Niobium complexes paramagnetic complex

The structure of the compound, 7.30, has been confirmed by X-ray diffraction [209a]. The complexes (3r-C5H5)2M(o-C5H5)2, where M = Nb, blue-violet, Ta, red-violet or 3r-C5H5Mo(tantalum complexes are paramagnetic having one unpaired electron. 

Monomeric, paramagnetic chlorohydrides snch as MH2CI2 (PR3)4 derive from facile oxidative addition of H2 to MCl2(PR3)4 complexes. Of these 17e dodecahedral complexes, (32) is the most interesting (eqnation 17). Its thermolysis in solution offers a qnadruply bridged hydride (33) and it can also be rednced to a monomeric Ta 16e species (34). Ta hydrides display a hydridic character (see Hydride Complexes of the Transition Metals), as shown by the reduction of CO by cyclopentadienyl derivatives. (see Niobium Tantalum Organometallic Chemistry)... 

Last but not least, mention should be made of the use of redox active organometallic clusters for the formation of CT complex. An early example was reported by Eisenberg, Miller and co-workers who exploited the trinuclear niobium cluster [Nb3(/i-Cl)6(>7 -C6Me6)3] and prepared the [TCNQ] salt, upon oxidation to the dicationic form. This material was found to be paramagnetic and to display a relatively modest conductivity (urt = 0.001 Scm , semiconductor) [75]. Finally, the pentanuclear trigonal bipyramidal vanadium cluster [(MeCp)5V5(/r -S)6] was shown to undergo CT complex formation with TCNQ affording [(MeCp)5V5(/i -S)6] [(TCNQ)2] [76]. This material, which was structurally characterized, is an n-type semiconductor with a band gap of 0.25 eV. 

Table 8 gives the data on the electron structure of valence shells of atoms of the corresponding transition metals [86]. Taking into account the fact that the total number of electrons provided by three allyl (crotyl) ligands to the molecular orbitals of the complex is nine, it may be concluded that the complexes of Cr (chromium), Nb (niobium) and Ti (titanium) should be paramagnetic and those of Rh (rhodium) should be diamagnetic. In this case the total... 

A zeolite with MFI structure was synthesised with 3 different amounts of niobium ammonium complex (NAC) in the reaction mixture. The samples obtained were characterised by scanning electron microscopy (SEM) using secondary electron detector and energy dispersive spectrum (EDS) detector, X-ray diffraction (XRD), differential thermal analysis (DTA), and electron paramagnetic resonance (EPR). The increase of NAC in the reaction mixture results in the decrease of the crystal size of the zeolite. The characterisation shows evidence that the niobium was incorporated into MFI structure. 

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