Supported atomic metal sites have discrete molecular orbitals. Precise control over the energies of these sites is key to achieving novel reaction pathways with superior selectivity. Here, we achieve selective oxygen (O₂) activation by utilising a framework of cerium (Ce) cations to reduce the energy of 3d orbitals of isolated copper (Cu) sites. Operando X-ray absorption spectroscopy, electron paramagnetic resonance and density-functional theory simulations are used to demonstrate that a [Cu(I)O₂]³⁻ site selectively adsorbs molecular O₂, forming a rarely reported electrophilic η²-O₂ species at 298 K. Assisted by neighbouring Ce(III) cations, η²-O₂ is finally reduced to two O²⁻, that create two Cu–O–Ce oxo-bridges at 453 K. The isolated Cu(I)/(II) sites are ten times more active in CO oxidation than CuO clusters, showing a turnover frequency of 0.028 ± 0.003 s⁻¹ at 373 K and 0.01 bar P_CO. The unique electronic structure of [Cu(I)O₂]³⁻ site suggests its potential in selective oxidation.

The synthesis of new types of mono- and polynuclear ruthenium nitrosyl complexes is driving progress in the field of NO generation for a variety of applications. Light-induced Ru-NO bond dissociation in solution may involve transient linkage isomers MS1 (Ru-ON) and MS2 (Ru-η²-NO), which can be detected spectroscopically and analyzed computationally. The investigation of photoisomerization processes in the solid state may be useful for potential application of such complexes for data storage, photochromic or photomagnetic materials or even non-linear optics. Herein we describe the major developments in the synthesis of ruthenium nitrosyl complexes, their photoinduced linkage isomerization (PLI) processes, their NO release both in the solid state and in solution, and their application as potential anticancer drugs. Illustrative examples of such innovations made mainly in the last decade are provided.