Bridged species silicon-containing

Miller (90), King (209, 210), and Bruce (211) first observed the formation of neutral metal fluoride species and metal fluoride-containing ions in the mass spectra of pentafluorophenyl derivatives of phosphorus, germanium, silicon, and phosphido-bridged iron carbonyls (90) and aliphatic and aromatic fluorocarbon derivatives of iron, cobalt (209-211),... 

The new ternary compound SrMgSi2 shows a considerable disproportionation of the silicon atoms into terminal (lb)Si , bridging (2b)Si, and branching (3b)Si" species (Fig. 2b, [31]). As shown in figure 2b the whole polyanion contains a one dimensional planar chain of silicon atoms with syndiotactically arranged side chains [Si(Si3)] . The Si-Si distances vary somewhat between 235 and 249 pm, with the shortest distances between the side chain bridging atoms and those of the main backbone. 

Because of the close relationship between silicon and carbon, many attempts have been made to try to synthesize species containing multiple bonds to silicon (Si=C, Si=0, Si=Si, etc.). However, it was not until 1967 that compelling evidence was presented that Si=C might exist in the thermal reaction of 1,1-dimethyl-1-silacyclobutane (equation 90). The first evidence for the existence of Si=Si as transient intermediate was provided in the thermolysis of bridged disilane derivatives (equation 91). Since then, many studies have been published on these unsaturated species, but it was in 1981 that synthesis and characterization of relatively stable crystalline compounds containing Si=C (silene) (equation 92) and Si=Si (disilene) (equation 85) were reported (equations 90-92). 

Some possible silicate species present in aqueous potassium silicate solution with atomic ratio K Si = 1.0 and concentration I.4M identified by Si NMR. Vertices in diagrams represent positions of silicon atoms that are bridged by oxygens. Additional oxygen (or OH groups) are present as required for valency fulfillment. Chemical shifts, given in ppm with respect to the monomer resonance, are included for positively identified species. Subscripts denote the number of individual Q" species contained in each structure. After Harris et at. [18]. 

Some Si chemical shifts and shift ranges for the systems indicated. Species (a) to (e) are shown below. The tropolonato complexes (b) and the silatranes (c) involve pentacoordinate silicon, while the diketone and ketoester systems (d) contain hexacoordinate silicon, as does [SiF ] . The shaded part of the ranges for Me Si(-0-) jj, n = 0-3, refers to compounds in which all the oxygens are involved in siloxane bridges. 

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