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

Abstract

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.

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

“…The structures of multinuclear zinc carboxylate complexes 9 – 13 represented by Zn a (O) b (OH) c (OAc) d L f (2a=b/2+c+d) have been reported (Figure 1C), in which Lewis basic neutral ligands (L) are often used to isolate them as single molecular structures. Tri‐, [26] tetra‐, [27] penta‐, [28,29] hexa‐, [29] and heptanuclear [30–33] zinc carboxylate complexes 9 – 13 contain oxido‐ or hydroxido bridge(s). Among them, tetranuclear complex 10 has been widely used as an SBUs for PCPs/MOFs since the pioneering work by Yaghi [34,35] and is also known to act as a biomimetic catalyst with unique chemoselectivity [36,37] .…”