Reactions of [ReX5(NO)]2- with triphenylstibine. Spectroscopic investigations of [ReX2(NO)(SbPh3) 3], X-ray structures of [ReCl2(NO)(SbPh3) 3] and [ReBr2Cl(SbPh3)3] and DFT calculations for [ReCl2(NO)(SbPh3)3]

Article abstract of DOI:10.1016/j.poly.2004.11.028

The reactions of [NBu₄]₂[ReX₅(NO)] (X = Cl, Br) with triphenylstibine have been examined and three new rhenium complexes - [ReCl₂(NO)(SbPh₃)₃] (1), [ReBr ₂(NO)(SbPh₃)₃] (2) and [ReBr ₂Cl(SbPh₃)₃] (3) - have been obtained. The last one has been isolated in a low yield during slow recrystallization of the complex 2 from a mixture of chloroform and ethanol. The stibine rhenium nitrosyls have been characterized by IR and UV-vis spectroscopy. The X-ray structures of 1 and 3 have been determined. The geometric parameters of 1 have been examined using the density functional theory (DFT) method.

Full text of DOI:10.1016/j.poly.2004.11.028

Polyhedron 24 (2005) 419–426
www.elsevier.com/locate/poly
Reactions of [ReX5(NO)]2ꢀ with triphenylstibine.
Spectroscopic investigations of [ReX2(NO)(SbPh3)3], X-ray
structures of [ReCl2(NO)(SbPh3)3] and [ReBr2Cl(SbPh3)3] and
DFT calculations for [ReCl2(NO)(SbPh3)3]
a,
c
B. Machura *, R. Kruszynski b,1, M. Jaworska
a
Department of Inorganic and Radiation Chemistry, Institute of Chemistry, University of Silesia, 9th Szkolna Street, 40006 Katowice, Poland
Department of X-ray Crystallography and Crystal Chemistry, Institute of General and Ecological Chemistry, Lodz University of Technology,
b
_
116 Zeromski Street, 90-924 Ło´dz´, Poland
c
Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia, 9th Szkolna Street, 40006 Katowice, Poland
Received 9 November 2004; accepted 30 November 2004
Abstract
The reactions of [NBu4]2[ReX5(NO)] (X = Cl, Br) with triphenylstibine have been examined and three new rhenium complexes –
[ReCl2(NO)(SbPh3)3] (1), [ReBr2(NO)(SbPh3)3] (2) and [ReBr2Cl(SbPh3)3] (3) – have been obtained. The last one has been isolated
in a low yield during slow recrystallization of the complex 2 from a mixture of chloroform and ethanol. The stibine rhenium nitrosyls
have been characterized by IR and UV–vis spectroscopy. The X-ray structures of 1 and 3 have been determined. The geometric
parameters of 1 have been examined using the density functional theory (DFT) method.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Rrhenium; Stibine; Nitrosyl complexes; X-ray structure; DFT calculations
1. Introduction
[10–18]. The [ReOX3L2] complexes react with NO to
give various products, depending on the reaction
conditions: [ReX3(NO)(OPPh3)2], [ReX3(NO)(PPh3)2],
[ReX2(NO)2(PPh3)2], [ReBr3(NO)(MeCN)(PPh3)], [Re-
The introduction of bꢀ emitting isotopes 188Re and
186Re in radiotherapy, the similarity with technetium
[1–5], and the key role of nitric oxide in human cardio-
vascular and nervous systems and in immune response
to pathogen invasion [6–9] are the main reasons of the
still growing interest in rhenium nitrosyl complexes.
Previously, we reported the preparation, spectro-
scopic and structural characterization of rhenium nitros-
yls with triphenylphosphine and triphenylarsine ligands
Cl3(NO)(PPh3)(OPPh3)],
[ReCl4(PPh3)2],
[Re-
Br3(NO)(dppe)][ReBr4(dppe)], [ReX3(NO)(OAsPh3)2],
[ReCl4(OAsPh3)2] and [ReCl3(NO)(AsPh3)2] [Re-
Cl4(AsPh3)2]. The reactions of [NBu4]2[ReX5(NO)]
with PPh3 and AsPh3 lead to [ReX3(NO)(PPh3)2], [Re-
Br3(NO)(AsPh3)2] and [ReCl3(NO)(AsPh3)2][ReCl4
(AsPh3)2].
Now we are extending our studies to the examina-
tion of the reactivity of [NBu4]2[ReX5(NO)] (X = Cl,
Br) compounds towards triphenylstibine, and here we
report the syntheses of the [ReX2(NO)(SbPh3)3] com-
plexes and X-ray structures of [ReCl2(NO)(SbPh3)3]
(1) and [ReBr2Cl(SbPh3)3] (3). The latter has been
*
Corresponding author. Tel.: +48 322582441; fax: +48 322599978.
E-mail addresses: bmachura@poczta.onet.pl (B. Machura), krus-
zyna@p.lodz.pl (R. Kruszynski), mj@tc3.ich.us.edu.pl (M. Jaworska).
1
A holder of the Foundation for Polish Science (FNP) scholarship.
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.11.028

420
B. Machura et al. / Polyhedron 24 (2005) 419–426
isolated in a low yield during slow recrystallization of
the [ReBr2(NO)(SbPh3)3] (2) complex from a mixture
of chloroform and ethanol. The formation of 3 is
particularly interesting since substitution reactions of
the nitrosyl ligand are rarely observed [19–21]. This
paper also includes the results of the DFT calculations
for [ReCl2(NO)(SbPh3)3] based on the B3LYP func-
tional, carried out by using the GAUSSIAN 03 program
package.
Gancheff et al. [22] have performed extended tests of
the ability of the B3LYP method in the LANL2DZ basis
set for rhenium compounds in a geometry optimization
and calculation of spectral properties. Although this is
not a very extended basis set, its use with DFT has
shown it to be sufficient for geometry optimization
and calculation of spectral properties. It gives good
agreement with the experimental data and its use is espe-
cially justified in the case of large molecules.
Anal. Calc. for C54H45Sb3Cl2 NORe: C, 48.18; H,
3.37; N, 1.04. Found: C, 48.3; H, 3.5; N, 1.1%.
2.3. Synthesis of [ReBr2(NO)(SbPh3)3] (2) and
[ReBr2Cl(SbPh3)3] (3)
A procedure similar to that for 1 was used with
[t-Bu4N]2[ReBr5(NO)] (1.27 g, 1.15 mmol) and SbPh3
(5.3 g, 15 mmol). A yellow–green precipitate of 2 was
collected in 38% yield.
IR (KBr, cmꢀ1) 3049 (m), 1681 (vs), 1576 (w), 1479
(m), 1431 (s), 1332 (w), 1302 (w), 1265 (w), 1186 (m),
1157 (w), 1066 (m), 1020 (w), 997 (w), 727 (vs), 692
(vs), 450 (m).
Anal. Calc. for C54H45Sb3Br2NORe: C, 45.19; H,
3.16; N, 0.98. Found: C, 45.3; H, 3.2; N, 1.1%.
Slow recrystallization of 2 from a mixture of chloro-
form and ethanol leads to the formation of the
[ReBr2Cl(SbPh3)3] complex (3) in low yield (ꢁ3%).
2. Experimental
2.4. Crystal structure determinations and refinement
2.1. General procedure
The X-ray intensity data of 1 and 3 were collected
on a KM-4-CCD automatic diffractometer equipped
with a CCD detector. 32- and 29-s exposure times
were used, respectively, and all the Ewald sphere
was collected up to h = 25.11ꢁ. The unit cell parame-
ters were determined from least-squares refinement of
the setting angles of 16321 and 7104 strongest reflec-
tions, respectively, for 1 and 3. Details concerning
crystal data and refinement are given in Table 1. Lor-
entz, polarization and numerical absorption correc-
tions [24] were applied. The structures were solved
by the Patterson method and subsequently completed
by difference Fourier recycling. All the non-hydrogen
atoms were refined anisotropically using full-matrix,
least-squares techniques. The hydrogen atoms of the
phenyl rings were treated as ‘‘riding’’ on their parent
All the reagents used for the syntheses were com-
mercially available and were used without further
purification. The [t-Bu4N]2[ReX5(NO)] (X = Cl, Br)
complexes were synthesized according to the literature
methods [23]. Gaseous NO was generated in the reac-
tion:
2NaNO2 + 3H2SO4 + FeSO4 ! 2NO + 2NaH-
SO4 + Fe2(SO4)3 + 2H2O, and was purified by passing
through washers with concentrated KOH solution
and a column containing solid NaOH. The reactions
were performed under argon atmosphere.
IR spectra were recorded on a Nicolet Magna 560
spectrophotometer in the spectral range 4000–
400 cmꢀ1 with the samples in the form of KBr pellets.
Electronic spectra were measured on a Lab Alliance
UV–VIS 8500 spectrophotometer in the range 800–
200 nm in deoxygenated dichloromethane solution.
Magnetic susceptibilities were measured at 296 K by
the Faraday method. Elemental analyses (C, H, N) were
performed on a Perkin–Elmer CHN-2400 analyzer.
˚
carbon atoms [d(C–H) = 0.96 A] and assigned isotro-
pic temperature factors equal to 1.2 times the value
of the equivalent temperature factor of the parent car-
bon atom. SHELXS 97 [25], SHELXL 97 [26] and SHEL-
XTL [27] programs were used for all the calculations.
Atomic scattering factors were those incorporated in
the computer programs.
2.2. Synthesis of [ReCl2(NO)(SbPh3)3] (1)
A mixture of [t-Bu4N]2[ReCl5(NO)] (1 g, 1.15 mmol)
and SbPh3 (5.3 g, 15 mmol) in ethanol (50 cm3) was re-
fluxed for 12 h. The yellow–green precipitate thus
formed was filtered and washed with ether. X-ray qual-
ity crystals were obtained by recrystallization from a
mixture of chloroform and ethanol. Yield 35%.
IR (KBr, cmꢀ1) 3049 (m), 2924 (w), 1683 (vs), 1477
(m), 1430 (s), 1333 (w), 1300 (w), 1261 (w), 1183 (w),
1157 (w), 1066 (m), 1020 (w), 995 (w), 728 (vs), 691
(vs), 449 (m).
2.5. Computational details
The GAUSSIAN 03 program [28] was used in the calcu-
lations. The geometry optimization was carried out with
the DFT method with the use of the B3LYP functional
[29,30].
The LANL2DZ basis set [31] was used on the rhe-
nium and antimony atoms, 6-31G(d) on the nitrogen,
chlorine, oxygen and carbon atoms, and 6-31G basis
on the hydrogen atoms in the calculations.

B. Machura et al. / Polyhedron 24 (2005) 419–426
421
Table 1
Crystal data and structure refinement for 1 and 3
The yield of the [ReX2(NO)(SbPh3)3] complexes de-
pends on: (i) the mole ratio of [NBu4]2[ReX5(NO)] to tri-
phenylstibine (it is the highest when it is ꢁ1:13) and (ii)
the reaction time (it drops considerably when the reac-
tion is carried out in less than 12 h). Compounds 1
and 2 were recrystallized from a mixture of CHCl3/
EtOH. The crystals of 1 were of good quality, whereas
the crystals of 2 were small and badly shaped. More-
over, in the case of the bromine nitrosyl, the formation
of a small amount of well-shaped yellow crystals of 3
was observed during the slow recrystallization. The oxi-
dation reactions of rhenium complexes by halogen-
containing solvents have been known for years [34].
Substitution reactions of nitrosyl ligands by halogen
ligands, however, are very sparse [19–21].
The structure of 1 has been modelled with the Cl and
NO ligands disordered over two sites using fractional
occupancies equal to 0.45 for Cl(1), N(2), O(2) atoms
and 0.55 for Cl(3), N(1) and O(1) atoms. A similar dis-
order of NO ligands has also been reported for iridium,
rhodium and ruthenium complexes [35]. The SbPh3 li-
gands are arranged in a meridional fashion, and the
Cl(3) ligand is involved in weak intramolecular hydro-
gen bonds with the H(36) and H(54) atoms of the phenyl
rings [36–38]. Fig. 1 shows a displacement ellipsoid plot
of 1 and selected bond lengths and angles of this com-
pound are summarized in Table 2.
1
3
Empirical formula
Formula weight
Temperature (K)
C54H45Sb3Cl2NORe C54H45Sb3Br2ClRe
1346.26
293(2)
1440.62
293(2)
˚
Wavelength (A)
0.71073
monoclinic
P21/n
0.71073
orthorhombic
P212121
Crystal system
Space group
Unit cell dimensions
˚
a (A)
18.8063(5)
13.1913(3)
19.8266(5)
91.738(2)
4916.3(2)
4
13.3916(4)
16.2378(5)
22.6870(9)
˚
b (A)
˚
c (A)
b (ꢁ)
Volume (A )
3
˚
4933.3(3)
4
1.940
Z
Density (calculated)
(Mg/m3)
Absorption coefficient
1.819
4.232
5.780
(mmꢀ1
)
F(000)
2584
0.15 · 0.15 · 0.29
2.77–25.11
2736
0.07 · 0.10 · 022
3.29–25.11
Crystal size (mm)
h range for data
collection (ꢁ)
Index ranges
ꢀ22 6 h 6 22
ꢀ15 6 k 6 14
ꢀ23 6 l 6 23
50963
ꢀ15 6 h 6 15
ꢀ19 6 k 6 19
ꢀ27 6 l 6 21
57700
Reflections collected
Independent reflections
8760 (0.0471)
8765 (0.0566)
(Rint
)
Completeness to 2h (%)
Data/restraints/
parameters
Goodness-of-fit on F2
95.3
8760/0/587
99.6
8765/0/550
Two groups of ligands of 3 (halide ions and stibine
molecules) are arranged in a meridional fashion, the bro-
mine ligands occupy a cis position to each other. Fig. 2
shows the molecular structure of this compound, and se-
lected bond lengths and angles for 3 are summarized in
1.042
1.102
Final R indices [I > 2r(I)] R1 = 0.0270
wR2 = 0.0634
R1 = 0.0426
wR2 = 0.0986
R1 = 0.0439
wR2 = 0.0994
0.016(8)
R indices (all data)
R1 = 0.0352
wR2 = 0.0664
Absolute structure
parameter
Largest difference
0.751 and ꢀ0.677
1.166 and ꢀ1.577e
3
˚
peak and hole (e/A )
Natural bond orbital (NBO) calculations were per-
formed with the NBO code [32] included in GAUSSIAN
03.
3. Results and discussion
The [t-Bu4N]2[ReX5(NO)] complexes (X = Cl, Br) re-
act with PPh3 and AsPh3 to give [ReX3(NO)(PPh3)2],
[ReBr3(NO)(AsPh3)2] and [ReCl3(NO)(AsPh3)2][Re-
Cl4(AsPh3)2] [18]. The reactions of [t-Bu4N]2[ReX5(NO)]
with triphenylstibine in ethanol lead to the [Re-
X2(NO)(SbPh3)3] complexes. The smaller steric demand
of SbPh3 in comparison with PPh3 and AsPh3 explains
the formation of [ReX2(NO)(SbPh3)3]. The increase of
M–E and E–C (E = P, As or Sb) bond lengths in the or-
der P > As > Sb leads to the decrease of the EPh3 cone
angles [33].
Fig. 1. The molecular structure of 1.

422
B. Machura et al. / Polyhedron 24 (2005) 419–426
Table 2
˚
The experimental and optimized bond lengths (A) and angles (ꢁ) for 1
Bond lengths
Experimental
Optimized
Angles
Experimental
Optimized
175.35
Re(1)–Cl(1)
Re(1)–Cl(2)
Re(1)–Cl(3)
Re(1)–N(1)
Re(1)–N(2)
Re(1)–Sb(1)
Re(1)–Sb(2)
Re(1)–Sb(3)
N(1)–O(1)
2.353(5)
2.4443(10)
2.362(4)
1.832(19)
1.753(17)
2.6945(3)
2.6640(3)
2.6758(3)
1.13(4)
2.533
2.522
N(2)–Re(1)–N(1)
N(2)–Re(1)–Cl(1)
N(1)–Re(1)–Cl(3)
Cl(1)–Re(1)–Cl(3)
N(2)–Re(1)–Cl(2)
N(1)–Re(1)–Cl(2)
Cl(1)–Re(1)–Cl(2)
Cl(3)–Re(1)–Cl(2)
N(2)–Re(1)–Sb(1)
N(1)–Re(1)–Sb(1)
Cl(1)–Re(1)–Sb(1)
Cl(3)–Re(1)–Sb(1)
Cl(2)–Re(1)–Sb(1)
Sb(2)–Re(1)–Sb(1)
Sb(3)–Re(1)–Sb(1)
N(2)–Re(1)–Sb(2)
N(1)–Re(1)–Sb(2)
Cl(1)–Re(1)–Sb(2)
Cl(3)–Re(1)–Sb(2)
Cl(2)–Re(1)–Sb(2)
N(2)–Re(1)–Sb(3)
N(1)–Re(1)–Sb(3)
Cl(1)–Re(1)–Sb(3)
Cl(3)–Re(1)–Sb(3)
Cl(2)–Re(1)–Sb(3)
Sb(2)–Re(1)–Sb(3)
O(1)–N(1)–Re(1)
O(2)–N(2)–Re(1)
178.2(9)
177.0(7)
177.1(7)
176.3(2)
92.3(6)
1.754
2.762
2.723
2.752
1.195
99.99
84.38
89.77
92.46
86.6(7)
89.39(19)
91.85(10)
84.7(6)
N(2)–O(2)
1.32(4)
96.5(7)
97.95(17)
85.67(10)
84.29(3)
94.101(10)
169.638(10)
94.8(6)
81.46
97.23
165.74
97.37
86.4(7)
83.60(19)
95.31(9)
172.52(3)
89.3(6)
78.31
162.58
90.36
89.3(7)
88.30(17)
88.24(10)
87.54(3)
94.809(10)
178(2)
88.48
84.48
96.90
179.1
175(2)
Table 3
˚
Bond lengths (A) and angles (ꢁ) for 3
Bond lengths
Angles
Re(1)–Br(1)
Re(1)–Br(2)
Re(1)–Cl(1)
Re(1)–Sb(1)
Re(1)–Sb(2)
Re(1)–Sb(3)
2.5179(16)
2.5997(11)
2.436(4)
Cl(1)–Re(1)–Br(1)
Cl(1)–Re(1)–Br(2)
Br(1)–Re(1)–Br(2)
Cl(1)–Re(1)–Sb(2)
Br(1)–Re(1)–Sb(2)
Br(2)–Re(1)–Sb(2)
Cl(1)–Re(1)–Sb(1)
Br(1)–Re(1)–Sb(1)
Br(2)–Re(1)–Sb(1)
Sb(2)–Re(1)–Sb(1)
Cl(1)–Re(1)–Sb(3)
Br(1)–Re(1)–Sb(3)
Br(2)–Re(1)–Sb(3)
Sb(2)–Re(1)–Sb(3)
Sb(1)–Re(1)–Sb(3)
177.56(9)
87.24(8)
90.49(5)
86.72(8)
95.54(4)
173.93(4)
91.23(7)
87.72(4)
85.80(3)
93.70(2)
93.78(7)
86.90(4)
85.01(3)
96.02(2)
169.30(2)
2.6809(7)
2.6713(7)
2.6873(7)
weak hydrogen bond with the H(20) atom of the phenyl
ring, while the Br(1) ion interacts with the H(36) atom.
Due to steric repulsion of the three bulky SbPh3 mol-
ecules, the octahedral Re geometries of 1 and 3 show the
expected angular distortions. The angles between cis-
ligands vary between 83.60(19)ꢁ and 97.95(17)ꢁ for 1,
and 85.01(3)ꢁ and 96.02(2)ꢁ for 3; the trans-angles are
between 169.64(1)ꢁ and 178.2(9)ꢁ for 1, and 169.30(2)ꢁ
and 177.56(9)ꢁ for 3.
Fig. 2. The molecular structure of 3.
Table 3. The conformations of [ReBr2Cl(SbPh3)3] mole-
cules are stabilized by two weak intramolecular hydro-
gen bonds [35–37]. The Cl(1) ligand is involved in a

B. Machura et al. / Polyhedron 24 (2005) 419–426
423
Table 5
Band positions and molar absorption coefficients for 1 and 2
There are only a few Re–Sb distances reported in the
Cambridge Structural Database, with [ReCl2(NO)2
˚
(SbPh3)2] [39] [Re–Sb: 2.711(8) and 2.710(8) A] and [Re-
Band position (nm)
e
˚
Cl(CO)3(SbPh3)2] [40] [Re–Sb: 2.726(1) and 2.729(2) A]
Compound 1
420.0
378.5
560
740
being the closest chemical examples and showing little
longer Re–Sb bond lengths compared to the presented
compounds (Tables 2 and 3).
282.5
230.0
215.0
8440
14900
9760
Relative small C–Sb–C tetrahedral angles were
found: 94.78(17)ꢁ–102.48(17)ꢁ, 100.2ꢁ (av) for 1 and
95.2(4)ꢁ–102.1(4)ꢁ, 99.1ꢁ (av) for 3. This is most likely
due to the large Sb–C bond lengths making it possible
for the phenyl rings to be compressed a little more than
that which is encountered for the analogous phosphine
and arsine ligands. Table 4 presents the Re–E and
E–C bond lengths and C–E–C angles (E = P, As or
Sb) for the selected rhenium complexes.
Compound 2
415.0
381.0
530
490
290.5
232.0
223.5
8200
12580
7580
e is the molar absorption coefficient (dm3 molꢀ1 cmꢀ1).
˚
˚
The average Re–NO (1.793 A) and N–O (1.225 A)
bond lengths and the average value of the Re–N–O an-
gle (176.5ꢁ) for 1 confirm a linear coordination of the
nitrosyl group, and they are comparable with values
found for phosphine and arsine rhenium nitrosyls [13–
18].
A notable trans influence of the triphenylstibine li-
gand is observed in both 1 and 3; the Re–X(2) bond
˚
lengths are longer by about 0.08 A in comparison with
tronic absorption spectra of both rhenium (I) complexes
are very similar. They are dominated by three intense
bands below 300 nm due to interligand electronic transi-
tions of SbPh3. In addition, two less intense absorption
bands appear at ꢁ420 and ꢁ380 nm, and they can be as-
signed to d–d transitions and metal-to-ligand charge
transfer (MLCT) transitions from Re(I) to p* ligand
orbitals.
Considering the magnetic measurements, the geome-
try of 1 was optimized in the singlet state by the DFT
method with the B3LYP functional. The optimized
geometry is in quite good agreement with the experimen-
tal one, the largest differences are found for the Re–Cl
and Re–Sb bond distances. A similar elongation of the
rhenium–halogen bond lengths in the B3LYP with dif-
ferent basis sets has been found in other rhenium com-
plexes [41].
Table 6 presents the atomic charges from the natural
population analysis (NPA) for 1. The calculated charge
on the nitrogen atom of the nitrosyl group is positive,
whereas the oxygen atom is negatively charged. The to-
tal charge on the NO group of the title complex is neg-
ative: ꢀ0.176. The calculated charge on the rhenium
atom of 1 is far from the formal charge +1. It results
from charge donation from the chloride ions and triphe-
nylstibine ligand, which act as r-donors. There are large
positive charges on the Sb atoms, and the charges on the
chloride ions are significantly smaller than ꢀ1.
the corresponding Re–X distances in cis positions to
the SbPh3 ligand. A difference between Re–Cl(1) and
Re–Cl(3) in 1 is a consequence of the nitrosyl disorder.
The nitrosyl stretching frequency in [Re-
X2(NO)(SbPh3)3] compounds is independent of the hal-
ogen ligand, the strong band corresponding to mNO
appears at ꢁ1680 cmꢀ1 in the IR spectrum of the chloro
(1) and bromo (2) nitrosyl. The considerable lowering of
the mNO for [ReIX2(NO)(SbPh3)3] complexes in compar-
ison with the [ReIIX3(NO)(PPh3)2] and [ReIIX3
(NO)(AsPh3)2] nitrosyls [15,17,18] is consistent with
the lower oxidation state of the rhenium ion. It results
in an increased backdonation of electron density from
the filled rhenium d-orbitals into the p* antibonding
orbital of the NO group.
The complexes 1 and 2 are diamagnetic, which con-
firms the low-spin d6 configuration of the rhenium ion
in the Oh field.
Table 5 presents the positions and molar absorption
coefficients of the electronic bands for 1 and 2. The elec-
Table 4
The Re–E and E–C bond lengths and C–E–C angles (E = P, As or Sb) for the selected rhenium complexes
˚
Re–E bond length (average, A)
˚
E–C bond length (average, A)
Complex
C–E–C angle (average, ꢁ)
Reference
[Re(NO)Cl3(PPh3)2]
[Re(NO)Br3(PPh3)2]
[Re(NO)Cl3(AsPh3)2]
[Re(NO)Br3(APh3)2]
[ReCl2(NO)2(SbPh3)2]
[ReCl(CO)3(SbPh3)]
[ReCl2(NO)(SbPh3)3]
[ReBr2Cl(SbPh3)3]
2.530
2.540
2.612
2.595
2.711
2.728
2.678
2.680
1.822
1.822
1.942
1.935
2.114
2.137
2.133
2.135
104.3
104.3
103.4
103.7
102.5
100.1
100.2
99.1
[15]
[17]
[18]
[18]
[38]
[39]
this work
this work

424
B. Machura et al. / Polyhedron 24 (2005) 419–426
Table 6
Atomic charges from the natural population analysis (NPA) for 1
components: (i) a donation of electron density from a r-
type orbital on NO onto the metal orbital and (ii) a
donation of electron density from the occupied metal
d-orbitals into the p* antibonding orbitals of the NO li-
gand. The occupied dyz and dxz rhenium orbitals partic-
ipate in the back-donation from the central ion to the
nitrosyl ligand in complex 1. In the occupied orbitals,
the pꢂNO are distributed among several highest MOs. A
substantial contribution of pRe–NO orbitals are shown
in HOMO ꢀ 4, HOMO ꢀ 2 and HOMO ꢀ 1. Percent
participations of the d rhenium and pꢂNO orbitals in these
MOs are very similar. The LUMO + 1, LUMO + 2 and
LUMO + 3 orbitals are of pꢂRe–NO antibonding character.
The LUMO + 1 orbital has prevalent NO character,
whereas the LUMO + 2 and LUMO + 3 orbitals are
localised almost evenly on the d rhenium and pNꢂ O
orbitals.
Atom
Atomic charge
Re(1)
Cl(1)
Cl(2)
N(1)
O(1)
ꢀ0.271
ꢀ0.515
ꢀ0.498
0.148
ꢀ0.324
1.650
1.653
Sb(1)
Sb(2)
Sb(3)
1.665
The energies and characters of several highest occu-
pied and lowest unoccupied molecular orbitals of 1 are
presented in Table 7. The selected HOMO and LUMO
orbitals of 1 are depicted in Fig. 3. The investigated
complex is of a large size, the number of basis func-
tions is equal 956. Among the occupied MOs of 1
the largest numbers constitute orbitals of the phenyl
rings which are not relevant for the discussion of the
bonding. The others have complicated character. The
percent participations of the ligand atomic orbitals in
the selected HOMO and LUMO orbitals are shown
in Table 7.
The HOMO orbital of 1 is a dxy metal orbital with an
admixture of chlorine p orbitals. The LUMO is a dx2ꢀy2
orbital with an antibonding admixture of the chloride
and antimony lone pair orbitals.
Additional information about the binding in com-
plex 1 was obtained by NBO analysis. Table 8 presents
the occupancies and natural atomic orbital composi-
tions (NAO) of the selected NBOs for complex 1.
The occupancies of the bonding and antibonding Re–
N bond orbitals (BDRe–N and BDꢂRe–N orbitals) con-
firms a great donation of electron density from the
occupied rhenium d-orbitals into the p* antibonding
orbitals of the NO ligand. For compound 1, three nat-
ural bond orbitals were detected for the Re–N bond,
and one orbital – for the N–O bond. The Re–N bond
orbital of r-character is polarized towards the nitrogen
atom (ca. 73% at N) and the s- and d-orbitals of Re
take part in the bonding. In the case of the Re–N bond
orbitals of p-character, only d-orbitals of Re are in-
cluded in the bonding. The N–O bond orbital is
slightly polarized towards the oxygen end. In the va-
lence-bond treatment a linear bonding mode of the
nitrosyl group may be represented by the following
resonance forms [42]:
The bonding of NO to the rhenium center involves a
synergic interaction between the nitrosyl ligand orbitals
and the metal orbitals. The Re–NO bond consists of two
Table 7
The energy and character of selected molecular orbitals of 1
MO
E (eV) Character
HOMO ꢀ 14 ꢀ6.801
p
Ph(80.54), pCl(13.99)
HOMO ꢀ 13 ꢀ6.767 pPh
HOMO ꢀ 12 ꢀ6.740 pPh
HOMO ꢀ 11 ꢀ6.719 pPh
HOMO ꢀ 10 ꢀ6.715 pPh
HOMO ꢀ 9
HOMO ꢀ 8
HOMO ꢀ 7
HOMO ꢀ 6
HOMO ꢀ 5
HOMO ꢀ 4
HOMO ꢀ 3
HOMO ꢀ 2
HOMO ꢀ 1
ꢀ6.686 pPh
ꢀ6.675 pPh
ꢀ6.600 pPh
ꢀ6.591 pPh
ꢀ6.572 pPh
ꢀ6.500 pPhð59:61Þ; pClð11:93Þ; dxzð7:06Þ þ pꢂNOð11:59Þ
ꢀ6.410
pCl(58.88), pPh(28.31), nSb(5.69)
ꢀ6.123 dyzð23:13Þ þ pꢂNOð29:37Þ, pCl(37.64)
ꢀ5.866 pClð28:15Þ; pPhð27:48Þ; nSbð20:03Þ; dxzð13:0Þ
þpꢂNOð7:11Þ
M -
N
A
O
M
N
B
O
HOMO
LUMO
ꢀ5.409
dxy(60.45), pCl(24.02)
ꢀ1.006 dx2ꢀy2 ð28:52Þ ꢀ rSbð36:07Þ ꢀ rClð5:82Þ
ꢀ0.939 pꢂNOð40:54Þ ꢀ dxzð22:53Þ; pPꢂhð17:56Þ
ꢀ0.852 pꢂNOð18:82Þ ꢀ dyzð14:96Þ; pPꢂhð38:75Þ;
pClð10:04Þ
LUMO + 1
LUMO + 2
M -
N
O
M
N
D
O-
C
LUMO + 3
LUMO + 4
LUMO + 5
LUMO + 6
LUMO + 7
LUMO + 8
LUMO + 9
ꢀ0.809 pꢂNOð15:77Þ ꢀ dyzð17:44Þ; pPꢂhð30:76Þ
ꢀ0.795 pꢂPhð30:76Þ; pNꢂ Oð7:76Þ ꢀ dyzð7:29Þ
ꢀ0.572 pꢂPh
ꢀ0.498 pꢂPh
The results of the NBO analysis indicate that the reso-
nance structure D makes a significant contribution to
the structure of complex 1.
It is consistent with the charges on the nitrogen and
oxygen atoms of the nitrosyl group and the relatively
low nitrosyl stretching frequency.
ꢀ0.442 pꢂPh
ꢀ0.363 pꢂPh
ꢀ0.306 pꢂPh
LUMO + 10 ꢀ0.294 pPꢂh
LUMO + 11 ꢀ0.264 pPꢂh
LUMO + 12 ꢀ0.221 pPꢂh

B. Machura et al. / Polyhedron 24 (2005) 419–426
425
Fig. 3. Selected HOMO and LUMO orbitals for 1. The phenyl rings are omitted for clarity, they make no contribution to the presented orbitals.
Positive values of the orbital contour are represented in blue (0.04 a.u.) and negative values – in yellow (ꢀ0.04 a.u.).
Table 8
Selected results of the NBO analysis for 1
Bond orbital BD
Occupancy
1.965
NAO composition
BD*
Occupancy
0.419
Re„N(r)
% Re
% N
26.96
73.04
s(18.35%) d(81.48%)
s(57.54%) p(42.44%)
Re„N(r*)
Re„N(p)
Re„N(p)
NAO
1.944
1.974
1.996
% Re
% N
48.48
51.52
d(93.84%)
p(93.72%)
Re„N(p*)
Re„N(p*)
N–O(r*)
0.444
0.469
0.014
% Re
% N
55.55
44.45
d(99.42%)
p(99.94%)
% N
% O
45.47
54.53
s(36.19%) p(63.66%)
s(29.72%) p(70.14%)
4. Supplementary data
WCSS, Wrocław, Poland, under calculational Grant
No. 51/96.
Supplementary data are available from the CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223
336033; e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk) on request, quoting the Deposi-
tion Nos.: 254986 (C54H45Sb3Cl2NORe) and 254987
(C54H45Sb3Br2ClRe).
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