User:KendahlWalz/Group 7 element

For the History Section:
While Johan Gottlieb Gahn is credited with the isolation of magnesium in 1774, Ignatius Kaim reported his isolation of manganese in his dissertation in 1771.

Ida Tacke, Otto Berg, and Walter Noddack are credited with the discovery of rhenium. It was the last naturally-occurring stable element to be discovered. Ida Tacke and Walter Noddack initially isolated it from gadolinite ore.

For Occurrence Section:
Manganese is the most common element in Group 7 with the fifth largest abundance in the Earth's crust of any metal. It is most commonly found as manganese dioxide or manganese carbonate. While rhenium is naturally occurring, it is one of the rarest metals with approximately 0.001 parts per million of rhenium in the Earth's crust.

For the Applications Section:
The facial isomer of both rhenium and manganese 2,2'-bipyridyl carbonyl halide complexes have been extensively researched as catalysts for electrochemical carbon dioxide reduction due to their high selectivity and stability. They are commonly abbreviated as M(R-bpy)(CO)3X where M = Mn, Re; R-bpy = 4,4'-disubstituted 2,2'-bipyridine; and X = Cl, Br.

The catalytic activity of Re(bpy)(CO)3Cl for carbon dioxide reduction was first studied by Lehn et al. and Meyer et al. in 1984 and 1985, respectively. Re(R-bpy)(CO)3X complexes exclusively produce CO from CO2 reduction with Faradaic efficiencies of close to 100% even in solutions with high concentrations of water or Brønsted acids.

The catalytic mechanism of Re(R-bpy)(CO)3X involves reduction of the complex twice and loss of the X ligand to generate a five-coordinate active species, which binds CO2. These complexes will reduce CO2 both with and without an additional acid present; however, the presence of an acid increases catalytic activity. The high selectivity of these complexes to CO2 reduction over the competing hydrogen evolution reaction has been shown by density functional theory studies to be related to the faster kinetics of CO2 binding compared to H+ binding.

The rarity of rhenium has shifted research toward the manganese version of these catalysts as a more sustainable alternative. The first reports of catalytic activity of Mn(R-bpy)(CO)3Br towards CO2 reduction came from Chardon-Noblat and coworkers in 2011. Compared to Re analogs, Mn(R-bpy)(CO)3Br shows catalytic activity at lower overpotentials.

The catalytic mechanism for Mn(R-bpy)(CO)3X is complex and depends on the steric profile of the bipyridine ligand. When R is not bulky, the catalyst dimerizes to form [Mn(R-bpy)(CO)3]2 before forming the active species. When R is bulky, however, the complex forms the active species without dimerizing, reducing the overpotential of CO2 reduction by 200-300 mV. Unlike Re(R-bpy)(CO)3X, Mn(R-bpy)(CO)3X only reduces CO2 in the presence of an acid.