A route to small clusters: a twisted half-hexagram-shaped M4(OH)4 cluster and its capacity for hosting closed-shell metals.

By combining different oxidation states, coordination indices and bridging systems, it has been possible to obtain the structurally novel M4(OH)4 cluster core (M = transition metal) found in the organometallic compound (NBu4)2[PtIVPt(C6Cl5)8(μ2-OH)2(μ3-OH)2] (1). The cluster is formed by two (μ3-OH) and two (μ2-OH) units that bond platinum atoms in different oxidation states. The cluster core geometry can best be described as a half-hexagram. Compound 1 is an excellent precursor for preparing heterometallic clusters since it can host d10 or s2 Lewis-acid metal centers through Pt→M dative bonds, as demonstrated by its reaction with Ag(i) to produce the heterometallic [Ag2PtIVPt(C6Cl5)8(μ2-OH)2(μ3-OH)2] (2), which has four unbridged Pt-Ag bonds.