Oligomeric cluster complexes

TABLE 5 Cluster-Based Electron (CBE) and Mean Distances (in pm) for Oligomeric Cluster Complexes T(Rr Xx ... 

Historically, the first alkoxides of Ca, Sr, and Ba isolated were those containing sterically compact groups (OMe, OEt), which formed [M(OR)2] derivatives that are presumably oligomeric or polymeric. The use of somewhat more sterically bulky groups has led, in recent years, to the isolation of a variety of stmcturally characterized cluster complexes, such as Sr4(OPh)8(PhOH)2(THF)6, Ba4(Ar4-0)[/a2-0C6H2-2,4,6-... 

The complexes derived from simple monodentate carboxylates are not stable, and only one mononuclear complex with a sterically hindered carboxylate has been successfully isolated, [VCKCbC Bujs] (13).103 Attempts to prepare carboxylates in organic solvents often led to the formation of oligomeric cluster compounds with a variety of interesting structural types.103 In aqueous solutions, these vanadium complexes appear to contain six-coordinate vanadium.60,104 Even carbonate has been found to form a weak vanadiumtV) complex in solution.105... 

Conceivably, metal tetrachalcolenes of the types exemplified in Figure 3 for metal tetrathiolenes can be synthesized. For discrete polynuclear metal complexes, one can either build up the oligomeric clusters by forming in-plane, metal-ligand o- bonds with tetrathiolene and other... 

TABLE 4 Oligomeric R Cluster Complexes with Endohedral Transition Metal Atoms T... 

TABLE 10 Percentage Contributions to Hetero- (T-R and R-X) and Homoatomic (T-T and R-R) Bonding Interactions in Some Oligomeric and Chain Cluster Complexes TfRr Xx... 

In chronic myelogenous leukemia (CML) as well as in a subset of acute lymphoblastic leukemia (ALL) Bcr-Abl, a fusion protein of c-Abl and the breakpoint cluster region (bcr), is expressed in the cytosol of leukemic cells. This fusion protein forms homo-oligomeric complexes that display elevated kinase activity and is the causative molecular abnormality in CML and certain ALL. The transforming effect of Bcr-Abl is mediated by numerous downstream signaling pathways, including protein kinase C (PKC), Ras-Raf-ERK MAPK, JAK-STAT (see below), and PI3-kinase pathways. 

Kai Pii is formed quantitatively from Na3p7 and Pi (in en) in a well defined reaction. The colourless solvate Uai Pii 6en can be obtained from en in crystalline form by counter-current diffusion of THF (Figure 5)- Again we find a solvated molecule or ion-complex Nai Pii in the crystal. The polyanion Pi ", whose trimethyl-silyl substituted derivatives have already been observed in small quantities in mass-spectra ( ), constitutes the first methodically executed step to an oligomerization and finally to a complete polymerization of Pv clusters (I6). 

Many complexes involving iron are known, mostly clusters containing iron carbonyl fragments, and reports for some come from the early years of metal cluster chemistry. Perhaps the simplest compound is PbFe(CO)4 , described originally in I960 (59) and later in more detail by Marks in 1978 (60). The structure is unknown although it is postulated to be oligomeric on the basis of infrared spectroscopic data. 

Geribaldi and coworkers have examined the oligomerization of SiH4 with the rare earth ions Sc+, Y+ and Lu+60,61a. In these FT-ICR studies, clustering of up to seven silane molecules around a metal ion was observed. In the additions of silane molecules to the metal center, the excess energy of the initial complex was found to be dissipated via sequential H2 loss, thus giving rise to MSi H2n + ions among various other products (equation 3). 

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