Crystal Structures and Magnetic Properties of Nickel Complexes with Hydrotris(pyrazolyl)borate Ligand and Double Bridged by Phosphate Esters

The reaction between [NiTp*(μ-OH)]2 (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) and (RO)2P(O)OH (R = Et, Bu, 4-NO2-Ph) affords the dinuclear nickel phosphates [NiTp*(μ-O2P(OR)2)]2 (R = Et (1), Bu (2), 4-NO2-Ph (3)), which have been studied by spectroscopic methods (IR, UV−vis, and 1H NMR). In chloroform solution, those complexes exhibit isotropically shifted 1H 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. Magnetic 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.