deconvolution of supramolecular synthons and analysis of supramolecular isomerism for wheel-and-axle...
TRANSCRIPT
Deconvolution of supramolecular synthons and analysis of supramolecular isomerism for
wheel-and-axle silver complexes
Alessia Bacchi, Elsa Bosetti
University of Parma – Italy
Spirit of this work
Observed native crystalSupramolecular synthons
Structural motifs
In cerebro manipulationVirtual mutant crystal
A supramolecular synthon is a structural unit formed by intermolecular interactions (e.g. carboxylic acid H-bonded dimer)
Outline
• what are wheel-and-axle silver complexes
• extraction of fundamental synthons
• derivation of supramolecular motifs
• generation of tentative supramolecular isomers*
* Purely speculative exercise
Wheel-and-axle
OHOH
One organic model
dhmb-solv.mry
N OHNOHAg
Our molecule
[Ag(LOH)2]+
DHMB
(it’s ionic!!)
What a difference the anion makes…
BF4-
+PF6
-
[Ag(LOH)2]BF4
[Ag(LOH)2]PF6
Wheel-and-axle
We will look at the patterns arising from the different properties of the anions
Deconvolution of supramolecular motifs
• elencation of supramolecular synthons
• analysis of their assembly in supramolecular motifs
• two motifs are identified
Deconvolution of supramolecular motifs: [Ag(LOH)2]BF4 vs. [Ag(LOH)2]PF6
1) Hydrogen bond chains –OH…F-X-F…HO-
2) cyclic pattern comprising Ag…F, –OH…F, and Ag…
BF4- PF6
-
Deconvolution of supramolecular motifs
Hydrogen bond chains –OH…F-X-F…HO- : cis vs. trans
BF4-
PF6-
Deconvolution of supramolecular motifs
Anion interactions/imprinting : tetrahedral vs. octahedral
BF4- diamondoid PF6
- hexagonal
Supramolecular isomerism…
“ is the existence of more than one type of network superstructures for the same molecular building blocks”
“all sets of polymorphs can therefore be regarded as being supramolecular isomers of one another”
B. Moulton, M.J. Zaworotko, Chem. Rev., 101, 1629-1658 (2001)
Deconvolution of supramolecular motifs
–OH…F-X-F…HO- synthon: cis vs. trans
tetrahedral anion: cis
• e-f additional interaction
• supramolecular chirality
• pseudo twofold symmetry
• tetrahedral imprinting (angle between molecular long axes)=109°
octahedral anion: trans
•centre of symmetry
•octahedral imprinting
Engineering of supramolecular isomers
Engineering of supramolecular isomers starting from the synthons
The observed structures are generated by propagating the synthons via inversion centre on Ag atoms
Engineering of supramolecular isomers
We want to combine the supramolecular synthons according to other symmetry elements compatible with the molecular structure, to generate a landscape of possible alternative supramolecular formats
Engineering of supramolecular isomers
In the observed structures both the cations are centrosymmetric.
There are other potential symmetry conditions:
(a)
(b)(c)
Engineering of supramolecular isomers
Application on Ag of a two-fold symmetry axis perpendicular to the pyridine plane – anti OH –same chirality
Hexameric quasi-macrocyclic assembly
Ring closure requires the matching of Ag atoms WebLab ViewerPro
Molecule
BF4-
Engineering of supramolecular isomers
The influence of conformation
Application on Ag of a two-fold symmetry axis perpendicular to the pyridine plane - conformationally modified (=O-C(sp
3)-Cpy-Cpy=0°)
Homochiral helix (pitch 17Å), polar residues outside. Could be templated? Could use 6PE?
WebLab ViewerPro Molecule
BF4-
Engineering of supramolecular isomers
application on Ag of a two-fold symmetry axis belonging to the pyridine plane – syn OH – same chirality
homochiral helix (pitch 50Å) polar residues are hidden along the helix folding
WebLab ViewerPro Molecule
BF4-
Too loose: difficult to control
Engineering of supramolecular isomers
application on Ag of a mirror symmetry perpendicular to N-Ag-N - syn OH - opposite chirality
Pentameric quasi-macrocyclic assembly. Ring closure is symmetry forbidden.
WebLab ViewerPro Molecule
BF4-
Engineering of supramolecular isomers
(a)
(b)
(c)
PF6-
Potential polymorphs? Too similar: difficult to control and engineer
Conclusions
• local (< 3.6Å) and medium range (< 5.5 Å) metal environment is identical
• Anions make the difference
• BF4 gives a cis –OH…F-X-F…HO- synthon
• PF6 gives a trans –OH…F-X-F…HO- synthon
• Zig-zag chains of –OH…F H-bonds with cis/trans geometry are observed
• other combinations have been generated to explore possible supramolecular isomerism
Prof. Alessia Bacchi
Prof. Mauro Carcelli
Dr Paolo Pelagatti
Dr Dominga Rogolino
Dr Elsa Bosetti
People involved
Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica
University of Parma
A. Bacchi, E. Bosetti, M. Carcelli, P. Pelagatti, D. Rogolino, CrystEngComm, 2004, 6, 177-183