The title compounds were synthesized by using an alternative solid state route, and characterized by elemental analysis, infrared spectroscopy and thermogravimetry, The IR data are in agreement with a coordination through oxygen for ethyleneurea (EU) and propyleneurea (PU) and through nitrogen for ethylenethiourea (ETU). EU, PU and ETU adducts exhibit two mass loss steps, suggesting that the coordination positions are not equivalent for all adducts, and that there are two ligand molecules closer to the metal cation. This hypothesis is supported by quantum chemical (density functional, DF) calculations. The observed thermal stability sequence is ETU > PU > EU.