Ligand o- bonding

The valence bond picture for six-coordinate octahedral complexes involves dispi hybridization of the metal (Fig. I i.lc. d). The specific d orbitals that meet the symmetry requirements for the metal-ligand o bonds are the four-coordinate d complexes discussed above, the presence of unpaired electrons in some octahedral compounds renders the valence level ( — l)J orbitals unavailable for bonding. This is true, for instance, for paramagnetic [CoFJ3- (Fig. I I.lc). In these cases, the VR model invokes participation of -level dorbitals in the hybridization. 

All of the complexes are six-coordinate high-spin. A trans octahedral structure has been found, for example, in the two complexes [Ni(N02)2(NH3)4]1641 and [Ni(N02)2(en)2] (213).1642 This type of coordination is usually found in complexes where the ancillary ligands do not exert much interligand repulsion. On the other hand, when some steric repulsion is present in the amine ligands O-bonded nitrito coordination usually occurs, as exemplified by the complex [Ni(ONO)2(W,iV-Me2en)2] (214).1642... 

Conceivably, metal tetrachalcolenes of the types exemplified in Figure 3 for metal tetrathiolenes can be synthesized. For discrete polynuclear metal complexes, one can either build up the oligomeric clusters by forming in-plane, metal-ligand o- bonds with tetrathiolene and other... 

Chelation of cellulose ethers with metal ions increased their thermal stability, except for the case of CMC-Cu(II), HEC-Cr(III), and HEC-Cu(ll) complexes. The extent of increasing the thermal stability depends on the type of cellulose ether [anionic or neutral), electronegativity of metal ion, and the nephlauxetic parameter (degree of covalence in the metal-ligand-o bond). 

On comparison of the dielectric measurements with the previously calculated nephlauxetic parameter[11-13], Tables 7.10 and 7.11 show a good relation between the increase in the metal content, which is considered to be a measure for complex formation, and degree of covalence of metal-ligand-o bonds Q8-value) of cellulose ether complexes with Ni(II), Co(II) and Fe(III) ions. We excluded the complexes with Cu(II), because the geometry structure proposed for these complexes square planner Cu(II) complexes could not be calculated the j8-value. The decrease in the value of fi indicates considerable overlap with a strong covalent metal. 

Stronger metal-ligand o-bonding occurs when pyridines replace weak-base waters of hydration in the coordination sphere of Ni(II). 

Complexes with other Carbon-donor Ligands. The naphthyl hydrido Complexes of the type [MH(CioH,)(MejP CHg CHa-PMe2)2] (46), where M = Ru or Os , are isomorphous and isostructural. They are octahedral and contain a naphthyl ligand o-bonded to the metal atom and in a position cis to the hydrido hydrogen. The respective Ru-C, Os-C, and Ru-H distances are 2.16(1), 2.13(2), and 1.7 A in the osmium compound the hydrido hydrogen atom has not been located. The M-P distances range... 

For hypoligated complexes, either of the following valence-bond procedures is sometimes used to describe the metal-ligand o-bonding ... 

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