Trans effect in octahedral complexes

At this point, it is appropriate to mention some of the evidence that indicates a trans effect in octahedral complexes, but only a brief description will be given. In the reaction of Mo(CO)6 with pyridine, only three CO ligands undergo replacement, and the product has the structure... 

In addition to the indications of an octahedral trans effect presented, there exists structural information in the form of bond lengths and spectral data similar to that described earlier for square planar complexes. Although the trans effect in octahedral complexes is not the dominant influence that it is in square planar complexes, there is no doubt that there is such an effect. 

Elder, R. C., Heeg, M. J., Payne, M. D., Trkula, M., and Deutsch, E. (1978). trans Effect in octahedral complexes. 3. Comparison of kinetic and structural trans effects induced by coordinated sulfur in sulfito- and sulfinatopentaamminecobalt(III) complexes. Inorg. Chem. 17,431-440. 

Rhodium complex cations have proved particularly suitable for studying trans effects in octahedral complexes. 

Pt(II) metal complexes, are known to exhibit a structural trans effect. In octahedral complexes, trans effects can also occur, even if these effects are less pronounced... 

The rates of substitution reactions of trans-CRhenjCl ] are first-order in complex concentration and independent of the nature and concentration of the substituting group. They also proceed without stereochemical rearrangement (1). These reactions appear, therefore, to be free of the difficulties which complicate studies of Co(III) and Pt(IV) complexes and were accordingly chosen as suitable for systematic investigation of the trans-effect in octahedral complexes. 

For a recent review on trans-effects in octahedral transition metal complexes, see ... 

Coe BJ, Glenwright SJ (2000) Trans-effects in octahedral transibon metal complexes. Coord... 

Similarity with cobalt is also apparent in the affinity of Rh and iH for ammonia and amines. The kinetic inertness of the ammines of Rh has led to the use of several of them in studies of the trans effect (p. 1163) in octahedral complexes, while the ammines of Ir are so stable as to withstand boiling in aqueous alkali. Stable complexes such as [M(C204)3], [M(acac)3] and [M(CN)5] are formed by all three metals. Force constants obtained from the infrared spectra of the hexacyano complexes indicate that the M--C bond strength increases in the order Co < Rh < [r. Like cobalt, rhodium too forms bridged superoxides such as the blue, paramagnetic, fCl(py)4Rh-02-Rh(py)4Cll produced by aerial oxidation of aqueous ethanolic solutions of RhCL and pyridine.In fact it seems likely that many of the species produced by oxidation of aqueous solutions of Rh and presumed to contain the metal in higher oxidation states, are actually superoxides of Rh . ... 

Kinetic parameters for alcohol exchange have been deduced from H and studies on Co(ii), (296) Ni(ii), (297) and Mn(ii) (298) systems. The complex [Co(CH30H)5py] (296) provides a clear example of the operation of the trans effect in a labile octahedral complex, in that the exchange rate constants for cis and trans methanol sites with respect to pyridine are 410s and 1200s respectively. 

B.J. Coe and S.J. Glenwright (2000) Coordination Chemistry Reviews, vol. 203, p. 5 - TVawi-effects in octahedral transition metal complexes (includes both structural and kinetic trans-effects). 

Co(CN)5(S03)] this may show a trans effect (commonly noted in square-planar complexes) in octahedral complexes, although CIST is at or near the top of the usital hsts of tran -effect ligands. See 10.2.2 Reduced nitrogen. Of course other factors also intrade. 

The most important members of this class are the osmium nitrido, and the osmyl complexes. The reddish-purple K2[OsNCl5] mentioned above is the result of reducing the osmiamate. The anion has a distorted octahedral structure with a formal triple bond Os=N (161pm) and a pronounced /ram-influence (pp. 1163-4), i.e. the Os-Cl distance trans to Os-N is much longer than the Os-Cl distances cis to Os-N (261 and 236 pm respectively). The anion [OsNCls] also shows a rram-effect in that the Cl opposite the N is more labile than the others, leading, for instance, to the formation of [Os NCl4] , which has a square-pyramidal structure with the N occupying the apical position. 

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