Dihydrogen Phosphate and Hydrogen Sulphate of 1,4-Dimethyl-1,4-diazabicyclo[2.2.2]octane-1,4-diium: Crystal Structures, Hydrogen Bonding and Infrared Spectra.

The crystal structures of the title compounds consist of 1,4-dimethyl-1,4-diazabicyclo[2.2.2]octane-1,4-diium cation [CHN] and [HPO] or [HSO] anions. Both crystal structures are monoclinic, the structure of the dihydrogen phosphate ( I) is non-centrosymmetric ( P2) with a = 6.4090(2) Å, b = 13.6920(5) Å, c = 7.6140(3) Å, β = 94.620(2)°, V = 665.97(4) Å, Z = 2; whereas the unit cell of the hydrogen sulphate ( II) is centrosymmetric ( P2/ c) with a = 13.8460(2) Å, b = 12.6610(2) Å, c = 8.0360(2) Å, β = 99.5800(12)°, V = 1389.10(5) Å, Z = 4. Both the structures are formed by the different bonding patterns of the anions interlinked by strong and moderate O-H···O hydrogen bonds. While the structure of ( I) consists of a two-dimensional network of the hydrogen bonded dihydrogen phosphates, the infinite chains of the hydrogen bonded hydrogen sulphates are the basic building unit of the structure ( II). In addition to the dominant electrostatic interaction the divalent cations stabilize themselves in the structures by forming several C-H···O hydrogen bonds to the oxygen atoms of the anions. The IR spectra of both the compounds are strongly affected by the hydrogen bonds whose influence on OH stretching vibrations is analysed by means of the DFT calculations in the solid state. Graphical Abstract: The crystal structures of the 1,4-dimethyl-1,4-diazabicyclo[2.2.2]octane-1,4-diium dihydrogen phosphate and hydrogen sulphate comprise strong and moderate O-H···O hydrogen bonds significantly influencing the high energy region of IR spectra.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]