The reactivity of [ReBr3(MeCN)(dppe)] towards gaseous nitric oxide. The X-ray structure of [ReBr3(MeCN)(dppe)] and [ReBr 3(NO)(dppe)]0.57[ReOBr3(dppe)]0.43 and DFT calculations for [ReBr3(NO)(dppe)] and [ReOBr 3(dppe)]

Article abstract of DOI:10.1016/j.molstruc.2005.01.038

The [ReOBr₃(dppe)] (dppe=bis(diphenylophosphino)ethane) complex reacts with acetonitrile in the presence of excess of triphenylphpsphine to give a new monomeric nitrile rhenium(III) complex - [ReBr₃(MeCN)(dppe)] (1). The reaction of 1 with gaseous nitric oxide leads to the mixed [ReBr ₃(NO)(dppe)]_0.57[ReOBr₃(dppe)]_0.43 complex (2) with rhenium atoms on +2 and +5 oxidation states. This paper presents the synthesis, spectroscopic characterisation and X-ray structure of 1 and 2. The geometries of [ReBr₃(NO)(dppe)] and [ReOBr ₃(dppe)] have been optimized using the density functional theory (DFT) and the electronic transitions of [ReBr₃(NO)(dppe)] and [ReOBr₃(dppe)] have been calculated with the time-dependent DFT method (TDDFT). The UV-vis spectrum of 2 has been interpreted on the basis of the experimental data for [ReOBr₃(dppe)] and the calculated transitions for [ReOBr₃(dppe)] and [Re(NO)Br₃(dppe)].

Full text of DOI:10.1016/j.molstruc.2005.01.038

Journal of Molecular Structure 740 (2005) 107–117
www.elsevier.com/locate/molstruc
The reactivity of [ReBr3(MeCN)(dppe)] towards gaseous nitric oxide.
The X-ray structure of [ReBr3(MeCN)(dppe)]
and [ReBr3(NO)(dppe)]0.57[ReOBr3(dppe)]0.43 and DFT calculations
for [ReBr3(NO)(dppe)] and [ReOBr3(dppe)]
a,
B. Machura , R. Kruszynski , M. Jaworska
b
c
*
aDepartment 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
cDepartment of Theoretical Chemistry, Institute of Chemistry, University of Silesia, 9th Szkolna Street, 40-006 Katowice, Poland
Received 18 November 2004; revised 17 January 2005; accepted 17 January 2005
Abstract
The [ReOBr3(dppe)] (dppeZbis(diphenylophosphino)ethane) complex reacts with acetonitrile in the presence of excess of
triphenylphpsphine to give a new monomeric nitrile rhenium(III) complex—[ReBr3(MeCN)(dppe)] (1). The reaction of 1 with gaseous
nitric oxide leads to the mixed [ReBr3(NO)(dppe)]0.57[ReOBr3(dppe)]0.43 complex (2) with rhenium atoms on C2 and C5 oxidation
states. This paper presents the synthesis, spectroscopic characterisation and X-ray structure of 1 and 2. The geometries of
[ReBr3(NO)(dppe)] and [ReOBr3(dppe)] have been optimized using the density functional theory (DFT) and the electronic transitions of
[ReBr3(NO)(dppe)] and [ReOBr3(dppe)] have been calculated with the time-dependent DFT method (TDDFT). The UV–vis spectrum of
2 has been interpreted on the basis of the experimental data for [ReOBr3(dppe)] and the calculated transitions for [ReOBr3(dppe)] and
[Re(NO)Br3(dppe)].
q 2005 Elsevier B.V. All rights reserved.
Keywords: Rhenium; Acetonitrile; Nitric oxide; Nitrosyl complexes; DFT and TDDFT calculations
1. Introduction
a synthesis of rhenium nitrosyls. Previously, we reported
the structural and spectroscopic characterisation of the
nitrosyl rhenium complexes obtained in the reactions of
the [ReOX3L2] complexes (XZCl, Br and LZPPh3,
AsPh3, 1/2 dppe and 1/2 bipy) with gaseous nitric oxide
[10–21].
The nitrile complexes have been recognized as con-
venient substrates in the syntheses of organometallic
derivatives for many years. The R–ChN ligands can be
readily displaced by other isoelectronic unsaturated ligands
such as dinitrogen, carbon monooxide, isocyanides and
alkynes [1–5] or can be converted into other organic ligands
in such chemical processes as insertion and nucleophilic or
elektrophilic attack [1,6–9].
The finding that [ReCl3(PPh3)2], generated in situ from
[ReOCl3(PPh3)2] and PPh3, undergoes a direct reaction
with the triazenido anion Li(RN–NaNR) to give trans-
[ReCl2(PPh3)2(RN–N–NR)] [22], prompted us to explore
the reaction of [ReOBr3(dppe)] with acetonitrile in the
presence of excess of triphenylphosphine as a direct route to
the nitrile complex.
The main aim of the paper was the preparation of the
nitrile rhenium complex with bis(diphenylophosphi-
no)ethane (dppe) in coordination sphere and using it to
The [ReBr3(MeCN)(dppe)] complex (1) obtained in
the above method, reacts with gaseous nitric oxide to
give [ReBr3(NO)(dppe)]0.57[ReOBr3(dppe)]0.43 (2). Here
we present the synthesis, spectroscopic characterisation
* Corresponding author. Tel.: C48 322582441; fax: C48 322599978.
E-mail addresses: basia@ich.us.edu.pl (B. Machura), mj@ich.us.edu.pl
(M. Jaworska).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.01.038

108
B. Machura et al. / Journal of Molecular Structure 740 (2005) 107–117
and X-ray structure of 1 and 2. The UV–vis spectrum of
2 has been discussed on the basis of the experimental
data for [ReOBr3(dppe)] and the calculated transitions
for [ReOBr3(dppe)] and [Re(NO)Br3(dppe)]. The geome-
tries of [ReOBr3(dppe)] and [Re(NO)Br3(dppe)]
have been optimised with the density functional
theory (DFT) and their electronic spectra have been
calculated with the time-dependent DFT method
(TDDFT).
Anal. Found: C, 38.92; H, 3.18; N, 1.68. Calc. for
C28H27Br3NP2Re (1): C, 38.86; H, 3.14; N, 1.62.
2.2. Preparation of
[ReBr3(NO)(dppe)]0.57[ReOBr3(dppe)]0.43 (2)
NO was passing through a vigorously stirred and
refluxing solution of [ReBr3(MeCN)(dppe)] (1 g,
1.2 mmol) in toluene (50 cm3) for 4 h. The colour changed
gradually from brownish-orange to dark red. Then the
resulting solution was evaporated to the volume of 10 cm3.
The dark red crystalline precipitate of 2 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. Yield 60%.
IR (KBr, cmK1) 3052 (w), 2948 (w), 2910 (w) 1740 (vs)
1485 (m), 1435 (s), 1154 (w), 1128 (m), 1097 (s) 1027 (w),
998 (w), 970 (s), 820 (m), 740 (m), 725 (m), 689 (s), 655
(m), 546 (m), 521 (s), 495 (m), 444.
The calculations with TDDFT method for closed-shell
and open-shell organic, inorganic and organometallic
molecules (including 5d-metal complexes) are still
limited but a few studies have already appeared and
supported the TDDFT method to be applicable for such
systems giving good assignment of experimental spectra
[23–34].
2. Experimental
Anal. Found: C, 36.72; H, 2.73; N, 0.97. Calc. for
C26H24P2Br3ON0.5Re (2): C, 36.85; H, 2.85; N, 0.83.
Triphenylphosphine, bis(diphenylophosphino)ethane
and ammonium perrhenate were purchased from Aldrich
Chemical Co. and used without further purification.
Solvents were obtained from commercial sources and
thoroughly deoxygenated prior to use. [ReOBr3(dppe)]
was prepared according to the literature [35].
2.3. Physical measurements
UV–vis spectra were recorded on a spectrophotometer
Lab Alliance UV–vis 8500 in the range 800–220 nm in
deoxygenated dichloromethane solution. IR spectra were
recorded as KBr pellets with a Nicolet Magna 560
Gaseous NO obtained in the reaction:
spectrophotometer in the spectral range 4000–400 cmK1
.
2NaNO2 C3H2SO4 C2FeSO4 /2NO C2NaHSO4
The magnetic susceptibility was determined with a
superconducting quantum interference device (SQUID,
Quantum Design) magnetometer. Elemental analyses
(CHN) were performed on a Perkin-Elemer CHN-2400
analyzer.
CFe2ðSO4Þ3 C2H2O;
was purified by passing through the washers with concen-
trated KOH solution and over solid NaOH.
The reactions were performed under argon atmosphere.
2.4. Crystal structures determination and refinement
2.1. Preparation of [ReBr3(MeCN)(dppe)] (1)
The crystals of 1 and 2 suitable for X-ray structure
determination were obtained by slow evaporation from
acetonitrile. The X-ray intensity data were collected on
KM-4-CCD automatic diffractometer equipped with CCD
detector with u scan mode, 30 and 42 s exposure time
was used for 1 and 2, respectively and, respectively all
and a quarter of Ewald sphere up to 50.28 was collected.
The unit cell parameters were determined from least-
squares refinement of the setting angles of 8022 and
3139 of strongest reflections for 1 and 2 respectively.
Details concerning crystal data and refinement are given
in Table 1. Lorentz, polarization and numerical absorp-
tion corrections [36] were applied. The structures were
solved direct methods and subsequently completed by the
difference Fourier recycling. All the non-hydrogen atoms
were refined anisotropically using full-matrix, least-
squares technique. For compound 2 some restrains were
applied, for details see Section 3 and 4. All hydrogen
atoms were founded on difference Fourier synthesis
Triphenylphosphine (5 g, 19 mmol) was added to a
suspension of [ReOBr3(dppe)] (1 g, 1.2 mmol) in tetra-
hydrofurane (50 cm3) and acetonitrile (50 cm3). The
brownish-orange solution thus formed was refluxed for
4 h. The volume was condensed to 15 cm3 and upon
slow cooling to room temperature brownish-orange
microcrystalline solid was isolated. X-ray quality crystals
were obtained by recrystallization from acetonitrile. Yield
70%. The crystals of 1 are air stable in the solid state
and in the acetonitrile solution but they slowly decom-
pose with loss of acetonitrile in halogenated solvents
such as chloroform and dichloromethane. A solution of
1 in CH2Cl2 and CHCl3 can be stabilized by the addition
of acetonitrile.
IR (KBr, cmK1) 3053 (w), 2915 (w), 1484 (m), 1434 (s),
1418 (m), 1361 (w) 1332 (w), 1189 (w), 1157 (w), 1100 (s),
1027 (w), 998 (w) 870 (w), 815 (w), 752 (m), 741 (s), 697
(s), 653 (m), 522 (s), 501 (m), 458 (m).

B. Machura et al. / Journal of Molecular Structure 740 (2005) 107–117
109
Table 1
3. Results and discussion
Crystal data and structure refinement for 1 and 2
1
2
3.1. Preparation of complexes
Empirical formula
C28H27Br3NP2Re
C26H24Br3N0.
57OP2Re
848.31
The nitrile complex 1 has been prepared in high yield by
use of the procedure shown in Eq. (1).
Formula weight
Temperature (K)
865.38
293(2)
291(2)
˚
Wavelength (A)
0.71073
Monoclinic
P21/n
0.71073
Monoclinic
P21/n
½ReOBr3ðdppeފ CMeCN CPPh3 /½ReBr3ðMeCNÞ
Crystal system
Space group
!ðdppeފ COPPh3
(1)
˚
˚
Unit cell dimensions
aZ9.7848(4) A
bZ22.5565(9) A
cZ13.8442(5) A
bZ102.404(3)8
2984.2(2)
4
aZ11.8735(8) A
bZ14.3697(11) A
cZ16.4129(9) A
bZ93.389(5)8
2795.4(3)
4
˚
˚
It can be assumed that the [ReBr3(dppe)] compound,
generated from [ReOBr3(dppe)] and PPh3 in the first step of
the synthesis, reacts with MeCN to give 1. The mass ratio of
[ReOBr3(dppe)] and PPh3 equal to 1:5 ensures the
maximum yield of the product. In the case of smaller
excess of PPh3, some unreacted starting material has been
recovered from the reaction.
˚
˚
3
˚
Volume (A )
Z
Density (calculated, Mg/m3)
1.926
2.016
Absorption coefficient
(mmK1
8.270
8.768
)
F(000)
1648
1608
Complex 1 reacts easily with gaseous nitric oxide to give
the mixed [ReBr3(NO)(dppe)]0.57[ReOBr3(dppe)]0.43 com-
plex (2) with rhenium atoms on C2 and C5 oxidation
states. The reaction equation:
Crystal size (mm)
q range for data collection
Index ranges
0.54!0.13! 0.06 0.36!0.07!0.01
2.95–25.118
K11%h%9
K26%k%26
K16%l%16
30,654
3.26–25.108
K14%h%14
0%k%17
0%l%19
4970
2½ReIIIBr3ðMeCNÞðdppeފ C2NO/½ReIIBr3ðNOÞðdppeފ
C½ReVOBr3ðdppeފ C1=2N2 C2MeCN
Reflections collected
Independent reflections
5321 (RintZ0.
0439)
4970(RintZ0.
0000)
Completeness to 2q (%)
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
97.1
95.6
0.6562 and 0.0949 0.894 and 0.144
5321/0/317
1.056
4970/33/317
1.006
explains the formation of complex 2.
Final R indices [IO2s(I)]
R1Z0.0291
wR2Z0.0567
R1Z0.0433
wR2Z0.0610
R1Z0.0526
wR2Z0.1017
R1Z0.0951
wR2Z0.1216
3.2. Description of the crystal structure of 1
R indices (all data)
Compound 1 crystallises in the monoclinic space group
P21/n and its structure consists of discrete and well-separated
monomers linked via C(2)–H(2A)/Br(2)(xC1/2,KyC
Largest diff. peak and hole
K3
1.444 and K0.660 1.458 and K1.196
˚
(e A
)
˚
3/2,zC1/2) [D/A distance equals 3.858(5) A and
D–H/A angle 170.38], C(32)–H(32A)/Br(1)(Kx,KyC
˚
2,Kz) [D/A distance equals 3.513(6) A and D–H/A angle
and refined as ‘riding’ on their parent carbon atoms with
geometry idealisation after each cycle and assigned
isotropic temperature factors equal 1.2 times the value
of equivalent temperature factor of the parent non methyl
carbon atoms and 1.5 for methyl carbon atoms. SHELXS97
[37], SHELXL97 [38] and SHELXTL [39] programs were used
for all the calculations. Atomic scattering factors were
those incorporated in the computer programs.
135.88] and C(32)–H(32B)/Br(3)(KxC1,KyC2,Kz)
[D/A distance equals 3.624(6) A and D–H/A angle
149.68] intermolecular weak hydrogen bonds [45]. The
conformations of molecules of compound 1 are stabilised by
weak intramolecular hydrogen bond: C(16)–H(16)/Br(2)
˚
˚
[D/A distance equals 3.732(5) A and D–H/A angle
151.68]. The molecular structure of 1 is presented in Fig. 1.
The rhenium atom is in a distorted octahedral environ-
ment with terminal MeCN group [Re–N–C angle—
176.0(4)8] trans to one of the phosphorus atoms of the
chelate ligand—bis(diphenylophosphino)ethane and three
bromine ligands in meridional geometry.
2.5. Computational details
GAUSSIAN03 program [40] was used in the calculations.
The geometry optimization of [ReBr3(NO)(dppe)] and
[ReOBr3(dppe)] was carried out with the DFT method
with the use of B3LYP functional [41,42]. The spin-allowed
transitions with the TDDFT method [43] were calculated for
[ReOBr3(dppe)] and [Re(NO)Br3(dppe)]. LANL2DZ basis
set [44] was used on the rhenium atom, 6-31G(d) on the
bromine, nitrogen and carbon atoms and 6-31G basis on the
hydrogen atoms in the calculations.
The most important bond lengths and angles for 1 are
reported in Table 2.
˚
The Re–N(nitrile) bond length of 2.127(4) A in 1 agrees
well with the Re–N values found in the rhenium complexes
containing the nitrile ligand in trans position to a strong
p-acceptor, but it is significantly longer than the Re–N bond
lengths found for the complexes whose trans position to
the nitrile ligand is not occupied by a p-acceptor.

110
B. Machura et al. / Journal of Molecular Structure 740 (2005) 107–117
˚
Re–Br bonds are equal to 2.4801(5) and 2.4736(5) A,
respectively. The Re–P distances at 2.3991(13) and
˚
2.4021(12) A in 1 are shorter than those found in the
rhenium complexes with chelate phosphine ligands:
˚
2.450(4), 2.456(4) and 2.480(4) A in mer-[ReCl3(dppm-
0
˚
P,P )(dppom-P)] [48] and 2.479(1) and 2.458(2) A in trans-
[ReCl(NO)(dppe)2]2C [49]. The bond valences were
computed as nijZexp[(RijKdij)/B] [50–52], where Rij is
the bond-valence parameter (in the formal sense Rij is the
single-bond length between i and j atoms) [53]. The RRe–N,
RRe–P, RRe–O, RRe–Br were taken as 2.06, 2.46, 1.97 and 2.45
[50], respectively, and the value of B was taken as 0.37 [51].
The computed bond valences of the rhenium atom are nRe–
NZ0.834, nRe–PZ1.169 and 1.179, nRe–BrZ0.607, 0.922
and 0.938 v.u. (valence units), what means that dppe ligand
is the strongest bonded substituent, two bromide atoms and
nitrile substituent is bonded with comparable strength, and
one bromide atom is bonded distinctly weaker. The
significant shortening of the C–N bond length in 1
Fig. 1. The molecular structure of 1. The thermal ellipsoids are drawn at
50% probability level.
˚
[1.098(5) A] in comparison with free acetonitrile
˚
[1.155 A] [54] is observed and it is expected upon
In [ReBr3(NO)(MeCN)(PPh3)] [13] and [NEt4][ReBr4
(NO)(MeCN)] [46] with acetonitrile trans to nitrosyl
group the Re–N(nitrile) bond lengths are equal to 2.156(7)
coordination. The NC–CH3 distance is within the range
observed for other acetonitrile complexes [13,46,47].
˚
and 2.153(11) A, respectively, but for mer–trans-[ReCl3
˚
(MeCN)(PPh3)2] the Re–N distance is 2.068(5) A [47].
3.3. Description of the crystal structure of 2
A clear trans effect of dppe ligand is also observed in the
elongation of Re–Br(2) distance trans to the phosphorus
˚
atom of the dppe ligand [2.5980(5) A], the mutually trans
The results of the structural study on 2 show clearly that
the molecules of [ReBr3(NO)(dppe)] are packed together
with molecules of [ReOBr3(dppe)] in a not unambiguous
proportion. Depending on the scheme of disordered
substituents restraining it differs from 57:43 to 50:50. The
molecules of 2 are linked via C(20)–H(20)/Br(1)(KxC
Table 2
˚
Table 2 The experimental bond lengths (A) and angles (8) for 1
Bond lengths
Experimental
˚
3/2, yK1/2,KzC1/2) [D/A distance equals 3.642(14) A
Re(1)–N(31)
Re(1)–P(1)
Re(1)–P(2)
Re(1)–Br(1)
Re(1)–Br(2)
Re(1)–Br(3)
N(31)–C(31)
C(31)–C(32)
2.127(4)
and D–H/A angle 149.18] intermolecular weak hydrogen
bonds [45]. The numbering scheme of the disordered
complex 2 is shown in Fig. 2.
In the both molecules the rhenium atom has a distorted
octahedral coordination with the chelate phosphine ligand
2.3991(13)
2.4021(12)
2.4801(5)
2.5980(5)
2.4736(5)
1.098(5)
1.463(7)
Angles
N(31)–Re(1)–P(1)
N(31)–Re(1)–P(2)
P(1)–Re(1)–P(2)
N(31)–Re(1)–Br(1)
N(31)–Re(1)–Br(2)
N(31)–Re(1)–Br(3)
P(1)–Re(1)–Br(1)
P(1)–Re(1)–Br(2)
P(1)–Re(1)–Br(3)
P(2)–Re(1)–Br(1)
P(2)–Re(1)–Br(2)
P(2)–Re(1)–Br(3)
Br(1)–Re(1)–Br(2)
Br(3)–Re(1)–Br(1)
Br(3)–Re(1)–Br(2)
C(31)–N(31)–Re(1)
N(31)–C(31)–C(32)
95.56(10)
178.58(11)
83.50(4)
90.63(10)
84.42(10)
88.96(10)
84.80(3)
176.77(3)
90.95(3)
90.35(3)
96.58(3)
89.99(3)
91.971(18)
175.666(19)
92.282(18)
176.0(4)
178.4(5)
Fig. 2. The molecular structure of 2.

B. Machura et al. / Journal of Molecular Structure 740 (2005) 107–117
111
Table 3
˚
The experimental bond lengths (A) and angles (8) for 2 and [ReOBr3(dppe)] and the optimized bond lengths (A) and angles (8) for [Re(NO)Br3(dppe)] and
˚
˚
[ReOBr3(dppe)]. The experimental bond lengths (A) and angles (8) for [ReOBr3(dppe)] are taken from the paper [64]
Bond lengths
2 Experimental (this work)
[ReOBr3(dppe)]
[Re(NO)Br3(dppe)]
Optimized
[ReOBr3(dppe)] Optimized
1.687
Experimental [64]
Re(1)–O(2)
Re(1)–N(1)
Re(1)–P(1)
Re(1)–P(2)
Re(1)–Br(1)
Re(1)–Br(2)
Re(1)–Br(3)
N(1)–O(1)
1.72(3)
1.680
1.679(15)
2.463(3)
2.461(3)
2.5759(12)
2.5192(13)
2.5316(13)
1.18(2)
1.764
2.507
2.510
2.667
2.621
2.619
1.177
2.447
2.463
2.581
2.517
2.517
2.505
2.513
2.703
2.618
2.613
Angles
O(2)–Re(1)–P(1)
N(1)–Re(1)–P(1)
O(2)–Re(1)–P(2)
N(1)–Re(1)–P(2)
P(1)–Re(1)–P(2)
O(2)–Re(1)–Br(2)
N(1)–Re(1)–Br(2)
P(2)–Re(1)–Br(2)
P(1)–Re(1)–Br(2)
O(2)–Re(1)–Br(3)
N(1)–Re(1)–Br(3)
P(2)–Re(1)–Br(3)
P(1)–Re(1)–Br(3)
Br(2)–Re(1)–Br(3)
O(2)–Re(1)–Br(1)
N(1)–Re(1)–Br(1)
P(2)–Re(1)–Br(1)
P(1)–Re(1)–Br(1)
Br(2)–Re(1)–Br(1)
Br(3)–Re(1)–Br(1)
O(1)–N(1)–Re(1)
83.1(13)
96.8(9)
83.3
91.2
84.8
89.9
95.52
90.6(14
87.7(12)
82.49(10)
109.1(13)
95.0(9)
93.06
82.56
83.2
84.5
104.4
102.9
92.40
89.54
91.45(8)
166.46(8)
94.3(13)
98.5(11)
172.35(7)
92.25(8)
92.50(5)
162.2(14)
171.8(12)
84.64(7)
79.26(7)
88.16(4)
88.93(4)
162(3)
96.0
164.3
100.7
93.1
166.7
102.9
169.09
91.89
168.84
87.01
174.6
93.1
172.6
92.6
86.5
100.24
88.2
162.6
162.7
178.62
85.63
83.86
88.06
89.31
179.33
82.6
76.9
87.4
92.8
82.3
77.6
89.2
90.5
˚
the Re–O(2) distance [1.607(18) A] in comparison with other
and two bromide ions in the equatorial plane. The
axial positions of the molecules are occupied by the NO
group or oxo ligand and bromide Br(1) ion. The clear
distortions from octahedral symmetry of the Re center in 2
are induced by the nitrosyl/oxo compositional disorder, the
presence of bidentate (dppe) and multiply bonding (oxo,
nitrosyl) ligands. Significant deviations from linearity
are observed in O(2)–Re(1)–Br(1) [162.2(14)8] and P(1)–
Re(1)–Br(2) [166.46(8)8]. The bond angles between cis-
ligands vary between 82.49(10) and 109.1(13)8. The most
important bond lengths and angles for 2 are reported in
Table 3.
˚
Re(V) monooxocomplexes: 1.669(4) A in [ReOCl3(PPh3)
0
˚
(OPPh3)] [55] and 1.671(6) A in fac-[ReOCl3(dppm-P,P )]
(dppmZPh2PCH2PPh2) [56] is observed. The fact that
disorder cause violations in determined distances is also
confirmed by calculated bond valences, which are nRe–N
Z
1.460, nRe–OZ2.667 v.u. According to valence sum rule [52]
these values should be almost the same in correctly refined
disordered structures. Thus as the best one was selected
refinement with Re–N, N–O and Re–O distances fixed and
NO, O substituents restrained with effective standard
deviation 0.04 to have the same Uij components (after
approximating to isotropic behaviour). The Re(1)–Br(1)
distance, considerable longer than Re(1)–Br(2) and Re(1)–
Br(3) bond lengths, is determined by the presence of oxygen
atom or nitrosyl group in trans position. The structural trans
effect of oxo and nitrosyl ligands was observed in many
transition metal complexes [57]. According to the computed
bond valences (nRe–PZ0.997 and 0.992, nRe–BrZ0.711,
0.829 and 0.802 v.u) it can be stated that dppe ligand is
bonded distinctly weaker than in compound 1, and the Re–P
bonds are only slightly stronger than Re–Br bonds.
For compound 2, due to the nitrosyl/oxo compositional
disorder, in the no restrained refinement can be observed the
˚
elongation of Re–NO distance [1.92(4) A] and the shortening
˚
of N–O bond length [1.03(4) A] in comparison with other
rhenium nitrosyl complexes. In monoclinic polymorph of
mer–cis-[ReBr3(NO)(OPPh3)2] the Re–NO bond length is
˚
˚
1.757(12) A and N–O distance is 1.261(13) A [18] and in
[ReBr4(NO)(EtOH)]K the Re–NO bond length is 1.723(15)
˚
and N–O distance is 1.19(2) A][46]. As a consequence of
disorder in not restrained refinement the shortening of

112
B. Machura et al. / Journal of Molecular Structure 740 (2005) 107–117
Table 4
The possible oxidation numbers and spin multiplicities of Re and NO in [ReBr3(NO)(dppe)]
Re
Spin of Re
NO
Spin of NO
Total spin
Spin multiplicity
Re(II)
Re(III)
Re(IV)
5/2, 3/2, 1/2
2, 1, 0
NOC (pꢀ1 )0(pꢀ2 )0
NO (pꢀ1 )1(pꢀ2 )0
NOK(pꢀ1 )1(pꢀ2 )1
0
5/2, 3/2, 1/2
5/2, 3/2, 1/2
5/2, 3/2, 1/2
6, 4, 2
6, 4, 2
6, 4, 2
1
⁄
2
3/2, 1/2
1
3.4. Spectroscopic characterization and magnetochemical
measurements
The complex 1 shows room temperature magnetic
moments of 1.43 BM. This value is characteristic of the
mononuclear complexes with low-spin rhenium(III) (d4)
ions in Oh field [62], and arises because of the large spin-
orbit coupling (xZ2500 cmK1) [63]. Due to the large spin-
orbit coupling, the recording of X-band ESR spectra of
solutions of these complexes is impossible even at 100 K.
The IR spectra of 1 and 2 are governed by the vibrations
of the phosphine ligand. The n(ChN) vibration is absent in
1, as already noted for other monomeric rhenium(III) nitrile
complexes [58–60]. However, the absence of the charac-
teristic strong n(ReaO) band at w970 cmK1 is a clear
indication that there is no oxo-Re(V) starting material left in
the sample 1. The IR spectrum of 2 exhibits strong band at
970 cmK1 assignable to n(ReaO) mode and strong band at
1740 cmK1 corresponding to n(NO). The value of n(NO)
corresponds to linear NO range of Haymore and Ibers
[n(NO) above 1620–1610 cmK1 were assigned to linear M–
N–O systems, while n(NO) below 1610 cmK1 were
assigned to bent M–N–O systems] [61].
3.5. Geometry and electronic structure
The geometries of [ReOBr3(dppe)] and [ReBr3
(NO)(dppe)] were optimized with the DFT method in
singlet and doublet state, respectively. Table 4 shows the
possible electronic configurations and spin multiplicities of
the [ReBr3(NO)(dppe)] complex. Doublet state agrees well
with the magnetic measurements for 2. The most important
Table 5
The energy and character of upper valence molecular orbitals for [ReBr3(NO)(dppe)] and [ReOBr3(dppe)]
MO
[Re(NO)Br3(dppe)]
[ReOBr3(dppe)]
a
Character
b
Character
Character
HOMO-12
HOMO-11
HOMO-10
HOMO-9
HOMO-8
HOMO-7
HOMO-6
HOMO-5
HOMO-4
HOMO-3
HOMO-2
HOMO-1
HOMO
K7.465
K7.444
K7.345
K7.180
K7.111
K7.057
K6.981
K6.611
K6.306
K6.250
K6.119
K6.020
K5.872
K1.603
p(Ph)
K7.481
K7.465
K7.388
K7.327
K7.153
K7.096
K7.036
K6.956
K6.262
K6.224
K6.167
K6.094
K6.008
K3.673
p(Ph), n(P)
p(Ph)
K7.479
K7.364
K7.285
K7.221
K7.169
K7.087
K6.999
K6.779
K6.670
K6.366
K6.240
K6.099
K5.765
K2.991
p(Ph)
p(Ph)
p(Ph), n(P)
p(Ph)
p(Ph)
p(Ph), n(P)
p(Ph)
p(Ph)
p(Ph)
p(Ph)
p(Ph)
p(Ph)
p(Ph)
p(Ph), n(P)
p(Ph), n(P)
p(Br)
p(Ph)
p(Ph), n(P)
p(Ph), n(P)
p(Br)
p(Ph), n(P)
p(Br), p(O), n(P)
p(Br), p(O), n(P)
p(Br)
dxzCp*(NO); p(Br)
dyzCp*(NO); p(Br)
p(Br)
dxzCp*(NO); p(Br)
dyzCp*(NO); p(Br)
p(Br)
p(Br)
p(Br)
p(Br)
dxyCs*(P)Kp(Br)
dx2Ky2Ks(Br)Ks(P),
p*(NO)
p(Br)
dxyCs*(P)Kp(Br)
dxyKp(Br)
dxzKp(O)
LUMO
LUMOC1
LUMOC2
LUMOC3
K1.551
K1.439
K1.208
p*(NO)Kdxz
p*(NO)Kdyz
px(P)Cp*(Ph)
K1.560
K1.521
K1.379
p*(NO)Kdxz
p*(NO)Kdyz
dx2Ky2Ks(Br)Ks(P),
p*(NO)
K2.868
K1.549
K1.168
dyzKp(O)
dx2Ky2Ks(Br)Ks(P)
px(P)C p*(Ph)
LUMOC4
LUMOC5
LUMOC6
K1.180
K1.104
K0.703
py(P)C p*(Ph)
dz2Ks(Br)Ks(N)
s*(PKPh)
K1.167
K1.112
K1.056
px(P)C p*(Ph)
K1.161
K1.042
K0.548
py(P)C p*(Ph)
py(P)C p*(Ph)
s*(PKPh), d2zKs(Br)K
s(O)
p*(Ph)
s*(PKPh), d2zK
s(Br)Ks(N)
p*(Ph)
p*(Ph)
LUMOC7
LUMOC8
LUMOC9
LUMOC10
K0.538
K0.390
K0.318
K0.206
p*(Ph)
p*(Ph)
p*(Ph)
K0.695
K0.528
K0.368
K0.305
K0.499
K0.464
K0.360
K0.293
p*(Ph)
p*(Ph)
p*(Ph)
p*(Ph)
p*(Ph)
p*(Ph)
p*(Ph)
p*(Ph), dx2Ky2K
s(Br)Ks(P)
dz2Ks(Br)Ks(N)
LUMOC11
K0.169
K0.143
dx2Ky2Ks(Br)Ks(P),
p*(Ph)
0.072
dz2Ks(Br)Ks(O)

B. Machura et al. / Journal of Molecular Structure 740 (2005) 107–117
113
optimized bond lengths and angles for the [ReOBr3(dppe)]
and [ReBr3(NO)(dppe)] are reported in Table 3. For
[ReOBr3(dppe)] there is a good accordance of the
experimental data [64] with the calculated bond lengths
and angles. Some differences between the experimental and
calculated data can be noticed for the nitrosyl complex.
However, the disagreement results mainly from the nitrosyl/
oxo compositional disorder in 2. High electronic density
along the Re–O axis in [ReOBr3(dppe)] strongly influences
the positions of the adjacent bromine atoms, which are
pushed away. This feature causes a strong deviation from
linearity of the O–Re–Br(1) sequence. The elongation of
Re–Br(1) in comparison with Re(1)–Br(2) and Re(1)–Br(3)
bond lengths, determined by the presence of the oxygen
atom or nitrosyl group in trans position, is reproduced in the
optimized structures.
present the p-bonding interaction between dyz and dxz metal
orbitals and p* NO orbitals. However, the structure of these
orbitals is a little more complicated—in all them the lone
pair orbitals of bromine with p character have contribution.
The LUMOC1, LUMOC2 with a-spiꢀn and LUMOC1,
LUMOC2 with b-spin are of the pReꢁNO antibonding
character.
The dxy rhenium orbital and p orbitals of bromine
ligands in anti-bonding arrangement make main contri-
butions into the HOMO with a-spin and LUMO with b-spin.
The HOMO with b-spin is localised on the bromine ligand
in trans position to NO group.
The LUMO with a-spin and LUMOC3 with b-spin are
of dx2–y2KsBrKsP character with the contribution of pNꢀO
.
The selected HOMO and LUMO orbitals of the oxo
complex are depicted in Fig. 4.
The rhenium–oxygen interaction in [ReOBr3(dppe)] is
described as a triple bond. The p bonds arise from overlap of
the two occupied oxygen pp orbitals with the empty dxz and
dyz metal orbitals. The HOMO-34 and HOMO-33 of
[ReOBr3(dppe)] are of pRehO bonding character, whereas
the LUMO and LUMOC1 are ascribed as p-antibonding
rhenium–oxygen molecular orbitals. The HOMO is formed
by antibonding interaction between dxy rhenium orbital and
the lone pair orbitals of two bromineligands with p chatacter.
The energies and characters of the several HOMO and
LUMO orbitals of [ReBr3(NO)(dppe)] and [ReOBr3(dppe)]
are presented in Table 5. The selected HOMO and LUMO
orbitals of the nitrosyl complex with a spin are depicted in
Fig. 3. The z axis goes along the Br(1)–Re–N(1) linkage and
Br(1)–Re–O(2) in [ReBr3(NO)(dppe)] and ReOBr3(dppe)],
respectively. Due to the presence of dppe in the coordination
sphere, most of the MOs have complicated character.
The bonding of NO to the rhenium centre involves a
synergic interaction between the NO ligand orbitals and the
metal orbitals. The Re–NO bond consists of two com-
ponents: (i) a donation of electron density from a s-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 NO ligand. The HOMO-1,
HOMO-3 with a-spin and HOMO-3, HOMO-2 with b-spin
3.6. Electronic spectra
The electronic spectra of [ReOBr3(dppe)] and 2 are
presented in Fig. 5. The calculated electronic transitions of
[ReOBr3(dppe)] and [ReBr3(NO)(dppe)] and the exper-
imental absorption bands of the oxo-complex are gathered
Fig. 3. The selected HOMO and LUMO orbitals with a-spin for [ReBr3(NO)(dppe)].

114
B. Machura et al. / Journal of Molecular Structure 740 (2005) 107–117
Fig. 4. The selected HOMO and LUMO orbitals for [ReOBr3(dppe)].
in Tables 6 and 7, respectively. Except for the low energy
part of the spectra, only transitions with oscillator strengths
larger than 0.01 are listed. The assignment of the calculated
transitions to the experimental bands was based on the
criterion of the energy and oscillator strengths of the
calculated transitions. The longest wavelength experimental
bands are of low intensity and they are compared to the
calculated long-wave transitions with small oscillator
strengths. The remaining absorption experimental bands
are of much higher intensity and they are compared to the
calculated transitions with high oscillator strengths.
The longest wavelength experimental bands of
[ReOBr3(dppe)] at 640 and 535 nm may be attributed to
the calculated transitions of d/d character at 776.4 and
406.5 nm, respectively. The calculated at 453.5 nm elec-
tronic transition of pBr/d origin makes contribution into
the second of them. Basing on the CFT theory, three spin-
allowed singlet–singlet d/d transitions may be predicted
1
1
for d2 configuration in Oh field: A1/1E, A1/1A2 and
1A1/1B2. The third d/d transition of [ReOBr3(dppe)]
was calculated at higher energy—at 250.7 nm.
The experimental band at 354 nm is very broad (Fig. 5)
and it can be ascribed to the calculated transitions in the
range 392–275 nm with p(Br)/p(O)/n(P)/d character
(LMCT transitions). The most intense experimental
band at 242.8 nm is attributed to the calculated transitions
in the range 270–240 nm. These transitions are of LMCT
(pPh/d), MLCT (d/pꢀPh) and LLCT (pBr /pPꢀh)
Fig. 5. The electronic absorption spectra of [ReOBr3(dppe)] (a) and 2 (b).

B. Machura et al. / Journal of Molecular Structure 740 (2005) 107–117
115
Table 6
The energy and molar absorption coefficients of experimental absorption bands and the electronic transitions calculated with the TDDFT method for
[ReOBr3(dppe)]
The most important
orbital excitations
Character
l (nm)
E (eV)
f
Experimental L (nm)
(E (eV))3
H/LC1
HK3/LC1
H/LC2
d/d
p (Br)/d
d/d
p(Br), p(O), n(P)/d
p(Br), p(O), n(P)/d
p (Br)/ d
776.4
453.8
406.5
392.4
1.60
2.73
3.05
3.16
0.0001
0.0173
0.0301
0.0383
640.0(1.94)30
535.0(2.32)250
HK5/L
354.0(3.50)8965
HK4/LC1
HK15/LC1
HK17/L
299.3
282.5
4.14
4.39
0.0186
0.0175
s(Br)/d
HK4/LC2
HK5/LC2
HK5/LC2
HK2/LC3
HK2/LC5
HK3/LC5
HK17/LC1
H/LC7
H/LC6
H/LC7
HK6/LC2
H/LC9
HK7/LC2
H/LC11
p(Br), p(O), n(P)/d
p(Br), p(O), n(P)/d
p(Br), p(O), n(P)/d
p (Br)/ p*(Ph)
p (Br)/ p*(Ph))
p (Br)/ p*(Ph)
s(Br)/d
279.8
277.6
276.6
4.43
4.47
4.48
0.0172
0.0200
0.0529
242.8(5.11)24185
270.0
267.8
4.59
4.63
0.0104
0.0237
d/p*(Ph)
d/p*(Ph)
d/p*(Ph)
p (Ph)/d
d/p*(Ph)
p (Ph)/d
d/d
p(Br), p(O), n(P)/
p*(Ph)
265.7
254.5
250.7
249.9
248.5
4.67
4.87
4.94
4.96
4.99
0.0102
0.0117
0.0265
0.0160
0.0381
HK4/LC3
HK8/LC2
HK4/LC5
p (Ph)/d
p(Br), p(O), n(P)/
p*(Ph)
p (Br)/p*(Ph)
p (Br)/p*(Ph)
HK1/LC6
HK1/LC7
247.9
5.00
0.0139
character. The transitions from metal to pꢀPh orbitals and
from pPh orbitals to metal are mediated by phosphorus
orbitals, whereas the LLCT transitions (pBr /pꢀPh)—by
phosphorus and rhenium orbitals.
559.3 nm can be assigned to the transition of d/d origin in
[ReOBr3(dppe)] and the transition of pBr/d character (at
691.2 nm) in [Re(NO)Br3(dppe)]. The second experimental
band of 2 corresponds to d/pꢀNO charge transfers
transitions in [Re(NO)Br3(dppe)], the oxocomplex does
not show the absorption band in this range.
The experimental bands of 2 at 457.6 and 352.8 nm are of
The UV–vis spectrum of 2 exhibits four broad absorption
bands at 559.3(1070), 457.6(2980), 352.8(5440) and
232.8 nm(42250) (Fig. 5). The lowest energy band of 2 at
Table 7
The electronic transitions calculated with the TDDFT method for [ReBr3(NO)(dppe)]
The most import-
ant a-spin orbital
excitations
Character
The most import-
ant b-spin orbital
excitations
Character
l (nm)
E (eV)
f
H-4/L
HK3/LC2
p (Br)/d
dxz /pꢀNO
691.2
520.3
1.79
2.38
0.0291
0.0041
HK4/LC1
HK3/LC2
dxz /pꢀNO
dyz /pꢀNO
HK5/L
HK10/L
HK9/L
p(Ph), n(P)/d
p(Ph), n(P)/d
p (Ph)/d
484.8
462.6
2.56
2.68
0.0047
0.0238
H/L
d/d
424.9
417.5
405.6
382.4
362.1
357.8
318.5
313.4
312.7
2.92
2.97
3.06
3.24
3.42
3.47
3.89
3.96
3.97
0.0034
0.0107
0.0124
0.0014
0.0054
0.0035
0.0145
0.0029
0.0019
HK13/L
HK16/L
p (Br)/d
s(Br)/d
H/L
H/LC2
d/d
dxy /pꢀNO
HK18/L
HK17/L
HK1/LC1
s(Br)/d
s(Br)/d
pðBrÞ/pꢀNO
HK4/LC2
HK2/LC3
dxz /pꢀNO
dyz /pꢀNO

116
B. Machura et al. / Journal of Molecular Structure 740 (2005) 107–117
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4. Supplementary data
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the depositions numbers: 235798 ([ReBr3(MeCN)(dppe)])
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