The temperature dependencies of the vapor pressure of Sn(IV) complexes with tridentate iminopyridine ligands

Studying the thermal properties and obtaining the temperature dependences of the saturated vapor pressure of Sn (IV) complexes with tridentate iminopyridine ligands by differential scanning calorimetry and the Knudsen effusion method allows the studied compounds to be used to obtain films and coatings acting as luminescent materials, as well as components for nonlinear optics. The following coordination compounds of tin(IV) containing tridentate Schiff bases were selected as objects of research: 4-(tert-butyl)-2-((pyridin-2-ylmethylene)amino)phenolatotrichlorotin(IV) (1), 2,4-di-tert-butyl-6-((pyridin-2-ylmethylene)amino)phenolatotrichlorotin(IV) (2), 4-methyl-2-((pyridin-2-ylmethylene)amino)phenolatotrichlorotin(IV) (3), 5-methyl-2-((pyridin-2-ylmethylene)amino)phenolatotrichlorotin(IV) (4), and 4-chloro-2-((pyridin-2-ylmethylene)amino)phenolatotrichlorotin(IV) (5). These compounds were prepared by template synthesis from tin tetrachloride, various o-aminophenols and α-carbonyl substituted pyridines containing the iminopyridine functional group capable of covalently binding a phenolic group to a metal. The composition and structure of the complexes have been confirmed by elemental analysis, IR and NIR spectroscopy. The X-ray diffraction data, obtained at 120 K on an Agilent Xcalibur diffractometer (ω scanning, MoKα radiation, λ = 0.71073 Å) for crystals 2 [С20H25N2OCl3Sn, M = 534.502; monoclinic syngony, symmetry group P21/с; cell parameters: a = 13.9657(2), b = 12.12140(10), c = 14.3489(2) Å; β = 109.512(2) degrees; V = 2289.68 Å3; total reflections 45565; independent reflections 6696; R int 0.0525; R 1 = 0.0262, wR 2 = 0.0469]. The tin coordination polyhedron is a distorted octahedron, with heteroatoms of an organic ligand and one of the halide substituents in the equatorial plane. The remaining two chlorine ligands occupy an apical position. The tridentate ligand is almost flat. The structure is registered with the Cambridge Structural Data Bank (No. 1849152; ccdc.cam.ac.uk/getstructures). The phase transitions of compounds 1-5 have been studied in the temperature range 25-500 °C using the DSC method. For all the studied complexes an endothermic transition associated with melting has been revealed. The temperature dependences of the saturated vapor pressure of complexes 1-5 have been obtained using the Knudsen effusion method with weight recording of the sublimated substance amount in the temperature ranges 221-256, 240-270, 229-259, 220-260, and 204-240 °C for 1, 2, 3, 4, and 5, respectively. The thermodynamic parameters of sublimation processes have been calculated. The effect of the structure and substituents in the ligand on the volatility of the studied compounds has been established.