One-electron oxidation behavior of {MNO}6-type nitrosyl complexes having acetylacetonato ligand, [M(NO)Cl5-2n(acac)n]m (M=Ru, Os; N=1, 2; Acac=acetylacetonato)

Article abstract of DOI:10.1016/S0020-1693(96)05578-8

The electrochemical behavior of several complexes with the general formula [M(NO)Cl_5-2n(acac)_n]^m (M=Ru, Os; n=1, 2; acac=acetylacetonato) was investigated: mer-[Ru(NO)Cl₃(acac)]^- (1, n=1), cis-[Ru(NO)Cl(acac)₂] (2, n=2), mer-[Os(NO)Cl₃(acac)]^- (3, n=1), cis-[Os(NO)Cl(acac)₂] (4, n=2). The study includes the known corresponding n=0 complexes, [M(NO)Cl₅]^2- (M=Ru, Os), for comparison. All these complexes undergo a one-electron oxidation, which is rather unusual redox behavior in the {MNO}⁶-type nitrosyl complexes. The behavior of some of these complexes as electrophiles was also described. Molecular structures with a meridional configuration were established for the n=1 complexes ([Ru(NO)Cl₃(acac)]^- (1) and [Os(NO)Cl₃(acac)]^- (3)) by X-ray structure determinations. Crystal data for 1 (Bu₄N salt): C₂₁H₄₃N₂O₃Cl₃Ru, a=31.443(9), b=21.86(1), c=19.852(6) A, β=119.65(2)°, monoclinic, C2/c, Z=16. Crystal data for 3 (Cs salt): C₅H₇NO₃Cl₃OsCs, a=7.942(1), b=12.602(2), c=7.451(2) A, α=105.91(2), β=98.20(2), γ=90.31(1)°, triclinic, P1, Z=2.

Full text of DOI:10.1016/S0020-1693(96)05578-8

Inorganica Chimica Acta 261 (1997) 45–52
One-electron oxidation behavior of {MNO}6-type nitrosyl complexes
having acetylacetonato ligand, [M(NO)Cl5y2n(acac)n]m
(MsRu, Os; ns1, 2; acacsacetylacetonato)
Dai Ooyama, Noriharu Nagao 1, Hirotaka Nagao, Yuko Sugimoto, F. Scott Howell,
Masao Mukaida U
Department of Chemistry, Faculty of Science and Engineering, Sophia University, Kioi-cho 7-1, Chiyoda-ku, Tokyo 102, Japan
Received 18 July 1996; revised 27 September 1996; accepted 25 October 1996
Abstract
The electrochemical behavior of several complexes with the general formula [M(NO)Cl5y2n(acac)n]m (MsRu, Os; ns1, 2;
acacsacetylacetonato) was investigated: mer-[Ru(NO)Cl3(acac)]y (1, ns1), cis-[Ru(NO)Cl(acac)2] (2, ns2), mer-
[Os(NO)Cl3(acac)]y (3, ns1), cis-[Os(NO)Cl(acac)2] (4, ns2). The study includes the known corresponding ns0 complexes,
[M(NO)Cl5]2y (MsRu, Os), for comparison. All these complexes undergo a one-electron oxidation, which is rather unusual redoxbehavior
in the {MNO}6-type nitrosyl complexes. The behavior of some of these complexes as electrophiles was also described. Molecular structures
with a meridional configuration were established for the ns1 complexes ([Ru(NO)Cl3(acac)]y (1) and [Os(NO)Cl3(acac)]y (3)) by
˚
X-ray structure determinations. Crystal data for 1 (Bu4N salt): C21H43N2O3Cl3Ru, as31.443(9), bs21.86(1), cs19.852(6) A,
˚
bs119.65(2)8, monoclinic, C2/c, Zs16. Crystal data for 3 (Cs salt): C5H7NO3Cl3OsCs, as7.942(1), bs12.602(2), cs7.451(2) A,
#
as105.91(2), bs98.20(2), gs90.31(1)8, triclinic, P1, Zs2.
Keywords: Crystal structures; Nitrosyl complexes; Ruthenium complexes; Osmium complexes; Electrochemistry
1. Introduction
mer-[Os(NO)Cl3(acac)]y (3, ns1), cis-[Os(NO)Cl-
(acac)2] (4, ns2). This paper describes the syntheses,
structures and characteristics of such ruthenium and osmium
metal complexes. We paid special attention to the investiga-
tion of the electrochemical properties.
Various {MNO}6-type nitrosyl complexes have been
reported [1–4]. The complexes showed a characteristicelec-
trochemical behavior due to a ligand (nitrosyl)-based reduc-
tion, but no electrode oxidation could be observed in the
measurable potential region. This was true for ns0 nitrosyl
complexes [M(NO)Cl5y2n(acac)n]m, [M(NO)Cl5]2y
(MsRu, Os), until recent work by several researchers
appeared [5–7]. Tocher and co-workers and Sinitsyn and co-
workers have shown that [M(NO)Cl5]2y exhibits a revers-
ible one-electron oxidation to give [M(NO)Cl5]y, which is
believed to contain an(MIII(NOq))moiety[5,6]. Wereport
here that an electrochemical oxidation occurs also in the
2. Experimental
2.1. Materials
The following complexes were prepared by the literature
methods. The solutions of nitrosylruthenium (Ru(NO)Cln)
(used as starting material) and K2[Ru(NO)Cl5] were pre-
pared by a conventional method of Fletcher et al. [8].
(Bu4N)2[Ru(NO)Cl5] was obtained using Bu4NCl, instead
of KCl. Cis-[Ru(NO)Cl(acac)2] was prepared by modify-
ing a procedure that was reported previously [9].
following complexes of general formula [M(NO)Cl5y2n
-
(acac)n]m (MsRu, Os; ns1, 2; acacsacetylacetonato),in
addition to the reduction mentioned above: mer-[Ru(NO)-
Cl3(acac)]y (1, ns1), cis-[Ru(NO)Cl(acac)2] (2, ns2),
2.2. Measurements
U Corresponding author.
1 Present address: Department of Chemistry, Stanford University, Stan-
ford, CA 94305, USA.
Elemental analyses were performed by the Sophia Univer-
sity Analytical Facility. IR spectra were recorded with a Per-
0020-1693/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved
PII S0020-1693(96)05578-8

46
D. Ooyama et al. / Inorganica Chimica Acta 261 (1997) 45–52
kin-ElmerFT-1650 spectrophotometer.UV–Visspectrawere
was refluxed for 2 h; during this time the pH of the solution
was adjusted repeatedly. The reaction solution was trans-
ferred to an open beaker, and then was concentrated on a hot
plate until crystalline material deposited. The product was
collected by filtration, and washed with cold water. The prod-
uct wasrecrystallizedfromethanolcontainingasmallamount
of water. The purified black–brown product was collected by
filtration and washed with ether, and then air dried. Yield
30% (140 mg). Anal. Found: C, 32.6; N, 3.81; H, 3.80. Calc.
for [Ru(NO)Cl(C5H7O2)2]H2O: C, 32.9; N, 3.84; H,
3.87%.
1
obtained with a Hitachi 200-20 spectrophotometer. H and
13C NMR spectra were obtained with a JEOL GX-270
spectrophotometer. All NMR spectra were obtained in
CD3COCD3, CD2Cl2 or CDCl3; Me4Si wasusedasaninternal
1
reference in the measurements of both H and 13C NMR
spectra. For the electrochemical measurements, aHusopolar-
ograph model 312 was used; the current potential waveswere
recorded with a Riken-Denshi Instruments model F-3F
recorder. The experiments were performed in CH3CN, with
a supporting electrolyte concentration of 0.1 M (tetraethyl-
ammonium perchlorate). Three-electrode, one-compartment
bcells were used. They were equipped with a platinum work-
ing electrode (fs1.6 mm), a platinum auxiliary electrode,
and a silver reference electrode (AgNAgNO3, 0.01 mol
dmy3). The coulometricexperimentswereperformedintwo-
compartment cells, using a platinum-gauze working elec-
trode, with the auxiliary electrode in the second compartment
separated by a glass frit. The number of coulombs was
measured by a Huso model 343B digital coulometer.
2.3.4. Cs[Os(NO)Cl3(acac)] (3)
The complex was obtained from the reactionsolution,from
which cis-[Os(NO)Cl(acac)2] (4) was separated by the
procedure described below. The volume of the solution was
reduced by spontaneous evaporation at room temperature,
until just before the solution had dried up. The solid material
which deposited was collected by filtration, and then recrys-
tallized from acetone–MeOH solution. The reddish brown
product was collected by filtration, washed using cold water,
EtOH and ether, and then air dried. Yield 15% (50 mg).
Anal. Found: C, 10.74; N, 2.50; H, 1.16. Calc. for
Cs[Os(NO)Cl3(C5H7O2)]: C, 10.75; N, 2.51; H, 1.27%.
2.3. Syntheses
2.3.1. Cs[Ru(NO)Cl3(acac)]
This complex was prepared as a raw material for
(Ph4As)[Ru(NO)Cl3(acac)] (1). To a starting solution of
Ru(NO)Cln (20 cm3, 0.5 g as RuCl3) was added a mixed
solution of Hacac–MeOH (4–4 cm3). The reaction solution
was adjusted to pHs1.0 with an aqueous solution of NaOH,
using a pH meter. The mixture was refluxed for 2 h, and then
the reaction solution was transferred to an open beaker. It
was concentrated on a hot plate until the solution volume was
reduced to 10 cm3. Then the solution was allowed to stand at
room temperature for 3 days. After the solution had been
filtered, using a piece of filter paper, CsCl (500 mg) was
added to the filtrate. From this a pale reddish brown crystal-
line material deposited. The product was collected by filtra-
tion, and washed with cold water, EtOH, and ether, then air
dried. Yield 40% (350 mg). The product was used as a raw
material for the preparationof(Ph4As)[Ru(NO)Cl3(acac)]
(see the next procedure).
2.3.5. Cis-[Os(NO)Cl(acac)2] (4)
To a solution of Cs2[Os(NO)Cl5] (0.4 g) in water (15
cm3) was added a mixed solution of Hacac–MeOH (4–6
cm3). The mixed solution was adjusted to pHs3.5 with an
aqueous solution of NaOH, using a pH meter. The mixture
was refluxed for 6 days, during which time the pH of the
solution was adjusted repeatedly. The reaction solution was
transferred to an open beaker and was concentrated on a hot
plate until red–purple crystalline material deposited. The
product was collected by filtration, then washed with water.
The product was recrystallized from the mixed solution of
CH2Cl2–EtOH–H2O (7–4–1 cm3). The purified reddish pur-
ple product was collected by filtration and washedwithwater,
and then air dried. Yield 50% (140 mg). Anal. Found: C,
26.57; N, 3.04; H, 3.17. Calc. for [Os(NO)Cl(acac)2]: C,
26.46; N, 3.09; H, 3.12%.
2.3.2. (Ph4As)[Ru(NO)Cl3(acac)] (1)
To a hydrochloric acid solutionofCs[Ru(NO)Cl3(acac)]
(100 mg, H2O–HCl 10 cm3 (4:1)), Ph4AsCl (100 mg) was
added. A pale brown precipitate was formed immediately. It
was collected by filtration, washed with cold water, and then
air dried. Yield 70% (170 mg). Anal. Found: C, 48.24; N,
2.33; H, 3.66. Calc. for (Ph4As)[Ru(NO)Cl3(C5H7O2)]:C,
48.38; N, 1.95; N, 3.79%.
2.4. X-ray crystallographic study
The reflections of an X-ray analysis with Mo Ka radiation
˚
(ls0.71069 A) were collected by the v–2u technique for 1
(2u-45.08) and for 3 (2u-50.0) on a Rigaku AFC5S dif-
fractometer at room temperature (208C); the resultingcrystal
data and details concerning data collection and refinement
are given in Table 1. All calculations were carried out on
a Silicon Graphics Indy Computer, using the program
TEXSAN.
2.3.3. Cis-[Ru(NO)Cl(acac)2] (2)
To a starting solution of Ru(NO)Cln (20 cm3, 0.5 g as
RuCl3) was added a mixed solution of Hacac–MeOH (4–4
cm3). The reaction solution was adjusted to pHs3.7 with an
aqueous solution of NaOH, using a pH meter. The mixture

D. Ooyama et al. / Inorganica Chimica Acta 261 (1997) 45–52
47
Table 1
Selected crystallographic data
Compound
(Bu4N)[Ru(NO)Cl3(acac)] (1)
Cs[Os(NO)Cl3(acac)] (3)
Chemical formula
Formula weight
C21H43N2O3Cl3Ru
579.01
31.443(9)
21.86(1)
19.852(6)
90
119.65(2)
90
11856(8)
C2/c
16
1.297
8.20
293
0.048
0.031
C5H7NO3Cl3CsOs
558.58
7.942(1)
12.602(2)
7.451(2)
105.91(2)
98.20(2)
90.31(1)
709.1(2)
#
P1
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
˚
Volume (A )
Space group
Z
2
Density (calc.) (g cmy3
)
2.616
120.64
293
0.035
0.049
m (cmy1
T (K)
R
)
Rw
3. Results and discussion
[Ru(NO)Cl3(acac)]y (1) and cis-[Ru(NO)Cl(acac)2]
(2) are obtainable in different pH conditions: pHs1.0 for
mer-[Ru(NO)Cl3(acac)]y (1) and 3.7 for cis-[Ru(NO)-
Cl(acac)2] (2). The conditions for the synthesis of 1 must
be strictly adhered to, and the complex could be obtained
only when the solution was kept near pHs1, otherwise the
species was contaminated by 2.
The preparative conditions of the osmium analogues are
different from those of the ruthenium complexes: either mer-
[Os(NO)Cl3(acac)]y (3) or cis-[Os(NO)Cl(acac)2] (4)
was formed under the same acidicconditions, pHs3.5. Com-
plex 3 could be isolated only when a counter-ion was added
to the reaction solution, but 4 was precipitated as crystalline
material during the process of concentration of the reaction
solution. All these complexes were characterized according
to satisfactory elemental analyses, cyclic voltammetric par-
ameters, visible and UV spectra, and 1H and 13C NMR spec-
tra. The data used for the characterization are summarized in
Table 2.
3.1. Syntheses, characterization and structures
Both [Ru(NO)Cl5]2y and [Os(NO)Cl5]2y (ns0 com-
plexes for [M(NO)Cl5y2n(acac)n]m) have been reported
[1–4], but a detailed electrochemical investigation was not
completed until recently [5–7]. These authors showed that
[M(NO)Cl5]2y (MsRu, Os) could be oxidized to give a
one-electron oxidation species, [M(NO)Cl5]y, which was
believed to contain the (MIII(NOq))4q moiety. The isola-
tion of the one-electron oxidation product has succeeded
in the osmium case, as R[Os(NO)Cl5] (RsEt4N, Ph4As,
Ph4P) [6,7]. Thecorrespondingrutheniumspecies,however,
did not give such a solid material, due to chemical instability.
Our recent attempt to isolate [Ru(NO)Cl5]y also failed;but,
instead, we were able to characterize the self-decomposition
reaction of [Ru(NO)Cl5]y, which occurred along with
the one-electron oxidation of [Ru(NO)Cl5]2y [10]:
[Ru(NO)Cl5]y gave cis-[Ru(NO)Cl4(solvent)]y (at
258C in the dark), instead of the expected trans-
[Ru(NO)Cl4(solvent)]y, and then the cis-form product
changed further to trans-[RuCl4(solvent)2]y (at258Cunder
room light). Two more unidentified species were detected as
taking part in this reaction.
Several ruthenium complexes with the acetylacetonato
ligand have been investigated recently [11]. However, the
ruthenium complexes with the general formula
[M(NO)Cl5y2n(acac)n]m (ns1 and 2) have not been syn-
thesized, except for cis-[Ru(NO)Cl(acac)2] (2). Detailed
electrochemical investigations of the latter have not yet been
carried out. In addition, the corresponding osmium com-
plexes, either mer-[Os(NO)Cl3(acac)]y (3) or cis-
[Os(NO)Cl(acac)2] (4), have not been prepared. In the
course of our work on the isolation of the complexes, we
observed some differences between the ruthenium and
osmium complexes. As described in Section 2, both mer-
The {MNO}6-type nitrosyl complexes show well-defined
NMR spectra, which aid greatly in the identification of their
steric configurations: the cis-type of coordination mode of
the acetylacetonato ligand was established in both 2 and 4,
cis-[Ru(NO)Cl(acac)2] and cis-[Os(NO)Cl(acac)2]
(Table 2). Although two other different steric forms, mer-
and fac-configuration, are possible for the mono-acetyl-
acetonato complexes, [Ru(NO)Cl3(acac)]y (1) and
[Os(NO)Cl3(acac)]y (3), as precursor species of 2 and 4,
respectively, the NMR data suggested that 1 and 3 have the
meridional configuration.
The meridional assignments in both [Ru(NO)-
Cl3(acac)]y (1) and [Os(NO)Cl3(acac)]y (3) could also
be confirmed by X-ray structure determination. ORTEPs
drawings of the complex anions are shown in Fig. 1 and their
atomic coordinates are listed in Tables 3 and 4. Some of the
selected bond lengths and angles are listed in Tables 5 and 6.
The NO moiety is essentially linear with the Ru atom and the

48
D. Ooyama et al. / Inorganica Chimica Acta 261 (1997) 45–52
Table 2
Data used for the characterization
[Ru(NO)Cl5]2y
[Ru(NO)Cl3(acac)]y
[Ru(NO)Cl(acac)2]
n(NO) a
1850
1862
1873
lmax b (nm) (e (moly1 dm3 cmy1))
1H NMR (d)
520 (52)
486 (55)
505 (184) c
2.02, 2.07 (–CH3); 5.59 (–CH)
(CD3COCD3)
2.05, 2.14, 2.24, 2.29 (–CH3); 5.47,
5.73 (–CH) (CDCl3)
13C NMR (d)
26.49, 27.51 (–CH3); 100.4 (–CH);
206.0 d (–C_O) (CD3COCD3)
[Os(NO)Cl5]2y
[Os(NO)Cl3(acac)]y
[Os(NO)Cl(acac)2]
n(NO) a
1803
1814
1819, 1841
lmax b (nm) (e (moly1 dm3 cmy1))
1H NMR (d)
575 (40), 440 (57)
545 (96)
512 (14)
2.03, 2.06 (–CH3); 5.77 (–CH)
(CD3COCD3)
2.10, 2.22, 2.31, 2.58 (–CH3); 5.68,
5.90 (–CH) (CD2Cl2)
13C NMR (d)
25.88, 26.70, 26.99, 27.60 (–CH3);
101.6, 102.7 (–CH); 187.2, 193.3,
193.8, 194.9 (–C_O) (CD2Cl2)
a In CH3CN.
b In CH3CN.
c In CH3OH.
d Overlapped with the spectral line due to the solvent.
[Ru(NO)Cl(acac)2] (2) were produced under different pH
conditions: mer-[Ru(NO)Cl3(acac)]y (1) was obtained
from the solution of pHs1.0 and cis-[Ru(NO)Cl(acac)2]
(2) from that of pHs3.7. Further increasing the pH value
of the solution to give neutral conditions results in a nitrosyl
ligand reaction, in which a hydroxyiminoacetylacetonato
ligand (hia) is formed [17]:
[Ru(NO)Cl(acac)2]qHacacs[Ru(hia)(acac)2]
q2HqqCly (hiasCH3COC(NO)COCHy3 ) (1)
Although the hydroxyiminoacetylacetonato (hia) ligand
formation occurred relatively easily for cis-[Ru(NO)Cl-
(acac)2] (2), cis-[Os(NO)Cl(acac)2] (4) did not undergo
the reaction, even in neutral solution. We assume that this
difficulty in producing the hia ligand stems mainly from the
inertness of the chloro ligand in osmium complex 4. The
assumption is supported by a result of our previous work
[17]: the ligand formation occurred immediately at room
temperature in the reaction between cis-[Ru(NO)(H2O)-
(bpy)2]3q and Hacac, in which cis-[Ru(hia)(bpy)2]q was
isolated as the PF6 salt. However, a similar experiment using
cis-[Ru(NO)Cl(bpy)2]2q, instead of cis-[Ru(NO)(H2O)-
(bpy)2]3q, required at least 1 week for the completion of the
hia ligand formation under the same conditions [17].
Fig. 1. ORTEP drawings of the mer-[Ru(NO)Cl3(acac)]y ion (1) and
mer-[Os(NO)Cl3(acac)]y ion (3).
Ru–NO and N–O bond lengths are similar to typical values
in other {RuNO}6-type nitrosyl complexes [12,13].
In octahedral geometry, one of the oxygen atoms of the
acetylacetonato ligand in both complexes exists in the trans
position to the nitrosyl group, and another oxygen atom lies
in the cis position. Reports by other researchers have shown
that either the fac-form or the mer-form was available in
[Ru(NO)X3(L-L)]-type complexes (Xshalogeno, L-Ls
bidentate ligand), when ethylendiamine or 2,29-bipyridine
was employed as the bidentate ligand [14–16].
b
An acid–base interconversion reaction which occurs
3.2. Reactivity as an electrophile
between the nitrosyl and the nitro species (Eq. (2)) can be
regarded as one of the criteria for the electrophilic behavior
of the coordinated nitrosyl [1–4]:
Some differences in the nitrosyl reactivity between mer-
[Ru(NO)Cl3(acac)]y (1) and mer-[Os(NO)Cl3(acac)]y
(3) could be observed in their formation reactions. As
mentioned earlier, mer-[Ru(NO)Cl3(acac)]y (1) or cis-
(RuNO)3qq2OHy|(Ru(NO2))qqH2O
(2)

D. Ooyama et al. / Inorganica Chimica Acta 261 (1997) 45–52
49
Table 3
Table 4
Positional parameters for the non-hydrogen atoms in (Bu4N)-
[Ru(NO)Cl3(acac)] (1)
Positional parameters for the non-hydrogen atoms in Cs[Os(NO)-
Cl3(acac)] (3)
Atom
x
y
z
Beq
Atom
x
y
z
Beq
5.27(3)
Os
Cs
0.21771(5)
0.7142(1)
0.4225(4)
0.0413(4)
0.2620(4)
0.29359(3)
0.49163(7)
0.2804(3)
0.0006(3)
0.4883(2)
0.3022(9)
0.2899(6)
0.1260(6)
0.3007(7)
0.2031(9)
0.0955(9)
0.0615(9)
0.224(1)
0.12907(6)
0.2711(1)
2.714(9)
4.81(2)
457(8)
4.74(8)
4.18(7)
8.3(3)
3.2(2)
3.4(2)
4.0(2)
2.8(2)
3.5(3)
3.2(2)
3.7(3)
4.6(3)
Ru(1)
Ru(2)
Cl(1)
Cl(2)
Cl(3)
Cl(4)
Cl(5)
Cl(6)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
N(1)
N(2)
N(3)
N(4)
C(1)
C(2)
C(3)
0.01410(4)
0.70717(6)
0.50979(6)
0.48893(6)
0.3974(2)
0.6238(2)
0.4397(2)
0.5055(2)
0.4783(2)
0.5750(2)
0.5386(8)
0.4837(5)
0.5697(5)
0.3611(5)
0.5826(4)
0.4213(4)
0.5280(7)
0.4129(5)
0.6146(5)
0.1824(6)
0.4996(9)
0.5383(10)
0.5727(8)
0.468(1)
0.6193(8)
0.5851(7)
0.5203(8)
0.4440(7)
0.6656(7)
0.3823(8)
0.6727(6)
0.6942(7)
0.7376(8)
0.7571(7)
0.6390(6)
0.7106(7)
0.7257(7)
0.7904(8)
0.6033(6)
0.5384(7)
0.5470(7)
0.4790(8)
0.5365(6)
0.5016(6)
0.4162(7)
0.3774(8)
0.2022(8)
0.1948(8)
0.243(1)
0.21127(4) y0.00445(6)
5.14(3)
8.1(1)
9.2(1)
5.96(9)
6.8(1)
7.2(1)
6.78(10)
13.4(5)
7.1(2)
6.8(3)
10.1(4)
6.1(2)
7.1(3)
8.1(4)
6.0(3)
4.8(3)
6.3(3)
7.8(5)
9.0(6)
7.1(5)
12.8(6)
10.3(6)
6.6(4)
6.8(4)
6.8(4)
8.3(5)
11.7(6)
5.5(3)
7.4(4)
10.1(4)
11.0(5)
5.6(4)
7.6(4)
8.2(4)
10.8(5)
5.3(3)
6.0(4)
7.2(4)
12.0(5)
4.8(3)
6.3(4)
8.5(4)
10.6(5)
10.7(5)
12.7(6)
22.6(8)
24.6(9)
8.3(4)
8.7(4)
10.1(5)
13.3(6)
7.6(4)
9.8(5)
14.0(7)
19.9(8)
7.4(4)
7.3(4)
9.2(5)
11.0(5)
Cl(1)
Cl(2)
Cl(3)
O(1)
O(2)
O(3)
N(1)
C(1)
C(2)
C(3)
C(4)
C(5)
y0.0783(4)
0.3635(5)
0.2319(4)
y0.152(2)
0.326(1)
0.0215(1)
0.0091(1)
0.7115(2)
0.7162(2)
0.6731(2)
y0.1098(2)
0.1027(2)
y0.0074(2)
0.5821(5)
0.7911(4)
0.7416(4)
y0.0285(5)
0.0101(4)
0.0024(5)
0.6347(6)
y0.0175(5)
0.2085(5)
0.1744(6)
0.8404(7)
0.8456(8)
0.7973(8)
0.8976(6)
0.8098(8)
0.0097(6)
0.0083(7)
0.0041(8)
0.0143(7)
0.004(1)
y0.0675(1)
0.2015(1)
0.2155(1)
0.2956(1)
0.0442(4)
y0.0130(3)
0.0834(3)
0.2246(4)
0.2046(3)
0.1381(3)
0.0335(4)
0.2186(3)
0.3651(3)
0.3668(3)
0.0122(6)
0.0627(6)
0.0944(5)
y0.0186(5)
0.1487(4)
0.1642(5)
0.1182(4)
0.1078(5)
0.1722(5)
0.0532(5)
0.4014(4)
0.3816(4)
0.4231(5)
0.4043(5)
0.3296(4)
0.3512(4)
0.3096(5)
0.3260(5)
0.3937(3)
0.3650(4)
0.3968(4)
0.3753(5)
0.3326(3)
0.3600(4)
0.3230(4)
0.3467(5)
0.3716(6)
0.4106(5)
0.4281(6)
0.3963(7)
0.3211(5)
0.3185(5)
0.2737(4)
0.2628(5)
0.4122(4)
0.4119(5)
0.4589(7)
0.4601(6)
0.3601(4)
0.3192(4)
0.3132(5)
0.2679(4)
y0.069(1)
0.4171(9)
0.1968(9)
0.048(1)
0.484(1)
0.428(1)
0.291(1)
0.634(1)
0.240(2)
0.055(1)
y0.040(1)
0.358(1)
0.266(2)
0.124(2)
0.508(2)
0.041(2)
y0.0576(10)
Table 5
˚
Selected bond lengths (A) for 1 and 3
(Bu4N)[Ru(NO)Cl3(acac)] (1)
Ru1–N1
N1–O1
Ru1–Cl1
Ru1–Cl2
Ru1–Cl3
Ru1–O2
Ru1–O3
O2–C1
C1–C2
1.67(1)
1.19(1)
2.357(3)
2.354(4)
2.354(3)
1.980(8)
2.041(7)
1.28(1)
1.38(2)
1.38(2)
1.26(1)
1.51(2)
1.51(1)
Ru2–N2
1.661(9)
1.16(1)
2.367(4)
2.360(4)
2.339(3)
1.997(7)
2.016(7)
1.30(1)
1.38(1)
1.38(1)
1.24(1)
1.49(1)
1.54(1)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
N2–O4
Ru2–Cl4
Ru2–Cl5
Ru2–Cl6
Ru2–O5
Ru2–O6
O5–O6
C6–C7
C7–C8
O6–C8
C6–C9
C8–C10
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34)
C(35)
C(36)
C(37)
C(38)
C(39)
C(40)
C(41)
C(42)
0.2529(6)
0.3079(6)
0.3525(6)
0.4089(7)
0.1830(6)
0.1440(6)
0.1257(7)
0.0828(6)
0.1569(6)
0.1126(5)
0.0576(6)
0.0145(7)
0.2393(5)
0.2712(6)
0.2851(7)
0.3178(7)
0.2399(8)
0.2744(9)
0.340(1)
C2–C3
O3–C3
C1–C4
C3–C5
Cs[Os(NO)Cl3(acac)] (3)
Os–N1
N1–O1
Os–Cl1
Os–Cl2
Os–Cl3
Os–O2
1.729(9)
1.16(1)
2.375(3)
2.374(3)
2.370(3)
2.010(7)
Os–O3
O2–C1
C1–C2
C2–C3
C1–C4
C3-C5
2.031(7)
1.28(1)
1.38(1)
1.38(1)
1.48(1)
1.49(2)
Published data on the equilibria for several ruthenium and
osmium complexes show that the pK value is strongly
dependent upon both metal ion and co-existing ligands [18].
The effect on the steric factor of the complexes used for
measuring the pK value is estimated to be quite small: almost
the same pK values have been estimated for both cis-
[Ru(NO)Cl(bpy)2]2q and the corresponding trans-form
complex [19]. We attempted to measure the pK value of the
acid–base reaction in both cis-[Ru(NO)Cl(acac)2] (2) and
cis-[Os(NO)Cl(acac)2] (4) photometrically, buttheresults
were not useful, because partial decomposition of both com-
plexes occurred in basic media. The acetylacetonato com-
plexes seem to be insensitive to the nitrosyl–nitro conversion
reaction (Eq. (2)). This is in accord with the judgement of
0.369(1)
0.220(1)
0.1489(7)
0.1477(7)
0.1194(8)
0.1200(9)
0.1394(7)
0.0739(7)
0.0466(7)
y0.010(1)
0.1608(6)
0.1915(6)
0.1705(7)
0.1913(7)
0.1833(7)
0.2565(7)
0.2448(8)
0.3038(8)
0.2418(7)
0.2343(9)
0.305(1)
0.307(1)
0.1037(7)
0.0361(7)
y0.0395(7)
y0.1073(7)

50
D. Ooyama et al. / Inorganica Chimica Acta 261 (1997) 45–52
Table 6
y1.44 V. Multiple scanning showed that the reduction of
Selected bond angles (8) for 1 and 3
[Ru(NO)Cl5]2y at this potential results in the gradual
appearance of a new wave at 0.8 V. No experiments attempt-
ing the identification of the species responsible were under-
(Bu4N)[Ru(NO)Cl3(acac)] (1)
Ru1–N1–O1
Cl1–Ru1–Cl2
N1–Ru1–O2
Cl3–Ru1–O2
Ru1–O2–Cl
O2–C1–C2
C1–C2–C3
175(1)
Ru2–N2–O4
Cl4–Ru2–Cl5
N2–Ru2–O5
Cl6–Ru2–O6
Ru2–O5–C6
O5–C6–C7
C6–C7–C8
177(1)
taken. A reduction wave was also found in [Os(NO)Cl5]2y
,
172.7(2)
176.4(4)
176.8(3)
125.5(8)
127(1)
124(1)
127(1)
124.9(9)
173.8(1)
178.1(4)
175.2(3)
126.2(7)
123(1)
126(1)
126(1)
126.1(8)
but the wave was detected at the limited negative end of the
potential window, discouraging further investigation.
The CV pattern of [M(NO)Cl5y2n(acac)n]m, including
that of [M(NO)Cl5]2y, is quite different from those of other
{MNO}6-type nitrosyl complexes, such as cis-[Ru(NO)Cl-
(bpy)2]2q which has been well-investigated electrochemi-
cally [21]. In the latter nitrosyl complexes, we found usually
two one-electron reduction waves, without any electrodeoxi-
dation reaction. The site of the reduction is regarded to be a
nitrosyl ligand [21].
C2–C3–O3
Ru1–O3–C3
C7–C8–O6
Ru2–O6–C8
Cs[Os(NO)Cl3(acac)] (3)
Os–N1–O1
Cl1–Os–Cl2
N1–Os–O2
Cl3–Os–O3
Os–O2–C1
177(1)
O2–C1–C2
C1–C2–C3
C2–C3–O3
Os–O3–C3
125.8(9)
126(1)
124(1)
172.6(1)
178.3(4)
175.4(2)
126.3(6)
127.4(7)
3.3.2. The ns1 complexes, [M(NO)Cl3(acac)]y (1 and 3)
All electrochemical data are listed in Table 7. A typical
cyclic voltammogram of mer-[Os(NO)Cl3(acac)]y (3) is
shown in Fig. 2.
Bottomley et al. based on IR (n(NO)) data [20]: the IR
(n(NO)) data of cis-[Ru(NO)Cl(acac)2] (2) (1890
cmy1) and of cis-[Os(NO)Cl(acac)2] (4) (1860 cmy1
)
suggest that these are rather inactive nitrosyl complexes.
Either the reversible oxidation wave or the irreversible
reduction wave was found at 1.12 V (E1/2) and y1.60 V
(Epc), respectively. The reversible nature of the one-electron
oxidation wave was confirmed based on the data of ln plots
(26 mV), peak current ratio (ipc/ipas1), and peak potential
3.3. Electrochemical behavior of [Ru(NO)Cl5y2n(acac)n]m
(ns0, 1, 2) complexes
3.3.1. The ns0 complex, [M(NO)Cl5]2y
separation ( E s70 mV). Plots of peak current versus the
D
In line with previous reports [5–7], a well-defined revers-
ible one-electron oxidation wave was found in both
[Ru(NO)Cl5]2y and [Os(NO)Cl5]2y. [Ru(NO)Cl5]2y
showed also an irreversible one-electron reduction wave at
p
square root of the scan rate are linear, indicating that diffu-
sion-controlled redox processes are occurring at the electrode
surface. The reversibility indicates that the following
Table 7
Electrochemical data of [M(NO)Cl5y2n(acac)n]m-type complexes
[Ru(NO)Cl5]2y
[Ru(NO)Cl3(acac)]y
[Ru(NO)Cl(acac)2]
Oxid. E1/2 a,b (V)
Reduc. Epc a (V)
RT/nF (mV)
(30 ms)
(50 ms)
(70 ms)
1.19
y1.44
1.46 c
y1.08
1.67 c
y0.84, y1.34
26.7
26.6
26.2
0.85 d
25.1
25.0
33.2
32.9
25.1
32.0
Q/nF
(1.5) e
(3.1) e
[Os(NO)Cl5]2y
[Os(NO)Cl3(acac)]y
[Os(NO)Cl(acac)2]
Oxid. E1/2 a,b (V)
Reduc. Epc a (V)
RT/nF (mV)
(30 ms)
(50 ms)
(70 ms)
0.75
y2.0?
1.12
y1.60
1.43
y1.56, y1.72
32.2
32.4
30.7
0.82
32.0
32.1
26.5
27.1
32.8
26.7
Q/nF
(1.5) e
(3.3) e
a vs. AgNAgNO3 (0.1 mol dmy3 TEAP–CH3CN) at 298 K.
b E1/2s(EpaqEpc)/2.
c Epa.
d At 298 K.
e Decomposition occurred during the exhaust electrolysis.

D. Ooyama et al. / Inorganica Chimica Acta 261 (1997) 45–52
51
mV, ipc/ipas1, ln plotss26–27 mV), but that of cis-
[Ru(NO)Cl(acac)2] (2) showed an irreversible one-elec-
tron oxidation wave. Again, exhaustive oxidative electrolysis
of cis-[Os(NO)Cl(acac)2] (4) did not give useful data.
3.4. Summary
We can summarize the electrochemical featuresinosmium
and ruthenium complexes of [M(NO)Cl5y2n(acac)n]m
(ns0, 1, 2) as follows.
(i) The CV pattern of the oxidationprocessdiffersdepend-
ing on the central metal atom. Under the same conditions,
[Ru(NO)Cl5y2n(acac)n]m (ns1, 2) showed anirreversible
behavior, while that of the osmium complexes proved to be
reversible. This suggests that the species resulting from one-
electron oxidation of the nitrosylosmium complexes are
chemically more stable than those of nitrosylruthenium. A
similar result was found in previous work on the ns0 com-
plex; [Os(NO)Cl5]y is so stable that it could be isolated
as R[Os(NO)Cl5] (RsEt4N, Ph4As, Ph4P) [6,7], but
isolation of the corresponding salts of [Ru(NO)Cl5]y was
unsuccessful [10].
(ii) In agreement with (i), redox potentials move to the
negative direction when the central metal atom isalteredfrom
Ru to Os (Table 1). The oxidation potentials (Epa) of
[Ru(NO)Cl5y2n(acac)n]m (ns1, 2) were in the more pos-
itive potential region than those of the corresponding
[Os(NO)Cl5y2n(acac)n]m (ns1, 2). Despite a ligand
(NO)-based electrode reaction, the reduction potentials
(Epc) of [M(NO)Cl5y2n(acac)n]m (ns0, 1, 2) show a sim-
ilar trend. However, these irreversible potentials are affected
by the kinetic behavior of the reactions which are accompa-
nied by the one-electron oxidation–reduction of the com-
plexes. Although the same trend has also been found in some
ruthenium- and osmiumnitrosyl complexes with polypyridyl
ligands, the reductions of these complexes proceedreversibly
[18], which is the typical behavior of {MNO}6-type nitrosyl
complexes.
(iii) In the comparative study on the polypyridyl nitrosyl
complexes mentioned above, a linear correlation between IR
data (n(NO)) and the potentials for a ligand-basedreduction
(E1/2(1)) was found, although there is a significant scatter-
ing of the experimental points from the least-squares line
[18]. We obtained a similar relation for a series of
[M(NO)Cl5y2n(acac)n]m complexes, using the data of the
reduction (Fig. 3(a)). Such a relation, however, was not the
case in the oxidation. Plots of IR (n(NO)) versus E1/2(ox)
gave clearly two straight lines (Fig. 3(b)), depending on the
metal atoms of [M(NO)Cl5y2n(acac)n]m. This may reflect
mainly the different redox sites between the reduction and
the oxidation in [M(NO)Cl5y2n(acac)n]m: a ligand (nitro-
syl)-based electron transfer takes place in the reduction of
the {RuNO}6-type nitrosyl complexes [21], while the site of
the oxidation is believed to be mainly a central metal atom
[5–7].
Fig. 2. Typical cyclic voltammogram of the mer-[Os(NO)Cl3(acac)]y (3)
ion. [Complex] (1.0 mmol dmy3) in 0.1 mol dmy3 TEAP–CH3CN on a
stationary Pt electrode at 258C (200 mV sy1).
electrode reaction is operating, probably in the (OsNO)3q
moiety (Eq. (3)):
[Os(NO)Cl3(acac)]y°[Os(NO)Cl3(acac)]qey (3)
Oxidative controlled-potential electrolysis carried out on
the wave at 1.12 V did not give useful data. The one-electron
oxidation species, mer-[Os(NO)Cl3(acac)](3),underwent
a facile decomposition (see Table 7), even in the experiment
at y408C (Eq. (4)).
mer-[Os(NO)Cl3(acac)]™unidentified species
(4)
Clearly, the one-electron oxidation speciesof osmiumhav-
ing the acetylacetonato ligand, mer-[Os(NO)Cl3(acac)]
(3), is more chemically unstable than [Os(NO)Cl5]y,
which could be isolated, as mentioned earlier. In addition, the
CV experiment on mer-[Os(NO)Cl3(acac)]y (3) sug-
gested that a one-electron reduction occurred, but it was not
carried further, because the reduction wave appeared too near
the potential window of this solvent.
Almost the same CV pattern was found in mer-
[Ru(NO)Cl3(acac)]y (1), but, in this case, an irreversible
oxidation was found. The complex also underwent an irre-
versible reduction at y1.12 V. Multiple-scanning shows that
the reduction of mer-[Ru(NO)Cl3(acac)]y (1) causes for-
mation of an unidentified species, whose oxidation wave is
found at around 0.9 V (Eq. (5)).
[Ru(NO)Cl3(acac)]yqey™[Ru(NO)Cl3(acac)]2y
(5)
[Ru(NO)Cl3(acac)]2y™unidentified species
As in the case of mer-[Os(NO)Cl3(acac)]y (3), the
species generated in the reduction could not be identified.
3.3.3. The ns2 complexes, cis-[M(NO)Cl(acac)2] (2 and 4)
CV experiments show that both cis-[Ru(NO)Cl(acac)2]
(2) and cis-[Os(NO)Cl(acac)2] (4) undergo a one-elec-
tron oxidation, in addition to the expected reduction. The
oxidation wave of cis-[Os(NO)Cl(acac)2] (4) was revers-
ible in the cyclic voltammogram (E1/2s1.43 V, DEps70

52
D. Ooyama et al. / Inorganica Chimica Acta 261 (1997) 45–52
4. Supplementary material
Observed and calculated structure factors, all calculated
atomic coordinates, all anisotropic thermal parameters, com-
plete lists of bond lengths and angles, torsion angles, and
structure factor tables are available from the authors on
request.
References
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(iv) Additionally, the values of the potential differences
between the oxidation and the reduction waves
(NEpc(ox)yEpc(red)N) are different depending on the com-
plex, whether it has a nitrosyl ligand or not. The values fall
in the range 2.5–2.6 V for the ruthenium complexes, and in
the range 2.7–2.9 V for the osmium complexes. The extent
of the potential ranges is larger than that observed in tris-
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)
versus AgNAgNO3 for [Ru(acac)3]0/1y and q0.84 V
(E1/2) for [Ru(acac)3]q/0). The difference in the potential
range between cis-[M(NO)Cl(acac)2] (or mer-[M(NO)-
Cl3(acac)]y) (MsRu, Os) and [M(acac)3](MsRu)can
be attributed to their different redox sites: an electrode reac-
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either in the reduction or in the oxidation.
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