In:
Chemistry – A European Journal, Wiley, Vol. 20, No. 42 ( 2014-10-13), p. 13698-13709
Abstract:
In an investigation into the proton conductivity of crystallized water clusters confined within low‐dimensional nanoporous materials, we have found that water‐stable nanoporous crystals are formed by complementary hydrogen bonding between [Co III (H 2 bim) 3 ] 3+ (H 2 bim: 2,2′‐biimidazole) and TATC 3− (1,3,5‐ tricarboxyl‐2,4,6‐triazinate); the O atoms in the COO − groups of TATC 3− in the porous outer wall are strongly hydrogen bonded with H 2 O, forming two types of WMCs (water molecular clusters): a spirocyclic tetramer chain (SCTC) that forms infinite open 1D channels, and an isolated cyclic tetramer (ICT) present in the void space. The ICT is constructed from four H 2 O molecules as a novel C 2 ‐type WMC, which are hydrogen bonded with four‐, three‐, and two‐coordination spheres, respectively. The largest structural fluctuation is observed at elevated temperatures from the two‐coordinated H 2 O molecules, which begin to rapidly and isotropically fluctuate on heating. This behavior can be rationalized by a simple model for the elucidation of pre‐melting phenomena, similar to those in ice surfaces as the temperature increases. Moreover, high proton conductivity of SCTCs (ca. 10 −5 S cm −1 at 300 K with an activation energy of 0.30 eV) through a proton‐hole mechanism was observed for pellet samples using the alternating impedance method. The proton conductivity exhibits a slight enhancement of about 0.1×10 −5 S cm −1 at 274 K due to a structural transition upon approaching this temperature that elongates the unit cell along the b ‐axis. The proton‐transfer route can be predicted in WMCs, as O(4) of an H 2 O molecule at the center of an SCTC shows a motion that rotates the dipole in the b ‐axis direction, but not the c ‐axis; the thermal ellipsoids of O(4) based on anisotropic temperature factors obtained by X‐ray crystallography reflect a structural fluctuation along the b ‐axis direction induced by [Co III (H 2 bim) 3 ] 3+ .
Type of Medium:
Online Resource
ISSN:
0947-6539
,
1521-3765
DOI:
10.1002/chem.201402900
Language:
English
Publisher:
Wiley
Publication Date:
2014
detail.hit.zdb_id:
1478547-X
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