Probing the geometric, optical, and magnetic properties of 3d transition-metal endohedral Ge12M (M=Sc–Ni) clusters

Luminescence properties of endohedrally doped group-IV clusters

Endohedrally doped clusters form a large category of cage clusters, with unique structures, diverse elemental compositions, and highly tunable electronic structures and physisochemical properties. They have been widely achieved in laboratory and may serve as functional building blocks for assembling new supermolecular structures and devices. In this paper, for the first time, we disclosed the luminescence properties of endohedrally doped group-IV clusters by time-dependent density functional theory calculations. A total of 64 cage clusters have been explored in terms of stability, emission wavelength, and the energy difference between the first excited singlet and triplet states. The key geometric and electronic factors governing the photophysical properties of these cage clusters were unveiled, to provide crucial insights for crafting atomically precise nanoclusters for optical and optoelectronic applications.

Hexagonal Bipyramidal Mn3Ge5 Cluster and Its One-Dimensional Ferrimagnetic Sandwich Nanowire: Mn3Ge3 Rings as Structural Motifs

Bipyramidal structures featuring planar rings serve as potential building blocks for one-dimensional (1D) nanostructures. Pure Ge atoms typically prefer to form three-dimensional rather than planar structures. Although a few-metal-doped bipyramids with pure Ge planar rings are predicted for constructing Ge-based 1D nanostructures, there is limited knowledge about those with both Ge and doped atoms on the same planar rings. Here, we report a hexagonal bipyramidal Mn3Ge5 cluster containing a Mn3Ge3 six-membered ring with the potential to construct a 1D germanium-based nanostructure. We investigated the structures and properties of Mn3Ge5-/0 using anion photoelectron spectroscopy and theoretical calculations. Mn3Ge5- has a C3v symmetric distorted hexagonal bipyramidal structure, while Mn3Ge5 has a C2v symmetric hexagonal bipyramidal structure. Chemical bonding analyses show that Mn3Ge5- could be considered as a [Mn3]V[Ge5]6- complex. First-principles calculations indicate that Mn3Ge5 may be used to construct a 1D ferrimagnetic [Mn3Ge5]∞ nanostructure.

Investigation of the Structures and Chemical Bonding of Mn2Ge6- and Mn2Ge7- Clusters via Anion Photoelectron Spectroscopy and Theoretical Calculations

We present joint anion photoelectron spectroscopy and theoretical studies for Mn₂Ge₆^- and Mn₂Ge₇^-. Experimental results show that Mn₂Ge₆^- and Mn₂Ge₇^- have vertical electron detachment energies of 2.58 ± 0.08 and 2.88 ± 0.08 eV, respectively. Both Mn₂Ge₆^- and Mn₂Ge₆ have C_s symmetric structures with a Mn atom attached to a pentagonal bipyramid MnGe₆. Both Mn₂Ge₇^- and Mn₂Ge₇ have C_2v symmetric structures, which can be considered as two Mn₂Ge₄ tetragonal bipyramids sharing a MnGeMn face. According to chemical bonding analyses, Mn₂Ge₆ could be considered as a (Mn^II)(MnGe₆^2-) complex. Theoretical calculations predict that the extension of Mn₂Ge₇ to Mn_2nGe_4n+3 may be able to produce a new type of Mn-doped germanium nanostructure.

Investigation of highly ferromagnetic Mn2Ge4 and Mn2Ge5 clusters via photoelectron spectroscopy and theoretical calculations

We investigate the structures and properties of Mn₂Ge₄^-/0 and Mn₂Ge₅^-/0 by anion photoelectron spectroscopy and theoretical calculations. The vertical detachment energies (VDEs) of Mn₂Ge₄^- and Mn₂Ge₅^- are measured to be 2.69 eV and 2.49 eV, respectively. It is found that neutral Mn₂Ge₄ has an approximate quadrilateral bipyramidal structure with C_2v symmetry and ¹¹B₂ electronic state. Neutral Mn₂Ge₅ has a pentagonal bipyramidal structure with C_2v symmetry and ¹¹B₂ electronic state. The 4s-based molecular orbitals of the Mn atoms participate in the chemical bonding with the Ge₄ and Ge₅ fragments in Mn₂Ge₄ and Mn₂Ge₅. In Mn₂Ge₄, the two Mn atoms interact with the Ge₄ moiety via four GeGeMn 3c-2e σ bonds. In Mn₂Ge₅, the two Mn atoms interact with the Ge₅ moiety via one MnGeMn 3c-2e σ bond and four GeMnGe 3c-2e σ bonds. The analysis of magnetic properties reveals that both Mn₂Ge₄ and Mn₂Ge₅ exhibit highly ferromagnetic characteristics with a magnetic moment of 10 μ_B which mainly originated from the Mn atoms. These double Mn atom doped germanium clusters may provide new opportunities to design novel spintronic devices featuring high magnetic moments.

Quantum-Chemical Design of Molecular Structures of Tetra-, Penta- and Hexanuclear Metal Clusters Containing Aluminum and 3d-Element Atoms

Various data on the structural and thermodynamic characteristics of polynuclear metal clusters containing atoms of aluminum and various d-elements with the general formula Al_nM_m where (n + m) is 4, 5, or 6, and which can be precursors for the formation of nanoparticles of elemental metals or intermetallic compounds, have been systematized and discussed. It has been noted that each of these metal clusters in principle is able to exist in very diverse structural isomers, differing significantly among themselves in terms of the total energy and spin multiplicity of the ground state, the number of which is determined by both the specific values of n and m, and the nature of d-elements in their compositions. The presence of very complex dynamics with respect to the changes of the individual thermodynamic characteristics of the metal clusters under consideration as well as the thermodynamic parameters of the reactions of their formation, depending on the nature of the d-element, were also ascertained. In the main, the given review is devoted to the authors’ works published over the last 10 years. Bibliography – 96 references.

Structural evolution and magnetic properties of anionic clusters Cr2Ge n (n = 3-14): photoelectron spectroscopy and density functional theory computation

The structural, electronic and magnetic properties of dual Cr atoms doped germanium anionic clusters, [Formula: see text] (n  =  3-14), have been investigated by using photoelectron spectroscopy in combination with density-functional theory calculations. The low-lying structures of [Formula: see text] are determined by DFT based genetic algorithm optimization. For [Formula: see text] with n  ⩽  8, the structures are bipyramid-based geometries, while [Formula: see text] cluster has an opening cage-like structure, and the half-encapsulated structure is gradually covered by the additional Ge atoms to form closed-cage configuration with one Cr atom interior for n  =  10 to 14. Meanwhile, the two Cr atoms in [Formula: see text] clusters tend to form a Cr-Cr bond rather than be separated. Interestingly, the magnetic moment of all the anionic clusters considered is 1 μ _B. Almost all clusters exhibit antiferromagnetic Cr-Cr coupling, except for two clusters, [Formula: see text] and [Formula: see text]. To our knowledge, the [Formula: see text] cluster is the first kind of transition-metal doped semiconductor clusters that exhibit relatively stable antiferromagnetism within a wide size range. The experimental/theoretical results suggest high potential to modify the magnetic behavior of semiconductor clusters through introducing different transition-metal dopant atoms.

The Electronic Structures of CoGe n-/0 ( n = 1-3) Clusters from Multiconfigurational CASSCF/CASPT2 and RASSCF/RASPT2 Calculations

Density functional theory and multiconfigurational CASPT2 and RASPT2 methods are employed to investigate the low-lying states of CoGe _n^-/0 ( n = 1-3) clusters. With the RASPT2 approach, the active space is extended to 14 orbitals for CoGe^-/0, 17 orbitals for CoGe₂^-/0, and 20 orbitals for CoGe₃^-/0. These active spaces include the 3d, 4s, and 4d of Co and 4p of Ge. The 4d of Co is incorporated into these active spaces in order to account for the important double-shell effect of Co. The structural parameters, vibrational frequencies, and relative energies of the low-lying states of CoGe _n^-/0 ( n = 1-3) are reported. The ground states of CoGe _n^- ( n = 1-3) are computed to be ³Φ of linear CoGe^-, ³B₁ of cyclic CoGe₂^-, and ³B₁ of cyclic CoGe₃^- isomer. The ground states of the neutral clusters are calculated to be ²Δ of linear CoGe, ⁴B₁ of cyclic CoGe₂, and ⁴A″ of tetrahedral CoGe₃ isomer. The calculated adiabatic and vertical detachment energies of the anionic ground states are in agreement with the experimental values as observed in the 266 nm anion photoelectron spectra.

Structural and magnetic properties of FeGen-/0 (n = 3-12) clusters: Mass-selected anion photoelectron spectroscopy and density functional theory calculations

The structural, electronic, and magnetic properties of FeGe_n^-/0 (n = 3-12) clusters were investigated by using anion photoelectron spectroscopy in combination with density functional theory calculations. For both anionic and neutral FeGe_n (n = 3-12) clusters with n ≤ 7, the dominant structures are exohedral. The FeGe₈^-/0 clusters have half-encapsulated boat-shaped structures, and the opening of the boat-shaped structure is gradually covered by the additional Ge atoms to form Ge_n cage from n = 9 to 11. The structures of FeGe₁₀^-/0 can be viewed as two Ge atoms symmetrically capping the opening of the boat-shaped structure of FeGe₈, and those of FeGe₁₂^-/0 are distorted hexagonal prisms with the Fe atom at the center. Natural population analysis shows that there is an electron transfer from the Ge atoms to the Fe atom at n = 8-12. The total magnetic moment of FeGe_n^-/0 and local magnetic moment of the Fe atom have not been quenched.

Growth Behavior and Electronic Structure of Noble Metal-Doped Germanium Clusters

Structures, energetics, and electronic properties of noble metal-doped germanium (MGe_n with M = Cu, Ag, Au; n = 1-19) clusters are systematically investigated by using the density functional theory (DFT) approach. The endohedral structures in which the metal atom is encapsulated inside of a germanium cage appear at n = 10 when the dopant is Cu and n = 12 for M = Ag and Au. While Cu doping enhances the stability of the corresponding germanium frame, the binding energies of AgGe_n and AuGe_n are always lower than those of pure germanium clusters. Our results highlight the great stability of the CuGe₁₀ cluster in a D_4d structure and, to a lesser extent, that of AgGe₁₅ and AuGe₁₅, which exhibits a hollow cage-like geometry. The sphere-type geometries obtained for n = 10-15 present a peculiar electronic structure in which the valence electrons of the noble metal and Ge atoms are delocalized and exhibit a shell structure associated with the quasi-spherical geometry. It is found that the coinage metal is able to give both s- and d-type electrons to be reorganized together with the valence electrons of Ge atoms through a pooling of electrons. The cluster size dependence of the stability, the frontier orbital energy gap, the vertical ionization potentials, and electron affinities are given.

On the structural landscape in endohedral silicon and germanium clusters, M@Si12 and M@Ge12

Amongst the endohedral clusters of the tetrel elements, M@En, the 12-vertex species are unique in that three completely different geometries, the icosahedron (Ih, [Ni@Pb12](2-)), the hexagonal prism (HP, Cr@Si12) and the bicapped pentagonal prism (BPP, [Ru@Ge12](3-)) have been identified in stable molecules. We explore here the origins of this structural diversity by comparing stability patterns across isovalent and isoelectronic series, M@Si12, M@Ge12 and [M@Ge12](3-). The BPP structure dominates the structural landscape for high valence electron counts (57-60) while the HP has a rather narrower window of stability around the 54-56 count. Moreover the preference for an HP structure is unique to silicon: in no case is a rigorously D6h-symmetric structure the global minimum for M@Ge12. Distortions from the high-symmetry limits, where present, can be traced to degeneracies or near-degeneracies in the frontier orbital domains. In all cases the structure adopted is that which maximizes the delocalization of electron density between the metal and the cluster cage, such that both components attain stable electronic configurations.

Structural and magnetic properties of CoGe(n)- (n=2-11) clusters: photoelectron spectroscopy and density functional calculations

A series of cobalt-doped germanium clusters, CoGe(n)(-/0) (n=2-11), are investigated by using anion photoelectron spectroscopy combined with density functional theory calculations. For both anionic and neutral CoGe(n) (n=2-11) clusters, the critical size of the transition from exo- to endohedral structures is n=9. Natural population analysis shows that there is electron transfer from the Ge(n) framework to the Co atom at n=7-11 for both anionic and neutral CoGe(n) clusters. The magnetic moments of the anionic and neutral CoGe(n) clusters decrease to the lowest values at n=10 and 11. The transfer of electrons from the Gen framework to the Co atom and the minimization of the magnetic moments are related to the evolution of CoGe(n) structures from exo- to endohedral.

Structural and bonding properties of small TiGen− (n = 2–6) clusters: photoelectron spectroscopy and density functional calculations

The structures of small TiGe_n⁻ clusters can be considered as Ti-substituted Ge_n+1 or Ti-capped Ge_n clusters.