Hierarchical tandem assembly of planar [3×3] building units into {3×[3×3]} oligomers: mixed-valency, electrical conductivity and magnetism.

A hierarchical tandem assembly - coordination, oligomerisation and supramolecular organization - is identified using MALDI-TOF of the solid products of the solvothermal reaction of 5,5'-pyridyl-3,3'-bi-1H-pyrazole with CuSO4·5H2O in CH3OH-CH3CN. The initial coordination leads to a [3×3] [CuI4CuII5(L)6] (SO4)·2CH3OH (Cu9 ) grid followed by oligomerisation to a 3×[3×3] [CuI6CuII21(L)18(CN)6(SO4)](SO4)2·8CH3CN (Cu27 ) grid through bridging sulfate and in situ generated cyanide with time and subsequent supramolecular organization. The isolated silvery lustrous crystals, Cu9 and Cu27 , are good electrical conductors, with conductivities of 3.2 × 10-2 and 5.4 × 10-3 S cm-1, respectively, due to the mixed valency. Their magnetic properties are dominated by antiferromagnetic interactions. DFT and band structure calculations confirm their valence distribution and semiconducting behavior. The planarity of the large 3×[3×3] Cu27 and its electro-activity renders it suitable for the development of large surface area molecular devices.