Synthesis, characterization and molecular structures of the trichloro-η1-benzoyldiazenido [ReCl3{η1-NNC(O)Ph}(PPh3) 2] and oxorhenium [ReOCl2(OMe)(PPh3) 2] complexes derived from reactions of [ReCl2{η2-NNC(O)Ph}(PPh3) 2] with a peroxide or dioxygen

Article abstract of DOI:10.1016/j.ica.2006.06.032

The reactions of [ReCl₂{η²-NNC(O)Ph}(PPh₃) ₂] (1) with t-BuOOH, in C₆H₆ or chlorinated solvents, at room temperature or with MeOH upon reflux in air lead to the trichloro-η¹-benzoyldiazenido [ReCl₃{η¹-NNC(O)Ph}(PPh₃) ₂] (2) or the methoxy-oxo [ReOCl₂(OMe)(PPh₃)₂] (3) compound, respectively, which have been characterized by spectroscopic and FAB⁺-MS methods, elemental and single crystal X-ray diffraction analyses. They show distorted octahedral coordinaiton geometries with trans triphenylphosphine ligands, an essentially linear η¹-diazenido moiety in 2 and the methoxy group in 3 in trans position to the oxo ligand.

Full text of DOI:10.1016/j.ica.2006.06.032

Inorganica Chimica Acta 359 (2006) 4421–4426
www.elsevier.com/locate/ica
Note
Synthesis, characterization and molecular structures of the
trichloro-g1-benzoyldiazenido [ReCl3{g1-NNC(O)Ph}(PPh3)2] and
oxorhenium [ReOCl2(OMe)(PPh3)2] complexes derived from reactions
of [ReCl2{g2-NNC(O)Ph}(PPh3)2] with a peroxide or dioxygen
a
b
a,
*
Alexander M. Kirillov , Matti Haukka , Armando J.L. Pombeiro
a
Centro de Quı´mica Estrutural, Complexo I, Instituto Superior Te´cnico, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
b
University of Joensuu, Department of Chemistry, P.O. Box 111, FIN-80101 Joensuu, Finland
Received 30 May 2006; accepted 11 June 2006
Available online 27 June 2006
Abstract
The reactions of [ReCl2{g2-NNC(O)Ph}(PPh3)2] (1) with t-BuOOH, in C6H6 or chlorinated solvents, at room temperature or with
MeOH upon reflux in air lead to the trichloro-g1-benzoyldiazenido [ReCl3{g1-NNC(O)Ph}(PPh3)2] (2) or the methoxy-oxo [ReOCl2(O-
Me)(PPh3)2] (3) compound, respectively, which have been characterized by spectroscopic and FAB+-MS methods, elemental and single
crystal X-ray diffraction analyses. They show distorted octahedral coordinaiton geometries with trans triphenylphosphine ligands, an
essentially linear g1-diazenido moiety in 2 and the methoxy group in 3 in trans position to the oxo ligand.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Rhenium; Benzoyldiazenido complexes; Oxo complexes; Phosphine ligands; Crystal structures
1. Introduction
attempted the reaction of 1 with either an organic hydro-
peroxide or dioxygen (air), aiming at the isolation of some
peroxo complexes which hopefully could act as active
intermediate species in the above peroxidative oxidation
catalysis [15], towards getting a better understanding of
this catalytic process. However, instead of the expected
formation of peroxo complexes, we have obtained the
already known [17] trichloro-g1-benzoyldiazenido [ReCl3-
{g1-NNC(O)Ph}(PPh3)2] (2) complex and the new oxorhe-
nium [ReOCl2(OMe)(PPh3)2] (3) compound (Scheme 1).
Their syntheses, spectroscopic and FAB+-MS character-
ization, elemental and single crystal X-ray diffraction anal-
yses are now reported.
The benzoylhydrazido compound [ReCl2{g2-NNC(O)-
Ph}(PPh3)2] (1) is a well-known starting material for the
syntheses of a variety of Re complexes with significance
in the fields of nitrogen fixation [1–11] and nuclear-medi-
cal research [12–14]. Recently, we have reported [15] that
1 and some derived benzoylhydrazido and diazenido Re
complexes bearing N,O-ligands can catalyze the peroxida-
tive oxidation of cycloalkanes, which is expected to occur
via the formation of intermediate peroxo and/or oxo Re
species. Following observations [16] that the related meth-
yldiazenidocarboxylate compound [ReCl2{g1-NNC(O)-
OMe}(PPh3)2(dmf)]
{dmf = N,N-dimethylformamide}
can react with dioxygen to give the g2-peroxo [ReCl2-
{g1-NNC(O)OMe}(g2-O2)(PPh3)2] complex, we have
2. Experimental
2.1. Materials and methods
*
All chemicals were obtained from commercial sources
and used as received. The solvents were dried and degassed
Corresponding author. Fax: +351 21 846 4455.
E-mail address: pombeiro@ist.utl.pt (A.J.L. Pombeiro).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.06.032

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A.M. Kirillov et al. / Inorganica Chimica Acta 359 (2006) 4421–4426
PPh3
in air to produce a brown cloudy solution. The solid was
filtered off, washed with MeOH (3 · 5 mL), Et2O
(3 · 5 mL) and finally with Me2CO (5 · 10 mL), and then
dried in vacuo to yield complex 3 as a brownish pink
microcrystalline solid. Yield: 39% (35 mg) based on 1.
Mp = 155 ꢁC. IR (KBr), selected bands, cmꢀ1: 3047 m br
mas(CH) and 3022 w ms(CH), 1481 s and 1437 s m(PPh),
1094 s m(OMe), 946 s m(Re@O), 744 s and 692 s m(PPh).
1H NMR (CDCl3), d: 7.75–7.39 (m, 30H, PPh3), 2.26 (s,
3H, OMe). 31P{1H} NMR (CDCl3), d: 35.59 (s). FAB+-
MS, m/z 795 (M+ꢀCl+2H), 761 (M+ꢀClꢀMeOH). Anal.
Calc. for C37H33Cl2O2P2Re: C, 53.62; H, 4.01. Found: C,
53.93; H, 4.12%. X-ray quality crystals of 3 were obtained
by slow evaporation of the reaction filtrate at room
temperature.
C
O
N
Ph
Cl
Cl
N
t-BuOOH
Re
C6H6 or
chlorinated
solvent, r.t.
Cl
PPh3
Re
PPh3
Cl
Cl
N N
O
2
Ph
C
PPh3
PPh3
O
Cl
MeOH, air
reflux
Re
1
Cl
MeO
PPh3
3
Scheme 1.
(if necessary) by standard methods. [ReCl2{g2-
NNC(O)Ph}(PPh3)2] (1) was prepared by a published
method [17,18].
C, H and N elemental analyses were carried out by the
2.4. X-ray structural determinations
´
Microanalytical Service of the Instituto Superior Tecnico.
Melting points were determined on a Kofler table. The
FAB mass spectra were obtained on a Trio 2000 instru-
ment by bombarding 3-nitrobenzyl alcohol (m-NBA)
matrices of the samples with 8 keV (ca. 1.18 · 1015 J) Xe
atoms. Mass calibration for data system acquisition was
achieved using CsI. Infrared spectra (4000–400 cmꢀ1) were
recorded on a Jasco FT/IR-430 instrument in KBr pellets.
1H and 31P{1H} NMR spectra were measured on a Varian
The X-ray diffraction data of 2 and 3 were collected with
a Nonius Kappa CCD diffractometer using Mo Ka radia-
tion. The DENZO-SCALEPACK program package [19] was used
for cell refinements and data reductions. The structures
were solved by direct methods using the SIR-97 or SIR-
2002 programs [20,21] with the WinGX graphical user
interface [22]. An empirical absorption correction was
applied to all data (Tmax/Tmin: 0.28498/0.21664 and
0.16940/0.12578 for 2 and 3, respectively) using XPREP in
SHELXTL v.6.12 program [23]. Structural refinements were
carried out with SHELXL-97 [24]. All hydrogens were placed
UNITY 300 spectrometer at ambient temperature. The 31
P
chemical shifts are relative to external 85% H3PO4 solution.
2.2. Synthesis of [ReCl3{g1-NNC(O)Ph}(PPh3)2] (2)
To a deep green solution of 1 (100 mg, 0.109 mmol) in
C6H6 (6 mL), an excess of t-BuOOH (70% in H2O,
1.09 mmol, 150 lL) was added and the reaction mixture
was stirred under dinitrogen atmosphere and at room tem-
perature for 1.5 h. The resulting deep red cloudy solution
was filtered and concentrated under reduced pressure to give
a reddish brown oil. This was treated with MeOH (10 mL) to
afford a suspension which was filtered off, washed with
MeOH (3 · 5 mL) and dried in vacuo to yield complex 2 as
a brown solid. Yield: 50% (52 mg) based on 1. Higher yields
(up to ca. 70%) can be achieved by using a chlorinated sol-
vent, such as CH2Cl2, CHCl3 or CCl4, instead of C6H6.
Mp = 190 ꢁC. IR (KBr), selected bands, cmꢀ1: 3057 w
m(CH), 1688 s m(C@O), 1566 s m(N@N), 1483 m and 1435 s
m(PPh), 1227 s m(NC), 745 m and 693 s m(PPh). FAB+-MS,
m/z 950 (M++H), 914 (M+ꢀCl), 813 (M+ꢀ{NNCOPh}
ꢀ3H), 781 (M+ꢀ{NNCOPh}ꢀCl), 746 (M+ꢀ{NNCOPh}
ꢀ2Cl). Anal. Calc. for C43H35Cl3N2OP2Re: C, 54.35; N,
2.95; H, 3.71. Found: C, 54.66; N, 2.60; H, 3.68%. X-ray
quality crystals of 2 were grown by slow evaporation at
5 ꢁC of a C6H6–EtOH(MeOH) solution.
Table 1
Crystal data and structure refinement details for complexes 2 and 3
Compound
2
3
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
C
950.22
100(2)
43H35Cl3N2OP2Re
C37H33Cl2O2P2Re
828.67
100(2)
0.71073
triclinic
˚
0.71073
monoclinic
P21/c
21.5014(12)
9.8748(4)
19.9444(12)
90
113.417(2)
90
3885.9(4)
4
ꢀ
Space group
P1
˚
a (A)
11.4015(3)
16.8967(3)
25.8640(6)
92.5310(10)
90.4730(10)
96.091(2)
4949.26(19)
6
1.668
3.975
73538
22345
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalc (Mg/m3)
l(Mo Ka) (mmꢀ1
1.624
3.453
18906
6576
)
Number of reflections
Number of unique data
Rint
Final R1a, wR2 [I P 2r(I)]
R1, wR2 (all data)
Goodness-of-fit on F2
0.0766
0.0847
b
0.0628, 0.1264
0.0950, 0.1379
1.204
0.0464, 0.0809
0.0983, 0.0969
1.036
2.3. Synthesis of [ReOCl2(OMe)(PPh3)2] (3)
Largest difference in peak
1.687 and ꢀ1.208
1.148 and ꢀ1.661
ꢀ3
˚
and hole (e A
)
P
P
a
A green suspension of 1 (100 mg, 0.109 mmol) in 40 mL
MeOH (was not dried prior to use) was refluxed for 2 days
R1 = ||Fo| ꢀ |Fc||/ |Fo|.
P
P
2
2 1=2
b
wR2 ¼ ½ ½wðF 2o ꢀ F c2Þ ꢁ= ½wðF 2oÞ ꢁꢁ
.

A.M. Kirillov et al. / Inorganica Chimica Acta 359 (2006) 4421–4426
4423
Table 2
Selected bond lengths (A) and bond angles (ꢁ) for compounds 2 and 3
˚
Compound 2
Compound 3a
Re(1)–N(1)
Re(1)–Cl(1)
Re(1)–Cl(2)
Re(1)–Cl(3)
Re(1)–P(1)
Re(1)–P(2)
N(1)–N(2)
N(2)–C(1)
O(1)–C(1)
1.805(9)
2.404(3)
2.328(3)
2.337(3)
2.519(3)
2.546(3)
1.132(12)
1.446(15)
1.244(15)
Re(1)–O(1)
Re(1)–O(2)
Re(1)–Cl(1)
Re(1)–Cl(2)
Re(1)–P(1)
Re(1)–P(2)
O(1)–C(1)
1.898(4)
1.705(4)
2.4363(14)
2.3788(14)
2.5296(17)
2.5203(17)
1.404(7)
O(1)–Re(1)–Cl(1)
O(1)–Re(1)–Cl(2)
O(2)–Re(1)–Cl(1)
O(2)–Re(1)–Cl(2)
O(2)–Re(1)–O(1)
Cl(2)–Re(1)–Cl(1)
O(1)–Re(1)–P(1)
O(1)–Re(1)–P(2)
O(2)–Re(1)–P(1)
O(2)–Re(1)–P(2)
Cl(1)–Re(1)–P(1)
Cl(1)–Re(1)–P(2)
Cl(2)–Re(1)–P(1)
Cl(2)–Re(1)–P(2)
P(2)–Re(1)–P(1)
C(1)–O(1)–Re(1)
84.44(13)
89.98(13)
89.93(14)
95.72(14)
173.36(19)
175.87(6)
91.13(14)
87.87(13)
91.99(14)
89.21(14)
86.07(5)
95.78(5)
92.70(5)
85.35(5)
177.46(5)
145.5(4)
N(1)–Re(1)–Cl(1)
N(1)–Re(1)–Cl(2)
N(1)–Re(1)–Cl(3)
N(1)–Re(1)–P(1)
N(1)–Re(1)–P(2)
Cl(2)–Re(1)–Cl(1)
Cl(2)–Re(1)–Cl(3)
Cl(3)–Re(1)–Cl(1)
Cl(1)–Re(1)–P(1)
Cl(1)–Re(1)–P(2)
Cl(2)–Re(1)–P(1)
Cl(2)–Re(1)–P(2)
Cl(3)–Re(1)–P(1)
Cl(3)–Re(1)–P(2)
P(1)–Re(1)–P(2)
N(2)–N(1)–Re(1)
a
178.3(3)
97.1(3)
93.1(3)
90.4(2)
89.8(2)
83.55(10)
168.69(10)
86.35(10)
91.27(9)
88.57(9)
85.12(9)
95.44(10)
90.04(9)
89.37(9)
179.40(9)
173.3(9)
Fig. 2. Thermal ellipsoid view of complex 3 with atomic numbering
scheme. Thermal ellipsoids are drawn at 50% probability.
3. Results and discussion
The reaction of the rhenium(V) dichloro-g2-ben-
zoylhydrazido(3ꢀ) complex 1 with an excess of tert-butyl
hydroperoxide in benzene solution at room temperature
leads to the known [17] (see below) rhenium(IV) tri-
Average values within three independent molecules of 3 in the asym-
metric unit are given.
chloro-g1-benzoydiazenido(1ꢀ)
complex
[ReCl3{g1-
in idealized positions and constrained to ride on their par-
ent atom. The crystallographic data are summarized in
Table 1 and selected bond lengths and bond angles in Table
2. The molecular structures of complexes 2 and 3 are shown
in Figs. 1 and 2, respectively.
NNC(O)Ph}(PPh3)2] (2). It involves the unexpected overall
single-electron reduction and chlorination of the metal.
The mechanistic details of the conversion are still unknown
but the simple opening of the g2-NNC(O)Ph(3ꢀ) ring to
give the g1-NNC(O)Ph(1ꢀ) ligand with the uncoordinated
benzoyl group corresponds to a Re(V) ! Re(III) reductive
elimination. Oxidative chlorination (with another complex
molecule as the halogen source) would then lead to the
Re(IV) trichloro-complex 2. This chlorination conceivably
is assisted by the peroxo reagent in accord with the known
involvement of halide oxidation by peroxo-complexes in
peroxidative halogenation reactions catalyzed by haloper-
oxidases and their model complexes [25].
The yield of 2 can be increased on changing the reaction
solvent from benzene to a chlorinated one (e.g. CH2Cl2,
CHCl3 or CCl4). In fact, the formation of 2 was reported
earlier [17] by reacting 1 with Cl2 in tetrachloromethane
solution, albeit the crystallographic investigation of 2 has
not been performed before the current study.
On other attempts to obtain peroxo-complexes from the
reactions of t-BuOOH with different chloro-rhenium com-
pounds, we have also observed metal chlorination in non-
chlorinated solvents, for example in the formation of the
known complexes [ReCl4(OPPh3)2] [26] and [ReCl2-
(dppe)2]Cl [27,28] from [ReOCl3(PPh3)2] and trans-
[ReCl(N)2(dppe)2]
{dppe = 1,2-bis(diphenylphosphino)-
Fig. 1. Thermal ellipsoid view of complex 2 with atomic numbering
scheme. Thermal ellipsoids are drawn at 50% probability.
ethane-P,P0}, respectively.

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A.M. Kirillov et al. / Inorganica Chimica Acta 359 (2006) 4421–4426
In contrast to the related methyldiazenidocarboxylate
the trans Re–Cl2 and Re–Cl3 distances of 2.328(3) and
2.337(3) A, respectively, which is indicative of a stronger
compound [ReCl2{g1-NNC(O)OMe}(PPh3)2(dmf)] [16]
(see above), 1 does not afford a peroxo-complex upon
treatment with either bubbling air or dioxygen in various
solvents. Nevertheless, the prolonged reflux for ca. 2 days
in air of a suspension of 1 in methanol leads to the forma-
tion of the pink methoxyoxorhenium(V) complex [ReO-
Cl2(OMe)(PPh3)2] (3) (Scheme 1). The liberation of the
benzoyldiazenido ligand in 1 possibly occurs upon nucleo-
philic attack of methanol to the carbonyl carbon to give
methylbenzoate PhCOOMe and N2 [5,6].
˚
trans-influence of the g1-benzoyldiazenido ligand than that
of a chloro ligand. Other bonding parameters in 2 do not
differ significantly from the expected values found for
related dichloro bis(triphenylphosphine) rhenium com-
pounds bearing the g1-benzoyldiazenido ligand, e.g.
[ReCl2{g1-NNC(O)Ph}(PPh3)2(X)] {X = MeCN [35], pyr-
azole [36,37], pyridine [36], NH2CH2C„CH [38],
NH2NHC(@S)Ph [39], NH2NHC(@O)SMe [39], NH3
[40]}.
Both compounds 2 and 3 are stable in the solid state,
and 3 is also stable in solutions of common solvents, e.g.
CH2Cl2, CHCl3 or C6H6. Compound 2 decomposes to give
1 and some unidentified species within minutes/hours in
those solvents. Common features of the IR spectra of 2
and 3 comprise weak/medium m(CH) bands in the 3060–
3020 cmꢀ1 range, and strong bands due to the triphenyl-
phosphine ligands or phenyl rings are observed at ca.
1480, 1435, 745 and 690 cmꢀ1. In 2, the typical m(C@O)
and m(N@N) vibrations for the benzoyldiazenido ligand
are detected at 1688 and 1566 cmꢀ1, respectively. The IR
spectrum of 3 also exhibits characteristic strong m(OMe)
and m(Re@O) bands at 1094 and 946 cmꢀ1, respectively,
in agreement with other methoxy- and/or oxorhenium
complexes [29–33]. The monoprotonated molecular ion
(M++H) with the expected isotopic pattern is observed at
m/z = 950 in the FAB-MS+ spectrum of 2. Its fragmenta-
tion corresponds to the stepwise elimination of chloride
or/and benzoyldiazenido moieties. No molecular ion is
found in the FAB-MS+ spectrum of 3 and the heaviest
detected fragments correspond to (M+ꢀCl+2H) and
O
C
Ph
[Re]
N
N
a
As shown in Fig. 2, the molecular structure of 3 also
exhibits a distorted octahedral coordination geometry
about the rhenium centre with two trans PPh3 groups.
The oxo, methoxy and two trans chloride ligands are in
the equatorial positions. The Re–O2 bond length of
1.705(4) A is in agreement with the normal Re–Ooxo bond
distances (ca. 1.67–1.70 A) [41,42] in six-coordinated
monooxorhenium complexes. The Re–O1 distance of
1.898(4) A is also unexceptional for Re compounds with
˚
˚
˚
methoxy or ethoxy moieties [29–31,43]. The major devia-
tion from the octahedral geometry in 3 is that of the O2–
Re–O1 angle of 173.36(19)ꢁ, whereas the other bond angles
are relatively close to the idealized 90ꢁ and 180ꢁ. Thus,
both triphenylphosphine and chloride ligands are bound
almost linearly (i.e. P1–Re–P2 177.46(5)ꢁ and Cl1–Re–
Cl2 175.87ꢁ) with the average Re–P and Re–Cl distances
1
(M+ꢀClꢀMeOH). The H NMR spectrum of complex 3
shows expected resonances for the coordinated PPh3 or
OMe ligands [30–33], while the singlet in the 31P{1H} spec-
trum is consistent with trans coordination of the two tri-
phenylphosphine ligands. Elemental analyses agree with
the proposed formulations, which are authenticated by sin-
gle crystal X-ray diffraction studies, as indicated below.
The molecular structure of 2 (Fig. 1) is distorted octahe-
dral with the two phosphine ligands in trans position and
the equatorial sites occupied by three chlorides and the
g1-diazenido ligand. The Cl2–Re–Cl3 angle of
168.69(10)ꢁ represents the major deviation from the octahe-
dral geometry around the rhenium centre. The g1-diazen-
ido ligand is bound in an essentially linear fashion
exhibiting the Re–N1–N2 angle of 173.3(9)ꢁ. The Re–N1
˚
of 2.5250(17) and 2.4076(14) A, respectively. These and
other metrical parameters in 3 are in agreement with those
reported for resembling Re complexes such as
[ReOCl2(X)(PPh3)2] {X = OEt [43], OPri [44], Cl [45], F
[46]}.
4. Final comments
The g2-benzoylhydrazido complex 1 (commonly referred
to as the ‘‘green chelate’’), in spite of its recognized ability to
act as a convenient starting material for a wide variety of
rhenium coordination compounds, does not appear to be,
at least under the usual experimental conditions we have
applied, a suitable source of a Re centre for the preparation
of peroxo-complexes. Instead of leading to such a type of
product, an unexpected metal chlorination was observed
upon reaction with t-BuOOH, whereas metal oxygenation
resulted from the reaction with dioxygen.
˚
distance [1.805(9) A] is comparable to that of 1 [15] and
those of other diazenido Re complexes [34], whereas the
˚
N1–N2 bond length of 1.132(12) A is slightly shorter than
˚
typical N@N bonds [ca. 1.21–1.24 A] encountered in vari-
ous g1-diazenido compounds [15,34]. According to a clas-
sification of organohydrazido ligands [34], such a type of
bonding parameters in 2 is indicative of a linear, four-elec-
tron donor diazenido(1ꢀ) species (a). The Re–Cl1 bond
Nevertheless, the observed reactions have their own
interest and deserve to be further explored. Hence, the lat-
ter reaction can hopefully be extended to the synthesis of
other alkoxy-oxo complexes derived from O2 in an alcohol.
˚
length [2.404(3) A], involving the chloride trans to the
NNC(O)Ph ligand, is slightly elongated in comparison with

A.M. Kirillov et al. / Inorganica Chimica Acta 359 (2006) 4421–4426
[16] T. Nicholson, J. Zubieta, Inorg. Chim. Acta 134 (1987) 191.
4425
The former reaction may be particularly promising
towards the development of peroxide-assisted metal halo-
genations, still little explored in spite of the known metal-
catalyzed peroxidative halogenation of organic compounds
such as olefins (catalyzed by haloperoxidases and their
model complexes [25,47–49]) or alkanes (catalyzed by
Amavadine and some vanadium complexes [50]).
[17] J. Chatt, J.R. Dilworth, G.J. Leigh, V.D. Gupta, J. Chem. Soc. A
(1971) 2631.
[18] J. Chatt, W. Hussain, G.J. Leigh, H.M. Ali, C.J. Pickett, D.A.
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307–326.
[20] A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C. Giaco-
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Acknowledgments
[21] M.C. Burla, M. Camalli, B. Carrozzini, G.L. Cascarano, C.
Giacovazzo, G. Polidori, R. Spagna, J. Appl. Crystallogr. 36
(2003) 1103.
[22] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.
[23] G.M. Sheldrick, SHELXTL v. 6.12, Bruker Analytical X-ray Systems,
Bruker AXS, Inc., Madison, WI, USA, 2002.
This work has been partially supported by the Founda-
tion for Science and Technology (FCT) and its POCI 2010
programme (FEDER funded). A.M.K. is grateful to the
FCT and the POCTI programme for a fellowship (BD/
6287/01).
[24] G.M. Sheldrick, SHELXL-97: Program for Crystal Structure
Determination, University of Go¨ttingen, Go¨ttingen, Germany,
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Appendix A. Supplementary material
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