Solvent Exchange on d-Transition Metal Ions

The increase of the exchange rate constants for solvent exchange on [MS6]2+/3+ in the sequence MeOH MeCN DMF H20 is independent of the metal ion and cannot be linked to specific properties like dielectric constant, donor number or size. It appears to reflect the overall characteristics of the solvent. 

The Ia and A mechanisms are mutually exclusive, since the 7 -coordinate transition state has an imaginary mode that either describes a concerted entry/leaving of the ligands and the mechanism is Ia (Fig. 6a) or only the motion of the entering (or leaving ligand) and the mechanism is A (Fig. 6b) (104). The Id and D mechanisms are not mutually exclusive and up to now no Id has been computed, most probably due to the omission of the second coordination sphere (104). 

Rotzinger s calculations confirmed the mechanistic crossover for water exchange on the first-row transition metal ions. The calculations predict Ia mechanisms for V2+ Mn2+ and D (or Id) mechanisms for Mn2+, Fe2+, Cu2+, and Zn2+. A d-activated mechanism for water exchange 

Solvation of the divalent copper ion requires some special remarks. In solid state hexa-coordinate Cu2+ shows Jahn-Teller distortion the metal-ligand bonds of four ligands in the equatorial plane are shorter 

The important influence of the LFAE is also nicely demonstrated on the labilities of V2+ andV3+.The smaller LFAE of t g [V(H20)6]3+ makes it about six times more labile than t2g [V(H20)6]2+ despite the smaller charge of the 2+ complex (Fig. 5). Both exchange processes are a-acti-vated with negative volumes of activation of —8.9 (V3+) (113) and —4.1 cm3 mol-1 (V2+) (68). 

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