Tetrahedral metal complexes

Table 5 Dipole Moments ps (D) of Square-planar and Tetrahedral Metal Complexes [M(RCS=CHCOCF,),]...

The molecular orbital theory as applied to octahedral and tetrahedral metal complexes. 

The convention used to describe the absolute configurations of tetrahedral centres was originally developed for carbon atom centres (see Ref. 13 and Section P-91 of Ref. 1) but can be used for any tetrahedral centre. There is no need to alter the rules in treating tetrahedral metal complexes. 

Fig. 4. The Coulombic correlation of the z-component of the electric dipole induced in each of the ligands by the xy-component of the quadrupole moment of a metal ion d-d transition in a tetrahedral metal complex...

Metal ions are excellent templates to build >2 and octupolar second-order NLO chromophores therefore their associations with functionalized bip5nidyl ligands give rise to octahedral and tetrahedral metal complexes with large quadratic hyperpolarizabilities [76]. The adequate functionalization of these octupoles allows their incorporation into macromolecular architectures such as polymers and metal-lodendrimers [76]. Various octupolar tris chelated Ru complexes are characterized by a significant second-order NLO response as evidenced by HRS [18]. 

A simple example of a dissymetric molecule is one with a tetrahedral structure wherein the central atom is surrounded by four different atoms or groups. There are many examples of such molecules among organic compounds. The structures of optical isomers may be represented by the amino acids, structures XVI and XVII. Tetrahedral metal complexes are generally... 

A good example of a tetrahedral metal complex is VCU, the coordinate system for which is shown in Fig. 9-16. We have already discussed the role of s and f valence orbitals in a tetrahedral molecule (Chapter V). The 4s and 4p orbitals of vanadium can be used to form tr molecular orbitals. The 34, and orbitals are also situated properly for such use. In valence-bond language, jd and sp hybrid orbitals are both tetrahedrally directed. The and... 

Tetrahedral metal complexes Spin-allowed, partially Laporte-forbidden d d lO -lO ... 

Derive the MO diagram for a tetrahedral metal complex with cr-donor ligands. For the ligand SALCs, reference to the case of methane (in Section 7.4) may be useful here ... 

Tetrahedral metal complexes are very frequent. Such complexes can be formed by almost all elements with p electrons in the outer shell. F, Te, Bi, Po, At and the noble gases are exceptions. Almost all transition metals, except Nb, Ta, Sc, Y, La and Ac, build tetrahedral complexes. Substitution mechanisms of the tetrahedral complexes of Si, Ge, Sn and P have been most extensively studied. These substitutions are of the A or type, with an intermediate of the coordination number 5, their possible geometries being a square pyramid or a trigonal bipyramid. 

However, with the application in the 19, iOs of crystal held theory to transition-metal ehemistry it was realized that CFSEs were unfavourable to the lormation of tetrahedral d complexes, and previous assignments were re-examined. A typical ca.se was Ni(acac)i. which had often been cited as an example of a tetrahedral nickel complex, but which was shown - in I9. I6 to be trimeric and octahedral. The over-zealous were then inclined to regard tetrahedral d" as non-existent until Hrst L.. M. Venanz.i and then N., S. Gill and R. S. Nyholm" demonstrated the existence of discrete tetrahedral species which in some cases were also rather easily prepared. 

Four-coordinate metal complexes may have either of two different geometries (Figure 15.3). The four bonds from the central metal may be directed toward the comers of a regular tetrahedron. This is what we would expect from VSEPR model (recall Chapter 7). Two common tetrahedral complexes are Zn(NH3)42+ and C0CI42. ... 

Slovokhotov, Yu.L. and Struchkov, Yu.T (1984) X-ray crystal structure of a distorted tetrahedral cluster in the salt [(Ph P)4Au4N] BF4 . Geometrical indication of stable electronic configurations in post-transition metal complexes and the magic number 18-e in centred gold clusters. Journal of Organometallic Chemistry, 177, 143-146. 

In 2005, Carretero et al. reported a second example of chiral catalysts based on S/P-coordination employed in the catalysis of the enantioselective Diels-Alder reaction, namely palladium complexes of chiral planar l-phosphino-2-sulfenylferrocenes (Fesulphos). This new family of chiral ligands afforded, in the presence of PdCl2, high enantioselectivities of up to 95% ee, in the asymmetric Diels-Alder reaction of cyclopentadiene with A-acryloyl-l,3-oxazolidin-2-one (Scheme 5.17). The S/P-bidentate character of the Fesulphos ligands has been proved by X-ray diffraction analysis of several metal complexes. When the reaction was performed in the presence of the corresponding copper-chelates, a lower and opposite enantioselectivity was obtained. This difference of results was explained by the geometry of the palladium (square-planar) and copper (tetrahedral) complexes. 

Beryllium(II) is the smallest metal ion, r = 27 pm (2), and as a consequence forms predominantly tetrahedral complexes. Solution NMR (nuclear magnetic resonance) (59-61) and x-ray diffraction studies (62) show [Be(H20)4]2+ to be the solvated species in water. In the solid state, x-ray diffraction studies show [Be(H20)4]2+ to be tetrahedral (63), as do neutron diffraction (64), infrared, and Raman scattering spectroscopic studies (65). Beryllium(II) is the only tetrahedral metal ion for which a significant quantity of both solvent-exchange and ligand-substitution data are available, and accordingly it occupies a... 

L-piperidine-2-carboxylic acid is a non-proteinogenic amino acid that is a metabolite of lysine. The zinc complexes of DL-piperidine-2-carboxylic acid, DL-piperidine-3-carboxylic acid, and piperidine-4-carboxylic acid have been studied. The X-ray crystal structures have been determined for the latter two. [ZnCl2(DL-piperidine 3-carboxylate)2] (42) is monomeric with a tetrahedral metal center and monodentate carboxylates. [Zn2Cl4(piperidine-4-carboxylate)2] (43) contains two bridging carboxylates in a dimeric structure. IR studies suggest that the DL-piperidine-2-carboxy-lato zinc has monodentate carboxylate ligands coordinating.392... 

Varying ratios of the ligands 7V-(2-thiophenyl)-2,5-dimethylpyrrole and V-methylimidazole were used to form tetrahedral zinc complexes with S4, S3N, and S2N2 coordination spheres. X-ray structural analyses and IR spectra were recorded for all compounds and the relevance to zinc finger proteins was discussed. The comparison to cobalt and cadmium structures showed only minor differences, supporting the theory that changes on substituting these metals into zinc proteins would be minor.538... 

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