Trans-Square planar complexes

What physical tool could be employed to determine the configuration of [PdCl2(C6H5CN)2] as cis or trans (square planar complex). 

Figure 32 (a) Cis- and (b) trans-square planar complexes of monothiodiketone ligand. 

In the cis isomer, the two CH3 groups (or the two H atoms) are as close to one another as possible. In the trans isomer, the two identical groups are farther apart. The two forms exist because there is no free rotation about the carbon-to-carbon double bond. The situation is analogous to that with cis-trans isomers of square planar complexes (Chapter 15). In both cases, the difference in geometry is responsible for isomerism the atoms are bonded to each other in the same way. 

C20-0004. Platinum forms a large collection of square planar complexes. Draw ball-and-stick models similar to those in Example for the cis and trans Isomers of [Pt (NH3)2 CI2 ]. 

The study of rapid, intermolecular ligand exchange between square-planar complexes trans-Ir(CO)L2X (X = C1 or Me, L - PPh3, P(p-tolyl)3, or PMePh2) by variable-temperature 31P NMR spectroscopy indicates that the reaction proceeds through dissociation of phosphine from the metal center and a subsequent associative substitution with other complexes 559,560 Ligand exchange between square-planar Ir and Pt complexes is slow. 

The square-planar complex (383) shows a monotropic smectic A-phase, and the X-ray diffraction study of the yellow form shows that the whole molecule adopts an extended rod-like shape with an all-trans conformation of the decycloxy chain.616... 

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 ... 

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... 

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. 

A study on the nucleophilic substitution on the square planar complex trans-[Pt(PEt3)2Cl2], a substrate similar to cisplatinum and other compounds largely used as antitumoral agents [53,62-65], has been carried out spectrophotometrically while changing the concentration of the nucleophile with time. The reaction vessel was... 

Square planar complexes of the formula [Ma,B2l may exhibit cis-trans isomerism ... 

Fig, 13.4 Competition of trans ligand (T) and leaving group (X) for a metal p orbital in a square planar complex. 

Trialkylphosphines, in general, give square planar complexes. A trans planar structure (146) has been found in most complexes which have been crystallographically investigated.1136,1138,n77 A cis planar structure was found, for example, in [NiCl2(PCnH13)2] (147).1188... 

---