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 CuSO(4)·5H(2)O in CH(3)OH–CH(3)CN. The initial coordination leads to a [3×3] [CuI4CuII5(L)(6)] (SO(4))·2CH(3)OH (Cu(9)) grid followed by oligomerisation to a 3×[3×3] [CuI6CuII21(L)(18)(CN)(6)(SO(4))](SO(4))(2)·8CH(3)CN (Cu(27)) grid through bridging sulfate and in situ generated cyanide with time and subsequent supramolecular organization. The isolated silvery lustrous crystals, Cu(9) and Cu(27), 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] Cu(27) and its electro-activity renders it suitable for the development of large surface area molecular devices.