Metal atoms, displacement

A ruthenium(VI) nitrido complex containing a tetrapyrrolic macrocycle ligand, [Ru (N)(L)] (82) (H4L = mcio-octamethylporphyrinogen), has been synthesized by the reaction of diphewldiazomethane with [Ru"(L)] , which is prepared from [Ru(cod)(Cl)2] and Na4(L) 4THF. X-ray crystal studies reveal that [Ru (N)(L)] has a Cjv symmetry, and it has the usual saddle conformation, with the metal atom displaced 0.482 A out of the N4 mean plane. The reactivities and redox chemistry of this complex are summarized in Scheme 12 (see also Section 5.6.5.2). 

Within the dimer, each monomeric bis(dithiolene) unit retains similar values for bond distances and angles when compared to related, nondimeric species. However, metal atoms are drawn out of the monomeric unit plane by 0.1-0.45 A and the coordination geometry about the central atom is best described as square pyramidal. A consequence of metal atom displacement is that all c — M—c angles (Scheme 3) in dimeric structures are smaller than those for monomeric... 

Five-coordinate (square pyramidal) Fe" complexes " containing a single axial ligand are generally high-spin (5 = f) with the metal atom displaced from the porphyrin 1 plane in the direction of the apical ligand. " Structural data for some representative examples are in Table 8. 

It may be mentioned that the condensation in the presence of metallic sodium appears to be partly effected by the metal which displaces atomic hj drogen from the ketone ... 

Figure 22.5 Alternative representations of (a) the sheet structure of NbF4 and (b) the chain structure of MX4 (M = Nb, Ta X = Cl, Br, I) showing the displacement of the metal atoms which leads to diamagnetism.

In summary, NIS provides an excellent tool for the study of the vibrational properties of iron centers in proteins. In spectroscopies like Resonance Raman and IR, the vibrational states of the iron centers are masked by those of the protein backbone. A specific feature of NIS is that it is an isotope-selective technique (e.g., for Fe). Its focus is on the metal-ligand bond stretching and bending vibrations which exhibit the most prominent contributions to the mean square displacement of the metal atom. 

Metals behave differently since the metal atoms are embedded in an electron gas. The attractive forces remain active even after mutual displacement of parts of a crystal has occurred. Metals therefore can be deformed without fracture. 

It follows therefore that there is sufficient room around the metal atom to accommodate additional ligands. Also the displacement of the singlet peak on addition of increasing amounts of pyridine demonstrates that these... 

The difference in activity between metal carbon bonds in (VIII) and (XXXI) could also explain why only one benzyl group per metal atom is used. On kinetic grounds alone, quite apart from other objections to two polymer chains growing from one metal atom, the probability of a second benzyl group being displaced can only be comparable to the probability of chain termination. 

In general, these defect-free modulated structures can, to a first approximation, be divided into two parts. One part is a conventional structure that behaves like a normal crystal, but a second part exists that is modulated5 in one, two, or three dimensions. The fixed part of the structure might be, for example, the metal atoms, while the anions might be modulated in some fashion. The primary modulation might be in the position of the atoms, called a displacive modulation (Fig. 4.35a). Displacive modulations sometimes occur when a crystal structure is transforming from one... 

---