The synthesis and the solid-state structure of benzene-tris-(methylene-phosphonic acid) is reported in the following article. Surprisingly the three methylenephosphonic acid groups are located on the same side of the benzene ring leading to the formation of an octopus shaped molecule. Furthermore the number of proton per phosphonic acid function is different from the expected value of two per phosphophonic acid function. The single crystal X-ray diffraction reveals that this interesting behaviour arises from the formation of a dimer in the solid-state. Interestingly both charge-assisted hydrogen bonds and hydrogen bonds are observed in this dimer.