Studies in the stereochemistry of zinc(II). V. Zinc complexes with N-alkylsalicylaldimines

Bis(N-alkylsalicylaldiminato)zinc(II) complexes are monomeric and 4- coordinate in dilute solutions in toluene but some association is observed in concentrated solutions in diphenylamine. Spectroscopic studies in the ultraviolet region show that only the methyl and ethyl homologues form 5-coordinate pyridine adducts even in pyridine solutions. Only the methyl homologue forms a pyridine adduct stable enough to be isolated, and only this homologue forms a 5-coordinate dimer in the solid state. The ultraviolet reflectance spectra and infrared spectra of the solid compounds can be used to distinguish those compounds in which some or all of the phenolic oxygen atoms are bridging: such bridging is accompanied by a splitting of the ultraviolet absorption near 370 mμ and a shift of a very sharp infrared band from 1530 to 1550 cm-1. This band is tentatively assigned to the phenolic C-O stretching mode.