Group 12 Metal Complexes of an 18-Membered N2O2S2 Macrocycle Incorporating Two Pyridines:
First Examples of an Infinite Mercury(I) Complex and a Dumbbell-Shaped
Heteronuclear Complex with a Macrocyclic Ligand
posted on 2016-10-20, 14:04authored bySujin Seo, Huiyeong Ju, Seulgi Kim, In-Hyeok Park, Eunji Lee, Shim Sung Lee
Homo- and heteronuclear
group 12 metal (Zn2+, Cd2+, and Hg2+) complexes 1–6 containing a newly
designed 18-membered N2O2S2 macrocycle
incorporating two pyridine subunits (L) were prepared
and structurally characterized. The individual complexes isolated
exhibit unusual stoichiometries, geometries, oxidation states, and
structural topologies and include an infinite mercurous complex and
a heteronuclear dumbbell-shaped complex. Both the Zn(II) complex [Zn(L)][ZnBr4] (1) and the Cd(II) complex
[Cd(L)Br2] (2) are mononuclear,
with the metal ion located inside the macrocyclic cavity. The six-coordinated
Zn(II) center in 1 adopts an octahedral geometry and
is shielded from the anion and solvent by the strongly bound macrocycle.
The Cd(II) center in 2 is seven-coordinate, being bound
equatorially to two N donors, two O donors, and a S donor from the
macrocycle and axially to two bromide ions on opposite sides of the
macrocyclic plane, adopting a pentagonal-bipyramidal geometry. In
the Hg(II) complexations, the configuration adopted by the macrocycle L shows a dependence of the nuclearity on the anion used.
When mercury(II) bromide was used, the dinuclear complex [HgII2(L)Br4] (3) was
obtained, while the reaction with mercury(II) nitrate afforded the
unexpected Hg(I) complex {[HgI2(L)](NO3)2}n (4) with a one-dimensional polymeric structure. In heterometallic
complexation experiments, one-pot reaction of L with
a mixture of ZnBr2 and CdBr2·4H2O resulted in the stepwise isolation of two pure solubility-dependent
Cd(II) complexes (2 and 5), including the
half-dumbbell-type complex [Cd(L)(μ-Br)(CdBr3)] (5), while a mixture of CdBr2·4H2O and HgBr2 yielded the heterometallic bis(macrocycle)
product [(CdL)2(μ-Hg2Br6)](Hg2Br6) (6). This is
the first example of a heteronuclear dumbbell-shaped complex in which
two terminal macrocyclic Cd(II) complexes are linked by a hexabromodimercury(II)
cluster via Cd–Br–Hg bonds. The heterometallic dumbbell 6 can be considered as a good example of competition
and collaboration between Cd(II) and Hg(II) ions because
its formation is associated with the higher coordination affinity
of Cd(II) toward the macrocycle and the formation of the (Hg2Br6)2– cluster, which links the two
endocyclic Cd(II) complexes directly. Both NMR titration and comparative
NMR data indicate a relatively higher coordination affinity of Cd(II)
toward the macrocycle than occurs for Hg(II), in parallel to the situation
observed in the solid state.