Square-metal faces, capping

Addition of either nucleophilic or electrophilic metallic species can result in the capping of triangular- or square-metal faces in carbonyl clusters. These redox reactions provide high yield syntheses of higher nuclearity clusters and somewhat resemble surface reconstruction on metals. With a few examples,... 

Carbonyls.—A new type of metal cluster system has been synthesized, Nij(CO)g-( X4-PPh)6, which can be considered to be a metallic analogue of cubane, CgHg there is a cube of Ni atoms with each square Ni4 face symmetrically capped by a PPh ligand. 

The trimeric structure of [Th(TPP)(0H)2]3-2H20 has been confirmed by Kadish et al. (1988). The six hydroxyl ligands in the molecular unit form a trigonal prism of which the triangular faces are capped by two water molecules and the rectangular faces are capped with three thorium atoms (fig. 2a). The three domed TPP units lie parallel to the threefold axis (fig. 2b) and each of the thorium atom assumes a distorted square antiprismatic geometry. The Th-Th separation is 3.960(3) A and does not suggest any metal-metal interaction. 

The reaction of the preformed 16-electron clusters [ (Ph3P)Au 8M](N03)2 (M = Pt, Pd) with metallic Hg resulted in isolation of the isomorphous 20-electron clusters [ (Ph3P) Au 8M (Hg)2] (N03)2 in which two mercury atoms cap in a (i4-fashion the gold atoms of two opposite square faces in an M-centered square-antiprism [Au-Hg 2.915... 

The square face of cluster 5 is readily capped by a number of different metal fragments affording octahedral heteronuclear clusters in high yield. The dianion 5 reacts with the Group 6 complexes M(CO)3L3 (M = Cr,... 

Fig. 62. Two views of H2Os6(CO)j8, a rare example of a non-octahedral hexanuclear metal cluster (Ref. 241). There was originally some suspicion that one of the H atoms might cap the basal square face of this cluster...

---