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The inside and outside protonation of a 15-membered O2N2-macrocycle. Synthesis and structural characterization of the protonated ligand salts

Reactions of a mixed dioxa-diaza macrocycle 5, 6, 14, 15-dibenzo-1, 4-dioxa-8, 12-diazacyclopentadeca-5, 14-diene (L) and various sodium salts NaX (X = picrate, ClO4, BF4, PF6, SCN and BPh4) in methanol afford the ion-pair compounds containing the protonated macrocyclic ligand as cation and anion from the sodium salt as a counterion. The new compounds were identified and characterized on the basis of elemental analysis, spectroscopic studies (IR, 1H NMR and MS), conductivity data and X-ray structure analysis. The mode of ligand protonation, as well as hydrogen bond network which stabilizes the binding site of the proton in the protonated macrocyclic species, depend on the sodium salt used. It was found that the proton to ligand ratio is 1:1 in the picrate salt (1), 1:2 in the perchlorate (2), tetrafluoroborate (3), hexafluorophosphate (4) and thiocyanate (5) salts, and 2:3 in the tetraphenylborate salt (6), which was converted by recrystalization in acetonitrile into the 1:1 salt (7). In the 1:1 proton:ligand compounds, [H(L)]X, the intraligand monoprotonation occurs in two modes: proton is bound to one of the nitrogen atoms (1) or proton is disordered between two nitrogen atoms (7). In the compounds with 1:2, [H(L)2]X, and 2:3, [H2(L)3](X)2, proton to ligand ratios, there is interligand protonation where one proton is dislocated between nitrogen atoms from two macrocyclic molecules (2-5) or two protons are shared between nitrogens from three ligand moieties (6). Crystallographic and infrared spectroscopic data indicate some differences in location of the proton between nitrogen atoms in the monoprotonated ligand salts 2-5.

dioxa-diaza macrocycle; protonation; spectroscopy; crystal structure; hydrogen bonding

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