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 crystal Supramolecular synthons Structural motifs In cerebro manipulation Virtual 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 One organic model Our molecule [Ag(LOH) 2 ] + DHMB (it’s ionic!!)

What a difference the anion makes… BF PF 6 - [Ag(LOH) 2 ]BF 4 [Ag(LOH) 2 ]PF 6 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 ]BF 4 vs. [Ag(LOH) 2 ]PF 6 1) Hydrogen bond chains –OH…F-X-F…HO- 2) cyclic pattern comprising Ag…F, –OH…F, and Ag… BF 4 - PF 6 -

Deconvolution of supramolecular motifs Hydrogen bond chains –OH…F-X-F…HO- : cis vs. trans BF 4 - PF 6 -

Deconvolution of supramolecular motifs Anion interactions/imprinting : tetrahedral vs. octahedral BF 4 - diamondoid PF 6 - 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, (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 BF 4 -

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 ) -C py -C py =0°) Homochiral helix (pitch 17Å), polar residues outside. Could be templated? Could use 6PE? BF 4 -

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 BF 4 - 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. BF 4 -

Engineering of supramolecular isomers (a) (b) (c) PF 6 - 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 BF 4 gives a cis –OH…F-X-F…HO- synthon PF 6 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,