Reaction of 1H,2H,3H,4H-pyrido[4,3-d]pyrimidinium bromide derivatives with molecular iodine: Comparative structure and spectroscopic analysis

New salts C27H22N3O2BrI2 (1) and C27H19N3O2Br4I2 center dot 2CHCl(3)center dot 2H(2)O (2) were synthesized by the iodination of derivatives of 1,3-dimethyl-2,4-dioxo-5,6,7-R-1H,2H,3H,4H-pyrido[4,3-d]pyrimidinium bromide (R = phenyl (1 a), p-bromphenyl (2a)) with an equimolar amount of iodine. The positive values of enthalpy (Delta H) and entropy (Delta S) indicate that the complexation of organic bromide and iodine molecule in chloroform solution is mainly entropically driven. The molecular and crystal structures ( 1) and (2) are studied by X-ray diffraction analysis. The structure of diiodinebromide 1 is composed of separate almost liner BrI2- and 1,3-dimethyl-2,4-dioxo-5,6,7-thriphenyl-1H,2H,3H,4H-pyrido[4,3-d]pyrimidinium cation. The crystal structure 2 is built up of alternate layers of (C27H19N3O2Br3+) (I-3(-)) (A) and (Br2I-)(CHCl3) (B), connected to each other by hydrogen bonds Br(Br2I-)center dot center dot center dot H(C27H19N3O2Br3+). The formation of the I-3(-) ions and Br2I- occurs via the disproportionation of I2Br- under the action of solvent on C27H19N3O2Br4I2 center dot 2CHCl(3)center dot 2H(2)O (2) crystallization. (C) 2011 Elsevier B.V. All rights reserved.