The H+- and Cl--assisted dissociation
kinetics and the stabilities of the complexes
[Hg(sar)]2+ and
[Hg((NH2)2-sar)]2+ (sar =
3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane
and (NH2)2-sar = 1,8-diamino-sar) were
determined.
The Hg2+ dissociation rates depend on both the
proton and the chloride ion concentrations. H+
competes with
the metal ion for dissociated amine groups, and Cl-
competes with the amine for vacant coordination sites.
The
rate laws are complicated. For the
[Hg(sar)]2+ system (0.1 ≤ [H+] ≤
1.0 M, 0.01 ≤ [Cl-] ≤ 1.0 M, I = 2.0
M
(NaO3SCF3), 25.0 °C) the observed rate
law is
v
-
Hg
2+
= (a +
b[Cl-])[H+][Hg(sar)2+]/(1
+ c[Cl-]), with a
=
35(3) M-1 s-1,
b = 2.9(4) × 103
M-2 s-1, and
c = 33(5) M-1. For the
[Hg((NH3)2-sar)]4+ system
(0.001 ≤ [H+]
≤ 1.0 M, 0.01 ≤ [Cl-] ≤ 1.0 M, I = 1.0
M (LiClO4), 25.0 °C) the observed rate law is
v
-
Hg
2+
= (a + b[H+] +
c[H+]2)[Cl-][Hg((NH3)2-sar)4+])/((1
+ d[Cl-])(1 +
e[H+])), with a = 0.056(6)
M-1 s-1,
b = 8(3) M-2
s-1, c =
5(3) M-3 s-1,
d = 1.3(4) M-1, and
e = 1.1(5) × 102
M-1. Intimate mechanisms for the
dissociation reactions
are proposed. Using iodide ion or sar ligand as competing ligands
and the reported values for the stabilities of
HgI3
-and
HgI4
2- the stability constants at
25.0 °C were determined for [Hg(sar)]2+
(1028.1(1) M-1),
[Hg(sar)I]+
(1029.1(1) M-2),
[Hg((NH2)2-sar)I]+
(1028.5(1) M-2), and
[Hg(cyclam)I]+ (1030.8(1)
M-2) (cyclam = 1,4,8,11-tetraazacyclotetradecane) with [OH-] = 0.1 M,
I = 0.5 M (NaClO4) and for
[Hg((NH2)2-sar)]2+
(1026.4(3) M-1)
with [OD-] = 0.1 M, I = 0.1 M
(NaOD).