The effect of chlorine and fluorine substitutions on tuning the ionization potential of benzoate-bridged paddlewheel diruthenium(II, II) complexes

Article abstract of DOI:10.1039/c5dt00505a

A series of paddlewheel diruthenium(II, II) complexes with various chlorine-substituted benzoate ligands (Cl-series) was synthesized as tetrahydrofuran (THF) adducts [Ru₂(Cl_xPhCO₂)₄(THF)₂]; where Cl_xPhCO₂^- = o-chlorobenzoate, o-Cl; m-chlorobenzoate, m-Cl; p-chlorobenzoate, p-Cl; 2,3-dichlorobenzoate, 2,3-Cl₂; 2,4-dichlorobenzoate, 2,4-Cl₂; 2,5-dichlorobenzoate, 2,5-Cl₂; 2,6-dichlorobenzoate, 2,6-Cl₂; 3,4-dichlorobenzoate, 3,4-Cl₂; 3,5-dichlorobenzoate, 3,5-Cl₂; 2,3,4-trichlorobenzoate, 2,3,4-Cl₃; 2,3,5-trichlorobenzoate, 2,3,5-Cl₃; 2,4,5-trichlorobenzoate, 2,4,5-Cl₃; 3,4,5-trichlorobenzoate, 3,4,5-Cl₃; 2,3,4,5-tetrachlorobenzoate, 2,3,4,5-Cl₄. This Cl-series and the previously synthesized F-series together with four new fluorine-substituted derivatives, [Ru₂(F_xPhCO₂)₄(THF)₂] (where F_xPhCO₂^- = 2,3-difluorobenzoate, 2,3-F₂; 2,4-difluorobenzoate, 2,4-F₂; 2,5-difluorobenzoate, 2,5-F₂; 2,3,5-trifluorobenzoate, 2,3,5-F₃), were experimentally characterized with respect to solid-state structure, magnetic properties and electrochemistry. By tuning the substituents of the benzoate ligands using chlorine or fluorine atoms, the redox potential (E_1/2) for [Ru₂^II,II]/[Ru₂^II,III]⁺ varied over a wide range of potentials from -40 mV to 360 mV (vs. Ag/Ag⁺ in THF). This was dependent on (i) the number of ortho-substituents, i.e. non-, mono- and di-o-substituted groups, with quasi-Hammett parameters for ortho-Cl and -F substitutions (σ_o = -0.272 and -0.217, respectively) and (ii) the general Hammett constants, σ_m and σ_p, for each group. The HOMO energy level calculated on the basis of the atomic coordinates of the solid-state structure was strongly affected by Cl- and F-substitutions as well as the redox potential in solution, which emphasizes the steric contribution of ortho-substituents in the energy level giving a deviation of E_HOMO < 0.3 eV and <0.55 eV for the Cl- and F-series, respectively.

Full text of DOI:10.1039/c5dt00505a

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Page 1 of 34
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DOI: 10.1039/C5DT00505A
Submitted to Dalton Trans. as an article, January 14, 2015
<<Revised version on DT-ART-01-2015-000166>>
The effect of chlorine and fluorine substitutions on tuning the ionization
potential of benzoateꢀbridged paddlewheel diruthenium(II, II) complexes†
a,b
b
a,b
Wataru Kosaka, Masahisa Itoh and Hitoshi Miyasaka,*
a
Institute for Materials Research, Tohoku University, 2ꢀ1ꢀ1 Katahira, Aobaꢀku, Sendai 980ꢀ8577,
Japan. Eꢀmail: miyasaka@imr.tohoku.ac.jp
b
Department of Chemistry, Graduate School of Science, Tohoku University, 6ꢀ3 AramakiꢀAzaꢀAoba,
Aobaꢀku, Sendai 980ꢀ8578, Japan
†
Electronic supplementary information (ESI) available: Syntheses of several benzoate ligands,
crystallographic data, ORTEP drawings of several compounds, magnetic data, a total plot of E1/2 vs.
Σ(xσ + yσ + zσ ) for the Clꢀ, Fꢀ and Meꢀseries reported, plots of HOMO level vs. E1/2 for the
Clꢀseries and the Fꢀseries representing the average dihedral angle. CCDC reference numbers
041309–1041325. For ESI and crystallographic data in CIF or other electronic formats, see DOI:
XXXXXXXX.
m
p
o
1
1

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Page 2 of 34
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DOI: 10.1039/C5DT00505A
Abstract
A series of paddlewheel diruthenium(II, II) complexes with various chlorineꢀsubstituted benzoate
2 x 2 4 2
ligands (Clꢀseries) was synthesized as tetrahydrofuran (THF) adducts [Ru (Cl PhCO ) (THF) ];
−
2
where Cl
x
PhCO
= oꢀchlorobenzoate, oꢀCl; mꢀchlorobenzoate, mꢀCl; pꢀchlorobenzoate, pꢀCl;
2
2
2
2
,3ꢀdichlorobenzoate, 2,3ꢀCl
,6ꢀdichlorobenzoate, 2,6ꢀCl
2
; 2,4ꢀdichlorobenzoate, 2,4ꢀCl
; 3,4ꢀdichlorobenzoate, 3,4ꢀCl
2
2
; 2,5ꢀdichlorobenzoate, 2,5ꢀCl
; 3,5ꢀdichlorobenzoate, 3,5ꢀCl
2
;
;
2
2
,3,4ꢀtrichlorobenzoate, 2,3,4ꢀCl
3
; 2,3,5ꢀtrichlorobenzoate, 2,3,5ꢀCl
3
; 2,4,5ꢀtrichlorobenzoate,
,4,5ꢀCl ; 3,4,5ꢀtrichlorobenzoate, 3,4,5ꢀCl
3
3
; 2,3,4,5ꢀtetrachlorobenzoate, 2,3,4,5ꢀCl
4
. This Clꢀseries
and the previously synthesized Fꢀseries together with four new fluorineꢀsubstituted derivatives,
−
[
Ru
2
(F
x
PhCO
2
)
4
(THF)
2
] (where F
x
PhCO
2
2
= 2,3ꢀdifluorobenzoate, 2,3ꢀF ; 2,4ꢀdifluorobenzoate,
2
,4ꢀF
2
; 2,5ꢀdifluorobenzoate, 2,5ꢀF
2
; 2,3,5ꢀtrifluorobenzoate, 2,3,5ꢀF
3
), were experimentally
characterized with respect to solidꢀstate structure, magnetic properties and electrochemistry. By
tuning the substituents of the benzoate ligands using chlorine or fluorine atoms, the redox potential
II,II
II,III +
(E
1/2) for [Ru
2
]/[Ru
2
] varied over a wide range of potentials from −40 mV to 360 mV (vs.
+
Ag/Ag in THF). This was dependent on (i) the number of orthoꢀsubstituents, i.e. nonꢀ, monoꢀ and
diꢀoꢀsubstituted groups, with quasiꢀHammett parameters for orthoꢀCl and ꢀF substitutions (σ
o
=
−
0.272 and–0.217, respectively) and (ii) the general Hammett constants, σ and σ , for each group.
m
p
The HOMO energy level calculated on the basis of the atomic coordinates of the solidꢀstate structure
was strongly affected by Clꢀ and Fꢀsubstitutions as well as the redox potential in solution, which
emphasizes the steric contribution of orthoꢀsubstituents in the energy level giving a deviation of
EHOMO < 0.3 eV and < 0.55 eV for the Clꢀ and Fꢀseries, respectively.
2

Page 3 of 34
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DOI: 10.1039/C5DT00505A
Introduction
Chargeꢀtransfer complexes composed of electron donor (D) and acceptor (A) units have attracted
1
much attention as functional molecular materials that exhibit magnetic longꢀrange ordering, high
2
3
4
conductivity, ferroelectric properties and synergistic functionalities. When choosing D/A sets, the
most important issue to consider is the control of the chargeꢀtransfer (D A) followed by the
0
0
δ+ δ−
occurrence of electron transfer from the neutral state (D A ) to the ionic state (D A ), which is
largely affected by the ionization potential (I ) of D and the electron affinity (E ) of A.
Our groups have chosen a family of carboxylateꢀbridged paddlewheel diruthenium(II, II)
D
A
II,II
II,II
2
complexes, [Ru
2
(RCO
2
4
) ] (abbreviated as [Ru
]), as D for constructing covalently assembled
D
m
A
n
frameworks
with
7,7,8,8ꢀtetracyanoꢀpꢀquinodimethane
(TCNQ)
and
5
N,N’ꢀdicyanoquinodiimine (DCNQI) derivatives. We have chosen these complexes on the basis of
II,II
the following: i) [Ru
2
] itself also acts as a coordinating acceptor, while TCNQ and DCNQI
II,II
derivatives act as coordinating donors, which are needed to construct the framework; ii) [Ru
2
] and
II,III +
2
its oxidation species [Ru
] are paramagnetic, with S = 1 and S = 3/2, respectively, i.e. both species
are useful as magnetic building blocks; iii) the I
D
of these complexes is accurately tuneable by
II,II
modifying the carboxylateꢀbridging groups; and iv) the HOMO of the [Ru
2
] family is located at an
energy level close to the LUMO of TCNQ and DCNQI, with an adequate energy gap between the
6
HOMO of D and the LUMO of A. Focusing on these benefits, DAꢀ and D
2
Aꢀtype compounds of
[
2
Ru ]/TCNQ, DCNQI in multiꢀdimensional frameworks have been synthesized by tuning the
intraꢀframework charge transfer/electron transfer in order to design magnetic and conducting
5
,6
materials.
The ionization potential is a key factor for the rational design of charge transfer/electron transfer
frameworks, as well as tuning of the E
A
of the acceptor units (i.e. TCNQ and DCNQI derivatives)
3

Dalton Transactions
Page 4 of 34
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DOI: 10.1039/C5DT00505A
D
used. In our previous work, we demonstrated that the donor character (i.e. I ) of fluorineꢀsubstituted
II,II
II,II
benzoateꢀbridged [Ru
2
] complexes, [Ru
2
x 2 4 2
(F PhCO ) (THF) ], is systematically affected
depending on the position and number of substituted fluorine groups. This was analysed by
electrochemistry, HOMO levels calculated on the basis of the atomic coordinates of the crystal
7
II,II
structure and the Hammett law. Here, we present a series of [Ru
2
] complexes with various
−
chlorineꢀsubstituted benzoate ligands, [Ru (Cl PhCO (THF)
2
x
2
)
4
2
], where Cl
x
PhCO
2
=
oꢀchlorobenzoate, oꢀCl; mꢀchlorobenzoate, mꢀCl; pꢀchlorobenzoate, pꢀCl; 2,3ꢀdichlorobenzoate,
2
3
2
3
,3ꢀCl
,4ꢀdichlorobenzoate, 3,4ꢀCl
,3,5ꢀtrichlorobenzoate, 2,3,5ꢀCl
,4,5ꢀCl ; 2,3,4,5ꢀtetrachlorobenzoate, 2,3,4,5ꢀCl
2
; 2,4ꢀdichlorobenzoate, 2,4ꢀCl
; 3,5ꢀdichlorobenzoate, 3,5ꢀCl
; 2,4,5ꢀtrichlorobenzoate, 2,4,5ꢀCl
; THF = tetrahydrofuran (Chart 1). The chlorine
2
; 2,5ꢀdichlorobenzoate, 2,5ꢀCl
2
; 2,6ꢀdichlorobenzoate, 2,6ꢀCl
2
;
2
2
; 2,3,4ꢀtrichlorobenzoate, 2,3,4ꢀCl
3
;
3
3
; 3,4,5ꢀtrichlorobenzoate,
3
4
atom is known as a substituent with an electronꢀwithdrawing effect which is similar to the fluorine
atom but has slightly different properties owing to its higher electron affinity and larger atomic radius.
We also added new fluorineꢀsubstituted derivatives, [Ru
2
(F
x
PhCO
2
)
4
(THF)
2
], in order to increase the
−
number of compounds in the series for comparison with the Clꢀseries, where F
x
PhCO
2
=
2
,3ꢀdifluorobenzoate, 2,3ꢀF
2
;
2,4ꢀdifluorobenzoate, 2,4ꢀF
2
;
2
2,5ꢀdifluorobenzoate, 2,5ꢀF ;
2
,3,5ꢀtrifluorobenzoate, 2,3,5ꢀF
3
(Chart 1). All compounds were characterized by singleꢀcrystal
Xꢀray analyses, magnetic properties and electrochemical properties measured in THF. Finally, the
II,II
relationship between the electronꢀdonating ability of [Ru
such as pK
DFT), was investigated in comparison with the Fꢀseries (Chart 1).
2
] units and their chemical properties,
a
, redox potential and the HOMO energy level calculated by density functional theory
(
<<Insert Chart 1 here>>
4

Page 5 of 34
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DOI: 10.1039/C5DT00505A
Experimental Section
General Procedures and Materials
All synthetic procedures were performed under an inert atmosphere using standard Schlenk line
7
techniques and a commercial glovebox. All chemicals were reagent grade purchased from
commercial sources. Solvents were dried using common drying agents and distilled under nitrogen
II,III
8
II,III
2
9
before use. [Ru
2
(CH
3
CO
2
)
4
(THF)
2
4
]BF ,
[Ru
3 2 4
(CH CO ) Cl] and several benzoic acids
1
0
(RꢀPhCOOH, R = 2,3,4ꢀCl
3
, 2,3,5ꢀCl
3
, 2,4,5ꢀCl
3
and 3,4,5ꢀCl
3
) were prepared by methods noted in
7
the electronic supporting information and modified from a general procedure previously reported.
II,II
2
II,II
Synthesis of [Ru
(oꢀClPhCO
2
)
4
(THF)
2
] (oꢀCl), [Ru
2
2 4 2
(mꢀClPhCO ) (THF) ] (mꢀCl),
II,II
II,II
[Ru
[Ru
[Ru
[Ru
[Ru
[Ru
2
2
2
2
2
2
(2,3ꢀCl
(2,5ꢀCl
(3,4ꢀCl
2
2
2
PhCO
PhCO
PhCO
2
2
2
)
)
)
4
4
4
(THF)
(THF)
(THF)
2
2
2
]
]
]
(2,3ꢀCl
(2,5ꢀCl
(3,4ꢀCl
2
),
),
),
[Ru
[Ru
[Ru
2
2
2
(2,4ꢀCl
(2,6ꢀCl
(3,5ꢀCl
2
2
2
PhCO
PhCO
PhCO
2
2
2
)
)
)
4
4
4
(THF)
(THF)
(THF)
2
2
2
]
]
]
(2,4ꢀCl
(2,6ꢀCl
(3,5ꢀCl
2
),
2
),
2
),
3
),
2
),
II,II
II,II
II,II
II,II
II,II
II,II
II,II
2
2
II,II
(2,3,4ꢀCl
(2,4,5ꢀCl
3
3
PhCO
2
)
4
4
(THF)
2
2
] (2,3,4ꢀCl
3
), [Ru
2
(2,3,5ꢀCl
3
PhCO
2
)
4
(THF)
2
] (2,3,5ꢀCl
(2,5ꢀF
II,II
PhCO
2
)
(THF)
]
(2,4,5ꢀCl
3
), [Ru
2
(2,5ꢀF
2
PhCO
2
)
4
(THF)
2
]
3 2 4 2 3
(2,3,5ꢀF PhCO ) (THF) ] (2,3,5ꢀF )
1
1
The compounds were synthesized on the basis of a method reported by Furukawa and Kitagawa.
II,III
The procedure for oꢀCl is described as a representative example. [Ru
2
3 2 4 2 4
(CH CO ) (THF) ]BF (335
mg, 0.5 mmol) and oꢀchlorobenzoic acid (313 mg, 2.0 mmol) were refluxed in N,Nꢀdimethylaniline
NDMA, 20 mL) for 12 h. After removing the solvent in vacuo, the brown residue was washed with
(
nꢀhexane (10 mL × 3) and dissolved in a minimum amount of THF. The red solution was filtered,
layered with nꢀhexane and allowed to stand for at least one week, affording oꢀCl as brown crystals.
5

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DOI: 10.1039/C5DT00505A
Yield: 79%. Elemental analysis (%) calculated for C36
H
32
O10Cl
4
Ru
2
: C 44.64, H 3.33. Found: C 44.85,
−
1
H 3.31. IR (KBr): ν(CO
2
) = 1550, 1398 cm . For mꢀCl, yield: 64%. Elemental analysis (%)
Ru : C 44.64, H 3.33. Found: C 44.55, H 3.44. IR (KBr): ν(CO ), 1550,
, yield: 63%. Elemental analysis (%) calculated for C36 Ru : C 39.08,
, yield: 65%.
: C 39.08, H 2.55. Found: C 39.29, H 2.67. IR
, yield: 88%. Elemental analysis (%) calculated for
calculated for C36
H
32
O
10Cl
4
2
2
−1
1
390 cm . For 2,3ꢀCl
H 2.55. Found: C 39.11, H 2.76. IR (KBr): ν(CO
Elemental analysis (%) calculated for C36 Ru
2
2
H
28
O
10Cl
8
2
−1
2
) = 1548, 1407 cm . For 2,4ꢀCl
2
H
28
O
10Cl
8
−
1
(
KBr): ν(CO
2
) = 1544, 1385 cm . For 2,5ꢀCl
Ru : C 39.08, H 2.55. Found: C 39.46, H 2.62. IR (KBr): ν(CO
, yield: 8%. Elemental analysis (%) calculated for C36 Ru : C 39.08, H 2.55. Found:
, yield: 59%. Elemental analysis
: C 39.08, H 2.55. Found: C 39.04, H 2.72. IR (KBr): ν(CO ) =
·0.8Hexane, yield: 45%. Elemental analysis (%) calculated for
2
−1
C
36
H
28
O
10Cl
8
2
2
) = 1549, 1399 cm . For
2
,6ꢀCl
2
H
28
O
10Cl
8
2
−1
C 39.46, H 2.62. IR (KBr): ν(CO
2
) = 1579, 1389 cm . For 3,4ꢀCl
2
(%) calculated for C36
H
28
O
10Cl
8
Ru
2
2
−
1
1
544, 1401 cm . For 3,5ꢀCl
Ru : C 41.69, H 3.36. Found: C 41.77, H 3.46. IR (KBr): ν(CO
24 2
, yield: 12%. Elemental analysis (%) calculated for C36H O10Cl12Ru
2
−
1
C
40.8
H
39.2
O
10Cl
8
2
2
) = 1563, 1397 cm .
: C 34.75, H 1.94.
·0.8Hexane, yield: 36%.
: C 37.32, H 2.70. Found: C 37.16, H 2.87.
3
, yield: 36%. Elemental analysis (%) calculated
For 2,3,4ꢀCl
Found C 34.93, H 2.10. IR (KBr): ν(CO
Elemental analysis (%) calculated for C40.8
3
−1
2
) = 1575, 1395 cm . For 2,3,5ꢀCl
3
H
35.2
O
10Cl
8
Ru
2
−
1
IR (KBr): ν(CO
2
) = 1549, 1394 cm . For 2,4,5ꢀCl
: C 34.75, H 1.94. Found C 34.67, H 2.12. IR (KBr): ν(CO
32 8 2
·0.5THF, yield: 67%. Elemental analysis (%) calculated for C38H F O10.5Ru
−1
for C36
H
24
O
10Cl12Ru
2
2
) = 1576, 1390 cm .
For 2,5ꢀF : C 44.80, H
.17. Found: C 44.79, H 3.34. IR (KBr): ν(CO , yield: 21%.
24 12 2
Elemental analysis (%) calculated for C36H F O10Ru : C 41.31, H 2.31. Found: C 41.46, H 2.41. IR
2
−1
3
2 3
) = 1560, 1383 cm . For 2,3,5ꢀF
−1
(
2
KBr): ν(CO ) = 1576, 1399 cm .
6

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II,II
II,II
2
Synthesis of [Ru
2
(3,4,5ꢀCl
3
PhCO
2
)
4
(THF)
2
] (3,4,5ꢀCl
3
), [Ru
2 2 4 2
(2,3ꢀF PhCO ) (THF) ]
II,II
(2,3ꢀF
2
), [Ru
2
(2,4ꢀF
2
PhCO (THF)
2
)
4
2
] (2,4ꢀF )
2
The compounds were synthesized stepꢀbyꢀstep via a ligand substitution process involving
II,III +
II,II
12
[
Ru
2
] , followed by reduction to the corresponding [Ru
2
] products. As a representative
II,III
example, the procedure for 2,3ꢀF
2
is described. [Ru
2
(CH
3
CO Cl] (200 mg, 0.42 mmol) and
2 4
)
2
2
,3ꢀdifluorobenzoic acid (537 mg, 3.4 mmol) were refluxed in a 1:1 solution of MeOH and H O (20
II,III
mL) for 12 h under aerobic conditions to synthesize [Ru
2
2 2 4
(2,3ꢀF PhCO ) Cl]. The obtained red
precipitate was collected by filtration, washed with water and dried in vacuo. Without further
purification, a THF solution (15 mL) of the crude product and Zn powder (52 mg, 0.80 mmol) was
stirred for 24 h under a nitrogen atmosphere. During this time, most of the solid dissolved. The
reddishꢀcoloured solution was filtered, and the filtrate was layered with nꢀhexane and allowed to
stand for at least one week, affording 2,3ꢀF
calculated for C36 Ru : C 44.36, H 2.90. Found: C 43.96, H 3.01. IR (KBr): ν(CO
, yield: 68%. Elemental analysis (%) calculated for C36 Ru
, yield: 24.6%.
: C 34.75, H 1.94. Found C 34.64, H 2.08. IR
2
as brown crystals. Yield: 88%. Elemental analysis (%)
) = 1560,
: C 44.36,
H
28
O
F
10 8
2
2
−1
1
394 cm . For 2,4ꢀF
H 2.90. Found: C 44.32, H 2.97. IR (KBr): ν(CO
24 2
Elemental analysis (%) calculated for C36H O10Cl12Ru
2
H
28
O
10
F
8
2
−1
2
) = 1560, 1395 cm . For 3,4,5ꢀCl
3
−1
(
KBr): ν(CO
2
) = 1539, 1379 cm .
II,II
Synthesis of [Ru
2
2 4 2
(pꢀClPhCO ) (THF) ] (pꢀCl)
This compound was synthesized by a modified version of that for 3,4,5ꢀCl
3
, 2,3ꢀF
2
and 2,4ꢀF
2
II,III
II,III
because the solid product [Ru
2
(pꢀClPhCO
2
)
4
Cl] has low solubility in THF. [Ru
2
(CH
3
2 4
CO ) Cl]
(570 mg, 1.2 mmol) and pꢀchlorobenzoic acid (1497 mg, 9.6 mmol) were refluxed in a 1:1 solution of
II,III
MeOH and H
2
O (120 mL) for 12 h under aerobic conditions to synthesize [Ru
2
(pꢀClPhCO
2
)
4
Cl].
7

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The obtained red precipitate was collected by filtration, washed with water and dried in vacuo.
Without further purification, a solution of the crude product and Zn powder (288 mg, 4.4 mmol) in
THF (100 mL) was refluxed for 24 h under a nitrogen atmosphere. The reddishꢀcoloured solution
immediately underwent hot filtration. Once the filtrate was cooled to room temperature, it was
layered with nꢀhexane and allowed to stand for several days, affording pꢀCl·THF as brown crystals.
Yield: 78%. Elemental analysis (%) calculated for C40
H
40
4 2
O11Cl Ru : C 46.16, H 3.87. Found: C 46.50,
−1
2
H 3.86. IR (KBr): ν(CO ) = 1547, 1403 cm .
II,II
Synthesis of [Ru
2
(2,3,4,5ꢀCl
4
PhCO
2
)
4
(THF)
2
] (2,3,4,5ꢀCl
4
)
This compound was synthesized by a modified version of that for pꢀCl, where a pure MeOH
II,III
solution was used for the solvent in the ligand substitution process. [Ru
2
3 2 4
(CH CO ) Cl] (479 mg,
1
.0 mmol) and 2,3,4,5ꢀtetrachlorobenzoic acid (1039 mg, 4 mmol) were refluxed in MeOH (50 mL)
II,III
for 48 h under aerobic conditions to synthesize [Ru
2
4 2 4
(2,3,4,5ꢀCl PhCO ) Cl]. The obtained red
precipitate was collected by filtration, washed with water and dried in vacuo. Without further
purification, a solution of the crude product and Zn powder (130 mg, 2.0 mmol) in THF (40 mL) was
refluxed for 24 h under a nitrogen atmosphere. The reddishꢀcoloured solution immediately underwent
hot filtration. The filtrate was then layered with nꢀhexane and allowed to stand for one week,
affording 2,3,4,5ꢀCl
4
·THF as brown crystals. Yield: 84%. Elemental analysis (%) calculated for
−1
C
40
H
28
O
11Cl16Ru
2
: C 33.11, H 1.94. Found: C 33.11, H 2.06. IR (KBr): ν(CO ) = 1582, 1375 cm .
2
General Physical Measurements
Infrared spectra were measured on KBr disks with a Jasco FTꢀIR 620 spectrometer. Magnetic
susceptibility measurements were conducted with a Quantum Design SQUID magnetometer
8

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(MPMSꢀXL) at temperature ranges of 1.8–300 K and applying a magnetic field of 0.1 T, for which
polycrystalline samples embedded in liquid paraffin were used. Experimental data were corrected for
1
3
diamagnetic contributions of the sample holder and liquid paraffin using evaluated Pascal constants.
Cyclic voltammograms (CVs) were recorded in THF with tetraꢀnꢀbutylammonium
hexafluorophosphate (nꢀBu N(PF ), 0.1 M) as the supporting electrolyte under a nitrogen atmosphere
4
6
using an ALS/[H] CH Instruments Electrochemical Analyzer Model 600A. CVs of the solvent with
only the supporting electrolyte were measured first. The desired compounds were then added to this
−
3
solution ([Compound] = 1 × 10 M), and the CVs were acquired using a glassy carbon electrode as
the working electrode, a Pt counter electrode and a Ag/AgNO
3
reference electrode. Finally, CV
+
potentials were adjusted with the ferrocene/ferrocenium couple as an internal standard (Fc/Fc = 213
+
mV (ꢀE = 91 mV) in THF vs. Ag/Ag ).
Crystallography
Crystal data were collected on a Rigaku Saturn CCD area detector with a graphite or multiꢀlayer
mirror monochromated MoꢀKα radiation (λ = 0.71075 Å). The structures were solved by direct
1
4
15
16
17
18
methods (SHELXL 97, SIR2008, SIR92, SIR2002 and SIR2004 ) or by the heavyꢀatom
1
9
20
Patterson method (PATTY)
and expanded using Fourier techniques (DIRDIF99).
All
nonꢀhydrogen atoms were anisotropically refined. Hydrogen atoms were introduced as fixed
2
contributors. Fullꢀmatrix leastꢀsquares refinements on F were based on observed reflections and
variable parameters and converged with unweighted and weighted agreement factors of R1 =
2
2 2
2 2 1/2
Σ||F
o
|−|F
c
||/Σ|F
o
| (I > 2.00
σ
(I)) and wR2 = [Σw(F
o
−F
c
o
) /Σw(F ) ] (all data). All calculations were
2
1
performed using the CrystalStructure crystallographic software package. Details of the crystal
structure analyses are summarized in Table S1.
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Computational Details
Theoretical ab initio calculations were performed using the density functional theory (DFT)
2
2
formalism, as implemented in the Gaussian 09 software, employing Beck’s threeꢀparameter hybrid
2
3
functional with the correlation functional of Lee, Yang and Parr (B3LYP). Unrestricted openꢀshell
calculations were performed for the molecule containing [Ru ] units. The effective core potential
basis function LanL2TZ with polarization (LanL2TZ(f)) for Ru atoms and 6ꢀ31G basis sets with
2
2
4
2
5
polarization and diffuse functions (6ꢀ31+G(d)) for C, H, F, Cl and O atoms were adopted. In the
calculations, spin polarization with S = 1 (triplet spin multiplicity) for [Ru ] units was used. The
Z
2
atomic coordinates determined using Xꢀray crystallography were used in the calculations.
Results and Discussion
Syntheses and Characterization
II,II
Most of the compounds in the Clꢀsubstituted [Ru
2
] series were synthesized by a oneꢀpot reaction
11
using NDMA as both the solvent and the reducing agent. However, several compounds were
synthesized in higher yields through a carboxylate ligand substitution reaction from
II,III
+
12
[
Ru (CH
3
CO
2
)
4
] to the desired benzoic acid derivatives followed by reduction with Zn. Note
II,II
that except for 2,6ꢀCl
Cl
occupied by Cl atoms, although the corresponding [Ru
,4,6ꢀF , 2,3,5,6ꢀF and F
2
, we were not able to synthesize [Ru
2
x 2 4
(Cl PhCO ) ] (x ≥ 2) with
x
ꢀsubstituted benzoate ligands where both orthoꢀpositions (i.e. positions 2 and 6, see Chart 1) are
II,II
2
(F
x
PhCO
2
)
4
] compounds (2,6ꢀF
2 3
, 2,3,6ꢀF ,
7
2
3
4
5
) were successfully obtained. Indeed, even 2,6ꢀCl
2
was obtained in a low
yield (8%). This could be attributed to the difference in the steric effect of the orthoꢀpositions
between Clꢀ and Fꢀsubstituted groups explained as follows: many compounds having substituents at
1
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the orthoꢀpositions result in a large dihedral angle between the phenyl ring of the benzoate group and
the plane composed of the bridging carboxylate and Ru metals ( , Table 1) due to steric hindrance
between the orthoꢀsubstituents and the oxygen atoms of the bridging carboxyl group. Furthermore,
although ≈ 90° reduces the steric hindrance between the orthoꢀsubstituents and the oxygen atoms of
θ
θ
the bridging carboxyl group, another type of steric hindrance is possible, which is caused by the
II,II
2
orthoꢀsubstituents of neighbouring benzoate moieties on a [Ru
] complex. This should be much
more pronounced in the Clꢀseries than in the Fꢀseries because of longer C–Cl bond lengths and the
larger atomic radius of Cl compared to F: this is one of the main reasons for the lower reactivity of
2
,6ꢀCl substituted carboxylate ligands in the Clꢀsubstituted series.
<<Insert Table 1 here>>
Structures
All compounds were structurally characterized by singleꢀcrystal Xꢀray crystallography. Figure1
shows ORTEP drawings of the structures of mꢀCl, 2,3ꢀCl , 2,3,4ꢀCl and 2,3,4,5ꢀCl as representative
2
3
4
examples (other complexes are shown in Fig. S1). The bond lengths around the Ru centres for the
present compounds are summarized in Table 1, together with reported previously relevant
7
compounds. Except for 2,5ꢀCl
2
, 2,6ꢀF
2
, 2,3,5ꢀF
3
and 2,3,4,5ꢀF
4
, the diruthenium units have an
, 2,6ꢀCl , 3,4ꢀCl and F contain
two structurally independent units in a unit cell, which are very similar to each other. Except for
,4ꢀCl and 2,3,4ꢀCl , the Ru–Ru bond length of the complexes is in the range of 2.260–2.280 Å,
similar to those of previously reported [Ru
Ru–Ru bond lengths of 2.291 and 2.336 Å, and 2,3,4ꢀCl
inversion centre at the midpoint of the Ru–Ru bond. pꢀCl, 2,5ꢀCl
2
2
2
5
3
2
3
II,II
2
5,7,26
] compounds;
2
whereas 3,4ꢀCl has slightly longer
3
has a much shorter bond length of 2.189 Å.
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The Ru–Oeq (Oeq = equatorial oxygen atoms) bond length varies in the range of 2.05–2.07 Å, except
for 2,3,4ꢀCl , which shows a slightly longer Ru–Oeq bond length of 2.106 Å. For the [Ru ] units, the
3
2
Ru–Oeq bond distance is a good indicator for evaluating the oxidation state (Table 1). Generally,
II,II
Ru–Oeq bond lengths are found in the range of 2.06–2.08 Å for [Ru
2
] and in the range of 2.02–2.04
II,III + 5,7,26
II,II
Å for [Ru
,3,4ꢀCl
2
] .
Hence, all compounds should have the oxidation state of [Ru
2
], including
2
3
, as proved by its magnetic properties (see below). Bond lengths of ca. 2.25–2.35 Å
II,II
involving axial THF (Ru–Oax) are also characteristic to the [Ru
2
] valence state.
<<Insert Fig. 1 here>>
The dihedral angle (
θ) is critical for the electronic effect that should mainly be given by benzoate
substituents to Ru sites; the electronic conjugation between the phenyl ring and the carboxyl group
becomes most effective when
0. As such, the Hammett law was not discussed for orthoꢀsubstituted aromatics. The values of
for the Clꢀ and Fꢀseries are listed in Table 1. When the number of orthoꢀsubstituents defines the [Ru
units as nonꢀoꢀCl(F), monoꢀoꢀCl(F) and diꢀoꢀCl(F), the average value for each group is 9.1 ± 6.0°,
1.0 ± 16.2° and 57.9 ± 28.1° for nonꢀoꢀCl, monoꢀoꢀCl and diꢀoꢀCl, respectively, and 16.2 ± 6.9°, 18.3
8.7° and 43.1 ± 16.0° for nonꢀoꢀF, monoꢀoꢀF and diꢀoꢀF, respectively. Clearly, Clꢀsubstitutions
result in larger values than the corresponding Fꢀsubstitutions. In addition, the larger standard
θ
= 0, while substituent groups at the orthoꢀpositions mostly result in
θ
≠
θ
2
]
θ
3
±
θ
deviation in the Clꢀseries demonstrates that both intraꢀ and interꢀmolecular steric hindrances could be
critical, most likely due to the unique characteristics found in the Clꢀseries, such as longer C–Cl bond
lengths and the larger atomic radius of Cl.
1
2

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Magnetic Properties
2
The oxidation state of the [Ru ] unit and its electron configuration on the frontier orbitals made by
Ru–Ru bonding can be easily determined by measuring the magnetic properties of the compounds.
The temperature dependence of the dc susceptibility ( ) of all compounds was measured on
polycrystalline samples in the temperature range of 1.8–300 K at 0.1 T (the
shown in Fig. S2). The
χ
χ
and
χT vs T plots are
3
χ
T values at 300 K were determined to be in the range of 0.90–1.04 cm K
−
1
−2
−2
3
mol , which decreased smoothly upon cooling to be in the range of 1.04 × 10 –5.18 × 10 cm K
−
1
mol at 1.8 K. On the other hand, the
χ value at 300 K gradually increased upon decreasing the
temperature to about 100 K and reached a plateau, followed by an increase at temperatures below
approximately 10 K. These features of the
χ and χT vs. T plots are consistent with those for isolated
II,II
[
Ru
2
] complexes with an S = 1 ground state affected by strong zeroꢀfield splitting (ZFS; D ≈
−1
II,II
7, 27 , 28
2
30–320 cm for general [Ru
2
] complexes),
even though the increase of χ at low
II,III +
temperatures is ascribed to paramagnetic impurities such as [Ru
2
] species with S = 3/2. Thus, the
magnetic data were simulated using a Curie paramagnetic model with S = 1, taking into account ZFS,
2
9
temperatureꢀindependent paramagnetism (TIP) and an impurity with S = 3/2 (
ρ).
The
intermolecular interaction (zJ) was considered for many cases of magnetically isolated or weakly
II,II
30
interacting [Ru
2
] complexes in the framework of the meanꢀfield approximation but was not
required in the present case to obtain an adequate fit (zJ ≈ 0 for all complexes). The best fit of
parameters for the compounds are listed in Table S2, where the g value was fixed to 2.00. The
II,II
7,27,28
estimated D value is typical for general [Ru
2
] species.
The magnetic data indicate that all
2
4
2
*2 * 2 *0
complexes have an electron configuration of σ π
2
δ δ π
2
σ on Ru–Ru bond frontier orbital sets
*
*
with degenerated levels of δ and two π orbitals.
1
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Electrochemistry in Solution
2 4 6
CVs of the compounds were measured in N ꢀsaturated THF solutions with nꢀBu N(PF ) as the
+
supporting electrolyte and Ag/Ag as the reference electrode, as shown in Fig. 2. For all compounds,
II,II
II,III +
a reversible oneꢀelectron redox wave assigned to [Ru
2
]/[Ru
2
c a
] was observed, with I /I ≈ 1 and
ꢀ
E
p
≈ 85–171 mV for the Clꢀseries and ꢀE
p
≈ 47–183 mV for the Fꢀseries, including previously
7
reported compounds. The redox potential (E1/2) was observed over a wide range of potentials from
2
2 to 337 mV for the Clꢀseries and ꢀ39 to 360 mV for the F series, showing the substituent effect even
between the Clꢀ and Fꢀseries. The electrochemical data are summarized in Table 2 along with the pK
of the corresponding benzoic acids and the summation of the Hammett constants for mꢀ and pꢀCl(F)
groups, as well as Σ(xσ + yσ ), where σ = 0.373 and σ = 0.227 for the Clꢀseries and σ = 0.337 and
= 0.062 for the Fꢀseries. x and y represent the number of mꢀ and pꢀsubstituents present,
a
m
p
m
p
m
σ
p
3
1
respectively. One of the most pronounced effects on the substituents of benzoate moieties emerges
from their pK values, and this relationship is known as the Hammett law. The pK values of
a
a
substituted benzoate moieties is directly associated with the electronic effect that is propagated from
II,II
the carboxylate group to the Ru centres in the compound. Thus, I
D
for [Ru
2
] units and E1/2 of
II,II
II,III +
[
[
Ru
2
2
]/[Ru
2
] states are functions of the substituent effect of benzoate bridging moieties in
II,II
Ru
]; a stronger electronꢀwithdrawing character of the substituents makes it difficult to release an
II,II
electron from its [Ru
2
D
] unit to derive a higher I and E1/2.
<<Insert Fig. 2 here>>
<<Insert Table 2 here>>
a
Figure 3 shows plots of E1/2 values as a function of pK of the corresponding benzoic acids (i.e.
1
4

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x 2 x 2 a
Cl PhCO H and F PhCO H), where Fig. 3a is the Clꢀseries and Fig. 3b is the Fꢀseries. The E1/2 vs. pK
relationship is very clear in each series, which should be compared as nonꢀoꢀCl(F), monoꢀoꢀCl(F) and
diꢀoꢀCl(F) in order to exclude the effect of steric hindrance on orthoꢀsubstitutions (see the structural
description), confirming a linear relationship for each group (except for diꢀoꢀCl with only one plot of
2
2
,6ꢀCl ). Note that the slopes of the linear relationships in the series are nearly identical. The effect on
orthoꢀsubstitutions, which includes both structural and electronic effects, equally affect each group;
in other words, the slope of the linear relationship in each group can only be decided by the electronic
effect on metaꢀ and paraꢀsubstitutions, as described by the Hammett law (see below). The change in
pK between neighbouring lines (ꢀpKa1 between the lines of nonꢀoꢀCl(F) and monoꢀoꢀCl(F), ꢀpKa2
a
between the lines of monoꢀoꢀCl(F) and diꢀoꢀCl(F)) are almost identical, i.e. ꢀpKa1 ≈ ꢀpKa2, indicating
that the electronic effects on orthoꢀsubstituents are more pronounced than the steric effects in solution,
or the steric effects are proportional to the number of orthoꢀsubstituents in solution.
<<Insert Fig. 3 here>>
E
1/2 was plotted as a function of Σ(xσ
respectively. A linear trend was observed in nonꢀ, monoꢀ and diꢀoꢀsubstitutions on the Clꢀ and
Fꢀseries similar to their pK dependence. If the steric effect was negligible in solution, a change in
Σ(xσ + yσ ) between neighbouring lines should have resulted from the electronic effects on
orthoꢀsubstitutions (σ ). Thus, we evaluated the Hammett constant (σ ) for oꢀCl and oꢀF substitutions
as 0.272 and 0.217, respectively. This was accomplished by minimizing the error for the leastꢀsquares
m
+ yσ
p
), as shown in Figs. 4a and 4b for the Clꢀ and Fꢀseries,
a
m
p
o
o
linear fit in the plot of E1/2 vs. Σ(xσ
m
+ yσ
p
o
+ zσ ), as shown in Figs. 4c and 4d for the Clꢀ and Fꢀseries,
2
respectively (R = 0.976 and 0.866, respectively), where z is 0, 1 and 2 for the nonꢀ, monoꢀ and
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diꢀoꢀpositioned substitutions, respectively. The estimated σ
o
value, which is an intermediate between
the Hammett constants σ
m
p
and σ , is well suited to predict the E1/2 values in the framework of
Hammett analysis.
<<Insert Fig. 4 here>>
Finally, the E1/2 vs. Σ(xσ
m
+ yσ
p
o
+ zσ ) plots for the Clꢀ and Fꢀseries, which were independently
evaluated (Fig. 4c and Fig. 4d, respectively), were gathered into a plot to make a common diagram for
II,II
[
Ru
2
] complexes (Fig. S3). A linear relationship is still found in this case. This implies that the
(Cl) = 0.272 and σ (F) = 0.217, are still effective for predicting the redox
] units where both Clꢀ and Fꢀsubstituents are mixed; however, the slope of the
Hammett constants, σ
o
o
II,II
potential for the [Ru
2
leastꢀsquares fit (see Fig. S3) varied slightly from the respective lines for the independently evaluated
Clꢀ and Fꢀseries (Fig. 4c and 4d). This diagram is also expected to be valid for other substituents at the
metaꢀ and paraꢀpositions if their Hammett constants are available; for example,
+
[
Ru
2
(mꢀMePhCO
2
)
4
(THF)
2
] and [Ru
2
(pꢀMePhCO
)
2 4
(THF)
2
] (–99 and –116 mV in THF vs. Ag/Ag ,
respectively) were also plotted in Fig. S3. The same quantitative procedure discussed above was valid
for various [Ru ] units for which orthoꢀpositions of benzoate ligands were substituted with other
2
groups, which may allow a common Hammett analysis using all substitutions, even at
orthoꢀpositions.
DFT Calculations from Crystal Structures
To determine the energy levels of the molecular orbitals (MOs) of the present compounds,
calculations on the basis of density functional theory (DFT) were performed at the UB3LYP level
1
6

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with basis functions LANL2TZ(f) for Ru and 6ꢀ31+g(d) for other atoms. Note that this calculation
was also performed for the previously reported Fꢀseries complexes for comparison, as the calculation
7
in the previous work was performed with a different basis set. For all compounds except 2,3,4ꢀCl
3
,
II,II
II,III +
the HOMO level that is most likely involved in the [Ru
2
]/[Ru
2
] couple was assigned as the
*
*
δ (β) frontier orbital, whereas that for 2,3,4ꢀCl
3
corresponds to the π (β) frontier orbital. The HOMO
energy level of the complexes is listed in Table 3.
<<Insert Table 3 here>>
Figure 5 shows plots of the HOMO energy levels vs. pK
a
of the corresponding ligands. A linear
trend similar to that found in the plot of E1/2 vs. pK (Fig. 3) was also observed; three groups of nonꢀ,
a
monoꢀ and diꢀoꢀsubstituted complexes were classified following respective quasiꢀlinear relationships
dependent on mꢀ and pꢀsubstituents, where the solid line represents the leastꢀsquares fit for each
group. Thus, the Clꢀ and Fꢀsubstituent effects quantitatively influence the MO energy levels
estimated by DFT calculations on the basis of solidꢀstate structures. The HOMO level should be
directly associated with the I
the relationship between the HOMO level and E1/2 of a complex is essential for understanding the
importance of I in a target complex. In addition, as the MO levels were evaluated on the basis of their
D
of the complexes as well as E1/2 of complexes. Therefore, investigating
D
solidꢀstate structures, this investigation provides valuable information on the deviation of the HOMO
level caused by the steric effect, i.e. it clarifies the difference between nonꢀoꢀsubstituted groups and
oꢀsubstituted groups. Plots of the HOMO energy level vs. E1/2 for the Clꢀ and Fꢀseries are depicted in
Fig. 6, where the solid line is the leastꢀsquares fit on the basis of the nonꢀoꢀsubstituted group of each
series. As the line for the nonꢀoꢀsubstituted group was defined as the standard line that yields the
1
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minimum contribution to the steric effect, most of the compounds having substituents at the
orthoꢀpositions deviate from the standard line, many of which are in the upper region. Note that the
compounds lying far from the standard line tend to have large
the HOMO level obtained by the DFT calculations reflects the steric effect, which is < 0.3 eV for the
Clꢀseries and < 0.55 eV for the Fꢀseries. Complexes with a small are located near the line, although
θ values (Fig. S4). This indicates that
θ
a few exceptions are present (Fig. S4). Thus, the steric effect was identified in the HOMO level,
estimated from a static state of structure, whereas it could be quantitatively treated in the redox
potential as if the steric effect on orthoꢀsubstitutions were negligible. This is most likely due to the
2
fact that the benzoate ligand of the [Ru ] complexes can rotate freely in solution even in
orthoꢀsubstituted ligands. In such a case, the effect on orthoꢀsubstitutions could be regarded as the
electronic effect. Considering the fact that the HOMO levels of the orthoꢀsubstituted groups include
steric effects, the standard line given in Fig. 6 indicates a lower limit of HOMO levels of the [Ru
series in the solidꢀstate.
2
]
<
<Insert Fig. 5 here>>
<Insert Fig. 6 here>>
<
a
Finally, for the sake of comparison between the Clꢀ and Fꢀseries, pK , E1/2 and the HOMO level of
the series were plotted as the Clꢀseries vs. the Fꢀseries, as shown in Fig. 7, where the solid black line
with a slope of 1 is given as the substitution effects of Cl and F, which were considered to be identical.
Fig. 7a clearly indicates that the acidity of the corresponding benzoic acid is stronger in the Clꢀseries
than the Fꢀseries. This trend can also be predicted from the Hammett constants (σ
m
p o
, σ , σ = 0.373,
0
.227, 0.272 and 0.337, 0.062, 0.217 for the Clꢀ and Fꢀseries, respectively) and can be roughly seen
1
8

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for E1/2, as shown in Fig. 7b, where the electron donating ability of the Fꢀseries is somewhat higher
than that of the Clꢀseries in solution. This tendency is similar to the plot of the HOMO level (Fig. 7c),
where most of the points are located in the lower right region, coloured in blue; however, due to the
contribution of the steric effects, this is not certain.
<<Insert Fig. 7 here>>
It should be noted on the substitution effect in the vibrational modes of carboxylate groups of
–
1
benzoate ligands, which can be confirmed in infrared spectra in the range of 1370–1420 cm and
–
1
1
530–1600 cm for the symmetry (
see experimental section for the solid state of compounds); Fig. S5 shows the variation of
frequencies of respective vibrational modes as a function of pK . While the symmetric mode has no
significant shift in the entire series of compounds, the asymmetric mode seems to have a small pK
dependency, namely the substitution effect. However, because of the presence of large errors among
the series in addition to including the steric effect that induces large angles in the orthoꢀsubstituted
νsym) and asymmetry (νasym) stretching vibrations, respectively
(
a
a
θ
groups, we abandoned to evaluate the substitution effect using the vibrational modes.
Conclusion
To gain deeper insight into the variation of the electron donating ability of paddlewheelꢀtype
diruthenium(II, II) complexes tuned by bridging carboxylate ligands, we focused on two types of
series with Clꢀ and Fꢀsubstituted benzoate bridging ligands, [Ru
these complexes were isolated as crystals and structurally, magnetically and electrochemically
characterized. Analyses of the electron donating ability based on relevant parameters, pK
2 x 2 4 2 x 2 4
(Cl PhCO ) ] and [Ru (F PhCO ) ];
a
, E1/2, the
1
9

Dalton Transactions
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DOI: 10.1039/C5DT00505A
Hammett constant and the HOMO level calculated by DFT, revealed that the Clꢀ or Fꢀsubstituent
effect is in agreement with the electronic effect for [Ru ] following a linear relationship, which can be
2
treated in the framework of the general Hammett law. Note that quantitative analysis should be
performed for complexes in solution, because the solidꢀstate form of the complexes involves steric
effects caused by orthoꢀsubstitution and/or intermolecular interactions. The HOMO levels calculated
on the basis of solidꢀstate structures, especially for the orthoꢀsubstituted complexes, involve error
such as EHOMO < 0.3 eV and < 0.55 eV for the Clꢀ and Fꢀseries, respectively. As predicted from the
Hammett constant, the [Ru
abilities than those of the Fꢀseries, which is characteristic in complexes with one or two substitutions
on a benzoate bridge. Thus, the present families of [Ru (Cl PhCO ] and [Ru (F PhCO ] act as
good electronꢀdonor units of which the donating ability can be accurately tuned over a wide range of
1/2 = −50 –+350 mV and EHOMO =−4.2 −ꢀ5.2 eV.
2
] complexes in the Clꢀseries have slightly lower electron donating
2
x
2
)
4
2
x
2 4
)
E
Acknowledgements. We thank Dr. Satoshi Matsunaga (Faculty of Science, Kanagawa University)
for his help with compound synthesis. This work was supported by a GrantꢀinꢀAid for Scientific
Research (Grant No. 21350032, 26810029) from the Ministry of Education, Culture, Sports, Science
and Technology, Japan, ICCꢀIMR, LCꢀIMR and The Asahi Glass Foundation.
Supporting Information Available.
CIF files for Xꢀray crystallographic data and figures for structures for the compounds, magnetic data,
plot of halfꢀwave redox potential (E1/2) vs. Hammett constants, plot of HOMO level vs. E1/2 with
dihedral angles. This material is available free of charge via the Internet at http://pubs.acs.org.
2
0

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Table 1. Relevant bond lengths (Å) around Ru centres and dihedral
θ
angles (°) between the
leastꢀsquares planes defined by the phenyl ring of the benzoate ligand and the carboxylateꢀbridging
II,II
II,II
mode (i.e. atom set of Ru
2
O
2
C) in [Ru
2
(Cl
x
PhCO
2
)
4
(THF)
2
] and [Ru
2
x 2 4 2
(F PhCO ) (THF) ]
(Setꢀ1–Setꢀ4: benzoate ligands structurally determined as asymmetric groups).
Compound
Ru−Ru / Å Averaged
RuꢀOeq / Å
Ru−Oax / Å
2.325(2)
θ
/ ˚
Reference
5g
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Setꢀ1 Setꢀ2 Setꢀ3
40.40 29.99
Setꢀ4
Average
35.2
10.2
6.5
oꢀCl
mꢀCl
pꢀCl (unit 1)
2.2666(3)
2.2682(3)
2.2691(6)
2.2659(5)
2.2645(4)
2.2673(8)
2.2664(3)
2.2724(3)
2.2699(6)
2.2723(6)
2.2911(10)
2.3355(14)
2.2707(13)
2.1893(5)
2.2604(13)
2.2744(16)
2.2749(12)
2.2738(11)
2.2649(8)
2.2691(4)
2.2677(2)
2.2684(6)
2.2686(5)
2.2669(10)
2.2706(2)
2.2744(4)
2.2708(8)
2.2712(2)
2.2646(11)
2.2719(2)
2.2703(3)
2.2723(2)
2.2767(5)
2.2774(4)
2.2731(3)
2.2754(7)
2.2804(8)
2.065
2.066
2.064
2.067
2.066
2.068
2.066
2.060
2.071
2.065
2.059
2.046
2.066
2.106
2.062
2.062
2.065
2.063
2.068
2.065
2.061
2.066
2.064
2.065
2.065
2.064
2.073
2.066
2.059
2.070
2.068
2.071
2.067
2.068
2.065
2.070
2.068
2.3254(19) 16.44
3.92
6.61
8.64
2.320(4)
2.301(4)
2.306(3)
2.322(5)
6.38
4.53
20.43 15.10
21.31 1.22
18.57 28.37
29.36 40.79
79.62 34.71
84.70 32.49
7.95
6.30
4.45
55.31 74.20
27.06 37.51
39.79 15.66
25.90 14.01
26.46 49.28
37.49 17.69
(
unit 2)
,3ꢀCl
,4ꢀCl2
,5ꢀCl
unit 2)
,6ꢀCl (unit 1)
6.6
2
2
2
2
17.8
11.3
20.8
36.4
57.2
58.6
6.2
a
2
(unit 1)
2.283
8.44
34.35
27.90
40.94
a
(
2.304
2
3
2.311(3)
2.344(4)
2.323(9)
2.303(14)
2.320(3)
2.254(3)
2.306(5)
2.349(4)
2.330(5)
2.305(7)
2.312(2)
2.331(2)
2
(
unit 2)
,4ꢀCl (unit 1)
unit 2)
,5ꢀCl
2
4.52
8.27
9.35
(
7.3
6.9
3
2
2
2
3
2
2
,3,4ꢀCl
,3,5ꢀCl
,4,5ꢀCl
,4,5ꢀCl
3
3
3
3
64.8
32.3
27.7
20.0
37.9
27.6
11.3
17.6
19.0
14.9
10.5
37.4
16.9
14.1
20.2
13.0
51.6
13.3
64.2
23.0
26.2
31.5
29.6
40.3
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,3,4,5ꢀCl
4
oꢀF
mꢀF
pꢀF
7
7
7
3.17
19.52
2.3537(15) 19.48 15.78
2
2
2
2
3
3
2
2
2
2
2
3
2
2
,3ꢀF2
2.312(3)
2.324(3)
2.340(3)
21.86 16.07
21.99
9.49
41.99 32.68
19.80 14.04
20.11
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,4ꢀF
,5ꢀF
2
7.82
11.47
2
a
,6ꢀF2
2.332
31.25
17.01
43.65
7.11
7
7
7
7
,4ꢀF
,5ꢀF
2
2.354(3)
2.310(5)
8.08
2
,3,4ꢀF3
,3,5ꢀF
,3,6ꢀF
,4,5ꢀF3
,4,6ꢀF
,4,5ꢀF
2.3334(11) 22.62 17.68
a
2.308
2.3022(17) 61.17 41.92
2.329(2) 11.44 15.12
2.2829(16) 51.84 76.47
20.90
7.00
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3
7
7
7
7
7
7
7
7
3
3
2.307(2)
18.22 27.78
29.77 21.56
36.68 26.34
25.84 33.43
42.00 38.67
3
a
,3,4,5ꢀF4
,3,5,6ꢀF
2.299
35.45
18.03
2.298(2)
2.318(2)
2.308(3)
4
F
5
(unit 1)
(
unit 2)
a
averaged value
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1

Dalton Transactions
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II,II
II,II
Table 2. Electrochemical data of novel [Ru2 (Cl PhCO ) (THF) ] and [Ru (F PhCO ) (THF) ]
x
2 4
2
2
x
2 4
2
+
a
compounds measured in THF containing 0.1 M nꢀBu
4
N(PF
6
) under N
2
(mV vs. Ag/Ag ) .
ꢀ
E
p
/
Reference
b
c
Compound
Ea / mV
Ec / mV
E1/2 / mV
Ia / Ic
a
pK of benzoate
Σ(xσ + yσ )
Σ(xσ + yσ + zσ )
m
p
m
p
o
mV
121
107
171
104
120
109
150
104
94
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oꢀCl
mꢀCl
pꢀCl
96
−14
38
−58
107
57
118
60
67
179
201
240
180
195
300
−14
−15
−89
46
41
86
22
1.01
1.01
1.00
1.18
1.04
1.02
0.95
0.95
1.01
1.06
1.02
1.03
1.00
0.96
1.00
0.99
0.99
0.97
1.00
0.95
1.02
0.96
1.08
1.06
1.18
1.01
1.01
1.10
1.06
1.09
1.00
0.99
2.94
3.83
3.98
2.53
2.29
2.51
1.82
3.60
3.46
2.23
2.09
2.25
3.23
1.80
3.27
3.86
4.14
2.93
3.21
2.93
2.34
3.80
3.59
2.87
2.59
2.00
2.87
2.28
3.46
2.53
1.66
1.60
0
0.272
0.373
0.227
0.645
0.499
0.645
0.544
0.600
0.746
0.872
1.018
0.872
0.973
1.245
0.217
0.337
0.062
0.554
0.279
0.554
0.434
0.399
0.674
0.616
0.891
0.771
0.616
0.496
0.736
0.953
1.108
1.170
134
102
200
166
216
199
160
262
278
329
272
314
374
84
0.373
0.227
0.373
0.227
0.373
0.000
0.600
0.746
0.600
0.746
0.600
0.973
0.973
0
0.337
0.062
0.337
0.062
0.337
0
0.399
0.674
0.399
0.674
0.337
0.399
0.062
0.736
0.736
0.674
0.736
2
2
2
2
3
3
,3ꢀCl
,4ꢀCl2
,5ꢀCl
,6ꢀCl
,4ꢀCl
,5ꢀCl
2
154
112
167
130
112
221
240
296
226
266
337
35
42
−39
93
35
99
2
2
2
2
2
2
2
3
,3,4ꢀCl
,3,5ꢀCl
,4,5ꢀCl
,4,5ꢀCl
,3,4,5ꢀCl
oꢀF
3
3
3
3
88
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100
103
129
85
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2
4
7
98
7
mꢀF
pꢀF
99
11
142
98
114
100
106
138
130
129
183
105
139
108
117
99
145
121
137
104
142
7
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2
2
2
2
3
3
,3ꢀF
,4ꢀF
,5ꢀF
,6ꢀF
,4ꢀF
,5ꢀF
2
2
2
2
2
2
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−29
39
−14
52
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158
115
235
230
278
273
394
263
244
334
383
412
429
7
51
7
144
178
209
225
336
214
172
274
315
360
358
7
125
139
177
277
164
99
213
246
308
287
7
2
2
2
2
2
3
,3,4ꢀF3
,3,5ꢀF
,3,6ꢀF
,4,5ꢀF3
,4,6ꢀF
,4,5ꢀF
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3
7
7
7
7
7
7
7
3
3
3
2
2
,3,4,5ꢀF4
,3,4,5ꢀF
4
F
5
a
+
The ferrocene/ferrocenium couple, Fc/Fc = 213 mV, was observed under the same conditions
b
described in the Experimental Section. σ
m
= 0.373, σ
p
= 0.227 for Cl and σ
m
p
= 0.337, σ = 0.062 for
c
F, from Ref. 31. σ
o
= 272 and 217 for Cl and F, respectively, were experimentally estimated.
2
2

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II,II
Table 3. Calculated energy values of the HOMO level of [Ru2 (Cl PhCO ) (THF) ] and
x
2 4
2
II,II
[
Ru
2
x 2 4 2
(F PhCO ) (THF) ] using the density functional theory (DFT) at the UB3LYP level with basis
functions LANL2TZ(f) for Ru and 6ꢀ31+g(d) for other atoms, on the basis of the atomic coordinates
determined by Xꢀray crystallography.
Compound
HOMO energy (eV)
−4.1677
−4.5323
−4.5048
−4.5517
−4.6657
−4.5906
−4.4512
−4.7759
−4.9391
−5.1590
−4.9212
−4.9255
−5.0692
−5.0235
Compound
oꢀF
ΗΟΜΟ energy (eV)
−4.1840
−4.4219
−4.5114
−4.5223
−4.4874
−4.6401
−4.3242
−4.7677
−4.9566
−4.9432
−4.8785
−4.6502
−4.8893
−4.7424
−5.0679
−5.0578
−4.8518
−5.1144
oꢀCl
mꢀCl
mꢀF
pꢀCl
pꢀF
2
2
2
2
3
3
2
2
2
3
2
,3ꢀCl
2
2,3ꢀF
2
,4ꢀCl2
2,4ꢀF2
,5ꢀCl
,6ꢀCl
,4ꢀCl
,5ꢀCl
2
2
2
2
2,5ꢀF
2,6ꢀF
3,4ꢀF
3,5ꢀF
2
2
2
2
,3,4ꢀCl3
2,3,4ꢀF3
,3,5ꢀCl
,4,5ꢀCl
,4,5ꢀCl
3
3
3
2,3,5ꢀF
2,3,6ꢀF
2,4,5ꢀF
3
3
3
,3,4,5ꢀCl4
2,4,6ꢀF3
3
2
2
,4,5ꢀF
3
,3,4,5ꢀF
4
4
,3,5,6ꢀF
F
5
2
3

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II,II
II,II
Chart 1. The series of [Ru
2
(Cl
x
PhCO
2
)
4
(THF)
2
] and [Ru
2
(F
x
PhCO
2
)
4
(THF)
2
] described here,
where a) was referred from Ref. 7.
2
4

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Fig. 1. ORTEP drawings of the structures of (a) mꢀCl, (b) 2,3ꢀCl , (c) 2,3,4ꢀCl and (d) 2,3,4,5ꢀCl
4
2
3
(50% ellipsoid probability level), where red, grey, green and purple represent O, C, Cl and Ru,
respectively, and the grey bonds represent disordered atomic positions. Hydrogen atoms were omitted
for clarity.
2
5

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II,II
II,II
Fig. 2. CVs of newly synthesized [Ru
2
(Cl
x
PhCO
2
)
4
(THF)
2
] and [Ru
2
x 2 4 2
(F PhCO ) (THF) ]
compounds in THF containing 0.1 M nꢀBu
4
N(PF
6
2
) under N , where nonꢀ, monoꢀ and
diꢀorthoꢀsubstituted groups were classified in colours of red, green and blue, respectively. The
relevant values obtained from these CVs are summarized in Table 2.
2
6

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a
Fig. 3. Plots of halfꢀwave redox potential (E1/2) vs. pK for (a) the Clꢀseries and (b) the Fꢀseries, where
the green (yellow), violet (red) and pink (blue) points represent nonꢀCl(F), monoꢀCl(F) and
diꢀoꢀCl(F) substituted groups, respectively, and the solid lines represent the leastꢀsquares linear fit for
a
the respective groups. E1/2 and pK of all compounds are listed in Table 2.
2
7

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Fig. 4. Plots of (a and b) halfꢀwave redox potential (E ) vs. Σ(xσ + yσ ) and (c and d) Σ(xσ + yσ
1/2
m
p
m
p
+
zσ ) for (a, c) the Clꢀseries and (b, d) the Fꢀseries, respectively, where the green (yellow), violet
o
(red) and pink (blue) points represent nonꢀCl(F), monoꢀCl(F) and diꢀoꢀCl(F) substituted groups,
respectively, and the solid lines represent the leastꢀsquares fit for the respective plots. E1/2 and the
values of Σ(xσ + yσ ) and Σ(xσ + yσ + zσ ) of all compounds are listed in Table 2.
m
p
m
p
o
2
8

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Fig. 5. Plots of HOMO level vs. pK
yellow), violet (red) and pink (blue) points represent nonꢀCl(F), monoꢀCl(F) and diꢀoꢀCl(F)
substituted groups, respectively, and the solid lines represent the leastꢀsquares fit for the respective
a
for (a) the Clꢀseries and (b) the Fꢀseries, where the green
(
a
plots. The pK values and HOMO energy levels of all compounds are listed in Tables 2 and 3,
respectively.
2
9