Synthesis and crystal structure of di-aqua-(1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)zinc(II) bis-(hydrogen 4-phospho-natobiphenyl-4'-carboxyl-ato)(1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)zinc(II).

In the asymmetric unit of the title compound, trans -di-aqua-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ 4 N 1 , N 4 , N 8 , N 11 )zinc(II) trans -bis-(hydrogen 4-phospho-natobiphenyl-4'-carboxyl-ato-κ O )(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ 4 N 1 , N 4 , N 8 , N 11 )zinc(II), [Zn(C 10 H 24 N 4 )(H 2 O) 2 ][Zn(C 13 H 9 O 5 P) 2 (C 10 H 24 N 4 )], both Zn atoms lie on crystallographic inversion centres and the atoms of the macrocycle in the cation are disordered over two sets of sites. In both macrocyclic units, the metal ions possess a tetra-gonally elongated ZnN 4 O 2 octa-hedral environment formed by the four secondary N atoms of the macrocyclic ligand in the equatorial plane and the two trans O atoms of the water mol-ecules or anions in the axial positions, with the macrocyclic ligands adopting the most energetically favourable trans -III conformation. The average Zn-N bond lengths in both macrocyclic units do not differ significantly [2.112 (12) Å for the anion and 2.101 (3) Å for the cation] and are shorter than the average axial Zn-O bond lengths [2.189 (4) Å for phospho-nate and 2.295 (4) Å for aqua ligands]. In the crystal, the complex cations and anions are connected via hydrogen-bonding inter-actions between the N-H groups of the macrocycles, the O-H groups of coordinated water mol-ecules and the P-O-H groups of the acids as proton donors, and the O atoms of the phospho-nate and carboxyl-ate groups as acceptors, resulting in the formation of layers lying parallel to the (110) plane.