Spontaneous Reduction of Copper(II) to Copper(I) at Solid–Liquid Interface

Abstract

Oxidation and reduction reactions are of central importance in chemistry as well as vital to the basic functions of life and such chemical processes are generally brought about by oxidizing and reducing agents, respectively. Herein, we report the discovery of an interfacial reduction reaction (IRR) − without the use of any external reducing agent. In course of metal−ligand coordination, spontaneous reduction of Cu(II) to Cu(I) at a solid−liquid interface was observed−unlike in a liquid-phase reaction where no reduction of Cu(II) to Cu(I) was occurred. High-quality thin films of a new coordination network compound bearing a Fe(II)−CN−Cu(I) link were fabricated by IRR and employed for efficient electro-catalysis in the form of oxygen reduction reaction. Also, thermally activated reversible structural phase transition modulated the electron transport property in thin film. This work unveils the importance of chemical reactions at solid−liquid interfaces that can lead to the development of new functional thin film materials.

Achieving current rectification ratios ≥ 105 across thin films of coordination polymer

“…2d). 16,39 The bonding motif of TCNQ was investigated by Raman spectroscopy, and upon comparing the Raman spectra of the pristine and doped thin lm, a signicant red-shi from $1455 cm À1 to $1374 cm À1 (D n $ 80 cm À1 ) for the C]C wing stretching mode was observed which suggested charge transfer between the Cu-BTEC framework and TCNQ amounting to $1.3e charge for the TCNQ moiety ( Fig. S5 †).…”

Elucidation of the Structure of a Thiol Functionalized Cu-tmpa Complex Anchored to Gold via a Self-Assembled Monolayer

“…Formation of a stable Cu I species attached to a gold surface via a SAM has recently been observed by Ballav et al as well, albeit under different conditions. 59 The Cu I species was attached to a carboxylic acid functionalized gold thiolate alkyl chain cross-linked via bridging ferrocyanides. In the Cu 2p 3/2 region of the XPS spectrum of the stabilized Cu I species, only one signal with a BE of 932.0 eV was observed without the presence of any satellite features.…”

Perspective on the Interfacial Reduction Reaction

“…Thus, our combined XPS, Raman, and UV–vis spectroscopic data conclusively supported the spontaneous reduction of Cu­(II) to Cu­(I) at the solid–liquid interface. Notably, in the liquid phase, (i) no reduction of Cu­(II) to Cu­(I) took place upon mixing Cu­(OAc) 2 and K 4 [Fe­(CN) 6 ] solutions; instead, the Cu-HCF with Cu­(II)-CN-Fe­(II) coordination link was isolated; and (ii) the CP compound bearing a fully reduced Cu­(I)-CN-Fe­(II) link could not be isolated even upon mixing the solution of CuI and K 4 [Fe­(CN) 6 ], in which the gradual conversion to Cu-HCF with the Cu­(II)-CN-Fe­(II) coordination link took place …”

“…So far, the reduction of metal ions has not been observed in such LbL growth of CPs at the solid–liquid interface. Recently, we have discovered the spontaneous chemical reduction of the metal ion at the solid–liquid interface while growing thin films of CPs on functionalized substrates. , In this invited feature article, we are going to highlight the fundamental understanding and importance of such an interfacial reduction reaction (IRR), specifically, of Cu­(II) to Cu­(I).…”