title: Halogen bonding stabilizes a cis-azobenzene derivative in the solid state: a crystallographic study.
abstract: Crystals of trans- and cis-isomers of a fluorinated azobenzene derivative have been prepared and characterized by single-crystal X-ray diffraction. The presence of F atoms on the aromatic core of the azobenzene increases the lifetime of the metastable cis-isomer, allowing single crystals of the cis-azobenzene to be grown. Structural analysis on the cis-azobenzene, complemented with density functional theory calculations, highlights the active role of the halogen-bond contact (N...I synthon) in promoting the stabilization of the cis-isomer. The presence of a long aliphatic chain on the azobenzene unit induces a phase segregation that stabilizes the molecular arrangement for both the trans- and cis-isomers. Due to the rarity of cis-azobenzene crystal structures in the literature, our paper makes a step towards understanding the role of non-covalent interactions in driving the packing of metastable azobenzene isomers. This is expected to be important in the future rational design of solid-state, photoresponsive materials based on halogen bonding.
authors.affiliation: Laboratory of Chemistry and Bioengineering, Tampere University of Technology, PO Box 541, FI-33101 Tampere, Finland.
authors.forename: Marco
authors.initials: M
authors.lastname: Saccone
authors.affiliation: Laboratory of Chemistry and Bioengineering, Tampere University of Technology, PO Box 541, FI-33101 Tampere, Finland.
authors.forename: Antti
authors.initials: A
authors.lastname: Siiskonen
authors.affiliation: Laboratory of Nanostructured Fluorinated Materials (NFMLab), Department of Chemistry, Materials and Chemical Engineering `Giulio Natta', Politecnico di Milano, Via L. Mancinelli 7, 20131 Milano, Italy.
authors.forename: Franisco
authors.initials: F
authors.lastname: Fernandez-Palacio
authors.affiliation: Laboratory of Chemistry and Bioengineering, Tampere University of Technology, PO Box 541, FI-33101 Tampere, Finland.
authors.forename: Arri
authors.initials: A
authors.lastname: Priimagi
authors.affiliation: Laboratory of Nanostructured Fluorinated Materials (NFMLab), Department of Chemistry, Materials and Chemical Engineering `Giulio Natta', Politecnico di Milano, Via L. Mancinelli 7, 20131 Milano, Italy.
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Terraneo
authors.affiliation: Laboratory of Nanostructured Fluorinated Materials (NFMLab), Department of Chemistry, Materials and Chemical Engineering `Giulio Natta', Politecnico di Milano, Via L. Mancinelli 7, 20131 Milano, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Resnati
authors.affiliation: Laboratory of Nanostructured Fluorinated Materials (NFMLab), Department of Chemistry, Materials and Chemical Engineering `Giulio Natta', Politecnico di Milano, Via L. Mancinelli 7, 20131 Milano, Italy.
authors.forename: Pierangelo
authors.initials: P
authors.lastname: Metrangolo
keywords: azobenzene; halogen bonding; isomerization