Bismuth unusual complexes

Monomeric arrangements are rare for alkoxide complexes of bismuth and require excess anionic ligands or bulky substituents. Otherwise the alkoxide ligands typically impose dimerization or multinuclear clustering, which are expressed in a variety of currently unusual structural arrangements (Table I). 

Many of the multidentate features observed for aminocarboxylate complexes of bismuth are evident in a small, diverse group of complexes involving hydroxyamine and aminoalkoxides ligands (Table XVI). Most of the examples in this section may be considered unique and represent unusual structural arrangements. 

A diverse coordination chemistry is emerging for bismuth(III) made possible by a spacious and flexible coordination environment, allowing for coordination numbers in excess of 9. Although the available data are still limited, distinct trends are evident, and the polymeric solid-state features that may be assumed on the basis of high coordination numbers can be mediated by appropriate selection of organic-based ligands. The unusual structural arrangements observed for many types of complex may prove to be representative as the number of examples of such systems increases. 

A prototypical high-temperature superconductor is yttrium barium copper oxide, YBa2Cu307, in which two-thirds of the copper is in the +2 oxidation state and one-third is in the unusual +3 state. Another example is BijSrjlCaQgYoyjCujOgjys, in which the average oxidation state of copper is +2.105 and the average oxidation state of bismuth is +3.090 (which is formally a mixture of Bi3+ and Bi5+). The most reliable means to unravel these complex formulas is through wet oxidation-reduction titrations, described in this chapter. 

Tl -bismolyl derivative [Mn(CO)jL] (81) (L=2,5-Me2C4H2Bi). Two papers describe the formation of triiron complexes [ Fe(CO)4 3(p -BiR)] in which bismuth is tetrahedral, addition of acetic acid to which affords rectangular complexes [Fc(CO)4(p-BiR)]2 . Another publication details the preparation of a whole range of complexes in which a bismuth nitrate unit is linked to two metal centres , while thermolysis of NaBi03 and [Mo(CO)J in methanol for a day, followed by addition of Et4NBr yields the unusual cluster [Mo3(CO)9(p -Bi) p -(OMej)Mo(CX))3 ][NEt4]2, which contains a naked bismuth atom (82) . ... 

Bismuth as an adatom or alloying element with Pt has been proposed as an extremely active co-catalyst for HCOOH oxidation on Pt. The unusual activity of Bi has been attributed to a combination of geometric (third-body) and electronic effects [155-157]. However, the role of Bi is quite complex and in some cases contradictory results were obtained. Tripkovic et al. clearly showed flie activity of PtBi is dependent on flie redox behavior of Bi and on its surface arrangement [158]. Oxidized Bi species such as Bi203 and BiO(OH) were identified by XPS on the surface at both open circuit and anodic potentials. Furthermore, the possibility of Bi leaching was proposed, with subsequent underpotential deposition of the resulting Bi on flie surface forming in-situ an adlayer, which could also contribute to the enhanced catalytic activity, as shown by a shift of the HCOOH oxidation onset potential by -0.25 V compared to pure Pt [158]. 

As with azeotropes, eutectics maybe ternary, quaternary, and so on, but their phase diagrams get very complex very quickly. A few important eutectics have an impact on ordinary life. Ordinary solder is a eutectic of tin and lead (63% and 37%, respectively) that melts at 183 C, whereas the melting points of tin and lead are 232 C and 327 C. Wood s metal is an alloy of bismuth, lead, tin, and cadmium (50 25 12.5 12.5) that melts at 70 C (lower than the boiling point of water ) that can be used in overhead fire sprinkler systems. NaCl and H2O make a eutectic that melts at — 21 C, which should be of some interest to communities that use salt on icy roads in the winter. (The composition of this eutectic is about 23 weight percent NaCl.) An unusual eutectic exists for cesium and potassium. In a 77 23 ratio, this eutectic melts at —48 C This eutectic would be a liquid metal at most terrestrial temperatures (and be very reactive toward water). 

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