Electronic Configuration and Coordination Geometry

Coordination geometry for nanomaterials depends on the coordinating atom species and numbers, bond distances and bond orientation, and oxidation state. 

XAS does not rely on long-range order and is highly sensitive to the local electronic environment, coordination geometry, and bond distances of absorbed atoms in materials, which makes it a quite precise fingerprint for structure determination.  

Adora et al. found H2PtCl6 (IV) was reduced to PtC (II) and Pt atoms (0) during electrochemical preparation of metallic platinum nanocrystallites 

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The most common oxidation states, corresponding electronic configurations, and coordination geometries of iridium are +1 (t5 ) usually square plane although some five-coordinate complexes are known, and +3 (t7 ) and +4 (t5 ), both octahedral. Compounds ia every oxidation state between —1 and +6 (<5 ) are known. Iridium compounds are used primarily to model more active rhodium catalysts. 

In other instances, irradiation of the d-d transition leads to no observable reaction. Examples of this behavior are found for complexes having a variety of d electron configurations and coordinative geometries square planar Ni(II) (3d)3 in Ni(CN)42 124 and mww-Ni(gIy)2 124 square planar Pd(II) in Pd(CN)42-,124 and tra -Pd(gly)2 square planar Pt(II) in Pt(CN)42" (5d)3 124 octahedral Co(III) (3d)6 in a variety of complexes (cf. Sect. III-C and III-D). A striking example of this type of behavior is afforded by the nonreversible photoisomerization of cis-Pt(gly)2 (5d)8 to trans-Pt(g y)2 [reaction (2)].124 It has been proposed that irradiation of either of these square planar complexes leads to the same tetrahedral intermediate which decays exclusively to mwj-Pt(gly)2. This behavior may be contrasted with the reversible photoisomerization shown in reaction (3).3... 

The V(IIIj containing complexes V(R2magnetic moments of these air-sensitive compounds are characteristic of two unpaired electrons as is expected for a configuration, the coordination geometry is assumed to be a distorted octahedron (Dj). 

Organometallic compounds of rhodium have the metal center in oxidation states ranging from +4 to -3. but the most common oxidation states are +1 and +3. The Rh(I) species have a d electron configuration and both four coordinated square planar and five coordinated trigonal bipyramidal species exist. Oxidative addition reactions to Rh(I) form Rh(III) species with octahedral geometry. The oxidative addition is reversible in many cases, and this makes catalytic transformations of organic compounds possible. Presented here are important reactions of rhodium complexes in catalytic and stoichiometric transformations of organic compounds. 

Equation (116)). Complex 290 features a six-coordinate octahedral geometry, but other reported examples of Ni(iii) pincer compounds are five coordinate, square pyramidal. A four-coordinated, square-planar homoleptic Ni(iii) complex, 291, has been prepared by oxidation of the corresponding Ni(ii) precursor with CI2 at low temperature (Equation (117)). This complex has low thermal stability and slowly decomposes at room temperature, with the production of perchlorobiphenyl. Organometallic Ni(iii) compounds have low spin electronic configurations, and display well-resolved EPR spectra (Table 12). 

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