(14), have been determined by single-crystal X-ray crystallography. In the solid state, the complexes of the lighter lanthanide ions La 3+ −Dy 3+ show a 10-coordinated geometry close to a distorted bicapped antiprism, where the carboxylate pendants are situated alternatively above and below the best plane that contains the nitrogen donor atoms. The complexes of the heavier ions, Ho 3+ −Lu 3+ , have a 9-coordinated geometry close to distorted tricapped trigonal prism, with one of the pendant carboxylate groups uncoordinated. The ligand is in a "twist−fold" conformation, where the twisting of the pyridine units is accompanied by an overall folding of the major ring of the macrocycle so that the pyridine nitrogen atoms and the metal are far from linear. The aqueous solution structures of the complexes were thoroughly characterized, the diamagnetic ones (La 3+ and Lu 3+ ) by their COSY NMR spectra, and the paramagnetic complexes using a linear least-squares fitting of the 1 H LIS (lanthanide-induced shift) and LIR (lanthanide-induced relaxation) data with rhombic magnetic susceptibility tensors. The solution structures obtained for the La 3+ −Dy 3+ complexes (10-coordinate) and for the Tm 3+ −Lu 3+ complexes (9-coordinate) are in very good agreement with the corresponding crystal structures. However, the 10-coordinate structure is still exclusive in solution for the Ho 3+ complex and predominant for the Er 3+ complex.

New neutral and zwitterionic chiral NNO‐donor scorpionate ligands 1 and 2 were designed to obtain new mononuclear and dinuclear NNO‐heteroscorpionate aluminum complexes. Reaction of 1 with [AlR3] (R=Me, Et) in a 1:1 or 1:2 molar ratio afforded the neutral mononuclear alkyl complexes [AlR2(κ2‐bpzappe)] {R=Me (3), Et (4); bpzappeH=2,2‐bis(3,5‐dimethylpyrazol‐1‐yl)‐1‐[4‐(dimethylamino)phenyl]‐1‐phenylethanol} and bimetallic complexes [{AlR2(κ2‐bpzappe)}(μ‐O){AlR3}] [R=Me (5), Et (6)]. By reaction of complexes 3–6 with PhCH2Br, mononuclear and dinuclear cationic aluminum complexes [AlR2(κ2‐bbpzappe)]Br {R=Me (7), Et (8); bbpzappeH=N‐benzyl‐4‐[2,2‐bis(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)‐1‐hydroxy‐1‐phenylethyl]‐N,N‐dimethylbenzenaminium bromide} and [{AlR2(κ2‐bbpzappe)}(μ‐O){AlR3}]Br [R=Me (9), Et (10)] were synthesized. Both neutral aluminum complexes in the presence of Bu4NBr and cationic aluminum complexes were investigated as catalysts for cyclic carbonate formation from epoxides and carbon dioxide. Amongst them, complex 10 was found to be an efficient one‐component catalyst for the synthesis of cyclic carbonates from both monosubstituted and internal epoxides and was shown to have broad substrate scope.

A new lanthanum heteroscorpionate complex has shown exceptional catalytic activity for the synthesis of cyclic carbonates from epoxides and carbon dioxide. This catalyst system also promotes the reaction of bio-based epoxides to give an important class of bis(cyclic carbonates) that can be further used for the production of bio-derived non-isocyanate polyurethanes. The catalytic process requires low catalyst loading and mild reaction conditions for the synthesis of a wide range of cyclic carbonates.