Group 17 Ligands

Xenon Bonded to Nitrogen. Several ligand groups form compounds containing xenon-nitrogen bonds (12). The first xenon-nitrogen... 

Ceitain acid dyes can have thek fastness piopeities impioved by combining the dye with a metal atom (chelation). The most common metal is chromium, although cobalt is sometimes used, and this can be introduced in a number of ways. The basic mechanism is donation of electron pans by groups in the dye (ligands) to a metal ion. For example, has a coordination number of 6, and therefore will accept six lone pans of electrons. Typical ligand groups... 

Based on the above results they have concluded that the ligand groups circularly arranged on the lower rim of the calixarene cavity construct a novel cyclic metal receptor for selective extraction of transition metal cations. Results suggest that the fine tuning in molecular... 

Here the ligand (L) can be either a neutral molecule or a charged ion, and successive replacement of water molecules by other ligand groups can occur until the complex ML, is formed n is the coordination number of the metal ion and represents the maximum number of monodentate ligands that can be bound to it. 

Table 6-3. Labelling of metal and ligand group orbitals in O symmetry.

Symmetry Metal orbital Ligand group orbital... 

The three-fold degenerate set of p orbitals are labelled tiu t for three-fold, u for odd under inversion through the centre of symmetry). As shown in Fig. 6-6, each metal p orbital matches symmetry with ligand group orbitals comprising just two... 

The field of transition metal complexes of isocyanides developed slowly over more than a century to a respectable subarea in coordination chemistry, and in the process seems to have attracted very little attention. Even the remarkable resurgence of transition metal organometallic chemistry in the last 20 years, and the realization that isocyanides and carbon monoxide should be quite similar as ligand groups in organometallic complexes, did not initiate an extensive development of this area of chemistry. Only in the last several years has this potentially important subject begun to receive the attention it would seem to deserve. 

The complexes Fe(CNR)4(CN)2 (R = H, CH3, C2H5) are reported to form 1 2 complexes with boron trihalides (65). In these complexes the BX3 group coordinates to the cyanide nitrogen, giving the ligand group [CNBXj] . A mention of a similar complex was made earlier 161). 

A number of other ligand groups are found to add to [Ni(CNBu )2] t, including azobenzene, tetracyanoethylene, fumaronitrile, and maleonitrile, diphenylacetylene and dimethyl acetylenedicarboxylate 109,110) [Eq. (29)]. 

To illustrate this point, the contributions of the occupied molecular orbitals to the total electron density at the nucleus are summarized in Table 5.2 for Fep4 (S - 5/2). It is evident from the table that the contributions coming from the orbitals at —6,966 eV must be assigned to the iron Is orbital, those from orbitals at —816 eV to the iron 2s orbital, and those from orbitals at —95 eV to the iron 3s orbital. In this highly symmetric complex, only two valence orbitals contribute to p(0), i.e. the —25 eV contribution from the totally symmetric ligand-group orbital that is derived from the F 2s orbitals and the —1 eV contribution from the totally symmetric... 

Dialkylboron enolates cannot accommodate an additional aldehyde ligand group and chelated TSs are not expected. When BF3 is used as the Lewis acid, chelation is... 

The ligand group can be introduced either on the meso or on the /5-pyrrole position of the porphyrin ring, but the synthesis of the meso-functionalized derivatives is easier and has been more widely exploited. Balch (50-53) reported that the insertion of trivalent ions such as Fe(III) (32) and Mn(III) (33) into octaethyl porphyrins functionalized at one meso position with a hydroxy group (oxophlorins) leads to the formation of a dimeric head-to-tail complex in solution (Fig. 11a) (50,51). An X-ray crystal structure was obtained for the analogous In(III) complex (34), and this confirmed the head-to-tail geometry that the authors inferred for the other dimers in solution (53) (Fig. lib). The dimers are stable in chloroform but open on addition of protic acids or pyridine (52). The Fe(III) octaethyloxophlorin dimer (52) is easily oxidized by silver salts. The one-electron oxidation is more favorable than for the corresponding monomer or p-oxo dimer, presumably because of the close interaction of the 7r-systems in the self-assembled dimer. 

The 4s orbital on the metal has a positive sign that is invariant in all directions. The combination of ligand orbitals, which are referred to as symmetry adjusted linear combinations (SALC) or ligand group... 

In a similar way, we obtain the wave functions for combinations of ligand group orbitals with the py and pz orbitals from the metal ion. They can be written as... 

When we inspect the dxi 2 orbital, we see that the lobes have positive signs in the x direction and negative signs in the y direction as shown in Figure 17.15f. The ligand group orbitals that match the symmetry of the dx> 2 orbital will be... 

Orbitals on metal Molecular orbitals Ligand group orbitals... 

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