A flexible model for generating anisotropic atom-atom form of an atom-diatom potential is developed and used to fit the high-level ab initio PES (potential energy surface) of the ground state Ar-B₂ Van der Waals complex. The system is found to have only a well for the T-shaped geometry as a consequence of the sp-hybridisation of B within B₂. Comparison of the complex with similar Ar-X₂ species studied at the same level of theory exhibits some particular features of the boron system, originating from its electronic structure and interpreted in terms of the Ar-B interactions. A proper combination of the empirically adjusted potentials for isolated ArB and of the calculated effective atom-atom potentials acting in Ar-B₂ is employed to produce the ``real'' PES of the complex, used to predict its microwave spectrum.