The 1:2:1 adduct of DABCO dication, hydrogen squarate and water molecules studied by X-ray diffraction and FTIR spectroscopy

The molecular structure of 1:2:1 adduct of diprotonated 1,4-diazabicyclo[2.2.2]octane, (DABCO), hydrogen squarates (HSQ−) and water (1) has been characterized by single-crystal X-ray diffraction and infrared spectroscopy. The crystals of 1 are orthorhombic, space group Pnma. The non-equivalent HSQ− anions are bonded into zigzag chains (α-chain) by two short OH⋯O hydrogen bonds of 2.485(2) and 2.509(2) Å, and additionally H-bonded by water molecules linking the zigzag chains into ribbons. The diprotonated DABCO cations are located between the ribbons and interact with HSQ− anions by the NH⋯O trifurcated hydrogen bonds. The FTIR spectrum shows a very broad absorption in the 1740–550 cm−1 region, typical of short hydrogen bonds and it is attributed to the ν(OHO) and γ(OHO) vibrations. The second derivative spectrum distinguishes the νCO and γCC modes assigned to the π-delocalized squaric acid ring.