Towards the installation of transition metal ions on donor ligand decorated tin sulfide clusters

Article abstract of DOI:10.1039/c3cc43649g

Decoration of tetrelchalcogenide T-E clusters with chelating donor ligands was achieved to capture transition metal ions on their surfaces. We demonstrate that by covalent linking of bispyridyl ligands to an Sn-S complex, [ZnX] ⁺ units can be t

Full text of DOI:10.1039/c3cc43649g

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Towards the installation of transition metal ions on donor ligand
decorated tin sulfide clusters
Aiming at transition metal ion capturing on the surface of
tetrelchalcogenide clusters, bispyridyl ligands were bonded to an
organo-functionalized Sn/S complex. The chelate ligands trapped
[ZnX]+ units that were additionally incorporated in the cluster
framework. Intermediates were identified by spectroscopy and/or
X-ray diffraction to give insight into the formation processes.
See Stefanie Dehnen et al.,
Chem. Commun., 2013, 49, 6590.
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Towards the installation of transition metal ions on
donor ligand decorated tin sulfide clusters†
Cite this: Chem. Commun., 2013,
49, 6590
Beatrix E. K. Barth, Eliza Leusmann, Klaus Harms and Stefanie Dehnen*
Received 15th May 2013,
Accepted 1st June 2013
DOI: 10.1039/c3cc43649g
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Decoration of tetrelchalcogenide T–E clusters with chelating donor R = Me, Ph, tBu, CF3, C6F5, C(SiMe3)3.5 Aiming at the introduc-
ligands was achieved to capture transition metal ions on their tion of reactivity onto the cluster surfaces, we have recently
surfaces. We demonstrate that by covalent linking of bispyridyl synthesized species with functionalized ligands Rf, like
ligands to an Sn–S complex, [ZnX]+ units can be trapped and [(R1Sn)4S6] (A; R1 = CMe2CH2COMe), [(HR2Ge)4S6] (HR2
=
=
incorporated into the cluster framework. Intermediates that were C2H4COOH) and [(HR2,3Ge)4E5] (E
=
Se, Te; HR3
identified using spectroscopy and/or X-ray diffraction gave insight CH(CH2COOH)2), by reactions of RfTCl3 with a chalcogenide
into the formation processes.
source.6,4e Terminal keto groups in Rf readily react with hydra-
zines, leading to the generation of a variety of hybrid clusters,
In the search for new compounds with desired properties, cages or cavitands.6a,7 Reactions with transition metal com-
chemists and material scientists are continuously developing pounds served to extend the inorganic core and to form
new connections between different fields of chemistry. One multinary M–T–E clusters with organo-functionalized ligand
option is to combine inorganic core particles or clusters with shells.6a,7a,b,8 First insight into the coordinating role of donor
functional organic ligand shells. For example, the functionali- ligands on the cluster surface was gained via the carboxylate-
zation of nanoparticles with suitable ligands offered the possi- decorated cluster [(R2Ge)4S6], which captured Mn2+ ions to
bility to capture metal ions, as shown for gold nanoparticles generate a hybrid framework.9a
with a shell of bipyridine ligands that produce a phosphores-
Different to the approaches on the micro- or nanoscale quoted
cent nanomaterial upon reaction with Eu(III) or Tb(III) ions.1 above, it has so far not been possible to decorate molecular T–E or
Metals@ligands on inorganic surfaces are also present in M–T–E clusters with chelating donor groups to trap transition metal
photosensitive materials of dye-sensitized solar cells (DSSC);2 complexes (Scheme 1). This approach differs from the previously
this was achieved, for instance, by connecting terpyridine reported synthesis of clusters surrounded by ferrocenyl (Fc)
molecules to a silicon-surface, conversion of the material with ligands,8,10 since in that, Fe ions had never been introduced a
Fe(II) ions and addition of a terminal ligand.3
posteriori, but the Fc units were rather installed as a whole. While we
Tetrelchalcogenide T–E and related ternary M–T–E systems (M = intend to eventually attach redox-active or catalytically active metal
transition metal, T = tetrel, E = chalcogen) combine diverse struc- ions to the clusters, first investigations have been undertaken with
tural, (opto-)electronic and magnetic properties to make them redox-insensitive metal ions.
attractive for (photo-)catalysis and chemical sensing.4 Further diver-
Since the introduction of N-donor chelate ligands in an RfSnCl3
sity is achieved by covalently binding organic moieties to these precursor is not trivial, we employed condensation reactions of the
inorganic cores, to additionally include the chemical and physical ketone-functionalized cage A and corresponding hydrazine deriva-
properties of the organic substituent.
tives. Herein we present the first successful results of this approach,
First investigations on organo-functionalized chalcogenido- by attaching bispyridine ligands to Sn–S clusters.
tetrelate cages [(RT)xEy] were restricted to unreactive groups like
¨
Philipps-Universitat Marburg, Fachbereich Chemie and Wissenschaftliches Zentrum
¨
fur Materialwissenschaften (WZMW), Hans-Meerwein-Straße, D-35043 Marburg,
Germany. E-mail: dehnen@chemie.uni-marburg.de; Fax: +49 6421 2825653;
Tel: +49 6421 2825751
† Electronic supplementary information (ESI) available: Details of the syntheses
of 1–6, X-ray diffraction, spectroscopy and spectrometry. CCDC 934166–934170.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3cc43649g
Scheme 1 Metals@ligands on inorganic clusters with T–E or M–T–E cores
(T = tetrel, E = chalcogen, M = transition metal).
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Fig. 1 Molecular structure of the bispyridine-decorated Sn–S cluster in 3b.
Hydrogen atoms and solvent molecules are omitted for clarity. Thermal ellipsoids
are drawn at 50% probability.
Scheme 2 Suggested formation of 1+, 2, and
3 from A, indicating the
re-arrangement of relevant electron pairs in the preliminary step; identified by-
products are given. The scheme drawings refer to the exact atomic positions in
the crystal structures of A, 2 and 3b. For details see ESI;† the structure model of
1+ represents the most probable connectivity of the atoms within a defect-
heterocubane geometry.
towards the generation of the consecutive products 3 and 4–6
(see below).
According to single-crystal X-ray diffraction,‡ the molecular struc-
ture of 3b (space group C2/m, Fig. 1) comprises two (m-S)2-bridged
[{(R4Sn)2Sn}S4] defect-heterocubanes. As previously observed in reac-
tions of A with other bulky hydrazine derivatives,6a,7c,d the inorganic
core underwent a re-arrangement into an [Sn6S10] architecture.
Similar to the findings in the structure of A, with intramolecular
Lewis acid–base interaction between the heteroatoms of the organic
moiety with the parent Sn atom, the ketazine CQN–NQC groups in
3 coordinate back to the organo-substituted Sn atom. Five-membered
SnC3N rings are therefore generated, maintaining the coordination
number (c.n.) five at the respective Sn atoms. The pyridine rings are
twisted with respect to each other since they remain uncoordinated.
The inner Sn2S2 ring leads to penta-coordination also at the purely
inorganic [SnS5] units.
This led to the formation of the donor ligand-functionalized
clusters [(R4Sn)3S4]+ (1+, detected in solution) and [(R4Sn)2(R5SnS)S4]
(2), the second being obtained as single crystals besides the larger
cluster [(R4Sn)4Sn2S10] (3), upon layering of the reaction solution
(R4 = CMe2CH2C(Me)NNC(2-py)2, R5 = CMe2CH2C(Me)NHNC(2-py)2,
py = o-C5H4N). Reaction of 1+ with ZnX2 salts proved the trapping
capability of the new ligands, accompanied by coordinating sulfide
ions of the re-arranged cluster core in the products [(R4Sn)4S10Zn8X8]
(X = Cl, Br, I; 4–6).
Cation 1+ was generated by the reaction of A with bispyridyl-
hydrazone in CH2Cl2 (Scheme 2), as shown using electrospray ioniza-
tion (ESI†) mass spectrometry of the reaction solution. The mass peak
at 1321.0737 m/z (88% relative abundance) indicated 1+ to be the
predominant species. Defect-heterocubane [Sn3E4] scaffolds are com-
mon structural motifs in tin chalcogenide chemistry,6a,7c,9b,c,11 thus the
appearance of 1+ is probably not restricted to ESI-MS conditions.
However, an ionic compound with the cationic cluster 1+ seems to
have no crystallization tendency under the given conditions. In
contrast, layering of the orange-brown reaction solution with n-hexane,
or layering of a reaction solution in dioxane–methanol (2 : 1) with
n-pentane, respectively, yielded crystals of [(R4Sn)2(R5SnS)S4] (2) in
small amounts besides triclinic crystals of [(R4Sn)4Sn2S10]Á5CH2Cl2
(3Á5CH2Cl2; 3a), or monoclinic crystals of [(R4Sn)4Sn2S10]Á1,4-dioxaneÁ
5MeOH (3Á1,4-dioxaneÁ5MeOH; 3b), respectively.
Although crystals 3a or 3b do not re-dissolve in CH2Cl2, 1H and
13C NMR spectra of the clear reddish-brown reaction solution
yielding 3a or 3b indicate the presence of several species that point
toward equilibria between various Sn–S species. A summary of the
processes observed in the synthesis and transformations of the title
compounds, which were additionally rationalized by spectroscopic
methods (see ESI†), is sketched in Scheme 2.
In order to explore the ion capturing potential of the chelate-ligand
decorated clusters 1+, 2 or 3, which co-exist in solution as shown in
Scheme 2, we have performed reactions with Zn2+ ions, which are
known to form stable complexes with bispyridine ligands,12 and which
do not react with A or its derivatives reported previously.6,7 Upon
layering the reaction mixture that afforded compound 1+, 2 and 3 with
a methanolic solution of ZnX2 (X = Cl, Br, I), colorless crystals of
compounds 4, (X = Cl), 5 (X = Br) or 6 (X = I), respectively, were obtained
within four days (Scheme 3).
Whereas 2 could not be detected by means of ESI-MS in the
reaction solution, signals of 3 are found at 18% relative abundance
(2150.7861 m/z) besides 1+ (88%, Fig. S13, ESI†). However, 1+ also
represents the predominant species (100% relative abundance) in
the ESI mass spectrum upon re-dissolving single-crystals of 3 in
THF, whereas 3 is only found as a minor component (1%), suggest-
ing an equilibrium between 1 and 3. The neutral complex 2 (Fig. S16,
ESI†) crystallized as heavily twinned crystals (monoclinic space
group C2/c) besides 3a‡ (see ESI†). 2 represents a derivative of 1+,
by unprecedented expansion of the assumed defect-heterocubane
motif of 1+. 2 might have been formed upon nucleophilic attack by
an HSÀ anion and transfer of the proton to one of the azine nitrogen
atoms produced the zwitterionic organic moiety, which coordinates
back to the Sn atom via the extra S atom. While this attack could
occur at the strongly electrophilic azine C atom or directly at the Sn
atom, the formation of the Sn–S moiety is clearly the first step
Single crystal X-ray diffraction‡ revealed the following formulae,
crystal systems and space groups: [(R4Sn)4(Zn8Cl8)S10]Á2CHCl3Á2CH2Cl2
Scheme 3 Formation of 4, 5, and 6 from equilibria between 1+, 2, and 3;
identified by-products are given.
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supertetrahedral anions are present in [Na10(H2O)32][Zn5Sn5S20].15
In contrast to these supertetrahedra, which are based on barrelane-
type or adamantane-type motifs, the structural condensation of six-
membered rings is different in 4–6. Besides the fact that the Zn2+ ions
also contribute to the inorganic cluster core in 4–6, these compounds
are the first ones to demonstrate a successful trapping of metal ions
by a terminal organic ligand on a semi-metal cluster surface. Thereby,
they clearly point toward the possibility to form further examples of
metals@ligands on inorganic clusters with T–E or M–T–E cores.
Notes and references
‡ X-ray crystallographic data: Data collection on a STOE IPDS2 diffracto-
meter using graphite-monochromatized Mo Ka radiation (l = 0.71073 Å)
at 100 K. Structure solution and refinement by direct methods and full-
matrix least-squares on F2, respectively; SHELXTL software.16 The crystal-
lographic data are provided in the ESI.†
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6592 Chem. Commun., 2013, 49, 6590--6592
This journal is The Royal Society of Chemistry 2013