Anion Binding of Inorganic Phosphates by the Hexaaza Macrocyclic Ligand 3,6,9,17,20,23-Hexaazatricyclo[23.3.1.111,15]triaconta-1(29),11(30),12,14,25,27-hexaene

• Published in: Inorganic chemistry 1996-07, Vol.35 (16), p.4597-4603
• Main Authors: Nation, David A, Reibenspies, Joseph, Martell, Arthur E
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic9513090

The interaction of mono-, di-, and tripolyphosphate anions with the various protonated forms of the hexaaza macrocyclic ligand BMXD, 3,6,9,17,20,23-hexaazatricyclo[23.3.1.111,15]triaconta-1(29),11(30),12,14,25,27-hexaene, was investigated by potentiometric equilibrium studies. The protonated ligand forms a number of stable binary complexes in solution with each of the anionic substrates and the strength of interaction increases in the order mono- < di- < tripolyphosphate. Formation constants for all the species found are reported and compared with those of analogous systems. The hexahydrobromide salt of BMXD, (H6BMXD)Br6·7H2O crystallizes in the orthorhombic system, space group Pna21, with a = 11.597(4) Å, b = 12.604(4) Å, c = 27.361(7) Å, and Z = 4. The binary complex (H4BMXD-H2P2O7)Br2·5.2H2O crystallizes in the monoclinic system, space group C2/c, with a = 28.194(6) Å, b = 13.875(3) Å, c = 20.811(4) Å, β = 113.72(3)°, and Z = 8. The X-ray structure results reveal the nature of the interaction between the protonated macrocycle and anionic substrates to be that of multiple hydrogen bonding.