The synthesis and characterization of the platinum carbonyl dianions [Pt(CO)] (n = 1–10), also known as Chini clusters or more correctly Chini-Longoni clusters, are recognized by the scientific community as the most spectacular result of Chini's work.
Chini clusters follow the general formula of [Pt(CO)], 1  subunits. Although these clusters were first reported in 1969 by Chatt and Booth, their structure were not established until Chini and Longoni's work in 1976.
Chini clusters are based on a planar triangular building block that can be condensed as multiple units forming chains usually anywhere from two to ten units long. The chains are formed by stacking of the planar units, extending through platinum to platinum bonds forming trigonal prismatic clusters. Within a triangular unit, the platinum–platinum bond lengths are 2.65 Å and between units the Pt–Pt bond lengths are 3.05 Å. Cluster structure is easily disrupted by deposition onto surfaces such as carbon or silicon, where the chains are broken, but the triangular subunits remain intact. The tetramer [Pt(CO)] is the most common member of this series of clusters. These clusters undergo reversible redox. They catalyze the hydrogenation of alkenes, ketones, and aldehydes.
Chini clusters can also be converted heterometal clusters and catalyze pH driven redox reactions and transport. First, the Chini clusters are the source of platinum atoms for the mixed metal cluster synthesis. For instance, the reaction [Pt(CO)] with [Ag(PPh)] produces heterometal cluster [PtAg(CO)(PPh)]. Second, the Chini clusters with redox properties act as a catalyst that helps transport sodium ions and electrons in the same direction across a liquid membrane, driven by pH-gradient. The [Pt(CO)] platinum clusters, where n=4 – 6, are reduced by OH:
:(n-1)[Pt(CO)] + 2OH ↔ n[Pt(CO)] + HO + 1/2O