Group Vllb

The relatively high receptivity of Mn (0.175) and its medium size quadrupole moment (0.55 x 10 ) make this nucleus a favorable one for NMR detection. There is, however, only a restricted number of diamagnetic complexes except for the permanganate ion and a series of [Mn(NO)3L] and isonitrile complexes, the 

Phosphines, owing to their empty 2d orbitals, are efficient n acceptors and influence the paramagnetic deshielding term via the 7t-interacting e level d, dy ) of the Mn-3 / set under 4v symmetry. If the ligand is comparable to CO in its w-acceptor ability, as is PF3, or if the ligand-metal interaction does not allow for much n contribution (as is the case for the halogens and E R3, E = Si, Ge, Sn, Pb), a influences upon the HOMO-LUMO separation (vide infra) may become predominant for variations of S examples are [MnH(CO)5 (PF3) ], [Mn(Hal) 

Nuclear quadrupole coupling constants and asymmetry parameters [in brackets] are from single crystal studies. NQCC( Mn) values have also been predicted from partial quadrupole splitting parameters for [Mn(CO)5L] (L = CN, CNR, PPhj, NCS, N3, SbPhj, and and calculated from Wy2 of the NMR resonance for [MnH(CO)5  

Nakano and Nakatsuji et have calculated dia- and paramagnetic terms for [MnX(CO)s] (X = Hal, H, CN, Me), [Mn(CO)e]+, and [Mn04] . A qualitative agreement is found between the calculated paramagnetic r(para) term and the observed shielding. As expected, the local diamagnetic terms are practically con- 

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The halides are binary compounds of a halogen (elements of group Vllb of the periodic table) and a more electropositive element such as a metal. 

The halogens (Group Vllb) directly precede the rare gases in the Periodic Table. They are fiourine (Z — 9), chlorine (Z = 17), bromine (Z 35), iodine (Z = 53), and the recently discovered astatine (Z 86). 

He often based his organization on what were called triads of elements—groups of three elements in the same vertical column with extremely similar properties. Examples of triads include vanadium, niobium, and tantalum in group VA sulfur, selenium, and tellurium in group VIB and chlorine, bromine, and iodine in group VllB. 

It is suggested that there are two possible conformations for the bridging cyclopropyl groups the syn form (Vila) observed in the crystal and the anti form (Vllb) that appears from minimum energy calculations to be more stable in solution (100). These differences and some of the angles seem to result from crystal packing energies in the solid state versus the less constricted form in solution. 

As in Table Vllb, the IJn values for p electrons are divided into two groups, and the I jn values are slightly higherfor the last three p electrons. 

Supported oxides of transition metals, particularly of groups Vb (V), VIb (Cr, Mo, W) and Vllb (Re) are widely used as catalysts or catalyst precursors for vari-... 

The elements W and Re are in Groups VIb and Vllb of the periodic table under Mo and Tc, respectively, and similar to the Mo/Tc system, the most common generator is based on adsorption of W on alumina, where selective elution of Re is achieved by saline as the eluant (Kadina et al. 1990). The interaction of tungsten ions with alumina has been studied in some detail by Dadachova et al. (1995). The chromatographic generator is portable, simple to operate, and it provides Re with a radiopurity of 75-85% (Kamioki et al. 1994). Other proposed W/ Re generators include gel-type (Ehrhardt et al. 1990) and sublimation types. A review of the latter can be found in Boyd (1982) cf also O Chap. 40 in this Volume. 

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