Tetrahedral/square planar interconversions

Numerous aminotroponeimineate complexes of type e, with nickel (II), have been prepared and are found to undergo square planar-tetrahedral interconversion (27). Extensive nuclear magnetic resonance data have been accumulated on this system along with magnetic moment and electronic spectral measurements (27). 

Other kinetic studies concerned with square-planar nickel(ii) complexes include those of [Ni(trigly)] with Qfanide, redistribution reactions involving pairs of bis-bidentate nickel(n) complexes, and square-planar tetrahedral interconversions of [Ni(tertiary phosphine)2X2] compounds. ... 

In solution the cfl complexes of Ni11 are characterized by several rapid equilibria between species having different coordination numbers and/or geometries. Upon irradiation, these equilibria are perturbed and can be studied by relaxation techniques. A number of photoinduced changes have been investigated in this manner including square planar/tetrahedral, four-coordinate/five-coordinate and four-coordinate/six-coordinate interconversions.138... 

THE SQUARE PLANAR-TETRAHEDRAL ML4 INTERCONVERSION 307 TABLE 16.1. Mean Nickel-Ligand Distances (A) ... 

Three relaxation processes observed during the Q-switched laser photolysis of dibromo-[l,3-bis(diphenylphosphino)propane]nickel(ii) in acetonitrile have been assigned " to the relaxation of coupled equilibria involving planar and tetrahedral isomers of the complex together with ion pairs and free ions. The kinetics of the rapid square-planar-octahedral interconversion accompanying the addition of two unidentate ligands L to (14) in chlorobenzene are consistent with a two-step mechanism,... 

Figure 19.3 Schematic interconversion of square planar and tetrahedral geometries.

Tetraaza macrocycles usually coordinate with the N4 donor set approximately coplanar for square planar or trans octahedral arrangements. The more flexible macrocycles can also coordinate in folded arrangements, usually to accommodate an additional chelate ligand in an octahedral arrangement, and planar-folded interconversions are facile. In planar coordination some degree of tetrahedral distortion of the donor set is common, and this can become substantial for larger ring... 

Fig. 9 Dependences of the energies of the d-d transitions (NEVPT2 results) for CuC142 on the angle a (Fig. 4) describing the tetrahedral to square planar interconversion...

Some structures are complicated by interconversions between square planar and tetrahedral, or square planar and octahedral coordination as we discuss later. In addition, the potential of some ligands to bridge between metal centres may cause ambiguity. For example, alkali metal salts of [NiF3] , [NiF4] and [NiCl3] crystallize with extended... 

A specific example serves to illustrate the general properties of gated processes. Four-coordinate copper prefers different ligand geometries in the two oxidation states Cu generally exhibits a square planar coordination, while Cu ligands are generally tetrahedral. If interconversion between these confer-... 

In the first section of tills chapter wc built up the orbitals of a square planar ML complex. An alternative geometry would be a tetrahedral species. There arc two basic ways to convert a square planar complex into a tetrahedral one. The 16.29 to 16.30 interconversion involves twisting one pair of cis ligands about an axis shown in 16.29. That will conserve D2 symmetry along all points that interconnect 16.29 with 16.30. In the other path the two trans L—M—L angles arc decreased, as shown in 16.31, ultimately yielding the tetrahedron 16.32. This conserves D2J symmetry. The elements of this latter pathway have actually been developed in Section 15.4, so we shall briefly explore this distortion. A Walsh... 

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