We have applied low-temperature matrix-isolation IR spectroscopy to study the structures of the pyrimidine-2-hydroxypyrimidine and pyrimidine-phenol heterodimers isolated in low temperature argon matrices. IR spectra are registered for samples with different relative concentrations of the heterodimer components. Based on the measured IR intensities of the spectral bands of the monomer molecules and their heterodimers the presence of the OH center dot center dot center dot N hydrogen bond in the pyrimidine-phenol complex isolated in argon matrices is demonstrated. However this bond is not observed in the pyrimidine-2-hydroxypyrimidine complex. (c) 2014 Elsevier B.V. All rights reserved.