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

Abstract

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] [Cu^I₄Cu^II₅(L)₆] (SO₄)·2CH₃OH (Cu₉) grid followed by oligomerisation to a 3×[3×3] [Cu^I₆Cu^II₂₁(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.