New Multi-Ferrocenyl- and Multi-Ferricenyl- Materials via Coordination-Driven Self-Assembly and via Charge-Driven Electro-Crystallization

Abstract

Three new tetra-ferrocenylethynylpyridinyl copper complexes, L₄(CuI)₄ (<b>3</b>), L₄(CuBr)₂ (<b>4</b>), and L₄(CuCl)₂ (<b>5</b>) have been prepared from the reaction of ferrocenyl­ethynyl­pyridine (L)­(<b>2</b>) with copper halides CuX (with X = I^–, Br^–, Cl^–).The ligand <b>2</b> and the complexes <b>3</b>–<b>5</b> have been fully characterized by spectroscopic methods. The structures of <b>2</b>–<b>4</b> have been confirmed by single-crystal X-ray crystallography. <b>2</b> forms a dimer in the crystalline-state through C–H··N hydrogen bonds. <b>4</b> and <b>5</b> are dimers and <b>3</b> 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 <b>3</b>, <b>4</b>, and <b>5</b>, respectively, suggesting the formulas [<b>3</b>]⁴⁺(PF₆^–)₄, [<b>4</b>]²⁺(PF₆^–)₂, and [<b>5</b>]⁴⁺(PF₆^–)₄ for the electro-crystallized products