Selenium-containing heterocycles from isoselenocyanates: Synthesis of 5-amino-2,4-dihydro-3H-1,2,4-triazole-3-selones

Article abstract of DOI:10.1002/hlca.200790067

The reaction of S-methylisothiosemicarbazide hydroiodide (=S-methyl hydrazinecarboximido-thioate hydroiodide; 1), prepared from thiosemicarbazide by treatment with MeI in EtOH, and aryl isoselenocyanates 5 in CH ₂Cl₂ affords 3H-1,2,4-triazole-3-selone derivatives 7 in good yield (Scheme 2, Table 10). During attempted crystallization, these products undergo an oxidative dimerization to give the corresponding bis(4H-1,2,4-triazol-3-yl) diselenides 11 (Scheme 3). The structure of 11a was established by X-ray crystallography.

Full text of DOI:10.1002/hlca.200790067

Helvetica Chimica Acta – Vol. 90 (2007)
641
Selenium-Containing Heterocycles from Isoselenocyanates: Synthesis of
5-Amino-2,4-dihydro-3H-1,2,4-triazole-3-selones
by Geoffroy L. Sommen1), Anthony Linden, and Heinz Heimgartner*
Organisch-Chemisches Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich
(phone: þ 41446354282; fax: þ 41446356836; e-mail: heimgart@oci.uzh.ch)
The reaction of S-methylisothiosemicarbazide hydroiodide (¼ S-methyl hydrazinecarboximido-
thioate hydroiodide; 1), prepared from thiosemicarbazide by treatment with MeI in EtOH, and aryl
isoselenocyanates 5 in CH2Cl2 affords 3H-1,2,4-triazole-3-selone derivatives 7 in good yield (Scheme 2,
Table 1). During attempted crystallization, these products undergo an oxidative dimerization to give the
corresponding bis(4H-1,2,4-triazol-3-yl) diselenides 11 (Scheme 3). The structure of 11a was established
by X-ray crystallography.
1. Introduction. – The biochemistry and pharmacology of selenium is of current
interest, particularly with regard to public health. Selenium has long been recognized as
a dietary antioxidant and is now known to be an essential component to the active sites
of several enzymes, including glutathione peroxidase [1] and thioredoxine reductase,
which catalyze reactions essential for the protection of cellular components against
oxidative and radical damage [2]. A too low concentration of selenium in the plasma
has been identified as a risk factor for several diseases, including cancer [3],
cardiovascular disease [4], and osteoarthritis or AIDS [5]. Therefore, consumption
of Se-rich plants or yeast-based nutritional supplements is reported to reduce the risk of
cancer. It has also been suggested that plants are able to convert inorganic Se in the soil
or growth medium into organoselenium compounds, such as selenoamino acids [6], by
following a route similar to the sulfur assimilatory pathway [7].
In recent years, the interest in organoselenium chemistry increased remarkably.
There is no doubt that Se-containing organic molecules have played and continue to
play an important role in biology and medicine, and a large number of them are now
accepted as useful antioxidants [8], anticancer [9] and melanin-synthesis-regulating
agents [10], superoxide-anion scavengers [11], anti-inflammatory agents [12], and
compounds with antihypertensive [13], antinociceptive [14], antibiotic [15], and
antiviral activity [16], i.e., organoselenium compounds are nowadays an important class
of biologically active products [17] with pharmaceutical applications [18].
The interest in Se-compounds may also be attributed to their specific chemical
properties, which fit well into the requirements of modern organic synthesis, and many
of them are well adapted to chemo-, regio-, and stereoselective reactions [19][20].
1
)
Postdoctoral stay at the University of Zürich (08.2004 – 08.2005). Present address: Lonza AG,
Walliser Werke, CH-3930 Visp, Switzerland; e-mail: geoffroy.sommen@lonza.com.
ꢀ 2007 Verlag Helvetica Chimica Acta AG, Zürich

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Helvetica Chimica Acta – Vol. 90 (2007)
For all of these reasons, isoselenocyanates became a focus of interest in our research
group as building blocks in the synthesis of Se-containing heterocycles. Their special
chemical properties [21] make them very useful starting materials in heterocyclic
chemistry [22], as they are easy to prepare and safe to store [23]. Nevertheless, under
mild conditions, they undergo reactions, which are compatible with the presence of a
variety of unsaturated as well as multi-functional structural units. Therefore, they are
useful reagents in the preparation of natural products [24].
Within the family of triazoles, the corresponding thiones have gained special
importance. Several examples were described to be of pharmaceutical interest, e.g., as
agents with antibacterial activity [25]. A series of 1,2,4-triazolethiones have been
prepared by using isothiocyanates [25 – 27] (and refs. cited therein). For example, 2,4-
dihydro-3H-1,2,4-triazole-3-thione derivatives were synthesized by the reaction of
isothiocyanates with amidrazone hydrochlorides (¼carboximidic acid hydrazide
hydrochlorides) [26]. Correspondingly, 5-amino derivatives were obtained when S-
methylisothiosemicarbazide hydroiodide (¼ S-methyl hydrazinecarboximidothioate
hydroiodide; 1) [28] was reacted with primary aryl- or benzylamines, and the resulting
carbonohydrazonic diamide hydroiodide 2 was subsequently treated with aryl
isothiocyanates in EtOH [25b] (Scheme 1). Depending on the reaction temperature,
a 5-(arylamino)- (3) or 5-amino-2,4-dihydro-3H-1,2,4-triazole-3-thione (4) was iso-
lated.
Scheme 1
As for the reaction of isoselenocyanates with nucleophiles, it is known that N-, O-,
S-, and Se-nucleophiles add to the central C-atom [21a], whereas P-nucleophiles attack
either the central C-atom or the Se-atom [21b][29]. However, only a few examples
have been reported for the reaction of hydrazine derivatives with isoselenocyanates
[30], and nothing is known on the reaction with carbonohydrazonic diamide
compounds. Very recently, we have published the synthesis of 1,3,4-selenadiazine
derivatives from hydrazine, a-bromoacetophenones, and isoselenocyanates [31].
As a continuation of the previously published studies on the synthesis of Se-
containing heterocycles based on isoselenocyanate chemistry [32], we have recently
reported on the synthesis of 5-selenoxo-1,2,4-triazole-1-carboxylates by using a

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643
Mitsunobu strategy [33]. Following a similar strategy, Koketsu et al. have published the
preparation of 3-selenoxo-1,2,4-triazole derivatives by the reaction of acyl isoseleno-
cyanates with phenylhydrazine [30]. Furthermore, reactions of isoselenocyanates 5
with mercapto acids led to 2-selenoxo-1,3-thiazolidin-4-ones and 2-selenoxo-1,3-
thiazinan-4-ones in good yields [34].
In the present paper, the results of the investigations aimed at extending this
methodology to the synthesis of 5-amino-3H-1,2,4-triazole-3-selone derivatives are
reported.
2. Results and Discussion. – In the synthesis of the 1,3,4-selenadiazine derivatives
[31], hydrazine was used as a bis-nucleophilic reagent, which combined first with the
aryl isoselenocyanate 5 and, in a later reaction step, underwent the cyclization with the
acetophenone residue of the intermediate. In this case, cyclization occurred via a
condensation reaction. We report here the use of S-methylisothiosemicarbazide
hydroiodide (1) bearing a methylthio group, which will be the leaving group in the
cyclization step of the preparation of 5-amino-4-aryl-3H-1,2,4-triazole-3-selones 7
according to Scheme 2. After stirring for 12 h, the products were separated by filtration;
they were obtained in good yields and were pure enough to give unambiguous
spectroscopic data and elemental analyses (Table 1).
Scheme 2
The structures of compounds 7 were established on the basis of their spectroscopic
data, which correspond reasonably well with those of the previously described 5-
selenoxo-1,2,4-triazole-1-carboxylates [33]. In the IR spectra (KBr), the triazolese-
lones 7 show weak absorptions for NH at 3380 – 3150 cmꢀ1 and a strong C¼N
absorption at ca. 1640 cmꢀ1. The 1H-NMR signals for the NH and NH2 groups in CDCl3
appear at d(H) 13.6 – 12.9 and 6.5 – 5.3, respectively. Characteristic signals in the
13C-NMR spectra are observed for the triazole C-atoms (C(5) and C(3)) at d(C) 152 –
159). Furthermore, the ESI-MS show the [M þ Na]þ signal as the characteristic
ensemble of the peaks for the Se-isotopes.
A reaction mechanism for the formation of 7 is proposed in Scheme 2. After
deprotonation of the hydroiodide 1, nucleophilic addition of S-methylisothiosemicar-

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Helvetica Chimica Acta – Vol. 90 (2007)
Table 1. Preparation of 5-Amino-2,4-dihydro-3H-1,2,4-triazole-3-selones 7 from Isoselenocyanates 5
a
b
c
d
e
7
Yield [%] 78
72
80
82
75
bazide onto 5 leads to an intermediate 6, which undergoes a cyclization via elimination
of MeSH.
Although all analytical data are in accordance with structure 7, we cannot exclude
the tautomeric structures 8 and 9 with certainty. Even structure 10, which could be the
result of the alternative cyclization of 6 via the Se-atom, is compatible with the data.
Therefore, we decided to establish the structure by X-ray crystallography. However, the
triazoles 7, which were obtained directly from the reaction mixture after filtration, were
always amorphous, and the crystallization of these products proved to be a difficult
task. An explanation for this behavior could be the presence of NH groups with the
possibility of the formation of different tautomeric structures (i.e., 7 – 9). The
recrystallization needed rather polar solvents, and the formation of metallic Se and
decomposition of the product was observed even at low temperature. After several
attempts, crystallization of 7a from MeOH/CH2Cl2 gave orange crystals with a m.p.
206 – 2088 and a molecular mass of 478(ESI-MS). Therefore, the structure of the
recrystallized product was proposed to be the diselenide 11a, which could be formed
from the tautomeric triazoleselenol 9a by oxidative dimerization (Scheme 3). This
assumption was established by an X-ray crystal-structure determination (Fig. 1).
Scheme 3
The asymmetric unit in the crystal structure contains one molecule of 11a, one
MeOH molecule, and two molecules of H2O (Fig. 2). The five-membered heterocyclic
rings are planar, with the adjacent atoms N(3), Se(1) and N(14), C(17), respec-
tively, also being in the corresponding plane, while C(6) and Se(2) deviate by
0.213(2) and 0.114(1) Š, respectively, from these planes. The torsion angle
C(1)ꢀSe(1)ꢀSe(2)ꢀC(12) is ꢀ 96.08(9)8, as usually observed for oligosulfides and
di- and triselenides (see, e.g., [36][37]). The planes of the Ph groups at N(2) and N(13)

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645
Fig. 1. ORTEP Plot [35] of the molecular structure of 11a (arbitrary atom numbering; 50% probability
ellipsoids)
are significantly twisted out of the planes of their parent heterocyclic rings with the
dihedral angles between the planes being 87.95(11) and 55.67(11)8, respectively.
Intermolecular H-bonds link the molecules of 11a, MeOH, and H2O into a three-
dimensional framework. Each molecule of 11a donates H-bonds to one neighboring
molecule of 11a, as well as to three different H2O molecules. One of the two symmetry-
independent H2O molecules donates H-bonds to two different molecules of 11a. The
other H2O molecule donates one H-bond to a molecule of 11a and a second H-bond to
the O-atom of a MeOH molecule. The MeOH molecule donates a H-bond to one of the
H2O molecules. The H-bond acceptor atoms in 11a are the unsubstituted N-atoms in
the five-membered rings.
In conclusion, we have shown that isoselenocyanates 5 react with isothiosemicar-
bazide hydroiodide 1 in basic media to give an intermediate, which undergoes a ring
formation to give 4-aryl-2,4-dihydro-3H-1,2,4-triazole-3-selones 7 in good yields. These
products are easily oxidized to give bis(4H-triazol-3-yl) diselenides 11.

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Helvetica Chimica Acta – Vol. 90 (2007)
Fig. 2. Molecularpacking of 11a projected down the a-axis showing the H-bonding scheme (equivalent
isotropic spheres for atoms; uninvolved H-atoms are omitted for clarity)
We thank the analytical units of our institute for spectra and analyses. Financial support of this work
by the Dr. Helmut Legerlotz-Foundation and F. Hoffmann – La Roche AG, Basel, is gratefully
acknowledged.
Experimental Part
1. General. See [32e][32f]. TLC: silica gel 60 F254 plates (0.25 mm; Merck). Column chromatog-
raphy (CC): silica gel 60 (0.040 – 0.063 mesh; Merck). M.p.: Büchi B-540 apparatus, in capillaries;
uncorrected. 1H- (300 MHz) and 13C-NMR (75.5 MHz) Spectra: Bruker ARX-300 instrument; in
(D6)DMSO, unless otherwise specified; chemical shifts in ppm. ESI-MS: Finnigan MAT-TSQ-700
instrument; in m/z (rel. %).

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2. Starting Materials. Isoselenocyanates were prepared according to Bartonꢁs procedure starting from
formamides [23]. Formanilide (¼ N-phenylformamide) is commercially available (Fluka), N-(4-
bromophenyl)-, N-(4-chlorophenyl)-, N-(4-methylphenyl)-, and N-(4-methoxyphenyl)formamide were
prepared from the respective commercial anilines and 95% HCOOH [38]. The soln. was heated to reflux
for 30 min and concentrated. The residue was dissolved in Et2O and washed with 5% AcOH soln., H2O,
and 5% aq. NaHCO3 soln. The aq. phase was extracted with Et2O, the combined org. extract dried
(MgSO4), and concentrated, and the crude products purified by recrystallization in H2O.
S-Methylisothiosemicarbazide hydroiodide (1) was prepared by treatment of thiosemicarbazide
(¼ hydrazinecarbothioamide; 9.10 g, 0.10 mol) with MeI (14.20 g, 0.10 mol) in refluxing abs. EtOH for
2 h. The mixture was allowed to cool, and filtration and purification by recrystallization in abs. EtOH
1
yielded 18.71 g (80%) of 1. M.p. 137 – 1398 ([39]: 1388). H-NMR: 2.69 (s, Me). 13C-NMR: 12.7 (Me);
170.2 (C¼N). ESI-MS: 234 (2, [M þ 1]þ), 106 (100, C2H8N3Sþ), 92 (53). Anal. calc. for C2H8IN3S
(233.07): C 10.31, H 3.46, N 18.03, S 13.76; found: C 10.30, H 3.44, N 18.24, S 13.59.
3. 3H-1,2,4-Triazole-3-selones 7: General Procedure. To a soln. of 1 (233 mg, 1.0 mmol) and
isoselenocyanate 5 (1.0 mmol) in CH2Cl2 (20 ml), Et3N (0.28ml, 2.0 mmol) was added, whereby the
suspension became instantaneously colorless and then rapidly yellow. The evolution of a gas
(methanethiol) was detected. The mixture was stirred overnight, then, the white precipitate was filtered
and washed with cold CH2Cl2 to give anal. pure 7.
5-Amino-2,4-dihydro-4-phenyl-3H-1,2,4-triazole-3-selone (7a). From phenyl isoselenocyanate (5a):
187 mg (78%) of 7a. White crystals. M.p. 191 – 1938 (CH2Cl2). IR (KBr): 3363w, 3287w, 3249w, 3158m
(br.), 2970w, 2936w, 2785w, 1640s, 1593m, 1496s, 1450m, 1336m, 1237m, 1139w, 1071w, 1011w, 991w, 78 4w,
1
749m, 690s, 567m. H-NMR: 5.94 (br. s, NH2); 7.25 (d, J ¼ 8.1, 2 arom. H); 7.42 – 7.49 (m, 3 arom. H);
13.57 (br. s, NH). 13C-NMR: 128.4 (2 arom. CH); 129.2 (3 arom. CH); 133.3 (1 arom. C); 153.1 (C(5));
155.8(C ¼Se). ESI-MS: 265 (12), 264 (10), 263 (100, [M þ Na]þ), 262 (5), 261 (47), 260 (14), 259 (13).
Anal. calc. for C8H8N4Se (239.14): C 40.18, H 3.37, N 23.43; found: C 39.93, H 3.49, N 23.20.
5-Amino-2,4-dihydro-4-(4-methoxyphenyl)-3H-1,2,4-triazole-3-selone (7b). From 4-methoxyphenyl
isoselenocyanate (5b): 194 mg (72%) of 7b. White crystals. M.p. 177 – 1798 (CH2Cl2). IR (KBr): 3373w,
3307w, 3261w, 3200w, 3158w, 2999w, 2935w, 2808w, 1646s, 1604w, 1583w, 1513s, 1459m, 1442m, 1338m,
1302m, 1259s, 1240m, 1184w, 1170m, 1130m, 1103w, 1048w, 1021w, 1007w, 98 9w, 8 33m, 8 03w, 768w, 728w,
665w, 629w, 619w, 573w. 1H-NMR: 4.06 (s, MeO); 6.25 (br. s, NH2); 7.31, 7.49 (AA’BB’, J ¼ 8.1, 4 arom.
H); 13.52 (br. s, NH). 13C-NMR: 55.3 (MeO); 114.4 (2 arom. CH); 125.8(1 arom. C); 129.7 (2 arom.
CH); 153.3 (1 arom. C); 156.1 (C(5)); 159.5 (C¼Se). ESI-MS: 295 (12), 294 (11), 293 (100, [M þ Na]þ),
292 (9), 291 (45), 290 (16), 289 (18). Anal. calc. for C9H10N4OSe (269.17): C 40.16, H 3.74, N 20.82;
found: C 40.31, H 3.40, N 21.06.
5-Amino-2,4-dihydro-4-(4-methylphenyl)-3H-1,2,4-triazole-3-selone (7c). From 4-methylphenyl iso-
selenocyanate (5c): 203 mg (80%) of 7c. White crystals. M.p. 182 – 1848 (CH2Cl2). IR (KBr): 3367w,
3298w, 3255w, 3159w, 2999w, 2942w, 2798w, 1645s, 1599w, 1578w, 1500s, 1465m, 1443m, 1332m, 1295m,
1245m, 1240m, 1178w, 1165m, 1128m, 1105w, 1055w, 1018w, 1000w, 978w, 8 35w, 798w, 777w, 725w, 656w.
1H-NMR: 2.42 (s, Me); 5.28(br. s, NH2); 7.26, 7.30 (AA’BB’, J ¼ 8.1, 4 arom. H); 12.91 (br. s, NH).
13C-NMR: 20.6 (Me); 127.1 (2 arom. CH); 129.7 (1 arom. C); 129.8(2 arom. CH); 139.3 (1 arom. C);
156.1 (C(5), C¼Se). ESI-MS: 279 (12), 278(12), 277 (100, [ M þ Na]þ), 276 (7), 275 (55), 274 (12), 273
(17). Anal. calc. for C9H10N4Se (253.17): C 42.70, H 3.98, N 22.13; found: C 42.56, H 4.12, N 22.23.
5-Amino-4-(4-bromophenyl)-2,4-dihydro-3H-1,2,4-triazole-3-selone (7d). From 4-bromophenyl iso-
selenocyanate (5d): 261 mg (82%) of 7d. White crystals. M.p. 192 – 1948 (CH2Cl2). IR (KBr): 3383w,
3294w, 3080m (br.), 2927w, 2774w, 1633s, 1586m, 1573m, 1489m, 1450m, 1403w, 1330m, 1226m, 1103w,
1069w, 1005m, 98 5w, 8 35m, 8 20w, 771w, 741w, 715w, 570m. 1H-NMR: 6.46 (br. s, NH2); 7.63, 8.05
(AA’BB’, J ¼ 8.1, 4 arom. H); 13.42 (br. s, NH). 13C-NMR: 122.5 (1 arom. C); 130.8(2 arom. CH); 132.2
(2 arom. CH); 139.4 (1 arom. C); 152.9 (C(5)); 155.8(C ¼Se). ESI-MS: 345 (13), 344 (8), 343 (78), 342
(11), 341 (100, [M þ Na]þ), 340 (16), 339 (48), 338 (15), 337 (12). Anal. calc. for C8H7BrN4Se (318.04):
C 30.21, H 2.22, N 17.62; found: C 30.36, H 2.55, N 17.63.
5-Amino-4-(4-chlorophenyl)-2,4-dihydro-3H-1,2,4-triazole-3-selone (7e). From 4-chlorophenyl iso-
selenocyanate (5e): 205 mg (75%) of 7e. White crystals. M.p. 185 – 1878 (CH2Cl2). IR (KBr): 3379w,
3294w, 3084m (br.), 2958m, 2931m, 2778w, 1634s, 1587m, 1574m, 1493s, 1453m, 1409w, 1331m, 1230m,

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Helvetica Chimica Acta – Vol. 90 (2007)
1106w, 1091w, 1007m, 98 6w, 8 40m, 8 22w, 774w, 734w, 717w, 574m. 1H-NMR: 6.33 (br. s, NH2); 7.58, 7.79
(AA’BB’, J ¼ 8.7, 4 arom. H); 13.47 (br. s, NH). 13C-NMR: 129.3 (2 arom. CH); 130.5 (2 arom. CH); 132.2
(1 arom. C); 133.9 (1 arom. C); 153.0 (C(5)); 155.8(C ¼Se). CI-MS (NH3): 277 (3), 275 (7, [M þ 1]þ),
273 (4), 197 (34), 196 (12), 195 (100), 194 (6). Anal. calc. for C8H7ClN4Se (273.59): C 35.12, H 2.58, N
20.48; found: C 34.90, H 2.80, N 20.34.
Bis(5-amino-4-phenyl-4H-1,2,4-triazol-3-yl) Diselenide (¼ 5,5’-Diselenobis[4-phenyl-4H-1,2,4-tria-
zol-3-amine]; 11a). Repeated attempts to crystallize 7a from CH2Cl2 gave orange crystals of 11a. M.p.
1
206.0 – 208.38 (color change). H-NMR: 6.05 (br. s, 2 NH2); 6.97 (d-like, 4 arom. H); 7.42 – 7.50 (m, 6
arom. H). ESI-MS: 504 (9), 503 (29), 502 (20), 501 (100, [M þ Na]þ), 500 (21), 499 (77), 498(31), 497
(43), 496 (13), 495 (17), 479 (19, [M þ 1]þ), 477 (17).
X-Ray Crystal-Structure Determination of 11a (see Fig. 1 and Table 2)2). All measurements were
made on a Nonius-KappaCCD diffractometer [40] by using graphite-monochromated MoKa radiation (l
0.71073 Š) and an Oxford-Cryosystems-Cryostream-700 cooler. Data reduction was performed with
HKL Denzo and Scalepack [41]. The intensities were corrected for Lorentz and polarization effects, and
an absorption correction based on the multi-scan method [42] was applied. Equivalent reflections were
merged. Data collection and refinement parameters are given in Table 2, and a view of the molecule is
shown in Fig. 1. The structure was solved by direct methods with SHELXS97 [43], which revealed the
positions of all non-H-atoms. The asymmetric unit contains one molecule of the Se-compound, one
MeOH molecule and two molecules of H2O. The non-H-atoms were refined anisotropically. The NH2,
H2O, and hydroxy H-atoms were placed in the positions indicated by a difference electron density map,
and their positions were allowed to refine together with individual isotropic displacement parameters. All
remaining H-atoms were placed in geometrically calculated positions and refined by using a riding model
where each H-atom was assigned a fixed isotropic displacement parameter with a value equal to 1.2 Ueq
of its parent C-atom (1.5 Ueq for the Me group of the MeOH molecule). Refinement of the structure was
carried out on F2 by full-matrix least-squares procedures, which minimized the function Sw(Fo2 ꢀ Fc2)2. A
Table 2. Crystallographic Data of Compound 11a
Crystallized from
Empirical formula
Mr
Crystal color, habit
Crystal dimensions [mm]
Temperature [K]
Crystal system
Space group
CH2Cl2/MeOH Dx [g cmꢀ3
C17H22N8O3Se2 m(MoKa) [mmꢀ1
]
1.667
3.447
f and w
60
0.492; 0.717
55961
]
544.33
Scan type
orange, tablet
2q(max) [8]
0.10 ꢁ 0.22 ꢁ 0.28Transmission factors (min; max)
160(1)
monoclinic
P21/n
Total reflections measured
Symmetry-independent reflections 6352
Reflections with I > 2s (I)
Reflections used in refinement
Parameters refined
5010
6348
309
Z
4
Reflections for cell determination 65007
2q Range for cell determination [8] 4 – 60
Final R(F) (I > 2s(I) reflections) 0.0340
Unit cell parameters a [Š]
8.6743(1)
wR(F2) (all data)a)
Goodness of fit
0.0841
1.034
b [Š]
c [Š]
b [8]
V [Š3]
14.3351(1)
17.8878(2)
102.8824(6)
2168.31(4)
Secondary extinction coefficient
0.0010(3)
0.001
0.62; ꢀ 0.91
Final Dmax/s
D1 (max; min) [e Š
ꢀ3
]
a) Weights: w ¼ [s2(Fo2) þ (0.0433P)2 þ 0.7378P]ꢀ1, where P ¼ (Fo2 þ 2Fc2)/3
2
)
CCDC-631597 contains the supplementary crystallographic data for this paper. These data can be
obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.

Helvetica Chimica Acta – Vol. 90 (2007)
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correction for secondary extinction was applied. Four reflections, whose intensities were considered to be
extreme outliers, were omitted from the final refinement. Neutral-atom scattering factors for non-H-
atoms were taken from [44], and the scattering factors for H-atoms were taken from [45]. Anomalous
dispersion effects were included in Fc [46]; the values for f’ and f’’ were those of [47]. The values of the
mass attenuation coefficients are those of [48]. All calculations were performed with the SHELXL97 [49]
program.
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Received December29, 2006