Novel rhenium(III) complexes with the picolinate ligand: Synthesis, spectroscopic investigations, X-ray structures and DFT calculations for [ReX2(pic)(PPh3)2] complexes

Article abstract of DOI:10.1016/j.poly.2009.05.032

The paper presents a combined experimental and computational study of novel rhenium(III) complexes with the picolinate ligand - [ReCl₂(pic)(PPh₃)₂] (1) and [ReBr₂(pic)(PPh₃)₂] (2). Both complexes 1 and 2 have been characterised spectroscopically and structurally (by single-crystal X-ray diffraction). Complex 1 has been additionally studied by magnetic measurement. The magnetic behavior is characteristic of a mononuclear d⁴ low-spin octahedral Re(III) complex (³T_1g ground state) and arises because of the large spin-orbit coupling (ζ = 2500 cm^-1), which gives a diamagnetic ground state. DFT and time-dependent (TD)DFT calculations have been carried out for complex 1, and UV-vis spectra of the [ReX₂(pic)(PPh₃)₂] compounds have been discussed on this basis.

Full text of DOI:10.1016/j.poly.2009.05.032

Polyhedron 28 (2009) 2377–2384
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Polyhedron
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Novel rhenium(III) complexes with the picolinate ligand: Synthesis,
spectroscopic investigations, X-ray structures and DFT calculations
for [ReX2(pic)(PPh3)2] complexes
a
b
c
d
B. Machura a, , M. Wolff , R. Kruszynski , J. Mrozinski , J. Kusz
*
´
a Department of Crystallography, Institute of Chemistry, University of Silesia, 9th Szkolna St., 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 St., 90-924 Łódz, Poland
c Faculty of Chemistry, Wroclaw University, F. Joliot-Curie 14 St., 50-383 Wrocław, Poland
d Institute of Physics, University of Silesia, 4th Uniwersytecka St., 40-006 Katowice, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
The paper presents a combined experimental and computational study of novel rhenium(III) complexes
with the picolinate ligand – [ReCl2(pic)(PPh3)2] (1) and [ReBr2(pic)(PPh3)2] (2). Both complexes 1 and 2
have been characterised spectroscopically and structurally (by single-crystal X-ray diffraction). Complex
1 has been additionally studied by magnetic measurement. The magnetic behavior is characteristic of a
mononuclear d4 low-spin octahedral Re(III) complex (3T1g ground state) and arises because of the large
spin–orbit coupling (f = 2500 cmꢀ1), which gives a diamagnetic ground state. DFT and time-dependent
(TD)DFT calculations have been carried out for complex 1, and UV–vis spectra of the [ReX2(pic)(PPh3)2]
compounds have been discussed on this basis.
Received 24 March 2009
Accepted 1 May 2009
Available online 23 May 2009
Keywords:
Keywords
Rhenium complexes
Picolinate ligand
X-ray
Ó 2009 Elsevier Ltd. All rights reserved.
Electronic structure
DFT calculations, magnetic measurement
1. Introduction
[CH3ReO(pic)2] complex is an active precursor in olefin oxidation
and forms epoxides in a two-phase H2O2–H2O/CH2Cl2 system [10].
The coordination chemistry of rhenium is a field of current
growing interest from various viewpoints. The attention of scien-
tists concentrates on synthetic aspects, structural, physicochemical
properties and reactivity, as well as on topics with an applied char-
acter such as the development of radiotherapeutic cancer agents,
nitrogen fixation and catalysis [1]. The 186Re (1.07 MeV b-emitter,
t1/2 90 h) and 188Re (2.12 MeV b-emitter, t1/2 17 h) isotopes are
among the most attractive isotopes for applications in targeted
radionuclide therapy [2,3].
Generally, chelation of nitrogenous p
-acidic ligands to ReVO
facilitates the oxygen atom transfer to oxophilic substrates via
electron withdrawal from the metal [11]. In this context, the de-
sign, synthesis and reactivity of oxorhenium complexes has be-
come the aim of several laboratories, including ours.
Previously, we investigated the reactivity of [ReOX3(EPh3)2]
(X = Cl, Br; E = P or As) oxorhenium(V) species towards 1,10-phe-
nanthroline and 5,6-diphenyl-3-(2-pyridyl)-1,2,4-trazine. The
products of these reactions include both Re(V) oxocomplexes –
Diazenido and dinitrogen rhenium complexes are important in
view of their significance in the field of nitrogen fixation [4–6].
Methyltrioxorhenium is one of the most versatile catalysts for olefin
oxidation reactions, aldehyde olefination and olefin metathesis
[7,8]. The mer, trans-[ReOCl3(PPh3)2] and its derivatives catalyze
the oxidation of sulfides to sulfoxides, thiols to disulfides and cata-
lyze oxygen-transfer from sulfoxides to phosphines [8]. The [ReO-
Cl2(O–N)(PPh3)] chelates with pyridinecarboxylate ligands exhibit
a remarkable catalytic activity for the conversion of ethane to a mix-
ture of propionic and acetic acids in a single-pot process [9]. The
[ReOCl3(phen)] and Re(III) compounds
–
[ReCl2(phen)(P-
Ph3)2](ReO4)ꢁ½H2O, [ReCl3(OPPh3)(dppt)] [12,13]. In this report
we focus on the examination of the reactions of [ReOX3(PPh3)2]
with 1-(2-pyridylcarbonyl)benzotriazole. Potentially, 1-(2-pyridyl-
carbonyl)benzotriazole can bind to the metal center ion via one of
two modes: either through the two nitrogen atoms located in the
pyridine and triazole rings or through one pyridyl nitrogen and
the carbonyl oxygen (Scheme 1).
The reactions of [ReOX3(PPh3)2] with 1-(2-pyridylcarbonyl)ben-
zotriazole lead to novel Re(III) [ReX2(pic)(PPh3)2] complexes
(Scheme 2).
The 1-(2-pyridylcarbonyl)benzotriazole hydrolyzes in the reac-
tion with [ReOX3(PPh3)2], and the formed picolinic acid coordi-
nates to the rhenium ion. With much higher yield, however,
* 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. Mrozin´ ski).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.05.032

2378
B. Machura et al. / Polyhedron 28 (2009) 2377–2384
2.2.2. Method B
ReOCl3(PPh3)2] (0.50 g, 0.6 mmol) was added to picolinic acid
(0.075 g, 0.61 mmol) and PPh3 (0.30 g, 1.15 mmol) in ethanol
(100 ml) and the reaction mixture was refluxed for 4 h. The result-
ing reaction mixture was reduced in volume to ꢂ10 ml and al-
lowed to cool to room temperature. An orange crystalline
precipitate of 1 was filtered off and dried in air. Yield 80%.
IR (KBr;
and
m
/cmꢀ1): 1697 (vs) masymCO ; 1616 (m) and 1596 (w) mCN
2
m
C@C; 1288(s) masymCO .
2
Scheme 1. Structure of 1-(2-pyridylcarbonyl)benzotriazole.
Anal. Calc. for C42H34Cl2NO2P2Re: C, 55.82; H, 3.79; N, 1.55%.
Found: C, 55.61; H, 3.56; N, 1.72%.
PPh3
2.3. Preparation of [ReBr2(pic)(PPh3)2] (2)
A procedure similar to that for [ReCl2(pic)(PPh3)2] was used
with [ReOBr3(PPh3)2] (0.50 g, 0.52 mmol) and 1-(2-pyridylcar-
bonyl)benzotriazole (0.12 g, 0.53 mmol) in method A, and [Re-
OBr3(PPh3)2] (0.50 g, 0.52 mmol), picolinic acid (0.068 g,
0.55 mmol) and PPh3 (0.29 g, 1.10 mmol) in method B.
O
N
X
X
O
C
Re
IR (KBr;
and
m
/cmꢀ1): 1684 (vs) masymCO ; 1608 (m) and 1586 (w) mCN
2
m
C@C; 1281(s) masymCO .
PPh3
2
Anal. Calc. for C42H34Br2NO2P2Re: C, 50.82; H, 3.45; N, 1.41%.
Found: C, 50.59; H, 3.32; N, 1.34%.
Scheme 2. Structure of [ReCl2(pic)(PPh3)2]; X = Cl for 1 and X = Br for 2.
2.4. Crystal structure determination and refinement
[ReCl2(pic)(PPh3)2] (1) and [ReBr2(pic)(PPh3)2] (2) were isolated
from the reactions of [ReOX3(PPh3)2] with picolinic acid in the
presence of PPh3 in ethanol.
The X-ray intensity data of 1 and 2 were collected on a KM-4-
CCD automatic diffractometer equipped with a CCD detector and
graphite monochromated Mo Ka radiation (k = 0.71073 Å) at room
The molecular orbital diagram of 1 has been calculated with the
density functional theory (DFT) method. Currently the density
functional theory (DFT) is commonly used to examine the elec-
tronic structure of transition metal complexes. It meets with the
requirements of being accurate, easy to use and fast enough to al-
low the study of relatively large molecules of transition metal com-
plexes [14]. The electronic spectrum of 1 has been discussed on the
basis of the time-dependent DFT calculations. Recent studies have
supported the TDDFT method to be applicable for open- and
closed-shell 5d-metal complexes (including rhenium complexes),
giving good assignments of the experimental spectra [15–17].
temperature. Details concerning crystal data and refinement are gi-
ven in Table 1. Lorentz, polarization and absorption corrections
[19] were applied. The structures were solved by the Patterson
method and subsequently completed by difference Fourier recy-
cling. All the non-hydrogen atoms were refined anisotropically
using the full-matrix, least-squares technique. The hydrogen atoms
were treated as ‘‘riding” on their parent carbon atoms and assigned
isotropic temperature factors equal to 1.2 times the value of equiv-
alent temperature factor of the parent atom. SHELXS97 [20], SHELXL97
[21] and SHELXTL [22] programs were used for all the calculations.
Atomic scattering factors were those incorporated in the computer
programs.
2. Experimental
2.5. Computational details
2.1. General procedure
The gas phase geometry of 1 was optimized without any sym-
metry restrictions in the singlet and triplet ground-states with
the DFT method using the hybrid B3LYP functional of GAUSSIAN-03
[23–25]. The calculations were performed using the ECP basis set
LANL2DZ [26] with an additional d and f function with the exponent
The reagents used in the syntheses were commercially available
and were used without further purification. The [ReOX3(PPh3)2]
complexes were prepared according to the literature methods
[18]. IR spectra were recorded on a Nicolet Magna 560 spectropho-
tometer 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–
180 nm in acetonitrile solution. Elemental analyses (C, H, N) were
performed on a Perkin–Elmer CHN-2400 analyzer. The 1H NMR
spectrum was obtained in d6-DMSO using a Bruker Avance 400
spectrometer.
a
= 0.3811 and a = 2.033 [27] for rhenium and the standard 6-31G
basis set for the other atoms. For chloride, oxygen, nitrogen and
phosphorous atoms, diffuse and polarization functions were added
[28–33]. The vibrations in the calculated vibrational spectrum of 1
were real, thus the geometry corresponds to a true energy
minimum.
The electronic spectrum of 1 was calculated with the TDDFT
method, and the solvent effect (acetonitrile) was simulated using
the polarizable continuum model with the integral equation for-
malism (IEF-PCM) [34–37].
2.2. Preparation of [ReCl2(pic)(PPh3)2] (1)
2.2.1. Method A
[ReOCl3(PPh3)2] (0.50 g, 0.6 mmol) was added to 1-(2-pyridyl-
carbonyl)benzotriazole (0.135 g, 0.6 mmol) in ethanol (100 ml)
and the reaction mixture was refluxed for 4 h. The resulting reac-
tion mixture was reduced in volume to ꢂ10 ml and allowed to cool
to room temperature. An orange crystalline precipitate of 1 was fil-
tered off and dried in air. Yield 55%.
2.6. Magnetic measurement
Magnetic measurements of 1 in the temperature range 1.8–
300 K were performed using a Quantum Design SQUID-based
MPMSXL-5-tpe magnetometer. The superconducting magnet was
generally operated at a field strength ranging from 0 to 5 T.

B. Machura et al. / Polyhedron 28 (2009) 2377–2384
2379
Table 1
gand to Re(V), formation of [ReOCl2(pic)(PPh3)2] and subsequent
reduction of [ReOCl2(pic)(PPh3)2] to [ReCl3(pic)(PPh3)2]. The low
yield of [ReX2(pic)(PPh3)2] in the reactions of [ReOX3(PPh3)2] with
1-(2-pyridylcarbonyl)benzotriazole results from an insufficient
amount of PPh3.
With a much higher yield, compounds 1 and 2 were isolated
from the reactions of [ReOX3(PPh3)2] with picolinic acid in the
presence of PPh3. In this case, similar reaction models can be pos-
tulated. The more probable one seems to involve coordination of
the picolinate ligand to Re(V), formation of [ReOCl2(pic)(PPh3)2]
and subsequent reduction of [ReOCl2(pic)(PPh3)2] to [Re-
Cl3(pic)(PPh3)2]. It has been previously proven that [ReOCl3(PPh3)2]
easily reacts with picolinic acid to give [ReOCl2(pic)(PPh3)] [9].
However, the other reaction course involving reduction of Re(V)
to Re(III) followed by coordination of picolinate ion to the Re(III)
is also possible.
Crystal data and structure refinement for complexes 1 and 2.
1
2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C42H34Cl2NO2P2Re
903.74
293.0(2)
0.71073
orthorhombic
Abm2
C42H34Br2NO2P2Re
992.66
100(2)
0.71073
orthorhombic
Abm2
Unit cell dimensions
a (Å)
b (Å)
9.3610(2)
25.0585(10)
15.8943(6)
3728.4(2)
4
1.610
3.526
1792
9.3877(2)
24.7704(8)
15.8178(3)
3678.23(17)
4
c (Å)
Volume, Å3
Z
Density (calculated) (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
1.793
)
5.6011
1936
Crystal size, mm
h Range for data collection (°)
0.004 ꢃ 0.006 ꢃ 0.093 0.052 ꢃ 0.056 ꢃ 0.34
The IR spectra of 1 and 2 show features comparable to those of
mononuclear picolinato species [40]. The bands assigned to msym
1.63–25.04
3.06–25.03
(CO2) and m
as(CO2) appear at 1697 and 1288 cmꢀ1 for 1, and 1984
Index ranges
ꢀ11 6 h 6 11
ꢀ29 6 k 6 29
ꢀ15 6 l 6 18
18 291
ꢀ11 6 h 6 11
ꢀ29 6 k 6 29
ꢀ18 6l 6 11
12 642
and 1281 cmꢀ1 for 2. The value of
D
m(CO2) =
m
as(CO2) ꢀ
ms(CO2),
equal to ꢄ400 cmꢀ1 for the [ReX2(pic)(PPh3)2] compounds, con-
Reflections collected
firms a unidentate coordination mode of the carboxylate group.
Independent reflections
Completeness to 2h (%)
Max. and min. transmission
Data/restraints/parameters
Absolute structure parameter
Goodness-of-fit on F2
3131 (Rint = 0.0583)
100
2347 (Rint = 0.0243)
99.7
Characteristic bands corresponding to the m(CN) and m(C@C) modes
of the pic ligand appear in the range 1620–1550 cmꢀ1 [41]. The
0.990 and 0.971
3131/1*/244
ꢀ0.022(9)
0.751 and 0.688
2347/1*/244
0.002(6)
absence of the strong
indication that there is no oxo-Re(V) starting material left in the
m
(Re@O) band at ꢂ980 cmꢀ1 is a clear
1.088
1.042
samples of 1 and 2.
Final R indices [I > 2(I)]
R1 = 0.0292
wR2 = 0.0609
R1 = 0.0379
wR2 = 0.0777
R1 = 0.0147
wR2 = 0.0349
R1 = 0.0152
wR2 = 0.0349
0.632 and ꢀ0.452
The proton spectrum of 1 shows features comparable to those of
mononuclear Re(III) with tertiary phosphines. The 1H NMR signals
of 1 are relatively narrow due to short electron-spin relaxation
time of the Re(III) center, but the signals are spread over the
ppm range [42]. The ortho protons of two PPh3 coordinated mole-
cules appear as a doublet at 12.02 ppm, and they are downfield
from the meta and para protons (8.5–8.7 ppm). The three protons
of the picolinate ion appear as a triplet at 10.15 ppm and two dou-
blets at 7.13 and 6.81 ppm, respectively.
R indices (all data)
Largest difference in peak and hole 1.288 and ꢀ0.869
(e Åꢀ3
)
*
Restraint of floating origin.
Measurements were made at a magnetic field of 0.5 T. Corrections
are based on subtracting the sample-holder signal and the contri-
bution vD estimated from Pascal constants equals – 499 ꢃ 10ꢀ6
cm3molꢀ1 for complex 1. The effective magnetic moment was cal-
3.1. Crystal structures
culated from the equation, leff = 2.83(v
MT)1/2 (B.M.).
A definite proof for the structure is provided by the X-ray dif-
fraction results. The crystallographic data of the complexes 1 and
2 are summarized in Table 1. The [ReX2(pic)(PPh3)2] complexes
are isostructural, crystallise in the orthorhombic Abm2 space
group (No. 39) with rhenium, halogen and all the picolinate anion
atoms located on the special position c with site symmetry m. Thus
both the polyhedron ReCl2NO base and picolinate anion are planar
by symmetry.
3. Results and discussion
The [ReCl2(pic)(PPh3)2] (1) and [ReBr2(pic)(PPh3)2] (2) com-
plexes were first isolated from the reactions of [ReOX3(PPh3)2]
(X = Cl or Br) with 1-(2-pyridylcarbonyl)benzotriazole in ethanol.
Although mechanism of the reaction has not been examined in de-
tail, two reaction courses can be supposed.
The short intra- and intermolecular contacts, which can be clas-
sified as weak hydrogen bonds [43,44], are gathered in Table 2. The
The first one is thought to occur via reduction of [ReOX3(PPh3)2]
by triphenylphosphine and coordination of 1-(2-pyridylcar-
bonyl)benzotriazole to the Re(III) center. After the coordination
of 1-(2-pyridylcarbonyl)benzotriazole to the Re(III) ion, hydrolysis
of 1-(2-pyridylcarbonyl)benzotriazole occurs and the picolinic acid
formed coordinates to the Re(III) ion to give [ReCl2(pic)(PPh3)2],
whereas the benzotriazole remains uncoordinated. The oxygen
atom transfer is believed to proceed via initial nucleophilic attack
Table 2
Hydrogen bonds for 1 and 2.
D–Hꢁ ꢁ ꢁA
1
D–H
Hꢁ ꢁ ꢁA
Dꢁ ꢁ ꢁA
D–Hꢁ ꢁ ꢁA
C(2)–H(2)ꢁ ꢁ ꢁCl(1)
C(18)–H(18)ꢁ ꢁ ꢁO(1)
C(23)–H(23)ꢁ ꢁ ꢁCl(2)
2
C(2)–H(2)ꢁ ꢁ ꢁBr(1)
C(18)–H(18)ꢁ ꢁ ꢁO(1)
C(23)–H(23)ꢁ ꢁ ꢁBr(2)
C(20)–H(20)ꢁ ꢁ ꢁBr(2)#1
C(22)–H(22)ꢁ ꢁ ꢁO(2)#2
C(23)–H(23)ꢁ ꢁ ꢁBr(1)#3
0.93
0.93
0.93
2.66
2.36
2.80
3.479(8)
3.105(10)
3.378(11)
147.9
136.9
121.7
on the Re„O p
* orbitals, and many instances of formation of phos-
phine oxides from ReVO and tertiary phosphines can be given
[11,38,39]. The starting oxo complex is synthesised using a large
excess of triphenylphosphine and it can be impure with PPh3.
The [ReCl3(L-L)(PPh3)] complex with coordinated 1-(2-pyridylcar-
bonyl)benzotriazole (L-L) has not been isolated from the reaction,
but many instances of the formation of [ReCl3(L-L)(PPh3)] in re-
lated syntheses can be given [11,38,39].
0.93
0.93
0.93
0.93
0.93
0.93
2.71
2.31
2.83
2.83
2.54
2.77
3.548(4)
3.068(4)
3.450(6)
3.615(6)
3.320(7)
3.488(6)
149.8
138.9
125.2
142.4
141.5
135.1
Symmetry transformations used to generate equivalent atoms: #1 ꢀ1 + x, y, z; #2
ꢀx, y, 1/2 + z; #3 1ꢀx, y, 1/2 + z.
The second probable reaction model involves hydrolysis of 1-(2-
pyridylcarbonyl)benzotriazole, coordination of the picolinate li-

2380
B. Machura et al. / Polyhedron 28 (2009) 2377–2384
Table 4
hydrogen bonding scheme in the both structures is similar due to
the isostructurality, however, in 2 some more short contacts exist
due to the larger radius of the Br atom. The planar, in the range of
experimental error, phenyl rings of the PPh3 ligands are inclined at
62.4(3), 71.3(3), 81.5(3)° in 1 and at 61.23(3), 71.98(4), 81.25(3)° in
2. The O–C@O bonds of the carboxylate groups show significant
delocalization in both structures (the C(24)–O(1) distances are
1.264(18) and 1.292(8) Å, and the C(24)–O(2) distances are
1.22(2) and 1.248(9) Å, respectively, in 1 and 2).
The molecular structure of 1 is presented in Fig. 1, and selected
bond distances and angles of 1 and 2 are collected in Tables 3 and
4, respectively. The [ReX2(pic)(PPh3)2] complexes show a distorted
octahedral geometry about Re with bidentate N,O donors of the
picolinato ligand, two halide ions arranged in cis geometry and
two PPh3 molecules in trans arrangement.
The experimental and optimized bond lengths [Å] and angles [°] for 2.
Bond lengths
Experimental
Bond angles
Experimental
Re(1)–O(1)
Re(1)–N(2)
Re(1)–Br(1)
Re(1)–Br(2)
Re(1)–P(1)
2.044(4)
2.131(5)
2.5205(6)
2.4906(6)
2.4530(8)
O(1)–Re(1)–N(2)
O(1)–Re(1)–Br(2)
N(2)–Re(1)–Br(2)
O(1)–Re(1)–Br(1)
N(2)–Re(1)–Br(1)
Br(2)–Re(1)–Br(1)
O(1)–Re(1)–P(1)
N(2)–Re(1)–P(1)
Br(2)–Re(1)–P(1)
Br(1)–Re(1)–P(1)
P(1)–Re(1)–P(1)#1
76.20(15)
170.51(12)
94.31(14)
85.44(12)
161.65(14)
104.04(3)
93.99(2)
90.93(3)
86.06(3)
90.34(3)
172.03(5)
3.2. Magnetic properties
The magnetic properties of 1, in the form
effective magnetic moment) is shown in Fig. 2. The rhenium(III)
complex shows a room temperature magnetic moment of 1.68
B.M. The magnetic moment of the solid is temperature dependent
The bond lengths and angles of 1 and 2 do not differ signifi-
cantly from the expected values for related mononuclear rhenium
complexes [9]. The Re–Cl(1) bond trans to N is far longer than the
Re–Cl(2) bond trans to O, indicating a structural trans effect of the
pyridine ring.
l
eff versus T (leff is the
between 300 and 1.8 K and the value of the vMT product decreases
on lowering the temperature. This behavior is characteristic of
mononuclear d4 low-spin pseudo-octahedral Re(III) complexes
(3T1g ground state) [45–54] and arises because of the large spin–or-
bit coupling (f = 2500 cmꢀ1 [55]), which gives a diamagnetic
ground state. It seems that at room temperature, in accordance
1.6
1.2
0.8
0.4
0.0
0
50
100
150
T (K)
200
250
300
Fig. 2. Plots of experimental effective magnetic moment
l
eff (s) vs. temperature for
Fig. 1. The molecular structure of 1.
1.
Table 3
The experimental and optimized bond lengths [Å] and angles [°] for 1.
Bond lengths
Experimental
Optimized
Bond angles
Experimental
Optimized
Re(1)–O(1)
Re(1)–N(2)
Re(1)–Cl(1)
Re(1)–Cl(2)
Re(1)–P(1)
2.039(9)
2.143(10)
2.395(3)
2.347(3)
2.4572(16)
1.941
2.082
2.503
2.442
2.481
O(1)–Re(1)–N(2)
O(1)–Re(1)–Cl(2)
N(2)–Re(1)–Cl(2)
O(1)–Re(1)–Cl(1)
N(2)–Re(1)–Cl(1)
Cl(2)–Re(1)–Cl(1)
O(1)–Re(1)–P(1)
N(2)–Re(1)–P(1)
Cl(2)–Re(1)–P(1)
Cl(1)–Re(1)–P(1)
P(1)–Re(1)–P(1)#1
O(1)–Re(1)–P(1)#1
N(2)–Re(1)–P(1)#1
Cl(2)–Re(1)–P(1)#1
Cl(1)–Re(1)–P(1)#1
75.6(3)
169.7(3)
94.1(3)
76.20
168.47
92.27
95.51
171.71
96.02
91.16
94.46
89.72
85.61
171.09
91.70
94.46
89.72
85.61
87.6(3)
163.3(3)
102.66(15)
93.15(6)
91.01(7)
86.94(7)
89.90(9)
173.68(10)
93.15(6)
91.01(8)
86.94(7)
89.90(9)

B. Machura et al. / Polyhedron 28 (2009) 2377–2384
2381
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
Character
HOMOꢀ5
HOMOꢀ4
HOMOꢀ3
HOMOꢀ2
HOMOꢀ1
HOMO
ꢀ6.818
ꢀ6.779
ꢀ6.396
ꢀ6.139
ꢀ5.821
ꢀ5.818
ꢀ2.048
ꢀ1.246
ꢀ1.028
ꢀ0.969
ꢀ0.900
ꢀ0.811
p
p
p
(PPh3)
(PPh3)
(Cl), n(P)
ꢀ6.849
ꢀ6.820
ꢀ6.809
ꢀ6.776
ꢀ6.342
ꢀ5.298
ꢀ3.148
ꢀ2.482
ꢀ1.932
ꢀ1.239
ꢀ0.995
ꢀ0.891
p
p
p
p
p
(PPh3),
(PPh3)
(PPh3)
(PPh3)
p(Cl)
p
(PPh3), dxz(Re)
(pic)
(pic)
(pic)
dxz(Re),
dxy(Re),
dyz(Re),
p*(pic)
p*(pic)
p
p
p
(Cl),
(Cl),
(Cl),
p
p
p
(Cl), n(P)
p
(PPh3)
dyz(Re),
p
(Cl), p(pic)
LUMO
p*(Re–Cl), p*(pic)
p*(Re–Cl), p*(pic)
p*(pic), dyz
p*(pic)
LUMO +1
LUMO+2
LUMO+3
LUMO+4
LUMO+5
d2z , p*(PPh3)
p*(PPh3), d2z
p*(PPh3)
p*(PPh3)
p*(PPh3)
p*(PPh3)
with Boltzmann’s distribution, the higher magnetic state is popu-
lated, and it is depopulated with temperature lowering, and a de-
crease of the magnetic moment is observed.
The magnetization indicates a value of only 0.001 B.M. at 5 T.
The magnetization of the sample confirms that the ground state
is diamagnetic and the rhenium(III) compound is of a very high
purity.
mated to a certain extent or may indicate the influence of the crys-
tal packing on the values of the experimental bond lengths. The
theoretical calculations do not consider the effects of chemical
environment. However, a similar elongation of the rhenium–chlo-
rine bond lengths (up to 0.25 Å) in the B3LYP with different basis
sets has been found in other rhenium–chlorine complexes [56].
3.4. Molecular orbitals
3.3. Geometry optimisation
The energies and characters of several of the highest occupied
and lowest unoccupied molecular orbitals of 1 are presented in Ta-
ble 5. Among the highest occupied MOs of 1, the largest numbers
The gas phase geometry of 1 was optimized in the triplet and
singlet states using the DFT method with the B3LYP functional.
The total energy of the triplet state is 5.8 kcal/mol smaller in com-
parison with the singlet state. The optimized geometric parameters
of the triplet state are gathered in Table 3. Generally, the predicted
bond lengths and angles are in agreement with the values based
upon the X-ray crystal structure data, and the general trends ob-
served in the experimental data are well reproduced in the calcu-
lations. The largest differences are found for the Re–Cl bond
distances. This may come from the basis sets which are approxi-
constitute
the Cl atoms. The three highest molecular orbitals with
can be represented as a combination of p*Re–Cl and
pic, with pre-
p
orbitals of the phenyl rings with a contribution from
a
-spin
p
dominant involvement of the former component. The HOMO orbital,
with b-spin, has the same character. The LUMO+1 and LUMO+3 b
orbitals of 1 are also to a large extent formed by rhenium d atomic
p
orbitals (dxz, dyz or dxy). Among the lowest unoccupied MOs of 1, the
most are constituted of p* orbitals of the pic and phenyl rings. The
HOMO-2
HOMO-1
HOMO
LUMO
LUMO+1
LUMO+2
Fig. 3. The selected HOMO and LUMO orbitals with a-spin for 1.

2382
B. Machura et al. / Polyhedron 28 (2009) 2377–2384
HOMO-2
HOMO-1
HOMO
LUMO
LUMO+1
LUMO+2
Fig. 4. The selected HOMO and LUMO orbitals with b-spin for 1.
LUMO and LUMO+1 with
spin have
triphenylphosphine ligands participate in the higher unoccupied
orbitals. The contours of the selected occupied and unoccupied
molecular orbitals of 1 with a-spin and b-spin are presented in Figs.
3 and 4, respectively.
a
-spin and LUMO+2 and LUMO+3 with b-
In the 350–600 nm region, complex 1 displays multiple transi-
tions of moderate intensity in the form of peaks and shoulders.
The low-energy absorption band of 1 originates from the tran-
sitions between HOMO-1, HOMO, LUMO and LUMO+2 with b-spin.
As can be seen from Fig. 4, the b HOMOꢀ1 is composed of ligand
(chloride and triphenylphosphine) orbitals, b HOMO is delocalized
on the central ion and ligands, and b LUMO and b LUMO+2 are
p
*(pic) character. The p* phenyl ring orbitals of the
3.5. Electronic spectra
2.00
1.60
1.20
0.80
0.40
0.00
The experimental and calculated electronic spectra of 1 are pre-
sented in Fig. 5. Each calculated transition is represented by a
2
gaussian function y ¼ ceꢀbx with the height (c) equal to the oscil-
lator strength and b equal to 0.04 nmꢀ2. The electronic spectrum
of 2 is very similar in terms of the position, intensity and shape
of the bands in the whole region 1000–180 nm; with maxima at
514.1, 458.8, 341.4, 251.5 and 201.7 nm.
Table 6 presents the most important spin-allowed triplet–trip-
let electronic transitions calculated with the TDDFT method, as-
signed to the observed absorption bands of 1. For the high
energy part of the spectrum, only transitions with oscillator
strengths larger than 0.020 are listed in Table 6. The investigated
complex is of a large size; the numbers of basis functions are equal
to 832. The calculated electron transitions (1 1 0) do not comprise
all the experimental absorption bands; the UV–vis spectrum was
calculated to ꢂ270 nm. Thus the shortest wavelength experimen-
tal bands of 1 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.
200.00
400.00
600.00
800.00
1000.00
The assignment of the calculated orbital excitations to the
experimental bands was based on an overview of the contour plots
and relative energy to the HOMO and LUMO involved in the elec-
tronic transitions.
Fig. 5. The experimental (black) and calculated (red) electronic absorption spectra
of a solution of 1 in acetronitrile. (For interpretation of the references to colour in
this figure legend, the reader is referred to the web version of this article.)

B. Machura et al. / Polyhedron 28 (2009) 2377–2384
2383
Table 6
The energy and molar absorption coefficients of experimental absorption bands and the electronic transitions calculated with the TDDFT method for 1.
The most important orbital excitations
Character
Calculated
k (nm)
Experimental K (nm) (E [eV]) e
E (eV)
f
H(b) ? L+2(b)
H-1(b) ? L(b)
H-1(b) ? L(b)
H(b) ? L+2(b)
d/
n(P)/
n(P)
p
(Cl)/
(PPh3)/
(PPh3)/
p
(pic) ? p*(pic)/d
(Cl) ? d/p*(pic)
542.6
2.28
0.0145
510.5 (2.43) 3600
p
p
p
p
(Cl) ? d/p*(pic)
537.8
2.31
0.0067
d/
p(Cl)/
p
p
(pic) ? p*(pic)/d
(pic) ? p*(pic)
H(
a) ? L(a)
d/
p(Cl)/
422.7
2.93
0.0389
427.7 (2.90) 5350
379.3 (3.27) 6150
H-2(
a
) ? L(
a
a
)
)
d/
d/
p
p
(Cl)/
(Cl)/
p
p
(pic) ? p*(pic)
395.4
388.0
3.14
3.20
0.0383
0.0162
H-2(a
) ? L(
(pic) ? p*(pic)
H(b) ? L+3(b)
H(
H(
a
) ? L+2(
a
a
)
d/
p
(Cl)/
p
(pic) ? d/p*(PPh3)
345.9
325.2
3.58
3.81
0.0296
0.0273
328.2 (3.78) 6650
a) ? L+11(
)
H(b) ? L+5(b)
d/
d/
p
p
(Cl)/
(Cl)/
p
p
(pic) ? p*(PPh3)
(pic) ? p*(pic)
H(
H-2(
H(
H(b) ? L+9(b)
H-5( ) ? L(
a) ? L+1(
a
)
a) ? L+1(
a
)
d/
d/
d/
p
p
p(Cl)/
p(Cl)/
p(Cl)/
p
p
p
(pic) ? p*(pic)
300.4
297.0
295.9
4.13
4.17
4.19
0.0100
0.0100
0.0154
247.9 (5.00) 87 000
a) ? L+3(
a
)
(pic) ? p*(PPh3)/d
(pic) ? p*(PPh3)
a
a
)
(PPh3) ? p*(pic)
(Cl) ? d
H-14(b) ? L+1(b)
291.9
288.9
4.25
4.29
0.0146
0.0179
H-3(b) ? L+2(b)
p
(PPh3) ? p*(pic)/d
204.8 (6.05) 270 000
e
– Molar absorption coefficient [dm3 molꢀ1 cmꢀ1].
f – Oscillator strength.
H – Highest occupied molecular orbital.
L – Lowest unoccupied molecular orbital.
*
formed from dRe orbitals and
p
-bonding orbitals of the picolinate
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
ligand. Accordingly, these transitions can be seen as delocalized
MLLCT (Metal–Ligand-to-Ligand CT) transitions.
The transitions assigned to the experimental bands at 427.7 and
Acknowledgements
379.3 nm can be seen as mixed Re ?
Transfer; LMCT) and (Cl)/ (pic) ?
Transfer; LLCT) transitions. The experimental absorption band at
328.2 nm is mainly attributed to the d/ (Cl)/ (pic) ? d/
*(PPh3)
p
*(pic) (Metal–Ligand Charge
p
p
p
*(pic) (Ligand–Ligand Charge
The GAUSSIAN-03 calculations were carried out in the Wrocław
Centre for Networking and Supercomputing, WCSS, Wrocław, Po-
land, http://www.wcss.wroc.pl, under calculational Grant No. 51/
96.
p
p
p
transition, whereas the transitions assigned to the experimental
band at 247.9 are mainly of LLCT character.
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