The host-guest interactions between ortho-, pyro-, and tripolyphosphate anions and the mono and dinuclear copper(II) complexes of the hexaaza macrocyclic ligand BMXD (3,6,9,17,20,23-hexaazatricyclo[23.3.1.1(11,15)]triaconta-1(29),11(30),12,14,25,27-hexaene) were investigated by potentiometric equilibrium methods. Ternary complexes are formed in aqueous solution as a result of coordinate bonding, hydrogen bond formation, and Coulombic attraction between the host and guest. Formation constants for all the species found are reported. The dinuclear copper(II) complexes of BMXD show strong selectivity for pyrophosphate ions in the presence of orthophosphate ions over the whole p[H] range; the pyrophosphate/tripolyphosphate selectivity is p[H] dependent. The dinuclear copper(II) complex of BMXD, (Cu-2-BMXD)(SO4)(2), crystallizes in the orthorhombic space group Pccn, with a = 15.73(2) Angstrom, b = 20.27(1) Angstrom, c = 9.045(5) Angstrom, and Z = 4. The sulfate counterions are found to bridge the copper(II) ions in adjacent molecules leading to an extended polymeric structure.