Cryptates copper

The subject molecules are obtained as dinuclear copper complexes with the octa-aza cryptate ligands L1 and L2 shown in Scheme 1. 

Much more pronounced is the macrocyclic or [l]-cryptate effect found in 10 as compared with 2 the stability constant for K+ complexation increases by about 104 (in methanol) on ring formation. A similar increase has been observed between copper-(II) complexes of acyclic and macro-cyclic tetra-aza ligands (139). 

Motekaitis, R. J., Martell, A. E., Murase, I., Cascade halide binding by multiprotonated bistren and copper(II) bistren cryptates. Inorg. Chem. 1986, 25, 938-944. 

Menif, R. Reibenspies, J. Martell, A. E. Synthesis, protonation constants, and copper(II) and cobalt(II) binding constants of a new octaaza macrobicylic cryptand (MX)3crystal structures of the cryptand and of the carbonato-bridged dinuclear copper(II) cryptate, Inorg. Chem. 1991, 30, 3446-3454. 

Fabbrizzi and co-workers have demonstrated the use of bis-copper(II) cryptates to sense ambidentate anions [49]. On titrating molecule 71 with NaN3 in aqueous solution, the colour changed from pale blue to bright green and an anion-metal LMCT absorption appeared at 400 nm. X-ray diffraction studies have shown that the azide anion is held colinear with the two Cu(II) centres, coordinated through the two terminal sp2-hybridised nitrogen atoms. Stability constants for 71 with a variety of anions in aqueous solution were calculated and the selectivity of this anion sensor was found to be controlled by the bite distance between the two copper atoms (Fig. 1). 

Cryptate 72, in which the aryl spacer of 71 is replaced with a furanyl unit, acts a colorimetric sensor for anions. UV-vis titrations in aqueous solution gave log K values for the 1 1 halide/receptor adducts of 3.98 for chloride, 3.01 for bromide and 2.39 for iodide. X-ray diffraction studies confirm that bromide is held between the two copper atoms. Under the same conditions 72 also interacts strongly with azide (log K=4.7) and thiocyanate (log X=4.28) anions. This receptor is interesting because of its lack of selectivity compared to 71. The complex appears to be able to expand and contract its bite length in order to accommodate anions of various sizes. 

Cryptand 193 forms a cryptate containing two copper(II) ions. The reduction potentials of the two ions would be expected to be vastly different, because the Cu2 + complex of 194 is reduced at a potential 500 mV less positive than the Cu2 + complex of 195. This is indeed found to be the case. The dinuclear Cu2+ complex of 193 undergoes a one-electron reduction at +550 mV, The second Cu2+ ion is reduced at +70 mV. Therefore, the first reduction must be that of the Cu2+ ion complexed by the [12]-N2S2 subunit, resulting in the facile formation of a Cu(I)-Cu(II) mixed valence dinuclear cryptate (196). This system suggests the possibility of the formation of heterometallic dinuclear complexes120). 

Many Class II complexes are known for which the EPR signal shows localization occurring at low temperatures (169,170) but only one (167) other synthetic example in which the seven-line signal is still evident at 77 K is known. Delocalization is most evident in systems in which the ligand imposes very similar geometry at both copper centers and the small, dinuclear cryptate achieves this very effectively. The properties observed are those of the encapsulated [Cu(1.5)-Cu(1.5)] unit and are independent of the details of ligand structure. 

Copper(II) trifluoromethanesulfonate, 110 Coriolin, 271, 272 Coronafacic acid, 443 Costunolide, 58 Coumarochromanone, 156 Crobarbatine, 109 Crotyltriphenyltin, 451 Crown ethers, 110-111, 322, 323 Cryptates, 112, 378 (J-Cuparenone, 153, 154 2-Cyanoaziridines, 174 Cyanocuprates, 287-288 Cyanoimines, 324 Cyanotrimethylsilanc, 1, 112-113 Cyanotrimethylsilane-Triethylaluminum, 113-114... 

The macrobicyclic cryptand BISTREN (3), as discussed earlier, binds anions when hexaprotonated. This compound is also capable of binding pairs of transition metal ions [e.g. the bis-copper(Il) Complex (55)] when unprotonated (39, 138). The bis-copper(II) based receptor (55) was observed to bind a chloride ion cascaded between the two metal ions. In fact, receptor 55 bound chloride more strongly (log K = 3.55) than the hexaprotonated form of 3 (log K = 2.36), and this was attributed to the formation of strong coordinate bonds. Hydroxide was also cascade bound forming a thermodynamically very stable complex (log K = 11.56), the resulting complex being of a different type from that formed by non-cryptate complexes of the Cu(II) ion. 

Polyaza macrobicyclic cryptands synthesis, crystal structures of a cyclophane type macrobicyclic cryptand and of its dinuclear copper(I) cryptate, and anion binding features, J. Jazwinski, J.-M. Lehn, D. Lilienbaum, R. Ziessel, J. Guilhem and... 

A further step in complexity was aecomplished by designing ligands able to eomplex more than one cation eryptand 8 (Fig. 8), for example, forms a homodinuclear complex with silver or copper.The erystal stracture of the dinuclear Cu(I) eomplex formed with the hexaimine macrobicycle 8 shows the inelusion of the two copper ions, which are tetracoordinated at each end of the cavity, the Cu...Cu distance being very large (11.07 A). The small hexaimine macrobicycle 9 (Fig. 9) forms a Cu(l) dinuclear complex in which the Cu(I)... Cu(l) distance is short (2.45 A). In the reduced hgand 10 (Fig. 10), the Cu(I) is not stable, and only the [Cu2 (lO)] " cryptate was obtained. The Cu... Cu distance in this complex is 2.42 A, and on the basis of ESW measurements, an average redox state (di Cu ) was postulated rather than a Cu(I)... Cu(II) dinuclear complex. ... 

Synthesis, crystal structure of a cyclophane type macrobicyclic cryptand and of its dinuclear copper(I) cryptate,... 

Motekaitis. R.J. Martell. A.E. Dietrich. B. Lehn. J.-M. Anion binding in macrobicyclic metal cryptate complexes Copper(II)-bistren. Inorg. Chem. 1984. 23. 1588-1591. 

Hydroxide ion is more strongly bound than fluoride ion as bridging donor groups (guests) in hosts consisting of dinuclear copper(II) cryptates of O-BISTREN and C-BISTREN. 

Motekaitis RJ, Martell AE, Lehn JM, Watanabe E (1982) Bis(2,2, 2"-triaminotriethylamine) cryptates of cobalt(II), nickel(II), copper(II), and zinc(II). Protonation constants, formation constants, and hydroxo bridging. Inorg Chem 21 4253 257... 

Motekaitis R, Martell AE, Murase I (1986) Cascade halide binding by multiprotonated 7,19,30-trioxa-l,4,10,13,16,22,27,33-octaazabicyclo[ll.ll.ll] pentatiiacontane (BISTREN) and copper(II) BISTREN cryptates. Inorg Chem 25 938-944... 

Motekaitis R, Martell AE, Murase I, Lehn JM, Hosseini MW (1988) Comparative study of the copper(II) cryptates of C-BISTREN and 0-BISTREN. Protonation constants, formation constants, and secondary anion bridging by fluoride and hydroxide. Inorg Chem 27 3630-3636... 

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