Structure investigations of group 13 derivatives of N-phenylsalicylideneimine

The reaction of MMe3 with 1 molar equiv of N-phenylsalicylideneimine (HsaldPh) yields the 0,N-chelate complexes Me2M(saldPh) (where M = Al (1), Ga (2), In (3)) in high yields. The reaction of 1 with gamma-picoline results in a ligand redistribution reaction and the formation of the five-coordinate complex MeAl(saldPh)(2) (4), while the gallium and indium compounds are stable in the presence of gamma-picoline. The resulting compounds have been characterized in a solution by NMR and IR spectroscopy and cryoscopic molecular weight measurements, and their molecular and crystal structure have been determined by X-ray crystallography. Compounds 1 and 2 exist as monomeric tetrahedral complexes, while the indium analogue 3 is dimeric with the In-2(mu-O)(2) bridges and five-coordinate metal centers. The five-coordinate methylaluminum compound 4 exhibits trigonal-bipyramidal geometry of the metal center. The obtained results show that a Schiff base acts as a strongly coordinating chelate ligand and, in this regard, it resembles the symmetrical acetylacetonato ligand and related beta-diketonates. An extended crystal structure analysis reveals that the isostructural crystalline complexes 1 and 2 comprise monomeric four-coordinate molecules linked by C-H-imino...O hydrogen bonds, forming helical chains. Parallel left- and right-handed helices joined by C-H...pi interactions give rise to the 3D extended tetragonal framework, with voids filled by solvent molecules. In the crystalline complex 4 the C-H-aryl...O hydrogen bonds organize molecules into H-bonded dimers.