Macrocyclic dinuclear Zn(II) complexes: synthesis, structure and hydrolysis of tris(p-nitrophenyl) phosphate

A series of mono- and dinuclear zinc complexes of 3,6,9,17,20,23-hexaaza-29,30-dihydroxy-13,27-dimethyl-tricyclo[23,3,111,15]triaconta-1(28),11,13,15(30),25,26-hexaene (H2L or BDBPH) have been defined in solution by potentiometry. The crystal structure of [Zn2C26H40N6O2(CH3OH)2]·Br2 has been determined by X-ray. Each zinc ion is coordinated to three nitrogen atoms, a bridged-phenolic oxygen atom, and a methanolic oxygen atom, which define a six-coordinated octahedron. Bond lengths of ZnN are in the range of 2.104(3)–2.120(3) Å and distances between Zn and O (bridged-phenolic oxygen) are 2.052(2), 2.062(2) Å, respectively. The dinuclear complexes: [Zn2L]2+ and [Zn2L(OH)]+ play crucial roles in hydrolytic reaction of tris(4-nitrophenyl)phosphate. A possible mechanism showed that [Zn2L(OH)]+ acts as a nucleophile and [Zn2L]2+ stabilizes the formation of the intermediate: [Zn2L–BNP].