Ni sub(3) versus Ni sub(30): A Truncated Octahedron Metal-Organic Cage Constructed with [Ni sub(5)(CN) sub(4)] super(6+) Squares and Tripodal Tris-tacn Ligands That are Large and Flexible

• Published in: Chemistry : a European journal 2016-12, Vol.22 (49), p.17576-17580
• Main Authors: Zhang, Zongyao, Zheng, Kunyi, Xia, Tianlong, Xu, Lijin, Cao, Rui
• Format: Article
• Language: English
• Subjects: Acetonitrile; Bonding; Cage; Cleavage; Ligands; Magnetic properties; Octahedrons; Phosphates
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201604598

Reactions of trinickel complex of tripodal tris-tacn ligand N(CH sub(2)-m-C sub(6)H sub(4)-CH sub(2)tacn) sub(3) (L, tacn=1,4,7-triazacyclononane) in acetonitrile-methanol solution with and without phosphate led to two complexes of distinct nuclearities, [(Ni super(II)Cl) sub(3)(CH sub(3)OH) sub(3)(HPO sub(4))L](PF sub(6)) (Ni sub(3), 1) and [(Ni super(II) sub(5)(CN) sub(4)(H sub(2)O) sub(8)Cl) sub(6)L sub(8)] Cl sub(30) (Ni sub(30), 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 Ni sub(3)L to form 1. In the absence of phosphate, Ni sub(3)L assembles with cyanide ions, which are formed by Ni-catalyzed C-CN bond cleavage of acetonitrile, to give a nano-sized Ni sub(30) cage. Complex 2 represents a discrete truncated octahedron cage assembled with [Ni sub(5)(CN) sub(4)] super(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. Unique coordination cage: A trinickel complex of the tripodal tris-tacn (tacn=1,4,7-triazacyclononane) ligand assembles with cyanide ions, which are formed in situ by Ni-catalyzed C-CN bond cleavage of acetonitrile, to give a nano-sized Ni sub(30) cage under mild conditions. This molecular cage is unique because it represents a discrete truncated octahedron assembled with pentanuclear [Ni sub(5)(CN) sub(4)] super(6+) squares and large and flexible triangular tris-tacn ligands.