Butterfly metallic cores

Most tetranuclear clusters exhibit butterfly metallic cores, for example, Au(CoFe)... 

The butterfly metal core (type 4) is the most frequently found geometry in tetranuclear clusters with skeletal isomerism (Scheme 2). It is worth noting that for metals... 

The reaction of the acetylide cluster [Os3(/z-H)(/x-G=Me)(CO)9] with [Ru3(CO)i2] in refluxing hexane gave [RuOs3(/X4-HC2Me)(GO)i2] with a butterfly metal core. Alkynyl complexes such as [Oss(CO)() fj,-CO)(ii3-ri, 7]. rf-Me3SiG=GG2G=GSiMc3)] also formed mixed-metal clusters 226 when treated with [Ru3(GO)i2] (Table 13). ... 

The synthesis of [HFe4(CO),3] from [Fe4(CO),3]2 (186,187) is interesting because of the major structural rearrangement that occurs following protonation (184). The parent dianion has a tetrahedral metal framework (Section II,C,4) (153) which undergoes metal-metal bond scission and formation of the II —CO upon protonation. The metal core geometry for [HFe4(CO)13] is butterfly shaped, and the proper 62-electron count for a butterfly metal cluster is achieved if the II —CO is assumed to be a 4-electron donor. 

OssC(CO) (C02R)X] (X = H or I) has been determined, and the metal core shown to exhibit the expected bridged-butterfly geometry. Another preliminary report on nucleophilic attack at a coordinated CO of a carbido carbonyl cluster compound has also appeared. The heterometallic carbido cluster anion [Co6Ni2C2 (C0)i6 ] results from the reaction of [003(00)9(001)] with [Nig (C0)i2 ] and contains two C atoms located in a cavity in the cluster and separated by only... 

Tetranuclear PtsRu cluster 67 is formed when the platinum triangle 20 reacts with [HRu(GO)4] . At low temperature 67 is formed cleanly, and can be identified by NMR and IR spectroscopies however, at room temperature, it isomerizes to 68 in a matter of hours (Scheme 15). Dark purple crystalline samples of 68 can be isolated, and are thermally and air stable. An X-ray structure of 68 shows the metal core to be closer to a butterfly structure than a tetrahedron the unique Pt-Ru distance is a long 2.9951(6) A, whereas the other two are 2.7031(6) and 2.7649(6) A Pt-Pt distances are in the range 2.61-2.73 A. Both 67 and 68 are fluxional in solution, with the NMR spectra of 67 showing fast exchange even at —30 °C. 

Core expansion of the /.ts-oxotriiron cluster 107 is reported (Scheme 8). Interaction with Mn and Re electrophiles leads to the formation of the heterotetranuclear /X4-0X0 clusters with the butterfly metal array 108 and the ji -oxo clusters with expanded metal frameworks 111-113, " which arise by Fe20 108 and Fes face capping 111-113, respectively. Interstitial clusters (e.g., 14- and 15-type complexes Scheme I) are rare for the 0x0 cluster compounds (see below) in contrast to the related carbido and nitrido clusters. 

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