Spin-catalysis phenomena

Abstract

DOn the grounds of results from quantum chemical calculations, we introduce spin-catalysis as a new concept, and classify different types of chemical reactions according to this concept. We propose a general definition of spin-catalysis as phenomena in which chemical reactions are promoted by substances which assist in overcoming spinprohibition or in which the activation barrier is lowered through spin uncoupling induced by a paramagnetic catalyst. A number of known phenomena fall into this definition and can be classified according to two main categories: (1) spin-orbit coupling induced and (2) paramagnetic-exchange induced spin-catalysis. Other types of spincatalysis are also discussed: (3) processes with participation of substances which assist in (a) photochemical and Cb) thermal or electrochemical generation of active particles by energy and-by electron transfer [radicals, diradicals, O,(' La,1, etc.], reacting further without spin-prohibition: (4) processes induced by an external magnetic field. Processes (3) and (4) are quite general and well known; their inclusion in the spin-catalysis classification does not introduce any new findings for the chemical kinetics, but the general features, which unite them with the important catalytic processes of the first two types, serve as a useful guide in catalysis theory. Few models of spin-catalytic processes have been simulated for the purpose of illuminating the principles of spin-catalysis; the cis-trans isomerization of ethylene catalyzed by molecular oxygen, the external heavy atom effect in ethylene photochemistry, and some others.

Molecular Propensity as a Driver for Explorative Reactivity Studies

“…Sometimes, the molecular system undergoes another spin inversion back to the original spin surface. Spin catalysis 24,25 is another concept to describe reactions involving more than one spin state. Both two-state reactivity and spin catalysis become relevant when spin states of different multiplicities have comparable energies.…”

Electrocatalytic oxygen evolution from water on a Mn(iii–v) dimer model catalyst—A DFT perspective

“…The conservation of spin during internal redox steps is facilitated by the half-metallicity of the ferromagnetically coupled manganese ions provided by the double-exchange mechanism. 55,56 The spin conservation starting with the m-peroxo moiety and, in particular the change of spin state from a doublet superoxo ligand to a triplet oxygen, emphasizes the role of spin catalysis 63 as facilitated by the unpaired electrons on manganese.…”

Hydroxide oxidation and peroxide formation at embedded binuclear transition metal sites; TM = Cr, Mn, Fe, Co

“…3 The efficiency of a water oxidation catalyst is, finally, also controlled by the ability to release molecular oxygen, which in turn requires spin catalysis. 4 For this purpose, transition metals are natural candidates. Indeed, the performance of several transition metal based compounds in photo-and electrocatalytic OER applications has been reported.…”