X-ray crystal structure of the 1∶2∶2 pentaethyleneglycol dimethyl ether(pentaglyme)∶dichloropicric acid∶water complex. Infrared studies of the 1∶2∶2 complexes with tri-, tetra-, and pentaglyme

Abstract

The 1∶2∶2 pentaglyme∶dichloropicric acid∶water adduct crystallizes in two polymorphic forms. Polymorph I is triclinic, space groupP¯1; at −96°Ca=11.629(6),b=12.566(8),c=12.877(16)Å,α=89.19(8),β=83.76(8), γ=85.95(5)°,D _x =1.599 g cm⁻³,V=1866(5)ų,Z=2. Refinement on 7729 observed reflections yielded a finalR value of 0.045. Polymorph II is orthorhombic, space groupP2₁2₁2₁; at −87°Ca=13.631(7),b=26.441(8),c=5.182(6)Å,D _x =1.597(3) g cm⁻³,V=1868(3)ų,Z=2. Refinement of 1610 observed reflections yielded a finalR of 0.071 for a disordered structure. The hydrogen bonding pattern in I is similar to that found in the analogous 18-crown-6 complex. Two pairs of alternate O atoms in the polyether are hydrogen bonded to two water molecules, each of which is hydrogen bonded to the phenol O atom of a neutral dichloropicric acid molecule. The bond distances and torsion angles in the S shaped polyether are similar to those in the cyclic polyether with C-C-O-C angles near 180° and O-C-C-O near±60°. The complex in II resembles that in I in overall shape and dimensions, also having normal bond distances and angles. The nonhydrogen atoms in water and the dichloropicric acid can be located unambiguously. However, the polyether molecule is disordered, and a satisfactory model for the disorder could not be found. Comparison of the IR spectra of the 1∶2∶2 tri-, tetra-, and pentaglyme∶dichloropicric acid∶water complexes suggests that the hydrogen-bonding in the tetraglyme complex is weaker than in the pentaglyme complex, but that in the triglyme complex is as strong or stronger.