Synthesis, structural characterization and semiempirical calculations of the ruthenium azide complex [Ru(tpy)(PPh3)2(N3)][ClO4]

Article abstract of DOI:10.1016/S0022-328X(98)00408-2

The reaction of [Ru(tpy)(PPh₃)₂Cl][PF₆] (tpy, 2,2′:6′,2″-terpyridine) with NaN₃/NaClO₄ in acetone/water produced the ruthenium(II) complex [Ru(tpy)(PPh₃)₂(N₃)][ClO₄] (1), which contains a coordinated azide unit with Ru-N = 2.132(5) A. The new Ru azide complex 1 was identified and characterized by elemental analysis, IR, Raman and multinuclear NMR (¹H, ¹⁴N, ³¹P) data. Crystals were grown from an acetonitrile/diethyl ether solution and the crystal structure was determined by a low-temperature single crystal X-ray diffraction study. Crystallographic data for 1: triclinic, P1, a = 10.9905(5), b = 13.4741(6), c = 17.8532(9) A, α = 90.6760(10), β= 96.4000(10), γ = 105.5270(10)°, V = 2529.07(21) A³, ρ = 1.422 g cm^-3, Z = 2. The experimentally obtained structural parameters for compound 1 compare reasonably well with those calculated at the semi-empirical ZINDO/1 level of theory.

Full text of DOI:10.1016/S0022-328X(98)00408-2

Journal of Organometallic Chemistry 559 (1998) 165–171
Synthesis, structural characterization and semiempirical calculations of
the ruthenium azide complex [Ru(tpy)(PPh3)2(N3)][ClO4]
Won K. Seok a, Sun Bin Yim a, Thomas M. Klapo¨tke b,*, Peter S. White c
a Department of Chemistry, Dongguk Uni6ersity, 26 Pil-Dong, Chung-Ku, Seoul 100-715, South Korea
b Institute of Inorganic Chemistry, Uni6ersity of Munich (LMU), Meiserstraße 1, D-80333 Munich, Germany
c Department of Chemistry, Uni6ersity of North Carolina, Chapel Hill, NC 27599-3290, USA
Received 27 November 1997
Abstract
The reaction of [Ru(tpy)(PPh3)2Cl][PF6] (tpy, 2,2%:6%,2%%-terpyridine) with NaN3/NaClO4 in acetone/water produced the rutheni-
˚
um(II) complex [Ru(tpy)(PPh3)2(N3)][ClO4] (1), which contains a coordinated azide unit with Ru–N=2.132(5) A. The new Ru
azide complex 1 was identified and characterized by elemental analysis, IR, Raman and multinuclear NMR (1H, 14N, 31P) data.
Crystals were grown from an acetonitrile/diethyl ether solution and the crystal structure was determined by a low-temperature
˚
single crystal X-ray diffraction study. Crystallographic data for 1: triclinic, P1, a=10.9905(5), b=13.4741(6), c=17.8532(9) A,
h=90.6760(10), i=96.4000(10), k=105.5270(10)°, V=2529.07(21) A , z=1.422 g cm−3, Z=2. The experimentally obtained
3
˚
structural parameters for compound 1 compare reasonably well with those calculated at the semi-empirical ZINDO/1 level of
theory. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Azides; Raman Spectra; Ruthenium; ZINDO Calculations
1. Introduction
the preparation and structural characterization of inor-
ganic and organometallic transition metal azide com-
plexes. For example, trans-[Ru(depe)2(N3)2] (depe,
1,2-bis(diethylphosphino)ethane) ([2]b) and the closely
related complex [Fe(dmpe)(N3)2] (dmpe, 1,2-bis(-
dimethylphosphino)ethane) [3], as well as the Cp
derivative [Ru(C5H5)2(N3)], have been prepared and
structurally characterized [4]. Very recently, four new
inorganic titanium azide complexes, [Ti(NMe2)2(N3)2]n,
[Ti(NMe2)2(N3)2(py)2]n, [Ti(NMe2)2(N3)2(bipy)]n and
[Ti(NMe2)3(N3)(bipy)]n were reported ([5]a). Moreover,
quite recently also diazido complexes of manganese
were synthesized ([5]b,c).
Cationic ruthenium complexes with tridentate
(N,N%,N%%) and also with bidentate (N,N%) 2,2%:6%,2%%-ter-
pyridine (tpy) ligand systems have been known for
several years. For example, [Ru(NO2)(PMe3)2(tpy)]
[ClO4] ([1]a) and [Ru(N,N%,N%%-tpy)(N,N%-tpy)Cl][PF6]
([1]b) have been reported recently. Cationic azidoruthe-
nium(III) complexes with additional NH3 have already
been reported as early as in 1970 ([1]c).
After early work in transition metal azide chemistry
where the characterization was largely based on 14N-
NMR data {see for example [Pd(PPh3)2(N3)2] and cis-
[Pt(PBu3)2(N3)2] ([2]a)}, recently interest has emerged in
In this contribution we wish to report the synthesis,
spectroscopic and structural characterization as well as
results from semi-empirical calculations of the new
ruthenium(II) azide complex [Ru(tpy)(PPh3)2(N3)
][ClO4] (1).
* Corresponding author. Fax: +49 89 5902382.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00408-2

166
W.K. Seok et al. / Journal of Organometallic Chemistry 559 (1998) 165–171
Fig. 1. Raman spectrum of [Ru(tpy)(PPh3)2(N3)][ClO4] (1) (for details see Section 3)
2. Results and discussion
at 3064 cm−1 for the aromatic C–H stretching modes.
In addition there are well resolved signals for the C–C
stretches of the aromatic phenyl rings and the tpy
ligand system (1466–1600 cm−1). The totally symmet-
ric w1 stretching mode of the ClO4− anion appears as
the strongest Raman peak of this tetrahedral system at
932 cm−1 [7].
The ruthenium(II) complex [Ru(tpy)(PPh3)2(N3)]
[ClO4] (1) was prepared from the chloro hex-
afluorophosphate precursor ([6]a) in a convenient two-
step one-pot reaction according to Eqs. (1a) and (1b)
(cf. also the chemistry and preparation of the isovalent
electronic [Re(tpy)(PPh3)2(Cl)]) [6b].
1
The H-NMR spectrum showed a complex multiplet
in the area between 6.9 and 8.1 ppm for the aromatic
protons of the phenyl rings and the tpy ligand system.
This multiplet appeared nearly unchanged compared to
the precursor complex [Ru(tpy)(PPh3)2Cl][PF6]. How-
ever, the low-field pseudo-doublet of the 2 or 6%% pro-
tons significantly changed from 9.02 and 9.03 ppm in
[Ru(tpy)(PPh3)2Cl][PF6] to 8.72 and 8.75 ppm in
[Ru(tpy)(PPh3)2(N3)][ClO4].
[Ru(tpy)(PPh3)2Cl][PF6]
+NaN3 “
acetone/water[Ru(tpy)(PPh3)2(N3)][PF6]+NaCl
(1a)
[Ru(tpy)(PPh3)2(N3)][PF6]
+NaClO4 (saturated solution in H2O)
“
acetone/water[Ru(tpy)(PPh3)2(N3)][ClO4]¡+NaPF6
(1b)
Complex 1 was also characterized by 14N-NMR spec-
troscopy (Table 1). For the covalently bound azide
species three well resolved resonances have been found
in the 14N-NMR spectrum and assignment of the indi-
vidual resonances to Na, Nb and Nc (connectivity:
Ru–Na–Nb–Nc) was made on the basis of the argu-
ments given in earlier work by Witanowski [8] and
other reports on 14N data of covalent azides [9–13].
The individual chemical shifts as well as line-widths
found for [Ru(tpy)(PPh3)2(N3)][ClO4] nicely compare to
related covalently bound metal–azide complexes (Table
1) ([2]a, [12,14]). Presumably as a result of the large
2.1. Spectroscopy
The new ruthenium azide complex 1 was identified
and characterized by elemental analysis, IR, Raman
and multinuclear NMR (1H, 14N, 31P) data (see Section
3). As the most intense and characteristic absorptions
the IR spectrum shows the asymmetric azide stretching
mode at 2042 cm−1
.
The Raman spectrum of 1 (Fig. 1) shows the very
characteristic symmetric azide stretching mode as an
intense peak at 1335 cm−1 and also a very strong peak

W.K. Seok et al. / Journal of Organometallic Chemistry 559 (1998) 165–171
167
Table 1
14N-NMR spectroscopic data of [Ru(tpy)(PPh3)2(N3)][ClO4] (1) and related compounds chemical shifts l in ppm relative to MeNO2 (connectivity:
X–Na–Nb–Nc)
Na
Nb
Nc
Ref.
[Ru(tpy)(PPh3)2(N3)][ClO4] (1)
(CF3)3GeN3
As(N3)3
[Pd(PPh3)2(N3)2]
cis-[Pt(PBu3)2(N3)2]
−337 (300)a
−332.8 (350)
−318.0 (150)
−363 (145)
−326 (220)
−136 (20)
−224 (60)
−186.8 (54)
−165.2 (30)
−230 (75)
−226 (110)
This work
[12]
[11]
[14]
[14]
−145.1 (28)
−131.1 (15)
−140 (110)
−135 (145)
a Line-widths Dw in Hz (in perentheses).
quadrupole moment of 14N, spin–spin splitting which
has been estimated to be B30 Hz was not observed
(cf. line-widths, Table 1) [15]. The three N atoms of
the tpy ligand system, however, could not be ob-
served. In this context it should be noted that the
relative line-widths in the 14N-NMR spectra are re-
lated to the local symmetry around the nitrogen atom,
with highly symmetric N atoms (i.e. Nb, central N of
N3) having sharper lines, whilst the more asymmetric
nitrogen atoms (i.e. Nc, terminal N of N3) have
broader lines and the very asymmetric N atoms (i.e.
Na, bound to Ru and tpy N atoms) have very broad
lines [16].
those of some related and recently characterized ruthe-
nium and iron azide complexes. For example, in trans-
[Ru(depe)2(N3)2]
ethane) the Ru1–N1 bond length is 2.354(1) A and the
(depe,
1,2-bis(diethylphosphino)
˚
˚
N–N distances are N1–N2=1.180(5) A and N2–
˚
N3=1.170(5) A, respectively ([2]b). The closely related
complex [Fe(dmpe)(N3)2] (dmpe, 1,2-bis(dimethylphos-
phino)ethane) displays a Fe1–N1 bond length of
˚
˚
2.024(3) A and a N1–N2 bond length of 1.162(5) A [3].
The molecule [Ru(C5H5)2(N3)] again has a similar
˚
Ru1–N1 bond length of 2.135(3) A [4]. The azide
group is slightly bent (175.2(3)°) and there is a small
difference between the N–N distances [1.186(3)
The 31P-NMR spectrum of 1 showed a singlet reso-
nance at 26.5 ppm for the coordinated PPh3 groups
(cf. the free PPh3 ligand shows resonance at −4
ppm). Therefore, the 31P resonance of 1 appears at
slightly lower field than that of the starting material
[Ru(tpy)(PPh3)2Cl][PF6] (22.4 ppm).
and 1.164(3) A], the longer being adjacent to the Ru
˚
atom [4].
2.2. X-ray structure
The structure of the ruthenium azide complex,
[Ru(tpy)(PPh3)2(N3)][ClO4] (1), was determined experi-
mentally by X-ray diffraction analysis at low tempera-
ture using a Siemens SMART area detector system.
Fig. 2 shows a formula unit of the ruthenium azide
cation and Fig. 3(a,b) show the packing diagrams of
the ruthenium azide complex, [Ru(tpy)(PPh3)2(N3)]
[ClO4]. Table 2 summarizes the most important ex-
perimentally obtained structural parameters for com-
plex 1.
As expected for a covalently bound azide (i.e. a coor-
dinated and not an ionic N3 unit), the [Ru(tpy)
(PPh3)2(N3)]+cation displays a bent trans configuration
with an N–N–N bond angle of 177.8°. The two N–N
distances are identical within the standard deviation
˚
(1.16 A). This can be explained by only a weak coordi-
native bond between N1 and Ru1 which is also in
agreement with the only slight bending of the azide
group (cf. typical covalent azides show NNN angles of
17292°) [17,18].
Fig. 2. Structure of a formula unit of a [Ru(tpy)(PPh3)2(N3)]+ cation
in the crystal (ORTEP representation) [19].
The structural parameters compare also well with

168
W.K. Seok et al. / Journal of Organometallic Chemistry 559 (1998) 165–171
As expected the cis and the trans isomers of 1 are
very close in their total energy with the trans form
being thermodynamically slightly favored over the cis
isomer (DE(cis–trans)=5 kcal mol−1; Table 3). It has
to be stressed, however, that the calculations were
performed for isolated ions in the gas phase and that
the stability might be reversed in the condensed phase
due to cation–anion interactions, molecule/ion–solvent
interactions or crystal packing effects [21].
For both isomers of 1 (cis and trans) the stationary
points were characterized as true minima (within the
ZINDO/1 model) by frequency analyses (in all cases
NIMAG=0; NIMAG, number of imaginary frequen-
cies) [22]. The asymmetric N3 stretching mode which is
very strong in the IR spectra was also calculated (Table
3).
To assign the experimentally observed IR frequencies
of the complex cation trans-[Ru(tpy)(PPh3)2(N3)]+in
the compound [Ru(tpy)(PPh3)2(N3)][ClO4] the structure
of the cation trans-[Ru(tpy)(PPh3)2(N3)]+was opti-
mized in C1 symmetry and the vibrational frequencies
and their intensities were calculated at the semi-empiri-
cal ZINDO/1 level of theory using a VSTO-3G* basis
set. Molecular frequencies depend on the second deriva-
tive of the energy with respect to the nuclear positions.
Due to the harmonic potential applied (and due to the
neglect of electron correlation) raw frequencies com-
puted at the HF and ZINDO levels contain systematic
errors. Therefore, it is usual to scale calculated frequen-
cies by empirical factors (F) smaller than unity. Use of
such factors has been demonstrated to produce good
agreement with experiment for a wide range of systems
[22,27,28].
Table 2
˚
Selected measured (X-ray) bond lengths (A) and angles (°) of
[Ru(tpy)(PPh3)2(N3)][ClO4] (1)a
˚
Atoms
Bond length (A) Atoms
Bond angle (°)
Fig. 3. Top: 2-D packing diagram of [Ru(tpy)(PPh3)2(N3)][ClO4]
(PLUTO representation) [20]. Bottom: 3-D packing diagram of
[Ru(tpy)(PPh3)2(N3)][ClO4] (PLUTO representation) [20].
Ru1–P1
Ru1–P2
Ru1–N11 2.102(4)
Ru1–N21 1.965(4)
Ru1–N31 2.087(4)
Ru1–N1
N1–N2
N2–N3
2.4013(14)
2.3972(14)
P1–Ru1–P2
176.52(5)
89.69(12)
89.51(11)
90.97(12)
91.57(11)
87.90(12)
88.41(11)
91.36(12)
91.40(11)
99.03(17)
177.83(18)
102.77(18)
78.92(17)
P1–Ru1–N1
P1–Ru1–N11
P1–Ru1–N21
P1–Ru1–N31
P2–Ru1–N1
P2–Ru1–N11
P2–Ru1–N21
P2–Ru1–N31
N1–Ru1–N11
N1–Ru1–N21
N1–Ru1–N31
N11–Ru1–N21
2.132(5)
1.157(7)
1.159(8)
2.3. Semi-empirical calculations
The structure of the ruthenium azide complex 1
(trans isomer) as well as the structure of the corre-
sponding cis isomer and their total energies were calcu-
lated at the semi-empirical ZINDO/1 level of theory.
For both calculated ruthenium complexes the
triphenyl phosphine ligand was modeled by the elec-
tronically very similar and closely related PMe3 (Me=
CH3) ligand in order to reduce the number of
parameters and to save cpu time.
N11–Ru1–N31 158.18
N21–Ru1–N31
Ru1–N1–N2
N1–N2–N3
79.28(18)
139.6(4)
177.8(6)
a Atomic labeling analogous to Fig. 1.

W.K. Seok et al. / Journal of Organometallic Chemistry 559 (1998) 165–171
169
Table 3
Semi-empirically calculated structural parameters and total energies for the cis and trans isomers of complex 1 (ZINDO/1/VSTO-3G* level of
theory)
E (kcal mol−1
)
NIMAG w(N3, asym) [cm−1] (Int.)a
˚ ˚ ˚
Ru–N1 (A) N1–N2 (A) N2–N3 (A) N1–N2–N3 (°)
Complex
1 (trans)
ZINDO/ 1
Experimental
−17473
0
2034
2053
1.97
2.13
1.24
1.16
1.19
1.16
175.2
177.8
1 (cis)
ZINDO/ 1
−17468
0
2084
1.92
1.24
1.18
173.2
a Scaled with an empirical factor of 0.62.
1
The H-NMR spectra were recorded in 5 mm NMR
tubes in DMSO-d6 solution (saturated solution) at 25°C
using a Varian Gemini 200 MHz spectrometer. 1H-
NMR (ppm): 6.9–8.8 m; 8.72 and 8.75 ‘d’.
In the present study a factor of F(w)=0.60 for the
stretching modes and F(l)=0.80 for in plane (l) and
out of plane (k) deformation modes was applied. The
results are summarized in Table 4.
3.1.1. 14N-NMR spectroscopy
The 14N-NMR spectrum was recorded in a 10 mm
NMR tube in CD2Cl2 solution (saturated solution) at
−20°C using a Bruker SY 200 spectrometer operating
at 14.462 MHz. A good spectrum could be obtained
with a pulse width of 45 ms after 90000 scans and is
reported ppm in the l scale referred to external MeNO2
in CD2Cl2 solution. Peak positions appearing downfield
(high-frequency) of the reference are reported as plus
and those upfield (low-frequency) of the reference are
reported as minus. A routine baseline correction was
applied. 14N-NMR [ppm, Dw1/2 (Hz)]: −136 (20), −
224 (60), −337 (300).
3. Experimental
All reactions were carried out using standard Schlenk
techniques.
3.1. Preparation of [Ru(tpy)(PPh3)2(N3)][ClO4] (1)
A sample of [Ru(tpy)(PPh3)2Cl][PF6] (100 mg, 0.10
mmol) [6] was dissolved in acetone (ca. 15 cm3) and
subsequently sodium azide (18.8 mg, 0.29 mmol) in
water (ca. 1 cm3) was added. The reaction mixture was
refluxed for 1 h and was then allowed to cool to room
temperature yielding a purple solution. At this stage the
precipitation of any solid must be avoided. Subse-
quently, a saturated solution of sodium perchlorate in
water (excess) was added at 0°C and the reaction
mixture was stirred for five minutes. At this time the
solution turned darker and the color slowly changed
from purple to dark-brown. The reaction product
which was insoluble in the acetone/water mixture was
filtered off and carefully washed with small amounts of
acetone and ether and then dried in vacuo. Recrystal-
lization of the crude material from dry acetonitrile/
ether (ca. 10 cm3) yielded dark brown crystals of
complex 1 (84 mg, 84%).
The 31P-NMR spectra were recorded in 5 mm NMR
tubes in DMSO-d6 solution (saturated solution) at 25°C
using a Varian Gemini 300 MHz spectrometer operat-
ing at 121.44 MHz and are referred to H3PO4 (85%
solution in water). 31P-NMR (ppm): 26.53 s.
3.2. Crystallography
3.2.1. X-ray structural determination of
[Ru(tpy)(PPh3)2(N3)][ClO4] ·2CH3CN (1)
Crystal data for the ruthenium azide complex,
[Ru(tpy)(PPh3)2(N3)][ClO4]·2CH3CN: Molecular for-
mula RuP2C55H47ClN8O4, M=1082.49, triclinic, a=
Elemental analysis (Carlo Erba, EA 1180),
RuP2C55H47ClN8O4, (1082.49) Anal. Calc.: C 60.5, H
4.2 , N 9.4. Found: C 61.0, H 4.4, N 10.3%.
˚
10.9905(5), b=13.4741(6), c=17.8532(9) A, and
h=90.6760(10), i=96.4000(10), k=105.5270(10)°;
3
˚
V=2529.07(21) A , space group P1, Z=2, Dcalc.
=
IR (Hartmann and Braun, KBr, cm−1): 3058 m,
2042 vs, 1604 w, 1561 m, 1481 m, 1434 s, 1386 m, 1281
w, 1089 s, 771 m, 747 s, 698 s, 624 m, 517 s, 493 m.
1.422 g cm−1. Crystal dimensions 0.20×0.15×0.10
mm. v(Mo–Kh)=0.48 mm−1
F(000)=1110.75.
,
u=0.71073 A,
˚
Raman (1064 nm, 200 mW, 20°C, 5000 scans, cm−1
,
Data collection and processing: Siemens SMART
diffractometer, −100°C (173 K), scan mode,
(Int.)): 3064 (6), 1600 (6), 1588 (5), 1466 (3), 1335 (8),
1270 (5), 1186 (4), 1096 (5), 1038 (6), 1004 (10), 932 (3),
726 (2), 644 (2). A Raman spectrum was also recorded
at −150°C which showed virtually an identical
spectrum.
ꢀ
2qmax. =50.0°, graphite monochromated Mo–Kh radia-
tion, 18108 independent measured reflections, 8738
unique reflections, 6236 reflections with [I\3.0|(I)].
Absorption corrections were made using SADABS.

170
W.K. Seok et al. / Journal of Organometallic Chemistry 559 (1998) 165–171
Table 4
Calculated (ZINDO/1/VSTO-3G*) and experimentally observed IR frequencies of the cation [Ru(tpy)(PPh3)2(N3)]+
Experimental IR (cm−1
)
Calc. IR (cm−1
)
Calc. Raint
Scaled IR (cm−1 b
)
Assignment
3058 m
2042 vs
1604 w
1561 m
1481 m
1434 s
4814
3313
42
956
2985
2054
w(CH, Ph+tpy)
was (NNN)
2540
2524
2517
2503
2106
2102
2101
1163
973
33
31
30
41
48
38
23
35
21
31
21
1575
1565
1560
1552
1306
1303
1302
930 (F=0.8)
779
wsym(CN, tpy)
wsym(CC+CN, tpy)+some w(CC, Ph)
wsym(CC+CN, tpy)+some w(CC, Ph)
w(CNC, tpy); w(CC, Ph)
wsym(NNN)
was(CC+CN, tpy)
was(CC+CN, tpy)
w(PC); l(PRuP); k(Ph); w(CC, Ph)
k(tpy)
1386 m
1281 w, br
1089 sc
771 m
747 s
698 s
624 mc
517 s
493 m
585
939
856
751
685
l(CPC)
k(Ph)
ClO−4
835
822
26
32
23
468
518 (F=0.62)
510
l(NNN)
w(RuN); l(NNN)
w(RuN); l(NNN); l(CC, Ph+tpy)
a Only calc. Rint\20 are listed.
b F(w)=0.60 for the stretching modes and F(l)=0.80 for in plane (l) and out of plane (k) deformation modes.
c Absorptions (partly) due to the ClO−4 anion, w1=928 (IR−, Ra+), w2=459 (IR−, Ra+), w3=1119 (IR+, Ra+), w4=625 (IR+, Ra+) [29].
Structure analysis and refinement: The structure was
solved by direct methods, and all non-H atoms refined
anisotropically. Refinement was by least-squares with
118 atoms, 640 parameters and 6142 out of 8738 reflec-
tions to RF=0.053, (RF=S[Fo−Fc]/S[Fo]), wR=
0.056, (wR=[S{w[Fo−Fc]2}/S{wFo2}]1/2); for all reflec-
tions: RF=0.091, wR=0.068. In the last D-map, the
model is within the unrestricted Hartree–Fock
formalism.
Acknowledgements
The authors thank Dr A. Schulz and W. Wu¨n-
schheim for the installation of the quantumchemical
programs. This work was financially supported by the
Dongguk University, the University of Munich and the
North Atlantic Treaty Organization (NATO, CRG
920034-3 to T.M. Klapo¨tke and P.S. White).
deepest hole was −0.58 e A−3, and the highest peak
˚
was 0.95 e A−3. Computations were carried out using
˚
the NRCVAX program system and published scatter-
ing factors [23,24].
Further details of the crystal structure determinations
are available upon request from the Fachinformation-
szentrum Karlsruhe, Gesellschaft fu¨r wissenschaftlich-
technische Information mbH, D-76344 Eggenstein-
Leopoldshafen, Germany, on quoting the journal, the
title, the authors and the depository numbers CSD-
407523.
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