Synthesis and Structure of Mercurous Ion and Dinuclear Lead(II) Complexes of the 28-Membered Selenaaza Macrocycle: Dominance of the Chelate Ring Size Effect and Conformational Requirement over Soft−Soft Interactions

The flexible and larger ring size macrocycle 4 (C36H46N6Se2) afforded stable complex 5 [Hg2(PF6)2{C36H46N6Se2}]
on treatment with 1 equiv of mercuric acetate followed by addition of NH4PF6. The reaction of Pb(OCOCH3)2·4H2O
with 4 followed by treatment with NH4PF6 resulted in a dinuclear lead complex (6) [Pb2(PF6)2(OCOCH3)2{C36H46N6Se2}]. The crystal structures of complexes 5 and 6 are described:  C36H46F12Hg2N6P2Se2 a = 9.5106(5) Å, b =
11.5222(6) Å, c = 11.8161(6) Å, α = 115.6110(10)°, β = 96.5190(10)°, γ = 106.2910(10)°, monoclinic, P1̄, Z
=1; C44H57F12N8O4P2Pb2Se2 a = 9.4668(5) Å, b = 11.9937(6) Å, c = 25.2319(14) Å, α = 102.4130(10)°, β =
97.6130(10)°, γ = 94.8540(10)°, monoclinic, P1̄, Z = 2. The crystal structure of 5 revealed that Hg22+ is trapped
inside the cavity of the macrocycle. The geometry around the mercurous ion is antiprismatic with Hg22+ coordinating
to six nitrogen atoms forming four five-membered rings, and there is no interaction between the mercurous ion and
the selenium donor atoms. The single crystal X-ray crystal structure of 6 indicates a distorted octahedral geometry
around each lead atom in the cavity of the macrocycle due to presence of the sterochemically active lone pair on
Pb(II). The octahedral geometry around each Pb(II) is satisfied by coordination to 3 nitrogen atoms, two oxygen
atoms of the chelating acetate group, and bridging of one of the oxygen atoms of the nearby acetate.