μ-2,3,5,6-Tetrakis(2-pyridyl)pyrazine-κ6N6,N1,N2:N3,N4,N5]bis[diaqua(dihydrogenm-phenylenediphosphonato-κO)nickel(II)] dihydrate

Abstract

The title compound [Ni2(C6H6O6P2)2(C24H16N6)(H2O)4]·2H2O or [Ni2(tpyprz)(1,3-HO3PC6H4PO3H)2(H2O)4]·2H2O [tpyprz = tetra­kis­(2-pyrid­yl)pyrazine, C24H16N6] 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 {NiO3N3} octa­hedral coordination, with the three nitro­gen donors of each terminus of the tpyprz ligand in a meridional orientation. An aqua ligand occupies the position trans to the pyrazine nitro­gen donor, while the second aqua ligand is trans to the oxygen donor of the dihydrogen-1,3-phenyl­diphospho­nate 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 organo­phospho­nate ligand are evident in the significantly longer P—O bonds compared to the unprotonated sites. In the crystal structure, the complex mol­ecules and the solvent water mol­ecules are linked into a three-dimensional hydrogen-bonded framework through O—H⋯O inter­actions between the aqua ligands, the protonated organo­phospho­nate oxygen atoms and the water mol­ecules of crystallization. Intra­molecular π-stacking between the phenyl group of the phospho­nate ligand and a pyridyl group of the tpyprz ligand, at a distance of 3.244 (5) Å between ring centroids, is also observed.