Metal fulminates, structure

Hg(CNO)2 is decomposed by heat (equation 8).4 It crystallizes in the orthorhombic form and contains linearly coordinated mercury.21 It reacts with alkali metal fulminate solutions to form the highly explosive compounds M2Hg(CNO)4 (M = K, Rb, Cs) with larger cations such as Ph4As+ more stable complexes are formed.219,220 Besides the homogeneous anionic mercury(II) fulminato complexes there are a few mixed species with unknown structures, e.g. Na Hg(CNO)2X (X = Cl, Br) or Na2S203-2Hg(CNO).221... 

All the crystalline metal fulminates and the heavy metal azides explode and detonate on the application of thermal shock and in some cases in the presence of an electric field, while the heavy metal cyanates and thiocyanates only deflagrate at high temperatures. According to Bowden and Williams (83) the stability to thermal shock increases in the order fulminate heavy metal salts are more thermally unstable. During the last decade Yoffe and co-workers have tried to explain the thermal and photochemical behaviour of these meterials in terms of their electronic structure. This work has been extensively reviewed by Yoffe (2) and will not be considered here. We will however explore briefly a few ideas which qualitatively correlate the geometry of the electronic and atomic configurations with the kinetic stability of these materials. 

The fulminate ion, CNO", where N is the central atom, is highly unstable. In feet, metal fulminates are explosive and have been used in percussion caps. Sketch all the possible resonance structures for the fulminate ion, determine the FCs on each atom in every canonical structure, and discuss why you think the fulminate ion is so unstable. 

All these tetracooidinated bisphosphine metal fulminates are, like the tettafiilminato complexes, diamagnetic and hence have planar structures. Also the cyanide compound (PEtj) Ni(CN)j is planar whereas Ni(Il) halides... 

The fulminate ion, CNO-, probably has a structure intermediate between C N O and C N 6 for since these two bond types have the same bond angles and term symbols ( 2), they can form intermediate structures lying anywhere between the two extremes. Which extreme is the more closely approached could be determined from a study of the bond angles in un-ionized fulminate molecules, such as AgCNO or ONCHgCNO, for the first structure would lead to an angle of 125° between the CNO axis and the metal-carbon bond, the second to an angle of 180°. 

N 49 01% wh ndls, sol in warm w. Structure not known. Prepd by heating Mercury Fulminate with ammonia at 70°. Completely decomposed to CO2 and NHa by dil HCl at 150°. Neutral in water, but will react with metal oxides giving, eg, a Silver salt, Ag/)6HgN903 Refs 1) Beil 1, 723 2) A. Steiner, Ber 8 ... 

Fulminates are salts of fulminic or para-cyanic acid (qv), which is isomeric with iso-cyanic acid. Fulminates should not be confused with Fulminating Compounds (qv). Structural formulas of fulminic acid and of its salts have not yet been definitely established. The free fulminic acid has not been isolated from its solns, as it undergoes polymerization very rapidly both in aqueous and in ethereal solns. The acid and its metallic salts, M(ON C)n, are very poisonous and explosive. The best known and most used salt is Mercuric Fulminate (qv)... 

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. ... 

The structures of the azide ion (Nj ), the cyanamide ion (CN/ ) and the fiilminate ion (CNO ) are closely related and the decompositions of some metal cyanamides and fulminates are therefore considered here. 

The heavy metal pseudohtilides fall in this group since covalent forces are partially present. The structural parameters listed in Table 4 show that thallous azide, fulminate and cycmate are isostructural with the tetragonal alkali metal salts, while thallous thiocyanate is isostructural with the room temperature phase of potassium thiocyanate. The lattice constants of the salts axe all indicative of abnormally short metal-anion distances. The silver salts form an interesting series where the subtle interactions which result as a function of the electron affinity, electronic structure and size of the anions, stimulate somewhat predictable variations of crystal geometry. Silver azide is an example of a distortion of the tetragonal D4 (Fig. 1) lattice due to covalent metal-emion interaction which lowers the space symmetry of the crystal to D2 (29), while silver thiocyanate is mainly covalent with bidentate metal-anion chains... 

Detailed crystal structures of only a few of the other heavy metal pseudohalides are available in the literature. Among them are, cuprous azide which has a relatively simple tetragonal lattice and cupric azide, mercuric fulminate and a-lead azide which have increasingly complex orthorhombic lattices. a-Lead azide has four types of anion sites of varying amounts of as5nnmetry (33) while cupric azide (35) and mercuric fulminate (72) have two such sites. The structure of cupric azide which is built up of distorted octahedra of asymmetric Ns ions about the central cupric ion is analogous to that of a transition metal complex. 

In contrast to the cyanate ion (NCO ), which is stable and found in many compounds, the fulminate ion (CNO ), with its different atom sequence, is unstable and forms compounds with heavy metal ions, such as Ag and Hg " ", that are explosive. Like the cyanate ion, the fulminate ion has three resonance structures. Which is the most important contributor to the resonance hybrid Suggest a reason for the instability of fulminate. 

Acetylides and fulminates form highly explosive shock- and heat-sensitive salts with many metals. Acetylides are the metal derivatives of acetylene. Hydrogen attached to carbon atoms bearing a triple bond is acidic in nature. It can be substituted by a metal ion to form acetylides, with the general structure M-C=C-M. These substances are made from acetylene, HC=CH, or alkyl acetylene, RC=CH, by passing acetylene gas or aUcyl acetylene vapors over the aqueous solutions of ammoniacal metal salts, as shown in the following reactions ... 

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