Molecular tectonics: Homochiral 3D cuboid coordination networks based on enantiomerically pure organic tectons and ZnSiF6

Article abstract of DOI:10.1039/c3cc41140k

Upon combining enantiomerically pure bis-monodentate organic tectons with ZnSiF₆, homochiral 3D cuboid architectures displaying chiral channels are formed.

Full text of DOI:10.1039/c3cc41140k

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Molecular tectonics: homochiral 3D cuboid
coordination networks based on enantiomerically
pure organic tectons and ZnSiF6†
Cite this: Chem. Commun., 2013,
49, 4468
Received 11th February 2013,
Accepted 27th March 2013
Patrick Larpent, Abdelaziz Jouaiti,* Nathalie Kyritsakas and Mir Wais Hosseini*
DOI: 10.1039/c3cc41140k
www.rsc.org/chemcomm
Upon combining enantiomerically pure bis-monodentate organic
tectons with ZnSiF6, homochiral 3D cuboid architectures displaying
chiral channels are formed.
Coordination polymers1 or Metal–Organic Frameworks (MOFs)
are promising solid materials for separation, storage, catalysis and
sensing, for example.2 It is interesting to note that the majority of
the reported examples are achiral. Although chiral architectures
are of interest for chiral separation or enantio- or stereo-selective
transformations, only a small number of chiral coordination
polymers have been reported.3 The design of coordination
polymers may be achieved using concepts developed in molecular
tectonics.4 Indeed, such hybrid periodic architectures in the
crystalline phase may be obtained under self-assembly conditions
upon combinations of organic and metallic tectons.5
Fig. 1 Schematic representations of 3D cuboid coordination networks (a and b)
and their square bases (c and d) composed of non-symmetric bismonodentate
chiral tectons and ZnSiF6. + and À indicate clockwise and anticlockwise orienta-
tion of the organic tectons.
Here we report the design and structural characterisation of
three new enantiomerically pure chiral coordination polymers
based on combinations of enantiomerically pure asymmetric
organic tectons with ZnSiF6 (Fig. 1).
ZnSiF6 (Scheme 1). Tectons 1–3 are similar chiral bismonodentate
units differing in the nature of their chiral group. Tectons 1 (R,R
isomer) and 2 (S,S isomer) differ in both handedness of chiral
centres and their distance to the O-phenyl moiety i.e. insertion
of a methylene unit between the O atoms and the chiral centre
ZnSiF6 is an interesting salt because in the presence of
bismonodentate organic tectons bearing N donor atoms, it forms
an infinite pillar through mutual bridging between SiF62À anions
and Zn2+ cations with a Zn–Zn distance of ca. 7.5 Å.6 Interestingly,
the cation adopts a distorted Oh geometry with the two apical
positions occupied by two F atoms belonging to two consecutive
2À
SiF6 anions. The remaining four coordination sites occupying
the square base of the octahedron serve as connecting nodes
leading thus to a variety of architectures depending on the nature
of the organic tecton.7 One may exploit this particular arrange-
ment for the design of chiral 3D networks by combining ZnSiF6
with chiral organic tectons (Fig. 1).
The design of the 3D cuboid chiral networks is based
on combinations of enantiomerically pure tectons 1–3 with
Laboratoire de Chimie de Coordination Organique, UMR CNRS 7140,
´
Universite de Strasbourg, F-67000, Strasbourg, France. E-mail: hosseini@unistra.fr;
Fax: +33 368851325; Tel: +33 368851323
† Electronic supplementary information (ESI) available. CCDC 923939–923944.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3cc41140k
Scheme 1
c
4468 Chem. Commun., 2013, 49, 4468--4470
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in 2. Tecton 3 (R,R isomer) bears an extra OH group located on were performed using X-ray diffraction on single crystals (see crystal-
the chiral centre. It is worth noting that, by construction, the lographic tables in ESI†). In all three cases, the crystal (space group
chiral fragments should be oriented towards the channels.
P4 for 1ÁZnSiF6 and 3ÁZnSiF6 and I4 for 2ÁZnSiF6) is composed of the
All three tectons, owing to the location of the two chiral centres at organic tecton, Zn2+ cation, SiF62À anion and solvent molecules (3, 2
positions 2 and 5 and the pyridyl units at positions 1 and 4, are non- and 1 CHCl3 molecules for 1, 2 and 3 respectively).
symmetric units. Consequently, upon bridging two consecutive Zn2+
cations they may adopt clockwise (Fig. 1c) or anticlockwise (Fig. 1d) disordered over two positions. Owing to the large disorder of CHCl3
relative orientation. Thus, for the 3D cuboid architecture, many solvent molecules located within the channels, the data were
possibilities may be encountered. Two of the most symmetrical ones processed using the Squeeze command. Unfortunately, all three
The alkyl chains in 1ÁZnSiF6 and 2ÁZnSiF6 were found to be
are schematically presented in Fig. 1a and b.
crystalline materials were found to be rather unstable and upon
Tectons 1–3 were synthesized in good yields starting from removal of the solvents molecules they irreversibly collapsed within
commercially available enantiomerically pure alcohols 4, 6 a few seconds. Consequently, no PXRD studies could be carried out.
and 8 (Scheme 1). The activation of alcohols 4 and 6, achieved at
In all cases, a 3D cuboid architecture is formed. The latter may be
RT in CH2Cl2 by treatment with p-TsCl in the presence of Et3N and a described as follows: the Zn2+ cation behaving as an octahedral node
catalytic amount of DMAP, afforded compounds 5 and 7 in 79 and is surrounded by a 4N2F set of atoms. The interconnection of
98% yields respectively. For compound 8, owing to the presence of consecutive cations through the four corners of the square base of
both primary and secondary OH groups, the activation process using the octahedron by four pyridyl moieties belonging to four enantio-
1 equiv. of p-TsCl at À20 1C yielded, in addition to the desired merically pure organic tectons 1, 2 or 3 leads to the formation of a 2D
compound 9 (50%), the di-tosylated by-product which was removed square grid type arrangement in the ab plane (Zn–N distance in the
using column chromatography. The OH protected 10 was obtained range 2.12–2.15 Å). Within the sheet, the Zn–Zn distance is in the
at RT in 98% yield by reacting 9 with DHP in the presence of a 15.58–15.62 Å range (Fig. 3a, 4a and 5a). The pyridyl units are tilted
catalytic amount of PPTS in CH2Cl2. The dibromo intermediates 11 with respect to the phenyl group by ca. 48.71 and 51.11 for 1, 52.91 and
and 12 were obtained in 86 and 84% yields, respectively, upon 56.61 for 2, 50.21 and 48.41 for 3. As stated above, owing to the non-
condensation of 2,5-dibromohydroquinone with 5 or 7 in the symmetric nature of tectons 1–3, within the square grid, among many
presence of Cs2CO3 in DMF at 100 1C. Compound 13 was prepared relative orientation possibilities, in all three cases, the organic tectons
in 60% yield by reaction of 2,5-dibromohydroquinone with 10 adopt either clockwise (Fig. 1c) or anticlockwise dispositions (Fig. 1d).
followed by a deprotection step using HCl in MeOH. Finally, tectons
To reach the cuboid type architecture, in all three cases the
1, 2 and 3 were obtained in 75, 74 and 75% yields, respectively, by a consecutive square grid type arrangements are further interconnected
Pd(PPh3)4 catalyzed Suzuki coupling reaction between 11, 12 or 13 along the c axis by SiF62À dianions through Zn–F bonds located at the
and 4-pyridylboronic acid under anaerobic conditions.
apical positions of the octahedral nodes (distance in the 2.10–2.14 Å
In addition to classical characterization in solution, the structures range). Along the third dimension, the distance between consecutive
of all three enantiomerically pure tectons 1–3 were studied in the Zn2+ cations is in the 7.55–7.65 Å range (Fig. 3b, 4b and 5b).
solid state using X-ray diffraction on single crystals. Colorless crystals
Alternatively, the 3D architecture may be described as the
of 1 and 2 were obtained upon slow diffusion of n-pentane vapors interconnection of consecutive pillars, formed upon bridging of
into a CHCl3 solution of 1 or 2. Yellowish crystals of 3 were obtained
upon slow evaporation of a CH2Cl2–MeOH solution of 3. As expected,
all three tectons crystallized in a chiral space group (P212121, P1 and
P21 for 1, 2 and 3 respectively) (see ESI† for crystallographic tables).
The pyridyl units are tilted with respect to the central phenyl group
by ca. 49.671 and 48.201 for 1, 39.581 and 43.661 for 2 and 39.141 and
35.461 for 3. In all three cases, no solvent molecules are present in
the crystal. The length of the tectons i.e. the distance between the two
N atoms is around 11.4 Å for 1–3 (Fig. 2).
Upon slow diffusion through a buffered layer of DMSO of an
EtOH solution of ZnSiF6ÁxH2O into a CHCl3 solution of the organic
tecton 1, 2 or 3, colorless crystalline materials were obtained after a
few days (see ESI†). For all three combinations, structural studies
Fig. 3 Views along the c (a, c and d) and a (b) axes of a portion of the X-ray
structure of the cuboid architecture formed by combining tecton 1 with ZnSiF6. The
Fig. 2 X-ray structures of tectons 1–3. H atoms are omitted for clarity. For bond
view along the c axis (a) clearly shows that in consecutive planes, tectons 1 are
distances and angles, see text.
either anticlockwise (c) or clockwise (d) oriented.
c
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Finally, it is worth noting that whereas for 1ÁZnSiF6 and 2ÁZnSiF6
the chiral pores are hydrophobic, in the case of 3ÁZnSiF6 they are
hydrophilic owing to the convergent orientation of the OH groups.
In conclusion, considering the pillar formed upon bridging of Zn2+
cations by SiF62À anions as an infinite tecton, using enantiomerically
pure bis-monodentate organic tectons a series of homochiral 3D
cuboid architectures were designed and generated. Owing to the
localisation of the chiral centres, the porous crystals display chiral
channels occupied by solvent molecules. With the aim of forming
robust crystalline materials, the replacement of Zn(II) by Co(II) or Cu(II)
and of Si(IV) by Ti(IV) or Sn(IV) is currently under investigation.
We thank the University of Strasbourg, the Institut Universitaire
de France, the International centre for Frontier Research in Chemistry
`
(icFRC, scholarship to P.L.), the C.N.R.S. and the Ministere de
´
l’Enseignement Superieur et de la Recherche for financial support.
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hedral coordination geometry by SiF62À anions, by four organic
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(Fig. 4c and d) they are only anticlockwise disposed.
c
4470 Chem. Commun., 2013, 49, 4468--4470
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