cg300669t_si_002.cif (240.45 kB)

Halogen Bonding-Based “Catch and Release”: Reversible Solid-State Entrapment of Elemental Iodine with Monoalkylated DABCO Salts

Download (240.45 kB)
dataset
posted on 01.08.2012 by Anssi Peuronen, Arto Valkonen, Minna Kortelainen, Kari Rissanen, Manu Lahtinen
The halogen bonding (XB) between elemental iodine (I2) and neutral 1,4-diazabicyclo[2.2.2]­octane (DABCO) and its monoalkylated PF6 salts was studied by X-ray crystallographic, thermoanalytical, and computational methods. DABCO was found to form both 1:1 and 1:2 complexes with I2 showing an exceptionally strong halogen bond (ΔEcp = −73.0 kJ/mol) with extremely short N···I distance (2.37 Å) in the 1:1 complex (1a). In the more favored 1:2 complex (1b), the XB interaction was found to be slightly weaker [ΔEcp = −64.4 kJ/mol and d(N···I) = 2.42 Å] as compared to 1a. The monoalkylated DABCO salts (2PF67PF6) form corresponding 1:1 XB complexes with I2 {[2···I2]­PF6–([7···I2]­PF6} similarly to the parent free base DABCO, but both X-ray diffraction and calculated (M05-2X/def2-TZVPP) geometrical parameters indicate that the XB interactions are somewhat weaker than with DABCO itself but can nonetheless be considered as moderately strong halogen bonds. The solid -state packing of the monoalkyl DABCO complexes is greatly affected by the length of the lipophilic hydrocarbon chain as the long-tail cations show increasing amphiphilic character. However, partly as a consequence of the amphiphilic nature of parent monoalkyl DABCO PF6 salts, their I2 complexes exhibit a reversible binding of I2 into their originally nonporous crystal lattices. This was verified by thermal analysis and X-ray powder diffraction studies of 2PF67PF6 and their corresponding I2 complexes. By varying the length of the alkyl chain, the release temperature of I2 can be tuned from 75 °C ([4···I2]­PF6) to 100 °C ([7···I2]­PF6). Furthermore, these highly stable (preservable for months in normal laboratory conditions) I2 complexes can be prepared with three different routes: by mixing in solution, by mechanochemical grinding of the components, and via gas-to-solid reaction (i.e., I2 vapor to solid PF6 salts).

History

Exports