New aspects for modeling supramolecular interactions in vanadium haloperoxidases: β-cyclodextrin inclusion compounds of cis-dioxovanadium(V) complexes

Article abstract of DOI:10.1002/ejic.200601225

The reaction of potassium vanadate and the hydrazone ligand derived from Schiff base condensation of salicylaldehyde and biphenyi-4-carboxylic acid hydrazide (H₂salhybiph) in the presence of β-cyclodextrin (β-CD) in water yields the 1:1 inclusi

Full text of DOI:10.1002/ejic.200601225

SHORT COMMUNICATION
DOI: 10.1002/ejic.200601225
New Aspects for Modeling Supramolecular Interactions in Vanadium
Haloperoxidases: β-Cyclodextrin Inclusion Compounds of cis-
Dioxovanadium(V) Complexes
Ines Lippold,[a] Helmar Görls,[a] and Winfried Plass*[a]
Keywords: Cyclodextrins / Host–guest systems / Inclusion compounds / Vanadium / X-ray diffraction
The reaction of potassium vanadate and the hydrazone li-
gand derived from Schiff base condensation of salicyl-
aldehyde and biphenyl-4-carboxylic acid hydrazide
(H2salhybiph) in the presence of β-cyclodextrin (β-CD) in
water yields the 1:1 inclusion compound K[VO2(salhybiph)@
β-CD]. The characterization in solution confirmed the integ-
rity of the inclusion compound in different polar solvents
such as DMSO and water. The inclusion compound crys-
tallizes with additional water molecules in the triclinic space
group P1. The supramolecular aggregation of the inclusion
compound in the solid state is established through hydrogen
bonding interactions between adjacent β-CD hosts and the
π–π stacking ability of the ligand side chain of the guest com-
plexes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
with hydrophobic cavities and hydrophilic outer walls and
generate inclusion complexes with various apolar groups
that are included partially or completely in the cavity.[9]
CDs are well known to form a variety of hydrogen bonds
because of their free OH-groups. Parts of the guest protrud-
ing out of the CD ring opening could take part in this hy-
drogen bonding system. CDs and their substituted deriva-
tives could be considered artificial enzymes as a result of
their ability to react as catalysts for several asymmetric re-
actions, such as oxidation reactions, hydrolyses, and race-
mate separation.[10] Moreover, CDs are known to bind or-
ganometallic complexes containing aromatic constituents
and such encapsulated complexes often exhibit markedly
different physical and chemical properties.[11] Nevertheless,
only very few examples of such inclusion complexes re-
ported in the literature have been successfully characterized
by single-crystal X-ray diffraction.[12]
We have recently reported the application of the N-salicy-
lidene hydrazide ligand system for generating vanadium(V)
complexes with a variety of functional groups attached to
the ligand core.[7,8,13,14] Extending this approach, we report
herein the synthesis and structure of a cis-dioxovanadi-
um(V) complex containing an appropriate apolar biphenyl
group in the ligand side chain, and its inclusion compound
with β-CD.
Introduction
Vanadium haloperoxidases (V-HPO) are enzymes that
catalyze the oxidation of halides to the corresponding hypo-
halous acids. These oxidized intermediates then readily ha-
logenate organic substrates or convert hydrogen peroxide to
singlet oxygen.[1] In addition, these enzymes can also cata-
lyze the oxidation of organic sulfides to sulfoxides.[2] The
active site of this class of enzymes consists of a vanadate
moiety with a proposed trigonal bipyramidal geometry co-
valently bound to a histidine residue and held within the
protein by strong hydrogen-bonding interactions with sev-
eral amino acid residues.[3] Furthermore, this active site
architecture is also found for certain acid phosphatases,[4]
but with subtle distinctions concerning the relative posi-
tions of the amino acid residues.[5] The catalytic activity of
V-HPO enzymes is proposed to be driven by this hydrogen-
bonding network.[6] Therefore, V-HPO model systems need
to be designed that provide a polar protic surrounding in
order to offer the possibility for such relevant hydrogen-
bonding interactions. Examples for such vanadium com-
plexes derived from N-salicylidene hydrazides with a hy-
droxy substituted side chain have recently been reported.[7,8]
An alternative method to provide such an environment
for the complex moieties can be through their interaction
with appropriate host molecules, which would generate
host–guest assemblies. Cyclodextrins (CDs) represent hosts
Results and Discussion
[a] Institut für Anorganische und Analytische Chemie,
Friedrich-Schiller-Universität Jena,
The N-salicylidene hydrazide ligand with apolar side
chain used in this study is derived from Schiff base conden-
sation of salicylaldehyde and biphenyl-4-carboxylic acid hy-
drazide (H2salhybiph; Figure 1). Reaction of potassium
Carl-Zeiss-Promenade 10, 07745 Jena, Germany
Fax: +49-3641-948132
E-mail: Sekr.Plass@uni-jena.de
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2007, 1487–1491
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1487

I. Lippold, H. Görls, W. Plass
SHORT COMMUNICATION
vanadate with the H2salhybiph ligand in a methanol/ace-
The solution structure of the inclusion compound
tone solution leads to the potassium salt of the correspond- K[VO2(salhybiph)@β-CD] can be unambiguously estab-
1
ing cis-dioxovanadium(V) complex K[VO2(salhybiph)]. The lished by H NMR spectroscopy. Proton diffusion-ordered
addition of acetone to the reaction solution is required ow- NMR spectroscopy (DOSY) clearly proves the integrity of
ing to the very poor solubility of the H2salhybiph ligand the inclusion compound in solution, as only one species can
system in methanol. After a reaction time of 2 d, K[VO2- be detected. The NOESY NMR spectra exhibit cross-peaks
(salhybiph)] can be isolated as a yellow crystalline solid ma- between the proton signals of the biphenyl side chain of the
terial. Notably, the analogous reaction for ammonium van- vanadium complex and those of the β-CD host (Figure 2).
adate affords the neutral cis-dioxovanadium(V) complex In particular for the 3-H and 5-H protons of the β-CD that
[VO2(Hsalhybiph)] as the isolated product in a much lower extend into the β-CD host cavity, strong interactions with
yield. This is due to the fact that the ligand system under the aromatic protons of the biphenyl side chain of the guest
study is prone to variable protonation states at the amide are observed. The absence of cross-peaks between the 5-H
group, which along with the presence of the protolytically protons of the β-CD and the Hbp7 and Hbp8 protons of
active ammonium ions allows the generation of various the biphenyl group of the guest complex strongly suggests
complex species.[13] Therefore, the potassium vanadate that the guest penetrates into the β-CD cavity from the pri-
route seems to be more promising for the generation of the mary hydroxy side. This is confirmed by the intense cross-
relevant inclusion compounds.
peaks that are observed between the 6-H protons of the β-
CD host and the Hbp2 and Hbp3 protons of the biphenyl
side chain of the guest complex. Moreover, the lack of
cross-peaks between the aromatic protons of the salicylid-
ene moiety and the β-CD host proves that this part of the
guest complex is distant from the β-CD. This also corrobo-
rates the presence of a 1:1 inclusion compound with a clear
Figure 1. Synthesis of the inclusion compound K[VO2(salhybiph)
@β-CD].
The inclusion compound K[VO2(salhybiph)@β-CD] was
synthesized by a one-pot reaction of potassium vanadate
with the H2salhybiph ligand and β-CD in a water/acetone
solution (Figure 1). The presence of β-CD results in a con-
siderably shorter reaction time of about 2 h, and the reac-
tion can be visually followed by the dissolution of the li-
gand. The 1:1 inclusion compound K[VO2(salhybiph)@β-
CD] can be isolated as yellow crystals, which have been fully
characterized in solution and in the solid state.
Figure 2. NOESY spectrum of K[VO2(salhybiph)@β-CD] in D2O
and labeling schemes for host and guest.
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 1487–1491

Modeling Supramolecular Interactions in Vanadium Haloperoxidases
SHORT COMMUNICATION
preference for the interaction of the biphenyl side chain
with the β-CD host cavity.
For the solid state characterization of the inclusion com-
pound K[VO2(salhybiph)@β-CD], crystals suitable for X-
ray analysis were grown by slowly cooling a hot aqueous
solution of the inclusion compound. For different batches,
a considerable variation in the water content was found.
Thermogravimetric analysis (TGA) of these materials re-
veals a weight loss of about 6.5% (16.6%) in the tempera-
ture range form room temperature up to 140 °C, assigned
to the removal of water molecules in the interstices between
the inclusion compounds. In agreement with the elemental
analysis, this indicates anywhere between 6.5 and 18 water
molecules of crystallization per host–guest unit in the solid
state. Above 200 °C, the inclusion compound starts to de-
compose. This temperature is somewhat lower than that ob-
served for plain β-CD hydrate which starts to decompose
at around 270 °C.[15] This difference can be attributed to the
promoting effect of the metal complex host on the decom-
position of the β-CD, and this provides further evidence for
significant host–guest interaction in the inclusion com-
pound. The final residual masses at 750 °C of 8.8 and 7.1%
observed for different batches correspond very well to the
values calculated for the formation of potassium orthovan-
adate, KVO3 (8.1 and 7.3%, respectively; cf. Experimental
Section).[16]
Crystallographic investigation shows that this inclusion
compound crystallizes in the triclinic space group P1. The
asymmetric unit contains two inclusion compounds to-
gether with the solvent water molecules, with the latter as
well as the potassium cations disordered over several crys-
tallographic positions. The molecular structure of the in-
clusion compound is shown in Figure 3. As expected from
the solution NMR spectra, the cis-dioxovanadium(V) com-
plex intrudes only partially into the β-CD cavity. Only the
biphenyl side chain is located within the hydrophobic cavity
of the host, whereas the remaining polar part of the com-
plex is situated outside the primary hydroxy side of the β-
CD host.
The vanadium atom of the guest complex exhibits an al-
most ideal square pyramidal environment with the coordi-
nated H2salhybiph ligand in its dianionic form, which is
characterized by τ values lower than 0.10 (τ = 0 for ideal
tetragonal pyramid; τ = 1 for ideal trigonal bipyramid). The
basal plane of the square pyramid is given by atoms Ni1,
Oi3, and Oi4 (i = 1, 2) of the ligand and the oxo group Oi2;
the apical position is occupied by the oxo group Oi1. Rela-
tive to the mean plane given by the donor atoms of the
chelate ligand system, the vanadium atom is displaced
towards the apical oxo group Oi1 by about 40 pm, whereas
the oxo group Oi2 is slightly tilted towards the opposite
side of the ligand plane with a deviation by about 15 pm
from that plane. The structural parameters are consistent
with those observed for other vanadium(V) complexes con-
taining similar N-salicylidene hydrazide ligands, in particu-
lar the V=O (Oi1 and Oi2) as well as the V–N (Ni1) and
V–O (Oi3 and Oi4) bond lengths are within the expected
range for such cis-dioxovanadium(V) complexes.[8,13]
Figure 3. Representation of the molecular structure of the inclusion
compound K[VO2(salhybiph)@β-CD] that shows the two indepen-
dent host–guest assemblies in the asymmetric unit. Selected bond
lengths [pm] and angles [°]: V1–O11 159.6(9), V1–O12 159.8(8),
V1–O13 189.3(7), V1–O14 196.7(6), V1–N11 215.5(7), N11–N12
139.3(9), O14–C18 127.8(10), N12–C18 129.7(11), O11–V1–O12
106.0(7), O11–V1–O13 102.4(4), O11–V1–O14 104.0(4), O12–V1–
O13 98.5(4), O12–V1–O14 94.0(4), O13–V1–O14 146.3(3), O11–
V1–N11 99.8(5), O12–V1–N11 153.4(5), O13–V1–N11 82.2(3),
O14–V1–N11 73.0(3).
In the solid state, the inclusion compound K[VO2-
(salhybiph)@β-CD] forms head-to-head dimers with the
secondary hydroxy sides of both β-CD hosts linked by hy-
drogen bonds as depicted in Figure 4. This arrangement
leads to a π–π interaction of the biphenyl side chains of the
corresponding guest molecules at a distance of 363 pm. The
cis-dioxovanadium moieties of the guest molecules protrude
from their hosts on the primary hydroxy group side and
thereby generate a gap with a distance of about 910 pm be-
tween the adjacent head-to-head dimers. The protruding
complex fragments of the adjacent dimers possess a stag-
gered arrangement with a nearly coplanar orientation of
their ligand planes (defined by Ni1, Oi3, and Oi4 with i =
1, 2), which are about 340 pm apart. The overall packing
of the head-to-head dimers can be described as a so-called
“channel-type” arrangement[17] which is built from host
guest dimers that are stringed together. These channels are
oriented along the [001] direction and linked through hy-
drogen bonds between primary hydroxy groups (C-6) of
neighboring β-CDs as depicted in Figure 5.
Figure 4. Packing of the inclusion compound K[VO2(salhybiph)
@β-CD] viewed approximately perpendicular to the [001] direction
of the β-CD channel alignment. Hydrogen bonds between neigh-
boring β-CDs are drawn as broken lines.
Eur. J. Inorg. Chem. 2007, 1487–1491
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1489

I. Lippold, H. Görls, W. Plass
SHORT COMMUNICATION
1000 °C with a heating rate of 5 °C/min. Atomic absorption spec-
trometry (AAS) was performed with an AA-6800 from Shimadzu.
K[VO2(salhybiph)]: A suspension of biphenyl-4-carboxylic acid sal-
icylidene hydrazide (0.200 g, 0.63 mmol) in an acetone/methanol
mixture (30:5, 35 mL) was heated to 60 °C. After the addition of
KVO3 (0.087 g, 0.63 mmol), the suspension turned yellow–orange,
and after 2 d of continuous stirring a clear solution was obtained.
Upon removal of the solvent, the crude product was redissolved in
hot methanol (30 mL), filtered, and kept for crystallization. Yield:
1
0.170 g (62%). H NMR (400 MHz, [D6]DMSO): δ = 6.78 (t, J =
7.3 Hz, 1 H, Ha5), 6.80 (d, J = 8.4 Hz, 1 H, Ha3), 7.35 (t, J =
7.8 Hz, 1 H, Ha4), 7.39 (tt, J = 7.4 and 2.1 Hz, 1 H, Hbp8), 7.48 (t,
J = 7.5 Hz, 2 H, Hbp7), 7.57 (d, J = 6.8 Hz, 1 H, Ha6), 7.52 (d, J
= 8.2 Hz, 2 H, Hbp3), 7.75 (t, J = 8.9 Hz, 2 H, Hbp6), 8.10 (d, J =
8.3 Hz, 2 H, Hbp2), 9.00 (s, 1 H, CH=N) ppm. 13C NMR
(100 MHz, [D6]DMSO): δ = 116.65 (HCa5), 119.45, 119.86 (HCa3
and Ca1), 126.34, 126.65 (HCbp3 and HCbp6), 127.78 (HCbp8),
128.29 (HCbp2), 128.93 (HCbp7), 131.85 (Cbp1), 132.47 (HCa6),
133.03 (HCa4), 139.33 (Cbp4), 141.91 (Cbp5), 155.51 (C=N), 164.59
(Ca2), 169.48 (C=O) ppm. 51V NMR (105 MHz, [D6]DMSO): δ =
Figure 5. View of the crystal packing along the β-CD channels in
the [001] direction. Hydrogen bonds between neighboring β-CDs
are drawn as broken lines.
–532 (ν1/2 = 1122 Hz) ppm. IR (KBr): ν = 3447 (s), 3055 (w), 3028
˜
(w), 2929 (w), 1615 (vs), 1550 (m), 1513 (m), 1476 (w), 1446 (m),
1383 (w), 1344 (s), 1278 (m), 1204 (w), 1157 (w), 950 (s), 904 (s),
875 (s), 760 (m), 740 (s), 696 (m) cm–1. MS (ESI–, MeOH): m/z
(%) = 397 (100) [VO2(salhybiph)]–.C20H14KN2O4V (436.38): calcd.
C 55.05, H 3.23, N 6.42; found C 55.05, H 3.25, N 6.28.
Conclusions
K[VO2(salhybiph)@β-Cyclodextrin]·xH2O: Biphenyl-4-carboxylic
acid salicylidene hydrazide (0.100 g, 0.32 mmol) was suspended in
a solution of β-cyclodextrin (0.359 g, 0.32 mmol) in water (15 mL)
at 60 °C. Acetone (15 mL) was added for better solubility of the
ligand. Upon addition of KVO3 (0.044 g, 0.32 mmol), the suspen-
sion turned yellow and, after stirring for 2 h at 60 °C, became a
clear solution. The hot solution was filtered, and acetone was re-
moved under reduced pressure. The solution was heated to 70 °C,
allowed to slowly cool to room temperature, and the product pre-
cipitated as pale yellow cubic crystals. The water content of the
isolated crystalline material varies considerably for different
We present the first supramolecular inclusion compound
of a cis-dioxovanadium(V) complex with cyclodextrins. To
facilitate this, a new vanadium complex derived from N-
salicylidene hydrazide containing a hydrophobic biphenyl
side chain matching the β-CD host cavity was synthesized.
The integrity of the isolated inclusion compound K[VO2-
(salhybiph)@β-CD] in solution was confirmed by NMR
spectroscopy. The solid-state structure reveals a channel-
type packing of the head-to-head β-CD dimers which is
cross-linked through hydrogen bonds and intercalated po-
tassium cations. Through modification of the CD-host, it
should be possible to utilize this concept for the generation
of novel systems in oxidation catalysis, including the poten-
tial influence of the sugar backbone on chiral induction of
vanadium-catalyzed oxidation reactions.
synthetic
batches.
Yield:
0.29 g
(50%).
Batch
1:
C62H84KN2O39V·6.5H2O (1697.47): calcd. C 44.10, H 5.79, N 1.67;
found C 44.04, H 5.94, N 1.39. TGA: Weight loss up to 140 °C of
6.5% (calcd. 6.9%), residual mass at 750 °C of 8.8% (calcd. 8.1%
for KVO3). Batch 2: C62H84KN2O39V·18H2O (1895.64): calcd. C
39.28, H 6.38, N 1.48, K 2.06; found C 39.79, H 6.39, N 1.21, K
1.2–2.3. TGA: Weight loss up to 140 °C of 16.6% (calcd. 17.1%),
residual mass at 750 °C of 7.1% (calcd. 7.3% for KVO3). 1H NMR
(400 MHz, [D6]DMSO): δ = 3.25–3.40 (m, 2 H, 2-H and 4-H),
3.50–3.70 (m, 4 H, 3-H, 5-H, and 6-H), 4.44 (t, J = 5.5 Hz, 1 H,
C6-OH), 4.82 (d, J = 3.3 Hz, 1 H, 1-H), 5.66 (d, J = 2.2 Hz, 1 H,
C3-OH), 5.71 (d, J = 6.9 Hz, 1 H, C2-OH), 6.77 (t, J = 7.2 Hz, 1
H, Ha5), 6.78 (d, J = 7.4 Hz, 1 H, Ha3), 7.34 (dt, J = 7.7 and 2.0 Hz,
1 H, Ha4), 7.38 (tt, J = 7.5 Hz and 1.2 Hz, 1 H, Hbp8), 7.48 (t, J =
7.6 Hz, 2 H, Hbp7), 7.56 (dd, J = 8.1 and 1.8 Hz, 1 H, Ha6), 7.75
(t, J = 8.2 Hz, 4 H, Hbp3 and Hbp6), 8.08 (d, J = 8.4 Hz, 2 H, Hbp2),
Experimental Section
General Remarks: The synthesis of the ligand biphenyl-4-carboxylic
acid salicylidene hydrazide (H2salhybiph) and its neutral cis-di-
oxovanadium(V) complex [VO2(Hsalhybiph)] is described in the
1
Supporting Information. H, 13C and 51V as well as NOESY and
DOSY NMR spectra were recorded with a 400 MHz Bruker
AVANCE spectrometer. For notation used in the assignment of the
atoms, see Figure 2. The chemical shift values for the 51V NMR
spectra are reported relative to VOCl3 as an external standard. Ele-
mental analyses (C, H, N) were carried out with a Leco CHNS-932
elemental analyzer. Mass spectra were measured with a MAT95XL
Finnigan instrument utilizing electron spray ionization and obser-
vation in the negative mode. IR spectra were recorded with a
Bruker IFS55/Equinox spectrometer on samples prepared as KBr
pellets. Thermogravimetric analysis (TGA) for powdered samples
was performed with a Netzsch STA409PC Luxx apparatus under
a constant flow of air ranging from room temperature up to
1
8.98 (s, 1 H, CH = N) ppm. H NMR (400 MHz, D2O): δ = 3.43
(dd, J = 9.9 Hz and 3.4 Hz, 1 H, 2-H), 3.45–3.50 (m, 2 H, 4-H and
5-H), 3.70–3.80 (m, 3 H, 3-H and 6-H), 4.90 (d, J = 3.5 Hz, 1 H,
1-H), 6.91 (d, J = 8.4 Hz, 1 H, Ha3), 6.94 (t, J = 7.6 Hz, 1 H, Ha5),
7.04 (br. s, 1 H, Hbp8), 7.11 (s, 2 H, Hbp7), 7.35 (d, J = 6.2 Hz, 2
H, Hbp6), 7.42 (t, J = 8.0 Hz, 1 H, Ha4), 7.57 (t, J = 8.0 Hz, 2 H,
Hbp3), 7.57 (t, J = 8.0 Hz, 1 H, Ha6), 7.95 (d, J = 8.0 Hz, 2 H, Hbp2),
8.89 (s, 1 H, CH=N) ppm.13C NMR (100 MHz, [D6]DMSO): δ
= 59.92 (C-6), 72.04 (C-5), 72.41 (C-2), 73.05 (C-3), 81.54 (C-4),
101.93 (C-1), 116.70 (HCa5), 119.51, 119.92 (HCa3 and Ca1),
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Eur. J. Inorg. Chem. 2007, 1487–1491

Modeling Supramolecular Interactions in Vanadium Haloperoxidases
SHORT COMMUNICATION
[2] a) M. Andersson, A. Willetts, S. Allenmark, J. Org. Chem.
1997, 62, 8455; b) H. B. ten Brink, A. Tuynman, H. L. Dekker,
W. Hemrika, Y. Izumi, T. Oshiro, H. E. Schoemaker, R. Wever,
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[3] a) A. Messerschmidt, R. Wever, Proc. Natl. Acad. Sci. USA
1996, 93, 392–396; b) A. Messerschmidt, L. Prade, R. Wever,
Biol. Chem. 1997, 378, 309–315; c) M. N. Isupov, A. R. Dalby,
A. A. Brindley, Y. Izumi, T. Tanabe, G. N. Murshudov, J. A.
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126.43, 126.72 (HCbp3 and HCbp6), 127.85 (HCbp8), 128.33
(HCbp2), 129.00 (HCbp7), 131.78 (Cbp1), 132.51 (HCa6), 133.11
(HCa4), 139.43 (Cbp4), 141.94 (Cbp5), 155.60 (C=N), 164.69 (Ca2),
169.51 (C=O) ppm. 51V NMR (105 MHz, [D6]DMSO): δ =
–532 ppm (ν1/2 = 1067 Hz). 51V NMR (105 MHz, D2O): δ =
–533 ppm. IR (KBr): ν = 3392 (vs), 2929 (m), 1612 (m), 1550 (w),
˜
1509 (w), 1490 (w), 1448 (w), 1388 (w), 1156 (m), 1079 (m), 1028
(s), 945 (m), 906 (m), 759 (w) cm–1. MS (ESI–, MeOH): m/z (%) =
2667 (8) {[VO2(salhybiph)] +2β-CD}–, 1532 (42) {[VO2(salhybiph)]
+ β-CD}–, 1134 (30) [β-CD–H]+, 397 (100) [VO2(salhybiph)]–.
X-ray
Crystallographic
Study
of
K[VO2(salhybiph)@β-
[4] W. Plass, Angew. Chem. 1999, 111, 960–962; Angew. Chem. Int.
Ed. 1999, 38, 909–912.
Cyclodextrin]·xH2O: Crystals suitable for X-ray analysis were
grown by slow cooling of a hot water solution of the inclusion
compound. C62H84KN2O39V(·8H2O), Mr = 1715.48 gmol–1, tri-
clinic, space group P1, a = 1535.37(5), b = 1545.54(7), c =
2146.64(8) pm, α = 94.710(2), β = 98.484(2), γ = 102.994(2)°, V =
4873.9(3)ϫ106 pm3, Z = 2, µ(Mo-Kα) = 0.229 mm–1, 32730 reflec-
tions measured with a Nonius KappaCCD diffractometer at
183(2) K in the 2.49 to 27.50° Θ range. The structure was solved
by direct methods and subsequently refined against F2 with the
SHELXL-97 program,[18] which converged at R1 = 0.1126 for 20029
observed reflections with IϾ2σ(I) and wR2 = 0.3385 for all unique
reflections with a goodness-of-fit on F2 of 1.165. All non-hydrogen
atoms were refined with anisotropic displacement parameters. All
hydrogen atoms bonded to carbon atoms were introduced in theo-
retical positions but not refined. As known from the analytical data
of different batches the content of water molecules is varying. For
the measured crystals an overall content of eight water molecules
could be assigned. The potassium cations and the water molecules
were found to be disordered over several crystallographic positions
and refined with partial occupancy factors. The discrimination be-
tween potassium and water sites is made on the basis of the poten-
tial coordination numbers and hydrogen bonding interactions. For
the water molecules, no attached hydrogen atoms were considered.
Additional disorder was found for one of the included anionic va-
nadium complexes (V2) which was refined with a relative ratio of
about 1:2. The largest positive and negative residual Fourier peaks
after the refinement were equal to 0.82 and –0.51, respectively.
CCDC-629924 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.
[5] K. Ishikawa, Y. Mihara, K. Gondoh, E. Suzuki, Y. Asano,
EMBO J. 2000, 19, 2412–2423.
[6] a) M. Bangesh, W. Plass, J. Mol Struct. THEOCHEM 2005,
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Supporting Information (see footnote on the first page of this arti-
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Acknowledgments
The authors gratefully acknowledge the financial support of this
study by the Deutsche Forschungsgemeinschaft. We wish to thank
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Received: December 22, 2006
Published Online: March 6, 2007
Eur. J. Inorg. Chem. 2007, 1487–1491
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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