Axial-site modifications of paddlewheel diruthenium(II, II) complexes supported by hydrogen bonding

Article abstract of DOI:10.1021/ic401030r

The reactions of paddlewheel-type diruthenium(II, II) complexes, [Ru ₂^II,II(x-FPhCO₂)₄(THF)₂] (x-FPhCO₂^- = x-fluorobenzoate with x- = o-, m-, p-), with 2,6-diaminopyridine (dapy) and 7-azaindole (azain) afford axially capped discrete compounds, [Ru₂^II,II(x-FPhCO₂) ₄(dapy)₂] (x = o-, 1; m-, 2; p-, 3) and [Ru ₂^II,II(o-FPhCO₂)₄(azain) ₂] (4), respectively. In these compounds, intramolecular hydrogen bonds are observed between NH₂ groups for 1-3 or imine NH groups for 4 and oxygen atoms of carboxylate groups. In addition, hydrogen bonds of NH ₂···F are also observed for 1 and 4 with an o-positioned F atom on benzoate. This coordination mode, i.e., a dual bonding mode with σ-bonding and hydrogen bonding, should assist ligand coordination to the axial position of the [Ru₂] unit. The Ru-N bond distance in 1-4 is shorter than that observed in related compounds reported previously. In a similar fashion, reactions with planar M^II dithiobiuret (dtb) complexes, [M^II(dtb)₂] (M^II = Pd^II and Pt^II), were carried out. One-dimensional alternating chains, [{Ru₂^II,II(o-FPhCO₂) ₄}{M^II(dtb)₂}] (M^II = Pd ^II, 5; Pt^II, 6), were obtained, in which the hydrogen-bonding modes of NH₂···O and NH ₂···F are present, as expected. DFT calculations for the [M^II(dtb)₂] unit revealed that the LUMO of [M^II(dtb)₂] lies at -2.159 and -1.781 eV for M = Pd and Pt, respectively, which is much higher than HOMO energy at -4.184 eV calculated for [Ru₂^II,II(o-FPhCO₂)(THF)₂], proving that the respective units are essentially electronically isolated in the chains.

Full text of DOI:10.1021/ic401030r

Article
pubs.acs.org/IC
Axial-Site Modifications of Paddlewheel Diruthenium(II, II)
Complexes Supported by Hydrogen Bonding
Wataru Kosaka,† Naoto Yamamoto,† and Hitoshi Miyasaka*,‡
†Department of Chemistry, Division of Material Sciences, Graduate School of Natural Science and Technology, Kanazawa University,
Kakuma-machi, Kanazawa 920-1192, Japan
‡Institute for Materials Research, Tohoku University, 2−1−1 Katahira, Aoba-ku, Sendai 980-8577, Japan
S
* Supporting Information
ABSTRACT: The reactions of paddlewheel-type
diruthenium(II, II) complexes, [Ru2II,II(x-FPhCO2)4(THF)2]
(x-FPhCO2− = x-fluorobenzoate with x- = o-, m-, p-), with 2,6-
diaminopyridine (dapy) and 7-azaindole (azain) afford axially
capped discrete compounds, [Ru2II,II(x-FPhCO2)4(dapy)2] (x
= o-, 1; m-, 2; p-, 3) and [Ru2II,II(o-FPhCO2)4(azain)2] (4),
respectively. In these compounds, intramolecular hydrogen
bonds are observed between NH2 groups for 1−3 or imine
NH groups for 4 and oxygen atoms of carboxylate groups. In
addition, hydrogen bonds of NH2···F are also observed for 1
and 4 with an o-positioned F atom on benzoate. This coordination mode, i.e., a dual bonding mode with σ-bonding and
hydrogen bonding, should assist ligand coordination to the axial position of the [Ru2] unit. The Ru−N bond distance in 1−4 is
shorter than that observed in related compounds reported previously. In a similar fashion, reactions with planar MII dithiobiuret
(dtb) complexes, [MII(dtb)2] (MII = PdII and PtII), were carried out. One-dimensional alternating chains, [{Ru2II,II(o-
FPhCO2)4}{MII(dtb)2}] (MII = PdII, 5; PtII, 6), were obtained, in which the hydrogen-bonding modes of NH2···O and NH2···F
are present, as expected. DFT calculations for the [MII(dtb)2] unit revealed that the LUMO of [MII(dtb)2] lies at −2.159 and
−1.781 eV for M = Pd and Pt, respectively, which is much higher than HOMO energy at −4.184 eV calculated for [Ru2II,II(o-
FPhCO2)(THF)2], proving that the respective units are essentially electronically isolated in the chains.
electron donors (D) to derive [Ru2II,III]+ without significant
structural change in reactions with adequate electron acceptors
INTRODUCTION
■
The rational design of functional molecular assemblies and
frameworks is a crucial issue in the field of solid-state chemistry
and physics. Recently, we proposed a method to synthesize on-
demand frameworks using a linear-type coordinating-acceptor
(A), but also contribute as a paramagnetic source with multiple
spin states of S = 1, as well as [Ru2II,III]+ with S = 3/2,10 due to
the formation of Ru−Ru bonds with frontier orbitals.7 The D/
A assemblies with organic polycyano acceptors such as 7,7,8,8-
building block (CABB) as “edge” of frameworks and a
tetracyano-p-quinodimethane (TCNQ) and N,N′-dicyanoqui-
nodiimine (DCNQI) have demonstrated electron-transfer-
driven magnetic ordering and electron transport properties in
D/A frameworks such as one-dimensional (1-D; the
selectable coordinating-donor building block (CDBB) as
“node” of frameworks.1,2 In this way, the topology of
constructed frameworks is modulated, dependent only on the
shape and number of coordination sites of CDBB (i.e., node)
used, as was systematized for finite cages by Stang et al.,3 in
dimensionality of the lattice, 1-D, 2-D, and 3-D, is hereafter
written in italics to distinguish it from “D” as donor) ladder-
cases where all coordination sites on CABB and CDBB are
mutually saturated for bonding of frameworks (Figure 1). For
type chains,12,13 1-D linear chains,14 2-D networks,15−19 and 3-
D infinite networks,20,21 well organized by the concept
the linear-type CABB, which is fixed in the above strategy, the
mentioned above (see Figure 1).2 Meanwhile, the bonding
family of paddlewheel-type dinuclear metal complexes ([M2])
is useful for the purpose. The latter not only act as a good
affinity at the axial sites of [Ru2II,II] is selective, rather
linear-type CABB,4−6 but also provide electronic/magnetic
disadvantageous for ligands/CDBBs with a weak donation
functional centers involving metal−metal bonding,7 flexible
such as neutral TCNQ and DCNQI, where the assembly
charge ordering,8 redox activity,7,9 and paramagnetism, based
reactions with ligands/CDBBs should, therefore, be well
on the frontier orbitals.7,10,11 Thus, the use of such a simple
controlled to exclude competing ligands such as solvents
capable of coordinating from reaction media. To obtain a more
rigid core with selectable functionalities enables the simpler
design of on-demand frameworks complete with functionalities.
flexible organization at the axial sites of the [Ru2II,II] unit,
The family of carboxylate-bridged paddlewheel-type
diruthenium(II, II) complexes ([Ru2II,II]) is suitable for
functional linear-type CABBs. Such complexes not only act as
Received: April 29, 2013
Published: August 20, 2013
© 2013 American Chemical Society
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RESULTS AND DISCUSSION
■
Synthesis and Characterization of Discrete Molecules
1−4. The reaction of [Ru2II,II(x-FPhCO2)4(THF)2] (x = o-, m-,
p-) with excess dapy or azain (1:4 mol ratio) leads to the
formation of discrete paddlewheel-type Ru dimers axially
capped by the corresponding pyridine derivatives: [Ru2II,II(x-
FPhCO2)4(L)2] (L = dapy, x = o-, 1; m-, 2; p-, 3; L = azain, x =
o-, 4). IR spectra of 1−3 show two N−H stretching peaks in
the range 3370−3480 cm−1, which are blue-shifted compared to
those for dapy (3308 and 3391 cm−1). An IR spectrum of 4
shows one N−H stretching peak at 3333 cm−1, similarly blue-
shifted compared to that for azain (3123 cm−1). Meanwhile, the
peak positions of symmetric and antisymmetric CO
stretching vibrations are unchanged after the addition of
pyridine derivatives. In powder reflection spectra of 1−4, no
specific charge transfer between [Ru2] unit and capping ligand
is observed (Figure S1).
Structures of 1−4 and Description on Hydrogen
Bonding. The structures of 1−4 were determined by single-
crystal X-ray diffraction. Their crystallographic data, selected
bond lengths and angles, and hydrogen bond distances are
summarized in Tables S1, S2, and S3, respectively.
All compounds have an identical motif: a discrete Ru dimer
axially capped by the corresponding pyridine derivatives.
Compounds 1, 2, and 4 crystallize in the triclinic P1 space
̅
group, where 1 and 4, respectively, have two crystallo-
graphically unique [Ru2] units (Z = 2), and 3 crystallizes in
the monoclinic P21/c with Z = 4 (Figure 2 and S2 for another
unit in 1 and 4). For each unit in 1, 2, and 4, an inversion
center is located at the midpoint of the Ru−Ru bond, forming a
centrosymmetric [Ru2(x-FPhCO2)4(L)2] molecule; thus the
half set of respective units forms an asymmetric unit, whereas
all atoms of the formula unit were determined as an asymmetric
unit for 3 (Z = 4). The Ru−Ru length is in the range 2.28−2.30
Å, slightly longer than that for [Ru2(x-FPhCO2)4(THF)2]
(2.2669(7) Å for x = o-, 2.2691(9) Å for m-, 2.2677(3) Å for p-
):9 when the Ru−N bond is strengthened, the Ru−Ru bond in
general tends to lengthen. The average Ru−Oeq length (Oeq
=
carboxylate oxygen atoms) is typical for [Ru2II,II] species (Table
II,III +
S2), because the Ru−Oeq lengths in the [Ru2II,II] and [Ru2
]
Figure 1. Expected structural topologies constructed by the
combination of a linear-type CABB (red) and various types of
CDBB (blue) following the rule that all coordination sites of building
blocks are saturated for bonding (i.e., without vacant sites).
complexes are generally found in the ranges 2.06−2.08 Å and
2.02−2.03 Å, respectively.7,9,14 The Ru−N length in the
quasilinear Ru−Ru−N linkage is in the range 2.32−2.44 Å,
II,II
which tends to be slightly shorter than N-capped [Ru2
]
complexes with no hydrogen bonding reported previously, e.g.,
[Ru2(CF3CO2)4(phz)] (phz = phenazine; 2.425(2) Å),25
[Ru2(2,3,5,6-F4PhCO2)4(acridine)2] (2.450 Å),26 and [Ru2(p-
FPhCO2)4(phz)] (2.450(7) Å).27 Except for one unit in 4 with
ψ = 8.6° (vide infra), the two L planes at the axial positions
almost bisect the paddlewheel arrangement, as similarly found
in the phz-bridged [Ru2II,II] chain [Ru2II,II(CF3CO2)4(phz)],25
where a dihedral angle ψ, which is defined by an angle between
L plane versus the O1−O2−O1*−O2* and/or O5−O6−
O5**−O6** planes (see inset figure in Table S2), is found
with ca. 45−50°. This configuration enables hydrogen bonding
between one amino group on L and two oxygen atoms of the
bridging carboxylate groups with N···O distances in the range
2.8−3.4 Å (only one unit in 4 has a one-site hydrogen bonding
mode; see Figure 2d) (Figures 2 and S2, and Table S3). The
position of amino groups in dapy and imino groups of azain
also enables the formation of hydrogen bonds with fluorine
groups of the o-FPh moiety, so only in 1 and 4, with N···F
hydrogen bonding, in addition to the general covalent bond, is
an efficient support, i.e., forming a dual bonding manner. In
fact, several [M2] complexes, in which hydrogen bonding is
involved, have already been discussed,22,23 and a unique 1-D
alternating chain with [Rh2II,II] and [Ni(bpbg)2] (bpbg =
biphenylbiguanide) has been synthesized,24 although the
instance for multidimensional networks is limited in this case.
Here we used hydrogen bonding to create assemblies with
[Ru2II,II] units. Discrete molecules axially capped by 2,6-
diaminopyridine (dapy) and 7-azaindole (azain), [Ru2II,II(x-
FPhCO2)4(dapy)2] (x = o-, 1; m-, 2; and p-, 3) and [Ru2II,II(o-
FPhCO2)4(azain)2] (4), and 1-D alternating chains with planar
MII dithiobiuret (dtb) complexes [MII(dtb)2] (MII = PdII, PtII),
[{Ru2II,II(o-FPhCO2)4}{MII(dtb)2}] (MII = PdII, 5; PtII, 6), are
reported.
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Figure 2. Thermal ellipsoid plots (50% probability) showing the formula unit for one unit of 1 (a), 2 (b), 3 (c), and one unit of 4 (d) (another unit
for 1 and 4 is given in Figure S2), where atoms of N, O, C, F, and Ru are represented in colors of blue, red, gray, green, and purple, respectively, and
blue dotted lines represent hydrogen bonds. Hydrogen atoms and crystallization solvents were omitted for clarity.
distances in the range 2.90−3.54 Å. An interesting aspect is that
the average dihedral angle, θav, defined by the plane of the
benzoate phenyl group and the plane composed of a carboxyl
group and two Ru atoms (inset figure in Table S2) is relatively
small even in 1 and 4 where the steric hindrance according to o-
F groups is expected (7.4° for 1 and 16.1° for 4), which is much
smaller than the 27.6° observed in [Ru2(o-FPhCO2)4(THF)2]
that has no such characteristic intramolecular hydrogen bonds.9
This is probably because the fixing by the hydrogen bonds of
NH2···F somewhat stabilizes such anomalous arrangements. As
described above, the shorter Ru−N bond found in all
compounds is probably due to the effect of hydrogen bonding.
Synthesis, Characterization, and Structures of 5 and
6. The dithiobiuret Pd and Pt complexes, [MII(dtb)2] (M = Pd,
Pt),28 which have structural character similar to that of dapy,
i.e., the presence of an imino nitrogen atom and two adjacent
amine groups, are expected to act as bridgeable CDBBs, i.e.,
metalloligands.29 To the best of our knowledge, however, there
is no example that exhibits such a bridging mode as M−dtb−
M′ (M′ meaning other metal ions). This is because of that the
imino nitrogen atom of [MII(dtb)2] complexes does not have a
strong coordination ability.
consequently competing for coordination at the axial sites of
[Ru2]; hence the use of such polar solvents should generally be
avoided in assembly reactions with [Ru2II,II] complexes where
possible, as done in previous studies.1,12−21,27 Nevertheless, the
1-D chain compounds 5 and 6 were selectively synthesized in
high yield in a THF-containing medium from the reaction of
[Ru2(o-FPhCO2)4(THF)2] and [MII(dtb)2] in a 1:1 molar
ratio. This may be due to the support of hydrogen bonding of
NH2···Oeq, which must strengthen the N−Ru bond, as is
evident in the discrete compounds 1−4 (vide infra).
IR spectra of compounds 5 and 6 show two characteristic
N−H stretching peaks in the range 3180−3370 cm−1, which are
blue-shifted compared to those in [MII(dtb)2] (3150 and 3310
cm−1 for M = Pd and Pt, respectively), whereas the peak
positions of CO stretching vibrations are almost unchanged,
proving that the charge distribution remains the same without
significant charge transfer between [Ru2] and the [MII(dtb)2]
unit. Powder reflection spectra of 5 and 6 could be interpreted
by a simple summation of respective components (Figure S3).
This can be realized by a relationship between the HOMO level
of [Ru2(o-FPhCO2)4(THF)2] and LUMO level of [MII(dtb)2]
(vide infra).
For assembly reactions with [MII(dtb)2] (M = Pd, Pt), polar
solvents such as THF, DMF, and MeCN are used because the
[MII(dtb)2] complexes are only soluble in polar solvents. Such
polar solvents, however, simultaneously act as ligands,
Compounds 5 and 6 are isostructural in the triclinic P1 space
̅
group. Crystallographic parameters, selected bond lengths and
angles, and hydrogen bond distances for 5 and 6 are
summarized in Tables S4, S5, and S6, respectively. The formula
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unit is composed of one [Ru2] unit and one [M(dtb)2] unit,
each of which has an inversion center on the midpoint of the
Ru−Ru bond and Pd (5) or Pt (6) center, respectively (Z = 1,
Figure 3 for 5 and Figure S4 for 6). The [M(dtb)2] unit
Ru−N angle is almost linear, but the overall feature of the chain
is a zigzag with a significant Ru−N···M angle of 145.68(11)° for
5 and 145.74(14)° for 6. The Ru−Ru distance for 5 and 6 is
2.2835(11) and 2.2894(10) Å, respectively, and the average
Ru−Oeq (Oeq = equatorial oxygen atoms) bond distance is
II,II
2.064 and 2.063 Å, respectively, consistent with the [Ru2
]
oxidation state.9 The average M−S distance is 2.2913 Å for 5
with M = Pd and 2.2926 Å for 6 with M = Pt, similar to those in
the original [MII(dtb)2] complexes (2.304 Å for M = Pd and
2.295 Å for M = Pt).28 The [MII(dtb)2] unit is not planar
because of the presence of large bending and twisting at the
bonds of C−S−M, albeit almost flat for the coordination plane
around Pd and Pt (i.e., MS4 plane). As the C15−N1−C16
plane was taken to evaluate the value of ψ, the coordinating dtb
ligand does not bisect the paddlewheel arrangement equally,
although it nearly does, with ψ = 35.1° and 35.4° for 5 and 6,
respectively, versus the O1−O2−O1*−O2* planes (symmetry
operations (*) −x + 1, −y + 1, −z + 1). This results in the
hydrogen bond formation between one amino group and two
oxygen atoms of different carboxylate bridges with N···O
distances in the ranges 2.86−3.31 and 2.84−3.32 Å for 5 and 6,
respectively (Figures 3 and S4). The amino group of dtb forms
hydrogen bonds with fluorine of the o-FPh moiety with N···F
distances in the ranges 3.11−3.94 and 3.09−3.98 Å for 5 and 6,
respectively, where the relatively long distances are found for
the minor-occupied F atoms in the positional disordering
fluorine atoms. The average dihedral angle θav, defined by the
plane of the benzoate phenyl group and the plane composed of
a carboxyl group and a diruthenium unit, is 8.6° and 8.8° for 5
and 6, respectively. These values are very low, as observed in 1
and 4, even though they apply to the o-F benzoate moiety.
The chains run along the ⟨011⟩ direction, where the chains
are arranged in an in-phase manner along the ⟨010⟩ direction
(the interchain distance corresponds to the length of the b axis)
and an antiphase manner along the ⟨01−1⟩ direction
([Ru2]···M = 9.66 Å for 5 and 6). The intermolecular π−π
interaction, through contacts between phenyl groups of
benzoate moieties, exists along the ⟨100⟩ direction (distance
between π planes = 3.42 and 3.40 Å for 5 and 6, respectively).
Four THF molecules locate between chains as crystallization
solvents, which strongly interact with NH2 groups of a dtb
ligand by hydrogen bonding. The THF molecules are finally
released above 340 K (in thermal gravimetric analyses) (Figure
S6), followed by a structural decomposition, indicating that the
presence of crystallization solvents with hydrogen bonding
plays an important role in stabilizing the structures of 5 and 6.
Consideration of Electronic Structures of 5 and 6. The
Figure 3. Thermal ellipsoid plot (50% probability) showing the
formula unit for 5, where atoms of N, O, C, F, S, Pd, and Ru are
represented in colors of blue, red, gray, green, yellow, brown, and
purple, respectively, dashed bonds for the o-F atom represent
positional disorder, and blue dotted lines represent hydrogen bonds.
Hydrogen atoms and crystallization solvents were omitted for clarity.
coordinates to the axial positions of the [Ru2] unit via the
imino nitrogen atom of the dtb ligand with a Ru−N bond
length of 2.406(5) and 2.443(3) Å for 5 and 6, respectively,
forming a 1-D chain motif with a [−{Ru2}−{M(dtb)2}−]
repeating unit (Figure 4 for 5 and Figure S5 for 6). The Ru−
electronic state of both [Ru2(o-FPhCO2)4] and [M(dtb)2]
II,II
units remains unchanged in 5 and 6, even though the [Ru2
]
unit often functions as an electron donor.2,14−21 It therefore
warrants a mention with regards to the relationship of
electronic structures between [Ru2(o-FPhCO2)4] and [M-
(dtb)2] units. We have reported that such charge transfers
can be well predicted by evaluating the gap between the
HOMO level of donor and the LUMO level of acceptor,2 and
DFT calculation for respective original units (e.g., [Ru2(o-
FPhCO2)4(THF)2]) is useful for obtaining such HOMO/
LUMO energy values. In this context, we obtained the frontier
orbital energy of [MII(dtb)2] by DFT calculation. A list of the
energy levels of HOMO and LUMO for [Ru2(o-
FPhCO2)4(THF)2]9 and [MII(dtb)2] with M = Pd and Pt
reported previously28 is given in Table 1. The LUMO energies
of the [MII(dtb)2] unit are −2.190 and −1.781 eV for M = Pd
Figure 4. Packing diagram of 5 projected along the [011] direction (a)
and the a axis (b), where atoms of N, O, C, F, S, Pd, and Ru are
represented in colors of blue, red, gray, green, yellow, brown, and
purple, respectively, and the THF molecules as crystallization solvents
are colored in cyan. Hydrogen atoms were omitted for clarity.
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Found: C, 46.24; H, 3.05; N, 9.32. IR(KBr): ν(CO), 1550, 1402
cm−1; ν(N−H), 3376 cm−1. Compound 2 was synthesized by the same
way as for 1, where [Ru2(m-FPhCO2)4(THF)2] (30 mg, 33 mmol)
and 2,6-diaminopyridine (14 mg, 130 mmol) were solved in 5 mL
THF. Yield 30 mg, 81%. Elemental analysis (%) calcd for
C46H46N6F4O10Ru2: C, 49.28; H, 4.14; N, 7.49. Found: C, 49.82; H,
4.58; N, 6.92. IR(KBr): ν(CO), 1553, 1397 cm−1; ν(N−H), 3476,
3388 cm−1.
Table 1. Estimated Energy Levels (eV) of the HOMO and
LUMO of the Related Compounds
compd
HOMO
LUMO
[Ru2II,II(o-FPhCO2)4(THF)2]
[PdII(dtb)2]
[PtII(dtb)2]
−4.184
−5.854
−5.498
−1.724
−2.159
−1.781
Synthesis of 3. A solid of 2,6-diaminopyridine (24 mg, 224 mmol)
was added to a solution of [Ru2(p-FPhCO2)4(THF)2] (50 mg, 56
mmol) in 15 mL of CH2Cl2. After being stirred for 1 h at room
temperature, the pale-brown solution was filtered and separated into 1
mL portions (bottom layer) in narrow diameter glass tubes (ϕ: 8
mm). n-Hexane (15 mL) was carefully placed in 1 mL portions on the
bottom layer, and the layer was allowed to stand for one week to form
3 as pale-brown block-type crystals. Yield: 16 mg, 29%. Elemental
analysis (%) calcd for C39H32N6Cl2F4O8Ru2: C, 43.11; H, 3.03; N,
7.91. Found: C, 42.99; H, 3.07; N, 8.53. IR(KBr): ν(CO), 1549,
1403 cm−1; ν (N−H), 3479, 3379 cm−1.
Synthesis of 4. A solid of 7-azaindole (22 mg, 200 mmol) was
added to a solution of [Ru2(o-FPhCO2)4(THF)2] (50 mg, 50 mmol)
in 10 mL of CH2Cl2. After being stirred for 1 h at room temperature,
the pale-brown solution was filtered and separated into 1 mL portions
(bottom layer) in narrow diameter glass tubes (ϕ: 8 mm). n-Hexane
(15 mL) was carefully placed in 1 mL portions on the bottom layer,
and the layer was allowed to stand for one week to form 4 as pale-
brown block-type crystals. Yield: 36 mg, 65%. Elemental analysis (%)
calcd for C42H26N4F4O8Ru2: C, 50.80; H, 2.64; N, 5.64. Found: C,
50.34; H, 3.04; N, 5.39. IR(KBr): ν(CO), 1551, 1401 cm−1; ν(N−
H), 3333 cm−1.
Syntheses of 5 and 6. Compound 5 was synthesized by the
following method: a 30 mL THF solution containing a solid of
[PdII(dtb)2] (21 mg, 50 mmol) was refluxed for 2 h to dissolve the
solid completely, and, then, cooled at room temperature. A solid of
[Ru2(o-FPhCO2)4(THF)2] (50 mg, 50 mmol) was added to this
solution and stirred for 1 h at room temperature. After being filtered,
the brown solution was placed in a Schlenk tube (bottom layer), which
was layered with 60 mL of n-hexane (top layer). The layer was left
undisturbed for 3 days to form red block-type crystals of 5. Yield: 28
mg, 41%. Elemental analysis (%) calcd for C40H40N6F4O10PdRu2S4
(5·2THF): C, 37.60; H, 3.16; N, 6.58. Found: C, 37.84; H, 3.80; N,
6.59. IR(KBr): ν(CO), 1549, 1402 cm−1; ν(N−H) 3366, 3187
cm−1. Compound 6 was synthesized by the same method, where
[PtII(dtb)2] (24 mg, 50 mmol) was used instead of [PdII(dtb)2]. Yield:
36 mg, 53%. Elemental analysis (%) calcd for C40H40N6F4O10PtRu2S4
(6·2THF): C, 35.16; H, 2.95; N, 6.15. Found: C, 35.49; H, 3.04; N,
6.78. IR(KBr): ν(CO), 1549, 1403 cm−1; ν(N−H) 3331, 3188
cm−1.
and Pt, respectively, which are much higher than the HOMO
energy at −4.184 eV calculated for [Ru2II,II(o-FPhCO2)-
(THF)2], proving the isolated feature of [Ru2II,II(o-FPhCO2)]
and [MII(dtb)2] from a viewpoint of charge. This result is in full
agreement with the reflection spectra and the magnetic
behavior of 5 and 6 (see Supporting Information).
CONCLUSION
■
Hydrogen-bond-assisted paddlewheel-type [Ru2II,II] assemblies
axially capped by pyridine derivatives for discrete complexes
(1−4) and with planar [MII(dtb)2] units for 1-D alternating
chains (5 and 6), which have seldom been reported to date,
were synthesized and structurally characterized. In all cases, the
formation of hydrogen bonds between the oxygen atoms of
carboxylate and amino groups of the axially coordinating
ligand/metalloligand was found, and furthermore, hydrogen
bonding as NH2···F was observed when fluorine is located at
the ortho position of the benzoate ligand. These hydrogen-
bonding forms should strengthen the σ-type coordination bond
of Ru−N, i.e., support the complexation of the axial site of
[Ru2II,II]. The Ru−N bond length in the present complexes is
relatively short compared with similar [Ru2II,II] complexes
reported previously.
Compounds 5 and 6 were selectively synthesized even in
THF, which should compete with the building block [M(dtb)2]
for the coordinating sites. Unfortunately, no significant
interaction between [Ru2] and [M(dtb)2] units or between
[Ru2] units via [M(dtb)2] as charge transfers and magnetic
correlations was observed in 5 and 6 because of the presence of
a large energy gap between HOMO of [Ru2] and LUMO of
[M(dtb)2]. Nonetheless, such a dual bonding assembly,
supported by hydrogen bonding, is quite an efficient strategy
for the design of multidimensional network compounds, such
as metal−organic frameworks and porous coordination
polymer compounds and functional metal-complex assemblies,
with paddlewheel-type dimetal building units.
Physical Measurements. Infrared spectra were measured on a
KBr disk using HORIBA FT-IR 720 (for 1−4) and JASCO FT/IR−
4200 (for 5 and 6) spectrophotometers. Powder reflection spectra
were measured on the basis of a reference of BaSO4 using a Shimadzu
UV−3150 spectrophotometer with an attachment for reflection
spectra. TG-DTA data were conducted on a Shimadzu DTG−60H
instrument with a temperature sweep rate of 5 °C/min at a N2
atmosphere. Magnetic susceptibility measurements were performed
using a Quantum Design SQUID magnetometer (MPMS−XL−7T).
Direct current measurements were conducted over the temperature
range 1.8−300 K and at 0.5 or 0.1 T. The measurements were
performed on finely ground polycrystalline samples restrained by
Nujol. Diamagnetic contributions were corrected for the sample
holder, Nujol, and for the sample using Pascal’s constants.30
Computational Details. Theoretical ab initio calculations of 1−4,
and [M(dtb)2] with M = Pt and Pd were performed using the density
functional theory (DFT) formalism, as implemented in the Gaussian
09 software,31 with the Beck’s three parameter hybrid functional with
the correlation functional of Lee, Yang, and Parr (B3LYP).32
Unrestricted open-shell calculations were performed in the calculations
of the molecule containing [Ru2] units. An effective core potential
basis set LanL2TZ with polarization (LanL2TZ(f))33 for Ru, Pt and
EXPERIMENTAL SECTION
■
General Procedures. All synthetic procedures were performed
under an inert atmosphere using standard Schlenk-line techniques and
a commercial glovebox. All chemicals were purchased from
commercial sources and were of reagent grade quality. Solvents were
dried using common drying agents and distilled under an ultrapure
nitrogen gas before use. The starting materials of [Ru2II,II] units,
[Ru2(x-FPhCO2)4(THF)2] (x- = o-, m-, p-), were prepared according
to the previously reported method.9 The [M(dtb)2] complexes with M
= Pd, Pt were synthesized according to the literature procedure.28
Syntheses of 1 and 2. Compound 1 was synthesized by the
following procedure: a solid of 2,6-diaminopyridine (24 mg, 224
mmol) was added to a solution of [Ru2(o-FPhCO2)4(THF)2] (50 mg,
56 mmol) in 10 mL of THF. After being stirred for 1 h at room
temperature, the pale-brown solution was filtered and separated into 1
mL portions (bottom layer) in narrow diameter glass tubes (ϕ: 8
mm). n-Hexane (10 mL) was carefully placed in 1 mL portions on the
bottom layer, and the layer was allowed to stand for one week to form
1 as pale-brown block-type crystals. Yield: 33 mg, 89%. Elemental
analysis (%) calcd for C38H30N6F4O8Ru2: C, 46.72; H, 3.10; N, 8.60.
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Pd atoms and 6-31G basis sets with polarization and diffuse functions
(6-31+G(d))34 for C, H, F, N, O, and S atoms were adopted. In the
calculations, spin polarization with SZ = 1 (triplet spin multiplicity) for
[Ru2] units was used. The atomic coordinates determined by using X-
ray crystallography with those for [M(dtb)2] (M = Pt, Pd) being taken
from ref 28 and [Ru2(x-FPhCO2)4(THF)2] (x- = o-, m-, p-) being
taken from ref 9 were used in the calculations of those units.
X-ray Crystallographic Study. Single crystals of 1−6 were
mounted on a thin Kapton film with Nujol and were cooled to 93(1)
or 109(1) K by a stream of cooled N2 gas. Data collections were
carried out on a Rigaku CCD diffractometer (Rigaku Saturn+VariMax
or Mercury) with graphite-monochromated Mo Kα radiation (λ =
0.710 70 Å). The structures were solved using direct methods
(SIR200835) and expanded using Fourier techniques. The full-matrix
least-squares refinement on F2 was performed on the basis of observed
reflections and variable parameters, and the refinement cycle was
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2
Σ∥Fo| − |Fc∥/Σ|Fo| (I > 2.00σ(I) and all data) and wR2 = [Σ(w(Fo
−
2
Fc2)2)/Σw(Fo )2]1/2 (all data). A Sheldrick weighting scheme was used.
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graphic software package,40 except for refinement, which was
performed using SHELXL-97.41 The crystallographic data for 1−4
and 5 and 6 were summarized in Tables S1 and S4, respectively. The
CIF data have been deposited at the Cambridge Data Centre as
supplementary publication nos. CCDC−935883, 935879, 935884,
935882, 935880, and 935881 for 1−6, respectively. Copies of the data
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deposit@ccdc.cam.ac.uk).
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ASSOCIATED CONTENT
* Supporting Information
■
S
X-ray crystallographic data in CIF format for 1−6, figures for
powder reflection spectra for 1−6, structures for one unit in 1
and 4 and for 6, TGA profiles for 5 and 6, magnetic properties
of 1−6, and tables associated with crystallography and
structural details and magnetic data for 1−6. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: miyasaka@imr.tohoku.ac.jp. Phone: +81-22-215-2030.
Fax: +81-22-215-2031.
■
(23) Kitamura, H.; Ozawa, T.; Jitsukawa, K.; Masuda, H.; Aoyama,
Y.; Einaga, H. Inorg. Chem. 2000, 39, 3294.
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Chem. Lett. 1999, 1225.
Notes
(25) Miyasaka, H.; Cler
R. J. Chem. Soc., Dalton Trans. 2001, 858.
́ ́
ac, R.; Campos-Fernandez, C. S.; Dunbar, K.
The authors declare no competing financial interest.
(26) Kosaka, W.; Ishii, Y.; Miyasaka, H. Polyhedron 2013, 52, 1213.
(27) Kosaka, W.; Yamagishi, K.; Yoshida, H.; Matsuda, R.; Kitagawa,
S.; Takata, M.; Miyasaka, H. Chem. Commun. 2013, 49, 1594.
(28) Girling, R. L.; Amma, E. L. Acta Crystallogr. 1976, B32, 2903.
(29) Noro, S.; Miyasaka, H.; Kitagawa, S.; Wada, T.; Okubo, T.;
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P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
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ACKNOWLEDGMENTS
■
This work was supported by a Grant-in-Aid for Scientific
Research (No. 21350032; 24245012) and on Innovative Areas
(“Coordination Programming” Area 2107, No 24108714) from
the Ministry of Education, Culture, Sports, Science, and
Technology, Japan, The Sumitomo Foundation, and The
Asahi Glass Foundation.
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