Thermodynamics of metal-ligand bond formation. XV. Adducts of mercury(II) halides with bidentate bases

Abstract

Thermodynamic data are reported for the reaction of mercury(11) halides with a range of potentially bidentate bases in benzene solution. The enthalpy data show that in 1 : 1 adducts with tetramethyl-alkanediamines and bis(diphenylphosphino)ethane both donor atoms are coordinated, the mercury being four-coordinate with two Hg-N or Hg-P bonds, each of comparable strength to those in 1 : 1 adducts with unidentate bases. N-Methylmorpholine and dioxan are almost certainly unidentate. 1,10-Phenanthroline, 2,2'-bipyridine and N,N'-dimethylpiperazine gave 1 : 1 adducts of higher stability than those of unidentate bases, but the enthalpies of adduct formation were similar or smaller; the most satisfactory explanation of this seems to be that both nitrogen atoms arecoordinated but that the two Hg-N bonds are unusually weak because of steric misfitting of the bidentate base with the mercury atom.