Multi‐metal oxide (MMO) materials have significant potential to facilitate various demanding reactions by providing additional degrees of freedom in catalyst design. However, a fundamental understanding of the (electro)catalytic activity of MMOs is limited because of the intrinsic complexity of their multi‐element nature. Additional complexities arise when MMO catalysts have crystalline structures with two different metal site occupancies, such as the spinel structure, which makes it more challenging to investigate the origin of the (electro)catalytic activity of MMOs. Here, uniform‐sized multi‐metal spinel oxide nanoparticles composed of Mn, Co, and Fe as model MMO electrocatalysts are synthesized and the contributions of each element to the structural flexibility of the spinel oxides are systematically studied, which boosts the electrocatalytic oxygen reduction reaction (ORR) activity. Detailed crystal and electronic structure characterizations combined with electrochemical and computational studies reveal that the incorporation of Co not only increases the preferential octahedral site occupancy, but also modifies the electronic state of the ORR‐active Mn site to enhance the intrinsic ORR activity. As a result, nanoparticles of the optimized catalyst, Co0.25Mn0.75Fe2.0‐MMO, exhibit a half‐wave potential of 0.904 V (versus RHE) and mass activity of 46.9 A goxide−1 (at 0.9 V versus RHE) with promising stability.

Density Functional Theory (DFT) calculations coupled with several exchange-correlation functionals were used for the prediction of Mossbauer hyperfine parameters of 36 bisaxially coordinated iron(II) phthalocyanine complexes with the general formulas PcFeL 2 , PcFeL′L″, and [PcFeX 2 ] 2− , including four new compounds. Both gas-phase and PCM calculations using BPW91 and MN12L exchange-correlation functionals were found to accurately predict both Mossbauer quadrupole splittings and the correct trends in experimentally observed isomer shifts. In comparison, hybrid exchange-correlation functionals underestimated quadrupole splittings, while still accurately predicted isomer shifts. Out of ∼40 exchange-correlation functionals tested, only MN12L was found to correctly reproduce quadrupole splitting trends in the PcFeL 2 complexes coordinated with phosphorus-donor axial ligands (i.e., P(OnBu) 3 ≈ P(OEt) 3 < PMe 3 < P[(CH 2 O) 2 CH 2 ]-p-C 6 H 4 NO 2 < PEt 3 ≈ PnBu 3 ). Natural Bond Orbital (NBO) analysis was successfully used to explain the general trends in the observed quadrupole splitting for all compounds of interest. In particular, the general trends in the quadrupole splitting correlate well with the axial ligand dependent, NBO-predicted population of the 3d z2 orbital of the Fe ion and are reflective of the hypothesis proposed by Ohya and co-workers (Inorg. Chem., 1984, 23, 1303 on the adaptability of the phthalocyanine's π-system toward Fe-L ax interactions. The first X-ray crystal structure of a PcFeL 2 complex with axial phosphine ligands is also reported.

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The synthesis, structures and electronic characterization of three strongly coloured, pseudo-octahedral Ni(ii) complexes supported by redox-active diarylamido ligands featuring benzannulated N-heterocyclic donor arms are reported.

We have synthesized three different shapes of $$\hbox{Co}_{3}\hbox{O}_{4}$$ Co 3 O 4 nanoparticles to investigate the relationships between the surface Co$$^{2+}$$ 2 + and Co$$^{3+}$$ 3 + bonding quantified by exploiting the known exposed surface planes, terminations, and coordiations of $$\hbox{Co}_{3}\hbox{O}_{4}$$ Co 3 O 4 nanoparticle spheres, cubes and plates. Subsequently this information is related to the unusual behaviour observed in the magnetism. The competition of exchange interactions at the surface provides the mechanism for different behaviours in the shapes. The cubes display weakened antiferromagnetic interactions in the form of a spin-flop that occurs at the surface, while the plates show distinct ferromagnetic behaviour due to the strong competition between the interactions. We elucidate the spin properties which are highly sensitive to bonding and crystal field environments. This work provides a new window into the mechanisms behind surface magnetism.

Graphene-based magnetic materials exhibit novel properties and promising applications in the development of next-generation spintronic devices. Modern synthesis techniques have paved the way to design precisely the local environments of metal atoms anchored onto a nitrogen-doped graphene matrix. Herein, it is demonstrated that grafting cobalt (Co) into the graphene lattice induces robust and stable room-temperature ferromagnetism. These comprehensive experiments and first-principles calculations unambiguously identify that the mechanism for this unusual ferromagnetism is π-d orbital hybridization between Co d xz and graphene p z orbitals. Here, it is found that the magnetic interactions of Co-carbon ions are mediated by the spinpolarized graphene p z orbitals, and room temperature ferromagnetism can be stabilized by electron doping. It is also found that the electronic structure near the Fermi level, which sets the nature of spin polarization of graphene p z bands, strongly depends on the local environment of the Co moiety. This is the crucial, previously missing, ingredient that enables control of the magnetism. Overall, these observations unambiguously reveal that engineering the atomic structure of metal-embedded graphene lattices through careful d to p orbital interactions opens a new window of opportunities for developing graphene-based spintronics devices.

Fe and Fe–O dispersed on nanoscale CeO supports are considered promising catalysts for oxidation and reduction catalysis and regarded as one of the better alternatives to precious metal catalysts for NO reduction. To understand the role of Fe ions, promoters, and factors that control the NO x reduction, we probed the local environments of Fe, Ce, and O using a range of spectroscopies. The order of Na promotion (sequential vs simultaneous) resulted in a significant difference in the catalytic activity by changing the local electronic structure around the Fe ions in reaction the conditions. The Ce M4,5- and O K-edge X-ray spectroscopy results suggest stabilization of the 4f, eg orbitals, where Fe and promotor ions are affecting the t2g orbitals. Optimizing this bonding environment around the Fe active species with a promoter ion enables tuning of the NO reduction activity.

The elusive PcFe(DABCO)2 (Pc = phthalocyaninato(2-) ligand; DABCO = 1,4-diazabicyclo[2.2.2]octane) complex was prepared and characterized by UV-Vis, MCD, 1H NMR, and Mössbauer spectroscopies. The X-ray crystal structure of this complex indicates the longest Fe-N(DABCO) bond distance among all known PcFeL2 complexes with nitrogen donors as the axial ligands. The target compound is only stable in the presence of large access of the axial ligand and rapidly converts into the (PcFe)2O [Formula: see text]-oxo dimer even at a modest temperature. The electronic structure of the PcFe(DABCO)2 complex was elucidated by DFT and TDDFT methods. The DFT calculations predicted a very small singlet-triplet gap in this compound. The femtosecond transient absorption spectroscopy is indicative of extremely fast ([Formula: see text]200 fs) deactivation of the first excited state in PcFe(DABCO)2 with a lack of formation of the long-lived low-energy triplet state.