Complexation of formaldoxime with water. Infrared matrix isolation and theoretical studies

The 1:1, 1:2 and 2:1 formaldoxime-water complexes isolated in the argon matrices have been studied by help of FTIR spectroscopy and MP2/6-311++G(2d,2p) method. The calculations predicted the stability of the three CH2NOH⋯H2O isomeric complexes, three CH2NOH⋯(H2O)2 ones and one (CH2NOH)2⋯H2O complex. The analysis of the experimental spectra and their comparison with theoretical ones indicated that both the 1:1 and 1:2 complexes trapped in solid argon have the most stable cyclic structures stabilized by the O–H⋯O and O–H⋯N bonds between the formaldoxime and water molecules. In the 1:2 complex formaldoxime interacts with the water dimer, one H2O molecule acts as a proton acceptor for the OH group of formaldoxime whereas the second H2O molecule acts as a proton donor toward the nitrogen atom of the formaldoxime molecule. In the (CH2NOH)2⋯H2O complex the OH group of the water molecule acts as a proton donor toward one of the oxygen atoms of the formaldoxime cyclic dimer.

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► The 1:1, 1:2 and 2:1 formaldoxime–water complexes are formed in the argon matrices.
► The 1:1 and 1:2 cyclic CH2NOH–H2O complexes are stabilized by N⋯H–O and O–H⋯O bonds.
► The deviation of hydrogen bonds from linearity decreases the hydrogen bond strength.
► In the 2:1 complex water is attached to an oxygen atom of the formaldoxime cyclic dimer.