No abstract

The majority of self-assembled metallic helicates contain two metal centers, whilst those containing three or more remain quite rare.[1] The limitation to synthesizing high-nuclearity helicates appears to be the design of the organic ligand, since double-and quadruple-stranded helicates containing five [2] and nine [3] metal centers, respectively, have been reported. This is in contrast to triple-stranded helicates, which have not progressed beyond the inclusion of three metal centers.[4] The apparent lack of high-nuclearity helicates has undoubtedly limited the exploitation of these systems, which is currently driven towards the development of molecular devices having predetermined properties and functions such as chirality, [5] energy transfer, [6] metal-metal bonding, [7] and DNA groove binding. [8] Surprisingly, helicates exhibiting magnetic exchange remain scarce, [9] since the adjacent metal ions are often bridged by long spacers that preclude viable superexchange pathways. However the preparation of high-nuclearity helicates with adjacent metal centers bridged by a single atom, or groups of atoms, provide an ideal opportunity to study the magnetic exchange between fixed numbers of paramagnetic metal centers in an isolated finite one-dimensional (1D) system. These systems could serve as useful models to provide further insights into the magnetic properties of infinite 1D magnetic-chain compounds, [10] which occupy an intermediate position between zero-dimensional clusters and 3D extended lattices, and as building blocks for future supramolecular devices.[11] Consequently we have embarked upon a program to exploit the helical structural

The majority of self-assembled metallic helicates contain two metal centers, whilst those containing three or more remain quite rare.[1] The limitation to synthesizing high-nuclearity helicates appears to be the design of the organic ligand, since double-and quadruple-stranded helicates containing five [2] and nine [3] metal centers, respectively, have been reported. This is in contrast to triple-stranded helicates, which have not progressed beyond the inclusion of three metal centers.[4] The apparent lack of high-nuclearity helicates has undoubtedly limited the exploitation of these systems, which is currently driven towards the development of molecular devices having predetermined properties and functions such as chirality, [5] energy transfer, [6] metal-metal bonding, [7] and DNA groove binding. [8] Surprisingly, helicates exhibiting magnetic exchange remain scarce, [9] since the adjacent metal ions are often bridged by long spacers that preclude viable superexchange pathways. However the preparation of high-nuclearity helicates with adjacent metal centers bridged by a single atom, or groups of atoms, provide an ideal opportunity to study the magnetic exchange between fixed numbers of paramagnetic metal centers in an isolated finite one-dimensional (1D) system. These systems could serve as useful models to provide further insights into the magnetic properties of infinite 1D magnetic-chain compounds, [10] which occupy an intermediate position between zero-dimensional clusters and 3D extended lattices, and as building blocks for future supramolecular devices.[11] Consequently we have embarked upon a program to exploit the helical structural