Coordinative metal-ligand bonding

5 Coordinative metal-ligand bonding 4.5.1 A preliminary overview of metal-ligand coordination 

Much confusion in the early history of aqueous transition-metal chemistry stemmed from the inability to distinguish free formula ions (serving merely as solvent-separated counterions) from those that remain in direct coordinated contact with 

Species Symmetry Angles (degrees) ctmn 7Tmn ctmh  

Surprisingly, the compound (4.66c) can be obtained in two distinct isomeric forms (of distinct colors, etc.) whereas (4.66a) and (4.66b) each correspond to unique chemical species. Plausible structural formulas for such species presented a great mystery to nineteenth-century chemists. 

The structural and formulaic questions concerning compounds such as (4.66a)-(4.66c) were largely resolved by Alfred Werner,31 the first inorganic chemist to receive a Nobel Prize (1913). Werner carefully studied the total number of free ions contributing to ionic conductivity, as well as the number of free chloride ions that could be precipitated (exchanged with a more soluble ion) under conditions of excess Ag+, namely 

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Abstract This review presents an overview of the area of anion-templated synthesis of molecules and supramolecular assemblies. The review is divided into two main sections the first part deals with anion-templated systems where the final products are linked by bonds that are not reversible under the conditions of the experiment Several recent examples of macrocycles, cages and interlocked species are presented in this section. The second part of the chapter, presents a discussion of anion-templation in systems containing reversible bonds that give rise to dynamic combinatorial libraries (either by formation of coordination metal-ligand bonds or by reversible covalent bonds). 

Figures 11a and 11b were constructed assuming that the one-electron orbital energies depend on the nuclear coordinates. Metal-ligand bond lengths tend to be different in different oxidation states of most transition metal complexes. As a result, the bridging ligand will tend to move in a concerted manner away from one metal towards the other as the electron is transferred,...

Scheme 3.40 Procedure to immobilize Pd +NPs on amino modified GO by means of coordinative metal-ligand bonds.

The mutual influence of ligands in transition metal coordination compounds with multiple metal-ligand bonds. E. M. Shustorovich, M. A. Porai-Koshits and Y. A. Buslaev, Coord. Chem. Rev., 1975,17,1-98 (345). 

As briefly stated in the introduction, we may consider one-dimensional cross sections through the zero-order potential energy surfaces for the two spin states, cf. Fig. 9, in order to illustrate the spin interconversion process and the accompanying modification of molecular structure. The potential energy of the complex in the particular spin state is thus plotted as a function of the vibrational coordinate that is most active in the process, i.e., the metal-ligand bond distance, R. These potential curves may be taken to represent a suitable cross section of the metal 3N-6 dimensional potential energy hypersurface of the molecule. Each potential curve has a minimum corresponding to the stable... 

Four-coordinate complexes exhibit lower isomer shifts than six-coordinate compounds. Metal-ligand bonds are shorter and more covalent if the coordination number is smaller because of less steric hindrance and less overlap with antibonding 2g orbitals in the case of four as compared to six bonds. 

Two other publications on Ir (73 keV) Mossbauer spectroscopy of complex compounds of iridium have been reported by Williams et al. [291,292]. In their first article [291], they have shown that the additive model suggested by Bancroft [293] does not account satisfactorily for the partial isomer shift and partial quadrupole splitting in Ir(lll) complexes. Their second article [292] deals with four-coordinate formally lr(l) complexes. They observed, like other authors on similar low-valent iridium compounds [284], only small differences in the isomer shifts, which they attributed to the interaction between the metal-ligand bonds leading to compensation effects. Their interpretation is supported by changes in the NMR data of the phosphine ligands and in the frequency of the carbonyl stretching vibration. 

A unique aspect of the G-quartets 34 and 16 is that their assembly involves only metal-ligand bond formation. Since the sites on the nucleobase involved in coordination are either N7 or [N7 + N3] this... 

X-ray structural studies of the diamagnetic anion (406) confirm that the Ir(-I) center is in a distorted coordination geometry intermediate between square planar and tetrahedral, with the P donor atoms in a cis position. The metal-ligand bond distances do not show significant changes among (404), (405), and (406). The Ir1/0 and Ir0/(-1) redox couples are measured at easily accessible potentials and are solvent dependent. 

From the localized Lewis-like perspective, we can picture coordinative metal-ligand interactions as involving two distinct types of localized bonding (which have already been discussed in the context of main-group chemistry Sections 3.2.11 and 3.5) ... 

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