Characterization, crystal structure, and solution studies of a proton transfer compound obtained from 2,6-pyridinedicarboxylic acid and 1,4,10,13-tetraoxa-7,6-diazacyclooctadecane

The pro ton trans fer com pound, (DA18C6H2)(pydcH)2×0.25H2O, has been pre pared from the re ac tion be tween 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, diaza-18-crown-6 (DA18C6), and 2,6-pyridinedicarboxylic acid, dipicolinic acid (pydcH2). The char ac ter iza tion was per formed us ing 1H and 13C NMR, IR spec tros copy and sin gle crys tal X-ray dif frac tion anal y sis. The asym met ric unit con sists of one (DA18C6H2)2+ cat ion adopt ing a sigmoidal con for ma tion which in ter acts with two (pydcH)– an ions via hy dro gen bonds in volv ing the protonated amine groups of the diazacrown ether. –COOH···–OOC– head-to-tail hy dro gen bonds gen er ate 2D un du lat - ing lay ers along [100] and [001] in the crys tal lat tice. The protonation con stants of DA18C6 and pydcH2 and equi lib rium con stants for the re ac tion of the two re ac tants were de ter mined by potentiometric pH ti tra tion. The so lu tion stud ies sup ported the for ma tion also in so lu tion of (DA18C6H2)(pydcH)2 as the most abun dant spe cies at pH = 3.4.