Copper -cyclam complex structures

Structures of l,4,8,ll-tetraazacyclotetradecanecopper(II) complexes ([Cu(cyclam)] ) with F", Cl, and Br" have been determined in crystals (1-3). The effect of solvents on the axial ligation constants of (C-meso- (C) and C-rac-5,5,7,12,12,14-hexamethyl-cyclam (L ) )copper(II) complexes with Cl and Br have been studied in water and in methanol, suggesting an interesting... 

In the present study, we synthesized dibromo(l,4,8,ll-tetraazacyclotetradecane)copper(II) ([CuBr2(cyclam)]) and diaqua(l,4,8,ll-tetraazacyclotetradecane)copper(II) difluoride four hydrate ([Cu(cyclam)-(H20)2]F2 4H20) complexes and performed single crystal structure analysis and X-ray absorption near-edge structure (XANES) measurements in crystals and in aqueous solution. Furthermore, DV-Xa molecular orbital calculations have been made for models based on these results, and the structures and electronic states of the [Cu(cyclam)] complexes in crystals and in aqueous solution are discussed, in particular, on the axial coordination to Cu(II). 

Scheme 5.2 Synthesis of tetra (hydroxy propyl) cyclam (5.21) via Michael addition followed by reduction, and X-ray crystal structure of its 1 1 copper(II) acetate complex.19...

Mixed aza-thiamacrocyclic derivatives of ferrocene 71 and 72 have also been prepared and the X-ray crystal structures of 72 and its copper complex reported [90]. Electrochemical studies revealed that the redox couples of 71 and 72 were perturbed to more positive potentials by 60 and 40 mV, respectively, on coordination with Cu ", even though the X-ray structure of the complex with 72 showed square planar coordination of the Cu " by the four sulfur atoms rather than by nitrogen. The cyclam ligand 73 derived from ferrocene has also been prepared and shown to recognise Ni and cations electrochemically [90]. 

Although the term dynamical combinatorial chemistry has only been coined at the end of the last century, the template effect has been used for a much longer time. Some of the best known macrocyclic ligands such as cyclam probably would not have been known so well if their synthesis had not implied the template effect. Probably the first example of a metal ion template for the formation of imino-macrocycles N. F. Curtis, D. A. House, Structure of some aliphatic Schiff-base complexes of nickel (II) and copper (II), Chem. and End., 1961, 42, 1708-1709. 

As mentioned before, Copper prefers macrocyclic chelators like cyclam-14 and its derivatives. Cyclam-14 forms thermodynamically stable complexes and its X-ray structure shows a square-plane configuration with four equal Cu-N bonds (Tasker and Sklar 1975). This complex with coordination number four lose less than 0.5% metal when incubated for 24 h in human serum. Open chain chelators do not reach this stability. Its bifunctional derivative CPTA (O Fig. 45.17) coupled to an antibody and labeled with Cu shows a half-life for copper exchange in phosphate buffer >1,000 days (Smith-Jones et al. 1991). 

On the other hand, it is also apparent that apart from fundamental spectroscopic, photophysical, and photochemical studies, as well as molecular and electronic structure investigations, the long-lived luminescence of d metal complexes also allows this class of compounds to be used as a luminescent probe and sensory material. For example, studies on the interaction of copper(I) [94] and gold(I) [135] complexes with DNA have been reported recently. The attachment of organic receptor type molecules such as crown ethers [157,177,178] and cyclams [145,169] to these metal centers has also been carried out. The binding of different cations to these complexes has been shown to be specific and selective. Studies along these lines will definitely provide a new generation of luminescent sensory materials. 

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