Synthesis and structures of 3,5-disubstituted 1,2,4-triazole head units and incorporation of 3,5-dibenzoyl-1,2,4-triazolate into new [2 + 2] Schiff-base macrocyclic complexes

The synthesis and characterization of sodium 3,5-diacetyl-1,2,4-triazolate (4Me) and sodium 3,5-dibenzoyl-1,2,4-triazolate (4Ph), both of which can be used as head unit building blocks in Schiff-base reactions, are reported. The crystal structures of sodium 3,5-diacetyl-1,2,4-triazolate, as [4Me(H2O)], and sodium 3,5-dibenzoyl-1,2,4-triazolate, as [4Ph(CH3OH)2]2, have been determined. The former is a helical polymer whilst the latter is a methanol-bridged dimer. The lead(II) templated cyclization reaction of sodium 3,5-dibenzoyl-1,2,4- triazolate (4Ph) with 1,3-diaminopropane or 1,4-diaminobutane, respectively, leads to the formation of two new [2+2] Schiff-base macrocycles as their lead(II) complexes, [Pb2L3Ph(-OH)]ClO4 (5) and [Pb2L4Ph(-OH)]ClO4 (6), respectively. Transmetallation of 5 with nickel(II) ions yields a novel, structurally characterized, dinickel(II) macrocyclic complex, [Ni2L3Ph(NCS)2] (7), which features double triazolate bridging of the two five-coordinate nickel(II) ions.