[μ-2,3,5,6-Tetra-kis(2-pyrid-yl)pyrazine-κN,N,N:N,N,N]bis-[diaqua(dihydrogen m-phenylene-diphospho-nato-κO)nickel(II)] dihydrate.

The title compound [Ni(2)(C(6)H(6)O(6)P(2))(2)(C(24)H(16)N(6))(H(2)O)(4)]·2H(2)O or [Ni(2)(tpyprz)(1,3-HO(3)PC(6)H(4)PO(3)H)(2)(H(2)O)(4)]·2H(2)O [tpyprz = tetra-kis-(2-pyrid-yl)pyrazine, C(24)H(16)N(6)] is a binuclear complex with a crystallographic inversion center located at the center of the pyrazine ring. The equivalent nickel(II) sites exhibit a distorted {NiO(3)N(3)} octa-hedral coordination, with the three nitro-gen donors of each terminus of the tpyprz ligand in a meridional orientation. An aqua ligand occupies the position trans to the pyrazine nitro-gen donor, while the second aqua ligand is trans to the oxygen donor of the dihydrogen-1,3-phenyl-diphospho-nate ligand. The Ni-O and Ni-N bond lengths fall in the range 2.011 (3) to 2.089 (3) Å. The protonation sites on the organo-phospho-nate ligand are evident in the significantly longer P-O bonds compared to the unprotonated sites. In the crystal structure, the complex mol-ecules and the solvent water mol-ecules are linked into a three-dimensional hydrogen-bonded framework through O-H⋯O inter-actions between the aqua ligands, the protonated organo-phospho-nate oxygen atoms and the water mol-ecules of crystallization. Intra-molecular π-stacking between the phenyl group of the phospho-nate ligand and a pyridyl group of the tpyprz ligand, at a distance of 3.244 (5) Å between ring centroids, is also observed.