Novel oxorhenium complexes with 2-(2′-hydroxyphenyl)-2-benzothiazolinato ligand: X-ray studies, spectroscopic characterization and DFT calculations

Article abstract of DOI:10.1016/j.poly.2008.02.018

The [ReOX₂(hbt)(EPh₃)] (X = Cl, Br; E = As, P) chelates have been prepared in the reactions of [ReOX₃(EPh₃)₂] complexes (X = Cl, Br; E = P, As) with 2-(2′-hydroxyphenyl)-2-benzothiazole (hbtH) in acetone. From the reactions of [ReOX₃(PPh₃)₂] with hbtH two kind of crystals [ReOX₂(hbt)(PPh₃)] · MeCN and [ReOX₂(hbt)(PPh₃)] with different arrangement of halide ions (cis and trans) were isolated, whereas the [ReOX₃(AsPh₃)₂] oxocompounds react with hbtH to give only cis-halide isomers. The complexes were structurally and spectroscopically characterised. The electronic structures of both [ReOBr₂(hbt)(PPh₃)] isomers have been calculated with the density functional theory (DFT) method. The TDDFT/PCM calculations have been employed to produce a hundred of singlet excited-states starting from the ground-state geometry optimized in the gas phase of cis- and trans-halide isomers of [ReOBr₂(hbt)(PPh₃)] and the UV-Vis spectra of these complexes have been discussed on this basis.

Full text of DOI:10.1016/j.poly.2008.02.018

Available online at www.sciencedirect.com
Polyhedron 27 (2008) 1679–1689
www.elsevier.com/locate/poly
Novel oxorhenium complexes with
2-(20-hydroxyphenyl)-2-benzothiazolinato ligand: X-ray studies,
spectroscopic characterization and DFT calculations
a,
b
c
*
B. Machura , R. Kruszynski , J. Kusz
a Department of Crystallography, 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
Received 10 January 2008; accepted 2 February 2008
Available online 26 March 2008
Abstract
The [ReOX2(hbt)(EPh3)] (X = Cl, Br; E = As, P) chelates have been prepared in the reactions of [ReOX3(EPh3)2] complexes (X = Cl,
Br; E = P, As) with 2-(20-hydroxyphenyl)-2-benzothiazole (hbtH) in acetone. From the reactions of [ReOX3(PPh3)2] with hbtH two kind
of crystals [ReOX2(hbt)(PPh3)] ꢀ MeCN and [ReOX2(hbt)(PPh3)] with different arrangement of halide ions (cis and trans) were isolated,
whereas the [ReOX3(AsPh3)2] oxocompounds react with hbtH to give only cis-halide isomers. The complexes were structurally and spec-
troscopically characterised. The electronic structures of both [ReOBr2(hbt)(PPh3)] isomers have been calculated with the density func-
tional theory (DFT) method. The TDDFT/PCM calculations have been employed to produce a hundred of singlet excited-states
starting from the ground-state geometry optimized in the gas phase of cis- and trans-halide isomers of [ReOBr2(hbt)(PPh3)] and the
UV–Vis spectra of these complexes have been discussed on this basis.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Rhenium oxocomplexes; 2-(20-Hydroxyphenyl)-2-benzothiazole; X-ray and electronic structure; DFT calculations; NBO analysis
1. Introduction
known to date [3,4]. The mer,trans-[ReOCl3(PPh3)2] and
its derivatives catalyze the oxidation of sulfides to sulfox-
ides, thiols to disulfides and catalyze oxygen-transfer from
sulfoxides to phosphines [4]. The [ReOCl2(O–N)(PPh3)]
chelates with pyridinecarboxylate ligands exhibit a remark-
able catalytic activity for the conversion of ethane to a mix-
ture of propionic and acetic acids in a single-pot process
[5]. The [CH3ReO(pic)2] complex is an active precursor in
olefin oxidation and forms epoxides in a two-phase
H2O2–H2O/CH2Cl2 system [6].
Transition metal oxocomplexes are of considerable
interest in both biological and industrial catalysis. These
compounds can transfer an oxygen atom to reductants
such as phosphines, sulfides, and alkenes. Oxygen atom
transfer chemistry has been implicated in various reactions
of industrial and biological importance, including olefin
epoxidation and catalysis by cytochrome P-450 [1,2].
The chemistry of oxorhenium complexes arouses partic-
ular interest among these compounds. Methyltrioxorhe-
nium are among the most versatile oxidation catalysts
Furthermore, 186Re (1.07 MeV b-emitter, t1/2 90 h) and
188Re (2.12 MeV b-emitter, t1/2 17 h) are two of the most
attractive isotopes for applications in targeted radionuclide
therapy [7,8].
In this context, the design, synthesis and reactivity of
novel rhenium oxocomplexes has become the aim of several
laboratories, including ours.
*
Corresponding author.
E-mail addresses: basia@ich.us.edu.pl (B. Machura), rafal.kruszyns-
ki@p.lodz.pl (R. Kruszynski).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.02.018

1680
B. Machura et al. / Polyhedron 27 (2008) 1679–1689
UV–VIS 8500 in the range 1100–180 nm in acetonitrile
HO
solution. Elemental analyses (C,H,N) were performed on
a Perkin–Elmer CHN-2400 analyzer.
N
S
2.2. Preparation of [ReOBr2(hbt)(PPh3)] ꢀ MeCN and
[ReOBr2(hbt)(PPh3)] (1a and 1b)
Scheme 1. Structure of hbtH ligand.
Continuing our researchers we focus on the synthesis and
characterization of oxorhenium(V) chelates [ReOX2(O–
N)(PPh3)] and [ReOX2(O–N)(AsPh3)] with 2-(20-hydroxy-
phenyl)-2-benzothiazolinato ligand (hbtH, Scheme 1). Some
other mono- and bis(2-(20-hydroxyphenyl)-2-benzothiazoli-
nato) complexes of Re(V) have been reported previously
[9,10].
The [ReOX2(hbt)(EPh3)] (X = Cl, Br; E = As, P) che-
lates have been prepared in the reactions of [ReOX3(EPh3)2]
complexes (X = Cl, Br; E = P, As) with 2-(20-hydroxy-
phenyl)-2-benzothiazole in acetone. From the reactions of
[ReOX3(PPh3)2] with 2-(20-hydroxyphenyl)-2-benzothiazole
(hbtH) two kind of crystals [ReOX2(hbt)(PPh3)] ꢀ MeCN
and [ReOX2(hbt)(PPh3)] with different arrangement of
halide ions (cis and trans, respectively) were isolated,
whereas the [ReOX3(AsPh3)2] oxocompounds react with
hbtH to give only cis-halide isomers [ReOX2(hb-
t)(AsPh3)] ꢀ MeCN. The cis and trans geometry of the halide
ligands in the oxorhenium complexes of the [ReOX2(O–
N)(PPh3)] and [ReOX2(O–P)(py)] type has been confirmed
previously [11,12]. The number of the structurally character-
ized [ReOX2(O–N)(AsPh3)] complexes is relatively small
and all they are cis stereoisomers [13–15].
Here, we presents results of our studies on the structural
and spectral properties of [ReOX2(hbt)(EPh3)] ꢀ MeCN
(1a, 2a, 3 and 4) and [ReOX2(hbt)(EPh3)] (1b and 2b).
The electronic structures of 1a and 1b have been calcu-
lated with the density functional theory (DFT), and
TDDFT/PCM calculations have been employed to pro-
duce a hundred of singlet excited-states starting from the
ground-state geometries optimized in the gas phase.
Currently, density functional theory (DFT) is commonly
used to examine the electronic structure of transition metal
complexes. It meets with the requirements of being accu-
rate, easy to use and fast enough to allow the study of rel-
atively large molecules of transition metal complexes,
including rhenium compounds [16,17].
A mixture of [ReOBr3(PPh3)2] (0.50 g, 0.52 mmol), hbtH
(0.125 g, 0.55 mmol) and acetone (70 ml) was stirred for 3 h.
50 ml of acetone was distilled off and 100 ml of diethyl ether
was added. [ReOBr2(hbt)(PPh3)] was filtered off, washed
with ethanol, diethyl ether, dried and recrystallized from
acetonitrile. Green crystals of [ReOBr2(hbt)(PPh3)] ꢀ MeCN
(1a) and red crystals of [ReOBr2(hbt)(PPh3)] (1b) were col-
lected in 70% and 10% yield, respectively. Crystals of 1a
and 1b were separated using microscope.
IR of 1a (KBr; m/cmꢁ1): 1596 (m) and 1561 (m) mCN and
m
m
C@C; 961 (s) mRe@O
IR of 1b (KBr; m/cmꢁ1): 1595 (m) and 1561(m) mCN and
C@C; 960 (s) mRe@O
Anal. Calc. for C33H26Br2N2O2PSRe: C, 44.45; H, 2.94;
.
.
N, 3.14. Found: C, 44.80; H, 3.05; N, 3.35%.
Anal. Calc. for C31H23Br2NO2PSRe: C, 43.78; H, 2.73;
N, 1.65. Found: C, 44.10; H, 2.96; N, 1.84%.
2.3. Preparation of [ReOCl2(hbt)(PPh3)] ꢀ MeCN and
[ReOCl2(hbt)(PPh3)] (2a and 2b)
A procedure similar to that for 1a and 1b was used with
[ReOCl3(PPh3)2] (0.50 g, 0.60 mmol) and hbtH (0.145 g,
0.64 mmol). Green crystals of [ReOBr2(hbt)(PPh3)] ꢀ MeCN
(2a) and red crystals of [ReOBr2(hbt)(PPh3)] (2b) were col-
lected in 68% and 8% yield, respectively. Crystals of 2a
and 2b were separated using microscope.
IR of 2a (KBr; m/cmꢁ1): 1597 (m) and 1566 (m) mCN and
m
m
C@C; 965 (s) mRe@O
IR of 2b (KBr; m/cmꢁ1): 1597 (m) and 1567 (m) mCN and
C@C; 966 (s) mRe@O
UV–Vis of 2a (CH3CN; kmax [nm] (e; [dm3 molꢁ1 cmꢁ1])):
.
.
647.0 (50), 454.0 (400), 370.0 (2500), 323.0 (4680), 256.0
(6740) and 207.5 (25900).
UV–Vis of 2b (CH3CN; kmax [nm] (e; [dm3 molꢁ1 cmꢁ1])):
638.5 (60), 453.0 (560), 365.5 (3100), 318.0 (4450), 259.0
(9960) and 207.5 (28950).
Anal. Calc. for C33H26Cl2N2O2PSRe: C, 49.38; H, 3.26;
N, 3.49. Found: C, 49.82; H, 3.06; N, 3.30%.
Anal. Calc. for C31H23Cl2NO2PSRe: C, 48.88; H, 3.04;
N, 1.84. Found: C, 48.15; H, 2.87; N, 1.92%.
2. Experimental
2.1. General procedure
All the reagents used to the synthesis were commercially
available and were used without further purification. The
[ReOX3(PPh3)2] and [ReOX3(AsPh3)2] complexes were pre-
pared according to the literature methods [18].
IR spectra were recorded on a Nicolet Magna 560 spec-
trophotometer in the spectral range 4000–400 cmꢁ1 with
the samples in the form of KBr pellets. Electronic spectra
were measured on a spectrophotometer Lab Alliance
2.4. [ReOCl2(hbt)(AsPh3)] ꢀ MeCN (3)
A procedure similar to that for phosphine analogues
was used with [ReOCl3(AsPh3)2] (0.50 g, 0.54 mmol) and
hbtH (0.13 g, 0.57 mmol). Crystalline green precipitate of
[ReOCl2(hbt)(AsPh3)] ꢀ MeCN was collected in 85% yield.
IR (KBr; m/cmꢁ1): 1598 (m) and 1566 (m) mCN and mC@C
;
965 (s) mRe@O
.

B. Machura et al. / Polyhedron 27 (2008) 1679–1689
1681
UV–Vis (CH3CN; kmax [nm] (e; [dm3 molꢁ1 cmꢁ1])):
2.6. Crystal structures determination and refinement
688.0 (95), 443.5 (640), 359.5 (6500), 313.0 (10,500), 242,5
(16150) and 203.5 (47500).
Anal. Calc. for C33H26Cl2N2O2AsSRe: C, 46.81; H,
3.10; N, 3.31. Found: C, 46.52; H, 3.16; N, 3.42%.
The X-ray intensity data of 1a, 1b, 2a, 2b, 3 and 4 were
collected on a KM-4-CCD automatic diffractometer
equipped with CCD detector and graphite monochromated
˚
Mo Ka radiation (k = 0.71073 A) at room temperature.
2.5. Preparation of [ReOBr2(hbt)(AsPh3)] ꢀ MeCN (4)
Details concerning crystal data and refinement are given
in Table 1. Lorentz, polarization and absorption correction
[19] were applied. The structures were solved by the Patter-
son method and subsequently completed by the difference
Fourier 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 (non-methyl) and 1.5 (methyl) times the
value of equivalent temperature factor of the parent atom.
The methyl groups were allowed to rotate about their local
threefold axis. In containing solvent compounds the MeCN
molecules show symptoms of disorder, what exhibits in rel-
atively large displacement parameters and residual density
A procedure similar to that for phosphine analogues
was used with [ReOBr3(AsPh3)2] (0.50 g, 0.47 mmol) and
hbtH (0.115 g, 0.50 mmol). Crystalline green precipitate
of [ReOBr2(hbt)(AsPh3)] ꢀ MeCN was collected in 80%
yield.
IR (KBr; m/cmꢁ1): 1597 (m) and 1566 (m) mCN and mC@C
;
966 (s) mRe@O
.
UV–Vis (CH3CN; kmax [nm] (e; [dm3 molꢁ1 cmꢁ1])):
672.0 (70), 439.5 (900), 358.5 (6700), 315.0 (12400), 245,5
(18100) and 210.5 (52500).
Anal. Calc. for C33H26Br2N2O2AsSRe: C, 42.37; H,
2.80; N, 2.99. Found: C, 42.92; H, 3.13; N, 3.22%.
Table 1
Crystal data and structure refinement for [ReOX2(hbt)(EPh3)] ꢀ MeCN and [ReOX2(O–N)(PPh3)] (X = Cl, Br; E = P, As) complexes
1a 2a 1b
33H26Br2N2O2PSRe C33H26Cl2N2O2PSRe C33H26AsCl2N2O2SRe C33H26AsBr2N2O2SRe C31H23Br2NO2PSRe C31H23Cl2NO2PSRe
3
4
2b
Empirical formula
Formula weight
Temperature (K)
C
891.61
293(1)
802.69
293(1)
846.64
935.56
850.55
761.63
291.0(3)
0.71073
triclinic
291.0(3)
0.71073
triclinic
291.0(3)
0.71073
monoclinic
P21=n
291.0(3)
0.71073
monoclinic
P21=n
˚
Wavelength (A)
0.71073
0.71073
Crystal system
Space group
Unit cell dimensions
triclinic
triclinic
ꢀ
ꢀ
ꢀ
ꢀ
P1
P1
P1
P1
˚
a (A)
11.197(2)
87.71(3)
11.532(2)
85.39(3)
13.221(3)
65.59(3)
1549.4(5)
2
11.1730(3)
88.030(2)
11.4490(3)
85.780(2)
13.1280(2)
65.700(2)
1526.38(6)
2
11.4176(7)
87.937(6)
11.5447(8)
86.158(6)
13.1933(10)
65.521(7)
1579.11(19)
2
11.5857(5)
86.558(3)
11.6384(4)
87.335(4)
13.2846(6)
64.872(4)
1618.40(12)
2
18.6496(5)
18.3899(5)
a (°)
˚
b (A)
9.1939(2)
113.959(3)
19.0220(4)
9.1125(2)
113.743(3)
18.7215(5)
b (°)
˚
c (A)
c (°)
Volume (A )
3
˚
2980.53(12)
4
2871.77(13)
4
Z
Dcalc (Mg/m3)
1.911
1.746
1.781
1.920
1.895
6.911
1.762
4.576
Absorption coefficient
(mmꢁ1
6.653
4.311
5.156
7.335
)
F(000)
860
788
824
896
1632
1488
Crystal size (mm)
h Range for data
collection (°)
0.02 ꢂ 0.10 ꢂ 0.20
3.09–25.00
0.07 ꢂ 0.10 ꢂ 0.13
3.11–25.00
0.379 ꢂ 0.158 ꢂ 0.132
3.28–25.10
0.271, 0.009, 0.007
1.54–25.02
0.04 ꢂ 0.19 ꢂ 0.20
1.98–25.00
0.007 ꢂ 0.009 ꢂ 0.197
2.01–25.05
Index ranges
ꢁ9 6 h 6 13,
ꢁ13 6 k 6 13,
ꢁ14 6 l 6 15
9884
ꢁ12 6 h 6 13,
ꢁ10 6 k 6 13,
ꢁ15 6 l 6 14
9474
ꢁ13 6 h 6 13,
ꢁ13 6 k 6 13,
ꢁ12 6 l 6 15
15,624
ꢁ13 6 h 6 12,
ꢁ13 6 k 6 13,
ꢁ12 6 l 6 14
16,504
ꢁ22 6 h 6 22
ꢁ10 6 k 6 10
ꢁ22 6 l 6 22
28,699
ꢁ21 6 h 6 21
ꢁ10 6 k 6 10
ꢁ21 6 l 6 22
28,280
Reflections collected
Independent reflections
5322 (Rint = 0.0257)
5198 (Rint = 0.0890)
96.6%
5598 (Rint = 0.0343)
99.6%
5717 (Rint = 0.0237)
100%
5236 (Rint = 0.0456) 5091 (Rint = 0.0262)
Completeness to 2h = 50° 98.6%
100.0%
100.0%
Minimum and maximum
0.442 and 0.878
0.599 and 0.765
0.599 and 0.181
0.920 and 0.963
0.286 and 0.751
0.955 and 0.972
transmission
Data/restraints/
parameters
Goodness-of-fit on F2
5322/0/380
1.087
5198/0/380
5598/0/380
5717/0/380
5236/0/352
5091/0/352
0.964
1.052
1.114
1.073
0.972
Final R indices [I > 2r(I)] R1 = 0.0622
wR2 = 0.1945
R1 = 0.0751
wR2 = 0.1649
R1 = 0.1262
wR2 = 0.1724
3.827 and ꢁ2.483
R1 = 0.0274
wR2 = 0.0626
R1 = 0.0310
wR2 = 0.0643
0.988 and ꢁ1.177
R1 = 0.0479
wR2 = 0.1654
R1 = 0.0587
wR2 = 0.1780
1.330 and ꢁ1.218
R1 = 0.0206
wR2 = 0.0475
R1 = 0.0308
wR2 = 0.0628
0.674 and ꢁ0.861
R1 = 0.0154
wR2 = 0.0333
R1 = 0.0235
wR2 = 0.0353
0.641 and ꢁ0.542
R indices (all data)
R1 = 0.0744
wR2 = 0.2020
1.844 and ꢁ2.366
Largest diffraction
ꢁ3
˚
peak and hole (e A
)

1682
B. Machura et al. / Polyhedron 27 (2008) 1679–1689
around acetonitrile atoms. This is probably caused by
absence of strong intermolecular interactions, which could
stabilise the solvent in the crystal net. SHELXS97 [20], SHEL-
XL97 [21] and SHELXTL [22] programs were used for all the
calculations. Atomic scattering factors were those incorpo-
rated in the computer programs.
3. Computational details
The gas phase geometries of 1a and 1b were optimized
without any symmetry restrictions in the singlet ground-
state with the DFT method using the hybrid B3LYP
functional of GAUSSIAN-03 [23–25]. The calculations were
performed by using ECP basis set on the rhenium atom,
Fig. 1. The molecular structure of 1a. Displacement ellipsoids are drawn
at 50% probability.
Fig. 2. The molecular structure of 1b. Displacement ellipsoids are drawn
at 50% probability.
Table 2
˚
The selected experimental and optimized bond lengths (A) and angles (°)
Table 3
˚
for 1a
The experimental and optimized bond lengths (A) and angles (°) for 1b
Bond lengths
Experimental
Optimized
Bond lengths
Experimental
Optimized
Re(1)–O(1)
Re(1)–O(2)
Re(1)–N(1)
Re(1)–Br(1)
Re(1)–Br(2)
Re(1)–P(1)
1.698(9)
1.932(8)
2.176(10)
2.472(3)
2.437(2)
2.491(3)
1.682
1.987
2.218
2.581
2.572
2.602
Re(1)–O(1)
Re(1)–O(2)
Re(1)–N(1)
Re(1)–Br(1)
Re(1)–Br(2)
Re(1)–P(1)
1.690(3)
1.933(3)
2.158(4)
2.5371(5)
2.5479(5)
2.4701(11)
1.684
1.977
2.179
2.622
2.647
2.540
O(1)–Re(1)–O(2)
O(1)–Re(1)–N(1)
O(2)–Re(1)–N(1)
O(1)–Re(1)–Br(2)
O(2)–Re(1)–Br(2)
N(1)–Re(1)–Br(2)
O(1)–Re(1)–Br(1)
O(2)–Re(1)–Br(1)
N(1)–Re(1)–Br(1)
Br(2)–Re(1)–Br(1)
O(1)–Re(1)–P(1)
O(2)–Re(1)–P(1)
N(1)–Re(1)–P(1)
Br(2)–Re(1)–P(1)
Br(1)–Re(1)–P(1)
167.6(4)
90.6(4)
82.1(4)
98.8(3)
89.4(2)
169.9(3)
99.1(3)
90.5(3)
87.2(3)
87.47(8)
84.1(3)
86.5(3)
94.4(3)
90.50(9)
176.44(9)
163.80
90.22
81.13
99.50
90.57
169.03
102.07
90.87
85.11
87.88
82.62
84.66
95.81
90.51
175.24
O(1)–Re(1)–O(2)
O(1)–Re(1)–N(1)
O(2)–Re(1)–N(1)
O(1)–Re(1)–Br(2)
O(2)–Re(1)–Br(2)
N(1)–Re(1)–Br(2)
O(1)–Re(1)–Br(1)
O(2)–Re(1)–Br(1)
N(1)–Re(1)–Br(1)
Br(2)–Re(1)–Br(1)
O(1)–Re(1)–P(1)
O(2)–Re(1)–P(1)
N(1)–Re(1)–P(1)
Br(2)–Re(1)–P(1)
Br(1)–Re(1)–P(1)
174.16(13)
99.02(15)
81.86(14)
89.72(11)
84.61(8)
84.52(9)
97.30(11)
88.50(8)
173.97
100.12
81.61
90.13
84.25
85.00
97.36
88.48
87.11
169.07
90.93
87.49
168.91
96.00
90.57
88.00(9)
170.476(17)
91.96(11)
87.23(9)
169.01(11)
95.80(3)
90.41(3)

B. Machura et al. / Polyhedron 27 (2008) 1679–1689
1683
the standard 6-31+G** basis for bromine, phosphorous,
oxygen and nitrogen, 6-31G* for carbon and 6-31G for
hydrogen atoms [26,27]. 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) [28] was
used for the valence electrons. Additional d function with
pounds react with hbtH to give only [ReOX2(hbt)
(AsPh3)] ꢀ MeCN with halide ligands in cis arrangement.
The examined previously reactions of [ReOX3(EPh3)2]
(E = P, As) with 2-(20-hydroxyphenyl)-2-benzoxazole, 8-
hydroxyquinoline and quinoline-2-carboxylic acid resulted
in the isolation only [ReOX2(N–O)(EPh3)] with cis halide
arrangement [13–15].
exponent a = 0.3811 and
f function with exponent
a = 2.033 on the rhenium atom were added [29]. All vibra-
tions in the calculated vibrational spectrum of 1a and 1b
were real thus the both geometries correspond to true
energy minimum.
The electronic spectrum of 1a and 1b were calculated
with the TDDFT method, and the solvent effect was simu-
lated using the polarizable continuum model with the inte-
gral equation formalism (IEF-PCM) [30].
All the isolated complexes are air stable and slightly sol-
uble in acetonitrile, dichloromethane, chloroform, spar-
ingly soluble in benzene and toluene. The solubility of
the trans stereoisomers are somewhat better than the cis
ones. All the crystals suitable for X-ray investigation were
obtained by recrystallization from acetonitrile.
The IR spectroscopic measurements outlined in the Sec-
tion 2 are not distinctive for molecular structure determina-
tion. The IR spectra of the cis and trans stereoisomers are
very similar in terms of the position, intensity and shape of
the bands in the whole region 4000–400 cmꢁ1. The strong
m(Re@O) stretching bands of both cis and trans stereoiso-
mers of [ReOX2(hbt)(EPh3)] are found in the narrow range
960–966 cmꢁ1, similar to those observed for the other
[ReOX2(O–N)(PPh3)] chelates [13–15]. Relatively high
wavenumbers of the m(Re@O) absorption bands suggest
that the Re–hydroxy bond trans to the oxo ligand does
not compete effectively for the Red orbitals and indicate
the presence of very stable {O„Re–O} structural moiety
in the examined structures.
Natural bond orbital (NBO) calculations were per-
formed with the NBO code [31] included in GAUSSIAN03.
4. Results and discussion
4.1. Preparation and infrared data
The [ReOX2(hbt)(EPh3)] (X = Cl, Br; E = As, P) com-
plexes were prepared in good yield by ligand exchange
reactions starting from [ReOX3(EPh3)2] complexes and 2-
(20-hydroxyphenyl)-2-benzothiazole (hbtH) in acetone:
The calculated (non-scaled) vibrational spectra of the cis
and trans stereoisomers are in a reasonable agreement with
the experimental data. Similar to the experimental, the cal-
culated IR spectra of both isomers are very similar in terms
of the position, intensity and shape of the bands. The cal-
culated m(Re@O) values (1019 cmꢁ1 for of 1a and
1024 cmꢁ1 for 1b) are higher than the experimental ones
by ꢄ7%, what is usual for this approach.
½ReOX3ðEPh3Þ2ꢃ þ hbtH ! ½ReOX2ðhbtÞðEPh3Þꢃ þ HX
þ EPh3 X ¼ Cl; Br; E ¼ As; P
From the reactions of [ReOX3(PPh3)2] with 2-(20-hydroxy-
phenyl)-2-benzothiazole two kind of crystals [Re-
OX2(hbt)(PPh3)] ꢀ MeCN and [ReOX2(hbt)(PPh3)] with
different arrangement of halide ions (cis and trans, respec-
tively) were isolated, whereas the arsine starting oxocom-
Table 4
Electron population of the valence core for 1a and 1b
Complex
Re(1)
6s
O(1)
2s
O(2)
2s
Br(1)
4s
Br(2)
4s
N(1)
2s
P(1)
3s
5d
2p
2p
4p
4p
2p
3p
1a
1b
0.43
0.43
5.58
5.57
1.83
1.83
4.62
4.60
1.63
1.63
5.02
5.02
1.93
1.93
5.41
5.46
1.92
1.94
5.40
5.47
1.30
1.29
4.16
4.18
1.15
1.12
2.42
2.40
Table 5
The occupancy and composition of the calculated natural bond orbitals (NBOs) between the rhenium and the oxo ligand for 1a and 1b
BD
Occupancy
Composition of NBO
BDa
Occupancy
1a
Re–Ot
Re–Ot
1.992
1.986
0.566(d)Re + 0.825(p)O
0.569(d)Re + 0.822(p)O
0.825(d)Re ꢁ 0.566(p)O
0.822 (d)Re ꢁ 0.569(p)O
0.257
0.313
1b
Re–Ot
Re–Ot
1.990
1.984
0.557(d)Re + 0.831(p)O
0.579(d)Re + 0.816(p)O
0.831(d)Re ꢁ 0.557(p)O
0.816(d)Re ꢁ 0.579(p)O
0.322
0.200
BD denotes 2-center bond.
a
Denotes antibond NBO.

1684
B. Machura et al. / Polyhedron 27 (2008) 1679–1689
4.2. Crystal structures
The 2-hydroxyphenyl moiety is inclined to the ben-
zothiazolie moiety at 11.2(9)°, 10.3(9)°, 11.0(3)°, 12.9(6)°,
12.2(3)°, 12.62(15)°, respectively, for compound 1a, 2a, 3,
4, 1b, 2b.
No extraordinary features in terms of bond lengths and
angles can be noticed between cis- and trans-halide
[ReOX2(hbt)(PPh3)] complexes. The Re–Ot (Ot = terminal
The crystallographic data of [ReOX2(hbt)(EPh3)] ꢀ
MeCN and [ReOX2(O–N)(PPh3)] (X = Cl, Br; E = P, As)
complexes are summarized in Table 1. The cis-halide com-
plexes are isostructural and crystallise as acetonitrile sol-
ꢀ
vates in the triclinic P1 space group. The trans
stereoisomers are also isostructural but consist of discrete
and well-separated [ReOX2(O–N)(PPh3)] monomers and
crystallise in the monoclinic P21=n space group.
The perspective drawing of [ReOBr2(hbt)(PPh3)] ꢀ
MeCN (1a) is presented in Fig. 1, and the selected bond
distances and angles of 1a are collected in Table 2. Fig. 2
presents the molecular structure of [ReOBr2(hbt)(PPh3)]
(1b), and its selected bond distances and angles are gath-
ered in Table 3.
All the complexes show octahedral geometry about the
central rhenium atom defined by the terminal oxo-group,
two halide ions, the phosphorus or arsine atom of EPh3
molecule, and the bidentate N,O donors of the hbt ligand.
The halide ions of [ReOX2(hbt)(PPh3)] ꢀ MeCN (1a, 2a, 3
and 4) are arranged in cis geometry, whereas the halide
ligands of [ReOX2(hbt)(PPh3)] occupy trans positions to
each other. In all the complexes triphenylphosphine or
triphenylarsine molecule with their p-acidity adopts cis
position with respect to the linear O„Re–O unit. Conse-
quently, the O„Re–O core with multiply bonded oxo
ligand is stabilized to some extent due to accessible p-dona-
tion from rhenium to phosphine or arsine molecule. The
multiple bonding ligand (terminal oxo) and narrow bite
angle of the chelating ligand contribute to clear distortions
of the pseudooctahedral environment of Re center in both
cis- and trans-halide complexes.
Fig. 3. The experimental (black) and calculated (red) electronic absorp-
tion spectra of 1a. (For interpretation of the references to colour in this
figure legend, the reader is referred to the web version of this article.)
2.00
1.60
1.20
0.80
0.40
0.00
In complexes 1a, 2a, 3 and 4 the rhenium atom is dis-
placed, respectively, 0.121(3), 0.128(3), 0.1289(10),
˚
0.133(2) A from the plane formed by the two halogen, one
nitrogen and one phosphorous (or arsine) atoms (plane A),
˚
0.043(3), 0.033(4), 0.0396(10), 0.037(2) A from the plane
formed by the two oxygen, one halogen and one phospho-
rous (or arsine) atoms (plane B) and 0.029(4), 0.049(8),
˚
0.0667(14), 0.061(3) A from the plane formedby two oxygen,
one halogen and one nitrogen atoms (plane C). Least squares
planeAisinclinedat89.78(23)°, 89.3(2)°, 89.75(7)°, 89.77(18)°
to plane B and at 87.38(24)°, 86.5(3)°, 87.38(8)°, 87.15(18)° to
plane C; planes B and C are inclined at 89.53(13)°, 89.08(14)°,
89.42(4)°, 89.92(9)°, respectively as above.
In complexes 1b and 2b the rhenium atom is displaced,
˚
respectively, 0.1834(10), 0.1855(7) A from the plane formed
by the two halogen, one nitrogen and one phosphorous
˚
atoms (plane A), 0.0636(11), 0.0480(7) A from the plane
formed by the two oxygen and two halogen ions (plane
˚
B) and 0.0379(14), 0.0380(9) A from the plane formed by
two oxygen, one nitrogen and one phosphorous atoms
(plane C). Least squares plane A is inclined at 87.33(7)°,
87.21(4)° to plane B and at 89.07(6)°, 89.39(4)° to plane
C; planes B and C are inclined at 87.66(7)°, 87.90(4)°,
respectively as above.
400.00
800.00
[nm]
Fig. 4. The experimental (black) and calculated (red) electronic absorp-
tion spectra of 1b. (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 27 (2008) 1679–1689
1685
˚
oxygen) bond lengths fall in the range 1.639–1.76 A, typical
of mononuclear complexes of rhenium(V) having [ReO]3+
core, and indicate the presence of a triple bond Re„O [32].
The interatomic distances between the rhenium atom
and the oxygen atom of 2-(20-hydroxyphenyl)-2-ben-
zothiazolinato ligand are somewhat shorter than an ideal
optimized geometric parameters of 1a and 1b are gathered
in Tables 2 and 3, respectively. In general, the predicted
bond lengths and angles are in agreement with the values
based upon the X-ray crystal structure data, and the gen-
eral trends observed in the experimental data are well
reproduced in the calculations.
˚
single Re–O bond length (ca. 2.04 A) [33], indicating only
Table 4 presents electron population of the valence core of
metal and donor atoms for 1a and 1b. The population at Re
center and oxygen O(1) and O(2) atoms of both isomers
remains almost constant. The calculated charges on the rhe-
nium atoms in 1a and 1b are considerably lower than the for-
mal charge +5, which results from significant charge
donation from the oxygen atoms, bromine ions and triphen-
ylphosphine molecule. The considerable differences in values
of charges are observed for the terminal oxo ligand and the
oxygen atom of hbt ligand – less negative are the terminal
oxo ligands, which indicate the higher electron density delo-
calization from the terminal ligands towards the rhenium
centers and correspond to differences in the Re–Ot and Re–
Ohbt bonds lengths. The higher charge donation from the
bromide ions can be noticed for the cis-halide
[ReOBr2(hbt)(PPh3)] complex, whereas the population at
small delocalization in the O(2)–Re(1)–O(1) moiety.
For cis-halide [ReOX2(hbt)(PPh3)] complexes clear dif-
ference between Re(1)–X(1) and Re(1)–X(2) bond lengths
can be noticed. The Re(1)–X(1) distances trans to the phos-
phorus or arsine atom of EPh3 molecule are slightly longer
than the Re(1)–X(2) bonds trans to the nitrogen atom of
the hbtꢁ ligand. It indicates structural trans effect of the
EPh3 ligands. A similar trend was observed in the other
[ReOCl2(O–N)(PPh3)] chelates [13–15].
4.3. Geometry optimisation, charge distribution, electronic
structure and NBO analysis
The geometries of 1a and 1b were optimized in a singlet
state by the DFT method with the B3LYP functional. The
Table 6
The energy and molar absorption coefficients of experimental absorption bands and the electronic transitions calculated with the TDDFT method for 1a
The most important orbital excitations
Character
k [nm]
E [eV]
f
Experimental
K [nm]
(E [eV])
e
H ? L
H ? L + 1
H-1 ? L
H-1 ? L + 1
H-1 ? L
H-1 ? L + 1
H ? L + 2
H-5 ? L + 1
H-5 ? L + 1
H-6 ? L
H-1 ? L + 2
H-8 ? L
H-1 ? L + 2
H-8 ? L
d/p(Br)/p(hbt) ? d
d/p(Br)/p(hbt) ? d
d/p(Br)/p(hbt) ? d
695.0
644.0
486.3
1.78
1.93
2.55
0.0024
0.0002
0.0106
649.5
(1.91)
50
446.0
361.2
324.5
(2.78)
450
d/p(Br)/p(hbt) ? d
469.4
368.0
2.64
3.37
0.0425
0.0561
d/p(Br)/p(hbt) ? p*(hbt)
p(Br)/p(PPh3) ? d
p(Br)/p(PPh3) ? d
(3.43)
(3.82)
2700
4080
362.4
359.7
341.0
3.42
3.45
3.64
0.0308
0.0401
0.0926
p(PPh3) ? d
d/p(Br)/p(hbt) ? p*(hbt)
p(PPh3) ? d
d/p(Br)/p(hbt) ? p*(hbt)
p(PPh3) ? d
338.2
3.67
0.0757
H-1 ? L + 3
H-2 ? L + 2
H-3 ? L + 2
H-2 ? L + 3
H-3 ? L + 3
H-5 ? L + 3
H-4 ? L + 3
H-15 ? L + 1
H-6 ? L + 3
H-1 ? L + 5
H-5 ? L + 4
H-16 ? L + 1
H-1 ? L + 9
H-14 ? L + 3
H ? L + 11
H-5 ? L + 5
H-14 ? L + 3
H-2 ? L + 7
d/p(Br)/p(hbt) ? d
329.9
310.4
296.9
288.6
282.4
276.2
3.76
3.99
4.18
4.30
4.39
4.49
0.0565
0.0730
0.0639
0.0303
0.0447
0.0766
p(hbt)/p(Br)/n(P) ? p*(hbt)
p(hbt)/p(Br)/p(PPh3) ? p*(hbt)
p(hbt)/p(Br)/n(P) ? d
p(hbt)/p(Br)/p(PPh3) ? d
p(Br)/p(PPh3) ? d
p(Br)/p(hbt)/p(PPh3) ? d
p (hbt)/n(P)/r(Br) ? d
p(PPh3) ? d
271.2
269.0
260.6
235.9
233.8
4.57
4.61
4.76
5.26
5.30
0.0339
0.0491
0.0345
0.0304
0.0348
d/p(Br)/p(hbt) ? p*(PPh3)
p(Br)/p(PPh3) ? p*(PPh3)
d/p(Br)/p(hbt) ? p*(hbt)/p*(PPh3)
p(Br)/p(PPh3) ? d
269.5
(4.60)
5640
p(Br)/p(bthoz)/n(P) ? d
d/p(Br)/p(hbt) ? p*(hbt)/p*(PPh3)
p(Br)/p(PPh3) ? p*(PPh3)
p(Br)/p(hbt)/n(P) ? d
p(hbt)/p(Br)/n(P) ? p*(hbt)/p*(PPh3)
233.0
228.4
228.4
226.6
5.32
5.43
5.43
5.47
0.0454
0.0367
0.0798
0.0319
209.0
(5.93)
23000
e – molar absorption coefficient [dm3 molꢁ1 cmꢁ1]; f – oscillator strength; H – highest occupied molecular orbital; L – lowest unoccupied molecular orbital.

1686
B. Machura et al. / Polyhedron 27 (2008) 1679–1689
the p-orbitals of the phosphorous atom of trans-halide is
smaller.
natural Re–Ot bond orbitals were detected for 1a and 1b,
whereas the NBO analysis of [ReOX3(N–N)] oxocom-
pounds [34,35] confirms three natural bond orbitals
between metal and oxygen. As the results for the last ones
are very clear (one r-bond and two p bonds), the interpre-
tation of NBO analysis for 1a and 1b is not straightfor-
ward. The both detected natural Re–Ot bond orbitals of
1a and 1b are similar in energy and they are composed of
the p oxygen and d rhenium orbitals. The terminal oxo
ligand of 1a and 1b has two lone pair orbitals, and electron
density from one of them is strongly delocalized into non-
Lewis rhenium orbital. It can be assumed that the detected
natural Re–Ot bond orbitals are of p character and not
detected rRe–Ot bond has ionic character, similar as Re–N
bond orbital in [ReCl4(MeCN)2] [17]. However, another
interpretation may be also concluded from the NBO anal-
ysis for the examined isomers. Instead of the mentioned tri-
ple bond, the double Re–Ot bond with relevant negative
hyperconjugation may be proposed for 1a and 1b.
The nature of rhenium–terminal oxygen (Ot) interaction
in 1a and 1b has been studied by NBO analysis. The occu-
pancy and composition of the calculated Re–Ot natural
bond orbitals (NBOs) are given in Table 5. The Re–Ohbt
bond orbital were not detected indicating a conceivable
predominant Coulomb-type Re–ligand interaction in both
isomers.
Each natural bond orbital (NBO) rAB can be written in
terms of two directed valence hybrids (NHOs) hA and hB on
atoms A and B:
rAB ¼ cAhA þ cBhB
where cA and cB are polarization coefficients. Each valence
bonding NBO must in turn be paired with a corresponding
valence anti-bonding NBO:
rꢅAB ¼ cBhA ꢁ cAhB
to complete the span of the valence space. The Lewis-type
(donor) NBOs are thereby complemented by the non-Le-
wis-type (acceptor) NBOs that are formally empty in an
idealized Lewis picture. The interactions between ‘filled’
Lewis-type NBOs and ‘empty’ non-Lewis NBOs lead to
loss of occupancy from the localized NBOs of the idealized
Lewis structure into the empty non-Lewis orbitals, and
they are referred to as ‘delocalization’ corrections to the
zeroth-order natural Lewis structure [31].
4.4. Electronic spectra
The experimental electronic spectra of 1a and 1b are pre-
sented in Figs. 3 and 4, respectively. The positions of
absorption bands for the other [ReOX2(hbo)(EPh3)] com-
plexes are given in the experimental part. As can be seen
from Figs. 3 and 4 the UV–Vis spectra of the cis and trans
stereoisomers are very similar in terms of the position,
intensity and shape of the bands in the whole region
1100–180 nm. Similar to the IR measurements they are
Similar to the previous described [ReOX2(O–N)(PPh3)]
chelates [13–15], two strongly polarized to the oxygen atom
Table 7
The energy and molar absorption coefficients of experimental absorption bands and the electronic transitions calculated with the TDDFT method for 1b
The most important orbital excitations
Character
k [nm]
E [eV]
f
Experimental
K [nm]
E [eV]
e
H ? L + 1
H-1 ? L
H-1 ? L + 1
H-2 ? L
H-4 ? L
H-5 ? L
H ? L + 2
H-9 ? L + 1
H-8 ? L
d/p(hbt)/p(Br) ? d
p(hbt)/p(Br)/d ? d
p(hbt)/p(Br)/d ? d
p(hbt) ? d
644.9
533.7
451.6
414.9
405.2
391.5
369.3
361.5
1.92
2.32
2.74
2.99
3.06
3.17
3.36
3.43
0.0003
0.0010
0.0772
0.0104
0.0165
0.0130
0.0530
0.0130
638.5
(1.94)
80
445.0
359.0
(2.79)
(3.45)
550
p(PPh3)/n(P) ? d
p(PPh3) ? d
3450
d ? p*(hbt)
p(Br)/p(Ot) ? d
p(PPh3)/p(Br) ? d
p (PPh3)/p(Br) ? d
p(hbt)/p(Br)/d ? p*(hbt)
p(hbt)/p(Br)/d ? d
p (PPh3)/p(Br) ? d
p (PPh3)/p(Br) ? d
p(Cl)/p(Ot)/p (PPh3) ? d
p(hbt) ? p*(hbt)
H-10 ? L
346.2
340.4
3.58
3.64
0.1086
0.0392
317.0
(3.91)
4650
H-1 ? L + 2
H-2 ? L + 3
H-8 ? L + 1
H-8 ? L + 1
H-12 ? L
H-2 ? L + 2
H-3 ? L + 2
H-4 ? L + 3
H-16 ? L + 1
H-7 ? L + 4
H-4 ? L + 4
H-4 ? L + 4
H-4 ? L + 5
H-13 ? L + 3
H-13 ? L + 3
339.0
335.0
309.1
302.4
278.9
277.8
238.2
3.66
3.70
4.01
4.10
4.31
4.46
5.21
0.0701
0.0439
0.0597
0.1055
0.0645
0.0960
0.0236
274.0
222.0
(4.52)
(5.58)
10950
18400
p(hbt)/p(Br)/p(PPh3) ? p*(hbt)
p(PPh3)/n(P) ? d
p(Br)/p(hbt)/p(Ot)/n(P) ? d
p(PPh3)/p(Br) ? p*(PPh3)
p(PPh3)/n(P) ? p*(PPh3)
p(PPh3)/n(P) ? p*(PPh3)
p(PPh3)/n(P) ? p*(PPh3)
p(hbt)/p(Br) ? d
236.3
232.2
5.25
5.34
0.0342
0.0276
p(hbt)/p(Br) ? d
232.2
5.34
0.0442
206.0
(6.02)
29980

B. Machura et al. / Polyhedron 27 (2008) 1679–1689
1687
indistinctive for molecular structure determination. In
order to discussion this observation in more detail, the
time-dependent density functional calculations (TDDFT)
were employed to produce a hundred of singlet excited-
states starting from the ground-state geometries of 1a
and 1b optimized in the gas phase. The calculated elec-
tronic spectra of 1a and 1b are presented in Figs. 3 and
and relative energy to the orbitals HOMO and LUMO
involved in the electronic transitions. The simplified molec-
ular orbital diagrams of 1a and 1b with several contours of
occupied and unoccupied MOs (active in the electronic
transitions) are presented in Figs. 5 and 6, respectively.
The TDDFT/PCM calculations show that the longest
wavelength experimental bands of 1a and 1b (at 649.5 for
cis and 638.5 nm for trans) originate in the HOMO ?
LUMO and HOMO ? LUMO + 1 transitions. The
HOMO, LUMO and LUMO + 1 orbitals are delocalized
among rhenium ion, bromide, oxo and hbt ligands, so a
delocalized MLLCT (metal-ligand-to-ligand CT) descrip-
tion also can be used. However, considering that these
molecular orbitals comprise mainly rhenium 5d atomic
orbitals (Figs. 5 and 6), the HOMO ? LUMO and
4, respectively. Each calculated transition is represented
2
by a gaussian function y ¼ ceꢁbx with the height (c) equal
to the oscillator strength and b equal to 0.04 nmꢁ2
.
Tables 6 and 7 present the most important electronic
transitions calculated with the TDDFT method assigned
to the observed absorption bands of 1a and 1b. The assign-
ment of the calculated orbital excitations to the experimen-
tal bands was based on an overview of the contour plots
L+5
L+4
π
*(PPh3)
-1.00
-2.00
-3.00
-4.00
-5.00
-6.00
-7.00
π*(PPh3)
2
2
L+3
L+2
dx -y
π*(bthoz)
dyz, π(Ot), π(Obthoz)
d
L+1
LUMO
xz, π(Ot), π(Obthoz)
dxy, π(Cl), π(bthoz)
xy, π(Cl), π(bthoz)
HOMO
H-1
d
π(bthoz), π(PPh3), n(P)
H-3
π(Cl), π(PPh3)
H-2
H-4
H-5
π(Cl), π(bthoz), π(PPh3)
Fig. 5. The energy (eV), character and some contours of the unoccupied molecular orbitals of 1a. Positive values of the orbital contour are represented in
blue (0.04 a.u.) and negative values – in yellow (ꢁ0.04 a.u.). (For interpretation of the references to colour in this figure legend, the reader is referred to the
web version of this article.)

1688
B. Machura et al. / Polyhedron 27 (2008) 1679–1689
L+5
L+4
π*(PPh3)
π*(PPh3)
-1.00
-2.00
-3.00
-4.00
-5.00
-6.00
-7.00
2
2
dx -y
L+3
L+2
π*(bthoz)
dyz, π(Ot), π(Obthoz)
L+1
dxz, π(Ot), π(Obthoz)
LUMO
dxy, π(Cl), π(bthoz)
HOMO
H-1
π(bthoz), π(Cl), dxy
π(bthoz)
H-2
H-3
H-4
H-5
π(bthoz), π(Cl), π(PPh3)
π(PPh3), n(P)
π(PPh3)
Fig. 6. The energy (eV), character and some contours of the unoccupied molecular orbitals of 1b. Positive values of the orbital contour are represented in
blue (0.04 a.u.) and negative values – in yellow (ꢁ0.04 a.u.). (For interpretation of the references to colour in this figure legend, the reader is referred to the
web version of this article.)
HOMO ? LUMO+1 transitions may be ascribed as tran-
sitions of d ? d character.
Acknowledgement
The observed absorptions at 446.0 nm (cis-Br) and
445.0 nm (trans-Br) can be assigned to Ligand-Metal
Charge Transfer transitions occurring from the bromide
and hbtꢁ ligand for cis and bromide, hbtꢁ and phosphine
ligand for trans halide complex.
The Gaussian03 calculations were carried out in the
Wrocł aw Centre for Networking and Supercomputing,
WCSS, Wrocław, Poland.
Appendix A. Supplementary data
The absorption band at 361.2 nm (cis-Br) and 359.0 nm
(trans-Br) can be related to HOMO ? LUMO + 2 excita-
tion of d/p(Br)/p(bthoz) ? p*(bthoz) character with a cer-
tain contribution of Ligand-Metal Charge Transfer
transitions.
For both stereoisomers the experimental bands below
300 nm result mainly from Ligand–Ligand Charge Transfer
and interligand (IL) transitions.
CCDC 673361, 673362, 673363, 673364, 673365, and
673366 contain the supplementary crystallographic data
for this paper. 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. Supplemen-

B. Machura et al. / Polyhedron 27 (2008) 1679–1689
1689
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