Cobalt compounds octahedral clusters

Because of possible catalytic and biological relevance of metal-sulfur clusters, several such compounds of cobalt have been prepared. The action of H2S or M2S (M = alkali metal) on a non-aqueous solution of a convenient cobalt compound (often containing, or in the presence of, a phosphine) is a typical route. Diamagnetic [Co6Ss(PR3)6] (R = Et, Ph) comprise an octahedral array of metal atoms (Co-Co in the range 281.7 to 289.4pm), all faces capped by atoms,and show facile redox behaviour... 

Reaction 6 is formally identical for cobalt and rhodium, however, in the cobalt case the octahedral cluster [Co6N(CO)i3] is produced first (according to Eq. (5)) and then the condensation step occurs. The two compounds, which share the same metal skeleton (a trigonal prism capped on a square face), have also a different ligand disposition which yields an idealized C2 symmetry in the cobalt case and for the rhodium compound. 

Chelation of ixo-maleonitriledithiolate (imdt) has been structurally characterized in the octahedral cobalt(III) complex trmw-[Co(imdt)2(P(ra-Bu)3)2], formed via reaction of cobalt(II) ion with K2(imdt) in the presence of the phosphine.1037 Simple chelating thiolates such as SCH2CH2S not only form mononuclear compounds, but participate in bridging in clusters such as [Co3(SCH2CH2S)3(PEt3)3]3+ (243).1038... 

Within the tris-chelate type of chiral coordination compound, the most extensively studied are the series of diamine chelates of cobalt(III), containing the octahedral [Cot )N6] cluster. The principal d—d transition of interest for the optical activity of these complexes is the Aj -> Tj octahedral excitation near 465 nm (Fig. 2), made up of the three single-orbital promotions, dxy dx -y , and the analogues obtained by the cyclic permutations of the electronic coordinates. The leading moments of the one-electron transition, dxy - , are the z-component of a magnetic dipole... 

Cobalt and rhodium also form a series of high nuclearity carbido-cluster compounds. Contrasting with carbido compounds of the iron group which have a clear tendency to put the carbide atom in octahedral cavities, carbides of the group 9 often place it in trigonal prismatic cavities. As shown in scheme in Fig. 3.12, the parent compound [Co6(CO)i5C] of a series of encapsulated car-bido-cobalt species may be prepared by the reaction of Co3(CO)9CCl with [Co(CO)4]. The same scheme also describes some carbido-cobalt cluster interconversions. Rhodium carbide clusters are in general similar to the cobalt ones. 

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