Sublimation Thermodynamics of 5,10,15,20–Tetraphenyl-21-X, 23-Y-Heteroporphyrins (X=O or S; Y= N or S). The Molecular structure of 5,10,15,20-Tetraphenyl-21-thiaporphyrin

Sublimation enthalpies of 10,15,20–tetraphenyl-21-oxa- (I), 5,10,15,20-tetraphenyl-21-thia- (II) and 5,10,15,20-tetraphenyl-21,23-dithia- (III) porphyrines were measured by Knudsen effusion mass spectrometry: ΔHsubl.(T) = 209±2 (561 K), 224±2 (552 K) and 219±2 (577 K) kJ/mol, respectively. A structure of a free molecule of II was studied by quantum chemistry and gas-phase electron diffraction. The molecular structures of the dimeric associates of I-III were tested by quantum chemical calculations.