Metal ion bridges

Some representative systems. A further type of binuclear species incorporates two metal ions bridged by one or two small groups within the macrocyclic ring. Such complexes differ from the previous type in that the bridges between the metal ions do not involve donor groups which are directly attached to the macrocycle - see (122) and (123). A variety of... 

Fe oxidation, 36 425-426 Fe release, 36 426-427 metal ion bridges, 36 472 molecule packing, 36 471-472 outer-sphere electron transfer, 36 429-433 comparison of cytochrome c and cytochrome C551, 36 431 cytochrome b 36 429 ferrihemoprotein reduction rates, 36 430-431... 

Metalloenrymes have tightly bound metal ions, such as Zn " or Fe ", that serve as metal ion bridges between the enzyme and substrate. 

The formation of an M—C hond is the one common feature. In these structures, /i indicates that the CO2 molecule bridges two or more metals with the subscript indicating the number of metal ions bridged. 

Sandstrom (146) has established by X-ray analysis unidentate coordination of two of the perchlorates to one of the metal ions (Hg—O length = 2.78, 3.04 A Hg—O—Cl angle = 161,123°) in the binuclear complex Hg2(dmso)8(C104)4 The metal ions bridged through two of the eight dmso molecules assume distorted octahedral geometries. X-ray evidence has been presented by Epstein et al. (147) for the presence of a weakly bonded perchlorate in a seven-coordinate mercury(II) complex... 

The alkaline-earth metal -diketonates are less volatile than other metal / -diketonates because they exist as oligomers. For example, one Ba / -diketonate consists of a clnster of five metal ions bridged by S-drketonate carbonyl O atoms and H2O. Several such metal /3-diketonates which are used for metallorganic chemistry vapor deposition (MOCVD) of thin-film superconductors were characterized by GC-MS as well as by TGA and MS. It was proved that the addition of the -diketone to the carrier gas stream improves the GC behavior of these alkaline earth metal chelates, probably owing to adduct formation accompanying the dissociation of the oligomers . 

Sigel, H. and Naumartn, C. F., Ternary complexes in solution. XXIV. Metal ion bridging of stacked purine-indole adducts. The mixed-ligand complexes of adenosine 5 -triphosphate, tryptophan, and manganese(II), copper(II), or zinc(II), /. Am. Chem. Soc., 98(3], 730, 1976. 

Two adjacent pairs of histidines have been introduced in alanyl, alanyl/ homoalanyl, homoalanyl, and alanyl/norvalyl PNA duplexes, which have a duplex width of 14, 15, 16.5, and 18 A, respectively (141). A hypothesis was set forth, but not proven, that the four histidines coordinate one metal ion in the narrower duplexes and a dimer of metal ions bridged by water ligands in... 

Luminescent coordination compounds continue to attract considerable attention. Zink recently reported a new mixed-ligand copper(I) polymer that shows interesting photoluminescence (232). The complex [CuCl(L44)Ph3P] consists of a one-dimensional chain lattice of metal ions bridged by both Cl" ions and pyrazine molecules. The compound shows conductivity of less than 10-8 S cm 1. The absorption spectrum of the complex shows a band at 495 nm, which could be interpreted as the promotion of an electron from the valence band to the conduction band. On the basis of resonance Raman spectra, the lowest excited state in the polymer is assigned to the Cu(I)-to-pyrazine metal-to-ligand charge-transfer excited state. 

One of the most successful families is represented by a series of polymers built from the linkage of metallic carboxylate chains through 4,4 -bipyridine spacers [ 176]. As an example, the coordination polymer [Cu(C4H O )(4,4 -bpyifH O) ] is formed by the connection of chains of Cu(II) metal ions bridged by succinate ligands through 4,4 -bipyridine molecules. This 3-D framework shows weak ferromagnetic interactions and channels, in which the water molecules are located. 

Almost similar connectivity and magnetic properties are observed in the porous solid [Fe(C 0 )(4,4 -bpy)(H30)j] 3HjO [177]. Chains of Fe(II) metal ions bridged by squarate ligands are connected through 4,4 -bipyridines to form a framework with 1-D channels fiUed with water molecules. Interestingly, the dehydration/rehy-dration process in this coordination polymer, as well as in other isostructural polymers with other metal ions, is fuUy reversible and accompanied with a continuous change of the colour [178]. 

The columnar one-dimensional, or network two-dimensional, polymeric motifs can be further varied in different ways to construct three-dimensional lattices of interlinked porphyrin species with better-defined pore sizes. One way to achieve this goal is to apply external transition metal-bridging auxiliaries with three-dimensional coordination features. These include, for example, zinc," " copper, and molybdenum,metal ion bridges that can associate... 

Henry Taube showed that electron transfer between two different metal ions bridged by a shared ligand in solution was faster if the ligand was conjugated than if it was saturated, i.e., nonconjugated. In Milestone... 

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