Fulminic acid metal complexes

Formamidine, N,N -di-2-anthraquinonyl-metal complexes, 275 Formamidine, JV,iV -diaryl-metal complexes, 275 Formamidine, N,N -dibenzyl-metal complexes, 276 Formamidine, N,N -diisopropyl-metal complexes, 276 Formic acid metal complexes, 436 Fulminates... 

CNO The isomeric fulminate ion, CNO (Figure 3-5), can be drawn with three similar structures, but the resulting formal charges are unlikely. Because the order of electronegativities is C < N < O, none of these are plausible structures and the ion is predicted to be unstable. The only common fulminate salts are of mercury and silver both are explosive. Fulminic acid is linear HCNO in the vapor phase, consistent with structure C, and coordination complexes of CNO with many transition metal ions are known with MCNO structures. ... 

Fulminates other than those of Hg and Ag (and also complex Na[Au(CNO)2] from AuCls [110]) cannot be prepared directly by reaction of the metal with nitric acid and subsequently with ethanol like MF or SF [15, 33]. Several reasons exist that make direct formation of other fulminates impossible. Wohler and Martin reported that solubility of most fulminates in the reaction mixture is a reason why only MF and SF can form directly. Most other fulminates are soluble and unstable in the reaction mixture, in which they decompose [57]. Another reason is that the fulminic acid too readily forms complex salts and therefore simple fulminates cannot be isolated [35]. A catalytic effect of noble metals (Hg, Ag) on some of the reaction steps of fulminate formation was reported by Krauz. He mentioned the analogy of the catalytic effect of mercuric ions on hydrocarbons that are oxidized to the relevant nitrophenols in dilute nitric acid [35]. 

Metallic fulminates (except mercury and silver) have never been practically used as explosives due to the difficulties with their preparation and generally low physical and chemical stability. However, the sodium salt can be used for many applications in organic chemistry. This salt is more suitable for this applicaticm than the more easily accessible mercury or silver salts due to their tendency to form complexes in solutions. For example, the sodium salt is useable in the preparation of free fulminic acid by acidification of its solution with dilute sulfuric acid [2]. 

The only directly accessible metal fulminates are those of mercury(II) and silver(I), very dangerously exposive solids obtained by the action of nitric acid and ethanol on the metals or their salts. Most modern preparations of fulminato complexes involve the conversion of a known amount of mercury fulminate into aqueous sodium fulminate by the action of sodium amalgam and ice-cold water the sodium fulminate solution is then allowed to react with the appropriate amount of a transition metal salt, and the resulting complex fulminato ion is precipitated as the salt of a large cation, most frequently Ph4As+ or R4N+ these are not explosive,4,35 Alkali and alkaline earth metal salts containing complex fulminato anions may be isolated from aqueous solutions, but they are reported to be as exposive as the binary silver and mercury fulminates, and are therefore usually avoided. 

Other metallic fulminates cannot be synthesized directly by reaction of metal with nitric acid and sequentially with ethanol in the same way as mercury or silver fulminates (and probably also complex Na[Au(CNO)2]). They are therefore mostly prepared by reaction of mercuric fulminate with the relevant amalgam. 

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