Molecular orbitals square planar complex

FIGURE 17.20 A molecular orbital energy level diagram for a square planar complex. 

Determine the qualitative form of the molecular orbitals for the square-planar complex Ni(CN)48-. (Assume that each CN ligand provides one e-type and two vr-type orbitals to the system.)... 

It is the purpose of this paper to develop a molecular orbital theory for square planar metal complexes. Both the spectral and magnetic properties of typical square planar complexes of Ni2+, Pda+, Pts+ and Au8+ will be considered m order to arrive at consistent values for the molecular orbital energies. However, in contrast to previous workers, effort will be concentrated on the assignments of the charge transfer bands of representative square planar complexes. 

Molecular Orbitals for Square Planar Complexes.— Figure 1 shows a square planar complex in a coordinate system with the central atom at the origin, and the four ligands along the x- and y-axes. The orbital transformation scheme in the D4h symmetry is given in Table I. 

The general molecular orbital energy level schemes arrived at for square planar complexes are given in Fig. 2 (case 1) and Fig. 3 (case 2). Group molecular orbital overlap integrals (for Ni(CN)42-) and ligand exchange interactions are summarized in Table II. 

A coordinate system for a square-planar complex ML4 (Z>4h symmetry) is displayed in Fig. 8.9.1. The linear combinations of ligand orbitals, matched in symmetry with the metal orbitals, and the molecular orbitals they form, are summarized in Table 8.9.1. A schematic energy level diagram for this type of complexes is given in Fig. 8.9.2. 

Table 8.9.1. Summary of the formation of molecular orbitals in square-planar complexes ML4...

One always begins with the monomer. What are its frontier levels The classical crystal field or molecular orbital picture of a square planar complex (Fig. 2) leads to a 4 below 1 splitting of the d block.11 For 16 electrons we have z2, xz, yz, and xy occupied and x2-y2 empty. Competing with the ligand field-destabilized x2-y2 orbital for being the lowest unoccupied molecular orbital (LUMO) of the molecule is the metal z. These two orbitals can be manipulated in understandable ways x acceptors push z down, x donors push it up. Better a donors push x2-y2 up. 

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. " ... 

FIGURE 13-11 Molecular Orbital Energy Levels for a Square-Planar Complex. 

Figure 1. Examples of distortions caused by populating antibonding molecular orbitals. Top Totally symmetric expansion of a square planar complex caused by populating the molecular orbital involving the d 2 2 metal orbital shown under the arrow. Bottom Totally symmetric expansion of a six coordinate complex caused by populating the molecular orbital involving the d 2 metal orbital shown under the arrow.

Large geometrical distortion in the lowest excited states of Pt(gly)2 is also suggested by spectroscopic studies, which have indicated that similar square planar complexes have pseudotetra-hedral excited states (93a), by semi-empirical molecular orbital calculations (56), and also by recent quenching and sensitization studies of the cis trans reaction (Section lII-D-1). ... 

Molecular Orbitals of Square Planar Complexes (Only o donor and it acceptor interactions are shown.)... 

In the structure of Zeise s salt, the ethylene occupies the fourth coordination site of the square planar complex with the CC axis perpendicular to the platinum-ligand plane. In this compound, the dsp2 hybridised s orbital of Pt overlaps with / -bonding molecular orbitals of ethylene. Simultaneously, the filled dp orbital of Pt overlaps with p orbital of C2H4. 

We have seen in Chapter 11 that the square planar configuration is particularly stable because Tour of the mostly metal nd molecular orbitals are stabilized relative to the dxj.yS-derived orbital. IW> Three of the four orbitals (metal-ligand it bonding, but to a first approximation, the interact with any other orbitals in an isolated square planar complex.147 Suppose, however, we configure the complex so that the is farced into interaction. By bridging two square planar complexes, the two systems are forced to lie parallel (face-to-face) at a fixed distance ... 

Many of the complexes for which 7p M data have been collected are those of platinum(II) and rhodium(I) compounds. These are square planar complexes and the highest microsymmetry corresponding to this stereochemistry is In this symmetry group, the d 2 orbital and the s orbital on the acceptor transform as A g, so there will be three molecular orbitals involving the s orbital of the metal instead of... 

---