Group metallic radii

The hydrogenation of unfunctionalized alkenes is readily performed by Group III and lanthanide cyclopentadienyl hydride derivatives, one key feature being the high TOFs of these systems (up to 120000 IT1 for hydrogenations catalyzed by Lu, Tables 6.8 and 6.9) [119, 120]. The reaction rate depends heavily on the metal and the ligands. It is inversely proportional to the metal radius (Lu>Sm>Nd>La), and it is faster for the Cp M derivatives than for the ansa di-... 

Because of the large number of carbonyl groups required to satisfy the noble gas rule and the relatively small metallic radius, serious steric limitations are present for manganese tetranuclear closed clusters12). The only known tetranuclear compounds are some mixed clusters, MnOs3(CO)16H and MnOs3(CO)13H3 (see later), which have been prepared from Os3(CO)12 and [Mn(CO)s] 161). 

Acrylic Polymers. Burrows et al. [95] showed by the Integral Procedural Decomposition Temperature (IPDT) method that for main group metal ions -the stabilizing effect in regard to polyacrylamide is inversely proportional to the radius of the metal ion reemphasizing that the strength of the complex between the ion and the polymer is of importance in deciding the stability. 

Electronic configuration 1. v22522/763 23/7 3 l04 24/764 /5.s 1. Ionic rad ius Ru4+ 0,60 A. Metallic radius 1,3251 A. First ionization potential 7.5 eV. Other physical properties of ruthenium will be found under Platinum and Platinum Group. See also Chemical Elements,... 

Some writers feel it important to distinguish carefully between covalent and metallic radii. Others suggest that a self-consistent set of atomic radii - some covalent, others metallic - can be devised. Such a collection is presented in Table 4.1. In cases where both a covalent and a metallic radius can be obtained, the agreement is variable. For example, the metallic radii of atoms of the Group 1 elements are 20-30 pm greater than the corresponding covalent radii, taken from the M-M distances in M2(g). The Mn-Mn distance in (CO)5Mn—Mn(CO)5 is 293 pm, which compares with 274 pm calculated from the metallic radius of Mn. The electronic environment of the Mn atom in the carbonyl complex is, of course, very different from that in the elemental substance. 

The figures in Table 29.6 imply valences of 5-78 for the transition metals Cr, Mn, Fe, Co, and Ni, and the same is assumed for the series Mo-Pd, W-Pt, and U-Cm. It is less easy to justify the valences of 5-44,4-44, and 3-44 respectively for the elements of Groups IB, IIB, and IIIB, which follow from the interpretation of interatomic distances in terms of an essentially empirical equation. This relates the metallic radius R n) for a bond of order n (i.e. one involving n electron pairs) to the single-bond radius 7 (1) ... 

All complexes mentioned above were highly effective single-component catalysts for the ROPs of e-caprolactone (Scheme 8) and rac-lactide (Scheme 14) without the need of an activator. The metal radius was influential to the catalytic activity. Both polymerization catalysis rates decreased in the trend of 96 >99 >98 >97, in agreement with the decrease in metal ion radii (La > Nd > Sm > Y). The investigation of polymer end group showed that the polymer chain growth was initiated by allyl transfer to monomer [77]. 

For any particular type of Lewis base, say an amine or carboxylate group, metals of smaller radius generally form the stronger complex. This produces the well-known Irving-Williams series of complexing strength for the divalent metal ions ... 

Because the radius of an octahedral cavity is 0.414 times the metallic radius of the metal atoms on the surface of the cluster, only the first-row main-group atoms can be incorporated in this site. There are several octahedral carbido- and nitrido-clusters, but examples are also known that incorporate hydrogen and boron. A series of related clusters include [Ru6H(CO)i8] , [Ru6B(CO)i7] , [RueQCO)] ], and [Ru6N(CO)i6] , all of whieh contain a fully encapsulated interstitial heteroatom lodged in the center of the octahedral cavity. 

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