Organic Complexes Built by Halogenated Molecules: Unexpected in Situ C–N Bond Formation in Metal-Free Solvothermal Conditions

Reactions of two halogenated derivatives of bis(4-hydroxyphenyl)sulphone (BPS, 1), tetrabromobisphenol-S (TBBPS, 2), and tetrachlorobisphenol-S (TCBPS, 3), with piperazine (PZ, 4), were investigated by means of the combinational usage of solvothermal and mechanochemical methods. The resultant organic complexes, [(C6H2OBr2)2SO2]·[(C4H10N2)2CH2] (5), [(C6H2OBr2)2SO2]2·(C4H12N2)2·3(CH3OH) (6), [(C6H2OCl2)2SO2]·[(C4H10N2)2CH2] (7), and [(C6H2OCl2)2SO2]2·(C4H12N2)2·3(CH3OH) (8), were fully characterized by single crystal and powder X-ray diffractions. In the cases of complexes 5 and 7 that were prepared from solvothermal conditions, a rare metal-free in situ ligand formation has been observed, in which the new organic molecule 1,2-bispiperazinylmethane was presumably originated from the double C–N coupling of two piperazines on a carbon atom coming from methanol. In addition, the relevant concomitants 6 and 8 were also isolated from the solutions of 5 and 7, respectively. Complexes 6 and 8 contain 1:1 starting molecules of 2/3 with 4 assembled into helical structures.