Olivier Jeannin

Oxidation of a bis(selenomethyl)-substituted TTF with TCNQF ₂ activates Se⋯N chalcogen bonding, when compared with the neutral TCNQMe ₂ charge-transfer complex.

Strong Se⋯Cl/Br chalcogen bond interactions are found in the cation radical salts of a naphthalene peri -diselenide with the paramagnetic FeCl ₄ ⁻ /FeBr ₄ ⁻ anions and their diamagnetic Ga analogs.

S/Se differentiation through chalcogen bonding interactions is achieved in oxidized tetrathiafulvalenes with MeS- and MeSe-substituents.

With their rigid and preorganized skeleton, bispidine (3,7-diazabicyclo[3.3.1]nonane) chelators are very appealing for the preparation of metal complexes with high kinetic inertness. With the aim to develop new Tb(III)-based medical imaging probes, this study describes the synthesis and physicochemical properties of two novel terbium(III) complexes with octadentate bispidine-based ligands substituted with either pyridine-phosphonate (H₆L¹) or picolinate (H₄L²) subunits. Thermodynamic stability constants of the corresponding Tb(III) complexes have been determined by potentiometric, UV-visible absorption spectrophotometric and spectrofluorimetric methods. Despite their apparent similarity, these two octadentate ligands differ in their most stable conformation: chair-chair conformation for H₄L² and boat-chair conformation for H₆L¹, as confirmed by ¹H NMR studies and suggested by physicochemical investigations. This conformational change induces different protonation schemes for the two ligands. The kinetic inertness of the Tb complexes has been studied in various media and assessed by transmetalation and transchelation experiments. In particular, Tb(L²) displayed a remarkable kinetic inertness with no measurable dissociation over two months in mouse serum at 10^-5 M concentration. The complex was also very inert in the presence of a 50-fold excess of Zn(II) in H₂O at pH = 7.4 (7% of dissociation over two months). The complexes with ligand L¹ are significantly less inert, emphasizing the influence of the ligand conformation on the kinetic inertness of the Ln(III) complexes. Finally, the luminescence properties of the isolated complexes have also been investigated. A bright green luminescence was observed, especially for Tb(L²), which displays a high quantum yield value of 50% in H₂O (60% in D₂O; λ_exc = 263 nm). In addition, luminescence lifetimes of 1.9(2) and 1.7(2) ms have been measured for Tb(L¹) and Tb(L²), respectively, hence confirming the formation of nona-coordinated complexes with one inner-sphere water molecule. These data on a bispidine scaffold pave the way for developing bright, inert luminescent probes for bioimaging and for radiolabeling applications with Tb(III) radioisotopes.

Two zinc(II) complexes with azopyridine or azopyrimidine featuring dodecyl chains have been synthesized, crystallographically characterized and analyzed in the framework of quantum chemistry. In the mononuclear complex 1, the metal centre has a distorted octahedral geometry with two molecules of 2-(4-dodecyloxyphenylazo)pyrimidine connected in a bidentate fashion, while the remaining coordination sites are occupied by two monodentate nitrate anions. Considering the complex 2, a linear arrangement of three zinc atoms linked by acetate ions was observed. The central zinc atom, situated on the inversion center, is in a nearly perfect octahedral environment, while the outer symmetry-related zinc atoms have a distorted octahedral geometry and they coordinate to three acetate groups and to one molecule of 2-(4-dodecyloxyphenylazo)pyridine in a bidentate manner. In 1, enantiomers locally deracemize so that the coordinated units form homochiral ribbons, while the dodecyl chains from the neighbouring ribbons interdigitate to form layers of molecules. Compound 2 shows a comparable layered packing arrangement. Theoretical investigations of the supramolecular energetic landscape were conducted using density-functional theory (DFT) formalism, quantum theory of atoms in molecules (QTAIM), and natural bond orbital (NBO) computational tools. Quantifying the strength of polar and hydrophobic interactions revealed that H⋯H interactions, hydrophobic in nature, dominate the crystal arrangement of these molecules. The obtained results pave a pathway towards understanding self-organized molecular systems that reach the nano- and micrometer scales.