Lanthanide(II) complexes of the dihydrotriazinido ligand [N{C(Ph)=N} 2C(tBu)Ph]-

Article abstract of DOI:10.1002/zaac.200800089

The potassium dihydrotriazinide K(L^Ph,tBu) (1) was obtained by a metal exchange route from [Li(L^Ph,tBu)(THF)₃] and KOtBu (L^Ph,tBu = [N{C(Ph)=N}₂C(tBu)Ph]). Reaction of 1 with 1 or 0.5 equivalents of SmI₂(thf)₂ yielded the monosubstituted Sm^II complex [Sm(L^Ph,tBu)I(THF)₄] (2) or the disubstituted [Sm(L^Ph,tBu)₂(THF)₂] (3), respectively. Attempted synthesis of a heteroleptic Sm^II amido-alkyl complex by the reaction of 2 with KCH₂Ph produced compound 3 due to ligand redistribution. The Yb^II bis(dihydrotriazinide) [Yb(L ^Ph,tBu)₂(THF)₂] (4) was isolated from the 1:1 reaction of YbI₂(THF)₂ and 1. Molecular structures of the crystalline compounds 2, 3·2C₆H₆ and 4·PhMe were determined by X-ray crystallography.

Full text of DOI:10.1002/zaac.200800089

DOI: 10.1002/zaac.200800089
Lanthanide(II) Complexes of the Dihydrotriazinido Ligand
[N{C(Ph)؍N}2C(tBu)Ph]؊
Peter B. Hitchcock, Alexei V. Khvostov, Michael F. Lappert* and Andrey V. Protchenko
Brighton/United Kingdom, University of Sussex
Received February 28th, 2008.
Dedicated to Professor Heinrich Nöth on the Occasion of his 80th Birthday
Abstract. The potassium dihydrotriazinide K(LPh,tBu) (1) was ob-
tained by a metal exchange route from [Li(LPh,tBu)(THF)3] and
KOtBu (LPh,tBu ϭ [N{C(Ph)ϭN}2C(tBu)Ph]). Reaction of 1 with 1
or 0.5 equivalents of SmI2(thf)2 yielded the monosubstituted
SmII complex [Sm(LPh,tBu)I(THF)4] (2) or the disubstituted
[Sm(LPh,tBu)2(THF)2] (3), respectively. Attempted synthesis of a
heteroleptic SmII amido-alkyl complex by the reaction of 2 with
KCH2Ph produced compound 3 due to ligand redistribution. The
YbII bis(dihydrotriazinide) [Yb(LPh,tBu)2(THF)2] (4) was isolated
from the 1:1 reaction of YbI2(THF)2 and 1. Molecular structures
of the crystalline compounds 2, 3·2C6H6 and 4·PhMe were deter-
mined by X-ray crystallography.
Keywords: Samarium; Ytterbium; Amido ligands; Crystal struc-
tures
Introduction
Likewise, it is long established that benzonitrile with LiR
in benzene or Et2O gave R-substituted dihydrotriphenyl-
triazines after aqueous work-up (R ϭ Me, Et, nPr, iPr, nBu
or Ph) [3]. Mulvey and coworkers showed that in hexane
the main product of such a reaction was the sym-tri-
phenyltriazine A, whereas in presence of THF the product
was the lithium dihydrotriazinide [Li(LPh,nBu)(THF)3]
[4a,b]; for the related LitBu reaction, affording the LPh,tBu
analogue, see eqn. (2) [4a]. Liu and coworkers found that
LiCH(SiMe3)2 with an N-cyanodialkylamine RCN yielded
the 1,3,5-triazine (RCN)3 in hexane, while in Et2O the prod-
uct was the β-diketiminate Li[{N(SiMe3)C(R)}2CH] (R ϭ
NMe2 or NC5H10) [5]. Wakefield and coworkers have sug-
gested that the reaction of the triazine A with a lithium
alkyl LiR followed by an aqueous work-up is a convenient
way of preparing H(LPh,R) [6].
The reaction of bis(trimethylsilyl)methyllithium with an α-
hydrogen-free nitrile is solvent dependent, yielding either a
lithium β-diketiminate (exemplified in eqn. (1) for PhCN as
the nitrile) or, in a stronger donor solvent, an enamide, e.g.,
[Li{N(SiMe3)C(Ph)ϭC(H)SiMe3}(THF)]2 [1a]. The former
compound is a versatile precursor to numerous s-, p-, d-
and f-metal analogues [1b,c]. Similar solvent effects were
first demonstrated by Sanger in a related system, Scheme
1 [2a,b].
The compounds Li(LR,RЈ) contain the bulky N-centred
monoanionic ligand LR,RЈ with two flanking Ph groups,
which can be used as an alternative to such sterically de-
manding amido ligands as terphenylamides featured, for ex-
ample, in low-coordinate Li and Tl complexes [7]. However,
only Li [4a,b], Na [4c], K [4c,8a], Rb [8b] and Mg [4a] di-
hydrotriazinido derivatives have been synthesized up to
date; the structure of [Sn(LPh,nBu)Ph3] has been deposited
at the Cambridge Database [8c]. A calcium derivative of the
doubly-metallated LPh,Ph ligand is also known [9].
Scheme 1 Solvent effects in the PhCN/LiNMe2 system [2a,b]
* Prof. Dr. M. F. Lappert
Department of Chemistry
University of Sussex
Brighton BN1 9QJ/UK
E-mail: m.f.lappert@sussex.ac.uk
Z. Anorg. Allg. Chem. 2008, 634, 1373Ϫ1377
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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P. B. Hitchcock, A. V. Khvostov, M. F. Lappert, A. V. Protchenko
Here we describe synthesis and structure of SmII and
Attempted synthesis of a mixed-ligand amido-alkyl com-
plex by the reaction of 2 with KCH2Ph led to a mixture of
products, which upon crystallization from hot benzene gave
dark brown [Sm(LPh,tBu)2(THF)2]·2C6H6 (3·2C6H6).
Apparently, the initially formed mixed-ligand species was
unstable and underwent a ligand redistribution reaction
during isolation or recrystallization. Complex 3 was better
obtained by the 2:1 reaction of 1 and SmI2(THF)2 (Scheme
2). Despite its paramagnetism, complex 3 showed well-
YbII derivatives of the ligand LPh,tBu
.
Results and Discussion
In order to prepare Ln(II) dihydrotriazinides we first trans-
formed the known Li derivative [4a] into the K salt
K(LPh,tBu) (1) because the latter was expected to be a better
ligand-transfer agent than its Li analogue. A metal ex-
change route, similar to that used in the synthesis of
[Rb(LnBu,tBu)(THF)2]4 [8b], produced 1 in a good yield, eqn.
(3). Treatment of the raw product with hot hexane allowed
the isolation of a virtually THF-free material (Li, Na and
K salts of the related LnBu,tBu ligand contained variable
amounts of coordinated THF [4c]).
1
resolved resonances in the H NMR spectrum.
Reaction in a 1:1 ratio of compound 1 with YbI2(THF)2
in THF was carried out in a similar manner to that of the
Sm analogue. However, in this case the product crystallized
from a THF solution was not a single compound as evident
1
from its H and especially 171Yb NMR spectra. The latter
showed two signals of approximately equal intensity (but of
a different shape) in the temperature range 218Ϫ338 K, one
of which split into 3 broad signals at 203 K. Recrystalliza-
tion of this mixture from pyridine gave [YbI2(Py)4]
identified by X-ray crystallography (only the molecular
connectivity was determined). From the THF mother
liquor a small amount of the disubstituted YbII complex
[Yb(LPh,tBu)2(THF)2] (4) was isolated by evaporating the
solvent and crystallizing from toluene (Scheme 2).
The molecular structures of the complexes 2, 3·2C6H6
and 4·PhMe are shown in Figures 1, 2 and 3, respectively.
The LPh,tBu ligand has a boat conformation and its
structural parameters are very similar in all three complexes
and are comparable to those of the LnBu,tBu ligand in
[Li(LnBu,tBu)(THF)3] [4a,b]. The flanking Ph rings of the
LPh,tBu ligand in each compound are nearly coplanar; the
largest deviation was found in the more crowded Yb com-
plex 4 with the dihedral angle between C4-C9 and C20-C25
rings being at 14°.
Compound 1 was used as a convenient precursor to lan-
thanide(II) complexes containing the LPh,tBu ligand. Thus,
reaction of 1 with one equivalent of SmI2(THF)2 in THF
produced a dark blue solution, from which the expected
monosubstituted complex [Sm(LPh,tBu)I(THF)4] (2) was iso-
lated (Scheme 2). Complex 2 was characterized by micro-
analysis, its UV-VIS absorption spectrum and X-ray crys-
1
tallography, but its H NMR spectrum was uninformative
due to significant line-broadening. Complex 2 represents a
rare example of a SmII mixed-ligand amide; such com-
pounds have previously been shown to undergo a facile li-
gand redistribution reaction producing bis(amido) com-
plexes. The only other SmII mixed-ligand amide featuring a
monodentate amido ligand is [Sm{N(SiMe3)2}(μ-I)(DME)-
(THF)]2 (B), which was shown to be a dimer in the solid
state [10].
Figure 1 ORTEP representation of the molecular structure of 2
(20 % ellipsoids; H atoms omitted).
Complex 2 has a monomeric structure in the solid state,
which is rather unusual for SmII mixed-ligand iodo com-
pounds. Thus, both the bulky amido complex B [10] and
the amido-pyridine complex [Sm{N(Ar)(2-C5H3NArЈ-
6)}(μ-I)(THF)2]2 (Ar ϭ C6H3iPr2-2,6, ArЈ ϭ C6H2iPr3-
Scheme 2 Synthesis of complexes 2Ϫ4 (O ϭ THF)
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© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 1373Ϫ1377

Lanthanide(II) Complexes of the Dihydrotriazinido Ligand
˚
Table 1 Selected bond lengths (A) and angles (°) for complex 2.
Bond lengths
Bond angles
SmϪN1
SmϪI
2.574(4)
3.3457(5)
2.604(4)
2.597(4)
2.583(4)
2.556(4)
1.399(6)
1.388(6)
N1ϪSmϪI
100.25(9)
72.79(13)
72.19(13)
73.30(13)
79.68(14)
124.8(3)
123.3(3)
110.4(4)
O1ϪSmϪO2
O1ϪSmϪO4
O2ϪSmϪO3
O3ϪSmϪO4
SmϪN1ϪC1
SmϪN1ϪC2
C1ϪN1ϪC2
SmϪO1
SmϪO2
SmϪO3
SmϪO4
N1ϪC1
N1ϪC2
˚
Table 2 Selected bond lengths (A) and angles (°) for complexes 3
and 4.
Figure 2 ORTEP representation of the molecular structure of 3
(20 % ellipsoids; H atoms omitted).
Bond
3
4
Bond
3
4
lengths
(Ln ϭ Sm) (Ln ϭ Yb) angles
(Ln ϭ Sm) (Ln ϭ Yb)
LnϪN1 2.524(4)
LnϪN4 2.543(4)
LnϪO1 2.476(4)
LnϪO2 2.496(4)
N1ϪC1 1.394(6)
N1ϪC3 1.372(6)
N4ϪC26 1.385(6)
N4ϪC28 1.381(6)
2.389(3)
2.426(3)
2.334(3)
2.386(2)
1.387(4)
1.383(4)
1.393(4)
1.383(4)
N1ϪLnϪN4 151.61(13) 132.95(9)
O1ϪLnϪO2 76.04(13)
80.40(9)
N1ϪLnϪO1 102.37(13) 96.98(9)
N1ϪLnϪO2 105.58(12) 94.56(9)
N4ϪLnϪO1 105.48(13) 129.43(9)
N4ϪLnϪO2 86.52(12)
99.80(9)
lated silylamido complex [Sm{N(SiMe3)2}2(THF)2]
(118.0(3)°) [10], which may be due to the increased steric
bulk of the LPh,tBu ligand with its flanking Ph groups. The
SmϪN bond lengths are similar to that in compound 2.
The ligands in the Yb complex 4 are more distorted with
one Ph group approaching the Yb atom to form a relatively
Figure 3 ORTEP representation of the molecular structure of 4
(20 % ellipsoids; H atoms omitted).
˚
close contact at 3.060 A (Yb···C50, o-C). The YbϪN bond
lengths (especially YbϪN4) are on the long end of the
range of terminal YbIIϪN distances; similarly long bonds
were found in the crowded trinuclear complex
2,4,6) [11] are iodo-bridged dimers. Similar dimers were ob-
tained with C5Me5- [12] and C5HiPr4- [13] SmII derivatives.
Only for a multi-functional triazacyclononane-tethered
cyclopentadienyl ligand was the isolation of a monomeric
SmII iodide possible [14]. The Sm coordination environment
in 2 can be described as a slightly distorted trigonal prism
(N1, O1, O2 and I, O3, O4 are at the apices). It is note-
worthy that four neutral ligands (THF) are on one side of
the Sm atom and the two anionic ligands on the other, while
a nearly linear (anion)-lanthanide-(anion) unit surrounded
by neutral ligands appears to be favourable in a variety of
other systems [15]. The SmϪN1 bond in 2 (Table 1) is
˚
Yb[Yb{N(SiMe3)2}(μ-DAC)]2 (2.43(3) and 2.44(3) A; DAC
is deprotonated 4,13-diaza-18-crown-6) [17].
In conclusion, we have shown that a bulky dihydrotriazi-
nido ligand, which was previously featured only in Group
1 and 2 metal complexes, can be successfully used for the
preparation of homo- and heteroleptic LnII complexes.
Thus, the salt metathesis reaction of K(LPh,tBu) and
SmI2(thf)2 produced [Sm(LPh,tBu)I(THF)4], a rare mixed-
ligand monomeric SmII compound stabilised by a non-
chelating amido ligand. The disubstituted SmII and YbII
compounds [Sm(LPh,tBu)2(THF)2] and [Yb(LPh,tBu)2(THF)2]
were obtained by a similar route.
˚
longer than in the silylamido complexes B (2.455(7) A) and
˚
[Sm{N(SiMe3)2}2(THF)2] (2.442(9) and 2.424(9) A) [10],
but it is similar to the SmϪN bond in [Sm(NPh2)2(THF)4]
(2.550(4) A) [16]. The SmϪI and SmϪO distances are simi-
Experimental Section
˚
General
lar to those in B.
Complexes 3 and 4 have similar molecular structures, but
they are not isostructural. Selected structural parameters
for both complexes are given in Table 2. Two oxygen and
two nitrogen atoms form a very distorted tetrahedral coor-
dination environment around the metal atoms. The
NϪLnϪN angle is significantly wider than that in the re-
All manipulations were carried out in an atmosphere of dry argon
using standard vacuum line and Schlenk techniques. Solvents were
dried from the appropriate drying agent, distilled, degassed and
stored over a potassium mirror. The NMR spectra were recorded
on a DPX 300 or AM-500 Bruker spectrometer with residual sol-
vent signals as internal reference (1H and 13C{1H}) or with an ex-
Z. Anorg. Allg. Chem. 2008, 1373Ϫ1377
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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1375

P. B. Hitchcock, A. V. Khvostov, M. F. Lappert, A. V. Protchenko
ternal reference ([Yb(C5Me5)2(thf)] for 171Yb). Elemental analyses
were carried out by Medac Ltd. (Brunel University); good micro-
analytical data for compounds 3 and 4 were not obtained due to
(0.16 g, 1.23 mmol). The mixture was stirred for 24 h to give a
dark-brown solution with a grey precipitate (KI). The mixture was
filtered, the filtrate was evaporated to dryness and extracted with
Et2O. Storing the extract at Ϫ25 °C overnight gave a brown micro-
crystalline powder, which was identified as compound 3 contami-
their high air-sensitivity. The compounds Li(LPh,tBu
) [4a],
SmI2(THF)2 [18] and YbI2(THF)2 [18] were prepared by pub-
lished procedures.
1
nated with Sm(CH2Ph)2(THF)x. H NMR (C6D6/THF-d8, 293 K):
δ 16.34 (br d, 4 H, Ph2 of L), 13.64 (br t, 2 H, Ph2 of L), 6.11 (br m,
5 H, Ph2 and Ph1 of L), 5.78 (t, 2 H, Ph1 of L), 2.25 (d, 2 H, Ph1
of L), Ϫ3.73 (s, 9 H, tBu of L); 7.92 (br, 1 H, CH2Ph), 7.22 (br,
2 H, CH2Ph), 1.26 (br, 3 H, CH2Ph) (integration of the CH2Ph sig-
nals was approximate due to broadening and partial overlapping
with solvent signals). Recrystallisation of a sample of this material
from hot benzene produced X-ray quality crystals of 3·2C6H6.
Synthetic procedures
K(LPh,tBu) (1). KOtBu (1.67 g, 14.9 mmol) was added to a solution
of [Li(LPh,tBu)(THF)3] (8.78 g, 14.9 mmol) in tetrahydrofuran
(100 mL) and the mixture was stirred for 2 h. The solution volume
was then reduced in a vacuum to ca. 20 mL and hexane (80 mL)
was added producing a light yellow precipitate. The mixture was
filtered using a cannula with a glass microfibre filter; the precipitate
was suspended in hexane (80 mL), warmed to 60 °C, stirred for
15 min and filtered again. This procedure was repeated twice; the
product was then dried in a vacuum yielding 1 as a pale yellow
powder (5.38 g, 89 %).
1H NMR (C6D6/THF-d8, 293 K): δ 8.57 (d, 4 H, o-H of Ph2), 8.09 (d, 2 H,
o-H of Ph1), 7.26 (t, 4 H, m-H of Ph2), 7.19 (t, 2 H, m-H of Ph1), 6.99 (t,
2 H, p-H of Ph2), 6.87 (t, 1 H, p-H of Ph1), 3.51 (m, 0.2 H, THF), 1.48 (m,
0.2 H, THF), 1.34 (s, 9 H, tBu). 13C NMR (C6D6/THF-d8, 293 K): δ 162.17
(NϭC(Ph)N), 154.70 (ipso-C of Ph1), 143.49 (ipso-C of Ph2), 129.47, 128.01,
127.50, 125.75, 124.72 (CH of Ph1 and Ph2), 80.79 (C(Ph)tBu), 40.56 (CMe3),
26.65 (CMe3).
[Sm(LPh,tBu)2(THF)2] (3) b). SmI2(thf)2 (2.17 g, 3.96 mmol) was ad-
ded to a stirred solution of K(LPh,tBu) (3.21 g, 7.91 mmol) in tetra-
hydrofuran (100 mL). The mixture was stirred for 24 h, and the
resulting dark-brown suspension was filtered. The filtrate was eva-
porated to dryness. The residue was dissolved in Et2O and stored
at Ϫ25 °C overnight yielding dark-brown crystals of 3 (1.40 g,
1
59 %). The H NMR spectrum in C6D6/THF-d8 showed a set of L
resonances nearly identical to those reported in a). The compound
crystallised as very thin wool-like crystals that hampered its purifi-
cation.
[Yb(LPh,tBu)2(THF)2] (4). YbI2(thf)2 (2.47 g, 4.33 mmol) was added
to a stirred solution of K(LPh,tBu) (1.65 g, 4.08 mmol) in tetrahydro-
furan (100 mL). The mixture was stirred for 24 h and then the red-
orange suspension was filtered. The filtrate was concentrated in a
vacuum to ca. 40 mL. Storing the filtrate at Ϫ25 °C overnight gave
a red microcrystalline powder tentatively identified as an Yb ana-
logue of 2; we failed to obtain X-ray quality crystals or analytically
pure samples of this product (the 1H NMR spectra showed two
sets of ligand signals at and below 273 K, while the 171Yb NMR
spectra showed two signals in the whole of the studied temperature
range, 218-338 K, with δ 491.2 and 449.1 at 298 K). The mother
liquor was evaporated in a vacuum and the residue was dissolved
in toluene. Storing the solution at Ϫ25 °C for several days yielded
[Sm(LPh,tBu)I(THF)4] (2). SmI2(thf)2 (1.40 g, 2.55 mmol) was added
to a stirred solution of K(LPh,tBu) (1.03 g, 2.55 mmol) in tetrahydro-
furan (100 mL). The mixture was stirred for 24 h and then the grey-
black suspension was filtered. The filtrate was concentrated in a
vacuum to ca. 40 mL. Black (dark-blue in thin layer) crystals of 2
(1.43 g, 60 %) were deposited upon cooling to Ϫ10 °C. UV-VIS
(thf), λmax: 553 nm. C41H56N3IO4Sm: C, 52.3; H, 6.03; N, 4.72
1
(calcd. C, 52.8; H, 6.05; N, 4.51) %. The H NMR spectrum was
uninformative due to signal broadening.
[Sm(LPh,tBu)2(THF)2] (3) a). To a stirred solution of 2 (1.18 g,
1.27 mmol) in tetrahydrofuran (100 mL) was added dry KCH2Ph
Table 3 Crystal data and structure refinement for 2, 3·2C6H6 and 4·PhMe.
Compound
2
3·2C6H6
4·PhMe
Empirical formula
Formula weight
Crystal system
Space group
C41H56IN3O4Sm
932.14
orthorhombic
Pbca (No. 61)
11.5636(5)
16.8479(6)
42.0506(16)
C70H76N6O2Sm
1183.72
C65H72N6O2Yb
1142.33
monoclinic
P21/n(No. 14)
17.6926(3)
18.1941(2)
19.1724(3)
triclinic
¯
P1 (No. 2)
˚
a/A
11.2600(6)
13.7664(10)
19.3855(14)
˚
b/A
c/A
Ͱ/°
85.917(3)
88.128(5)
88.868(5)
2995.3(3)
β/°
114.389(1)
γ/°
U/A3
8192.4(6)
5620.88(14)
Z
8
1.51
2.23
3760
2
1.31
1.03
1232
4
1.35
1.71
2360
Dc/Mg mϪ3
μ(Mo-Kα)/mmϪ1
F(000)
Crystal size
0.40ϫ0.15ϫ0.10
29171
9639 [R(int) ϭ 0.085]
5808
9639/0/451
0.869
R1 ϭ 0.046, wR2 ϭ 0.105
R1 ϭ 0.101, wR2 ϭ 0.127
0.76 and Ϫ0.80
0.30ϫ0.10ϫ0.05
17060
10239 [R(int) ϭ 0.062]
8098
10239/0/688
1.028
R1 ϭ 0.057, wR2 ϭ 0.123
R1 ϭ 0.079, wR2 ϭ 0.134
1.26 and Ϫ1.22 (near Sm)
0.15ϫ0.15ϫ0.10
78083
9931 [R(int) ϭ 0.065]
7991
9931/0/667
1.012
R1 ϭ 0.034, wR2 ϭ 0.066
R1 ϭ 0.051, wR2 ϭ 0.073
1.14 and Ϫ1.55 (near Yb)
Reflections collected
Independent reflections
Reflections with I > 2σ(I)
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
Largest diff. peak and hole/ e AϪ3
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© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 1373Ϫ1377

Lanthanide(II) Complexes of the Dihydrotriazinido Ligand
a small amount of red crystals of complex 4·PhMe suitable for X-
ray crystallography. H NMR (C5D5N, 373 K): δ 8.88 (br d, 8 H,
Ph2 of L), 8.53 (d, 4 H, Ph1 of L), 7.28-7.64 (m, 23 H, CHarom of
L and PhMe), 3.90 (br s, 8 H, THF), 2.49 (s, 3 H, PhMe) 1.92 (br
s, 8 H, THF), 1.66 (s, 18 H, tBu).
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Diffraction data for compounds 2, 3·2C6H6 and 4·PhMe were col-
lected on a Nonius Kappa CCD diffractometer using monochrom-
˚
ated Mo-Kα radiation, λ 0.71073 A at 173(2) K. Crystals were co-
ated in oil and then directly mounted on the diffractometer under
a stream of cold nitrogen gas. The structures were refined on all F2
using SHELXL-97 [19]; absorption corrections were applied using
MULTISCAN. Further details are found in Table 3. Crystallo-
graphic data for the structures have been deposited with the Cam-
bridge Crystallographic Data Centre, CCDC 677251Ϫ677253.
Copies of the data can be obtained free of charge on application
to The Director, CCDC, 12 Union Road, Cambridge CB21EZ, UK
(fax: ϩ44-1223-336-033; e-mail: deposit@ccdc.cam.ac.uk or
www.http:/ccdc.cam.ac.uk).
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© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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