Polymerization Isomerism in Co-M (M = Cu, Ag, Au) Carbonyl Clusters: Synthesis, Structures and Computational Investigation

The reaction of [Co(CO)(4)](-) (1) with M(I) compounds (M = Cu, Ag, Au) was reinvestigated unraveling an unprecedented case of polymerization isomerism. Thus, as previously reported, the trinuclear clusters [M{Co(CO)(4)}(2)](-) (M = Cu, 2; Ag, 3; Au, 4) were obtained by reacting 1 with M(I) in a 2:1 molar ratio. Their molecular structures were corroborated by single-crystal X-ray diffraction (SC-XRD) on isomorphous [NEt4][M{Co(CO)(4)}(2)] salts. [NEt4](3)represented the first structural characterization of 3. More interestingly, changing the crystallization conditions of solutions of 3, the hexanuclear cluster [Ag-2{Co(CO)(4)}(4)](2-) (5) was obtained in the solid state instead of 3. Its molecular structure was determined by SC-XRD as Na-2(5)center dot C4H6O2, [PPN](2)(5)center dot C5H12 (PPN = N(PPh3)(2)](+)), [NBu4](2)(5) and [NMe4](2)(5) salts. 5 may be viewed as a dimer of 3 and, thus, it represents a rare case of polymerization isomerism (that is, two compounds having the same elemental composition but different molecular weights) in cluster chemistry. The phenomenon was further studied in solution by IR and ESI-MS measurements and theoretically investigated by computational methods. Both experimental evidence and density functional theory (DFT) calculations clearly pointed out that the dimerization process occurs in the solid state only in the case of Ag, whereas Cu and Au related species exist only as monomers.

Automated summary

The study revealed a case of polymerization isomerism in cluster chemistry when [Co(CO)(4)](-) reacts with M(I) compounds (M = Cu, Ag, Au), resulting in the formation of trinuclear clusters with unique molecular structures. This phenomenon was further explored both experimentally and theoretically, demonstrating that dimerization occurs in the solid state only with Ag species, while Cu and Au species exist as monomers.