Mole ratio dependent formation of mononuclear versus pentanuclear zinc(II) pivalate complexes and the ‘carboxylate shift’ process

Linear, Planar, Orbicular, and Macrocyclic Multinuclear Zinc (Meth)acrylate Complexes

Zinc carboxylate complexes are widely utilized as artificial models of metalloenzymes and as secondary building units of PCPs/MOFs. However, the relationship between the structure of the monodentate carboxylato ligand and the molecular arrangement of multinuclear zinc carboxylate complexes is not fully understood because of the coordination flexibility of the Zn ion and carboxylato ligands. Herein, we report the structural analysis of a series of complexes derived from zinc (meth)acrylate which has a linear infinite chain structure. The molecular structure of μ4-oxido-bridged tetranuclear complexes [Zn4(μ4-O)(OCOR)6] revealed a distorted Zn4O core. Crystallization of zinc acrylate under aqueous conditions afforded a μ3-hydroxido-containing pentanuclear complex [Zn5(μ3-OH)2(OCOR)8] as the repeating unit of an infinite sheet-like structure in the solid state. It was also obtained by the hydrolysis of the μ4-oxido-bridged tetranuclear complex. In sharp contrast, the methacrylate analog retained the methacrylato ligands under aqueous crystallization conditions to form a macrocyclic dodecanuclear complex with methacrylato as the sole ligand.

Combining valproate and bipyridyl ligands to construct a 0D core-shell Zn5(μ3-OH)2 cluster and a 2D layered coordination network with a [Zn3(μ3-OH)]2 SBU

Starting from the proposed zinc carboxylate cluster tetrakis(μ-2-propylpentanoato)dizinc(II), Zn₂(μ₂-valp)₄ (I), of valproic acid, a branched short-chain fatty acid, and bipyridine ligands, two new mixed-ligand coordination compounds, namely, bis(2,2'-bipyridine)di-μ₃-hydroxido-hexakis(μ-2-propylpentanoato)bis(2-propylpentanoato)pentazinc(II), [Zn₅(C₈H₁₅O₂)₈(OH)₂(C₁₀H₈N₂)₂] (II), and poly[[bis(μ-4,4'-bipyridine)di-μ₃-hydroxido-octakis(μ-2-propylpentanoato)bis(2-propylpentanoato)hexazinc(II)] dimethylformamide disolvate], {[Zn₆(C₈H₁₅O₂)₁₀(OH)₂(C₁₀H₈N₂)₂]·2C₃H₇NO}_n (III), were synthesized. Compound II is a core-shell-type zero-dimensional discrete Zn₅(μ₃-OH)₂ metal-organic cluster with Zn ions in double-triangle arrangements that share one Zn ion coincident with an inversion centre. The cluster contains three crystallographically non-equivalent Zn ions exhibiting three different coordination geometries (tetrahedral, square pyramidal and octahedral). The cluster cores are well separated and embedded in a protective shell of the aliphatic branched short chains of valproate. As a result, there is no specific interaction between the discrete clusters. Conversely, compound III, a 2D layered coordination network with a secondary building unit (SBU), is formed by Zn₆(μ₃-OH)₂ clusters exhibiting a chair-like hexagonal arrangement. This SBU is formed from two Zn₃(μ₃-OH) trimers related by inversion symmetry and connected by two syn-anti bridging carboxylate groups. Each SBU is connected by four 4,4'-bipyridine ligands producing a 6³-hcb net topology. 2D coordination layers are sandwiched within layers of dimethylformamide molecules that do not interact strongly with the network due to the hydrophobic protection provided by the valproate ligands.

Synthesis, crystal structure, DNA binding and molecular docking studies of zinc(II) carboxylates

New zinc(II) carboxylate complexes [Zn(3-F-C₆H₄CH₂COO)₂]_n (1), [Zn₃(3-F-C₆H₄CH₂COO)₆(Phen)₂] (2) and [Zn₃(3-F-C₆H₄CH₂COO)₆(bipy)₂] (3) were synthesized and characterized by atomic absorption, single crystal structural analysis and IR studies. Complex 1 crystallizes as a coordination polymer constituting a web of μ-η¹,η¹ carboxylate bridged tetrahedral zinc centers. Complexes 2 and 3 comprise trinuclear zinc centers with two terminal fivefold coordinated slightly distorted square-pyramidal and central sixfold coordinated octahedral zinc centers. The complexes were also assessed for their DNA binding ability by UV/-Vis spectroscopy and their behavior rationalized theoretically by molecular docking studies. A DNA binding study has shown groove binding interactions with the complexes.