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

Abstract

Homo- and heteronuclear group 12 metal (Zn, Cd, and Hg) complexes 1-6 containing a newly designed 18-membered NOS 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)][ZnBr] (1) and the Cd(II) complex [Cd(L)Br] (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 [Hg(L)Br] (3) was obtained, while the reaction with mercury(II) nitrate afforded the unexpected Hg(I) complex {[Hg(L)](NO)} (4) with a one-dimensional polymeric structure. In heterometallic complexation experiments, one-pot reaction of L with a mixture of ZnBr and CdBr·4HO 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)(CdBr)] (5), while a mixture of CdBr·4HO and HgBr yielded the heterometallic bis(macrocycle) product [(CdL)(μ-HgBr)](HgBr) (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 (HgBr) 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.

Tetrazine-Based Ligand Transformation Driving Metal–Metal Bond and Mixed-Valence HgI/HgII

“…Because Hg II ions forming metal bonds are rare, Hg2 and Hg3 can be assigned, as Hg I forms the well-known dication {Hg I 2 } 2+ . 9 This is consistent with the charge-balance considerations as well as the presence of a lower coordination geometry, which is typically assigned to Hg I oxidation states in Hg II/ Hg I mixed-valence clusters. 9 When considering the charge balance of Hg1 and Hg4, bond valence sum (BVS) calculations indicate that the outermost metal ions of the compound are Hg II (Hg1 = 1.80 and Hg4 = 2.13).…”

“…9 This is consistent with the charge-balance considerations as well as the presence of a lower coordination geometry, which is typically assigned to Hg I oxidation states in Hg II/ Hg I mixed-valence clusters. 9 When considering the charge balance of Hg1 and Hg4, bond valence sum (BVS) calculations indicate that the outermost metal ions of the compound are Hg II (Hg1 = 1.80 and Hg4 = 2.13). BVS calculations could not be performed on Hg2 and Hg3 because no reference values have been reported for an Hg–C bond.…”

Endo- and Exocyclic Coordination of a 20-Membered N2O2S2-Macrocycle and Cascade Complexation of a 40-Membered N4O4S4-Macrocycle

“…We have reported several dumbbell-type disilver­(I) complexes of oxathiamacrocycles linked with different diamine spacers such as dabco (1,4-diazabicyclo­[2,2,2]­octane, bpy, bpp (1,4-bis­(4-pyridyl)­piperazine) . The preparations of the dumbbell-type macrocyclic complexes with inorganic linkers are serendipitous because they are associated with the cluster formations which are hardly predictable . We recently have reported the first heteronuclear dumbbell complex [(CdL) 2 (μ-Hg 2 Br 6 )]­(Hg 2 Br 6 ) (L = 18-membered N 2 O 2 S 2 macrocycle) .…”

Influence of the Reaction Sequence on the Complexation of an NS4-Macrocycle with CdII and CuI Salts Leading to the Formation of Supramolecular Isomers and an Endo/Exocyclic CuI Complex

“…We have been interested in merging the metal substitution chemistry elucidated previously with the preparation of endo/exocoordinated complexes of macrocycles by choosing the appropriate metal ions. Soft metal ions (M = Cu + , Ag + , and Hg 2+ ) very often form exocyclic complexes with thiaazamacrocycles (route I in Scheme ), while borderline metal ions (for example, M′ = Cd 2+ , Zn 2+ , and Pb 2+ ) tend to form endocyclic complexes (route III) via the formation of M′–N pyd bond(s). , Unlike the one-pot synthesis of the endo/exocyclic Cu II complex with L (Chart b), the corresponding Cu I complex is not able to be obtained by traditional synthetic routes. The hard–soft acid–base (HSAB) concept is also useful in predicting and discussing metal substitution in this situation.…”