Reactivity of [ReOX3(PPh3)2] complexes towards 1,4-diaminobenzene: X-ray structure and DFT calculations of the [Re(4-NC6H4NH2)Cl3(PPh 3)2]·PPh3 c

Article abstract of DOI:10.1016/j.poly.2005.03.094

The reaction of [ReOX₃(PPh₃)₂] (X = Cl and Br) complexes with 1,4-diamnobenzene has been examined and novel imido rhenium complexes - [Re(4-NC₆H₄NH₂)X ₃(PPh₃)₂

Full text of DOI:10.1016/j.poly.2005.03.094

Polyhedron 24 (2005) 1454–1460
www.elsevier.com/locate/poly
Reactivity of [ReOX3(PPh3)2] complexes towards
1,4-diaminobenzene: X-ray structure and DFT calculations
of the [Re(4-NC6H4NH2)Cl3(PPh3)2] Æ PPh3 complex
a,
b
c
B. Machura *, R. Kruszynski , M. Jaworska
a
Department of Inorganic and Radiation Chemistry, Institute of Chemistry, University of Silesia, 9th Szkolna Street, 40-006 Katowice, Poland
b
´
´
X-ray Crystallography Laboratory, Institute of General and Ecological Chemistry, Technical University of Łodz,
_
´
´
116 Zeromski Street, 90-924 Łodz, Poland
Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia, 9th Szkolna Street, 40-006 Katowice, Poland
c
Received 23 February 2005; accepted 18 March 2005
Available online 5 July 2005
Abstract
The reaction of [ReOX3(PPh3)2] (X = Cl and Br) complexes with 1,4-diamnobenzene has been examined and novel imido rhenium
complexes – [Re(4-NC6H4NH2)X3(PPh3)2] – havebeen obtained. The crystal and molecularstructure of [Re(4-NC6H4NH2)Cl3(PPh3)2]
has been determined, and its molecular diagram has been calculated with the density functional theory (DFT) with the use of the B3LYP
functional. Additional information about the binding in the [Re(4-NC6H4NH2)Cl3(PPh3)2] complex has been obtained by NBO anal-
ysis. The time-dependent DFT method (TDDFT) has been used for calculations of spin-allowed singlet–singlet electronic transitions of
[Re(4-NC6H4NH2)Cl3(PPh3)2], and on this basis the UV–Vis spectrum has been interpreted.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Rhenium imido complexes; X-ray structure; DFT calculations; NBO analysis
1. Introduction
Recently, high-valent imido complexes of Tc and Re
have been also proposed as potential radiopharmaceuti-
cals as alternatives to oxo and nitrido compounds, ow-
ing to the possibility of incorporating specific targeting
molecules on the substituents at the nitrogen site [14].
The coordinated imido ligand can adopt a variety of
geometries: terminal linear (A), terminal bent (B), dou-
bly bridging (C) and triply bridging (D) [15].
For many years much attention has been focused on
the synthesis and study of a variety of imido transition
metal complexes. These compounds have been in the cen-
ter of interest of scientists both engaged in basic research
and trying to employ these complexes in catalysis [1–7].
Imido compounds have been successfully employed
in the catalytic hydroamination of alkynes, the synthesis
of various nitrogen heterocycles, alkene methathesis,
activation of hydrocarbons including methane, and in
cycloaddition reactions with unsaturated organic sub-
strates [8–13].
M
M
M
N
R
M
N
B
N
R
N
C
M
R
R
M
M
D
A
*
Corresponding author. Tel.: +48 322582441; fax: +48 322599978.
E-mail addresses: bmachura@poczta.onet.pl (B. Machura),
kruszyna@p.lodz.pl (R. Kruszynski), mj@tc3.ich.us.edu.pl (M.
Jaworska).
The R group can be varied widely and rhenium deriva-
tives with R = alkyl, aryl, OMe, halogen, COPh, NH2,
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.03.094

B. Machura et al. / Polyhedron 24 (2005) 1454–1460
1455
C(O)NHCH2C(O)OEt, (CH2)3C(O)OH, (CH2)3C(O)-
OEt groups are known [6].
Anal. Calc. for C60H51Cl3N2P3Re: C, 60.79; H, 4.34;
N, 2.36. Found: C, 60.85; H, 4.40; N, 2.30%.
This paper presents the syntheses and spectroscopic
properties of the [Re(4-NC6H4NH2)X3(PPh3)2] (X = Cl
and Br) complexes, obtained in the reaction of [Re-
OX3(PPh3)2] with 1,4-diaminobenzene. The crystal and
molecular structure of [Re(4-NC6H4NH2)Cl3(PPh3)2]
has been determined, and its molecular diagram has been
calculated with the density functional theory (DFT).
Additional information about the binding in the [Re
(4-NC6H4NH2)Cl3(PPh3)2] complex has been obtained
by NBO analysis. The spin-allowed singlet–singlet elec-
tronic transitions of [Re(4-NC6H4NH2)Cl3(PPh3)2] have
been calculated with the time-dependent DFT method
(TDDFT), and the UV–Vis spectrum has been discussed
on this basis.
2.3. Preparation of [Re(4-NC6H4NH2)Br3(PPh3)2]
A procedure similar to that for the chloro analogue
was used with trans-[ReOBr3(PPh3)2] (0.97 g, 1 mmol)
and 1,4-diaminobenzene (0.43, 4 mmol). Yield: 55%.
IR (KBr, cmꢀ1) 3452 (w), 3334 (s), 3047 (w), 1613 (s),
1587 (s), 1483 (m), 1434 (m), 1369 (s), 1327 (m), 1163 (s),
1091 (m), 838 (w), 745 (m), 695 (s), 602 (w), 999 (m), 520
(s), 505 (sh), 480 (w).
1H NMR (CDCl3, ppm): d = 7.274 (s, 2H, NH2);
7.270–7.254 (m, 4H of imido ligand and 30H of coordi-
nated PPh3 ligands).
Anal. Calc. for C42H36Br3N2P2Re: C, 47.74; H, 3.43;
N, 2.65. Found: C, 47.87; H, 3.55; N, 2.55%.
2. Experimental
2.4. Crystal structure determination and refinement
2.1. General procedure
Crystals suitable for X-ray investigation were ob-
tained by recrystallization from acetonitrile. The X-ray
intensity data of the title complex were collected on a
KM-4-CCD automatic diffractometer equipped with a
CCD detector with 40 s exposure time, and all reflec-
tions of the Ewald sphere were collected up to h = 25ꢁ.
The unit cell parameters were determined from least-
squares refinement of the setting angles of the 6795
strongest reflections. Details concerning crystal data
and refinement are given in Table 1. Lorentz polariza-
tion and numerical absorption corrections [17] were ap-
plied. The structure was solved by the Patterson method
and subsequently completed by difference Fourier recy-
cling. All the non-hydrogen atoms were refined aniso-
tropically using the full-matrix least-squares technique.
All the hydrogen atoms were found from difference Fou-
rier synthesis after four cycles of anisotropic refinement,
and refined as ‘‘riding’’ on the adjacent atom with an
individual isotropic temperature factor equal to 1.2
times the value of the equivalent temperature factor of
the parent atom. Carbon-bonded hydrogen atom posi-
tions were idealized after each cycle of refinement
All synthetic manipulations were carried out open to
the atmosphere. All solvents were of reagent grade and
used as received. Ammonium perrhenate, triphenylphos-
phine and 1,4-diaminobenzene were purchased from Al-
drich. The [ReOX3(PPh3)2] complexes were prepared
according to the literature methods [16].
Infrared spectra were recorded on a Nicolet Magna
560 spectrophotometer in the spectral range 4000–400
cmꢀ1, with the samples in the form of potassium bro-
mide pellets. Electronic spectra were measured on a
spectrophotometer Lab Alliance UV–Vis 8500 in the
range 900–200 nm in deoxygenated dichloromethane
solution. 1H NMR spectra were obtained in CDCl3
using an INOVA 300 spectrometer. Magnetic suscepti-
bility was measured at 296 K by the Faraday method.
Elemental analysis (C, H, N) was performed on a
Perkin–Elmer CHN-2400 analyzer.
2.2. Preparation of [Re(4-NC6H4NH2)Cl3(PPh3)2] Æ
PPh3
˚
[d(C–H) = 0.96 A]. SHELXS-97 [18], SHELXL-97 [19] and
A mixture of trans-[ReOCl3(PPh3)2] (0.83 g, 1 mmol),
1,4-diaminobenzene (0.43, 4 mmol) and acetone (100 ml)
was stirred for 2 days, and then 50 ml of acetone was
distilled off. [Re(4-NC6H4NH2)Cl3(PPh3)2] was filtered
off, washed with ethanol, diethyl ether and dried. Yield:
60%.
SHELXTL [20] programs were used for all the calculations.
Atomic scattering factors were those incorporated in the
computer programs.
2.5. Computational details
IR (KBr, cmꢀ1) 3466 (m), 3360 (s), 3050 (w), 1614 (s),
1588 (s), 1482(m), 1433 (s), 1365 (s), 1327 (m), 1169 (s),
1089 (m), 832 (w), 749 (s), 696 (s), 606 (w), 560 (w), 522
(s), 480 (w).
1H NMR (CDCl3, ppm): d = 7.26 (s, 2H, NH2); 7.38–
7.46 (m, 30H, coordinated PPh3 ligands); 7.77–7.81 (m,
4H of imido ligand and 15H of uncoordinated PPh3).
The GAUSSIAN-03 program [21] was used in the calcu-
lations. The geometry optimization was carried out with
the DFT method with the use of the B3LYP functional
[22,23]. The electronic spectrum was calculated with the
TDDFT method [24].
In the calculations, the LANL2DZ basis set [25] with
additional d (a = 0.3811) and f (a = 0.2033) functions

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B. Machura et al. / Polyhedron 24 (2005) 1454–1460
Table 1
Crystal data and structure refinement for [Re(4-NC6H4NH2)-
complexes. [Re(4-NC6H4NH2)X3(PPh3)2] are formally
rhenium(V) compounds with the arylimido unit as a
dianionic NR2ꢀ ligand.
Cl3(PPh3)2] Æ PPh3.
Empirical formula
Formula weight
T (K)
C60H51Cl3N2P3Re
1185.49
293(2)
3.2. Description of the structure of [Re(4-NC6H4NH2)-
Cl3(PPh3)2] Æ PPh3
˚
k (A)
Crystal system
0.71073
monoclinic
P21/n
Space group
Unit cell dimensions
The [Re(4-NC6H4NH2)Cl3(PPh3)2] complex crystal-
lizes as the [Re(4-NC6H4NH2)Cl3(PPh3)2] Æ PPh3 adduct
in the monoclinic space group P21/n. The starting oxo
complex is synthesized using a large excess of triphenyl-
phosphine, and [ReOCl3(PPh3)2] can be impure with
PPh3. It explains the presence of PPh3 in the adduct.
There are no significant contacts between the uncoordi-
nated triphenylphosphine and the imido complex.
Table 1 presents crystal data and structural refinement
for [Re(4-NC6H4NH2)Cl3(PPh3)2] Æ PPh3.
˚
a (A)
11.0688(5)
32.6510(16)
14.7331(7)
91.114(4)
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
5323.6(4)
4
1.479
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
Crystal size (mm)
)
2.564
2384
0.22 · 0.05 · 0.05
2.95–25.11
ꢀ13 6 h 6 13,
ꢀ38 6 k 6 38,
ꢀ17 6 l 6 17
56075
h Range for data collection (ꢁ)
Index ranges
A displacement ellipsoids plot of [Re(4-NC6H4-
NH2)Cl3(PPh3)2] is shown in Fig. 1. The rhenium atom
of [Re(4-NC6H4NH2)Cl3(PPh3)2] is in a distorted octahe-
dral environment with the chloride ions in a meridional
geometry and two mutually trans-triphenylphosphine li-
gands, and the shortest Reꢂ ꢂ ꢂRe distance is equal to
Reflections collected
Independent reflections (Rint
Completeness to 2h (%)
Maximum and minimum transmission
Data/restraints/parameters
Goodness-of-fit on F2
)
9473 (0.0716)
97.8
0.8804 and 0.6061
9473/0/623
1.161
˚
9.678(1) A (the second Re atom is obtained by ꢀx, ꢀy,
ꢀz + 1 symmetry transformation).
The weak intramolecular hydrogen bonds; C(12)–
˚
and
Final R indices [I > 2r(I)]
R1 = 0.0598,
wR2 = 0.0659
R1 = 0.0906,
wR2 = 0.0726
0.499 and ꢀ0.717
H(12)ꢂ ꢂ ꢂCl(1) [Dꢂ ꢂ ꢂA distance = 3.393(2)
A
R indices (all data)
D–Hꢂ ꢂ ꢂA angle = 147.0ꢁ], C(24)–H(24)ꢂ ꢂ ꢂCl(2) [Dꢂ ꢂ ꢂA
˚
distance = 3.548(6) A and D–Hꢂ ꢂ ꢂA angle = 154.0ꢁ],
ꢀ3
˚
Largest difference in peak and hole (e A
)
˚
C(32)–H(32)ꢂ ꢂ ꢂCl(2) [Dꢂ ꢂ ꢂA distance = 3.527(2) A and
D–Hꢂ ꢂ ꢂA angle = 134.2ꢁ] and C(32)–H(32)ꢂ ꢂ ꢂCl(3)
˚
[Dꢂ ꢂ ꢂA distance = 3.378(2) A and D–Hꢂ ꢂ ꢂA angle =
was used on the rhenium atom, 6-31G(d) on the chlo-
rine, nitrogen, phosphorous and carbon atoms and
6-31G basis on the hydrogen atoms.
Natural bond orbital (NBO) calculations were per-
formed with the NBO code [26] included in GAUSSIAN-03.
3. Results and discussion
3.1. Synthesis
The reaction of trans-[ReOX3(PPh3)2] with an excess
of 1,4-diaminobenzene in acetone leads to the formation
of [Re(4-NC6H4NH2)X3(PPh3)2] in good yield (Eq. (1)).
½ReOX3ðPPh3Þ ꢁ þ H2N–C6H4–NH2
2
! ½Reð4-NC6H4NH2ÞX3ðPPh3Þ ꢁ þ H2O
ð1Þ
2
The complexes are air stable. Their solubilities in most
polar solvents are low, but they can be crystallized from
acetonitrile. Room temperature magnetic susceptibility
measurements show the complexes to be diamagnetic.
The lack of paramagnetic broadening or shifts of
Fig. 1. A displacement ellipsoid plot of [Re(4-NC6H4NH2)Cl3(PPh3)2]
showing the atom numbering scheme (50% probability ellipsoids). The
hydrogen atoms of the phenyl rings are omitted for clarity.
1
resonances in the H NMR spectra of [Re(4-NC6H4-
NH2)X3(PPh3)2] also confirms diamagnetism of the

B. Machura et al. / Polyhedron 24 (2005) 1454–1460
1457
126.1ꢁ] provide additional conformational stabilization
3.3. Optimized geometry and charge distribution
of the [Re(4-NC6H4NH2)Cl3(PPh3)2] molecule [27,28].
The most important bond lengths and angles for
[Re(4-NC6H4NH2)Cl3(PPh3)2] are reported in Table 2.
The geometry of the [Re(4-NC6H4NH2)Cl3(PPh3)2]
complex was optimized in a singlet state using the
DFT method with the B3LYP functional. The opti-
mized geometric parameters are gathered in Table 2.
The calculated bond lengths and angles are in agreement
with the values based upon the X-ray crystal structure
data, and the general trends observed in the experimen-
tal data are well reproduced in the calculations.
Table 3 presents the atomic charges from the natural
population analysis (NPA) for [Re(4-NC6H4NH2)Cl3-
(PPh3)2]. The calculated charge on the rhenium atom
is considerably lower than the formal charge of +5.
The populations of the dxy; dxz; dyz; dx2ꢀy2 and dz2 orbi-
tals of the central atom are 1.300, 1.957, 0.904, 1.145
and 1.042, respectively. This is a result of significant
charge donation from the imido ligand, chloride ions
and triphenylphosphine molecules. Small differences in
values of charges can be noticed between the chloride
ion in the trans position to the imido group and two
mutually trans Cl(1) and Cl(3) ligands. The Cl(2) ligand
is less negative, which indicates higher electron density
delocalization towards the rhenium atom.
˚
The Re(1)–N(1)–C(37) bond angle [177.2(4) A] agrees
with the linear coordination mode of the 4-NC6H4NH2
˚
ligand, and the Re–N(1) distance [1.719(4) A] is typical
for Re„NR of rhenium(V) complexes [6]. Similar to
the d2 complexes mer,trans-[Re(NR)Cl3(PEt2Ph)2]
(R = C6H4-4-OMe or C6H4-4-COMe) [29] and mer,
trans-[Re(NMe)Cl3(PEt2Ph)2] [30], no structural trans
effect of the imido ligand is observed in [Re-
(4-NC6H4NH2)Cl3(PPh3)2]. The Re–P bond distances
fall within the normal range of Re–P distances observed
in six-coordinate tertiary phosphine complexes – 2.45–
˚
2.51 A [31].
The bond valences were computed as mij = exp
[(Rij ꢀ dij)/b] [32–34], where Rij is the bond-valence
parameter (in the formal sense the Rij parameter value
can be considered as the idealized single-bond length be-
tween i and j atoms). The RRe–N, RRe–P, RRe–Cl were taken
as 2.06, 2.46 and 2.23 [34], respectively, and b was taken as
0.37 [33]. The computed bond valences of rhenium are
m
Re–N = 2.513; mRe–P = 0.905 and 0.915; mRe–Cl = 0.554,
0.552 and 0.602 v.u. (valence units), which means that
the Re–P bonds are two times stronger than the Re–Cl
bonds, the Re–N bond is the strongest one and in a for-
mal sense can be considered as a triple bond.
3.4. Electronic structure
The rhenium atom of [Re(4-NC6H4NH2)Cl3(PPh3)2]
possesses a d2 configuration, the highest MO of this
compound is of dxz type with antibonding contributions
from pp chloride orbitals. The remaining four d-type
orbitals of the rhenium are found among the unoccupied
MOs. The dyz; dxy; dz2 and dx2ꢀy2 orbitals of the central
atom constitute mainly the LUMO, LUMO + 1,
LUMO + 2 and LUMO + 10, respectively. The dyz and
dxy rhenium orbitals bear antibonding character to-
wards the pp nitrogen orbitals of the imido ligand; the
LUMO, LUMO + 1 can be considered as pRꢃ eBNR
orbitals.
Table 2
˚
The experimental and optimized bond lengths (A) and bond angles (ꢁ)
for [Re(4-NC6H4NH2)Cl3(PPh3)2]
Experimental
Optimized
˚
Bond length (A)
Re(1)–N(1)
Re(1)–Cl(1)
Re(1)–Cl(2)
Re(1)–Cl(3)
Re(1)–P(1)
Re(1)–P(2)
1.719(4)
1.715
2.506
2.496
2.508
2.549
2.549
2.4554(13)
2.4498(12)
2.4180(14)
2.4969(14)
2.4929(14)
3.5. NBO analysis
Bond angle (ꢁ)
Table 4 presents the occupancies and natural atomic
orbital compositions (NAO) of the calculated NBOs
N(1)–Re(1)–Cl(1)
N(1)–Re(1)–Cl(2)
N(1)–Re(1)–Cl(3)
N(1)–Re(1)–P(1)
N(1)–Re(1)–P(2)
Cl(1)–Re(1)–P(1)
Cl(1)–Re(1)–P(2)
Cl(2)–Re(1)–Cl(1)
Cl(2)–Re(1)–P(1)
Cl(2)–Re(1)–P(2)
Cl(3)–Re(1)–Cl(1)
Cl(3)–Re(1)–Cl(2)
Cl(3)–Re(1)–P(1)
Cl(3)–Re(1)–P(2)
P(2)–Re(1)–P(1)
Re(1)–N(1)–C(37)
90.31(13)
177.97(14)
92.71(14)
92.39(13)
93.78(13)
91.00(5)
88.61(5)
88.26(4)
86.19(4)
87.63(4)
176.70(5)
88.76(5)
90.19(5)
89.87(5)
173.82(4)
177.2(4)
90.70
179.75
90.45
94.58
94.68
90.41
89.36
89.55
85.42
85.32
178.85
89.30
89.46
89.46
170.74
179.66
Table 3
Atomic charges from the natural population analysis (NPA) of [Re(4-
NC6H4NH2)Cl3(PPh3)2]
Atom
Atomic charge
Re(1)
Cl(1)
Cl(2)
Cl(3)
P(1)
0.326
ꢀ0.481
ꢀ0.463
ꢀ0.482
1.415
P(2)
1.414
ꢀ0.234
ꢀ0.806
N(1)
N(2)

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B. Machura et al. / Polyhedron 24 (2005) 1454–1460
Table 4
The selected results of the NBO analysis of [Re(4-NC6H4NH2)-
Cl3(PPh3)2]
Table 5 summarizes the most important delocaliza-
tions in [Re(4-NC6H4NH2)Cl3(PPh3)2] with their stabil-
ization energy E(2) values. Some of them concern the
imido ligand. The electron density of the lone pair of
the Cl(2) ligand (in the trans position to the imido li-
gand) is delocalized into the rꢃReð1Þ–Nð1Þ bond orbital. A
significant loss of occupancy concerns the pp orbital of
the C(37) atom in the imido group. The elꢃectron density
of this orbital is delocalized into the pReð1Þ–Nð1Þ bond
orbital and pꢃC–C bond orbitals of the imido ring.
Bond orbital BD Occupancy NAO composition
Re(1)–N(1) (r)
Re(1)–N(1) (p)
Re(1)–N(1) (p)
Re(1)–Cl(1) (r)
Re(1)–P(1) (r)
1.95644
1.97310
1.93278
1.95214
1.87547
% Re 26.20 s(23.28%) d(76.52%)
% O 73.80 s(53.61%) p(46.35%)
% Re 39.38 d(99.49%)
% O 60.62 p(99.98%)
% Re 48.46 (98.95%)
% O 51.54 p(99.97%)
% Re 26.29 s(30.29%) d(69.17%)
% Br 73.71 s(16.84%) p(83.03%)
3.6. Spectroscopic properties
% Re 35.48 s(43.37%) d(56.43%)
% Br 64.52 s(26.63%) p(73.20%)
The IR spectra of [Re(4-NC6H4NH2)Cl3(PPh3)2] and
[Re(4-NC6H4NH2)Br3(PPh3)2] are characterized by
strong absorptions at 1169 and 1163 cmꢀ1, respectively,
which is within the region (1000–1200 cmꢀ1) expected
for a linearly coordinated phenylimido moiety with a tri-
ple bond [36]. The absorption bands at ꢄ3400 cmꢀ1 cor-
respond to the N–H stretching vibrations and confirm
the presence of the uncoordinated NH2-group.
between the rhenium and the donor ligand atoms for
[Re(4-NC6H4NH2)Cl3(PPh3)2]. Some of the Re–L bonds
were not detected indicating predominant Coulomb-
type interactions between the central ion and the
ligands.
The NBO analysis confirms the presence of a triple
bond between the rhenium and the imido ligand in
[Re(4-NC6H4NH2)Cl3(PPh3)2]. The Re–N bond orbital
of r-character is strongly polarized towards the nitrogen
atom (ca. 74% at N), and the s and p nitrogen orbitals
and s and d rhenium orbitals take part in the bond for-
mation. The Re–N bond orbitals of p-character are the
result of overlapping of the empty dxy and dyz rhenium
orbitals with the occupied px and pz orbitals of the
deprotonated nitrogen of the imido ligand.
The experimental and calculated electronic spectra of
the chloro complex are represented graphically in Fig. 2.
Each calculated transition in Fig. 2 is represented by a
The NBO analysis also takes into consideration all
possible interactions between ꢀfilledꢁ (donor) Lewis-type
NBOs and ꢀemptyꢁ (acceptor) non-Lewis NBOs and esti-
mates their energetic importance by second-order per-
turbation theory. Since these interactions lead to a loss
of occupancy from the localized NBOs of the idealized
Lewis structure into the empty non-Lewis orbitals, they
are referred to as ꢀdelocalizationꢁ corrections to the zer-
oth-order natural Lewis structure. The stabilization en-
ergy E(2) associated with delocalization is estimated as
2
Eð2Þ ¼ DEij ¼ qiðF ði; jÞ Þ=ðej ꢀ eiÞ;
where qi is the donor orbital occupancy, ei, ej are diago-
nal elements (orbital energies) and F(i,j) is the off-diag-
onal NBO Fock matrix element [35].
200.00
400.00
600.00
800.00
Fig. 2. The experimental (——) and calculated (------) electronic
absorption spectrum of [Re(4-NC6H4NH2)Cl3(PPh3)2].
Table 5
The most important delocalizations observed for [Re(4-NC6H4NH2)Cl3(PPh3)2] and their stabilization energies (kcal/mol)
Donor natural bond orbital Occupancy of donor NBO Acceptor natural bond orbital Occupancy of acceptor NBO Stabilization energy
LP of Cl(2) (r)
pp of C(37)
pp of C(37)
1.66073
1.08447
r* of Re(1)–N(1)
p* of Re(1)–N(1)
p* of C(38)–C(39)
p* of C(41)–C(42)
r* of Re(1)–Cl(1)
r* of Re(1)–P(1)
0.40280
0.37253
0.27819
0.27864
0.44406
0.51972
137.39
171.49
64.81
pp of C(37)
LP of Cl(3) (r)
LP of P(2)
64.90
136.88
139.84
1.55618
1.33608
LP, lone pair.

B. Machura et al. / Polyhedron 24 (2005) 1454–1460
1459
Table 6
The energy and molar absorption coefficients of experimental absorption bands and the electronic transitions calculated with the TDDFT method for
[Re(4-NC6H4NH2)Cl3(PPh3)2]
The most important orbital excitations
Character
k (nm)
E (eV)
f
Experimental K (nm) (E (eV)) e
H ! L + 1
H ! L + 2
H-1 ! L + 1
H-3 ! L
d ! d
678.4
431.9
409.0
392.6
372.1
355.0
337.4
336.8
326.6
326.3
302.5
301.6
297.9
290.4
1.83
2.87
3.03
3.16
3.33
3.49
3.67
3.68
3.80
3.80
4.10
4.11
4.16
4.27
0.0007
0.0001
0.0015
0.0219
0.2250
0.0836
0.0506
0.0183
0.0098
0.0125
0.0822
0.0141
0.0291
0.0128
790.0 (1.60) 25
9
d ! d
>
>
>
>
>
p(imido)/p(Cl) ! d
p(Ph)/p(Cl) ! d
p(imido)/p(Cl) ! d
p(Ph)/p(Cl) ! d
p(Ph)/p(Cl) ! d
p(Ph) ! d
>
>
>
>
>
>
>
=
H-1 ! L
419.2 (2.96) 19800
H-5 ! L
>
>
>
>
H-3 ! L + 1
H-7 ! L
>
>
>
>
>
>
>
>
;
H-5 ! L + 1
H-7 ! L
p(Ph)/p(Cl) ! d
p(Ph) ! d
9
H-9 ! L + 1
H ! L + 7
H-17 ! L
p(Cl) ! d
>
>
>
>
d ! p*(Ph)
>
>
>
>
p(Ph)/p(Cl) ! d
p(Cl)/p(Cl)/r(Cl) ! d
p(Ph) ! d
>
>
>
>
H-13 ! L + 1
H-11 ! L + 1
H-1 ! L + 2
H-2 ! L + 2
H ! L + 11
H-17 ! L
>
>
>
>
>
>
>
>
>
p(imido)/p(Cl) ! d
n(P)/p(Cl) ! d
d ! p*(Ph)
288.5
277.3
274.1
273.1
265.5
255.6
250.0
249.2
249.0
248.7
247.5
245.0
244.5
4.30
4.47
4.52
4.54
4.67
4.85
4.96
4.97
4.98
4.98
5.01
5.06
5.07
0.0207
0.2661
0.0410
0.0108
0.0135
0.0106
0.0243
0.0160
0.0196
0.0257
0.0229
0.0232
0.0135
>
>
=
256.2 (4.84) 24600
>
>
>
>
p(Ph)/p(Cl) ! d
p(Ph)/p(Cl) ! d
p(Ph)/p(Cl) ! d
p(imido)/p(Cl) ! d
p(Ph) ! d
>
>
>
>
>
H-3 ! L + 2
H-5 ! L + 2
H-1 ! L + 10
H-6 ! L + 2
H ! L + 15
H-2 ! L + 6
H-1 ! L + 7
H-3 ! L + 3
H-2 ! L + 7
>
>
>
>
>
>
>
>
>
>
>
>
>
>
;
d ! p*(Ph)
9
n(P)/p(Cl) ! p*(Ph)
p(imido)/p(Cl) ! p*(Ph)
p(Ph)/p(Cl) ! p*(Ph)
n(P)/p(Cl) ! p*(Ph)
>
=
228.4 (5.43) 42700
216.4 (5.73) 27000
>
;
H, HOMO; L, LUMO.
Gaussian function with the height equal to the oscillator
strength and width equal to 0.04. The shape of the UV–
Vis spectrum of [Re(4-NC6H4NH2)Br3(PPh3)2] is the
same as for the chloro analogue; the absorption bands
of the bromo complex were recorded at 788.0, 421.0,
267.4, 237.0 and 224.8 nm.
Table 6 shows the energy and molar absorption
coefficients of the experimental absorption bands of
[Re(4-NC6H4NH2)Cl3(PPh3)2] and the spin-allowed sin-
glet–singlet electronic transitions calculated with the
TDDFT method. Except for the low energy part of
the spectrum, only transitions with oscillator strengths
larger than 0.01 are listed in Table 6.
The investigated complex is of large size, and the
number of basis functions is equal to 812. Eighty elec-
tron transitions calculated by the TDDFT method do
not comprise all the experimental absorption bands.
The UV–Vis spectrum of [Re(4-NC6H4NH2)Cl3(PPh3)2]
was calculated to ꢄ240 nm, so the shortest wavelength
experimental band is not assigned to the calculated tran-
sitions, and the assignment of the band at 228.4 nm is
probably not complete. Considering that the solution
spectra of PPh3 and 1,4-diaminobenzene exhibit intense
absorption bands in 250–200 nm region, some addi-
tional intraligand and interligand transitions are
expected to be found at higher energies in the calcula-
tions for [Re(4-NC6H4NH2)Cl3(PPh3)2].
The longest wavelength experimental band at 790 nm
may be attributed to the transition of d ! d character
with small oscillator strength, calculated at 678.4 nm.
The absorption band at 419.2 nm corresponds to the
LMCT transitions calculated in the range 432–326 nm.
These transitions occur from the chloride, imido and
phosphine ligand orbitals to the d rhenium orbitals.
The next experimental band at 256.2 nm may be as-
signed to the transitions calculated between 305 and
249 nm with large oscillator strengths. These are LMCT
transitions from the chloride, imido and phosphine li-
gand orbitals to the d rhenium orbitals and MLCT tran-
sitions from the dRe to the acceptor orbitals of PPh3.
The absorption band at 228.4 nm is attributed to the
LLCT transitions with large oscillator strengths. They
comprise intra- and interligand transitions.
4. Supplementary data
Supplementary data for C60H51Cl3N2P3Re are avail-
able from the CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: +44 1223 336 033; e-mail:

1460
B. Machura et al. / Polyhedron 24 (2005) 1454–1460
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263918.
[18] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467.
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Acknowledgements
[21] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A.
Robb, J.R. Cheeseman, J.A. Montgomery Jr., T. Vreven, K.N.
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The GAUSSIAN-03 calculations were carried out in the
Wrocław Centre for Networking and Supercomputing,
WCSS, Wrocław, Poland under calculational Grant
No. 51/96.
The crystallographic part was financed by funds allo-
cated by the Ministry of Scientific Research and Infor-
mation Technology to the Institute of General and
´ ´
Ecological Chemistry, Technical University of Łodz.
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