4
6
8
50
100
150
T/K
200
250
300
2
4
6
8
B/T
B/T
a) C1
b) C2

New Journal of Chemistry
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DOI: 10.1039/C7NJ00617A
6
5
.00
.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
6
5
4
3
2
1
0
.0
.0
.0
.0
.0
.0
.0
6.0
B
=
0.1
T
B
=
0.1
T
2
.0
K
2.0 K
5.0
4.0
3.0
2.0
1.0
0.0
3
2
2
1
1
0
5
0
5
0
5
0
4.00
3.00
2.00
1.00
0.00
30
25
20
15
10
5


4
.6
K
4.6 K


0
0
10
10
10
20
30
40
40
40
50
0
10
10
10
20
30
40
40
40
50
T/K
T/K
T/K
T/K
T/K
T/K
0
0
0
50
50
50
100
150
200
250
300
0
0
0
2
2
2
4
6
8
8
8
0
0
0
50
50
50
100
150
200
250
300
0
0
0
2
2
2
4
6
8
8
8
T/K
B/T
T/K
B/T
c) C3
d) C4
6
5
.00
.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
6
5
4
3
2
1
0
.0
.0
.0
.0
.0
.0
.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
2
.0
K
2.0 K
B
=
0.1
T
B
=
0.1
T
3
2
2
1
1
0
5
0
5
0
5
0
4.00
3.00
2.00
1.00
0.00
30
25
20
15
10
5
4.6
K
4.6 K
0
0
20
30
50
0
20
30
50
100
150
200
250
300
4
6
100
150
200
250
300
4
6
T/K
B/T
T/K
B/T
e) C5
f) C6
6
5
.00
.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
6
5
4
3
2
1
0
.0
.0
.0
.0
.0
.0
.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
B
=
0.1
T
B
=
0.1
T
2.0
K
2
.0
K
3
2
2
1
1
0
5
0
5
0
5
0
4.00
3.00
2.00
1.00
0.00
30
25
20
15
10
5
4.6
K
4.6
K
0
0
20
30
50
0
20
30
50
100
150
200
250
300
4
6
100
150
200
250
300
4
6
T/K
B/T
T/K
B/T
g) C7
h) C8
6
5
.00
.00
6
5
4
3
2
1
0
.0
.0
.0
.0
.0
.0
.0
B
=
0.1
T
2.0 K
3
2
2
1
1
0
5
0
5
0
5
0
4.00
3.00
2.00
1.00
0.00

4.6 K


0
10
20
30
40
50
T/K
0
50
100
150
T/K
200
250
300
0
2
4
6
8
B/T
i) C9
Fig. 11 Magnetic functions for C1-C9 and their theoretical analysis with D(-) alternative, effective
magnetic moment vs temperature (left), magnetization vs magnetic field (right), magnetic
susceptibility vs temperature (inset); grey circles: experimental data, solid line: fitted.

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DOI: 10.1039/C7NJ00617A
3
.4. DFT calculations
Both, the g-factors and exchange coupling parameters can be easily calculated with the help of
Density Functional Theory (DFT). The g-factors were obtained with the help of coupled-perturbed
34
Kohn-Sham approach. Because of its efficiency and reliability, the GGA functional PBE was chosen
in this work. Resulting g-factors are collected in Table 6. One can see that the values are very similar
each other and in all cases slightly higher compared to those extracted from experimental curves.
The exchange coupling parameters can be obtained employing the Ginsberg-Noodleman approach.35
In this work its weak bonding variant was used, which regarding to convention from Eq. (1) leads to
formula
2
(EBS  E )
HS
(2)
J 
2
S
where EHS and EBS is the energy of the high spin state (HS) and the broken-symmetry state (BS),
respectively, and S is the value of the total spin of the HS state, i.e. S = 5. The functional X3LYP was
36
shown to perform well for the H-bonds energy motivating thus its employment in this work. The
resulting calculated values of magnetic exchange coupling are collected in Table 6. Very good
agreement with the fitted values can be concluded.
The accurate calculation of very small zero-field splitting parameters is still very challenging task37
which exceeds the scope of present work, therefore we leave the question on their correct sign
open.
Tab. 6. Summary of calculated magnetic parameters of systems C1-C9.
Complex
J/cm-1
-0.361
g
C1
C2
C3
C4
C5
C6
C7
C8
C9
2.013
2.012
2.010
2.010
2.011
2.009
2.010
2.010
2.011
-0.649
-0.490
-0.373
-0.471
-0.447
-0.324
-
-

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DOI: 10.1039/C7NJ00617A
Conclusions
In the summary, nine novel mononuclear iron(III) complexes have been prepared and their
structural and magnetic properties were investigated in detail. The target-directed synthesis of Schiff
base ligands was focused on the formation of 2-hydroxybenzophenone derivatives capable to
condensate with aliphatic triamines and to form pentadentate N
3
O -donor ligands with enhanced
2
degree of aromaticity. Iron(III) complexation with corresponding Schiff bases allowed us to prepare
series of mononuclear compounds with terminal chlorido, azido or isocyanato ligand anions.
Unfortunately, despite our best efforts to create π-π contacts in the supramolecular structures of
presented compounds, the H-bonding interconnection between two complex molecules took the
place more preferably. Phenyl rings of neighbouring H-bonded pseudodimers are arranged in the
face-to-edge fashion to each other making the formation of π-π contacts impossible.
All nine complexes exhibit permanent HS state behaviour which was confirmed by structural as
-
1
well as magnetic investigation. A zero-field splitting with very small absolute value (D≈ 0.5 cm ) was
found in all complexes, however, its sign cannot be determined with employed methods. A small
magnetic exchange coupling was also determined by fitting experimental magnetic functions and its
H-bond pathway was confirmed by DFT calculations. Despite its small value a correlation between
the coupling and structural motif of related H-bonded pseudodimers was proven.
The presence of SCO phenomenon in the ferric complexes with N
4
O -coordination environment
2
is anticipated.1 However, this is not the case in herein reported compounds. Putting this into
perspective, over the fifty similar examples of iron(III) complexes with pentadentate Schiff bases and
pseudohalido terminal ligands can be found in the CCDC database. Among them, however, only less
than a half exhibits thermally induced SCO effect and it seems that the presence of asymmetric N,N-
(
ethyl)propylamine aliphatic part of the pentadentate Schiff base ligands is a common structural
feature in this family of SCO complexes. To the best of our knowledge, so far reported iron(III)
complexes containing either the symmetric aliphatic parts of Schiff base ligands (N,N-
bis(propyl)amine or N,N-bis(ethyl)amine moiety) lack the SCO bistability in favour of the HS state
behaviour. So it looks, that symmetry of pentadentate Schiff base ligands plays a crucial role and
presence of N,N-(ethyl)propylamine aliphatic bridge is necessary requirement for the observation of
SCO phenomenon. The synthesis of this type of ligands and iron(III) complexes is an ongoing work in
our laboratory.
Acknowledgements
Grant Agencies (Slovakia: APVV-14-0078, APVV-14-0073, VEGA 1/0522/14) and STU Grant
scheme for Support of Young Researchers, STU Grant scheme for Support of Excellent Teams of
Young Researchers and COST Action CM1305 (ECOSTBio)) are acknowledged for the financial

Page 23 of 25
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support. We are grateful to the HPC centre at the Slovak University of Technology in Bratislava, which
DOI: 10.1039/C7NJ00617A
is a part of the Slovak Infrastructure of High Performance Computing (SIVVP project, ITMS code
6230120002, funded by the European region development funds, ERDF), as well as the Department
2
of Physical Chemistry at the University of Geneva for the computational time and resources made
available.
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