Reaction of [Ni(1,5-cod)₂] (30 equiv.) with PEt₃ (46 equiv.) and S₈ (1.9 equiv.) in toluene, followed by heating at 115 °C for 16 h, results in the formation of the atomically precise nanocluster (APNC), [Ni₃₀S₁₆(PEt₃)₁₁] (1), in 14% isolated yield. Complex 1 represents the largest open-shell Ni APNC yet isolated. In the solid state, 1 features a compact "metal-like" core indicative of a high degree of Ni-Ni bonding. Additionally, SQUID magnetometry suggests that 1 possesses a manifold of closely-spaced electronic states near the HOMO-LUMO gap. In situ monitoring by ESI-MS and ³¹P{¹H} NMR spectroscopy reveal that 1 forms via the intermediacy of smaller APNCs, including [Ni₈S₅(PEt₃)₇] and [Ni₂₆S₁₄(PEt₃)₁₀] (2). The latter APNC was also characterized by X-ray crystallography and features a nearly identical core structure to that found in 1. This work demonstrates that large APNCs with a high degree of metal-metal bonding are isolable for nickel, and not just the noble metals.

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].

Reaction of FeBr₂ with Li(N═C^tBu₂) (0.5 equiv) and Zn⁰ (2 equiv) results in the formation of the formally mixed-valent cluster [Fe₄Br₂(N═C^tBu₂)₄] (1) in moderate yield. The subsequent reaction of 1 with Na(N═C^tBu₂) results in formation of [Fe₄Br(N═C^tBu₂)₅] (2), also in moderate yield. Both 1 and 2 were characterized by zero-field ⁵⁷Fe Mössbauer spectroscopy, X-ray crystallography, and superconducting quantum interference device magnetometry. Their tetrahedral [Fe₄]⁶⁺ cores feature short Fe-Fe interactions (ca. 2.50 Å). Additionally, both 1 and 2 display S = 7 ground states at room temperature and slow magnetic relaxation with zero-field relaxation barriers of U_eff = 14.7(4) and 15.6(7) cm^-1, respectively. Moreover, AC magnetic susceptibility measurements were well modeled by assuming an Orbach relaxation process.

Reaction of FeBr₂ with 1.5 equiv. of LiN[double bond, length as m-dash]CPh₂ and 2 equiv. of Zn, in THF, results in the formation of the tetrametallic iron ketimide cluster [Fe₄(N[double bond, length as m-dash]CPh₂)₆] (1) in moderate yield. Formally, two Fe centers in 1 are Fe(i) and two are Fe(ii); however, Mössbauer spectroscopy and SQUID magnetometry suggests that the [Fe₄]⁶⁺ core of 1 exhibits complete valence electron delocalization, with a thermally-persistent spin ground state of S = 7. AC and DC SQUID magnetometry reveals the presence of slow magnetic relaxation in 1, indicative of single-molecule magnetic (SMM) behaviour with a relaxation barrier of U _eff = 29 cm^-1. Remarkably, very little quantum tunnelling or Raman relaxation is observed down to 1.8 K, which leads to an open hysteresis loop and long relaxation times (up to 34 s at 1.8 K and zero field and 440 s at 1.67 kOe). These results suggest that transition metal ketimide clusters represent a promising avenue to create long-lifetime single molecule magnets.