Octahedral complexes, electron configurations

Polyatomic molecules cover such a wide range of different types that it is not possible here to discuss the MOs and electron configurations of more than a very few. The molecules that we shall discuss are those of the general type AFI2, where A is a first-row element, formaldehyde (FI2CO), benzene and some regular octahedral transition metal complexes. 

The most common oxidatiou states and corresponding electronic configurations of rhodium are +1 which is usually square planar although some five coordinate complexes are known, and +3 (t7 ) which is usually octahedral. Dimeric rhodium carboxylates are +2 (t/) complexes. Compounds iu oxidatiou states —1 to +6 (t5 ) exist. Significant iudustrial appHcatious iuclude rhodium-catalyzed carbouylatiou of methanol to acetic acid and acetic anhydride, and hydroformylation of propene to -butyraldehyde. Enantioselective catalytic reduction has also been demonstrated. 

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. 

The chemistry of Cr(III) in aqueous solution is coordination chemistry (see Coordination compounds). It is dominated by the formation of kineticaHy inert, octahedral complexes. The bonding can be described by Ss]] hybridization, and HteraHy thousands of complexes have been prepared. The kinetic inertness results from the electronic configuration of the Cr ion (41). This type of orbital charge distribution makes ligand displacement and... 

In general, octahedral complexes of transition-metal ions possessing 0, 1, or 2 electrons beyond the electronic configuration of the preceding noble gas, ie, i/, (P configurations, are labile. The (P systems are usually inert the relative lability of vanadium(II) may be charge and/or redox related. 

However, high spin (P and (P species, which possess 4, 5, and 4 unpaired electrons, respectively, are labile, as are (P through (P octahedral complexes. In addition to the inert (P systems, low spin (P and (P complexes are inert to rapid substitution. The (P species are the least labile of the configurations classed as labile. 

Predict the electron configuration of an octahedral eP complex with (a) strong-field ligands and (b) weak-field ligands, and state the number of unpaired electrons in each case. 

The electron configuration expected for Ni2+ is [Ar]3unpaired electrons it would have to be (c) square planar in its electronic geometry, as both the octahedral and tetrahedral geometries require a species to have two unpaired electrons. Square planar does not. 

A significant number of Ir111 complexes arise from the oxidative addition reactions of Ir1 species. Such reactions may proceed via routine addition, whereas some proceed by ligand expulsion in conjunction with oxidative addition. Complexes containing Ir111 have a low-spin d6 electronic configuration, and are usually to be found with an octahedral-based ligand set. 

Would Jahn-Teller distortion be as significant for tetrahedral complexes as it is for octahedral complexes For which of the electron configurations would Jahn-Teller distortion occur ... 

The kinetically-stabilized complexes of the cage ligands normally yield redox reagents free of the exchange problems often associated with simple complexes. Indeed, the redox chemistry of the complexes shows a number of unusual features for example, saturated cages of the type mentioned in Chapter 3 are able to stabilize rare (monomeric) octahedral Rh(n) species (d7 electronic configuration) (Harrowfield etal., 1983). In a further study, radiolytical or electrochemical reduction of the Pt(iv) complexes of particular cages has been demonstrated to yield transient complexes of platinum in the unusual 3+ oxidation state (Boucher et al., 1983). 

Since the octahedral and tetrahedral configurations have the same number of unpaired electrons (that is, 2 unpaired electrons), we cannot use magnetic properties to determine whether the ammine complex of nickel(II) is Octahedral or tetrahedral. But we can determine if the complex is square planar, since the square planar complex is diamagnetic with zero unpaired electrons. 

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