Mixed-Metal Coordination Cages Constructed with Pyridyl-Functionalized β-Diketonate Metalloligands: Syntheses, Structures and Host-Guest Properties

Abstract

The design and synthesis of mixed-metal coordination cages, which can act as hosts to encapsule guest molecules, is a subject of intensive research, and the utilization of metalloligand is an effective method to construct a designed heterometallic architecture. Herein, a series of heterometallic cages with half-sandwich Rh, Ir and Ru fragments using CuII-metalloligand as a building block by a stepwise approach is reported. The cavity sizes of the cages could be controlled easily by the lengths of the organic ligands. Because the metalloligands in the oxalate-based cage are somewhat distorted and concave, there are weak Cu...O interactions in the molecules, forming a binuclear copper unit. By increasing the height of the cages using longer ligands, 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (H2CA), the organometallic boxes display interesting host-guest behavior, which are made large enough to accommodate some large molecules, such as pyrene and [Pt(acac)2]. Interestingly, the heterometallic cage with larger cavity size can transfer into a homometallic hexanuclear prism in the presence of pyrazine.