Trinuclear arrays

For trinuclear cluster complexes, open (chain) or closed (cycHc) stmctures are possible. Which cluster depends for the most part on the number of valence electrons, 50 in the former and 48 in the latter. The 48-valence electron complex Os2(CO)22 is observed in the cycHc stmcture (7). The molecule possesses a triangular arrangement of osmium atoms with four terminal CO ligands coordinated in a i j -octahedral array about each osmium atom. The molecule Ru (00) 2 is also cycHc and is isomorphous with the osmium analogue. 

The structures are shown in Fig. 26.8c and d and differ in that, whereas the Ir compound consists of a tetrahedron of metal atoms held together solely by M-M bonds, the Rh and Co compounds each incorporate 3 bridging carbonyls. A similar difference was noted in the case of the trinuclear carbonyls of Fe, Ru and Os (p. 1104) and can be explained in a similar way. The M4 tetrahedra of Co and Rh are small enough to be accommodated in an icosahedral array of CO ligands whereas the larger Ir4 tetrahedron forces the adoption of the less dense cube octahedral array of ligands. 

The electrochemical and photophysical properties of a linear 2,2 6, 2"-terpyridine-based trinuclear Ru(ii)-Os(ii) nanometer-sized array 39 have been studied <2005JA2553>. 

As a kind of extension of this particular type of trinuclear structure, there are numerous compounds that contain two such units fused together on a common edge to give either a discrete molecule as in W4(OEt)i6 (Fig. 16-23), and Mo408(OPr )4py4 or extended arrays of such a unit, joined by shared nonmetal atoms, as in MNb4Cln (Fig. 18-B-13) or certain mixed oxides of molybdenum such as Bai.i4Mo80i6. 

Pope, S.J.A., Coe, B.J., and Faulkner, S. (2004) Re(l) sensitised near-infrared lanthanide luminescence from a hetero-trinuclear Rc2Ln array. Chemical Communications, 1550. 

The trinuclear framework with three metal-metal bonds is remarkably stable and supports a rich array of chemical reactions. A related triangular complex with a remarkable bridging PF3 group is obtained by disproportionation reaction [eq. (b)] which produces two new Pd-Pd bonds with rearrangement of the diphosphine ligands. ... 

The trinuclear species Ari3(Tmsingle crystal study of [Au3(Tm Bu )2 J SbF indicated a cationic complex [Au3(Tm Bu)2]+ in which a triangular array (Fig. 5.11) of three gold atoms is coordinated simultaneously by two Tm Bu ligands.52... 

Human ceruloplasmin consists of a single polypeptide chain with a MW of 132 kDa folded in six cupredoxin domains arranged in a triangular array. Each domain comprises a p-barrel, constructed in a Greek key motif, typical for the cupredoxins. Three of the six copper ions are bound to T1 sites present in domains 2, 4, and 6, whereas the other three copper ions form a trinuclear cluster, bound at the interface between domains 1 and 6 (Fig. 10). The spatial relation between the trinuclear center and the nearest T1 site (A, in domain 6) closely resembles that found in AO and was taken to further support the proposal that hCp has an oxidase function. The three T1 sites are separated from each other by a distance of 1.8 nm, a distance that might still allow for internal ET at reasonable rates and could also increase the probability for electron uptake. The coordination sphere of the T1 site in domain 4 (TIB) is identical with that of domain 6 (TIA). The third type 1 center (TIC), however. 

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