The synthesis, spectroscopic characterisation, crystal and molecular structure of the [ReCl3(NO)(OPPh3)(pyz)] complex. DFT calculations for [ReCl3(NO)(OPPh3)(pyz)] and [ReCl 3(NO)(OPPh3)(PPh3)]

Article abstract of DOI:10.1016/j.poly.2004.11.024

A new rhenium nitrosyl - [ReCl₃(NO)(OPPh₃)(pyz)] - has been obtained by two different routes: (i) in the substitution reaction of [ReCl₃(NO)(OPPh₃)(PPh₃)] with pyrazine, and (ii) in the nitrosylation reaction of [ReOCl₃(PPh₃) ₂] by gaseous nitric oxide in the presence of an excess of pyrazine. The crystal, molecular and electronic structure of the [ReCl₃(NO) (OPPh₃)(pyz)] complex has been determined. The geometric parameters of [ReCl₃(NO)(OPPh₃)(pyz)] have been examined using the density functional theory (DFT) method. The UV-Vis spectrum of the pyrazine complex has been interpreted on the basis of the electronic transitions of [ReCl₃(NO)(OPPh₃)(pyz)] calculated with the time-dependent DFT method (TDDFT). The paper also includes the results of the DFT and TDDFT calculations for [ReCl₃(NO)(OPPh₃)(PPh₃)].

Full text of DOI:10.1016/j.poly.2004.11.024

Polyhedron 24 (2005) 267–279
www.elsevier.com/locate/poly
The synthesis, spectroscopic characterisation, crystal and
molecular structure of the [ReCl3(NO)(OPPh3)(pyz)] complex.
DFT calculations for [ReCl3(NO)(OPPh3)(pyz)] and
[ReCl3(NO)(OPPh3)(PPh3)]
a,
b
c,1
B. Machura *, M. Jaworska , R. Kruszynski
a
Department of Inorganic and Radiation Chemistry, Institute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice, Poland
b
Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice, Poland
c
Department of X-ray Crystallography and Crystal Chemistry, Institute of General and Ecological Chemistry,
_
Lodz University of Technology, 116 Zeromski St., 90-924 Łodz, Poland
´
´
Received 8 September 2004; accepted 9 November 2004
Abstract
A new rhenium nitrosyl – [ReCl3(NO)(OPPh3)(pyz)] – has been obtained by two different routes: (i) in the substitution reaction of
[ReCl3(NO)(OPPh3)(PPh3)] with pyrazine, and (ii) in the nitrosylation reaction of [ReOCl3(PPh3)2] by gaseous nitric oxide in the
presence of an excess of pyrazine. The crystal, molecular and electronic structure of the [ReCl3(NO)(OPPh3)(pyz)] complex has been
determined. The geometric parameters of [ReCl3(NO)(OPPh3)(pyz)] have been examined using the density functional theory (DFT)
method. The UV–Vis spectrum of the pyrazine complex has been interpreted on the basis of the electronic transitions of
[ReCl3(NO)(OPPh3)(pyz)] calculated with the time-dependent DFT method (TDDFT). The paper also includes the results of the
DFT and TDDFT calculations for [ReCl3(NO)(OPPh3)(PPh3)].
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Rhenium nitrosyl complexes; Pyrazine; X-ray structure; DFT and TDDFT calculations
1. Introduction
One of the most important aspects of the research on
nitrosyl complexes is determination of the bonding nat-
ure of NO to the metal center. Terminal NO ligands
may adopt either linear or bent geometries. Although
the bonding in the M–NO moiety is largely of covalent
nature and the electron distribution is more or less
evenly distributed in this group, the bonding of the
M–NO unit is often described by assigning formal oxi-
dation states to the metal centre and the nitrosyl ligand.
In such an assignment nitric oxide can be coordinated as
NO+, NO or NOꢀ. The M–NO core can be also de-
scribed using the {M(NO)x}n formalism proposed by
Enemark and Feltham, in which n is taken as the total
number of electrons associated with the metal d and
p*(NO) orbitals [1,3,9,11].
For many years nitrosyl compounds of transition
metals have been the centre of interest of scientists both
engaged in basic research and trying to employ these
complexes as catalysts of polymerisation, oligomeri-
sation, metathesis, epoxidation, oxidation and reduction
[1–11].
*
Corresponding author. Tel.: +48322582441; fax: +48322599978.
E-mail addresses: bmachura@poczta.onet.pl (B. Machura),
mj@tc3.ich.us.edu.pl (M. Jaworska), kruszyna@p.lodz.pl (R.
Kruszynski).
1
A holder of the Foundation for Polish Science (FNP) scholarship.
0277-5387/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.11.024

268
B. Machura et al. / Polyhedron 24 (2005) 267–279
Due to the favourable nuclear properties of 186Re and
2NaNO2 þ 3H2SO4 þ FeSO4
! 2NO þ 2NaHSO4 þ Fe2ðSO4Þ þ 2H2O
was purified by passing through washers with concen-
trated KOH solution and over solid NaOH.
188Re nuclides in diagnostic nuclear medicine and appli-
cations in radioimmunotheraphy [12,13], the chemistry
of nitrosyl rhenium complexes arouses particular
interest.
ð1Þ
3
The IR spectrum of 1 was recorded on a Nicolet
Magna 560 spectrophotometer in the spectral range
4000–400 cmꢀ1 with the sample in the form of a KBr
pellet. The electronic spectrum of 1 was measured on a
Lab Alliance UV–Vis 8500 spectrophotometer in the
range 800–220 nm in deoxygenated dichloromethane
solution. Magnetic susceptibility was measured at
296 K by the Faraday method. Elemental analyses (C,
H, N) were performed on a Perkin–Elmer CHN-2400
analyzer.
The papers [14–22] present the preparation, structural
and spectroscopic characterisation of rhenium mononi-
trosyls with phosphine and arsine ligands in the coordi-
nation sphere.
Here we present the synthesis, crystal, molecular and
electronic structure of a new rhenium nitrosyl with pyr-
azine (pyz) in the coordination sphere – [ReCl3(NO)
(OPPh3)(pyz)] (1). The electronic structure of 1 has been
determined on the basis of density functional theory
(DFT) calculations. The spin-allowed doublet–doublet
electronic transitions of [ReCl3(NO)(OPPh3)(pyz)] have
been calculated with the time-dependent DFT (TDDFT)
method, and the UV–Vis spectrum of the title complex
has been discussed on this basis. For comparison, the
paper includes also the results of the DFT and TDDFT
calculations for [ReCl3(NO)(OPPh3)(PPh3)] (2). The
crystal, molecular structure and spectroscopic properties
of 2 were presented in paper [17].
Recent calculations with the TDDFT method for
open- and closed-shell 5d-metal complexes have sup-
ported the TDDFT method to be applicable for such
systems giving good assignment of experimental spectra
[23–29]. Some theoretical investigations have also been
carried out on rhenium compounds. The electronic
structures of nitrido, oxo, carbonyl and nitrile rhenium
complexes, as well as their spectroscopic properties,
bonding and reactivity have been theoretically studied
at the HF, MP2, EHT and DFT levels of theory using
various basis sets [30–37]. Gancheff et al. [32] have per-
formed extended tests of the ability of the B3LYP method
in the LANL2DZ basis set for rhenium compounds in a
geometry optimisation and calculation of spectral prop-
erties. Although this is not a very extended basis set, its
use with DFT has been shown to be sufficient for geom-
etry optimisation and calculation of spectral properties.
It gives good agreement with the experimental data and
its use is especially justified in the case of large
molecules.
2.2. Preparation of [ReCl3(NO)(OPPh3)(pyz)] (1)
2.2.1. Method A
[Re(NO)Cl3(OPPh3)(PPh3)] (1 g, 1.15 mmol) and pyz
(0.5 g, 0.62 mmol) in chloroform (100 cm3) were refluxed
for 12 h. The volume was condensed to 20 cm3 and a
dark green microcrystalline solid was formed by addi-
tion of 100 cm3 of diethyl ether. The product was
washed with EtOH and cold ether, and dried in vacuo
(Yield: 40%).
2.2.2. Method B
NO was passed through a vigorously stirred and
refluxing solution of [ReOCl3(PPh3)2] (1.05 g, 1 mmol)
and pyz (0.25 g, 3.1 mmol) in acetone (100 cm3). The
reaction was carried out for 4 h. The colour changed
gradually from bright green to dark green. Then
the resulting solution was evaporated to a volume of
10 cm3. A green precipitate was formed by an addition
of 40 cm3 of EtOH and after 15 min it was filtered off.
The product was washed with cold ether and dried in
vacuo. Crystals suitable for X-ray investigation were
obtained by recrystallisation from CHCl3–EtOH (Yield:
70%).
IR (KBr, cmꢀ1) 3059 (w), 1762 (s), 1589 (m), 1484 (s),
1440 (s), 1416 (3), 1354 (w), 1316 (w), 1270 (w), 1163(m),
1122 (s), 1060 (s), 1027 (m), 1001 (m), 807 (m), 753 (s),
727 (s), 691 (s), 616 (w), 552 (s), 536 (s), 466(s). Calc.
for C21H19N3Br3OAsRe: C, 38.80; H, 2.81; N, 6.1.
Found: C, 38.92; H, 2.75; N, 6.15%.
2. Experimental
2.3. Crystal structure determination and refinement
2.1. General procedure
The X-ray intensity data of complex 1 were col-
lected on a KM-4-CCD automatic diffractometer
equipped with a CCD detector with 50 s exposure time
and all reflections of the Ewald sphere were collected
up to h = 25ꢁ. The unit cell parameters were deter-
mined from least-squares refinement of the setting an-
gles of 9937 strongest reflections. Details concerning
The reactions were carried out under an argon atmo-
sphere. All the reagents used for the syntheses of the com-
plexes are commercially available and were used without
further purification. [Re(NO)Cl3(PPh3)(OPPh3)] and
[ReOCl3(PPh3)2] complexes were prepared according to
the literature methods [17,38]. Gaseous NO, obtained
in reaction (1)

B. Machura et al. / Polyhedron 24 (2005) 267–279
269
crystal data and refinement are given in Table 1. Lor-
entz, polarisation and numerical absorption correc-
tions [39] were applied. The structure was solved by
the Patterson method and subsequently completed by
difference Fourier recycling. All the non-hydrogen
atoms were refined anisotropically using the full-
matrix, least-squares technique. The hydrogen atoms
of the phenyl rings were treated as ‘‘riding’’ on their
nitrogen, phosphorous, oxygen and carbon atoms and
6-31G basis on the hydrogen atoms.
Natural bond orbital (NBO) calculations were per-
formed with the NBO code [48] included in
GAUSSIAN03.
3. Results and discussion
˚
parent carbon atoms [d(C–H) = 0.96 A] and assigned
3.1. Preparation
isotropic temperature factors equal to 1.2 times the va-
lue of the equivalent temperature factor of the parent
carbon atom. SHELXS97 [40], SHELXL97 [41] and
SHELXTL [42] programs were used for all the calcula-
tions. Atomic scattering factors were those incorpo-
rated in the computer programs.
Two different routes have been employed for the
preparation of 1. The refluxing of [ReCl3(NO)
(OPPh3)(PPh3)] with pyrazine (pyz) (Eq. (2)) in chloro-
form gives complex 1 in a moderate yield
½ReCl3ðNOÞðOPPh3ÞðPPh3Þꢁ þ pyz
! ½ReCl3ðNOÞðOPPh3ÞðpyzÞꢁ þ PPh3
ð2Þ
2.4. Computational details
A much higher yield of 1 has been reported for the
nitrosylation reaction of [ReOCl3(PPh3)2] by gaseous ni-
tric oxide in the presence of an excess of pyrazine.
The GAUSSIAN03 program [43] was used in the calcu-
lations. The geometry optimisation was carried out with
the DFT method with the use of the B3LYP functional
[44,45]. The electronic spectra were calculated with the
TDDFT method [46].
3.2. Crystal structure
In the calculations, the LANL2DZ basis set [47] was
used on the rhenium atom, 6-31G(d) on the chlorine,
A thermal ellipsoid plot of 1 is shown in Fig. 1.
The rhenium atom of 1 is in a distorted octahedral
Table 1
Crystal data and structure refinement for [ReCl3(NO)(OPPh3)(pyz)]
Empirical formula
Formula weight
Temperature (K)
C22H19Cl3N3O2PRe
680.92
293(2)
˚
Wavelength (A)
0.71073
orthorhombic
Pbcn
Crystal system
Space group
Unit cell dimensions
˚
a (A)
29.2078(14)
10.2887(4)
16.6705(7)
5009.7(4)
8
˚
b (A)
˚
c (A)
3
˚
Volume (A )
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢀ1
F(0 0 0)
1.806
5.259
2632
)
Crystal size (mm)
h Range for data collection
Index ranges
0.041 · 0.180 · 0.194
2.81–25.11
ꢀ28 6 h 6 34;
ꢀ2 6 k 6 12;
ꢀ19 6 l 6 19
51 246
Reflections collected
Independent reflections (Rint
Completeness to 2h (%)
Maximum and minimum
transmission
)
4464 (0.0558)
89.4
0.867 and 0.739
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
4464/0/289
1.117
R1 = 0.0311; wR2 = 0.0473
R1 = 0.0486; wR2 = 0.0522
0.918 and ꢀ0.660
Largest differential peak
ꢀ3
Fig. 1. Thermal ellipsoid plot of [ReCl3(NO)(OPPh3)(pyz)] showing
the atom numbering scheme (50% probability ellipsoids).
˚
and hole (e A
)

270
B. Machura et al. / Polyhedron 24 (2005) 267–279
environment with the chloride ligands in meridional
geometry and the linear N–O group trans to the pyr-
azine molecule and cis to the OPPh3 ligand.
and thus is longer than the Re–Npyrazine distances de-
tected in [ReO(OEt)Cl2(pyz)2] (2.152(16) and 2.103(16)
˚
A) with a trans arrangement of the N-heterocyclic mol-
The molecules of 1 are linked via one C(12)–
H(12)ꢂ ꢂ ꢂO2(x, ꢀy, z + 1/2) intermolecular interaction,
which according to Desiraju and Steiner [50] can be con-
sidered as a weak hydrogen bond with a Dꢂ ꢂ ꢂA distance
ecules [51]. The OPPh3 ligand affects the Re–Cl(2) bond
length and causes its shortening. A similar trend is ob-
served for the [ReCl3(NO)(OPPh3)2] and [Re-
Br3(NO)(OPPh3)2] complexes with the halogen ligand
in a trans position to the OPPh3 molecule. The Re–
˚
equal to 3.317(6) A and a D–Hꢂ ꢂ ꢂA angle of 143.9ꢁ. The
˚
weak intramolecular interaction C(19)–H(19)ꢂ ꢂ ꢂCl(1)
OPPh3 [2.058(2) A] and P–O [1.521(3)] bond lengths in
1 are in good agreement with values found for [Re-
˚
with a Dꢂ ꢂ ꢂA distance equal to 3.264(4) A and a
˚
Cl3(NO)(OPPh3)2] (Re–O = 2.055(6) A, P–O = 1.493(6)
D–Hꢂ ꢂ ꢂA angle of 112.0ꢁ can also be treated as a weak
hydrogen bond [49,50]. It provides additional conforma-
tional stabilisation of the [ReCl3(NO)(OPPh3)(pyz)]
molecule.
˚
A) and [ReBr3(NO)(OPPh3)2] (Re–O = 2.048(4) A, P–
˚
˚
O = 1.505(4) A) [18,21]. In complex 2, the Re–OPPh3
˚
distance (2.103(5) A) is affected by the nitrosyl group
and thus is longer than the Re–OPPh3 bond length in 1.
Table 1 presents the crystal data and structural refine-
ment for complex 1. The most important experimental
bond lengths and angles of 1 are reported in Table 2.
3.3. Infrared data and magnetochemical measurements of
complex 1
˚
˚
The Re–NO (1.740(4) A) and N–O (1.184(4) A) bond
distances and the Re–N–O angle (176.0(6)ꢁ) indicate
the nitrosonium character of the NO group. They are
well compared with values previously found for other
rhenium nitrosyls [14–22]. In comparison with the
[ReCl3(NO)(OPPh3)(PPh3)] compound [1.747(5) and
The IR spectrum of 1 exhibits a strong band at 1762
cmꢀ1, assignable to m(NO). The value of m(NO) corre-
sponds to the linear NO range of Haymore and Ibers
[52]. In the IR spectrum of complex 2, the strong band
corresponding to the stretching vibration of the nitrosyl
˚
1.165(8) A] [25], an insignificant shortening of the Re–
N distance and elongation of the N–O bond length
can be noticed for complex 1. The Re–Npyrazine distance
is affected by the trans influence of the nitrosyl group
group appears at 1745 cmꢀ1
.
The sharp absorption band at 1598 cmꢀ1 in the spec-
trum of 1 is typical of mono-coordinated diaza ligands
[53]. The strong bands at 1163 and 1122 cmꢀ1 confirm
the presence of the coordinated OPPh3 molecule.
The complex 1 is a paramagnetic compound with a
room temperature magnetic moment of 1.8 BM, corre-
sponding to one unpaired electron.
Table 2
˚
The experimental and optimised bond lengths (A) and angles (ꢁ) for
[ReCl3(NO)(OPPh3)(pyz)]
Experimental
Optimised
Bond lengths
Re(1)–N(1)
Re(1)–N(2)
Re(1)–Cl(1)
Re(1)–Cl(2)
Re(1)–Cl(3)
Re(1)–O(1)
N(1)–O(2)
P(1)–O(1)
3.4. Optimised geometries of 1 and 2
1.740(4)
2.231(3)
1.758
2.245
2.453
2.409
2.458
2.105
1.171
1.536
The geometries of 1 and 2 were optimised in a dou-
blet state by the DFT method with the B3LYP func-
tional. The doublet state agrees well with the
experimental values of the effective magnetic moment
for complexes 1 and 2. The geometric parameters of 1
and 2 optimised by the DFT method are gathered in
Tables 2 and 3, respectively. For comparison, the exper-
imental bonds and bond angles of 2 are also included in
Table 3. The structure and atomic numbering scheme of
the complex 2 are shown in Fig. 2. The optimised geom-
etries of 1 and 2 are in good agreement with the exper-
imental ones, and the general trends observed in the
experimental data are well reproduced in the
calculations.
2.3656(11)
2.3472(11)
2.3734(11)
2.058(2)
1.184(4)
1.521(3)
Bond angles
N(1)–Re(1)–O(1)
N(1)–Re(1)–N(2)
O(1)–Re(1)–N(2)
N(1)–Re(1)–Cl(2)
O(1)–Re(1)–Cl(2)
N(2)–Re(1)–Cl(2)
N(1)–Re(1)–Cl(1)
O(1)–Re(1)–Cl(1)
N(2)–Re(1)–Cl(1)
Cl(2)–Re(1)–Cl(1)
N(1)–Re(1)–Cl(3)
O(1)–Re(1)–Cl(3)
N(2)–Re(1)–Cl(3)
Cl(2)–Re(1)–Cl(3)
Cl(1)–Re(1)–Cl(3)
P(1)–O(1)–Re(1)
O(2)–N(1)–Re(1)
98.49(14)
178.87(15)
81.31(11)
94.00(12)
167.47(8)
86.21(9)
99.93
177.50
82.56
91.70
168.36
85.81
93.86
86.09
86.11
92.66
95.24
86.89
85.04
92.59
169.35
141.72
176.34
94.03(12)
86.53(8)
87.07(9)
91.74(4)
93.72(12)
89.52(8)
85.17(9)
3.5. Charge distribution and spin densities of 1 and 2
Table 4 presents the atomic charges from the natural
population analysis (NPA) and spin densities for 1 and
2. For both complexes the calculated charges on the rhe-
nium atoms are considerably lower than the formal
90.55(4)
171.75(4)
142.36(16)
178.2(3)

B. Machura et al. / Polyhedron 24 (2005) 267–279
271
Table 3
Table 4
Atomic charges from the natural population analysis (NPA) and spin
densities of 1 and 2
˚
The experimental and optimised bond lengths (A) and angles (ꢁ) for
[ReCl3(NO)(OPPh3)(PPh3)]
Experimental
Optimised
Atom
1
2
Bond lengths
Re(1)–N(1)
Re(1)–P(2)
Re(1)–Cl(1)
Re(1)–Cl(2)
Re(1)–Cl(3)
Re(1)–O(1)
N(1)–O(2)
P(1)–O(1)
Atomic charge Spin density Atomic charge Spin density
1.747(5)
1.751
2.589
2.425
2.453
2.453
2.149
1.172
1.530
Re(1)
0.830
1.079
0.036
0.066
0.593
ꢀ0.402
ꢀ0.441
ꢀ0.430
0.255
1.034
0.080
0.054
2.5288(18)
2.3579(18)
2.377(2)
Cl(1) ꢀ0.453
Cl(2) ꢀ0.380
Cl(3) ꢀ0.466
0.033
0.061
2.3502(18)
2.103(5)
1.165(8)
N(1)
O(2)
O(1)
P(1)
N(2)
N(3)
P(2)
0.254
ꢀ0.225
ꢀ1.097
2.339
ꢀ0.125
ꢀ0.105
0.0144
0.002
ꢀ0.112
ꢀ0.092
ꢀ0.001
ꢀ0.000
ꢀ0.235
ꢀ1.123
2.338
1.506(5)
ꢀ0.479
ꢀ0.400
ꢀ0.009
0.001
Bond angles
N(1)–Re(1)–O(1)
N(1)–Re(1)–Cl(3)
O(1)–Re(1)–Cl(3)
N(1)–Re(1)–Cl(1)
O(1)–Re(1)–Cl(1)
Cl(3)–Re(1)–Cl(1)
N(1)–Re(1)–Cl(2)
O(1)–Re(1)–Cl(2)
Cl(2)–Re(1)–Cl(3)
Cl(3)–Re(1)–Cl(1)
N(1)–Re(1)–P(2)
O(1)–Re(1)–P(2)
Cl(3)–Re(1)–P(2)
Cl(1)–Re(1)–P(2)
Cl(2)–Re(1)–P(2)
P(1)–O(1)–Re(1)
O(2)–N(1)–Re(1)
176.6(2)
93.3(2)
177.66
94.87
87.33
93.17
84.68
171.18
91.87
87.32
90.33
90.33
91.44
89.53
85.25
90.95
174.69
148.76
176.63
1.385
ꢀ0.031
90.05(15)
91.9(2)
84.77(15)
174.26(6)
93.5(2)
coordinated triphenylphosphine in complex 2. The oxy-
gen atoms of the OPPh3 ligands in 1 and 2 are negatively
charged. The calculated charges on the nitrogen atoms
of the nitrosyl groups are positive, whereas the oxygen
atoms are negatively charged. The total charges on the
NO groups are positive, being 0.029 and 0.020 for 1
and 2, respectively.
For both complexes, there are positive spin densities
of about 1 on the rhenium atoms and small negative spin
densities of about ꢀ0.1 on the nitrogen and oxygen
atoms of the nitrosyl ligands. The spin densities on the
donor atoms of the other ligands are below 0.1 for com-
plexes 1 and 2.
85.74(14)
90.76(8)
91.32(8)
93.0(2)
87.98(14)
85.18(7)
92.14(6)
171.75(4)
150.2(3)
176.0(6)
3.6. Electronic structure
The energies and characters of several highest occu-
pied and lowest unoccupied molecular orbitals of 1
and 2 are presented in Tables 5 and 6, respectively. Most
of the MOs of 1 and 2 have complicated characters. The
percent participation of atomic orbitals in the selected
HOMO and LUMO orbitals for 1 and 2 are shown in
Tables 5 and 6, respectively.
3.7. [ReCl3(NO)(OPPh3)(pyz)] (1)
In the molecular orbital approach, the bonding of
NO to a metal is considered to be made up of two com-
ponents. The first involves donation of electron density
from a r-type orbital on NO to the metal, and the sec-
ond – backdonation from the filled dxz and dyz metal
orbitals to the p* orbitals of the NO ligand. Among
the MOs of 1 there are no orbitals of pure pRe–NO char-
acter. The pRe–NO bonding interaction makes the largest
contribution into HOMO ꢀ 2 and HOMO ꢀ 1 with a-
spin and HOMO ꢀ 1, HOMO orbitals with b-spin. A
substantial contribution of pRe–NO orbitals are also vis-
ible in HOMO ꢀ 16 and HOMO ꢀ 15 with a-spin and
HOMO ꢀ 15 and HOMO ꢀ 12 with b-spin. In
Fig. 2. Atomic numbering scheme of [ReCl3(NO)(OPPh3)(PPh3)].
charge of +2. This is the result of charge donation from
Clꢀ ions, the charges on the chloride ligands are signif-
icantly smaller than ꢀ1. The rhenium atom of 2 is less
positive than the Re atom of 1. It results from the pres-
ence of triphenylphosphine in the coordination sphere of
2. The PPh3 molecule acts as a strong r-donor; there is a
large positive charge on the phosphorus atom of the

Table 5
The energy and character of the selected occupied molecular orbitals with a- and b-spin for 1 and 2
1
2
a MO
E (eV)
b MO
E (eV)
ꢀ9.464
a MO
E (eV)
ꢀ7.832
b MO
E (eV)
Character
Cl, pO, pPh, ppyz
Character
Cl, rC–P, rC–C
Character
Character
HOMO ꢀ 19 ꢀ9.456
r
r
p
Cl(34.3), pO(21.4), pPh(25.2),
ꢀ8.202 rCl
dxzð10:5Þ þ pꢃNOð5:1Þ
HOMO ꢀ 18 ꢀ8.885
HOMO ꢀ 17 ꢀ8.709
p
p
Cl(43.8), pO(19.2), dxy(7.8)
Cl(48.4), pO(13.7), dxy(12.3)
ꢀ9.328
ꢀ8.841
p
Ph(50.4), pO(21.0), rCl(8.5)
Cl(50.1), pO(16.6)
ꢀ7.706
ꢀ7.613
ꢀ7.527
ꢀ7.475
ꢀ7.421
p
Ph(35.4), pCl(26.6), pO(12.1),
ꢀ7.772
ꢀ7.650
ꢀ7.579
ꢀ7.496
pCl(38.5), pO(19.5),
dyzð14:7Þ þ pꢃNOð9:1Þ
dyzð8:7Þ þ pꢃNOð5:7Þ
p
p
p
p
p
Ph(41.9), pCl(40.0), pO(9.8)
Ph(53.5), pCl(37.2)
pPh(55.5), pCl(22.4),
dyzð7:9Þ þ pꢃNOð6:4Þ
HOMO ꢀ 16 ꢀ8.496 dxzð32:1Þ þ pꢃNOð16:8Þ, pCl(36.9) ꢀ8.486
rCl, pCl
pCl(36.7), pPh(36.9), pO(12.7),
dyzð5:8Þ þ pꢃNOð5:0Þ
HOMO ꢀ 15 ꢀ8.220
p
pyz(37.0), pCl(32.8),
ꢀ8.362 dxzð24:1Þ þ pꢃNOð19:1Þ,
Ph(54.6), pCl(33.0)
pPh(60.5), pCl(33.6)
dyzð14:8Þ þ pꢃNOð8:4Þ
pCl(47.7)
ppyz(59.4), pCl(25.2)
pPh(69.7), pCl(18.3)
HOMO ꢀ 14 ꢀ8.082
HOMO ꢀ 13 ꢀ8.007
r
Cl(50.1), pPh(19.3), pO(11.1)
ꢀ8.168
ꢀ7.977
Ph(71.2), pCl(15.6), pO(8.9)
ꢀ7.418
ꢀ7.406
p
p
Ph(57.1), pCl(27.1), pO(6.6)
Ph(71.0), pCl(20.6), pO(4.5)
p
pyz(30.8), pCl(26.8),
ꢀ7.317 pPh
dyzð12:6Þ þ pꢃNOð7:1Þ
HOMO ꢀ 12 ꢀ7.915
HOMO ꢀ 11 ꢀ7.752
p
Ph(60.9), pCl(19.4), pO(8.3)
ꢀ7.941
p
Cl(41.1), ppyz(23.0),
ꢀ7.277 pPh
ꢀ7.295 pPh
dyzð13:0Þ þ pꢃNOð9:3Þ
p
Ph(55.6), pCl(29.6)
ꢀ7.860
ꢀ7.728
pCl(44.6), pO(13.7)
pyz(44.6), pPh(43.8)
ꢀ7.221
p
Ph(68.1), pCl(26.8)
ꢀ7.259 pPh
ꢀ7.158 pPh
ꢀ7.144 pPh
ꢀ7.058 pPh
ꢀ7.004 pPh
ꢀ6.951 pPh
ꢀ6.914 pPh
HOMO ꢀ 10 ꢀ7.734 npyz
p
ꢀ7.156 pPh
ꢀ7.073 pPh
ꢀ7.013 pPh
ꢀ6.983 pPh
ꢀ6.924 pPh
ꢀ6.918 pPh
HOMO ꢀ 9
HOMO ꢀ 8
HOMO ꢀ 7
HOMO ꢀ 6
HOMO ꢀ 5
HOMO ꢀ 4
HOMO ꢀ 3
HOMO ꢀ 2
HOMO ꢀ 1
HOMO
ꢀ7.703 pPh
ꢀ7.644 pPh
ꢀ7.714 npyz(54.4), pPh(35.2)
ꢀ7.694 pPh
ꢀ7.565
p
Cl(49.1), pPh(35.7)
ꢀ7.628 pPh
ꢀ7.564 pPh
ꢀ7.562 pPh
ꢀ7.489
p
Cl(62.9), pPh(29.4)
ꢀ7.535
ꢀ7.438
p
p
Cl(48.5), pPh(33.8)
Ph(56.0), pCl(36.1)
ꢀ7.441 Ph(75.7), pCl(20.0)
ꢀ6.767
ꢀ6.681
p
p
Cl(65.7), pPh(32.0)
Ph(54.1), pCl(28.2), np.(8.7)
ꢀ6.856
ꢀ6.645
p
p
p
Ph(70.5), pCl(23.5)
Ph(42.5), pCl(40.6), np.(10.8)
Cl(77.7), pPh(19.1)
ꢀ7.094 pCl
ꢀ7.371 pCl
ꢀ6.573 dyzð30:4Þ þ pꢃ ð20:2Þ, pCl(42.8) ꢀ6.873 pCl
ꢀ6.425 dyzð24:9Þ þ pꢃ ð15:4Þ, pCl(44.6) ꢀ6.569
ꢀ6.465 dxzð30:3Þ þ pNꢃ Oð19:6Þ, pCl(48.2) ꢀ6.462 dyzð25:9Þ þ pꢃ ð30:5Þ, pCl(37.2) ꢀ6.235 dxzð30:1Þ þ pNꢃ Oð22:0Þ, pCl(41.7) ꢀ6.326 dyzð23:3Þ þ pꢃ ð23:1Þ, pCl(39.4)
NO
NO
ꢀ5.899
d
xy(59.1), pCl(34.9)
ꢀ6.361 dxzð28:8Þ þ pNꢃ Oð29:9Þ, pCl(42.6) ꢀ5.822 dxy(53.4), pCl(41.8)
ꢀ6.140 dxzð25:1Þ þ pNꢃ Oð31:8Þ, pCl(38.9)
NO
NO

Table 6
The energy and character of the selected unoccupied molecular orbitals with a- and b-spin for 1 and 2
1
2
a MO
E (eV)
b MO
E (eV)
a MO
E (eV)
b MO
E (eV)
Character
Character
Character
Character
LUMO
ꢀ2.322 pꢃ ð77:8Þ;
ꢀ2.909 dxy(72.4), pCl(19.4)
ꢀ1.340 dx2ꢀy2 ð22%Þ ꢀ rClð13:2Þ ꢀ rPð15:3Þ;
pꢃPhð36:3Þ
ꢀ3.096 dxy(65.4), pCl(25.9)
ppꢃNyOz ð13:5Þ ꢀ dyzð2:3Þ
LUMO + 1
LUMO + 2
LUMO + 3
LUMO + 4
LUMO + 5
LUMO + 6
ꢀ1.724 pPð14:6Þ þ pꢃPhð58:1Þ;
ꢀ2.353 pꢃ ð76:6Þ;
ꢀ1.290 pPð6:6Þ þ pꢃPhð56:7Þ; dx2ꢀy2 ð11:8Þ
ꢀ1.296 pPð12:7Þ þ pꢃPhð72:5Þ
pꢃNOð6:4Þ ꢀ dyzð7:9Þ
ppꢃNyOz ð13:1Þ ꢀ dyzð4:2Þ
ꢀ1.572 pPð10:7Þ þ pꢃPhð79:2Þ
ꢀ1.698 pPð15:1Þ þ pꢃPhð61:5Þ;
pꢃNOð5:9Þ ꢀ dyzð6:6Þ
ꢀ1.200 pꢃNOð47:7Þ ꢀ dyzð19:2Þ; pPꢃhð18:6Þ
ꢀ1.102 pꢃNOð45:4Þ ꢀ dxzð22:5Þ; pPꢃhð18:1Þ
ꢀ0.922 pꢃPh
ꢀ1.211 pꢃNOð39:2Þ ꢀ dyzð21:5Þ; pPꢃhð22:9Þ
ꢀ1.336 pꢃNOð30:3Þ ꢀ dxzð21:2Þ;
ꢀ1.570 pPð10:4Þ þ pꢃPhð80:2Þ
ꢀ1.175 dx2ꢀy2 ð24:0Þ ꢀ rClð15:9Þ ꢀ rPð16:7Þ;
pꢃPhð34:9Þ
pꢃPhð29:1Þ
ꢀ1.245 pꢃNOð21:4Þ ꢀ dxzð15:3Þ;
pꢃPhð46:7Þ
ꢀ1.309 pꢃNOð30:6Þ ꢀ dxzð22:4Þ;
ꢀ1.074 pꢃNOð37:9Þ ꢀ dxzð26:3Þ; pPꢃhð22:1Þ
pꢃPhð32:0Þ
ꢀ1.130 pꢃNOð29:5Þ ꢀ dyzð22:3Þ;
pꢃPhð25:4Þ
ꢀ1.225 pꢃNOð13:7Þ ꢀ dxzð10:4Þ;
pꢃPhð63:9Þ
ꢀ0.876 pPð7:7Þ þ pꢃPhð82:8Þ
ꢀ0.845 pPð7:1Þ þ pꢃPhð68:4Þ
ꢀ0.801 pꢃPh
ꢀ0.909 pꢃPh
ꢀ1.078 dx2ꢀy2 ð29:1Þ ꢀ rClð23:5Þ;
pꢃ ð17:9Þ; ppꢃyzð17:4Þ
ꢀ1.042 pPpꢃyhzð68:2Þ; dx2ꢀy2 ð9:5Þ
ꢀ0.943 pꢃPh
ꢀ1.066 pꢃNOð29:3Þ ꢀ dyzð24:8Þ;
pꢃPhð22:4Þ
ꢀ0.872 pPð8:5Þ þ pꢃPhð85:8Þ
LUMO + 7
LUMO + 8
LUMO + 9
ꢀ1.047 pꢃpyz
ꢀ0.803 pꢃPhð68:8Þ; pꢃ ð9:4Þ ꢀ dxzð10:0Þ
ꢀ0.769 pꢃPhð70:6Þ; pNNꢃ OOð4:0Þ ꢀ dyzð9:3Þ
ꢀ0.687 pꢃPh
ꢀ0.947 pꢃPhð77:3Þ; pNꢃ Oð7:0Þ ꢀ dyzð7:1Þ ꢀ0.692 pꢃPh
ꢀ0.793 pꢃPh
ꢀ0.836 dx2ꢀy2 ð39:7Þ ꢀ rClð33:6Þ;
ꢀ0.511 dz2 ð16:5Þ ꢀ rNð4:1Þ ꢀ rClð18:2Þ;
pꢃPhð16:5Þ
pꢃPhð79:8Þ
LUMO + 10 ꢀ0.579 pPꢃh
ꢀ0.788 pꢃPh
ꢀ0.474 pꢃPh
ꢀ0.482 pꢃPh
LUMO + 11 ꢀ0.281 dz2(30.5) ꢀ rCl(20.8)
ꢀ0.580 pꢃPh
ꢀ0.265 pꢃPh
ꢀ0.353 dz2 ð21:3Þ ꢀ rClð23:0Þ; pꢃPhð39:3Þ

274
B. Machura et al. / Polyhedron 24 (2005) 267–279
HOMO ꢀ 16, HOMO ꢀ 2 and HOMO ꢀ 1 with a-spin
and HOMO ꢀ 15, HOMO ꢀ 1 and HOMO orbitals
with b-spin, the pRe–NO orbitals are mixed with pCl orbi-
tals. HOMO ꢀ 15 with a-spin and HOMO ꢀ 12 with
b-spin have also a significant contribution of ppyz orbi-
tals. The bonding pRe–NO orbitals with a- and b-spin
are localised mainly on the rhenium d orbitals. The
anti-bonding pꢃRe–NO interaction makes the largest con-
tribution into LUMO, LUMO + 3, LUMO + 4 and
LUMO + 5 with a-spin and LUMO, LUMO + 4,
LUMO + 5 and LUMO + 6 with b-spin. The pRꢃ e–NO
orbitals have prevalent NO character and they are
mixed with pꢃpyz or pPꢃh orbitals. Considering the molecu-
lar orbital composition and positive total charge on the
NO group, the character of the nitrosyl ligand in 1 may
be described as NO+.
3.9. NBO analysis
Additional information about the binding in com-
plexes 1 and 2 was obtained by NBO analysis. In
open-shell systems, the density operator separates into
distinct components for a- and b-spin, leading to the
possibility of different NBOs for different spins [54]. Ta-
ble 7 presents the occupancies and NAO compositions
of the selected a- and b-spin NBOs for complexes 1
and 2. For compound 1, six natural bond orbitals (three
with a-spin and three with b-spin) were detected for the
Re–N bond, and two orbitals (one with a-spin and one
with b-spin) for the N–O bond. The Re–N bond orbitals
of r-character with a- and b-spins are polarised towards
the nitrogen atom (ca. 77% at N) and the s and d orbi-
tals of Re take part in the bonding. The Re–N bond
orbitals of p-character are mainly polarised toward the
metal atom and only d-orbitals of Re are included in
the bonding. The N–O bond orbitals with a- and b-spins
are slightly polarised towards the oxygen end. In the va-
lence-bond treatment a linear bonding mode of the
nitrosyl group may be represented by the following res-
onance forms [1]:
The dxy rhenium orbital and p orbitals of the chloride
ligands in an anti-bonding arrangement make the main
contribution into the HOMO with a-spin and LUMO
with b-spin. The LUMO with b-spin is mainly localised
on the pyrazine ligand with the admixture of pRꢃ e–NO
anti-bonding orbitals. LUMO + 6 with a-spin and
LUMO + 9 with b-spin are mainly of dx2 ꢀ y2 ꢀ rCl ꢀ rO
character with
a
substantial contribution from
M
M -
M -
N
D
O-
N
C
O
N
A
O
M
N
B
O
pꢃpyz and pPꢃh orbitals. The participation of the dz2 rhe-
nium orbital is visible in LUMO + 11 with a-spin and
LUMO + 12 with b-spin.
The results of the NBO analysis indicate that the res-
onance structure of D makes a significant contribution
to the structure of complex 1.
3.8. ReCl3(NO)(OPPh3)(PPh3)] (2)
For complex 2, the pꢃNO orbitals are also distributed
among several occupied MOs, and the largest contribu-
tion of pRe–NO bonding orbitals is noticed for
HOMO ꢀ 2 and HOMO ꢀ 1 with a-spin and
HOMO ꢀ 1, HOMO orbitals with b-spin. The percent
participations of pꢃNO orbitals in HOMO ꢀ 20 and
HOMO ꢀ 18 with a-spin and HOMO ꢀ 19 and
HOMO ꢀ 17 with b-spin do not reach 10%.
LUMO + 2 and LUMO + 3 with a-spin and
LUMO + 2 and LUMO + 4 are mainly composed of
pꢃRe–NO orbitals (about 60%). Based on the molecular
orbital composition and small spin densities on the
nitrogen and oxygen atoms of the nitrosyl ligand, the
character of the NO group in 2 may be described as
NO+.
Similar to complex 1, HOMO with a-spin and
LUMO with b-spin are dxy rhenium orbitals with the
admixture of chlorine p orbitals. The LUMO with
a-spin is mainly of dx2 ꢀ y2 ꢀ rCl ꢀ rP character with a
substantial contribution from pꢃPh orbitals. The dz2 rhe-
nium orbital makes a contribution into LUMO + 9 with
a-spin and LUMO + 11 with b-spin. HOMO ꢀ 3 with a
and HOMO ꢀ 3 with b-spin are localised on the chlo-
ride and phenyl ligands with a substantial contribution
from the free electron pair on the phosphorous atom
of the PPh3 molecule.
For complex 2, significantly different NBOs for differ-
ent spins are observed. One natural bond orbital for the
Re–N bond and three orbitals for the N–O bond were de-
tected in the case of orbitals with a-spin, whereas three
NBOs for the Re–N bond and one orbital for the N–O
bond were detected for orbitals with b-spin. For complex
2, the a and b natural Lewis structure can be represented
by the resonance structure of A and D, respectively. The
total occupancy number of the natural bond orbitals for
the Re–N bond is larger for complex 1, whereas the total
occupancy number of the NBOs for the N–O bond is lar-
ger for 2. It indicates that the p-backdonation is stronger
for complex 1. The changes of Re–N and N–O bond dis-
tances, listed in Tables 1 and 2, also confirm the above-
discussed results. An insignificant shortening of the
Re–N distance and elongation of the N–O bond length
can be noticed for complex 1.
3.10. Electronic spectra
The experimental and calculated electronic spectra of
1 are presented in Fig. 3. Each calculated transition in
Fig. 3(b) was represented by a gaussian function with
the height equal to the oscillator strength and width
equal to 0.06.

B. Machura et al. / Polyhedron 24 (2005) 267–279
275
Table 7
Results of the NBO analysis of complexes 1 and 2
Bond orbital
1
2
a-Spin orbitals
b-Spin orbitals
a-Spin orbitals
b-Spin orbitals
Re–N/BD
r
occ.
%Re
%N
0.986
22.96; sd68.73
77.04; sp37.11
0.987
22.14; sd59.14
77.86; sp36.55
0.982
24.79; sd74.11
75.21; sp37.55
0.982
24.23; sd73.96
75.77; sp40.39
p
p
occ.
%Re
%N
0.989
64.20; d99.92
35.80; p99.90
0.991
53.43; d99.89
46.57; p99.92
0.990
52.03; d99.32
47.97; p99.91
occ.
%Re
%N
0.981
63.14; d98.93
36.86; p99.88
0.998
44.82; d99.19
47.24; p99.91
0.983
52.95; d99.21
47.07; p95.95
N–O/BD
r
occ.
%N
%O
0.998
44.84; sp62.92
55.16; sp68.69
0.998
44.82; sp63.43
55.18; sp68.86
0.998
44.95; sp63.07
55.05; sp68.66
0.998
44.89; sp63.45
55.11; sp68.83
p
p
occ.
%N
%O
0.999
33.66; p99.47
66.34; p99.55
occ.
%N
%O
0.999
34.05; p99.44
65.95; p99.59
Re–N/BD*
r
p
p
occ.
occ.
occ.
0.144
0.269
0.268
0.137
0.226
0.226
0.178
0.136
0.230
0.237
N–O/BD*
r
p
p
occ.
occ.
occ.
0.007
0.006
0.006
0.305
0.295
0.006
The hybridisation of the atoms is indicated with the percent contribution of the metal-centered d or (and) p orbitals as a superscript.
Tables 8 and 9 show the energy and molar absorption
coefficients of the experimental absorption bands and
the spin-allowed doublet–doublet electronic transitions
calculated with the TDDFT method for 1 and 2, respec-
tively. The positions and molar absorption coefficients
of the electronic bands for complex 2 have been taken
from paper [17].
The investigated complexes are of large size and the
number of basis functions are equal to 510 and 718
for 1 and 2, respectively. Eighty electron transitions cal-
culated by the TDDFT method do not comprise all the
experimental absorption bands. The UV–Vis spectra of
1 and 2 were calculated to ꢄ260 nm, so the shortest
wavelength experimental bands cannot be assigned to
the calculated transitions. However, considering that
the solution spectra of PPh3, OPPh3 and pyrazine exhi-
bit intense absorption bands in the 260–200 nm region,
some additional intraligand and interligand transitions
are expected to be found at higher energies in the
calculations.
The calculations result in many transitions with very
small oscillator strengths. Except for the electronic tran-
sitions of d ! pꢃNO character and the low energy part of
the spectrum, only transitions with oscillator strengths
larger than 0.0040 are listed in Tables 7 and 8.
The assignment of the calculated transitions to
the experimental bands is based on the criterion
of the energy and oscillator strength of the calcu-
lated transitions. In the description of the electronic
transitions, the main components of the molecular
orbital are used. The bonding pRe–NO orbitals are
assigned as d orbitals, and the antibonding pRꢃ e–NO
orbitals as pꢃNO
.
3.11. ReCl3(NO)(OPPh3)(pyz)] (1)
In the description of the electronic transitions of 1
the main components of the molecular orbital are used:
the LUMO with b-spin is assumed as an orbital of d

276
B. Machura et al. / Polyhedron 24 (2005) 267–279
character with small oscillator strengths, calculated at
449.0 and 437.3 nm, respectively.
The experimental absorption band at 359.4 nm is
assigned to the transition calculated between 420 and
335 nm. These transitions are mainly of LMCT
(pCl ! d) character. The electronic transitions from
the rhenium d orbitals onto p* orbitals of the
nitrosyl group calculated in the range 420–335 nm
have small oscillator strengths and they do not
contribute significantly to the overall shape of the
spectrum.
The experimental band at 309.0 nm is attributed to
the calculated transition of pCl ! pꢃpyz character at
326.7 nm and some LMCT (pCl/pPh/pO ! d) transi-
tions. LUMO + 1 with b-spin has a substantial admix-
ture of the rhenium d orbitals, so the transition from
chloride ligand to pꢃpyz orbitals are mediated by the
metal.
3.12. ReCl3(NO)(OPPh3)(PPh3)] (2)
In the description of the electronic transitions of 2 the
main components of the molecular orbital are used: the
LUMO with b-spin is assumed as an orbital of d charac-
ter. LUMO + 1 and LUMO + 2 with a-spin and
LUMO + 2 and LUMO + 4 with b-spin are described
as pꢃNO orbitals.
The longest wavelength experimental bands at 719.9
and 656.2 nm may be attributed to transitions of
d/p(Cl) ! d character with small oscillator strengths,
calculated at 756.8 and 671.3 nm, respectively.
Fig. 3. The experimental (a) and calculated (b) electronic absorption
spectrum of 1.
The experimental absorption bands at 421.0 and
356.0 nm are assigned to the LMCT (pCl ! d,
pPh ! d and n(P) ! d) transitions with large oscillator
strengths. In comparison with complex 1, the LMCT
(pCl ! d, pPh ! d and n(P) ! d) electronic transitions
character, LUMO withꢃa-spin and LUMO + 1 with b-
spin are described as pPh orbitals, LUMO + 4 with a-
spin and LUMO + 5 with b-spin are treated as pPꢃh
orbitals.
The longest wavelength experimental bands at 646.2
and 603.6 nm may be attributed to the transitions of
are
bathochromically
shifted.
The
electronic
transitions from the rhenium d orbitals onto p* orbi-
tals of the nitrosyl group have small oscillator
strengths and they do not contribute significantly to
the overall shape of the bands at 421.0 and 356.0
nm. Similar to complex 1, they are hidden under the
more intense transitions of LMCT character. How-
ever, such small values of the oscillator strengths seem
to be typical of d ! pꢃNO transitions, and they have
been supported by the calculations for other metal
nitrosyls [55,56].
The experimental band at 279.0 is mainly attributed
to the calculated transition of pCl ! d character at
298.5 nm.
The intense absorption band at 266.0 is assigned to
the interligand charge transfer transitions, but this
assignment is probably not complete. Similar to com-
plex 1, some additional intraligand and interligand tran-
sitions can be expected at higher energies in the
calculated spectrum.
d
Re/pCl ! d character with small oscillator strengths,
calculated at 621.3 and 600.9 nm, respectively.
The weak absorption band at 458.9 nm is assigned
to the calculated transitions with small oscillator
strengths at 526.4 and 463.2 nm. The first one corre-
sponds mainly to the electronic transition from the
rhenium d orbitals onto p* orbitals of the nitrosyl
group. Considering that the bonding pRe–NO and
anti-bonding pꢃRe–NO orbitals are mixed with the p
chloride and pꢃPh orbitals respectively, the character
of the transition at 526.4 nm is determined as
dRe=pCl ! pꢃNO=pPꢃh. The transition at 463.2 nm is of
dRe=pCl ! pꢃpyz origin.
The experimental band at 408.5 nm is also attributꢃed
to transitions of d=pCl ! pꢃPh and d=pCl ! d=pPꢃh=ppyz

B. Machura et al. / Polyhedron 24 (2005) 267–279
277
Table 8
The energy and molar absorption coefficients of the experimental absorption bands and the electronic transitions calculated with the TDDFT
method for 1
The most important orbital excitations Character
k (nm) E (eV)
f
Experimental, K [nm] (E [eV]) e
H(b) ! L(b)
dxz/p(Cl) ! dxy
621.3
600.9
526.4
2.00
2.06
2.36
0.0002
0.0001
0.0002
646.2 (1.92) 50
603.6 (2.05) 60
H ꢀ 1(b) ! L(b)
H ꢀ 1(a) ! L + 3(a)
H(b) ! L + 4(b)
H ꢀ 1(b) ! L + 6(b)
H(a) ! L(a)
d
yz/p(Cl) ! dxy
dxz/p(Cl) ! p*(NO)/p*(Ph)
dxz/p(Cl) ! p*(NO)/p*(Ph)
458.9 (2.70) 30
408.5 (3.04) 70
d
yz/p(Cl) ! p*(NO)/p*(Ph)
g
g
dxy/p(Cl) ! p*(pyz)
dxy/(Cl) ! p*(Ph)
463.2
449.0
2.68
2.76
0.0002
0.0001
H(a) ! L + 1(a)
H(a) ! L + 6(a)
H(b) ! L + 4(b)
H ꢀ 1(b) ! L + 1(b)
H ꢀ 2(b) ! L(b)
H(a) ! L + 3(a)
H ꢀ 2(a) ! L(a)
H(a) ! L + 5(a)
H ꢀ 3(b) ! L(b)
H ꢀ 5(b) ! L(b)
H ꢀ 2(a) ! L + 3(a)
H ꢀ 1(b) ! L + 4(b)
H ꢀ 2(b) ! L + 1(b)
H ꢀ 11(b) ! L(b)
H(a) ! L + 2(a)
H(a) ! L + 11(a)
H ꢀ 116(b) ! L(b)
d
d
xy/p(Cl) ! dx2 ꢀ y2/p*(Ph)/p*(pyz)
xz/p(Cl) ! p*(NO)/p*(Ph)
437.3
2.84
0.0001
dyz/p(Cl) ! p*(pyz)
p(Cl) ! dxy
416.1
399.4
362.4
358.8
357.9
354.4
339.4
2.98
3.10
3.42
3.45
3.46
3.50
3.65
0.0175
0.0011
0.0080
0.0045
0.0204
0.0061
0.0016
dxy/p(Cl) ! p*(NO)/p*(Ph)
d
yz/p(Cl) ! p*(pyz)
dxy/p(Cl) ! p*(NO)/p*(Ph)
p(Cl) ! dxy
359.4 (3.45) 1040
g
p(Cl)/p(Ph) ! dxy
dyz/p(Cl) ! p*(NO)/p*(Ph)
dyz/p(Cl) ! p*(NO)/p*(Ph)
p(Cl) ! p*(pyz)
326.7
3.79
0.0143
(Cl)/p(O) ! dxy
dxy/p(Cl) ! p*(Ph)
dxy/p(Cl) ! dz2
324.7
316.2
282.8
3.82
3.92
4.43
0.0042
0.0049
0.0045
309.0 (4.01) 3850
g
r(Cl)/p(Cl) ! dxy
275.4 (4.51) 9890
230.4 (5.38) 22000
e, Molar absorption coefficient (dm3 molꢀ1 cmꢀ1).
Table 9
The energy and molar absorption coefficients of the experimental absorption bands and the electronic transitions calculated with the TDDFT
method for 1
The most important orbital excitations Character
k (nm) E (eV)
f
Experimental, K [nm] (E [eV]) e
H(b) ! L(b)
d
xz/p(Cl) ! dxy
756.8
671.3
497.3
485.9
469.5
426.2
415.5
413.2
404.0
403.1
383.1
371.6
366.1
352.7
1.64
1.85
2.49
2.55
2.64
2.91
2.98
3.00
3.07
3.08
3.24
3.34
3.39
3.51
0.0001
0.0002
0.0002
0.0093
0.0198
0.0011
0.0001
0.0103
0.0002
0.0022
0.0046
0.0009
0.0015
0.0001
719.9 (1.72) 17
656.2 (1.89) 40
H ꢀ 1(b) ! L(b)
H ꢀ 1(a) ! L + 3(a)
H ꢀ 2(b) ! L(b)
H ꢀ 3(b) ! L(b)
H(a) ! L(a)
dyz/p(Cl) ! dxy
d
xz/p(Cl) ! p*(NO)
p(Cl)/p(Ph) ! dxy
p(Ph)/p(Cl)/n(P) ! dxy
dxy/p(Cl) ! dx2 ꢀ y2/p*(Ph)
dxz/p(Cl) ! p*(NO)
p(Ph)/p(Cl) ! dxy
421.0 (2.94) 2100
g
H(b) ! L + 2(b)
H ꢀ 4(b) ! L(b)
H ꢀ 1(b) ! L + 2(b)
H ꢀ 5(b) ! L(b)
H ꢀ 6(b) ! L(b)
H(a) ! L + 2(a)
H(a) ! L + 3(a)
H ꢀ 1(a) ! L + 2(a)
H(b) ! L + 2(b)
H ꢀ 2(a) ! L + 2(a)
H ꢀ 1(a) ! L + 3(a)
H ꢀ 2(a) ! L + 3(a)
H ꢀ 21(b) ! L(b)
H ꢀ 2(a) ! L + 3(a)
H ꢀ 2(b) ! L + 3(b)
H ꢀ 3(a) ! L + 2(a)
H ꢀ 4(a) ! L + 2(a)
d
yz/p(Cl) ! p*(NO)
p(Ph) ! dxy
p(Ph) ! dxy
d
xy/p(Cl) ! p*(NO)
dxy/p(Cl) ! p*(NO)
xz/p(Cl) ! p*(NO)
dxz/p(Cl) ! p*(NO)
yz/p(Cl) ! p*(NO)
dxz/p(Cl) ! p*(NO)
356.0 (3.48) 1793
d
d
315.2
3.93
0.0004
d
yz/p(Cl) ! p*(NO)
308.6
298.5
298.1
268.2
4.02
4.15
4.16
4.62
4.67
4.75
0.0002
0.0206
0.0057
0.0071
0.0134
0.0050
p(Cl) ! dxy
279.0 (4.44) 7 811
266.0(4.66)15 800
g
g
dyz/p(Cl) ! p*(NO)
p(Cl)/p(Ph) ! dx2 ꢀ y2/p*(Ph)
p(Ph)/p(Cl)/n(P) ! p*(NO)/p*(Ph) 265.5
p(Cl)/p(Ph) ! p*(NO)
261.2
e, Molar absorption coefficient (dm3 molꢀ1 cmꢀ1).

278
B. Machura et al. / Polyhedron 24 (2005) 267–279
ˇ
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4. Conclusions
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The [ReCl3(NO)(OPPh3)(pyz)] (1) complex has been
obtained by two different routes, and characterised by
IR, UV–Vis and magnetic measurements. Its crystal
and molecular structure has been determined. Theoreti-
cal studies of [ReCl3(NO)(OPPh3)(pyz)] and the related
complex [ReCl3(NO)(OPPh3)(PPh3)] (2) have been per-
formed by the DFT method with the aim to investigate
their molecular and electronic structures, spectral prop-
erties and bonding. Most of the MOs of 1 and 2 have
complicated character. The electronic configuration of
the metal center in the investigated complexes is as fol-
lows: (dxz)2(dyz)2(dxy)1. The dxy rhenium orbital makes
the main contributions into the HOMO with a-spin
and LUMO with b-spin. The occupied dyz and dxz rhe-
nium orbitals participate in back-donation from the cen-
tral ion to the NO ligand. However, the dyz/dxz and pNꢃ O
orbitals are distributed among several occupied MOs to
give a considerable contribution into several HOMO
and LUMO orbitals. For both complexes, the bonding
pRe–NO orbitals are localised mainly on the rhenium d
orbitals, whereas the pꢃRe–NO orbitals have prevalent
NO character. The results of the NBO analyses indicate
a stronger p-backdonation in complex 1. A shortening
of the Re–N distance and elongation of the N–O bond
length observed for complex 1 confirms it. The TDDFT
calculations for complexes 1 and 2 reveal that the elec-
tronic transitions from the rhenium d orbitals onto the
p* orbitals of the nitrosyl group have small oscillator
strengths and they do not contribute significantly to
the overall shape of the spectrum. They are hidden un-
der the more intense transitions of LMCT character.
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The GAUSSIAN03 calculations were carried out in the
Wrocław Centre for Networking and Supercomputing,
WCSS, Wrocław, Poland under calculational Grant
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