Ni₃ versus Ni₃₀ : A Truncated Octahedron Metal-Organic Cage Constructed with [Ni₅ (CN)₄ ]⁶⁺ Squares and Tripodal Tris-tacn Ligands That are Large and Flexible

Reactions of trinickel complex of tripodal tris-tacn ligand N(CH₂ -m-C₆ H₄ -CH₂ tacn)₃ (L, tacn=1,4,7-triazacyclononane) in acetonitrile-methanol solution with and without phosphate led to two complexes of distinct nuclearities, [(Ni^II Cl)₃ (CH₃ OH)₃ (HPO₄ )L](PF₆ ) (Ni₃ , 1) and [(Ni^II₅ (CN)₄ (H₂ O)₈ Cl)₆ L₈ ]Cl₃₀ (Ni₃₀ , 2). Ligand L takes upward and downward conformation in the structure of 1 and 2, respectively. It is proposed that phosphate directs the upward conformation of Ni₃ L to form 1. In the absence of phosphate, Ni₃ L assembles with cyanide ions, which are formed by Ni-catalyzed C-CN bond cleavage of acetonitrile, to give a nano-sized Ni₃₀ cage. Complex 2 represents a discrete truncated octahedron cage assembled with [Ni₅ (CN)₄ ]⁶⁺ squares and large and flexible triangular ligands, which is scarcely observed for self-assembled metal-organic cages. The magnetic properties of 1 and 2 were examined, showing intriguing magnetic properties.