The Honeysuckle and the Bindweed Revisited: Synthesis and Stereochemistry of Extended Helical Structures from Coordination Complexes

We report structural studies of a chiral tridentate ligand which forms helical cubanes with cobalt(II) and manganese(II). A quadruple helicate with (P)-chirality is obtained using a (S)-ligand with cobalt(II) but the ligand binds manganese(II) in one of two possible orientations and either (P)- or (M)-quadruple helicates may be observed for a given ligand enantiomer. The helicates may be linked into extended structures by p-nitrobenzoate capping ligands which show stacking interactions with neighbouring complexes. With cobalt(II) we find an extended helical structure with (M)-chirality linking helicates which themselves have (P)-chirality. With manganese(II) we observe a remarkable structure with extended (M)-helices coexisting with extended (P)-helices.     

Symmetry and Rigidity for Boosting Erbium-Based Molecular Light-Upconversion in Solution

Previously limited to highly symmetrical homoleptic triple-helical complexes [Er( Lk )₃]³⁺, where Lk are polyaromatic tridentate ligands, single-center molecular-based upconversion using linear optics and exploiting the excited-state absorption mechanism (ESA) greatly benefits from the design of stable and low-symmetrical [ Lk Er(hfa)₃] heteroleptic adducts (hfa⁻=hexafluoroacetylacetonate anion). Depending on (i) the extended π-electron delocalization, (ii) the flexibility and (iii) the heavy atom effect brought by the bound ligand Lk , the near-infrared (801 nm) to visible green (542 nm) upconversion quantum yield measured for [ Lk Er(hfa)₃] in solution at room temperature can be boosted by up to three orders of magnitude.     

Microdeformation in Heterogeneous Polymers,Revealed by Electron Microscopy

Recent investigations of the tensile fracture behaviour of representative glassy and semicrystalline impact-resistant polymers are reviewed, with emphasis on the microdeformation behaviour as revealed by electron microscopy of sections from bulk specimens, where the crack-tip damage zone has been embedded and/or stained under load, and on thin films deformed in situ. The insight that such techniques have provided into the toughening mechanisms is discussed.