Thermodynamic data have
been obtained from spectroscopic and calorimetric measurements for the addition
of pyridine and 4- methylpyridine to bis(O,O?-diethyl thiomalonato)nickel(II),
Ni(etm)2, in solution in cyclohexane,
benzene, 1,2-dichloroethane, acetonitrile, butan-2-one and carbon tetra-chloride.
In each solvent two base molecules add successively, giving Ni(etm)2B then Ni(etm)2B2.
There are only small variations in K1 and K2 in different
solvents; typically K1 ≈ 200, K2 ≈ 100 l. mol-1,
ΔH�1+2 ≈ -65, ΔH�2 ≈ 0 kJ mol-1
at 30�C, but in benzene and cyclohexane ΔH�2 ≈ -25 and in
cyclohexane ΔH�1+2 ≈ -100 kJ mol-1. The main
driving force for adduct formation is apparently the formation of the first
Ni-N bond, which is accompanied by a spin change.
Mechanistic Insights into Co and Fe Quaterpyridine-Based CO2 Reduction Catalysts: Metal–Ligand Orbital Interaction as the Key Driving Force for Distinct Pathways
