Host-guest interaction between the dinuclear copper(II) complex of the hexaaza macrocyclic ligand 3,6,9,17,20,23-hexaazatricyclo[23.3.1.1 11,15]triaconta-1(29),11(30),12,14,25,27-hexaene and malonate, maleate, fumarate, pyrophosphate and orthophosphate anions

Abstract

The hexaaza macrocyclic ligand 3,6,9,17,20,23-hexaazatricyclo[23.3.1.1]triaconta-1(29),11(30),12,14,25,27-hexaene (L), forms strong dinuclear complexes, as well as several protonated and hydroxo chelates, with Cu(II) ions. The host-guest interactions between the dinuclear copper(II) complexes of L and malonate, maleate, fumarate, pyrophosphate and orthophosphate anions were investigated by potentiometric conventional pH-metry as well as by spectrophotometric titrations in 2:1:1 molar ratio for Cu(II), L and guest. Several ternary complexes are found in aqueous solution as a result of coordinate bonding, hydrogen bond formation and Columbic attraction between the host and guest. The stability constants for all the species found are reported. The dinuclear copper(II) complex of L shows stronger complexation with the maleate anion than with malonate and fumarate anions. It is suggested that the presence of the double bond in maleate offers a more favourable geometry for coordination to the Cu 2L host. Complexation with pyrophosphate and orthophosphate anions show little difference in stability. The big, flexible, pyrophosphate anion probably coordinates outside the macrocycle.