Superatomic states in nickel clusters: Revising the prospects for transition metal based superatoms

[Ni8(CNtBu)12][Cl]: A nickel isocyanide nanocluster with a folded nanosheet structure

The reaction of 1.75 equiv of ^tBuNC with Ni(1,5-COD)₂, followed by crystallization from benzene/pentane, resulted in the isolation of [Ni₈(CN^tBu)₁₂][Cl] (2) in low yields. Similarly, the reaction of Ni(1,5-COD)₂ with 0.6 equiv of [Ni(CN^tBu)₄], followed by addition of 0.08 equiv of I₂, resulted in the formation of [Ni₈(CN^tBu)₁₂][I] (3), which could be isolated in 52% yield after work-up. Both 2 and 3 adopt folded nanosheet structures in the solid state, characterized by two symmetry-related planar Ni₄ arrays, six terminally bound ^tBuNC ligands, and six ^tBuNC ligands that adopt bridging coordination modes. The metrical parameters of the six bridging ^tBuNC ligands suggest that they have been reduced to their [^tBuNC]^2- form. In contrast to the nanosheet structures observed for 2 and 3, gas phase Ni₈ is predicted to feature a compact bisdisphenoid ground state structure. The strikingly different structural outcomes reveal the profound structural changes that can occur upon addition of ligands to bare metal clusters. Ultimately, the characterization of 2 and 3 will enable more accurate structural predictions of ligand-protected nanoclusters in the future.

5-Fold symmetry in superatomic scandium clusters: exploiting favourable orbital overlap to sequester spin

The geometries and electronic structures of icosahedral A₁₃^C (A = Sc, Y; C = 0, ±1, ±2) clusters have been determined at a range of multiplicities at each cluster charge, using density functional theory methods. These clusters demonstrate a complex electronic structure which provides insight into the anomalously high magnetic moment of icosahedral group 3 clusters and further contextualises the role of transition metals and d-electrons within the superatomic model. Embedded deeply within the density of states for these clusters are typical superatom orbitals which are populated up to the 2S level. Above the 2S-state there are three states of apparent F symmetry, which are preferentially singly occupied, followed by an abundance of approximately degenerate P-, G-, D- and F-states at the Fermi energy, which are at most singly occupied. In spite of apparent angular symmetry and a nodal structure reminiscent of superatomic orbitals these states are actually formed from preferential overlap of the valence d-orbitals of the cluster atoms. This analysis was further contextualised through analysis of the Sc₁₉ cluster, which shows a similar construction of Kohn-Sham states, but with the breaking of 5-fold symmetry along one of its Cartesian axes. Finally, this work clearly demonstrates the ability of d-electrons to give rise to superatomic orbitals is not just constrained by atomic species but also by the local environment of the atoms.

On the influence of exact exchange on transition metal superatoms

The electronic structure of A7C (A = Hg, Pd, V, Cr, Mn, Fe, Ni, Cu; C = 0, ±1, ±2) clusters has been determined using density functional theory methods. The A7C (A = Hg, Pd, Cr, Cu; C = 0, ±1, ±2) clusters all conform to the existing superatomic model, with a sufficiently stabilised local structure to prevent perturbation upon the introduction of exact exchange to the exchange correlation functional. For the A7C (A = Mn, Fe, Ni; C = 0, ±1, ±2) clusters the incorporation of exact exchange separates the atomic s- and d-electrons, leading to a net increase in the number of superatomic electrons. Conversely the incorporation of exact exchange into the exchange correlation functional decreases the number of superatomic electrons for the V7C (C = 0, ±1, ±2) clusters, owing to the radial extension of the d-orbitals influencing their ability to contribute into superatomic shells.

On the involvement of d-electrons in superatomic shells: the group 3 and 4 transition metals

The geometries and electronic structures of small M₇^C (M = Sc, Y, La, Ti, Zr, Hf; C = 0, ±1, ±2) clusters have been calculated at a range of multiplicities at each cluster charge, using density functional theory methods. These clusters conform to the existing superatom model, with some contextual differences. There are a range of states which are populated by the outermost s and d-electrons of the constituent atoms, with an irregular Aufbau rule for the states formed from the atomic d-electrons. The states comprised of d-electrons present themselves as two states of P-symmetry and two states of F-symmetry, which are nearly degenerate, followed by states of D-symmetry, a shell ordering which arises due to the symmetry, and favourable overlap, of the contributing states. The effect of exact exchange in modulating the localisation of these states is also discussed. In addition, this study shows pseudo-superatomic states which arise due to the 5-fold symmetry of the clusters, materialising as either a ring or plane of electron density. In summary, these observations allow for an expansion of the role that early transition metals have within the existing superatom framework.

Account of chemical bonding and enhanced reactivity of vanadium-doped rhodium clusters toward C–H activation: a DFT investigation

The chemical bonding and enhanced reactivity of vanadium-doped rhodium clusters toward C–H activation were investigated using DFT.

Stability of small cationic platinum clusters

The relative stability of small cationic platinum clusters is investigated by photofragmentation experiments and density functional theory calculations.