U. Siemeling, T. Klemann, C. Bruhn, B. Neumüller, K. Dehnicke
˚
˚
a short (2.34 A) and a long HgϪN bond (2.47 A). Closer
inspection of the crystal packing reveals that the molecular
units of [μ-(3)(HgCl2)2] are aggregated through Hg···Cl con-
tacts in such a way that the coordination environment of
the Hg atom can be considered as a 4 ϩ 1 type (Figure 9).
Experimental Part
4-Hydroxy-2,3,4,5-tetra(pyrid-2-yl)cyclopent-2-en-1-one was pre-
pared according to the published procedure [4]. BeCl2 was prepared
from the elements using a quartz tube and subsequent sublimation
in vacuo [12]. All other materials were procured from commercial
sources and used as received. NMR spectra were recorded at 300 K
with a Varian Unity INOVA 500 spectrometer (500.13 MHz for 1H,
ext. TMS). Elemental analyses were performed by the Microana-
lytical Laboratory of the University of Kassel.
2,3,4,5-Tetra(pyrid-2-yl)cyclopent-2,4-dien-1-one (3):
A mixture of 4-hydroxy-2,3,4,5-tetra(pyrid-2-yl)cyclopent-2-en-1-
one (849 mg, 2.0 mmol) and silica gel (ca. 8.5 g, previously dried
in vacuo at ca. 250 °C) was heated to ca. 200 °C under a stream of
N2. After 0.5 h the dark red mixture was allowed to cool to room
temperature and was subsequently subjected to Soxhlet extraction
with diethyl ether (ca. 400 mL). Crystallization afforded the prod-
uct (621 mg, 78 %) as a red, crystalline solid. If the reaction was
carried out in air, mixtures of 3 and 1,3,4,5-tetra(pyrid-2-yl)-6-oxa-
bicyclo[3.1.0]hex-3-en-1one (4) with varying ratios of the two com-
pounds were obtained in similar overall yield.
Fig. 9 Aggregation of [μ-(3)(HgCl2)2] by chloro-bridging in the
crystal. Selected bond angles/°:
1H NMR (CDCl3): δ ϭ 7.03 (m, 2 H), 7.12 (m, 2 H), 7.36 (m, 2 H), 7.41 (m,
2 H), 7.50 (m, 2 H), 7.59 (m, 2 H), 8.27 (m, 2 H), 8.45 (m, 2 H). 13C{1H}
NMR (CDCl3): δ ϭ 122.4, 122.5, 125.3, 125.4, 126.1, 135.2, 135.7, 148.5,
149.4, 150.0, 152.8, 156.3, 199.5.
Cl(1)ϪHgϪCl(1Ј) 88.43(6), Cl(1)ϪHgϪN(2) 102.2(1), N(1)ϪHgϪN(2)
77.8(2),
N(1)ϪHgϪCl(2)
102.3(1),
Cl(2)ϪHgϪCl(1Ј)
88.12(6),
N(1)ϪHgϪCl(1) 116.9(1), Cl(1Ј)ϪHgϪN(2) 152.9(4), Cl(1)ϪHgϪCl(2)
138.24(7).
˚
[μ-(3)(MX2)2] (M ؍
Zn, Hg; X ؍
Cl, Br) (general procedure)
The Hg···Cl distance is ca. 3.15 A, which is shorter than
the sum of the estimated van der Waals radii. This contact
could largely result from crystal packing forces [9], but may
also be due to a long intermolecular bond. Such intermo-
lecular contacts are quite common in inorganic chemistry,
a well-known example being ReOCl4, which forms centro-
symmetric chloro-bridged dimers in the solid state with par-
3 (39 mg, 0.1 mmol) was dissolved in ethanol (10 mL). MX2
(0.2 mmol) was added. The mixture was stirred at 65 °C for 14 h
and was subsequently allowed to cool to room temperature. The
product was isolated by filtration, washed with small amounts of
diethyl ether and n-hexane and dried in vacuo.
˚
ticularly long M···Cl distances of 3.55 A [10]. In the coordi-
MX2 ؍
ZnCl2: red microcrystalline solid (62 mg, 95 %). An analyti-
cal sample was obtained by recrystallization from dichloromethane.
Elemental analysis: C26H16N4Cl4OZn2 ·CH2Cl2 (745.92): C 41.63
(calcd. 41.87), H 2.85 (2.43), N 6.95 (7.51) %.
1H NMR (CDCl3): δ ϭ 7.54 (m, 2 H), 7.68 (m, 6 H), 7.75 (m, 2 H), 8.09 (m,
2 H), 9.12 (m, 2 H), 9.17 (m, 2 H).
nation chemistry of mercury, a weak intermolecular bond
has been reported, for example, for [NEt4]2[Hg2PtCl8],
whose anion is aggregated in the solid state to form poly-
meric zig-zag chains of [Hg2PtCl8]n2nϪ [11]. The intermolec-
˚
ular Hg···Cl distances of 3.15 A are very similar to the dis-
tance present in [μ-(3)(HgCl2)2]. If the Hg atom in this com-
plex is considered to be pentacoordinate, its coordination
polyhedron is best described as distorted trigonal bipyrami-
dal, which renders nitrogen atom N(1) equatorial and N(2)
axial. Not surprisingly, the equatorial HgϪN(1) distance is
considerably smaller than the axial HgϪN(2) distance
MX2 ؍
ZnBr2: dark orange microcrystalline solid (80 mg, 95 %).
Elemental analysis: C26H16N4Br4OZn2 (838.79): C 35.02 (calcd.
35.80), H 2.27 (1.92), N 6.02 (6.68) %.
1H NMR (CDCl3): δ ϭ 7.55 (m, 4 H), 7.66 (m, 4 H), 7.73 (m, 2 H), 8.08 (m,
2 H), 9.23 (m, 4 H).
˚
˚
MX2 ؍
HgCl2: orange microcrystalline solid (81 mg, 87 %). An
analytical sample was obtained by recrystallization from di-
chloromethane. Elemental analysis: C26H16N4Cl4Hg2O·2CH2Cl2
(1101.30): C 29.34 (calcd. 29.45), H 1.82 (1.83), N 4.76 (5.09) %.
1H NMR (CDCl3): δ ϭ 7.29 (m, 2 H), 7.38 (m, 2 H), 7.50 (m, 4 H), 7.56 (m,
2 H), 7.89 (m, 2 H), 8.80 (m, 4 H). 13C{1H} NMR (CDCl3): δ ϭ 124.9, 125.3,
125.4, 127.7, 127.9, 138.3, 138.6, 148.0, 148.4, 148.8, 150.2, 155.4, 200.4.
(2.34 A versus 2.47 A, vide supra).
We note that two isomers are possible for mononuclear
chelates of 3, depending on whether the metal atom is che-
lated by the pyridyl units in position 2 and 3 or 3 and 4.
However, attempts to obtain mononuclear complexes of 3
by using one equivalent of the respective metal dihalide
invariably afforded the isolation of the corresponding di-
nuclear [μ-(3)(MX2)2]. It is as yet unclear whether this is
due to the comparatively low solubility of the dinuclear
species or rather to cooperative metal binding, similar to
allosteric effects observed in functional proteins. Studies
concerning the complexation equilibria in solution will be
performed in due course.
MX2 ؍
HgBr2: orange microcrystalline solid (72 mg, 65 %).
Elemental analysis: C26H16N4Br4Hg2O (1109.23): C 26.73 (calcd.
27.07), H 1.82 (1.45), N 4.20 (5.05) %.
1H NMR (CDCl3): δ ϭ 7.21 (m, 2 H), 7.38 (m, 2 H), 7.50 (m, 4 H), 7.55 (m,
2 H), 7.89 (m, 2 H), 8.81 (m, 2 H), 8.85 (m, 2 H). 13C{1H} NMR (CDCl3):
δ ϭ 125.1, 125.5, 125.6, 128.1, 128.4, 138.5, 138.9, 148.3, 148.7, 149.1, 150.4,
155.4, 199.5.
898
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 895Ϫ900