Dicopper(II) Schiff base aminobenzoates with discrete molecular and 1D-chain polymeric structures

Abstract

Dicopper(II) complexes [Cu₂L(O₂CC₆H₄-o-NH₂)] (1) and [Cu₂L(O₂CC₆H₄-p-NH₂)] (2) are prepared from a reaction of [Cu₂L(O₂CMe)] with the corresponding aminobenzoic acid and a base in MeOH, where L is a trianionic pentadentate Schiff base ligand N,N'-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine). The complexes are structurally characterized by X-ray crystallography. The crystal structures show the presence of an asymmetrically dibridged {Cu₂^II(μ-OR)(μ-O₂CR)} core where the endogenous mono-atomic bridging alkoxo group is derived from the Schiff base and the aminobenzoate ligand displays syn-syn bridging mode. The CuCu separation and Cu-OR-Cu bond angle in 1 and 2 are 3.472(1) Å, 131.02(18)° and 3.511(1) Å, 132.20(17)°, respectively. The o-aminobenzoate complex is discrete dimeric nature. The pendant o-amino group is involved in an intramolecular hydrogen bonding interaction with one carboxylate oxygen atom. The crystal structure of the p-aminobenzoate species 2 shows the formation of a one-dimensional polymeric chain resulting from the axial binding of the pendant p-amino group to one copper center belonging to another dimeric unit. Magnetic studies show that both the complexes are antiferromagnetic in nature giving a singlet-triplet energy separation of -130 and -150 cm^-1 for 1 and 2, respectively. The 1D chain complex 2 magnetically behaves like the discrete dimeric complex 1.