New multi-ferrocenyl- and multi-ferricenyl- materials via coordination-driven self-assembly and via charge-driven electro-crystallization

Three new tetra-ferrocenylethynylpyridinyl copper complexes, L₄(CuI)₄ (3), L₄(CuBr)₂ (4), and L₄(CuCl)2 (5) have been prepared from the reaction of ferrocenylethynylpyridine (L)(2) with copper halides CuX (with X = I–, Br–, Cl–).The ligand 2 and the complexes 3–5 have been fully characterized by spectroscopic methods. The structures of 2–4 have been confirmed by single-crystal X-ray crystallography. 2 forms a dimer in the crystalline-state through C–H··N hydrogen bonds. 4 and 5 are dimers and 3 a tetramer, in all cases linked through Cu–X··Cu bridging interactions. Cyclic voltammetry in dichloroethane showed chemically reversible multiferrocenyl oxidation signals with evidence for product electro-crystallization. The oxidation products were isolated by electrodeposition onto a Pt disc electrode and investigated by scanning electron microscopy which confirmed the spontaneous formation of crystalline oxidation products with distinctive morphologies. Energy dispersive X-ray elemental analysis shows the presence of hexafluorophosphate (counterion) with the P:Fe ratio of 1:1, 0.5:1, and 1:1 for the electrocrystallized products 3, 4, and 5, respectively, suggesting the formulas [3]⁴⁺(PF₆–)₄, [4]²⁺(PF₆–)₂, and [5]⁴⁺(PF₆–)⁴ for the electro-crystallized products.