No abstract

The reaction of neutral iron(II) complexes of tetradentate Schiff base like ligands with the pseudohalogenides SCN -, OCN -, and CNas monodentate axial ligands was investigated. In solution the formation of octahedral complexes could be confirmed and it was pos-1093 sible to follow a spin transition by T-dependent 1 H NMR spectroscopy.In the solid only pentacoordinate complexes were obtained and the Xray structure of five monoanionic pentacoordinate iron(II) complexes and an interesting trinuclear complex are discussed.

Crystals of the bis(tert‐butyl)silylene (DTBS) derivatives of the tartaric acids were synthesized from D‐, L‐, rac‐, and meso‐tartaric acid and DTBS bis(trifluoromethanesulfonate): two polymorphs of Si2tBu4(L‐Tart1,2;3,4H–4) (L‐1a and L‐1b), the mirror image of the denser modification (D‐1b) as well as the racemate (2), and the meso analogue Si2tBu4(meso‐Tart1,3;2,4H–4) (3). The structures were determined by single‐crystal X‐ray diffraction. The threo‐configured D‐ and L‐ (and rac‐) tartrates were coordinated by two tBu2Si units forming five‐membered chelate rings, whereas the erythro‐configured meso‐tartrate formed six‐membered chelate rings. The new compounds were analyzed by NMR techniques, including 29Si NMR spectroscopy, and single‐crystal X‐ray crystallography.

Sialic acid represents a group of thirty derivates of neuraminic acid with various substituents at the amino residue and the alcoholic hydroxy groups. We analysed the behaviour of the tetracoordinated metal ions palladium(II) and silicon(IV) against the most important derivative N-acetylneuraminic acid (NANA). The molecular 77 structures were assigned by a combined 1 H, 13 C and 29 Si NMR-spectroscopic approach. Despite the presence of many different functional groups, the coordination chemistry of NANA with Pd II follows established rules. Coordination via the N-acetyl-group -sterically impossible with Pd II -was realised with Si IV .