We review the reservoirs of methane clathrates that may exist in the different bodies of the Solar System. Methane was formed in the interstellar medium prior to having been embedded in the protosolar nebula gas phase. This molecule was subsequently trapped in clathrates that formed from crystalline water ice during the cooling of the disk and incorporated in this form into the building blocks ...

Hybrid carbon-silicon, carbon-nitrogen, and carbon-boron clathrates are new classes of Type I carbon-based clathrates that have been identified by first-principles computational methods by substituting atoms on the carbon clathrate framework with Si, N, and/or B atoms. The hybrid framework is further stabilized by embedding appropriate guest atoms within the cavities of the cage structure. Seri...

The pristine crystalline type-I, type-II, and type-VIII silicon clathrates have been studied using state of the art first-principles calculations based on density functional theory and density functional perturbation theory. We apply quasi-harmonic approximation to study structural stability, the possibility of temperature or pressuredriven phase transitions, along with Grüneisen parameters, co...

In various studies, Hofmann-type clathrates, given by the general formula ML2Ni(CN)4·G, were produced. Here M is a transition metal atom, L a ligand molecule or half of a bidentate ligand molecule, and G a guest molecule [1]. The clathrates are of interest because of their inclusion behavior and use as catalysts, anti-oxidants and stabilizing agents [2]. Infrared spectroscopy is one of the best...

In addition to their ground state, diamond structure, Si, Ge and Sn can form crystalline solids called clathrates. As in the diamond structure, in the clathrates, the Group IV atoms are tetrahedrally coordinated and sp covalently bonded to their neighbors. However, the clathrates contain pentagonal atomic rings and have open-framework lattices containing 20-, 24and 28-atom ‘‘cages’’. There are ...

Clathrates are crystalline inclusion compounds formed by a physically stable reaction between host and guest molecules. Gas hydrate and hydroquinone (HQ) clathrate are one of the most studied and welldefined clathrate compounds. In this study, guest-free, CO2-loaded, CH4-loaded and CO2/CH4-loaded HQ clathrates were synthesized by gas-phase reaction and recrystallization. In addition, pure CO2 a...

New Hofmann type benzene clathrates in the form of M(CyHEA)2Ni(CN)4·2benzene (where CyHEA=2-(1-cyclohexenyl)ethylamine and M=Ni or Cd) have been prepared in powder form and FT-IR and Raman spectra have been reported. The results suggest that title compounds are similar in structure to Hofmann type clathrates and their structures consist of polymeric layers of |M-Ni(CN)4|∞ with the CyHEA molecul...

We review the electronic properties of pure and doped silicon and carbon clathrates. Using accurate quasiparticle calculations within the GWapproximation, we show that undoped clathrates are 1.8 eV band gap semiconducting compounds. Further, the effect of doping by elements more electronegative than Si is shown to lead to p-type doped semiconductors with a 2.3–2.5 eV band gap in the visible ene...

The thermodynamics of binary sII hydrogen clathrates with secondary guest molecules is studied with Monte Carlo simulations. The small cages of the sII unit cell are occupied by one H(2) guest molecule. Different promoter molecules entrapped in the large cages are considered. Simulations are conducted at a pressure of 1000 atm in a temperature range of 233-293 K. To determine the stabilizing ef...