Dimetal systems

Metal ions can be inserted to the diporphyrin ligands by standard procedures. If a metal complex of the diamine 10 or 11 was coupled with a free base porphyrin, the resultant dimer would have only one metal ion while subsequent metal insertion could lead to a mixed dimetal system. Using this approach, we have successfully prepared Cu—H2, Fe Cu, Mg-H2, and Fe-Mg diporphyrins. The stability of most of the dimetal complexes appears rather similar to the monomers. The Mg—Mg... 

The phenomenon of bridge-terminal carbonyl exchange can occur in any dimetal system that can exist in CO-bridged and metal-metal bonded forms, such as COjfCO), ... 

The dimetal systems M2X6 (M = Mo, W X = R, NR2, OR) have been first characterized by Chisholm and coworkers [20,21]. Two dynamic processes are typical of these molecules rotation about the metal-metal bond, and possible restricted ligand mobility. 

Using fs laser excitation at 620 nm, a 2PC in Y of 0.5ps [399] implicates hot electrons, probably thermalized at Te, as the mechanism for desorption induced by the fs laser (Section 2.6.2). Rotational state distributions are nearly Boltzmann characterized by Tf. The 2PC of internal state distributions was also obtained. Rather surprisingly, significant differences in these 2PC were obtained for T and the state-resolved yield for the two spin-orbit states and this was qualitatively rationalized by a DIMET picture [399]. Where overlap in experiments exist, the qualitative results are similar to those for fs laser induced desorption of NO/Pd(lll) [400,401]. For this latter system, the absolute yield Y is large at typical fluencies used in the experiments and a very hot vibrational distribution was observed (Tv = 2900 K). 

Thus, in this review we present the desorption phenomena focused on the rotational and translational motions of desorbed molecules. That is, we describe the DIET process stimulated by ultraviolet (UV) and visible nanosecond pulsed lasers for adsorbed diatomic molecules of NO and CO from surfaces. Non-thermal laser-induced desorption of NO and CO from metal surfaces occurs via two schemes of DIET and DIMET (desorption induced by multiple electronic transitions). DIET is induced by nanosecond-pulsed lasers and has been observed in the following systems NO from Pt(0 0 1) [4, 5],... 

Most of the electron attacks eventually lead to anti addition of hydrogen to the triple bond. Therefore, it has often been assumed that a irons dianion is a necessary intermediate. Because both free dianions and dimetal adducts may be isolated or detected, either or both may be important in different systems. 

Saalfrank, P. (1997) Open-system quantum dynamics for laser-induced DIET and DIMET. Surf. Set., 390, 1-10. 

The inherent steric bulk of the porphyrin directly affects the amount of the bridging a-diketone complex that is formed. At pco = 1 atm and T = 298K, formation of the dimer is favored in all but the bulkiest system (TTiPP). In the case of the least sterically demanding porphyrin, (OEP)Rh, reaction with CO produces the dimetal ketone, (OEP)Rh-C(0)-Rh(OEP).98... 

A second relevant aspect here is the consideration of models for the various dimetal species that could be important in the reactions at the ferroxidase centers. The area of di-iron metallosites has received a great deal of attention from the early 1980s since the identification of such sites in hemerythrin and the production of the first coordination chemistry model compounds for these (Chapters 8.12 and 8.13). Subsequently several other systems with this motif have been studied and the ones of most relevance to the ferroxidase centers would appear to be those involved in oxygen activation rather than transport. ... 

In other systems, N—cleavage gives bis(/i-nitrido)dimetal diamond cores as the products of N2 cleavage. A reduced niobium complex of calix[4]arene reduces N2 in the presence of sodium metal, and a number of intermediates can be isolated. A related tridentate aryloxide ligand also splits N2 to give a diamond core with lithium ions bound to the nitrides. A vanadium diamidoamine complex reacts with N2 to give a product with a similar core structure, which may be further reduced by potassium graphite to a compound with one unpaired electron. This... 

Scheme 9.4 The more flexible ligand system 3 leading only to formation of the dimetal-lic complex 34.

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