Stepwise charge transfer complexation of some pyrimidines with σ-acceptor iodine involving a new unconventional acceptor

Interactions of some aminopyrimidines, as electron donors, with the σ-acceptor, iodine, have led to the formation of CT complexes having the stoichiometric ratio 2:2 (donor (P):acceptor(I 2)), or formally 1:1. Thus, the well known triiodide complex, P +I.I 3 −, resulting in situ, is a new acceptor that interacts with another molecule of the donor (P) to form a CT complex having the form, (P).(P +I.I 3 −). Spectral tracking of these interactions have shown the stepwise formation of the triiodide CT complex. ▪ Interactions of some pyrimidine derivatives, 4-amino-2,6-dimethylpyrimidine, kyanmethin, (4AP), 2-amino-4,6-dimethylpyrimidine (2AP), 2-aminopyrimidine (AP), 2-amino-4-methylpyrimidine (AMP), 2-amino-4-methoxy-6-methylpyrimidine (AMMP), and 4-amino-5-chloro-2,6-dimethylpyrimidine (ACDP) as electron donors, with iodine (I 2), as a typical σ-electron acceptor, have been studied. Electronic absorption spectra of these interactions in several organic solvents of different polarities have performed instant appearance of clear charge transfer (CT) bands. Formation constants ( K CT), molar absorption coefficients ( ɛ CT) and thermodynamic properties, Δ H, Δ S, and Δ G, of these interactions have been determined and discussed. Electronic absorption spectra of the solutions of the synthesized pyrimidines–iodine, P–I 2, CT complexes have shown the characteristic bands of the triiodide ion, I 3 −. UV/vis spectral tracking of these interactions have shown that by lapse of time the first formed CT complex, P–I 2, is transformed to the corresponding triiodide complex, P +I.I 3 −, then, the later interacts as a new unconventional acceptor and it forms a CT complex of the form (P).(P +I.I 3 −). Elemental analyses of these solid complexes have indicated the stoichiometric ratio 2:2, or formally 1:1, P:I 2.