Combining valproate and bipyridyl ligands to construct a 0D core-shell Zn-5(mu(3)-OH)(2) cluster and a 2D layered coordination network with a [Zn-3(mu(3)-OH)](2) SBU

摘要

Starting from the proposed zinc carboxylate cluster tetrakis(mu-2-propylpentanoato)dizinc(II), Zn-2(mu(2)-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-mu(3)-hydroxido-hexakis(mu-2-propylpentanoato)bis(2-propylpentanoato)pentazinc(II), [Zn-5(C8H15O2)(8)(OH)(2)(C10H8N2)(2)] (II), and poly[[bis(mu-4,4'-bipyridine)di-mu(3)-hydroxido-octakis(mu-2-propylpentanoato)-bis(2-propylpentanoato)hexazinc(II)] dimethylformamide disolvate], {[Zn-6(C8H15O2)(10)(OH)(2)(C10H8N2)(2)]center dot 2C(3)H(7)NO}(n) (III), were synthesized. Compound II is a core-shell-type zero-dimensional discrete Zn-5(mu(3)-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 Zn-6(mu(3)-OH)(2) clusters exhibiting a chair-like hexagonal arrangement. This SBU is formed from two Zn-3(mu(3)-OH) trimers related by inversion symmetry and connected by two synanti bridging carboxylate groups. Each SBU is connected by four 4,4'-bipyridine ligands producing a 6(3)-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.