A Re-examination of the Synthesis of Monolayer-Protected Co x(SCH2CH2Ph) m Nanoclusters: Unexpected Formation of a Thiolate-Protected Co(II) T3 Supertetrahedron

A Theoretical Benchmark of the Geometric and Optical Properties for 3d Transition Metal Nanoclusters via Density Functional Theory

Understanding structure-property relationships in atomically precise metal nanoclusters is vital in finding selective and tunable catalysts. In this study, density functional theory (DFT) was used to benchmark seven exchange correlation functionals at different basis sets for 17 atomically precise nanoclusters against experimentally determined geometries, band gaps, and optical gaps. The set contains both monometallic and bimetallic clusters that possess at least two types of 3d transition metals (specifically, Cu, Ni, Fe, or Co). The benchmark highlights that PBE0 is a good functional to use regardless of the basis set, and Minnesota functionals do well with respect to specific metals. Further, while long-range corrected functionals overestimate band and optical gaps, they model absorption features better than the other considered functionals. The study additionally looks at the photoinduced hydrogen evolution reaction (HER) and the CO2 reduction mechanism on nanoclusters reported from the literature.

Platonic and Archimedean solids in discrete metal-containing clusters

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

[Ni23Se12(PEt3)13] Revisited: Isolation and Characterization of [Ni23Se12Cl3(PEt3)10]

The reaction of [Ni(1,5-COD)₂] (1.0 equiv), PEt₃ (0.04 equiv), SePEt₃ (0.52 equiv), and [NiCl₂(PEt₃)₂] (0.07 equiv) in a mixture of toluene and THF results in the formation of [Ni₂₃Se₁₂Cl₃(PEt₃)₁₀] (1), which can be isolated in moderate yield after workup. Complex 1 was characterized by NMR spectroscopy, ESI-MS, and X-ray crystallography. This open-shell nanocluster features a central [Ni₁₃]⁷⁺ anticuboctahedral kernel, which is encapsulated by a [Ni₁₀(μ-Se)₉Cl₃]^- shell, along with ten PEt₃ ligands and three (μ₄-Se)^2- ligands. On the basis of our spectroscopic and crystallographic analysis, coupled with in situ spectroscopic monitoring, we believe that the previously reported nanocluster, [Ni₂₃Se₁₂(PEt₃)₁₃], is actually better formulated as [Ni₂₃Se₁₂Cl₃(PEt₃)₁₀].

Understanding the Early Stages of Nickel Sulfide Nanocluster Growth: Isolation of Ni3 , Ni4 , Ni5 , and Ni8 Intermediates

Addition of sub-stoichiometric quantities of PEt₃ and diphenyl disulfide to a solution of [Ni(1,5-cod)₂ ] generates a mixture of [Ni₃ (SPh)₄ (PEt₃ )₃ ] (1), unreacted [Ni(1,5-cod)₂ ], and [(1,5-cod)Ni(PEt₃ )₂ ], according to ¹ H and ³¹ P{¹ H} NMR spectroscopic monitoring of the in situ reaction mixture. On standing, complex 1 converts into [Ni₄ (S)(Ph)(SPh)₃ (PEt₃ )₃ ] (2), via formal addition of a "Ni(0)" equivalent, coupled with a CS oxidative addition step, which simultaneously generates the Ni-bound phenyl ligand and the μ₃ -sulfide ligand. Upon gentle heating, complex 2 converts into a mixture of [Ni₅ (S)₂ (SPh)₂ (PEt₃ )₅ ] (3) and [Ni₈ (S)₅ (PEt₃ )₇ ] (4), via further addition of "Ni(0)" equivalents, in combination with a series of C-S oxidative addition and CC reductive elimination steps, which serve to convert thiophenolate ligands into sulfide ligands and biphenyl. The presence of 1-4 in the reaction mixture is confirmed by their independent syntheses and subsequent spectroscopic characterization. Overall, this work provides an unprecedented level of detail of the early stages of Ni nanocluster growth and highlights the fundamental reaction steps (i.e., metal atom addition, CS oxidative addition, and CC reductive elimination) that are required to grow an individual cluster.

Tetrahedral μ4-chloride and in situ generated octahedral μ6-sulfide templating Co8 complexes with different distortions of the cube

Herein two unprecedented octanuclear Co8 clusters are presented, [Cl@Co8 (TEOA)4(CH3CN)Cl3] (1) and [S@Co8(DEOA)6(NCS)2] (2) (H3TEOA = triethanolamine, H2DEOA = diethanolamine), in which tetrahedral μ4-chloride and in situ generated octahedral μ6-sulfide are used as templates. In spite of them being derivatives of cubes, eight Co atoms in 1 consist of two co-centered tetrahedra of different sizes, whereas in 2 they appear as a rhombohedron formed via elongating a cube along the C3-axis direction. Strong intra-cluster antiferromagnetic interactions were found.

Case Studies in Nanocluster Synthesis and Characterization: Challenges and Opportunities

Atomically precise nanoclusters (APNCs) are an emerging area of nanoscience. Their monodispersity and well-defined arrangement of capping ligands facilitates the interrogation of their fundamental physical properties, allowing for the development of structure-function relationships, as well as their optimization for a variety of applications, including quantum computing, solid-state memory, catalysis, sensing, and imaging. However, APNCs present several unique synthetic and characterization challenges. For example, nanocluster syntheses are infamously low yielding and often generate complicated mixtures. This combination of factors makes nanocluster purification and characterization more difficult than that of typical inorganic or organometallic complexes. Yet, while this fact is undoubtedly true, the past lessons learned from the characterization of inorganic complexes are still useful today. In this Account, we discuss six case studies taken from the recent literature in an attempt to identify common challenges and pitfalls encountered in APNC synthesis and characterization. For example, we show that several reducing agents employed in APNC synthesis, including the commonly used reagent NaBH₄, do not always behave as anticipated. Indeed, we highlight one case where NaBH₄ reduces the ligand and not the metal center, and other cases where NaBH₄ acts as a Brønstead base instead of a reducing agent. In addition, we have identified several instances where the use of phase transfer agents, which were added to mediate APNC formation, played no role in the nanocluster synthesis, and likely made the isolation of pure material more difficult. We have also identified several cases of cluster misidentification driven by spurious or ambiguous characterization data, most commonly collected by mass spectrometry. To address these challenges, we propose that the nanocluster community adopt a standard protocol of characterization, similar to those used by the organometallic and coordination chemistry communities. This protocol requires that many complementary techniques be used in concert to confirm formulation, structure, and analytical purity of APNC samples. Two techniques that are underutilized in this regard are combustion analysis and NMR spectroscopy. NMR spectroscopy, in particular, can provide information on purity and formulation that are difficult to collect with any other technique. X-ray absorption spectroscopy is another powerful method of nanocluster characterization, especially in cases where single crystals for X-ray diffraction are not forthcoming. Chromatographic techniques can also be extremely valuable for assessing purity, but are rarely used during APNC characterization. Our goal with this Account is to begin a discussion with respect to the best protocols for nanocluster synthesis and characterization. We believe that embracing a standard characterization protocol would make APNC synthesis more reliable, thereby accelerating their integration into a variety of technologies.