The new synthesized complexes of neodimium, samarium and gadolinium with o-phthalic acid were studied by X-ray, DTA and IR spectroscopic analysis methods. Clathrate compounds were obtained on the basis of these complexes. Formic acid (for samarium complexes) and the acetic acid (for gadolinium complexes) were chosen as ²guest² molecules. According to X-ray, elemental, IR spectroscopic and derivatographic analyses the identity of complexes and clathrates on their basis, form of coordination of o-phthalic acid, existence and amount of ²guest² molecules in a clathrate, as well as processes of thermal decomposition and formation of supramolecular compounds: {Sm₂[C₆H₄(COO)₂]₃×2H₂O}·3HCOOH and {Gd₂[C₆H₄(COO)₂]₃×5H₂O}×2CH₃COOH  were established.