Reactivity of phosphonodithioato NiII complexes:: solution equilibria, solid state studies and theoretical calculations on the adduct formation with some pyridine derivatives

The reaction between trans-bis[O-methyl-(4-methoxyphenyl)phosphonodithioato]nickel (6) and pyridine (1), and o-, m-, and p-aminopyridines (II-IV) leads to the 1:2 adducts 7-10. The corresponding formation constants have been determined by UV-visible spectroscopy. DFT calculations performed on the free I-IV ligands, and EHT-FMO calculations on their interactions with 6 predict an increase in the donor ability on passing from I to IV. The formation equilibrium constants follow the expected trend [log beta (eq) = 3.20, (7); 3.46, (9); 4.71 (10)], except for 8, which exhibits the lowest constant (log beta (eq) = 1.88), possibly due to steric effects. The adducts have also been obtained in the solid state, again with the exception of 8, and compounds 7 and 10 have been characterised by single crystal X-ray diffraction.