Nickel(II) chelates with tridentate O,N,S- and O,N,O-ligands: Synthesis, magnetic properties, and stereochemistry

Nickel(II) chelates with the tridentate O,N,S-ligands prepared by condensation of 2-mercaptoethylamine with thenoyltrifluoroacetone (I) and 5-bromosalicylaldehyde (II) and with the O,N,O-ligands prepared by the reaction of ethanolamine with salicylaldehyde (III) and its 4-methyl- (IV) and 5-chloro- (V) derivatives were synthesized. All chelates are paramagnetic. Compounds I and II are monomeric and exhibit unusually high, for nickel(II) compounds, mu(eff) values because of the zero-field splitting of the nickel ground state in the low-symmetry (H3O)(2)[Ni(ONS)(2)] anion. Compounds III-V relate to the mixed-ligand type H-2[H2O(O2N)Ni(mu-CH3COO)(2)Ni(O2N)H2O], with the distance between the Ni2+ ions excluding exchange interactions.