Whereas, commonly, Langmuir monolayers are structurally dominated by the aliphatic chains, we present here the first case of monolayers where the chains merely serve anchoring at the air/water interface and the organization is dictated by the hydrophilic head group self-assembling in a hexagonal lattice. These head groups are polyoxometalates known for their multifunctional potential. The chain length has been systematically varied, allowing for a general study of the impact of the chain length on the supramolecular structure. These model structures are studied here by a combination of modern techniques, the leading ones being X-ray reflectivity and grazing incidence X-ray diffraction. The quantitative structural insights offered in this Letter might represent a starting point for the rational design and study of a new class of emulsions, including an organic tail and a multifunctional inorganic polar head.