Order in disorder: solution and solid-state studies of [(M2M5II)-M-III] wheels (M-III = Cr, Al; M-II = Ni, Zn).

A family of heterometallic Anderson-type ‘wheels’ of general formula [(M2M5II)-M-III(hmp)(12)](ClO4)(4) (where M-III = Cr or Al and M-II = Ni or Zn giving [Cr2Ni5] (1), [Cr2Zn5] (2), [Al2Ni5] (3) and [Al2Zn5] (4); hmpH = 2-pyridine-methanol) have been synthesised solvothermally. The metallic skeleton common to all structures describes a centred hexagon with the MIII sites disordered around the outer wheel. The structural disorder has been characterised via single crystal X-ray crystallography, 1-3D H-1 and C-13 solution-state NMR spectroscopy of the diamagnetic analogue (4), and solid-state Al-27 MAS NMR spectroscopy of compounds (3) and (4). Alongside ESI mass spectrometry, these techniques show that structure is retained in solution, and that the disorder is present in both the solution and solid-state. Solid-state dc susceptibility and magnetisation measurements on (2) and (3) reveal the Cr-Cr and Ni-Ni exchange interactions to be J(Cr-Cr) = -1 cm(-1) and J(Ni-Ni),(r) = -5 cm(-1), J(Ni-Ni,c) = 10 cm(-1). Fixing these values allows us to extract J(Cr-Ni,r) = -1.2 cm(-1), J(Cr-Ni,c) = 2.6 cm(-1) for (1), the exchange between adjacent Ni and Cr ions on the ring is anti-ferromagnetic and between Cr ions on the ring and the central Ni ion is ferromagnetic.