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Edited by Mark H. Thiemens, University of California San Diego, La Jolla, CA, and approved July 26, 2012 (received for review April 12, 2012)
Article Figures & SI
Figures
- Fig. 1.
The large and small cages of the cubic structure II THF-ammonia binary clathrate hydrate from single crystal X-ray diffraction. The ammonia guest has moved a water molecule out of its normal position by pulling it into the small cavity by forming a H2N-H⋯OH2 or H3N⋯HOH hydrogen bond.
- Fig. 2.
PXRD patterns of NH3 and H2O co-deposition sample (A) recorded at 100, 140, and 150 K; (B) expansion of the pattern at 150 K. Lattice parameters (150 K) are: a = 0.4527(1) nm, b = 0.5586(1) nm, c = 0.9767(3) nm for ammonia monohydrate (space group: P212121); a = 0.4496(1) nm and c = 0.7339(1) nm for ice Ih (space group P63/mmc); a = 1.1818(2) nm for sI ammonia clathrate hydrate (space group Pm-3n); a = 0.8404(2) nm, b = 0.8441(3) nm, and c = 5.345(1) nm for ammonia hemihydrate (space group Pbnm); and a = 0.7125(1) nm for ammonia dihydrate (space group P213).
- Fig. 3.
PXRD patterns of NH3, CH4, and H2O co-deposition sample (A) recorded at 112, 143, 160, and 180 K; (B) expansion of the pattern at 160 K. Vertical thin red lines and arrows indicate the peaks from sII hydrate and blue lines and arrows indicate the peaks from sI hydrate. Lattice parameter (160 K): a = 0.4491(3) nm and c = 0.7333(5) nm for Ih (space group P63/mmc), a = 0.6361(3) nm for Ic (space group Fd-3m), a = 1.1847(8) nm for sI hydrate (space group Pm-3n), and a = 1.7161(9) nm for sII hydrate (space group: Fd-3m).
- Fig. 4.
Sample configurations of the NH3 guests hydrogen bonding with the water molecules of the large (L) and small (S) cages of the sI and sII clathrate hydrate (Top: sI, Bottom: sII cages). The snapshots of the cages were extracted from the periodic simulation cell. In cases where NH3 is incorporated into the water lattice, the displaced water molecule is also shown.
Tables
- Table 1.
The average percent (H3N⋯H-OH) hydrogen bonding configurations calculated from RDFs and the enthalpy of hydrogen bond formation for pure sI and sII NH3 hydrates and binary sII CH4 (large cages) + NH3 (small cages) hydrate at different temperatures
Guests 100 K 120 K 140 K 160 K 170 K ΔHHB/kJ·mol-1 NH3 (pure sI, large cages) 4.6 12.9 34.5 54.4 68.9 7.66 NH3 (pure sI, small cages) 1.4 2.1 15.0 32.0 49.8 8.90 NH3 (pure sII, large cages) 7.8 17.1 28.3 51.5 61.8 5.85 NH3 (pure sII, small cages) 1.4 4.3 6.1 24.4 33.6 6.95 NH3 (binary sII, small cages) ∼0 0.6 1.3 1.8 2.9 5.09
Data supplements
Supporting Information
Files in this Data Supplement:
Ammonia clathrate hydrates
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