Coordination compounds linear complexes

Gold Compounds. The chemistry of nonmetallic gold is predominandy that of Au(I) and Au(III) compounds and complexes. In the former, coordination number two and linear stereochemistry are most common. The majority of known Au(III) compounds are four coordinate and have square planar configurations. In both of these common oxidation states, gold preferably bonds to large polarizable ligands and, therefore, is termed a class b metal or soft acid. 

Like Ag, Au also readily forms linear 2-coordinate complexes such as [AuX2] (X = Cl, Br, I) " and also the technologically important [Au(CN)2] . But it is much more susceptible to oxidation and to disproportionation into Au and Au which renders all its binary compounds, except AuCN, unstable to water. It is also more clearly a class b or soft metal with a preference for the heavier donor atoms P, As and S. Stable, linear complexes are obtained when tertiary phosphines reduce Au in ethanol. 

Cations [(RR C=Se)2I]+ In the case of A-methylbenzothiazole-2(3//)-selone (mbts), one equivalent of iodine provides a molecular adduct in dichloromethane solution 50 crystallisation, however, leads to a ionic compound of the type [(RR C Se)2I]+I3, 43 This compound was the first one reported in the literature featuring a two coordinated iodine(I) complex with two donor molecules containing selenocarbonyl groups. In the solid state two molecules of mbts are linearly coordinating a central I+ ion to give a slightly... 

The geometry of the coordination compounds can be similarly predicted based on the coordination number of the central atom. Coordination numbers 2 and 3 are both relatively rare and give linear and planar or pyramidal geometries, respectively. The most important coordination numbers are 4, 5 and 6 with the latter being the most important one as nearly all cations form 6-coordinate complexes. Table 2.4 shows the geometries corresponding to the commonest coordination numbers in biological systems. 

Severin and Buryak have utilized mixtures of commercial dyes and simple metals [Cu(II) and Ni(II)] to generate DCLs capable of distinguishing closely related di- and tripeptides [11]. The DCL was generated by the combination of metal and dye, which created a complex mixture of uniquely UV-Vis-absorbing coordination compounds. Addition of the analyte (usually a di- or tripeptide) shifted the library speciation that then created a new UV-Vis spectrum (Fig. 5.10). Combining this principle with linear discriminant analysis of the spectrum (in conjunction with learning datasets)... 

There are mercury compounds with mercury oxidation numbers lower than +1, e.g. +0.5,16,21 +0.6713,15,27 or +0.35.18,20 Yellow crystals of Hg3(AsF6)2 have been formed by the reaction of metallic mercury with AsFs in liquid S02.13 X-Ray structure determination showed a linear polycation Hg+—Hg—Hg+ with Hg—Hg distances of 255 pm.15 Metallic mercury and SbF5 react in liquid S02 to form Hg3(Sb2Fu)2.15,23 The Hg—Hg distances in the complex Hg3(AlCU)2 are 256 pm 14 the Hg—Cl distances are 251 and 256 pm the Hg—Hg—Hg angle is 174°. Dark red crystals of Hg4(AsF6)2 were obtained in liquid S02. This coordination compound contains centrosymmetric Hg4+ ions, which are connected to chains (see l).21... 

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