Deconvolution of supramolecular synthons and analysis of supramolecular isomerism for wheel-and-axle...

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