The reaction between [NiTp*(mu-OH)](2) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) and (RO)(2)P(O)OH (R = Et, Bu, 4-NO2-Ph) affords the dinuclear nickel phosphates [NiTp*(mu-O2P(OR)(2))](2) (R = Et (1), Bu (2), 4-NO2-Ph (3)), which have been studied by spectroscopic methods (IR, UV vis, and H-1 NMR). In chloroform solution, those complexes exhibit isotropically shifted H-1 NMR resonances. Their molecular structures reveal that they all have an eight-membered Ni2O4P2 ring which possesses two nickel centers bridged to each other by two isobidentate phosphate ligands. Magretic studies on 1-3 and other similar complexes (4 and 5) reveal antiferromagnetic behavior at low temperatures as well as an interesting correlation between calculated D values and the planarity of eight-membered Ni2O4P2 rings.