Square planar molecules

Discernible associative character is operative for divalent 3t5 ions through manganese and the trivalent ions through iron, as is evident from the volumes of activation in Table 4. However, deprotonation of a water molecule enhances the reaction rates by utilising a conjugate base 7T- donation dissociative pathway. As can be seen from Table 4, there is a change in sign of the volume of activation AH. Four-coordinate square-planar molecules also show associative behavior in their reactions. 

The example of COj discussed previously, which has no vibrations which are active in both the Raman and infrared spectra, is an illustration of the Principle of Mutual Exclusion For a centrosymmetric molecule every Raman active vibration is inactive in the infrared and any infrared active vibration is inactive in the Raman spectrum. A centrosymmetric molecule is one which possesses a center of symmetry. A center of symmetry is a point in a molecule about which the atoms are arranged in conjugate pairs. That is, taking the center of inversion as the origin (0, 0, 0), for every atom positioned at (au, yi, z ) there will be an identical atom at (-a ,-, —y%, —z,). A square planar molecule XY4 has a center of symmetry at atom X, whereas a trigonal planar molecule XYS does not possess a center of symmetry. 

C09-0131. Imagine a square planar molecule, X Y2Z2, in which X is the central atom and Z is more... 

Complex 4a (see Fig. 1) differs from these catalytically active complexes only in the substitution of the complexed olefin molecules and hydrogen atom by a 7r-allyl group. The ligands in these square-planar molecules can adopt two different arrangements around the central nickel atom The olefin can either be trans (31a) or cis (31b) to the phosphine molecule. Because precedent exists for both these arrangements [e.g., 12 (84) and 30 (82)]. it is difficult to decide which of the two structures (31a or 31b) represents the catalytically active species. It is of course possible that the differences observed in the catalytic properties of systems having different ligands L and Y (Section IV) is due (at least in part) to differences in the population of 31a and 31b. 

Next, take the square planar molecule AB4 (say, PtClJ ), it is not linear, it does not have two or more Cn with 3 (though it does have one), its principal axis is CA and there are four axes perpendicular to this axis, the plane of the molecule is a ah plane and therefore it belongs to the point group. Notice that this molecule also possesses aA planes, hut the ah plane is enough to associate it with the point group. 

Xe 90" F F Square planar molecule with two nonbonding electron pairs, one above and one below the plane of the molecule... 

This group includes in particular the square planar molecules of [CuOR]4, R = Bu , SiPh3, C6H3Ph2-2,6 (analogs of[Cu404]4- oxocuprates), where the Cu atoms have linear coordination, the vertexes of the squares being occupied by the oxygen atoms [676, 1094, 1027]. In the cluster molecules of Mo, W, and... 

Determine the MOs for the square planar molecule ML4 of D4h symmetry. [Hint. Set up right-handed axes a, n 1, % on each ligand.]... 

When XeF4 was first prepared it was thought to be highly symmetrical, but it was not known whether it was a tetrahedral or a square-planar molecule. The infra-red absorption spectrum of XeF4 consists of three fundamental bands and the vibrational Raman spectrum also has three bands. Determine the symmetry of the normal modes of a... 

In coordination chemistry, many square planar species are known (for example, PtCl4 ). For a square planar molecule, use the appropriate character table to determine the types of hybridization possible for a metal surrounded in a square planar fashion by four ligands (consider hybrids used in a bonding only). 

Examples of square-planar complexes include the d, 16-electron complexes shown in Figure 13-10. To understand why 16-electron square-planar complexes might be especially stable, it is necessary to examine the molecular orbitals of such a complex. An energy diagram for the molecular orbitals of a square-planar molecule of formula ML4 (L = ligand that can function as both a donor and v acceptor) is shown in Figure 13-11. " ... 

A main objective of this work is to develop the relationship between the many reaction pathways leading to ligand substitution at square-planar molecules. Concentrating on more recent results to illustrate the processes under discussion, we examine in detail the evidence for operation of the less common and sometimes controversial routes such as dissociative ligand exchange (6). It cannot be stressed too much, however, that the field is still dominated by associative reactions, so to maintain a balance, as well as to provide the now necessary comparative evidence, we also cover the essential features of nucleophilic ligand replacements. 

The ki term, then, can be generally regarded as representing an associative solvation step, an important conclusion in view of the mounting evidence that some ligand replacements at square-planar molecules proceed dissociatively. Measures of the true magnitudes of ki for comparisons with 2 are obtained by dividing by the solvent concentration. ... 

Nucleophilic catalysis is known to lead to isomerization at square-planar molecules, but for many years it was believed that the only mechanism operating was consecutive displacement two sequential stereoretentive ligand substitutions (Scheme 5 A — B, then B C). A major argument in favor of this interpretation was the lack of examples of nonstereoretentive ligand replacements. It is now generally accepted, however, that pseudorotation can be, and sometimes is, the mechanism of such isomerization processes (50). The recognition that... 

A number of cases of oxidative additions of halogen molecules to square-planar molecules are also believed to proceed by forming... 

The picture regarding solvation of square-planar molecules remains obscure. From the associative reactions, there is no evidence that solvation at the metal is important, though entering group solvation is clearly indicated. The dissociative reactions show the relative importance of solvation of the leaving groups and substrates, and solvent interaction with the substrate elsewhere than at the metal ion is probably common. 

Two Lewis structures can be written for the square planar molecule PtCl2Br2 ... 

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