Osmium-carbonyl complexes of naphthylazoimidazoles. Single crystal X-ray structure of [Os(H)(CO)(PPh3)2(α-NaiEt)](PF6) {α-NaiEt = 1-ethyl-2-(naphthyl-α-azo)imidazole}

Article abstract of DOI:10.1016/j.poly.2006.08.028

1-Alkyl-2-(naphthyl-α/β-azo)imidazole (α-NaiR 1; β-NaiR, 2) react with [Os(H)(Cl)(CO)(PPh₃)₃] in THF and synthesise [Os(H)(CO)(PPh₃)₂(α/β-NaiR)](PF₆) (3, 4). The X-ray structure of [Os(H)(CO)(PPh₃)₂(α-NaiEt)](PF₆) (3c) shows a distorted octahedral geometry. Other spectroscopic studies (IR, UV-Vis, NMR) support the stereochemistry of the complexes. Addition of Cl₂ in MeCN to 3 or 4 gives [Os(Cl)(CO)(α/β-NaiR)(PPh₃)₂](PF₆) (5, 6), which were characterized by spectroscopic studies. The redox properties of the complexes show Os(III)/Os(II), Os(IV)/Os(III) and azo reductions.

Full text of DOI:10.1016/j.poly.2006.08.028

Polyhedron 26 (2007) 600–606
www.elsevier.com/locate/poly
Osmium-carbonyl complexes of naphthylazoimidazoles.
Single crystal X-ray structure of [Os(H)(CO)(PPh3)2(a-NaiEt)](PF6)
{a-NaiEt = 1-ethyl-2-(naphthyl-a-azo)imidazole}
a
a
b
T.K. Mondal , Joydev Dinda , Alexandra M.Z. Slawin ,
b
a,
*
J. Derek Woollins , C. Sinha
a
Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, West Bengal, India
b
Department of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK
Received 18 August 2006; accepted 21 August 2006
Available online 7 September 2006
Abstract
1-Alkyl-2-(naphthyl-a/b-azo)imidazole (a-NaiR 1; b-NaiR, 2) react with [Os(H)(Cl)(CO)(PPh3)3] in THF and synthesise [Os(H)-
(CO)(PPh3)2(a/b-NaiR)](PF6) (3, 4). The X-ray structure of [Os(H)(CO)(PPh3)2(a-NaiEt)](PF6) (3c) shows a distorted octahedral geom-
etry. Other spectroscopic studies (IR, UV–Vis, NMR) support the stereochemistry of the complexes. Addition of Cl2 in MeCN to 3 or 4
gives [Os(Cl)(CO)(a/b-NaiR)(PPh3)2](PF6) (5, 6), which were characterized by spectroscopic studies. The redox properties of the com-
plexes show Os(III)/Os(II), Os(IV)/Os(III) and azo reductions.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Naphthylazoimidazoles; Hydrido-osmium-carbonyl; X-ray structure; Electrochemistry
1. Introduction
sized the azoimidazole in the azoimine family [9,10].
Imidazole and its derivatives are chosen because of their
chemical and biological ubiquity [11], whilst the azo group
enhances the p-acidity and is responsible for photochro-
mism [12], pH—responsive and redox activity of the mole-
cules [3]. It is important to stabilize M–H bonds in the
presence of a p-acidic chelating framework in the com-
plexes [13–15].
In this work we have used 1-alkyl-2-(naphthyl-a/b-azo)-
imidazoles (a/b-NaiR) as a chelating azoimine function
[10,16]. We have synthesized [Os(H)(CO)(PPh3)2(a/b-
NaiR)]+, an osmium-hydrido-carbonyl compound, and
the structure has been established by single crystal X-ray
diffraction study in one case. The complexes have been
reacted with chlorine in acetonitrile. The products, [Os(Cl)-
(CO)(PPh3)2(a/b-NaiR)](ClO4), were characterised by spec-
troscopic and electrochemical techniques.
Polypyridyl complexes of ruthenium and osmium are an
active area of current research [1–7]. There are a number of
M–polypyridine complexes which bear M–H bonds
(M = Ru, Os) [8]. The functional group is the diimine,
–N@C–C@N–, and the key feature of these heterocycles
is their p-acidity. Recent years have witnessed a great deal
of interest in the synthesis of new ligands in the framework
of the diimine function (–N@C–C@N–) or the functional
modification to design an isoelectronic chelating motif.
We have been engaged for the last few years in the design
of the azoimine function (–N@C–C@N–) which is a func-
tional modification of the diimine unit. We have synthe-
*
Corresponding author. Fax: +91 033 2413 7121.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
0277-5387/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2006.08.028

T.K. Mondal et al. / Polyhedron 26 (2007) 600–606
601
4
2.2. Molecular structure
5
N
N
R' / H
N
N
N
H/R
The X-ray structure of [Os(H)(CO)(PPh3)2(a-NaiEt)]-
(PF6) (3c) is shown in Fig. 1; selected bond parameters
are listed in Table 1. The molecule consists of a central
Os atom surrounded by six coordination centers and the
arrangement is distorted octahedral. The atomic arrange-
ment involves two trans-phosphine, a chelated 1-ethyl-2-
(naphthyl-a-azo)imidazole (a-NaiEt), hydrido (Hꢀ) and a
CO within the OsP2N2CH coordination sphere. The Hꢀ
is located trans to the azo-N coordination. The a-naphthyl
ring is inclined at an angle of 46.07(11)ꢁ with respect to the
chelate ring (Os, N(1), C(2), N(2), N(8)). The trans-phos-
phine angle, P(1)–Ru–P(2) of 167.29 (2)ꢁ lies in the range
of reported data [17,18]. The steric crowding of phenyl
and naphthyl groups may provide this large deviation from
the perfect trans-angle value. The chelate angle N(1)–Os–
N(8) is 74.49(8)ꢁ. Other angles about Os define the dis-
torted octahedral geometry.
N
8
N
N
7
N/
N
9
6
13
10
12
11
9
13
12
8
10
11
α-NaiR(1)
β-NaiR(2)
H (a), Me (b), CH2CH3 (c), CH2Ph (d)
2. Results and discussion
2.1. Synthesis and formulation
There is no statistically significant difference in the two
˚
Os–N bonds; Os(1)–N(8), [(N8) is azo-N] is 2.1117(19) A
˚
The reaction of [Os(H)(Cl)(CO)(PPh3)3] and 1-alkyl-2-
(naphthyl-a/b-azo)imidazoles (a-NaiR (1), b-NaiR (2)
where R = H (a), Me (b), CH2CH3 (c), CH2Ph (d)) in
dry THF under dinitrogen yielded a dark red coloured
solution. On evaporation of the solvent to half of its ori-
ginal volume and addition of NH4PF6, a dark precipitate
appeared after cooling in a deep freezer for overnight.
The formulation of the complex, [Os(H)(CO)(PPh3)2-
(a/b-NaiR)](PF6) (3 for a-NaiR; 4 for b-NaiR) is sup-
ported by microanalytical data (see Section 3). Although
two geometrical isomers (3 and 30 or 4 and 40) are pos-
sible [CO trans to N(azo) or N(imidazole)] we have iso-
lated only one isomer, CO trans to N(imidazole) (3 and
4). The complexes, 3 and 4, are diamagnetic and show
1:1 conductivity in acetonitrile solution (KM = 90–
105 Xꢀ1 molꢀ1 cm2). The reaction of a/b-NaiH and
[Os(H)(Cl)(CO)(PPh3)3] also gave dark coloured crystal-
line compounds in the presence of NH4PF6, but their
solubility was too low to carry out any spectral measure-
ments, thus they were not studied further. Reaction of
[Os(H)(CO)(PPh3)2(a/b-NaiR)](PF6) with Cl2 in MeCN
gave red coloured [Os(Cl)(CO)(PPh3)2(a/b-NaiR)](PF6)
(5, 6) in high yield (>70%). The hydrido complexes (3,
4) can be regenerated from the chloro complexes (5, 6)
by refluxing with NaBH4 in EtOH for 2 h. The forma-
tion of hydrido complexes from 5/6 has been confirmed
by elemental and spectral analysis.
and Os(1)–N(1) (N(1) is imidazole) is 2.109(2) A. The
˚
–N@N– bond length is 1.306(3) A and is longer than
˚
the free ligand azo distance (1.267(3) A) [16] which is in
support of dp(Os) ! p*(azo) charge transmission. The
Fig. 1. Single crystal X-ray structure of [Os(H)(CO)(PPh3)2(a-NaiEt)]+.
NH4PF6 in THF
[Os(H)(Cl)(CO)(PPh3)3]
(3, 4)
[Os(H)(CO)(PPh3)2(NaiR)]PF6
+ NaiR (1, 2)
exc. NaBH4 in EtOH
Cl2 in acetonitrile
(5, 6)
[Os(Cl)(CO)(PPh3)2(NaiR)]PF6

602
T.K. Mondal et al. / Polyhedron 26 (2007) 600–606
Table 1
dimer. PPh3 protons form several hydrogen bonding inter-
actions with F–P(F5) and form a 3-D arrangement.
Selected bond distances and angles of [Os(H)(CO)(PPh3)2(a-NaiEt)](PF6)
(3b) along with their esd in parentheses
˚
Distances (A)
Angles (ꢁ)
2.3. Spectra and bonding
Os(1)–C (18)
Os (1)–N(1)
Os (1)–N(8)
Os (1)–P(1)
Os(1)–P(2)
N(2)–N (8)
N(8)–C(8)
N(2)–C(2)
C(18)–O(18)
Os(1)–H(1)
1.855(3)
2.109(2)
2.1117(19)
2.3916(7)
2.3670(7)
1.306(3)
1.438(3)
1.362(3)
1.160(3)
1.600
N(1)–Os(1)–N(8)
N(1)–Os(1)–C(18)
N(8)–Os (1)–C(18)
P(1)–Os(1)–P(2)
P(1)–Os(1)–C(18)
P(2)–Os (1)–C(18)
P(1)–Os(1)–N(1)
P(1)–Os (1)–N(8)
P(2)–Os (1)–N(1)
P(2)–Os(1)–N(8)
C(18)–Os(1)–H(1)
N(1)–Os(1)–H(1)
P(1)–Os(1)–H(1)
P(2)–Os(1)–H(1)
N(8)–Os(1)–H(1)
74.49(8)
177.46(9)
103.08(9)
167.29(2)
95.03(8)
89.17(8)
84.50(6)
94.43(5)
91.82(6)
96.30(5)
88.4(10)
94.1(10)
85.8(9)
The complexes [Os(H)(CO)(PPh3)2(a/b-NaiR)](PF6)
(3,4) show a sharp stretch at 1920–1940 cmꢀ1, which corre-
sponds to m(CO). The m(Os–H) band is observed at ca.
2080–2100 cmꢀ1. Other significant vibrations are m(N@N)
and m(C@N) at 1350–1380 and 1560–1580 cmꢀ1, respec-
tively. The azo stretching is significantly shifted to the
lower frequency region compared to the free ligand value
(1400–1410 cmꢀ1) [16] and is in support of back donation,
dpOs(II) ! p*(azo). The single crystal structure determina-
tion in one of the complexes also supports a retro-bonding
process (vide supra). For the chlorinated complexes (5/6)
m(CO) is shifted to 1960–1970 cmꢀ1 which is higher than
the precursor complexes (3/4). This is corroborated with
the absence of r-donation of Os–H to the Os–CO motif.
The electronic spectra of the complexes 3 and 4 in
MeCN show two high intensity transitions at 310–350
and 410–440 nm and these are assigned to ligand-centred
charge transfer transitions. An intense broad band at
490–505 nm (Table 2) (Fig. 3), absent in the free ligand,
is obviously assigned to a dp(Os) ! p*(azoimine) transi-
tion [10]. The solution spectra of 5 and 6 show blue shifting
by 10–30 nm compared to the hydrido analogues, 3 and 4
respectively.
82.3(9)
168.5(10)
Os–H is trans to the Os–N@N-(azo) group. The trans
effect of the Os–H bond may cause elongation of the
–N@N– bond. The trans Os–H bond enhances the charge
transfer to the N@N function and causes the increase in
the N@N distance. The Os–C and C–O bond lengths
are 1.855(3) and 1.160(3) A, respectively. The observed
Os–P distances, 2.3916(7), 2.3670 (7) A, are short in the
series of Os(PPh3) chemistry [17,18].
The intramolecular hydrogen bonding interaction gener-
ates a supramolecule. A hydrogen bonded dimer serves as a
˚
˚
1
ꢀ
The H NMR spectra of the complexes are taken in
motif (Fig. 2). An F atom in PF6 acts as a bridging agent
CDCl3 (the proton numbering pattern is shown in Scheme
1) and have been assigned (Table 3) on the basis of spin-
spin interactions and on comparison with the free ligand
values [10,16]. The X-ray structure determination aids the
unambiguous assignment of the protons. The most signifi-
cant observation is the appearance of a triplet Os–H signal
at ꢀ9.55 to ꢀ9.65 ppm (2JP–H = 22–25 Hz) for [Os(H)-
(CO)(PPh3)2(a/b-NaiR)](PF6). Imidazole protons 4- and
5-H appear as a broad singlet at 7.2–7.3 and 7.0–7.1 ppm,
respectively. The singlet nature of the imidazole protons
may be due to rapid proton exchange on the NMR time
scale. 1-R signals of (a/b)-NaiR in [Os(H/Cl)(CO)(PPh3)2-
(a/b-NaiR)]+ appear at their usual position [16]; 1-Me
appears as a singlet at 4.10–4.15 ppm; 1-CH2–CH3 gives a
quartet at 4.45–4.50 ppm, (J = 8.0 Hz) and a triplet at
1.5 ppm (J = 8.0 Hz) for –CH2– and –CH3, respectively;
1-CH2–(Ph) gives a singlet at 5.65–5.75 ppm. PPh3 shows
multiplets at 7.2–7.4 ppm.
between two complex units. A bifurcated hydrogen
bond [(naph)C(14)–H(14)–F(6)(PF5)–H(27)–C(27)(PPh3):
C(14)–H(14a), 0.95; H(14a)–F(6), 2.520(2); C(14)–F(6),
˚
3.231(3) A; \C–H–F, 132.0ꢁ and C(27)–H(27a), 0.95;
˚
H(27a)–F(6), 2.400(1); C(27)–F(6), 3.319(3) A and \C–
H–F 163.0ꢁ] bridges two molecules and forms a supracyclic
2.4. Electrochemistry
The redox data are summarised in Table 2. [Os(H)(CO)-
(PPh3)2(a/b-NaiR)](PF6) (3, 4) and [Os(Cl)(CO)(PPh3)2-
(a/b-NaiR)](PF6) (5, 6) show two successive redox
responses (Fig. 4) in MeCN solution with a Pt-working
electrode (+ve to Ag/AgCl) between 0.0 and 1.8 V. The
voltammogram is quasireversible in nature as is evident
from the peak-to-peak separation data (for a reversible
Fig. 2. H-Bonded dimer showing the C–H---F---H–C unit.

T.K. Mondal et al. / Polyhedron 26 (2007) 600–606
603
Table 2
UV–Vis spectrala and cyclic voltammetric dataa
Complex
UV–Vis spectra kmax (nm) (10ꢀ3 2 Mꢀ1 cmꢀ1
)
Cyclic voltammetry
EM1
EM2
Ligand reductions
3b
3c
3d
4b
4c
4d
5b
5c
5d
6b
6c
6d
a
334(8.46), 410(12.88), 495(5.34)
350(5.42), 415(5.98), 500(5.47)
332(4.76), 442(5.64), 504(3.94)
352(6.25), 421(7.29), 492(8.20)
350(3.88), 428(6.19), 496(2.94)
328(4.82), 438(6.34), 498(3.26)
337(5.48), 458(7.09), 506(5.38)
358(5.48), 430(5.94), 534(5.38)
336(5.24), 454(4.78), 520(3.86)
338(8.22), 425(9.26), 510(6.36)
356(3.68), 468(5.07), 512(6.19)
336(4.94), 356(5.44), 505(3.44)
0.68(160)
0.58(160)
0.70(140)
0.68(130)
0.60(160)
0.70(160)
0.77(130)
0.68(120)
0.81(130)
0.75(130)
0.78(120)
0.80(130)
1.18(190)
1.20(170)
1.32(170)
1.35(180)
1.22(170)
1.22(170)
1.30(160)
1.27(170)
1.40(160)
1.30(180)
1.36(180)
1.36(170)
ꢀ0.82(160), ꢀ1.24b
ꢀ0.88(180), ꢀ1.22b
ꢀ0.78(160), ꢀ1.32b
ꢀ0.87(160), ꢀ1.35b
ꢀ0.85(180), ꢀ1.30b
ꢀ0.82(160), ꢀ1.35b
ꢀ0.80(150), ꢀ1.25b
ꢀ0.74(150), ꢀ1.23b
ꢀ0.72(160), ꢀ1.20b
ꢀ0.90(180), ꢀ1.40b
ꢀ0.77(170), ꢀ1.32b
ꢀ0.78(160), ꢀ1.37b
Solvent MeCN, Pt-disk working electrode, Ag/AgCl reference electrode, Pt wire auxiliary electrode, [n-Bu4N][ClO4] supporting electrolyte. E1M ¼ 0:5
(Epa + Epc), V for Os(III)/Os(II) couple, E2M for Os(IV)/Os(III) couple in unit of V, DEp = jEpa ꢀ Epcj, mV; Epc (cathodic-peak-potential), Epa (anodic-
peak-potential).
b
Epc (cathodic-peak-potential).
(a/b-NaiR)](PF6) (3, 4) at 0.6–0.70 and 1.1–1.3 V are
shifted to 0.7–0.8 and 1.2–1.4 V, respectively, in [Os(Cl)-
(CO)(PPh3)2(a/b-NaiR)](PF6) (5, 6). The effect of the elec-
tron withdrawing Cl in the latter complexes may be the
reason for this redox shifting.
On scanning to the negative direction (0 to ꢀ1.8 V), two
redox responses are observed (Fig. 4). First response is
quasireversible (DEp P 120 mV) and the second one
appears at <ꢀ1.2 V which is irreversible in nature. Ligand
reduction of azoimidazole complexes appears at negative
potential [16b]. The chelated ligand belongs to the azoi-
mine family and can accommodate two electrons centred
at the azo group (–N@N–). On comparing with the litera-
ture [13,16,19], the reductive responses may be due to
accommodation of electrons in the azo dominated function
[–N@N]/[–N'N–]ꢀ and [–N'N]ꢀ/[–N–N–]2ꢀ
.
Fig. 3. Absorption spectra of [Os(H)(CO)(PPh3)2(a-NaiEt)](PF6)] (3c)
(—) [Os(Cl)(CO)(PPh3)2(a-NaiEt)](PF6)] (5c) (- - -) (in acetonitrile).
3. Experimental
cyclic voltammogram DEp is 60 mV and in the present
complexes DEp > 120 mV and is quasi-reversible). The nat-
ure of the voltammogram does not change with scan rate
(50–250 mV Sꢀ1). Os(II) can sequentially exhibit Os(III)/
Os(II) and Os(IV)/Os(III) redox processes at positive to
Ag/AgCl reference electrode. Thus, two redox couples
are referred to metal centred oxidations: Os(III)/Os(II)
and Os(IV)/Os(III). Redox couples of [Os(H)(CO)(PPh3)2-
3.1. Materials
The 1-alkyl-2-(naphthyl-a/b-azo)imidazoles were syn-
thesized following a previously published procedure [16].
[Os(H)(Cl)(CO)(PPh3)3] was also prepared by a reported
method [20]. Imidazole and all other organic chemicals and
inorganic salts were available from Sisco Research Lab,
PPh3
+
PPh3
PPh3
Os
+
+
H
Cl
N
N
N
CO
Os
Os
N/
CO
N/
H
N/
CO
PPh3
PPh3
PPh3
3 /4
3' /4'
5 /6
Scheme 1.

604
T.K. Mondal et al. / Polyhedron 26 (2007) 600–606
Table 3
1H NMR spectral data of the compounds in CDCl3 at 298 K
Complex
4-Ha
5-Ha
6-Ha
7-Ha
8-H
9-12-Hd
13-Hb
N(1)–R
Os–Hc,g
PPh3
3b
3c
3d
4b
4c
4d
5b
5c
5d
6b
6c
6d
a
7.18
7.15
7.18
7.16
7.14
7.21
7.36
7.38
7.34
7.34
7.22
7.41
7.05
7.06
7.09
7.04
7.00
7.11
7.21
7.23
7.25
7.18
7.16
7.27
7.68
7.66
7.73
7.68c(7.0)
7.66c(7.0)
7.73c(7.0)
7.59b(7.5)
7.55b(7.5)
7.67b(7.5)
7.86c(7.0)
7.88c(7.0)
7.87c(7.0)
7.76b(7.5)
7.68b(7.5)
7.84b(7.5)
7.55
7.46
7.61
7.50
7.43
7.56
7.74
7.61
7.82
7.62
7.57
7.72
7.86(7.5)
7.84(7.0)
7.90(7.0)
7.80(7.0)
7.76(7.0)
7.87(7.0)
7.94(7.0)
7.98(7.0)
7.90(7.0)
7.96(7.0)
7.88(7.5)
7.97(7.0)
4.14f
ꢀ9.63(23.4)
ꢀ9.59(22.8)
ꢀ9.55(24.0)
ꢀ9.67(22.0)
ꢀ9.60(23.6)
ꢀ9.56(22.0)
7.25–7.35
7.20–7.35
7.30–7.40
7.25–7.35
7.20–7.30
7.25–7.35
7.30–7.45
7.30–7.40
7.40–7.52
7.35–7.45
7.35–7.45
7.35–7.45
4.46(9.0), 1.50(7.5)e
5.78f
4.09f
7.93
7.89
7.98
4.51(9.0), 1.52(7.0)e
5.68f
4.23f
7.86
7.88
7.90
4.57(8.5), 1.58(7.5)e
5.87f
4.19f
8.05
8.02
8.10
4.62(9.0), 1.64(8.0)e
5.76f
Broad singlet.
b
c
d
e
f
Doublet.
Triplet.
Multiplet.
d(–CH2–CH3) quartet for –CH2– and triplet for –CH3.
Singlet.
Coupling constant 2J refers to 31P–1H coupling.
g
electrodes. All measurements were carried out under a
nitrogen environment at 298 K with reference to Ag/AgCl
in acetonitrile using [n-Bu4N][ClO4] as the supporting elec-
trolyte. The reported potentials are uncorrected for junc-
tion potentials. Magnetic properties were measured using
a PAR-155 vibrating sample magnetometer fitted with a
Walker scientific magnet. EPR spectra were recorded on
a Varian E-109C spectrometer.
3.3. Synthesis of [Os(H)(CO)(PPh3)2(a-NaiMe)](PF6)
(3b)
Fig. 4. Cyclic voltammogram of [Os(H)(CO)(PPh3)2(a-NaiEt)](PF6) (3c)
(—); [Os(Cl)(CO)(PPh3)2(a-NaiEt)](PF6)] (5c) (–-–) in acetonitrile using a
Pt-working electrode and a Ag/AgCl reference electrode.
To a suspension of [Os(H)(Cl)(CO)(PPh3)3] (0.250 g,
0.230 mmol) in dry THF (20 ml) 1-methyl-2-(naphthyl-a-
azo)imidazole (a-NaiMe) (0.065 g, 0.28 mmol) was added
in the same solvent (10 ml). The solution was stirred and
refluxed for 15 h under dinitrogen. The orange red solution
turned deep red. It was then cooled and filtered. The filtrate
was then evaporated slowly in air to half of its original vol-
ume. A THF solution (5 ml) of NH4PF6 (0.2 g) was added
into this solution and the resulting solution was kept in a
deep freezer overnight. A dark precipitate appeared which
was filtered, washed with cold THF and then dried in a
CaCl2 desiccator in vacuo. Purification was carried out
by column chromatography over a silica gel column pre-
pared in benzene. The desired red band was eluted by ace-
tonitrile. It was then evaporated and dried over CaCl2 in
vacuo. The yield was 0.16 g (63%).
The other complexes were prepared following an identi-
cal procedure. The yield varied between 55% and 65%.
Microanalytical data: Calc. (found) for C51H43N4OF6P3Os
(3b): C, 54.44 (54.35); H, 3.82 (3.76); N, 4.98 (5.11%). For
C52H45N4OF6P3Os (3c): C, 54.82 (54.95); H, 3.95 (3.88); N,
4.92 (5.01%). For C57H47N4OF6P3Os (3d): C, 56.99 (56.89);
H, 3.92 (3.86); N, 4.67 (4.63%). For C51H43N4OF6P3Os
(4b): C, 54.44 (54.39); H, 3.82 (3.78); N, 4.98 (4.94%).
Mumbai, India. The purification of acetonitrile and prepara-
tion of n-tetra-butylammonium perchlorate [n-Bu4N][ClO4]
for the electrochemical work were done as reported before
[9]. Dinitrogen was purified by bubbling through an alkaline
pyrogallol solution. All other chemicals and solvents were of
reagent grade and were used without further purification.
Commercially available SRL silica gel (60–120 mesh) was
used for column chromatography.
3.2. Physical measurements
Microanalytical data (C, H, N) were collected on a Per-
kin–Elmer 2400 CHNS/O elemental analyzer. Spectroscopic
data were obtained using the following instruments: UV–
Vis spectra, Perkin–Elmer; model Lambda 25. IR spectra
(KBr disk, 4000–450 cmꢀ1), Perkin–Elmer; model RX-1.
1H NMR spectra, Bruker (AC) 300 MHz FTNMR spec-
trometer. Molar conductances were measured using a Sys-
tronics conductivity meter 304 model using ca. 10ꢀ3 M
solutions in acetonitrile. Electrochemical measurements
were performed using computer-controlled PAR model
250 VersaStat electrochemical instruments with Pt-disk

T.K. Mondal et al. / Polyhedron 26 (2007) 600–606
605
Table 4
For C52H45N4OF6P3Os (4c): C, 54.82 (54.78); H, 3.95
(3.98); N, 4.92 (4.94%). For C57H47N4OF6P3Os (4d): C,
56.99 (57.05); H, 3.92 (3.94); N, 4.67 (4.71%).
Summarised crystallographic data for [Os(H)(CO)(PPh3)2(a-NaiEt)](PF6)
Empirical formula
Formula weight
Crystal system
Space group
C52H45F6N4OP3Os
1139.03
monoclinic
P2(1)/n
12.0841(14)
25.549(3)
15.7643(18)
103.684(3)
0.20 · 0.10 · 0.10
4728.8(9)
0.71073
1.600
4
93(2)
2.865
30568
9226(0.0287)
609
3.4. Reaction of [Os(H)(CO)(PPh3)2(a/b-NaiR)](PF6)
(3, 4) with Cl2 in MeCN
˚
a (A)
˚
b (A)
˚
c (A)
To a MeCN solution of [Os(H)(CO)(PPh3)2(a/b-NaiR)]-
(PF6), a few drops of Cl2 saturated MeCN was added and
the resulting solution was stirred. The solution colour
changed immediately from red to red-violet. The volume
was reduced by slow evaporation and addition of NH4PF6
separated out crystalline compounds. A red-violet band
was separated by chromatography. The eluent was evapo-
rated to dryness, then the dark mass was water washed and
dried over CaCl2. Microanalytical data of the complexes
support the composition [Os(Cl)(CO)(PPh3)2(a/b-NaiR)]-
b (ꢁ)
Size (mm3)
3
˚
V (A )
˚
k (A)
qcalc. (Mg mꢀ3
)
Z
T (K)
l Mo-Ka (mmꢀ1
Total reflection collected
Unique reflections (Rint
)
)
Refined parameters
ꢀ3
˚
(PF6) and conductivity data (KM = 100–110 Xꢀ1 cm2 molꢀ1
)
Largest differences in peak and hole (e A
)
2.151 and ꢀ0.763
Ra (I > 2r(I))
wRb
0.0235
suggests a 1:1 electrolyte.
0.0500
1.043
Goodness-of-fitc
½OsðHÞðCOÞðPPh3Þ ða=b-NaiRÞꢁþ
2
P
P
a
R = jFo ꢀ Fcj/ Fo.
Cl2 in MeCN
P
P
½OsðClÞðCOÞðPPh Þ ða=b-NaiRÞꢁþ
1=2
2
b
wR ¼ ½ wðF 2o ꢀ F c2Þ= wF o4ꢁ where w ¼ 1=½r2ðF 2oÞ þ ð0:0183PÞ þ
ꢀꢀꢀꢀꢀꢀ!
3
2
4:1609Pꢁ, where P ¼ ðF 2o þ 2F c2Þ=3.
1=2
c
Goodness-of-fit (GOF) is defined as ½wðF 2o ꢀ F c2Þ=ðn0 ꢀ npÞꢁ
where
Microanalytical data: Calc. (found) for C51H42N4OClF6-
P3Os (7b): C, 52.83 (52.79); H, 3.62 (3.59); N, 4.83
(4.80%). For C52H44N4OClF6P3Os (7c): C, 53.22 (53.24);
H, 3.75 (3.76); N, 4.77 (4.78%). For C57H46N4OClF6P3Os
(7d): C, 55.41 (55.38); H, 3.73 (3.71); N, 4.54 (4.52%).
For C51H42N4OClF6P3Os (8b): C, 52.83 (52.87%); H,
3.62 (3.64%); N, 4.83 (4.86%). For C52H44N4OClF6P3Os
(8c): C, 53.22 (53.19); H, 3.75 (3.73); N, 4.77 (4.79). For
C57H46N4OClF6P3Os (8d): C, 55.41 (55.36); H, 3.73
(3.69); N, 4.54 (4.52%).
n0 and np denote the number of data and variables, respectively.
4. Conclusion
1-Alkyl-2-(naphthyl-a/b-azo)imidazole (a/b-NaiR,
1
and 2) has been reacted with [Os(H)(Cl)(CO)(PPh3)3] in
THF to synthesise [Os(H)(CO)(PPh3)2(a/b-NaiR)](PF6)
(3, 4). The structure of the complexes has been determined
by spectroscopic data (FTIR, UV–Vis, 1H NMR) and
redox activity was examined by cyclic voltammetry. Single
crystal X-ray diffraction measurement in the case of
[Os(H)(CO)(PPh3)2(a-NaiEt)](PF6) confirmed the struc-
ture. Cl2 (in MeCN) addition to the hydrido-Os compounds
(3, 4) has synthesized [Os(Cl)(CO)(PPh3)2(a/b-NaiR)](PF6)
(5, 6).
3.5. X-ray crystal structure determination
Crystals of [Os(H)(CO)(PPh3)2(a-NaiEt)](PF6) (3c)
were grown by slow diffusion of a CH2Cl2 solution of
the complex into hexane. The prismatic red crystal was
of dimensions 0.20 · 0.10 · 0.10 mm. Data were collected
using a CCD area detector rotating anode radiation
source and a confocal optics monochromator of Mo-
Acknowledgements
˚
Ka radiation (k = 0.71073 A) at 93(2) K. Data collections
were performed in the 2h range 3.1–52.74ꢁ Absorption
corrections were carried out by the multiscan process.
Out of a total of 30,568 reflections, 9226 unique data
(8451 of I > 2r(I)) were used for the structure determina-
tion. Data reduction were carried out using Crystalclear
1.3.6 (Rigaku Corporation). The structure solution
and refinement were carried out using the programs
SHELXS-97 [21] and SHELXL-97 [22]. The structure was solved
by direct method and refined by full-matrix least-squares
refinement based on F2. All non-hydrogen atoms were
refined anisotropically. The hydridic H atom was fixed
Financial support from the Department of Science and
Technology, New Delhi and Jadavpur University Potential
for Excellence unit are gratefully acknowledged. One of us
(T.K.M.) thanks UGC, New Delhi for a fellowship. We
thank Dr. G. Mostafa, Department of Physics, Jadavpur
University, Kolkata for his help in the structure solution.
Appendix A. Supplementary material
CCDC 288383 contains the supplementary crystallo-
graphic data for 3c. These data can be obtained free of
charge via htpp://www.ccdc.cam.ac.uk/conts/retrieving.
html, or from the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
˚
at a distance of 1.60 A from the metal [23]. Crystal
parameters and refinement results are summarized in
Table 4.

606
T.K. Mondal et al. / Polyhedron 26 (2007) 600–606
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