Triangular {Ni3} coordination cluster with a ferromagnetically coupled metal-ligand core

Article abstract of DOI:10.1016/j.poly.2018.01.014

The coordination characteristics of a tridentate, π-conjugated Schiff base (HL·SMe) combined with 4-(methylthio)benzoic acid (Hbza·SMe) were explored in methanol solution. A two-step aerobic process involving the precursor NiCl₂·6H₂O afforded the trinuclear coordination compound [Ni^II₃(L·SMe)₄(bza·SMe)(MeOH)₂]Cl_0.5(CH₃O)_0.5·5.5MeOH·H₂O (1), while the precursor Ni(ClO₄)₂·6H₂O resulted in [Ni^II₃(L·SMe)₄(bza·SMe)(MeOH)₂](ClO₄)_0.75(CH₃O)_0.25·1.5MeOH·0.75H₂O (2); in both cases the thioether-containing ligands are key to isolation of crystalline products. Their solvent-free cationic motif [Ni₃(L·SMe)₄(bza·SMe)]⁺, supported by two different types of monodeprotonated chelate ligands, has been studied by electrospray ionization mass spectrometry. 1 and 2 crystallize in the triclinic space group P1ˉ and monoclinic space group Cc, respectively, and feature a hitherto not observed triangular metal-ligand skeleton that is characterized by predominantly ferromagnetic exchange coupling between Ni(II) ions. Proof-of-concept infrared reflection–absorption spectroscopy measurements of 1 deposited on a gold substrate indicate that this moisture-stable compound retains its main structural features upon adsorption on the metal surface, which enables subsequent studies of catalytic properties of 1 on a solid support.

Full text of DOI:10.1016/j.poly.2018.01.014

Polyhedron 144 (2018) 144–151
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Triangular {Ni3} coordination cluster with a ferromagnetically coupled
metal-ligand core
Sebastian Schmitz a, Jan van Leusen a, Natalya V. Izarova b, Svenja D.M. Bourone a, Arkady Ellern c,
Paul Kögerler a,b, , Kirill Yu. Monakhov a,
⇑
⇑
a Institut für Anorganische Chemie, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
b Jülich-Aachen Research Alliance (JARA-FIT) and Peter Grünberg Institute (PGI-6), Forschungszentrum Jülich, 52425 Jülich, Germany
c Chemistry Department, Iowa State University, 1711 Gilman Hall, Ames, IA 50011, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The coordination characteristics of a tridentate,
p
-conjugated Schiff base (HLꢀSMe) combined with 4-
Received 6 December 2017
Accepted 16 January 2018
Available online 31 January 2018
(methylthio)benzoic acid (HbzaꢀSMe) were explored in methanol solution. A two-step aerobic process
involving the precursor NiCl2ꢀ6H2O afforded the trinuclear coordination compound [NiI3I(LꢀSMe)4(bzaꢀSMe)
(MeOH)2]Cl0.5(CH3O)0.5ꢀ5.5MeOHꢀH2O (1), while the precursor Ni(ClO4)2ꢀ6H2O resulted in
[NiI3I(LꢀSMe)4(bzaꢀSMe)(MeOH)2](ClO4)0.75(CH3O)0.25ꢀ1.5MeOHꢀ0.75H2O (2); in both cases the thioether-
containing ligands are key to isolation of crystalline products. Their solvent-free cationic motif
[Ni3(LꢀSMe)4(bzaꢀSMe)]+, supported by two different types of monodeprotonated chelate ligands, has been
Keywords:
Polynuclear metal complexes
Sulfur
ꢀ
studied by electrospray ionization mass spectrometry. 1 and 2 crystallize in the triclinic space group P1
Schiff base
and monoclinic space group Cc, respectively, and feature a hitherto not observed triangular metal-ligand
skeleton that is characterized by predominantly ferromagnetic exchange coupling between Ni(II) ions.
Proof-of-concept infrared reflection–absorption spectroscopy measurements of 1 deposited on a gold sub-
strate indicate that this moisture-stable compound retains its main structural features upon adsorption on
the metal surface, which enables subsequent studies of catalytic properties of 1 on a solid support.
Ó 2018 Elsevier Ltd. All rights reserved.
Carboxylates
Magnetochemistry
1. Introduction
co-ligand (Fig. 2) and the ligand periphery was functionalized with
thioether groups. Such structurally exposed thioether groups (–
The excellent reactivity and versatility of combined Schiff base
and carboxylate ligands toward metal ions provide a reliable path
towards a plethora of metal complexes with different nuclearity
and physicochemical properties [1]. A synthetic expansion of such
species is motivated by a better understanding of structure-prop-
erty relations between their structural parameters, shape, size
and dependent intraelectronic and magnetic exchange interactions
[2,3] as well as optical and ferroelectric properties [4]. Coordina-
tion clusters with intricate spin structures in particular continue
to be of interest for the experimental and computational commu-
nities [5].
SMe) usually do not increase the coordination versatility of such
equipped ligands in high nuclearity metal complexes [6–8], but
rather are used to induce eventual chemisorptive interactions of
coordination clusters with a solid support [9,10]. Our current study
showcases a further attractive aspect of these prosthetic groups,
namely their key role in the isolation of the targeted compounds
as single-crystalline material.
We thus describe the preparation of two nickel(II) coordination
clusters isolated as [Ni3(LꢀSMe)4(bzaꢀSMe)(MeOH)2]Cl0.5(CH3O)0.5
ꢀ
5.5MeOHꢀH2O (1) and [Ni3(LꢀSMe)4(bzaꢀSMe)(MeOH)2](ClO4)0.75
(CH3O)0.25ꢀ1.5MeOHꢀ0.75H2O (2), which are supported by monode-
Herein, we explore a Schiff base (HL) that has rarely been used
in the coordination chemistry of transition metals because of its
low denticity as ligand (Fig. 1). To result in a multinuclear coordi-
nation complex, a carboxylic acid (Hbza) has been introduced as
protonated anions of the
p
-conjugated Schiff base (HLꢀSMe) and
carboxylate (HbzaꢀSMe) ligands augmented by –SMe functionali-
ties (Fig. 2). Compounds 1 and 2 were characterized by IR spec-
troscopy, electrospray ionization mass spectrometry (ESI-MS) and
thermogravimetric analysis (TGA). Their solid-state molecular
structures were determined from single-crystal X-ray diffraction
and the magnetic properties were studied by dc susceptibility
measurements. The molecular deposition of compound 1 on a solid
⇑
Corresponding authors at: Institut für Anorganische Chemie, RWTH Aachen
University, Landoltweg 1, 52074 Aachen, Germany.
E-mail addresses: paul.koegerler@ac.rwth-aachen.de (P. Kögerler), kirill.mona-
khov@ac.rwth-aachen.de (K.Yu. Monakhov).
https://doi.org/10.1016/j.poly.2018.01.014
0277-5387/Ó 2018 Elsevier Ltd. All rights reserved.

S. Schmitz et al. / Polyhedron 144 (2018) 144–151
145
(ca. 62%) which is well-soluble in MeCN, THF or CH2Cl2. Specifi-
cally, the first synthetic step included a four-component reaction
where 4-(methylthio)benzaldehyde, 2-aminophenol, NiCl2ꢀ6H2O
and Et3N in a 1:1:1:2.5 ratio were dissolved in methanol and the
formed clear solution was stirred under reflux conditions for 30
min. In the second step, a methanolic solution of one equivalent
of HbzaꢀSMe was added to the brown reaction solution and
refluxed for further 30 min (see Section 4 for details on work-up
of the reaction solution). Interestingly, utilization of the freshly
prepared HLꢀSMe, instead of its corresponding in situ form, under
otherwise identical reaction conditions does give the same com-
plex 1, but does not increase the quality of the crystals or the yield
of the product. The use of thioether-functionalized ligands how-
ever turned out to be a crucial factor, as replacing 4-(methylthio)
benzaldehyde with benzaldehyde and/or 4-(methylthio)benzoic
acid with benzoic acid does not lead to any crystalline material.
Contrary to the nickel(II) complexes [Ni6(Lig)3(CO3)(MeOH)6(-
THF)2]Clꢀ2MeOH and [Ni8(HLig)2(LꢀSMe)2(OH)4(MeCN)4(H2O)4]
(NO3)2ꢀ11MeCNꢀ2PhCN comprising pentadentate Schiff base
ligands (H3Lig = 2,20-(((2-hydroxy-5-(methylthio)-1,3-phenylene)
Fig. 1. Left: A rare bidentate Schiff base ligand used for coordination with transition
metals, with only 6 hits (5 mononuclear, 1 dinuclear complexes) in the Cambridge
Structural Database [18–23]. Right: A much more common tridentate Schiff base
ligand used for transition metal coordination, with >100 hits in the CSD.
bis(methanylylidene))bis(azanylylidene))diphenol;
C21H18N2O3S)
in our preceding report [7], the identity of the nickel precursor salt
(e.g., using Ni(ClO4)2ꢀ6H2O instead of NiCl2ꢀ6H2O) does not influ-
ence the nuclearity and structure of the formed metal complex
Fig. 2. Ligands used in this work.
(see compound
2
with the formula [Ni3(LꢀSMe)4(bzaꢀSMe)
(MeOH)2](ClO4)0.75(CH3O)0.25ꢀ1.5MeOHꢀ0.75H2O in Section 4). This
suggests that the triangular metal–ligand core in 1 and 2 is rigid
and stable, which is also indicated by our ESI-MS measurements
of these two compounds, revealing the molecular ion peak of the
solvent-free [Ni3(LꢀSMe)4(bzaꢀSMe)]+ fragment (Fig. 3). Thermo-
gravimetric analysis (TGA) shows different thermal stability of
compound 1 against degradation under a N2 atmosphere or in air
(see also Supporting Information). Two undefined steps with a
total mass loss of 8.5% (N2) and 10.8% (air) are observed in the tem-
perature ranges of 25–230 °C (N2) and 25–130 °C (air), which cor-
respond to a loss of uncoordinated and coordinated solvent
molecules, thus pointing to the relative stability of the solvent-free
[Ni3(LꢀSMe)4(bzaꢀSMe)]+ fragment. At higher temperatures the
complex decomposes in one wider step 230–600 °C (51.5% mass
loss) under N2 and in two distinct steps 230–410 °C (34.6% mass
loss) and 410–600 °C (33.7% mass loss) under air.
support (gold substrate) was probed via infrared reflection–
absorption spectroscopy (IRRAS).
2. Results and discussion
2.1. Synthesis
In a two-step aerobic synthesis, 4-(methylthio)benzoic acid
(HbzaꢀSMe, denoted as co-ligand in Fig. 1) was added to a
methanolic mixture containing the nickel(II) salt precursor, the tri-
dentate Schiff base HLꢀSMe (denoted as ligand A) and triethy-
lamine (Et3N) as an auxiliary base (Scheme 1). This reaction
yielded the moisture-stable compound [Ni3(LꢀSMe)4(bzaꢀSMe)
(MeOH)2]Cl0.5(CH3O)0.5ꢀ5.5MeOHꢀH2O (1) in comparably high yield
Scheme 1. Synthesis of the trinuclear nickel(II) complexes 1 and 2 supported by thioether-functionalized Schiff base and carboxylate ligands.

146
S. Schmitz et al. / Polyhedron 144 (2018) 144–151
(Table 1); for crystallographic details of compounds 1 and 2 see
the Supporting Information. Compound 1 crystallizes in the tri-
ꢀ
clinic space group P1 and consists of the [Ni3(LꢀSMe)4(bzaꢀSMe)
(MeOH)2]+ coordination cluster counterbalanced by a chloride
anion that is shared by two cationic complexes in the extended
structure and a partially deprotonated methanol solvent molecule,
in which H13 has an occupancy factor of 0.5. The Ni3 core of com-
pound 1 displays an isosceles triangle with non-bonding Niꢀ ꢀ ꢀNi
distances of 2.8584(16) Å and 2.8678(16) Å between Ni2/Ni3 and
Ni1 and 3.135(2) Å between Ni2 and Ni3 atoms. Two nickel atoms
(Ni2 and Ni3) bridged by 4-(methylthio)benzoic acid (bzaꢀSMeꢁ)
are in an octahedral NO5 coordination environment. Each of them
binds three of the four Schiff base ligands, an oxygen atom of
bzaꢀSMeꢁ and a methanol molecule. The third Ni2+ center (Ni1) is
coordinated to all four Schiff base ligands (LꢀSMeꢁ) and exhibits a
highly distorted octahedral N2O4 coordination sphere.
In the lattice of 1 the complexes are arranged in a one-dimen-
sional chain via hydrogen bonds that are generated between coor-
dinated and uncoordinated (‘‘free”) methanol molecules, water
molecules, and the chloride counterion (Fig. 5). The corresponding
closest Oꢀ ꢀ ꢀO distances between coordinated and ‘‘free” methanol
molecules constitute 2.602 Å (O7–O9), while the separations
between ‘‘free” methanol and the chloride ion are 3.071 Å (see
Fig. 5a and c). The additional connection is achieved due to
{MeOHcoordꢀ ꢀ ꢀMeOHfreeꢀ ꢀ ꢀMeOHfreeꢀ ꢀ ꢀH2Ofree
}
interactions with
2
the hydrogen bond distances of 2.641 Å (O8–O10), 2.645 Å (O10–
O11) and 2.970 Å (O11–O15), respectively (see Fig. 5b and c). The
sulfur atoms of the thioether groups situated at the periphery of
the Schiff base (LꢀSMeꢁ) and carboxylate (bzaꢀSMeꢁ) ligands are
not engaged in any intermolecular interactions or coordination
bonds in the crystal structure of compound 1.
Fig. 3. Experimental and simulated ESI-MS diagram of compound 1 in MeOH
featuring the integrity of the solvent-free [Ni3(LꢀSMe)4(bzaꢀSMe)]+ fragment (m/z =
1311.076). The complete ESI-MS diagram of compound
Supporting Information.
1 is provided in the
Compounds 1 and 2 feature a central nickel-oxygen motif
(Fig. 6a) that has not been observed previously according to a
CSD search. A few structurally related nickel-oxygen moieties
(Fig. 6b/c) have been however observed as constituents of larger
nickel coordination clusters (e.g., Ni6, Ni9, and Ni11) [17,18,21].
One of the Schiff base-supported {Ni3}-oxygen moieties (Fig. 6c)
similar to the one observed herein was obtained by Zhang et al.
in 2009 [20]. The reaction described by these authors was per-
formed in a MeOH : MeCN solvent mixture (1:1 volume ratio)
using Ni(ClO4)2ꢀ6H2O as metal source and 2-hydroxybenzaldehyde
together with methylamine as ligand precursors to form the Schiff
base ligand (Hmimp). This synthesis was carried out in a PTFE-
2.2. X-ray crystal structure
The solid-state molecular structures of compounds 1 and 2
were established by single-crystal X-ray diffraction and the catio-
nic fragment of these metal complexes is illustrated in Fig. 4. As
this central motif is virtually isostructural between 1 and 2, only
the structural characteristics of 1 are discussed in the following
Table 1
Selected bond lengths (in Å) and angles (in °) of compound 1.
Nickel-ligand bonds
Ni1–OLꢀSMe
Ni1–NLꢀSMe
Ni2–OMeOH
2.008(5) – 2.179(6)
2.066(7) and 2.074(7)
2.041(5)
Ni2–Obza SMe
ꢀ
2.002(6)
2.050(6) – 2.079(6)
2.095(7)
Ni2–OLꢀSMe
Ni2–NLꢀSMe
Ni3–OMeOH
2.041(6)
Ni3–Obza SMe
Ni3–OLꢀSMe
Ni3–NLꢀSMe
ꢀ
2.011(6)
2.028(5) – 2.153(6)
2.103(8)
Nickel-ligand angles
Ni1–O1–Ni2
Ni1–O1–Ni3
Ni2–O1–Ni3
Ni1–O3–Ni2
Ni1–O3–Ni3
Ni2–O3–Ni3
Ni1–O2–Ni2
Ni1–O4–Ni3
85.4(2)
83.2(2)
96.4(2)
84.3(2)
85.9(2)
99.5(2)
89.1(2)
89.1(2)
Fig. 4. Molecular structure of the cationic complex [Ni3(LꢀSMe)4(bzaꢀSMe)
(MeOH)2]+ in compounds 1 and 2. Hydrogen atoms and counterions are omitted
for clarity. Color code: C of bzaꢀSMeꢁ, turquoise; other C, dark gray; N, blue; O, red;
S, yellow; Ni, green. The nickel, sulfur and coordinated methanol atoms are
represented as ball-and-stick models. (Color online.)

S. Schmitz et al. / Polyhedron 144 (2018) 144–151
147
Fig. 5. A combined ball-and-stick and polyhedral representation of segments of the extended crystal structure of compound 1, highlighting the association of {Ni3}
coordination clusters via (a) O–HMeOHꢀ ꢀ ꢀCl and (b) O–HMeOHꢀ ꢀ ꢀO–HMeOHꢀ ꢀ ꢀOH2O hydrogen bonding interactions. A segment (c) featuring both interactions (a) and (b) is also
shown. Hydrogen atoms are omitted for clarity. Color code: C, gray; N, blue; O, red; S, yellow; Cl, light green; Ni coordination octahedra, transparent green. (Color online.)
lined autoclave under microwave irradiation, and a crystalline
compound with reported formula [Ni3(mimp)5(MeCN)]ClO4 was
obtained after 6 days in 87% yield. For comparison, our compound
1 has been obtained from a pure methanolic solution after one day
using reflux conditions. Following up on the work of Zhang et al.
[20] who used 2-hydroxybenzaldehyde and methylamine, we syn-
thesized a constitutional isomer of HLꢀSMe (denoted as ligand B;
for details on its structure, synthesis and characterization see the
Supporting Information) to access its coordination ability in our
designed reaction process. However, replacing HLꢀSMe with ligand
B does not result in the formation of any crystalline product.
2.3. Magnetism and magnetochemical modeling
The magnetic properties of 1 were analyzed on the basis of the
temperature- and field-dependent dc susceptibility data. The
vmT
versus T data are shown in Fig. 7 for applied magnetic fields of
0.1, 1.0, and 3.0 T. At 290.0 K, the values of
v
mT = 4.77 cm3 K molꢁ1
(0.1 T) and 4.67 cm3 K molꢁ1 (3.0 T), respectively, are slightly
above the range 2.94–4.60 cm3 K molꢁ1 that is expected for three
non-interacting high-spin Ni(II) centers [11]. Upon lowering the
temperature,
vmT continuously increases, reaching a maximum
value of 7.79 cm3 K molꢁ1 at 3.6 K and 0.1 T, of 7.38 cm3 K molꢁ1

148
S. Schmitz et al. / Polyhedron 144 (2018) 144–151
Fig. 6. (a) The nickel-oxygen core moiety in compounds 1 and 2 obtained in this work (zero CSD hits). (b) The nickel-oxygen moiety reported as part of {Ni9} and {Ni11}-
nuclearity complexes (three CSD hits) [24,25]. (c) The nickel-oxygen moiety reported as part of {Ni3}- and {Ni6}-nuclearity complexes (three/one CSD hits, respectively) [26–28].
The least-squares fit of the magnetic data is depicted as dashed
lines in Fig. 7. The respective fit parameters are geff = 2.25, J1 = +3.0
cmꢁ1, J2 = +42.3 cmꢁ1. Since the fit is of relatively low quality (SQ =
2.7%, relative root mean square error), we employ the ‘‘full” model
Hamiltonian to also account for ligand field and anisotropy effects.
As for the isotropic model calculations, the Ni(II) centers are con-
sidered as approximately identical in local C4v-symmetric ligand
fields. Calculations considered all 120 states of a 3d8 electron con-
figuration for single-ion contributions, and the 21 states of the 3F
ground multiplet per Ni(II) center for exchange interactions. The
results of the isotropic model fit are taken as starting values. In
addition, we set the ratio of the ligand field parameters B44/B04 =
(5/14)ꢁ1/2 as for exact octahedral symmetric metal complexes. The
one-electron spin–orbit coupling parameter f3d = 649 cmꢁ1 and
Racah parameters B = 1084 cmꢁ1 and C = 4831 cmꢁ1 are taken from
literature [13]. The least-squares fit using this model yields a good
SQ of 1.0%, thus demonstrating that the magnetism of 1 is signifi-
cantly influenced by the ligand field effect of the single Ni(II) centers.
The corresponding calculated data are shown in Fig. 7 as solid lines
Fig. 7. Temperature dependence of
vmT at 0.1 T, 1.0 T, and 3.0 T of 1; inset: molar
and match the data much better. The fit parameters for these data
are B20 = 6500 cmꢁ1, B04 = 15960 cmꢁ1, and B44 = (5/14)ꢁ1/2ꢀB40 (ligand
field parameters in Wybourne notation), J1 = +2.1 cmꢁ1, J2 = +19.3
cmꢁ1. In terms of an effective anisotropic spin-1 model, the ligand
field parameters, the Racah parameters, and f3d translate to D =
magnetization Mm vs. B at 2.0 K: experimental data (open circles), least-squares fit
(dashed lines (isotropic model), solid lines (anisotropic model).
at 8.0 K and 1.0 T, and of 6.75 cm3 K molꢁ1 at 15.0 K and 3.0 T. The
comparably large
indicative of dominant ferromagnetic exchange interactions
between the three Ni(II) centers. The sharp decrease of mT may
vmT values at 290.0 K as well as the maxima are
+2.64 cmꢁ1
,
(E ꢂ 0), g = 2.309 cmꢁ1 and g\ = 2.322 cmꢁ1 corre-
k
v
sponding to a small magnetic anisotropy of the Ni(II) centers. In
addition, the fit shows small to moderate ferromagnetic exchange
interaction between the Ni(II) centers forming a triangle. The total
spin of the ground state is calculated to be S = 3, consistent with
above expectations.
be to some extent due to the ligand-field effect, i.e. thermal depop-
ulation of the energy states of a single center, but is mainly due to
the introduction of saturation effects which is reflected by the field
dependency of the
Mm at 2.0 K as a function of the applied magnetic field B is depicted
in Fig. 7 (inset) and remains linear up to ca. 0.5 T, reaching 6.9 NA
B at 5.0 T. At this field, the magnetization is not fully saturated but
hints at a ground state of a total effective spin S = 3.
vmT curve for T < 30 K. The molar magnetization
-
2.4. Immobilization on gold substrate
l
To assess the stability of the obtained magnetic {Ni3} coordina-
tion cluster on a solid metal support, we performed IRRAS mea-
surements for compound 1 (for details see Section 4). Our
comparison of the IR spectrum with the IRRAS spectrum recorded
from an immobilized thin layer of compound 1 on a gold substrate
(Fig. 8) shows that the metal complex retains its major structural
integrity on this solid support. Determination of the type of inter-
action (chemisorptive or physisorptive) between the thioether
groups of 1 and the Au surface remains a target of future studies.
Small shifts of the main vibrations bands between the measured
IRRAS and IR spectra of compound 1 (Table 2) are indeed observed
and expected due to the different sample forms (Au substrate ver-
sus KBr) and measurement methods (reflective versus through-
beam, respectively) [14]. Additionally, the supramolecular H-
Next, we used the computational framework CONDON 2.0 [12]
to model the magnetic data of 1. Since it is often sufficient to
employ an isotropic spin-only model (SNi = 1 per Ni(II) center) to
describe the magnetism of many Ni(II) compounds with approx.
octahedral ligand fields, we start our analysis with such a model.
Based on the structure of the compound, we identified two differ-
ent exchange pathways, and we assign the exchange parameter J1
to the Ni1–Ni2 and Ni1–Ni3 pathway, respectively, while J2
describes the Ni2–Ni3 exchange interaction. The corresponding
spin Hamiltonian is:
3
X
b
b
b
b
b
b
b
b
H ¼ ꢁ2J1ðSNi1 ꢀ SNi2 þ SNi1 ꢀ SNi3Þ ꢁ 2J2 SNi2 ꢀ SNi3
þ
lBgeff B ꢀ SNiJ
J¼1

S. Schmitz et al. / Polyhedron 144 (2018) 144–151
149
The IR spectra of compounds 1, 2 and A were recorded on a Nicolet
Avatar 360 FTIR spectrometer by using KBr pellets (mKBr ꢃ 250 mg)
in the range ṽ = 4000–400 cmꢁ1. TGA curves for compounds 1, 2
and A were obtained under a nitrogen atmosphere and in air with
a heating rate of 5 K minꢁ1 in the temperature range 25–800 °C by
using a Mettler Toledo TGA/SDTA 851e instrument. The ESI-MS
spectra of compounds 1, 2 and A in the positive ion mode were
recorded on a 4000 QTRAP mass spectrometer system by using
the LC/LC–MS method with direct infusion.
4.2. Synthesis of (E)-2-((4-(methylthio)benzylidene)amino)phenol
(HLꢀSMe = A)
2-Aminophenol (0.820 g; 7.5 mmol) and 4-(methylthio)ben-
zaldehyde (1.00 mL; 7.5 mmol) were dissolved in 16 mL of ethanol.
Four drops of acetic acid were added as a catalyst. The reaction
solution was refluxed for 4 h. The solution was stored at 4 °C over-
night and pale yellow crystals were formed. The product was
washed with ice cold ethanol and pentane. Yield: 1.135 g (4.7
mmol; 62.6%).
Fig. 8. IRRAS (red) and IR (black) spectra of compound 1 in the 1700–765 cmꢁ1
region. (Color online.)
Elemental analysis: Calcd. for C14H13NOS (243.32 gꢀmolꢁ1; dis-
regarding solvent) C, 69.11; H, 5.39 and N, 5.76%. Found: C,
69.22; H, 5.26 and N, 5.62%.
Table 2
Comparison between bulk IR (as KBr pellet) and IRRAS (on gold substrate) spectra of
compound 1 [29].
IR wavenumbers/cmꢁ1
IRRAS wavenumbers/cmꢁ1
Assignment
IR (KBr pellet), ṽmax/cmꢁ1: 3354 (w), 3301 (w, br), 3059 (vw),
3039 (w), 3022 (w), 2984 (w), 2914 (m), 1622 (s), 1605 (vw),
1585 (vs), 1552 (s), 1494 (s), 1480 (vs), 1433 (m), 1406 (m),
1379 (s), 1320 (w), 1290 (m), 1280 (m), 1246 (vs), 1224 (m),
1198 (m), 1168 (m), 1150 (s), 1122 (w), 1087 (s), 1028 (m), 1009
(w), 970 (m), 924 (m), 880 (m), 850 (m), 814 (vs), 831 (m), 792
(m), 752 (s, sh), 745 (vs), 708 (vw), 671 (m), 606 (s), 507 (vs),
447 (m), 410 (w).
3058
3020
2984
2919
3061
3022
2988
2921
2856
1619
1593
1541
1479
1452
1402
1291
ṽ
ṽ
ṽ
ṽ
ar(CAH)
ar(CAH)
as(CH3)
as(CH3)
ṽs(CH3)
ṽar(C@C)
ṽ
as(COOꢁ)
ṽar(C@C)
ṽar(C@C)
1591
1547
1476
1451
1407
1296
1278
1254
1174
1089
865
MS (MeOH, ESI): m/z = 244.079 (C14H14NOS+, 100%; HLꢀSMeH+).
1H NMR (in CD2Cl2; 400 MHz): d = 8.67 (s, 1H, N=CH–ar), 7.85
(m, 2H, H–ar), 7.33 (m, 3H, H–ar), 7.25 (s, 1H, OH), 7.18 (tdd, 1H,
H–ar), 6.98 (dd, 1H, H–ar), 6.91 (m, 1H, H–ar) and 2.54 (s, 3H,
H3C–S–R).
das(CH3)
ṽs(COOꢁ)
ṽ
ṽ
ip(OAH)
ip(OAH)
1251
1174
1092
865
816
773
dip(@CAH)
dip(@CAH)
dip(@CAH)
dop(@CAH)
dop(@CAH)
dop(@CAH)
13C NMR (in CD2Cl2; 100 MHz): d = 157.2, 152.9, 144.6, 136.2,
133.0, 129.6, 129.2, 126.1, 120.6, 116.4, 115.3 and 15.4 ppm.
810
771
4.3. Synthesis of [Ni3(LꢀSMe)4(bzaꢀSMe)(MeOH)2]
Cl0.5(CH3O)0.5ꢀ5.5MeOHꢀH2O (1)
bonded zig-zag chain formation in the crystal structure of com-
pound 1 is anticipated to break by treatment of the sample with
the CH2Cl2 solvent, which may also lead to some shifts of the vibra-
tional bands.
NiCl2ꢀ6H2O (0.095 g, 0.4 mmol) and 2-aminophenol (0.044 g,
0.4 mmol) were dissolved in 6 mL of methanol. 4-(methylthio)ben-
zaldehyde (0.054 mL, 0.4 mmol) and triethylamine (0.140 mL, 1.0
mmol) were added to this solution, which resulted in a color
change from light-green to light-brown. The reaction mixture
was stirred for 30 min under reflux, following the addition of 4-
(methylthio)benzoic acid (0.068 g, 0.4 mmol) in 4 mL of methanol.
After refluxing for further 30 min the MeOH solution was filtered
off and the filtrate was kept in a capped vial at room temperature.
Brown needle-shaped single crystals of compound 1 were obtained
after three days via slow evaporation and then washed with a small
amount of ice cold methanol. Yield of air-dried crystals: 0.089 g
(62.4% based on HLꢀSMe; calcd. for: [Ni3(LꢀSMe)4(bzaꢀSMe)
3. Conclusions
We have demonstrated that ligand augmentation with
thioethers, leading to HLꢀSMe and HbzaꢀSMe ligands is crucial for
the isolation of a triangular nickel coordination cluster under aer-
obic reflux reaction conditions. The resulting structure features a
novel metal–ligand core framework and is characterized by all-fer-
romagnetic exchange interactions. Due to its remarkable structural
stability on the gold substrate, the {Ni3} system represents an
interesting target for future immobilization and catalysis studies.
(MeOH)2]Cl0.5(CH3O)0.5
,
C66.5Cl0.5H64.5N4Ni3O8.5S5,
1409.88
gꢀmolꢁ1; disregarding solvent). Elemental analysis: Calcd. for [Ni3(-
LꢀSMe)4(bzaꢀSMe)]Cl0.5(CH3O)0.5ꢀ4H2Oꢀ1.5MeOH (C66Cl0.5H70.5N4-
Ni3O12S5, 1465.91 gꢀmolꢁ1): C, 54.08; H, 4.85; N, 3.82 and Ni,
12.01%. Found: C, 53.70; H, 4.48; N, 3.88 and Ni, 12.24%.
4. Experimental
4.1. Materials and general methods
IR (KBr pellet), ṽmax/cmꢁ1: 3426 (s, br), 3058 (w), 2919 (w),
1590 (s), 1580 (sh), 1547 (m), 1476 (s), 1451 (m), 1408 (m),
1384 (sh), 1296 (sh), 1279 (s), 1255 (sh), 1174 (w), 1149 (w),
1111 (w), 1089 (s), 1038 (w), 966 (w), 899 (w), 866 (m), 810 (m),
772 (sh), 747 (m), 589 (w), 521 (w), 479 (w), 431 (w).
The syntheses of compounds 1–2 and A were carried out under
aerobic conditions. All starting materials were commercial and
used as received. Solvents were used without further purification.

150
S. Schmitz et al. / Polyhedron 144 (2018) 144–151
MS (MeOH, ESI): m/z = 543.071 (C28H25N2Ni1O2S+2, 22%; [Ni
Hg-Cd-Te (MCT) detector and an A513/Q variable-angle reflection
accessory including an automatic rotational holder for MIR polar-
izer. The IR beam was polarized with a KRS-5 polarizer with 99%
degree of polarization. Double-sided interferograms were collected
with a sample frequency of 20 kHz, an aperture of 1.5 mm and a
nominal spectral resolution of 4 cmꢁ1. The interferograms were
apodized by a Blackmann–Harris 3-term apodization and zero
filled with a zerofilling factor of 2. The angle of incidence was set
to 80°, and p-polarized IR radiation was used to record the spectra.
For the background measurements, the sample chamber was
purged with argon for 5 min, then 1024 scans were collected while
continuing to purge. For the sample measurements, argon purging
was started at the moment the first scan was recorded. The scans
were averaged until the peaks arising from the water vapor in
the sample chamber were compensated, for what typically 800–
1500 scans were necessary. The spectra were processed using
OPUS software (Bruker). Where necessary, scatter correction was
applied to the spectra.
(LꢀSMe)2H]+), 842.062 (C42H36N3Ni2O3S+3, 60%; [Ni2(LꢀSMe)3]+),
1311.076 (C64H55N4Ni3O6S+5, 100%; [Ni3(LꢀSMe)4(bzaꢀSMe)]+ – 2
MeOH).
4.4. Synthesis of [Ni3(LꢀSMe)4(bzaꢀSMe)(MeOH)2]
(ClO4)0.75(CH3O)0.25ꢀ1.5MeOHꢀ0.75 H2O (2)
Compound 2 was synthesized following the procedure described
for compound 1, replacing NiCl2ꢀ6H2O by Ni(ClO4)2ꢀ6H2O (0.146 g,
0.4 mmol). Brown block-shaped single crystals of compound 2 were
obtained after three days via slow evaporation and then washed
with a small amount of ice cold methanol. Yield of air-dried crys-
tals: 0.084 g (57.6% based on HLꢀSMe; calcd. for: [Ni3(LꢀSMe)4
(bzaꢀSMe)(MeOH)2](ClO4)0.75(CH3O)0.25
,
C66.25Cl0.75H63.75N4Ni3
O11.25S5, 1458.98 gꢀmolꢁ1; disregarding solvent). Elemental analy-
sis: Calcd. for [Ni3(LꢀSMe)4(bzaꢀSMe)](ClO4)0.75(CH3O)0.25ꢀ6H2O
(C64.25Cl0.75H67.75N4Ni3O15.25S5, 1502.99 gꢀmolꢁ1): C, 51.34; H, 4.54
and N, 3.73%. Found: C, 51.19; H, 4.24 and N, 3.96%.
IR (KBr pellet), ṽmax/cmꢁ1: 3423 (m, br), 3058 (w), 3020 (w),
2984 (w), 2919 (w), 1590 (s), 1546 (m), 1491 (m, sh) 1476 (s),
1451 (m), 1436 (vw), 1410 (m), 1296 (m), 1278 (m), 1254 (m),
1174 (w), 1150 (w), 1089 (s, br), 1013 (vw), 965 (w), 900 (w),
865 (m), 847 (w), 812 (m), 802 (m), 770 (sh), 749 (m), 590 (w),
521 (w), 478 (w), 430 (w).
4.7.1. General procedure for the preparation of Au substrates for IRRAS
The gold substrates were fabricated by sputtering a 10 nm
adhesive film of Ti and a 100 nm thick layer of Au on <100> ori-
ented silicon wafers with a native SiO2 layer. The freshly prepared
gold substrates were cleaned in oxygen plasma (p(O2) = 0.4 mbar, f
= 40 kHz and P = 75 W) for 4 min immediately prior to the deposi-
tion of compound 1. For the deposition a solution (ꢅ1.0 mM) of 1
was prepared using CH2Cl2 with analytical reagent grade (purity:
99.99%). The Au substrate was stored for 24 h in this solution
and dried for 24 h in a desiccator.
MS (MeOH, ESI): m/z: 1311.075 (C64H55N4Ni3O6S+5, 100%;
[Ni3(LꢀSMe)4(bzaꢀSMe)]+ – 2 MeOH).
4.5. X-ray crystallography
Single-crystal diffraction data for 1 were collected on an APEX2
Acknowledgment
Suite (Bruker AXS, 2013) diffractometer at 173 K with Mo K
ation (k = 0.71073 Å). The data for 2 were measured on a Super-
Nova (Agilent Technologies) instrument at 120 K (Mo K ). The
a radi-
K. Y. M. thanks the Excellence Initiative of the German federal
and state governments for an RWTH Start-Up grant. The authors
express their gratitude to Prof. U. Simon (RWTH Aachen Univer-
sity) for access to the IRRAS equipment and Dr. B. Santiago-Schübel
(Forschungszentrum Jülich) for assistance with the ESI-MS
measurements.
a
crystals were mounted in a Hampton cryoloop with Paratone-N
oil to prevent water loss. Absorption corrections were applied
empirically using the SADABS program [15] for 1 and numerically
based on multifaceted crystal model using CrysAlis software for 2
[16]. The SHELXTL software package [17] was used to solve and refine
the structures. The structures were solved by direct method and
refined by full-matrix least-squares method against |F|2 with aniso-
tropic thermal parameters for all atoms besides hydrogens.
The hydrogen atoms of the solvent methanol and water mole-
cules in 2 were not located. All the other hydrogen atoms in 1
and 2 were placed in geometrically calculated positions. The rela-
tive site occupancy factors for the disordered positions of oxygen,
carbon and chlorine atoms of co-crystallized solvent water and
methanol molecules and ClOꢁ4 counteranions were first refined in
an isotropic approximation with Uiso = 0.05 and then fixed at the
obtained values and refined without the thermal parameters
restrictions.
Appendix A. Supplementary data
CCDC 1579948 and 1579949 contains the supplementary crys-
tallographic data for compounds 1 and 2, respectively. These data
can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
data associated with this article can be found, in the online version,
at https://doi.org/10.1016/j.poly.2018.01.014.
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