Novel rhenium(III) complexes with 5,6-diphenyl-3-(2-pyridyl)-1,2,4-trazine: X-ray structures and DFT calculations for [ReCl3(OPPh3)(dppt)] and [ReCl3(PPh3)(dppt)] complexes

Article abstract of DOI:10.1016/j.poly.2007.05.053

The reaction of [ReOCl₃(PPh₃)₂] with 5,6-diphenyl-3-(2-pyridyl)-1,2,4-trazine (dppt) has been examined and [ReCl₃(OPPh₃)(dppt)] has been obtained. The triphenylphosphine oxide can be easily replaced b

Full text of DOI:10.1016/j.poly.2007.05.053

Polyhedron 26 (2007) 4427–4435
www.elsevier.com/locate/poly
Novel rhenium(III) complexes with
5,6-diphenyl-3-(2-pyridyl)-1,2,4-trazine: X-ray structures
and DFT calculations for [ReCl3(OPPh3)(dppt)]
and [ReCl3(PPh3)(dppt)] complexes
a,
b
c
d
d
*
´
B. Machura , R. Kruszynski , J. Kusz , J. Kłak , J. Mrozinski
a
Department of Inorganic and Coordination Chemistry, Institute of Chemistry, University of Silesia, 9th Szkolna Street, 40-006 Katowice, Poland
b
Department of X-ray Crystallography and Crystal Chemistry, Institute of General and Ecological Chemistry, Lodz University of Technology,
_
116 Zeromski Street, 90-924 Ło´dz´, Poland
c
Institute of Physics, University of Silesia, 4th Uniwersytecka Street, 40-006 Katowice, Poland
Faculty of Chemistry, Wroclaw University, F. Joliot-Curie 14 Street, 50-383 Wrocław, Poland
d
Received 20 March 2007; accepted 31 May 2007
Available online 15 June 2007
Abstract
The reaction of [ReOCl3(PPh3)2] with 5,6-diphenyl-3-(2-pyridyl)-1,2,4-trazine (dppt) has been examined and [ReCl3(OPPh3)(dppt)]
has been obtained. The triphenylphosphine oxide can be easily replaced by PPh3 in the reaction of [ReCl3(OPPh3)(dppt)] with an excess
of triphenylphosphine. The [ReCl3(OPPh3)(dppt)] and [ReCl3(PPh3)(dppt)] complexes have been structurally and spectroscopically char-
acterized. Their molecular orbital diagrams have been calculated with the density functional theory (DFT) method, and their electronic
spectra have been discussed on the basis of time-dependent DFT calculations. The compound [ReCl3(OPPh3)(dppt)] has been studied
additionally by magnetic measurement. The magnetic behavior is characteristic of mononuclear complexes with d4 low-spin octahedral
Re(III) complexes (3T1g ground state) and arise because of the large spin–orbit coupling (f = 2500 cmꢀ1), which gives diamagnetic
ground state.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Rhenium complexes; 6-Diphenyl-3-(2-pyridyl)-1,2,4-trazine; X-ray and electronic structure; DFT calculations; Magnetic measurement
1. Introduction
and biological importance, including olefin epoxidation
and catalysis by cytochrome P-450 [1–3].
For many years inorganic compounds containing an
oxygen atom multiply bonding to a transition metal have
been in the centre of interest to those scientists engaged
in basic research and to those trying to employ these com-
plexes in catalytic processes. Oxygen atom transfer chemis-
try has been implicated in various reactions of industrial
The chemistry of oxo rhenium complexes arouses partic-
ular interest among these compounds. It results from the
favourable nuclear properties of 186Re and 188Re nuclides,
which make the radioisotopes useful for diagnostic nuclear
medicine and applications in radioimmunotheraphy [4,5].
In this context, the design, synthesis and reactivity of
rhenium oxocomplexes has become the aim of several lab-
oratories, including ours.
Previously, we investigated the reactivity of oxorhe-
nium(V) species – [ReO(OEt)X2(PPh3)2], [ReOX3(PPh3)2]
and [ReOX3(AsPh3)(OAsPh3)] (X = Cl or Br) – towards
pyrazole, 3,5-dimethylopyrazole and benzotriazole [6].
*
Corresponding author.
E-mail addresses: basia@ich.us.edu.pl (B. Machura), rafal.kruszynski@
´
p.lodz.pl (R. Kruszynski), jmroz@wchuwr.chem.uni.wroc.pl (J. Mrozinski).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.05.053

4428
B. Machura et al. / Polyhedron 26 (2007) 4427–4435
In this report we focus on the examination of the reaction
of [ReOCl3(PPh3)2] with 5,6-diphenyl-3-(2-pyridyl)-1,2,4-
trazine (dppt). The isolated [ReCl3(OPPh3)(dppt)] complex
easily reacts with an excess of triphenylphosphine to give
[ReCl3(PPh3)(dppt)]. The last one can be also prepared in
the reaction of [ReCl3(MeCN)(PPh3)2] with 5,6-diphenyl-
3-(2-pyridyl)-1,2,4-trazine. Here we present spectroscopic
characterization, crystal, molecular and electronic struc-
ture of [ReCl3(OPPh3)(dppt)] (1) and [ReCl3(PPh3)(dppt)]
(2) complexes. The molecular orbital diagrams of 1 and 2
have been calculated with the density functional theory
(DFT) method. Currently density functional theory
(DFT) is commonly used to examine the electronic struc-
ture of transition metal complexes. It meets with the
requirements of being accurate, easy to use and fast enough
to allow the study of relatively large molecules of transition
metal complexes [7]. The electronic spectra of 1 and 2 have
been discussed on the basis of time-dependent DFT calcu-
lations. Recent studies have supported the TD-DFT
method to be applicable for open- and closed-shell of 5d-
metal complexes (including rhenium complexes) giving
good assignment of experimental spectra [8–10].
2.3. Preparation of [ReCl3(PPh3)(dppt)] (2)
Method A: To a solution of complex 1 (0.20 g,
0.23 mmol) in chloroform (20 ml), PPh3 (0.24 g,
0.92 mmol) was added and the solution was refluxed for
1 h. The solvent was then removed under reduced pressure.
The precipitate was washed several times with ethanol and
hexane, and finally dried in vacuo. The crystals of 2 suitable
for X-ray investigation were obtained by recrystallization
from chloroform (yield 95%).
Method B: [Re(MeCN)Cl3(PPh3)2] (0.5 g, 0.58 mmol)
and dppt (0.19 g, 0.61 mmol) in chloroform (40 cm3) were
refluxed for 4 h. The starting material gradually dissolved
and the colour of the reaction solution became dark red.
The volume was condensed to 10 cm3, diethyl ether
(100 cm3) was added and dark violet microcrystalline solid
was filtered. The product was washed with EtOH and cold
ether, and dried in vacuo (yield 90%).
IR (KBr; m/cmꢀ1): 1599(m), 1572(w) and 1507 (w) mCN
and mC@C
.
Anal. Calc. for C38H29Cl3N4PRe: C, 52.75; H, 3.38; N,
6.48. Found: C, 52.62; H, 3.45; N, 6.37%.
2. Experimental
2.4. Crystal structures determination and refinement
2.1. General procedure
The X-ray intensity data of 1 Æ CH2Cl2 and 2 were col-
lected on a KM-4-CCD automatic diffractometer equipped
with CCD detector and graphite-monochromated Mo Ka
The reagents used to the synthesis were commercially
available and were used without further purification. The
[ReOCl3(PPh3)2] complex was prepared according to the
literature method [11].
IR spectra were recorded on a Nicolet Magna 560 spec-
trophotometer in the spectral range 4000-400 cmꢀ1 with
the samples in the form of KBr pellets. Electronic spectra
were measured on a spectrophotometer Lab Alliance
UV–VIS 8500 in the range 1000–200 nm in chloroform
solution. Elemental analyses (C, H, N) were performed
on a Perkin–Elmer CHN-2400 analyzer.
˚
radiation (k = 0.71073 A) at room temperature. Details
concerning crystal data and refinement are given in Table 1.
Lorentz polarization and absorption correction [12] were
applied. The structures were solved by the Patterson
method and subsequently completed by the difference Fou-
rier recycling. All the non-hydrogen atoms were refined
anisotropically using full-matrix, least-squares technique.
The hydrogen atoms were treated as ‘‘riding’’ on their par-
ent carbon atoms and assigned isotropic temperature fac-
tors equal 1.2 times the value of equivalent temperature
factor of the parent atom. SHELXS-97 [13], SHELXL-97 [14]
and SHELXTL [15] programs were used for all the calcula-
tions. Atomic scattering factors were those incorporated
in the computer programs.
2.2. Preparation of [ReCl3(OPPh3)(dppt)] Æ CH2Cl2
(1 Æ CH2Cl2)
To a solution of [ReOCl3(PPh3)2] (0.50 g, 0.6 mmol) in
30 ml dichloromethane was added 0.19 g (0.61 mmol) of
5,6-diphenyl-3-(2-pyridyl)-1,2,4-trazine (dppt). The result-
ing solution was magnetically stirred for 2 h at room tem-
perature, and during this time the colour changed from
light green to violet. 20 ml of CH2Cl2 was distilled off
and 50 ml of diethyl ether was added. [ReCl3(OPPh3)-
(dppt)] Æ CH2Cl2 was filtered off, washed with ethanol,
diethyl ether and dried (yield 90%). The dark violet crystals
of 1 Æ CH2Cl2 for X-ray investigation were obtained by
recrystallization from dichloromethane.
2.5. Computational details
GAUSSIAN-03 program [16] was used in the calculations.
The geometry optimizations of 1 and 2 were carried out
with the DFT method with the use of B3LYP functional
[17,18]. The electronic spectra of 1 and 2 were calculated
with the TD-DFT method [19]. The calculations were per-
formed by using ECP basis set on the rhenium atom, the
standard 6-31+G** basis for chlorine, oxygen, and nitro-
gen, 6-31G* for carbon and 6-31G for hydrogen atoms.
The Xe core electrons of Re were replaced by an effective
core potential and DZ quality Hay and Wadt Los Alamos
ECP basis set (LANL2DZ) [20] was used for the valence
electrons. Additional d function with exponent a = 0.3811
IR (KBr; m/cmꢀ1): 1601 (m), 1590(m) and 1504 (m) mCN
and mC@C; 1141(s) and 1115(s) mP@O
.
Anal. Calc. for C39H31Cl5N4OPRe: C, 48.48; H, 3.23; N,
5.80. Found: C, 48.60; H, 3.18; N, 5.85%.

B. Machura et al. / Polyhedron 26 (2007) 4427–4435
4429
Table 1
Crystal data and structure refinement for complexes 1 and 2
3. Results and discussion
Compound
1 Æ CH2Cl2
39H31Cl5N4OPRe
2
3.1. Preparation and infrared data
Empirical formula
Formula weight
Temperature (K)
C
C38H29Cl3N4PRe
865.17
295(2)
0.71073
monoclinic
P21/c
966.10
The [ReCl3(dppt)(OPPh3)] (1) complex has been pre-
pared in good yield in the reaction of [ReOCl3(PPh3)2] with
5,6-diphenyl-3-(2-pyridyl)-1,2,4-trazine (dppt) in dichloro-
methane:
291.0(3)
0.71073
monoclinic
P21/c
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions
˚
[ReOCl3(PPh3)2] + dppt ! [ReCl3(dppt)(OPPh3)] + PPh3
a (A)
9.7664(4)
18.9933(8)
21.7652(8)
94.151(3)
4026.8(3)
4
10.2122(4)
12.1143(3)
28.2982(12)
90.834(3)
3500.5(2)
4
˚
b (A)
˚
c (A)
It can be supposed that the [ReOCl3(dppt)] oxocompound,
formed in the first step reaction, is an oxidant transferring
an oxygen atom to PPh3. The oxygen atom transfer is be-
lieved to proceed via initial nucleophilic attack on the
Re„O p* orbitals, the p acidity of the dppt ligand facili-
tates the attack of triphenylphosphine [22]. The produced
triphenylphosphine oxide remains bonded to the reduced
rhenium ion in complex 1. Many instances of formation of
phosphine oxides from ReVO and tertiary phosphines can
be given, but examples when the phosphine oxide remain
firmly bonded to the reduced metal centre are rare [22–25].
The complex 1 easily reacts with an excess of PPh3 to give
[ReCl3(dppt)(PPh3)] (2). The last one has been also isolated
in the reaction of [ReCl3(MeCN)(PPh3)2] with dppt.
The elemental analyses of the 1 Æ CH2Cl2 and 2 com-
plexes are in good agreement with their formulation. The
characteristic bands corresponding to the m(CN), m(C@C)
modes of the dppt ligand appear in the range 1610-
1500 cmꢀ1in the IR spectrum of 1 and 2. The absence of
the characteristic strong m(Re@O) band at ꢁ980 cmꢀ1 is
clear indication that there is no oxo-Re(V) starting material
left in the samples 1 and 2. The strong bands at 1141 and
1115 cmꢀ1 in the IR spectrum of 1 confirm the presence
of the coordinated OPPh3 molecule [26].
b (ꢁ)
Volume (A )
3
˚
Z
Dcalc (Mg/m3)
Absorption coefficient
(mmꢀ1
1.594
3.425
1.642
3.780
)
F(000)
1904
0.13 · 0.28 · 0.50
2.91–25.11
1704
0.03 · 0.08 · 0.30
2.97–25.00
Crystal size (mm)
h Range for data
collection (ꢁ)
Index ranges
ꢀ11 6 h 6 11,
ꢀ22 6 k 6 22,
ꢀ25 6 l 6 25
42201
ꢀ11 6 h 6 6,
ꢀ14 6 k 6 7,
ꢀ26 6 l 6 33
10927
Reflections collected
Independent reflections 7169 (0.0575)
(Rint
Completeness to 2h (%) 99.5
Maximum and
minimum
transmission
Data/restraints/
parameters
Goodness-of-fit on F2
Final R indices
[I > 2r(I)]
6168 (0.0374)
)
99.9
0.888 and 0.711
0.586 and 0.260
7169/0/460
6168/0/424
1.116
0.893
R1 = 0.0338,
wR2 = 0.0788
R1 = 0.0389,
wR2 = 0.0815
1.358 and ꢀ0.803
R1 = 0.0279,
wR2 = 0.0439
R1 = 0.0555,
wR2 = 0.0462
1.013 and ꢀ0.815
R indices (all data)
Largest difference in
peak and hole
ꢀ3
˚
(e A
)
3.2. Crystal structures
The complex 1 crystallises as dichloromethane solvate
1 Æ CH2Cl2, and the dichloromethane molecule is not
bonded to any atom of the Re(III) complex. The structure
of 2 consist of discrete and well-separated [ReCl3(dppt)-
(PPh3)] monomers. Any intermolecular interactions with
enough strength to govern crystal packing or molecule con-
formation were not found in the structures of 1 and 2. Only
weak intramolecular and intermolecular hydrogen bonds
[25–27] were detected in crystals 1 and 2, and they are gath-
ered in Table 2.
The molecular structures of 1 and 2 are presented in
Figs. 1 and 2, respectively, and the selected bond distances
and angles are collected in Tables 3 and 4, respectively.
Both complexes show distorted octahedral geometry about
Re with the three chloride ions arranged in meridional fash-
ion in complex 1 and in facial configuration in complex 2.
The coordination polyhedron least squares planes are
inclined at 88.54(6)ꢁ, 82.95(11)ꢁ, and 74.58(13)ꢁ in
compound 1 and at 89.05(5)ꢁ, 86.90(8)ꢁ, and 87.87(5)ꢁ in
and f function with exponent a = 2.033 on the rhenium
atom were added.
2.6. Magnetic measurement
Magnetic measurements in the temperature range 1.8–
300 K were performed using a Quantum Design SQUID-
based MPMSXL-5-type magnetometer. The SQUID
magnetometer was calibrated with the palladium rod sam-
ple (Materials Research Corporation, measured purity
99.9985%). The superconducting magnet was generally
operated at a field strength ranging from 0 to 5 T. Mea-
surements were made at a magnetic field of 0.5 T. Correc-
tions are based on subtracting the sample – holder signal
and contribution vD estimated from the Pascal constants
[21] and equal – 425 · 10ꢀ6 cm3 molꢀ1 for complex
[ReCl3(OPPh3)(dppt)]. The effective magnetic moment
was calculated from the equation, leff = 2.83(vMT)1/2
(BM).

4430
B. Machura et al. / Polyhedron 26 (2007) 4427–4435
Table 2
Hydrogen bonds for 1 and 2
compound 2 what shows that polyhedron distortion is dis-
tinctly smaller in compound 2. The OPPh3 ligand is pure
donor and PPh3P@O ! Re ! p*(dppt) interaction is sui-
ted to the meridional configuration. In the presence of
PPh3 the electronic situation is affected by p acidity of
the phosphine ligand. In complex 2, two good p acceptor,
dppt and PPh3, are coordinated to rhenium (III) centre,
and the back-bonding effect is maximized in the facial dis-
position which ensures minimum competition between the
two ligands for identical metal orbitals. It is significant that
the Re–N distances in 2 are longer than those in 1 where
the dppt ligand alone is available for back bonding. The
presence of Re–PPh3 back-bonding diminishes the demand
on p*(dppt) orbitals. Some differences are observed
between the Re–N(pyridine) and Re–N(triazine) bond
lengths in 1 and 2 complexes. It indicates different p acidity
strength of the two rings – the triazine ring favours p-back
donation from the rhenium ion. Nevertheless, the Re–N
bond lengths of both complexes are similar to those found
for the other rhenium(III) polypirydyl compounds: in
˚
˚
D
A
d(Hꢂ ꢂ ꢂA) (A)
d(Dꢂ ꢂ ꢂA) (A)
\D–Hꢂ ꢂ ꢂA (ꢁ)
Compound 1
C(6)
C(8)
C(30)
Cl(3)#1
Cl(1)#2
Cl(2)#3
2.81
2.80
2.77
3.467(4)
3.655(5)
3.593(7)
129.1
153.5
147.5
Compound 2
C(9) Cl(3)#4
2.73
3.562(6)
149.2
Symmetry codes: #1: 1 ꢀ x, ꢀy, ꢀz; #2: ꢀx, ꢀy, ꢀz; #3: ꢀ1 + x, y, z; #4:
ꢀx, y-1/2, ꢀz + 1/2.
˚
[ReCl2(bipy)2]PF6 – 2.094(5) and 2.096(5) A [27] and in
the [ReL(terpy)2]2+ (L = Cl, OH, NCS) complexes – about
˚
2.10 A [28]. These values are significantly shorter than
comparable distances for saturated amine complexes,
where metal-to-ligand p-back bonding is not possible, for
instance, the Re–NH2 distance in the [Re(N2)(ampy)-
(tbpy)(PPh3)]PF6 compound is 2.197(7) [29].
The Re–Cl(3) distance of 2 is affected by trans influence
of triphenylphospnie and is therefore longer than the Re–
Cl(1) and Re–Cl(2) bond lengths located in trans positions
to the dppt ligand. In both compounds the 3-(2-pyridyl)-
1,2,4-trazine moiety is close to planarity (maximum least
˚
˚
squares plane atom deviation of 0.073(3) A exists for
C(2) atom in compound 1 and of 0.122(3) A exists for
N(4) atom in compound 2). The dppt phenyl rings are
Fig. 1. The molecular structure of 1.
Fig. 2. The molecular structure of 2.

B. Machura et al. / Polyhedron 26 (2007) 4427–4435
4431
Table 3
The experimental and optimized bond lengths (A) and angles (ꢁ) for 1
˚
Bond lengths
Experimental
Optimized
Bond angles
Experimental
Optimized
Re(1)–O(1)
Re(1)–N(2)
Re(1)–N(4)
Re(1)–Cl(1)
Re(1)–Cl(2)
Re(1)–Cl(3)
2.054(3)
2.016(3)
2.068(3)
2.3664(11)
2.3900(11)
2.3856(11)
2.06
2.03
2.08
2.42
2.42
2.43
N(2)–Re(1)–O(1)
N(2)–Re(1)–N(4)
O(1)–Re(1)–N(4)
N(2)–Re(1)–Cl(1)
O(1)–Re(1)–Cl(1)
N(4)–Re(1)–Cl(1)
N(2)–Re(1)–Cl(3)
O(1)–Re(1)–Cl(3)
N(4)–Re(1)–Cl(3)
Cl(1)–Re(1)–Cl(3)
N(2)–Re(1)–Cl(2)
O(1)–Re(1)–Cl(2)
N(4)–Re(1)–Cl(2)
Cl(1)–Re(1)–Cl(2)
Cl(3)–Re(1)–Cl(2)
98.22(12)
76.94(12)
175.15(12)
90.34(9)
89.31(8)
90.95(9)
89.54(9)
86.32(8)
93.34(9)
175.57(4)
171.34(9)
90.43(9)
94.41(10)
89.57(4)
91.22(4)
96.26
77.18
173.38
90.32
90.00
90.91
89.78
87.09
91.95
177.09
171.97
91.76
94.79
90.03
90.27
Table 4
˚
The experimental and optimized bond lengths (A) and angles (ꢁ) for 2
Bond lengths
Experimental
Optimized
Bond angles
Experimental
Optimized
Re(1)–P(1)
Re(1)–N(2)
Re(1)–N(4)
Re(1)–Cl(1)
Re(1)–Cl(2)
Re(1)–Cl(3)
2.4505(11)
2.044(4)
2.117(4)
2.3600(13)
2.3386(14)
2.4009(10)
2.54
2.06
2.13
2.43
2.38
2.42
N(2)–Re(1)–N(4)
N(2)–Re(1)–Cl(2)
N(4)–Re(1)–Cl(2)
N(2)–Re(1)–Cl(1)
N(4)–Re(1)–Cl(1)
Cl(2)–Re(1)–Cl(1)
N(2)–Re(1)–Cl(3)
N(4)–Re(1)–Cl(3)
Cl(2)–Re(1)–Cl(3)
Cl(1)–Re(1)–Cl(3)
N(2)–Re(1)–P(1)
N(4)–Re(1)–P(1)
Cl(2)–Re(1)–P(1)
Cl(1)–Re(1)–P(1)
Cl(3)–Re(1)–P(1)
75.91(15)
95.36(11)
171.27(10)
168.43(11)
92.73(11)
95.98(5)
87.58(9)
88.48(9)
90.85(4)
89.95(4)
94.53(9)
91.24(9)
89.77(4)
87.82(4)
177.73(4)
76.26
94.28
170.52
168.39
92.18
97.26
87.97
86.20
92.85
90.21
96.73
94.45
87.28
85.09
175.27
inclined to the 3-(2-pyridyl)-1,2,4-trazine moiety at
presented in Tables 5 and 6. The selected HOMO and
LUMO orbitals of 1 and 2 with a spin are depicted in
Figs. 3 and 4. Among the highest occupied MOs of 1 and
2, the largest numbers constitute p orbitals of the dppt
and phenyl rings of PPh3 or OPPh3 with a contribution
from the Cl and O (for 1) atoms. For both 1 and 2, the
highest molecular orbital with a-spin can be represented
as a combination of p*Re–Cl, and pd*ppt, with predominant
involvement of the former component. The same character
have the HOMO orbitals with b-spin of 1 and 2, but con-
tribution of p orbitals of dppt ligand is considerable larger.
The H-2 and H-1 a molecular orbitals of 1 correspond to
combination of p*Re–Cl and p*Re–OPPh3 interaction, whereas
the H-2 and H-1 a molecular orbitals of 2 have p*Re–Cl char-
acter. To a large extent, the L + 1 and L + 3 b orbitals of 1
and L and L + 2 b orbitals of 2 are also formed by rhenium
dp atomic orbital (dxz, dyz or dxy). Among the lowest unoc-
cupied MOs of 1 and 2, the largest numbers constitute
p orbitals of the dppt and phenyl rings of PPh3 or OPPh3.
For both complexes the LUMO and LUMO + 1 with
a-spin have p*(dppt) character. The p* phenyl ring orbitals
37.95(16)ꢁ and 50.37(16)ꢁ in compound
32.37(13)ꢁ and 39.62(16)ꢁ in compound 2.
1 and at
3.3. Geometry optimization
The geometries of 1 and 2 were optimized in triplet and
singlet states using the DFT method with the B3LYP func-
tional. The energies of the singlet states are of 15.2 and
15.7 kcal/mol higher for 1 and 2, respectively. The opti-
mized geometric parameters of the triplet states are gath-
ered in Tables 3 and 4. In general, the predicted 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 experimental data are well repro-
duced in the calculations.
3.4. Molecular orbitals
The energies and characters of several highest occupied
and lowest unoccupied molecular orbitals of 1 and 2 are

4432
B. Machura et al. / Polyhedron 26 (2007) 4427–4435
Table 5
The energy and character of the selected molecular orbitals with a and b spins for 1
MOs with a spin
MOs with b spin
E (eV)
E (eV)
Character
xy(Re), p(Cl), p(O)
Character
HOMO ꢀ 2
HOMO ꢀ 1
HOMO
ꢀ6.065
ꢀ5.622
ꢀ5.399
ꢀ2.520
ꢀ2.331
ꢀ1.624
ꢀ1.471
d
ꢀ6.840
ꢀ6.475
ꢀ4.566
ꢀ2.754
ꢀ2.556
ꢀ2.359
ꢀ2.086
p(dppt), p(Cl)
p(Cl)
dxz(Re), p(Cl), p(O)
dyz(Re), p(Cl), p*(dppt)
p*(dppt)
dxz(Re), p(Cl), p*(dppt)
p*(dppt), dxz(Re)
dxy(Re), p(Cl), p(O)
p*(dppt), dxz(Re)
dyz(Re), p*(dppt)
LUMO
LUMO + 1
LUMO + 2
LUMO + 3
p*(dppt)
p*(PhOPPh3
p*(PhOPPh3
)
)
Table 6
The energy and character of the selected molecular orbitals with a and b spins for 2
MOs with a spin
MOs with b spin
E (eV)
E (eV)
Character
Character
HOMO ꢀ 2
HOMO ꢀ 1
HOMO
ꢀ5.721
ꢀ5.680
ꢀ5.515
ꢀ2.647
ꢀ2.411
ꢀ1.448
ꢀ1.098
d
d
xy(Re), p(Cl)
xz(Re), p(Cl)
ꢀ6.417
ꢀ6.403
ꢀ4.851
ꢀ2.904
ꢀ2.577
ꢀ2.467
ꢀ2.295
p(Cl), n(P)
p(Cl), n(P), p(PhPPh3
dyz(Re), p(Cl), p*(dppt)
dxz(Re), p*(dppt), p(Cl)
p*(dppt), dyz
)
dyz(Re), p(Cl)
p*(dppt)
p*(dppt)
p*(dppt)
p*(PhPPh3), dz2 ðReÞ
LUMO
LUMO + 1
LUMO + 2
LUMO + 3
dxy(Re), p(Cl)
p*(dppt), dyz
Fig. 3. The selected HOMO and LUMO orbitals with a-spin for 1. HOMO ꢀ 2 HOMO ꢀ 1 HOMO LUMO LUMO + 1 LUMO + 2.
of the triphenylphosphine or triphenylphosphine oxide
ligands participates in the higher unoccupied orbitals.
trum, only transitions with oscillator strengths larger than
0.020 are listed in Tables 7 and 8.
The investigated complexes are of large size; the num-
bers of basis functions are equal to 969 and 799 for 1
and 2, respectively. The calculated electron transitions
(110 and 100 for 1 and 2) do not comprise all the experi-
mental absorption bands. The UV–Vis spectrum was calcu-
lated to ꢁ290 nm for 1, and to 300 nm for complex 2. Thus
3.5. Electronic spectra
The spin-allowed triplet–triplet electronic transitions
calculated with the TD-DFT method for 1 and 2 are gath-
ered in Tables 7 and 8. For the high energy part of the spec-

B. Machura et al. / Polyhedron 26 (2007) 4427–4435
4433
Fig. 4. The selected HOMO and LUMO orbitals with a-spin for 2. HOMO ꢀ 2 HOMO ꢀ 1 HOMO LUMO LUMO + 1 LUMO + 2.
Table 7
The energy and molar absorption coefficients of experimental absorption bands and the electronic transitions calculated with the TD-DFT method for 1
The most important orbital excitations
Character
k (nm)
E (eV)
f
Experimental K (nm) (E (eV)) e
H(b) ! L + 3(b)
d ! d/p*(dppt)
929.2
1.33
0.0242
840.0 (1.48) 450
705.9 (1.76) 1150
H(a) ! L(a)
d ! p*(dppt)
d ! d/p*(dppt)
d ! p*(PhOPPh3
d ! p*(dppt)
d ! p*(dppt)
d ! p*(dppt)
575.6
514.6
2.15
2.41
0.0227
0.0586
H(b) ! L + 6(b)
H(b) ! L + 4(b)
H(a) ! L + 1(a)
H-1(a) ! L + 1(a)
H(b) ! L + 7(b)
H-5(b) ! L(b)
)
502.1
481.6
443.3
352.7
2.47
2.57
2.80
3.52
0.0736
0.0926
0.0216
0.0247
549.7 (2.26) 1700
420.8 (2.95) 1070
p(PhOPPh3)/p(Cl) ! p*(dppt)
H-1(a) ! L + 4(a)
H-1(b) ! L + 3(b)
H-3(a) ! L + 1(a)
H-6(b) ! L + 1(b)
H-1(b) ! L + 3(b)
H-1(a) ! L + 3(a) H(b) ! L + 14(b)
H-4(a) ! L(a)
d ! (PhOPPh3
)
p(Cl) ! d/p*(dppt)
p(Cl) ! p*(dppt)
345.8
342.9
334.0
3.59
3.62
3.71
0.0228
0.0618
0.0338
328.3 (3.78) 5380
p(PhOPPh3)/p(Cl) ! d
p(Cl) ! d/p*(dppt)
d ! p*(PhOPPh3
)
333.0
329.1
3.72
3.78
0.0315
0.0243
p(dppt)/p(Cl) ! p*(dppt)
H(a) ! L + 2(a)
H(b) ! L + 15(b)
H-1(a) ! L + 7(a)
d ! p*(PhOPPh3
d ! p*(PhOPPh3
d ! p*(PhOPPh3
)
)
)
321.5
292.9
3.86
4.23
0.0230
0.0210
274.0 (4.52) 9775
226.6 (5.47) 23650
e, molar absorption coefficient (dm3 molꢀ1 cmꢀ1); f, oscillator strength; H, highest occupied molecular orbital; L, lowest unoccupied molecular orbital.
the shortest wavelength experimental bands of 1 and 2 are
not assigned to the calculated transitions; some additional
intraligand and interligand transitions are expected to be
found at higher energies in the calculations for 1 and 2.
In the visible region (400–1000 nm), complexes 1 and 2
display multiple transitions of moderate intensity in the
form of peaks and shoulders. The longest wavelength
experimental band of 1 with maximum at 705.9 nm and
shoulder at 840 nm is very broad. It is assigned to the tran-
sition of d ! d/p*(dppt) character with relatively large
oscillator strength. The calculated transition (at
929.2 nm) lies in the low energy end of the experimental
band. For complex 2, two absorption bands are observed
in this range, and this arrangement is reproduced in the cal-
culations. The experimental bands of 2 at 998.9 and
674.1 nm are attributed to the d ! d/p*(dppt) transitions

4434
B. Machura et al. / Polyhedron 26 (2007) 4427–4435
Table 8
The energy and molar absorption coefficients of experimental absorption bands and the electronic transitions calculated with the TD-DFT method for 2
The most important orbital excitations
Character
k (nm)
E (eV)
f
Experimental K (nm) (E (eV)) e
H(b) ! L + 1(b)
H(b) ! L + 3(b)
H(a) ! L(a)
d ! d/p*(dppt)
976.3
806.0
562.0
505.1
486.4
431.9
370.3
1.27
1.54
2.21
2.45
2.55
2.87
3.35
0.0211
0.0137
0.0226
0.1167
0.0549
0.0225
0.0427
998.9 (1.24) 80
674.1 (1.84) 4400
d ! d/p*(dppt)
d ! d/p*(dppt)
H(a) ! L + 1(a)
H-1(a) ! L + 1(a)
H-5(b) ! L(b)
d ! d/p*(dppt)
520.3 (2.38) 5400
432.9 (2.86) 4750
d ! d/p*(dppt)
p(Cl)/p(PhPPh3)/p(dppt) ! d/p*(dppt)
p(Cl)/p(dppt) ! d/p*(dppt)
H-4(a) ! L + 1(a)
H-3(b) ! L(b)
H-7(a) ! L(a)
p(Cl)/p(PhPPh3)/p(dppt) ! d/p*(dppt)
356.6
354.6
3.48
3.50
0.0235
0.0363
H-5(a) ! L(a)
H-3(a) ! L + 1(a)
H-3(b) ! L + 1(b)
H-4(b) ! L + 1(b)
H-7(a) ! L(a)
p(Cl)/n(P)/p(PhPPh3) ! d/p*(dppt)
p(Cl)/p(dppt) ! d/p*(dppt)
p(Cl)/p(PhPPh3) ! d/p*(dppt)
p(Cl)/p(PhPPh3)/p(dppt) ! d/p*(dppt)
p(PhPPh3) ! d/p*(dppt)
345.2
340.5
337.3
3.59
3.64
3.68
0.0537
0.0474
0.0664
328.3 (3.78) 18240
H-6(a) ! L(a)
H-3(b) ! L + 3(b)
H-7(b) ! L + 1(b)
H-8(a) ! L(a)
p(Cl)/p(dppt) ! d/p*(dppt)
p(Cl)/p(dppt) ! d/p*(dppt)
p(dppt) ! d/p*(dppt)
317.6
316.1
3.90
3.92
0.0299
0.0250
H-12(b) ! L + 2(b)
H(a) ! L + 4(a)
p(Cl)/p(PPh3)/p(dppt) ! d
d ! p*(PhPPh3
)
300.0 (4.13) 23200
258.5 (4.80) 23680
228.2 (5.43) 38850
calculated at 976.3 and 806.0 nm. The same character
[d ! d/p*(dppt)] have the experimental absorption bands
at 549.7 nm for complex 1 and at 520.3 nm for complex
2. The observed shift of the d ! d/p*(dppt) bands to higher
energy in going from triphenylphosphine oxide (1) to tri-
phenylphosphine (2) coordination is consistent with the
stabilization of the t2g shell of complex 2 via back-bonding.
Some differences can be noticed in the assignment of the
experimental absorption bands at 420.8 nm and 432 nm for
1 and 2, respectively. The first one is assigned to the d ! d/
p*(dppt) transition, whereas the absorption band of com-
plex 2 corresponds to ligand–ligand charge transfer
(p(Cl)/p(PPh3)/p(dppt) ! d/p*(dppt)) transitions.
For both complexes the absorption bands below 400 nm
are attributed to metal–ligand charge transfer, ligand–
metal charge transfer and ligand–ligand charge transfer
and interligand (IL) transitions (Tables 7 and 8).
3.6. Magnetic properties
The magnetic properties of 1 complex under the form
leff versus T (leff the effective magnetic moment) is shown
in Fig. 5. The chloro-derivative of the rhenium(III) shows
room
temperature
magnetic
moment
2.01 BM
(0.502 cm3 molꢀ1 K). The magnetic moment of the solid
is temperature independent between 300 and 60 K. In the
temperature range 55–14 K it is observed only slightly
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.016
0.014
0.012
0.010
0.008
0.006
0.004
0.002
0.000
0.0
0
100
150
200
250
300
0
10000
20000
30000
40000
50000
T [K]
H [Oe]
Fig. 6. Field dependence of the magnetization for complex 1 at 2 K.
Fig. 5. Plots of the experimental effective magnetic moment leff (d) vs.
temperature for complex 1.

B. Machura et al. / Polyhedron 26 (2007) 4427–4435
[13] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467.
4435
magnetic anomaly and below 14 K the value of vM product
increases with temperature lowering. This behavior is char-
acteristic of mononuclear complexes with d4 low-spin
octahedral Re(III) complexes (3T1g ground state) [30–38]
and arise because of the large spin–orbit coupling
(f = 2500 cmꢀ1 [39]), which gives diamagnetic ground
state. It seems that in room temperature, in accordance
Boltzmann’s distribution, it is populated higher magnetic
state, which is depopulated with temperature lowering
and decreasing of the magnetic moment is observed.
The variation of the magnetization M versus the mag-
netic field H for complex 1 at 2 K is shown in Fig. 6. The
M versus H curve for complex very slowly increases and
indicates value of the magnetization near zero (0.014 BM)
at 5 T. Magnetization of the sample confirms that the
ground state is diamagnetic.
[14] G.M. Sheldrick, SHELXL-97: Program for the Refinement of Crystal
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Burant, J.M. Millam, S.S. Iyengar, J. Tomasi, V. Barone, B.
Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene,
X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, C. Adamo, J.
Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin,
R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma,
G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S.
Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D.
Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G.
Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A.
Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T.
Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challa-
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Gonzalez, J.A. Pople, GAUSSIAN-03, Revision B.03, Gaussian, Inc.,
Pittsburgh, PA, 2003.
4. Supplementary material
CCDC 640907 and 640908 contain the supplementary
crystallographic data for C39H31Cl5N4OPRe and
C38H29Cl3N4Pr. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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Acknowledgements
The GAUSSIAN-03 calculations were carried out in the
Wrocław Centre for Networking and Supercomputing,
WCSS, Wrocław, Poland. The work was supported by
the Polish Ministry of Science and Higher Education Grant
No. 1T09A12430.
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