Metal—ligand bonds formation

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... 

Besides reactions with alkali salts, there are several groups investigating metal-ligand bond formation by mechanochemical methods. For example Orita et al. have shown that the supramolecular self-assembly of a number of complexes can take place under solvent-free conditions, leading to higher-order fabrications of two- or three-dimensional topology and even double... 

Figure 2.3 Schematic presentation of orbital overlaps for metal-ligand bond formations.

A Figure 23.27 Metal-ligand bond formation. The ligand acts as a Lewis base by donating its nonbonding electron pair to an empty orbital on the metal ion. The bond that results is strongly polar with some covalent character. 

Self-assembly can also be induced by metal-ligand interactions [33,34], In this case, supramolecular coordination complexes that are thermodynamically favored products can be obtained from spontaneous metal—ligand bond formation in a mixture of soluble metal and ligand precursors [19]. These self-assembled capsules, which are known as coordination-driven self-assembly, are more robust than hydrogen bond capsules [13,35]. 

The data for the 1,2-diaminoethane complexes now parallels the trends in ionic radius and LFSE rather closely, except for the iron case, to which we return shortly. What is happening Copper(ii) ions possess a configuration, and you will recall that we expect such a configuration to exhibit a Jahn-Teller distortion - the six metal-ligand bonds in octahedral copper(ii) complexes are not all of equal strength. The typical pattern of Jahn-Teller distortions observed in copper(ii) complexes involves the formation of four short and two long metal-ligand bonds. 

Ligand substitution reactions of NO leading to metal-nitrosyl bond formation were first quantitatively studied for metalloporphyrins, (M(Por)), and heme proteins a few decades ago (20), and have been the subject of a recent review (20d). Despite the large volume of work, systematic mechanistic studies have been limited. As with the Rum(salen) complexes discussed above, photoexcitation of met allop or phyr in nitrosyls results in labilization of NO. In such studies, laser flash photolysis is used to labilize NO from a M(Por)(NO) precursor, and subsequent relaxation of the non-steady state system back to equilibrium (Eq. (9)) is monitored spectroscopically. 

Under these conditions, the formation rate constant, k, can be estimated from the product of the outer sphere stability constant, Kos, and the water loss rate constant, h2o, (equation (28) Table 2). The outer sphere stability constant can be estimated from the free energy of electrostatic interaction between M(H20)q+ and L and the ionic strength of the medium [5,164,172,173]. Consequently, Kos does not depend on the chemical nature of the ligand. A similar mechanism will also apply to a coordination complex with polydentate ligands, if the rate-limiting step is the formation of the first metal-ligand bond [5]. Values for the dissociation rate constants, k, are usually estimated from the thermodynamic equilibrium constant, using calculated values of kf ... 

In the chemistry of main-group element sulfoxide complexes, a relationship between Aj/(S=0) and the enthalpy of formation of the sulfoxide complex has been derived (159). The applicability of the equation has only been examined for O-l SO complexes, and the constraints on using Ai (S=0) as a measure of metal-ligand bond strength should be borne in mind during its application. 

This monograph contains enthalpies of formation, heat capacities, entropies, and metal-ligand bond dissociation enthalpies of organometallic compounds of transition and main group elements. 

In order to understand the basic aspects of an electrochemical investigation on inorganic molecules (in its widest meaning, of any molecule which contains at least one metal centre) it must be taken into account that in these molecules the metal-ligand bonds are prevailingly covalent type. Since electrochemical techniques allow one to add or remove electrons in a controlled manner, it is conceivable that the addition or removal of electrons inside these molecules can lead to the formation of new bonds or to the breakage of existing bonds. 

Two additional points that are self-evident are discussed below for the sake of completeness. The coordination number of a metal ion counting all ligands other than the adjacent metal involved in multiple metal bonding is less than the maximum coordination number possible for that metal center. Furthermore, the number of d-electrons on the metal is nearly equal to the number of metal valence orbitals not involved in metal-ligand bonding to optimize metal-metal bond formation by filled bonding MOs. 

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