There has been a considerable interest in the transition metal nitrosyls and the reactions of the nitrosyl lignad. Thus no can function as an electron donor giving NO+ or an electron acceptor, giving NO- and N2O2-2. Another stimulus to investing NO reactivity has been the developments in pollution control. Largely steaming from attempts to remove, or at least diminish the concentration of NO- in exhaust gases, emitted by the internal combustion engines. The long search for NO- complexes predicted as by Sidgwick, culminated in the complex, [Ir(Cl)(CO)(NO)(Ph3)2]BF4. In this case NO+ is believed to be coordinated as a Lewis acid accepting an electron pair from the week base Iridium. Cyano nitrosyl complexes have drawn a distinction from other metal nitrosyl, although they are not basically different from other nitrosyl complexes. Among these [M(CN)5NO]n+ species have received attention. A diamagnetic cyano nitrosyl complex of composition Ag3[Re(CN)6(NO)] is also reported. This red brown compound on further reduction with sodium amalgam gives very green [Fe(NO)2(CN)2]2-. Different physical methods used so far for the elucidation of structural aspects of the starting complexes along with the trends observed with the alike complexes of the other transition metals. Therefore, some general comments of results of X-ray diffraction studies, magnetic measurements along with electronic spin resonance, vibration electronic, photo-electronic and mass spectra redox properties and kinetic studies are used. The synthesis bonding and reactivity of the nitrocyl complexes are complexed and varied. Mononitrosyl complexes containing {MNO}n group having cyanide as coligand are comparatively less explored regarding substitution reaction keeping the (MNO) moiety intact.
