Bis{P,P'-1,5-diphenyl-3,7-bis[(4-hydrogenphosphonate)phenyl]-1,5,3,7-diazadiphosphocine} nickel(II) bromide (hydrogen bromide adduct) can be used as Synthetic nickel catalyst used for photocatalytic reduction of aqueous protons to hydrogen and catalyst containing phosphonate anchor groups for immobilation on metal oxide semiconductor surfaces, enabling light-driven hydrogen evolution.