To make large molecules that can perform specific tasks, it is necessary to direct the assembly of simpler molecular blocks in a spatially controlled fashion. In particular, if multiple metallic centres can be incorporated into supramolecular aggregates, macromolecules can be created with magnetic, redox and catalytic properties. Richard Winpenny and colleagues at the University of Manchester, l'Institut Néel and the Lawrence Berkeley National Laboratory have now developed a conceptually simple, yet powerful, strategy for making multimetallic assemblies.
The researchers start with a ring-shaped compound that contains seven chromium atoms and one nickel atom arranged in an octagon. The nickel atom is attached to a Lewis base, which can be used to link the 8-centre ring to various other compounds using common acid–base coordination chemistry. For the Lewis acid, the team choose compounds containing a labile group (typically water or tetrahydrofuran) that can be easily displaced by the Lewis base to form a new covalent bond.
Three examples are used to highlight the generality of the approach. In the first, a 3-centre ring comprising three manganese atoms attached to a labile group is reacted with three equivalents of the 8-centre ring to create a multimetallic 27-centre compound. In the second, a bitetrahedral, 6-centre ring is reacted with four equivalents of the 8-centre ring to give a 38-metal centre aggregate containing 4 different metals. Finally, a compound with 60 metal centres is synthesized from a 12-centre hexagonal ring and six equivalents of the 8-centre ring.