Trans influence square planar complexes

Titanium, tris(acetylacetone)-structure, 65 Titanium(III) complexes magnetic behavior, 271 spectra, 250 Titanium tetrachloride photoreactivity, 406 Titrimetry, 552 T oluene-3,4-dithiol in gravimetry, 534 metal complexes liquid-liquid extraction, 547 Topochemical reactions, 463 Topotactic reactions, 463 Trans effect, 16, 26,315 six-coordinate compounds, 49 Trans influence square planar complexes, 38 Transition metal complexes d... 

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. 

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... 

The evidence cited previously shows clearly that there is a trans influence in square planar complexes and that the magnitude depends on the nature of the ligand. In fact, the trans directing influence is a factor of major importance in the structures and substitution reactions of square planar complexes. It is now necessary to provide an explanation of how this phenomenon is caused and how it is related to the nature of the ligands. 

Pearson, in elaborating upon these ideas, distilled the essence of the ir competition theory to two soft ligands in mutual trans positions will have a destabilizing influence on each other when attached to class (h) soft) metal atoms. He also provided additional examples of the rule that symbiosis prevails in octahedral complexes. antisymbiosis in square planar complexes. Tetrahedral complexes are expected to show antisymbiosis but on a much reduced scale compared with the square planar complexes. - 2... 

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. 

Palladium(II) and platinum(II) form a wealth of square planar complexes a tendency for Pt—Pt interactions (i.e. for the heaviest group 10 metal) is quite often observed. The mechanisms of substitution reactions in Pt(II) complexes and the trans-effect have been much studied and we return to this in Section 25.3. However, for the discussion that follows, it is important to note that mutually trans ligands exert an effect on one another, and this dictates the order in which ligands are displaced and, therefore, the products of substitution reactions. A word of caution do not confuse trans-eSect with trani-influence (see Box 22.9). 

The trans influence of a ligand is the ability of a ligand to weaken the bond trans to itself in a complex. Gold(I) and gold(III) complexes are, in the simplest treatment, considered to use sp and dsp hybrid orbitals in forming linear and square planar complexes respectively. A good o donor, L, tends to concentrate gold 6s character in the AuL bond and the trans bond must then overlap with an orbital of low s character. A weaker and more ionic bond is then formed. 

Values of i>(Pt-H) show that the Pt—H bond is weakest for X = [CN] and the trawi-influence of the X ligands follows the order [CN] > F > Br > Cl . The signal for the hydride in the H NMR spectrum moves to lower frequency (higher field) with a decrease in the tra 5-influence of X . The traw-influence is not unique to square planar complexes, and may be observed wherever ligands are mutually trans, e.g. in octahedral species. 

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