Macrocycles dimethylglyoxime

An enormous, wide-ranging literature on NF macrocyclic chemistry is now available (see Section 5.7). The H-bonded dimethylglyoxime complex [Ni(dmgH)2] (64) is one of the more important, since this species is used for the gravimetric determination of Ni. Tike many square-planar nF complexes it stacks in the solid state with a Ni-Ni separation of 3.24A. Related nF complexes of functionalized dmg ligands frequently show this type of stacking interactions. 

Fe complex of 2,2 -bipyridine-3,5 -dicarboxylic acid but the pyridine-4-carboxylic acid was observed not to be photosensitive in the presence of Fe ions. The photochemistry of low-spin Fe complexes with macrocyclic ligands continues to be a field that attracts interest. Irradiation of the charge-transfer bands of [Fe(TIM)(OMe)(MeOH)] + (TIM = 2,3,9,10-tetramethyl-l,4,8,ll-tetraazacyclotetradeca-l,3,8,10-tetraene) and of [Fe(DMG)2(OMe)(MeOH)] (DMG = dimethylglyoxime), was found to lead to oxidation of the co-ordinated MeOH and reduction of the metal centre. These photoreactions have been attributed to the population of methoxy-to-Fe CT states. 

A similar picture is reflected by the stability constants of the mixed complexes formed in various donor solvents between iodide ions and nickel macrocyclic systems with inner coordination spheres analogous to those of the dimethylglyoxime complexes. 

This second inlcrprclalion is in accordance with the observation that nickel dimethylglyoximate, which is a perfect analogue of the macrocyclic complex with the two propylene bridges, except for the difference that both propylene bridges arc replaced with O—H—O groups, is completely unable to coordinate monofunctional ligands [Bu 63]. 

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