Transition metal complexes of the novel hexadentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine

Article abstract of DOI:10.1039/c0dt01406k

The novel polydentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl) phthalazine, bimptz, has been synthesized and its coordination chemistry was investigated. Bimptz is neutral and contains a central phthalazine unit, to which two di-(N-methylimidazol-2-yl)methyl groups are attached in the 1,4-positions. This ligand therefore provides up to 6 donor sites for coordination to metal ions. A series of metal complexes of bimptz was prepared and their molecular structures were determined by X-ray diffraction. Upon reaction of bimptz with two equivalents of MnCl₂·4H ₂O, CoCl₂·6H₂O and [Ru(dmso) ₄Cl₂], the dinuclear complexes [Mn₂(bimptz)(- Cl)₂Cl₂] (1), [Co₂(bimptz)(CH ₃OH)₂(-Cl)₂](PF₆)₂ (3) and [Ru₂(bimptz)(dmso)₂(-Cl)₂](PF ₆)₂ (4), respectively, were isolated. The latter were found to have similar solid state structures with octahedrally coordinated metal centers bridged by the phthalazine unit and two chloro ligands. The cobalt and ruthenium complexes 3 and 4 were isolated as PF₆^- salts and contain neutral methanol and dmso ligands, respectively, at the terminal coordination sites of the metal centres. The mononuclear ruthenium complex [Ru(Hbimptz)₂](PF₆)₄ (6) was obtained from the reaction of two equivalents bimptz with [Ru(dmso)₄Cl₂]. In complex 6, three donor sites per ligand molecule are used for coordination of the Ru(ii) center. In each bimptz ligand, one of the remaining, dangling N-methylimidazole rings is protonated and forms a hydrogen bond with the unprotonated N-methylimidazole ring of the other bimptz ligand.

Full text of DOI:10.1039/c0dt01406k

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PAPER
Transition metal complexes of the novel hexadentate ligand
1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine†
Stefan Roggan,a Christian Limberg,a Christina Knispela and T. Don Tilley*b
Received 17th October 2010, Accepted 18th February 2011
DOI: 10.1039/c0dt01406k
The novel polydentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine, bimptz, has been
synthesized and its coordination chemistry was investigated. Bimptz is neutral and contains a central
phthalazine unit, to which two di-(N-methylimidazol-2-yl)methyl groups are attached in the
1,4-positions. This ligand therefore provides up to 6 donor sites for coordination to metal ions. A series
of metal complexes of bimptz was prepared and their molecular structures were determined by X-ray
diffraction. Upon reaction of bimptz with two equivalents of MnCl2·4H2O, CoCl2·6H2O and
[Ru(dmso)4Cl2], the dinuclear complexes [Mn2(bimptz)(m-Cl)2Cl2] (1), [Co2(bimptz)(CH3OH)2(m-
Cl)2](PF6)2 (3) and [Ru2(bimptz)(dmso)2(m-Cl)2](PF6)2 (4), respectively, were isolated. The latter were
found to have similar solid state structures with octahedrally coordinated metal centers bridged by the
phthalazine unit and two chloro ligands. The cobalt and ruthenium complexes 3 and 4 were isolated as
-
PF6 salts and contain neutral methanol and dmso ligands, respectively, at the terminal coordination
sites of the metal centres. The mononuclear ruthenium complex [Ru(Hbimptz)2](PF6)4 (6) was obtained
from the reaction of two equivalents bimptz with [Ru(dmso)4Cl2]. In complex 6, three donor sites per
ligand molecule are used for coordination of the Ru(II) center. In each bimptz ligand, one of the
remaining, dangling N-methylimidazole rings is protonated and forms a hydrogen bond with the
unprotonated N-methylimidazole ring of the other bimptz ligand.
occurs in the oxygen-evolving complex (OEC) of photosystem
Introduction
II. It is believed that the catalytic site in the OEC consists of a
cubane-like Mn4Ca oxocluster, but the detailed mechanism of this
four-electron oxidation process is still under intense discussion.6
A growing interest in electrocatalytic water splitting, which results
from the motivation to establish viable strategies for conversion of
solar energy to chemical fuels, has led to the synthesis of dinuclear
manganese and ruthenium complexes which have been reported
to catalyze the oxidation of water in the presence of an oxidant
such as Ce(IV).7,8 More generally, the interest in dinuclear metal
complexes stems from possible cooperative effects that may be of
use in the design of more efficient catalytic transformations.9
For exploration of cooperative effects in dinuclear complexes, it
is important to utilize ligands that possess the desired property of
rigidly binding two metals such that they are in close proximity.
Thus, there has been considerable interest in binucleating ligands
which place the metal fragments at a desired distance and with a
predetermined orientation. This should allow tuning of the steric
and electronic properties of the dinuclear core.
Di- and polynuclear metal complexes play an important role
in many areas of chemistry, and for this reason investigations
of ligand systems tailored for the complexation of more than
one metal centre continues to be an active area of research.1
Since many enzymes possess two or more metal centres at
their active sites, the bioinorganic community has significantly
advanced this area of research, in search of synthetic models
and biomimetic complexes. Attractive targets include artificial
mimics for methane monooxygenase and [FeFe]-hydrogenase,
which catalyze the oxidation of methane to methanol, and the
reduction of H+ to H2, respectively. In both cases the catalytic site
contains a diiron centre that has been the focus of considerable
research efforts, given the desire to develop efficient synthetic
catalysts for these reactions.2–5 Another important enzyme-based
reaction in biology is the oxidation of water to oxygen, which
aInstitut fu¨r Chemie, Humboldt-Universita¨t zu Berlin, Brook-Taylor-Straße
2, 12489, Berlin, Germany. E-mail: christian.limberg@chemie.hu-berlin.de;
Fax: +49 30 2093 6966; Tel: +49 30 2093 7382
Previous studies have shown that the phthalazine group is a
versatile building block for the synthesis of dinuclear complexes,
and dinucleating ligands based on this moiety have been used
bDepartment of Chemistry, University of California-Berkeley, Berkeley,
CA 94720, USA; Chemical Sciences Division, Lawrence Berkeley Na-
tional Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA. E-mail:
tdtilley@berkeley.edu; Fax: +1 510 642 8940; Tel: +1 510 642 8939
˚
to obtain metal–metal separations ranging from 2.550 A to
10,11
˚
4.045 A.
Here we present the results of investigations on the
† Electronic supplementary information (ESI) available. CCDC reference
numbers 765494–765497. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt01406k
synthesis and coordination chemistry of the ligand 1,4-bis(di(N-
methylimidazol-2-yl)methyl)phthalazine, bimptz, which is based
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on a central phthalazine unit, to which two di-N-methylimidazol-
2-ylmethyl groups are attached in the 1- and 4-positions
(Scheme 1). The bimptz ligand provides up to six N-donor
functions for binding metal ions and possesses four imidazolyl
groups, which in principle have the potential to mimic biologically
relevant histidine residues.
Scheme 1 Synthesis of the ligand bimptz.
Fig. 1 Molecular structure of [Mn2(bimptz)(m-Cl)2Cl2] (1). All hydrogen
atoms as well as one methanol solvent molecule of crystallization were
omitted for clarity. See Table 1 and Table 2 for selected bond lengths and
angles. For crystal parameters see Table 4.
Results and discussion
The bimptz ligand was obtained in high yield by reaction of 2
equivalents of lithiated bis-(N-methylimidazol-2-yl)methane and
1,4-dichlorophthalazine in THF at -70 ◦C (Scheme 1). The
monosubstituted 1-chloro-4-(bis-(N-methylimidazolyl)methane)-
phthalazine and unreacted Im¢CH2Im¢ were identified as side
˚
Table 1 Selected bond lengths [A] for the complexes 1, 3 and 4
1
products by H NMR spectroscopy after workup. This suggests
that the intermediate mono-substitution product, ClptzCH(Im¢2),
may react with Li(CHIm¢2) via a competing proton-transfer
process. Further support for this was observed in the use
of benzylpotassium for the deprotonation of Im¢CH2Im¢ (to
generate K(CHIm¢2) as the nucleophilic agent in the reaction
mixture), which gave only mono-substituted ClptzCH(Im¢2) and
Im¢CH2Im¢, in equimolar amounts, as isolated compounds after
work up. In the latter case, nucleophilic substitution of the second
chlorine atom of the pthalazine unit appears to be significantly
slower than protonation of K(CIm¢2) by Clptz(CHIm¢2).
To investigate the properties of bimptz as a binucleating ligand,
the latter was allowed to react with various metal salts. Addition
of a solution of bimptz in ethanol to 2 equivalents of man-
ganese(II)chloride hydrate in ethanol resulted in precipitation of a
light yellow solid. Crystallization of this solid from MeOH/Et2O
provided X-ray quality crystals of the compound, identified
by an X-ray diffraction analysis as the dinuclear manganese
complex [Mn2(bimptz)(m-Cl)2Cl2] (1; Scheme 2), and the molecular
structure is shown in Fig. 1.
1
3
4
(M = Mn)
(M = Co)
(M = Ru)
M1–N1
M2–N2
M1–N3
M1–N4
M2–N5
M2–N6
M1–Cl1
M2–Cl2
M1–Cl2
M2–Cl1
M1–X3
2.432(5)
2.514(5)
2.205(5)
2.287(5)
2.268(5)
2.179(5)
2.484(2)
2.493(2)
2.595(2)
2.595(2)
X3 = Cl3
2.433(2)
X4 = Cl4
2.443(2)
M = Mn
3.549(2)
2.190(3)
2.192(3)
2.073(3)
2.077(3)
2.103(3)
2.107(3)
2.449(2)
2.449(2)
2.469(2)
2.437(2)
X3 = O1
2.069(3)
X4 = O2
2.098(3)
M = Co
3.255(2)
2.105(9)
2.093(8)
2.03(2)
2.053(9)
2.05(1)
2.039(7)
2.439(3)
2.422(2)
2.418(2)
2.431(3)
X3 = S1
2.221(4)
X4 = S2
2.229(7)
M = Ru
3.273(2)
M2–X4
M1–M2
Each manganese atom resides in a distorted octahedral coor-
dination environment, in which the observed bond angles about
the metal center deviate significantly from the ideal values (e.g.
N5–Mn2–N6 82.9◦) (Table 2). The Mn atoms are bridged by
two chloride ligands and the phthalazine unit, resulting in a
˚
metal–metal distance of 3.549(2) A. This distance is shorter than
the analogous one found in [Mn2(bdptz)(m-OBz)2(H2O)2](OTs)2,
˚
(3.754(2) A, bdptz = 1,4-bis(2,2¢-dipyridylmethyl)phthalazine)), in
Scheme 2 Synthesis of the dimanganese complex [Mn2(bimptz)(m-
Cl)2Cl2] (1).
which the m-benzoate ligands induce a larger separation of the two
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Table 2 Selected bond angles [◦] for the complexes 1, 3 and 4
1
3
4
(M = Mn)
(M = Co)
(M = Ru)
Cl1–M1–Cl2
N1–M1–X3
84.85(5)
X3 = Cl3
171.7(2)
86.6(2)
84.67(5)
82.9(2)
164.9(2)
X4 = Cl4
172.1(2)
86.09(4)
X3 = O1
177.6(2)
87.21(8)
86.78(4)
85.9(2)
173.25(9)
X4 = O2
173.8(2)
84.35(9)
X3 = S1
174.9(3)
87.9(2)
84.44(9)
88.2(3)
172.1(2)
X4 = S2
173.8(2)
N1–M1–Cl1
Cl1–M2–Cl2
N5–M2–N6
Cl2–M2–N6
N2–M2–X4
Scheme 3 Synthesis of the dinuclear cobalt complexes 2 and 3.
metal ions.12 The Mn2(m-Cl)2 unit is unsymmetrical, and exhibits
˚
two comparatively short (Mn2–Cl2 2.493(2); Mn1–Cl1 2.484(2) A)
˚
and two longer (Mn1–Cl2 2.595(2); Mn2–Cl1 2.595(2) A) Mn–Cl
bonds. This suggests a relatively weak bridging character for the
m-Cl ligands, since the terminal Mn–Cl bond distances (Mn1–Cl3
˚
2.433(2); Mn2–Cl4 2.443(2) A) are only slightly shorter than the
shorter distances involving the bridging Cl atoms.
The reaction of bimptz with two equivalents of CoCl2·6H2O
in ethanol led to a deep green-blue solution, which contained a
very fine precipitate. After workup single crystals were grown by
recrystallization from methanol/THF. Although the quality of
the dataset obtained from an X-ray diffraction experiment was
too poor to determine accurate geometrical parameters, the atom
connectivity of the complex was clearly determined. Thus, this
complex is the dinuclear cobalt species [Co2(bimptz)2(CH3OH)2(m-
Cl)2][CoCl4] (2), with a structure that is comparable to that of 1.
However, in contrast to 1, 2 does not contain terminal chloride
ligands. Instead, methanol (solvent) molecules are coordinated to
the cobalt atoms, in positions trans to the phthalazine nitrogen
atoms. The reaction also results in formation of tetrachloro-
cobaltate(II) as the counter anion. The reaction was repeated
using three equivalents of CoCl2·6H2O and methanol as the
solvent. A pink solution was obtained, from which pink crystals
of [Co2(bimptz)2(CH3OH)2(m-Cl)2](PF6)2 (3) precipitated after
addition of NH4PF6 and cooling to -30 ◦C (Scheme 3). Single
crystals suitable for X-raydiffraction were grown byether diffusion
intoasolutionof 3inmethanolat4 ◦C, andthemolecularstructure
of 3 is shown in Fig. 2.
Fig. 2 Molecular structure of [Co2(bimptz)(m-Cl)2(CH3OH)2](PF6)2 (3).
Hydrogen atoms, except those for the methanol ligands, as well as the PF6
counter anions have been omitted for clarity. For selected bond lengths
and angles see Table 1 and Table 2. For crystal parameters see Table 4.
-
An ESI-MS analysis of 3 in acetonitrile solution indi-
cates that the methanol ligands are somewhat labile, as no
signals were detected for species containing methanol, such
as [Co2(bimptz)(CH3OH)2Cl2]2+. Instead, only peaks for the
+
methanol-free species {[Co2(bimptz)Cl2](PF6)} (m/z = 811.0) and
As expected, the coordination geometry of the cationic dicobalt
complex of 3 is very similar to that of the dimanganese complex
1. The two cobalt(II) ions are located at the centers of two
slightly distorted, edge-sharing octahedrons. However, in 3 the
bond angles about the metal centers are closer to ideal octahedral
values. In contrast to the Mn2Cl2 unit of 1, the Co2(m-Cl)2 core is
diamond-like, with no pronounced differences in the Co–Cl bond
[Co2(bimptz)Cl2]2+ (m/z = 333.0), as well as for [Co2(bimptz)-
Cl2(CH3CN)]2+ (m/z = 353.5), were observed.
Initial attempts to obtain a ruthenium complex of bimptz were
based on a protocol which had been successfully employed by
˚
Thummel et al. and Akermark et al. for the synthesis of dinuclear
ruthenium complexes containing a bridging phthalazine unit.13,14
Accordingly, two equivalents of [Ru(dmso)4Cl2] were heated
together with bimptz, LiCl and NEt3 in an ethanol–water mixture
for 48 h. However, the crude product that was isolated after
addition of NH4PF6 was found to consist of an inseparable
˚
distances which range from 2.437 to 2.469 A. The metal–metal
˚
distance in 3 (3.255(2) A) is shorter than the corresponding value
˚
in 1 (3.549(2) A).
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mixture of several products. Better results were obtained when
a 2 : 1 mixture of [Ru(dmso)4Cl2] and bimptz in ethylene glycol
was heated in a microwave reactor for 15 min. After addition of
excess NH4PF6, the reaction mixture was subjected to column
chromatography (silica gel). Initially, a deep red component was
eluted, followed by a broad yellow band that contained the main
product. NMR (1H and 13C) and ESI-MS analyses identified the
latter as the dinuclear complex [Ru2(bimptz)(dmso)2(m-Cl)2](PF6)2
(4), and an X-ray diffraction analysis confirmed this formulation
(Fig. 3).
1H NMR spectroscopy and high resolution ESI-mass spectrom-
etry. This information suggests that the complex is the dinu-
clear ruthenium complex [Ru2(bimptz)(m-Cl)2(dmso)(dms)](PF6)2
(5), which differs from 4 in that one of the dmso ligands
has been replaced by dimethylsulfide (dms, Scheme 4). Ac-
cordingly, the mass spectrum showed two peaks correspond-
ing to the mono- and dicationic species {[Ru2(bimptz)(m-
+
Cl)2(dmso)(dms)](PF6)} (m/z = 1036.9750, calc. 1036.9777)
and [Ru2(bimptz)(m-Cl)2(dmso)(dms)]2+ (m/z = 446.0057, calc.
446.0068), respectively. In the 1H NMR spectrum of 5 a new
signal for the (CH3)2S protons was detected, while in comparison
to the spectrum of 4 the integration for the (CH3)2SO protons was
reduced by half. The relatively harsh reaction conditions employed
for the preparation of 4 are possibly responsible for the partial
deoxygenation of dimethylsulfoxide, which leads to the formation
of 5 as a byproduct.
Fig. 3 Molecular structure of [Ru2(bimptz)(m-Cl)2(dmso)2](PF6)2 (4). Hy-
drogen atoms, the PF6 counterions, and cocrystallized solvent molecules
-
Scheme 4 Synthesis of the dinuclear ruthenium complexes 4 and 5.
have been omitted for clarity. For selected bond lengths and angles see
Table 1 and Table 2. For crystal parameters see Table 4.
Particularly interesting bimetallic complexes might incorporate
two different metal atoms. Thus, it was of interest to investigate
the 1 : 1 reaction of bimptz with [Ru(dmso)4Cl2], to see if only one
Ru center could be selectively introduced onto the ligand. These
compounds were allowed to react in refluxing ethylene glycol,
and upon addition of excessive NH4PF6 to the reaction mixture,
a microcrystalline, dark purple solid precipitated. Single crystals
of this complex were grown by slow evaporation of a methanol–
acetone solution. An X-ray diffraction analysis revealed a molec-
ular structure that features one ruthenium atom coordinated by
two bimptz ligands (Scheme 5). In addition, not two but four
As in the case of the manganese (1) and cobalt (2, 3) complexes,
the two ruthenium ions are located at the centers of edge-
sharing octahedra. The Ru2(m-Cl)2 core is symmetrical (Ru–Cl
˚
distances of 2.418(2)–2.439(3) A and the metal–metal distance
˚
˚
(3.273(2) A) is very similar to that found for 3 (3.255(2) A).
As for 3, the neutral ligands (dmso) are positioned trans to the
phthalazine nitrogen atoms. The dmso ligands are coordinated to
the ruthenium centers via donation from sulfur, as is usually the
case in ruthenium chemistry.15 An ESI-MS analysis for 4 in ace-
tonitrile revealed a signal for the dication [Ru2(bimptz)(dmso)2(m-
Cl)2]2+ (m/z = 454.0053, calc. 454.0037) along with a peak
-
PF6 counterions were found to be contained in the structure. As
an oxidation of the metal center from Ru(II) to Ru(IV) seemed
+
corresponding to {[Ru2(bimptz)(dmso)2(m-Cl)2](PF6)} (m/z =
1052.9733, calc. 1052.9721). Heating 4 to reflux in CH3CN induces
the successive substitution of the dmso ligands by CH3CN. After
one day the solution contained 4, [Ru2(bimptz)(dmso)(CH3CN)(m-
Cl)2]2+ and [Ru2(bimptz)(CH3CN)2(m-Cl)2]2+ in a 1 : 4 : 2 ratio (as
determined by ESI-MS), while after 2 days the formation of
[Ru2(bimptz)(CH3CN)2(m-Cl)2]2+ was nearly complete and only
minor amounts (20%) of [Ru2(bimptz)(dmso)(CH3CN)(m-Cl)2]2+
could be detected (by ESI-MS and 1H NMR spectroscopy).
The dark red solid isolated as a minor component during the
chromatographic purification of 4 (vide supra) was analyzed by
Scheme 5 Synthesis of [Ru(Hbimptz)2](PF6)4 (6).
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Table 3 CVa data of the ruthenium complexes 4 and 6
unreasonable, the structural data were examined for the presence
of additional protons, and indeed it proved possible to locate two
“new” hydrogen atoms (H7, H7¢) within the structure (Fig. 4).
In each bimptz ligand, one of the dangling N-methylimidazole
rings is protonated and these protons are hydrogen-bonded to
an imidazole ring of the other bimptz ligand (e.g. N7–H7–N9¢,
ox
Complex
E1/2 (DE)
[Ru2(bimptz)(dmso)2(m-Cl)2](PF6)2 4
[Ru(Hbimptz)2](PF6)4 6
0.78 (68), 1.58(78)
0.79 (70)
a Measured with a platinum electrode at 100 mV s-1 in dry CH3CN
containing 0.1 M (n-Bu4)PF6 and reported in volts relative to SCE. E1/2
(Epa + Epc)/2 in V, DE = (Epa - Epc) in mV.
+
see Fig. 4). A comparison of the pKa values for NH4 and N-
methylimidazolium (HIm¢) suggests that under normal conditions
=
the ammonium cation would not be expected to be acidic enough
+
+
to protonateN-methylimidazole(pKa(NH4 ) = 9.25; pKa(HIm¢ ) =
6.6).16 Thus, formation of the hydrogen bond undoubtedly drives
this proton-transfer reaction.
The electrochemical properties of the ruthenium complexes
4 and 6 were studied by cyclic voltammetry (CV, Table 3).
The CV of the dinuclear complex 4, recorded in anhydrous
acetonitrile, exhibits two reversible one-electron waves at E1/2
=
0.78 and 1.58 V vs. the saturated calomel electrode (SCE). These
waves can be assigned to the stepwise one-electron oxidations
RuIIRuII to RuIIRuIII and RuIIRuIII to RuIIIRuIII, respectively. The
marked difference in the two oxidation potentials observed for
4 indicates a strong coupling of the two Ru centers. When
negative potentials were applied, only irreversible, ligand reduction
bands were observed. The oxidation potentials found for 4 are
comparable to those reported by Thummel et al. for a series
of pyridazine-bridged dinuclear ruthenium(II) complexes.13 These
values are, however, much more positive than the oxidation
˚
potentials observed by Akermark et al. for a diruthenium complex
that contains a negatively charged pyridazine based ligand.14 For
the mononuclear complex 6 a reversible one-electron oxidation
wave was observed at E1/2 = 0.79 V, which is a potential very
close to that found for oxidation of the first Ru(II) centre
in 4.
-
Conclusions
Fig. 4 Molecular structure of 6. The four PF6 counterions and all
hydrogen atoms except H7/H7¢ were omitted for clarity. The hydrogen
Here we describe the synthesis and coordination properties of
the neutral ligand bimptz, which is accessible in three steps
starting from N-methylimidazole and diethoxycarbonate. Bimptz
contains a bridging phthalazine unit with four tethered imidazolyl
rings, and it is therefore able to provide up to 6 donor sites
for the coordination of metal ions. The potential of bimptz for
the synthesis of dinuclear metal complexes was demonstrated in
reactions with MnCl2·4H2O, CoCl2·6H2O and [Ru(dmso)4Cl2],
from which the corresponding dimetallic complexes 1, 3 and 4
could be obtained. The molecular structures of the latter are
similar and contain two metal ions in a more or less distorted
octahedral ligand environment. In all structures the two metal
ions are bridged by the phthalazine moiety and two m-chloro
ligands. Diamond-like M2(m-Cl2) units are found in the cobalt
and ruthenium complexes 3 and 4, while the M–Cl bond lengths
within the corresponding core of the manganese complex 1 reflect
a significant bond alternation. The electrochemical properties of
the two ruthenium complexes were investigated by means of cyclic
voltammetry, which shows two reversible one electron oxidations
for 4 and one reversible oxidation wave for 6. Further work
will focus on the synthesis of chlorine free, dinuclear complexes
of bimptz and on investigations of the ability of 6 to act as
a precursor for the preparation of heteronuclear metal comp-
lexes.
atom H7 was found from a difference Fourier map and freely refined in
˚
the subsequent least square cycles. Selected bond distances [A] and angles
[◦]: Ru–N1 2.035(2), Ru–N3 2.052(2), Ru–N5 2.054(2), N7–H7 0.89(4),
N9¢–H7 1.79(4); N5–Ru–N1¢ 177.10(9), N3–Ru–N3¢ 178.1(2), N1–Ru–N1¢
93.4(2), N1–Ru–N3¢ 96.18(8), N7–H7–N9¢ 174(4).
Further evidence for the presence of two additional protons in 6
is provided by high-resolution ESI-MS analysis. For an acetonitrile
solution of the complex, signals were observed for the complex
cation [Ru(Hbimptz)2]4+ (m/z = 265.0968; calc. 265.0965), and
-
2+
for its PF6 salt {[Ru(Hbimptz)2](PF6)2} . Peaks corresponding
to the trication [Ru(Hbimptz)(bimptz)]3+ (m/z = 353.1265; calc.
-
2+
353.1263) and its PF6 adduct {[Ru(Hbimptz)(bimptz)](PF6)}
provide evidence that deprotonation occurs to a certain degree
in solution.
In 6 each of the two bimptz ligands contributes three N-
donor sites to the slightly distorted octahedral coordination of
the Ru(II) center, leaving the other three nitrogen donors available
for further reactivity. Complex 6 is C2-symmetric and contains
a crystallographic axis of symmetry that passes through the
ruthenium center and bisects the angle spanned by N1, Ru and
N1¢. As mentioned above, two of the dangling imidazolyl rings are
protonated and are involved in hydrogen bonds to the nitrogen
atoms of additional imidazolyl rings.
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(m), 1579 (m), 1546 (m), 1523 (m), 1490 (vs), 1458 (m), 1412 (s),
1396 (s), 1361 (s), 1284 (s), 1271 (s), 1244 (m), 1177 (w), 1136 (s),
1082 (w), 1047 (w), 936 (w), 923 (w), 872 (m), 859 (s), 810 (m), 763
(s), 750 (vs), 717 (m), 695 (s), 678 (m), 662 (s), 650 (m), 586 (m), 550
(s), 525 (w), 490 (w), 441 (w). UV-Vis (CH3CN): lmax/nm, (loge) =
Experimental section
General considerations
Bis(N-methylimidazol-2-yl)methane, Im¢CH2Im¢, was synthesized
following a procedure given by Ru¨ther et al.17 and purified by
sublimation (110 ◦C, 10-4 mbar). The C, H, N microanalyses were
performed with a Leco CHNS-932 element analyzer. Chlorine
was determined using Scho¨niger’s method followed by titration
with Hg(ClO4)2. NMR spectra were recorded on a Bruker AV
400 NMR spectrometer (1H: 400.13 MHz, 13C: 100.6 MHz) at
25 ◦C. Chemical shifts are reported relative to residual proton sig-
nals and natural abundance 13C resonances of the corresponding
deuterated solvents. Chemical electronic absorption spectra were
recorded with a Varian Cary 100 Scan UV-Vis spectrometer at
room temperature using quarz cuvettes. IR spectra were measured
between 400 and 4000 cm-1 with a Shimadzu FTIR-8400S spec-
trometer using KBr pellets. The ESI-mass spectra were recorded
using a Finnigan LTQ-FT spectrometer. Cyclic voltammograms
were recorded on a Gamry Reference 600 Potentiostat using a
platinum working electrode, a platinum counter electrode and a
Ag/AgCl reference electrode. The half potentials were referenced
against the Fc/Fc+ couple and the values conversed to SCE
(saturated calomel electrode) by adding + 0.40 V.18
269 (3.87), 218 (4.78). MS (EI): 478 (100%, M∑+), 303 (90%, M∑+
CHIm¢2), 176 (60%, [Im¢CH2Im¢]+).
-
Preparation of [Mn2(bimptz)Cl4] (1)
A light yellow solid precipitated when a solution of bimptz
(0.100 g, 0.21 mmol) in 10 mL absolute ethanol was added
dropwise to a solution of MnCl2·4H2O (0.083 g, 0.42 mmol) in
5 mL of ethanol. The suspension was stirred for 30 min, and the
precipitate was isolated by filtration and dried in vacuo to give
analytically pure 1. Yield: 0.117 g (0.16 mmol, 77%). Anal. calc.
for C26H32Cl4Mn2N10O3, [Mn2(bimptz)Cl4]·3H2O: C 39.82, H 4.11,
N 17.86. Found: C 39.95, H 3.76, N 17.56%.
IR: n/cm-1 = 3433 (br), 3145 (w), 3119 (m), 3072 (m), 2960 (m),
1622 (br), 1567 (w), 1532 (m), 1509 (s), 1466 (w), 1405 (s), 1351
(m), 1284 (s), 1174 (m), 1161 (m), 1135 (m), 1089 (m), 1040 (m),
952 (m), 875 (m), 851 (s), 801 (w), 762 (s), 715 (m), 672 (w), 658
(m), 633 (m), 614 (m), 558 (m), 452 (m). MS (FAB+, m/z): 693
(5%, M∑+ - Cl], 658 (5%, M∑+ - 2Cl), 568 (3%, M∑+ - Mn - 3Cl).
Preparation of 1,4-Bis(di(N-methylimidazol-2-
yl)methyl)phthalazine (bimptz)
Preparation of [Co2(bimptz)(CH3OH)2Cl2][CoCl4] (2)
Im¢CH2Im¢ (4.02 g, 22.8 mmol) was dissolved in dry THF
(200 mL) and cooled to -78 C. It is possible that a part of the
◦
A solution of bimptz (0.100 g, 0.21 mmol) in 8 mL of ethanol
was added dropwise to a dark blue solution of CoCl2·6H2O
(0.149 g, 0.63 mmol) in 8 mL of ethanol, which led to a
color change to green-blue and the formation of a fine blue-
green powder. After stirring the suspension for 3.5 h at room
temperature, all volatile material was removed in vacuo, and
the blue-green residue was washed with CH2Cl2 and recrystal-
lized from methanol–ether. Anal. calc. for C30H40Cl6Co3N10O3,
[Co2(bimptz)(CH3OH)2Cl2][CoCl4]·EtOH: C 36.83, H 4.12, N
14.32. Found: C 37.01, H 4.38, N 14.06%.
IR: n/cm-1 = 3412 (br,s), 3146 (sh), 3120 (s), 2977 (m), 2951 (sh),
2897 (m), 1624 (s, br), 1567 (m), 1536 (s), 1513 (s), 1459 (m), 1411
(s), 1350 (m), 1286 (m), 1175 (m), 1140 (m), 1092 (m), 1018 (m),
961 (m), 882 (m), 852 (m), 763 (s), 717 (s), 673 (m), 660 (m), 634
(m), 599 (m), 564 (m), 529 (m), 448 (m).
Im¢CH2Im¢ precipitates again at this temperature. n-BuLi (2.5 M
in hexane, 9.31 mL, 23.3 mmol) was added during a period of
15 min and the resulting clear yellow solution was stirred for
2 h at -45 ◦C. After cooling the reaction mixture to -78 ◦C
a solution of 1,4-dichlorophthalazine in dry THF (100 ml) was
added dropwise through an addition funnel over a period of
35 min. A rubiginous suspension formed, which was stirred for
1 h at -78 ◦C before it was allowed to warm to room temperature.
Stirring was continued for an additional 45 min, and subsequently
water (8 mL) was added to the reaction mixture. The resulting
cream-colored suspension was filtered and the sticky residue was
washed with THF. Drying in vacuo yielded 5.66 g of a light brown
crude product. In order to separate LiCl from crude bimptz, the
latter was stirred in a mixture of 100 mL water and 300 mL CH2Cl2
until all solid had dissolved. The solution was transferred to a
separatory funnel and the yellow organic layer was separated.
The aqueous phase was repeatedly extracted with CH2Cl2 and the
combined organic extracts were dried over Na2SO4. After filtration
the solution was evaporated to dryness to give bimptz as a light
yellow powder, which is pure according to 1H NMR spectroscopy.
Yield: 4.41 g (9.22 mmol, 81%). Further purification can be
achieved by recrystallization from boiling acetonitrile. Anal. calc.
for C26H28N10O, [bimptz·H2O]: C 62.89, H 5.68, N 28.21. Found:
C 62.48, H 5.34, N 28.37%.
Preparation of [Co2(bimptz)(CH3OH)2Cl2](PF6)2 (3)
A yellow solution of bimptz (0.200 g, 0.42 mmol) in 15 mL of
methanol was added dropwise to a pink solution of CoCl2·6 H2O
(0.298 g, 1.25 mmol) in 10 mL methanol. The reaction mixture
initially darkened and then turned pink-red after 15 min at room
temperature. Stirring was continued for 2 h, whereupon a solution
of NH4PF6 (0.204 g, 1.25 mmol) in 5 mL of methanol was added
quickly. After an additional 1.5 h the solution was concentrated
in vacuo until a solid started to precipitate. The precipitate was
redissolved by gentle heating and the resulting solution was then
cooled to - 30 ◦C. After several days 3 was isolated as a pink-
red solid by filtration, which was washed with cold methanol and
dried on standing in air. Further amounts of 3 could be obtained
by concentrating the mother liquor and cooling to - 30 ◦C. Yield:
1H NMR (CDCl3): d/ppm = 8.18 (m, 2H, CHptz), 7.72 (m,
3
2H, CHptz), 6.96 (d, 4H, J(H,H) = 1.2 Hz, CHim), 6.85 (d, 4H,
3J(H,H) = 1.2 Hz, CHim), 6.64 (s, 2H, CHIm2), 3.45 (s, 12H,
NCH3). 13C NMR (CDCl3): d/ppm = 156.5, 143.9, 132.3, 127.5,
126.5, 125.6, 122.4, 44.8, 33.6. IR: n/cm-1 = 3437 (br), 3149 (m),
3131 (s), 3115 (m), 3106 (m), 3092 (m), 2947 (m), 2881 (m), 1613
4320 | Dalton Trans., 2011, 40, 4315–4323
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0.248 g (0.24 mmol, 58%). Anal. calc. for C28H38Cl2Co2F12N10O4P2,
[Co2(bimptz)(CH3OH)2Cl2](PF6)2·2H2O: C 31.81, H 3.62, N 13.25,
Cl 6.71. Found: C 31.38, H 3.57, N 13.23, Cl 6.72%.
Preparation of [Ru2(bimptz)(dmso)(dms)(l-Cl)2][PF6]2 (5)
The evaporated dark red second fraction obtained from the
purification of 4 was worked up analogously as described for 4
yielding 5 as dark red crystalline solid. Yield: 0.053 g (45 mmol,
21%).
IR: n/cm-1 = 3634 (m), 3163 (m), 2966 (m), 1616 (m),
1569 (w), 1539 (m), 1516 (s), 1464 (m), 1414 (s), 1352 (m),
1288 (m), 1177 (m), 1169 (m), 1140 (m), 1090 (m), 1038
(w), 960 (m), 842 (vs), 760 (s), 740 (m), 719 (m), 675 (w),
660 (m), 635 (m), 557 (s), 447 (m). MS (ESI+(CH3CN),
1H-NMR (CD3CN): d/ppm = 9.03 (m, 2H, CHptz), 8.38
(m, 2H, CHptz), 7.09 (d, 2H, 3J(H,H) = 1.4 Hz, CHim), 7.03
(d, 2H, 3J(H,H) = 1.4 Hz, CHim), 7.00 (d, 2H, 3J(H,H) =
+
m/z): 811.0 (100%, {[Co2(bimptz)Cl2](PF6)} ), 353.5 (40%,
3
1.4 Hz, CHim), 6.98 (d, 2H, J(H,H) = 1.4 Hz, CHim) 6.93 (s,
[Co2(bimptz)Cl2(CH3CN)]2+), 333.0 (45%, [Co2(bimptz)Cl2)]2+).
HRMS (ESI+(CH3CN), m/z): Calc. for C26H26N1035Cl259Co2F6P1
({[Co2(bimptz)Cl2]}(PF6)+): 811.0019. Found: 811.0007. Calc.
for C28H29N1135Cl259Co2 ([Co2(bimptz)Cl2(CH3CN)]2+): 707.0648.
Found: 707.0630.
1H, (Ptz)(Im)2CH), 6.89 (s, 1H, (Ptz)(Im)2CH), 3.93 (s, 12H,
NCH3), 3.38 (s, 6H, Hdmso), 2.37 (s, 6H, Hdms). IR: n/cm-1
=
3147 (w), 2959 (m), 2920 (m), 2851 (m), 1624 (br), 1541 (m),
1519 (m), 1464 (w), 1427 (m), 1348 (w), 1286 (m), 1261 (w),
1236 (w), 1176 (w), 1088 (m), 1060 (w), 1018 (m), 982 (m),
912 (w), 840 (vs), 756 (m), 715 (w), 688 (w), 661 (w), 578
(w), 557 (s), 427 (w). UV-Vis (CH3CN): lmax/nm, (loge) =
503 (sh), 416 (3.71), 292 (3.85), 234 (4.67), 209 (4.53). HRMS
(ESI+(CH3CN), m/z): Calc. for C30H38O1N1035Cl2F6P1102Ru232S2
Preparation of [Ru2(bimptz)(dmso)2(l-Cl)2](PF6)2 (4)
Bimptz (0.100 g, 0.21 mmol) and [Ru(dmso)4Cl2] (202.5 mg,
0.41 mmol), each dissolved in 12 mL of ethylene glycol, were
mixed to yield an orange-colored solution, which was degassed by
evacuation and purging with argon three times. After refluxing
the reaction mixture in a microwave reactor under argon for
15 min, a solution of NH4PF6 (1.36 g) in 10 mL of water was
added to the still hot brown-red solution. Cooling to 0 ◦C and
filtering yielded a brown crude product, which was washed with
cold water and THF. The crude product was purified by column
chromatography on silica and the column eluted with acetonitrile–
aqueous saturated KPF6 (9 : 1). The first pale red fraction was
rejected, the following narrow dark red and broad yellow bands
were collected. 4 was contained in the third (yellow) fraction
(along with KPF6), which was evaporated to dryness using a
rotovap. The residue was stirred in approximately 40 mL of
water in order to dissolve the KPF6 salt. After filtration a dark
brown solid of crude 4 was obtained, which was washed with a
minimum amount of cold water, followed by tetrahydrofuran and
ether. 4 was dried in vacuo and recrystallized by slow diffusion of
tetrahydrofuran into a solution of 4 in acetonitrile. Yield: 0.122 g
(0.1 mmol, 48%). Anal. calc. for C30H38Cl2F12N10O2P2Ru2S2,
[Ru2(bimptz)(dmso)2Cl2](PF6)2: C 30.08, H 3.20, N 11.69, Cl
5.92, S 5.35. Found: C 30.32, H 3.33, N 11.23, Cl 6.46,
S 4.52%.
+
({[Ru2(bimptz)(dmso)(dms)Cl2](PF6)} ): 1036.9777. Found:
1036.9750. Calc. for C30H38O1N1035Cl2102Ru232S2 ([Ru2(bimptz)-
(dmso)(dms)Cl2]2+): 446.0068. Found: 446.0057.
Preparation of [Ru(Hbimptz)2](PF6)4 (6)
Bimptz (0.200 g, 0.42 mmol) and [Ru(dmso)4Cl2] (0.101 g,
0.21 mmol), each dissolved in 25 mL ethylene glycol were mixed
and heated to 100 ◦C in an oil bath under argon. After 10 min at
this temperature the red solution was refluxed for an additional
5 h. Solid NH4PF6 (1.36 g) was then added to the still hot
reaction mixture. After cooling to room temperature 6 was isolated
as a fine microcrystalline dark purple solid, which was washed
subsequently with cold water and ether and dried in vacuo. Yield:
0.155 g (0.11 mmol, 55%). Anal. calc. for C52H54N20F24P4Ru,
[Ru(Hbimptz)2](PF6)4: C 38.08, H 3.32, N 17.08. Found C 37.68,
H 3.52, N 16.58%.
3
1H-NMR (CD3CN): d/ppm = 8.96 (d, 1H, J(H,H) = 8.6 Hz,
CHptz), 8.24 (m, 1H, CHptz), 7.93 (m, 1H, CHptz), 7.36 (d, 1H,
3J(H,H) = 8.3 Hz, CHptz), 7.17 (d, 1H, 3J(H,H) = 1.2 Hz, CHim),
3
3
7.08 (d, 1H, J(H,H) = 1.4 Hz, CHim), 7.03 (d, 1H, J(H,H) =
1.4 Hz, CHim), 6.88 (s, 1H, (Ptz)(Im)2CH), 6.66 (d, 1H, 3J(H,H) =
1.9 Hz, CHim), 6.64 (s, 1H, (Ptz)(Im)2CH), 6.36 (d, 1H, 3J(H,H) =
1.4 Hz, CHim), 6.27 (d, 1H, 3J(H,H) = 1.3 Hz, CHim), 6.07 (d, 1H,
1H-NMR (CD3CN): d/ppm = 9.10 (m, 2H, CHptz), 8.47 (m,
3
2H, CHptz), 7.08 (d, 4H, J(H,H) = 1.6 Hz, CHim), 7.01 (d, 4H,
3J(H,H) = 1.6 Hz, CHim), 6.95 (s, 2H, (Ptz)(Im)2CH), 3.93 (s,
12H, NCH3), 3.37 (s, 12H, Hdmso). 13C-NMR (CD3CN): d/ppm =
164.5, 140.4, 137.6, 132.5, 127.4, 125.9, 124.5, 47.2, 35.7, 35.5.
IR: n/cm-1 = 3144 (m), 3021 (w), 2968 (m), 2923 (m), 2851 (w),
1628 (m, br), 1545 (m), 1521 (s), 1448 (m), 1424 (m), 1412 (m),
1350 (m), 1320 (w), 1287 (m), 1177 (m), 1150 (w), 1088 (s), 1018
(s), 982 (w), 965 (w), 910 (w), 839 (vs), 758 (m), 742 (m), 715
(m), 687 (w), 668 (w), 662 (w), 638 (w), 577 (m), 558 (s), 439
(m), 426 (m). UV-Vis (CH3CN): lmax/nm, (loge) = 458 (sh, 3.61),
396 (3.93), 286 (4.05), 236 (4.79). MS (ESI+(CH3CN), m/z):
3J(H,H) = 1.4 Hz, CHim), 5.30 (d, 1H, J(H,H) = 1.9 Hz, CHim),
3
4.15 (s, 3H, NCH3), 4.03 (s, 3H, NCH3), 3.65 (s, 3H, NCH3), 3.47
(s, 3H, NCH3). 13C-NMR (CD3CN): d/ppm = 159.5, 155.3, 142.1,
141.5, 140.1, 140.0, 136.1, 134.0, 130.7, 129.8, 128.1, 126.9, 126.6,
125.0, 124.7, 124.3, 124.1, 123.8, 123.7, 119.4, 39.0, 35.9, 35.2,
35.1, 34.9, 34.4. IR: n/cm-1 = 3163 (m), 2956 (m), 2927 (m), 2869
(w), 2854 (w), 1610 (m), 1576 (w), 1543 (s), 1521 (s), 1500 (m), 1460
(m), 1441 (w), 1427 (m), 1358 (w), 1323 (w), 1288 (s), 1238 (w),
1170 (m), 1148 (m), 1092 (m), 1051 (w), 1041 (w), 1016 (w), 957
(w), 834 (vs), 756 (s), 715 (m), 704 (w), 694 (w), 669 (w), 663(w),
640 (w), 621 (w), 601 (w), 557 (s), 538 (w). UV-Vis (CH3CN):
+
1052.7 (15%, {[Ru2(bimptz)(dmso)2Cl2](PF6)} ), 453.9 (100%,
[Ru2(bimptz)(dmso)2Cl2]2+). HRMS (ESI+(CH3CN), m/z): Calc.
lmax/nm, (loge) = 515 (4.21), 421 (4.00), 293 (4.15), 224 (5.02). MS
C30H38O2N1035Cl2F6P1102Ru232S2
{([Ru2(bimptz)(dmso)2]-
(ESI+(CH3CN), m/z): 674.9 (10%, {[Ru(Hbimptz)2](PF6)2} ),
2+
for
+
2+
Cl2(PF6)} ): 1052.9721. Found: 1052.9733. Calc. for
C30H38O2N1035Cl2102Ru232S2 ([Ru2(bimptz)(dmso)2Cl2]2+): 454.0037.
Found: 454.0053.
601.9 (15%, {[Ru2(Hbimptz)(bimptz)](PF6)} ), 353.3 (100%,
[Ru2(Hbimptz)(bimptz)]3+), 265.2 (85%, [Ru2(Hbimptz)2]4+).
HRMS (ESI+(CH3CN), m/z): Calc. for C52H54F12N20P2102Ru
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Table 4 Crystal and refinement data for 1, 3, 4, 6
1·2MeOHa
3b
4·thf·2(CH3CN)
6
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
C28H34Cl4Mn2N10O2
794.33
100(2)
Monoclinic
P21/n
C28H34Cl2Co2F12N10O2P2
1021.35
100(2)
Monoclinic
C2/c
C38H52Cl2F12N12O3P2Ru2S2
1352.02
100(2)
Orthorhombic
Pna21
C52H54F24N20P4Ru
1640.10
100(2)
Monoclinic
C2/c
˚
Cell dimensions/A
a = 13.1972(6)
b = 16.7605(7)
c = 15.8055(8)
a = 90◦
a = 32.2485(7)
b = 11.1423(2)
c = 27.0595(6)
a = 90◦
a = 33.468(2)
b = 13.7678(5)
c = 11.1687(7)
a = 90◦
a = 22.7921(8)
b = 14.6642(4)
c = 21.0070(8)
a = 90◦
b = 104.000(4)◦
b = 101.431(2)◦
g = 90◦
b = 90◦
b = 114.484(3)◦
g = 90◦
g = 90◦
g = 90◦
3
˚
Cell volume/A
3392.2(3)
9530.2(3)
5146.3(4)
6389.8(4)
Z
4
8
4
4
Calc. density/ Mg m-3
Absorption coefficient/mm-1
F(000)
1.555
1.103
1624
1.424
0.958
4112
1.745
0.928
2720
1.705
0.472
3304
Crystal size/mm
Measured region/◦
Index region
0.36 ¥ 0.24 ¥ 0.20
3.41–25.25
- 15 £ h £ 15
0 £ k £ 20
- 18 £ l £ 18
6116
0.20 ¥ 0.12 ¥ 0.08
2.58–25.63
- 39 £ h £ 38
0 £ k £ 13
0 £ l £ 32
0.45 ¥ 0.2 ¥ 0.08
3.38–26.02
- 39 £ h £ 41
- 16 £ k £ 17
- 14 £ l £ 14
40 436
0.20 ¥ 0.12 ¥ 0.08
2.39–28.02
- 30 £ h £ 29
- 19 £ k £ 18
- 27 £ l £ 27
35 726
No of reflections
8967
No of independent reflections
Data/restrains/parameters
Goodness-of-fit on F2
6116 [Rint = 0.1548]
6116/15/396
0.963
R1 = 0.0724
wR2 = 0.0968
R1 = 0.1409
wR2 = 0.1103
0.477; - 0.488
8967 [Rint = 0.0000]
8967/175/566
0.886
R1 = 0.0452
wR2 = 0.1121
R1 = 0.0611
wR2 = 0.1157
0.781; - 0.652
9913 [Rint = 0.0897]
9913/11/630
1.153
R1 = 0.0754
wR2 = 0.1682
R1 = 0.0867
wR2 = 0.1761
0.878; - 1.401
7643 [Rint = 0.0640]
7643/4/482
0.974
R1 = 0.0418
wR2 = 0.0734
R1 = 0.0695
wR2 = 0.0792
0.539, - 0.583
Final R values [I > 2s(I)]
R values (all data)
Max/min electron
-3
˚
density/eA
a Including crystal solvent (methanol) removed by the programme SQUEEZE (Platon). b Data reflect unit cell content only.
2+
tetrahydrofuran into a diluted solution of 4 in acetonitrile. 6: slow
evaporation of the solvent from an acetone–methanol solution of
6. Crystallographic data for the structures 1, 3, 4 and 6 have been
deposited with the Cambridge Crystallographic Data Centre as
supplementary publication no. 765497 (1), 765495 (3), 765496 (4),
765494 (6).†
({[Ru(Hbimptz)2](PF6)2} ): 675.1584. Found: 675.1589. Calc. for
C52H54N20102Ru ([Ru2(Hbimptz)2]4+): 265.0965. Found: 265.0968.
Crystal structure determinations†
All data were collected on a Stoe IPDS-2T diffractometer using
˚
MoKa radiation, l = 0.71073 A. In all cases, the structures were
solved by direct methods (SHELXS-97)19 and refined versus F2
(SHELXL-97)20 with anisotropic temperature factors for all non-
hydrogen atoms (Table 4). In 1 one of the two co-crystallized
methanol molecules could not be modeled satisfactory and was
excluded using the program SQUEEZE (Platon)21 In the crystal
structure of 3 there is a region of disordered solvent molecules
which could not be modeled successfully (trial modeling attempts
indicated a mixture of methanol and diethyl ether). The program
SQUEEZE (Platon)21 was used to remove the contribution of these
Acknowledgements
This work was funded by the Deutsche Forschungsgemeinschaft
as well as the Helios Solar Energy Research Center, which is
supported by the Director, Office of Science, Office of Basic
Energy Sciences of the U.S. Department of Energy under Contract
No. DE-AC02-05CH11231. S.R thanks the DAAD (German
Academic Exchange Service) for a postdoctoral fellowship.
diffusely scattering species from the structure factor calculations.
3
References
˚
The program calculated a solvent accessible region of 2404 A
per unit cell (25% of the total unit cell volume). The reported
formula weight, F(000) and density reflect only the known unit
cell contents. In 6 all hydrogen atoms except H7 were added
geometrically and refined by using a riding model. Single crystals
suitable for X-ray diffraction were obtained by the following
procedures. 1: slow diffusion of degassed ether into a solution of 1
in degassed methanol at 4 ◦C. 2: slow diffusion of tetrahydrofuran
into a solution of 2 in methanol at rt. 3: slo◦w diffusion of ether into
a diluted solution of 3 in methanol at 4 C. 4: slow diffusion of
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4322 | Dalton Trans., 2011, 40, 4315–4323
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