Monolayer formation and aggregation of nickel(II) complexes coordinated with salen substituted by non-linear alkyl side chains

In order to investigate the effect of alpha-methylene groups of alkyl-substituted [Ni(salen)] on the aggregating nature, the monolayers of nickel(II) complexes coordinated with N,N'-disalicylideneethylenediamine (salen) substituted by propyl, 1-methylpropyl and 1,1-dimethylpropyl side chains have been prepared at a water-air interface using the Langmuir-Blodgett (LB) method. The pi-A isotherm measurement revealed the formation of two different types of monolayers, condensed phase and expanded phase. When the hydrogen atoms of alpha-methylene groups were totally substituted by the methyl groups, the transition pressure of the expanded phase to the condensed phase decreased considerably from 5.4 to 1.0 mN m (- 1), and the critical area of the expanded phase increased by ca. 20%. This observation suggests the presence of CH-pi: interaction between the alpha-methylene group and the pi-conjugated system in the monolayer state as has been found in the crystalline state. (C) 2000 Elsevier Science S.A. All rights reserved.