Low-melting cationic 3d-transition metal complexes of azole-based ligands

Article abstract of DOI:10.1016/j.poly.2015.03.020

Ligands N-methylimidazole (MIm) and N-ethylimidazole (EIm) were used for the preparation of [Fe^II(L)₆](NTf₂)₂·0.5EtOH·0.5H₂O. With T_fus = 83°C, the EIm complex was characterised as paramagn

Full text of DOI:10.1016/j.poly.2015.03.020

Polyhedron 93 (2015) 28–36
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Low-melting cationic 3d-transition metal complexes of azole-based
ligands
⇑
Timo Huxel, Michael Skaisgirski, Julia Klingele
Institut für Anorganische und Analytische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, D-79104 Freiburg, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Ligands N-methylimidazole (MIm) and N-ethylimidazole (EIm) were used for the preparation of
[FeII(L)6](NTf2)2ꢀ0.5EtOHꢀ0.5H2O. With Tfus = 83 °C, the EIm complex was characterised as paramagnetic
MeIL. Using bidentate imidazole ligands 2-(2-pyridyl)-1-ethylimidazole (L1) and 2-(2-pyridyl)-
1-(2-methoxyethyl)imidazole (L2) 3:1 type complexes [MII(Li)3]X2 (M = Fe; Li = L1; X = ClO4, BF4, NTf2;
M = Fe; Li = L2, X = ClO4, BF4; M = Co; X = ClO4; Li = L1, L2; M = Ni; X = ClO4; Li = L1, L2) were prepared.
All complexes of L2 and complex [FeII(L1)3](NTf2)2 were low-melting with Tfus < 200 °C. Complexes of
L2 additionally had glass transition temperatures below 75 °C upon reheating.
Received 11 February 2015
Accepted 20 March 2015
Available online 27 March 2015
Keywords:
Ionic liquid
N-ligand
Chelating ligand
Iron(II)
Ó 2015 Elsevier Ltd. All rights reserved.
Bis(trifluoromethylsulfonyl)imide
1. Introduction
with imidazolium-based cations, like [CnMIm][FeCl4] (CnMIm+
=
1-alkyl-3-methylimidazolium) [14,15] or [BMIm]2[Co(NCS)4]
(BMIm+ = 1-butyl-3-methylimidazolium) [19]. Far less common
is the latter type of MeILs that contains the metal center in the
cationic part. Here specially designed side chains are tagged to
the ligand core to increase the entropy of fusion. For example
Murray and co-workers used the strategy of tagging a ligand core
with side chains exhibiting high torsion and rotational degrees of
freedom and introduced polyether-tags to bipy-based ligands
(bipy = 2,20-bipyridine). These new ligands had up to 16
CH2CH2O- or up to three CH(Me)CH2O-units and formed highly
viscous MeILs of ruthenium(II) [20–24], iron(II) [21,25–27],
copper(II) [23], nickel(II) [27] and especially cobalt(II) [22,23,25–
35], mostly with ClOꢁ4 anions. Even using the rigid porphyrin-
frame Murray and co-workers were able to prepare an iron(III)
MeIL with an exceptionally low melting point of Tfus = 7 °C, intro-
ducing polyether-tags [36]. With simple alkyl chains tagged to
monodentate imidazole ligands, Reedijk and co-workers prepared
in the 1980s complexes of the type [MII(L)6]X2 (M = Co, Ni, Cu;
L = MIm, EIm; X = ClO4, BF4), some of them low-melting
(MIm = N-methylimidazole, EIm = N-ethylimidazole) (Table 1)
[37]. The corresponding iron(II) complexes [FeII(L)6](ClO4)2 were
recently reported by us and the EIm compound was found to be
low-melting, whereas the MIm complex melted somewhat above
200 °C (Table 1) [38]. Corresponding NTf2-salts, however, had not
been prepared at that point, even so, by experience, NTf2-salts usu-
ally melt at least 60 K lower than their ClOꢁ4 analogues. In 2012
Binnemans and co-workers isolated NTf2-salts [MII(MIm)6](NTf2)2
Commonly, salts that melt at the boiling point of water, or
lower, are regarded as Ionic Liquids (IL). On the basis of this con-
cept ionic coordination compounds that melt in a common melting
point tube, before they decompose, at 200 °C or lower, will be clas-
sified as ‘‘low-melting’’ hereupon [1]. In general low melting points
Tfus in ionic compounds will be achieved in salts that have unusu-
ally high entropies of fusion
DSfus, which will be reached with a
high number of torsion angles and relatively low symmetry [2].
Therefore IL-cations are usually organic ions with low symmetry
and side chains with especially high torsion and rotational degrees
of freedom. To minimise ionic pair formation IL-anions are usually
monoanionic with high distribution of charge density, like bis(tri-
fluoromethylsulfonyl)imide (NTfꢁ2 ).
Compared to conventional liquids, ILs have extremely low
vapor pressures, high ionic conductivities and good solvent prop-
erties. They are therefore popular alternative reaction media for
several applications [3–13]. In this context, lately Ionic Liquids
containing metal ions, so-called MeILs, have been described that,
additionally to the IL nature, feature typical properties of the metal
ion, like paramagnetism, luminescence or catalytic activity
[14–18]. As the metal center can be introduced in the anion or
cation part of the MeIL, two types of MeILs exist. The first is
composed of halido or pseudohalido metallates in combination
⇑
Corresponding author. Tel.: +49 (0)761 203 6128; fax: +49 (0)761 203 6001.
E-mail address: julia.klingele@ac.uni-freiburg.de (J. Klingele).
http://dx.doi.org/10.1016/j.poly.2015.03.020
0277-5387/Ó 2015 Elsevier Ltd. All rights reserved.

T. Huxel et al. / Polyhedron 93 (2015) 28–36
29
Table 1
Melting points in degrees Celsius of complexes [MII(L)6]X2 (M = Fe, Co, Ni; L = MIm,
EIm; X = ClO4, NTf2).
[MII(L)6]X2
X = ClO4
X = NTf2
L = MIm
L = EIm
L = MIm
L = EIm
M = Ni
M = Co
M = Fe
293[37]
214[37]
147[39]
–
–
258[37]
173[37]
137[39]
218–219[38]
160–162[38]
decomp.[this
83[this
work]
work]
of cobalt(II), nickel(II) and copper(II) and consequently all featured
melting points below 200 °C (Table 1) [39]. Here we describe the
synthesis and characterisation of the homoleptic iron(II) NTf2-salts
[Fe(L)6](NTf2)2 (L = MIm, EIm).
Additionally the 2-(2-pyridyl)-imidazole unit was chosen for
the synthesis of bidentate chelating ligands with alkyl tag, in order
to study their complexation behavior. Ligands 2-(2-pyridyl)-1H-
imidazole (I) [40–42] and 2-(2-pyridyl)-1-methylimidazole [43]
are known to form iron(II) spin crossover (SCO) compounds
[Fe(L)3]2+. However, melting points of the studied perchlorate,
tetraphenylborate, chloride, thiocyanate, thiosulfate, selenate and
sulfate complexes have not been reported.
2. Results and discussion
Iron(II) bis(trifluoromethylsulfonyl)imide was prepared react-
ing iron powder with the free acid HNTf2 in water and was isolated
in the form of its analytically pure hexahydrate Fe(NTf2)2ꢀ6H2O,
which was used for further complexation reactions. A single crystal
of [Fe(H2O)6](NTf2)2ꢀ2H2O suitable for X-ray diffraction analysis
was obtained from dichloromethane at ꢁ40 °C (Fig. 1).
Scheme 1. Synthesis of (a) complexes [FeII(L)6](NTf2)2 (L = MIm, EIm); (b) ligands
2-(2-pyridyl)-1-ethylimidazole (L1) and 2-(2-pyridyl)-1-(2-methoxyethyl)im-
idazole (L2); (i) MeOH, NaOMe; (ii) 2,2-dimethoxyethylamine, EtOH, reflux; (iii)
MeOH, HCl, reflux; (iv) K2CO3, H2O; (v) H2O, KOH, EtI, reflux; (vi) H2O, KOH,
MeOCH2CH2Cl, reflux; (c) 3:1-type complexes [MII(L1)3]X2 (3, 4, 7: M = Fe; X = ClO4,
BF4, NTf2; 8: M = Co; X = ClO4; 10: M = Ni; X = ClO4) and [M(L2)3]X2 (5, 6: M = Fe;
X = ClO4, BF4; 9: M = Co; X = ClO4; 11: M = Ni; X = ClO4).
Reacting Fe(NTf2)2ꢀ6H2O with the monodentate N-alkyl substi-
tuted imidazole ligands MIm and EIm in the appropriate 6:1
ligand-to-metal ion stoichiometry in EtOH solution, homoleptic
complexes of the composition [Fe(L)6](NTf2)2ꢀ0.5EtOHꢀ0.5H2O (1:
L = MIm; 2: L = EIm) were obtained as colorless and tan
Fig. 1. Molecular structure of [Fe(H2O)6](NTf2)2ꢀ2H2O including the hydrogen bonding pattern of the asymmetric unit. Selected distances (Å): O(1)–Hꢀ ꢀ ꢀO(8) 2.762, O(1)–
Hꢀ ꢀ ꢀN(1B) 2.926, O(1)–Hꢀ ꢀ ꢀO(4) 2.970, O(2)–Hꢀ ꢀ ꢀO(6) 3.038, O(2)–Hꢀ ꢀ ꢀO(5C) 2.782, O(3)–Hꢀ ꢀ ꢀO(7B) 2.840, O(3)–Hꢀ ꢀ ꢀO(8A) 2.720, O(8)–Hꢀ ꢀ ꢀO(6D) 2.851, O(8)–Hꢀ ꢀ ꢀO(4) 2.849.
Symmetry operations used to generate equivalent atoms: (A) ꢁx, ꢁy, ꢁz + 1; (B) ꢁy, x ꢁ 0.5, z + 0.5; (C) ꢁy, x ꢁ 0.5, z ꢁ 0.5; (D) x, y, z + 1.

30
T. Huxel et al. / Polyhedron 93 (2015) 28–36
amorphous powders, respectively, as confirmed by elemental
analyses, ESI-MS spectrometry and IR spectroscopy (Scheme 1).
Whereas 1 of the methyl substituted ligand decomposed at ele-
vated temperatures in a melting point tube, its ethyl substituted
higher homologue melted at about 85 °C. This exceptionally low
melting point was subsequently reassured by differential scanning
calorimetry (DSC).
bonds, as commonly observed for complexes of 2-pyridyl substi-
tuted azoles [45,46,50]. In both complexes the pyridine and imida-
zole rings, with angles of 8.2(2)–11.6(1)° and 11.0(1)–15.5(2)° for
8ꢀ2MeOH and 9, respectively, are basically coplanar. Table 2 sum-
marises the crystallographic data of [Fe(H2O)6](NTf2)2ꢀ2H2O,
8ꢀ2MeOH and 9. Table 3 contains the bond lengths and angles of
the cobalt(II) complexes.
Following this result the bidentate 2-pyridyl substituted ligand
2-(2-pyridyl)-1-ethylimidazole (L1) was prepared as simple deriva-
tive of EIm, capable to exploit the chelate effect. Additionally
ligand 2-(2-pyridyl)-1-(2-methoxyethyl)imidazole (L2), where the
ethyl side chain is formally extended by a methoxy group was pre-
pared. Formation of the N-substituted 2-(2-pyridyl)-imidazole
ligands L1 and L2 was achieved by treatment of the ligand precur-
sor 2-(2-pyridyl)-imidazole (I) with EtI or MeOCH2CH2Cl, respec-
tively, in aqueous KOH solution. Both compounds were oils at RT.
Ligand precursor I was prepared from 2-cyanopyridine, following
a literature procedure (Scheme 1) [44].
3.1. UV-Vis and moessbauer spectroscopy
Results of UV–Vis spectroscopy of 1 and 2 in propylene carbon-
ate suggest both compounds to be in the hs state at RT. No color
change of the tan materials was observed upon cooling with liquid
nitrogen, which is a strong argument against the occurrence of a
thermally induced SCO. Both spectra exhibit a broad extremely
weak absorption at 863 and 858 nm (5, 6
assigned to the 5T2g ? 5Eg transition expected for hs iron(II) com-
plexes. Hence 10Dq was calculated to 11,600 and 11,700 cmꢁ1
M
ꢁ1 cmꢁ1), respectively,
,
Compounds [FeII(L1)3]X2ꢀH2O (3ꢀH2O, 4ꢀH2O: X = ClO4, BF4) and
[FeII(L2)3]X2 (5, 6: X = ClO4, BF4) precipitated upon addition of a
MeOH ligand solution to a MeOH solution of the respective
iron(II) salt, whereas [FeII(L1)3](NTf2)2 (7) was precipitated with
the addition of TBME and pentane. A similar iron(II) triflimide
complex of L2 unfortunately could not be isolated. However, similar
3:1-type complexes of cobalt(II) and nickel(II) perchlorate were
prepared with both ligands, via slow diffusion of MeOH metal
perchlorate and ligand solutions. Single crystals suitable for X-ray
diffraction analysis were obtained for both the cobalt(II) complexes
mer-[CoII(L1)3](ClO4)2ꢀ2MeOH (8ꢀ2MeOH) and mer-[CoII(L2)3]
(ClO4)2 (9) and affirmed the 3:1-type composition of the com-
pounds. Formation of respective fac-isomers of the complex cores
has not been observed. This fact concords with previous reports
about 3:1-type complexes of 2-pyridyl substituted azole ligands,
which are generally found to predominantly exist in their mer-con-
formation [45–49]. Exceptions have merely been reported with
thiadiazole- [50,51] or thiazole-based [52] such ligands that may
additionally form 3:1-type fac-isomers. Bulk material of 8ꢀ1.5H2O
and 9 was obtained upon drying the crystalline material in vacuo.
Similar procedures, but using Ni(ClO4)2ꢀ6H2O instead of the respec-
tive cobalt salt resulted in the formation of [NiII(L1)3](ClO4)2ꢀ0.5H2O
(10ꢀ0.5H2O) and [NiII(L2)3](ClO4)2 (11), which were obtained in the
form of crystalline materials.
respectively. These values are comparable to the ones observed
for the respective perchlorate compounds [FeII(MIm)6](ClO4)2 and
[FeII(EIm)6](ClO4)2 reported before (10Dq = 11,547 cmꢁ1 in both
cases) [38]. The UV–Vis spectrum of 2 is exemplarily shown in
Fig. 3a.
UV–Vis spectroscopy of the bidentate chelating ligands and their
complexes was performed in MeOH or MeCN solution. All spectra
show strong absorption bands in the UV region that were therefore
correlated to inner-ligand absorptions. Apart from these bands two
rather strong (e = 2000–3387 and 5680–6600 M
ꢁ1 cmꢁ1), and there-
fore presumably CT transition absorption bands, are present in the
spectra of the iron(II) compounds 3–7 in the range of kmax = 392–
396 and 494–498 nm, as exemplarily shown in Fig. 3b for the tri-
flimide compound 7. Similar transitions have been observed in
the electronic spectra of [FeII(I)3]2+ species, of the unsubstituted
ligand backbone [41,42,54]. They occur in the range, where typi-
cally low-spin (ls) iron(II) d–d-transitions (1A1g ? 1T1g and
1A1g ? 1T2g) are expected (Fig. 3b). However, as these transitions
are generally very weak, in the case of 3–7 they are presumably
masked by the stronger CT transitions [42]. The UV–Vis spectra of
bulk samples of the cobalt(II) complexes 8ꢀ1.5H2O and 9 exhibit
very weak absorptions (e = 16, 17 and 38, 38 M
ꢁ1 cmꢁ1, respec-
tively) at kmax = 474, 487 and 552, 544 nm, respectively, assigned
4
4
to the expected T1g(F) ? 4A2g(F) (
m
2) and T1g(F) ? 4T1g(P) (m3
)
4
d–d-transitions of hs cobalt(II) (Fig. 3c). A respective T1g(F) ?
4T2g(F) (
therefore not observed [55]. One equally weak
21 absorption band is observed at kmax = 530 and
ꢁ1 cmꢁ1
m
1) transition is expected to occur in the IR region and is
3. Description of the crystal structures
(
e
= 15,
Iron salt [Fe(H2O)6](NTf2)2ꢀ2H2O crystallises in the tetragonal
space group P4(2)/n with half a complex molecule, one triflimide
counterion and one water solvent molecule in the asymmetric
unit (Fig. 1). The iron(II) ion is octahedrally coordinated by six
water molecules, which are hydrogen bonded to the triflimide
counterions and the water solvent molecules.
M
)
538 nm in the UV–Vis spectra of the nickel compounds 10ꢀ0.5H2O
and 11, respectively (Fig. 3d). For a nickel(II) d8 ion three d–d
3
3
transitions, A2g(F) ? 3T2g(F)
(m
1), A2g(F) ? 3T1g(F)
(m2)
and
3A2g(F) ? 3T1g(P) (
m3), are expected. The m2 transition usually
absorbs in the region of 13,000–19,000 cmꢁ1 and was therefore
expected to be the cause of the observed transition at 530
(18,868) and 538 nm (18,587 cmꢁ1) in the spectra of 10ꢀ0.5H2O
and 11, respectively. The m3 absorptions are presumably masked
The 3:1-type complexes [CoII(L1)3](ClO4)2ꢀ2MeOH (8ꢀ2MeOH)
and [CoII(L2)3](ClO4)2 (9) crystallise in the monoclinic space group
ꢀ
P2(1)/n and the triclinic space group P1 with one complex cation
and two perchlorate counterions, respectively, and two MeOH sol-
vent molecules in the case of 8ꢀ2MeOH. The coordination environ-
ments of the cobalt(II) ions are best described as N6 distorted
octahedral, formed by mer-coordinated bidentate NPy–NIm com-
partments of three ligands (Fig. 2a and b).
The Co–NPy and Co–NIm distances compare well within and
between the complexes and are in the range of 2.007(2)–2.088(2)
and 2.100(2)–2.106(2) Å for Co–NIm and 2.148(2)–2.159(2) and
2.138(2)–2.163(2) Å for Co–NPy, in 8ꢀ2MeOH and 9, respectively.
A Jahn–Teller distortion is not observed. These findings suggest
the cobalt(II) ions to reside in the high spin (hs) state at 100 K
[53]. The Co–NPy distances are slightly longer than the Co–NIm
by inner-ligand transition bands of the ligands, whereas m1 presum-
ably lies beyond 900 nm, the higher end of the range investigated.
For these reasons, unfortunately 10Dq cannot be established by this
method for either of the complexes, but the iron(II) compounds 3–7
are expected to be in the ls state, whereas the cobalt(II) complexes 8
and 9 presumably reside in the hs state.
Moessbauer spectroscopy was performed exemplarily on the
iron(II) triflimide compound 7 at 287 and 3 K (Fig. 4). The spectra
recorded at these temperatures were very similar and both exhib-
ited symmetrical doublets with isomeric shifts d = 0.32 and
0.40 mm sꢁ1 and quadrupole splittings
D
Eq = 0.57 and 0.59 mm sꢁ1
for 287 and 3 K, respectively. These data clearly indicate ls iron(II)

T. Huxel et al. / Polyhedron 93 (2015) 28–36
31
Fig. 2. View of the molecular structures of (a) [CoII(L1)3]2+, the complex cation of 8ꢀ2MeOH; (b) [CoII(L2)3]2+, the complex cation of 9. Hydrogen atoms have been omitted for
clarity.
Table 2
Crystallographic data for [Fe(H2O)6](NTf2)2ꢀ2H2O, [CoII(L1)3](ClO4)2ꢀ2MeOH (8ꢀ2MeOH) and [CoII(L2)3](ClO4)2 (9).
[Fe(H2O)6](NTf2)2ꢀ2H2O
8ꢀ2MeOH
9
Empirical formula
Formula weight (g molꢁ1
Crystal system
Space group
a (Å)
C4H16F12FeN2O16S4
760.28
Tetragonal
P4(2)/n
20.079(8)
20.079(8)
6.313(3)
90
C32H41Cl2CoN9O
841.57
Monoclinic
P2(1)/n
8.5392(2)
28.2904(6)
15.8193(4)
90
95.9320(11)
90
C33H39Cl2CoN9O11
867.56
)
Triclinic
ꢀ
P1
8.9130(2)
12.8828(3)
17.9445(5)
71.1580(10)
89.3090(10)
72.0760(10)
1846.66(8)
2
b (Å)
c (Å)
a
(°)
b (°)
90
90
c
(°)
V (Å3)
2545.2(19)
4
1.984
3801.12(15)
4
1.471
Z
qcalc. (g cmꢁ3
)
1.560
0.683
l
(mmꢁ1
)
1.077
0.659
T (K)
100(2)
100(2)
100(2)
F(000)
1520
1748
898
Crystal color and shape
Colorless plate
0.66 ꢂ 0.18 ꢂ 0.05
1.43/29.57
ꢁ25 ? 25
ꢁ27 ? 26
ꢁ5 ? 8
Orange block
0.22 ꢂ 0.05 ꢂ 0.02
1.48/26.37
ꢁ10 ? 10
ꢁ35 ? 35
ꢁ19 ? 16
49,914
Orange block
0.08 ꢂ 0.05 ꢂ 0.05
1.20/29.58
ꢁ12 ? 12
ꢁ17 ? 17
ꢁ24 ? 24
46,099
Crystal size (mm3)
hmin./hmax. (°)
h
k
l
Reflections collected
13,107
Independent reflections
3518 [Rint = 0.0316]
98.4
3518/34/203
1.074
7764 [Rint = 0.0417]
99.7
7764/0/491
1.072
10,248 [Rint = 0.0190]
99.0
10,248/0/505
1.026
Completeness to hmax. (%)
Data/restraints/parameters
GOOF
R1/wR2 [I > 2
r
(I)]
0.0313/0.0885
0.0332/0.0899
0.513/ꢁ0.436
0.0436/0.0927
0.0605/0.0990
0.483/ꢁ0.542
0.0495/0.1292
0.0556/0.1337
1.305/ꢁ0.934
R1/wR2 (all data)
Max. peak/hole/(e Åꢁ3
)
even at 287 K and give no evidence of a thermally induced SCO.
Table 4 summarises the spin states of the complexes described in
this chapter.
observed up to 97 °C, the higher end of the range measured.
With Tfus < 100 °C this hs iron(II) compound hence is characterised
as paramagnetic Ionic Liquid.
DSC measurements were also carried out on the isolated 3:1-
type iron(II) tetrafluoroborate and triflimide complexes 4ꢀH2O, 6
and 7 and the nickel and cobalt perchlorate complexes 8–11 that
did not decompose in the melting-point apparatus up to 220 °C.
Both the cobalt(II) and nickel(II) perchlorate complexes of L1
(8ꢀ1.5H2O and 10ꢀ0.5H2O) did not melt up to 235 °C, the highest
temperature measured. The respective L2 complexes 9 (Fig. S2,
Supporting information, bottom) and 11, however, showed a melt-
3.2. DSC measurements
Differential scanning calorimetry was performed on the EIm-
NTf2 complex [FeII(EIm)6](NTf2)2ꢀ0.5EtOHꢀ0.5H2O (2). The DSC
showed one endothermic melting and exothermic solidifying peak
at 83 (D
Hfus = 67 kJ molꢁ1) and 50 °C in the heating and cooling
mode, respectively, reproducible in various heating and cooling
cycles (Fig. S1, Supporting information). A loss of solvent is not
ing process at Tfus = 181 (D
Hfus = 58) and 189 (48 kJ molꢁ1) °C,

32
T. Huxel et al. / Polyhedron 93 (2015) 28–36
Table 3
respectively, in the first DSC heating cycle. A glass transition could
not be undoubtedly detected in the cooling mode but in further
two heating cycles presumably a glass transition with relaxation
occurred upon heating, at Tg = 66 (Fig. S2, Supporting information,
top) and 72 °C, respectively. A further melting process at higher
temperatures was no longer observed. Both the tetrafluoroborate
(4ꢀH2O) and triflimide (7) iron(II) complexes of L1 exhibited sharp
Selected distances in Å and angles in degrees in [CoII(L1)3](ClO4)2ꢀ2MeOH (8ꢀ2MeOH)
and [CoII(L2)3](ClO4)2 (9).
8ꢀ2MeOH
9
Co(1)–N(1)
Co(1)–N(2)
Co(1)–N(11)
Co(1)–N(12)
Co(1)–N(21)
Co(1)–N(22)
2.159(2)
2.088(2)
2.148(2)
2.077(2)
2.156(2)
2.080(2)
76.44(9)
86.81(8)
94.90(8)
101.85(8)
169.28(8)
98.82(8)
170.80(8)
88.06(8)
92.85(8)
77.32(8)
170.07(8)
95.35(8)
96.88(8)
95.81(8)
77.05(8)
Co(1)–N(1)
Co(1)–N(2)
Co(1)–N(21)
Co(1)–N(22)
Co(1)–N(41)
Co(1)–N(42)
2.138(2)
2.102(2)
2.146(2)
2.106(2)
2.163(2)
2.100(2)
77.25(7)
93.34(7)
95.68(7)
172.47(7)
96.40(6)
94.24(7)
168.25(7)
100.69(7)
96.91(7)
76.64(7)
94.04(7)
166.57(7)
87.49(7)
93.18(7)
76.57(6)
melting peaks at Tfus = 239 (D
Hfus = 36) and 153 (55 kJ molꢁ1) °C,
respectively. A change of color was not observed during the heat-
ing process of the red compounds, which would be strong evidence
of a thermally induced SCO. The tetrafluoroborate complex 4ꢀH2O,
in the first heating cycle, additionally had a second, much smaller
endothermic peak, presumably due to loss of solvent, as it was no
longer observed on reheating. Upon cooling 4ꢀH2O of L1 solidified
at 216 °C, giving rise to an exothermic doublet peak (Fig. S3,
Supporting information). A glass transition of the triflimide com-
pound 7 could not be detected undoubtedly upon cooling but in
following four heating cycles, before the melting process, presum-
ably a cold crystallisation occurred at 51 °C (Fig. S4, Supporting
information). In the first cycle of the tetrafluoroborate compound
6 of L2 a phase transition occurred, as suggested by an endothermic
peak at 95 °C, followed by an exothermic process at 102 °C, before
N(1)–Co(1)–N(2)
N(1)–Co(1)–N(11)
N(1)–Co(1)–N(12)
N(1)–Co(1)–N(21)
N(1)–Co(1)–N(22)
N(2)–Co(1)–N(11)
N(2)–Co(1)–N(12)
N(2)–Co(1)–N(21)
N(2)–Co(1)–N(22)
N(11)–Co(1)–N(12)
N(11)–Co(1)–N(21)
N(11)–Co(1)–N(22)
N(12)–Co(1)–N(21)
N(12)–Co(1)–N(22)
N(21)–Co(1)–N(22)
N(1)–Co(1)–N(2)
N(1)–Co(1)–N(21)
N(1)–Co(1)–N(22)
N(1)–Co(1)–N(41)
N(1)–Co(1)–N(42)
N(2)–Co(1)–N(21)
N(2)–Co(1)–N(22)
N(2)–Co(1)–N(41)
N(2)–Co(1)–N(42)
N(21)–Co(1)–N(22)
N(21)–Co(1)–N(41)
N(21)–Co(1)–N(42)
N(22)–Co(1)–N(41)
N(22)–Co(1)–N(42)
N(41)–Co(1)–N(42)
Fig. 3. UV-Vis spectra of (a) [Fe(EIm)6](NTf2)2ꢀ0.5EtOHꢀ0.5H2O (2) in propylene carbonate (10 m
M
) (inset: enlarged region 700–1000 nm); (b) [FeII(L1)3](NTf2)2 (7) in MeOH
(0.1 m
M
); (c) [Co(L1)3](ClO4)2ꢀ1.5H2O (8ꢀ1.5H2O) in MeCN (0.1 m
M
) (inset: 10 m
M
); (d) [Ni(L1)3](ClO4)2ꢀ0.5H2O (10ꢀ0.5H2O) in MeOH (0.01 m
M) (inset: 10 mM). Point charge
splitting diagrams of hs d6, hs d7 and d8 ions, depicting the expected d–d transitions.

T. Huxel et al. / Polyhedron 93 (2015) 28–36
33
crystal X-ray diffraction and corroborated the 3:1-type nature of
the compounds. Differential scanning calorimetry revealed that
even L1 with the relatively short ethyl tag, in combination with
NTfꢁ2 , is able to form low-melting complexes. And, with the excep-
tion of [FeII(L2)3](ClO4)2 (5) that decomposed at elevated tempera-
tures, all complexes of the methoxyethyl-tagged ligand L2 isolated
were low-melting with Tfus < 200 °C and had glass transitions
below 75 °C upon reheating. With these results the viability of this
ligand system to form low-melting complexes was affirmed.
Table 4 summarises the spin states and temperatures of the melt-
ing and glass transition processes of the complexes described in
this work.
5. Experimental part
Fig. 4. 57Fe Moessbauer spectrum of [FeII(L1)3](NTf2)2 (7) recorded at 3 K.
5.1. General remarks
All chemicals and reagents were purchased from commercial
sources and used as received. All solvents used were laboratory
reagent grade. MIm and EIm were purchased from commercial
sources. If not stated otherwise, reactions were performed under a
protective atmosphere of argon. Melting points were determined
using a Setaram DSC 131 evo differential scanning calorimeter or
a Thiele melting point apparatus. Elemental analyses were carried
out using an Elementar Vario EL analyzer. IR spectra were recorded
over the range 4000–400 cmꢁ1 using a Nicolet Magna 760 FTIR
spectrometer. Raman spectra were recorded over the range of 50–
4000 cmꢁ1 using a Bruker Vertex 70 FT-Raman spectrometer.
Mass spectra were recorded with a Thermo Exactive device with
Orbitrap-analysator. UV–Vis/NIR spectra were recorded with a
Thermo Scientific Evolution 600 over the range 200–900 nm or in
the range 300–1000 nm by using an Analytik Jena Specord S 300
VIS spectrometer. Moessbauer spectra were recorded with a 57Co
source in a Rh matrix using an alternating constant acceleration
Wissel moessbauer spectrometer operated in the transmission
mode and equipped with a Spectromag 4000 cryostat. Isomer shifts
are given relative to iron metal at ambient temperature. Simulation
of the experimental data was performed with the Mfit program [56].
Single crystal X-ray diffraction data were collected using a Bruker
Smart APEX-II CCD Quazar diffractometer with an Incoatec micro-
Table 4
List of complexes described in the main text, summarising their spin state, melting
points and glass transition temperatures.
Compound
Spin state
hs
Tfus (°C)
Tg (°C)
[FeII(MIm)6](NTf2)2ꢀ0.5EtOHꢀ0.5H2O (1)
185
(decomp.)
83
218
(decomp.)
239
153
187
(decomp.)
175
>235
181
–
[FeII(EIm)6](NTf2)2ꢀ0.5EtOHꢀ0.5H2O (2)
[FeII(L1)3](ClO4)2ꢀH2O (3ꢀH2O)
hs
ls
–
–
[FeII(L1)3](BF4)2ꢀH2O (4ꢀH2O)
ls
ls
ls
–
–
–
[FeII(L1)3](NTf2)2 (7)
[FeII(L2)3](ClO4) (5)
[FeII(L2)3](BF4)2(6)
ls
hs
hs
–
73
–
66
–
[CoII(L1)3](ClO4)2ꢀ1.5H2O (8ꢀ1.5H2O)
[CoII(L2)3](ClO4)2 (9)
[NiII(L1)3](ClO4)2ꢀ0.5H2O (10ꢀ0.5H2O)
[NiII(L2)3](ClO4)2 (11)
>235
189
–
72
the melting process was detected at Tfus = 175 °C (49 kJ molꢁ1). A
change of color was not observed during the heating process of
the red compound. A glass transition of the compound could not
be detected undoubtedly upon cooling, but in further two heating
cycles presumably occurred at 73 °C, before the melting process
reoccurred (Fig. 5, Supporting information). However, a residual
part of the compound presumably remained in the crystalline state
and melted at the same temperature as in the first cycle. Table 4
summarises the melting and glass transition temperatures of the
complexes described in this work.
fused sealed tube radiation source, with mirror optics (Mo K radia-
a
tion, k = 0.71073 Å). The structures were solved by direct methods
with SHELXS-97 [57] and refined against F2 using all data by full-
matrix least-squares techniques with SHELXL-97 [57]. All non-hydro-
gen atoms were refined anisotropically. All hydrogen atoms were
placed at calculated positions using riding models. CCDC 1042804,
1042805 and 1042803 contain the supplementary crystallographic
data for [Fe(H2O)6](NTf2)2ꢀ2H2O, 8ꢀ2MeOH and 9, respectively.
These data can be obtained free of charge at www.ccdc.cam.ac.
uk/data_request/cif or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK.
4. Conclusions
With the iron(II) salt Fe(NTf2)ꢀ6H2O two homoleptic N-alkylim-
idazole complexes, namely [FeII(MIm)6](NTf2)2ꢀ0.5EtOHꢀ0.5H2O (1)
and [FeII(EIm)6](NTf2)2ꢀ0.5EtOHꢀ0.5H2O (2), have been synthesised
and characterised. Even so the imidazole side chain of EIm is
merely composed of the relatively short ethyl substituent, its
homoleptic triflimide complex 2, with Tfus < 100 °C, has been iden-
tified as paramagnetic hs iron(II) MeIL and had the lowest melting
point in the series [MII(L)6]X2 (M = Fe, Co, Ni; X = ClO4, NTf2)
(Table 1) [37–39]. Following these results two new bidentate 2-
(2-pyridyl)-1H-imidazole ligands, L1 and L2 with ethyl or methox-
yethyl side chain, respectively, have been prepared. With these
ligands 3:1-type complexes of iron(II), cobalt(II) and nickel(II), fea-
turing different counterions, have been prepared, and their spin
state and melting behavior has been determined. All iron(II) com-
plexes of L1 and L2 were ls at RT, whereas the cobalt(II) complexes
were hs at 100 K. Exemplarily, the molecular structure of the
cobalt(II) complexes 8ꢀ2MeOH and 9 was determined by single
5.1.1. [Fe(H2O)6](NTf2)2
To
a suspension of iron powder (559 mg, 10.0 mmol) in
degassed water (8.5 ml) was slowly added an aqueous solution of
bis(trifluoromethylsulfonyl)imid (80%, 21.0 mmol). The mixture
was stirred at RT for 2 h, before it was filtered. The solvent was
removed under reduced pressure. Drying the residue at 80 °C in
vacuo gave a colorless powder of Fe(NTf2)2ꢀ6H2O. Yield: 75%.
Tfus = 115–116 °C. Elemental analysis (%) Anal. Calc. for
C4H12N2O14F12S4Fe (724.21 g molꢁ1): C, 6.63; H, 1.67; N, 3.87.
Found: C, 7.00; H, 1.43; N, 3.85%. ESI-MS (negative mode, MeCN):
m/z (intensity, fragment) = 280.1 (100% [(CF3SO2)2Nꢁ]) (Fig. S6,
~
Supporting information). Raman:
1367, 1240, 1148, 1105, 752 (vs SNS), 659, 559, 425, 332, 290,
v = 3235, 2933, 2847, 2759,

34
T. Huxel et al. / Polyhedron 93 (2015) 28–36
243, 193, 127, 99 cmꢁ1 (Fig. S20, Supporting information). Single
crystals of [Fe(H2O)6](NTf2)2ꢀ2H2O, suitable for X-ray diffraction
analysis, were obtained in an attempted complexation reaction
with 1-ethyltetrazole in DCM at ꢁ40 °C.
(10 ml) was added to the reaction mixture and the organic phase
was separated. The aqueous layer was further extracted several
times with DCM and the combined organic layer was washed with
water and dried over Na2SO4. The solvent was removed under
reduced pressure and the residue was purified by column chro-
matography (DCM:MeOH = 9:1). L2 was obtained as a slightly yel-
low liquid. Yield: 34%. 1H NMR (200.13 MHz, DMSO-d6): d = 8.58
(ddd, 1 H, 6-pyH), 8.09 (ddd, 1 H, 3-pyH), 7.87 (ddd, 1 H, 4-pyH),
7.32 (d, 1 H, 5-imH), 7.34 (ddd, 1 H, 5-pyH), 7.03 (d, 1 H, 4-imH),
5.1.2. 2-(2-Pyridyl)-1H-imidazole (I)
2-Pyridinecarbonitrile (10.4 g, 100 mmol) was added to a solu-
tion of NaOMe (0.54 g, 10.0 mmol) in abs. MeOH (40 ml). The mix-
ture was stirred for 1 h at 40 °C before it was allowed to cool down.
2,2-Dimethoxyethylamine (10.5 g, 100 mmol) and glacial acetic
acid (11 ml) was added drop wise and the resulting mixture was
refluxed for 1 h and was afterwards allowed to cool down before
4.75 (t, 2 H, NCH2CH2OCH3), 3.65 (t, 2 H, NCH2CH2OCH3), 3.19 (s,
3 H, CH3) ppm. 13C NMR (50.33 MHz, DMSO-d6): d = 151.0 (2-
pyC), 149.3 (6-pyC), 143.9 (2-imC), 137.8 (4-pyC), 128.5 (4-imC),
MeOH (50 ml) and 6
M HCl (50 ml) was added. The mixture was
125.5 (5-imC), 123.3 (5-pyC), 122.9 (3-pyC), 72.1 (NCH2CH2OCH3),
then refluxed for further 4 h before the solvent was removed under
reduced pressure. The residue was digested in a solution of K2CO3
(50 g) in H2O (50 ml) before DCM (50 ml) was added to the resulting
suspension. The mixture was filtered and the organic phase sepa-
rated. The aqueous phase was extracted several times with DCM
and the combined organic layers were dried over Na2SO4 before
removal of the solvent under reduced pressure and recrystallisation
of the residue from ethyl acetate (50 ml) gave a tan amorphous
powder of I. Yield: 62%. 1H NMR (200.13 MHz, DMSO-d6):
d = 12.77 (bs, 1 H, 1-imH), 8.58 (d, 1 H, 6-pyH), 8.04 (d, 1 H, 3-
pyH), 7.87 (ddd, 1 H, 4-pyH), 7.34 (ddd, 1 H, 5-pyH), 7.22 (s, 1 H,
5-imH or 4-imH), 7.08 (s, 1 H, 5-imH or 4-imH) ppm. 13C NMR
(50.33 MHz, DMSO-d6): d = 149.2 (2-pyC), 148.9 (6-pyC), 145.5 (2-
imC), 137.1 (4-pyC), 129.5 (4-imC or 5-imC), 123.0 (5-pyC), 119.4
(3-pyC), 118.7 (4-imC or 5-imC) ppm. EI-MS (MeOH) m/z (rel. abun-
~
58.6 (CH3), 47.6 (NCH2CH2OCH3) ppm (Fig. S35, Supporting infor-
~
v
mation). IR (diamond, ATR):
= 2892, 1588 (s), 1566, 1486 (s),
1459 (vs), 1407, 1298, 1277, 1211, 1117 (vs), 1038, 1012, 992,
969, 917, 833, 791 (vs), 743 (vs), 708 (vs), 667, 624, 404 cmꢁ1
(Fig. S22, Supporting information). APCI-MS (MeOH) m/z (rel. abun-
dance, fragment) = 204.1132 (100%, [HL2]+) (Fig. S8, Supporting
information). Elemental analysis (%)Anal. Calc. for
(203.24 g molꢁ1): C, 65.01; H, 6.45; N, 20.67. Found: C, 64.69; H,
6.46; N, 20.79%. UV–Vis (MeCN): kmax ) = 294 (15,850), 266
(12,180) nm (
ꢁ1 cmꢁ1) (Fig. S37, Supporting information).
C11H13N3O
(e
M
Caution! While no problems were encountered in the course of this
work, ClOꢁ4 salts are potentially explosive and should be handled with
appropriate care.
5.1.5. [FeII(MIm)6](NTf2)2 (1)
dance, fragment) = 145.0 (100%, I+). IR (diamond, ATR):
v = 3046,
In an argon atmosphere a solution of MIm (493 mg, 6.00 mmol)
in EtOH (2 ml) was added to a solution of Fe(NTf2)2ꢀ6H2O (724 mg,
1.00 mmol) in EtOH (5 ml) and the resulting suspension was stirred
for 1 h at RT. The precipitate of [FeII(MIm)6](NTf2)2ꢀ0.5EtOHꢀ0.5 H2O
(1) was collected by filtration, washed with EtOH and dried in vacuo.
Yield: 20%. Tfus = 183–185 °C (decomp.). Elemental analysis (%) Anal.
Calc. for C29H40F12N14O9S4Fe (1140.79 g molꢁ1): C, 30.53; H, 3.53; N,
17.19. Found: C, 30.22; H, 3.94; N, 17.47%. ESI-MS (MeOH): m/z (rel.
abundance, fragment) = 499.9577 (100%, [Fe(MIm)2NTf2]+) (Fig. S9,
~
2983, 2887, 2821, 2743, 1594 (s), 1568, 1479 (vs), 1458 (vs),
1415, 1382, 1308, 1139, 1109 (s), 992, 954 (s), 909, 786 (vs), 758,
736 (vs), 706 (vs), 630 (s), 621, 504, 464, 403 cmꢁ1. Elemental analy-
sis (%) Anal. Calc. for C8H7N3 (145.16 g molꢁ1): C, 66.19; H, 4.86N,
28.95. Found: C, 65.89, H, 4.97; N, 29.09%.
5.1.3. 2-(2-pyridyl)-1-ethylimidazole (L1)
solid I (2.61 g, 18.0 mmol) was added to a solution of KOH in H2O
(50%, 10 ml). Ethyl iodide (2.81 g, 18.0 mmol) was added drop wise
and the reaction mixture was refluxed for 6 h before it was
extracted with DCM. The combined organic layer was washed with
water and dried over Na2SO4 before the solvent was removed under
reduced pressure. The residue was purified by column chro-
matography (DCM:MeOH = 9:1) to obtain L1 as a slightly yellow liq-
uid. Yield: 72%. 1H NMR (200.13 MHz, DMSO-d6): d = 8.61 (ddd, 1 H,
6-pyH), 8.08 (ddd, 1 H, 3-pyH), 7.87 (ddd, 1 H, 4-pyH), 7.34 (ddd, 1
H, 5-pyH), 7.36 (d, 1 H, 5-imH), 7.03 (d, 1 H, 4-imH), 4.58 (q, 2 H,
Supporting information). IR (diamond, ATR):
v = 3139, 1532, 1517,
1424, 1349 (s), 1331, 1286, 1233 (vs), 1174, 1140, 1107 (s), 1087,
1052 (vs), 936, 830, 791, 756, 746, 662 (vs), 610 (vs), 569 (s), 514,
410 cmꢁ1 (Fig. S23, Supporting information). UV–Vis (PC): kmax
(e) = 360 (132), 863 (5) nm (M ) (Fig. S38, Supporting
ꢁ1 cmꢁ1
information).
5.1.6. [FeII(EIm)6](NTf2)2 (2)
In an argon atmosphere a solution of EIm (559 mg, 6.00 mmol)
in EtOH (2 ml) was added to a solution of Fe(NTf2)2ꢀ6H2O (724 mg,
1.00 mmol) in EtOH (5 ml). Addition of pentane (10 ml) resulted in
precipitation of [FeII(EIm)6](NTf2)2ꢀ0.5EtOHꢀ0.5H2O (2), which was
collected by filtration, washed with pentane and dried in vacuo.
Yield: 37%. Tfus = 83–85 °C. Elemental analysis (%) Anal. Calc. for
NCH2CH3), 1.33 (t, 3 H, CH3) ppm. 13C NMR (50.33 MHz, DMSO-
d6): d = 150.1 (2-pyC), 148.1 (6-pyC), 142.9 (2-imC), 136.6 (4-pyC),
127.8 (4-imC), 123.3 (5-imC), 122.2 (5-pyC), 121.9 (3-pyC), 42.2
(NCH2CH3), 16.5 (CH3) ppm (Fig. S34, Supporting information). IR
~
v
(diamond, ATR):
= 2979, 1588 (vs), 1565, 1487 (vs), 1463 (vs),
C
35H52F12N14O9S4Fe (1224.95 g molꢁ1): C, 34.32; H, 4.78; N,
1438 (s), 1408, 1380, 1355, 1300, 1277, 1257, 1148, 1091 (s),
1051 (s), 1039, 992, 959, 918, 848, 790 (vs), 742 (vs), 708 (vs),
662, 623,402 cmꢁ1 (Fig. S21, Supporting information). APCI-MS
(MeOH) m/z (rel. abundance, fragment) m/z = 174.1024 (100%,
[HL1]+) (Fig. S7, Supporting information). Elemental analysis (%)
Anal. Calc. for C10H11N3 (173.21 g molꢁ1): C, 69.34; H, 6.40; N,
24.26. Found: C, 69.19; H, 6.42; N, 24.27%. UV–Vis (MeOH): kmax
16.27. Found: C, 33.95; H, 4.63; N, 16.27%. ESI-MS (MeOH): m/z
(rel. abundance, fragment) = 527.9890 (100%, [Fe(EIm)2NTf2]+)
~
v
(Fig. S10, Supporting information). IR (diamond, ATR):
= 3138,
1521, 1469, 1457, 1405, 1345 (s), 1321 (s), 1288, 1232, 1175 (vs),
1133 (vs), 1113, 1103, 1092 (s), 1060 (s), 1033, 965, 932, 843,
788, 762, 752, 741, 664, 651 (s), 624, 597 (s), 570, 530, 506, 443,
404 cmꢁ1 (Fig. S24, Supporting information). UV-Vis (PC): kmax
(
e
) = 290 (12,810), 264 (8870), 210 (5360), 204 (4680) nm
(e) = 372 (156), 858 (6) nm (M
ꢁ1 cmꢁ1).
(M
ꢁ1 cmꢁ1) (Fig. S36, Supporting information).
5.1.4. 2-(2-pyridyl)-1-(2-methoxyethyl)imidazole (L2)
solid I (2.02 g, 13.9 mmol) was added to a solution of KOH in H2O
(50%, 10 ml). 2-Chloromethyl ethyl ether (1.46 g, 15.4 mmol) was
added drop wise and the mixture was refluxed for 3.5 h. Water
5.1.7. [FeII(L1)3](ClO4)2 (3)
A solution of L1 (109 mg, 630
to a solution of Fe(ClO4)2ꢀ6H2O (74.3 mg, 205
(5 ml) and the resulting red precipitate of 3ꢀH2O was collected by
l
mol) in MeOH (10 ml) was added
mol) in MeOH
l

T. Huxel et al. / Polyhedron 93 (2015) 28–36
35
filtration, washed with Et2O and dried in vacuo. Yield: 48%.
Tfus = 218–220 °C (decomp.). Elemental analysis (%) Anal. Calc. for
30H35Cl2N9O9Fe (792.42 g molꢁ1): C, 45.47; H, 4.45; N, 15.91.
5.1.11. [FeII(L1)3](NTf2)2 (7)
A solution of L1 (116 mg, 670
l
mol) in MeOH (1 ml) was added
C
to a solution of Fe(NTf2)2ꢀ6H2O (145 mg, 206
lmol) in MeOH
Found: C, 45.65; H, 4.27; N, 15.83%. ESI-MS (MeOH) m/z (rel. abun-
dance, fragment) = 174.1026 (100%, [HL1]+), 287.6095 (55%,
[Fe(L1)3]2+), 501.0717 (6%, [[Fe(L1)2]ClO4]+) (Fig. S11, Supporting
~
(1 ml). After 48 h pentane (1 ml) and TBME (200 lml) was added.
The resulting red precipitate of 7 was collected by filtration
washed with Et2O and dried in vacuo. Yield: 70%. Tfus = 148–
151 °C. Elemental analysis (%) Anal. Calc. for C34H33F12N11O8S4Fe
(1135.78 g molꢁ1): C, 35.95; H, 2.93; N, 13.57. Found: C, 35.91; H,
2.74; N, 13.63%. ESI-MS (MeOH) m/z (rel. abundance, frag-
ment) = 174.1025 (100%, [HL1]+), 287.6096 (71%, [Fe(L1)3]+),
682.0414 (23%, [[Fe(L1)2](NTf2)]+) (Fig. S15, Supporting informa-
~
information). IR (diamond, ATR):
v = 3144, 3124, 2987, 1607,
1535, 1491, 1473 (s), 1445, 1385, 1353, 1311, 1264, 1166, 1073
(vs), 1042, 960, 880, 781 (s), 752 (m), 705 (m), 673, 646, 620 (s),
514, 459, 422 cmꢁ1 (Fig. S25, Supporting information). UV–Vis
(MeOH): kmax(e) = 214 (22,090), 264 (23,870), 300 (41,160), 392
(2310), 498 (6440) nm
(
M
ꢁ1 cmꢁ1
)
(Fig. S39, Supporting
tion). IR (diamond, ATR): v = 3129, 1608, 1538, 1498, 1478, 1449,
information).
1393, 1349 (s), 1330 (s), 1268, 1228, 1178 (vs), 1132 (vs), 1052
(vs), 967, 883, 781 (s), 750, 739, 720, 704, 661, 600 (s), 568 (s),
506 (s), 407 cmꢁ1 (Fig. S29, Supporting information). UV–Vis
5.1.8. [FeII(L1)3](BF4)2 (4)
(MeOH): kmax
(3034), 494 (5680) nm (
(
e
) = 16 (18,440), 262 (21,900), 300 (38,040), 396
A solution of L1 (118 mg, 680
lmol) in MeOH (1 ml) was added
M
ꢁ1 cmꢁ1).
to a solution of Fe(BF4)2ꢀ6H2O (69.2 mg, 205
l
mol) in MeOH (1 ml).
The resulting red solid of 4ꢀH2O was collected by filtration, washed
5.1.12. [Co(L1)3](ClO4)2 (8)
A solution of L1 (105 mg, 605
added to a solution of Co(ClO4)2ꢀ6H2O (75.8 mg, 207
with Et2O and dried in vacuo. Yield: 67%. Tfus = 225–228 °C.
lmol) in MeOH (2.5 ml) was
Elemental analysis (%) Anal. Calc. for
C30H35F8B2N9OFe
(767.11 g molꢁ1): C, 46.97; H, 4.60; N, 16.43. Found: C, 47.18; H,
4.42; N, 16.62%. ESI-MS (MeOH) m/z (rel. abundance, frag-
ment) = 174.1023 (100%, [HL1]+), 146.0711 (19%, [HI]+) (Fig. S12,
~
v = 3150, 3129,
lmol) in
MeOH (2.5 ml) and the resulting orange colored crystalline mate-
rial of 8ꢀ1.5H2O was collected by filtration after 20 h, washed with
Et2O and dried in vacuo. Yield: 49%. Tfus > 235 °C. Elemental analy-
sis (%) Anal. Calc. for C30H36Cl2N9O9.5Co (804.50 g molꢁ1): C, 44.79;
H, 4.51; N, 15.67. Found: C, 44.81; H, 4.67; N, 15.85%. ESI-MS
(MeOH) m/z (rel. abundance, fragment) = 289.1092 (100%,
[Co(L1)3]2+), 202.5611 (47%, [Co(L1)2]2+), 174.1025 (25%, [HL1]+),
504.0711 (11%, [[Co(L1)2](ClO4)]+) (Fig. S16, Supporting informa-
~
Supporting information). IR (diamond, ATR):
2989, 1607, 1536, 1493, 1474 (s), 1446, 1385, 1354, 1313, 1265,
1168, 1106, 1050 (vs), 1034 (vs), 961, 875, 783 (s), 752, 720, 707,
674, 645, 636, 519, 425 cmꢁ1 (Fig. S26, Supporting information).
UV–Vis (MeOH): kmax(e) = 204 (18,400), 214 (15,800), 268
(29,200), 292 (37,100), 392 (2000), 494 (5920) nm (
M )
ꢁ1 cmꢁ1
tion). IR (diamond, ATR):
v = 3120, 2985, 1603, 1574, 1490, 1468
(Fig. S40, Supporting information).
(s), 1444, 1387, 1350, 1290, 1264, 1169, 1072 (vs), 1005, 959,
947, 787 (s), 746, 719 (s), 707 (s), 667, 638, 620 (s), 506, 459,
449, 411 cmꢁ1 (Fig. S30, Supporting information). UV–Vis
5.1.9. [FeII(L2)3](ClO4)2 (5)
A solution of L2 (129 mg, 634
lmol) in MeOH (2.5 ml) was
(MeCN): kmax
(e) = 288 (46,200), 474 (38), 542 (16) nm
(M
ꢁ1 cmꢁ1). Single crystals of 8ꢀ2MeOH, suitable for single crystal
added to a solution of Fe(ClO4)2ꢀ6H2O (74.1 mg, 204 mol) in
l
MeOH (2.5 ml) and the resulting red precipitate of 5 was collected
by filtration after 24 h, washed with Et2O and dried in vacuo. Yield:
55%. Tfus = 187–190 °C (decomp.). Elemental analysis (%) Anal. Calc.
for C33H39Cl2N9O11Fe (864.47 g molꢁ1): C, 45.85; H, 4.55; N, 14.58.
Found: C, 45.72; H, 4.70; N, 14.65%. ESI-MS (MeOH) m/z (rel. abun-
dance, fragment) = 332.6255 (100%, [Fe(L2)3]2+), 204.1130 (10%,
[HL2]+), 561.0950 (8%, [[Fe(L2)2](ClO4)]+) (Fig. S13, Supporting
~
X-ray diffraction analysis, were obtained by this method.
5.1.13. [Co(L2)3](ClO4)2 (9)
A solution of L2 (80.5 mg, 396
lmol) in MeOH (2.5 ml) was
added to a solution of Co(ClO4)2ꢀ6H2O (49.5 mg, 135 mol) in
l
MeOH (2.5 ml) and the resulting orange colored crystalline mate-
rial of 9 was collected by filtration after 72 h, washed with Et2O
and dried in vacuo. Yield: 30%. Tfus = 180–183 °C. Elemental analy-
sis (%) Anal. Calc. for C33H39Cl2N9O11Co (867.56 g molꢁ1): C, 45.69;
H, 4.53; N, 14.53. Found: C, 45.69; H, 4.69; N, 14.57%. ESI-MS
(MeOH) m/z (rel. abundance, fragment) = 334.1245 (100%,
[Co(L2)3]2+), 232.5717 (42%, [Co(L2)2]2+), 204.1131 (20%, [HL2]+),
564.0910 (11%, [Co(L2)2](ClO4)]+) (Fig. S17, Supporting informa-
~
information). IR (diamond, ATR):
v = 3121, 2889, 1607, 1534,
1471 (s), 1448, 1354, 1305, 1273, 1212, 1165, 1071 (vs), 1011,
959, 832, 781 (s), 746 (s), 721, 703 (s), 674, 646, 620 (s), 494,
457 cmꢁ1 (Fig. S27, Supporting information). UV-Vis (MeOH):
kmax
(e) = 262 (24,620), 296 (41,510), 392 (3387), 496 (6600) nm
(M
ꢁ1 cmꢁ1) (Fig. S41, Supporting information).
tion). IR (diamond, ATR):
v = 3118, 2893, 2814, 1604, 1574, 1474
5.1.10. [FeII(L2)3](BF4)2 (6)
(s), 1445, 1392, 1359, 1273, 1211, 1184, 1167, 1070 (vs), 1009
(s), 971, 945, 830, 785 (s), 764, 746, 722, 706 (s), 670, 636, 620
(vs), 548, 411 cmꢁ1 (Fig. S31, Supporting information). UV–Vis
A solution of L2 (127 mg, 627
lmol) in MeOH (3 ml) was added
to a solution of Fe(BF4)2ꢀ6H2O (67.8 mg, 201
l
mol) in MeOH (3 ml).
(MeCN): kmax
(e) = 266 (28,860), 302 (35,380), 487 (38), 544
After 96 h at 7 °C a red precipitate of 6 had formed, which was col-
lected by filtration, washed with Et2O and dried in vacuo. Yield:
52%. Tfus = 170–173 °C. Elemental analysis (%) Anal. Calc. for
(17) nm (
M
ꢁ1 cmꢁ1) (Fig. S43, Supporting information).
33H39F8B2N9O3Fe (839.18 g molꢁ1): C, 47.23; H, 4.68; N, 15.02.
5.1.14. [Ni(L1)3](ClO4)2 (10)
C
A solution of L1 (109 mg, 628
lmol) in MeOH (2.5 ml) was
Found: C, 47.17; H, 4.66; N, 14.91%. ESI-MS (MeOH) m/z (rel. abun-
dance, fragment) = 332.6253 (100%, [Fe(L2)3]2+), 204.1131 (50%,
[HL2]+), 231.0726 (28%, [Fe(L2)2]2+) (Fig. S14, Supporting informa-
~
added to a solution of Ni(ClO4)2ꢀ6H2O (79.1 mg, 216
lmol) in
MeOH (2.5 ml) and the resulting purple crystalline material of
10ꢀ0.5H2O was collected by filtration after several days, washed
with Et2O and dried in vacuo. Yield: 40%. Tfus > 235 °C. Elemental
analysis (%) Anal. Calc. for C30H34Cl2N9O8.5Ni (786.25 g molꢁ1): C,
45.83; H, 4.36; N, 16.03. Found: C, 45.93; H, 4.60; N, 15.93%. ESI-
MS (MeOH) m/z (rel. abundance, fragment) = 288.6099 (100%,
[Ni(L1)3]2+), 202.0622 (68%, [Ni(L1)2]2+), 503.0720 (28%,
tion). IR (diamond, ATR):
v = 3130, 2895, 2819, 1607, 1536, 1495,
1474 (s), 1451, 1358, 1308, 1273, 1211, 1169, 1027 (vs), 833, 781
(s), 746 (s), 721, 704 (s), 674, 640, 519, 455 cmꢁ1 (Fig. S28,
Supporting information). UV–Vis (MeOH): kmax
(e
) = 262 (23,450),
302 (36,870), 392 (2929), 496 (5860) nm (
Supporting information).
M
ꢁ1 cmꢁ1) (Fig. S42,

36
T. Huxel et al. / Polyhedron 93 (2015) 28–36
[[Ni(L1)2](ClO4)]+) (Fig. S18, Supporting information). IR (diamond,
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[6] T. Welton, Chem. Rev. 99 (1999) 2071.
~
ATR):
v
= 3142, 3117, 2970, 1606, 1575, 1493, 1472 (s), 1444,
1382, 1353, 1314, 1291, 1263, 1174, 1071 (vs), 1042 (s), 960,
949, 881, 787 (s), 746, 721, 706 (s), 669, 641, 619 (s), 510,
412 cmꢁ1 (Fig. S32, Supporting information). UV–Vis (MeOH): kmax
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(e) = 246 (64,200), 302 (51,100), 530 (21) nm (M
ꢁ1 cmꢁ1).
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5.1.15. [Ni(L2)3](ClO4)2 (11)
A solution of L2 (121 mg, 596
to a solution of Ni(ClO4)2ꢀ6H2O (73.2 mg, 200
l
mol) in MeOH (2.5 ml) was added
l
mol) in MeOH
(2.5 ml) and the resulting purple crystalline material of 11 was col-
lected by filtration after several days, washed with Et2O and dried in
vacuo. Yield: 56%. Tfus = 188–191 °C. Elemental analysis (%) Anal.
Calc. for C33H39Cl2N9O11Ni (867.32 g molꢁ1): C, 45.70; H, 4.53; N,
14.53. Found: C, 45.64; H, 4.76; N, 14.52%. ESI-MS (MeOH) m/z
(rel. abundance, fragment) = 333.6255 (100%, [Ni(L2)3]2+),
232.0728 (20%, [Ni(L2)2]2+), 563.0942 (12%, [[Ni(L2)2](ClO4)]+),
204.1133 (10%, [HL2]+) (Fig. S19, Supporting information). IR (dia-
~
´
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v = 3118, 2891, 2814, 1605, 1474 (s), 1445, 1392,
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1359, 1273, 1211, 1186, 1168, 1119, 1071 (vs), 1010 (s), 971, 947,
830, 785 (s), 747, 722, 707 (s), 671, 635, 620 (s), 543, 501,
420 cmꢁ1 (Fig. S33, Supporting information). UV–Vis (MeCN):
kmax(e) = 262 (26,510), 304 (37,440), 538 (15) nm (M )
ꢁ1 cmꢁ1
(Fig. S44, Supporting information).
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This work was supported by the European Social Fund and the
Ministry of Science, Research and the Arts Baden-Württemberg
within the Margarete-von-Wrangell-Program and by the
Deutsche Forschungsgemeinschaft (DFG). Financial support from
the University Freiburg is also gratefully acknowledged. The
authors are indebted to Dr. Dominic Kaase and Dr. Daniel
Kratzert for support on X-ray crystallography, to Dr. Valeriu
Mereacre for the measurements and interpretation of the
Moessbauer spectra and to Maximilian Schmucker and Carla
Gotzmann for technical assistance. J.K. thanks Prof. Ingo Krossing
and Prof. Harald Hillebrecht for their support.
Appendix A. Supplementary data
CCDC 1042804, 1042805 and 1042803 contain the supplemen-
tary crystallographic data for [Fe(H2O)6](NTf2)2ꢀ2H2O, 8ꢀ2MeOH
and 9, 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 http://dx.doi.org/10.
1016/j.poly.2015.03.020.
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