STERIC, ELECTRONIC AND SOLVATION EFFECTS IN THE COORDINATION OF AMINES BY THE [FE(CN)(5)(OH2)](3-) ION

Equilibrium constants K for the substitution of co-ordinated H2O in [F e-II(CN)(5)(OH2)](3-) by sterically hindered amines (both alpha and be ta branching, viz. NH2Me-NMe3 and NH2Me-NH2But) and by aniline have be en determined in aqueous solution with I = 0.1 mol dm(-3) (NaClO4) at 25 degrees C by UV/VIS spectrophotometry. Comparison with published da ta on the rates of Fe-N bond fission and their further correlation wit h the energetics of protonation of the free amines shows that the obse rved variation in log K for aliphatic amines reflects 'solvation' as w ell as more typically steric effects. Aniline differs from the aliphat ic amines both in its smaller crystal-field splitting(shared by other aromatic amines) and a low value of log K comparable to that of NMe3.