Square planar complexes trans effect

The preparation of the dinuclear complexes is readily achieved by taking advantage of the well-established trans effect in square-planar complexes. For example, the treatment of two equivalents... 

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. 

Isomerization involving a square planar complex is also known. Because of the trans effect, it is easier to synthesize the trans isomer of many complexes than it is to prepare the cis complex. The following reactions lead to the formation of an unusual platinum complex ... 

Briefly, as Prof. Basolo points out in his paper, and Prof. Basolo and Pearson pointed out nicely in a review on the trans effect, the situation in the ir-bonding theory is a stabilization of the trigonal bipyramidal intermediate because there are more orbitals in the trigonal plane available for 7r-bonding in the trigonal bipyramid than in the square planar complex. The same is also true in the --system. The trans effect is directional, and in my opinion, it has to be orbital or quantum mechanical. 

As described earlier, the trans effect is indicated by the fact that the products obtained when NH3 and N02 are substituted for Br- in [PtBr4]2- depend on the order of addition. If NH3 is added first followed by N02 , the product is cA-[PtBr2NH3N02] , but if N02 is added first, the product is trans- PtBr2NH3N02r. Clearly the stereochemistry of the product is the result of a trans effect. If this trans directing influence is manifested in this way, it should also be evident from other properties of square planar complexes. In fact, there should be kinetic as well as thermodynamic and structural evidence to indicate the difference in trans influence exerted by different ligands. In the case of square planar complexes, much... 

It should also be pointed out that the trans effect is not limited to complexes of Pt(II) but should exist in any square planar complex. Generally, the trans effect is smaller in complexes of Pd(II) than in those of Pt(II) and this is exactly as would be expected from the fact that Pd(II) is less polarizable (harder) than Pt(II). In terms of the n bonding hypothesis, the Pd(II) is a harder acid than Pt(II) (and less likely to participate in back donation) and does not form covalent bonds as well. By either way of explaining the trans effect, the effect should be smaller in complexes of Pd(II) than in those of Pt(II). The trans... 

Why is the trans effect less important for square planar complexes of Ni2+ than it is for complexes of Pt2+ ... 

Figure 7 Overview of the trans effect for square planar complexes...

Square-planar Exchange in square-planar complexes is associative, and is influenced by the trans effect, complexes whereby some ligands facilitate substitution of trans ligands. 

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