Calculations of NMR properties for sI and sII clathrate hydrates of methane, ethane and propane

Abstract

Calculations of NMR parameters (the absolute shielding constants and the spin-spin coupling constants) for 512, 51262 and 51264 cages enclathrating CH4, C2H6 and C3H8 molecules are presented. The DFT/B3LYP/HuzIII-su3 level of theory was employed. The 13C shielding constants of guest molecules are close to available experimental data. In two cases (the ethane in 512 and the propane in 51262 cages) the 13C shielding constants are reported for the first time. Inversion of the methyl/methylene 13C and 1H shielding constants order is found for propane in the 51262 cage. Topological criteria are used to interpret the changes of values of NMR parameters of water molecules and they establish a connection between single cages and bulk crystal.Electronic supplementary materialThe online version of this article (doi:10.1007/s00894-014-2511-2) contains supplementary material, which is available to authorized users.

13C Chemical Shift in Natural Gas Hydrates from First-Principles Solid-State NMR Calculations

“…24 The shielding constants and spin−spin coupling constants of CH 4 , C 2 H 6 , and C 3 H 8 encapsulated in the 5 12 , 5 12 6 2 , and 5 12 6 4 water cages were calculated at the level of B3LYP/HuzIII-su3 by Siuda and Sadlej. 25,26 The chemical shifts of methane trapped in water clusters (H 2 O) 19−25 were studied using B3LYP by Terleczky and Nyulaśzi. 27 Several limitations are present in the theoretical studies on NMR parameters of hydrocarbon molecules in clathrate hydrates.…”

“…Ida et al calculated the 13 C chemical shielding constants of methane enclosed in the small and large cage of sI hydrate using coupled perturbed Hatree–Fock method, and the electronic environments experienced by methane were also studied . The shielding constants and spin–spin coupling constants of CH 4 , C 2 H 6 , and C 3 H 8 encapsulated in the 5 12 , 5 12 6 2 , and 5 12 6 4 water cages were calculated at the level of B3LYP/HuzIII-su3 by Siuda and Sadlej. , The chemical shifts of methane trapped in water clusters (H 2 O) 19–25 were studied using B3LYP by Terleczky and Nyulászi …”

“…Several limitations are present in the theoretical studies on NMR parameters of hydrocarbon molecules in clathrate hydrates. For example, usually only isolated cluster models are employed in the simulations. − The influences of the molecules beyond those of the cage wall are thus neglected. In addition, the dispersion interaction between guest hydrocarbon molecules and host water lattice is one of the most fundamental interactions in NGHs, which cannot be appropriately described by B3LYP. , The experimental studies mainly focus on the guest molecules CH 4 , C 2 H 6 , and C 3 H 8 in the sI and sII phases.…”

“…For example, usually only isolated cluster models are employed in the simulations. [24][25][26][27] The influences of the molecules beyond those of the cage wall are thus neglected. In addition, the dispersion interaction between guest hydrocarbon molecules and host water lattice is one of the most fundamental interactions in NGHs, which cannot be appropriately described by B3LYP.…”

Clathrate Hydrates

“…For example, Lasich and Ramjugernath used a simple lattice gas approximation with classical DFT coupled with Platteeuw theory to model clathrate hydrate phase equilibria for several hydrate guest molecules [33]. Standard DFT calculations were used by Chattaraj et cages hosting methane, ethane, and propane guests) [35]. Mondal and Chattaraj used ab initio molecular dynamics (AIMD) via atom-centered density matrix propagation (ADMP) methodologies to study time-dependent structural behavior of noble gas hydrates on the timescale of ~500 fs [36].…”