Inorganic Chemistry
Article
alternation has been reported for the self-assembly of linear
After the ligands, py
3
CR and py
3
COC(O)R, were separated and
11b
purified, complex formation with iron(II) chloride, lithium
thiocyanate, and tetramethylammonium chloride in methanol gave
corresponding target complexes, Me N[Fe(py CC H2n+1)(NCS)3]
1a− 7a for n = 1−7) and Me N[Fe(py COC(O)C H2n+1)(NCS)3]
1e− 6e for n = 1−6) as light brown to red polycrystals. They turned
dark red at 100 K. The molar ratio of the reactants was optimized for
decreasing bis(tripod) complexes as a byproduct. The samples were
subjected to elemental, spectroscopic, and magnetic analyses without
further purification. The absence of solvent molecules was confirmed
by means of elemental analysis and infrared spectroscopy. X-ray
quality crystals were applied to the structural study.
X-ray diffraction data of a single crystal were collected on a
RIGAKU Saturn70 CCD diffractometer with graphite monochro-
mated Mo Kα radiation (λ = 0.71073 Å) at 100 K. Selected
bis(benzamides). The odd−even effects on the mesophase
transition temperature have been studied for some liquid
12
4
3
n
crystalline materials having a linear alkyl bridge. The alkyl-
substituted tetracenes are yellow to red in their solid state,
depending on the parity of the atom number of the alkyl
(
(
4
3
n
1
3a
carbon atoms. Aggregation-induced emissive materials also
1
3b
exhibited an odd−even effect in chiral assembly.
Further-
more, the odd−even behavior affects the molecular assembly
and macroscopic crystal morphology. A number of surface
14
and interfacial materials carrying alkyl chains have many odd−
1
5
even phenomena in the structures and properties. Assuming
the trans zigzag conformation of the alkyl group in the
isomorphous crystal lattice, the end chain interaction is
3
alternating by an sp -hybridized angle, 109.5°, with an increase
16
of the number of carbon atoms.
993179 are for 3a, 4a, 5a, 1e, 4e, 5e, and 6e, respectively. For the
Thermodynamic parameters exhibited an odd−even effect
1
0,11,17
ester compounds, the structures were also determined at 296 K.
Magnetic susceptibilities of polycrystalline samples were measured
on a Quantum Design MPMS-XL7 SQUID magnetometer with an
applied field of 5000 Oe. No thermal hysteresis was recorded in
across phase transition phenomena.
The transition
temperature is regulated by the relation Ttr = Δ H/Δ S.
tr
tr
The odd−even effects are explained in terms of the crystal
11−17
packing and alkyl conformation.
However, if T is
tr
elevated/lowered, one can hardly tell whether an origin resides
in enhanced/reduced Δ H, reduced/enhanced Δ S, or both. A
tr
tr
combined study from structural and thermodynamic experi-
ments is required to obtain further insight into this question.
We have so far developed the SCO complexes using
−
[
Fe(py CR)(NCS) ] building blocks, where py CR stands for
RESULTS
3
3
3
■
tris(2-pyridyl)methyl derivatives with R = H, OH, CH , py,
and so on (Scheme 1). Anionic SCO complex ions are
3
18
Crystal Structures. Crystal structures have successfully
been determined for 3a, 4a, 5a, 1e, 4e, 5e, and 6e (Table 1),
and the space groups are P1, P1, P2 /c, P2 /c, P2 /n, P1, and
P1, respectively. The molecular structures (except side chains)
are quite similar to each other, as shown in Figure 1 (left
1
1
1
Scheme 1. Structural Formulas of py CR (Left) and
3
3
panels). A tripodal N,N′,N″-tridentate donor, py CR, and
3
−
three NCS coligands afforded an FeN coordination sphere.
Although the Fe-NCS portions were somewhat bent, the
Fe(py CR)(NCS) ] core possesses an approximate C3v
6
−
−
[
3
3
symmetry. The Fe−N bond lengths in these compounds
varied in ca. 1.92−1.99 Å at 100 K, being assignable to LS
+
iron(II) ions. The countercation Me N is usually found near
4
−
configured NCS groups (Figure S1, Supporting Information).
−
−
somewhat rare, and furthermore the [Fe(py CR)(NCS) ]
3
3
family exhibits a range of interesting SCO properties;
Me N[Fe(py COH)(NCS) ](H O) showed thermal hystere-
We have to pay attention to the molecular arrangement in each
crystal, especially folding patterns of alkyl side chains, as
described below. Very interestingly, various packing motifs
appeared (Figure 1, right panels).
As Table 1 and Figure 1a show, 3a crystallizes in a triclinic
P1 space group. The propyl groups, having an anti
conformation, are arranged in a layer structure parallel to the
4
3
3
2
18a
sis with a temperature-scan rate dependence, [Fe(py C) ]-
4
2
[
Fe(py C)(NCS) ] exhibited efficient light-induced excited
4 3 2
18d
spin-state trapping, Me N[Fe(py C-n-C H )(NCS) ] dis-
4
3
18 37
3
played an order−disorder structural transition accompanied by
1
8e
SCO,
and the first FeN S SCO compounds were
4 2
discovered in dinuclear [{Fe(py COH)(NCS)(μ-NCS)} ]-
crystallographic ac plane, together with NCS ligands and Me N
3
2
4
1
8f
19
(
PrOH)2 and polynuclear derivatives. In this study, on
ions. Two nearest-neighboring propyl groups are related with a
crystallographic centrosymmetry and arranged in a head-to-
head manner, not side-by-side. The interatomic distance
between the alkyl terminal carbon atoms is 3.777(3) Å. No
disorder was found, and the thermal displacement of every
atom was considerably small at 100 K. Since the present series
has an anionic charge at the iron(II) complex, we checked
varying the length of the R portions (Scheme 1), we
systematically investigated the SCO temperature depending
on n, the number of carbon atoms in R.
MATERIALS AND METHODS
■
Derivatization of py CR from 2-picoline has been established in the
3
20
18e
line of R = CH3 and C H (stearyl).
The tripodal alkylated
22
18
37
possible S···H−C interactions. The shortest distances are
ligands py CC H
(n = 1−7) were thus prepared according to the
i
ii
3
n
2n+1
2
.82 Å for S1···H14 and 2.94 Å for S1···H2 (the symmetry
established method. The key step is a double aromatic nucleophilic
substitution of 2-halopyridine, and the yields were often low.
operation codes of i and ii are −x, −y+1, −z+1 and x, y+1, z,
respectively, being shorter than the sum of the van der Waals
Esterification on py COH can be subjected to a manner for the
3
23
2
1
known acetate py COC(O)CH . The tripodal ester ligands
radii (S/H: 3.0 Å). The contacting hydrogen atoms belong
3
3
py COC(O)C H
(n = 1−6) were prepared in reasonable yields.
to pyridine rings in neighboring molecules, and this finding
3
n
2n+1
B
Inorg. Chem. XXXX, XXX, XXX−XXX