First-known high-nuclearity silver–nickel carbonyl cluster: nanosized [Ag16Ni24(CO)40]4− possessing a new 40-atom cubic Td closed-packed metal-core geometry

Abstract

The redox reaction of silver acetate with [Ni₆(CO)₁₂]²⁻ (2) in acetonitrile has afforded in low yields (≤10%) a close-packed silver–nickel carbonyl cluster: namely, the pseudo-T_d [Ag₁₆Ni₂₄(CO)₄₀]⁴⁻ tetraanion (1) as the [PPh₃Me]⁺ salt. This well-defined, dark brown bimetallic cluster, which is air-unstable and light-sensitive, is the first example of a microscopic ccp chunk of quasi-silver metal that is stabilized by close-packed carbonyl-ligated transition-metal layers. The overall 40-atom metal-core geometry, which corresponds to a heretofore unknown 36-atom T_d polyhedron encapsulating four interior atoms, may be described as a central ccp Ag₁₆ kernel that is connected by direct Ag–Ni bonding with four tetrahedrally disposed equilateral triangular Ni₆(CO)₁₀ fragments. The particular close-packed condensation mode of each ν₂ Ni₆ triangular layer to one of the four tetrahedrally oriented Ag-centered hexagonal Ag₇ layers of the Ag₁₆ kernel results in each of the four tetrahedrally-connected interior Ag atoms in the Ag₁₆Ni₂₄ core having a localized hcp environment. Of the 10 carbonyl groups per ν₂ Ni₆ equilateral triangle, three are each terminally coordinated to a corner Ni atom, six are each edge-connected to one of the two pairs of linked Ni atoms along the three Ni₃ edges, and the remaining one caps the inner triangle of the Ni₆ triangle. Both its structure and composition were unambiguously established via a single-crystal X-ray diffraction analysis with a SMART CCD area detector diffractometry system. The maximum metal-core diameter in 1 is ca. 0.98 nm (av.) along each of the four three-fold axes.