Formation of 0D M5L2 helicate cage and 1D loop-and-chain complexes: stepwise assembly and catalytic activity

Abstract

The reactions of pyridyl-substituted tripodal ligand 3-TPyMNTB (tris((pyridin-3-ylmethyl)benzimidazol-2-ylmethyl)amine) with Cu(II) chloride give rise to two supramolecular complexes, namely, [Cu₅(3-TPyMNTB)₂Cl₁₀H₂O]·6C₃H₇NO·11H₂O (1), and [Cu₅(3-TPyMNTB)₂Cl₈(H₂O)₂]Cl₂·2CHCl₃·2CH₂OH (2). The assembly of the two complexes takes place in a stepwise route, including: (1) identical monomeric ML building units are firstly formed in both cases by the coordination of Cu(II) with 3-TPyMNTB using its four central N donors, and (2) the ML units are further linked by the 2-connecting Cu(II) ions through extending pyridyl terminals on the ligands into 0D discrete or 1D infinite structures in complexes 1 and 2, respectively. As a result, 1 presents a unique example of a M₅L₂ coordination cage which shows a triple helicate shape. Three Bim–Py–Cu(II)–Py–Bim coordination chains constitute the strands of the helicate, which can be outlined by an extending “molecular clip” approach, and such structural character is analyzed in detail in comparison with other known helicate examples. On the other hand, a 1D loop-and-chain structure is formed in complex 2, which can be seen as one strand of the helicate cage in complex 1 being opened up to undergo polymerization. The oxidation catalytic properties of complexes 1 and 2 are tested.