Syntheses and structural studies of polynuclear copper (II) complexes of Schiff-base macrocycles and related ligands (1996)
AuthorsLingga, Novalinashow all
Two diimine-diamine ligands derived from the [2+1] template condensation of 1,3-diaminopropane with 2,6-diformyl-4-R-phenol [R = Me, (L¹)-; R = tBu, (L⁸)-], have been isolated as their dicopper(II) hydroxo-bridged complex cations. The ring-closure condensation reaction of the dicopper complex cation of (L¹)- with 2,5-diformylfuran produced a new asymmetric tetraimine macrocycle, (L³)- as the methoxo-, hydroxo- and ethoxo-bridged dicopper(II) complexes. The hydroxo- and ethoxo-bridged dicopper(II) complexes of (L³)- were isolated from the recrystallisation of the methoxo-bridged analogue using N,N-dimethylformamide, in the absence or presence of ethanol, respectively. The structures of the dicopper(II) acyclic complexes of (L¹)- and of the ethoxo-bridged complex of (L³)- have been determined by X-ray crystallography. Two hexacopper(II) complexes of a new acyclic Schiff-base ligand, derived from the [3+2] condensation of 1,3-diamino-2-hydroxypropane with 4-t-butyl-2,6- diformylphenol, were isolated. Preliminary X-ray crystallographic investigations on these hexacopper(II) complexes revealed a CU₆ ring templating the ligand such that the primary amine groups are held in an appropriate orientation and separation for ring-closure with a dicarbonyl compound. Two tetracopper(II) macro cyclic complexes were obtained from the [2+2] template condensation of 1,5-diarnino-3-hydroxypentane and 2,6-diformyl-4- Methylphenol. One of the complexes was isolated as a tetrafluoroborate complex, while the other as a formate complex. The formate complex, whose crystal structure has been determined, is believed to have been generated by the hydrolysis of N,N-dimethylformamide at room temperature, promoted by the tetrafluoroborate complex. The tetrafluoroborate complex underwent dimerisation to give an octacopper(II) complex. Another tetracopper(II) complex was synthesised by the template condensation of 1,5-diamino-3-hydroxypentane and 2,6-diformyl-methylphenol. X-ray structure determination of this complex revealed that it is a dimer of two dinuclear macro cyclic complexes. The two copper(II) ions in one unit of the dimer are bound inside the macro cycle "laterally". In contrast, two copper(II) ions are found to be held "diagonally" within the cavity of another Schiff-base macrocycle, derived from the [2+2] template condensation of 2,6-diformyl-4-methylphenol with triethylenetetramine.