Energy production and consumption without the use of fossil fuels are amongst the biggest challenges currently facing humankind and the scientific community. Huge efforts have been invested in creating technologies that enable closed carbon or carbon neutral fuel cycles, limiting CO₂ emissions into the atmosphere. Formic acid/formate (FA) has attracted intense interest as a liquid fuel over the last half century, giving rise to a plethora of studies on catalysts for its efficient electrocatalytic oxidation for usage in fuel cells. However, new catalysts and catalytic systems are often difficult to compare because of the variability in conditions and catalyst parameters examined. In this review, we discuss the extensive literature on FA electrooxidation using platinum, palladium and non-platinum group metal-based catalysts, the conditions typically employed in formate electrooxidation and the main electrochemical parameters for the comparison of anodic electrocatalysts to be applied in a FA fuel cell. We focused on the electrocatalytic performance in terms of onset potential and peak current density obtained during cyclic voltammetry measurements and on catalyst stability. Moreover, we handpicked a list of the most relevant examples that can be used for benchmarking and referencing future developments in the field.

Here we present the synthesis, structure and magnetic properties of complexes of general formula (Mn)(Me₂NH₂)₄][Mn₃(μ-L)₆(H₂O)₆] and (Me₂NH₂)₆[M₃(μ-L)₆(H₂O)₆] (M = Co^II, Ni^II and Cu^II); L⁻² = 4-(1,2,4-triazol-4-yl) ethanedisulfonate). The trinuclear polyanions were isolated as dimethylammonium salts, and their crystal structures determined by single crystal and powder X-ray diffraction data. The polyanionic part of these salts have the same molecular structure, which consists of a linear array of metal(II) ions linked by triple N1-N2-triazole bridges. In turn, the composition and crystal packing of the Mn^II salt differs from the rest of the complexes (with six dimethyl ammonia as countercations) in containing one Mn⁺² and four dimethyl ammonia as countercations. Magnetic data indicate dominant intramolecular antiferromagnetic interactions stabilizing a paramagnetic ground state. Susceptibility data have been successfully modeled with a simple isotropic Hamiltonian for a centrosymmetric linear trimer, H = −2J (S₁S₂ + S₂S₃) with super-exchange parameters J = −0.4 K for Mn^II, −7.5 K for Ni^II and −45 K for Cu^II complex. The magnetic properties of these complexes and their easy processing opens unique possibilities for their incorporation as magnetic molecular probes into such hybrid materials as magnetic/conducting multifunctional materials or as dopant for organic conducting polymers.

A series of new Ru^II complexes has been synthesised, with different azo ligands as additional chromophore. The dyes are all intensely colored due to MLCT and ILCT transitions in the visible region. The photophysical study of the dyes, carried out by UV/Vis absorption and emission spectroscopy, showed unusual features such as intense solvatochromism and solvent‐dependent extinction coefficients. The energies of these excited states have been tuned by changing the electron density across the series of azo ligands, and this results in different contributions from each charge transfer process for the different complexes and consequently, different emission behavior. The detailed behaviour of these dyes was further studied and interpreted through electrochemical, structural and computational techniques. The dyes do not work well as sensitisers for DSSCs and this is investigated by emission spectroscopy on TiO₂ and ZrO₂ films, suggesting poor charge injection to TiO₂.

The Front Cover shows the molecular structure of an iron(II)‐triazole trimer that undergoes a single‐crystal to single‐crystal transformation following its spin transition between low spin (LS) and high spin (HS) upon immersion in different solvents. Magnetic and spectroscopic changes are represented here as almond tree branches in bloom. The reversible structural changes responsible for this solvent‐responsive behavior in the solid state were identified by comparison of the crystal structure after immersion in acetonitrile or in toluene. Image credits: Irene Sánchez‐Molina, David Nieto and Andrea Moneo. More information can be found in the Full Paper by I. Sánchez‐Molina, J. R. Galán‐Mascarós and co‐workers.