Cyclopentadienyl complexes structures

Cationic cyclopentadienyl complexes are not common in this group, but recent examples whose structures have been determined include [Nb ( j -C5H5)2Cl2]BF4< > and [Nb( j -C5H5)2L2](BF4)2 (L = CNMe and NCMe),< > which have pseudo-tetrahedral symmetry. 

Kopf-Maier P, Kopf H (1988) Transition and Main-Group Metal Cyclopentadienyl Complexes Preclinical Studies on a Series of Antitumor Agnets of Different Structural... 

Metallocenes with substituted cyclopentadienyl rings. Metallocenes with methylated rings were among the first heavy alkaline earth metallocenes to be structurally characterized, but many other substituents have been incorporated into bis(cyclopentadienyl) complexes. Under this classification are included compounds with indenyl ligands, which in... 

One other structure of a tricyclopentadienide has appeared (57) and it provides a further demonstration of the correlation between ionic size and coordination. Neodymium tris(methylcyclopentadienide) crystallizes as a tetramer (Fig. 10). The Nd + ion (which is slightly larger than Sm3+) is pentahapto bound to three cyclopentadienyl rings and monohapto bound to a fourth ring. This fourth ring is in turn j -bonded to another Nd + ion, until the tetramer is generated. The distances between tetramers are those expected for van der Waals contact. The crystal and molecular parameters are compared with the other tris cyclopentadienyl complexes in Table 5. 

The tetramethylethanediyl-bridged, f-butyl-substituted bis-cyclopentadienyl complex Me4C2(3-f-BuC5H3)2Mg(THF) (129) is present in the solid state as a me o-diastere-oisomer. It has a structure in which both cyclopentadienyl groups are /7 -bonded to magnesium while only one THF molecule is coordinated to magnesium (Figure 62) . 

Cyclopentadienyl complexes reactions of, 700-703 structures of, 673-678 synthesis of, 680-681 Cytochromes, 569-572, 891-895... 

X-ray analysis of complex 9 shows two independent molecules in the unit cell. The Hf—Si bonds of 2.881(4) A and 2.888(4) A are longer than those found in other d° Zr—Si derivatives (Table 1), reflecting the steric hindrance in 9. The crystal structure of the mixed cyclopentadienyl complex CpCp Hf(SiH2Ph)Cl reveals a Hf—Si bond length of 2.729(3) A, which is shorter than in 9, presumably due to a lower steric interaction... 

Two classes of material will be described here - the metal dithiolenes and rare earth metallocenes. In the metal dithiolenes a strong, low energy pi-pi transistion occurs in the near IR (9.10). This can be tuned from about 700 nm to 1400 nm by altering the metal ion, substituents or charge state of the dithiolene. The dithiolenes are particularly attractive because of their optical stability which has been exploited in their use as laser Q-switch materials. In the rare earth complexes the near IR band is provided by/-/transistions of the rare earth ion rather than the cyclopentadienyl ring structure various nonlinear optical phenomena have been observed in glasses incorporating similar ions. Previous studies have shown that dicyclopentadienyl complexes such as ferrocene have off-resonant nonlinearities similar to nitrobenzene or carbon disulphide (11-13)... 

Optimal synthetic methods for obtaining these complexes have been developed including, for example, the interaction of acetylene derivatives, atomic selenium, and cyclopentadienyl complexes [638,640]. In some derivatives of 1,2,3-selenodia-zole, structure 343 can be transformed to 339, as shown by reaction (2.7) [641] ... 

Cyclopentadienyl complexes of Ge, Sn, and Pb exist in a wide variety of composition and structure, such as half-sandwiches CpM and CpMX, bent and parallel sandwiches Cp2M, and polymeric (Cp2M)x. 

As mentioned above, polymorphism may also arise for compounds formed by isomers whose structures are related by low-energy interconversion pathways, e.g. cluster carbonyls with different distributions of bridging and terminal ligands, or substituted metallo-arenes and metallo-cyclopentadienyl complexes [60]. In such cases, the structural isomers correspond to different energetic minima along the interconversion pathway and the cohesion of the respective crystals may stabilize the less thermodynamically stable isomers. Crystals of structural isomers may (or may not) interconvert via a phase transition. 

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