Arsenic-antimony bonds

Arsinidene and stibinidene complexes. Arsenic and antimony in their +1 oxidation state can be stabilized by a metal-arsenic (or antimony) n bond with a trigonal planar coordination. PhE[Mn(CO)2Cp]2 was prepared as its arsenic " and antimony derivatives . 

In the semimetals antimony, arsenic and bismuth, bonding effects are more pronounced, and the structures are not related to the simple structures of most metals. Bismuth, the heaviest, is the most metallic , and phosphorus, lying above antimony in the periodic table, is not even considered to be a semimetal. 

The ylides have been classified on the basis of the heteroalom covalently bonded to the carbanion. Accordingly, they can be differentiated into nitrogen ylide (Scheme 2), sulfur ylide Scheme 3, phosphorus ylide Scheme 4, arsenic ylide Scheme 5, antimony ylide (Scheme 6), bismuth ylide (Scheme 7) and thallium ylide (Scheme 8). 

Phosphorus, arsenic, antimony and bismuth multiply bonded systems with low coordination number — their role as complex ligands. O. J. Scherer, Angew. Chem., Int. Ed. Engl., 1984, 24, 924 (85). 

Arsenic and antimony are metalloids. They have been known in the pure state since ancient times because they are easily obtained from their ores (Fig. 15.3). In the elemental state, they are used primarily in the semiconductor industry and in the lead alloys used as electrodes in storage batteries. Gallium arsenide is used in lasers, including the lasers used in CD players. Metallic bismuth, with its large, weakly bonded atoms, has a low melting point and is used in alloys that serve as fire detectors in sprinkler systems the alloy melts when a fire breaks out nearby, and the sprinkler system is activated. Like ice, solid bismuth is less dense than the liquid. As a result, molten bismuth does not shrink when it solidifies in molds, and so it is used to make low-temperature castings. 

The magnetic criterion is particularly valuable because it provides a basis for differentiating sharply between essentially ionic and essentially electron-pair bonds Experimental data have as yet been obtained for only a few of the interesting compounds, but these indicate that oxides and fluorides of most metals are ionic. Electron-pair bonds are formed by most of the transition elements with sulfur, selenium, tellurium, phosphorus, arsenic and antimony, as in the sulfide minerals (pyrite, molybdenite, skutterudite, etc.). The halogens other than fluorine form electron-pair bonds with metals of the palladium and platinum groups and sometimes, but not always, with iron-group metals. 

Six elements are metalloids B, Si, Ge, As, Sb, and Te. Of these, silicon is by far the most abundant, making up over 27% of the Earth s crust, more than any other element except oxygen, hi fact, S1O2 and silicate minerals account for 80% of the atoms near the Earth s surface. Despite its great abundance, silicon was not discovered until 1824, probably because the strong bonds it forms with oxygen makes silicon difficult to isolate. Two much rarer metalloids, antimony (known to the ancients) and arsenic (discovered ca. 1250 ad) were isolated and identified long before silicon. 

Many of the properties of the group 15 element diheteroferrocences are very similar to ferrocenes and other metallocenes. It seems justified to regard the diheteroferrocenes as perturbed ferrocenes just as we regard the group 15 heterobenzenes as perturbed benzenes. Thus, it is very clear that the elements phosphorus, arsenic, antimony, and bismuth can take part in 7r-bonding in a manner similar to carbon. 

---