Scientists in Japan have shown the intercalation of metal (aza)porphines into an organic-pillared coordination box, forming metal arrays with unusual spin properties.

Makoto Fujita and colleagues from the University of Tokyo and Michito Yoshizawa from Japan Science and Technology Agency have synthesised homo (Cu-Cu-Cu) and hetero (Cu-Pd-Cu or Cu-Co-Cu) metal arrays within an organic-pillared coordination box by inserting M(II)-azaporphine/porphine cartridges (where M = Cu(II), Pd(II) or Co(II)). 

The organic-pillared coordination box self assembles from two panels, three pillars and six Pd(II) hinges. The box can then selectively encapsulate the M(II)-azaporphine/porphine units and generate the corresponding homo- or hetero-metal arrays.

The resulting metal arrays show unique spin interactions by electron spin resonance (ESR), which is a spectroscopic technique that can be used to study the unpaired electrons found in transition metals. Interestingly, an unusual spin interaction was reported for the homo-metal array (Cu-Cu-Cu), as the 'forbidden' Dm_s= 3 transition was observed between the three interacting Cu(II) centers.

Fujita said that 'the strict control of the quantity and order of discrete metal arrays is a very important technology that leads to the development of, for example, molecular-based memory devices.   The data storage density of memory devices is expected to increase by several orders if the current bulk materials in memory devices are replaced by a molecular-based one.'

The groups' future targets are 'to switch the spin-spin interaction by external stimuli and to make single molecular magnets and conductors by this reported approach.' In particular the challenge will be to find the 'right ordering of spin-active metal ions which is expected to lead towards data storage at the molecular level,' explained Fujita.

Emma Shiells