Crystal structure of silver fulminate

Polymorphism and thermodynamic ground state of silver fulminate studied from van der Waals density functional calculations

Silver fulminate (AgCNO) is a primary explosive, which exists in two polymorphic phases, namely, orthorhombic (Cmcm) and trigonal (R3) forms at ambient conditions. In the present study, we have investigated the effect of pressure and temperature on relative phase stability of the polymorphs using planewave pseudopotential approaches based on Density Functional Theory (DFT). van der Waals interactions play a significant role in predicting the phase stability and they can be effectively captured by semi-empirical dispersion correction methods in contrast to standard DFT functionals. Based on our total energy calculations using DFT-D2 method, the Cmcm structure is found to be the preferred thermodynamic equilibrium phase under studied pressure and temperature range. Hitherto Cmcm and R3 phases denoted as α- and β-forms of AgCNO, respectively. Also a pressure induced polymorphic phase transition is seen using DFT functionals and the same was not observed with DFT-D2 method. The equation of state and compressibility of both polymorphic phases were investigated. Electronic structure and optical properties were calculated using full potential linearized augmented plane wave method within the Tran-Blaha modified Becke-Johnson potential. The calculated electronic structure shows that α, β phases are indirect bandgap insulators with a bandgap values of 3.51 and 4.43 eV, respectively. The nature of chemical bonding is analyzed through the charge density plots and partial density of states. Optical anisotropy, electric-dipole transitions, and photo sensitivity to light of the polymorphs are analyzed from the calculated optical spectra. Overall, the present study provides an early indication to experimentalists to avoid the formation of unstable β-form of AgCNO.

First structural characterization of solvate-free silver dinitramide, Ag[N(NO(2))(2)]

The crystal structure of solvate-free silver dinitramide (Ag[N(NO(2))(2)]) was determined by X-ray diffraction for the first time and displays secondary contacts between silver and oxygen as well as between silver and nitrogen, furnishing different coordination modes of the dinitramide moiety.

Electronic structure and stability of the inorganic fulminates

The fulminates form a class of compounds isoelectronic with the azides and cyanamides. They are, however, extremely sensitive materials and even the ionic salts explode. A study has been made of some of the optical properties of small crystals and thin deposited films, and of the solid state infrared spectra, in order to determine the nature of the bonds in the sodium, potassium, thallous, silver and mercury salts. Structural data is also available and it is concluded that while sodium, potassium and thallous fulminates are ionic solids, the mercury salt is covalent. It is likely that in the silver salt there is also a high degree of directed bonding in the solid state. The nature of the bond between the metal and the carbon atom of the fulminate group can, however, be different in the silver and mercury salts and this will be reflected in the order of the stability of the salts.