Over the past few years the interest on the organic compounds of thiosemicarbazones class has increased due to their pronounced capacity to form complexes with transition metal. Initially it seems that the thiosemicarbazones coordination chemistry with metals presents purely theoretical interest. This is due to the fact that different metals coordinate differently and form a large variety of coordination polyhedron. Various oxidation states can be stabilized in these compounds. But the practical interest is caused by the fact that a number of the coordination compounds, from this class of organic substances with transition metals, exhibit catalytic properties, are biologically active showing important antitumor and antiviral pharmacological properties. It is also known that the coordination compounds of platinum metals with thiosemicarbazide derivatives have a relatively high stability coloring intensively the solutions. This properties places them among the perspective reagents for elaboration of the spectrophotometric determination of these metals. According to the results of previous studies [1], salicylaldehyde S-methyl-thiosemicarbazones (HL) in coordination compounds with palladium(II), acts as a monoanionic tridentate ligand coordinating to the metal ion through the set of donor atoms O, N(1) and S. Such type of coordination corresponds to Pearson's theory, according to which the ligands of type R2S (Ralkyl groups, S-sulfur) represents “soft” bases and coordinate to a "soft" acids as Pd(II). However there are described and deviations from this theory. The interaction of 8-formylquinoline N(4)-2-methylphenylthiosemicarbazone (HL1) with K2[PdCl4] in the presence of an excess of KNCS affords the compound [Pd(L1)(NCS)] containing two ligands potentially able to coordinate via sulfur atom. X-ray investigation of the structure shown that the organic ligand adopted really the N,N,S mode of coordination, traditional for the tridentate thiosemicarbazones. The anionic ligand NCS prefers the formation of the bound Pd – N. The use of the S-alkylated derivative - 8-formylquinoline S-methyl-N(4)-phenylthiosemicarbazone (HL2), in the reaction with K2[PdCl4] give rise to the formation of [Pd(L2)Cl] close by composition to the compound described in [1]. X-ray investigation of the structure of this one shown that the organic ligand adopted the coordination via N,N,N donor atom set. Even the presence of a bulk substituent such as 2methylphenyl was not an obstacle to use the nitrogen atom for coordination. Mode of coordination, traditional for the tridentate thiosemicarbazones. Acquires a coordination compound with the molar ratio Pd:L1 1:1, where the ligand is tridentate and coordinates to the metal ion via atoms: N quinoline, N(1) and N(4) from thiosemicarbazone fragment. In order to establish the possibility of modifying the mode of coordination of the ligand to the palladium ion (II), interaction study of K2[Pd(SCN)4] with N(4)-2-methylphenylthiosemicarbazone was carried out. Where for "lockout" N(4) atom was changed substituent, while sulfur atom in contrast to L1 has been "unlocked". X-ray study of the obtained crystalline compound (PdL2) showed that the ligand is tridentate coordinated to the metal ion via atoms: N quinoline, N(1) and S from thiosemicarbazone fragment (Fig.1). In order to establish the influence of factors which cause the mode of coordination of the ligand to the metal ion it is necessary to perform an additional study.