Multinuclear structures

Shilov and collaborators discovered136 considerable yields of hydrazine and ammonia when dinitrogen reacts with a suspension of freshly prepared VK and Mg11 hydroxides. The magnesium is essential and yields of hydrazine and ammonia depend on temperature, pH, dinitrogen pressure and solvent (Scheme 4). The system has been used to reduce acetylene to ethylene and ethylene to ethane.137 Shilov and collaborators assumed a multinuclear structure for the centre where N2 reduction occurs and suggested the mechanism shown in Scheme 5. 

The structures of the complexes formed by the Schiff bases (162) depend upon the nature of R when R is a simple alkyl or aryl group the complexes are of the type CuL2 with an essentially planar structure,701 but when R contains a potential donor, CH2CH20 or CH2CH2CH20, a multinuclear structure results, whilst when R = MeC02, the ligand is terdentate, and produces a mononuclear complex. 

In addition to geometrical factors, lability is a critical parameter for self-assembly. While many reported structures contain labile ions, several ions that are normally not considered labile, such as Ti, Cr , Co , and Pt have been successfully incorporated into elaborate multinuclear structures by forcing reaction conditions to reach thermodynamic equilibrium. 

The structures of doubly bonded compounds containing tin readily lend themselves to study by multinuclear NMR spectroscopy, as tin has two NMR active isotopes ll7Sn and ll9Sn. The chemical shifts of doubly bonded tin species in the 119Sn NMR spectrum cover a broad range from 6 = -150 to +835 (Table VI) however, the majority of the signals occur at low field S = 400 or above. 

Reaction of [Ircp Cl2]2 with AgBF4 and (SPPh2)3CH in CH2C12 or Me2CO to which Et3N is added yields [Ircp ( 73-(SPPh2)3C]BF4, which has been structurally characterized.271 The Irm complexes [Ircp L3](PF6)2 (L3 = MeC(CFl2ER)3, E = Se, R = Me E = Te, R = Me, Ph) have been prepared and characterized by IR and multinuclear NMR spectroscopy.647... 

Linear multinuclear metal complexes are attracting attention in the context of molecular electronics due to their projected use as molecular wires. 01igo(pyridyl)amido ligands are efficient scaffolds for lining up several Ni11 ions like a string. The first structurally characterized trinickel complex of this type, [Ni3(dpa)4Cl2] (dpa = bis(2-pyridyl)amide), showed a nearly linear Ni3 unit with Ni—Ni distances of around 244 pm.209 Penta-, hepta-, and nonanuclear systems have... 

Phosphido-bridged multinuclear complexes have been formed from zinc chloride of the form [Zn4(PPh2)4Cl4(PRR 2)2], where R and R are alkyl or phenyl groups. Related tetrameric structures can be formed with a bridging dialkyl phosphide or (trimethyl)silylphenyl phosphide.303... 

Zinc boryloxides with a tetrameric Zn404 core (45) have only recently been characterized. The single-crystal X-ray structure and multinuclear NMR spectroscopy studies were used as a basis for discussion of deformation of the central core.435 Alkali metal zinc orthoborates MZn4(B03)3 (M = K, Rb, Cs) have been synthesized and single-crystal X-ray structures determined for M = K and Rb.436... 

TMEDA can also participate in the formation of multinuclear zinc telluride complexes with Znio, Zni4, and Zni6 complexes structurally characterized. A comparison was carried out by Pfistner et al. replacing the diamine with a diphosphorus ligand, bis(diphenylphosphino)methane,... 

The simplest possible coordination compounds of Cd and Hg with chalcogen donors are the anions MCh22. Multinuclear NMR studies of these species (Ch = Se, Te) in NH3 or en solutions with [K(2.2.2-cryptand)]+ counterions have been reported.314 Structural studies31, also combined with new multinuclear NMR measurements, have been performed.316... 

Independently, triangulo-Hg3 compounds with stabilizing chelating diphosphine and diarsine ligands have been prepared, 82-387 crystal-structure analyses have been solved (the Hg—Hg bonds, 280 pm, are longer than before), and careful multinuclear NMR spectra measured and analysed. 

Multinuclear ( H, 13C, nB) NMR spectroscopy is undoubtly the most useful and powerful method for the investigation of the organoboration of 1-alkynyltin, -germanium, and -silicon compounds allowing not only the structure of the final products to be determined but also the product ratio to be ascertained (Tables 6-8). 

In addition to the influence of neighbors on 29Si chemical shifts, the geometrical effects (such as Si-O-T angles) already described above are also evident of mixed frameworks with elements other than Si on tetrahedral positions. This is reflected by the broadness of the bars shown in Fig. 1. Multinuclear NMR investigations on a large set of sodalite structures with various framework compositions show that T-O-T bond angle (T = Si, Al, Ga) and dTT distance chemical shift dependences exist, and mutual correlations between chemical shift of these NMR nuclei can be observed [68],... 

One difficulty with many synthetic preparations of semiconductor NCs that complicates any interpretation of NMR results is the inevitable distribution of sizes (and exact shapes or surface morphologies). Therefore attempts to make semiconductors as a sort of molecular cluster having a well-defined stoichiometry are of interest to learn potentially about size-dependent NMR parameters and other properties. One approach is to confine the semiconductor inside a template, for instance the cuboctahedral cages of the sodalite framework or other zeolite structures, which have been characterized by multinuclear NMR methods [345-347], including the mesoporous channel material MCM-41 [341, 348]. 

Multinuclear NMR data have been recorded for molsidomine 12 and its metabolite SIN-1 13, confirming that both are closed ring structures and that the positive charge is accommodated at the N3 position <1996CHE1358>. The c C4-C5 coupling constants for selected 1,2,3-oxadiazoles lie between 69.4 and 89 Hz, but correlation of these values with measures of bond order and aromaticity is difficult due to substituent effects <2000MRC617, 2002JST269>. 

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