Isomer Effect on the Structure and Chemical Reactivity of Diruthenium Complexes. Synthesis and Characterization of the (4,0), (3,1), and (2,2) Trans Isomers of Ru2(F5ap)4Cl and Ru2 (F5ap)4(C≡CC65)2 Where F5ap Is the 2-(2,3,4,5,6-Pentafluoroanilino)pyridinate Anion

Article abstract of DOI:10.1021/ic9602658

The syntheses and characterization of the (4,0), (3,1), and (2,2) trans isomers of Ru₂(F₅ap)₄Cl and Ru₂(F₅ap)_4- (C≡CC₆H₅)₂ are reported where F₅ap is the 2-(2,3,4,5,6-pentafluoroanilino)pyridinate anion. The (4,0), (3,1), and (2,2) trans isomers of Ru₂ (F₅ap)₄Cl were separated on a silica gel column following the reaction between Ru₂(CH₃COO)₄Cl and molten HF₅ap under argon. The (4,0), (3,1), and (2,2) trans isomers of Ru₂(F₅ap)₄(C≡CC₆H ₅)₂ were obtained by reaction of their respective isomer of Ru₂(F₅ap)₄Cl with LiC≡CC₆H₅) in THF at room temperature. The three isomers of Ru₂(F₅ap)₄Cl and Ru₂(F₅ap)₄(C≡CC₆H ₅)₂ were characterized by ¹H and ¹⁹F NMR, ESR, and IR spectroscopy, mass spectrometry and electrochemistry. Each Ru^IIRu^III isomer of Ru₂(F₅-ap)₄Cl is paramagnetic and undergoes two oxidations and one reduction in CH₂Cl₂, 0.1 M TBAP while each Ru^III₂ isomer of Ru₂(F₅ap)₄(C≡CC₆H ₅)₂ is diamagnetic and undergoes one oxidation and two reductions under the same solution conditions. All of the redox processes are reversible and involve metal-centered one-electron transfers. The singly reduced products of the (4,0), (3,1), and (2,2) trans isomers of Ru₂(F₅ap)₄(C≡CC₆H ₅)₂ were electrogenerated and display ESR signals consistent with the presence of a single unpaired electron. Molecular structures of the three isomers of Ru₂(F₅ap)₄(C≡CC₆H ₅)₂ were also determined. The (4,0) isomer crystallizes in the monoclinic space group P2₁/c with a = 23.436(6) ?, b = 20.640(6) ?, c = 23.504(6) ?, β= 105.82(2)°, and Z = 8, while the (3,1) isomer crystallizes in the monoclinic space group P2₁/n with a = 15,621(3) ?, b = 16.427(3) ?, c = 21.166(5) ?, β = 93.91(2)°, and Z = 4. The (2,2) trans isomer crystallizes in the triclinic space group P1 with a = 12.819(5) ?, b = 13.390(4) ?, c = 17.827(5) ?, α = 85.04(2)°, β= 72.66(2)°, γ = 68.47-(2)°, and Z = 2. The average Ru-Ru bond distances in the (4,0), (3,1), and (2,2) trans isomers of Ru₂(F₅ap)_4- (C≡CC₆H₅)₂ are 2.450(1), 2.475(1), and 2.473(1) ?, respectively.

Full text of DOI:10.1021/ic9602658

Inorg. Chem. 1997, 36, 5449-5456
5449
Isomer Effect on the Structure and Chemical Reactivity of Diruthenium Complexes.
Synthesis and Characterization of the (4,0), (3,1), and (2,2) Trans Isomers of Ru2(F5ap)4Cl
and Ru2(F5ap)4(CtCC6H5)2 Where F5ap Is the 2-(2,3,4,5,6-Pentafluoroanilino)pyridinate
Anion
John L. Bear,* Yulan Li, Baocheng Han,† Eric Van Caemelbecke, and Karl M. Kadish*
Department of Chemistry, University of Houston, Houston, Texas 77204-5641
ReceiVed March 8, 1996X
The syntheses and characterization of the (4,0), (3,1), and (2,2) trans isomers of Ru2(F5ap)4Cl and Ru2(F5ap)4-
(CtCC6H5)2 are reported where F5ap is the 2-(2,3,4,5,6-pentafluoroanilino)pyridinate anion. The (4,0), (3,1),
and (2,2) trans isomers of Ru2(F5ap)4Cl were separated on a silica gel column following the reaction between
Ru2(CH3COO)4Cl and molten HF5ap under argon. The (4,0), (3,1), and (2,2) trans isomers of Ru2(F5ap)4-
(CtCC6H5)2 were obtained by reaction of their respective isomer of Ru2(F5ap)4Cl with LiCtCC6H5 in THF at
room temperature. The three isomers of Ru2(F5ap)4Cl and Ru2(F5ap)4(CtCC6H5)2 were characterized by 1H and
19F NMR, ESR, and IR spectroscopy, mass spectrometry and electrochemistry. Each RuIIRuIII isomer of Ru2(F5-
ap)4Cl is paramagnetic and undergoes two oxidations and one reduction in CH2Cl2, 0.1 M TBAP while each
RuIII isomer of Ru2(F5ap)4(CtCC6H5)2 is diamagnetic and undergoes one oxidation and two reductions under
2
the same solution conditions. All of the redox processes are reversible and involve metal-centered one-electron
transfers. The singly reduced products of the (4,0), (3,1), and (2,2) trans isomers of Ru2(F5ap)4(CtCC6H5)2
were electrogenerated and display ESR signals consistent with the presence of a single unpaired electron. Molecular
structures of the three isomers of Ru2(F5ap)4(CtCC6H5)2 were also determined. The (4,0) isomer crystallizes in
the monoclinic space group P21/c with a ) 23.436(6) Å, b ) 20.640(6) Å, c ) 23.504(6) Å, â ) 105.82(2)°, and
Z ) 8, while the (3,1) isomer crystallizes in the monoclinic space group P21/n with a ) 15.621(3) Å, b )
16.427(3) Å, c ) 21.166(5) Å, â ) 93.91(2)°, and Z ) 4. The (2,2) trans isomer crystallizes in the triclinic space
group P1h with a ) 12.819(5) Å, b ) 13.390(4) Å, c ) 17.827(5) Å, R ) 85.04(2)°, â ) 72.66(2)°, γ ) 68.47-
(2)°, and Z ) 2. The average Ru-Ru bond distances in the (4,0), (3,1), and (2,2) trans isomers of Ru2(F5ap)4-
(CtCC6H5)2 are 2.450(1), 2.475(1), and 2.473(1) Å, respectively.
Introduction
sulfate, to strongly basic,12-29 in the case of 2-anilinopyridinate
and N,N′-diphenylformamidinate and can be classified into two
categories, symmetrical1-10,14-20 and unsymmetrical.11-13,21-29
Dimetal complexes bridged by four symmetrical ligands are
represented by a single structural formula, but four different
geometric isomers are possible for dimetal complexes containing
four unsymmetrical bridging ligands. This is schematically
shown in Chart 1, where the solid and open circles represent
two different types of donor atoms.
Several dimetal complexes bridged by four identical equato-
rial ligands have been synthesized and characterized over the
last two decades.1-29 The bridging ligands in these complexes
vary from slightly basic,1-11 in the case of carboxylates and
† Present address: Department of Chemistry, University of Wisconsin,
Whitewater, Whitewater, WI 53190.
X Abstract published in AdVance ACS Abstracts, October 1, 1997.
(1) Cotton, F. A.; Pedersen, E. Inorg. Chem. 1975, 14, 388.
(2) Stephenson, T. A.; Wilkinson, G. J. Inorg. Nucl. Chem. 1966, 28,
2285.
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1985, 107, 7195.
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1175.
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1996, 35, 3012.
(20) Bear, J. L.; Li, Y. L; Han, B. C.; Kadish, K. M. Inorg. Chem. 1996,
35, 1395.
(3) Kuz’menko, I. V.; Zhilyaev, A. N.; Fomina, T. A.; Porai-Koshits, M.
A.; Baranovskii, I. B. Russ. J. Inorg. Chem. 1989, 34, 1457.
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(5) Aquino, M. A. S.; Macartney, D. H. Inorg. Chem. 1987, 26, 2696.
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H.; Guest, M. F. Chem. Phys. Lett. 1989, 154, 326.
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Trans. 1988, 3059.
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24, 172.
(22) Malinski, T.; Chang, D.; Feldmann, F. N.; Bear, J. L.; Kadish, K. M.
Inorg. Chem. 1983, 22, 3225.
(23) Chavan, M. Y.; Feldmann, F. N.; Lin, X. Q.; Bear, J. L.; Kadish, K.
M. Inorg. Chem. 1984, 23, 2373.
(10) Cogne, A.; Grand, A.; Rey, P.; Subra, R. J. Am. Chem. Soc. 1989,
111, 3230.
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1383.
(12) Best, S. P.; Chandley, P.; Clark, R. J. H.; McCarthy, S.; Hursthouse,
M. B.; Bates, P. A. J. Chem. Soc., Dalton Trans. 1989, 581.
(13) Seeber, R.; Piu, P.; Piraino, P.; Zanello, P. Inorg.Chim. Act. 1989,
155, 27.
(24) Chakravarty, A. R.; Cotton, F. A. Inorg. Chim. Acta 1986, 113, 19.
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(26) (a) Yao, C.-L.; Park, K. H.; Khokhar, A. R.; Jun, M.-J.; Bear, J. L.
Inorg. Chem. 1990, 29, 4033. (b) Bear, J. L.; Liu, L.-M.; Kadish, K.
M. Inorg. Chem. 1987, 26, 2927.
(27) Bear, J. L.; Yao, C. L.; Liu, L. M.; Capdevielle, F. J.; Korp, J. D.;
Albright, T. A.; Kang, S. K.; Kadish, K. M. Inorg. Chem. 1989, 28,
1254.
(14) Cotton, F. A.; Ren, T. Inorg. Chem. 1995, 34, 3190.
(15) Cotton, F. A.; Matusz, M. J. Am. Chem. Soc. 1988, 110, 5761.
(16) Cotton, F. A.; Ren, T. Inorg. Chem. 1991, 30, 3675.
(28) Bear, J. L.; Liu, L. M.; Kadish, K. M. Inorg. Chem. 1987, 26, 2927.
(29) Li, Y. L.; Han, B. C.; Bear, J. L.; Kadish, K. M. Inorg. Chem. 1993,
32, 4175.
S0020-1669(96)00265-0 CCC: $14.00 © 1997 American Chemical Society

5450 Inorganic Chemistry, Vol. 36, No. 24, 1997
Bear et al.
1H NMR spectra were recorded on a QE-300 FT NMR spectrometer
while 19F NMR spectra were obtained with a NT-200 spectrometer. IR
spectra were obtained on an IBM Model IR/32 FTIR spectrometer.
ESR spectra were recorded with an IBM ER 100D spectrometer. The
g values were calculated with respect to the diphenylpicrylhydrazyl
radical (DPPH) which has a signal at g ) 2.0036 ( 0.0003.30 Magnetic
susceptibility measurements were carried out at room temperature with
a Johnson Matthey Model MSG-1 magnetic susceptibility balance which
was calibrated with Hg[Co(NCS)4].
Chart 1
Cyclic voltammograms were obtained with an IBM Model EC 225
voltammetric analyzer. The working electrode was a platinum button
with a surface area of 0.19 mm2, and a homemade saturated calomel
electrode (SCE) was used as the reference electrode. The counter
electrode was a platinum wire. Controlled-potential electrolysis was
carried out with a BAS Model SP-2 potentiostat. An “H” type cell
was used for bulk electrolysis. Two cylindrically shaped platinum
gauze electrodes, separated by a fine-fritted disk, served as the working
and counter electrodes, respectively.
The isomer with four equivalent donor atoms on each metal
atom is designated as the (4,0) isomer while that with three
equivalent donor atoms on each metal is designated as the (3,1)
isomer.26-28 The notations of (2,2) trans and (2,2) cis indicate
that these geometrical isomers have two equivalent donor atoms
on each metal in trans and cis arrangements, respectively.26-28
The energy and ordering of the metal-centered molecular
orbitals of diruthenium complexes are highly dependent on the
donor/acceptor properties of the bridging and axial ligands. For
this reason, a large number of diruthenium complexes containing
bridging and axial ligands which vary significantly in their σ
and π donor/acceptor properties have been synthesized and
studied in recent years.1,2,15,16,18-22,27,29 Diruthenium complexes
with unsymmetrical ligands such as anilinopyridine (ap) and
2-(2,3,4,5,6-pentafluoroanilino)pyridinate (F5ap) have been syn-
thesized, but little is known on how the bonding orientations
of these ligands would affect the reactivity and stucture of these
complexes. For this reason, the synthesis and characterization
of geometric isomers containing the diruthenium unit in a +6,
+5, or +4 oxidation state are of interest.
Each Ru2(F5ap)4(CtCC6H5)2 derivative can theoretically exist
in four geometric isomer forms due to the unsymmetrical F5ap
bridging ligand (see Chart 1). The synthesis and preliminary
characterization of the (4,0) isomer have been reported,29 and
we now describe the syntheses and characterization of the (3,1)
and (2,2) trans isomers of Ru2(F5ap)4(CtCC6H5)2. A more
detailed description of the synthetic procedure and characteriza-
tion of the (4,0) isomer is also presented in this paper in addition
to new data on the (4,0), (3,1), and (2,2) trans isomers of Ru2(F5-
ap)4Cl, the starting compounds used in synthesis of the three
isolated isomers of Ru2(F5ap)4(CtCC6H5)2.
HF5ap. A 0.25 mL (ca. 2.5 mmol) portion of 2-bromopyridine was
added to 5.0 equiv of sodium 2-methyl-2-propanoxide in 100 mL of
THF under an argon atmosphere. The solution was refluxed overnight,
after which 10.0 g (ca. 54.6 mmol) of 2,3,4,5,6-pentafluoroaniline was
added and the solution refluxed for another 10 h. The mixture was
then extracted by using CH2Cl2 and H2O. The organic layer was
collected, and anhydrous CaCl2 was added. The solution was filtered,
and the crude product was recovered after removal of the solvent. Pure
2-(2,3,4,5,6-pentafluoroanilino)pyridine, HF5ap, was obtained by sub-
limation at 110 °C under a pressure of 5 × 10-3 Torr. The yield of
the product was extremely variable and ranged between 5 and 70%
despite what appeared to be constant reaction conditions. This problem
of variable ligand yield is not understood and still under investigation.
Mass spectral data (m/e, fragment): 260.5, [HF5ap]+. NMR data in
CD2Cl2 (δ, ppm): 8.14 (d, 1H), 7.58 (t, 1H), 6.85 (t, 1H), 6.66 (d,
1H), 6.20 (s, b, 1H), (s ) singlet; d ) doublet; t ) triplet; b ) broad).
(4,0), (3,1), and (2,2) Trans Isomers of Ru2(F5ap)4Cl.31 Ru2(CH3-
COO)4Cl (0.18 g, ca. 0.4 mmol) and molten HF5ap (4.00 g, ca. 15.4
mmol) were stirred under an argon atmosphere at 140 °C for 20 min.
Excess HF5ap ligand was sublimed off under vacuum at 110 °C and
the residue twice chromatographed on a silica gel column, using CH2-
Cl2 and then acetone/n-hexane (1:9) as eluent. Three bands, which
were yellow, brown, and green were collected, and these corresponded
to the (4,0), (3,1), and (2,2) trans isomers of Ru2(F5ap)4Cl, respectively.
The crude products were washed using methanol and recrystallized three
times using acetone/n-hexane (2:8). Only the (4,0) isomer of Ru2(F5-
ap)4Cl was characterized in detail, and the data are as follows. Infrared
spectrum (CsI pellet), cm-1: 1660.9 (w), 1558.7 (m), 1460.3 (s), 1420.2
(s), 1380.4 (s), 1288.6 (m), 1230.8 (m), 1124.6 (m), 1080.4 (w), 1003.7
(s), 972.2 (s), 854.6 (m), 780.4 (m), 742.7 (m), 718.6 (m), 682.9 (w),
634.7 (w), 588.4 (w), 511.2 (w) (s ) strong; m ) medium; w ) weak).
Mass spectral data (m/e, fragment): 1275.0, [Ru2(F5ap)4Cl]+; 1240.0,
[(Ru2(F5ap)4]+; 1016.2, [Ru2(F5ap)3Cl]+; 980.4, [(Ru2(F5ap)3]+. Anal.
Calcd for C44H16N8F20Ru2Cl: C, 41.46; H, 1.26; N, 8.80; F, 29.84.
Found: C, 41.55; H, 1.14; N, 8.77; F, 27.49.
Both series of diruthenium compounds were characterized
by 1H and 19F NMR, ESR, and IR spectroscopy, mass
spectrometry and electrochemistry. Molecular structures of the
(4,0), (3,1), and (2,2) trans isomers of Ru2(F5ap)4(CtCC6H5)2
were also determined by single-crystal X-ray diffraction.
Experimental Section
(4,0) Isomers of Ru2(F5ap)4(CtCC6H5) and Ru2(F5ap)4(CtC-
C6H5)2. A 4.0 mL (ca. 4.0 mmol) sample of LiCtCC6H5 was added
to 0.10 g (ca. 0.08 mmol) of Ru2(F5ap)4Cl in 100 mL of deaerated
THF. The solution was stirred overnight at room temperature as its
color changed from yellow-brown to red. The reaction mixture was
then exposed to air and the solvent evaporated under vacuum. The
residue was purified on a silica gel column using CH2Cl2/n-hexane (1:
9) as eluent. A red and a blue band were observed on the column.
The red band was collected and the solvent evaporated under vacuum.
The solid was then recrystallized from CH2Cl2/n-hexane (2:8), and
Ru2(F5ap)4(CtCC6H5) was recovered in an isolated yield of 40%.
Crystals suitable for X-ray single-crystal analysis were obtained by slow
diffusion of n-hexane into a THF solution of the (4,0) isomer of
Chemicals and Reagents. Deuterated dichloromethane (CD2Cl2)
and chloroform (CDCl3) were purchased from Aldrich Chemical Co.
and used as received. CH2Cl2 was obtained as HPLC grade from Fisher
Scientific Co. and distilled over phosphorus pentoxide (P2O5). Spec-
troscopic grade THF, purchased from Aldrich Chemical Co., was
purified by distillation under Ar from sodium/benzophenone just prior
to use. Analytical grade n-hexane (Mallinckrodt Chemical Co.) was
used without further purification. Tetra-n-butylammonium perchlorate
(TBAP, Fluka Chemical Co.) was twice recrystallized from absolute
ethanol and dried in the oven at 40 °C. Sodium 2-methyl-2-
propanoxide, 2-bromopyridine, 2,3,4,5,6-pentafluoroaniline, lithium
phenylacetylide, RuCl3‚3H2O, and 1,4-phenylene diisocyanide, pur-
chased from Aldrich Chemical Co., were used as received.
Physical Measurements. Mass spectra were obtained from a high-
resolution hybrid tandem VG Analytical Model 70-SEQ (EEQQ
geometry) mass spectrometer. A standard fast atom bombardment
(FAB) source was used with m-nitrobenzyl alcohol (NBA) as the liquid
matrix. Elemental analyses were carried out by Galbraith Laboratories,
Inc., Knoxville, TN.
(30) Drago, R. S. Physical Methods in Chemistry; W. B. Saunders:
Philadephia, PA, 1977; p 324.
(31) The (2,2) cis isomer of Ru2(F5ap)4Cl was apparently present in the
reaction mixture, but we could not isolate an adequate amount of
product to further characterize this compound. The low yield for the
(2,2) cis isomer of Ru2(F5ap)4Cl is not yet understood.

Isomer Effect on Diruthenium Complexes
Inorganic Chemistry, Vol. 36, No. 24, 1997 5451
Ru2(F5ap)4(CtCC6H5). Infrared spectrum (CsI pellet), cm-1: 1660.9
(w), 1554.8 (w), 1466.1 (s), 1423.6 (s), 1385.1 (m), 1334.9 (w), 1286.7
(m), 1265.5 (w), 1223.0 (w), 1126.6 (w), 993.5 (s), 970.3 (s), 858.4
(m), 765.8 (m), 740.8 (m), 723.4 (m), 681.0 (w), 588.4 (w), 509.3.
Anal. Calcd for C52H21N8F20Ru2: C, 46.60; H, 1.57; N, 8.36; F, 28.38.
Found: C, 46.65; H, 1.65; N, 8.08; F, 28.36.
The blue band was also collected and the solvent evaporated under
vacuum. Pure Ru2(F5ap)4(CtCC6H5)2 was obtained in an isolated yield
of 40% after elution with CH2Cl2/n-hexane (2:8) and further purification
on an alumina column using pure CH2Cl2. Dark-green crystals suitable
for X-ray analysis were obtained by recrystallization in a 9:1 mixture
of CH2Cl2 and benzene. Infrared spectrum (CsI pellet), cm-1: 1545.2
(m), 1454.5 (s), 1367.7 (m), 1325.2 (m), 1115.0 (w), 956.8 (s), 833.4
(m), 727.3 (m), 665.5 (w), 513.1 (w). Anal. Calcd for C60H26N8F20-
Ru2: C, 50.07; H, 1.93; N, 7.63; F, 26.31. Found: C, 50.00; H, 1.81;
N, 7.78; F, 26.39.
Table 1. Crystal Data and Data Collection and Processing
Parameters of the (4,0), (3,1), and (2,2) Trans Isomers of
Ru2(F5ap)4(CtCC6H5)2
(4,0)
(3,1)
(2,2) trans
space group
a, Å
b, Å
P21/c (monoclinic) P21/n (monoclinic) P1h (triclinic)
23.436(6)
20.640(6)
23.504(6)
15.621(3)
16.427(3)
21.166(5)
12.819(5)
13.390(4)
17.827(5)
85.04(2)
72.66(2)
68.47(2)
2716
c, Å
R, deg
â, deg
γ, deg
V, Å3
105.82(2)
93.91(2)
10939
5459
mol formula
fw
C60H26N8F20Ru2
1441.08
8
1.75
6.55
C60H26N8F20Ru2
1441.08
4
1.77
6.62
C60H26N8F20Ru2
1441.08
2
1.76
6.60
Z
F, g/cm3
µ, cm-1
(3,1) and (2,2) Trans Isomers of Ru2(F5ap)4(CtCC6H5)2. Both
isomers were obtained using reaction conditions similar to those
described above for preparation of the (4,0) isomer of Ru2(F5ap)4-
(CtCC6H5)2. To 0.1 g (0.08 mmol) of the (3,1) or (2,2) trans isomer
of Ru2(F5ap)4Cl in 100 mL of deaerated THF was added 2.0 mL (2.0
mmol) of LiCtCC6H5.
λ (Mo KR), Å 0.710 73
data coll range 4 e 2θ e 50
(2θ), deg
0.710 73
4 e 2θ e 45
0.710 73
4 e 2θ e 50
temp, °C
-50
-50
0.031
0.024
-50
0.027
0.028
Ra
Rw
0.039
0.036
b
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
.
2
The mixture containing the (3,1) isomer was stirred at room
temperature for 8 h as the color of the solution changed from yellow-
brown to red. The solvent was then removed under vacuum and the
residue purified on a silica gel column using CH2Cl2/n-hexane (3:7) as
eluent. A red and a blue band were observed on the column. The red
band was collected and, after evaporation of the solvent under vacuum,
gave the pure (3,1) isomer of Ru2(F5ap)4(CtCC6H5) in a 7% isolated
yield. The blue band was also eluted from the column and the solvent
evaporated under vacuum. The solid residue was further purified on
an alumina column using CH2Cl2 as eluent and gave pure Ru2(F5ap)4-
(CtCC6H5)2 in a 60% isolated yield after evaporation of the solvent.
The (2,2) trans isomer of Ru2(F5ap)4(CtCC6H5)2 was isolated in a
yield of 85% using a procedure similar to that described above for the
(3,1) isomer of Ru2(F5ap)4(CtCC6H5)2. The only difference was that
the mixture was stirred for 4 h rather than 8 h as the color of the solution
changed from green to red. Infrared spectrum for the (3,1) isomer of
Ru2(F5ap)4(CtCC6H5)2 (CsI pellet), cm-1: 2093.0 (w), 1606.9 (m),
1512.4 (s), 1468.0 (s), 1423.6 (m), 1340.7 (w), 1307.9 (w), 1026.3 (s),
995.4 (s), 723.2 (w), 756.2 (m), 6932.5 (w). Infrared spectrum for the
(2,2) trans isomer of Ru2(F5ap)4(CtCC6H5)2 (CsI pellet), cm-1: 2093.0
(m), 1608.8 (s),1512.4 (s), 1469.9 (s), 1423.6 (m) 1342.6 (m), 1307.9
(m), 1286.7 (w), 1155.5 (w), 1024.3 (s), 1012.8 (s), 995.4 (s), 864.2
(m), 765.2 (s), 692.5 (w).
X-ray Crystallography of the (4,0), (3,1), and (2,2) Trans Isomers.
Single-crystal X-ray crystallographic studies were performed at the
University of Houston X-ray Crystallographic Center. Since the
material was subject to a slow decomposition, the sample was placed
in a stream of dry nitrogen gas at -50 °C in a random orientation on
a Nicolet R3m/V automatic diffractomer. The radiation used was Mo
KR monochromatized by a highly ordered graphite crystal. Final cell
constants, as well as other information pertinent to data collection and
refinement, are summarized in Table 1. Intensities were measured using
an ω scan technique, with a scan rate dependent on the count obtained
in rapid prescans of each reflection. Two standard reflections were
monitored after every 2 h or 100 data collected, and these showed no
significant change, indicating that the crystal does not decompose during
the data collection. During data reduction, Lorentz and polarization
corrections were applied to the intensity data, but because of the small
linear absorption coefficient, absorption corrections were not applied.
The structures were solved by the SHELXTL direct methods program
which revealed the positions of many of the atoms in the asymmetric
unit. Remaining non-hydrogen atoms were found in subsequent
difference Fourier syntheses. The usual sequence of isotropic and
anisotropic refinement was followed, after which all hydrogens were
entered in ideal calculated positions and constrained to riding motion,
with a single variable isotropic temperature factor for all of them. After
all shift/esd ratios were less than 0.1, convergence was reached at the
agreement factors listed in Table 1. No unusually high correlations
were noted between any of the variables in the last cycle of full-matrix
least-squares refinement, and the final difference density map showed
a maximum peak of about 0.6, 0.7, or 0.5 e/Å3 for the (4,0), (3,1), or
(2,2) trans isomer, respectively. All calculations were made using the
Nicolet SHELXTL PLUS (1987) series of crystallographic programs.
For the (4,0) isomer, all the carbons of the F5ap ligand were refined
isotropically in order to reduce the number of variables to a manageable
value. One of the phenyl groups (C(53) to C(60)) was also found to
be disordered over two positions, with this being modeled by using
ideal rigid-body phenyl groups. The variation in the location of C(53)
was too small to separate, and therefore it was refined common to both
orientations. The occupancy factors refined to 62% for the C(54) to
C(60) orientation and 38% for C(54′) to C(60).
The Laue symmetry of the (4,0) isomer was determined to be 2/m,
and from the systematic absences, the space group was shown to be
unambiguously P21/c. For the (3,1) and (2,2) trans isomers, the Laue
symmetries were determined to be 2/m and 1h, respectively. From the
systematic absences, the space groups were shown to be unambiguously
P21/n for the (3,1) isomer and either P1 or P1h for the (2,2) trans isomer.
Successful refinement in P1h showed it to be the correct setting.
Results and Discussion
Synthesis and Reaction. The affinities of the three isomers
of Ru2(F5ap)4Cl for LiCtCC6H5 are different under the same
experimental conditions. For example, the formation of the (4,0)
isomer of Ru2(F5ap)4(CtCC6H5) or Ru2(F5ap)4(CtCC6H5)2
from the (4,0) isomer of Ru2(F5ap)4Cl could be easily controlled
by changing the amount of LiCtCC6H5, but this was not the
case for the (3,1) or (2,2) trans isomer. The (4,0) isomer of
Ru2(F5ap)4(CtCC6H5)2 was the major product in the presence
of a large excess of LiCtCC6H5 (>100 equiv), while the (4,0)
isomer of Ru2(F5ap)4(CtCC6H5) was the major product when
only 2-5 equiv of LiCtCC6H5 was used. On the other hand,
when stoichometric amounts (1:1) of LiCtCC6H5 and the (3,1)
isomer of Ru2(F5ap)4Cl were used, the major product isolated
was the (3,1) isomer of Ru2(F5ap)4(CtCC6H5)2 and only 7%
of the (3,1) isomer of Ru2(F5ap)4(CtCC6H5) was obtained. No
(2,2) trans isomer of Ru2(F5ap)4(CtCC6H5) could be obtained
by a reaction between the (2,2) trans isomer of Ru2(F5ap)4Cl
and LiCtCC6H5. Only the (2,2) trans isomer of Ru2(F5ap)4-
(CtCC6H5)2 and the parent complex Ru2(F5ap)4Cl were isolated
from the reaction mixture. It is not clear at present whether
this is due to kinetic or thermodynamic effects, but the ease of
adding two σ-bonded axial ligands to the Ru25+ core of Ru2(F5-
ap)4Cl follows the order (4,0) < (3,1) < (2,2) trans.
Molecular Structures of the (4,0), (3,1), and (2,2) Trans
Isomers of Ru2(F5ap)4(CtCC6H5)2. Selected bond lengths and
bond angles for the three isomers of Ru2(F5ap)4(CtCC6H5)2

5452 Inorganic Chemistry, Vol. 36, No. 24, 1997
Bear et al.
Table 2. Selected Bond Lengths (Å) for the (4,0), (3,1), and (2,2) Trans Isomers of Ru2(F5ap)4(CtCC6H5)2
(4,0) isomera
(3,1) isomer
(2,2) trans isomer
Ru(1)-Ru(2)
2.441(1)
2.069(6)
2.030(6)
2.030(8)
2.110(7)
2.036(6)
2.115(6)
2.123(7)
2.032(7)
1.955(12)
1.951(11)
1.212(17)
1.446(17)
1.211(28)
1.451(28)
1.238(45)
1.478(44)
Ru(1)-Ru(2)
2.475(1)
2.003(4)
2.147(4)
2.018(5)
2.087(4)
2.125(4)
1.970(4)
2.054(4)
2.085(4)
1.987(6)
1.979(6)
1.208(8)
1.445(8)
1.220(8)
1.425(8)
Ru(1)-Ru(2) 2.473(1)
Ru(1)-N(1)
Ru(2)-N(2)
Ru(1)-N(3)
Ru(2)-N(4)
Ru(1)-N(5)
Ru(2)-N(6)
Ru(1)-N(7)
Ru(2)-N(8)
Ru(1)-C(45)
Ru(2)-C(53)
C(45)-C(46)
C(46)-C(47)
C(53)-C(54)
C(54)-C(55)
C(53)-C(54′)
C(54′)-C(55′)
Ru(1)-N(1)
Ru(2)-N(2)
Ru(1)-N(3)
Ru(2)-N(4)
Ru(1)-N(5)
Ru(2)-N(6)
Ru(2)-N(7)
Ru(1)-N(8)
Ru(1)-C(45)
Ru(2)-C(53)
C(45)-C(46)
C(46)-C(47)
C(53)-C(54)
C(54)-C(55)
Ru(1)-N(1)
Ru(2)-N(2)
Ru(1)-N(3)
Ru(2)-N(4)
Ru(1)-N(5)
Ru(2)-N(6)
Ru(2)-N(7)
Ru(1)-N(8)
Ru(1)-C(45)
Ru(2)-C(53)
C(45)-C(46)
C(46)-C(47)
C(53)-C(54)
C(54)-C(55)
2.147(2)
1.979(3)
2.159(2)
1.982(2)
2.012(2)
2.120(2)
2.016(2)
2.120(2)
1.990(3)
2.001(3)
1.201(4)
1.440(4)
1.204(4)
1.446(4)
a Data for molecule 2 of the (4,0) isomer are included in the Supporting Information.
Table 3. Selected Bond Angles (deg) for the (4,0), (3,1), and (2,2) Trans Isomers of Ru2(F5ap)4(CtCC6H5)2
(4,0) isomera
(3,1) isomer
(2,2) trans isomer
Ru(2)-Ru(1)-N(1)
Ru(2)-Ru(1)-N(1)
84.7(2)
91.0(3)
89.7(3)
91.1(3)
175.9(3)
90.4(3)
83.8(2)
89.8(3)
174.8(3)
89.7(3)
170.6(3)
89.7(4)
96.5(4)
94.4(3)
88.7(4)
88.3(2)
82.9(2)
90.2(3)
82.8(2)
171.2(3)
88.6(3)
89.6(2)
91.6(3)
172.3(3)
88.5(3)
172.2(3)
96.6(3)
91.1(4)
92.1(3)
96.2(4)
177.7(9)
176.6(11)
173.6(12)
173.4(23)
166.4(23)
166.4(36)
Ru(2)-Ru(1)-N(1)
97.5(1)
92.7(1)
90.5(2)
78.6(1)
175.4(2)
87.4(2)
81.7(1)
90.7(2)
174.2(2)
91.0(2)
163.5(2)
95.9(2)
96.8(2)
88.4(2)
88.6(2)
78.3(1)
81.8(1)
93.6(2)
95.0(1)
171.2(2)
91.3(2)
93.1(1)
88.0(2)
174.1(2)
86.4(2)
163.0(1)
87.2(2)
90.4(2)
100.3(2)
95.3(2)
171.8(5)
176.3(7)
174.3(5)
178.7(6)
80.3(1)
95.9(1)
88.6(1)
97.2(1)
176.1(1)
88.6(1)
79.0(1)
93.7(1)
173.9(1)
88.8(1)
160.6(1)
87.8(1)
99.2(1)
95.4(1)
86.6(1)
95.1(1)
79.7(1)
88.6(1)
79.0(1)
172.0(1)
95.5(1)
97.41(1)
87.4(1)
174.9(1)
88.1(1)
160.9(1)
99.7(2)
88.7(1)
87.2(1)
95.2(1)
174.6(2)
173.2(3)
172.3(3)
177.7(4)
Ru(2)-Ru(1)-N(3)
N(1)-Ru(1)-N(3)
Ru(2)-Ru(1)-N(5)
N(1)-Ru(1)-N(5)
N(3)-Ru(1)-N(5)
Ru(2)-Ru(1)-N(7)
N(1)-Ru(1)-N(7)
N(3)-Ru(1)-N(7)
N(5)-Ru(1)-N(7)
Ru(2)-Ru(1)-C(45)
N(1)-Ru(1)-C(45)
N(3)-Ru(1)-C(45)
N(5)-Ru(1)-C(45)
N(7)-Ru(1)-C(45)
Ru(1)-Ru(2)-N(2)
Ru(1)-Ru(2)-N(4)
N(2)-Ru(2)-N(4)
Ru(1)-Ru(2)-N(6)
N(2)-Ru(2)-N(6)
N(4)-Ru(2)-N(6)
Ru(1)-Ru(2)-N(8)
N(2)-Ru(2)-N(8)
N(4)-Ru(2)-N(8)
N(6)-Ru(2)-N(8)
Ru(1)-Ru(2)-C(53)
N(2)-Ru(2)-C(53)
N(4)-Ru(2)-C(53)
N(6)-Ru(2)-C(53)
N(8)-Ru(2)-C(53)
Ru(1)-C(45)-C(46)
C(45)-C(46)-C(47)
Ru(2)-C(53)-C(54)
C(53)-C(54)-C(55)
Ru(2)-C(53)-C(54′)
C(53)-C(54′)-C(55′)
Ru(2)-Ru(1)-N(3)
N(1)-Ru(1)-N(3)
Ru(2)-Ru(1)-N(5)
N(1)-Ru(1)-N(5)
N(3)-Ru(1)-N(5)
Ru(2)-Ru(1)-N(8)
N(5)-Ru(1)-N (8)
N(3)-Ru(1)-N(8)
N(5)-Ru(1)-N(8)
Ru(2)-Ru(1)-C(45)
N(1)-Ru(1)-C(45)
N(3)-Ru(1)-C(45)
N(5)-Ru(1)-C(45)
N(8)-Ru(1)-C(45)
Ru(1)-Ru(2)-N(2)
Ru(1)-Ru(2)-N(4)
N(2)-Ru(2)-N(4)
Ru(1)-Ru(2)-N(6)
N(2)-Ru(2)-N(6)
N(4)-Ru(2)-N(6)
Ru(1)-Ru(2)-N(7)
N(2)-Ru(2)-N(7)
N(4)-Ru(2)-N(7)
N(6)-Ru(2)-N(7)
Ru(2)-Ru(1)-C(53)
N(2)-Ru(2)-C(53)
N(4)-Ru(2)-C(53)
N(6)-Ru(2)-C(53)
N(7)-Ru(2)-C(53)
Ru(1)-C(45)-C(46)
C(45)-C(46)-C(47)
Ru(2)-C(53)-C(54)
C(53)-C(54)-C(55)
Ru(2)-Ru(1)-N(4)
N(1)-Ru(1)-N(4)
Ru(2)-Ru(1)-N(5)
N(1)-Ru(1)-N(5)
N(4)-Ru(1)-N(5)
Ru(2)-Ru(1)-N(8)
N(1)-Ru(1)-N (8)
N(4)-Ru(1)-N(8)
N(5)-Ru(1)-N(8)
Ru(2)-Ru(1)-C(45)
N(1)-Ru(1)-C(45)
N(4)-Ru(1)-C(45)
N(5)-Ru(1)-C(45)
N(8)-Ru(1)-C(45)
Ru(1)-Ru(2)-N(2)
Ru(1)-Ru(2)-N(3)
N(2)-Ru(2)-N(3)
Ru(1)-Ru(2)-N(6)
N(2)-Ru(2)-N(6)
N(3)-Ru(2)-N(6)
Ru(1)-Ru(2)-N(7)
N(2)-Ru(2)-N(7)
N(3)-Ru(2)-N(7)
N(6)-Ru(2)-N(7)
Ru(2)-Ru(1)-C(53)
N(2)-Ru(2)-C(53)
N(3)-Ru(2)-C(53)
N(6)-Ru(2)-C(53)
N(7)-Ru(2)-C(53)
Ru(1)-C(45)-C(46)
C(45)-C(46)-C(47)
Ru(2)-C(53)-C(54)
C(53)-C(54)-C(55)
a Data for molecule 2 of the (4,0) isomer are included in the Supporting Information.
are summarized in Tables 2 and 3, and their crystal structures
are presented in Figures 1 and 2. All intramolecular bond
lengths and angles as well as other structural data for the (4,0)
isomer of Ru2(F5ap)4(CtCC6H5) are given in the Supporting
Information.
The X-ray structure of the (4,0) isomer consists of two
independent molecules located in general positions (see Figure
1). The geometry of each Ru atom is nearly octahedral, with
one set of four pyridyl nitrogens (for Ru(1) or Ru(3)), and
another set of four anilino nitrogens (for Ru(2) or Ru(4)),
forming the equatorial planes. The Ru-Ru-C angle is
distinctly nonlinear, having an average value of 171.4° for
molecule 1 and 167.7° for molecule 2. Other crystallographic
differences between the two molecules can also be noted. For
example, the variations in bond lengths and angles involving
Ru(3) and Ru(4) (molecule 2) are more pronounced than those
involving Ru(1) and Ru(2) (molecule 1). Also, the N-Ru-
Ru-N torsion angles show a wider variation in molecule 2 than
in molecule 1.
The coordination of each Ru atom is essentially octahedral
in both the (3,1) and (2,2) trans isomers of Ru2(F5ap)4-
(CtCC6H5)2 (see Figure 2), and only a single molecule of each

Isomer Effect on Diruthenium Complexes
Inorganic Chemistry, Vol. 36, No. 24, 1997 5453
isomer, with values averaging 163.3° for the (3,1) and 160.8°
for the (2,2) trans isomer. The four N-Ru-Ru-N individual
torsion angles are quite different from each other in the (3,1)
isomer, ranging from 10.3 to 18.5°. The N(1)-Ru-Ru-N(2)
and N(3)-Ru-Ru-N(4) torsion angles average 12.7°, while
the N(5)-Ru-Ru-N(6) and N(7)-Ru-Ru-N(8) values aver-
age 15.5°. On the basis of steric hindrance alone, one would
have expected to see the -CtCC6H5 axial ligands of the (3,1)
isomer bend closer to the pyridyl groups than the anilino rings,
but the opposite is observed.
In all three isomers, there is a 50:50 mixture of left-handed
and right-handed molecules in the crystal with respect to the
N-Ru-Ru-N torsion angles. Each Ru atom has two long
Ru-N bonds and two short ones. This fact is illustrated by
comparing the Ru-Np bond lengths (Np ) pyridyl nitrogen) to
the Ru-Na bond lengths (Na ) anilino nitrogen) for the four
F5ap equatorial ligands in the (2,2) trans isomer. The Ru-Na
bond lengths are shorter than the Ru-Np bond lengths for only
two of the F5ap ligands (see Table 2).
The crystal structures of the three compounds also reveal the
following interesting geometric features:
(i) Three arrangements of bridging ligands are obtained for
Ru2(F5ap)4(CtCC6H5)2, suggesting that each parent compound
of Ru2(F5ap)4Cl should also have the corresponding (4,0), (3,1),
or (2,2) trans arrangement.
Figure 1. View of the (4,0) isomer of Ru2(F5ap)4(CtCC6H5)2 with
the H and F atoms omitted in molecule 1 and molecule 2 but with
both orientations of the disordered axial phenyl ring being shown.
(ii) The Ru-Ru bond distance in the (2,2) trans isomer is
2.473(1) Å, which is comparable to the value of 2.475(1) Å in
the (3,1) isomer, and both values are slightly longer than the
2.441(1) and 2.460(1) Å values in the two molecules of the
(4,0) isomer (see Table 2). These Ru-Ru bond distances are
all significantly shorter than the 2.556(1) Å Ru-Ru distance
in Ru2(dpf)4(CtCC6H5)2. However, as compared to the Ru-
6+
Ru bond distances of several Ru24+, Ru25+, and Ru2 com-
plexes,19 these bond distances are still much longer than
6+
expected for a Ru2 complex of this structural type.
(iii) For each isomer of Ru2(F5ap)4(CtCC6H5)2, the smallest
Ru-Ru-N and N-Ru-C bond angles are observed for the
longest Ru-N bond lengths. This is illustrated in the case of
the (3,1) isomer by the following data: The Ru(1)-N(5) bond
length is longer than the Ru(1)-N(1) bond length (see Table
2), and subsequently the Ru(2)-Ru(1)-N(5) and the C(45)-
Ru(1)-N(5) bond angles are both smaller than their respective
Ru(2)-Ru(1)-N(1) and C(45)-Ru(1)-N(1) bond angles (see
Table 3).
(iv) The deviation from linearity for the average Ru-Ru-C
bond angles in the three geometric isomers follows the order
(2,2) trans, 160.8° < (3,1), 163.3° < (4,0), 171.4° (or 167.7°)
The three isomers of Ru2(F5ap)4(CtCC6H5)2 are also ordered
in the same way if one compares the steric hindrance between
the phenyls of the equatorial ligands and the axial ligand and/
or the polarization of the Ru-Ru bond. The fact that the
average Ru-Ru-C bond angle differs from 180° results from
electronic effects rather than a steric hindrance between the axial
and equatorial ligands.19
Figure 2. Views of (a) the (3,1) isomer and (b) the (2,2) trans isomer
of Ru2(F5ap)4(CtCC6H5)2 with H and F atoms omitted.
(v) The arrangement of the equatorial ligands in the (4,0),
(3,1), and (2,2) trans isomers leads to a severe twist in geometry
of the structure, with the average N-Ru-Ru-N torsion angles
being 19.9° for the (4,0), 14.4° for the (3,1), and 8.35° for the
(2,2) trans isomer.
isomer is present in the crystal. In the (3,1) isomer of Ru2(F5-
ap)4(CtCC6H5)2, (Figure 2a), either three pyridyl and one
anilino nitrogens or one pyridyl and three anilino nitrogens form
the equatorial planes of each ruthenium while in the (2,2) trans
isomer (Figure 2b) these planes are formed by two pyridyl and
two anilino nitrogens in a trans arrangement. Again, the Ru-
Ru-C units are not linear in either the (3,1) or the (2,2) trans
(vi) Suprisingly, in the case of the (4,0) isomer, the two axial
phenylacetylide ligands have nearly the same geometries. For
instance, the same distances are seen between C(45) and C(46)

5454 Inorganic Chemistry, Vol. 36, No. 24, 1997
Bear et al.
Table 4. 1H and 19F NMR Chemical Shifts (δ, ppm)a of the (4,0), (3,1), and (2,2) Trans Isomers of Ru2(F5ap)4(CtCC6H5)2 in CD2Cl2
1H NMR
19F NMR
isomer
(4,0)
9.85 (4H, d)
8.18 (4H, t)
8.10 (2H, t)
8.03 (2H, t)
9.83 (1H, d)
9.57 (2H, d)
9.23 (1H, d)
7.41 (4H, t)
7.38 (2H, d)
9.31 (4H, d)
7.34 (8H, m)
5.92 (2H, d)
5.66 (1H, t)
5.12 (1H, t)
4.85 (2H, d)
4.54 (4H, d)
4.11 (4H, t)
-134.0 (4F, d)
-143.2 (4F, d)
-153.8 (4F, t)
-158.3 (4F, t)
-158.5 (4F, t)
(3,1)
7.35 (2H, d)
7.29 (2H, t)
7.27 (2H, d)
7.05 (4H, t)
6.85 (1H, t)
7.09 (2H, t)
6.90 (4H, d)
6.79 (2H, d)
6.66 (2H, t)
6.59 (2H, d)
6.45 (1H, d)
6.35 (1H, t)
6.65 (4H, d)
6.55 (4H, t)
-136.3 (2F, q)
-139.2 (2F, q)
-140.7 (2F, t)
-143.9 (2F, t)
-154.8 (2F, t)
-145.2 (8F, d)
-159.1 (4F, t)
-155.7 (1F, t)
-157.2 (1F, t)
-159.2 (2F, t)
-160.4 (2F, t)
-160.8 (4F, q)
-163.6 (8F, t)
(2,2)
a s ) singlet; d ) doublet; t ) triplet; q ) quartet; m ) multiplet.
(1.212 Å) and between C(53) and C(54) (1.211 Å) (Table 2),
while the Ru(2)-Ru(1)-C(45) and Ru(1)-Ru(2)-C(53) units
have almost the same angles (see Table 3). This could also
suggest that electronic effects play an important role in the
structure.
1
1H and 19F NMR Characterization. Well-defined H and
19F NMR spectra are obtained for the three isomers of Ru2(F5-
ap)4(CtCC6H5)2, indicating that the compounds are all dia-
magnetic. A summary of 1H and 19F NMR data is presented in
Table 4. Ten distinct 1H NMR resonances are seen for the (4,0)
isomer of Ru2(F5ap)4(CtCC6H5)2. The four occurring at 9.85,
8.18, 4.54, and 4.11 ppm show an integration representative of
four H’s and can be assigned to the four nonequivalent pyridyl
protons of the equatorial ligands. Due to the different electronic
environment created by the totally polar arrangement of the four
equatorial ligands in the (4,0) isomer, chemical shifts of the
protons on each of the phenyl rings in the axial ligand of Ru2(F5-
ap)4(CtCC6H5)2 differ from one another, thus appearing in
pairs.
The magnitude of the related chemical shifts in the 1H NMR
spectrum of the (3,1) and (2,2) trans isomers is similar to that
1
1
found in the H NMR spectrum of the (4,0) isomer. The H
NMR spectrum of the (3,1) isomer shows nine doublets and
six triplets while that of the (2,2) trans isomer exhibits three
doublets and two triplets. The NMR data clearly indicate that
the four bridging F5ap ligands, as well as the two -CtCC6H5
axial ligands, are identical in the (2,2) trans isomer, giving four
nonequivalent pyridyl protons and three nonequivalent axial
phenyl protons. The two equatorial ligands in the trans position
of the (3,1) isomer are equivalent but the other two equatorial
ligands and the two axial ligands are not equivalent in this
compound.
Figure 3. Cyclic voltammograms of each investigated isomer of
Ru2(F5ap)4Cl and Ru2(F5ap)4(CtCC6H5)2 in CH2Cl2 containing 0.1 M
TBAP. Scan rate ) 0.1 V/s.
cores can be accomplished by the redox reactions shown in (1)-
(3).
The three isomers of Ru2(F5ap)4(CtCC6H5)2 were also
characterized by 19F NMR. The 19F NMR spectrum of the (4,0)
isomer shows five peaks at -134.0, -143.2, -153.8, -158.3,
and -158.5 ppm. This implies that the fluorine atoms of the
pentafluorophenyl ring are nonequivalent due to restricted
rotation, which is also observed in the X-ray structure. As
illustrated in Table 4, the 19F NMR spectrum of the (3,1) isomer
shows more resonances than the spectrum of the (4,0) or (2,2)
trans isomer. Also, the 19F NMR spectrum of the (2,2) trans
isomer displays only three peaks with a ratio of 1:2:2, which
indicates that there is a free rotation of the pentafluorophenyl
rings, thus making the two ortho and two meta fluorines
equivalent.
4+
Ru25+ + e H Ru2
Ru26+ + e H Ru2
Ru27+ + e H Ru2
(1)
(2)
(3)
5+
6+
Cyclic voltammograms of the three isomers of Ru2(F5ap)4Cl
and Ru2(F5ap)4(CtCC6H5)2 in CH2Cl2 are shown in Figure 3,
and a summary of half-wave potentials for each electrode
reaction is given in Table 5. Each complex undergoes three
reversible reactions. The three isomers of Ru2(F5ap)4Cl undergo
two one-electron oxidations (reactions 2 and 3) and a single
one-electron reduction (reaction 1) while the three isomers of
Ru2(F5ap)4(CtCC6H5)2 undergo a single one-electron oxidation
Electrochemistry. Four oxidation states are possible for each
of the six investigated compounds. A stepwise interconversion
4+
between the compounds with Ru27+, Ru26+, Ru25+, or Ru2

Isomer Effect on Diruthenium Complexes
Inorganic Chemistry, Vol. 36, No. 24, 1997 5455
E1/2, V vs SCEa
Table 5. Half-Wave Potentials of Investigated Compounds in CH2Cl2, 0.1 M TBAP
6+
5+
4+
Ru27+/Ru2
Ru26+/Ru2
Ru25+/Ru2
compd
Ru2(F5ap)4Cl
isomer
(4,0)
(3,1)
(reaction 3)
(reaction 2)
(reaction 1)
1.68
1.61
1.59
0.95
0.78
0.63
-0.35
-0.35
-0.45
(2,2) trans
Ru2(F5ap)4(CtCC6H5)2
(4,0)
(3,1)
(2,2) trans
0.90
1.00
1.04
-0.05
-0.14
-0.18
-1.18
-1.20
-1.21
Ru2(F5ap)4(CtCC6H5)
(4,0)
0.80
-0.53
a See Figure 3 for labeling of reactions 1-3.
Figure 4. ESR spectra (77 K) in CH2Cl2, 0.2 M TBAP of the
electrogenerated (4,0), (3,1), and (2,2) trans isomers of
[Ru2(F5ap)4(CtCC6H5)2]-.
(reaction 3) and two one-electron reductions (reactions 2 and
1) under the same solution conditions.
Figure 5. ESR spectra (77 K) of the electrogenerated (4,0) isomer of
[Ru2(F5ap)4(CtCC6H5)2]- in CH2Cl2, 0.1 M TBAP and Ru2(F5ap)4-
(CtCC6H5) in CH2Cl2 containing excess 1,4-phenylene diisocyanide.
By comparing the cyclic voltammograms of the monochloro
and bis(phenylacetylide) compounds, one can illustrate how the
metal-centered molecular orbitals (HOMO and LUMO) are
sensitive to the donor/acceptor properties and number of axial
ligands. The average difference in E1/2 between the monochloro
and the corresponding bis(phenylacetylide) compound is 0.65
V for reaction 3, 0.91 V for reaction 2, and 0.81 V for reaction
(see Table 5). A small isomer effect on E1/2 is also seen for all
three electrode reactions of Ru2(F5ap)4(CtCC6H5)2 (see E1/2
values in Table 5).
ESR of Electrogenerated [Ru2(F5ap)4(CtCC6H5)2]-.
Ru2(F5ap)4Cl contains three unpaired electrons as evidenced by
the fact that the solid compound has a room-temperature
magnetic moment of 3.94 µB. This result is consistent with a
ground state electronic configuration of σ2π4δ2(δ*π*)3. The
three isomers of Ru2(F5ap)4(CtCC6H5)2 are unambiguously
5+
1. Thus, the Ru26+/Ru2 process has the largest variation in
7+
half-wave potentials while the Ru26+/Ru2 process has the
smallest.
The E1/2 of a given electrode reaction is also dependent upon
the type of isomer with the largest variation being seen in the
case of the Ru6+/Ru5+ reaction of the monochloro compound
(reaction 2). As seen in Table 5, the E1/2 for the first oxidation
of Ru2(F5ap)4Cl shifts cathodically by 170 mV upon going from
the (4,0) to the (3,1) isomer and by another 150 mV upon going
from the (3,1) to the (2,2) trans isomer. This contrasts with
reactions 1 and 3 of Ru2(F5ap)4Cl where E1/2 shifts by only ca.
100 mV upon going from the (4,0) to the (2,2) trans isomer
1
diamagnetic (as shown by their well-defined H and 19F NMR
spectra), and no ESR signals could be observed between room
temperature and 77 K. This is not the case, however, for the
singly reduced products of the (4,0), (3,1), or (2,2) trans isomer
of Ru2(F5ap)4(CtCC6H5)2 in CH2Cl2, 0.1 M TBAP which can
be electrogenerated by bulk electrolysis of the neutral isomers
at -0.60 V under argon.

5456 Inorganic Chemistry, Vol. 36, No. 24, 1997
Bear et al.
The 77 K ESR spectrum of each [Ru2(F5ap)4(CtCC6H5)2]-
isomer is shown in Figure 4. Interestingly, the (4,0) isomer of
[Ru2(F5ap)4(CtCC6H5)2]- exhibits a rhombic signal while the
(3,1) and (2,2) trans isomers both show an axial signal.
However, all ESR spectra in Figure 4 are characteristic of
species containing one rather than three unpaired electrons since,
in the latter case, either no signal or a broad and ill-resolved
ESR spectrum is observed.1,32
signal for this species is due to an extremely fast relaxation
time when the unpaired electron is in an orbital doublet, i.e.
when the ground state is an orbitally degenerate Eg state.
2
Several experiments were performed in order to determine
whether correlations might exist between the nature of the axial
ligand and the magnetic properties of the diruthenium(II,III)
complexes. For instance, it was observed that addition of more
than 100 equiv of 1,4-phenylene diisocyanide to a CH2Cl2
solution of the (4,0) isomer of Ru2(F5ap)4(CtCC6H5) leads to
an ESR spectrum (77 K) which is similar to that of [Ru2-
(F5ap)4(CtCC6H5)2]- (see Figure 5). On the other hand, no
ESR spectrum was observed when methanol, CH3CN, or F-,
was added to a CH2Cl2 solution of Ru2(F5ap)4(CtCC6H5). The
1,4-phenylene diisocyanide ligand is similar to the acetylide ion
in that both are good σ donors and π acceptors. This is not the
case for CH3OH, CH3CN, and F-, which are mainly σ donors.
Our data thus imply that the Ru25+ species should show an ESR
spectrum only if each ruthenium ion were complexed by an
axial ligand which is both a good σ donor and a good π acceptor.
As shown in Figure 4, the g3 component in the ESR spectrum
of each isomer consists of two signals which arise from the
two isotopes of the ruthenium atoms. One isotope has a spin
5
constant of /2 (29.8%) and has a six-line hyperfine splitting,
while the other has a spin constant of 0 (70.2%) and appears as
a singlet. The singlet signal is the most intense owing to the
natural abundance of the isotope population of the ruthenium
atoms. Interestingly, the most intense signal in the g3 compo-
nent of the (3,1) isomer of [Ru2(F5ap)4(CtCC6H5)2]- does not
appear as a single peak, as is the case of the (4,0) or (2,2) trans
isomer (see Figure 4), but rather is split into two closely-spaced
peaks of unequal magnitude. The origin of the splitting is not
known, but a similar splitting is also seen in at least one
dirhodium complex where the single unpaired electron can be
either localized on one rhodium atom or delocalized over the
two rhodium metals.28
Acknowledgment. The support of the Robert A. Welch
Foundation (J.L.B., Grant E-918; K.M.K., Grant E-680) is
gratefully acknowledged. We also acknowledge Dr. J. D. Korp
for X-ray crystallography.
Supporting Information Available: Tables of data collection
parameters, atomic coordinates, anisotropic displacement parameters,
H atom coordinates and isotropic displacement parameters, and all
molecular bond lengths and angles and figures showing various views
(including space filling views) of the molecule and molecular packing
diagrams (72 pages). Ordering information is given on any current
masthead page.
It should also be pointed out that all but one previously
reported Ru2 complex of the structural type investigated in
5+
this study have three unpaired electrons. The only exception
is Ru2[(p-tolyl)NNN(p-tolyl)]4(CH3CN)(BF4) ((p-tolyl)NNN(p-
tolyl) ) di-p-tolyltriazenate) which is ESR silent from room
temperature to 77 K33 but has one unpaired electron and an
electronic configuration of σ2π4δ2π*3. The lack of an ESR
IC9602658
(32) Smith, K. M. Porphyrins and Metalloporphyrins; Elsevier Scientific
(33) Cotton, F. A.; Falvello, L. R.; Ren, T.; Vidyasagar, K. Inorg. Chim.
Acta 1992, 194, 163.
Publishing Co: New York, 1975; p 582.