Strategic synthesis of [Cu2], [Cu4] and [Cu5] complexes: inhibition and triggering of ligand arm hydrolysis and self-aggregation by chosen ancillary bridges

The Schiff base ligand HL1 (2,6-bis(allylimino)methyl-4-methylphenol) having no coordinating donor arm has been examined for its reaction medium and ancillary bridge dependent reactivity for a hierarchical family of CuII complexes. The ligand showed a unique reactivity pattern toward CuII in solution. The bridging nature of in situ generated HO− ions in the absence and presence of externally added carboxylates (RCOO−; R = CF3, C6H5 and CH3) has been utilized to produce complexes [Cu2(μ-L2)2(H2O)]2[Cu2(μ-L2)2(H2O)2](ClO4)6 (1) (HL2 = 3-(allylimino)methyl-2-hydroxy-5-methylbenzaldehyde), [Cu4(μ4-O)(μ-L1)2(μ1,3-O2CCF3)4] (2), [Cu4(μ4-O)(μ-L1)2(μ1,3-O2CC6H5)4]·H2O (3), and [Cu5(μ3-OH)2(μ-L1)2(μ1,3-OAc)2(OAc)2(H2O)4][Cu5(μ3-OH)2(μ-L1)2(μ1,3-OAc)2(OAc)3(H2O)](ClO4)3·2C2H5OH (4). The absence of carboxylate anions did not yield HO− ions in situ and triggered single ligand arm hydrolysis. The formation of tetra- and pentanuclear aggregates as well as ligand hydrolyzed dinuclear products has been rationalized to identify the possible roles of carboxylate anions in solution. Detailed characterization of the complexes in the solid state and in solution has been carried out using spectroscopic measurements, X-ray crystallography, variable temperature magnetic measurements and functional behavior. In MeOH solutions at 298 K, the complexes 1-4 showed catalytic oxidation of 3,5-di-tert-butyl catechol (3,5-DTBCH2) saturated with O2 from the air.