First order effects, coordination numbers

So, first-order effects determine the coordination number in species such as LnCl and [Ln(H20)9] +, whereas bulky ligands with high second-order steric effects lead to crowding and impose low coordination numbers in [Ln (CH(SiMe3)2 3] and [Ln (N(SiMe3)2 j]. 

It is possible to consider first the coordination numbers, and then the atomic numbers, or to proceed in the reverse order. If there are more differences in atomic numbers than in coordination numbers the first mode is more effective, while the existence of many atoms of the same element with different coordination number favors the use of the second. Most atoms of a given chemical element have the same coordination number, particularly in organic compounds. If the H-atoms are, however, disregarded, one obtains constitutional formulas which can be indexed quite well by primary consideration of the degrees of the nodes0), i.e., the number of immediate covalent neighbors. 

A number of studies have also been made of the hydrolysis of nitriles in the coordination sphere of cobalt(III). Pinnell et al.3 4 found that benzonitrile and 3- and 4-cyanophenol coordinated to pentaamminecobalt(III) are hydrolyzed in basic solution to the corresponding N-bonded carboxamide (equation 22). The reaction is first order in hydroxide ion and first order in the complex with koH= 18.8M 1s 1 at 25.6 °C for the benzonitrile derivative. As fc0H for the base hydrolysis of benzonitrile is 8.2 x 10-6 M-1 s at 25.6 °C, the rate acceleration is ca. 2.3 x 106-fold. The product of hydrolysis is converted to [(NH3)5CoNH2COPh]3+ in acidic solution and the pJC of the protonated complex is 1.65 at 25 °C. Similar effects have been observed with aliphatic nitriles.315 Thus, base hydrolysis of acetonitrile to acetamide is promoted by a factor of 2 x 106 on coordination to [Co(NH3)5]3+. 

A number of interesting studies have also been carried out using labile metal ions. The effect of metal ions on the mechanism of the condensation of the salicylaldehydato ion (sal) with primary amines has been studied kinetically.385-387 Under suitable experimental conditions, the reaction of sal- with diethylenetriamine (dien) in the presence of copper(II) occurs by first order kinetics.387 The reaction is envisaged to occur by prior coordination of the reactants to copper,... 

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