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

The redox reaction of silver acetate with [Ni-6(CO)(12)](2-) (2) in acetonitrile has afforded in low yields (less than or equal to10%) a close-packed silver-nickel carbonyl clusters 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 Ag-16 kernel that is connected by direct Ag-Ni bonding with four tetrahedrally disposed equilateral triangular Ni-6(CO)(10) fragments. The particular close-packed condensation mode of each v(2) Ni-6 triangular layer to one of the four tetrahedrally oriented Ag-centered hexagonal Ag-7 layers of the Ag-16 kernel results in each of the four tetrahedrally-connected interior Ag atoms in the Ag16Ni24 core having a localized hep environment, Of the 10 carbonyl groups per v(2) Ni-6 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 Ni-3 edges, and the remaining one caps the inner triangle of the Ni-6 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.