Controlled Self-Assembly of a 2‑D Sheet Coordination Polymer and Monomer Containing an Eight-Membered Cu₄I₄ Crown Motif

The reaction of Ni­(mnt)₂ (mnt = 1,2-dicyano-1,2-ethylenedithiolate) with CuI in THF results in the formation of a Ni­(mnt)₂Cu₄I₄ unit with an eight-membered Cu₄I₄ crown motif. Coordination polymers with Ni­(mnt)₂Cu₄I₄ building units, having doubly bridged 1-D chains, were formed with bulky NBu₄ counterions. To pack the bulky NBu₄ cations into the crystal structure, no direct interactions between the 1-D chain structures are observed. When the bulky NBu₄ cations are exchanged for small sodium cations, direct interactions between the 1-D chain structures dominate. A doubly bridged 2-D sheet structure is formed through the bridging of the cyano groups of the Ni­(mnt)₂Cu₄I₄ units of neighboring 1-D chain structures by sodium atoms. The monomeric [Na₂(18-crown-16)]₂[Ni­(mnt)₂Cu₄I₄] complex is formed when the sodium cations of the 2-D sheet structure are captured by 18-crown-6. The configuration of the coordination polymer or the monomer is controlled through the selection of the appropriate countercation to the Ni­(mnt)₂Cu₄I₄ building unit. Furthermore, the eight-membered Cu₄I₄ crown motifs in the 2-D sheet structure captures sodium cations. In this regard, we propose that the flexible Cu₄I₄ crown motif is capable of capturing atoms or molecules of various sizes; such a material may act as a useful molecular adsorbent through electrostatic interactions.