Stereochemistry of bis(salicylaldiminato)metal(II) compounds. Part I. Bis[N-(2,6-dialkylphenyl)salicylideneiminato]nickel(II) compounds and five- and six-co-ordinate pyridine and picoline complexes

Abstract

The compounds bis[N-(2,6-dimethylphenyl)salicylideneiminato]nickel(II), bis[N-(2,6-diethylphenyl)salicylideneiminato]nickel(II), and analogous species with substituents at the 3 and/or 5 positions of the salicyl moiety, strongly prefer the four-co-planar geometry in the solid state and in non-donor solvents. They are forced into tetrahedral structures only by bulky substitution (NO₂, but not Me, OMe, Br, or Cl) at the 3 position of the salicyl moiety; and they do not form six-co-ordinate oligomers as do the N-phenyl and 3- and 4-substituted N-phenyl compounds. In pyridine and the picolines, however, in spite of bulk steric effects (B-strain), they form five- and six-co-ordinate complexes with the bases, to an extent determined by (a) the steric effect {Me > Et (on N-phenyl); and γ-pic py > α-pic}; and (b) the electron-withdrawing substituents on the salicyl moiety (NO₂ > OMe > Br Cl > Me H > 5,6-benzo; and 3- > 5-). Electronic spectra (5–30 10³ cm^–1), bulk magnetic susceptibility, and ¹H n.m.r. data (including paramagnetic shifts) have been used to define structures.