Tetranuclear Mixed-Metal Clusters

In mixed metal clusters, redistributions can occur in the mass spectrometer so that the highest observed peak arises from such a product. This is clearly exemplified by the heterometallic dodecacarbonyls containing metals of the cobalt triad. The thermal stability of this series of clusters decreases as the rhodium content increases and facile redistributions result in the formation of tetranuclear species containing less rhodium the very thermally stable Q I CO) does not rearrange184. ... 

Most of the reported reactions between tetranuclear clusters and alkynes involve mixed-metal cluster species. In these systems hydride and carbon monoxide substitution generally occurs [Eq. (11)] (194-200), although in some cases Me3NO has been used to activate the starting material (201, 202), and in still others cluster breakdown takes place even under mild reaction conditions (203). Rh4(CO)12 (204) and Ir4(CO)12 (205) retain their nuclearity in reactions with alkynes, but in the latter case the metal framework geometry is altered (Fig. 7). The use of [Ir4(CO)11Br] instead of Ir4(CO)12 in reactions with alkenes produces alkene-substituted tetranuclear complexes (189), as shown in Fig. 7. Few other homonuclear clusters have been found to react with alkynes (206-208). In the reaction between the tetranuclear cluster Cp2W2Ir2(CO) 0 and diphenylacetylene two independent processes... 

Figure 9.22 The structure of [Fe2Ho2(OH)2(teaH)2(02CPh)4(N03)2]-6CH3CN and its hysteresis loops measured in micro-SQUID [110]. (Reprinted from Polyhedron, 25, M. Murugesu, et al., Mixed 3d/4d and 3d/4f metal clusters tetranuclear image and image complexes, and the first Fe/4f single-molecule magnets, 613-625, 2006, with permission from Elsevier.)...

D. PLANAR TETRANUCLEAR CLUSTERS WITH MIXED-METAL CORES, MiMo2(Ti5-C5H5)2(CO)6(PPh3)2 M =Pd or Pt... 

Taking advantage of both aurophilicity and argentophilicity, tetranuclear mixed-metal complexes which contain pairs of Au and Ag atoms have been prepared, as shown in Fig. 19.6.3. In the preparation of mixed gold/silver polynuclear complexes, aurophilicity and argentophilicity have been utilized to promote cluster formation. Figure 19.6.4 shows the cores of several mixed gold-silver clusters. 

Table I. Fragmentation of Mixed-Metal Tetranuclear Clusters with Carbon Monoxide at 1 Atmosphere Pressure (17)...

H. Stoeckli-Evans, M. Hemy, G. Laurenczy, R. Roulet, Amphiphilic organoruthenium oxomolybdenum and oxovanadium clusters. Polyhedron 17 2817 (1998) c) L. Plasseraud, H. Stoechli-Evans, G. Siiss-Fink, [(Ti6-p-Pr C6H4Me)2Ru2Mo206(OMe)4]-A new tetranuclear mixed-metal 0x0 cluster presenting a cube-based chair structure, Inorg. Chem. Commun. 2 44 (1999). 

Metal carbonyl clusters are also numerous. In addition to dinuclear carbonyls such as M2(CO)io (M = Mn, Tc, Re), many hydrido clusters and ionic species exist which contain three or more metal atoms [M3H3(CO)i2] (M = Mn, Tc, Re), Mn3(CO)i (linear compound, 1)4 ), and Re3(/i-H)(CO)i4 (the Re —Re —Re angle is 90°). Rhenium forms a number of tetranuclear compounds. Some of them have a butterfly structure while others adopt a triangle of rhenium atoms with one Re attached to it Re4(/i3-H)4(CO)i2, [(Re4( -H)4(CO)i3] , [Re4( -H)6(CO)i4], and [Re4(CO)i6]. Rhenium also forms mixed metal carbonyls possessing several metal atoms (Table 3.14). There are numerous clusters of the group 7 metals containing cyclopentadienyl groups, ... 

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