Metal nitrosyl molecule

This reaction is driven by the formation of the stable metal nitrosyl molecule PdNO. Pd+, as well as Cu+, Rh+, Ag+, Cd+, and Pt+ that also induce NO ionization, thus do not catalyze the reduction of nitric oxide. 

Distortions along non-totally symmetric modes may occur in certain excited states. These distortions are non-symmetry preserving the point group of the molecule changes in the excited state. The specific examples in this paper are the linear to bent geometry changes of metal nitrosyls (e.g., from Ci(V to C3 in [Fe(CN)5N0]2+.)... 

Reduction of metal-nitrosyl complexes is a prominent subject in the redox chemistry of small nitrogenated molecules, most relevant to biochemistry and to natural nitrogen-redox cycles.11 MnNO+ complexes have low-energy LUMOs and undergo facile one-electron reduction, usually showing reversible CV waves associated with MNO+/MNO redox couples.4"-6 The MNO 6 complexes yield fairly stable MNO 7 species in solution, as evident from UV-vis, IR, and EPR. Some of the latter species release NO in the minute time scale alternatively, the [Fe(CN)5NO]3 and [Ru(NH3)5NO]2+ ions may lose cyanide or ammonia.4"-6 Some metallopor-phyrins also afford reversible conversion between MNO1 / MNO forms.21 The NiR enzymes release NO after nitrite coordination and reduction.11... 

Returning to question (c), whether the difference in activity between Mo and W complexes is determined by molecular electronic "design" and/or by molecular packing in the crystal, it seems from the above data that the similarities between the crystal structures and 0m indicate that the explanation for the variations in SHG efficiency must lie in electronic factors. This is reasonable in view of the differences between Ef for the reduction of the respective complexes, the tungsten compounds having reduction potentials between 450 and 500 mV more cathodic than their Mo analogues. It would appear that on photo-excitation of these molecules, electron transfer from the ferrocenyl "donor" to the metal nitrosyl "acceptor" occurs, and the SHG efficiency mirrors the ease or otherwise of this process. 

In order to understand the bonding in metallic nitrosyls, let us first see the molecular orbital (MO) diagram of a nitric oxide (NO) molecule, shown in Figure 1. 

Structural studies of large molecules may be illustrated by cyclopentadienyl chromium dicarbonyl nitrosyl ( ) —C5 H5)Cr(CO)2NO, a simple piano-stool-type configuration. Interest in these metal-nitrosyl compounds arises since NO is a neurotransmitter. A study of various iso-tomers gives the overall molecular configuration and structure of Fig. 15. 

As briefly alluded to, there are different classes of redox-active ligands in addition to the above mentioned ones. For example, we have seen in Chapter 5, Section 8, that azo-groups (in particular, 2-(phenylazo)pyr-imidine) are able to undergo two separate one-electron reduction processes. Conjugated polynitriles (mnt, tcne, tcnq) also constitute an important class of redox-active molecules and the electrochemical behaviour of their metal complexes has been reviewed.107 The same holds as far as alkyldithiocarbamates (Rdtc) and their metal complexes are concerned,108 or nitrosyl complexes in their possible NO+[NO fNO redox sequence.109 Thus, we would like to conclude the present Chapter by discussing a few less known redox non-innocent ligands. 

This picture can qualitatively account for the g tensor anisotropy of nitrosyl complexes in which g = 2.08, gy = 2.01, and g == 2.00. However, gy is often less than 2 and is as small as 1.95 in proteins such as horseradish peroxidase. To explain the reduction in g from the free electron value along the y axis, it is necessary to postulate delocalization of the electron over the molecule. This can best be done by a complete molecular orbital description, but it is instructive to consider the formation of bonding and antibonding orbitals with dy character from the metal orbital and a p orbital from the nitrogen. The filled orbital would then contribute positively to the g value while admixture of the empty orbital would decrease the g value. Thus, the value of gy could be quite variable. The delocalization of the electron into ligand orbitals reduces the occupancy of the metal d/ orbital. This effectively reduces the coefficients of the wavefunction components which account for the g tensor anisotropy hence, the anisotropy is an order of magnitude less than might be expected for a pure ionic d complex in which the unpaired electron resides in the orbital. 

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