An Alternate [2×2] Grid Constructed Around TiO4 N2 Units.

ABSTRACT

The formation of a tetranuclear self-assembled species constructed around a TiO4 N2 motif is reported. This aggregate is generated from Ti(Oi Pr)4 , 2,2'-bipyrimidine (bpym) and a bis-biphenol strand (L2 H4 ) where two 2,2'-biphenol units are connected with a biphenyl spacer. The solid-state structure of the [Ti4 (L2 )4 (bpym)4 ] architecture reveals the formation of an unprecedented chiral alternate [2×2] grid. In addition to the structural characterization of the [Ti4 (L2 )4 (bpym)4 ] architecture, geometry optimisation on various possible isomeric tetrameric assemblies ([2×2] grid, alternate [2×2] grid, circular helicate or cyclic hemihelicate) is performed using DFT calculations. These results confirm the higher stability of the alternate [2×2] grid over the other possible tetranuclear isomers and allow examining the replacement of the bpym ligands by two novel diimine chelates within the tetranuclear assembly (2,2'-bipyridine=bipy and 2,2'-bipyrazine=bipyraz). From this initial theoretical investigation, the competition between these three nitrogen ligands in the course of the self-assembly process is next evaluated. Overall, this investigation shows that the exclusive formation of the alternate [2×2] grid is driven by CH⋅⋅⋅N interactions.