X-ray structural characterizations of the reaction products between ZnCl2 and 6-benzylaminopurine derivatives in different acidic conditions

The reaction between ZnCl2 and the corresponding 6-benzylaminopurine derivative, Ln, [where L1 = 6-(4-fluorobenzylamino)purine, L2 = 6-(2-fluorobenzylamino)purine or L3 = 6-(4-chlorobenzylamino)purine] in 0.1 M or 2 M HCl afforded various products in dependence on a pH of the reaction medium. X-ray structures of the reaction products have been determined by a single crystal X-ray analysis. It has been found that the reaction led to the formation of [Zn(HL1)Cl3]·H2O (1) in 0.1 M HCl in which the L1 ligand acts as the single N1–H protonated N9–H tautomer and is coordinated to Zn through N7 atom of a purine skeleton. On the other hand, ion-paired compounds of the composition (H2L2)[ZnCl4]·H2O (2) and (H2L3)[ZnCl4] (3) have been formed during the reactions in 2 M HCl. Each of the organic molecules L2 and L3 is twice protonated and its positive charge is compensated by the presence of the [ZnCl4]2− anion. The cation exists as the N1–H, N7–H protonated N9–H tautomer in (2), and as the N3–H, N7–H protonated N9–H one in (3). It has been found that the extent of protonation has a significant impact on the coordination ability of the discussed organic molecules, and as a result of this finding, also on selected interatomic parameters as well as non-bonding interactions present in their crystal structures. Moreover, the compounds have been characterized by elemental analyses (C, H, N), FTIR and Raman spectroscopies, and thermogravimetric (TG) and differential thermal (DTA) analyses.