Dicopper complex, structure

Figure 13.3 A bis(/i,-oxo)dicopper complex represented using Eq. (13.6) where each boxed R group is H for the small QM system and benzyl for the large MM system. The structure on the right is a TS structure for H-atom transfer from C to O found by optimization at the hybrid level of theory. All other H atoms have been removed for clarity...

An important precursor of such studies is the investigation of model compounds that are fully characterized. For instance, the end-on mode of dioxygen binding in dicopper complexes has been investigated by molecular mechanics 3961. The successful reproduction of the structures of such model compounds provides a sound basis for the modeling of similar sites in metalloenzymes13971. 

Fig. 37. Proposed structures for some /u-peroxo-dicopper complexes.

A series of j8-diketonate Schiff base complexes (87 M = Ni, Cu, Pd, VO n=10, 12, 16) having a half disc-shape, was synthesised [164]. All the complexes, except the oxovanadium complexes, were mesomorphic (Colh), at relatively low temperatures. This approach was also applied to half-discshaped homodinuclear and heterodinuclear 1,3,5-triketonate Schiff base complexes, 88, and 1,3,5,7-tetraketonate Schiff base dicopper complexes, 89 [165]. The homodinuclear complexes 88, with M = M = Cu, X = OR, were mesomorphic showing Colh phases, whereas those with four chains (88 X = H) were not liquid-crystalline. Amongst the five heterodinuclear prepared (88 X = OR,n=14, Y = —CH2—CH2—, M = Cu, Pd, Ni, Mn, Co and M =Ni), only those with M = Cu, M = Ni and M = Pd, M =Ni, showed a mesophase, namely a Colh phase. A Colh phase was also observed for a structurally related compound, 89, (n=12, X = OR). 

Liquid-crystalline 1,3,5,7-tetraketonate dicopper complexes 90 and 91 also showed Colh phases [163, 164], In these cases, the neighbouring molecules must be rotated by 90° in respect to each other, in order to give rise to a time-averaged disc-shaped structure (Fig, 9a),... 

Table 1 Spectroscopic and structural data for monocopper superoxo, hydroperoxo, alkylperoxo, and acylperoxo complexes. Selected dicopper complexes are also listed... 

Martell and co-workers have shown that the BISTREN macrobicyclic structures can form dicobalt or dicopper complexes bound by nitrogens at opposite ends of the cryptand <82IC4253, 84IC1588, 86IC938, 88IC3630). Placement of the two Cu " ions within the macrocycle reduces the remaining cavity size and permits complexation of such small anions as fluoride and hydroxide. 

The large cavity of cryptand 17 allows another approach to anion coordination, the "cascade anion binding. " In a first step, the ligand binds by its tren subunits two Cu(II) cations. In a secorui step, the axial vacant hollow between the two alrecufy bound Cu(IT) cations will allow the binding of cn anion. An early example was based on computer analysis of potentiometric titrations data, and the efficientbinding of the chloride anion by the dicopper complex of 1 was postulated. Many other bis-tren-type figands were studied, and the cascade binding of anions such as Br, OH, N3, WCO. etc. was demonstrated. Many x-ray structures confirm the location of the anions between the various meted cations. ... 

The latest developments in this class of metal complexes were concerned with the structural modification of the triketone ligands to the [3, 6-type. Two series of dicopper complexes were obtained with six and eight peripheral chains respectively ((68) R = H or OC H2 +i)." Not surprising, they all showed a Coin phase, the complexes with eight chains having lower transition... 

Another series of metallodendrimers with a closely related molecular structure to (152) has been reported. " The dendritic ligand was obtained by condensation of the corresponding 1,3-dione with aminopropanol, and the dicopper complex was then formed by the reaction with copper(II) acetate. The ligand itself was not mesomorphic, but upon complexation, mesophases were observed whose stability was found to be dependent on the number of chains, and their length. 

Figure 12 Phenoxo-bridged dicopper complex (a) and a portion of the 2D square grid structure (b) in 82.

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